Seismic Protection
Civil and architectural engineers are protecting buildings (and their occupants) with LORD MR technology. MR fluid devices enlarge the control envelope of base-isolation and distributed-damping systems that protect against earthquakes — against both initial shocks and aftershocks.
The Value LORD MR Provides
High dissipative force at low velocity. Unlike with variable orifice dampers, force is not wholly dependent upon velocity, enabling superior mitigation of a broader range of seismic activity. This capability is especially important in mitigating aftershocks, which can be even more damaging than the initial shock.
Continual optimization. Unlike passive systems that are tuned once according to an inferred optimum setting, MR devices continually optimize the rheology (stiffness) of their fluid up to 100 Hz. Further, this controllable re-tuning occurs more quickly with MR than with alternative semi-active solutions.
High dynamic range. The ratio of the maximum force to the minimum force that MR devices provide is much greater than that of any other controllable damper, particularly at low velocities. Unlike friction dampers, MR dampers experience comparatively very low levels of stiction.
Inherent stability and failure-safety. Unlike active dampers that require large power sources, semi-active MR dampers fail-safe to a passive damping mode.
Mechanical simplicity. MR damper valves have no moving parts, reducing maintenance concerns and potential expense.
Fast response-time. Because MR damper valves have no moving parts, their response time is significantly faster than that of variable-orifice dampers.
Small device size. MR technology enables smaller device sizes than with hydraulic or mechanical systems, leading to aesthetic and practical benefits.
Large temperature range. Importantly, MR materials can operate under the extreme conditions often associated with catastrophic events; MR dampers have an operating temperature range of 40° C to 130° C, with no significant variation in performance.
LORD MR Technology at Work
Seismic motion causes on floor to shear relative to the next floor as low-order modes of the building are excited. Excessive motion that is potentially damaging to the building and its contents is controlled by dissipating mechanical energy in a distributed array of dampers. See and AVI video demo.
The LORD MR 180 kN damper is a large-scale MR fluid damper. Real-time damping is controlled by the increase in yield stress of the MR fluid in response to magnetic field strength. The response time of the fluid damping is 60 milliseconds on average as the magnetic field is changed.
See also G. Yang, “Large-Scale Magnetorheological Fluid Damper for Vibration Mitigation: Modeling, Testing and Control,” Ph.D. dissertation, University of Notre Dame, 2001.