![[Full-Scale 20-ton
Seismic MR Damper Experiment Setup]](damper_setup.jpg)
Magnetorheological (MR) dampers are semi-acitve control devices that use MR fluids to produce controllable dampers. MR fluids recently developed by the Lord Corporation have many attractive features, including high yield stress, low viscosity and stable hysteretic behavior over a broad temperature range. A typical MR fluid consists of 20-40% by volume of relatively pure, soft iron particles, e.g. carbony iron, suspended in an appropriate carrier liquid such as mineral oil, synthetic oil, water or a glycol. MR fluids made from iron particles exhibit a yield strength of 50-100 kPa for an applied magnetic field of 150-250 kA/m. As a controllable fulid, the primary advantages of an MR fluid are:
MR fluid is able to achieve large, controlled yield stresses.
MR devices can be powered directly from common, low voltage sources. Standard electrical connectiors, wires and feedthroughs can be reliably used, even in mechanically aggressive and dirty environments, without fear of dielectric breakdown.
MR fluid is relative insensitivity to temperature extremes and contaminants. MR fluids can operate at temperatures from -40 to 150 degrees with only slight variations in the yield stress.
To prove the scalability of MR fluid technology to devices of appropriate size for civil engineering applcations, a full-scale, MR fluid damper has been designed and built. For the nominal design, a maximum damping force of 200,000 N and a dynamic range equal to ten were chosen. The damper uses a particularly simple geometry in which outer cylindrical housing is part of the magnetic circuit. The effective fluid orifice is the entire annular space between the piston outside diameter and the inside of the damper cylinder housing. The damper is double-ended. This arrangement has the advantage that a rod-volume compensator does not need to be incorporated into the damper, although a small pressurized accumulator is provided to accommodate thermal expansion of the fluid. The basic parameters for the 20-ton damper are given in the following table.
| Stroke | ±8 cm |
| Fmax/Fmin | 10.1@10 cm/s |
| Cylinder Bore (ID) | 20.32 cm |
| Max. Input Power | <50 watts |
| Max. Force (nominal) | 200,000 N |
| Effective Axial Pole Length | 8.4 cm |
| Coils | 3 x 1050 turns |
| Fluid hp/t2y(field) | 2 x 10-10 s/Pa |
| Fluid Viscosity hp | 1 Pa-s |
| Maximum Fluid Yield Stress ty(field) | 70 kPa |
| Gap | 2 mm |
| Active Fluid Volume | ~90 cm3 |
| Wire | 16 gauge |
| Inductance (L) | 6.6 henries |
| Coil Resistance (R) | 3 x 7.3 ohms |
The experiment setup for the 20-ton MR fluid damper is shown in the following picture. The damper was attached to a 7.5 cm thick pate that was grouted to a 2m thick strong floor. The damper is driven by a 560 kN actuator configured with a 305 lpm servo-valve with bandwidth of 80 Hz. A Schenck-Pegasus 5910 servocontroller is employed in conjuction with a 200 MPa, 340 lpm hydraulic pump.
Research papers relevant
to the pilot MR damper studies can be download from here.
Page designed by Guangqiang
Yang (gyang2@uiuc.edu)
.