The derivatives of the Lagrange shape functions are nonzero on the element faces. This is why you are seeing dphi_face != 0
> On May 16, 2014, at 12:07 PM, walter kou <walter4c...@gmail.com> wrote: > > Hi all, > > Really appreciate it if any one can tell what get_dphi() is for the element > at the boundary, and point out the reason for my issue. > > >> On Thu, May 15, 2014 at 10:58 PM, walter kou <walter4c...@gmail.com> wrote: >> >>> Hi all, >>> >>> For the 2D boundary element of the 3D domain, what is dphi_face = >>> fe_face->get_dphi(); ?? >>> >>> The strange thing to me is as below: >>> >>> 1) I use Hex8 for the 3D box, thus get 2D quad4 at the boundary face >>> (i.e. side element) . Notice the side element is shown below with nodes on >>> the x-y plane: >>> >>> /************ show the nodes on boundary element: side-element >>> [side-elem]:node: 0 coordinates:(x,y,z)=1,0,0 >>> [side-elem]:node: 1 coordinates:(x,y,z)=1,1,0 >>> [side-elem]:node: 2 coordinates:(x,y,z)=2,1,0 >>> [side-elem]:node: 3 coordinates:(x,y,z)=2,0,0 >>> >>> 2) I print out the Jxw- face, phi_face dphi_face. >>> >>> 3) Why do I get non-zero dphi_face[*][*](2)? should dphi/dz ==0 since the >>> 2D face is on the x-y plane? >>> >>> 4) Why is dphi_face[7][3](2) is non-zero, even nodes 4-7 are not on the >>> face? >>> >>> 5) Is dphi-face[*][*](0,1,2) = dphi/d(x,y,z) for both bulk and boundary >>> elements? >>> >>> Thanks >>> >>> /*************** show Jxw_face, phi, dphi >>> >>> Jxw_face[0]:=0.25 >>> Jxw_face[1]:=0.25 >>> Jxw_face[2]:=0.25 >>> Jxw_face[3]:=0.25 >>> >>> phi_face[0][0]:0.622008 dphi_face[0][0]:(x,y,z)=(-0.788675, -0.788675, >>> -0.622008) >>> phi_face[0][1]:0.166667 dphi_face[0][1]:(x,y,z)=(-0.211325, -0.788675, >>> -0.166667) >>> phi_face[0][2]:0.166667 dphi_face[0][2]:(x,y,z)=(-0.788675, -0.211325, >>> -0.166667) >>> phi_face[0][3]:0.0446582 dphi_face[0][3]:(x,y,z)=(-0.211325, -0.211325, >>> -0.0446582) >>> phi_face[1][0]:0.166667 dphi_face[1][0]:(x,y,z)=(0.788675, -0.211325, >>> -0.166667) >>> phi_face[1][1]:0.0446582 dphi_face[1][1]:(x,y,z)=(0.211325, -0.211325, >>> -0.0446582) >>> phi_face[1][2]:0.622008 dphi_face[1][2]:(x,y,z)=(0.788675, -0.788675, >>> -0.622008) >>> phi_face[1][3]:0.166667 dphi_face[1][3]:(x,y,z)=(0.211325, -0.788675, >>> -0.166667) >>> phi_face[2][0]:0.0446582 dphi_face[2][0]:(x,y,z)=(0.211325, 0.211325, >>> -0.0446582) >>> phi_face[2][1]:0.166667 dphi_face[2][1]:(x,y,z)=(0.788675, 0.211325, >>> -0.166667) >>> phi_face[2][2]:0.166667 dphi_face[2][2]:(x,y,z)=(0.211325, 0.788675, >>> -0.166667) >>> phi_face[2][3]:0.622008 dphi_face[2][3]:(x,y,z)=(0.788675, 0.788675, >>> -0.622008) >>> phi_face[3][0]:0.166667 dphi_face[3][0]:(x,y,z)=(-0.211325, 0.788675, >>> -0.166667) >>> phi_face[3][1]:0.622008 dphi_face[3][1]:(x,y,z)=(-0.788675, 0.788675, >>> -0.622008) >>> phi_face[3][2]:0.0446582 dphi_face[3][2]:(x,y,z)=(-0.211325, 0.211325, >>> -0.0446582) >>> phi_face[3][3]:0.166667 dphi_face[3][3]:(x,y,z)=(-0.788675, 0.211325, >>> -0.166667) >>> phi_face[4][0]:0 dphi_face[4][0]:(x,y,z)=( 0, 0, 0.622008) >>> phi_face[4][1]:0 dphi_face[4][1]:(x,y,z)=( 0, 0, 0.166667) >>> phi_face[4][2]:0 dphi_face[4][2]:(x,y,z)=( 0, 0, 0.166667) >>> phi_face[4][3]:0 dphi_face[4][3]:(x,y,z)=( 0, 0, 0.0446582) >>> phi_face[5][0]:0 dphi_face[5][0]:(x,y,z)=( 0, 0, 0.166667) >>> phi_face[5][1]:0 dphi_face[5][1]:(x,y,z)=( 0, 0, 0.0446582) >>> phi_face[5][2]:0 dphi_face[5][2]:(x,y,z)=( 0, 0, 0.622008) >>> phi_face[5][3]:0 dphi_face[5][3]:(x,y,z)=( 0, 0, 0.166667) >>> phi_face[6][0]:0 dphi_face[6][0]:(x,y,z)=( 0, 0, 0.0446582) >>> phi_face[6][1]:0 dphi_face[6][1]:(x,y,z)=( 0, 0, 0.166667) >>> phi_face[6][2]:0 dphi_face[6][2]:(x,y,z)=( 0, 0, 0.166667) >>> phi_face[6][3]:0 dphi_face[6][3]:(x,y,z)=( 0, 0, 0.622008) >>> phi_face[7][0]:0 dphi_face[7][0]:(x,y,z)=( 0, 0, 0.166667) >>> phi_face[7][1]:0 dphi_face[7][1]:(x,y,z)=( 0, 0, 0.622008) >>> phi_face[7][2]:0 dphi_face[7][2]:(x,y,z)=( 0, 0, 0.0446582) >>> phi_face[7][3]:0 dphi_face[7][3]:(x,y,z)=( 0, 0, 0.166667) > ------------------------------------------------------------------------------ > "Accelerate Dev Cycles with Automated Cross-Browser Testing - For FREE > Instantly run your Selenium tests across 300+ browser/OS combos. > Get unparalleled scalability from the best Selenium testing platform available > Simple to use. 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