FEATool Multiphysics  v1.16.5 Finite Element Analysis Toolbox
ex_multiphase1.m File Reference

## Description

EX_MULTIPHASE1 Static bubble example.

[ FEA, OUT ] = EX_MULTIPHASE1( VARARGIN ) Sets up and solves a stationary static bubble example where the pressure jump should be equal to sigma/r. Accepts the following property/value pairs.

Input       Value/{Default}        Description
-----------------------------------------------------------------------------------
rho         scalar {1e4}           Density
miu         scalar {1}             Molecular/dynamic viscosity
sigma       scalar {1}             Coefficient of surface tension
lbi         scalar 1/{0}           Exact or transformed surface tension source term
igrid       scalar 0/{1}           Cell type (0=quadrilaterals, 1=triangles)
hmax        scalar {1/30}          Max grid cell size
ischeme     scalar {3}             Time stepping scheme
sf_u        string {sflag2}        Shape function for velocity
sf_p        string {sflag1}        Shape function for pressure
iplot       scalar 0/{1}           Plot solution and error (=1)
.
Output      Value/(Size)           Description
-----------------------------------------------------------------------------------
fea         struct                 Problem definition struct
out         struct                 Output struct


# Code listing

 cOptDef = { ...
'rho',      1e4; ...
'miu',      1; ...
'sigma',    1; ...
'r',        0.25; ...
'lbi',      0; ...
'igrid',    1; ...
'hmax',     1/30; ...
'ischeme'   3; ...
'sf_u',     'sflag2'; ...
'sf_p',     'sflag1'; ...
'iplot',    1; ...
'tol',      0.3; ...
'fid',      1 };
[got,opt] = parseopt(cOptDef,varargin{:});
fid       = opt.fid;

% Geometry and grid generation.
fea.sdim = { 'x' 'y' };   % Coordinate names.
fea.grid = rectgrid(round(1/opt.hmax),round(2/opt.hmax),[0 1;0 1]);
if ( opt.igrid==1 )
end
n_bdr = max(fea.grid.b(3,:)) + 1;   % Increment number of boundaries.
fea.grid.b(3,1) = n_bdr;            % Set first boundary edge to boundary n_bdr.

% Problem definition.
phi   = ['(sqrt((x-0.5)^2+(y-0.5)^2)-',num2str(opt.r),')'];   % Level set function.
dh    = num2str(1*opt.hmax);   % Smoothing region width.
dw    = ['(',phi,'/',dh,')'];
smhs  = ['((0.5*(1+',dw,'+1/pi*sin(pi*',dw,')))*(',dw,'>-1)*(',dw,'<1)+(',dw,'>=1))'];   % Smooth heaviside function.
smdel = ['0.5*(1+cos(pi*',dw,'))/',dh,'*(',dw,'>-1)*(',dw,'<1)'];                        % Smooth delta function.
sigma = num2str(opt.sigma);
nx    = ['(2*x-1)/(2*sqrt((x-0.5)^2+(y-0.5)^2+eps))'];
ny    = ['(2*y-1)/(2*sqrt((x-0.5)^2+(y-0.5)^2+eps))'];

% Surface tension force source term.
if ( ~opt.lbi )   % Exact curvature.
kappa = ['1/sqrt((x-0.5)^2+(y-0.5)^2+eps)'];
fx1   = ['-',sigma,'*',kappa,'*',nx,'*',smdel];
fy1   = ['-',sigma,'*',kappa,'*',ny,'*',smdel];
else   % With Laplace-Beltrami transformation.
fx1   = ['-',sigma,'*(1-(',nx,')^2)*',smdel];
fx2   = ['-',sigma,'*(-(',nx,')*(',ny,'))*',smdel];
fy1   = ['-',sigma,'*(-(',ny,')*(',nx,'))*',smdel];
fy2   = ['-',sigma,'*(1-(',ny,')^2)*',smdel];
end

% Add Navier-Stokes equations physics mode.
fea.phys.ns.eqn.coef{1,end} = { opt.rho };
fea.phys.ns.eqn.coef{2,end} = { opt.miu };
fea.phys.ns.sfun            = { opt.sf_u opt.sf_u opt.sf_p };
fea.phys.ns.eqn.coef{3,end} = { fx1 };
fea.phys.ns.eqn.coef{4,end} = { fy1 };
fea.phys.ns.bdr.sel(n_bdr)  = 4;   % Set pressure to zero on last boundary segment.

% Parse problem.
fea = parsephys(fea);
if ( opt.lbi )
fea.eqn.f.form{1} = [2 3];
fea.eqn.f.form{2} = [2 3];
fea.eqn.f.coef{1} = {fx1 fx2};
fea.eqn.f.coef{2} = {fy1 fy2};
end
fea = parseprob(fea);

% Call to time-dependent solver.
fea.sol.u = solvetime( fea, ...
'fid',     fid, ...
'tmax',    0.3, ...
'tstep',   0.1, ...
'icub',    3, ...
'ischeme', opt.ischeme );

% Postprocessing.
if ( opt.iplot>0 )
postplot(fea,'surfexpr','p')
title('Pressure')
end

% Error checking.
ind_p    = [fea.eqn.ndof(1)+fea.eqn.ndof(2)+1:fea.eqn.ndof(1)+fea.eqn.ndof(2)+fea.eqn.ndof(3)];
dp       = max(fea.sol.u(ind_p,end)) - min(fea.sol.u(ind_p,end));
out.err  = abs(opt.sigma/opt.r - dp)/(opt.sigma/opt.r);
out.pass = out.err<opt.tol;

if ( nargout==0 )
clear fea out
end