In this work, the performance of barrel-shaped laser-textured piston rings is numerically investigated. The surface texture, parameterized by the dimple density, dimple depth, and dimple distribution pattern, is optimized to minimize the friction coefficient for piston rings of variable curvature. We consider fully textured as well as partially textured piston rings with two different dimple distributions patterns: a central dimple distribution, and a distribution along the piston ring edges. Finally, the sensitivity of the optimal surface parameters to the piston ring curvature is assessed.
In this article, a laser partially textured thrust bearing is theoretically and experimentally analyzed. An adiabatic model is developed in order to theoretically investigate the performances of the bearing. The bearing sample is partially textured both in radial and circumferential direction using the laser texturing process. The performance of the bearing (fluid film thickness and friction torque) is evaluated on a specially adapted test rig and the experimental results are compared with the theoretical model. A good agreement is found between the theoretical model and the experimental data. Also a comparison between a laser textured bearing and a bearing textured using the photolithographic method is presented.
The electric conductivities of different tissues are important parameters of the head model and their precise knowledge appears to be a prerequisite for the localization of electric sources within the brain. To estimate the error in source localization due to errors in assumed conductivity values, parameter variations on skull conductivities are examined. The skull conductivity was varied in a wide range and, in a second part of this paper, the effect of a nonhomogeneous skull conductivity was examined. An error in conductivity of lower than 20% appears to be acceptable for fine finite element head models with average discretization errors down to 3 mm. Nonhomogeneous skull conductivities, e.g., sutures, yield important mislocalizations especially in the vincinty of electrodes and should be modeled.
The paper focuses on the numerical determination of Patir and Cheng’s flow factors for general roughness patterns. Improved procedures for the generation of surface roughness and flow simulation are presented. It is shown that application of these techniques resolves differences to analytical solutions of Elrod and Tripp and reduces the scatter in the results to a reasonable degree. Flow factor charts are given for the ‘standard’ Gaussian/Peklenik roughness and for sintered surfaces with high skewness.
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