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DEVELOPMENT OF MR DAMPER
The design of the bypass-flow-type MR damper, which was developed by fifth author for semi-active
control of base isolation, is shown in Figure 6 and TABLE 3. It is composed of three parts: bypassflow,
pressure chambers and a reservoir. The bypass flow portion has an orifice for effectively
magnetizing the fluid. The uniform magnetic field is applied perpendicularly to the MR fluid flow at
the annular orifice. The thermal expansion due to the temperature rise of the MR fluid is absorbed by
the reservoir.
Cyclic loading tests were conducted to clarify the performance of the MR damper. Figure 7 shows
the force-displacement relationship. The electric current to the electromagnet was set at a constant
value of OA~ 3 A in the 0.3A interval. The hysteretic loop shows rigid-plastic like characteristics
caused by friction force of the MR fluid with magnetic field. The force increases almost
proportionally to the increase in the electric current. Figure 8 shows the force-velocity relationship.
The velocity is the maximum velocity of the piston in the case of sinusoidal loading. This figure also
shows that the force increases almost proportionally to the increase in the electnc current, and the
force does not depend so much on the piston velocity.
Bypass Fbw
.Reservoir TABLE 3
DESIGN SPECIFICATION
Coil
Figure 6: Structure of MR damper
M ax Force
Stroke
Cy Inder Bore
Secton
Orifce
Length
Inductance
E lectrom agnet Res stance
M ax.Curreni
MR fliri
40kN
± 295m in
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1 "^
T
OA
-15 -10 -5 0 5 10 15
Displacement (m)
(a) O.lHz, 10cm, 6.28cm/sec
40
^20
z;
A*
o 0
CJ
O
i,
-20
-40
T
3.0A
T
OA
-30 -20 -10 0 10 20 30
Displacement