Improvement of open-close iteration in DDA

This paper corrects Open-Close Iteration for the convergence of block contacts in DDA. In conventional open-close iteration, each contact pattern converges at Time Step n when the contact pattern at Iteration i is the same as the one at previous iteration of i - 1. When the number of iteration equals to 6, but the contact pattern is not converged, the time interval decreases, and a new iteration cycle is performed. At the Iteration 1 of the new iteration cycle, the previous contact pattern is defined as that at Iteration 5 in the old iteration cycle, which may be different from the contact pattern at the end of Step n - 1. As the number of block in DDA increases, the contacts are difficult to converge. The time interval changes significantly and unexpectedly when calculating the stress distribution of a blocky assembly. Therefore, we improved the open-close iteration that the contact information at the end of previous step, Step n - 1, is reloaded as the previous iteration when the iteration is 1 in the new iteration cycle. With the new open-close iteration algorithm, the time interval for the blocky assembly calculations can be expected. This is the first step to investigate the appropriate time interval or contact spring stiffness for DDA in the future.