The direct method for performing a coupled-field analysis involves a single analysis using a coupled-field element. Table 2.1: Coupled-Field Elements lists the elements that have coupled-field capability.

Coupled-field elements contain all the necessary degrees of freedom. They handle the field coupling by calculating the appropriate element matrices (strong, or matrix coupling) or element load vectors (weak, or load vector coupling). In linear problems with strong coupling, coupled-field interaction is calculated in one iteration. Weak coupling requires at least two iterations to achieve a coupled response. Nonlinear problems are iterative for both strong and weak coupling. Table 2.2: Coupling Methods Used in Direct Coupled-Field Analyses lists the different types of coupled-field analyses available using the direct method, and which type of coupling is present in each. See Coupling Methods in the Theory Reference for more information about strong versus weak coupling.

Your finite element model may intermix certain coupled-field elements with the VOLT degree of freedom. To be compatible, the elements must have the same reaction solution for the VOLT degree of freedom. Elements that have an electric charge reaction solution must all have the same electric charge reaction sign. For more information, see Element Compatibility.

Weak coupling effects are ignored in a substructure analysis, because an iterative solution is not available within the substructure generation pass.

Because of the possibly extreme nonlinear behavior of weakly coupled field elements, you may need to use the predictor and line-search options to achieve convergence. Nonlinear Structural Analysis in the Structural Analysis Guide describes these options.

To speed up convergence in a coupled-field transient analysis, you can disable the time integration effects for any degrees of freedom that are not a concern. For example, if structural inertial and damping effects can be ignored in a thermal-structural transient analysis, you can issue TIMINT,OFF,STRUC to turn off the time integration effects for the structural degrees of freedom.

Contact elements may also be included in a direct coupled-field analysis. For more information, see the following sections in the Contact Technology Guide:

For information about coupled physics circuit simulations, see Coupled Physics Circuit Simulation.