软体连续机械臂动力学建模与仿真

由于软体机械臂的质量是沿臂的长度连续分布,因此采用拉格朗日方法建立软体机械臂的动力学模型时,涉及计算复杂的积分运算,采用离散化的集中质量模型降低了计算的复杂性,但准确性不足.为了提高软体机械臂动力学建模与仿真的准确度和计算效率,本文采用模态方法对软体机械臂进行运动学描述,并从能量的角度分析软体机械臂动力学特性,研究发现...     

On the Static Equilibrium of a Multi-Legged Robot on a Rough Surface in Zero-Gravity Conditions

The problem of the equilibrium of a multi-legged robot in zero-gravity is investigated. The robot has several points of support and is located on a flat rough surface. The influence of an arbitrarily directed force applied to the center of mass of a robot on its equilibrium is considered.     

非线性转子-轴承系统涡动的机械化数学分析

为研究转子一轴承系统中非线性油膜力引起的半速涡动，本文给出了将吴文俊消去法和符号计算相结合的分析方法。基于短轴承假设，得到了单盘转子系统涡动时盘心、轴心及涡动角速度相对于无量纲转速的关系式。分析研究了转子涡动角速度变化规律及出现的双稳态现象。     

多机械臂搬运同一物体的协调动态载荷分配

针对多机械臂共同搬运同一物体形成闭运动链的协调系统,研究了多机械臂协调动态载荷分配存在冗余情况下的实时性分配方法文中提出了“应集中惯性质量棒”的概念,进而根据各机械臂的承载能力,采用线性加权的方法发展了一种操作物体质心处零内力的载荷分配原则。最后给出了系统载荷分配的解析表达式,有效地解决了多机械臂搬运同一物体时其动态载荷分配的实时性问题。     

Modeling the effect of liquid movement on the center of gravity calculation of agricultural vehicles

Due to a high center of gravity (CG) location, agricultural vehicles are more vulnerable to overturns. The CG location can be calculated using the lifting axle method of ISO 16231-2:2015. But, as a vehicle is lifted, its liquid payloads are not entirely contained. The liquids will shift both in position and form, affecting the CG height calculation.A mathematical model was developed to predict the effect of liquid movement on the CG height calculation of a tilted vehicle. The model was validated using an agricultural utility tractor and a prototype. The developed model was applied to calculate the CG location considering the effect of the liquid shift.Results showed tilting produced a higher calculated center of gravity due to liquid movement, but by increasing the tilting angle, the calculated CG height decreased. The effect of the liquid shift on CG height measurement for the wagon with 16.0% liquid mass was 14.8% and for the tractor with 1.2% liquid mass was 0.41%. The model error was less than 1.3% for all tests. Considering the effect of the liquid shift in CG height calculation, the error in CG height calculation decreased from 11.9% to 2.6% for the wagon.     

螺旋式输液管道振动的有限元法分析

本文采用有限元法分析螺旋式输液管道流固耦合振动。基于哈密顿变分式推导了单元质量矩阵、刚度矩阵及科里奥利力引起的阻尼矩阵,讨论了不同的流体速度、边界条件及螺距角对输液管固有频率的影响。文内还提出用于非经典非对称阻尼系统的双边里兹向量方法,并给出该方法与HQR法在计算精度与计算时间上的比较。     

基于RGB颜色模型的玉米淀粉爆燃火焰传播速度

采用小尺度粉尘爆炸实验装置对不同质量浓度的玉米淀粉爆燃火焰传播过程进行了实验研究,建立了基于RGB颜色模型的火焰重构及形态学重建的粉尘火焰传播速度计算方法,计算了不同质量浓度下的玉米淀粉爆燃火焰传播速度。结果表明:采用基于RGB颜色模型的速度计算方法能够快速准确地计算出玉米淀粉爆燃火焰传播速度,火焰像素范围的确定是火焰速度计算的关键;管道内火焰传播速度受粉尘云质量浓度的影响,最大火焰传播速度随粉尘云质量浓度的增大先增大后减小,到达速度峰值的时间先缩短后增长,当质量浓度为0.63 kg/m3时,出现该实验条件下火焰传播速度最大值7.03 m/s。     

Studies of dynamics of a lightweight wheeled mobile robot during longitudinal motion on soft ground

The paper is concerned with the study of longitudinal motion of a lightweight wheeled mobile robot on soft ground. The study is focused on the influence of the desired longitudinal velocity of a robot on both the longitudinal slip of the wheels and the ratio of wheel-terrain contact angles. Design of the four-wheeled skid-steered robot and research environment are described. Experimental investigations were conducted on a dedicated test stand with dry sand. A dynamics model of the robot-ground system taking into account properties of soft ground is presented. The classical terramechanics models of Bekker and Janosi-Hanamoto are used. Results of simulation research of robot motion and of the analogous experimental investigations are presented. Actual motion parameters of the robot and the values of longitudinal slip ratio of the wheels are determined. The results of simulation and experimental investigations are compared and discussed. A formula to describe front-to-back wheel-terrain contact angle ratio dependency on the desired velocity is proposed.     

Stability of the rectilinear motion of a railway Wheelset

A railway wheelset rolling on rails without slip is studied with consideration of the creep hypothesis. The wheelset is represented by two cones having a common base; the rails are represented by two circular cylinders with parallel axes. The kinematic characteristics of undisturbed rolling for the wheelset are determined when its center of mass moves along a straight line; these characteristics are also determined in the case of disturbed motion when the mass center of the wheelset moves along a sinusoidal trajectory. For these modes of motion, the constraint reactions are found with an accuracy up to the second order of smallness with respect to the values of disturbed variables. When the absolutely rigid point contact is replaced by the elastic contact, the creep hypothesis is used, the method of averaging with respect to the fast variables is applied, and a critical velocity above which the rectilinear rolling becomes unstable is determined on the basis of the averaged equations.     

基于能力评估的空间翻滚目标抓捕策略优化

由于目标的翻滚运动, 空间双臂机器人对动态目标的抓捕相比于静态目标更具有挑战性. 对抓捕策略进行优化可以提高空间双臂机器人对翻滚目标的操作能力以保证任务的成功. 本文提出了一种基于能力评估的抓捕策略优选方法. 空间双臂机器人捕获目标时, 双臂末端执行器与目标同时接触形成闭链系统, 闭链约束的引入使操作能力的评估更加复杂. 在对双臂空间机器人协调操作翻滚目标的运动学与动力学分析基础上, 建立了考虑闭链约束的协调工作空间, 并分析了基于任务兼容度的消旋能力评估指标. 建立的协调工作空间同时包含位置和姿态信息, 可以用于灵巧度的计算. 接着, 基于协调工作空间的全局灵巧度指标确定机械臂末端执行器对目标的最优抓捕点, 以及考虑相机视角约束和末端执行器对目标速度跟踪约束下的力任务兼容度指标确定空间双臂机器人捕获翻滚目标时的最优抓捕构型. 利用能力评估确定抓捕策略可以充分利用双臂的协调性以增加对动态目标的操作能力, 通过仿真验证了所提抓捕策略的可行性和有效性.      

COORDINATED PATH PLANNING BY INTEGRATING IMPROVED RRT$^{\small*}$ AND QUARTIC SPLINE$^{\bf 1)}$

针对空间机器人抓捕空间非合作目标的在轨服务任务,同时考虑机器人运动学约束和动力学约束,提出一种分层式的自由漂浮双臂空间机器人协调路径规划方法. 首先,在路径规划层面上基于 RRT* 算法分别规划双臂末端执行器在笛卡尔空间下的初始可行路径,为双臂设置独立的采样空间,保证路径规划过程中双臂系统不发生自身碰撞. 然后,在轨迹规划层面上利用四次样条曲线平滑 RRT* 算法生成的初始路径,设计满足样条曲线的一阶、二阶及三阶微分连续约束,同时考虑机械臂末端执行器的初末速度约束条件、初始加速度约束条件,得到适合于空间机器人执行的动力学可行的平滑 轨迹.最后,计算所规划路径的最大速度、最大加速度与机械臂末端执行器物理极限值的比值,取最小上限,即为最少路径规划时间. 所提路径规划方法能够设计出满足特定路径点约束的协调路径,且所设计的路径考虑了机械臂的物理限制条件,通过对自由漂浮双臂空间机器人进行仿真试验,验证了所提路径规划算法的有效性.     

一种改进 RRT* 结合四次样条的协调路径规划方法

针对空间机器人抓捕空间非合作目标的在轨服务任务,同时考虑机器人运动学约束和动力学约束,提出一种分层式的自由漂浮双臂空间机器人协调路径规划方法. 首先,在路径规划层面上基于 RRT* 算法分别规划双臂末端执行器在笛卡尔空间下的初始可行路径,为双臂设置独立的采样空间,保证路径规划过程中双臂系统不发生自身碰撞. 然后,在轨迹规划层面上利用四次样条曲线平滑 RRT* 算法生成的初始路径,设计满足样条曲线的一阶、二阶及三阶微分连续约束,同时考虑机械臂末端执行器的初末速度约束条件、初始加速度约束条件,得到适合于空间机器人执行的动力学可行的平滑 轨迹.最后,计算所规划路径的最大速度、最大加速度与机械臂末端执行器物理极限值的比值,取最小上限,即为最少路径规划时间. 所提路径规划方法能够设计出满足特定路径点约束的协调路径,且所设计的路径考虑了机械臂的物理限制条件,通过对自由漂浮双臂空间机器人进行仿真试验,验证了所提路径规划算法的有效性.      

控压钻井中三相流体压力波速传播特性

考虑虚拟质量力、相间阻力、气相溶解度及滑脱速度等因素,在双流体模型基础上,建立了控压钻井中油-气-钻井液三相流体压力波速模型. 将溢流气体视为气相,将溢流油相及钻井液相视为液相,液相弹性模量及密度等参数为油相及钻井液相中各参数的加权和,利用半隐式差分及小扰动理论等数学方法,借助计算机编程对其求解. 结果表明,当井底气侵量从0.36m3/h 增至3.6m3/h,波速减小峰值为498.59m/s,而相同的油侵增加量,波速呈缓慢减小趋势,波速减小峰值为19.21m/s;当回压从0.1MPa 增至9.0MPa,波速呈增大趋势,波速增大峰值为233.15m/s;不考虑虚拟质量力,在低频段引起的波速误差呈增大趋势,在高频段引起的波速误差峰值稳定于10.03%.      

弹体侵彻厚混凝土靶迎弹面成坑效应

为研究弹体侵彻厚混凝土靶的迎弹面成坑效应,总结了侵彻实验中的成坑现象,分析了经验公式对成坑深度、成坑直径和成坑角等成坑效应的预测效果;考虑了撞击速度、靶板强度、配筋以及弹体直径和质量等因素的影响,采用量纲分析方法建立了新型成坑效应计算公式及成坑阶段耗能计算公式;基于新型成坑效应计算公式,对成坑效应的影响因素和成坑耗能进行了参数化分析。结果表明:无量纲成坑深度受靶板强度、配筋率和弹体质量的影响较大;对于钢筋混凝土,成坑深度随撞击速度提升呈先增大后减小再增大的变化规律;在常见的侵彻速度和质量范围内,成坑角为15°～24°,质量对成坑角影响较小;迎弹面成坑耗能占弹体总动能的10%～25%,且配筋率和靶板强度对成坑耗能比例的影响较小;弹体质量越小,成坑阶段耗能占比越大。新型成坑效应计算公式对成坑深度、直径和角度的计算结果与实验数据吻合较好,可为侵彻弹体设计和工程防护提供参考。     

RESEARCH ON PRESSURE WAVE PROPAGATION CHARACTERISTICS IN THREE-PHASE FLOW DURING MANAGED PRESSURE DRILLING

考虑虚拟质量力、相间阻力、气相溶解度及滑脱速度等因素,在双流体模型基础上,建立了控压钻井中油-气-钻井液三相流体压力波速模型. 将溢流气体视为气相,将溢流油相及钻井液相视为液相,液相弹性模量及密度等参数为油相及钻井液相中各参数的加权和,利用半隐式差分及小扰动理论等数学方法,借助计算机编程对其求解. 结果表明,当井底气侵量从0.36m³/h 增至3.6m³/h,波速减小峰值为498.59m/s,而相同的油侵增加量,波速呈缓慢减小趋势,波速减小峰值为19.21m/s;当回压从0.1MPa 增至9.0MPa,波速呈增大趋势,波速增大峰值为233.15m/s;不考虑虚拟质量力,在低频段引起的波速误差呈增大趋势,在高频段引起的波速误差峰值稳定于10.03%.     

Rotation of an elastic sphere about its mass center in the gravitational field of two attracting points

A planet model as a uniform elastic sphere in the gravitational field of two mass points whose mutual motion causes tidal deformations is considered. The sphere rotation about its mass center is studied with consideration of its deformations caused by the centrifugal force field and the gradient fields of gravitational forces. The sphere’s inertia tensor whose components are time dependent is found. The sphere’s angular velocity projections onto the axes associated with the sphere according to an integral law are determined. The results obtained are illustrated for the case of the Earth. For this case, the equivalent values of the elasticity modulus and Poisson’s ratio and the angular velocity disturbances are found.     

轴向分布式药包激发地震波场模型

炸药震源激发地震波场幅频特性直接影响地震勘探精度,本文通过计算研究轴向分布式药包激发地震波场幅频特征规律:以球形空腔震源模型为基础,采用叠加方法获得轴向分布式药包激发地震波场计算方法,并与数值模拟结果进行对比。研究表明:该方法误差在7%以内;在爆心距大于药柱总长度9.8倍时轴向分布式药包所激发地震波速度场与球形药包基本一致,但地震波的频率更高。     

Parameterization of the in-water motions of falling cylinders using high-speed video

A methodology to observe the motions of large cylinders falling freely at large (~10⁶) Reynolds numbers using a stereometric, high-speed video technique is presented. Parameter variation in length, weight, center of mass, and nose shape combined with changes in release height and initial inclination angle were used to estimate the influence of net drag forces on six cylinder bodies. Cylinders with coincident centers of volume and mass typically assumed body orientations with the major axis aligned normal to the path of descent indicating that buoyancy forces and turbulent drag balanced the inertia of the body and displaced water. Displacement of the center of mass resulted in more vertical orientations and more complex motions. Abrupt changes in position, orientation, and velocity were also observed when air-dropped cylinders separated from a trapped cloud of bubbles signifying the onset of less predictable behaviors.     

固体差动随行装药高初速火炮内弹道理论分析

提出了一种基于差动原理的固体差动随行装药的高初速火炮发射方案,该方案能有效克服传统随行装药技术提高初速必将伴随射弹底部最大压力增加的缺点。它的主要特点是运用差动原理,实现不同组合件之间的速度不同,自动压缩储能室使随行工质向弹后连续喷射,有效抑制和消除了弹丸运动引发的稀疏波影响,提高了火炮工作容积利用率。推导了差动随行组合弹丸不同组合件动力学模型,给出了弹载工质物理量分布关系式。计算结果表明,在最大膛压、飞行弹丸底部最大压力、弹重及弹丸行程等不变条件下,随行药量取10.2 kg,某大口径火炮的弹丸初速可提高26%,火炮工作容积利用率提高约44%。该方案可为火炮提高初速和实现超远程发射提供新的途径。     

Error Analysis in Trifilar Inertia Measurements

Accurate calculation of the moment of inertia of an irregular body is made difficult by the large number of quantities which must be measured. A popular method is to use a trifilar suspension system to measure the period of oscillation of the body in the horizontal plane. In this paper, some sources of error are discussed with particular attention given to the alignment of the test object’s center of mass on the trifilar platform. The procedure is described, the necessary calculations are derived and the relative importance of accuracy in different measurements is assesed. It is determined that the accurate alignment of the centre of mass of the body being tested with the centre of the trifilar plate is insignificant compared to the accuracy of the other measurements required in the calculations.