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ACTIVE VIBRATION CONTROL Professor Mike Brennan Institute of Sound and Vibration Research University of Southampton, UK.

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Presentation on theme: "ACTIVE VIBRATION CONTROL Professor Mike Brennan Institute of Sound and Vibration Research University of Southampton, UK."— Presentation transcript:

1 ACTIVE VIBRATION CONTROL Professor Mike Brennan Institute of Sound and Vibration Research University of Southampton, UK

2 Active Vibration Control WHY ? Structures become lighter Space and weight constraints ActuatorsSensors Controlled Structure Controller

3 Active Vibration Control Active control strategies Semi-active/adaptive-passive control changing damping changing stiffness changing mass tunable vibration neutralisers Fully-active control where to place the control force feedforward control feedback control control of waves

4 Active Vibration Control Control strategy Disturbance Physical objective Deterministic Random Global control Blocking structural path Local Control Feedback Feedforward Semi-active Fully-active

5 Active Vibration Control m k c m k c m k c fpfp fpfp fpfp fsfs Passive Semi-active /Adaptive-passiveFully- active Passive – Mass, stiffness and damping (quantity and distribution) fixed at the design stage Fully-active – Dynamic forces applied to the system to minimise the response Semi-active / Adaptive-passive – Stiffness and/or damping properties changed to adjust internal dynamic forces to minimise the response

6 SEMI-ACTIVE / ADAPTIVE-PASSIVE VIBRATION CONTROL

7 Semi-Active / Adaptive-Passive Vibration Control Strategies Change Stiffness – low frequencies (air spring) Change mass – high frequencies ?? m k c f Change damping – resonance (hydraulics, electro / magneto rheological fluids frequency |Displacement/force| stiffness controlled mass controlled damping controlled high damping low damping

8 ADAPTIVE DAMPING

9 Electro / Magneto -Rheological Fluids micron sized, polarizable particles in oil What do they do? Newtonian in absence of applied field develop yield strength when field applied What are they ? ER fluids respond to electric field MR fluids respond to magnetic field

10 Basic ER/MR Device Configurations hydraulic controls servo valves dampers shock absorbers actuators clutches and brakes chucking/locking devices dampers breakaway devices structural composites Direct Shear Mode force velocity N S applied magnetic field E Valve Mode flow pressure N S applied magnetic field applied electric field

11 Typical MR Fluid Behaviour at 25°C Shear Stress (kPa) Shear Strain Rate (sec ) 0 kA/m 80 kA/m 160 kA/m 240 kA/m Bingham Model Total damping = Viscous Damping + Coulomb Damping ConstantDue to MR effect

12 Magneto-Rheological Fluids - Applications Ride Mode Switch MR Fluid Damper Sensor/Controller

13 Magneto-Rheological Fluids - Applications Seat Sensor Controller Spring Controllable shock absorber Road input Acceptable motion transmitted Off-state Random pattern On-State Ordered pattern Single Degree of Freedom System - Heavy Duty Vehicle Suspended Seats off-highway, construction and agricultural vehicles class 8 trucks ("eighteen wheelers") buses

14 Magneto-Rheological Fluids - Applications Seismic excitation Nihon-Kagaku-Miraikan National Museum of Emerging Science and Innovation Opened July, 2001 Tokyo, Japan 2 30-ton MR dampers installed between 3rd and 5th floors Dong Ting Lake Bridge Hunan Province, PRC Wind excitation

15 ADAPTIVE STIFFNESS

16 mTmT Change in Stiffness Table systems mAmA pneumatic isolators Stiffness of a pneumatic spring = where = pressure in the pneumatic spring = cross-sectional area of the bellows = air volume = ratio of specific heats …………………..(1)

17 Change in Stiffness Consider a single mass on a pneumatic spring m k The natural frequency is given by: ………………………….(2) Substituting for k from (1) gives: But PA=F=mg, therefore: Thus provided that the area and volume remain constant, then the natural frequency is independent of the mass Normally designed to have a natural frequency of

18 Change in Stiffness – shape memory alloys When the memory metal is pulled apart, it deforms. When placed into hot water, the metal "remembers" its original shape, and again forms the letters ICE. Memory metal is a nickel-titanium alloy This piece has been formed into the letters ICE, heat- treated, and cooled.

19 Change in Stiffness – shape memory alloys Soft Stiff Stiffness increases With temperature

20 Change in Stiffness – shape memory alloys Material whose Youngs modulus changes with temperature Composite panel } Embedded SMA wires Activating the fibres (by passing a current through them and hence causing a temperature change) causes local stiffening and hence the natural frequencies can be shifted to avoid troublesome excitation frequencies.

21 Variable Stiffness Civil Engineering

22 TUNABLE VIBRATION ABSORBERS

23 structure Tunable Vibration Absorbers The Vibration Absorber – What does it do? m k c frequency

24 Tuned Vibration Absorber frequency

25 Tunable Vibration Absorbers Some Terminology frequency Natural frequency Absorber: Tuned to suppress the response at a troublesome resonance frequency Forcing frequency Neutraliser: Tuned to suppress the response at a troublesome forcing frequency

26 The Absorber – some key parameters m k c mama kaka caca Mass ratio Optimum Damping frequency

27 Location of absorbers Land-Mark Tower Yokohama mama kaka caca m k c Tunable Vibration Absorbers

28 Land-Mark Tower Yokohama Largest building in Japan (earthquake zone)

29 mama kaka caca m k c Acvtive Tunable Vibration Absorbers K Λ + _ Relative displacement z(t) measured using a stroke transducer Measured value of z(t) Desired value of z(t) Computer model of second order system with variable natural frequency And damping ratio A secondary force f s (t) is used to tune a vibration absorber

30 Tunable Vibration Absorbers 63 rd floor of the Citicorp Centre, New York City

31 Citicorp Centre New York City

32 frequency Forcing frequency Tunable Vibration Neutralisers Change damping Change stiffness frequency

33 mama kaka caca m Some Important Parameters Tunable Vibration Neutralisers

34 Pneumatically Controlled Vibration Neutraliser (50-100Hz) Too much damping

35 Beam-Type Neutraliser excitation L effective mass of the beam Change E, I or L k m

36 Beam-Type Neutraliser h=distance between beams d=thickness of one beam

37 35% change in natural frequency Servo motor Beam-Type Neutraliser

38 Shape Memory Alloy Beam-Like Neutraliser shaker neutraliser shape memory alloy wires impedance head

39 Change in Stiffness – Shape Memory Alloys

40 Change in Stiffness – shape memory alloys Elastic modulus changes from 40 to 59 MPa Hysteresis of about 10°C Temperature EmEm EaEa Cooling Heating Soft Stiff Stiffness increases With temperature

41 Shape Memory Alloy Beam-Like Neutraliser Cold state Hot state Frequency [Hz] Force/Velocity [Ns/m] mama kaka caca m

42 Shape Memory Alloy Beam-Like Neutraliser Steady-State Experimental Results 63.9 Hz77.6 Hz+17.5% Temperature below 35°CTemperature above 67°C

43 Shape Memory Alloy Beam-Like Neutraliser temperature ( ºC) frequency (Hz) increasing temperature natural frequency

44 Shape Memory Alloy Beam-Like Neutraliser temperature ( ºC) frequency (Hz) decreasing temperature natural frequency

45 Performance Time cos( ) D[cos( )] I Time V(Host) V(TVA) Good performance also with the real ATVA No oscillation around the equilibrium point Constant excitation frequency 59Hz from amb

46 Change in natural frequency by shape change mass Host structure Low natural frequency mass Host structure Change curvature High natural frequency Curved beams

47 Change in stiffness by change in curvature p h s u

48 Adaptive Neutraliser using shape change natural frequency: 39 Hz - 50 Hz

49 Adaptive Neutraliser using shape control

50 Control mama kaka caca m Adjust stiffness so that natural frequency=forcing frequency Large steps small steps

51 Control Algorithm The controller updates the output current every T n seconds e n is the evaluation of cosΦ at the n th time step The current at the (n+1) th time step: P: Constant of the non-linear proportional part D: Constant of the derivative part

52 Control Measure phase angle and set mama kaka caca m

53 Frequency sweep test input/output board voltage amplifier electrodynamic shaker ATVA PC variable frequency harmonic excitation signal amplifier accelerometers controller output Adaptive Neutraliser using shape control amplifier

54 Frequency sweep test – NO CONTROL P-D CONTROL time (s) cos(phase) time (s) frequency (Hz) 38 Hz 52 Hz 2 Hz/s at 0 V

55 Boeing CH - 47C Three adaptive self- tuning absorbers (neutralisers) are installed and tuned to the blade passage frequency of approximately 11 Hz

56 Upper chamber Lower chamber Decoupler Primary rubber Rubber bellows Inertia track Hydraulic engine mount High damping at low frequencies Low damping at high frequencies

57 Hydraulic engine mount Amplitude sensitive device Damping peaks at a low frequency which is controlled by the mass of the fluid in the inertia track and stiffness of the rubber elements Increased stiffness at high frequencies stiffness damping

58 Adaptive hydraulic engine mount damping m Engine side Structure side Effective length of inertia track is adjusted in real-time

59 Freudenburg active engine mount actuator working reservoir outer reservoir balance reservoir bellows rubber element diaphragm At low frequencies (<20Hz) the mount behaves as a conventional hydromount At high frequencies the inertia of the fluid is high decoupling the working and balance reservoirs At high frequencies the generated forces are in anti-phase with the dynamic forces generated by the engine

60 Combined active noise/engine mount system

61 Engine speed (RPM) dB re 20 μ Pa Drivers position 3 rd gear acceleration

62 Active mount driven with a piezo actuator Chassis acceleration (dB) Engine speed (RPM)

63 FULLY-ACTIVE VIBRATION CONTROL

64 FEEDFORWARD CONTROL OF VIBRATION Used where it is possible to get advance information on the vibration to be controlled eg. To control machinery vibration which is generally periodic in nature Mechanical system Controller + + Excitation Response

65 Fully-Active Systems – where to place the secondary force? - SDOF example m k c receiver m k c m k c (1)Secondary source applied to source (2) Secondary source applied to receiver (3) Secondary source applied between source and receiver Where to apply the secondary force to bring the receiver to rest with a minimum applied force?

66 Fully-Active Systems – where to place the secondary force? - SDOF example m k c receiver (1)Secondary source applied to source

67 Fully-Active Systems – where to place the secondary force? - SDOF example m k c receiver (2) Secondary source applied to receiver Or in non-dimensional terms as where

68 Fully-Active Systems – where to place the secondary force? - SDOF example Or in non-dimensional terms as m k c receiver (3) Secondary source applied between source and receiver

69 Fully-Active Systems – where to place the secondary force? - SDOF example Force applied to the receiver Force applied to the source Force applied between the receiver and the source

70 Application of ACSR to the Westland/Agusta EH101 Helicopter. Active Control of Structural Response (Westlands, 1989)

71 Active Control of Rotor Vibration rotor fuselage Hydraulic actuators Active control at rotor blade passing frequency at about 18 Hz + harmonics Feedforward control

72 ACSR ACSR - Actuator Installation for Production EH101 sa Steel downtube Composite Compliant Element Titanium Lug End ACSR Actuator Hydraulic Supply Main Gearbox Installation Fwd Support Strut/ACSR Actuator Assembly

73 FEEDBACK CONTROL OF VIBRATION Used where it is not possible to get advance information on the vibration to be controlled Often used to control random vibration Mechanical system Controller + + Disturbance Response

74 Feedback Control of a Single-degree-of-freedom System X Y c m H(j ) k FsFs equipment actuator controller vibrating base accelerometer Can feed back displacement, velocity or acceleration Feedback gains Closed-loop response is given by

75 Feedback Control of a Single-degree-of-freedom System – base excitation Constant gain feedback control Non-dimensional frequency dB X Y c m H(j ) k fsfs equipment actuator controller vibrating base accelerometer

76 Open-Loop FRF – Nyquist Plots (simulations) No high-pass filterOne high-pass filter All are unconditionally stableVelocity feedback is the most stable

77 Active Vibration Isolation – Feedback Control Equipment Controller Base plate Primary shaker Secondary shaker Electromagnetic actuator - relatively low forces and large displacements Objective To isolate the delicate piece of equipment using active vibration control

78 The Control Problem Decentralised Control

79 imaginary real Stability of the Decentralised Control System (measurements) Stability criterion: None of the eigenvalues i should encircle the Nyquist point (-1,0) as varies from – infinity to +infinity

80 Performance of the Decentralised Control System (measurements)

81 Overall Performance Decentralised velocity feedback control Electromagnetic actuators in parallel with resilient mounts Feedback of absolute velocity in 4 local loops Analogue controller – still effective if one channel fails

82 Example: Feedback (displacment) control of circular saw vibrations (Ellis and Mote, 1979)

83 Example: Ride comfort improvement o an aircraft (Sensburg et al, 1980) Frequency (Hz) Discomfort due to fuselage bending Mode at 9 Hz Velocity feedback to the taileron 9Hz vibration reduced by 2/3

84 Flexural waves in a beam power

85 Active control of waves in beams Equivalent block diagram

86 Active control of waves in beams Frequency (Hz) PSD at error sensor (dB) Poor performance at low frequencies because of noise and presence of near field wave Poor performance at high frequencies because of high group velocity causing causality problems

87 Concluding Remarks Active control of vibration is being used as an alternative to passive control in many different applications Weight /space constraints Novelty factor Many more current and potential applications: Dynamic control of large space structures Flutter control in aircraft Vibration isolation Vibration control of rotating machines

88 References C.R. FULLER, S.J. ELLIOTT and P.A. NELSON Active Control of Vibration. Academic Press P.A. NELSON and S.J. ELLIOTT Active Control of Sound. Academic Press C.H. HANSEN and S.D. SNYDER 1997 Active Control of Noise and Vibration. E & F.N. Spon R.L. CLARK, W.R. SAUNDERS and G.P. GIBBS Adaptive Structures. Wiley Interscience A.V. SRINIVASAN and D. MICHAEL McFARLAND Smart Structures. Cambridge University Press


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