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ex_linearelasticity2.m File Reference

Description

EX_LINEARELASTICITY2 Example for deflection of a bracket.

[ FEA, OUT ] = EX_LINEARELASTICITY2( VARARGIN ) Example to calculate displacements and stresses for a bracket with a circular hole.

Accepts the following property/value pairs.

Input       Value/{Default}        Description
-----------------------------------------------------------------------------------
E           scalar {200e9}         Modulus of elasticity
nu          scalar {0.3}           Poissons ratio
force       scalar {1e4}           Load force
l           scalar {0.2}           Length of bracket
t           scalar {0.02}          Thickness of bracket
r           scalar {0.08}          Radius of bracket hole
hmax        scalar {0.01}          Max grid cell size
sfun        string {sflag2}        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',        200e9; ...
   'nu',       0.3; ...
   'force',    1e4; ...
   'l',        0.2; ...
   't',        0.02; ...
   'r',        0.08; ...
   'hmax',     0.01; ...
   'sfun',     'sflag2'; ...
   'iplot',    1; ...
   'tol',      0.05; ...
   'fid',      1;
   'igeomb',   0 };
 [got,opt] = parseopt(cOptDef,varargin{:});
 fid       = opt.fid;


% Geometry definition.
 fea.sdim = { 'x' 'y' 'z' };   % Coordinate names.
 gobj1    = gobj_block( 0, opt.t, 0, opt.l, 0, opt.l, 'B1' );
 gobj2    = gobj_block( 0, opt.l, 0, opt.l, (opt.l-opt.t)/2, (opt.l+opt.t)/2, 'B2' );
 gobj3    = gobj_cylinder( [opt.l/2 opt.l/2 opt.l/2-opt.t], opt.r, 2*opt.t, 3, 'C1' );
 fea.geom.objects = { gobj1 gobj2 gobj3 };
 fea              = geom_apply_formula( fea, 'B1+B2-C1' );
 if( ~opt.igeomb )
   fea.geom.objects{1} = rmfield( fea.geom.objects{1}, 'boundaries' );
 end

% Grid generation.
 fea.grid = gridgen( fea, 'hmax', opt.hmax, 'sortbdr', opt.igeomb, 'fid', fid );


% Problem definition.
 fea = addphys(fea,@linearelasticity);
 fea.phys.el.eqn.coef{1,end} = { opt.nu };
 fea.phys.el.eqn.coef{2,end} = { opt.E  };
 fea.phys.el.sfun            = { opt.sfun opt.sfun opt.sfun };


% Boundary conditions.
 dtol     = 1e-5;
 fixbdr   = findbdr( fea, ['x<=',num2str(dtol)] );         % Right boundary number.
 forcebdr = findbdr( fea, ['x>=',num2str(opt.l-dtol)] );   % Left boundary number.

% Fix right edge (set zero Dirichlet BCs).
 n_bdr  = max(fea.grid.b(3,:));        % Number of boundaries.
 bctype = num2cell( zeros(3,n_bdr) );  % First set homogenous Neumann BCs everywhere.
 [bctype{:,fixbdr}] = deal( 1 );       % Set Dirchlet BCs for right boundary.
 fea.phys.el.bdr.coef{1,5} = bctype;

% Apply negative z-load to left edge.
 bccoef = num2cell( zeros(3,n_bdr) );
 bccoef{3,forcebdr} = -opt.force;
 fea.phys.el.bdr.coef{1,end} = bccoef;


% Parse and solve problem.
 fea       = parsephys( fea );
 fea       = parseprob( fea );
 fea.sol.u = solvestat( fea, 'fid', fid );


% Postprocessing.
 if ( opt.iplot>0 )
   DSCALE = 5000;

   subplot(2,2,1)
   postplot( fea, 'surfexpr', 'u' )
   title( 'x-displacement' )
   view([30 20])

   subplot(2,2,3)
   postplot( fea, 'surfexpr', 'v' )
   title( 'y-displacement' )
   view([30 20])

   subplot(2,2,2)
   postplot( fea, 'surfexpr', 'w' )
   title( 'z-displacement' )
   view([30 20])

   subplot(2,2,4)
   dp = zeros(size(fea.grid.p));
   for i=1:3
     dp(i,:) = DSCALE*evalexpr( fea.dvar{i}, fea.grid.p, fea );
   end
   fea_disp.grid   = fea.grid;
   fea_disp.grid.p = fea_disp.grid.p + dp;
   plotgrid( fea, 'facecolor', [.95 .95 .95], 'edgecolor', [.8 .8 1], ...
                  'selcells', selcells(fea,['x>',num2str(1.5*opt.t)]) )
   hold on
   plotgrid( fea_disp )
   title(['Displacement plot (at ',num2str(DSCALE),' times scale)'])
   view([30 20])

 end


% Error check.
 xdisp = fea.sol.u(fea.eqn.dofm{1}(:));
 ydisp = fea.sol.u(fea.eqn.dofm{2}(:)+fea.eqn.ndof(1));
 zdisp = fea.sol.u(fea.eqn.dofm{3}(:)+sum(fea.eqn.ndof(1:2)));
 xdisp = [ min(xdisp) max(xdisp) ];
 ydisp = [ min(ydisp) max(ydisp) ];
 zdisp = [ min(zdisp) max(zdisp) ];
 xdisp_ref = [ -8.971e-7 8.971e-7 ];
 ydisp_ref = [ -9.556e-8 9.605e-8 ];
 zdisp_ref = [ -1.09e-5  1.065e-8 ];
 svm_ref = [ 6.252756 1.779065e6 ];
 out.xdisp = xdisp;
 out.ydisp = ydisp;
 out.zdisp = zdisp;
 out.err   = abs(zdisp(1) - zdisp_ref(1))/abs(zdisp_ref(1));
 out.pass  = out.err<opt.tol;


 if ( nargout==0 )
   clear fea out
 end