This document presents a model of an electrohydraulic fatigue testing system that focuses on components upstream of the servovalve and actuator, including the supply and return lines. The model allows prediction of pressure fluctuations in these lines in the time domain using a modular approach. Experiments showed significant pressure fluctuations at the servovalve ports due to supply and return line dynamics. The model was then used to evaluate potential design changes to improve system bandwidth by reducing pressure dynamics from flexible hoses.
Oil & Gas Pipelines are often subjected to an operation called ‘Pigging’ for maintenance purposes (For e.g., cleaning the pipeline of accumulated liquids or waxes). A pig is launched from a pig launcher that scrapes out the remnant contents of the pipeline into a vessel known as a ‘Slug catcher’. The term slug catcher is used since pigging operations produces a Slug flow regime characterized by the alternating columns of liquids & gases. Slug catcher’s are popularly of two types – Horizontal Vessel Type & Finger Type Slug catcher. However irrespective of the type used, the determination of the slug catcher volume becomes the primary step before choosing the slug catcher type.
Natural Gas Pipeline Transmission Cost & EconomicsVijay Sarathy
In any pipeline project, an economic analysis has to be performed to ensure the project is a viable investment. The major capital components of a pipeline system consists of the pipeline, Booster station, ancillary machinery such as mainline valve stations, meter stations, pressure regulation stations, SCADA & Telecommunications. The project costs would additionally consist of environmental costs & permits, Right of Way (ROW) acquisitions, Engineering & Construction management to name a few.
The following tutorial is aimed at conducting a pipeline economic analysis using the method of Weight Average Capital Cost (WACC) to estimate gas tariffs, project worth in terms of Net Present Value (NPV), Internal Rate of Return (IRR), Profit to Investment Ratio (PIR) and payback period. The cost of equity is estimated using the Capital Asset Pricing Model (CAPM).
Prediction of flow characteristics through a circular port of a spool valve u...eSAT Journals
Abstract Hydraulic spool valves are used in a variety of industrial equipment’s like earth moving machinery, aircrafts and machine tools etc. A hydraulic spool valve is a switching device used for controlling hydraulic devices. A spool valve can turn the flow of hydraulic fluid from a hydraulic pump to an actuator in forward or reverse directions or on and off by blocking offthe route of the fluid takes. A controller moves the valve back and forth in its case to slide the spools into different positions. As the spool moves across the inlet port, the port which is initially fully open, circular in shape and permitting the fluid flow, is getting closed gradually. Once the spool starts moving, the inlet port becomes non circular and continues to be so till closure. The shape and the area of the port that is still left open for the oil to flow is steadily changing. The area which is originally circular is becoming far away from circularity. It is required to study the flow in such port-spool combination. The purpose of the dissertation is to compute the flow for different port openings. ANSYS CFD FLOTRAN software is used to predict the flow characteristics. The exact flow path is simulated. The predicted results are compared with the analytical calculations. Key words- Spool valve, Simulation, Flow Characteristics, CFD
Oil & Gas Pipelines are often subjected to an operation called ‘Pigging’ for maintenance purposes (For e.g., cleaning the pipeline of accumulated liquids or waxes). A pig is launched from a pig launcher that scrapes out the remnant contents of the pipeline into a vessel known as a ‘Slug catcher’. The term slug catcher is used since pigging operations produces a Slug flow regime characterized by the alternating columns of liquids & gases. Slug catcher’s are popularly of two types – Horizontal Vessel Type & Finger Type Slug catcher. However irrespective of the type used, the determination of the slug catcher volume becomes the primary step before choosing the slug catcher type.
Natural Gas Pipeline Transmission Cost & EconomicsVijay Sarathy
In any pipeline project, an economic analysis has to be performed to ensure the project is a viable investment. The major capital components of a pipeline system consists of the pipeline, Booster station, ancillary machinery such as mainline valve stations, meter stations, pressure regulation stations, SCADA & Telecommunications. The project costs would additionally consist of environmental costs & permits, Right of Way (ROW) acquisitions, Engineering & Construction management to name a few.
The following tutorial is aimed at conducting a pipeline economic analysis using the method of Weight Average Capital Cost (WACC) to estimate gas tariffs, project worth in terms of Net Present Value (NPV), Internal Rate of Return (IRR), Profit to Investment Ratio (PIR) and payback period. The cost of equity is estimated using the Capital Asset Pricing Model (CAPM).
Prediction of flow characteristics through a circular port of a spool valve u...eSAT Journals
Abstract Hydraulic spool valves are used in a variety of industrial equipment’s like earth moving machinery, aircrafts and machine tools etc. A hydraulic spool valve is a switching device used for controlling hydraulic devices. A spool valve can turn the flow of hydraulic fluid from a hydraulic pump to an actuator in forward or reverse directions or on and off by blocking offthe route of the fluid takes. A controller moves the valve back and forth in its case to slide the spools into different positions. As the spool moves across the inlet port, the port which is initially fully open, circular in shape and permitting the fluid flow, is getting closed gradually. Once the spool starts moving, the inlet port becomes non circular and continues to be so till closure. The shape and the area of the port that is still left open for the oil to flow is steadily changing. The area which is originally circular is becoming far away from circularity. It is required to study the flow in such port-spool combination. The purpose of the dissertation is to compute the flow for different port openings. ANSYS CFD FLOTRAN software is used to predict the flow characteristics. The exact flow path is simulated. The predicted results are compared with the analytical calculations. Key words- Spool valve, Simulation, Flow Characteristics, CFD
Using a Hydraulic Ram to Pump Livestock Water - British Columbia
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For more information, Please see websites below:
`
Organic Edible Schoolyards & Gardening with Children =
http://scribd.com/doc/239851214 ~
`
Double Food Production from your School Garden with Organic Tech =
http://scribd.com/doc/239851079 ~
`
Free School Gardening Art Posters =
http://scribd.com/doc/239851159 ~
`
Increase Food Production with Companion Planting in your School Garden =
http://scribd.com/doc/239851159 ~
`
Healthy Foods Dramatically Improves Student Academic Success =
http://scribd.com/doc/239851348 ~
`
City Chickens for your Organic School Garden =
http://scribd.com/doc/239850440 ~
`
Huerto Ecológico, Tecnologías Sostenibles, Agricultura Organica
http://scribd.com/doc/239850233
`
Simple Square Foot Gardening for Schools - Teacher Guide =
http://scribd.com/doc/239851110 ~
[7] a generalized parameter tuning method of proportional resonant controller...Ngoc Dinh
Phuong Vu, Ngoc Dinh, Nam Hoang, Quan Nguyen, Minh Tran; “A Generalized Parameter Tuning Method of Proportional-Resonant Controllers for Dynamic Voltage Restorers”; International Journal of Power Electronics and Drive System (IJPEDS).
Analysis and compensation for the cascade dead-zones in the proportional cont...ISA Interchange
The four-way proportional directional control valve has been widely used as the main stage spring constant for the two-stage proportional control valve (PDV). Since a tradeoff should be made between manufacturing costs and static performance, two symmetry dead-zones are introduced in the main stage spring constant: the center dead-zone caused by the center floating position and the intermediate dead- zone caused by the intermediate position. Though the intermediate dead-zone is much smaller than the center dead-zone, it has significant effect on the dynamic position tracking performance. In this paper, the cascade dead-zones problem in a typical two-stage PDV is analyzed and a cascade dead-zones model is proposed for the main stage spring constant. Then, a cascade dead-zones inverse method is improved with gain estimation and dead-zone detection to compensate the dead-zone non-linearity. Finally, a digital controller is designed for verification. The comparative experimental results indicate that it is effective to reduce the large position tracking error when the proposed method is applied.
Study on a linear relationship between limited pressure difference and coil c...ISA Interchange
On/off solenoid valves with PWM control are widely used in all types of vehicle electro-hydraulic control systems respecting to their desirable properties of reliable, low cost and fast acting. However, it can hardly achieve a linear hydraulic modulation by using on/off valves mainly due to the nonlinear behaviors of valve dynamics and fluid, which affects the control accuracy significantly. In this paper, a linear relationship between limited pressure difference and coil current of an on/off valve in its critical closed state is proposed and illustrated, which has a great potential to be applied to improve hydraulic control performance. The hydraulic braking system of case study is modeled. The linear correspondence between limited pressure difference and coil current of the inlet valve is simulated and further verified experimentally. Based on validated simulation models, the impacts of key parameters are researched. The limited pressure difference affected by environmental temperatures is experimentally studied, and the amended linear relation is given according to the test data.
Jest wiele wewnętrznych i zewnętrznych sił, które kształtują twoich pracowników. Jeśli pozostawisz grupę pracowników o wysokim potencjale rozwojowym bez nadzoru jej skład i jakość zmienią się samoczynnie i staną się niespójne z potrzebami organizacji.
Using a Hydraulic Ram to Pump Livestock Water - British Columbia
`
For more information, Please see websites below:
`
Organic Edible Schoolyards & Gardening with Children =
http://scribd.com/doc/239851214 ~
`
Double Food Production from your School Garden with Organic Tech =
http://scribd.com/doc/239851079 ~
`
Free School Gardening Art Posters =
http://scribd.com/doc/239851159 ~
`
Increase Food Production with Companion Planting in your School Garden =
http://scribd.com/doc/239851159 ~
`
Healthy Foods Dramatically Improves Student Academic Success =
http://scribd.com/doc/239851348 ~
`
City Chickens for your Organic School Garden =
http://scribd.com/doc/239850440 ~
`
Huerto Ecológico, Tecnologías Sostenibles, Agricultura Organica
http://scribd.com/doc/239850233
`
Simple Square Foot Gardening for Schools - Teacher Guide =
http://scribd.com/doc/239851110 ~
[7] a generalized parameter tuning method of proportional resonant controller...Ngoc Dinh
Phuong Vu, Ngoc Dinh, Nam Hoang, Quan Nguyen, Minh Tran; “A Generalized Parameter Tuning Method of Proportional-Resonant Controllers for Dynamic Voltage Restorers”; International Journal of Power Electronics and Drive System (IJPEDS).
Analysis and compensation for the cascade dead-zones in the proportional cont...ISA Interchange
The four-way proportional directional control valve has been widely used as the main stage spring constant for the two-stage proportional control valve (PDV). Since a tradeoff should be made between manufacturing costs and static performance, two symmetry dead-zones are introduced in the main stage spring constant: the center dead-zone caused by the center floating position and the intermediate dead- zone caused by the intermediate position. Though the intermediate dead-zone is much smaller than the center dead-zone, it has significant effect on the dynamic position tracking performance. In this paper, the cascade dead-zones problem in a typical two-stage PDV is analyzed and a cascade dead-zones model is proposed for the main stage spring constant. Then, a cascade dead-zones inverse method is improved with gain estimation and dead-zone detection to compensate the dead-zone non-linearity. Finally, a digital controller is designed for verification. The comparative experimental results indicate that it is effective to reduce the large position tracking error when the proposed method is applied.
Study on a linear relationship between limited pressure difference and coil c...ISA Interchange
On/off solenoid valves with PWM control are widely used in all types of vehicle electro-hydraulic control systems respecting to their desirable properties of reliable, low cost and fast acting. However, it can hardly achieve a linear hydraulic modulation by using on/off valves mainly due to the nonlinear behaviors of valve dynamics and fluid, which affects the control accuracy significantly. In this paper, a linear relationship between limited pressure difference and coil current of an on/off valve in its critical closed state is proposed and illustrated, which has a great potential to be applied to improve hydraulic control performance. The hydraulic braking system of case study is modeled. The linear correspondence between limited pressure difference and coil current of the inlet valve is simulated and further verified experimentally. Based on validated simulation models, the impacts of key parameters are researched. The limited pressure difference affected by environmental temperatures is experimentally studied, and the amended linear relation is given according to the test data.
Jest wiele wewnętrznych i zewnętrznych sił, które kształtują twoich pracowników. Jeśli pozostawisz grupę pracowników o wysokim potencjale rozwojowym bez nadzoru jej skład i jakość zmienią się samoczynnie i staną się niespójne z potrzebami organizacji.
Internet Rzeczy? W polskich firmach to wciąż fikcjaBPSC
Internet Rzeczy to w polskich przedsiębiorstwach raczej puste hasło niż realna potrzeba – wynika z danych Urzędu Komunikacji Elektronicznej. Zaledwie 3% firm korzysta z Internetu Rzeczy. Niewiele więcej, bo 6% przedsiębiorstw zamierza w przyszłości wprowadzić rozwiązania M2M.
“Artículo 208.- Contratación de profesores
208.1 La contratación de profesores en las
Instituciones Educativas Públicas de Educación Básica
y Técnico Productiva se realiza mediante concurso
público convocado cada dos (2) años, bajo los principios
de calidad, capacidad profesional y oportunidad. Este
concurso determina los cuadros de méritos vigentes para
los procesos de contratación anuales que se realicen en
dicho periodo.
208.2 En las Instituciones Educativas Públicas de
Educación Básica, la contratación de profesores se lleva
a cabo a través de la aplicación de una Prueba Única
Nacional, a cargo del MINEDU. Los cuadros de mérito
se determinan considerando el puntaje fi nal obtenido por
cada postulante en la citada prueba y la elección de UGEL
que realizó
The KING-GAGE 780XD Purge Control is an extremely rugged unit designed specifically for hazardous areas requiring flameproof or ATEX (Ex d) rating. A proprietary wet check assembly ensures positive seal of fluids to ensure containment integrity. Loop powered transmitter provides 4-20mAdc output while components are isolated from the process media by a continuous air purge. Total consumption rate is less than 0.083 scfm for energy saving operation with external air/gas supply.The only internal element is a simple length of pipe extending into the tank.
Steam traps are the hardest working components in the steam system. Maintenance or replacement of steam traps must be as quick and efficient as possible to avoid unnecessary disruption to related processes.
Traditional steam trapping assemblies often require the plant to be shut down for traps to be maintained or replaced taking significant time and reducing production output.
The PC3000 and PC4000 incorporate isolation valves, strainer, two-bolt steam trap connection and blowdown valves, all in a single unit for quick and easy installation and operation.
Insertion turbine flow meters measure flow of liquid, gas, and
steam by detecting the frequency of rotation of the turbine blades. The frequency of turbine rotation is directly proportional to the flow velocity. Insertion turbine flow meters measure flow by detecting the local velocity within the pipe. The fluid velocity is combined with other parameters to calculate the average pipe velocity and volumetric flow rate.
2016-03-17 Structural Value EngineeringPiet Lambert
Presentatie van Piet Lambert (Lambert Engineering) tijdens 5-jarig verjaardagsevent op 17 maart 2016.
Structural Value Engineering is de methode om als stabiliteitsingenieur ruwbouwkosten in de uitvoering reeds in ontwerp te verlagen. Zo worddt extra (architecturale) waarde gecreëerd
Temporary voltage swells and sags appear with high frequency in electric power systems, and they significantly affect sensitive loads such as industrial manufacturing or communication devices. This paper presents a strategy to design proportional-resonant controllers for three full-bridge voltage-source converters with a common DC-link in dynamic voltage restorer systems. The proposed controllers allow the system to quickly overcome temporary unbalanced voltage sags. Simulation results carried out in MATLAB/Simulink and experimental results implemented in a Typhoon HIL402 device demonstrate the ability of the proposed design method. The results show that the system with the proposed controllers can ride-through single-phase or double-phase voltage sags up to 55% and three-phase voltage sags up to 70% in a duration less than one grid-voltage cycle.
Adaptive terminal sliding mode control strategy for dc–dc buck convertersISA Interchange
This paper presents an adaptive terminal sliding mode control (ATSMC) strategy for DC–DC buck converters. The idea behind this strategy is to use the terminal sliding mode control (TSMC) approach to assure finite time convergence of the output voltage error to the equilibrium point and integrate an adaptive law to the TSMC strategy so as to achieve a dynamic sliding line during the load variations. In addition, the influence of the controller parameters on the performance of closed-loop system is investigated. It is observed that the start up response of the output voltage becomes faster with increasing value of the fractional power used in the sliding function. On the other hand, the transient response of the output voltage, caused by the step change in the load, becomes faster with decreasing the value of the fractional power. Therefore, the value of fractional power is to be chosen to make a compromise between start up and transient responses of the converter. Performance of the proposed ATSMC strategy has been tested through computer simulations and experiments. The simulation results of the proposed ATSMC strategy are compared with the conventional SMC and TSMC strategies. It is shown that the ATSMC exhibits a considerable improvement in terms of a faster output voltage response during load changes.
Analysis, control and design of a non-inverting buck-boost converter: A bump-...o_almasi
In this paper, a new modified fuzzy Two-Level Control Scheme (TLCS) is proposed to control a non inverting buck-boost converter. Each level of fuzzy TLCS consists of a tuned fuzzy PI controller. In addition, a Takagi–Sugeno–Kang (TSK) fuzzy switch proposed to transfer the fuzzy PI controllers to each other in the control system. The major difficulty in designing fuzzy TLCS which degrades its performance is emerging unwanted drastic oscillations in the converter output voltage during replacing the controllers. Thereby, the fuzzy PI controllers in each level of TLCS structure are modified to eliminate these oscillations and improve the system performance. Some simulations and digital signal processor based experiments are conducted on a non-inverting buck-boost converter to support the effectiveness of the proposed TLCS in controlling the converter output voltage.
A Shunt Active Power Filter for 12 Pulse Converter Using Source Current Detec...IAES-IJPEDS
A shunt Active Power Filter (APF) with current detection at the source side
is considered as a closed-loop system from the view of the whole power
distribution system, which is expected with better harmonics filtering
performance compared with conventional current detection methods such as
load current detection and open loop control. This paper introduces an
efficient source current detection method (direct) control scheme to mitigate
the grid current harmonics generated by the twelve pulse converter. The
proposed system uses Control Rectifier (12 –pulse converter) which
efficiently regulates the DC voltage by varying the angle of each 6 pulse
converter. Moreover, the proposed system uses three winding transformer
which eliminates the harmonics during equal angles switching at each six
pulse converter which in turn simplifies the operation of the SAPF. The
proposed system is simulated in MATLAB SIMULINK to evaluate the
performance of the proposed system.
This paper presents the further developments and working principle of the speed-variable switched differential pump (SvSDP) concept proposed, designed and produced in [1]. The SvSDP system is designed to remove the throttling losses associated with typical valve driven control (VDC) systems. The hydraulic and mechanical system is modelled and linearised. The linearisation point is studied to provide an usable basis for controller design. It is proposed, in this paper, to model the converter and motor using a black box approach, where designed and informative input sequences are used to estimate the mathematical behaviour of the electrical drive based on the equivalent output data. The complete non linear model is verified against available trajectory data from the physical system, obtained from [1]. The linear model is analysed through a relative gain array (RGA) analysis to map the input output couplings present in the system. The results show that the system includes heavy cross-couplings. Results presented in [1] indicate, that it is possible to utilise a input output compensated decoupling to redefine the MIMO system into multiple SISO systems. The SvSDP concept is over-determined in relation to the amount of control inputs compared to possible outputs.
It is proposed in [1] to introduce two new input states and two new output states. The decoupling approach has been investigated in this paper. The decoupling results provided a basis of using decentralised control. The linear control strategies are designed independently based on the notion of decoupling. The first controller is related to the level flow, designed to maintain a desired minimum pressure level. The second load flow controller is related to the cylinder motion. The controller results indicate, that it is possible to achieve a good dynamic tracking performance with an error of maximum 0.5 mm for a given position trajectory.
This paper is also considering the energy consumption issues stated in [1], where two conceptual solutions are proposed, to solve the power loss associated with holding a load at a constant cylinder position. This paper is written as the product of an appendix report describing the whole project.
International Journal of Engineering Research and Applications (IJERA) is an open access online peer reviewed international journal that publishes research and review articles in the fields of Computer Science, Neural Networks, Electrical Engineering, Software Engineering, Information Technology, Mechanical Engineering, Chemical Engineering, Plastic Engineering, Food Technology, Textile Engineering, Nano Technology & science, Power Electronics, Electronics & Communication Engineering, Computational mathematics, Image processing, Civil Engineering, Structural Engineering, Environmental Engineering, VLSI Testing & Low Power VLSI Design etc.
H6 Transformer less Topology and Its Modulation Strategy for Mitigating Cm Cu...IJERA Editor
MATLABbasedsingle-phase three-level topology for a transformer less photovoltaic system is presented in this paper. Compared with the conventional H-bridge topology, it only needs two additional asymmetrically distributed switches, and the system common-mode voltage can be kept constant with a simple modulation scheme. Family of H6 transformer less inverter topologies with low leakage currents is proposed and highly efficient and reliable inverter concept (HERIC) topology is also presented in this paper. The proposed inverter can also operate with high frequency by retaining high efficiency which enables reduced cooling system. Finally, the proposed new topology is simulated by MATLAB/Simulink software to validate the accuracy of the theoretical explanation.
HARMONIC MITIGATION USING D STATCOM THROUGH A CURRENT CONTROL TECHNIQUEJournal For Research
The harmonic mitigation using shunt active filters are most widely used in industrial and commercial applications. In this paper a Multi-Level Inverter is considered as DSTATCOM to compensate harmonics. The mathematical modeling of the system and design of the controller using synchronous reference frame theory is also presented. The nonlinear load generally known as diode rectifier load and an unbalanced load is simulated with the system using MATLAB/SIMULINK.
CONTROL VALVE SIZING AND SELECTION FOR ANY APPLICATION.pptNagalingeswaranR
CONTROL VALVE BASICS.INCLUDING SIZIND, DETAILING AND SELECTION OF MATERIAL.THIS IS APPLICABLE FOR ALL APPLICATIONS LIKE UTILITY, POWER, WATER AND REFINERY. FROM THE PRESENTATION THE DESIGN ENGINEER CAN DECIDE THE TYPE OF CONTROL VALVE AND ITS CHARACTER TO BE SELECTED FOR THE GIVEN APPLICATION.
Analysis of symmetrical & asymmetrical pwm based three phase ac to ac con...eSAT Journals
Abstract
A Three phase bidirectional AC to AC buck converter circuit using power MOSFET operating in high frequency chopping mode is simulated and analyzed for electrical parameters such as output phase voltage, input line current, input power factor, harmonic profile and efficiency using MATLAB/simulink software package. The various PWM techniques such as symmetrical ramp-DC PWM (SRDPWM), asymmetrical ramp-triangular PWM (ARTPWM), asymmetrical sinusoidal PWM type-1 [ASPWM1] and asymmetrical sinusoidal PWM type-2 [ASPWM2] techniques are adopted to analyze the harmonic profile, input power factor and efficiency of the converter. The rms value of the output phase voltage, output line current and source current can be significantly increased by varying the duty ratio K in case of symmetrical PWM control strategy and modulation index MI in case of asymmetrical PWM control strategies independent of variation in switching frequency. It is observed from the simulation results that the ASPWM1 switching strategy gives more output phase voltage, input power factor, efficiency by increasing modulation index MI and reduced low order harmonics of output voltage and source current by increasing the number of pulses per half cycle P compared to other PWM techniques rendering easy and economical filteration.
Keywords: Three phase AC chopper, symmetrical ramp-DC PWM, asymmetrical ramp-triangular PWM, asymmetrical sinusoidal PWM technique, harmonic profile, power factor, efficiency
Analysis of symmetrical & asymmetrical pwm based three phase ac to ac con...eSAT Journals
Abstract
A Three phase bidirectional AC to AC buck converter circuit using power MOSFET operating in high frequency chopping mode is simulated and analyzed for electrical parameters such as output phase voltage, input line current, input power factor, harmonic profile and efficiency using MATLAB/simulink software package. The various PWM techniques such as symmetrical ramp-DC PWM (SRDPWM), asymmetrical ramp-triangular PWM (ARTPWM), asymmetrical sinusoidal PWM type-1 [ASPWM1] and asymmetrical sinusoidal PWM type-2 [ASPWM2] techniques are adopted to analyze the harmonic profile, input power factor and efficiency of the converter. The rms value of the output phase voltage, output line current and source current can be significantly increased by varying the duty ratio K in case of symmetrical PWM control strategy and modulation index MI in case of asymmetrical PWM control strategies independent of variation in switching frequency. It is observed from the simulation results that the ASPWM1 switching strategy gives more output phase voltage, input power factor, efficiency by increasing modulation index MI and reduced low order harmonics of output voltage and source current by increasing the number of pulses per half cycle P compared to other PWM techniques rendering easy and economical filteration.
Keywords: Three phase AC chopper, symmetrical ramp-DC PWM, asymmetrical ramp-triangular PWM, asymmetrical sinusoidal PWM technique, harmonic profile, power factor, efficiency
An optimal general type-2 fuzzy controller for Urban Traffic NetworkISA Interchange
Urban traffic network model is illustrated by state-charts and object-diagram. However, they have limitations to show the behavioral perspective of the traffic information flow. Consequently, a state space model is used to calculate the half-value waiting time of vehicles. In this study, a combination of the general type-2 fuzzy logic sets and the modified backtracking search algorithm (MBSA) techniques are used in order to control the traffic signal scheduling and phase succession so as to guarantee a smooth flow of traffic with the least wait times and average queue length. The parameters of input and output membership functions are optimized simultaneously by the novel heuristic algorithm MBSA. A comparison is made between the achieved results with those of optimal and conventional type-1 fuzzy logic controllers.
Embedded intelligent adaptive PI controller for an electromechanical systemISA Interchange
In this study, an intelligent adaptive controller approach using the interval type-2 fuzzy neural network (IT2FNN) is presented. The proposed controller consists of a lower level proportional - integral (PI) controller, which is the main controller and an upper level IT2FNN which tuning on-line the parameters of a PI controller. The proposed adaptive PI controller based on IT2FNN (API-IT2FNN) is implemented practically using the Arduino DUE kit for controlling the speed of a nonlinear DC motor-generator system. The parameters of the IT2FNN are tuned on-line using back-propagation algorithm. The Lyapunov theorem is used to derive the stability and convergence of the IT2FNN. The obtained experimental results, which are compared with other controllers, demonstrate that the proposed API-IT2FNN is able to improve the system response over a wide range of system uncertainties.
State of charge estimation of lithium-ion batteries using fractional order sl...ISA Interchange
This paper presents a state of charge (SOC) estimation method based on fractional order sliding mode observer (SMO) for lithium-ion batteries. A fractional order RC equivalent circuit model (FORCECM) is firstly constructed to describe the charging and discharging dynamic characteristics of the battery. Then, based on the differential equations of the FORCECM, fractional order SMOs for SOC, polarization voltage and terminal voltage estimation are designed. After that, convergence of the proposed observers is analyzed by Lyapunov’s stability theory method. The framework of the designed observer system is simple and easy to implement. The SMOs can overcome the uncertainties of parameters, modeling and measurement errors, and present good robustness. Simulation results show that the presented estima- tion method is effective, and the designed observers have good performance.
Fractional order PID for tracking control of a parallel robotic manipulator t...ISA Interchange
This paper presents the tracking control for a robotic manipulator type delta employing fractional order PID controllers with computed torque control strategy. It is contrasted with an integer order PID controller with computed torque control strategy. The mechanical structure, kinematics and dynamic models of the delta robot are descripted. A SOLIDWORKS/MSC-ADAMS/MATLAB co-simulation model of the delta robot is built and employed for the stages of identification, design, and validation of control strategies. Identification of the dynamic model of the robot is performed using the least squares algorithm. A linearized model of the robotic system is obtained employing the computed torque control strategy resulting in a decoupled double integrating system. From the linearized model of the delta robot, fractional order PID and integer order PID controllers are designed, analyzing the dynamical behavior for many evaluation trajectories. Controllers robustness is evaluated against external disturbances employing performance indexes for the joint and spatial error, applied torque in the joints and trajectory tracking. Results show that fractional order PID with the computed torque control strategy has a robust performance and active disturbance rejection when it is applied to parallel robotic manipulators on tracking tasks.
Fuzzy logic for plant-wide control of biological wastewater treatment process...ISA Interchange
The application of control strategies is increasingly used in wastewater treatment plants with the aim of improving effluent quality and reducing operating costs. Due to concerns about the progressive growth of greenhouse gas emissions (GHG), these are also currently being evaluated in wastewater treatment plants. The present article proposes a fuzzy controller for plant-wide control of the biological wastewater treatment process. Its design is based on 14 inputs and 6 outputs in order to reduce GHG emissions, nutrient concentration in the effluent and operational costs. The article explains and shows the effect of each one of the inputs and outputs of the fuzzy controller, as well as the relationship between them. Benchmark Simulation Model no 2 Gas is used for testing the proposed control strategy. The results of simulation results show that the fuzzy controller is able to reduce GHG emissions while improving, at the same time, the common criteria of effluent quality and operational costs.
Design and implementation of a control structure for quality products in a cr...ISA Interchange
In recent years, interest for petrochemical processes has been increasing, especially in refinement area. However, the high variability in the dynamic characteristics present in the atmospheric distillation column poses a challenge to obtain quality products. To improve distillates quality in spite of the changes in the input crude oil composition, this paper details a new design of a control strategy in a conventional crude oil distillation plant defined using formal interaction analysis tools. The process dynamic and its control are simulated on Aspen HYSYS dynamic environment under real operating conditions. The simulation results are compared against a typical control strategy commonly used in crude oil atmospheric distillation columns.
Model based PI power system stabilizer design for damping low frequency oscil...ISA Interchange
This paper explores a two-level control strategy by blending a local controller with a centralized controller for the low frequency oscillations in a power system. The proposed control scheme provides stabilization of local modes using a local controller and minimizes the effect of inter-connection of sub-systems performance through a centralized control. For designing the local controllers in the form of proportional-integral power system stabilizer (PI-PSS), a simple and straight forward frequency domain direct synthesis method is considered that works on use of a suitable reference model which is based on the desired requirements. Several examples both on one machine infinite bus and multi-machine systems taken from the literature are illustrated to show the efficacy of the proposed PI-PSS. The effective damping of the systems is found to be increased remarkably which is reflected in the time-responses; even unstable operation has been stabilized with improved damping after applying the proposed controller. The proposed controllers give remarkable improvement in damping the oscillations in all the illustrations considered here and as for example, the value of damping factor has been increased from 0.0217 to 0.666 in Example 1. The simulation results obtained by the proposed control strategy are favorably compared with some controllers prevalent in the literature.
A comparison of a novel robust decentralized control strategy and MPC for ind...ISA Interchange
Abstract: In this work we have developed a novel, robust practical control structure to regulate an industrial methanol distillation column. This proposed control scheme is based on a override control framework and can manage a non-key trace ethanol product impurity specification while maintaining high product recovery. For comparison purposes, an MPC with a discrete process model (based on step tests) was also developed and tested. The results from process disturbance testing shows that, both the MPC and the proposed controller were capable of maintaining both the trace level ethanol specification in the distillate (XD) and high product recovery (β). Closer analysis revealed that the MPC controller has a tighter XD control, while the proposed controller was tighter in β control. The tight XD control allowed the MPC to operate at a higher XD set point (closer to the 10 ppm AA grade methanol standard), allowing for savings in energy usage. Despite the energy savings of the MPC, the proposed control scheme has lower installation and running costs. An economic analysis revealed a multitude of other external economic and plant design factors, that should be considered when making a decision between the two controllers. In general, we found relatively high energy costs favor MPC.
Fault detection of feed water treatment process using PCA-WD with parameter o...ISA Interchange
Feed water treatment process (FWTP) is an essential part of utility boilers; and fault detection is expected for its reliability improvement. Classical principal component analysis (PCA) has been applied to FWTPs in our previous work; however, the noises of T2 and SPE statistics result in false detections and missed detections. In this paper, Wavelet denoise (WD) is combined with PCA to form a new algorithm, (PCA- WD), where WD is intentionally employed to deal with the noises. The parameter selection of PCA-WD is further formulated as an optimization problem; and PSO is employed for optimization solution. A FWTP, sustaining two 1000 MW generation units in a coal-fired power plant, is taken as a study case. Its operation data is collected for following verification study. The results show that the optimized WD is effective to restrain the noises of T2 and SPE statistics, so as to improve the performance of PCA-WD algorithm. And, the parameter optimization enables PCA-WD to get its optimal parameters in an auto- matic way rather than on individual experience. The optimized PCA-WD is further compared with classical PCA and sliding window PCA (SWPCA), in terms of four cases as bias fault, drift fault, broken line fault and normal condition, respectively. The advantages of the optimized PCA-WD, against classical PCA and SWPCA, is finally convinced with the results.
Model-based adaptive sliding mode control of the subcritical boiler-turbine s...ISA Interchange
As higher requirements are proposed for the load regulation and efficiency enhancement, the control performance of boiler-turbine systems has become much more important. In this paper, a novel robust control approach is proposed to improve the coordinated control performance for subcritical boiler-turbine units. To capture the key features of the boiler-turbine system, a nonlinear control-oriented model is established and validated with the history operation data of a 300 MW unit. To achieve system linearization and decoupling, an adaptive feedback linearization strategy is proposed, which could asymptotically eliminate the linearization error caused by the model uncertainties. Based on the linearized boiler-turbine system, a second-order sliding mode controller is designed with the super-twisting algorithm. Moreover, the closed-loop system is proved robustly stable with respect to uncertainties and disturbances. Simulation results are presented to illustrate the effectiveness of the proposed control scheme, which achieves excellent tracking performance, strong robustness and chattering reduction.
A Proportional Integral Estimator-Based Clock Synchronization Protocol for Wi...ISA Interchange
Clock synchronization is an issue of vital importance in applications of wireless sensor networks (WSNs). This paper proposes a proportional integral estimator-based protocol (EBP) to achieve clock synchronization for wireless sensor networks. As each local clock skew gradually drifts, synchronization accuracy will decline over time. Compared with existing consensus-based approaches, the proposed synchronization protocol improves synchronization accuracy under time-varying clock skews. Moreover, by restricting synchronization error of clock skew into a relative small quantity, it could reduce periodic re-synchronization frequencies. At last, a pseudo-synchronous implementation for skew compensation is introduced as synchronous protocol is unrealistic in practice. Numerical simulations are shown to illustrate the performance of the proposed protocol.
An artificial intelligence based improved classification of two-phase flow patte...ISA Interchange
Flow pattern recognition is necessary to select design equations for finding operating details of the process and to perform computational simulations. Visual image processing can be used to automate the interpretation of patterns in two-phase flow. In this paper, an attempt has been made to improve the classification accuracy of the flow pattern of gas/ liquid two- phase flow using fuzzy logic and Support Vector Machine (SVM) with Principal Component Analysis (PCA). The videos of six different types of flow patterns namely, annular flow, bubble flow, churn flow, plug flow, slug flow and stratified flow are re- corded for a period and converted to 2D images for processing. The textural and shape features extracted using image processing are applied as inputs to various classification schemes namely fuzzy logic, SVM and SVM with PCA in order to identify the type of flow pattern. The results obtained are compared and it is observed that SVM with features reduced using PCA gives the better classification accuracy and computationally less intensive than other two existing schemes. This study results cover industrial application needs including oil and gas and any other gas-liquid two-phase flows.
New Method for Tuning PID Controllers Using a Symmetric Send-On-Delta Samplin...ISA Interchange
In this paper we present a new method for tuning PI controllers with symmetric send-on-delta (SSOD) sampling strategy. First we analyze the conditions that produce oscillations in event based systems considering SSOD sampling strategy. The Describing Function is the tool used to address the problem. Once the conditions for oscillations are established, a new robustness to oscillation performance measure is introduced which entails with the concept of phase margin, one of the most traditional measures of relative stability in closed-loop control systems. Therefore, the application of the proposed robustness measure is easy and intuitive. The method is tested by both simulations and experiments. Additionally, a Java application has been developed to aid in the design according to the results presented in the paper.
Load estimator-based hybrid controller design for two-interleaved boost conve...ISA Interchange
This paper is devoted to the development of a hybrid controller for a two-interleaved boost converter dedicated to renewable energy and automotive applications. The control requirements, resumed in fast transient and low input current ripple, are formulated as a problem of fast stabilization of a predefined optimal limit cycle, and solved using hybrid automaton formalism. In addition, a real time estimation of the load is developed using an algebraic approach for online adjustment of the hybrid controller. Mathematical proofs are provided with simulations to illustrate the effectiveness and the robustness of the proposed controller despite different disturbances. Furthermore, a fuel cell system supplying a resistive load through a two-interleaved boost converter is also highlighted.
Effects of Wireless Packet Loss in Industrial Process Control SystemsISA Interchange
Timely and reliable sensing and actuation control are essential in networked control. This depends on not only the precision/quality of the sensors and actuators used but also on how well the communications links between the field instruments and the controller have been designed. Wireless networking offers simple deployment, reconfigurability, scalability, and reduced operational expenditure, and is easier to upgrade than wired solutions. However, the adoption of wireless networking has been slow in industrial process control due to the stochastic and less than 100% reliable nature of wireless communications and lack of a model to evaluate the effects of such communications imperfections on the overall control performance. In this paper, we study how control performance is affected by wireless link quality, which in turn is adversely affected by severe propagation loss in harsh industrial environments, co-channel interference, and unintended interference from other devices. We select the Tennessee Eastman Challenge Model (TE) for our study. A decentralized process control system, first proposed by N. Ricker, is adopted that employs 41 sensors and 12 actuators to manage the production process in the TE plant. We consider the scenario where wireless links are used to periodically transmit essential sensor measurement data, such as pressure, temperature and chemical composition to the controller as well as control commands to manipulate the actuators according to predetermined setpoints. We consider two models for packet loss in the wireless links, namely, an independent and identically distributed (IID) packet loss model and the two-state Gilbert-Elliot (GE) channel model. While the former is a random loss model, the latter can model bursty losses. With each channel model, the performance of the simulated decentralized controller using wireless links is compared with the one using wired links providing instant and 100% reliable communications. The sensitivity of the controller to the burstiness of packet loss is also characterized in different process stages. The performance results indicate that wireless links with redundant bandwidth reservation can meet the requirements of the TE process model under normal operational conditions. When disturbances are introduced in the TE plant model, wireless packet loss during transitions between process stages need further protection in severely impaired links. Techniques such as re-transmission scheduling, multi-path routing and enhanced physical layer design are discussed and the latest industrial wireless protocols are compared.
Fault Detection in the Distillation Column ProcessISA Interchange
Chemical plants are complex large-scale systems which need designing robust fault detection schemes to ensure high product quality, reliability and safety under different operating conditions. The present paper is concerned with a feasibility study of the application of the black-box modeling method and Kullback Leibler divergence (KLD) to the fault detection in a distillation column process. A Nonlinear Auto-Regressive Moving Average with eXogenous input (NARMAX) polynomial model is firstly developed to estimate the nonlinear behavior of the plant. Furthermore, the KLD is applied to detect abnormal modes. The proposed FD method is implemented and validated experimentally using realistic faults of a distillation plant of laboratory scale. The experimental results clearly demonstrate the fact that proposed method is effective and gives early alarm to operators.
Neural Network-Based Actuator Fault Diagnosis for a Non-Linear Multi-Tank SystemISA Interchange
The paper is devoted to the problem of the robust actuator fault diagnosis of the dynamic non-linear systems. In the proposed method, it is assumed that the diagnosed system can be modelled by the recurrent neural network, which can be transformed into the linear parameter varying form. Such a system description allows developing the designing scheme of the robust unknown input observer within H1 framework for a class of non-linear systems. The proposed approach is designed in such a way that a prescribed disturbance attenuation level is achieved with respect to the actuator fault estimation error, while guaranteeing the convergence of the observer. The application of the robust unknown input observer enables actuator fault estimation, which allows applying the developed approach to the fault tolerant control tasks.
A KPI-based process monitoring and fault detection framework for large-scale ...ISA Interchange
Large-scale processes, consisting of multiple interconnected sub-processes, are commonly encountered in industrial systems, whose performance needs to be determined. A common approach to this problem is to use a key performance indicator (KPI)-based approach. However, the different KPI-based approaches are not developed with a coherent and consistent framework. Thus, this paper proposes a framework for KPI-based process monitoring and fault detection (PM-FD) for large-scale industrial processes, which considers the static and dynamic relationships between process and KPI variables. For the static case, a least squares-based approach is developed that provides an explicit link with least-squares regression, which gives better performance than partial least squares. For the dynamic case, using the kernel re- presentation of each sub-process, an instrument variable is used to reduce the dynamic case to the static case. This framework is applied to the TE benchmark process and the hot strip mill rolling process. The results show that the proposed method can detect faults better than previous methods.
An adaptive PID like controller using mix locally recurrent neural network fo...ISA Interchange
Being complex, non-linear and coupled system, the robotic manipulator cannot be effectively controlled using classical proportional integral derivative (PID) controller. To enhance the effectiveness of the conventional PID controller for the nonlinear and uncertain systems, gains of the PID controller should be conservatively tuned and should adapt to the process parameter variations. In this work, a mix locally recurrent neural network (MLRNN) architecture is investigated to mimic a conventional PID controller which consists of at most three hidden nodes which act as proportional, integral and derivative node. The gains of the mix locally recurrent neural network based PID (MLRNNPID) controller scheme are initi- alized with a newly developed cuckoo search algorithm (CSA) based optimization method rather than assuming randomly. A sequential learning based least square algorithm is then investigated for the on- line adaptation of the gains of MLRNNPID controller. The performance of the proposed controller scheme is tested against the plant parameters uncertainties and external disturbances for both links of the two link robotic manipulator with variable payload (TL-RMWVP). The stability of the proposed controller is analyzed using Lyapunov stability criteria. A performance comparison is carried out among MLRNNPID controller, CSA optimized NNPID (OPTNNPID) controller and CSA optimized conventional PID (OPTPID) controller in order to establish the effectiveness of the MLRNNPID controller.
A method to remove chattering alarms using median filtersISA Interchange
Chattering alarms are the most found nuisance alarms that will probably reduce the usability and result in a confidence crisis of alarm systems for industrial plants. This paper addresses the chattering alarm reduction using median filters. Two rules are formulated to design the window size of median filters. If the alarm probability is estimated using process data, one rule is based on the probability of alarms to satisfy some requirements on the false alarm rate, or missed alarm rate. If there are only historical alarm data available, the other rule is based on percentage reduction of chattering alarms using alarm duration distribution. Experimental results for industrial cases testify that the proposed method is effective.
Discover the innovative and creative projects that highlight my journey throu...dylandmeas
Discover the innovative and creative projects that highlight my journey through Full Sail University. Below, you’ll find a collection of my work showcasing my skills and expertise in digital marketing, event planning, and media production.
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2. 330 Beshahwired Ayalew, Bohdan T. Kulakowski / ISA Transactions 44 (2005) 329–343
3. Beshahwired Ayalew, Bohdan T. Kulakowski / ISA Transactions 44 (2005) 329–343 331
Fig. 1. Schematic of test system ͑HPϭhigh pressure, LPϭlow pressure͒.
supply and return lines are usually flexible hoses output stage. The servovalve is close coupled with
rated for the appropriate working pressure. a 10-kN, 102-mm-stroke symmetric actuator,
Aside from the extensive presentation by Vier- which is mounted on a load frame. Pressure trans-
sma ͓7͔, not much has been reported on the analy- ducers are used for sensing the pressures at the
sis of a hydraulic servosystem including supply four ports of the servovalve. A linear variable dif-
pressure variations at the servovalve. Viersma’s ferential transformer ͑LVDT͒ is mounted on the
analysis was done in the frequency domain and the actuator piston for position measurement.
emphasis was to provide design rules for the loca- Control and signal processing is done with a
tion and sizing of the components of hydraulic ser- dSpace® 1104 single processor board, which in-
vosystems. Yang and Tobler ͓10͔ developed a cludes onboard A/D and D/A converters and a
modal approximation technique that enables slave digital signal processor ͑DSP͒. An amplifier
analysis of fluid transmission lines in the time do- circuit converts a 0–10-V control output from the
main via state space formulations. Modal approxi- dSpace® D/A to a high-impedance Ϯ50-mA cur-
mation results provide modular and simpler alter- rent input to the torque motor coils of the servov-
natives to direct numerical time-domain solutions alve.
of the flow equations. The unit labeled hydraulic services manifold
In this paper, the authors present and use modal ͑HSM͒ is connected to the servovalve using 3.048-
approximation results within a model of an elec- m-long SAE-100R2 hoses. The hydraulic power
trohydraulic actuation system to investigate supply supply ͑HPS͒ unit, including its heat exchanger
and return pressure variations at the servovalve and drive units, is housed separately and is con-
due to transmission line dynamics. Open-loop and nected to the HSM via 3.048-m-long SAE-100R2
closed-loop tests were conducted to validate the hoses. The HSM provides basic line pressure regu-
model. The model was then used to make a quick lation via the accumulators. In addition, the HSM
evaluation of alternative layouts of the supply and is equipped with a control manifold circuitry to
return lines. permit selection of high- and low-pressure operat-
ing modes, low-pressure level adjustment, slow
2. Description of test system pressure turn-on and turn-off, and fast pressure un-
loading. The drain line provides a path for oil that
The hydraulic system shown schematically in seeps past the seals in the actuator and also for
Fig. 1 was designed for fatigue testing applica- draining oil from the HSM pressure gage.
tions. The servovalve is a 5-gpm ͑19 lpm͒ two- During a normal fatigue testing operation, both
stage servovalve employing a torque motor driven the low-pressure and high-pressure solenoids are
double nozzle-flapper first stage and a main spool energized, the main control valve is completely
4. 332 Beshahwired Ayalew, Bohdan T. Kulakowski / ISA Transactions 44 (2005) 329–343
Fig. 2. Simplified system.
wide open, and the circuitry of the HSM allows pressed from the pump output pressure. Therefore,
flow at full system pressure ͓11͔. We therefore in the following analysis, it is assumed that the
model the HSM by considering the lumped non- output pressure just after the accumulator and
linear resistance arising from change of flow di- pressure relief valve connection points in the HPS
rections, flow cross sections, as well as flow in the unit can be set as a known pressure input to the
filter element. The total pressure drop between the rest of the system. In fact, this is not a very restric-
pressure inlet and outlet ports of the HSM is given tive assumption, since the modeling approach pre-
in manufacturer specifications. The available data sented here is modular and models of the upstream
satisfy a nonlinear expression relating flow rate to components of the whole HPS unit can be incor-
pressure drop. While the HSM unit is rated for a porated if needed.
wide range of flow rate capacities, the rated flow For the simplified system, we now have two sec-
rate through the servovalve is within 10% of tions of transmission hoses to model. The first sec-
nominal flow rate of the HSM. We therefore use a tion is for the supply and return hoses between the
local linear approximation to account for losses in HPS and the HSM and the second is for the hoses
the HSM, between the HSM and the servovalve. A model
applicable for each section is discussed next.
⌬p HSM ϭR HSM q. ͑1͒
We further assume that the check valve is an 3. Model of transmission lines
ideal one, so that its own dynamics are fast enough
to be neglected and its backflow restriction has a To model the hydraulic hoses for our system, we
large enough parallel resistance that the permitted refer to previous rigorous results on validated so-
backflow is very small. We also consider the drain lutions of the mass and momentum conservation
flow to be negligible. With these simplifications, equations governing flow in one-dimensional fluid
the system reduces to the one shown in Fig. 2. It transmission lines having a circular cross section
should be noted that the resistances were lumped ͓5,6,8͔. In general, some assumptions are neces-
in the HSM excluding the gas-charged accumula- sary for the basic results to hold. These assump-
tors. tions include laminar flow in the lines, negligible
We make one more assumption before we pro- gravitational effects, negligible tangential velocity,
ceed. Through extensive frequency domain analy- and negligible variations of pressure and density
sis, Viersma ͓7͔ has shown that, provided that the in the radial and tangential directions. We also as-
accumulator and the pressure relief valve on the sume constant and uniform temperature and ignore
hydraulic power supply unit are located suffi- heat transfer effects in the fluid line. We thereby
ciently close to the pump outlet ͑within 0.3 m͒, the limit the discussion to the linear friction model,
pump flow pulsation frequencies can be sup- which does not include distributed viscosity and
5. Beshahwired Ayalew, Bohdan T. Kulakowski / ISA Transactions 44 (2005) 329–343 333
other input ͓12͔. Since we have already assumed
the pressure just after the connection point of the
pressure relief valve and first accumulator to be
taken as an input to the system, the desired causal
Fig. 3. A fluid transmission line. form of the four-pole equations for the supply line
is the so-called pressure-input/pressure-output
causality form ͓15͔. It can be derived by defining
the boundary conditions for the distributed param-
heat transfer effects ͓6,10͔. Corrections are applied eter model as the upstream pressure and flow rate
to account for the frequency dependence of vis- ( p u ,q d ) and the downstream pressure and flow
cosity on the linear friction model, following the rate ( p d ,q u ) at the opposite ends of the line,
work of Yang and Tobler ͓10͔.
The flow lines are assumed to have rigid walls
in some derivations ͓1,7͔. However, Blackburn et
al. ͓12͔ and McCloy and Martin ͓13͔ arrive at the
ͫ ͬ
P d͑ s ͒
Q u͑ s ͒
ͫ ͬ
same governing equations as the rigid wall case 1 Z c ͑ s ͒ sinh ⌫ ͑ s ͒
͑for a frictionless flow͒ by allowing for wall flex- Ϫ
cosh ⌫ ͑ s ͒ cosh ⌫ ͑ s ͒
ibility and defining an effective bulk modulus ϭ
combining the flexibility of the wall and that of sinh ⌫ ͑ s ͒ 1
the oil. Their definition of effective bulk modulus Z c ͑ s ͒ cosh ⌫ ͑ s ͒ cosh ⌫ ͑ s ͒
is the same as that derived by Merritt ͓4͔, where
the effective bulk modulus is viewed as a series
interconnection of the ‘‘stiffness’’ of the oil, of a
ͫ ͬ
P u͑ s ͒
ϫ Q s͒ .
d͑
͑2͒
container wall and even of entrapped air volume in
the oil. Following this approach, we consider flex- The definitions of the propagation operator ⌫ ( s )
ibility effects via the effective bulk modulus  e . and the line characteristic impedance Z c ( s ) de-
The model parameters required for any section of pend on the friction model chosen ͓6,9͔. In this
the transmission line reduce to the ones shown in paper, the authors use the approach of Yang and
Fig. 3. For the hydraulic hoses in this work, nomi- Tobler ͓10͔ that incorporated frequency-dependent
nal values of the bulk modulus were taken from damping and natural frequency modification fac-
Ref. ͓13͔. tors into analytically derived modal representa-
Using the above assumptions for the single tions of the four-pole equations for the linear fric-
transmission line, the conservation laws can be in- tion model. ⌫ ( s ) and Z c ( s ) are defined by
tegrated in the Laplace domain to yield a well-
known distributed parameter model commonly ex-
pressed as a two-port matrix equation and
⌫ ͑ s ͒ ϭD n
d 2s
4
ͱ ␣ 2ϩ
32␣
sd 2
, ͑3͒
sometimes known as the four-pole equation ͓1,7͔.
The four-pole equations can take four physically
realizable causal forms ͓6,9,12͔. Two of these four
are readily relevant to the problem at hand: one for
Z c ͑ s ͒ ϭZ 0 ͱ 32␣
sd 2
ϩ ␣ 2. ͑4͒
the supply line hoses and another one for the re-
turn line hoses. The third one also finds use with The frequency-dependent correction factors ␣
accumulator connection lines, as discussed by Ay- and  are obtained by comparing the modal un-
alew and Kulakowski ͓14͔. damped natural frequencies and damping coeffi-
Taking the supply line case first, we notice that cients of the modal approximations of the dissipa-
in most hydraulic servosystem applications, a con- tive ͑‘‘exact’’͒ model, which is described in detail
trol signal modulates the servovalve consumption in Ref. ͓16͔, against the modal representation of
flow rate downstream of the supply line, q d ( t ) , the linear friction model ͓10͔. Corrected kinematic
following the excursions of the ͑loaded͒ actuator viscosity ͑͒ values are used ͓8͔. The dimension-
piston. Then q d ( t ) is a preferred input to the trans- less numbers D n and Z 0 are the dissipation num-
mission line model, and a realizable causality form ber and the line impedance constant, respectively,
requires that either p u ( t ) or q u ( t ) should be the and are given by
6. 334 Beshahwired Ayalew, Bohdan T. Kulakowski / ISA Transactions 44 (2005) 329–343
ͫ ͬ
n
4l
D nϭ , ͑5͒ ͚ p di
cd 2
ͫ ͬ
pd
qu ϭ
iϭ1
n ϭ ͓ I 2 I 2 ¯I 2 ͔
4c iϭ1
͚ q ui
Z 0ϭ , ͑6͒
d2 ϫ͓ p d1 q u1 p d2 q u2 ¯p dn q un ͔ .
͑10͒
where c is the speed of sound in the oil,
It should be noted that the truncation to finite
number of modes will introduce steady-state er-
cϭ ͱ . e
͑7͒ rors. Some methods have been suggested to re-
cover the steady-state output based on the fact that
at steady state the original four-pole equation, Eq.
The three causal functions 1/cosh ⌫(s), ͑2͒, reduces to
Z c ( s ) sinh ⌫(s)/cosh ⌫(s), and sinh ⌫(s)/
Zc(s)cosh ⌫(s) can be represented as infinite sums
of quadratic modal transfer functions. The goal is ͫ ͬ ͫ
pd
qu ss
ϭ
1
0
Ϫ8D n p u
1 qd ͬͫ ͬ ss
. ͑11͒
to use a finite number of modes to approximate the
otherwise infinite sum of the modal contributions Hsue and Hullender ͓16͔ discussed rescaling the
for the outputs. Of particular interest for the time truncated sum of the modal approximation for the
domain models sought in this paper is the state dissipative model by its zero-frequency magnitude
space formulation ͓10,15͔, to bring about Eq. ͑11͒. Van Schothorst ͓9͔ and
Hullender et al. ͓15͔ described an additive ap-
ͫ ͬͫ ͬ
0 ͑ Ϫ1 ͒ iϩ1 Z 0 ci proach where the steady-state error is eliminated
ͫ ͬ
˙ di
p
q ui ϭ Ϫ
˙ ͑ Ϫ1 ͒ iϩ1 ci
2
Ϫ 2
32 
p di
q ui
by adding a corrective feed-through term on the
output equation ͑10͒. However, the transfer func-
tions so implemented will no longer be strictly
Z 0␣ d ␣
ͫ ͬ
proper. This may entail the need for off-line alge-
8Z0 braic manipulations when the transmission line is
0 Ϫ connected to static source and/or load linear resis-
ϩ
8
d 2D n
ͫ ͬ
pu
qd ,
tances or other transmission line models with their
own direct feed-through gains. The eigenvalues of
0 the coupled system may then be altered by the
d 2Z 0D n␣ 2 steady-state correction ͓15͔.
Yang and Tobler ͓10͔ introduced methods that
iϭ1,2,3...n. ͑8͒ modify the input-matrix or use a state similarity
transformation matrix to affect the steady-state
The ci are the modal undamped natural frequen- correction while preserving the modal eigenvalues
cies of blocked line for the linear friction model of the truncated model. Since comparable results
given by are obtained by the use of either method, we adopt
the input-matrix modification method here. Sup-
ͩ ͪ
pose matrices A i and B i represent, respectively,
1
4 iϪ the feedback and input matrices in the modal state
2 space Eq. ͑8͒. Introducing the input-matrix modi-
ci ϭ , iϭ1,2,3,...n. ͑9͒
d 2D n fier G,
The modification factors ␣ and  are given as
functions of the dimensionless modal frequencies
ͫ ͬ ͫ ͬ
˙
p di
q
p di pu
˙ ui ϭA i q ui ϩB i G q d . ͫ ͬ ͑12͒
d 2 ci /4 ͓10͔. The output is the sum of the modal The steady-state value of the n-mode approxima-
contributions and is expressed as tion is then
7. Beshahwired Ayalew, Bohdan T. Kulakowski / ISA Transactions 44 (2005) 329–343 335
ͫ ͬ ͫ ͬ ͫ ͬ
n n
pd p di pu
qu ϭ͚ q ui ϭϪ ͚ ͑ A Ϫ1 B i ͒ G q
i .
ss iϭ1 ss iϭ1 d ss
͑13͒
Comparing with the desired steady-state value
given by Eq. ͑11͒ and solving for G,
GϭϪ ͚ͩ n
iϭ1
A Ϫ1 B i
i ͪͫ
Ϫ1
1
0
Ϫ8Z 0 D n
1
ͬ . ͑14͒
The number of modes n to be chosen depends on
the frequency range of interest for the application.
Similarly, for the return line from the servo-
valve, we can define the flow rate at the servov-
alve end and the pressure at the downstream ͑to-
ward the tank͒ end as inputs to the model of the
return line based on the other four-pole equation
of causality dual to Eq. ͑2͒ ͓6͔. Equally, we can
use the observation that switching the sign con-
vention of the flow direction for just the return line
and using the four-pole equation dual to Eq. ͑2͒
yields the same set of four-pole equations as Eq. Fig. 4. Piston accumulator.
͑2͒, provided the inputs to the model remain flow
rate toward the servovalve end and pressure at the
other end. This fact can easily be shown math- plied after initial transients have died down. In
ematically, but we omit it here for brevity and general ‘‘steady’’ simulations, like those involving
state that for the return line model all of the deri- sinusoidal fatigue test wave forms, the modal ini-
vations presented above for modeling the supply tial conditions of the interconnected system are
line hold. The caveat is to exercise care in using less important.
the proper signs for the input and output flow rates As shown in Fig. 3, the model described in this
at both ends of the return line when forming inter- section requires few parameters to set up and
connections with other system components. simulate each transmission line section using lin-
For step response simulations, it is desirable to ear state space models in the time domain. This is
have good estimates of the initial conditions of the particularly more convenient than finite difference
modal states, especially when the interconnected approaches, which may require rigorous descreti-
system model contains nonlinearities. Usually, for zation methods.
a single pipeline section, the derivative of the
modal output can be assumed to be zero just be-
fore the application of the step change in the input, 4. Modeling accumulators
and modal initial conditions can be computed
from For the nitrogen gas-charged accumulators,
which are of piston type for our system ͑Fig. 4͒,
ͫ p di ͑ 0 Ϫ ͒
q ui ͑ 0 Ϫ ͒ͬ i ͫ
p u͑ 0 Ϫ ͒
ϭϪA Ϫ1 B i G q 0 Ϫ ͒ ,
d͑
ͬ ͑15͒
we assume that the piston mass and seal friction
are negligible. Under this assumption, the gas
pressure and the oil pressure are equal. We also
where the ͓ p u ( 0 Ϫ ) ,q d ( 0 Ϫ ) ͔ T are the inputs just neglect the compressibility of the oil volume in
before the step change. For an interconnected the accumulator compared to the compressibility
pipeline system, the inputs to one pipeline section of the gas. Furthermore, we consider the gas to
may be outputs of another section, in which case undergo a polytropic expansion and compression
the determination of proper initial values for the process with polytropic exponent m.
modal states of each section can be done by trial
and error. The step disturbances can also be ap- p g V m ϭconst.
g ͑16͒
8. 336 Beshahwired Ayalew, Bohdan T. Kulakowski / ISA Transactions 44 (2005) 329–343
Fig. 5. Model interconnections for the supply line ͑Version I͒.
The exponent m approaches 1 for a slow ͑nearly can be estimated as the HSM pressure minus the
isothermal͒ process and the specific heat ratio of pressure drop in the connection lines.
the gas for a rapid ͑adiabatic͒ process on an ideal
gas. However, it should be noted that if heat trans-
fer effects were to be included, then real gas equa- 5. Model interconnections for the supply line
tions of state should be used together with appro-
priate energy conservation laws. For the work The components on the supply line of the sim-
presented here, the present model was found to be plified model shown in Fig. 2 can be intercon-
sufficiently accurate. nected as shown in Figs. 5 or 6. The arrows indi-
Given initial gas pressure p g0 and gas volume, cate the input-output causality assigned for each
V g0 , the gas pressure is computed from Eq. ͑16͒, subsystem. Each of the blocks section I and sec-
which is equivalent to tion II implement Eqs. ͑8͒–͑14͒ for the corre-
sponding sections of the supply line.
mpg Integration causality is the desired form for the
˙
p gϭ qa , p g ͑ 0 ͒ ϭp g0 , ͑17͒ model of the accumulator, which is given by Eq.
V g0 Ϫ ͐ t0 q a dt ͑17͒. It was pointed out by Viersma ͓7͔ that the
where q a is the flow rate of the hydraulic oil to the flow dynamics in the short branch-away connec-
accumulator. For simulations involving distur- tion lines to the accumulators are significant in
bances applied at the servovalve, it is reasonable most cases. Under the linear resistance assumption
to assume that the accumulator already develops given by Eq. ͑1͒, the subsystem ‘‘manifold and
an initial gas pressure through a slow isothermal check valve loss’’ can be configured either as a
process1 ( mϭ1 ) . The initial gas volume V g0 can pressure-input/flow rate-output subsystem ͑in ver-
be estimated by applying Eq. ͑16͒ between the sion I, Fig. 5͒ or as a pressure-input/pressure-
pre-charge state ͑the gas pre-charge pressure at ac- output subsystem ͑in version II, Fig. 6͒. As a con-
cumulator capacity͒ and the initial state at the on- sequence, the model of the short accumulator
set of the disturbance. The initial gas pressure p g0 connection line changes between version I and
version II. The model of the short connection line
1 in version I has the same structure as the one de-
The present system has an additional slow turn-on/turn-
off accumulator that enables the HSM to come to full sys-
scribed above for the sections of the main supply
tem pressure from an off state in a slow and controlled line. The model for the short connection line in
manner. The servovalve disturbances considered in this version II is derived using the modal approxima-
study are applied after the whole system has reached nor- tion for the relevant four-pole equations with
mal operating conditions. ( p u ,p d ) as input and ( q u ,q d ) as output, as de-
9. Beshahwired Ayalew, Bohdan T. Kulakowski / ISA Transactions 44 (2005) 329–343 337
Fig. 6. Model interconnections for the supply line ͑Version II͒.
scribed by Ayalew and Kulakowski ͓14͔. It was 6. Model for servovalve and actuator
shown there that the dynamics of the short connec-
tion line can be approximated by a first-order term Physical models of electrohydraulic servoactua-
that reduces to a series interconnection of hydrau- tors are quite widely available in the literature
lic resistance and inertance. This result goes along ͓1– 4,7,9,17͔. The model presented here is adapted
with the convenient assumption that the oil side to apply to a four-way servovalve close coupled
compressibility in the accumulator is negligible with a double-ended piston actuator.
compared to that of the gas side. This result also Fig. 7 shows a double-ended translational piston
makes version II preferable to version I, since it actuator with hydraulic flow rates q t from the top
reduces the order of the overall system and verifies chamber and q b to the bottom chamber of the cyl-
a physically supported model order reduction. inder. Leakage flow between the two chambers is
The model for the return line is developed in a either internal ( q i ) between the two chambers or
similar way noting the reverse direction of the external from the top chamber ( q e,t ) and from the
flow, as mentioned earlier. It should be noted that bottom chamber ( q e,b ) . A t and A b represent the
the modularity of the subsystem model intercon- effective piston areas of the top and bottom face,
nections allows changes to be made to the system respectively. V t and V b are the volumes of oil in
model with ease. the top and bottom chamber of the cylinder, re-
spectively, corresponding to the center position
( x p ϭ0 ) of the piston. These volumes are also
considered to include the respective volumes of oil
in the pipelines between the close-coupled servo-
valve and actuator as well as the small volumes in
the servovalve itself.
We assume that the pressure dynamics in the
lines between the servovalve and the actuator are
negligible due to the close coupling.2 Furthermore,
even for a long-stroke actuator used in a flight
simulator application, Van Schothorst ͓9͔ has
2
This is to say that any resonances introduced by the
short-length lines are well above the frequency range of
interest for our system. In fact, this can be verified using
the model development presented earlier or referring to the
Fig. 7. Schematic of a rectilinear actuator and servovalve. results of Van Schothorst ͓9͔.
10. 338 Beshahwired Ayalew, Bohdan T. Kulakowski / ISA Transactions 44 (2005) 329–343
shown that the pressure dynamics in the actuator
chambers need not be modeled using distributed
parameter models. It is therefore assumed that the
pressure is uniform in each cylinder chamber and
is the same as the pressure at the respective port of
the servovalve.
Starting with the continuity equation and intro-
ducing the state equation with the effective bulk
modulus for the cylinder chambers, it can be Fig. 8. Actuator with a simple load model.
shown that the pressure dynamics are given by
͑see, for example Ref. ͓2͔͒
dpb c
ϭ ˙
͑ q ϪA b x p ϩq i Ϫq e,b ͒ , K v ,i ϭc d,i w i ͱ2/ , iϭ1,2,3,4. ͑20͒
dt V b ϩA b x p b
͑17a͒ These coefficients could be computed from data
for the discharge coefficient c d,i , port widths w i ,
dpt c and oil density . If we assume that all orifices are
ϭ ˙
͑ Ϫq t ϩA t x p Ϫq i Ϫq e,t ͒ .
dt V t ϪA t x p identical with the same coefficient K v , then the
͑17b͒ value of K v can also be estimated from manufac-
turer data for the rated valve pressure drop ( ⌬p N ) ,
These equations show that the hydraulic capaci- rated flow ( Q N ) , and maximum valve stroke
tance, and hence the pressure evolution in the two ( x v max) using the following equation ͓1,4͔:
chambers, depends on the piston position. The
leakage flows q i , q e,b , and q e,t are considered QN
negligible. K v ,i ϭK v ϭ , iϭ1,2,3,4.
The predominantly turbulent flows through the x v maxͱ1/2⌬p N
sharp-edged control orifices of a spool valve, to ͑21͒
and from the two sides of the cylinder chambers, As an approximation of the servovalve spool dy-
are modeled by nonlinear expressions ͓1,2,4͔. As- namics, a second-order transfer function or
suming positive flow directions as shown in Fig. equivalently a second-order state space was ex-
7, we have tracted from manufacturer specifications,
q b ϭK v ,1sg ͑ x v ϩu 1 ͒ sgn͑ p S Ϫp b ͒ ͱ͉ p S Ϫp b ͉ X v͑ s ͒ G v 2 v
n,
ϭ . ͑22͒
ϪK v ,2sg ͑ Ϫx v ϩu 2 ͒ sgn͑ p b Ϫp R ͒ ͱ͉ p b Ϫp R ͉ , I v ͑ s ͒ s 2 ϩ2 v n, v sϩ 2
n, v
͑18a͒ The state equations governing piston motion are
derived considering the loading model for the ac-
q t ϭK v ,3sg ͑ x v ϩu 3 ͒ sgn͑ p t Ϫp R ͒ ͱ͉ p t Ϫp R ͉ tuator. For the test system, the actuator cylinder is
rigidly mounted on a load frame, which we use as
ϪK v ,4sg ͑ Ϫx v ϩu 4 ͒ sgn͑ p S Ϫp t ͒ ͱ͉ p S Ϫp t ͉ , an inertial frame as shown in Fig. 8.
͑18b͒ The upward force on the actuator piston due to
the oil pressure in the two cylinder chambers is
where the sg ( x ) function is defined by given by
sg ͑ x ͒ ϭ ͭ x, xу0
0, xϽ0
. ͑19͒
F p ϭA b p b ϪA t p t .
The friction force on the piston in the cylinder is
͑23͒
denoted by F f and the external loading including
The parameters u 1 , u 2 , u 3 , u 4 are included to specimen damping and stiffness forces are lumped
account for valve spool lap conditions as shown in together in F ext . The equations of motion are eas-
Fig. 7. Negative values represent overlap while ily derived by applying Newton’s second law:
positive values represent underlap. The valve co-
efficients K v ,i are given by ˙
x pϭ v p , ͑24͒
11. Beshahwired Ayalew, Bohdan T. Kulakowski / ISA Transactions 44 (2005) 329–343 339
1
˙
v pϭ ͓ A p ϪA t p t ϪF ext ϪF f Ϫm p g ͔ .
mp b b
͑25͒
Eqs. ͑17a͒, ͑17b͒, ͑24͒, and ͑25͒ with q b and q t
given by Eqs. ͑18a͒ and ͑18b͒ constitute the state
space model for the servovalve and loaded actua-
tor subsystem under consideration. These equa-
tions also contain the major nonlinearities in the
system: the variable capacitance and the square
root flow rate versus pressure drop relations. Non-
linearity is also introduced in Eq. ͑25͒ by the non-
linear friction force, which includes Coulomb,
static, and viscous components ͓1,18͔ as discussed
next.
Fig. 9. Piston friction force.
7. Modeling and identification of friction
behavior of friction. For simplicity, we use the
Friction affects the dynamics of the electrohy- common memory-less analytical model of friction
draulic servovalve as well as the dynamics of the ͑without hysteresis͒ as a function of velocity,
actuator piston. Friction in the servovalve is gen- given by Eq. ͑26͒ and included in Fig. 9,
erally considered to be of Coulomb type acting on
˙
the spool of the valve and can in practice be suf- F f ϭF Ϯ x p ϩsgn͑ x p ͒͑ F Ϯ ϩ ͑ F s ϪF Ϯ ͒ e ͑ x p /C s ͒ ͒ .
v
˙ ˙ c
Ϯ
c
ficiently eliminated by using dither signals ͓9͔. ͑26͒
The particular friction effect of interest in this sec-
The asymmetry of the friction force with respect
tion is the model of the frictional forces that ap-
to the sign of the velocity observed in the mea-
pear in the equations of motion of the actuator
sured data is taken into account by taking different
piston. The literature offers various empirical
coefficients in Eq. ͑26͒ for the up and down mo-
models applied to specific hydraulic actuators
tions. The strong scatter in the estimation data is
͓1,3,18,19͔. In the most general case, friction in
typical of friction phenomena.
the actuator cylinder is considered to be a function
of the position and velocity of the piston, the
chamber pressures ͑the differential pressures when 8. Experimental validation of the model
the piston is sticking near zero velocity͒, the local
oil temperature and also running time. The model described in the previous sections
In this study, open-loop and closed-loop tests was implemented in MATLAB/SIMULINK, and base-
were performed to identify the friction force on line open-loop and closed-loop experiments were
the actuator piston by assuming it to be a function conducted to validate it. In these experiments, a
of velocity. Open-loop tests involved changing the simple load mass is rigidly attached to the piston
set current input to the servovalve while measur- rod. For the models of each of the sections of the
ing the steady-state piston velocity and cylinder supply and return line hoses, only six modes are
chamber pressure responses. The system behaves retained in the modal approximation. This was de-
as a velocity source in the open loop. The closed- cided considering the actuator hydraulic natural
loop test involved tracking a 2-Hz 35-mm sine frequency of 172 Hz computed using formulas
wave piston position command under P control from linear models ͑see Merritt ͓4͔͒ and selecting
while measuring acceleration, velocity, and cham- the natural frequency of the highest mode of the
ber pressures. In both the open-loop and closed- approximation for each section to be close to twice
loop tests, the friction is then estimated using this value. From manufacturer frequency response
Newton’s second law. Fig. 9 shows the result of data for the servovalve, the natural frequency for
multiple open-loop tests and a closed-loop test. the servovalve was estimated to be 140 Hz with a
The closed-loop test clearly shows the hysteretic damping ratio of 1.
12. 340 Beshahwired Ayalew, Bohdan T. Kulakowski / ISA Transactions 44 (2005) 329–343
Fig. 10. Supply and return pressure following a step change Fig. 11. Open-loop cylinder chamber pressure responses.
in servovalve current.
namics introduced by the long sections of hoses
are reflected in the individual cylinder chamber
To measure the supply and return pressure fluc- pressures.
tuation, pressure transducers were mounted on the In the open-loop piston velocity response shown
supply and return ports at the servovalve and a in Fig. 12, the velocity signal was obtained by
50-mA rated step current was supplied to the ser- low-pass filtering and differentiating the LVDT
vovalve in the open-loop. Fig. 10 shows a com- position signal. The figure shows that the model
parison of the supply and return pressure from does a fairly good job of predicting the piston ve-
measurement and simulation. Two observations locity response as well. The differences are again
can be made from this figure. First, the supply and attributed to uncertainties in the servovalve model
return pressure fluctuations contain the fundamen- and also errors in friction estimation, which has a
tal periods of 25 and 32 ms, respectively. These considerable scatter, as shown in Fig. 9.
correspond to fundamental frequencies of about 40
and 31 Hz, respectively. The implication of these 9. Predicting system performance
fluctuations is that the bandwidth of the actuator is
limited by the dynamics of the supply and return It should be recalled that, for the present system,
hoses, since the other dynamic elements including the fundamental frequencies of oscillation of the
the servovalve and the actuator have higher corner
frequencies. Second, the model follows the mea-
surement well. In particular, the frequency con-
tents match nicely. The discrepancies can be at-
tributed to errors in the estimation of effective
bulk moduli for the different hose sections, and
the estimation of manifold pressure drops as well
as unknown but estimated parameters in the
adopted simplified model of the servovalve.
The open-loop response of the system can be
investigated further by looking at the cylinder
chamber pressures shown in Fig. 11 and the piston
velocity response shown in Fig. 12 following the
same step-rated current input to the servovalve. It
can be seen from Fig. 11 that the simulation pre-
dictions of chamber pressures follow the measure-
ments and that the supply and return pressure dy- Fig. 12. Open-loop piston velocity response.
13. Beshahwired Ayalew, Bohdan T. Kulakowski / ISA Transactions 44 (2005) 329–343 341
Table 1
Summary of step response simulation results.
Fundamental fre-
quency of oscillation Peak amplitude of
in oscillation
step response ͑Hz͒ ͑Mpa͒
Lengths of
sections II Supply Return Supply Return
͑m͒ pressure pressure pressure pressure
3.048 40 31 1 0.94
2.286 49 39 0.97 0.91
1.524 76 57 0.94 0.88
0.7512 147 115 0.87 0.71
0 N/A N/A 0.0 0.0
Fig. 13. Supply and return pressures with 1.524-m-long
lines. return line. The settling times are reduced by
about 20 ms or about 22% compared to the origi-
nal setup with 3.048 m lengths of sections II of the
supply and return line pressures are lower than the supply and return line hoses. The peak amplitude
natural frequencies of both the actuator and the of the oscillation is also slightly reduced, as shown
servovalve. This implies that the bandwidth of the in Table 1. The bandwidth of the hydraulic actua-
test system is limited by supply and return line tor can therefore be expected to be improved ac-
dynamics. The model described in this paper was cordingly. However, the accumulators were not
used to predict pressure fluctuations in the supply shown to be effective in filtering the fluctuations
and return lines by running simulations for con- completely.
templated modifications to the layout of the test As a second case, the sections II of the hoses are
system. In particular, it was desired to see if re- considered to be removed from the system and by
ducing the lengths of sections II of both the supply so doing the HSM is close-coupled with the actua-
and return hoses in the layout ͑Fig. 2͒ produces tor. This consideration would need significant
significant changes in the supply and return line changes to the physical design of the load frame to
pressure dynamics at the servovalve. The lengths allow the HSM to be mounted on it together with
of sections I were kept unchanged since the physi- the actuator. In the model, the corresponding sub-
cal constraints of housing the HPS required about
3.048 m of hose lengths for sections I of both the
supply and return lines. The goal of the study was
to see if actually there will be significant gains
from these measures in terms of increasing the ef-
fective bandwidth for the actuator.
As a first case, the hoses of sections II were
reduced to half the original length of 3.048 m. A
length of 1.524 m was considered sufficient to still
place the HSM unit on the ground while the ac-
tuator was mounted on the load frame. Fig. 13
shows the supply and return line pressures at the
servovalve following the open-loop test described
previously with the lengths now at 1.524 m.
It can be seen from Fig. 13 that the fundamental
period of pressure fluctuation shifts to 13.3 and
18.5 ms, respectively, for the supply and return
lines. These correspond to fundamental frequen- Fig. 14. Supply and return pressures with close-coupled
cies of 75 Hz on the supply line and 54 Hz on the HSM and shorter lines.
14. 342 Beshahwired Ayalew, Bohdan T. Kulakowski / ISA Transactions 44 (2005) 329–343
system of section II was removed from the sche- without ignoring supply and return line pressure
matic in Fig. 6. Fig. 14 shows simulation results variations introduced by transmission line dynam-
for this case as well as a hypothetical case for ics.
which the hoses are shortened further to 0.7512 m. 3. The model of the overall hydraulic system
It can be seen that the effect of the accumulators in was modular. Subsystem models can easily be
filtering out the dynamics of the sections I from changed for desired emphasis observing only the
the supply and return lines is particularly evident input-output causality. For example, a detailed
in the close-coupled HSM case. In addition, the model of the servovalve can be used in place of
steady-state pressure drops in the supply and re- the simplified model used in this paper, thereby
turn line are smaller in this case compared to the improving the predictive power of the overall
original setup ͑Fig. 10͒ and to the case with model.
1.524-m lengths for sections II ͑Fig. 13͒. The im- Simulation results for some open-loop step re-
provements predicted by the case of lengths 1.524 sponses were compared against experimental re-
and 0.7512 m seem rather small compared to the sults for the test system. It is felt that the model
case of close coupling the HSM with the actuator. performs well, given the minimal amount of infor-
Table 1 summarizes these results, including one mation it uses to enable a time domain simulation.
more additional length for sections II. It can be The use of constant bulk modulus values for the
seen that the peak amplitudes of the supply and hose material, which in reality depends on pres-
return pressure oscillations are progressively re- sure and frequency, may explain some of the dif-
duced as the length of the hoses becomes shorter ference between the simulation and measurement.
while the fundamental frequency of the oscilla- A more detailed servovalve model with measured
tions for the step responses becomes larger. In the operating characteristics, instead of the rated
limit case of 0-m length for sections II, which specifications, could also improve the accuracy of
means the HSM accumulators are close coupled the overall electrohydraulic system model pre-
with the servovalve, the oscillations are elimi- sented here.
nated. In this case, the accumulators effectively A simulation analysis of the effects of the
suppress the oscillations arising out of the sections lengths of sections of the supply and return lines
I of the supply and return line hoses. between the HSM accumulators and the servo-
valve was done. It was concluded that reducing
10. Conclusions the lengths of these lines progressively reduces the
supply and return pressure fluctuation at the servo-
In this paper, a model of an electrohydraulic ac- valve during dynamic excursions by the actuator.
tuator system focusing on supply and return line The test system bandwidth was correspondingly
dynamics was presented. A model of hydraulic improved. The best scenario was shown to be one
transmission lines based on modal approximation where the accumulators were close coupled with
techniques was adopted yielding state space de- the servovalve, thereby employing the accumula-
scriptions suitable for time domain simulations. tors effectively in filtering out the effects of the
The interconnection model of the electrohydraulic sections of the supply and return lines between the
system developed here is an attractive simulation pump ͑HPS͒ and the accumulators.
tool for the following reasons. In conclusion, it is recommended that hydraulic
1. The distributed parameter transmission line control system design and analysis include the
model requires only aggregate line parameters modeling approach presented here, to account for
such as line length, diameter, and effective bulk the effects of supply and return line dynamics
modulus in state space dynamic models. It there- rather than assuming constant values for the sup-
fore enables a quick investigation of line effects in ply and return pressure as has been usually done in
a time domain analysis. It was used here to model the literature. It was also demonstrated that the
hydraulic hoses with experimental validation. approach could be used to make a quick assess-
2. The time domain simulation, in turn, makes ment of alternative layouts for supply and return
it possible to include nonlinear actuator models. lines in terms of minimizing transmission line dy-
This is particularly useful for the study of actuator namics. The method can easily be adopted to other
models with linear and nonlinear control systems applications of hydraulic machinery and test sys-
15. Beshahwired Ayalew, Bohdan T. Kulakowski / ISA Transactions 44 (2005) 329–343 343
tems where hydraulic oil supply and return lines of domain simulation of fluid transmission lines using
significant length are involved. minimum order state variable models. Fluid Transmis-
sion Line Dynamics. ASME special publication, 1983,
pp. 78 –97.
References ͓16͔ Hsue, C. Y.-Y. and Hullender, D. A., Modal approxi-
mations for the fluid dynamics of hydraulic and pneu-
͓1͔ Jelali, M. and Kroll, A., Hydraulic Servo-systems:
Modelling, Identification and Control ͑Advances in In- matic transmission lines, Fluid Transmission Line Dy-
dustrial Control͒. Springer-Verlag, London, 2003. namics, edited by M. E. Franke and T. M. Drzewiecki.
͓2͔ Kugi, A., Non-linear Control Based on Physical Mod- ASME special publication, 1983, pp. 51–77.
els, Lecture Notes in Control and Information Sci- ͓17͔ Dransfield, P., Hydraulic Control Systems: Design and
ences No. 260. Springer-Verlag, London, 2001. Analysis of their Dynamics, Springer-Verlag, Berlin,
͓3͔ Sohl, G. A. and Bobrow, J. E., Experiments and Simu- 1981.
lations on the Nonlinear Control of a Hydraulic Ser- ͓18͔ Alleyne, A. and Liu, R., A simplified approach to force
vosystem. IEEE Trans. Control Syst. Technol. 7͑2͒, control for electro-hydraulic systems. Control Eng.
238 –247 ͑1999͒. Pract. 8, 1347–1356 ͑2000͒.
͓4͔ Merritt, Herbert E., Hydraulic Control Systems. Wiley, ͓19͔ Manhartsgruber, B., Singular perturbation analysis of
New York, 1967. an electrohydraulic servo-drive with discontinuous re-
͓5͔ D’Souza, A. F. and Oldenburger, R., Dynamic re- duced dynamics. Proceedings of the 1999 ASME De-
sponse of fluid lines. J. Basic Eng. 86͑3͒, 589–598 sign Engineering Technical Conference, Las Vegas,
͑1964͒. Nevada, 1999, pp. 2001–2011.
͓6͔ Goodson, R. E. and Leonard, R. G., A survey of mod-
eling techniques for fluid line transients. J. Basic Eng.
94͑2͒, 474 – 482 ͑1972͒.
͓7͔ Viersma, T. J., Analysis, Synthesis and Design of Hy- Beshahwired Ayalew was
draulic Servosystems and Pipelines, Studies in Me- born in Goba, Ethiopia in
chanical Engineering I. Elsevier Publishing Co., Am- 1975. He earned his BS degree
in mechanical engineering
sterdam, the Netherlands, 1980. from Addis Ababa University,
͓8͔ Woods, R. L., Hsu, C. H., and Chung, C. H., Compari- Ethiopia and his MS degree,
son of theoretical and experimental fluid line re- also in mechanical engineer-
sponses with source and load impedance. Fluid Trans- ing, from the Pennsylvania
mission Line Dynamics, edited by M. E. Franke and T. State University, USA. He is
M. Drzewiecki. ASME Special Publications, New currently a Ph.D. candidate in
mechanical engineering at the
York, 1983, pp. 1–36. Pennsylvania State University.
͓9͔ Van Schothorst, G., Modeling of Long-Stroke Hydrau- His research interests include
lic Servo-Systems for Flight Simulator Motion Control dynamic systems and control,
and System Design. Ph.D. thesis, Delft University of energy systems, mechanical design, and vehicle dynamics.
Technology, Delft, The Netherlands 1997.
͓10͔ Yang, W. C. and Tobler, W. E., Dissipative modal ap-
proximation of fluid transmission lines using linear Bohdan T. Kulakowski ob-
friction model. J. Dyn. Syst., Meas., Control 113, tained his Ph.D. from the Pol-
152–162 ͑March 1991͒. ish Academy of Sciences in
͓11͔ MTS Corporation, Hardware Product Manual, 290.1X, 1972. He has been with Penn
290.2X, and 290.3X Hydraulic Service Manifold, State University since 1979,
where he is currently a profes-
1985. sor of mechanical engineering.
͓12͔ Blackburn, J. F., Reethof, G., and Shearer, J. L., Fluid Dr. Kulakowski teaches under-
Power Control. MIT Press, Cambridge, MA, 1960. graduate and graduate courses
͓13͔ McCloy, D. and Martin, H. R., Control of Fluid on engineering measurements,
Power: Analysis and Design, second edition. Halsted system dynamics, and controls.
Press, Chichester, UK, 1980. He is a co-author of the book
‘‘Dynamic Modeling and Con-
͓14͔ Ayalew, B. and Kulakowski, B. T., Transactions of the trol of Engineering Systems.’’
ASME, Journal of Dynamic Systems, Measurement Dr. Kulakowski is a Fellow of ASME. His research interests are in
and Control ͑in press͒. vehicle testing, vehicle dynamics, and vehicle interaction with envi-
͓15͔ Hullender, D. A., Woods, R. L., and Hsu, C.-H., Time ronment.