基于并联机构中医推拿机器人机型研究

 在对中医推拿手法运动学研究的基础上，依据中医推拿手法运动学特征并结合并联机构的特点，提出基于并联机构中医推拿机器人机型及输出矩阵。对基于三平移三转动并联机构、三平移两转动并联机构、两平移三转动并联机构、两平移两转动并联机构、两平移一转动并联机构的中医推拿机器人进行了概念设计，并利用Pro/E软件构建出各机型虚拟样机。最后从动平台输出矩阵、控制解耦性、结构对称性、工作空间及转动能力等方面对各机型进行了分析总结。为各中医推拿机器人的实际应用提供了理论依据。     

Thin plate elements with relaxed Kirchhoff constraints

An analysis of thin plates by C⁰ elements is presented. The fundamental part of it is the formulation of a set of constraints that relate the rotational degrees of freedom to the translational degrees of freedom and which are weaker than the usual Kirchhoff constraints. A penalty term associated with these constraints is then introduced instead of the usual expression for the shear strain energy. It is shown that the approach is effective for both quadrilateral and triangular elements.     

用于光滑/非光滑壳的稳定化新型协同转动4节点四边形壳单元

该文发展了一种适用于光滑壳和非光滑壳的新型协同转动4节点四边形壳单元。在单元中每个节点采用了3个平动自由度和2/3个矢量型转动自由度,每个光滑壳的节点或非光滑壳的非交界节点采用壳中性面法向矢量的2个最小分量作为矢量型转动变量,在非光滑壳中性面交界线上的节点采用3个矢量型转动变量,他们分别是节点定向矢量组中一个定向矢量的较小或最小分量和另一定向矢量的2个最小分量。在非线性增量求解过程中,这些矢量型转动变量可以采用简单的加法将增量累加到原矢量中直接进行更新,且采用了协同转动框架的单元在局部和整体坐标系下得到的切线刚度矩阵都是对称的,结构整体切线刚度矩阵可以采用一维线性存储,可节省大量的计算机存储资源和计算时间。为消除膜闭锁和剪切闭锁的不利影响,采用单点积分方案计算单元内力矢量和切线刚度矩阵,并借鉴Belytschko提出的物理稳定化零能模态控制法来消除可能出现的零能模态。通过对2个光滑壳和2个非光滑壳进行非线性分析,检验了单元的可靠性、计算效率与计算精度。     

A bilinear shell element with the cross-reduced integration technique

A bilinear shell element is presented. The element is based on the concepts of laminas and fibres. A cross-reduced integration technique is used to carry out the element integration. In this reduced integration technique, the Gauss points are chosen both on the reference lamina and along the central fibre. Spurious shear strains are averaged on the reference lamina to solve the shear locking problem and to eliminate any zero-energy mode associated with the rotational degrees of freedom. Due to the integration on the reference lamina, zero-energy modes associated with the translational degrees of freedom can also be removed. The behaviour of the element is examined in several numerical examples with various loading conditions and boundary conditions.     

The Effect of Inelastic Collisions of Molecules of a Diatomic Gas with Rotational Degrees of Freedom

The problem on Barnett slip of gas along a plane surface is solved within the suggested kinetic model for a diatomic gas with rotational degrees of freedom of molecules, which takes into account transitions from rotational degrees of freedom to translational and vice versa. The Barnett slip coefficient is obtained in the form of a function dependent on the frequency of inelastic collisions of gas molecules and on the coefficient of accommodation of tangential momentum.     

An assumed-stress hybrid 4-node shell element with drilling degrees of freedom

An assumed-stress hybrid/mixed 4-node quadrilateral shell element is introduced that alleviates most of the deficiencies associated with such elements. The formulation of the element is based on the assumed-stress hybrid/mixed method using the Hellinger-Reissner variational principle. The membrane part of the element has 12 degrees of freedom including rotational or ‘drilling’ degrees of freedom at the nodes. The bending part of the element also has 12 degrees of freedom. The bending part of the element uses the Reissner-Mindlin plate theory which takes into account the transverse shear contributions. The element formulation is derived from an 8-node isoparametric element by expressing the midside displacement degrees of freedom in terms of displacement and rotational degrees of freedom at corner nodes. The element passes the patch test, is nearly insensitive to mesh distortion, does not ‘lock’, possesses the desirable invariance properties, has no hidden spurious modes, and for the majority of test cases used in this paper produces more accurate results than the other elements employed herein for comparison.     

A New Locking Free Higher Order Finite Element Formulation for Composite Beams.

A refined 2-node, 7 DOF/node beam element formulation is presented in this paper. This formulation is based on higher order shear deformation theory with lateral contraction for axial-flexural-shear coupled deformation in asymmetrically stacked laminated composite beams. In addition to axial, transverse and rotational degrees of freedom, the formulation also incorporates the lateral contraction and its higher order counterparts as degrees of freedom. The element shape functions are derived by solving the static part of the governing equations. The element considers general ply stacking and the numerical results shows that the element exhibits super convergent property. The efficiency of the element in capturing both the static and dynamic inter-laminar stresses is demonstrated. The accuracy of the element to capture free vibration and wave propogation responses with small problem sizes is also demonstrated.     

一个适合于复合材料层合板分析的应力杂交单元

本文根据修正的余能变分原理构造了一个适合于复合材料层合板特点的三角形单元。此单元能够考虑横向剪切变形的影响和局部扭曲效应。三角形单元的三个顶点取为节点,每个节点具有5个自由度,三个位移自由度,二个转角自由度。文中用此单元计算了几种层合板的固有频率,并将结果与解析解进行了比较。计算表明,此单元计算精度较高,应用方便。     

可倾瓦滑动轴承系统线性稳定性分析

提出可倾瓦轴承系统解析模型并对其进行线性稳定性分析。采用Newton-Raphson和pad assembly这两种方法,可获得系统完整的动力特性系数。基于这些动力特性系数,建立系统的运动微分方程并进行复特征值分析,易求得用来检验系统稳定性的轴瓦临界质量和系统阻尼比。结果表明:预负荷、转速及支点位置均对可倾瓦轴承系统的稳定性有着较大的影响,合理选取这些参数有助于提高系统的稳定临界值。     

Simulation of tension fields with in-plane rotational degrees of freedom

This paper introduces a novel multigrid approach for the geometric non-linear simulation of tension fields on the basis of a three-node membrane finite element. The element possesses, in addition to the nodal displacement degrees of freedom, an in-plane rotational degree of freedom inside the element domain that controls the direction of the tension field. This rotational degree of freedom allows the enforcement of continuity and tension field boundary conditions on the basis of a coarser mesh with varying size.     

Dynamics of an elastic multibody chain: Part D—Modelling of joints

In the three previous papers in this series on the dynamics of a topological chain of arbitrary elastic bodies, rotational and translational displacements of arbitrary magnitude were allowed at all interbody joints. While this degree of generahty lends relevance withrespect to a diverse range of robotics applications, a careful specification of the displacement and force components at each joint becomes mandatory. In the present analysis, from one to six degrees of freedom are permitted at each joint, as reflected in the number of columns in its joint projection matrix. The special but practically important cases ofrotational (revolute) joints with one, two or three degrees of freedom are considered in detail, including physical interpretations for the coefficient matrices in the equations of motion. With robotics applications in mind, the many possibilities for sensors and actuators at the joints are catalogued and the four most important classes of ‘sensactor’ (a colocated sensor/actuator pair) are identified and their implications for the system equations presented.     

RxPzRy型2R1T部分解耦并联机构设计与分析

目的分析部分解耦的2R1T并联机构驱动副旋量特征,从而设计一类新型的部分解耦的RxPzRy型2R1T并联机构。方法基于完全解耦的并联机构的输入输出关系,将动平台角速度在定坐标系轴线方向的分量,变换为XYZ欧拉角角速度分量,得到角速度的完全解耦的分块雅可比矩阵,得到具有多个转动自由度机构的输出与输入部分解耦的关系。结果设计了一种新型部分解耦2R1T并联机构,分析表明该机构部分解耦。结论对于RxPzRy型2R1T并联机构在解耦设计时,使用旋量理论得到的关于角速度的雅克比矩阵不适用于具有多个转动自由度的并联机构完全解耦设计,使用文中提出的变换矩阵将其变换为关于欧拉角的角速度的雅克比矩阵,可以得到相应的对角矩阵,这种方法可以用来对具有多个转动自由度的并联机构完全解耦设计。     

An enhanced co‐rotational approach for large displacement analysis of plates

This paper presents a new co‐rotational approach for the large displacement analysis of plates employing 4‐noded quadrilateral flat shell elements. The proposed approach benefits from (i) a simple local co‐rotational system invariant to the element nodal ordering, (ii) the choice of the two smallest components of the nodal normal vector as global rotational degrees of freedom, and (iii) the use of hierarchic freedoms, that are unaffected by the co‐rotational transformations, for higher‐order accuracy. Important additional benefits that arise from the aforementioned features include symmetry of the tangent stiffness matrix and complete insensitivity of the large displacement transformations to the size of the incremental step. The applicability of the new approach to moderately thick as well as thin plates is illustrated by considering two alternative local formulations based on the Reissner–Mindlin and discrete Kirchhoff hypotheses. Several examples are finally presented which demonstrate the accuracy, step‐insensitivity and computational benefits of the proposed co‐rotational approach for large displacement analysis of plate structures. Copyright © 2005 John Wiley & Sons, Ltd.     

一种简单有效的通用薄壳结构分析单元

本文在简略讨论近年来平面膜元和薄板弯曲元的基础上,选用 IDKQ弯曲元和AQ平面应力元组合构造成一种任意4边形24自由度平壳单元.数值结果和工程分析实例表明,该壳元具有简单,高效、高精度的特点。由于具有统法线转动自由度,该壳元特别适合于复杂工程结构的有限元分析。     

The Smoluchowski problem in polyatomic gases

A model kinetic equation is constructed which describes the behavior of molecular (polyatomic) gases in which the vibrational degrees of freedom are “frozen” and the rotational degrees of freedom are treated quasiclassically. An analytical solution is obtained for the Smoluchowski problem of the temperature jump and weak evaporation above a planar surface in a half space. Numerical calculations are carried out. Pis’ma Zh. Tekh. Fiz. 24, 85–89 (September 12, 1998)     

Finite-rotation theories for composite laminates

Summary For the finite-element analysis of arbitrary composite laminates various finite-rotation theories are presented in a single formulation. First a refined theory is derived which allows a quadratic shear deformation distribution across the thickness. The so-called difference vector appearing in the kinematic relations is expressed in terms of rotational degrees of freedom permitting a clear determination of the deformed normal vector in every nonlinear range. The constitutive relations derived are applicable to orthotropic material properties varying arbitrarily across the thickness and to curvilinear laminate coordinates as well. This refined theory is then transformed into simplified theories of Kirchhoff-Love and Mindlin-Reissner types. Finally, the last formulation is used to formulate a layer-wise theory able to grasp the shear deformations very accurately. Kinematic relations and the corresponding constraints are presented in two alternative forms suitable for the application of isoparametric and classical finite-element formulations.     

Geometrically nonlinear analysis of shells by quadrilateral flat shell element with drill,shear, and warping

In this paper, a four‐node quadrilateral flat shell element is proposed for geometrically nonlinear analysis based on updated Lagrangian formulation with the co‐rotational kinematics concept. The flat shell element combines the membrane element with drilling degrees of freedom and the plate element with shear deformation. By means of these linearized elements, a simplified nonlinear analysis procedure allowing for warping of the flat shell element and large rotation is proposed. The tangent stiffness matrix and the internal force recovery are formulated in this paper. Several classic benchmark examples are presented to validate the accuracy and efficiency of the proposed new and more proficient element for practical engineering analysis of shell structures. Copyright © 2016 John Wiley & Sons, Ltd.     

力矩激励器功率输出特性

力矩激励器是一种新型传感器 ,用于研究结构声转动自由度的特性。本文利用互功率谱方法对力矩激励器的最大不失真力矩输出功率和相对应的输入电功率进行了测量 ,并计算了其电 力功率转换效率     

A rotation‐free corotational plane beam element for non‐linear analyses

This paper presents a plane beam element without rotational degrees of freedom that can be used for the analysis of non‐linear problems. The element is based on two main ideas. First, a corotational approach is adopted, which means that the kinematics of the element is decomposed into a rigid body motion part and a deformational part. Next, in the deformational part, the local nodal rotations are extrapolated as a function of the local displacements of the two nodes of the element and the first nodes to the left and right of the element. Six numerical applications are presented in order to assess the performance of the formulation. Copyright © 2007 John Wiley & Sons, Ltd.