The hysteresis behavior of a linear stroke magnetorheological damper is characterized for sinusoidal displacement excitation at 2.0 Hz (nominal). Four different modeling perspectives are discussed for purposes of system identification procedures, including: (1) equivalent viscous damping, (2) nonlinear Bingham plastic model, (3) nonlinear biviscous model, and (4) nonlinear hysteretic biviscous model. By progressively adding model parameters with which to better represent pre-yield damper behavior, the force vs. velocity hysteresis model is substantially improved. The three nonlinear models represent the force vs. displacement hysteresis behavior nearly equally well. Thus, any of the three nonlinear damper models could be used equally successfully if only a prediction of energy dissipation or damping were of interest. The nonlinear hysteretic biviscous model provides the best representation of force vs. velocity hysteresis of the four models examined here.

A frequency response notion comparable to the classical Bode gain and phase response for linear time invariant (LTI) systems has not been developed for linear time periodic (LTP) systems. In this paper, fundamental input and output signal spaces are identified that lead to a one-to-one map and a linear operator (transfer function). The LTP frequency response, including a characterization of gain, phase and their directional properties, is then presented in terms familiar to the multivariable LTI control theory.

~en,rh Assf. Assoc;ecir~liut A p e d Gessow Rofu,rrnfr Cerlfer Lor{/ C o r~~o r n f i o~~ fle/>flrf~~tee,~f ofAero.r/~<~cc Engir~eerirzg Tlzo,rcns Lord Research Center. U~ri~,ersif~' of Mnr)'lo,cd 110 Lod Drive College Park. MD 20742 C a r : NC 27511Magnetorheological fluid dampers are attractive candidates for augmentation oflag mode damping in helicopter rotors, where additional damping is required lo avert instabilities only during specific flight conditions. Magnetorheological (MR) fluids change properties dran~alically with application of a magnetic field. This active damping component presents an advantage over passive elastnmeric and fluid-elastomeric dampers. An extensive comparative study of fluid-elastomeric and MR dampers is presented. The study was conducted with four (a pair each) 116th Froude scale dampers. The MR dampers were tested with the magnetic field turned off (OFF condition) and with the magnetic field turned on (ON condition). The dampers were tested individually and in pairs, under different preloads, and under single and dual frequency excitation conditinns. The fluid-elastomeric and MR (OFF) damper hehavior was linear, while the MR (ON) hehavior was nonlinear with the sliffness and damping varying with the displacement amplitude. Under dual frequency conditions, the MR dampers (ON condition) showed a significant degradation in damping and stiffness as the dual frequency excitation was increased. The MR (OFF) damperssho~ved n o change in properlies. The fluid-elastonieric dampers showed a mild degradation in stiffness and damping under dual frequency excitation conditions. The MR (ON) damper hysleresis was modeled using a nonlincar viscoelaslic-plastic model. The model captures the nonlinear behavior accurately. Using the single frequency parameters, the dual frequency hysteresis hehavior was predicted, and it correlales well wilh experimental data.

This paper presents a case study of magnetorheological (MR) and electrorheological (ER) valve design within a constrained cylindrical volume. The primary purpose of this study is to establish general design guidelines for volume-constrained MR valves. Additionally, this study compares the performance of volume-constrained MR valves against similarly constrained ER valves. Starting from basic design guidelines for an MR valve, a method for constructing candidate volume-constrained valve geometries is presented. A magnetic FEM program is then used to evaluate the magnetic properties of the candidate valves. An optimized MR valve is chosen by evaluating non-dimensional parameters describing the candidate valves’ damping performance. A derivation of the non-dimensional damping coefficient for valves with both active and passive volumes is presented to allow comparison of valves with differing proportions of active and passive volumes. The performance of the optimized MR valve is then compared to that of a geometrically similar ER valve using both analytical and numerical techniques. An analytical equation relating the damping performances of geometrically similar MR and ER valves in as a function of fluid yield stresses and relative active fluid volume, and numerical calculations are provided to calculate each valve’s damping performance and to validate the analytical calculations.