Finite element analysis in moving coordinates

摘要

Computational modeling of welding thermal cycles using finite element analysis is usually performed as a transient problem with the heat source moveed incrementally to correspond to the motion of the welding arc. Considerable spatial detail is required to represent a moving source about which there are strong gradients. Problems are very time consuming, even on advanced modern computers, and make heavy demands on data storage. Analytical studies of welding frequently use moving coordinate frames to correspond to the motion of the arc. Because of actual or perceived limitations of available computing tools, most numerical computation has been in fixed coordinate frames. Reported use of moving coordinates has included signicant assumptions to fit the structure of the code and/or to restric the numerical analysis to symmetric matrices. This paper reports results obtained with the ANSYS computer program, which includes advective terms (introduced for purposes of treating mass transport) in its equations. By proper selectron of coefficients and boundary conditions, welding problems have been modeled in moving coordinates. Conventional fixed coordinate problems have been run to provide measures of gain. Moving and fixed coordinate problems have been found to provide identical solutions. For the same mesh detail, moving coordinate problems are found to be more accurate, relfecting the need to approximate source motion in fixed coordinates. Moving coordinate problems are found to reduce computer elapsed time by one or two orders of magnitude, depending on the number of time steps needed for the fixed coordinate problems.Mjaor reductions in data storage requirements also are observed. Problems too large to run in fixed coordinats can be run in moving coordinates. SOlution of moving coordinate problems improves dramatically the ability to analyze thermal cycle and thereby to study the material microstructure and properties resulting from these cycles.