Page 162 - Process Modelling and Simulation With Finite Element Methods

Extended Multiphysics 149

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Clearly, there are still undefined expression above, which are conveniently
defined in the Add/Edit Expressions selection of the Options menu.

Name I Type Defined Expression

U geometry Geoml 1 0,5*(uO+vO)/(Ufeed+Vfeed)

So here is the faultline. The subdomain coefficients will only accept an
expression defined on the whole geometry for the coefficient of x-velocity,
called u, to which we assigned the expression as u above. Unfortunately, u0 and
v0 cannot be defined as coupling variables in the whole geometry Geoml in the
GUI. Attempting to solve just elicits an error “Unknown variable or function
u0.” So here is the workaround. At this point, save a model m-file. Then edit
the equivalent lines in the m-file
elemcpl{7}.src.bnd.var={’uO’,{~uinlet’));
elemcpl{7}.src.bnd.ind={3};
%elemcpl{7}.dst.g=l;
%elemcpl{7}.dst.equ.ind={[l 21);
Comment out the dst fields. Do the same for v0. So what does this do? Page 5-
73 of the Reference Manual tells us - “By default, the variables defined in src
can be used everywhere in geometry 1. The optional field dst can be used to
specify the domains of the definition for the variables in detail.” So without the
dst fields, the coupling variables u0 and v0 will be available at the geometry
level, so that they can be used in defining u. Why the ‘u’ coefficient must be
defined at the geometry level is certainly a bug, since other PDE coefficients
need only be defined at the subdomain level. Read in this edited model m-file