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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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Journal of Marine Science and Application,Vol.5, No.3, September 2006 18

(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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(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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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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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.

mr damp

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