Design sensitivity analysis in large deformation elasto‐plastic and elasto‐viscoplastic problems

Implicit time integration algorithm derived by Simo for his large‐deformation elasto‐plastic constitutive model is generalized, for the case of isotropy and associative flow rule, towards viscoplastic material behaviour and consistently differentiated with respect to its input parameters. Combining it with the general formulation of design sensitivity analysis (DSA) for non‐linear finite element transient equilibrium problem, we come at a numerically efficient, closed‐form finite element formulation of DSA for large deformation elasto‐plastic and elasto‐viscoplastic problems, with various types of design variables (material constants, shape parameters). The paper handles several specific issues, like the use of a non‐algorithmic coefficient matrix or sensitivity discontinuities at points of instantaneous structural stiffness change. Computational examples demonstrate abilities of the formulation and quality of results. Copyright © 2005 John Wiley & Sons, Ltd.     

RAS: A Data-Driven Rigidity-Aware Skinning Model For 3D Facial Animation

We present a novel data-driven skinning model—rigidity-aware skinning (RAS) model, for simulating both active and passive 3D facial animation of different identities in real time. Our model builds upon a linear blend skinning (LBS) scheme, where the bone set and skinning weights are shared for diverse identities and learned from the data via a sparse and localized skinning decomposition algorithm. Our model characterizes the animated face into the active expression and the passive deformation: The former is represented by an LBS-based multi-linear model learned from the FaceWareHouse data set, and the latter is represented by a spatially varying as-rigid-as-possible deformation applied to the LBS-based multi-linear model, whose rigidity parameters are learned from the data by a novel rigidity estimation algorithm. Our RAS model is not only generic and expressive for faithfully modelling medium-scale facial deformation, but also compact and lightweight for generating vivid facial animation in real time. We validate the efficiency and effectiveness of our RAS model for real-time 3D facial animation and expression editing.     

Numerical analysis of partly wrinkled cylindrical inflated beams under bending and shear

This paper is aimed at assessing the nonlinear elastic response of an inflatable cylindrical beam through a simple mechanical model recently proposed by the authors for studying the equilibrium configurations of highly pressurised elastic membranes with general shapes. The attention is focused on beams loaded at mid-span with two different constraints, corresponding to simply-supported ends and built-in ends. The geometrical nonlinearities due to both the cross-sectional ovalization and wrinkling are carefully considered. In particular, the wrinkling of the membrane, clearly visible for load values much lower than the collapse load, is taken into account by means of an equivalent physical non-linearity. A two-states constitutive law for the material is assumed: when a fibre is stretched (the active state), its response is elastic, while when the fibre is contracted, no compressive force can be engendered in it (the passive state). The evolution of the cross-sectional ovalization, the size of the wrinkled regions and the magnitude of longitudinal and transverse stresses in the membrane are accurately determined for increasing levels of loads, up to collapse. The numerical results for the corresponding values of load and internal pressure, obtained through an expressly developed incremental-iterative algorithm, are compared with the experimental ones available in the literature.     

A convected particle domain interpolation technique to extend applicability of the material point method for problems involving massive deformations

A new algorithm is developed to improve the accuracy and efficiency of the material point method for problems involving extremely large tensile deformations and rotations. In the proposed procedure, particle domains are convected with the material motion more accurately than in the generalized interpolation material point method. This feature is crucial to eliminate instability in extension, which is a common shortcoming of most particle methods. Also, a novel alternative set of grid basis functions is proposed for efficiently calculating nodal force and consistent mass integrals on the grid. Specifically, by taking advantage of initially parallelogram‐shaped particle domains, and treating the deformation gradient as constant over the particle domain, the convected particle domain is a reshaped parallelogram in the deformed configuration. Accordingly, an alternative grid basis function over the particle domain is constructed by a standard 4‐node finite element interpolation on the parallelogram. Effectiveness of the proposed modifications is demonstrated using several large deformation solid mechanics problems. Copyright © 2011 John Wiley & Sons, Ltd.     

某服务中心平板式筏基优化设计

平板式筏基在带大面积地下车库的高层建筑中广泛应用,属于补偿性基础。文章结合工程实例,运用上部结构、基础和地基共同作用的分析原理对某服务中心的平板式筏基在不同区域进行优化设计,为类似工程基础设计提供了参考。     

核电站不锈钢衬里力学分析及焊接变形控制

采用ANSYS有限元程序建模进行力学分析,计算出不锈钢覆面在水压力作用下的变形值及应力值,同时采用现场相似模拟实验,模拟了不锈钢覆面的真实受力情况,并结合工程实践,给出了有效控制水池池底墙角处不锈钢弯折件焊接变形的方法和措施,为后续类似工程提供了良好的借鉴。     

Grid_strain and grid_strain3: Software packages for strain field computation in 2D and 3D environments

Two Matlab™ software packages for strain field computation, starting from displacements of experimental points (EPs), are here presented. In particular, grid_strain estimates the strain on the nodes of a regular planar grid, whereas grid_strain3 operates on the points of a digital terrain model (DTM). In both cases, the computations are performed in a modified least-square approach, emphasizing the effects of nearest points. This approach allows users to operate at different scales of analysis by introducing a scale factor to reduce or also exclude points too far from grid nodes. The input data are displacements (or velocities) that can be provided by several techniques (e.g. GPS, total topographical station, terrestrial laser scanner). The analysis can be applied to both regional- and local-scale phenomena, to study tectonic crustal deformations (strain ≈10⁻⁸−10⁻⁶) or rapid landslide collapses (10⁻⁴−10²), and to characterize the kinematics of the studied system. Errors on strains and geometric significance of the results are also provided.     

Thermal-mechanical model of the tube elongation process in Diescher''s mill

The steady-state finite element approach is used to model the tube elongation process in Diescher's mill. The material is deformed between two rotating cone shaped rolls and a plug. The material is dragged by the rolls, moves forward and rotates. The analysis of the process is performed in the cylindrical coordinates. Tube ovalness is neglected. The material flowing in the circumferential direction is accounted for. The velocity field components in r,θ,z directions are discretized using parabolic shape functions. An iterative algorithm is employed for correction of the outer and inner free surfaces that determine the control volume. The material flow and torsion, distribution of the effective strain and temperature are computed and analysed for the tube elongation process in Diescher's mill using a parabolic plug.