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This form reveals how to generalize the element stiffness to 3-D space trusses by simply extending the pattern that is evident in this formulation. After developing the element stiffness matrix in the global coordinate system, they must be merged into a single “master” or “global” stiffness matrix.
The full stiffness matrix A is the sum of the element stiffness matrices. In particular, for basis functions that are only supported locally, the stiffness matrix is sparse . For many standard choices of basis functions, i.e. piecewise linear basis functions on triangles, there are simple formulas for the element stiffness matrices.
The finite element method has been the tool of choice since civil engineer Ray W. Clough in 1940 derived the stiffness matrix of a 3-node triangular finite element (and coined the name). The precursors of FEM were elements built-up from bars (Hrennikoff, Argyris, Turner) and a conceptual variation approach suggested by R. Courant.
This type of element is suitable for modeling cables, braces, trusses, beams, stiffeners, grids and frames. Straight elements usually have two nodes, one at each end, while curved elements will need at least three nodes including the end-nodes. The elements are positioned at the centroidal axis of the actual members.
Examples of Galerkin methods are: the Galerkin method of weighted residuals, the most common method of calculating the global stiffness matrix in the finite element method, [3] [4] the boundary element method for solving integral equations, Krylov subspace methods. [5]
For some problems this is not the case. In order for a numerical method to give a reliable solution to the differential system sometimes the step size is required to be at an unacceptably small level in a region where the solution curve is very smooth. The phenomenon is known as stiffness. In some cases there may be two different problems with ...
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here is the mass matrix, is the damping matrix, and are internal force per unit displacement and external forces, respectively. Using the extended mean value theorem , the Newmark- β {\displaystyle \beta } method states that the first time derivative (velocity in the equation of motion ) can be solved as,