CFD Online Logo CFD Online URL
Home > Wiki > PFV convection matrix

PFV convection matrix

From CFD-Wiki

Revision as of 03:52, 29 June 2011 by Jonas Holdeman (Talk | contribs)
(diff) ← Older revision | Latest revision (diff) | Newer revision → (diff)
Jump to: navigation, search

Matlab function CMatW.m for pressure-free velocity convection matrix.

function [Cm,RowNdx,ColNdx]=CMatW(Xe,Elcon,nn2nft,Vdof)
%CMATW - Returns the affine-mapped element convection matrix for the simple cubic Hermite 
%   basis functions on 4-node straight-sided quadrilateral elements with 3 DOF 
%   per node using Gauss quadrature on the reference square and row/col indices. 
% The columns of the array Vdof must contain the 3 nodal degree-of-freedom 
%   vectors in the proper nodal order. 
% The degrees of freedom in Vdof are the stream function and the two components
%   u and v of the solenoidal velocity vector.
% The assumed nodal numbering starts with 1 at the lower left corner of the 
%   element and proceeds counter-clockwise around the element. 
% Usage:
%   [CM,Rndx,Cndx] = CMatW(Xe,Elcon,nn2nft,Vdof)
%   Xe(1,:) -  x-coordinates of corner nodes of element.  
%   Xe(2,:) -  y-coordinates of corner nodes of element.  
%   Elcon - this element connectivity matrix 
%   nn2nft - global number and type of DOF at each node 
%   Vdof  - (3x4) array of stream function, velocity components, and second 
%     stream function derivatives to specify the velocity over the element.
% Jonas Holdeman, August 2007, revised  June 2011 

% Constants and fixed data
nd = 3;  nd4=4*nd;  ND=1:nd;    % nd = number of dofs per node, 
nn=[-1 -1; 1 -1; 1 1; -1 1];    % defines local nodal order
% Define 5-point quadrature data once, on first call. 
% Gaussian weights and absissas to integrate 9th degree polynomials exactly. 
global GQ5;
if (isempty(GQ5))   % 5-point quadrature data defined? If not, define arguments & weights. 
  Aq=[-.906179845938664,-.538469310105683, .0,               .538469310105683, .906179845938664];
  Hq=[ .236926885056189, .478628670499366, .568888888888889, .478628670499366, .236926885056189];
  GQ5.size=25; GQ5.xa=[Aq;Aq;Aq;Aq;Aq]; GQ5.ya=GQ5.xa'; 
  wt=[Hq;Hq;Hq;Hq;Hq]; GQ5.wt=wt.*wt';

   xa=GQ5.xa; ya=GQ5.ya; wt=GQ5.wt; Nq=GQ5.size;  % Use GQ5 (5x5) for exact integration

% -----------------------------------------------
global Zs3412D2c;  global ZS3412c;

if (isempty(ZS3412c)|isempty(Zs3412D2c)|size(Zs3412D2c,2)~=Nq)
% Evaluate and save/cache the set of shape functions at quadrature pts. 
   Zs3412D2c=cell(4,Nq);  ZS3412c=cell(4,Nq);
   for k=1:Nq
      for m=1:4
      ZS3412c{m,k}= Sr(nn(m,:),xa(k),ya(k));
end  % if(isempty(*))

% --------------- End fixed data ----------------

for m=1:4
  JtiD=[Jt(2,2),-Jt(1,2); -Jt(2,1),Jt(1,1)];   % det(J)*inv(J)

% Move Jacobian evaluation inside k-loop for general convex quadrilateral. 
% Jt=[x_q, x_r; y_q, y_r];

Cm=zeros(nd4,nd4); Rcm=zeros(nd4,1);  
S=zeros(2,nd4); Sx=zeros(2,nd4); Sy=zeros(2,nd4);  % Pre-allocate arrays

% Begin loop over Gauss-Legendre quadrature points. 
for k=1:Nq  
  Jt=Xe*GBL(nn(:,:),xa(k),ya(k));         % transpose of Jacobian at (xa,ya)
  Det=Jt(1,1)*Jt(2,2)-Jt(1,2)*Jt(2,1);    % Determinant of Jt & J 
  TL=[Jt(2,2)^2, -2*Jt(2,1)*Jt(2,2),  Jt(2,1)^2; ... 
     -Jt(1,2)*Jt(2,2), Jt(1,1)*Jt(2,2)+Jt(2,1)*Jt(1,2), -Jt(1,1)*Jt(2,1); ... 
      Jt(1,2)^2, -2*Jt(1,1)*Jt(1,2),  Jt(1,1)^2 ]/Det^2;
% Initialize functions and derivatives at the quadrature point (xa,ya).
  for m=1:4 
    S(:,mm+ND) = Jtd*ZS3412c{m,k}*Ti{m};
    Ds = TL*Zs3412D2c{m,k}*Ti{m}; 
    Sx(:,mm+ND) = [Ds(2,:); -Ds(1,:)];     % [Pyx, -Pxx]
    Sy(:,mm+ND) = [Ds(3,:); -Ds(2,:)];     % [Pyy, -Pxy]
  end  % loop m
% Compute the fluid velocity at the quadrature point.
  U = S*Vdof(:);
% Submatrix ordered by psi,u,v 
  Cm = Cm + S'*(U(1)*Sx+U(2)*Sy)*(wt(k)*Det);
end    % end loop k over quadrature points 

for n=1:4                 % Loop over element nodes 
  gf(m+ND)=(nn2nft(1,Elcon(n))-1)+ND;  % Get global freedoms

RowNdx=repmat(gf,1,nd4);      % Row indices
ColNdx=RowNdx';               % Col indices
Cm = reshape(Cm,nd4*nd4,1);

% ----------------------------------------------------------------------------

function P2=D3s(ni,q,r)
% Second derivatives [Pxx; Pxy; Pyy] of simple cubic stream function.
 qi=ni(1); q0=q*ni(1); q1=1+q0; 
 ri=ni(2); r0=r*ni(2); r1=1+r0;
  P2=[-.75*qi^2*(r0+1)*q0, 0, -.25*qi*(r0+1)*(3*q0+1); ...
       .125*qi*ri*(4-3*(q^2+r^2)), .125*qi*(r0+1)*(3*r0-1), -.125*ri*(q0+1)*(3*q0-1); ...
      -.75*ri^2*(q0+1)*r0, .25*ri*(q0+1)*(3*r0+1), 0] ;  

function S=Sr(ni,q,r)
%S  Array of solenoidal basis functions on rectangle.
   qi=ni(1); q0=q*ni(1); q1=1+q0; 
   ri=ni(2); r0=r*ni(2); r1=1+r0;
   % array of solenoidal vectors 
S=[ .125*ri*q1*(q0*(1-q0)+3*(1-r^2)), .125*q1*r1*(3*r0-1),    .125*ri/qi*q1^2*(1-q0); ...
      -.125*qi*r1*(r0*(1-r0)+3*(1-q^2)), .125*qi/ri*r1^2*(1-r0), .125*q1*r1*(3*q0-1)];

function G=GBL(ni,q,r)
% Transposed gradient (derivatives) of scalar bilinear mapping function. 
% The parameter ni can be a vector of coordinate pairs. 
  G=[.25*ni(:,1).*(1+ni(:,2).*r), .25*ni(:,2).*(1+ni(:,1).*q)];
My wiki