Periodic Bcs in 3D

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Author Message   Dariusz Lydzba (darlydzba) New member Username: darlydzba Post Number: 1 Registered: 04-2006 Posted on Saturday, April 08, 2006 - 10:19 am:    Hi Dr. Nelson! I have a huge problem with setting the periodic BCs in 3D. My problem is to set the periodic BCs on all walls of cube. In 2D - the problem runs. In 3D, when i try with PERIODIC EXTRUSION, there appears a comment: "Incomplete Bounding Mesh". What shoul I do? Here is an input file: TITLE 'effective elasticity parameters' COORDINATES cartesian3 { coordinate system, 1D,2D,3D, etc } VARIABLES u v w SELECT painted errlim=1 DEFINITIONS zbottom=-0.3 ztop=0.3 B=0.3 A=30 G=30 Ex=1 Ey=0 Ez=0 Exy=0 Exz=0 Eyz=0 Sx=A*(Ex+Ey+Ez)+2*G*Ex+A*(dx(u)+dy(v)+dz(w))+2*G*dx(u) Sy=A*(Ex+Ey+Ez)+2*G*Ey+A*(dx(u)+dy(v)+dz(w))+2*G*dy(v) Sz=A*(Ex+Ey+Ez)+2*G*Ez+A*(dx(u)+dy(v)+dz(w))+2*G*dz(w) Txy=2*G*(Exy+0.5*(dx(v)+dy(u))) Txz=2*G*(Exz+0.5*(dx(w)+dz(u))) Tyz=2*G*(Eyz+0.5*(dy(w)+dz(v))) PERIODIC EXTRUSION SURFACE 'Bottom' z=zbottom LAYER 'All' SURFACE 'Top' z=ztop EQUATIONS u: dx(Sx)+dy(Txy)+dz(Txz)=0 v: dx(Txy)+dy(Sy)+dz(Tyz)=0 w:dx(Txz)+dy(Tyz)+dz(Sz)=0 CONSTRAINTS integral(u) = 0 integral(v) = 0 integral(w) = 0 BOUNDARIES REGION 1 START(-B,-B) PERIODIC(x,y+2*B) LINE TO (B, -B) NATURAL(U)=0 NATURAL(V)=0 NATURAL(W)=0 LINE TO (B, -0.29) PERIODIC(x-2*B,y) LINE TO (B, 0.29) NATURAL(U)=0 NATURAL(V)=0 NATURAL(W)=0 LINE TO (B,B) LINE TO (-B,B) NATURAL(U)=0 NATURAL(V)=0 NATURAL(W)=0 LINE TO(-B, 0.29) LINE TO (-B, -0.29) NATURAL(U)=0 NATURAL(V)=0 NATURAL(W)=0 LINE TO CLOSE PLOTS CONTOUR(Sx) on x=0 SUMMARY REPORT(Vol_Integral(Sx)/(2*B)^3) END   Robert G. Nelson (rgnelson) Moderator Username: rgnelson Post Number: 580 Registered: 06-2003 Posted on Tuesday, April 11, 2006 - 04:11 pm:    The current implementation of FlexPDE allows only a single periodic image of each mesh node. Corner nodes in multi-way periodicity require multiple image nodes, which is not supported. You have provided gaps in the XY corners to avoid this restriction, but you must do the same thing at XZ and YZ corners. Add thin layers top and bottom to separate the Z-periodicity from the X- and Y- periodicity.