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

Frame and cab suspension designs of Class 8 heavy trucks were investigated to see their effects on ride comfort. Four trucks were used in this study, each with a different frame: a factory low frame, a lightweight low frame, a factory high frame, and a lightweight high frame. There were two different frame heights and three thicknesses. Two different rear cab suspensions were also tried out on each truck. Both suspensions used two airsprings and two dampers mounted vertically to control the vertical motion. The first suspension used two horizontally mounted dampers to control the lateral motion, while the second used a panhard rod connected to a torsion spring. In addition, two different sets of airsprings and two sets of vertical shocks were tried with each suspension, giving eight suspension combinations. The trucks were shaken through the forward drive (second) axle using two 5500 lb hydraulic actuators with displacement control. The steering (first) axle was left in contact with the ground (through the tires) and the rear drive (third) axle was strapped to the truck's frame and acted solely as dead weight. The actuators were given various inputs including single frequency sinusoidal signals, step signals, and decreasing amplitude chirp signals. Both roll and heave modes of the truck were excited. The ride was measured using three accelerometers located at the B-post inside the truck cab. These accelerometers were oriented in the vertical, fore/aft (longitudinal), and lateral (left/right) directions. Numerous other accelerometers and LVDTs were used to measure frame and cab motion. This study found that there while the beaming frequency shifted downward with the lighter frames, there was only a small decrease in ride quality. The panhard suspension rod had significantly higher roll motion, but the heave amplitudes were similar to the lateral damper suspension. Switching vertical shocks had a significant effect on heave motion, but none on the cab's roll. Switching the airsprings on the cab suspension in this study had no effect. / Master of Science

Please read the abstract in the section, 00front, of this document Please note that the Compact disc with Vehsim2d (demonstration version) (Appendix B) is not included / Thesis (PhD (Mechanical Engineering))--University of Pretoria, 2008. / Mechanical and Aeronautical Engineering / unrestricted

This thesis deal with a suspension kinematics of racing vehicles a specialy group B. It processes an overview of axle suspensions of racing vehicles used at 80´ last century. Than it compare kinematics variables with actual axle suspensions systems.

One-, two- and three-phase mixing systems have been extensively studied. The experiments were performed in a range of standard (baffled) vessel geometries of diameter varying between 0.22 - 1.83 m. Rushton disc turbines and mixed flow impellers (both pumping directions) were fully investigated. Water and glucose solution (~ - 120 mPas) were employed. For single phase systems, the work has shown that the power number of disc turbines depends on disc thickness and scale of vessel. For the mixed flow agitators the power number is dependent upon the blade thickness and (D/T) ratio. Correlations enabling the ungassed power number to be calculated as a function of these parameters are given. For gassed systems, the power drawn by each type of impeller is explained by local impeller hyarodynamics (cavity structure) and the bulk flow pattern. The fiooding-Ioading transition (NF) and the complet~ dispersion condition (NeD) have also been studied. A large mixed flow impeller (6MFU45 ; D - T/2) with a large ring sparger is the most energy efficient at NF and NCD speeds as compared with the other geometries studied and correlations enabling the prediction of NF and NCD for all geometries studied are presented. Hold-up correlations are also given for each impeller firstly as a function of specific energy dissipation rate and superficial gas velocity and secondly as' a function of agitator speed and volumetric gassing rate. For each impeller, each method is equally good statistically for scale-up but the latter is more explicit. All impellers give approximately the same hold-up under equal specific power inputs and superficial gas velocity but there are small but statistically significant differences. These differences are discussed. For solid-liquid systems, correlations in the literature for the calculation of the minimum speed to just suspend solids, NJS ' are tested for each system geometry with glass Ballotini particles. The correlation proposed by Chapman et al. is shown to fit the present experimental data best. The specific power input per unit mass (ET)JS - constant, is proposed as a scale-up criterion for solids suspension. Large 6MFD45 (D - T/2) is the most energy efficient for suspension but 6MFU45 (D - T/2) is only slightly worse. In the three-phase mixing systems, the 6MFD 45 , D - T/2, is most energy efficient for solid suspension (ET)JSg' at low gassing rates (up to 1 vvm) but exhibits large flow pattern and torque fluctuations. Above _ 1 vvm, 6MFU45 (D = T/2) becomes the most energy efficient for solid suspension. In addition the minimum impeller speed for solid suspension NJSg for this impeller is almost independent of gassing rate and gives very stable flow patterns and torque. output throughout the whole gassing range. Again (eT)JSg - const is the recommended scale-up criterion for solids suspension under gassed conditions. Large (D - T/2) impellers are found to be more energy efficient and correlations for predicting N 45 45 . JSg for 6DT. 6MFD and 6MFU are obta~ned. Increase in liquid viscosity has a rather small effect on gas dispersion. Up to 120 mPas: (N) Q:I (N ) and (N ) Q:I F viscous F water CD viscous (NCD) water uO.06 On the other hand, viscosity has a significant effect on NJS and 3 to 5 times more energy is required for solid suspension at 120 ,mPas.

Strong trust based relationships are one of the pillars of the communitarian model of industrial districts. District literature calls upon trust in order to explain several elements of the model. The existence of trust may explain how a highly fragmented and essentially local value chain reduces transaction costs compared with an integrated firm. It may also allow for closer ties where up to date pertinent information and innovative ideas are transferred between firms. Trusting, long term relationships and district networks are also evoked in the literature as being, in themselves, sources of competitive advantage. Yet despite large sections of district literature calling upon trust to explain the existence and efficiency of industrial districts, few scholars have investigated empirically the sources of trust in local ties. In depth semi-directive interviews with small firm managers in the Arve Valley industrial district near Geneva were analysed in order to examine the context and quality of intra-district relationships (mainly supplier and peers) which were then ompared with extra-district links with clients. The sources of trust are analysed by applying Möllering’s (2006) model of trust based on reason, routine and reflexivity. Findings indicate that managers rely more on a rational calculation of partner’s motives than ‘blind’ adherence to local, historical norms of behaviour. This finding contributes to the view that districts are organizational fields where agents possess large amounts of information about markets, technologies and partners. Managers also demonstrate a willingness to maintain local links over the long term, thus ensuring a crucial element of their firms’ competitive advantage and will adjust their behaviour accordingly. This thesis contributes to district literature by examining detailing the existence and foundations of close intra-district ties created between managers mobilising resources based on cognitive, organisational and geographical proximities. A major contribution to trust literature is the 5 analysis and discussion of the complex interplay between the three antecedents outlined in Möllering’s model in the creation of local trust and proposes that while trust decisions in information rich districts are based more on rational calculation than on local norms and institutions, other trust decisions (with external clients), in the absence of sufficient information are founded on very different bases. This comparison of the foundations of trust in two different contexts highlights the role of identity and routine in the ‘leap of faith’ or suspension of doubt that is trust.

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