Browsing by Subject "Friction Coefficient"

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    Mechanics and charging of nanoparticle agglomerates.
    (2009-06) Shin, Weon Gyu
    This thesis consists of two parts. The first part concerns studies on mechanics of real agglomerate particles and the second part involves studies on unipolar diffusion charging of agglomerates. Understanding mechanics of real agglomerate particles consisting of multiple primary particles is important for aerosol sizing instrumentation using electrical mobility and nanoparticle manufacturing process where coagulation and sedimentation occur. A key quantity determining transport properties of agglomerates is the friction coefficient. However, quantitative studies for the friction coefficient of agglomerates are very limited. Transmission Electron Microscopy (TEM) image analysis results of silver agglomerates provides a basis for the comparison of experimental data with estimates based on free molecular models. A new quantitative method to determine the dynamic shape factor and the two exponents, η and Dfm, which characterize the power law dependence of friction coefficient on the number of primary spheres and the mass on the mobility diameter, was developed using Differential Mobility Analyzer (DMA)- Aerosol Particle Mass (APM) analyzer. Model predictions indicate that η is independent of agglomerate size while Dfm is sensitive to agglomerate size. Experimentally, it appears the opposite is true. Tandem DMA (TDMA) results also show that the massmobility diameter scaling exponent is not dependent on mobility size range. Estimates of non-ideal effects on the agglomerate dynamics were computed as perturbations to the Chan-Dahneke agglomerate model. After the corrections, an agreement between experimental data and model predictions becomes significantly improved. Unipolar diffusion charging becomes more attractive because it has higher charging efficiency than bipolar charging as well as important applications in aerosol sizing instrumentation using electrical mobility, powder coating, and the removal of toxic particles from air stream using Electrostatic Precipitator. It has been reported that the particle morphology affects both bipolar and unipolar charging processes. Nevertheless, knowledge about the charging of non-spherical particles such as asbestos fibers and fractal agglomerates is still lacking. From this study it was found that the effect of dielectric constant of materials on unipolar diffusion charging of nanoparticles is very small and the experimental results are in a good agreement with Fuchs (1963)’ theory. The effect of agglomerate morphology on unipolar charging characteristic was examined both experimentally and analytically in terms of the mean charge per particle. Both geometric surface area and electrical capacitance are known as two important parameters to determine the mean charge of non-spherical particles. A new model to predict the electrical capacitance of loose agglomerate particles as a function of mobility diameter was developed incorporating electrical mobility and electrostatics theories. This study shows that the electrical capacitance contributes to increase the mean charge per particle of agglomerates more than the geometric surface area, especially in the transition regime. The estimates of geometric surface area and electrical capacitance were used to predict the mean charge from Chang (1981)’s model and the predicted results are reasonably in good agreement with experimental data.
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    New sensors and estimation systems for the measurement of tire-road friction coefficient and tire slip variables.
    (2009-11) Erdogan, Gurkan
    This thesis introduces two new measurement systems developed for the estimation of tire-road friction coefficient and tire slip variables on highway vehicles. The first part of the thesis focuses on the development and experimental evaluation of a friction estimation system based on a novel adaptive feedforward vibration cancellation algorithm. The friction estimation utilizes a small instrumented wheel on the vehicle. Unlike other systems previously documented in literature, the developed system can provide a continuous measurement of the friction coefficient under all vehicle maneuvers, even when the longitudinal and lateral accelerations are both zero. A key challenge in the development of the estimation system is the need to remove the influence of vibrations and the influence of vehicle maneuvers from the measured signal of a force sensor. An adaptive feedforward algorithm based on the use of accelerometer signals as reference inputs is developed. The parameters of the feedforward model are estimated by the adaptive algorithm and serve to determine the value of the friction coefficient. The experimental performance of the adaptive feedforward algorithm is shown to be significantly superior to that of a simple cross-correlation based algorithm for friction estimation. The second part of the thesis introduces a simple approach for the analysis of tire deformations and proposes a new wireless piezoelectric tire sensor for the measurements of physically meaningful tire deformations. The tire deformation profile inside the contact patch can be used for the estimation of tire slip variables, tire forces and tire road friction coefficient. A wireless piezoelectric tire sensor for the specific case of slip angle and tire-road friction coefficient estimation is developed in this work. A sensor which decouples the lateral sidewall deformation from the radial and tangential sidewall deformations is designed. The slope of the lateral deflection profile at the leading edge of the contact patch is used to estimate the slip angle. A second order polynomial is used to model the lateral deflection profile of the sidewall. The parameters of this function are employed to estimate the lateral force and the conventional brush model is employed to estimate the tire road friction coefficient.