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.

In order to control the vibration response of high rise buildings during seismic events, energy absorbing passive damping devices are most commonly used for energy absorption. Today there are a number of types of manufactured dampers available in the market, which use a variety of materials and designs to obtain various levels of stiffness and damping. Some of these include friction, yielding, viscoelastic and viscous dampers. These dampers are usually installed between two load bearing elements (walls or columns) in new buildings. In existing buildings, which require retrofitting, they could be installed in cut-outs of shear walls, as evidenced from recent investigations. An effective damping system can result in higher levels of safety and comfort, and can also lead to considerable savings in the total cost of a building. This thesis treats seismic mitigation of multistorey buildings using embedded dampers. Three types of damping mechanisms, viz, friction, viscoelastic, and combined friction-viscoelastic were investigated. Finite element methods were employed in the analysis using the program ABAQUS version 6.3. A direct integration dynamic analysis was carried out to obtain the damped and undamped responses of the structure in terms of deflections and accelerations at all storeys in order to evaluate the effectiveness of the damping system in mitigating the seismic response. The damping mechanisms have been modelled as (i) a linear spring and dash-pot in parallel for the viscoelastic damper, (ii) a contact pair with friction parameter for a friction damper and (iii) a hybrid damper consisting of both a viscoelastic and a friction damper. The earthquake events used in this study have been applied as acceleration time-histories at the base of the structure in the horizontal plane. Concrete material properties were chosen to represent the model as many high-rise buildings are constructed by using reinforced concrete. Several medium and high-rise building structures with embedded dampers in different configurations and placed in various locations throughout the structure were subjected to different earthquake loadings. Influence of damper type and properties, configuration and location were investigated. Results for the reduction in tip deflection and acceleration for a number of cases demonstrate the feasibility of the technique for seismic mitigation of these structures for a range of excitations, even when the dominant seismic frequencies match the natural frequency of the structure. Results also provide information which can be used for optimal damper placement for seismic mitigation.

The increased prevalence of semi-active control systems is largely due to the emergence of cost effective commercially available controllable damper technology such as Magneto-Rheological (MR) devices. Unfortunately, MR dampers exhibit highly nonlinear behavior, thus presenting an often over-looked complexity to the control system designer. With regards to controlling dampers, the well-known Skyhook Damping control algorithm has enjoyed great success for both fully active and semi-active control problems. The Skyhook design strategy is to create a control force that emulates what a passive linear damper would create when connected to an inertial reference frame. Skyhook control is device independent since it generates a desired control force command output that must be produced by the control system. For simplicity, MR dampers are often assumed to have a linear relationship between the current input and the force output at a given relative velocity. Often this assumption is made implicitly and without knowledge of the underlying nonlinearity. This thesis shows that the overall performance of a semi-active Skyhook control system can be improved by explicitly inverting the nonlinear relationship between input current and output force. The proposed modification will work with any semi-active control algorithm, such as Skyhook, to insure that the controller performance is at least as good as the performance without the proposed modification. This technique is demonstrated through simulation on a quarter-vehicle system. Hysteretic damping effects are incorporated into the modification by application of simple open loop force compensation. Laboratory testing of the hysteretic inversion process was performed with the goal of emulating an ideal linear damper without hysteresis. These results are compared with the implicit assumption thus providing a basis for validating the benefits of the improved methodology. / Master of Science

In recent years, a flurry of interest has been shown for a relatively old technology called magneto-rheological fluids, or MR fluids. Multiple types of devices have been designed to implement this versatile fluid, including linear dampers, clutches, work-piece fixtures, and polishing machines. The devices have been used in automobiles, washing machines, bicycles, prosthetic limbs, and even smart structures. This thesis focuses on another application of MR dampers, involving super-sport motorcycles. This paper introduces the topics of MR dampers and motorcycle suspensions, and why the two would be a good combination. A detailed history of MR fluids, MR dampers, and motorcycle suspension technologies is given next. After a broad outline of MR dampers and motorcycle suspensions, the method of designing and manufacturing MR dampers is discussed. The damper design for this research is presented in detail, along with the design procedure used to make it. Next, laboratory testing for it is covered, including the test equipment, test procedure, and the laboratory test results. Upon laboratory test completion, the field test setup and procedure are presented. The results of field tests with stock dampers and MR dampers with a variety of control systems is discussed. The MR dampers provided a more stable ride than that of the OEM dampers. By reducing suspension displacement, settling time, and suspension oscillations, the MR dampers were able to reduce suspension geometry instability. Lastly, concluding remarks are made on the research presented. Design flaws are discussed, as well as recommendations for future work in the same area. / Master of Science

In Squeeze Film Dampers, (SFD), grooves (deep or shallow) are used to feed oil into the damper and prevent oil starvation within the fluid film lands. In oil seals with film land of clearance c, short shallow grooves (depth ≤ 15c, length ≤ 30c) are machined to reduce the cross-coupled stiffness coefficients, and thus improve the seal stability characteristics. Moreover, test stands for these devices can also incorporate grooves or recesses as part of oil feeding/ discharge arrangements. A common assumption is that these grooves do not influence the test system forced response. However, unexpected large added mass coefficients are reported in these configurations and not adequately predicted. In the case of grooved oil seals, experimental results also show that circumferential grooves do aid to reduce cross-coupled force coefficients but to a lesser extent than predictions otherwise indicate. A linear fluid inertia model for analysis of multiple-groove SFD or oil seal configurations is advanced. A perturbation analysis for small motion about a journal centered and off-centered position yields zeroth and first order flow equations defined at each individual flow region (land and grooves) of constant clearance ( c ).The analysis considers both the circumferential and axial dynamic pressure variations across the groove and land regions. At the groove regions, an effective groove depth ( dη ) and effective clearance (c d c η η = + ) are defined based on qualitative observations of the laminar flow pattern through annular cavities. This depth differs from the actual physical groove depth. The boundary conditions at the inlet and exit plane are a function of the geometric configuration. Integration of the resulting dynamic pressure fields on the journal surface yields the force coefficients (stiffness, damping, and inertia). Comparisons between predicted and experimental force coefficients for a grooved oil seal and a SFD show excellent correlation over a narrow range of effective groove depths. The results confirm that large added mass coefficients are associated to the feed/discharge grooves in the scrutinized test configurations. Furthermore, predictions, benchmarking experimental data, corroborate that short inner land grooves in an oil seal do not isolate the pressure field of the adjacent film lands, and hence contribute greatly to the force response of the seal.

Squeeze film dampers (SFDs) provide viscous damping to attenuate excessive vibrations and enhance system stability in turbomachinery. SFDs are of special importance in aircraft engines which use rolling element support bearings that, by themselves, do not provide enough damping to ensure safe operation. A modular test rig capable of simulating actual operating conditions in aircraft jet engines is used to test two centrally grooved, end sealed, SFDs. Both SFDs have diameter D and nominal radial clearance c and consist of two parallel squeeze film lands separated by a deep circumferential groove of length LG and depth dG. A short length damper with film land lengths L and a long damper with land lengths 2L are tested. Piston rings seal the damper lands. An ISO VG2 lubricant is supplied to the SFD via three radial holes that discharge lubricant into the central groove. The lubricant passes through the damper lands and across the piston ring seals to finally exit the damper at ambient pressure. Circular orbit tests of amplitude ~0.5c and for static eccentricities varying from 0 to ~0.36c are conducted on the two sealed dampers. The instrumental variable filter method (IVFM) serves to identify the SFD dynamic force coefficients. The parameter identification range is 50Hz to 210Hz for the short damper and 110Hz to 250Hz for the long damper. Large amplitude dynamic pressures measured in the central groove demonstrate that the central groove does not divide the damper in two separate film lands, but the lubricant in the groove interacts with the squeeze film lands, hence contributing significantly to the SFD forced response. Dynamic pressures in the film lands and in the central groove reveal that both dampers operate free of air ingestion or cavitation for the tested static eccentricities and amplitudes of motion. Comparisons to test results for the same SFD configurations but with open ends demonstrate the effectiveness of the end seals on increasing the direct damping coefficients. For the sealed ends short length damper, the added mass coefficients are ~2 times larger and the damping coefficients are ~3.8 times larger than the respective coefficients of the open ends long damper. For the sealed ends long damper, the damping coefficients are ~2.8 times, and the added mass coefficients are ~3.1 times larger than coefficients from the open ends configuration. The identified SFD direct stiffness coefficients are nearly zero except at the maximum static eccentricity for the long damper. Predictions from a novel computational model that include the effects of the central groove, the lubricant feed holes and the end seals are in excellent agreement with results from the short length damper. For the long damper, the predicted damping coefficients are in good agreement with the test results, while the added mass coefficients are under predicted by ~25 percent. Experimental results from the two sealed SFD configurations lead to a better understanding of the effects of end seals as well as central feed groves on the SFD forced performance. The results presented in this thesis will help improve the effectiveness of SFDs aircraft jet engines.

In recent years, many investigators have predicted that with a semiactive suspension it is possible to attain performance gains comparable to those possible with a fully active suspension. In achieving this, the method by which the damper is controlled is one of the crucial factors that ultimately determines the success or failure of a particular semiactive suspension. This study is an investigation into the effectiveness of a number of basic control strategies at controlling vehicle dynamics, particularly vehicle roll. The test vehicle is a Sport Utility Vehicle (SUV), a class of vehicle that regularly sees widely varying vehicle weight (as a result of passengers and load) and can exhibit undesirable levels of vehicle roll. This study includes a suspension system comprised of four controllable magneto-rheological dampers, associated sensors, and controller. There are three distinct phases in this investigation, the first of which is a numerical investigation performed on a four-degree-of-freedom vehicle roll-plane model. The model is subjected to a variety of road and driver induced inputs, and the vehicle response is characterized, with each semiactive control policy. The second phase of this study consists of laboratory testing performed on a Ford Expedition, with the front axle of the vehicle placed on a two-post dynamic rig (tire coupled), and a variety of road inputs applied. The third phase of this testing involves road testing the test vehicle to further evaluate the effectiveness of each of the semiactive control policies at controlling both vehicle comfort (vibration) and stability (roll). In each phase, the semiactive control policies that are investigated are tuned and modified such that the best possible performance is attained. The performance of each of these optimal semiactive systems is then compared. In the first phase of this investigation, two basic skyhook control strategies are investigated and two modified strategies are proposed. Upon numerically investigating the effectiveness of the four control strategies, it is found that the performance achievable with each of the control strategies is heavily dependent on the properties of the controllable damper. The properties of the controllable damper that were particularly important were the upper and lower levels of force that the controllable damper was able to apply. Based on numerical results, the controllable dampers were tuned for each control system. The results indicate that a velocity-based skyhook control policy, in conjunction with force control, is most effective at controlling both road-induced vibration and driver-induced roll. In the second phase of this investigation, the effects of the two skyhook control strategies were again examined. Multiple system inputs including step inputs, chirp inputs, and multi-sine inputs were used, and the results indicate that significant performance gains using the basic skyhook policies are unlikely. The third phase involved road testing the vehicle through specific maneuvers modeling a wide variety of common driving situations. In addition to the two basic skyhook policies, two additional policies augmented with steering wheel position feedback were also examined. It was found that the velocity based skyhook control policy augmented with steering wheel position feedback achieved performance superior to both the stock passive dampers and other control policies tested here. / Ph. D.

This study evaluates the performance of a semiactive magnetorheological primary suspension on a heavy truck application. A set of magnetorheological dampers is designed, fabricated, and characterized. The set of magnetorheological test dampers are implemented on a Volvo VN heavy truck. An embedded controller determines the level of damping to be supplied by the test dampers. The level of damping in each of the controllable magnetorheological dampers is determined according to a skyhook control scheme. Eleven PCB Piezotronics accelerometers are used to measure the acceleration at various points on the truck. The measurement positions include four measurements on the axles of the truck, and four measurements on the frame of the truck. This data is both recorded for post-test analysis and determining the damping level during testing. Q Additionally, three accelerometers measure the roll, heave, and pitch of the truck cab. The performance of the truck equipped with the semiactive magnetorheological suspension is primarily compared to the performance of the truck with the original (stock) passive system. Results from operation with the adjustable dampers fixed in both their on and off states are also given. The performance comparison between the semiactive and the original passive system is performed for two different driving situations. The first comparison between the two suspension types is for a test case where the truck is driven over a speed bump at approximately 6-7 mph. The second comparison is for the test case where the truck is driven at a constant speed along a stretch of straight and level highway at a constant speed of 55 mph. Acceleration data for both of these test cases is analyzed in the time domain (RMS and peak values of acceleration), and in the frequency domain (average peak intensity in different frequency bands). The findings presented here are confined to the specific magnetorheological dampers that were tested on the truck. Little effort was spent on tuning the high and low states of the adjustable dampers. In addition, the controller used was relatively crude, in the sense that it only implemented the on-off skyhook policy. The findings are meant to highlight some of the potential benefits, as well as shortcomings, of the magnetorheological dampers for heavy truck applications. The data for driving the truck over speed bumps indicate that the magnetorheological dampers used in this study with the skyhook control policy have only a small effect on the vehicle body and wheel dynamics, as compared to the passive stock dampers. The highway data shows that magnetorheological dampers and skyhook control policy are effective at reducing the RMS value of the measured acceleration at most measurement points, as compared to the stock dampers. / Master of Science

There are many active and passive vibration control techniques to reduce the effect of energy on structures which emerges during an earthquake and reduce the displacement of buildings that is caused by ground acceleration. Main advantage of passive vibration control techniques over active vibration control techniques is / no external power or a sensor is required for passive vibration control devices (PVCDs) and it results in lower installation and maintenance costs. However, PVCDs require a predefined optimum damping ratio and optimum damping distribution along the structure since they are not adaptive to changing ground acceleration values. During the design of the PVCDs numerous factors such as building properties and earthquake characteristics should be considered. Dry friction damper is an example of PVCD and has an extensive usage in many different fields due to its high energy damping capacity with low cost and ease of installation. In this thesis, damping of seismic energy at buildings with dry friction dampers is investigated and a new optimization method is developed in frequency domain by employing Describing Function Method (DFM) which reduces the computational effort compared to the time domain and finite element solutions drastically. The accuracy and verification of the presented method is investigated by comparing the frequency domain results with time marching solutions. Furthermore, damper placement and slip forces on the dampers are optimized for single and multi-story buildings equipped with dry friction dampers by utilizing the developed method.

This work deals with the springs and dampers questions. It focuses on their classification, characteristics and testing. The main part of this thesis describes the design and sizing dimensions of machine for measuring characteristics of automotive springs and conceptual design of machine for detection characteristics of hydraulic shock absorbers.