基于心肺复苏用途的上肢外骨骼助力机器人仿真研究

针对心肺复苏助力用途,设计了一种新型的上肢外骨骼助力机器人.以D-H矩阵为基础建立了上肢外骨骼助力机器人的运动学方程,得到机器人末端点的位姿矩阵并验证,利用代数解法求得逆运动学.通过Matlab编程求解出上肢外骨骼助力机器人的可达工作空间.运用ADAMS对机器人进行了运动学和动力学仿真,证明了结构的合理性以及运动学的正确性,同时动力学仿真得到的各关节最大力矩为电机选型和后续的运动控制提供依据.     

4-RRR冗余并联机构的动力学分析

为了分析冗余4-RRR并联机构在高速、高载荷下的的动力学特性和运动精度,利用坐标变换矩阵求解冗余4-RRR平面并联机构反解方程,推导机构雅克比矩阵。在此基础上,将并联机构分解为动平台和一、二连杆子系统,采用Lagrange法建立子系统动力学模型,然后推导出机构整体动力学模型。以Matalb/Simulink为工具,对该机构的动力学进行算例仿真,仿真结果表明:4-RRR平面并联机构各驱动构件在实现期望轨迹的运动过程中,驱动力和力矩的变化、数值大小各不相同,但均呈正余弦曲线规律变化。所提出的研究方法快速有效,为机构后续研究提供了理论依据。     

调径变矩抽油机驴头的跌落仿真研究

针对抽油机驴头的掉落事故呈高发态势,基于多体系统动力学分析理论,建立了调径变矩抽油机的复杂机械系统运动学和动力学程式化的数学模型,进行了整机动力学分析,确定了驴头裂纹产生的区域和掉落的成因。以不同的跌落方式对驴头跌落过程进行模拟仿真,得到了跌落过程中动能、应力及速度的变化情况。总结不同跌落方式下的变量规律,确定了最危险的跌落方式。通过仿真对比分析得出:当驴头竖直方式跌落时最危险,其结果和实际情况相符,为其进一步的结构优化设计和机械类构件跌落冲击的有限元模拟提供了重要的依据。     

A virtual machine concept for real-time simulation of machine tool dynamics

When designing CNC machine tools it is important to consider the dynamics of the control, the electrical components and the mechanical structure of the machine simultaneously. This paper describes the structure and implementation of a concept for real-time simulation of such machine tools using a water jet cutting machine as an application. The concept includes a real control system, simulation models of the dynamics of the machine and a virtual reality model for visualisation. The real-time capability of the concept, including the simulation of electrical and rather detailed mechanical component models is proofed. The validation process indicates good agreement between simulation and measurement, but suggests further studies on servo motor, connection and flexibility modelling. However, already from the initial simulation results presented in this paper it can be concluded that the influence of structural flexibility on manufacturing accuracy is of importance at desired feeding rates and accelerations. The fully automated implementation developed in this work is a promising base for dealing with this trade-off between productivity and accuracy of the manufacturing process through multidisciplinary optimisation.     

基于ADAMS的机床爬行问题的动力学仿真

应用机械系统动力学分析软件ADAMS对机床的爬行问题和运动不平稳性进行了动力学仿真。根据机床直线传动的力学模型,通过比较多种影响机床爬行因素的参数方案,分析了机床的爬行问题,获得了最优结果。     

Numerische Simulation disperser Gas/Flüssig‐Strömungen in Blasensäulen bei hohen Gasgehalten mit OpenFOAM®. Teil 2 – Numerische Simulation und Ergebnisse

The design of industrial gas/liquid reactors such as bubble columns requires detailed information with respect to the flow structure and characteristics of two‐ or multiphase systems in the reactor. The contribution is focused on the evaluation of the simulation results obtained by a selection of models. The results are further compared with those reported in literature. The simulations have been performed with the CFD software OpenFOAM®. The main focus of the numerical simulation was set on capturing the characteristic process and design parameters of bubble columns.     

PIV/PLIF Study of Impinging Jet Ozone Bubble Column with Mixing Nozzles

This paper introduces the results obtained from a particle image velocimetry/planer laser-induced fluorescence (PIV/PLIF) system used in characterizing an impinging jet ozone bubble column with mixing nozzles. This research aims at evaluating the mixing effect resulting from the nozzle diffusers attached to the outlets of the impinging jets' injectors. The PIV system was used to study the flow patterns of the liquid and gas phases under different superficial gas and liquid velocities (u_G and u_L, respectively) values (from 0.002 to 0.017 m/s and from 0.008 to 0.024 m/s, respectively). Furthermore, a particle dynamics analyzer (PDA) system was used to characterize the bubble sizes under the same operating conditions. The PLIF system was used to determine the liquid axial dispersion coefficient (D_L, m²/s) for the mentioned range of operating conditions. The column average gas hold-up (?_G) and specific interfacial area (a) were then determined in order to evaluate the column's mass transfer efficiency. The results showed that higher mass transfer rates can be obtained by using this column, as high ?_G, and were achieved.     

Ball screw drives with enhanced bandwidth by modification of the axial bearing

The bandwidth of the ball-screw drive is limited by the first natural frequency of the mechanical structure. As opposed to conventional drives where the axial bearing stiffness is kept high to obtain higher natural frequencies, this paper proposes to use lower axial bearing stiffness accompanied by a strong damper in parallel with the ball-screw structure. The proposed method, which is experimentally demonstrated, increases the bandwidth of the drive considerably provided that a cost effective and practical damper is available.     

Flow distribution and mass removal in floating treatment wetlands arranged in series and spanning the channel width

Floating treatment wetlands (FTWs) use plants’ roots for water quality improvement. The plants are supported by a buoyant structure deployed at the water surface. The roots form a porous zone beneath the structure and remove pollutants carried in suspension through filtering, absorption and uptake. This paper used CFD simulation to model FTWs arranged in series and spanning the channel width and to study the effects of root length and spacing between FTWs on flow distribution and mass removal. The root zone was modelled as a porous media, and removal was computed using first-order decay, for which a range of removal constants was tested. Longer roots increased the reactive volume of the root zone, which increased the fraction of pollutant inflow entering the FTWs. Increasing the distance between FTWs allowed greater mixing between water that went through and beneath the upstream FTW. This increased the concentration entering each FTW, which enhanced mass removal per FTW. However, a larger distance between FTWs reduced the number of FTWs in the channel, reducing the reactive volume. In the tradeoff between mixing and reactive volume, the reactive volume was more important, such that total removal in the channel increased with longer roots and more units of FTW (shorter gap distance). However, removing the gap entirely was detrimental, as FTWs in series removed more mass than a continuous FTW of same volume. This study points to two design recommendations for FTWs in series. First, if resources for building FTWs are not limiting, but the channel length is, it is preferable to prioritize higher reactive volume (shorter gap distance) to achieve maximum removal per channel length. Second, if resources for FTWs are limiting, but channel length is not, it is better to place the FTWs with a longer gap distance, preferably along enough to allow mixing over the full depth between FTWs, as this will achieve maximum removal per FTW.     

人工降雨试验中风速对落地雨强空间分布的影响研究

气候变化和城镇化发展使得极端暴雨发生频率增加,实验室降雨试验可为极端暴雨灾害的研究提供数据支撑。通过开展不同情景下的实验室降雨试验与数值模拟,研究了风对落地雨强分布的影响,分析了风导致试验区域平均落地雨强减小的原因。结果表明：（1）风会使试验区域的实际平均落地雨强减小,主要原因是降雨中不同粒径雨滴在风场作用下漂移距离的不同,导致了地面受雨面积扩张。（2）受雨范围内落地雨强的均匀性受风速影响,落地雨强均匀性随风速增加而下降。为提高试验数据的准确性,在进行降雨模拟试验时需要考虑风速的影响,结合实验室实际条件合理确定试验范围。