COMSOL Multiphysics™

multiphysics
Elements of fem1.***.(f/ga/g/r/weak/dweak/constr/c/da/ea/al/be/a/
q/h) which correspond to subsystems for which the corresponding field does not
exist are '0'. Elements of fem1.***.init in such cases are empty strings. Elements
in fem1.***.(gporder/cporder) in such cases are 1. The fields fem1.elemmph
and fem1.eleminitmph are obtained by concatenating the contents of the results
of calling elem_compute for each application. The field fem1.shape is obtained by
concatenating the contents of the fields fem.appl{:}.shape. Duplicate shape
functions are removed and the fields fem.***.shape are adjusted to take account
of this. The field fem1.sshape is obtained by taking the maximum of the fields
fem.appl{:}.sshape. The resulting value is overridden if the property Outsshape
is given. The fem1.border field is always 1 because coefficients for boundary
conditions that are not used due to border being on or off in the application mode
are set to zero and can be “applied”.
Suppose multiphysics has been called previously, and fem is the result of such a
call. If changes are made to fem.equ and it is wished to keep them (that is not allow
changes to be written over when multiphysics is called again), it is possible to
restrict the set of subdomains for which multiphysics writes over fem.equ. Thus
giving the property Sdl the value [1 2] in a call to multiphysics results in the
coefficients for subdomains 1 and 2 being “refreshed” from the applications, but all
the coefficients in fem.equ relating to other subdomains being kept and copied into
fem1.equ. The same principle holds for bnd/edg/pnt using the properties Bdl/
Edl/Pdl.
Example
The model “Resistive Heating” uses the multiphysics function. Note that the
structure fem contains the data that is common for the subsystems, that is, the
geometry and the mesh. The electrical subsystem and the heat transfer subsystem
are specified in the application structures a1 and a2, and the multiphysics
function is used to combine them.
clear fem a1 a2
fem.geom = geomcsg({square2(0,0,1)});
fem.mesh = meshinit(fem);
a1.mode = 'ConductiveMediaDC';
a1.assignsuffix = '_dc';
a1.bnd.V0 = {0.1 0 0};
a1.bnd.type = {'V' 'nJ0' 'V0'};
a1.bnd.ind = [1 2 2 3];
a1.equ.init = '0.1*(1-x)';
a1.equ.T0 = 293;
a1.equ.T = 'T';
a1.equ.alpha = 0.0039;
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