mr damp
TRANSCRIPT
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Journal of Marine Science and Application,Vol.5, No.3, September 2006, pp. 17-29
Review of magnetorheological (MR) fluids and
its applications in vibration control
MUHAMMAD Aslam, YAO Xiong-liang, and DENG Zhong-chao
College of Shipbuilding Engineering, Harbin Engineering University, Harbin 150001,China
Abstract: Magnetorheological ( MR ) fluids are now well established as one of the leading materials for
use in controllable structures and systems. Commercial application of MR fluids in various fields,
particularly in the vibration control, has grown rapidly over the past few years. In this paper, properties
of magnetorheological ( MR ) fluids ,its applications in suspensions of vehicles, suspension of trains, high
buildings cable-stayed bridges have been discussed. The scope of MR fluids in future, problems andsome suggestions are also presented. Finally, effectiveness of MR fluids in vibration control of marine
diesel engine through experiment is briefly discussed by the author.
Keywords: MR fluids, applications; properties; vibration control
CLC number:U661.44 Document code: A Article ID: 1671-9433(2006)03-0017-13
1 Introduction1
Magnetorheological is a branch of Rheology that deals
with the flow and deformation of the materials under
an applied magnetic field. The discovery of MR fluids
is credited to Jacob Rabinow[2,3] in 1949.Magnetorheological (MR) fluids are suspensions of
non-colloidal (0.05-10 µm), multi-domain, and
magnetically soft particles in organic or aqueous
liquids. Many different ceramic metals and alloys
have been described and can be used to prepare MR
fluids as long as the particles are magnetically
multi-domain and exhibit low levels of magnetic
coercivity. Particle size, shape, density, particle size
distribution, saturation magnetization and coercive
field are important characteristics of the magneticallyactive dispersed phase. Other than magnetic particles,
the base fluids, surfactants, anticorrosion additives are
important factors that affect the rheological properties,
stability and redispersibility of the MR fluid.
In the “off” state, in terms of their consistency, MR
fluids appear similar to liquid paints and exhibit
comparable levels of apparent viscosity (0.1 to 1 Pa-s
at low shear rates)[4]
. Their apparent viscosity
changes significantly
5 6
(10 10 times)−
within a fewmilliseconds when the magnetic field is applied. The
Received date :2006-03-13.
change in the viscosity is completely reversible when
the magnetic field is removed. Once the magnetic
field is applied, it induces a dipole in each of the
magnetic particles.
The inert-particle forces originating from the magnetic
interactions lead to a material with higher apparent
viscosity. This dipolar interaction is responsible for
the chain like formation of the particles in the
direction of the field (Fig. 1).
It is also believed that in addition to magnetic
interactions between two particles, the formation of
the particles contribute to a certain level to increase
the apparent viscosity. Particles held together by
magnetic field and the chains of the particles resist toa certain level of shear stress without breaking, which
make them behave like a solid. When this shear stress
exceeds a critical value, the structure breaks and the
material starts to flow. MR fluid effect is often
characterized by Bingham Plastic model, which is
discussed in Ref. [5]. The critical value of the shear
stress necessary to break the structure is the “apparent
yield stress” of the material. PHULE and GINDER
reported a yield stress of 100 kPa at a flux density of 1
T for (Fe) 40%ϕ =
Fe based fluids[6]
. WEISS andco-workers reported the yield stress of MR fluids with
an unknown concentration as 90~100 kPa for 30 kOe
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(3 T) of magnetic field[7]
.
(a) No magnetic field
(b) Magnetic field, H
Fig.1 Schematic of the formation of chain-like formation of
magnetic particles in MR fluids in the direction of an
applied magnetic field
2 Properties of MR fluids
2.1 Comparison of field responsive fluids
More recently MR fluids have gained considerably
more attention than their electric analogue
electrorheological (ER) fluids which were discovered
by WINSLOW in 1948[9, 10]
.
One of the advantages of MR fluids is the higher yield
stress value than ER fluids. The reason for having
higher yield stress for MR fluids is the higher magneto
static energy density,2
H µ of MR fluids compared
to electrostatic energy density, 2 E ε
of ER fluids.
Low voltage power supplies for MR fluids and relative
temperature stability between –40°C and +150 °C
make them more attractive materials than ER fluids.
Ferro fluids do not exhibit yield stress, but show an
increase in the viscosity. The viscosity under an
applied magnetic field increases almost twice as much
as the viscosity when there is no magnetic fieldapplied. Since Ferro fluids are synthesized by
colloidal magnetic particles, these fluids are more
stable than MR fluids based on non-colloidal magnetic
particles. The comparison of MR, ER fluids, and Ferro
fluids is discussed in detail in Ref. [66].
2.2 Magnetic materials for MR fluidsIn MR fluids, materials with lowest coercivity and
highest saturation magnetization are preferred,
because as soon as the field is taken off, the MR fluid
should come to its demagnetized state in milliseconds.
Due to its low coercivity and high saturation
magnetization, high purity carbonyl iron powder
appears to be the main magnetic phase of most
practical MR fluid compositions. Iron powders made
by the CVD decomposition of iron pentacarbonyl
(Fe(CO)5)[28, 29]
are preferred as opposed to for
example, those prepared using the electrolytic or spray
atomization process. This is because carbonyl iron is
chemically pure and the particles are meso-scale and
spherical in nature in order to eliminate the shape
anisotropy. The meso-scale particles are necessary
since they have many magnetic domains. The high
level of chemical purity (> 99.7%) means less domain
pinning defects. The spherical shape helps minimize
magnetic shape anisotropy. The impurities that cause
magnetic hardness in metals also cause mechanical
hardness, due to resistance to dislocation motion, and
make the iron particles mechanically harder. In MR
fluid based devices, it is preferred to have non-abrasive
particles. This is another reason why spherical, high
purity iron powders are more appropriate for
applications as a dispersed phase in MR fluids. Thus,
carbonyl iron is chosen because of its high saturation
magnetization (2.1 T, at room temperature)[30]
and
magnetic softness. Among other soft magnetic
materials, Fe-Co alloys (composition (Fe) 50%w = )
have a saturation magnetization of 2.43 T[36]. Although
some researchers reported an enhanced yield stress for
Fe-Co based fluid, the settling problem of the fluid
will be aggravated due to the higher bulk density (8.1
gr/cc) than that of Fe (7.8 gr/cc). Also the cost of these
alloys makes them undesirable for MR fluids.
CARLSON and WEISS reported that as well as
iron-cobalt alloys, iron-nickel alloys in ratio ranging
from 90:10 to 99:1 showed a significant increase in
the yield stress of MR fluids[31]
. MR fluids have been
prepared based on ferromagnetic materials such asmanganese-zinc ferrite and nickel zinc ferrite of an
average size of 2 µm. The saturation magnetization of
ceramic ferrites is relatively low (0.4~0.6 T)[27]
and
Surfactant
Magnetic phase Continuous phase
H
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MUHAMMAD Aslam, et al: Review of magnetorheological (MR) fluids and its applications in vibration control 19
therefore the yield stresses also tend to be smaller.
PHULE and co-workers reported a yield stress of 15 kPa
at a magnetic flux of 15 kPa[32]
.
Magnetic induction curves, or B-H curves of the four
commercial MR fluids are shown in Fig. 2.
Fig. 2 Flux density within MR fluids as a function of
applied field.
Inset: Intrinsic induction as a function of applied field.
Ascending order of the plots corresponds to increasing iron
volume fraction.(MARK,et.al )
2.3 Properties of commercial MR fluids
Magnetic, rheological, tribological and settling
properties of four commercial MR fluids are discussed.
The basic composition of these four fluidscommercially available is given in Table 1.
Table 1 Basic composition and density of four
commercial MR fluids (LORD, 1998)
Commercia
l MR fluid
Percent
iron
by volume
Carrier
fluid
Density
/ -1g mLi
MRX-126PD 26 Hydrocarbon oil 2.66
MRX-140ND 40 Hydrocarbon oil 3.64
MRX-242AS 42 Water 3.88
MRX-336AG 36 Silicone oil 3.47
The rheological properties of controllable fluids
depend on concentration and density of particles,
particle size and shape distribution, and properties of
the carrier fluid, additional additives, applied field,
temperature, and other factors. The interdependency
of all these factors is very complex, yet is important in
establishing methodologies to optimize the
performance of these fluids for particular applications.
Both linear models and models accounting for
nonlinear magnetic effects such as particle saturation
(Ginder, DAVIS and ELIE, 1995; JOLLY, CARLSON
and MUNOZ, 1996) predicted quadratic behavior at
very low flux densities. The non-linear model
proposed by GINDER, DAVIS and ELIE (1995)
predicted a power law index of 1.5 at intermediate
fields. Beyond flux densities of about 0.2~0.3 T, theeffects of magnetic saturation are revealed as a
departure from power law behavior. The stress
response ultimately plateaus as the MR fluids
approach complete magnetic saturation.
2.4 The volume fraction and particle size dependence
of viscosity
At high volume fractions, the particles are close
enough to each other that the flow field of one particle
is affected by the neighbors. Thus the particles aresaid to experience hydrodynamic interactions. At a
concentration of about 50%, a rapid increase in the
viscosity is noticeable[35]
(Fig. 3).
Fig. 3 Dependence of viscosity on the solid loading of alumina
of 0.7 µm mean particle size [35]
The loose packing of uniform spheres assuming
simple cubic packing corresponds to 52% by
volume. At this concentration, the friction due to
particle interactions would become a significant
factor and the resistance to shear seems to cause a
rapid increase in viscosity. At high volume fractions,
the maximum packing volume fraction Φm becomes
important and the relationship can be given by
KRIEGER-DOUGHERTY equation[36]
.
2.5 Linear viscoelasticity
Linear Viscoelasticity is the time dependent
mechanical response of a material to an applied stress.
Under constant deformation, the viscoelastic solid
stores part of the input energy and dissipates the restof this energy whereas a viscoelastic liquid dissipates
all of the energy eventually. An essential characteristic
T / B
0/T H µ
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of the viscoelastic behavior for various transient
experiments such as creep and stress relaxation. In
creep experiments, the stress is suddenly created and
maintained constant and the deformation is observed.
In the stress relaxation experiments, a strain issuddenly imposed and maintained constant and the
change in stress is observed. In a creep experiment, in
order to consider linear viscoelastic for the material,
one requirement is that the strain in the creep
experiment must be proportional to the applied stress.
The stress history of the linear viscoelastic material in
simple shear has to correspond to the strain history.
This most powerful law of polymer physics is known
as the Boltzmann Superposition Principle. If the strain
varies in a continuous function of time, then the strain
at any instant of time t depends on the stress of the
previous times.
2.6 Rheology of magnetorheological (MR) fluids
Many of the models developed for ER fluids can be
adopted for MR fluids in low magnetic fields.
However, at high magnetic fields, due to the
non-linearity and magnetic saturation of the particles,
the linear models used to treat ER fluids are no longer
valid for MR fluids.
In their Finite Element Analysis (FEA), GINDER and
co-workers determined the static yield stress as the
maximum shear stress, which was modeled as tensile
component in the shear direction of the linear infinite
single chains of spherical particles[38, 39]
. Rheology of
magnetic particle dispersions is generally analyzed in
2 steps which are known as pre-yield and post-yield
conditions, respectively (Fig. 4) [5]
.
Pre yield: 0, =′= γ γ σ G , y
σ σ < (1)
Post yield: y
σ γ η σ +=
, y
σ σ ≥ (2)
where η is the plastic viscosity , γ is the shear rate
and y
τ is the dynamic yield stress and G is storage
modulus. The MR fluids within the pre-yield region
exhibit viscoelastic properties and these are important
in understanding MR suspensions, especially for
vibration damping applications. For applied
stresses y
τ τ > , the material is able to flow.
(a) pre yield
(b) post yield
Fig.4 Bingham plastic model
Table 2 Equations of rheological properties for different geometries
Geometry Shear stress Shear rate Strain Viscosity
Concentriccylinder2
ave(2π )
M
R h
2 2
1 2
2 2 2
2 1
2
( )
R R
r R R
Ω
−
2 1
ave R
R R
θ
−
2 2
2 1
2 2
1 2
( )
4π
M R R
h R R
−
Ω
Parallel plate3
2π
M
R
R
h
Ω
R
h
θ
4π
2
MR
h
Ω
Cone and plate3
3
2π
M
R
α
Ω
θ
α
3
3
2π
M
R
α
Ω
Double concentric2 2
1 42π ( )
M
h R R+
2 2
4 1
2 2 2 2
4 3 2 1( ) ( )
R R
R R R R
Ω Ω+
− −
2 2
4 1
2 2 2 2
4 3 2 1( ) ( )
R R
R R R R
θ θ +
− −
2 2 2 2
4 3 2 1( )( )
2π
M R R R R
h
− −
Notes: In these equations, M is the torque, h is the height, R is the radius (Fig. 5, Ω is the angular velocity,θ is the angular displacement and α is the cone
angle [5, 50]
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MUHAMMAD Aslam, et al: Review of magnetorheological (MR) fluids and its applications in vibration control 21
(a) double concentric cylinder
(b) cone and plate
(c) parallel plate
(d) concentric cylinder
Fig. 5 Types of rheometer geometries
2.7 Stability of MR fluids
The stability and redispersibility of MR fluids have
been one of the most important issues of these
materials. Stable MR fluids are considered to exhibit
no or very little amount of particle settling. For dilute
systems, the dependence of the sedimentation velocity
of a spherical particle can be obtained from Stoke’s
law as follows[40]
:22 ( )
.9
s R g ρ
ν η
Δ= (3)
R s is the particle radius, ρ Δ is the difference in
density of the magnetic phase and carrier liquid,η is
the viscosity of the carrier liquid and g is the
gravitational acceleration (9.8 m/s2
). Since, less
viscous liquids will aggravate the settling of the
particles in an MR fluid, Rankin and co-workers
formulated a suspension with viscoplastic continuous phase (e.g., grease) to prevent sedimentation
[41].
When the yield stress of the viscoplastic medium is
bigger than the critical yield stress that was defined
for each particulate material and particle radius, the
particles are suspended. Although, for most of the
applications the figure of merit for MR fluids is to
keep the off state viscosity as small as possible, for
applications such as control of seismic vibrations,
paste-like MR fluids can be more appropriate since
the gravitational settling over an extended period can
be prevented.
2.8 Effect of temperature on MR fluids
When a magnetic field is applied across MR fluids[64]
,
a yield stress is developed, and their rheological
properties can then be categorized into two distinct
regimes: pre-yield and post-yield. The research in
Ref.[64] concerns the viscoelastic behavior of MR
fluids in the pre-yield region. Oscillatory tests were
carried out to determine the complex shear modulus
properties of MR fluids between the temperature
range of -20°C and +50°C. The test results show that
the storage modulus and loss modulus increased in
value as the excitation frequency was increased from
5Hz to 50Hz. The complex modulus was also found to
be influenced by changes in temperature; the higher
the temperature, the lower the complex modulus. This
is consistent with the behavior of viscoelastic
polymers. The sets of temperature-dependent and
frequency-dependent data were subsequently
condensed using the method of reduced variables intomaster curves of complex modulus, which effectively
extended the frequency coverage of the data at the
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reference temperature.
3 Applications of MR
3.1 Applications in automotive industry
A semi-active force tracking PI control scheme with acontrollable MR-damper was formulated and analyzed
[51]
to study its performance characteristics in terms of
vibration attenuation of a quarter-vehicle model
subject to idealized harmonic and transient base
excitations. The simulation results suggest that the
synthesized controller could achieve superior
vibration attenuation performance of the vehicle, and
it offers considerable advantage in view of
implementation since it requires only directly
measurable relative position and velocity signals.
Fig. 6 A car model[51]
Fig. 7 A quarter car model [51]
A semi-active force tracking control strategy is
proposed in Ref.[52-55] to realize desired variable and
asymmetric damping characteristics of a MR damper
used for vibration control of vehicles. The controller is
formulated on the basis of a modified “on-off” control
law, coupled with an inverse model of the hysteretic
MR-damper. An asymmetric force generation function
is further proposed and integrated within the controller
to achieve asymmetric damping properties in
compression and rebound.
A semi-active control for a car suspension system with
a MR damper has been proposed. For vibration
control of the car suspension system[56]
, sliding mode
controller has been used for the system controller and
the damper controller has been designed to adjust the
appropriate input voltage to the MR damper. Inaddition, the effectiveness of the MR suspension
system has been demonstrated via HILS. Under
sinusoidal excitation, it shows the improvement in
reducing the displacement and acceleration. These
results again show that the controlled MR suspension
system can improve the ride comfort quite effectively.
A similar research has been carried out by
Ref.[57-58].
3.2 Applications of MR for train suspension system
A detailed study for semi-active secondary train
suspension system[62]
with MR dampers has been
investigated by considering a full-size railway vehicle,
which includes three vibration motions (vertical, pitch
and roll) of the car body and trucks. The governing
equations of a nine degree-of-freedom railway vehicle
model integrated with MR dampers are developed. To
illustrate the feasibility and effectiveness of controlled
MR dampers on railway vehicle suspension systems,
the LQG control using the acceleration feedback is
adopted as the system controller, in which the state
variables are estimated from the measurable
accelerations with the Kalman estimator.
Fig. 7 Schematic of semi-active control system for railway
vehicle [62] 3.3 Application of MR for seismic protection of
buildings
The experimental study in Ref. [59] investigates
performance of a 12-ton mass supported by a hybrid
base-isolation system that includes rolling pendulum
system and a 20 kN MR damper. The system is tested
on a large shake table and numerous transducersmonitor motion and feedback data to a controller.
Fuzzy logic control is used to design the semi-active
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controller that modulates voltage to the MR damper.
The goal is to mitigate response of the mass with the
aid of the nonlinear base-isolation system. Different
passive and semi-active control cases are used to test
the effectiveness of each strategy.
Fig. 8 Photo of the 12-ton test structure—Hybrid controlled
base-isolation system composed with Ref. [59]
A comparison study[60]
covering two possible types of
‘intelligent’ base isolation systems, ideal fully active
and semi-active via MR damper, was performed. The
response to several earthquake excitations was
computed. This preliminary study suggests that MR
dampers show significant promise in base isolation
applications with greatly reduced power requirements.
A study was carried out by Ref.[61] for the
optimization problem of a complex control system of
a spatial structure with MR dampers by using the
PGA approach, which can suitably deal with not only
the system of large dimensions, but also limited
control force. And the performance index is not
differentiable. The control force is the complicated
nonlinear feedback of state variables. To obtain the
approximate solution, the nonlinear system is firstly
linearized, and then the p.3A is applied to solve the
problem.
A real computational case is given and it has been
shown that the proposed control method is effective in
structural vibration reduction using MR dampers
based on the proposed PGA.
Fig. 9 Comparative time history of effectiveness of vibration
reduction in structural vibration control in Y direction [61]
The performance of a smart isolation system for the
base-isolated two-degree-of-freedom structural model
employing MR fluid dampers has been investigated in
Ref. [63]. The efficacy of this smart base isolation
system in reducing the structural responses for a widerange of loading conditions has been demonstrated in
a series of experiments conducted at the Structural
Dynamics and Control/ Earthquake Engineering
Laboratory at the Univ. of Notre Dame. An analytical
model of the MR damper employing the Bouc-Wen
hysteresis has been presented. a modified
clipped-optimal control strategy has been proposed
and shown to be effective. By applying a threshold to
the control voltage for the MR damper, the controller
becomes robust for the ambient vibration. Thedynamic behavior of this system is also shown to be
predictable.
Fig. 10 Schematic of experimental setup of smart base isolation
model [63]
3.4 Applications in cable-stayed bridges
As primary members of cable-stayed bridges, cables
are susceptible to vibrations because of their low
intrinsic damping. Mechanical dampers[65]
have been
used to improve cable damping. Magnetorheological
(MR) dampers have been proven efficient for seismic
applications because of their large output damping
forces, stable performance, low power requirement,
and quick response from both laboratory research and
field practice. In this research, experimental work was
carried out to demonstrate that MR dampers are also
suitable for cable vibration control. First, a MR
damper was tested with various test parameters to
obtain the performance curves of the MR damper
under different loading conditions, including different
electric currents, loading frequencies, loading wave
types, and working temperatures. The MR damper
was then installed on a cable to reduce the cable
vibration. A 7.16 m long stay cable with a
prototype-to-model scale factor of 8 was established
for this study. The frequencies of the stay cable under
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different tension forces were measured and compared
with those obtained through theoretical calculations.
Then, a free vibration control test was carried out with
the MR damper being installed at the 1/4 point of the
cable. In the forced vibration test, a shaker wasinstalled at 0.18 m from the lower end of the cable.
The measured data show that the damper is efficient
for cable vibration control within its working current
range (zero to maximum) although there is a
saturation effect. It was also observed that the damper
could reduce cable vibration under a variety of
excitation frequencies, especially for resonant
vibrations.
3.5 Experimental research on vibration control of
diesel engine on board ship
Authors have designed an intelligent foundation and
used MR dampers to control the low frequency
vibration of diesel engine onboard ship, as low
frequency vibration can be detected by hostile
weapons and sensors.
It consists of a ship base to simulate the bilge and
engine base for housing the engine. The engine base is
connected with ship base by six passive spring wiredampers, three on each side, each having k =1.01e6
and four MR dampers, two on each side, each having
capacity of 10 kN. These MR dampers can sense the
response. The current was varied in steps to check the
response of the structure at different damping forces.
Fig. 11 shows the detailed dimensions of the
foundation. The super structure of the foundation is
attached by ship base through six springs, three on
each side and four MR dampers, two on each side.
Modal parameters were obtained from experiment by
various sensors, among which 11 in no accelerometers,
two velocity sensors, five in no displacement sensors,
and 5 in no force sensors were used to retrieve
displacement, velocity acceleration and force at
various points on the foundation in three directions.
Signal is amplified through amplifiers and fed to 32
channel FFT analyzer of Brüel & Kjær Company to
compute frequency response function and finally for
post-processing, modal software CAD-X-3.5 is used
for identifying modal parameters and displaying the
data in time history. Output from four MR dampers in
the form of force is also fed through amplifiers
through Modal analyzer to computer to process. A
voltage regulator is used to supply power to MR
dampers from 0A to 2A in steps of 0.25A.
Fig. 11 Dimensions of the foundation
A multi-purpose force simulator is used to apply
excitation force at frequency from 1 to 15 Hz in steps
of 400 from 400 kg to 2400 kg. All the tests are
operated through software with the controlled
computer.
For each test, the simulator machine is programmed to
move up and down in a sinusoidal wave at certain
displacement amplitude and frequency.
Generally, the resonance frequency and magnitude
decrease in a linear systems, the damping coefficient
increases. Both damping coefficient and stiffness of an
MR damper increase when the magnetic field is
applied.
Vibration experiments mainly test the control ability
of the transmission ratio and mainframe vibrating shift
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MUHAMMAD Aslam, et al: Review of magnetorheological (MR) fluids and its applications in vibration control 25
of the MR damper under different harmonic vibrations
in the experimental model.
Fig. 12 Experimental setup for vibration control of diesel engine
Fig.13 Model of intelligent foundation built in ANSYS
3.5.1 Experimental Results
Experiment was performed at various damping states,
excitation frequencies, excitation forces and at
different model mass. The simulations as shown in Fig
14 and 15 are performed at 2 t model mass , 2 400 kg
excitation force and foundation mass is 500 kg.
Fig. 14 Relationship between displacement transmission ratio
and frequency ratio at excitation force of 2400Kg
Fig 14 and 15 show displacement transmission ratio ß
and force transmission ratioη at different damping
states. It is clear that at low damping state, peak is
high and at high damping state, peak is significantly
low at critical frequency ratio, so MR dampers are
quite feasible to control low frequency vibration indiesel engines.
The natural frequency as calculated using ANSYS was
around 8 Hz, but in experiment, it’s around 9 Hz. It’s
because of the fact that hydraulic force simulator used
to input excitation force exerts pre-pressure on the
model due to apparent stiffness and changes of model
mass. From Fig. 14 and 15, it is clear that peak
response of force transmission ratio reduces by
310.9% and peak response of displacementtransmission ratio reduces by 188.6%.
Fig. 15 Relationship between Force transmission ratio and
frequency ratio at excitation force of 2 400 kg
3.5.2 Control System
Control system includes various sensors
(accelerometer, velocity sensors, displacement sensors
and force sensors), amplifiers, FFT analyzer, computer
to process and display modal parameters as shown in
Fig 16. A multi-point loading system with controlled
computer was used to apply sinusoidal load to
simulate excitation force of the engine at different
frequencies.
Displacement and velocity feedback control strategies
were used to control the vibration. Results of vibration
control experiment performed at 1 Ton model
mass, excitation force of 15 kN and at excitation
frequency of 1Hz are shown in Figs. 17 and 18.The
objective of vibration control was that displacement
should not exceed more then 1 mm.
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Fig. 17 Displacement Time history curve for vibration controlof the diesel engine foundation
Fig. 18 Time history curve of MR damper force during
vibration control of diesel engine foundation
From Fig 17 and 18, when vibration starts, the
oscillation amplitude is large in uncontrolled state andexceeded pre-set allowed limit. When control signal is
applied, the displacement decreases and MR damping
force increases to limit the vibration with in
predefined limit.
When MR dampers are used in parallel with spring
wire dampers, it provides better control at low
frequency, and reduces the power transmission rate
and displacement transmission ratio, and vibration
response reduces by 15.1 dB when MR dampers areused as compared to when single spring wire dampers
are used.
4 Perspective on future trends,
problems and suggestions
Commercial applications are clearly expanding and, in
future, will probably be driven by equipment
manufacturers looking to add value to their products
through the introduction of smart fluids. Three areas
where significant developments might be expected
will be mentioned – automotive, civil and aerospace
engineering.
The application of MR fluids to produce controllable
suspension struts in the 2002 model of the Cadillac
STS model is a great success. It was announced that
further Cadillac models, the SRX and XLR will follow,
as well as the Chevrolet Corvette sports car. Inaddition to vibration control of vehicle seats, there are
also likely to be significant developments in
components and systems associated with passenger
protection. Devices whose performance could be
enhanced through the introduction of smart fluids
include airbags, seatbelt retractors, steering column
dampers and external bumpers.
In the civil engineering field, the use of smart fluid
dampers for isolating buildings from seismic
disturbances was mentioned above. Along with the
control of cable stayed bridges subjected to wind and
rain excitation, this represents a key area of
applications where a significant number of further
applications might be expected. One intriguing
possibility is the application of smart fluids to
buildings which employ a significant amount of
structural glass.
With the advent of MR fluids, which obviates the need
for the high voltages associated with ER fluids,
various aerospace applications are currently being
re-appraised. The benefits of employing smart fluids
in aircraft landing gear are well understood and MR
fluid-based units are likely to be developed. The
steer-by-wire system for a forklift truck, which was
noted previously can readily be extended to a number
of control-by-wire functions in aerospace vehicles.
Brake-by-wire, throttle-by-wire and shift-by-wire are
all candidates for the application of MR fluids where
preserving tactile feedback is essential both for safetyand for operator acceptance.
Some problems with MR dampers and suggestions are
given by authors as follows:
1) Large size of MR dampers limits the application of
MR dampers in marine applications due to limited
space especially in submarines, so design of MR
dampers to reduce the size and power needs to be
further researched.2) Non-linear behavior of MR dampers makes it
difficult to devise control strategies to control the
vibration, so this effect further needs to be researched.
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MUHAMMAD Aslam, et al: Review of magnetorheological (MR) fluids and its applications in vibration control 27
3) Control strategies further need to be researched to
control the vibration in varying conditions.
4) Reliability and maintainability should be further
investigated to ensure success.
5) Implementation of MR dampers in real structures.6) To increase the self-sufficiency of the damping
system, investigations into development of a
self-powered MR damper should be pursued.
5 Conclusions
Recently, there has been some exciting development
in MR materials that can provide reasonable force and
long stroke. This material needs careful scrutiny by
researchers. There is great potential that this
revolutionary material might open up many new
frontiers of applications. There are many problems
still need to be addressed and researched. The longer
size of MR dampers restricts its applications in marine
industry, specially in submarines, where it can be
applied to attenuate low frequency harmonics which
are dangerous for submarine, and vulnerable to be
caught by hostile sensors and equipments. The
formulation of MR fluids involves the optimal
balancing of properties for particular applications or
class of applications. Several applications arediscussed to illustrate how various material properties
may be balanced. A comprehensive study has been
carried out on properties of MR fluids by various
researchers and research carried out on vibration
control of marine diesel engine by author is presented
here for reference.
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MUHAMMAD ASLAM, a Pakistani student
was born in 1979.He received the bachelor
degree in mechanical engineering from National
University of Science and Technology(Pakistan)
in 2002 .He is currently a master degree student
in Naval Architecture at Harbin Engineering
University Harbin, China. His primary research
includes active vibration control of marine diesel
engine and numerical solutions to vibration control.
YAO XIONG LIANG, professor, was born in
1963.He received his master degree and PhD in
1989 and 1992 from Harbin Engineering
University respectively. Now he is professor and
Dean of College of Shipbuilding Engineering,
Harbin Engineering University, China. He is the
authors or co-authors of many papers in national
and international journals and conference
proceedings. His research interest includes, ship building, vibration control,
flow induced vibration, structural analysis of ships and many other. He has
won many awards at national level.
DENG ZHONGCHAO was born in 1978 and
received M .S. degree in 2004 from Harbin
Engineering University, China. Now he is a
teacher and PhD candidate for Active Vibration
Control at Harbin Engineering University. His
research interest includes ship building, CAD and
vibration control.