Saturday, 1 August 2015

Element types



The eight node brick (SOLID45) element was used for comparison with other elements. In the eight node brick there is a node at each corner of the brick. Higher order of SOLID 45 is 20 node brick (SOLID 95)
For the axisymmetric model, plate elements were used. In the axisymmetric model, the solid remains two-dimensional and is treated much like a shell element. The major difference is that instead of inputting a thickness, the plate is made axisymmetric. Once again there are linear (PLANE42) and quadratic (PLANE82) elements.
The axisymmetric model had by far the shortest runtime with comparatively small computational error. In this approach the loading and geometry of cylinder must be symmetric with respect to Y-axis. Only a sectional area is considered for meshing. As the no of elements are much lower, the computational time required is low and computational error is minimal. If we have a flange on circumferential side of cylinder, this approach is not possible. In such cases we have to go with shell elements. We have to model the entire cylinder. As we model the entire model the no. of elements increase and computational time rise up. If the cylinder is symmetric with respect to any plane, simplification of model is possible by meshing half or quarter of cylinder and applies symmetric boundary conditions. In shell elements the major concern is thickness. For thin walled cylinder shell serves good. But for thick walled cylinders we have to go with SOLID elements (brick) as it is capable of providing no of elements on a line. If wall thickness is known, it is better to go with axisymmetric or solid approach. In such cases where we have to find wall thickness or to go with different wall thickness, it is better to go with shell elements.
If we compare the linear elements with quadratic element, quadratic element gives better results than linear elements in all cases as the quadratic element is much capable of absorbing the variations than linear elements. If we use same no of elements in linear and quadratic, quadratic consume more time as the element is higher order but captures results much accurately. So, while going with quadratic elements, less no. of elements is enough to obtain accuracy than linear mesh.
File space was dependent on model size. The axisymmetric models were the smallest. The standard mesh axisymmetric model was five times smaller than the next closest model. Doubling the mesh size resulted in slightly less than doubling the file size. A quadratic model was larger than a linear model of the same mesh size, but significantly smaller than a twice as refined linear model. The solid model was the largest of the initial mesh models.

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