Innovative magnetorheological devices for shock and vibration mitigation

Vibration and impact protection have been a popular topic in research fields, which could directly affect the passengers’ and drivers’ comfort and safety, even cause spines fracture. Therefore, an increasing number of vehicle suspensions and aircraft landing gears are proposed and manufactured. Magnetorheological fluids (MRFs), as a smart material, are growly applied into the above device owing to its unique properties such as fast response, reversible properties, and broad controllable range, which could improve the vibration/impact mitigation performance. MRF was utilized to achieve adaptive parameters of the vehicle suspensions by controlling the magnetic field strength of the MRF working areas. Generally, the magnetic field is provided by a given current, subsequently, it would consume massive energy from a long-term perspective. Thus, a self-powered concept was applied as well. This thesis reports a compact stiffness controllable MR damper with a self-powered capacity. After the prototype of the MR damper, its property tests were conducted to verify the stiffness controllability and the energy generating ability using a hydraulic Instron test system. Then, a quarter-car test rig was built, and the semi-active MR suspension integrated with the self-powered MR damper was installed on a test rig. Two controllers, one based on short-time Fourier transform (STFT) and a classical skyhook controller was developed to control the stiffness. The evaluation results demonstrate that the proposed MR damper incorporated with STFT controller or skyhook controller could suppress the response displacements and accelerations obviously comparing with the conventional passive systems

Investigation into low power active electromagnetic damping for automotive applications

Automobile suspension systems carry out two important functions; road handling and passenger comfort. Hydraulic passive dampers are the most common system employed on vehicles, yet it is well known that passive suspension systems are less effective on lightweight vehicles. Modern damper technologies such as semi-active and active dampers, offer potential benefits when used in these vehicles. An active electromagnetic (e.m.) damper could offer these same benefits with lower power consumption and with less mechanical complexity than existing active suspension systems. This research investigates the effectiveness of e.m. passive and active damping on the performance of lightweight electric vehicles and develops a novel, fully integrated model of the e.m. damper in both passive and active modes. The proposed e.m. damper consisted of one or more cylindrical permanent magnets that travelled axially through one or more cylindrical solenoids. A magnet/solenoid damper system was modelled for both the passive and active modes. The magnets were modelled as a current carrying solenoid and from Maxwell's Laws the magnetic field was determined. For the passive damper, the magnetic field was used with Faraday's Law to determine the forces generated. In the case of the active damper the magnetic field and the current in the damper solenoid were used to calculate the magnetic force. Both a passive and active e.m. damper were modelled for a small, one degree of freedom experimental system. The active e.m. damper was modelled as a pure Skyhook damper. There was a good correlation between the modelled and experimental data for the magnet, the passive and the active Skyhook dampers. The passive damper model was scaled up as a two degree of freedom system using realistic values for a road legal lightweight electric vehicle and demonstrated that sufficient passive damping could be achieved for automotive uses, but at the price of excessive mass. For the scaled up active damper model, sufficient force could be achieved with a mass similar to a commercial hydraulic damper. The power consumption was less than 5 % of an equivalent active hydraulic suspension system. This demonstrated that the passive damper was currently impractical for lightweight electric vehicles, but the active electromagnetic damper was of sufficiently low weight and power consumption: had enough authority and offered sufficient passenger comfort benefits to include in future lightweight electric vehicle designs

Shock isolation using magnetorheologically responsive technology

The purpose of this thesis is to develop a shock isolation system using magnetorheologically (MR) responsive technology to isolate shock input to various components in the light weight military vehicles susceptible to ballistic shock effects; Two methods are chosen for isolation of the shock. One is the friction damper based on MR fluid and the other is an elastomer based on magnetically responsive elastomer (MRE). Both approaches can be utilized for semi-active control schemes that have been widely used because of its unique feature of using variable damping and stiffness characteristics of the isolator; In this thesis, both computer simulation and experimental verification are presented to show the effectiveness of the technologies in isolating the shock and the performance is evaluated by the comparison with the passive isolator as a baseline

Modeling, analysis and non-linear control of a novel pneumatic semi-active vibration isolator: a concept validation study

Advanced suspension systems play a crucial role in the performance of vehicles. The essential problem in designing a vibration isolator for a system comprises of controlling the relative motion between the suspended mass and the base due to stroke limitations, while attenuating the vibration transmitted to the mass from the base. These two requirements being conflicting in nature results in a compromised suspension design when purely passive isolation technologies are employed. Active vibration isolation systems which totally eliminated this compromise have cost, maintenance and reliability issues precluding them from being used in many applications. Semi-active technologies on the other hand provide feasible alternative to the active systems, but employ oil based dampers, which deteriorates the performance over a wide range of operating regime.;The thesis presents a novel semi-active pneumatic vibration isolation technology, which is capable of alleviating the drawbacks of both the contemporary active and the semi-active systems currently being researched. The pneumatic system proposed was shown to have the capability to continuously alter its natural frequency and damping characteristics (CVNFD) without needing either a hydraulic actuator or oil based variable damping device. The computational study based on the non-linear mathematical model developed showed the CVNFD behavior of the pneumatic system and the experiments conducted on the research test-rig corroborated the result.;Two non-linear control schemes in the form of Skyhook control and sliding mode control were used to synthesize controllers for the pneumatic system. A modified skyhook control was derived and implemented on the pneumatic system. The performance of this controller was shown to rival that obtained for a conventional semi-active system using the Magneto-Rhealogical (MR) damper and controlled by skyhook control. A more advanced non-linear robust control scheme called sliding mode control was used for the second controller design. The controller was synthesized using the sliding mode control theory applied to the theory of model-matching. Lyapunov stability analysis was applied and the sliding mode controller was modified to guarantee global asymptotic stability. It was demonstrated computationally as well as experimentally that by suitably choosing the several controller design-parameters, the skyhook based sliding mode controller can recover the performance lost by implementing the model independent skyhook law.;In summary, the research conducted in this thesis demonstrated the availability and feasibility of a new and novel semi-active pneumatic vibration isolation technology that can replace and/or enhance the performance of contemporary passive and semi-active systems

MR Fluid Damper and Its Application to Force Sensorless Damping Control System

Vibration suppression is considered as a keyresearch field in civil engineering to ensure the safety and comfort of their occupants and users of mechanical structures. To reduce the system vibration, an effective vibration control with isolation is necessary. Vibration control techniques have classically been categorized into two areas, passive and active controls. For a long time, efforts were made to make the suspension system work optimally by optimizing its parameters, but due to the intrinsic limitations of a passive suspension system, improvements were effective only in a certain frequency range. Compared with passive suspensions, active suspensions can improve the performance of the suspension system over a wide range of frequencies. Semi-active suspensions were proposed in the early 1970s [1], and can be nearly as effective as active suspensions. When the control system fails, the semi-active suspension can still work under passive conditions. Compared with active and passive suspension systems, the semi-active suspension system combines the advantages of both active and passive suspensions because it provides better performance when compared with passive suspensions and is economical, safe and does not require either higher-power actuators or a large power supply as active suspensions do [2]

Magneto Rheological Dampers — A New Paradigm in Base Isolation Techniques in Earth Quake Engineering

Over the past three decades, a great deal of interest has been generated regarding the use of structural protective systems to mitigate the effects of dynamic environmental hazards, such as earth quakes and strong wind, on Civil Engineering structures. These systems usually employ supplemental damping devices to increase the energy dissipation capability of the protected structure. One of the most promising new devices proposed for structural protection is Magneto rheological (MR) fluid dampers because of their mechanical simplicity, high dynamic range, low pressure requirements, large force capacity and robustness, this class of devices has been shown to mesh well within application demands and constraints to offer an attractive means of protecting Civil infrastructure systems against dynamic loading. The focus of the paper is to develop a fundamental understanding of large scale MR dampers for the purpose of designing and implementing these “smart” damping devices in large- scale structures for natural hazard mitigation

Development and evaluation of a versatile semi-active suspension system for high-speed railway vehicles

With the increase in speed of high-speed trains, their vibration will become fiercer and fiercer, especially when the lateral resonance of the car body occurs. This paper develops a versatile semi-active suspension system with variable stiffness (VS) magnetorheological elastomer (MRE) isolators and variable damping (VD) magnetorheological (MR) dampers for high-speed trains, aiming to improve ride comfort by avoiding car body resonance and dissipating vibration energy. As the first step, a multifunction VSVD semi-active suspension system for high-speed railway vehicles was designed and prototyped, including four VS-MRE isolators and two VD-MR dampers. After that, a scaled train model, composing of a car body and a secondary lateral suspension system was designed and built to evaluate the performance of the new VSVD suspension system; a control strategy based on short-time Fourier transform (STFT) and sky-hook was proposed to control the new suspension system. Two different excitations, harmonic excitation and random excitation, were applied to evaluate the train\u27s VSVD suspension. As a comparison, four alternative suspension systems, including passive-off suspension, passive-on suspension, pure VS suspension, and pure VD suspension were also evaluated. The evaluation results verified that the VSVD suspension of the train can avoid lateral resonance of car body and dissipate the vibration energy efficiently. The comparison verified that the VSVD suspension system outperforms the passive-off suspension, passive-on suspension, pure VS suspension, and pure VD suspension