COMSOL Multiphysics™

elcontact
Cautionary
The elcontact element is only implemented for boundaries. That is, no edge-edge,
edge-boundary or similar contact can be detected and evaluated.
The computation of complete Jacobians rely on the availability of spatial derivatives
of the mapped expression with respect to local coordinate directions. These local
derivatives cannot be calculated for all variables, a notable example being any global
spatial derivatives. Therefore, for expressions like map(uTx) some Jacobian
contributions will be missing.
Examples
Evaluate and display the distance from a hard surface to the closest point of a
cylinder lying on its side on the surface.
clear fem;
fem.geom = ...
rect2(2,0.2,'pos',[-1,-0.2])+circ2(0.8,'pos',[0,0.8]);
fem.mesh = meshinit(fem);
fem.sshape = 2;
clear el;
el.elem = 'elcontact';
el.g = {'1'};
el.opname = {'map'};
el.gapname = {'gap'};
el.visname = {'vis'};
el.method = 'ball';
el.checkdist = '1';
el.srcframe = {'xy'};
el.srcn = {{'nx','ny'}};
el.dstx = {{'x','y'}};
el.dstn = {{'nx','ny'}};
clear src11
src11.ind = {{'3','4'}};
src11.src = {{'1'}};
el.geomdim{1} = {{},src11};
fem.elem = {el};
fem.xmesh = meshextend(fem);
fem.sol = asseminit(fem);
postcrossplot(fem,1,[6 8],'lindata','if(vis,gap,0)',...
'linxdata','if(vis,map(x),sign(x))');
% compare with the theoretical value
hold on;
x=-1:0.05:1;
plot(x,sqrt(x.^2+0.8^2)-0.8,'ro');
56 | CHAPTER 1: COMMAND REFERENCE