Topic
Direct stiffness method
About: Direct stiffness method is a research topic. Over the lifetime, 2584 publications have been published within this topic receiving 53131 citations.
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14 May 2012
TL;DR: The vsaUT-II, a novel rotational variable stiffness actuator, is presented and its kinematic structure guarantees that the output stiffness can be changed without changing the potential energy stored internally in the elastic elements.
Abstract: In this paper, the vsaUT-II, a novel rotational variable stiffness actuator, is presented. As the other designs in this class of actuation systems, the vsaUT-II is characterized by the property that the output stiffness can be changed independently of the output position. It consists of two internal elastic elements and two internal actuated degrees of freedom. The mechanical design of the vsaUT-II is such that the apparent output stiffness can be varied by changing the transmission ratio between the elastic elements and the output. This kinematic structure guarantees that the output stiffness can be changed without changing the potential energy stored internally in the elastic elements. This property is validated in simulations with the port-based model of the system and in experiments, through a proper control law design, on the prototype.
65 citations
TL;DR: In this article, an efficient method for stiffness matrix correction to match modal testing data is presented, where significant reduction of unknown parameters is achieved by grouping the elements of the same stiffness characteristics and representing them as a multiplication of a scaling factor and a submatrix.
Abstract: An efficient method six stiffness matrix correction to match modal testing data is presented. Significant reduction of unknown parameters is achieved by grouping the elements of the same stiffness characteristics and representing them as a multiplication of a scaling factor and a submatrix. A concise formulation to identify the scaling factors is found by utilizing a least squares solution. The formulation also incorporates a capability of reducing finite element mass and stiffness matrices to test degrees-of-freedom for a direct analysis/experiment correlation
65 citations
TL;DR: The results of the current study show that the parallel computing technique is a valuable tool for solving computationally intensive topology optimization problems and the memory requirement and computation time has been reduced by avoiding the assembly of the global stiffness matrix.
Abstract: Topology optimization is often used in the conceptual design stage as a preprocessing tool to obtain overall material distribution in the solution domain. The resulting topology is then used as an initial guess for shape optimization. It is always desirable to use fine computational grids to obtain high-resolution layouts that minimize the need for shape optimization and postprocessing (Bendsoe and Sigmund, Topology optimization theory, methods and applications. Springer, Berlin Heidelberg New York 2003), but this approach results in high computation cost and is prohibitive for large structures. In the present work, parallel computing in combination with domain decomposition is proposed to reduce the computation time of such problems. The power law approach is used as the material distribution method, and an optimality criteria-based optimizer is used for locating the optimum solution [Sigmund (2001)21:120–127; Rozvany and Olhoff, Topology optimization of structures and composites continua. Kluwer, Norwell 2000]. The equilibrium equations are solved using a preconditioned conjugate gradient algorithm. These calculations have been done using a master–slave programming paradigm on a coarse-grain, multiple instruction multiple data, shared-memory architecture. In this study, by avoiding the assembly of the global stiffness matrix, the memory requirement and computation time has been reduced. The results of the current study show that the parallel computing technique is a valuable tool for solving computationally intensive topology optimization problems.
65 citations
01 Jan 1989
TL;DR: In this article, the authors describe the circumstances that led to the formulation of the finite element method by members of the Structural Dyanmics Unit at the Boeing Airplane Company.
Abstract: Following a brief summary of the 1952 state of the art of structural analysis, the paper describes the circumstances that led to the formulation of the finite element method by members of the Structural Dyanmics Unit at the Boeing Airplane Company. It is noted that the central feature of the procedure that was developed is the evaluation of the stiffness properties of structural elements based on assumed sets of displacement interpolation functions.
65 citations
TL;DR: In this paper, a doubly curved axisymmetric shell element is constructed for use in the analysis of shells by the direct stiffness method, which is expected to remedy difficulties experienced with the conical shell element, developed by Grafton and Strome and extended by Percy et al., in the case of shells subjected to distributed loadings.
Abstract: A doubly curved axisymmetric shell element is constructed for use in the analysis of shells by the direct stiffness method. The new element is expected to remedy difficulties experienced with the conical shell element, developed by Grafton and Strome and extended by Percy et al., in the case of shells subjected to distributed loadings. The curved element provides a highly accurate approximation to the shapes of shells of revolution with arbitrarily curved meridians. Numerical illustrations of the shape approximations are given for spherical and elliptical shells. The direct stiffness method equations are derived, and calculations are given for the case of an internally pressurized spherical shell. Comparisons of these results with those provided by the conical element are presented and discussed.
64 citations