From CFD-Wiki
classdef ELG3412r < handle
% ELG3412r
% Container class for 4-node simple cubic Hermite finite elements
% on rectangle/quadrilateral (designated by 'G3412r').
% The scalar element is used for scalar fields such as pressure
% or temperature.
% The vector element is used for irrotational vector fields
% such as pressure or thermal gradients or irrotational fluid flow.
%
% Jonas Holdeman January 2013
properties (Constant)
name = 'Simple-cubic Hermite';
designation = 'G3412r';
shape = 'quadrilateral';
nsides = 4;
order = 3; % order of completeness
nnodes = 4; % number of nodes
nndofs = 3; % max number of nodal dofs
tndofe = 12; % total number of dofs for element
mxpowr = 3; % highest power/degree in g
hQuad = @GQuad2; % handle to quadrature rules on rectangles
cntr = [0 0]; % reference element centroid
nn = [-1 -1; 1 -1; 1 1; -1 1]; % standard nodal order of coords
end % properties
methods (Static)
% Four-node cubic-complete Hermite scalar potential function
% element on the reference square. The vector function is the gradient
% of this simple-cubic element (3412) with 3 dofs per corner node.
% Parameter ni is one of coordinate pairs (-1,-1),(1,-1),(1,1),(-1,1)
function g=g(ni,q,r)
qi=ni(1); q0=q*ni(1);
ri=ni(2); r0=r*ni(2);
g=[1/8*(1+q0)*(1+r0)*(2+q0*(1-q0)+r0*(1-r0)), ...
-1/8*qi*(1+q0)*(1+r0)*(1-q^2), -1/8*ri*(1+q0)*(1+r0)*(1-r^2)];
end % g
% Four-node quadratic-complete Hermite irrotational vector function
% element on the reference square. The vector function is the gradient
% of the cubic-complete element (3412) with 3 dofs per corner node.
% Parameter ni is one of coordinate pairs (-1,-1),(1,-1),(1,1),(-1,1)
function gv=G(ni,q,r)
qi=ni(1); q0=q*ni(1);
ri=ni(2); r0=r*ni(2);
gv=[1/8*qi*(1+r0)*(r0*(1-r0)+3*(1-q^2)), ...
-1/8*(1+r0)*(1+q0)*(1-3*q0), ...
-1/8*qi/ri*(1-r^2)*(1+r0); ...
1/8*ri*(1+q0)*(q0*(1-q0)+3*(1-r^2)), ...
-1/8/qi*ri*(1-q^2)*(1+q0), ...
-1/8*(1+q0)*(1+r0)*(1-3*r0)];
end % G
% First derivatives wrt q & r of four-node quadratic-complete Hermite
% gradient vector function element on the reference square.
% The vector function is the gradient of the cubic-complete element
% (3412) with 3 dofs at each corner node.
% Gq = array of q-derivatives of irrotational vectors
% Gr = array of r-derivatives of irrotational vectors
% Parameter ni is one of coordinate pairs (-1,-1),(1,-1),(1,1),(-1,1)
function [Gq,Gr]=DG(ni,q,r)
qi=ni(1); q0=q*ni(1);
ri=ni(2); r0=r*ni(2);
Gq=[-3/4*qi^2*q0*(1+r0), 1/4*qi*(1+r0)*(1+3*q0), 0; ...
1/8*qi*ri*(4-3*q0^2-3*r0^2), -1/8*ri*(1+q0)*(1-3*q0), ...
-1/8*qi*(1+r0)*(1-3*r0)];
Gr=[1/8*qi*ri*(4-3*q0^2-3*r0^2), -1/8*ri*(1+q0)*(1-3*q0), ...
-1/8*qi*(1+r0)*(1-3*r0); ...
-3/4*ri^2*r0*(1+q0), 0, 1/4*ri*(1+q0)*(1+3*r0)];
end % DG
% Transpose of the Jacobian matrix at (q,r)
function Jt=JacT(Xe,q,r)
Jt=Xe*Gm(ELG3412rr.nn(:,:),q,r);
end % JacT
% Test to see if transformation is affine, returns True or False
function isit=isaffine(Xe)
isit=sum(abs(Xe(:,1)-Xe(:,2)+Xe(:,3)-Xe(:,4)))<4*eps;
end % isaffine
% Post-multiplying matrix Ti^-1
function ti=Ti(Xe,m)
Jt=Xe*ELG3412r.Gm(ELS32r.nn(:,:),ELG3412r.nn(m,1),ELG3412r.nn(m,2));
JtiD=[Jt(2,2),-Jt(1,2); -Jt(2,1),Jt(1,1)]; % det(J)*inv(J)
ti=blkdiag(1,JtiD);
end % Ti
% Bilinear mapping function from (q,r) in the reference square
% [-1.1]x[-1,1] to (x,y) in the straight-sided quadrilateral
% finite elements.
% The parameter ni can be a vector of coordinate pairs.
function g=gm(ni,q,r)
g=.25*(1-ni(:,1).*q)*(1+ni(:,2).*r);
end % gm
% Transposed gradient (derivatives) of scalar bilinear mapping function
% The parameter ni can be a vector of coordinate pairs.
function G=Gm(ni,q,r)
G=[.25*ni(:,1).*(1+ni(:,2).*r), .25*ni(:,2).*(1+ni(:,1).*q)];
end % Gm
% Second (cross) derivative of scalar bilinear mapping function
% The parameter ni can be a vector of coordinate pairs.
function D=DGm(ni,~,~)
D=.25*ni(:,1).*ni(:,2);
end % DGm
end % method (Static)
end % classdef
