﻿ Tech Briefs
 Seamless Implicit-Explicit Dynamic Analysis ADINA uses the same reliable element formulations for all analysis types irrespective of whether the analysis is static, implicit or explicit dynamic, or harmonic. This makes switching between different analysis types direct and reliable. In this Tech Brief, we show how ADINA can be used to switch from implicit to explicit analysis in the same run at any given time, without using the restart option. ADINA can also automatically switch to explicit analysis if the implicit dynamic analysis fails to converge. An analyst might want to switch back and forth between implicit and explicit time integration to capture the advantages of each analysis type in different parts of a simulation. This switching can be difficult using other commercial programs because of the different element formulations, etc., that are typically used for implicit and explicit analysis. With ADINA, the switching is seamless. To demonstrate the analysis switch feature, we solve the rolling tire problem shown in Figure 1. In this analysis, the tire is modeled using solid elements while the road is modeled using rigid elements. Frictional contact is assumed between the road and tire. Figure 1  Tire-road model Figure 2  Tire model. Rigid links are used to model the rim First, the tire is inflated by applying a pressure to the tire inner surface. Then, the tire is accelerated by applying a torque to the center of the rim. The Bathe implicit time integration scheme is used to solve this part of the analysis. Tire inflation Tire starts rolling and implicit time integration is used The analysis is switched to explicit time integration just before the tire impacts the step. Explicit time integration is used in this part of the analysis as these methods simply march forward in time without any equilibrium iterations. ADINA automatically reduces the time step size to ensure the explicit integration is stable. Figure 3  During impact explicit time integration is used Once the tire jumps over the step, the analysis is switched back to implicit time integration. This switch can be specified by the user any number of times. It can also be performed automatically if the implicit dynamic analysis fails to converge. Tire impacts and then climbs the step Tire bounces after climbing the step The implicit-explicit analysis switch capability in ADINA is a powerful way to capitalize on the advantages of the different time integration schemes in different parts of the simulation. This capability is robust and reliable, and is of clear value for the efficient analysis of solids and structures. Keywords: Analysis switch, implicit analysis, explicit analysis, Bathe method, tire, contact, convergence difficulties