1) High vibration was detected in the structure of a large boiler and associated buildings, which was traced to resonance with nearby coal mills operating at 7.8Hz.
2) Attempts to balance the mills were not practical, so dynamic vibration absorbers were designed and installed to tune the structure to a different frequency range, successfully reducing the vibration.
3) Future plant designs incorporated vibration isolating foundations for each mill to prevent structural resonance from occurring.
Design of Variable Stiffness and Variable Damping Vibration Absorberijsrd.com
The vibration absorbers are frequently used to control and to minimize excess vibration in structural systems. To reduce the vibration of the main system or machine, the frequency of absorber should be equal to the excitation frequency. This result in subcomponent of total structure adding large input impedance to the primary structure, thus 'absorbing' the internal energy transferred to form primary structure. The aim of this work is to design the tunable vibration absorber (TDVA) for vibration control of primary beam system using finite element method through an Ansys Programming. Its stiffness can be varied to adapt the changes in excitation frequencies. Traditional means of vibration control have involved the use of passive and active methods. This study involves the design of variable stiffness vibration absorber by incorporating the use of lead screw for varying the stiffness of secondary system. Finite element analysis is done for the dynamic vibration absorber. FEA code is generated using Mat lab software to find numerical performance of beam structure with dynamic vibration absorber. The proposed absorber is suitable for vibration isolation of beam structure with uniform cross-section and facilitates vibration attenuation at variable excitation frequencies.
seminar related to chemical kinetics course in Master degree in Physical Chemistry In connection with shock waves in shock tubes From experimental methods.
The document outlines the user ordering process for a mobile app. It shows that customers can log into an existing account or register as new. If login is successful, they can choose a gift, fill out a questionnaire, and the platform will match their answers to suggested gifts from a database. Customers are then redirected to suppliers' websites to order, pay for, and receive the gift. Suppliers receive the order, wrap and send the gift, and get paid upon receipt of payment.
This document appears to be an assignment for an introduction to business class, submitted by student Qaimat karim with registration ID A1BM113020 and teacher Waqar Ahmad. The document covers topics related to the multinational consumer goods company Unilever including its history, vision, mission, strategies and goals, nature of work, geographical expansion, products, future planning, infrastructure, and HR structure.
Beebe - Balancing by timed oscillation (AUS)Ray Beebe
This document discusses methods for balancing rotating machinery using a mobile phone stopwatch to time oscillations. The Timed Oscillation Method involves attaching a swing mass to the rotor and using a phone stopwatch to time oscillations. Times are plotted against position and the maximum/minimum times are used to calculate an imbalance correction mass. This method was successfully used to balance pump impellers and fans. The document also discusses trial and error balancing without instrumentation by drilling holes in positions that cause rotor oscillations to vary.
Sustainable Production Design InstitutePhoebe Hewson
For my thesis I developed a Sustainable Production Design Institute in West Hollywood
Students learn to create sets while keeping the environment in mind.
Take a look at this institute and let me know what you think!
Design of Variable Stiffness and Variable Damping Vibration Absorberijsrd.com
The vibration absorbers are frequently used to control and to minimize excess vibration in structural systems. To reduce the vibration of the main system or machine, the frequency of absorber should be equal to the excitation frequency. This result in subcomponent of total structure adding large input impedance to the primary structure, thus 'absorbing' the internal energy transferred to form primary structure. The aim of this work is to design the tunable vibration absorber (TDVA) for vibration control of primary beam system using finite element method through an Ansys Programming. Its stiffness can be varied to adapt the changes in excitation frequencies. Traditional means of vibration control have involved the use of passive and active methods. This study involves the design of variable stiffness vibration absorber by incorporating the use of lead screw for varying the stiffness of secondary system. Finite element analysis is done for the dynamic vibration absorber. FEA code is generated using Mat lab software to find numerical performance of beam structure with dynamic vibration absorber. The proposed absorber is suitable for vibration isolation of beam structure with uniform cross-section and facilitates vibration attenuation at variable excitation frequencies.
seminar related to chemical kinetics course in Master degree in Physical Chemistry In connection with shock waves in shock tubes From experimental methods.
The document outlines the user ordering process for a mobile app. It shows that customers can log into an existing account or register as new. If login is successful, they can choose a gift, fill out a questionnaire, and the platform will match their answers to suggested gifts from a database. Customers are then redirected to suppliers' websites to order, pay for, and receive the gift. Suppliers receive the order, wrap and send the gift, and get paid upon receipt of payment.
This document appears to be an assignment for an introduction to business class, submitted by student Qaimat karim with registration ID A1BM113020 and teacher Waqar Ahmad. The document covers topics related to the multinational consumer goods company Unilever including its history, vision, mission, strategies and goals, nature of work, geographical expansion, products, future planning, infrastructure, and HR structure.
Beebe - Balancing by timed oscillation (AUS)Ray Beebe
This document discusses methods for balancing rotating machinery using a mobile phone stopwatch to time oscillations. The Timed Oscillation Method involves attaching a swing mass to the rotor and using a phone stopwatch to time oscillations. Times are plotted against position and the maximum/minimum times are used to calculate an imbalance correction mass. This method was successfully used to balance pump impellers and fans. The document also discusses trial and error balancing without instrumentation by drilling holes in positions that cause rotor oscillations to vary.
Sustainable Production Design InstitutePhoebe Hewson
For my thesis I developed a Sustainable Production Design Institute in West Hollywood
Students learn to create sets while keeping the environment in mind.
Take a look at this institute and let me know what you think!
The document discusses various pricing methods that can be used by businesses, including:
- Market oriented pricing, which involves comparing prices of similar products and adjusting based on competitors.
- Cost plus pricing, which calculates all costs and marks up the price to include a profit margin.
- Price sensitivity, which determines how price changes impact consumer demand to find the optimal price.
- Loss leader pricing, where certain products are priced below cost to attract customers and increase overall profits.
The document provides examples and definitions for each method to explain how and when businesses may utilize different approaches to set prices.
The document contains a SWOT analysis, market sizing, and list of competitors for a proposed gift-giving platform called Gift a Gift. The SWOT analysis notes strengths like an intuitive interface and personalized service, and weaknesses like cost and dependence on third parties. Market sizing estimates the total addressable market and serviceable obtainable market based on varying penetration rates of online shoppers adopting the platform over 5 years. Competitors include both direct online retailers and indirect traditional retailers.
Ray Beebe has over 50 years of experience in power generation and condition monitoring of steam turbines. He discusses several case studies where condition monitoring helped identify issues in steam turbines. Condition monitoring techniques like vibration analysis, performance analysis of parameters like valve output, stage pressures and enthalpy drop efficiency can help detect problems like blade deposits or damage. The case studies show how condition monitoring helped detect issues and schedule repairs before further degradation occurred. Mr. Beebe emphasizes that condition monitoring data should be used to only open turbines for repair when there are clear technical and economic reasons to do so.
The document describes chapter 14 of a textbook on organizational change and conflict management. It covers types of organizational change, individual reactions to change, reasons for employee resistance to change, strategies for overcoming resistance, approaches to planned change through organization development and grassroots efforts, and techniques for managing conflict. The key topics are anticipatory, reactive, incremental and strategic types of organizational change; the unfreezing-change-refreezing model of planned change; and competitive versus cooperative approaches to conflict.
Case Studies from 25 Years of Troubleshooting Vibration Problems.pdfssuser75ec351
This document summarizes several case studies over 25 years that used vibration analysis to troubleshoot problems with rotating and non-rotating equipment:
1) A hydroelectric dam would vibrate at certain turbine loads due to a phenomenon called Rheingan's Influence. Vibration spectra detected the issue but the system was not coupled properly. Modifications allowed operators to avoid problematic loads.
2) Stripes formed on steel strips during induction heating. The furnace frequency matched strip vibrations. Continuously varying the frequency instead of using one fixed frequency eliminated striping.
3) A microscope used in microsurgery vibrated, fatiguing surgeons. Vibration spectra found structural vibrations amplified by mismatched
The TAMU Turbomachinery Lab conducted research on wet annular seals subjected to two-phase flow. Their existing test rig assessed the dynamic force performance of these seals but had issues with shaker movement. To address this, they designed and constructed rigidly mounted shaker frames for the X and Y directions. Vibration testing found the natural frequencies of both mounts to be over 300 Hz, outside the 10-200 Hz excitation range, resolving the shaker movement issue.
Flow-induced vibration in heat exchangers has been a major problem for decades. Three main mechanisms that cause vibration are fluid-elastic instability, vortex shedding, and multi-phase buffeting. Fluid-elastic instability is the most important mechanism for shell and tube heat exchangers. Several studies have analyzed vibration experimentally and through computational fluid dynamics simulations. Parameters like damping ratios, tube properties, fluid properties, and flow velocities are important factors in vibration analysis and predicting the onset of instability.
This document contains lecture notes on mechanical vibrations. It covers topics such as two degree of freedom systems, principal modes, double pendulums, torsional systems with damping, coupled systems, vibration absorbers, centrifugal pendulum absorbers, vibration isolators, and dampers. Examples of two degree of freedom systems include two masses connected by springs. Equations of motion are derived using mass and stiffness matrices. Torsional vibrations in shafts can be caused by inertia forces or shock loads. Centrifugal pendulum absorbers have a natural frequency that varies with rotational speed, making them well-suited for applications like engines.
This document discusses the study of nonlinear behavior in vibrating systems. It begins with an abstract that defines vibration and explains why nonlinear models are needed to accurately describe real structures. The document then focuses on optimizing the vibration behavior of an absorber system with two degrees of freedom, a shock absorber, and nonlinear stiffness, subjected to harmonic loads. Both deterministic and stochastic cases are considered to find optimal response envelopes for nonlinear displacements, phases, and forces. Different types of nonlinear vibration isolators are also described, including ultra-low frequency isolators, Euler column isolators, and Gospodnetic-Frisch-Fay beam isolators.
Vibrations in data centers can be caused by nearby construction, traffic, railways, or cooling and equipment inside the data center. Vibrations above 0.5g can damage servers and disk drives, potentially causing data loss. Anti-vibration solutions like individual springs, metallic frames, and floating concrete slabs can isolate vibrations. Floating slabs distribute weight to maintain low resonance even with varying loads. Additional seismic protections like wire absorbers and walls can further isolate horizontal impacts during earthquakes. Proper isolation is needed to protect sensitive data center equipment from vibrations and seismic events.
Environmental stress screening (ESS) is a process that applies environmental stresses like vibration to products to induce latent defects. This helps improve quality and reliability. Vibration and temperature cycling are effective forms of ESS to stimulate flaws like loose connections or cracks. ESS is intended to find flaws, not simulate actual use, so failures during the process are encouraged and their causes must be identified and addressed. Random and quasi-random vibration are commonly used for ESS to induce a variety of motions that can cause failures through mechanisms like loose parts or solder joints. Thermal cycling and vibration work best together in ESS to find defects that one stress alone may not reveal.
This document summarizes research into designing a piezoelectric-actuated mirror mount with a servo bandwidth greater than 380kHz. Four different mount designs were tested: a cylindrical control mount and three designs intended to dampen mechanical resonances - a solid center of mass design, a design with a 0.125" tungsten-carbide core, and a design with a 0.25" tungsten-carbide core. Testing showed the thickness of the adhesive layer and mount material most affected resonance frequency. The optimal design was found to be a 0.25" tungsten-carbide filled brass mount, achieving a 392kHz servo bandwidth.
This presentation gives an introduction to mechanical vibration or Theory of Vibration for BE courses. Presentation is prepared as per the syllabus of VTU.For any suggestions and criticisms please mail to: hareeshang@gmail.com or visit:ww.hareeshang.wikifoundry.com.
Thanks for watching this presentation.
Hareesha N G
Experimental Analysis of Flow through Concentric Vane Swirler in Combustion C...IJSTA
This document describes an experimental analysis of flow through a concentric vane swirler in a combustion chamber using atmospheric air. The study examines the design of a swirler that can produce a central recirculation zone for flame stabilization. Experiments were conducted taking atmospheric cold air instead of hot gases through the combustion chamber. The results provide insight into the complex interactions between swirling flow, pressure gradients, and turbulent mixing in combustion systems.
Free Vibrational Analysis of Cracked and Un-cracked Cantilever BeamIRJET Journal
1. The document analyzes the free vibrational behavior of cracked and un-cracked cantilever beams through numerical analysis using ANSYS software, analytical solutions using Euler beam theory, and experimental modal analysis.
2. Natural frequencies of the beams are obtained for the first three vibration modes. Ten cracked beam models with varying cross-sections, crack locations, and crack depths are analyzed.
3. Curve fitting and fuzzy logic techniques are introduced to identify crack parameters like location and depth based on the natural frequencies. Results from finite element analysis, numerical analysis, fuzzy logic and experiments are compared.
OMAE2014 - 23661 Experimental Assessment of The Behaviour Of A Pipe Vibration...Luan Tochetto
The document describes experiments conducted to assess the behavior of a Pounding Tuned Mass Damper (PTMD) installed on a pipe underwater. A small-scale test apparatus was constructed to model a submarine pipe section. Free and forced oscillation tests were performed on the pipe both with and without a PTMD installed, in air and underwater conditions. The results showed that underwater, the natural frequency decreased due to added water mass, while damping increased due to fluid viscosity. With the PTMD installed, two natural frequencies were observed corresponding to the two-degree-of-freedom system. The PTMD was found to reduce pipe vibration amplitudes both in air and underwater through energy dissipation, though its performance was affected by surrounding fluid
In this study Dynamic property of a structural element which is frequency, damping and mode shapes are described by a process called modal analysis. Structural condition can be monitored by analyzing the changes in frequencies and mode shapes. All materials posses certain amount of internal damping. Similarly steel fibers also produce some internal damping. A system is a combination of elements, for example a structure is a system whose elements are beams, columns, slabs, footings .etc. In all those elements I have selected beam elements. Many research works are conducted on different type of materials under dynamic loading.
ACOUSTICALLY INDUCED VIBRATION (AIV) & FLOW INDUCED VIBRATION (FIV) ANALYSIS ...Journal For Research
Piping systems adapted for handling fluids such as steam and various process and hydrocarbon gases through a pressure-reducing device at high pressure and velocity conditions can produce severe acoustic and flow vibrations and metal fatigue in the system. The evaluation method for susceptibility of piping to AIV fatigue failure was first proposed by Carucci and Mueller around 35 years ago. Since then, several developments were reported. However, there has not been publication with reference to Finite Element Approach in relation to the AIV phenomena. This Paper Proposes a method to reduce the Acoustic & Flow Induced Vibrations in Piping system based on Actual operating conditions. This kind of AIV & FIV evaluation would be useful to determine the priority of the countermeasure to mitigate piping failure caused by AIV & FIV in the existing plant.
The document discusses various pricing methods that can be used by businesses, including:
- Market oriented pricing, which involves comparing prices of similar products and adjusting based on competitors.
- Cost plus pricing, which calculates all costs and marks up the price to include a profit margin.
- Price sensitivity, which determines how price changes impact consumer demand to find the optimal price.
- Loss leader pricing, where certain products are priced below cost to attract customers and increase overall profits.
The document provides examples and definitions for each method to explain how and when businesses may utilize different approaches to set prices.
The document contains a SWOT analysis, market sizing, and list of competitors for a proposed gift-giving platform called Gift a Gift. The SWOT analysis notes strengths like an intuitive interface and personalized service, and weaknesses like cost and dependence on third parties. Market sizing estimates the total addressable market and serviceable obtainable market based on varying penetration rates of online shoppers adopting the platform over 5 years. Competitors include both direct online retailers and indirect traditional retailers.
Ray Beebe has over 50 years of experience in power generation and condition monitoring of steam turbines. He discusses several case studies where condition monitoring helped identify issues in steam turbines. Condition monitoring techniques like vibration analysis, performance analysis of parameters like valve output, stage pressures and enthalpy drop efficiency can help detect problems like blade deposits or damage. The case studies show how condition monitoring helped detect issues and schedule repairs before further degradation occurred. Mr. Beebe emphasizes that condition monitoring data should be used to only open turbines for repair when there are clear technical and economic reasons to do so.
The document describes chapter 14 of a textbook on organizational change and conflict management. It covers types of organizational change, individual reactions to change, reasons for employee resistance to change, strategies for overcoming resistance, approaches to planned change through organization development and grassroots efforts, and techniques for managing conflict. The key topics are anticipatory, reactive, incremental and strategic types of organizational change; the unfreezing-change-refreezing model of planned change; and competitive versus cooperative approaches to conflict.
Case Studies from 25 Years of Troubleshooting Vibration Problems.pdfssuser75ec351
This document summarizes several case studies over 25 years that used vibration analysis to troubleshoot problems with rotating and non-rotating equipment:
1) A hydroelectric dam would vibrate at certain turbine loads due to a phenomenon called Rheingan's Influence. Vibration spectra detected the issue but the system was not coupled properly. Modifications allowed operators to avoid problematic loads.
2) Stripes formed on steel strips during induction heating. The furnace frequency matched strip vibrations. Continuously varying the frequency instead of using one fixed frequency eliminated striping.
3) A microscope used in microsurgery vibrated, fatiguing surgeons. Vibration spectra found structural vibrations amplified by mismatched
The TAMU Turbomachinery Lab conducted research on wet annular seals subjected to two-phase flow. Their existing test rig assessed the dynamic force performance of these seals but had issues with shaker movement. To address this, they designed and constructed rigidly mounted shaker frames for the X and Y directions. Vibration testing found the natural frequencies of both mounts to be over 300 Hz, outside the 10-200 Hz excitation range, resolving the shaker movement issue.
Flow-induced vibration in heat exchangers has been a major problem for decades. Three main mechanisms that cause vibration are fluid-elastic instability, vortex shedding, and multi-phase buffeting. Fluid-elastic instability is the most important mechanism for shell and tube heat exchangers. Several studies have analyzed vibration experimentally and through computational fluid dynamics simulations. Parameters like damping ratios, tube properties, fluid properties, and flow velocities are important factors in vibration analysis and predicting the onset of instability.
This document contains lecture notes on mechanical vibrations. It covers topics such as two degree of freedom systems, principal modes, double pendulums, torsional systems with damping, coupled systems, vibration absorbers, centrifugal pendulum absorbers, vibration isolators, and dampers. Examples of two degree of freedom systems include two masses connected by springs. Equations of motion are derived using mass and stiffness matrices. Torsional vibrations in shafts can be caused by inertia forces or shock loads. Centrifugal pendulum absorbers have a natural frequency that varies with rotational speed, making them well-suited for applications like engines.
This document discusses the study of nonlinear behavior in vibrating systems. It begins with an abstract that defines vibration and explains why nonlinear models are needed to accurately describe real structures. The document then focuses on optimizing the vibration behavior of an absorber system with two degrees of freedom, a shock absorber, and nonlinear stiffness, subjected to harmonic loads. Both deterministic and stochastic cases are considered to find optimal response envelopes for nonlinear displacements, phases, and forces. Different types of nonlinear vibration isolators are also described, including ultra-low frequency isolators, Euler column isolators, and Gospodnetic-Frisch-Fay beam isolators.
Vibrations in data centers can be caused by nearby construction, traffic, railways, or cooling and equipment inside the data center. Vibrations above 0.5g can damage servers and disk drives, potentially causing data loss. Anti-vibration solutions like individual springs, metallic frames, and floating concrete slabs can isolate vibrations. Floating slabs distribute weight to maintain low resonance even with varying loads. Additional seismic protections like wire absorbers and walls can further isolate horizontal impacts during earthquakes. Proper isolation is needed to protect sensitive data center equipment from vibrations and seismic events.
Environmental stress screening (ESS) is a process that applies environmental stresses like vibration to products to induce latent defects. This helps improve quality and reliability. Vibration and temperature cycling are effective forms of ESS to stimulate flaws like loose connections or cracks. ESS is intended to find flaws, not simulate actual use, so failures during the process are encouraged and their causes must be identified and addressed. Random and quasi-random vibration are commonly used for ESS to induce a variety of motions that can cause failures through mechanisms like loose parts or solder joints. Thermal cycling and vibration work best together in ESS to find defects that one stress alone may not reveal.
This document summarizes research into designing a piezoelectric-actuated mirror mount with a servo bandwidth greater than 380kHz. Four different mount designs were tested: a cylindrical control mount and three designs intended to dampen mechanical resonances - a solid center of mass design, a design with a 0.125" tungsten-carbide core, and a design with a 0.25" tungsten-carbide core. Testing showed the thickness of the adhesive layer and mount material most affected resonance frequency. The optimal design was found to be a 0.25" tungsten-carbide filled brass mount, achieving a 392kHz servo bandwidth.
This presentation gives an introduction to mechanical vibration or Theory of Vibration for BE courses. Presentation is prepared as per the syllabus of VTU.For any suggestions and criticisms please mail to: hareeshang@gmail.com or visit:ww.hareeshang.wikifoundry.com.
Thanks for watching this presentation.
Hareesha N G
Experimental Analysis of Flow through Concentric Vane Swirler in Combustion C...IJSTA
This document describes an experimental analysis of flow through a concentric vane swirler in a combustion chamber using atmospheric air. The study examines the design of a swirler that can produce a central recirculation zone for flame stabilization. Experiments were conducted taking atmospheric cold air instead of hot gases through the combustion chamber. The results provide insight into the complex interactions between swirling flow, pressure gradients, and turbulent mixing in combustion systems.
Free Vibrational Analysis of Cracked and Un-cracked Cantilever BeamIRJET Journal
1. The document analyzes the free vibrational behavior of cracked and un-cracked cantilever beams through numerical analysis using ANSYS software, analytical solutions using Euler beam theory, and experimental modal analysis.
2. Natural frequencies of the beams are obtained for the first three vibration modes. Ten cracked beam models with varying cross-sections, crack locations, and crack depths are analyzed.
3. Curve fitting and fuzzy logic techniques are introduced to identify crack parameters like location and depth based on the natural frequencies. Results from finite element analysis, numerical analysis, fuzzy logic and experiments are compared.
OMAE2014 - 23661 Experimental Assessment of The Behaviour Of A Pipe Vibration...Luan Tochetto
The document describes experiments conducted to assess the behavior of a Pounding Tuned Mass Damper (PTMD) installed on a pipe underwater. A small-scale test apparatus was constructed to model a submarine pipe section. Free and forced oscillation tests were performed on the pipe both with and without a PTMD installed, in air and underwater conditions. The results showed that underwater, the natural frequency decreased due to added water mass, while damping increased due to fluid viscosity. With the PTMD installed, two natural frequencies were observed corresponding to the two-degree-of-freedom system. The PTMD was found to reduce pipe vibration amplitudes both in air and underwater through energy dissipation, though its performance was affected by surrounding fluid
In this study Dynamic property of a structural element which is frequency, damping and mode shapes are described by a process called modal analysis. Structural condition can be monitored by analyzing the changes in frequencies and mode shapes. All materials posses certain amount of internal damping. Similarly steel fibers also produce some internal damping. A system is a combination of elements, for example a structure is a system whose elements are beams, columns, slabs, footings .etc. In all those elements I have selected beam elements. Many research works are conducted on different type of materials under dynamic loading.
ACOUSTICALLY INDUCED VIBRATION (AIV) & FLOW INDUCED VIBRATION (FIV) ANALYSIS ...Journal For Research
Piping systems adapted for handling fluids such as steam and various process and hydrocarbon gases through a pressure-reducing device at high pressure and velocity conditions can produce severe acoustic and flow vibrations and metal fatigue in the system. The evaluation method for susceptibility of piping to AIV fatigue failure was first proposed by Carucci and Mueller around 35 years ago. Since then, several developments were reported. However, there has not been publication with reference to Finite Element Approach in relation to the AIV phenomena. This Paper Proposes a method to reduce the Acoustic & Flow Induced Vibrations in Piping system based on Actual operating conditions. This kind of AIV & FIV evaluation would be useful to determine the priority of the countermeasure to mitigate piping failure caused by AIV & FIV in the existing plant.
TSI presentation for Bentley Nevada System, Vibration system of steam turbine for 150 MW unit. It demonstrates vibration in power plant. for BHEL turbine.
IRJET- Experimental Analysis of Boring Tool’s by using Viscous OilIRJET Journal
This document discusses experimental analysis of boring tool vibrations using passive damping. It begins with an introduction to boring operations, vibration basics, and definitions of problems like deflection that occur during boring. It then reviews past literature on topics like using viscous oil and particle dampers to reduce boring tool vibrations. The document describes the methodology used, which involves measuring vibration acceleration and surface roughness with and without passive dampers. Results showed that passive damping, like using teflon or nylon, reduced vibrations by up to 75% and improved surface finish compared to conventional boring tools. In conclusion, passive damping techniques are effective for vibration reduction during boring.
This document outlines a course on mechanical vibrations. It includes 5 course learning outcomes related to describing vibration principles, evaluating solutions for single and multi-degree of freedom vibration systems, and analyzing engineering implications of resonance. The course covers topics such as undamped and damped single-degree systems, forced vibrations, two-degree systems, and vibration resonance. Assessments include assignments, tests, and a final exam. References for the course are also provided.
Characteristics and stability threats of resonance caused by forced oscillati...Power System Operation
This paper studies the resonance interaction caused by
forcing oscillations occurring at frequencies near the
inter-area mode frequencies. The paper studies measured
incidents and analyses the resonance phenomenon with
simulations. The paper shows that observations, both
measured and simulated, are in line with the resonance
theory. The main issues that affect the resonance caused
by the forcing oscillations are investigated. According to
the results, in some power system states even relativ ely
small forcing oscillations in certain locations may create
a resonance with high amplitude oscillations and in this
way even cause instability. The resonance interaction
can be significant in systems where low damping limits
the transmission capacity (e.g. Nordic power system).
Thus, TSOs responsible for such systems should analyze
and mitigate the risk of forced oscillations.
My first paper to a journal. My boss then encouraged me to work at home while my wife was in hospital with birth of our second child and I had to babysit our toddler. Her 40th birthday reminded me....
A power station was experiencing annoying low frequency vibrations that caused glassware to vibrate and crash to the floor in the chem lab and shake the control room, disturbing operators. The vibrations occurred at around 8Hz and were found to be caused by coal mills that rotated at the same frequency, resonating with the steel structure of the building. Vibration absorbers using scrap mass and compression springs were installed and tuned to the structure's natural frequency, reducing vibrations to a non-problematic level. The absorbers solved the problem and remained effective for years without further issues.
My biggest success in balancing a fan was a few years agoRay Beebe
This document describes balancing a large fan impeller using the components method. It summarizes:
1) The fan being balanced was a 590 r/min boiler ID fan with a 11 ft diameter double entry impeller weighing 21.5 tons.
2) Vibration was measured at each bearing using a velocity transducer to determine the original vibration vectors. These were resolved into in-phase and anti-phase components.
3) Balancing first proceeded using a shared pair of masses to address the larger in-phase components. Additional stages could address residual anti-phase vibration using masses placed 180 degrees apart.
This document discusses condition monitoring techniques for various industrial machines, including vibration analysis, performance testing of steam turbines, and monitoring pump wear. It provides examples of how identifying issues through condition monitoring, such as resonant vibration in a generator or increased internal leakage in a pump, can help determine the root cause of problems and guide appropriate corrective actions like bearing modifications or pump overhauls. The case studies demonstrate how condition monitoring can help optimize equipment reliability and efficiency.
The document discusses condition monitoring techniques for various industrial machines, including vibration analysis, enthalpy-entropy plots, and performance testing. It provides examples of how analyzing vibration spectra, efficiency parameters, and test results helped diagnose issues like bearing instability, steam leakage, and internal pump wear. Catching problems early through condition monitoring techniques can help minimize downtime and reduce operating costs.
Getting started with condition monitoring for only $2000Ray Beebe
This document discusses how condition monitoring can be done for low cost using simple methods and techniques. It provides 10 case studies as examples of low-cost condition monitoring, such as using a $10 tool to view a damper around a bend, using a ruler to measure liner erosion depth, and using temperature sensitive paint or a spot temperature indicator. Overall vibration monitoring can be done for as little as $300. It emphasizes that proper documentation of measurement methods is important.
Study & career paths for Maintenance people (Ray Beebe)Ray Beebe
Presentation I was asked to give to a conference of condition monitoring and maintenance people. Outlines some of the postgrad programs available around the world, Many are taught using off-campus learning. (I led the Monash MRE for 16 years (now Federation Uni).
This document discusses how to optimize energy usage in pumps through condition monitoring techniques. Pumps use 25% of the world's motor-driven electricity, or around 6.5% of global electricity production. Condition monitoring can detect degradation in bearings, casing wear, misalignment, and internal wear in impellers and seals. Performance analysis by measuring head-flow curves is particularly useful for detecting internal wear and optimizing the timing of pump overhauls to balance repair costs and wasted energy. The document provides examples of using performance analysis on boiler feed pumps to schedule optimal overhaul times that minimize total costs.
Ray Beebe has learned many lessons over 45 years of condition monitoring experience:
1) Simple instruments and approaches can identify many issues, like finding a loose rubber bung caused erratic vibration.
2) Regularly review monitoring procedures to check if they are still needed, can be simplified, or test intervals extended.
3) Specialist test equipment requires full-time skilled operators to regularly maintain and use equipment properly.
1. Presented at ICOMS2002, International Conference of Maintenance Societies, Brisbane
CONTROL OF VIBRATION WITH DYNAMIC ABSORBER
Ray Beebe
Summary: High beating vibration was evident in the structure of a large boiler structure and associated
buildings. The level became high enough to be annoying to workers in the vicinity. Vibration analysis
was used to identify the frequency of the exciting vibration and its likely source. It was concluded that the
vibration was close to the resonant frequency of the structure, but reduction at the source of vibration was
neither sufficient nor practicable to control it. A vibration absorber system was designed. The paper
describes the investigation, the identification of the source, and the successful control measure - design
and installation of a series of dynamic absorbers. The feature used on later designs to prevent this
problem is also described.
Keywords: Vibration analysis, structural resonance, vibration absorber
1. INTRODUCTION
High beating vibration was evident in the structure of a large boiler structure and associated buildings. Although the amplitude
was well below that considered to be unacceptable for machines for their integrity, the level increased to became high enough
to be annoying to workers in the vicinity. Vibration analysis was used to identify the frequency of the exciting vibration and its
likely source. As the vibration was concluded to be at the resonant frequency of the structure, reduction of the source was not a
practicable was to control the vibration. A vibration absorber system was designed. This paper describes the investigation, the
identification of the source, and the successful control measure -design and installation of a series of dynamic absorbers. The
feature used on later designs to avoid this problem is also described.
2. THE PROBLEM
An annoying vibration was present in the boiler steelwork structure of a large power generation unit. Although barely
noticeable initially, this increased over some months to reach unacceptable levels from the viewpoint of its effect on people.
Initially, this only affected a chemical instrument room, where laboratory glassware left on a bench would eventually bounce
off and break on the floor! Eventually, the vibration caused annoyance to the shift operating staff in the plant control room.
The amplitude of vibration was low, and at no stage indicated a danger to the plant itself. However, vibration sufficiently high
to be annoying to people is one of the valid reasons for eliminating or reducing it. (Ref 1)
Vibration was measured at selected places on the structure, and analysed with a manually-tune vibration analyser. The
vibration was found to be at a frequency of close to 8Hz, and would behave in a cyclical fashion, increasing to a maximum,
then decreasing to almost nothing, over a two-minute period. Such behaviour is typical of classical “beating” behaviour,
where two frequencies that are very close together move into phase and out of phase, as described in texts on vibration such as
Ref 2.
Having read that the natural frequencies of large steel framed structures can be as low as in this range, the investigator
suspected that this structure, some 90m tall, was being excited to vibrate at its natural frequency. A search for the likely source
of the exciting vibration commenced. The regular vibration condition monitoring and previous investigations of the low speed
fan-type coal mills meant that their nominally constant speed of 465r/min, or 7.8Hz, was well known, and accordingly, they
were quickly identified as the likely source.
The unit has eight such mills arranged around the boiler. These mills provide the gas handling capacity to draw hot gas from
the boiler at furnace exit level at a temperature of the order of 1000°C. The coal (lignite) is added just before entry to the mill,
where it mixes with the hot gas as it impacts the blades of the mill wheel. The fan action then conveys the pulverised coal and
hot wet gas mixture at approximately 160°C to the burners. Shown opened up through its entry door in Figure I, the impeller
has a mass of about 20t, and wear occurs on the impeller blades in a fashion that is not unevenly distributed around the wheel.
Unbalance therefore increases with service.
2. 2
Figure I: fan-type coal mill, showing impeller
Study of the plant construction drawings revealed that each of the four corner columns of the main steel structure was
supported on a concrete raft. Each of these rafts also supported two of the fan-type mills. This foundation arrangement was
not readily evident to observers (mechanical engineers!), as the only visible floor concrete was clearly not connected
structurally to the mill foundations. The drawings showed that this reinforced concrete paving had been laid over the rafts
and the area between them, as in Figure II, and was designed to carry only the maintenance loads such as vehicles and cranes.
Figure II: main corner column and the two adjacent mills
It was therefore likely that the vibration from two corner-adjacent mills would be very well transmitted into the boiler
steelwork via the shared mill and column supports. It was decided to investigate further at its source how the vibration varied
with time. Therefore, a vibration transducer was fitted at the same location on the bearing casings of a pair of these adjacent
mills.
The time traces of the vibration were arranged to be viewed on a twin-beam oscilloscope. The time traces were clearly shown
as sine waves of approximately 8Hz. As the time traces moved into phase, the structural vibration was at a maximum, and
vanished when the traces were in anti-phase. This was the classic case of “beating” as suspected. The forces from the residual
unbalance in each of the two impellers apparently balanced each other when in anti-phase, but added together when in phase
to provide a large exciting force to the structure. It was also evident that the speeds of the mills varied slightly in service,
possibly due to slight variations in the intensity of coal flow.
The levels of vibration as measured at the bearings of these mills were not high, and not of a concern for the condition of the
mills themselves, according to available Standards (Ref 3). A common measure to reduce excessive vibration is to reduce the
3. 3
source, which in the case of rotating machinery usually means balancing. Balancing of these mills in-situ was possible, as it
had been successful on smaller mills of a similar design, but here it was considered too lengthy and cumbersome a process.
The state of balance would also be expected to decay as blade wear progressed, and frequent balancing was not practicable.
Given the large structure, the other common control measures of a change in system mass or stiffening were also not
practicable. It was decided to try the use of a vibration absorber.
3. THE SOLUTION
A vibration absorber consists of a mass connected to the original system by springs, such that is free to vibrate independently
of the original structure. The springs can be of any type. An absorber is useful where a structure or machine that can be
considered to have a single-degree-of-freedom vibrates at its natural frequency, usually due to some forcing or exciting
vibration.
The “absorber” adds a second mass-spring combination to the system, converting in into a two-degree-of-freedom system.
This new combined system now has two new natural frequencies, one above and one below the original natural frequency.
When the absorber system is tuned to the driving frequency and has reached steady state, the force provided by the absorber
mass is equal in magnitude and opposite in direction to the original disturbance force. With zero, or close to zero, net force
acting on the primary mass, it does not move and the motion is “absorbed” by motion of the absorber mass.
For the method to be successful, the harmonic excitation must be known and not change much from its constant value.
Damping must also be negligible. These conditions were considered to apply in this case. The theory behind the use of the
vibration absorber is given in textbooks on vibration analysis, such as Ref 2.
Defining these terms:
Ratio of mass of absorber to original system mass: μ (usually chosen in the range of 5% - 25% of the original system
mass, where this is known)
Natural frequency of the original system: p (assumed here from the symptoms to be close to 7.8Hz)
Natural frequency of the absorber system before it is attached to the original system
absorberofMass
springsabsorberofStiffness
m
k
a
a
a
Ratio of frequency of absorber system to that of original system:
p
a
(which for a tuned system =1)
The equation relating these gives the values of the natural frequencies of the new system normalised to the frequency of the
absorber system (Ref 2):
1)1(2)1(
2
1
2
11 224
22
2
2
a
The values that indirectly specify the mass and stiffness of an absorber system can be seen as the ratio of the absorber mass to
the initial system mass, and the ratio of the natural frequencies of the absorber mass system and the original system. The
greater the absorber mass compared with the mass of the original system, the wider the useful frequency range of the absorber.
In the more usual applications of a vibration absorber, where the masses of both original system and absorber are known, and
hence μ is readily found, the useful frequency range of the new system can also be calculated equating the following
expression to 1, and also to –1 (Ref 2). This results in four roots, the central pair of which define the useful frequency range.
As long as the exciting force remains inside the useful frequency range, the absorber will be effective. (If this expression is
greater than unity, the absorber will in fact increase the force to the original system).
With ωdr as the frequency of the driving force:
4. 4
]/1[
2
adr
22
/)/(1 paadr 22
//1 pdrpa
As in this case the effective mass of the total system was not known, and was too complex and too large to consider a single
absorber at any one position, some initial experimentation was done at a point of relatively high vibration in the chemical
instrument room. A combination of masses and springs tuned to as close to 7.8 Hz as could be obtained was tried and
eventually the correct combination was found to minimise the amplitude of vibration at that point. The same experimentation
was applied at mid-span of the steel floor supporting beams under the control room.
The final mass/spring system was designed as a frame holding lengths of scrap steel (a supply of worn mill lining plates was
readily available). Several of these arrangements were installed in locations at about mid-span of the beams underneath the
control room, with compression springs resting on the bottom flange of the beams as shown in Figure III.
Figure III: typical absorber supported on lower flange of control room beams
Another of a simple table design – plate with springs underneath - was installed in the chemical instrument room which is on
the same level as the control room.
The systems were successful in controlling the vibration in the areas where it had been causing annoyance. Detailed
measurements of the amplitudes were not necessary, as the criteria for success was to remove the annoyance, and this was
achieved. The systems have been operating successfully for some years.
4. THE FUTURE DESIGN
The design of future boiler-turbine units was well advanced, and it was not possible to redesign the structures, which in any
case were of a completely different arrangement to the earlier plant. The new mills were also to be variable speed.
It was decided to install the fan-type mills on vibration isolating foundations, designed by a specialist company. Each mill was
mounted on its own concrete block foundation, but instead of being supported directly connected with the main structural
system as in the plant described in this case study, the foundation blocks are supported on several large springs. Large simple
dampers are also provided. The effectiveness of these proprietary systems in service is readily apparent when standing with
one foot on the mill block and the other on the adjacent floor. It was not practicable to modify the initial plant to such an
isolating system.
5. CONCLUSION
An absorber system was successful applied on an unusually large structure. Such an application should encourage wider use of
this vibration control measure where the conditions require and allow it.
6. ACKNOWLEDGEMENT
5. 5
Following the initial identification of the problem, the work of colleagues, in particular Mr Carl Ross, in the experimentation
and design of the system were appreciated.
7. REFERENCES
(1) Beebe, RS Machine condition monitoring MCM Consultants 2001 reprint
(2) Inman, DJ Engineering vibration Prentice Hall 1996
(3) AS2625, Part 3 -1983 Rotating and reciprocating machinery –mechanical vibration Measurement and evaluation of
vibration severity of large machines in situ
Paper presented at the International Conference of Maintenance Societies (ICOMS), Brisbane, 2002.