Min Mao

A Magnetorheological Damper with Bifold Valves for Shock and Vibration Mitigation

This study presents the design and fabrication of a flow-mode bifold magnetorheological (MR) damper for shock and vibration mitigation for high piston velocity (15 mph or 6.75 m/s) as well as an evaluation of its performance at low speed. Based on a Bingham-plastic (BP) model, as well as a BP model coupled with a low speed hysteresis model, two theoretical MR damper models for flow-mode MR dampers are constructed. Using the design strategy associated with the Bingham-model based damper model, two MR damper designs for achieving the performance requirement with a limited space are considered: first, the conventional MR damper that has an MR valve inside the piston head and second, the bifold MR damper that has MR valves at each end of the damper. After numerically comparing the damping performances of the two MR damper designs, the bifold MR damper has been chosen because its dynamic range is better at high speed. The bifold MR damper was tested at a relatively low piston velocity using an MTS testing machine under sinusoidal loading. Experimental data compare well with the results predicted by the theoretical models.

Effective design strategy for a magneto-rheological damper using a nonlinear flow model

This paper presents an effective design strategy for a magnetorheological (MR) damper using a nonlinear flow model. The MR valve inside a flow mode MR damper is approximated by a rectangular duct and its governing equation of motion is derived based on a nonlinear flow model to describe a laminar or turbulent flow behavior. Useful nondimensional variables such as, Bingham number, Reynolds number, and dynamic (controllable) range are theoretically constructed on the basis of the nonlinear model, so as to assess damping performance of the MR damper over a wide operating range of shear rates. First, the overall damping characteristics of the MR damper are evaluated through computer simulation and, second, the effects of important design parameters on damping performance of the MR damper are investigated. Finally, the effective design procedure to meet a certain performance requirement is proposed. A high force-high velocity damper is fabricated and tested, and the resulting model and design procedure are experimentally validated.

Experimental validation of a magnetorheological energy absorber design analysis

A key challenge when designing linear stroke magnetorheological energy absorbers for high-speed impact is that high piston speeds in linear stroke magnetorheological energy absorbers induce high Reynolds number flows in the magnetic valve of the magnetorheological energy absorber, so that achieving high controllable dynamic range can be a design challenge. So far, the research on magnetorheological energy absorbers has typically assumed that the off-state force increases linearly with piston velocity. But at the higher piston velocities occurring in impact events, the off-state damping exhibits nonlinear velocity squared damping effects. This problem was recognized in our prior work, where it was shown that minor losses are important contributing factors to off-state damping. In this study, a nonlinear analytical magnetorheological energy absorber model is developed based on a Bingham-plastic nonlinear flow model combined with velocity squared dependent minor loss factors. This refined model is denoted as the Bingham-plastic nonlinear flow model with minor losses. From this Bingham-plastic nonlinear flow model with minor losses, an effective design strategy is presented for conventional magnetorheological energy absorbers. The Bingham-plastic nonlinear flow model with minor losses is validated via computational fluid dynamics simulation, so that magnetorheological energy absorber performance can be analytically verified before being manufactured. The magnetorheological energy absorber is fabricated and tested up to an effective piston velocity of 5 m/s by using the high-speed drop tower facility at the GM R&D Center. Comparison of our analysis with measured data is conducted, and the effective design of the magnetorheological energy absorber using the Bingham-plastic nonlinear flow model with minor losses is validated.

Nonlinear modeling of magnetorheological energy absorbers?under impact conditions

Magnetorheological energy absorbers (MREAs) provide adaptive vibration and shock mitigation capabilities to accommodate varying payloads, vibration spectra, and shock pulses, as well as other environmental factors. A key performance metric is the dynamic range, which is defined as the ratio of the force at maximum field to the force in the absence of field. The off-state force is typically assumed to increase linearly with speed, but at the higher shaft speeds occurring in impact events, the off-state damping exhibits nonlinear velocity squared damping effects. To improve understanding of MREA behavior under high-speed impact conditions, this study focuses on nonlinear MREA models that can more accurately predict MREA dynamic behavior for nominal impact speeds of up to 6 m s−1. Three models were examined in this study. First, a nonlinear Bingham-plastic (BP) model incorporating Darcy friction and fluid inertia (Unsteady-BP) was formulated where the force is proportional to the velocity. Second, a Bingham-plastic model incorporating minor loss factors and fluid inertia (Unsteady-BPM) to better account for high-speed behavior was formulated. Third, a hydromechanical (HM) analysis was developed to account for fluid compressibility and inertia as well as minor loss factors. These models were validated using drop test data obtained using the drop tower facility at GM R&D Center for nominal drop speeds of up to 6 m s−1.

Shock load mitigation using magnetorheological energy absorber with bifold valves

Magnetorheological energy absorbers (MREAs) have been identified as a candidate for tunable impact energy absorber applications, meaning those in which a high shock load is applied during a short time period. In this study, we focused on the theoretical analysis, design and laboratory implementation of a compact high force MREA for shock and impact loads. This study included the design and fabrication of a flow-mode bifold MREA (magnetorheological energy absorber) that operates under piston velocities up to 6.71 m/s and the development of a hydro-mechanical analysis to predict MREA performance. Experiments were conducted both in the laboratories at UMCP (sinusoidal excitation) and at GM R&D (drop tower tests), and these data were used to validate the analysis. The hydro-mechanical model for the MREA was derived by considering lumped hydraulic parameters which are compliances of MR fluids inside the cylinder and flow resistance through the MR bifold valves. The force behavior predicted by the hydro-mechanical analysis was simulated for two classes of inputs: sinusoidal displacement inputs, and shock loads using a drop tower. At UMCP, sinusoidal inputs ranging up to 12 Hz with an amplitude of 12.7 mm were used to excite the MREA using three different MR fluids, each having an iron volume fraction of nominally 35%, 40% and 45%. Subsequently, drop tower tests were conducted at GM R&D by measuring MREA performance resulting from the impact of a 45.5 kg (100 lb) mass dropped onto the MREA shaft at speeds of 1, 2 and 3 m/s. Comparison of the simulations with experimental data demonstrated the utility of the hydro-mechanical model to accurately predict MREA behavior for the specified ranges of sinusoidal and shock classes of inputs.

A Nonlinear Analytical Model for Magnetorheological Energy Absorbers Under Impact Conditions

Linear stroke magnetorheological energy absorbers (MREAs) can be used to adaptively control load-stroke profiles under impact loads. An appropriate and controllable dynamic range, defined as the ratio of the force at maximum field to the off-state force, as well as the off-state (minimum) damping force, must be specified in order to account for varying payload mass over a wide range of MREA operating velocities. A key challenge when designing MREAs for high speed impact conditions is that the high shaft speeds in linear stroke MREAs induce high Reynolds number flows in the magnetic valve of the MREA, so that high dynamic range canbe a design challenge. Previous studies demonstrated that the dynamic range, D, of an MREA under high speed drop impact test dramatically dropped to D≈1 as velocity rose to 6.6 m/s, where Reynolds number, Re>2000. Also, past research on MREAs typically assumed that the off-state force increases linearly with speed, but at the higher shaft speeds occurring in impact events, the off-state damping exhibits nonlinear velocity squared damping effects. This problem was recognized in our prior work where it was shown that minor losses are important contributing factors to off-state damping. In this study, a nonlinear analytical MREA model, based on the Bingham-plastic nonlinear flow model (BP model), is combined with semi-analytical minor loss factors to develop a BPM model. From this BPM model, an effective design strategy is presented for conventional MREAs and an MREA designed. The BPM model was validated via finite element analysis (FEA), so that MREA performance could be verified before manufacture. The MREA was fabricated and tested up to effective piston velocity of 5 m/s using the high speed drop tower facility at GM R&D Center. Comparison of our analysis with measured data shows that the BPM model can accurately predict off-state (passive) MREA performance under impact conditions, and the effective deign of the MREA using the BPM was validated.Copyright

Performance Analysis of Magnetorheological Energy Absorbers Under Impact Conditions

Magnetorheological energy absorbers (MREAs) can provide adaptive vibration and shock mitigation capabilities to adapt to varying payloads, vibration spectra, and shock pulses, as well as other environmental factors. To effectively utilize these adaptive capabilities, the dynamic range (defined as the ratio of the force at maximum field to the force in the absence of field) or turn-up ratio is a key issue. Previous studies found that the dynamic range of a MREA significantly degraded at velocities even as low as nominally 6 m/s. To improve understanding of MREA behavior and to enable effective MREA design, which implies maintaining sufficient dynamic range over its design speeds range, this study focuses on the design, fabrication, testing, and transient impact analysis of a MREA for which the primary design objective was a dynamic range, D≥2, for nominal impact speeds of up to 6.75 m/s. The MREA was tested using the drop tower facility at GM RD and 2) the hydromechanical analysis is a useful and accurate tool for predicting this MREA transient force behavior for these drop test data.Copyright

Adaptive Control of a Sliding Seat Using Magnetorheological Energy Absorbers

Feasibility of a sliding seat utilizing adaptive control of a magnetorheological (MR) energy absorber (MREA) to minimize loads imparted to a payload mass in a ground vehicle for frontal impact speeds as high as 7 m/s (15.7 mph) is investigated. The crash pulse for a given impact speed was assumed to be a rectangular deceleration pulse having a prescribed magnitude and duration. The adaptive control objective is to bring the payload (occupant plus seat) mass to a stop using the available stroke, while simultaneously accommodating changes in impact velocity and occupant mass ranging from a 5th percentile female to a 95th percentile male. The payload is first treated as a single-degree-of-freedom (SDOF) rigid lumped mass, and two adaptive control algorithms are developed: (1) constant Bingham number control, and (2) constant force control. To explore the effects of occupant compliance on adaptive controller performance, a multi-degree-of-freedom (MDOF) lumped mass biodynamic occupant model was integrated with the seat mass. The same controllers were used for both the SDOF and MDOF cases based on SDOF controller analysis because the biodynamic degrees of freedom are neither controllable nor observable. The designed adaptive controllers successfully controlled load-stroke profiles to bring payload mass to rest in the available stroke and reduced payload decelerations. Analysis showed extensive coupling between the seat structures and occupant biodynamic response, although minor adjustments to the control gains enabled full use of the available stroke.Copyright