The characteristics of an automotive passenger seat in response to vibrational excitations are examined and an active vibration isolation system incorporating smart materials is designed, built, and tested. Human sensitivity to vibration is discussed. Characteristics of road roughness are discussed and used to implement a representative test input to a passenger seat system. extsc{Matlab} is used to model the car seat and vehicle system with four degrees of freedom to determine actuator requirements. Selection and implementation of a low--profile, prestressed piezoceramic device into an active seat suspension system is described, and experimental results of the actuator assembly performance are presented. Vibration isolation is realized in an experimental setup representing one quarter of a seat and passenger's total mass, using one actuator assembly (representing one corner of the seat suspension). For an input power spectrum representative of a passenger vehicle environment, the smart material actuator assembly, as applied to a quarter seat experimental setup, is proven to be capable of isolating vibration with an isolation frequency of 2Hz and no resonant peak, versus 6Hz and a resonant peak of 2g/g for an actual passenger seat tested. / 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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Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1980. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING. / Includes bibliographical references. / by James Raymond Downer. / M.S.