Advantages of Using the Multiphysics Coupling Features

One advantage of using the predefined multiphysics couplings is that specific or modified settings are included with the physics interfaces and the coupling features. But if physics interfaces are added one at a time, followed by the coupling features, these modified settings are not automatically included.

For example, if you add single Electric Currents and Heat Transfer in Solids interfaces to the Model Builder, the COMSOL software adds an empty Multiphysics node. The applicable multiphysics couplings are then available as subnodes and can be added. Even more convenient, you can choose the predefined Joule Heating multiphysics coupling, for example, which then adds the Electromagnetic Heat Source, Boundary Electromagnetic Heat Source, and Temperature Coupling nodes under the Multiphysics node, so that you do not need to remember which multiphysics coupling nodes to add for a specific type of multiphysics. See The Add Multiphysics Window.

In general, it is useful to use any type of multiphysics coupling because you can turn multiphysics on and off (that is, enable and disable features), giving you more flexibility to test and observe multiphysics effects.

Even if you do not start with a predefined coupling, another benefit of this approach is that you are no longer constrained by the use of specific physics interfaces, nor do these have to be added in any specific order. With the new coupling approach, the order in which physics interfaces are added does not matter for the end result.

An example of this is if you start modeling by adding a Heat Transfer in Solids interface. As you continue to build the model, you add an Electric Currents interface. At this stage of the process, you have defined several boundary conditions, chosen materials, or experimented with other settings. You may have also solved the model successfully at this point and now you want to continue building on this design. The COMSOL software recognizes this and adds a Multiphysics node, which you can right-click to access and add multiphysics couplings.

For multiphysics interfaces that consist of participating physics interfaces, the default solver settings use a segregated solver approach with one segregated step for each physics interface and each of these steps calling an iterative solver. These solver settings are suitable for large models, but if possible, a fully-coupled solver approach using direct solvers can be more robust. You can switch to such solver settings by right-clicking the Study node and choosing Show Default Solver. Then the solver nodes that the multiphysics interface specifies appear under the Solver Configuration node, and you can right-click the solver node to add a Fully Coupled solver node to replace the Segregated node, for example.

For some multiphysics interfaces, a side effect of adding physics interfaces one at a time is that two study types — Frequency-Stationary and Frequency-Transient — are not available for selection until after at least one coupling feature is added. In this case, it is better to first add an Empty Study, then add the coupling features to the Multiphysics node, and lastly, right-click the Study node to add the study steps as needed.