The hysteresis behavior of a linear stroke magnetorheological damper is characterized for several magnetic fields and sinusoidal excitations over a nominal operational frequency range of 10-30 Hz The behavior of the damper is inadequately modeled using the equivalent viscous damping and the complex modulus Therefore, four different nonlinear modeling perspectives are discussed for purposes of system identification procedures, including the 1) nonlinear Bingham plastic model, 2) nonlinear biviscous model, 3) nonlinear hysteretic biviscous model, and 4) nonlinear viscoelastic plastic model The first three nonlinear models are piecewise continuous in velocity The fourth model is piecewise smooth in velocity The parameters for each model are identified from an identification set of experimental data; these parameters are then used to reconstruct the force vs displacement and the force vs velocity hysteresis cycles for the respective model Model performance is evaluated by calculating equivalent viscous damping and force time history errors between the model fit and the experimental data In addition to the identification study, a validation study was done Model parameters were calculated for offset values of current and frequency These intermediate parameters were used to calculate hysteresis cycles, which were compared with a second set of experimental data, a validation data set Identification and validation study results including damping levels and force time history errors

Characterization and Analysis of Magnetorheological Damper Behavior Under Sinusoidal Loading

Aircraft landing gears are subjected to a wide range of excitation conditions with conflicting damping requirements. A novel solution to this problem is to implement semi-active damping using magnetorheological (MR) fluids. In part 1 of this contribution, a methodology was developed that enables the geometry of a flow mode MR valve to be optimized within the constraints of an existing passive landing gear. The device was designed to be optimal in terms of its impact performance, which was demonstrated using numerical simulations of the complete landing gear system. To perform the simulations, assumptions were made regarding some of the parameters used in the MR shock strut model. In particular, the MR fluid's yield stress, viscosity, and bulk modulus properties were not known accurately. Therefore, the present contribution aims to validate these parameters experimentally, via the manufacture and testing of an MR shock strut. The gas exponent, which is used to model the shock strut's nonlinear stiffness, is also investigated. In general, it is shown that MR fluid property data at high shear rates are required in order to accurately predict performance prior to device manufacture. Furthermore, the study illustrates how fluid compressibility can have a significant influence on the device time constant, and hence on potential control strategies.

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Magnetorheological landing gear: 2. Validation using experimental data

The hysteresis behavior of a linear stroke magnetorheological damper is characterized for sinusoidal displacement excitation at 2.0 Hz (nominal). First, we characterize the linearized MR damper behavior using equivalent viscous damping and complex stifiness. Four difierent nonlinear modeling perspectives are then discussed for purposes of system identiflcation procedures, including: (1) nonlinear Bingham plastic model, (2) nonlinear biviscous model, (3) nonlinear hysteretic biviscous model, and (4) nonlinear viscoelastic-plastic model. The flrst three nonlinear models are piecewise continuous in velocity. The fourth model is piecewise smooth in velocity. By adding progressively more model parameters with which to better represent pre-yield damper behavior, the force vs. velocity hysteresis model is substantially improved. Of the three nonlinear piecewise continuous models, the nonlinear hysteretic biviscous model provides the best representation of force vs. velocity hysteresis. The nonlinear viscoelastic plastic model is superior for purposes of simulation to the hysteretic biviscous model because it is piecewise smooth in velocity, with a smooth transition from pre-yield to post-yield behaviors. The nonlinear models represent the force vs. displacement hysteresis behavior nearly equally well, although the nonlinear viscoelastic-plastic is quantiflably superior. Thus, any of the nonlinear damper models could be used equally successfully if only a prediction of energy dissipation or damping were of interest.

/pdf/analysis-and-testing-of-a-linear-stroke-magnetorheological-k87lawa4bu.pdf

Analysis and testing of a linear stroke magnetorheological damper

We experimentally validate nonlinear quasi-steady electrorheological (ER) and magnetorheological (MR) damper models, using an idealized Bingham plastic shear flow mechanism, for the flow mode of damper operation. An electrorheological valve or bypass damper was designed, and fabricated using predominantly commercial off-the-shelf hydraulic components. Both the hydraulic cylinder and the bypass duct have cylindrical geometry, and damping forces are developed in the annular bypass via Poiseuille (flow mode) flow. Damper models assume parallel plate geometry. Three nondimensional groups are used for damper analysis, namely, the Bingham number, Bi, the nondimensional plug thickness, 6, and the area coefficient defined as the ratio of the piston head area, AP, to the cross-sectional area of the annular bypass, Ad. In the flow mode case, the damping coefficient, which is defined as the ratio of equivalent viscous damping of the Bingham plastic material, Ceq, to the Newtonian viscous damping, C, is a function on...

Analysis and Testing of Electrorheological Bypass Dampers

The hysteresis behavior of a linear stroke magnetorheological damper is characterized for several magnetic fields and sinusoidal excitations over a nominal operational frequency range of 1.0 - 3.0 Hz. The behavior of the damper is inadequately modeled using the equivalent viscous damping and the complex modulus. Therefore, four different non-linear modeling perspectives are discussed for purposes of system identification procedures, including: (1) nonlinear Bingham plastic model, (2) nonlinear biviscous model, (3) nonlinear hysteretic biviscous model, and (4) nonlinear viscoelastic plastic model. The first three nonlinear models are piecewise continuous in velocity. The fourth model is piecewise smooth in velocity. The parameters for each model are identified from an identification set of experimental data, these parameters are then used to reconstruct the force vs. displacement and the force vs. velocity hysteresis cycles for the respective model. Model performance is evaluated by calculating equivalent viscous damping and force time history errors between the model fit and the experimental data. In addition to the identification study, a validation study was done. Model parameters were calculated for offset values of current and frequency. These intermediate parameters were used to calculate hysteresis cycles which were compared with a second set of experimental data, a validation data set. The results from both identification and validation studies of the MR damper behavior are presented in this paper, including calculated damping and force time history errors.

Characterization and analysis of magneto-rheological damper behavior due to sinusoidal loading

Electrorheological (ER) technology was explored for its suitability to the continuous control of force and motion in aircraft landing gear. Although the state of knowledge on all types of active suspensions was examined, the analytical and experimental portions of the study focused upon the control of damping, alone. A specific class of ER damper designs was selected by means of a generalized analysis that modeled the ER fluid as a "bingham" plastic material. This analysis reveals the advantage of ER damping devices that minimize shear rates such that static shear stresses tend to dominate the damper's response. A prototype damping device in this class was constructed and simplified response parameters of the device were measured. Alternative formulations of the ER fluid are discussed and the employed test fluid is described. An analysis of the landing transient for an example military aircraft was performed so that the nominal performance of an ER-based damping controller could be estimated. The study observes that although ER technology offers promise over the long term, current limitations in fluid performance severely constrain the application to aircraft landing gear.

R D Ervin

Papers

Electrorheology for smart landing gear