Gregory H. Hitchcock

A New Bypass Magnetorheological Fluid Damper

This study presents theoretical and experimental investigations of a novel external bypass, fail-safe, magnetorheological fluid (MRF) damper. A fail-safe MRF damper is referred to as a device that retains a minimum required damping capacity in the event of a power supply or electronic system failure. The new MRF device has a simple design, is compact, is capable of generating a considerable dynamic force range, and can be sized for specific vibration control applications. The theoretical formulation is developed based on the Herschel-Bulkley constitutive model for an annular flow. Experimental results are obtained to demonstrate the validity of the theoretical analysis.

New by-pass, fail-safe, magnetorheological fluid damper

This paper presents experimental results for a novel external by-pass, fail-safe, magneto-rheological fluid (MRF) damper. A fail-safe MRF damper is referred to as a device which retains a minimum required damping capacity in the event of a power supply or electronic system failure. The new MRF device has a simple design, is compact, can generate a considerable dynamic force range, and can be sized for specific vibration control applications. As an example of the performance of this by-pass valve, a MRF damper is presented that can be used for vibration mitigation in cable stay bridges under strong storms. Performance characteristics of the by-pass valve and the MRF damper are discussed.

Experimental study on fuzzy logic vibration control of a bridge using fail-safe magnetorheological fluid dampers

This study presents a semi-active vibration control of a scaled two-span bridge structure. Magneto-rheological fluid dampers are utilized as the semi-active energy absorbing devices, and a bridge vibration control system is developed. Closed-loop control system based on fuzzy logic is used to suppress the bridge deck motion under random excitation. It is demonstrated that this fuzzy logic control system can significantly reduce the relative deck displacement using about 60% less power compared to passive on state, while the absolute deck acceleration remains practically unchanged.

A Hysteresis Model for Magneto-rheological Damper

In this paper, a bi-linear hysteresis model is proposed to describe the nonlinear response of an electromagnetic activated magneto-rheological fluid (MRF) damper. The model parameters have significant effects on MRF damper. An analytical solution for the primary resonance of an SDOF system with skyhook damping is obtained. There exists a specific condition for the primary resonance for discussed system.

A new modular magnetorheological fluid valve for large-scale seismic applications

This study presents a modular, large-scale, magneto-rheological (MRF) by-pass valve to be used in seismic damper retrofits for energy mitigation. The by-pass valve is designed, constructed and tested. The MR valve can be used to retrofit a commercial passive seismic damper as a semi-active device. The performance of the MRF valve was characterized by means of quasi-static characterizations. A new MR fluid is also developed for the seismic by-pass MRF damper application. This MR fluid has low off-state viscosity and high field-dependent yield strength. The field-dependent rheology of the MR fluid is evaluated with a MR shear rheometer. In addition, a theoretical model is developed taking into account geometric dimensions, fluid properties and applied magnetic field strength. Three-dimensional electromagnetic finite element analysis is used to determine and maximize the magnetic field strength inside the by-pass MRF valving region. Both experimental and theoretical results show that the modular large-scale by-pass MRF damper can generate sufficient dynamic force range which meets the high-force requirements of large-scale structures subjected to seismic or other significant hazards.

Variable-structure-system-based logic fuzzy control of bridge vibration using fail-safe magnetorheological fluid dampers

This paper presents a semi-active vibration control of a scaled two-span bridge structure. Magneto-rheological fluid dampers are utilized as the semi-active energy absorbing deices and a bridge vibration control system is developed. Closed-loop control system based on fuzzy logic is used to suppress the bridge deck motion under random excitations. The sufficient condition for the closed-loop stability of the fuzzy control system is derived from the variable structure system theory. It is demonstrated that this stable fuzzy control system can significantly reduce the relative deck displacement using about 55 percent less power compared to passive-on state, while the absolute deck acceleration is relatively unaffected.

A magneto-rheological fluid-elastomer vibration isolator

A magneto-rheological (MR) fluid-elastomer vibration isolator is constructed by encapsulating a MR fluid inside an elastomer. The structural properties of this system are controllable by an applied magnetic field. Previous studies have shown that the damping capacity of this MR fluid-elastomer vibration isolator is a function of strain amplitude and field strength, and weakly dependent on the excitation frequency. The energy-dissipated mode, subjected to a magnetic field during oscillatory motion, is similar to a combined viscous and frictional damping. In this paper, a mechanical model is presented to account for the dynamic behavior of the MR fluid-elastomer vibration isolators under oscillatory compressive deformations. This model is a two-element analogy comprised of a variable friction damper and a nonlinear spring. The parameters of the model have been identified by a series of harmonic loading tests. The theoretical and experimental results are in excellent agreement.

Dynamic behaviors of magnetorheological fluid-elastomer composites under oscillatory compression

A new magnetorheological (MR) elastomer composite encapsulating MR fluid inside a polymer solid is presented. The mechanical properties of the MR composite sandwich system are controllable through an externally applied magnetic field. The dynamic behavior of the MR fluid-elastomer under various magnetic fields has been investigated by means of oscillatory compression cycles over a frequency range of 0.1 to 10Hz for various deformations (less than 1 mm). Energy dissipation in the material is analyzed as related to strain amplitude, strain frequency and magnetic field strength. The field induced damping mechanism is discussed in terms of the damping exponent. Such MR fluid-elastomer composites show promise in applications where tuning vibration characteristics of a system is desired such as altering natural frequencies, mode shapes, and damping properties.

Magneto-rheological fluid encased in flexible materials for vibration control

The disclosed device is directed toward magneto-rheological fluid encasement device. The magneto-rheological fluid encasement device comprises a body having at least one containment element defining an interior and an exterior. A magneto-rheological fluid is disposed in the interior of the at least one containment element. At least one magnetic field is in operative communication with the magneto-rheological fluid.

Semiactive control of a two-span bridge using field-controllable magneto-rheological dampers

This paper presents a semi-active control of a scaled two-span bridge structure. Magneto-rheological fluid (MRF) dampers are utilized as the semi-active devices and a bridge vibration control system is developed. Both open and closed-loop control systems are used to suppress the bridge deck motion under simple harmonic and simulated earthquake excitation. Effectiveness of each system is discussed. It is demonstrated that the closed-loop control systems can reduce the relative deck displacement of the bridge, while simultaneously limiting the peak damper forces.