requiring large power sources, semi-active control systems have attracted a great deal of attention in recent
years. Recent work by several researchers has indicated that semi-active control systems, when
appropriately implemented, achieve significantly better results than passive control systems; in fact, they
may even outperform fully active control systems, demonstrating significant potential for controlling
structural responses to a wide variety of dynamic loading conditions (Dyke [2] Jansen [3]; Johnson et al.
[4]; Ramallo et al. [5]; Spencer et al.[6]; Yi [7]Yoshioka [8]).
Moreover, MR fluids can be controlled with a low-power (e.g., less than 50 watts), low-voltage (e.g.,
~12-24 volts), current-driven power supply with ~1-2 amps output. Therefore, MR fluids are particularly
promising for natural hazard mitigation and cost sensitive applications. The interested reader is directed to
reviews on MR fluid characterization and their applications, as presented by (Carlson [9] and Yang et al.
[10]. Different techniques have been developed to model the behavior of the controllable fluid dampers.
Basically, two types of models have been investigated: non-parametric and parametric models. Chang [11]
developed a neural network model to emulate the dynamic behavior of MR dampers. However, the nonparametric damper models are quite complicated. Stanway et al. [12] proposed a simple mechanical
model, the Bingham model, in which a Coulomb friction element is placed in parallel with a dashpot. The
model consists of a Bingham model in series with a standard model of a linear solid model. Kamath [13],
Makris et al. [14], and Wereley et al. (1998) developed parametric models to characterize ER and MR
dampers. Bouc-Wen model versatility was utilized to describe a wide variety of hysteretic behavior.
Ramallo et al. [5] and Yoshioka et al. [8] incorporated an MR damper with a base isolation system such
that the isolation system would be effective under both strong and moderate earthquakes. Johnson et al. [4]
employed the MR damper to reduce wind-induced stay cable vibration. The objectives of this work were to
design and fabricate an low cost MR fluid based damper, to study the characteristic of an MR fluid with
different current and to design a controller to control the vibration.
HARDWARE DESIGN AND FABRICATION
The MR damper is very similar with conventional damper except with some additional electrical part.
Major components of MR damper are Piston, Housing, MR Fluid and induction coil. Since the actual
comprehensive construction of MR Damper is confidential from most manufacturers, we needed to
proceed with our own design of the MR Damper.
Magnetic Induction Coil
This is considered one of the most vital parts of the system which will provides the magnetic field for MR
fluid. By applying the correct amount of current, the MR fluid will change its state from a less viscous fluid
to a more viscous state. Coil is installed around the piston; this type of installation might be theoretically
offers better functionality as is consumes less space which leads to the whole system are lighter and smaller.
External Housing
We presumed that the external housing to encapsulate the whole system must be free from any magnetic
influence. For the external housing, we have used the conventional damper‟s housing (Fig. 2). The size also
is suitable just like usual damper for most vehicles with outer diameter of 5 cm and inner diameter of 3 cm
but more importantly it fits trough the vibration testing machine. Additional features have to be added to the
housing to make it capable to be mounting at the testing machine.
Fig. 3 Piston with Coil
Fig. 2 External housing
Piston also considered as major part of the system in providing the damping. The piston is made from a
material that is non metal to avoid any disturbance on the magnetic field from the coil. For that we have
several choices of material such as Teflon, fibre and Perspex but we finally chose aluminium since it is
easier to machine according to our design and also it is available for free at IIUM workshop.
Experimental Setup
After fabrication of MR damper, experimental setup was done using GANT Universal Vibration Machine
at Vibration and Dynamic Laboratory. In this experimental setup, the machine will excite testing substance
with an exciter motor and the damper will absorb the vibration, accordingly. This setup consists of a PIC
microcontroller 16F877 and relay circuit. Flowchart of the experimental work is shown in Fig 5
Exciter/ actuator
Accelerometer
MR Damper
PIC 16f877
Relay circuit
Fig 5 System setup
Start
Power on Exciter
motor
Damping start
Suppress damping
Controller
MR Damper
Reduced damping
End
Fig. 6 Flow chart of Experimental process.
The system was excited by the exciting motor at frequency of 7.7 Hz. Experimental results are shown
from Fig 7 to Fig 10.
Fig.7 The system vibration with MR Damper is off.
Fig. 8 System vibration when MR damper is ON.
Fig 9 Vibration suppression with MR damper
Fig 10 Vibration suppression with MR damper
From both of the graph obtained, it can be stated that when the vibration exciter frequency set at 7.7 Hz,
and the MR damper is off, the system vibrate at an amplitude of 0.6V. After the MR damper is switch ON,
and the exciter frequency is set as before, the amplitude is reduce to 0.4V.
7 DISCUSSIONS AND RECOMMENDATION.
This paper reports the design and the manufacture of a new MR damper based on a electromagnetic coil.
The paper provides also a description of the magnetizing device technology, characterization test results
and optimization criteria. This new MR damper prototype was designed and fabricated on a basis of
minimum component change from the original passive damper and to use for a semiactive vibration control.
The results obtained from laboratory tests and numerical simulations clearly show that the damping
coefficient could be increased up to three times when the exciting current inside the coils is around 1
ampere. As stated earlier in the objectives of this project, the amplitude of vibration of the system reduces
by applying MR damper has been established.
Reference
[1] Housner, G.W. et al. (1997). “Structural control: past, present, and future.” J. Engrg. Mech.,
ASCE, 123:897–971.
[2] Dyke, S.J., Spencer Jr., B.F., Quast, P., Sain, M.K., Kaspari, Jr., D.C., and Soong,, R., and Kar,
R. (2000). “Performance evaluation of friction
[3] E.A., Baker, G.A., Spencer Jr., B.F., and Fujino, Y. (2001a). “Semiactive Damping of Stay
Cables.” J. Engrg. Mech., ASCE,
[4] Johnson , E.A., Christenson R.E., and Spencer Jr., B.F. (2001b). “Semiactive damping of
cables with sag.” ASCE, 120:120–126
[5] Ramallo, J.C., Johnson, E.A., and Spencer Jr., B.F. (2001). “„Smart‟ base isolation systems.”
J. Engrg. Mech., ASCE, submitted.
[6] Spencer Jr., B.F., Suhardjo, J., and Sain, M.K. (1994). “Frequency domain optimal control
strategies for aseismic protection.” J. Engrg. Mech., ASCE, 120:135–159.
[7] Yi, F., and Dyke, S.J. (2000). “Structural control systems: performance assessment.”Proc. of
American Control Conf., Chicago, IL.
[8] Yoshioka, H., Ramallo, J.C., and Spencer Jr., B.F. (2001). “„Smart‟ base isolation strategies
employing magnetorheological dampers.” J. Engrg. Mech., ASCE, submitted.
[10] Carlson, J.D., Catanzarite, D.N. and St Clair, K.A. (1996). “Commercial Magneto- Rheological
Fluid Devices.” Proceedings 5th Int. Conf. on ER Fluids, MR Suspensions and Associated
Technology, W. Bullough, Ed., World Scientific, Singapore, pp. 20–28.
[11] Yang, G., Jung, H.J., and Spencer Jr., B.F. (2001c). “Dynamic model of full-scale MR dampers for
civil engineering applications.” Proc. US-Japan Workshop on Smart Structures for Improved
Seismic Performance in Urban Region, Seattle, WA
[12] Chang, C.C., and Roschke, P. (1998). “Neural network modeling of a magnetorheological damper.”
J. Intelligent Material Systems and Structures, 9:755–764.
[13] Stanway, R., Sproston, J.L., and Stevens, N.G. (1987). “Non-linear modeling of a
electrorheological vibration damper.” J. Electrostatics, 20:167–184.
[14] Kamath, G.M., and Wereley, N.M. (1997). “Nonlinear viscoelastic-plastic mechanisms based
model of an electrorheological damper” J. Guidance, Control, and Dynamics, 20(6):1125-1132.