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ex_planestress2.m File Reference

Description

EX_PLANESTRESS2 NAFEMS benchmark challenge 1 plane stress example.

[ FEA, OUT ] = EX_PLANESTRESS2( VARARGIN ) NAFEMS benchmark example to calculate von Mieses stress thin plate under plane stress assumption with loads all around.

Accepts the following property/value pairs.

Input       Value/{Default}        Description
-----------------------------------------------------------------------------------
E           scalar {210e9}         Modulus of elasticity
nu          scalar {0.3}           Poissons ratio
igrid       scalar 1/{0}           Cell type (0=quadrilaterals, 1=triangles)
hmax        scalar {1/20}          Max grid cell size
sfun        string {sflag1}        Shape function for displacements
iplot       scalar 0/{1}           Plot solution (=1)
                                                                                  .
Output      Value/(Size)           Description
-----------------------------------------------------------------------------------
fea         struct                 Problem definition struct
out         struct                 Output struct

Code listing

 cOptDef = { ...
   'E',        210e9; ...
   'nu',       0.3; ...
   'igrid',    0; ...
   'hmax',     1/20; ...
   'sfun',     'sflag1'; ...
   'iplot',    1; ...
   'fid',      1 };
 [got,opt] = parseopt(cOptDef,varargin{:});
 fid       = opt.fid;


% Geometry definition.
 gobj1 = gobj_rectangle( 0, 1, 0, 1, 'R1' );
 fea.geom.objects = { gobj1 };
 fea.sdim = { 'x' 'y' };


% Grid generation.
 if( opt.igrid==1 )
   fea.grid = gridgen(fea,'hmax',opt.hmax,'fid',fid);
 else
   nx = 1/opt.hmax;
   fea.grid = rectgrid( nx, nx );
 end

% Boundary conditions.
 dtol = 0.1;
 if( opt.igrid==1 )
   lbdr = findbdr( fea, ['x<',num2str(dtol)] );     % Left boundary number.
   rbdr = findbdr( fea, ['x>',num2str(1-dtol)] );   % Right boundary number.
   tbdr = findbdr( fea, ['y>',num2str(1-dtol)] );   % Top boundary number.
   bbdr = findbdr( fea, ['y<',num2str(dtol)] );     % Bottom boundary number.
 else
   lbdr = 4;
   rbdr = 2;
   tbdr = 3;
   bbdr = 1;
 end


% Add plane stress physics mode.
 fea = addphys(fea,@planestress);
 fea.phys.pss.eqn.coef{1,end} = { opt.nu };
 fea.phys.pss.eqn.coef{2,end} = { opt.E  };
 fea.phys.pss.sfun            = { opt.sfun opt.sfun };

% Set boundary condition types.
 bctype = mat2cell( zeros(2,4), [1 1], [1 1 1 1] );
 fea.phys.pss.bdr.coef{1,5}   = bctype;

% Set loads on boundary.
 bccoef = mat2cell( zeros(2,4), [1 1], [1 1 1 1] );
 bccoef{1,tbdr} = '-x';
 bccoef{2,tbdr} = 'x';
 bccoef{1,bbdr} = '-(1-x)';
 bccoef{2,bbdr} = '1-x';
 bccoef{1,lbdr} = '1-y';
 bccoef{2,lbdr} = '-(1-y)';
 bccoef{1,rbdr} = 'y';
 bccoef{2,rbdr} = '-y';
 fea.phys.pss.bdr.coef{1,end} = bccoef;


% Parse and solve problem.
 fea       = parsephys(fea);             % Check and parse physics modes.
 fea       = parseprob(fea);             % Check and parse problem struct.
 fea.sol.u = solvestat(fea,'fid',fid);   % Call to stationary solver.


% Postprocessing.
 s_vm = fea.phys.pss.eqn.vars{1,2};
 if ( opt.iplot>0 )
   figure
   postplot( fea, 'surfexpr', s_vm, 'isoexpr', s_vm )
   title('von Mieses stress')
 end

% Error checking.
 dtol = sqrt(eps);
 sm  = evalexpr( s_vm, [0.5;0.5], fea );
 s01 = evalexpr( s_vm, [dtol;1],    fea );
 s10 = evalexpr( s_vm, [1;dtol],    fea );
 s00 = evalexpr( s_vm, [dtol;dtol], fea );
 s11 = evalexpr( s_vm, [1;1],       fea );

 sol = [ sm s01 s10 s00 s11 ];
 ref = [  0   0   0   2   2 ];
 out.err    = norm(sol-ref)/norm(ref);
 out.pass   = out.err < 0.1;


 if ( nargout==0 )
   clear fea out
 end