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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 Actuators Sensors 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 Feedback Feedforward Semi-active Fully-active Deterministic Random Global control Blocking structural path Local Control

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

6 SEMI-ACTIVE / ADAPTIVE-PASSIVE VIBRATION CONTROL

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

8 ADAPTIVE DAMPING

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

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

11 Typical MR Fluid Behaviour at 25°C
Bingham Model Shear Stress (kPa) 20 40 60 80 100 120 25 50 75 Shear Strain Rate (sec -1 ) 0 kA/m 80 kA/m 160 kA/m 240 kA/m Total damping = Viscous Damping + Coulomb Damping Constant Due to MR effect

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

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

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 Change in Stiffness mA mT Stiffness of a pneumatic spring =
Table systems mA mT                                      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 m k Consider a single mass on a pneumatic spring
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
Memory metal is a nickel-titanium alloy This piece has been formed into the letters ICE, heat-treated, and cooled. 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.

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

20 Change in Stiffness – shape memory alloys
Material whose Young’s 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 Tunable Vibration Absorbers
The Vibration Absorber – What does it do? structure 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

26 The Absorber – some key parameters
Mass ratio Optimum Damping ma ka ca m k c frequency

27 Tunable Vibration Absorbers
Location of absorbers Land-Mark Tower Yokohama ma ka ca m k c

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

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

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

31 Citicorp Centre New York City

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

33 Tunable Vibration Neutralisers Some Important Parameters
ma ka ca m frequency

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

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

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

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

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
Temperature Em Ea Cooling Heating Soft Stiff Stiffness increases With temperature Elastic modulus changes from 40 to 59 MPa Hysteresis of about 10°C

41 Shape Memory Alloy Beam-Like Neutraliser
Cold state Hot state Frequency [Hz] Force/Velocity [Ns/m] ma ka ca m

42 Shape Memory Alloy Beam-Like Neutraliser
Steady-State Experimental Results Temperature below 35°C Temperature above 67°C 63.9 Hz +17.5% 77.6 Hz

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

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

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

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

47 Change in stiffness by change in curvature
p h

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

49 Adaptive Neutraliser using shape control

50 Control small steps Large steps ma ka ca m Adjust stiffness so that natural frequency=forcing frequency

51 The controller updates the output current every Tn seconds
Control Algorithm The controller updates the output current every Tn seconds en is the evaluation of cosΦ at the nth 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 ma ka ca m

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

54 Frequency sweep test – NO CONTROL P-D CONTROL
2 4 6 8 10 12 14 16 18 20 35 40 45 50 55 time (s) frequency (Hz) 38 Hz 52 Hz 2 Hz/s at 0 V 2 4 6 8 10 12 14 16 18 20 -10 time (s) acceleration (m/s ) 2 4 6 8 10 12 14 16 18 -1 1 time (s) cos(phase) 20

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

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

57 Hydraulic engine mount
stiffness damping 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

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

59 Freudenburg active engine mount
actuator 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 diaphragm working reservoir outer reservoir balance reservoir rubber element bellows

60 Combined active noise/engine mount system

61 Combined active noise/engine mount system
dB re 20 μPa Engine speed (RPM) Drivers position 3rd 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 Response Excitation Mechanical system + + Controller

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

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

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

69 Fully-Active Systems – where to place the secondary force
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 Active Control of Structural Response (Westlands, 1989)
Application of ACSR to the Westland/Agusta EH101 Helicopter.

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

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

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 Disturbance Response Mechanical system + + Controller

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

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

76 Open-Loop FRF – Nyquist Plots (simulations)
No high-pass filter One high-pass filter All are unconditionally stable Velocity feedback is the “most” stable

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

78 The Control Problem Decentralised Control

79 Stability of the Decentralised Control System (measurements)
imaginary real 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)
Discomfort due to fuselage bending Mode at 9 Hz Velocity feedback to the taileron 9Hz vibration reduced by 2/3 Frequency (Hz)

84 Flexural waves in a beam
power

85 Active control of waves in beams
Equivalent block diagram

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

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 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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