On solving the forward kinematics of 3RPR planar parallel manipulator using hybrid metaheuristics

Hybrid metaheuristics have been applied with success in solving many real-world problems. This work introduces hybrid metaheuristics to the field of kinematics problem, in particular, for solving the forward kinematics of the 3RPR parallel manipulator. It implements a combination of genetic algorithms and simulated annealing into two popular hybrid metaheuristic techniques. They are combined as teamwork and relay collaborative hybrid metaheuristics and compared to the performance of genetic algorithms and simulated annealing alone. The results show that the meta-heuristic approaches give robust and high quality solutions. Genetic algorithms and teamwork collaborative metaheuristics showed better performance than simulated annealing and relay collaborative metaheuristics. The given metaheuristic methods obtain all the unique solutions and comparisons with algebraic methods show promising results.     

融合神经网络与数值计算的人体逆向运动学求解

人体逆向运动学问题是人体运动合成、人体运动捕获和理解的基本问题.由于人体关节链式系统的复杂性,人体逆向运动学方程往往存在多解或无解的情形.传统的方法通常采用解析或数值迭代方法求解逆向运动学问题,在给定足够多约束的情形下能够得到比较好的解,但无法处理少量约束下生成自然的人体姿态问题.近年来,从大规模数据集中学习统计模型参数的思想被广泛运用,求解人体逆向运动学的机器学习方法中经典工作|混合Gauss逆向运动求解模型(Gaussian mixture model-inverse kinematics,GMM-IK)就提出利用混合Gauss模型建模人体姿态数据分布,并采用期望最大化方法求解参数.随着深度学习技术的发展,本文提出一种自编码神经网络与数值迭代融合的方法,在给定少量约束的情形下依然能够得到自然的人体姿态,相较于GMM-IK方法,本文所提出的方法通过神经网络自动学习姿态分布,省去了模型的假设和特征的设计,且量化实验显示本文方法的关节坐标和角度重建误差相较于GMM-IK模型平均减少了25%和39%.在应用方面,本文方法可处理光学运动捕获数据,也可用于图像视频的人体姿态估计等领域.     

Thermodynamics of finite strain elastic-inelastic deformation

The kinematic relations describing elastic-inelastic deformation that coincide in shape with the well-known Lie representation but are free from the drawback of the latter are extended to the case of thermo-elastic-inelastic deformation with finite strains. The limitations imposed on the kinematics by the principle of objectivity are considered. Relations for the stresses and entropy are derived from the laws of thermodynamics, and a heat-conduction equation is constructed. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 48, No. 4, pp. 144–153, July–August, 2007.     

Generatrices of rational curves

We investigate the one-parametric set of projective subspaces that is generated by a set of rational curves in projective relation. The main theorem connects the algebraic degree of , the number of degenerate subspaces in and the dimension of the variety of all rational curves that can be used to generate . It generalizes classical results and is related to recent investigations on projective motions with trajectories in proper subspaces of the fixed space. Received 9 May 2001.     

An application of Neustadt's abstract maximum principle to probability kinematics

An important class of problems in philosophy can be formulated as mathematical programming problems in an infinite-dimensional vector space. One such problem is that of probability kinematics: the study of how an individual ought to adjust his degree-of-belief function in response to new information. Much work has recently been done to establish maximum principles for these generalized programming problems (Refs. 3–4). Perhaps, the most general treatment of the problem presented to date is that by Neustadt (Ref. 1). In this paper, the problem of probability kinematics is formulated as a generalized mathematical programming problem and necessary conditions for the optimal revised degree-of-belief function are derived from an abstract maximum principle contained in Neustadt's paper.This work was supported by the National Research Council of Canada.The author is grateful to G. J. Lastman and J. A. Baker of the University of Waterloo for numerous suggestions made for improvement of this paper. The problem of probability kinematics was brought to the author's attention by W. L. Harper of the University of Western Ontario.     

Hunting η-bound nuclei

The η meson can be bound to atomic nuclei.Experimental search is discussed in the form of final state interaction for the reactions dp → 3 Heη and dd → 4 Heη.For the latter case tensor polarized deuterons were used in order to extract the s-wave strength.For both reactions complex scattering lengths are deduced: a 3 Heη = ± 10.7±0.8 +0.1 -0.5 +i· 1.5±2.6 +1.0-0.9 fm and a 4 Heη = [±(3.1±0.5)+i·(0±0.5)] fm.In a two-nucleon transfer reaction under quasi-free conditions,p 27 Al → 3 HeX,was investigated.The system X can be the bound 25 Mg  η at rest.When a possible decay of an intermediate N  (1535) is required,a highly significant bump shows up in the missing mass spectrum.The data give for a bound state a binding energy of 13.3±1.6 MeV and a width of σ=4.4±1.3 MeV.     

流动中边界面的识别

将流场的边界面定义为流动表面,在该表面上剪切率为0,并利用所建议的程序求解.该方法是基于速度向量场的计算,与坐标系的选择无关.     

Crown evolution kinematics of a camellia oil droplet impacting on a liquid layer

The phenomenon of droplet impact on an immiscible liquid is encountered in a variety of scenarios in nature and industrial production. Despite exhaustive research, it is not fully clear how the immiscibility of the liquid on which a droplet impacts affects the crown evolution. The present work experimentally investigates the evolution kinematics of a crown formed by the normal impact of a camellia oil droplet on an immiscible water layer. Based on discussion of dynamic impact behaviors for three critical Weber numbers (We), the radius of the crown and its average spreading velocity are compared with those of previous theoretical models to discuss their applicability to the immiscible liquid. The evolution kinematics (morphology and velocity) are analyzed by considering the effects of the We and layer thickness. Furthermore, the ability of crown expansion in radial and vertical directions is characterized by a velocity ratio. The results show that our experimental crown radius still follows a square-root function of evolution time, which agrees with the theoretical predictions. The dimensionless average spreading velocity decreases with We and follows a multivariate power law, while the dimensionless average rising velocity remains constant. The velocity ratio is shown to linearly increase with We, demonstrating that the rising movement in crown evolution gradually enhances with We. These results are helpful for further investigation on the droplet impact on an immiscible liquid layer.     

Optimal Control of a Ship for Collision Avoidance Maneuvers

We consider a ship subject to kinematic, dynamic, and moment equations and steered via rudder under the assumptions that the rudder angle and rudder angle time rate are subject to upper and lower bounds. We formulate and solve four Chebyshev problems of optimal control, the optimization criterion being the maximization with respect to the state and control history of the minimum value with respect to time of the distance between two identical ships, one maneuvering and one moving in a predetermined way.Problems P1 and P2 deal with collision avoidance maneuvers without cooperation, while Problems P3 and P4 deal with collision avoidance maneuvers with cooperation. In Problems P1 and P3, the maneuvering ship must reach the final point with a given lateral distance, zero yaw angle, and zero yaw angle time rate. In Problems P2 and P4, the additional requirement of quasi-steady state is imposed at the final point.The above Chebyshev problems, transformed into Bolza problems via suitable transformations, are solved via the sequential gradient-restoration algorithm in conjunction with a new singularity avoiding transformation which accounts automatically for the bounds on rudder angle and rudder angle time rate.The optimal control histories involve multiple subarcs along which either the rudder angle is kept at one of the extreme positions or the rudder angle time rate is held at one of the extreme values. In problems where quasi-steady state is imposed at the final point, there is a higher number of subarcs than in problems where quasi-steady state is not imposed; the higher number of subarcs is due to the additional requirement that the lateral velocity and rudder angle vanish at the final point.     

基于增强现实的物体运动仿真设计与实现

针对如何在增强现实(Augmented Reality, AR)的虚拟环境中体现物体运动仿真时运动学与动力学特性的问题, 设计了一套将AR技术与物体运动仿真集成, 通过模型建立、标记物注册、运动仿真交互控制、增强场景实时渲染等步骤设计物体AR运动仿真系统. 该系统由运动学仿真模块和动力学仿真模块组成. 运动学仿真模块的设计和实现以刚体绕定轴转动和平面四杆机构的几何运动为例, 通过移动标记物进行运动学仿真的交互控制. 动力学仿真模块的设计和实现以曲柄滑块机构惯性运动为例, 通过改变输入参数进行动力学仿真控制. 最后以机械类课程教学中平面四杆机构急回特性学习和曲柄滑块机构动力学方程求解为例进行实际应用. 结果表明, AR运动仿真系统提供了直观的高交互操作运动学与动力学仿真环境, 通过可视化能帮助学生理解相关的理论知识, 进而实现虚实融合的智慧化运动仿真教学.