COMSOL 6.4 - Physics Interface

Physics Interface

The Physics node contains the settings of the physics interfaces, including the domain and the boundary settings. Settings are grouped together according to the physics interface they belong to. To model the electrothermal interaction of this example, add the ConductiveMedia and HeatTransfer interfaces to the model. Apply a fixed electric potential to the upper bolt and ground the two lower bolts. In addition, assume that the device is cooled by convection, approximated by a heat flux with a defined heat transfer coefficient on all outer faces, except where the bolts are connected.

Create the HeatTransfer interface on the geom1 geometry:

ht = comp1.physics.create('ht', 'HeatTransfer', 'geom1');

Add a heat flux boundary condition to the physics interface and set the type to InwardHeatFlux:

hf1 = ht.feature.create('hf1', 'HeatFluxBoundary', 2);

hf1.set('HeatFluxType', 'InwardHeatFlux');

The third argument of the create method, the space dimension sdim, indicates which geometry level (domain, boundary, edge, or point) the feature should be applied to. In the above commands, the 'HeatFluxBoundary' feature applies to boundaries, which have the space dimension 2.

Now apply cooling to all exterior boundaries 1–43, except the bolt connection boundaries 8, 15, and 43. An InwardHeatFlux boundary condition requires a heat transfer coefficient. Set its value to the previously defined parameter htc:

hf1.selection.set([1:7 9:14 16:42]);

hf1.set('h', 'htc');

As you may have noticed, defining selections requires you to know the entity indices. To view the boundary indices, display the geometry with face labels:

mphgeom(model,'geom1','facemode','off','facelabels','on')

You can use the controls in the window to zoom and pan to read off the indices.

Alternative methods for obtaining entity indices are described in the LiveLink™ for MATLAB® User’s Guide. These include the use of point coordinates, selection boxes, or adjacency information.

Create the ConductiveMedia interface on the geom1 geometry:

ec = comp1.physics.create('ec', 'ConductiveMedia', 'geom1');

Now create an electric potential boundary condition and set the selection to boundary 43; then set the electric potential to Vtot:

pot1 = ec.feature.create('pot1', 'ElectricPotential', 2);

pot1.selection.set(43);

pot1.set('V0', 'Vtot');

Apply a ground boundary condition to boundaries 8 and 15:

gnd1 = ec.feature.create('gnd1', 'Ground', 2);

gnd1.selection.set([8 15]);

The model object includes default properties so you do not need to set properties for all boundaries. For example, the Conductive Media interface uses a current insulation as a default boundary condition for the current balance.