example38.edp

// example38 from book, Section 3.14, p. 53ff
verbosity = 1;
bool anew = true;  // fresh start (false means restart)
bool savefiles = false;
real x0=0.5, y0=0, rr=0.2;

border ccc(t=0,2){x=2-t; y=1;}
border ddd(t=0,1){x=0; y=1-t;}  // second border is no. 2
border aaa1(t=0,x0-rr){x=t; y=0;}
border circle(t=pi,0){ x=x0+rr*cos(t); y=y0+rr*sin(t);}
border aaa2(t=x0+rr,2){x=t; y=0;}
border bbb(t=0,1){x=2; y=t;}

int m=5; 
mesh Th;
if(anew){
  Th = buildmesh (ccc(5*m) + ddd(3*m) + aaa1(2*m) + circle(5*m)
                + aaa2(5*m) + bbb(2*m) );
  plot(Th, wait=true);
} else {
  Th = readmesh("Th_circle.mesh"); 
  plot(Th, wait=false);
}

real dt=0.01, u0=2, err0=0.00625;
fespace Wh(Th,P1);
fespace Vh(Th,P1);
Wh u, v, u1, v1, uh, vh;
Vh r, rh, r1;

macro dn(u) (N.x*dx(u) + N.y*dy(u) ) //  def the normal derivative

if(anew){ 
  u1= u0; 
  v1= 0; 
  r1 = 1;
} else {
  ifstream g("u.txt");
  g >> u1[];
  ifstream gg("v.txt");
  gg >> v1[];
  ifstream ggg("r.txt");
  ggg >> r1[];
  plot(u1, value=true ,wait=true);
  err0 = err0/10; 
  dt = dt/10;
}

problem  eul(u,v,r,uh,vh,rh)
   = int2d(Th)(  (u*uh + v*vh + r*rh)/dt
              + ((dx(r)*uh+ dy(r)*vh) - (dx(rh)*u + dy(rh)*v)) )
   + int2d(Th)(-(rh*convect([u1,v1],-dt,r1) + 
        uh*convect([u1,v1],-dt,u1) + vh*convect([u1,v1],-dt,v1))/dt)
   + int1d(Th,6)(rh*u)
   + on(2,r=0) + on(2,u=u0) + on(2,v=0);

int remesh=80;
for(int k=0;k<3;k++) {
  if(k==20){ 
    err0 = err0/10; 
    dt = dt/10; 
    remesh = 5;
  }
  for(int i=0;i<remesh;i++){
     eul; 
     u1=u; 
     v1=v; 
     r1=abs(r);
     cout<<"k="<< k <<"  E="<< int2d(Th)(u^2+v^2+r)<<endl;
     plot(r, wait=false, value=true);
  }
  Th = adaptmesh (Th, r, nbvx=40000, err=err0, abserror=true, 
      nbjacoby=2, omega=1.8, ratio=1.8, nbsmooth=3,
      splitpbedge=true, maxsubdiv=5, rescaling=true) ;
  plot(Th,wait=0);
  // interpolate solution from old to new mesh
  u = u;
  v = v;
  r = r;
  
  if (savefiles) {
    savemesh(Th,"Th_circle.mesh");
    ofstream f("u.txt");
    f << u[];
    ofstream ff("v.txt");
    ff << v[];
    ofstream fff("r.txt");
    fff << r[];
    r1 = sqrt(u*u+v*v);
    plot(r1, value=true);
    r1 = r;
  }
}