The document discusses various techniques for reducing vibration in helicopters, including passive, active, and semi-active methods. Passive techniques like tuned mass absorbers and blade design optimization provide moderate vibration reduction but with a significant weight penalty. Active concepts like higher harmonic control and individual blade control generate unsteady loads to cancel vibrations, but require external power. Semi-active systems modify structural properties using small amounts of power. The most successful current method is active control of structural response, which places actuators throughout an airframe to reduce vibrations measured by sensors.
Stress and fatigue analysis of landing gear axle of a trainer aircrafteSAT Journals
Abstract The undercarriage or landing gear of an aircraft is the structure that supports an aircraft on the ground and allows it to taxi, takeoff and land. Among the various parts of landing gear, axle is the most critical component where the loads (landing and ground loads) act on the axle first, then transferred to the structure. In this study stress and fatigue analysis of the axle is performed to meet the strength and life requirements. The modeling of the axle is done using UniGraphics (UG) software. Stress analysis is carried out using MSC Patran (pre-processing and post-processing)/Nastran (solver) for different landing loads (spin up, spring back, maximum vertical and drift) and ground handling loads (braking, taxing and turning). Stress analysis was carried out by both classical and FEM approaches and by comparing the results it was obvious that they were in correlation with one another. Fatigue analysis was also carried out for the axle using landing spectrum and ground handling spectrum to estimate the fatigue life. By the iteration process, the requirement of 10000 landings was satisfied. Keywords: Static, Fatigue, Axle, Fatigue life, UniGraphics, MSC Patran, MSC Nastran
Stress and fatigue analysis of landing gear axle of a trainer aircrafteSAT Journals
Abstract The undercarriage or landing gear of an aircraft is the structure that supports an aircraft on the ground and allows it to taxi, takeoff and land. Among the various parts of landing gear, axle is the most critical component where the loads (landing and ground loads) act on the axle first, then transferred to the structure. In this study stress and fatigue analysis of the axle is performed to meet the strength and life requirements. The modeling of the axle is done using UniGraphics (UG) software. Stress analysis is carried out using MSC Patran (pre-processing and post-processing)/Nastran (solver) for different landing loads (spin up, spring back, maximum vertical and drift) and ground handling loads (braking, taxing and turning). Stress analysis was carried out by both classical and FEM approaches and by comparing the results it was obvious that they were in correlation with one another. Fatigue analysis was also carried out for the axle using landing spectrum and ground handling spectrum to estimate the fatigue life. By the iteration process, the requirement of 10000 landings was satisfied. Keywords: Static, Fatigue, Axle, Fatigue life, UniGraphics, MSC Patran, MSC Nastran
PRELIMINARY DESIGN APPROACH TO WING BOX LAYOUT AND STRUCTURAL CONFIGURATIONLahiru Dilshan
This is an assignment that was done to design the basic layout of the aircraft wing and structural configuration. Key aspects of the assignment are to design the structural layout, identify the basic component, identify the structural arrangement
Abstract:
Landing gear is one of the critical subsystems of an aircraft. The need to design landing gear with minimum weight, minimum volume, high performance, improved life and reduced life cycle cost have posed many challenges to landing gear designers and practitioners. Further it is essential to reduce the landing gear design and development cycle time while meeting all the regulatory and safety requirements. Many technologies have been developed over the years to meet these challenges in design and development of landing gear. This paper presents a perspective on various stages of landing gear design and development, current technology landscape and how these technologies are helping us to meet the challenges involved in the development of landing gear and how they are going to evolve in future.
NAME : S. Srinivasa Phani Kumar
Branch : MECHANICAL
College : SWARNANDHRA COLLEGE OF ENGINEERING & TECHNOLOGY
The turbofan engine is a propulsive mechanism to combine the high thrust of a turbojet with the high efficiency of a propeller. Basically, a turbojet engine forms the core of the turbofan; the core contains the diffuser, compressor, burner, turbine, and nozzle. However, in the
turbofan engine, the turbine drives not only the compressor, but also a large fan external to the core. The fan itself is contained in a shroud that is wrapped around the core.
Offshore wind turbines are relatively complex structural and mechanical systems located ina highly demanding environment. In this study, the fundamental aspects and major issues related to the design of such structures are inquired. The system approach is proposed to carry out the design of the structural parts: in accordance with this philosophy, a decomposition of the system (environment, structure, actions/loads) and of the structural
performance is carried out, in order to organize the qualitative and quantitative assessment in various sub-problems. These can be faced by sub-models of different complexity both for the structural behavior and for the load models. Numerical models are developed to assess the safety performance under aerodynamic and hydrodynamic actions. In the structural analyses, three types of turbine support structures have been considered and compared: a
monopile, a tripod and a jacket.
PRELIMINARY DESIGN APPROACH TO WING BOX LAYOUT AND STRUCTURAL CONFIGURATIONLahiru Dilshan
This is an assignment that was done to design the basic layout of the aircraft wing and structural configuration. Key aspects of the assignment are to design the structural layout, identify the basic component, identify the structural arrangement
Abstract:
Landing gear is one of the critical subsystems of an aircraft. The need to design landing gear with minimum weight, minimum volume, high performance, improved life and reduced life cycle cost have posed many challenges to landing gear designers and practitioners. Further it is essential to reduce the landing gear design and development cycle time while meeting all the regulatory and safety requirements. Many technologies have been developed over the years to meet these challenges in design and development of landing gear. This paper presents a perspective on various stages of landing gear design and development, current technology landscape and how these technologies are helping us to meet the challenges involved in the development of landing gear and how they are going to evolve in future.
NAME : S. Srinivasa Phani Kumar
Branch : MECHANICAL
College : SWARNANDHRA COLLEGE OF ENGINEERING & TECHNOLOGY
The turbofan engine is a propulsive mechanism to combine the high thrust of a turbojet with the high efficiency of a propeller. Basically, a turbojet engine forms the core of the turbofan; the core contains the diffuser, compressor, burner, turbine, and nozzle. However, in the
turbofan engine, the turbine drives not only the compressor, but also a large fan external to the core. The fan itself is contained in a shroud that is wrapped around the core.
Offshore wind turbines are relatively complex structural and mechanical systems located ina highly demanding environment. In this study, the fundamental aspects and major issues related to the design of such structures are inquired. The system approach is proposed to carry out the design of the structural parts: in accordance with this philosophy, a decomposition of the system (environment, structure, actions/loads) and of the structural
performance is carried out, in order to organize the qualitative and quantitative assessment in various sub-problems. These can be faced by sub-models of different complexity both for the structural behavior and for the load models. Numerical models are developed to assess the safety performance under aerodynamic and hydrodynamic actions. In the structural analyses, three types of turbine support structures have been considered and compared: a
monopile, a tripod and a jacket.
Power consumption in room (split) airconditioning using alternative refrigera...eSAT Journals
Abstract
In this age of rapid economic development India is in need of huge of amount of energy including electricity. The prohibitive cost of setting up of new facilities for production of electricity led to the introduction of various means for saving electricity at every front. Airconditioners are huge consumers of electricity. So, reduction in use of electricity in airconditioner could be very much beneficial to the cause of the nation. At the same time all measures are being taken to save the environment from the hazards of global warming producing chemicals and burning of fossil fuels. All these purposes could be met by introduction of hydrocarbon refrigerants like Isobutane (R-600a). As such in the present work tests have been conducted to measure the saving in electrical energy when the existing-22 gas (refrigerant) is replaced by R-600a as refrigerant in the same system. It is found that substantial saving could be achieved in the consumption of electricity by this replacement without compromising the basic cooling effect. However, the flammability factor of R-600a is to be properly taken care of.
Keywords: refrigerant, alternative, electricity, consumption, isobutane, Montreal protocol, ozone depletion, global warming, flammability
The currently used refrigerant properties were recommended as unsuitable for the future use due to their high ozone-depleting rate. To abide with the Montrcal Protocol norms have been taken into account and suitable alternative, which is innocuous to ozone layer.
Performance of HFC-152a is researched to develop the HFC-152a as alternative mixture. The HFC-152a has been tested under various systems. Its properties, comparison with HFC-134a, cost, risk assessment, efficiency and technological issues have been discussed.
3M Silicone Cold Shrink Tubes - LSF Low Smoke Zero Halogen for Low Voltage Cable Splices, Cable Repair & Insulation Protection
3M 8443-2 Silicone Rubber Cold Shrink Tubes
Minimum diameter seal 8.86mm
Maximum diameter seal 14.22mm
Cold shrink tube length 36mm
*No tools or heat shrink gas torches required for installation of 3M cold shrink
*Seals tight, retains resilience and pressure even after aging and exposure
*Moisture resistant 3M silicone cold shrink
*Cold shrink resists acids and alkalies
*Resists ozone and UV ultraviolet light
*Fire resistant 3M silicone cold shrink tubings
3M Silicone Cold Shrink Applications
Primary electrical insulation of insulated wires and cable splices up to 1000 volts, insulation of electrical aircraft cables, suitable for indoor and outdoor applications, moisture sealing for high voltage (HV) air insulated cable connectors and cable lugs, insulation of secondary splices (copper and aluminium conductors), cable sheath repairs, insulation of line conductor transition connectors.
Flammability Testing of 3M Silicone Cold Shrink
3M Cold Shrink Insulators 8440 Series flammability testing was conducted with specimens positioned both vertically and horizontally per specification BSS 7230. The 3M silicone rubber cold shrink insulation passed the Flammability Test of BSS 7230 without supporting a flame. In addition, these cold shrink insulators were also subjected to a gas flame test as outlined in paragraph 4.4.15 of MIL-C-24643A and met the passing criteria as specified - no fuse was blown during the one hour flame exposure of the 3M Silicone Cold Shrink Tube.
During the Airbus Military Trade Media Briefing 2013, held on May 29th and 30th 2013,
Angel Barrio Cardaba Head of Engineering and Technology provided an overview on a number of technological developments at Airbus Military over the past year. But the key system highlighted was the C295 W.
According to Airbus Military:
Featuring winglets and uprated engines as standard, the new model will provide operators with enhanced performance in all flight phases but is particularly aimed at those operating at “hot and high“ airfields where payload increases in excess of 1,000kg are promised.
In intelligence, surveillance and reconnaissance (ISR) roles such as airborne early warning (AEW) the enhancements will increase endurance by 30-60min and permit an operating altitude up to 2,000ft higher than now.
The new features will also provide an overall reduction in fuel consumption of around 4% depending on configuration and conditions.
The C295W, assembled in Seville, Spain, is being offered to the market from now on and will be the standard version of the aircraft in all versions from the fourth quarter of 2014. Certification is expected in 2Q14.
Airbus Military is committing to the C295W following flight-trials with winglets fitted to its company development aircraft which showed positive results for a weight penalty of only around 90kg.
The engines are the Pratt & Whitney Canada PW127 turboprops which power all versions of the C295. New procedures recently certified by Canada and Spain permit operation in the climb and cruise phases at higher power settings at the discretion of the operator. As well as improved hot and high performance, the procedure improves operation over very high terrain such as the Andes or Himalaya mountains with only a minor influence on maintenance cost.
EASA Part 66 Module 5.13 : Software Management Controlsoulstalker
Software management in order the prevent catastrophic failure on aircraft.
Slide for student who want to take EASA part 66 exam.
Other presentation you can get at :
http://part66.blogspot.com/
Stall avoidance training and pilot evaluations of approach to stall recovery procedures must develop essential habit formations that instill recognition and proper recovery from imminent and full stall situations. Using power as the primary control without a reduction in elevator backpressure while recovering from an approach to stall does not instill habit formation for effective stall avoidance and aircraft upset recovery.
Modeling & Analysis of Centrifugal Blower using Composite MaterialIOSR Journals
Centrifugal blowers are used extensively for on-board naval applications which have high noise levels. The noise generated by a rotating component is mainly due to random loading force on the blades and periodic iteration of incoming air with the blades of the rotor. The Contemporary blades in naval applications are made up of Aluminium or Steel and generate noise that causes disturbance to the people working near the blower. The present work aims at observing the choice of E-Glass as an alternative to metal for better vibration control. E-Glass, known for their superior damping characteristics are more promising in vibration reduction compared to metals. The modeling of the blower was done by CATIA V5 R19. The blower is meshed with a three dimensional hex8 mesh is done using HYPERMESH 10. It is proposed to design blower with Epoxy glass, analyze its strength and deformation using FEM technique. In order to evaluate the effectiveness of E-Glass and metal blower using FEA packaged (ANSYS). Modal analysis is performed on both Aluminium and E-Glass blower to find out first five natural frequencies
The GENERATION of power units and CONSUMPTION of loads connected to the UCTE network
needs to be controlled and monitored for secure and high-quality operation of the
SYNCHRONOUS AREAS. The LOAD-FREQUENCY-CONTROL control, the technical reserves and
the corresponding control performances are essential to allow TSOs to perform daily
operational business.
Within the UCTE SYNCHRONOUS AREA, the control actions and the reserves are organised in
a hierarchical structure with CONTROL AREAS, CONTROL BLOCKS and the SYNCHRONOUS AREA
with two CO-ORDINATION CENTERS.(for the principle see Figure 1 below, see also UCTE
Pyramid in Policy
Design,Construction And Structure Analysis Of Twinrotor UAVijics
There have been many advancements in the field of aerospace and avionics. Scientists have increasingly
started to focus on VTOL (vertical take - off and landing) aircrafts. We have built a miniature VTOL
twinrotor UAV. UAVs have begun to grab a lot of attention these days due to its numerous applications
such as surveillance and relief. Twinrotor is a kind of a helicopter having two main propellers instead of
one and no tail fin. All three important motion of the aircraft i.e. roll, pitch, yaw are controlled by thrust
vectoring using servo motors and changing the magnitude of thrust using electronics speed controllers. The
paper deals with the design of a basic UAV based on application and the construction keeping in mind the
different concepts that govern its motion.
GDG Cloud Southlake #33: Boule & Rebala: Effective AppSec in SDLC using Deplo...James Anderson
Effective Application Security in Software Delivery lifecycle using Deployment Firewall and DBOM
The modern software delivery process (or the CI/CD process) includes many tools, distributed teams, open-source code, and cloud platforms. Constant focus on speed to release software to market, along with the traditional slow and manual security checks has caused gaps in continuous security as an important piece in the software supply chain. Today organizations feel more susceptible to external and internal cyber threats due to the vast attack surface in their applications supply chain and the lack of end-to-end governance and risk management.
The software team must secure its software delivery process to avoid vulnerability and security breaches. This needs to be achieved with existing tool chains and without extensive rework of the delivery processes. This talk will present strategies and techniques for providing visibility into the true risk of the existing vulnerabilities, preventing the introduction of security issues in the software, resolving vulnerabilities in production environments quickly, and capturing the deployment bill of materials (DBOM).
Speakers:
Bob Boule
Robert Boule is a technology enthusiast with PASSION for technology and making things work along with a knack for helping others understand how things work. He comes with around 20 years of solution engineering experience in application security, software continuous delivery, and SaaS platforms. He is known for his dynamic presentations in CI/CD and application security integrated in software delivery lifecycle.
Gopinath Rebala
Gopinath Rebala is the CTO of OpsMx, where he has overall responsibility for the machine learning and data processing architectures for Secure Software Delivery. Gopi also has a strong connection with our customers, leading design and architecture for strategic implementations. Gopi is a frequent speaker and well-known leader in continuous delivery and integrating security into software delivery.
Slack (or Teams) Automation for Bonterra Impact Management (fka Social Soluti...Jeffrey Haguewood
Sidekick Solutions uses Bonterra Impact Management (fka Social Solutions Apricot) and automation solutions to integrate data for business workflows.
We believe integration and automation are essential to user experience and the promise of efficient work through technology. Automation is the critical ingredient to realizing that full vision. We develop integration products and services for Bonterra Case Management software to support the deployment of automations for a variety of use cases.
This video focuses on the notifications, alerts, and approval requests using Slack for Bonterra Impact Management. The solutions covered in this webinar can also be deployed for Microsoft Teams.
Interested in deploying notification automations for Bonterra Impact Management? Contact us at sales@sidekicksolutionsllc.com to discuss next steps.
The Art of the Pitch: WordPress Relationships and SalesLaura Byrne
Clients don’t know what they don’t know. What web solutions are right for them? How does WordPress come into the picture? How do you make sure you understand scope and timeline? What do you do if sometime changes?
All these questions and more will be explored as we talk about matching clients’ needs with what your agency offers without pulling teeth or pulling your hair out. Practical tips, and strategies for successful relationship building that leads to closing the deal.
GraphRAG is All You need? LLM & Knowledge GraphGuy Korland
Guy Korland, CEO and Co-founder of FalkorDB, will review two articles on the integration of language models with knowledge graphs.
1. Unifying Large Language Models and Knowledge Graphs: A Roadmap.
https://arxiv.org/abs/2306.08302
2. Microsoft Research's GraphRAG paper and a review paper on various uses of knowledge graphs:
https://www.microsoft.com/en-us/research/blog/graphrag-unlocking-llm-discovery-on-narrative-private-data/
Encryption in Microsoft 365 - ExpertsLive Netherlands 2024Albert Hoitingh
In this session I delve into the encryption technology used in Microsoft 365 and Microsoft Purview. Including the concepts of Customer Key and Double Key Encryption.
Epistemic Interaction - tuning interfaces to provide information for AI supportAlan Dix
Paper presented at SYNERGY workshop at AVI 2024, Genoa, Italy. 3rd June 2024
https://alandix.com/academic/papers/synergy2024-epistemic/
As machine learning integrates deeper into human-computer interactions, the concept of epistemic interaction emerges, aiming to refine these interactions to enhance system adaptability. This approach encourages minor, intentional adjustments in user behaviour to enrich the data available for system learning. This paper introduces epistemic interaction within the context of human-system communication, illustrating how deliberate interaction design can improve system understanding and adaptation. Through concrete examples, we demonstrate the potential of epistemic interaction to significantly advance human-computer interaction by leveraging intuitive human communication strategies to inform system design and functionality, offering a novel pathway for enriching user-system engagements.
Smart TV Buyer Insights Survey 2024 by 91mobiles.pdf91mobiles
91mobiles recently conducted a Smart TV Buyer Insights Survey in which we asked over 3,000 respondents about the TV they own, aspects they look at on a new TV, and their TV buying preferences.
JMeter webinar - integration with InfluxDB and GrafanaRTTS
Watch this recorded webinar about real-time monitoring of application performance. See how to integrate Apache JMeter, the open-source leader in performance testing, with InfluxDB, the open-source time-series database, and Grafana, the open-source analytics and visualization application.
In this webinar, we will review the benefits of leveraging InfluxDB and Grafana when executing load tests and demonstrate how these tools are used to visualize performance metrics.
Length: 30 minutes
Session Overview
-------------------------------------------
During this webinar, we will cover the following topics while demonstrating the integrations of JMeter, InfluxDB and Grafana:
- What out-of-the-box solutions are available for real-time monitoring JMeter tests?
- What are the benefits of integrating InfluxDB and Grafana into the load testing stack?
- Which features are provided by Grafana?
- Demonstration of InfluxDB and Grafana using a practice web application
To view the webinar recording, go to:
https://www.rttsweb.com/jmeter-integration-webinar
2. Agendas Covered
1. INTRODUCTION
1.1 Background and Motivation
1.2 Overview of helicopter vibration
1.3 Objectives
2. LITERATURE REVIEW
2.1 Loads acting on a Helicopter in flight
3. HELICOPTER VIBRATION REDUCTION METHODS
3.1 Passive helicopter vibration reduction
3.1.1 Blade design optimization
3.1.2 Main Rotor Gearbox Mounting Systems
3.1.3 Dynamic Response of the Fuselage
2
3. Agendas ......... (Continued)
3.2. Active helicopter vibration reduction
3.2.1 Higher harmonic control
3.2.2 Individual blade control
3.2.3 Active Control of Structural
Response (ACSR)
3.3.Semi-active vibration reduction
technology
3.3.1 Overview of semi-active vibration
reduction concept
3
4. Agendas ..........(Continued)
3.3.3 Helicopter vibration reduction
using semi-active approach
3.3.2 Comparison between active and
semi-active concepts
4. CONCLUDING REMARKS
4
5. CHAPTER 1
INTRODUCTION
Helicopters play an essential role in
today’s aviation with unique abilities
to hover and take off/land vertically
These capabilities enable helicopters to
carry out many distinctive tasks in both
civilian and military operations.
5
6. Despite these attractive abilities,
helicopter trips are usually unpleasant
for passengers and crew because of
high vibration level in the cabin.
This vibration is also responsible for
degradation in structural integrity
as well as
reduction in component fatigue life
6
7. decrease the effectiveness of onboard
avionics or computer systems that
are critical for aircraft primary
control, navigation, and weapon
systems
Consequently, significant efforts have
been dedicated over the last several
decades for developing strategies to
reduce helicopter vibration
7
8. A review the various techniques used
by different helicopter companies to
control helicopter vibrations is
presented here
8
9. 1.2 Overview of Helicopter Vibration
Helicopter vibration generally originates from
many sources; for example,
transmission,
engine, and
tail rotor
but most of the vibration comes primarily from
the main rotor system, even with a perfectly
tracked rotor.
9
10. Figure 1.1 shows a typical vibration
profile of a helicopter, as a function of
cruise speeds,
severe vibration usually occurs in two distinct
flight conditions;
10
11. low speed transition flight (generally
during approach for landing) and
high-speed flight.
the severe vibration level is primarily
due to
impulsive loads induced by interactions
between rotor blades
and strong tip vortices dominating the
rotor wake (Fig. 1.2)
This condition is usually referred to as
Blade Vortex Interaction (BVI)
11
12. Figure 1.2: Blade Vortex Interaction (BVI) schematic
In moderate-to-high speed cruise, the BVI-induced
vibration is reduced since vortices are washed
further downstream from the rotor blades, and the
vibration is caused mainly by the unsteady
aerodynamic environment in which the rotor blades
are operating.
12
13. The control of vibration is important
for four main reasons:
1. To improve crew efficiency, and hence safety of
operation;
2. To improve comfort of passengers;
3. To improve the reliability of avionics and mechanical
equipments;
4. To improve the fatigue lives of airframe structural
components
Hence it is very important to control vibration
throughout
the design,
development and
in-service stages of a helicopter project 13
14. CHAPTER 3
HELICOPTER VIBRATION REDUCTION METHODS
3.1 Passive Helicopter Vibration Reduction
Most of the passive strategies produce moderate
vibration reduction in certain flight conditions, and
only at some locations in the fuselage (such as, pilot
seats or avionics compartments)
The major advantage of the passive concepts is that
they require no external power to operate
However, they generally involve a significant weight
penalty and are fixed in design, implying no ability to
adjust to any possible change in operating conditions
(such as changes in rotor RPM or aircraft forward14
speed).
15. Examples of these passive vibration reduction
strategies include
tuned-mass absorbers,
isolators, and
blade design optimizations.
tuned-mass absorbers
Tuned-mass vibration absorbers can be employed
for reducing helicopter vibration both in the
fuselage and on the rotor system. The absorbers
are generally designed using classical spring mass
systems tuned to absorb energy at a specific
frequency, for example at N/rev, thus reducing
system response or vibration at the tuned
frequency ( Fig. 3.1.1).
15
16. Figure 3.1.1: Frequency response of a dynamic system with and without an absorber
In the fuselage, the absorbers are usually employed to
reduce vibration levels at pilot seats or at locations where
sensitive equipment is placed.
Without adding mass, an aircraft battery may be used
as the mass in the absorber assembly.
16
17. For example, a helicopter known as sea
king uses its battery vibration absorber
or the mass may be parasitic, as in certain
models of the Boeing Vertol Chinook
helicopter, where five vibration absorbers
one in the nose,
two under the cockpit floor
and two inside the aft pylon are used
Sea King battery vibration absorber Boeing-Vertol CH-47 "Chinook"17
18. A centrifugal pendulum type of absorber mounted on
the rotor blade is another type . This type of absorber
has been used on the Bolkow Bo 105 and Hughes 500
helicopters
Next Figure shows the Hughes installation which
consists of absorbers tuned to the 3 and 5
excitation frequencies for the four-bladed rotor
version,
18
19. 3.2. Active Helicopter Vibration Reduction Method
Active vibration reduction concepts have been
introduced
with the potential to improve vibration
reduction capability and
to overcome the fixed-design drawback of the
passive designs
The majority of the active vibration reduction
concepts aim to reduce the vibration in the rotor
system,
and some active methods intend to attenuate/reduce
the vibration only in the fuselage
19
20. In general, an active vibration reduction
system consists of four main components;
sensors, actuators, a power supply unit,
and a controller (Figure)
Actuators Sensors
Controlled
Structure
Controller
The principle of operation is:
based on the sensor input and a mathematical model
of the system, generates an anti vibration field, that
is, as closely as possible identical to the uncontrolled
vibration field but with opposite phase
20
21. If these two vibration fields (the uncontrolled and the
actuator generated) were identical in amplitude and
had exact the opposite phase, then the addition of the
two fields would lead to complete elimination of the
vibrations levels
Also, the controller can be configured to adjust itself
for any possible change in operating conditions using
an adaptive control scheme.
The most commonly examined active vibration
reduction strategies include
Higher Harmonic Control (HHC),
Individual Blade Control (IBC), and
Active Control of Structural Response (ACSR).
21
22. 3.2.1 Higher Harmonic Control (HHC)
The main objective of this concept is to generate higher harmonic
unsteady aerodynamic loads on the rotor blades that cancel the
original loads responsible for the vibration
The unsteady aerodynamic loads are introduced by adding higher
harmonic pitch input through actuation of the swash plate at
higher harmonics
The rotor generates oscillatory forces which cause the fuselage
to vibrate. Transducers mounted at key locations in the fuselage
measure the vibration, and this data is analyzed by an onboard
computer
Based upon this data, the computer generates, using optimal
control techniques, signals which are transmitted to a set of
actuators
22
24. Conventionally, the swash plate is used to provide
rotor blade collective and first harmonic cyclic pitch
inputs (1/rev), which are controlled by the pilot to
operate the aircraft.
In addition to the pilot pitch inputs, the HHC system
provides higher harmonic pitch inputs (for example;
3/rev, 4/rev, and 5/rev pitch inputs for a 4-bladed
rotor) through hydraulic or electromagnetic actuators,
attached to the swash plate in the non-rotating frame
( Fig. 3.2.3).
24
25. 3.2.2 Individual Blade Control (IBC)
The main idea of IBC is similar to that of HHC
(generating unsteady aerodynamic loads to
cancel the original vibration), but with a
different implementation method.
Instead of placing the actuators in the non-
rotating frame (HHC concept), the IBC
approach uses actuators located in the rotating
frame to provide, for example, blade pitch,
active flap, and blade twist inputs for vibration
reduction.
25
26. Schemetics of Individual Blade Control
(IBC) systems are shown below:
(a) blade pitch, (b) active flap, and (c) blade twist controls
26
27. 3.2.3 Active Control of Structural Response (ACSR)
Unlike the HHC and IBC techniques that are intended
to reduce the vibration in the rotor system, ACSR
approach is designed to attenuate the N/rev vibration
in the fuselage, and is one of the most successful
helicopter vibration reduction methods at the present
time
Vibration sensors are placed at key locations in the
fuselage, where minimal vibration is desired (for
example, pilot and passenger seats or avionics
compartments)
Depending on the vibration levels from the sensors, an
ACSR controller will calculate proper actions for
actuators to reduce the vibration.
28. The calculated outputs will be fed to
appropriate actuators, located
throughout the airframe, to produce the
desired active forces
Figure 3.2.5 shows the basic concept of
ACSR.
28
29. The basis of ACSR is that, if a force F is applied to a
structure at a point P and an equal and opposite force
(the reaction) is applied at a point Q, then the effect
will be to excite all the modes of vibration of the
structure which possess relative motion between
points P and Q
This requirement for relative motion in the modal
response between the points where the actuator forces
are applied is an essential feature of ACSR.
Commonly used force actuators include
electro-hydraulic
Piezoelectric, and
inertial force actuators
Extensive studies on ACSR system have been
conducted analytically and experimentally.
29
30. Recently, the ACSR technology has been incorporated
in modern production helicopters such as the Westland
EH101 (Fig. Application of ACSR to the Westland/Augusta Helicopter)
Hydraulic Supply
Composite
Compliant Titanium
Element Lug End
ACSR Actuator
• sa
Steel downtube
30
31. 3.3. Semi-active Vibration Reduction Technology
Semi-active vibration reduction concepts are
developed to combine the advantages of both purely
active as well as purely passive concepts.
Like purely active concepts, semi-active concepts
have the ability to adapt to changing conditions,
avoiding performance losses seen in passive systems
in “off-design” conditions
In addition, like passive systems, semi-active systems
are considered relatively reliable and fail-safe, and
require only very small power (compared to active
systems)
31
32. Semi-active strategies achieve vibration reduction by
modifying structural properties, stiffness or damping,
of semi-active actuators
Semi-active vibration reduction concepts have already
been investigated in several engineering applications
but only very recently has there been any focus on
using them to reduce helicopter vibration
Major differences between active and semi-active
concepts are their actuators and associated
controllers.
Active actuators generally provide direct active force,
while semi-active actuators generate indirect semi-
active force through property modification.
There are several advantages for using the semi-
active concepts over the active concepts:
32
33. power requirement of the semi-active approaches
is typically smaller than that of the active
methods
B/c active actuators generate direct force to
overcome the external loads acting on the
system, while semi-active actuators only modify
the structural properties of the system
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34. Comparison Of the three
Techniques
1. Passive Techniques
Advantages
Require No external power
Disadvantages
Significant Weight Penalty
Fixed in Design-no ability to adjust to any
change in flight condition
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35. 2. Active Techniques
Advantage
Low weight Penalty
Disadvantage
Requirement for external power
3. Semi-active Technique
Advantage
like active-adapt to changing conditions
like passive- small power requirement
(compared to active)
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36. CHAPTER 4: CONCLUDING REMARKS
Figure 4.1 shows a comparison of the vibration
levels of the Westland W30 helicopter without
a vibration reduction system, and when fitted
with a Flexispring rotor head absorber, and an
ACSR system
36