Multifunctional optimization of random hollow sphere stackings

Random hollow sphere stackings present good performance for the seemingly contradictory requirements of a light structural material and good acoustic damping properties. A way to optimize the architectured materials parameters is described. The structural properties of random hollow sphere stacking have been measured using X-ray tomography and compared to an Artz compaction model. The mechanical properties are optimized according to the architectural parameters by way of coupled finite elements and discrete elements simulations, and acoustical properties are discussed based on tube absorption models.     

Characteristics of an evaporating thin film in a microchannel

An evaporating meniscus in a microchannel is investigated through an augmented Young–Laplace model and the kinetic theory-based expression for mass transport across a liquid–vapor interface. The complete expression for mass transport is employed without any approximations and boundary conditions for the film profile are developed. The thin film and the intrinsic-meniscus regions are distinguished based on the disjoining pressure variation along the meniscus. While heat transfer in the thin-film region is found to be relatively insensitive to channels larger than a few micrometers in radius, that in the intrinsic meniscus is quite sensitive to channel size. The role of evaporation suppression due to capillary pressure in both regions is discussed. Compared to the relatively small contribution to overall heat transfer from the thin-film region, the micro-region (defined here as extending from the non-evaporating region to a location where the film is 1 μm thick) is found to account for more than 50% of the total heat transfer.     

Wall-following control of a two-wheeled mobile robot

Wall-following control problem for a mobile robot is to move it along a wall at a constant speed and keep a specified distance to the wall.This paper proposes wall-following controllers based on Lyapunov function candidate for a two-wheeled mobile robot (MR) to follow an unknown wall. The mobile robot is considered in terms of kinematic model in Cartesian coordinate system. Two wall-following feedback controllers are designed: full state feedback controller and observer-based controller. To design the former controller, the errors of distance and orientation of the mobile robot to the wall are defined, and the feedback controller based on Lyapunov function candidate is designed to guarantee that the errors converge to zero asymptotically. The latter controller is designed based on Busawon’s observer as only the distance error is measured. Additionally, the simulation and experimental results are included to illustrate the effectiveness of the proposed controllers.     

建筑用抗震钢HRB400EⅢ级钢筋焊接接头的低周疲劳性能

采用轴向应变控制方法,在MTS809拉扭复合疲劳试验机上开展了HRB400EⅢ级钢筋母材及焊接接头的低周疲劳试验,获得了母材及焊接接头的低周疲劳性能,如循环应力响应特征、循环应力-应变关系以及寿命预测公式等.通过断口电镜扫描发现,HRB400EⅢ级钢筋焊接接头的裂纹萌生于试件表面,且存在多处裂纹源.研究结果表明,焊接接头与母材的低周疲劳寿命及微观断裂机理方面均存在明显差异,并从力学性能变化的角度对引起差异的原因进行了解释.