An MR damper moves fluid between two chambers through passages influenced by a magnetic field. Explore the piston and coil arrangement, then compare yield and viscous contributions in a separate ideal local shear-gap calculation.
Ideal Local Bingham-Gap Estimate
Enter an effective yield stress, plastic viscosity, active shear area, relative speed and gap. This local parallel-gap estimate is not a full annular-flow damper-force model or a current-to-force map.
Equation Used
- Entered yield stress is already known for the fluid, field, temperature and history of interest.
- Velocity is uniform and parallel to a gap of constant thickness over the entered active area.
- Yield and viscous stress contributions are added as an ideal steady Bingham estimate for nonzero speed.
The local estimate adds the force associated with entered yield stress to a viscous contribution based on speed, gap and active area. It does not convert coil current into force or calculate the complete damper response.
Piston coil, annular flow gap and two chambers
MR-damper patents describe a piston moving inside a fluid-filled cylinder, separating two chambers. Piston motion forces fluid through an annular passage. A coil and magnetic pole pieces drive flux through that passage, changing the fluid's flow resistance.
The animation identifies those parts schematically. It does not solve the magnetic circuit, fluid field or complete damper force.
Topology and local constitutive arithmetic
Use the calculator only when effective yield stress and plastic viscosity are already available for the relevant MR fluid and field condition. A real damper requires device-specific geometry, magnetic analysis, pressure-flow modelling, temperature and dynamic validation.
Declared local Bingham approximation
This is a uniform parallel-gap shear estimate. It is not the pressure-drop equation for the complete annular flow path and does not infer yield stress from coil current.
Arithmetic example
For tauy=20 kPa, eta=0.2 Pa s, A=30 cm2, v=100 mm/s and g=1 mm, shear rate is 100 s-1, yield contribution is 60.00 N, viscous contribution is 0.06 N and local total is 60.06 N. This is not a damper rating.
Model boundary
Current-to-yield-stress mapping requires the actual coil, magnetic circuit, fluid curve and temperature.
MR-damper model questions
Does entered yield stress come directly from current?
No. It must come from compatible measured or manufacturer data for the actual field and fluid state.
Is total force the damper's axial force?
No. It is a local parallel-gap shear estimate only.
How does gap enter the calculation?
Relative speed divided by gap thickness gives the local shear rate v/g in this uniform parallel-gap model. Magnetic field is not calculated.
Primary references
- US Patent 5,277,281, Magnetorheological fluid dampers: Carlson and Chrzan's piston, coil, MR-fluid and controllable-valve topology.
- US Patent 6,279,700, Magnetorheological fluid damper: documents two chambers, piston coil, pole pieces, flux ring and annular flow gap.
- US Patent 6,279,701, MR fluid damper with multiple annular flow gaps: documents controlled fluid passage and current-dependent magnetic flux through annular gaps.
- NIST/NEHRP report, Smart structural systems: describes MR fluids as magnetically polarizable particles in carrier fluid with field-controlled yield strength.
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