机件表面微槽内流体流动的数值研究

运用格子boltzmann方法(LBM)和Fluent软件分别对机械零件表面的微小沟槽内的流体流动进行了数值模拟。通过比较流体Re=200时主流速度及沟槽内X方向上不同截面的速度分布曲线,表明LBM能有效的对机件表面微小槽道流体流动进行数值模拟。针对三角形、矩形、梯形微槽道内流体的流动过程进行模拟,得到不同槽道的阻力系数,分析不同雷诺数对涡心位置的影响以及流场分布特点,数值计算结果表明了LBM方法能有效模拟微槽内的流体流动现象。

Method of Precise Auto Tool Setting for Micro Milling

Based on microscope and image processing, a new method of auto tool setting for micro milling was presented. Firstly, a realtime image of tool setting area was obtained by microscope and CCD camera, then image processing was carried out on this image and the gap between the tool and workpiece was calculated. The gap measurement was sent to motion controlling card to make the tool approach to the surface of workpiece. These steps were repeated until the gap is zero, which means that tool setting was finished. Moreover, a reliability verification test was conducted. Results indicated that the precision of tool setting is satisfactory.

Safety Analysis for Older Drivers at SignalizedIntersections

The proportions of older drivers continue to increase since baby boom generation is becoming old. The level of mobility of older drivers is also increasing. Older drivers begin to noticeably be over-involved in fatal crashes. Intersections appear to be hazardous to older drivers, particularly left turn due to one or more of. sensory, perceptual, cognitive, physical and general driving knowledge deficiencies. The safety concern of older drivers is also becoming significant. Ten years of crash data has been extracted from Kansas accident report system. It has been analyzed using SAS （statistical analysis system） software. Five different age groups have been considered. Comparison has been made between different age groups of the same gender, and the same age group for different gender. Effects of light condition, weather condition, surface type, surface condition, road character and construction/maintenance zone on older drivers＇ safety have also been considered in this study. It has been found out that proportion of older drivers in through movement involved in accident decreases as age increases whereas the proportion of left turn accidents increases with age, left turn is harder for females in all age groups, and proportion of right turn accidents has no specific trend. Most of the accidents have taken place during daylight when there are no adverse weather conditions on dry surface, straight and level road, and blacktop surface type.

Kinematics constrained five-axis tool path planning for high material removal rate

Traditional five-axis tool path planning methods mostly focus on differential geometric characteristics between the cutter and the workpiece surface to increase the material removal rate(i.e.,by minimizing path length,improving curvature matching,maximizing local cutting width,etc.) . However,material removal rate is not only related to geometric conditions such as the local cutting width,but also constrained by feeding speed as well as the motion capacity of the five-axis machine. This research integrates machine tool kinematics and cutter-workpiece contact kinematics to present a general kinematical model for five-axis machining process. Major steps of the proposed method include:(1) to establish the forward kinematical relationship between the motion of the machine tool axes and the cutter contact point;(2) to establish a tool path optimization model for high material removal rate based on both differential geometrical property and the contact kinematics between the cutter and workpiece;(3) to convert cutter orientation and cutting direction optimization problem into a concave quadratic planning(QP) model. Tool path will finally be generated from the underlying optimal cutting direction field. Through solving the time-optimal trajectory generation problem and machining experiment,we demonstrate the validity and effectiveness of the proposed method.

On-chip higher-order topological micromechanical metamaterials

Metamaterials with higher-order topological band gaps that exhibit topological physics beyond the bulkedge correspondence provide unique application values due to their ability of integrating topological boundary states at multiple dimensions in a single chip.On the other hand,in the past decade,micromechanical metamaterials are developing rapidly for various applications such as micro-piezoelectricgenerators,intelligent micro-systems,on-chip sensing and self-powered micro-systems.To empower these cutting-edge applications with topological manipulations of elastic waves,higher-order topological mechanical systems working at high frequencies(MHz)with high quality-factors are demanded.The current realizations of higher-order topological mechanical systems,however,are still limited to systems with large scales(centimetres)and low frequencies(k Hz).Here,we report the first experimental realization of an on-chip micromechanical metamaterial as the higher-order topological insulator for elastic waves at MHz.The higher-order topological phononic band gap is induced by the band inversion at the Brillouin zone corner which is achieved by configuring the orientations of the elliptic pillars etched on the silicon chip.With consistent experiments,theory and simulations,we demonstrate the emergence of coexisting topological edge and corner states in a single silicon chip as induced by the higher-order band topology.The experimental realization of on-chip micromechanical metamaterials with higherorder topology opens a new regime for materials and applications based on topological elastic waves.