Magnetorheological dampers, or as they are more commonly called, MR dampers, are being developed for a wide variety of applications where controllable damping is desired. These applications include dampers for automobiles, heavy trucks, bicycles, prosthetic limbs, gun recoil systems, and possibly others. This thesis first introduces MR technology through a discussion of MR fluid and then by giving a broad overview of MR devices that are being developed. After giving the reader an understanding of MR technology and devices, MR damper basics are presented. This section includes a discussion of MR damper types, mathematical fundamentals, and an approach to magnetic circuit design. With the necessary background information covered, MR dampers for automotive use are then discussed. Specifically, designs for MR dampers that were built for a Mercedes ML-430 and for a Ford Expedition are presented along with their respective test results. These test results are presented and compared with the original equipment hydraulic dampers. After discussing automotive MR dampers, designs for gun recoil applications are presented. Specifically, two different MR damper designs are discussed along with live-fire test results for the first damper. Finally, two hybrid dampers that were based on a modified adjustable hydraulic damper are presented. These hybrid dampers, if pursued further, may develop into controllable replacements for large hydraulic dampers such as those installed on large vehicles and field Howitzers. In conclusion, recommendations are made for materials as well as for seal selection and other design aspects. / Master of Science

Semi-active dampers utilizing various working principles have been developed for a variety of vehicles. These semi-active dampers have been designed to resolve the ride and handling compromise associated with conventional passive dampers, and increase vehicle stability. This thesis briefly reviews existing semi-active damper designs, including but not limited to MR dampers, before presenting two new prototype semi-active hydraulic dampers. Both prototype dampers are designed to provide a large force range while maintaining easily controllable valve characteristics. The first of these dampers served primarily as a proof of concept and a means of understanding the dynamics of a disc valve housed inside the main piston. The valve design is presented, along with other information concerning the fabrication of the Initial Prototype damper. Test results are presented and analyzed, and a second iteration of the valve is designed. The Final Prototype damper is a scaled up version of the initial design, with refinements made in piston geometry, internal disc profile, and dynamic seals. This large force range damper is tested and results are compared with existing MR dampers. The Final Prototype damper provides a significantly larger force range when compared with typical MR dampers. Finally, to conclude this research, the vehicle dynamics implications of the Final Prototype damper are discussed and recommendations for further study are made. / Master of Science

A TLD (tuned liquid damper) is a passive control devise on top of a structure that dissipates the input excitation energy through the liquid boundary layer friction, the free surface contamination, and wave breaking. In order to design an efficient TLD, using an appropriate model to illustrate the liquid behaviour as well as knowing optimum TLD parameters is of crucial importance. In this study the accuracy of the existing models which are able to capture the liquid motion behaviour are investigated and the effective range of important TLD parameters are introduced through real-time hybrid shaking table tests.

A TLD (tuned liquid damper) is a passive control devise on top of a structure that dissipates the input excitation energy through the liquid boundary layer friction, the free surface contamination, and wave breaking. In order to design an efficient TLD, using an appropriate model to illustrate the liquid behaviour as well as knowing optimum TLD parameters is of crucial importance. In this study the accuracy of the existing models which are able to capture the liquid motion behaviour are investigated and the effective range of important TLD parameters are introduced through real-time hybrid shaking table tests.

The present work describes experiments conducted on several pocket damper seal (PDS) designs using a high pressure annular gas seal test rig. Both rotating and non-rotating tests were conducted for a 12, 8, and 6 bladed PDS. The objective of the tests was to determine the rotordynamic force coefficients and leakage for the different PDS while varying parameters such as: (1) clearance ratio, (2) rotor surface speed, (3) PDS pressure differential, and (4) excitation frequency. Two different methods were used to determine frequency dependent force coefficients: (1) the impedance method, which involved using a baseline subtraction and (2) the dynamic pressure response method, which comprised of measuring seal cavity dynamic pressure and phase relationship to vibration. Both methods were used to determine coefficients, but the dynamic pressure response method revealed insights to the dynamics of the PDS that were the first of its kind and allowed the comparison to the damper seal theory at the most fundamental of levels. The results indicated that the conventional PDS possessed high positive damping, negative and positive stiffness, and same sign cross-coupled coefficients. Another objective of the work is to investigate a new fully partitioned PDS design and accompany experimental results with the development of a modified damper seal theory. The new fully partitioned PDS design was shown to give twice as much damping as the conventional design and revealed the ability to modify direct stiffness without degradation in direct damping. Finally, both the conventional theory and the newly proposed theory predictions are compared to experimentally determined force coefficients. The last objective was to evaluate the leakage characteristics of the different designs and to investigate the effect of blade profile on seal leakage. Results showed that beveled tooth blade profiles yield higher mass flow leakage compared to rectangular blade profiles.

Squeeze film dampers (SFDs) with low levels of external pressurization and poor end sealing are prone to air entrapment, thus reducing the damping capability. Furthermore, existing predictive models are too restrictive. Single frequency, unidirectional load and centered circular orbit experiments were conducted on a revamped SFD test rig. The damper journal is 1" in length and 5" in diameter, with nominal clearance of 5 mils (0.127 mm). The SFD feed end is flooded with oil, while the discharge end contains a recirculation groove and four orifice discharge ports to prevent air ingestion. The discharge end is fully sealed with a wave-spring that pushes a seal ring into contact with the SFD journal. The measurements conducted without and with lubricant in the squeeze film lands, along with a frequency domain identification procedure, render the mechanical seal dry-friction force and viscous damping force coefficients as functions of frequency and motion amplitude. The end seal arrangement is quite effective in eliminating side leakage and preventing air entrainment into the film lands. Importantly enough, the dry friction force, arising from the contact forces in relative motion, increases significantly the test element equivalent viscous damping coefficients. The identified system damping coefficients are thus frequency and amplitude of motion dependent, albeit decreasing rapidly as the motion parameters increase. Identified force coefficients, damping and added mass, for the squeeze film damper alone agree very well with predictions based on the full film, short length SFD model.

This thesis describes the implementation of a parametric model of an automotive damper. The goal of this research was to create a damper model to predict accurately damping forces to be used as a design tool for the Formula SAE racecar team. This study pertains to monotube gas charged dampers appropriate to Formula SAE racecar applications. The model accounts for each individual flow path in the damper, and employs a flow resistance model for each flow path. The deflection of the shim stack was calculated from a force balance and linked to the flow resistance. These equations yield a system of nonlinear equations that was solved using Newton's iterative method. The goal of this model was to create accurately force vs. velocity and force vs. displacement plots for examination. A shock dynamometer was used to correlate the model to real damper data for verification of accuracy. With a working model, components including the bleed orifice, piston orifice, and compression and rebound shims which were varied to gain an understanding of effects on the damping force.

Experiments conducted at the Texas A&M Turbomachinery Laboratory and field applications have shown that pocket damper seals (PDS) can be used to suppress vibrations in compressors. A mathematical model is presented for the notched PDS. The notch is a prominent feature in all the PDS manufactured in recent times. The notch is provided at the exit blades of the PDS to act as a diverging clearance, which is one of the conditions for the damper seal to perform satisfactorily The model to be presented has been adapted from a theory previously developed to predict the direct stiffness and damping coefficients. The flow equations are numerically solved and a computer program is developed correspondingly. The predictions from this notched model are compared with the existing model to highlight the effect of the notch in the analysis. These predictions correlate well with the experimental results from the notched PDS. Also experimental results from testing of a two bladed PDS are compared to the code predictions thus validating the notched model. The notched model performs satisfactorily to predict the direct damping coefficients. Coastdown tests are conducted on a four bladed eight pocket PDS with a partial arc notch of large radius across the exit blades. The PDS offers positive direct damping which increases with an increase in seal inlet pressure. The low stiffness of the test rig combined with the negative stiffness of the seal made it impracticable to conduct testing above inlet pressures of 64.7 psia (4.461 bar). The existing theoretical models are compared with the experimental data collected up to 64.7 psia (4.461 bar).

Damping in a multitude of engineering applications has a variable threshold requirement based on the input excitation given to the system. In most applications the desired system response is known but the input to the system is a time dependent function with fluctuating amplitudes and frequencies. Therefore for optimal performance the damping characteristics of a given system must be able to adapt to increase or decrease the amount of energy being absorbed by the system. In most mechanical systems (including vehicles) damping is achieved through a viscous medium; such as hydraulic oil. Although the oil is capable of absorbing the unwanted energy in the system, its passive nature limits its ability to achieve an optimal amount of damping given the excitation. To achieve the requisite functionality of variable damping; a multitude of solutions have been implemented, proposed, and evaluated at both commercial and academic research levels. These solutions have met the variable damping requirements but have significant cant drawbacks associated with them. To address the shortcomings associated with the aforementioned variable damping solutions, a hybrid design consisting of a conventional hydraulic damper and a linear motor topology was fused together to produce a hybrid variable damper. In this hybrid design, the oil in the system acts as bias and the linear motor topology allows for variability in the amount of damping being provided to the system. This hybrid design allows for the requisite variable damping requirement to be achieved. In addition to the hybrid design being able to achieve variable damping, it has the capacity to act as a generator and also provide fail-safe operation due to the viscous bias. Through analytical, FEM analysis and experimental modeling the hybrid damper has been characterized and with a high level of agreement between the various results. This work has also shown that the design is capable of achieving variable damping with the capacity to recover energy from the system.

Vehicle suspension systems have been extensively explored in the past decades, contributing to ride comfort, handling and safety improvements. The new generation of powertrain and propulsion systems, as a new trend in modern vehicles, poses significant challenges to suspension system design. Consequently, novel suspension concepts are required, not only to improve the vehicle’s dynamic performance, but also to enhance the fuel economy by utilizing regeneration functions. However, the development of new-generation suspension systems necessitates advanced suspension components, such as springs and dampers. This Ph.D. thesis, on the development of hybrid electromagnetic dampers is an Ontario Centres of Excellence (OCE) collaborative project sponsored by Mechworks Systems Inc. The ultimate goal of this project is to conduct feasibility study of the development of electromagnetic dampers for automotive suspension system applications. With new improvements in power electronics and magnetic materials, electromagnetic dampers are forging the way as a new technology in vibration isolation systems such as vehicle suspension systems. The use of electromagnetic dampers in active vehicle suspension systems has drawn considerable attention in the recent years, attributed to the fact that active suspension systems have superior performance in terms of ride comfort and road-handling performances compared to their passive and semi-active counterparts in automotive applications. As a response to the expanding demand for superior vehicle suspension systems, this thesis describes the design and development of a new electromagnetic damper as a customized linear permanent magnet actuator to be used in active suspension systems. The proposed electromagnetic damper has energy harvesting capability. Unlike commercial passive/semi-active dampers that convert the vibration kinetic energy into heat, the dissipated energy in electromagnetic dampers can be regenerated as useful electrical energy. Electromagnetic dampers are used in active suspension systems, where the damping coefficient is controlled rapidly and reliably through electrical manipulations. Although demonstrating superb performance, active suspensions still have some issues that must be overcome. They have high energy consumption, weight, and cost, and are not fail-safe in case of a power break-down. Since the introduction of the electromagnetic dampers, the challenge was to address these drawbacks. Hybrid electromagnetic dampers, which are proposed in this Ph.D. thesis, are potential solutions to high weight, high cost, and fail-safety issues of an active suspension system. The hybrid electromagnetic damper utilizes the high performance of an active electromagnetic damper with the reliability of passive dampers in a single package, offering a fail-safe damper while decreasing weight and cost. Two hybrid damper designs are proposed in this thesis. The first one operates based on hydraulic damping as a source of passive damping, while the second design employs the eddy current damping effect to provide the passive damping part of the system. It is demonstrated that the introduction of the passive damping can reduce power consumption and weight in an active automotive suspension system. The ultimate objective of this thesis is to employ existing suspension system and damper design knowledge together with new ideas from electromagnetic theories to develop new electromagnetic dampers. At the same time, the development of eddy current dampers, as a potential source for passive damping element in the final hybrid design, is considered and thoroughly studied. For the very first time, the eddy current damping effect is introduced for the automotive suspension applications. The eddy current passive damper, as a stand-alone unit, is designed, modeled, fabricated and successfully tested. The feasibility of using passive eddy current dampers for automotive suspension applications is also studied. The structure of new passive eddy current dampers is straightforward, requiring no external power supply or any other electronic devices. Proposed novel eddy current dampers are oil-free and non-contact, offering high reliability and durability with their simplified design. To achieve the defined goals, analytical modeling, numerical simulations, and lab-based experiments are conducted. A number of experimental test-beds are prepared for various experimental analyses on the fabricated prototypes as well as off-the-shelf dampers. Various prototypes, such as eddy current and electromagnetic dampers, are manufactured, and tested in frequency/time domains for verification of the derived analytical and numerical models, and for proof of concept. In addition, fluid and heat transfer analyses are done during the process of the feasibility study to ensure the durability and practical viability of the proposed hybrid electromagnetic dampers. The presented study is only a small portion of the growing research in this area, and it is hoped that the results obtained here will lead to the realization of a safer and more superior automotive suspension system.