[求助]运用hammer积分构建四面体单元质量矩阵，出现了这样的问题

yangmingsui

Me(i,j)=(1/c**2)∫(Ni*Nj)dV,  运用hammer积分，单元质量矩阵在积分点（体积坐标），可变为
Me(i,j)=Me(i,j)+((1/c**2) ∑（H(i,j)/6）*(Ni(L1,L2,L3)*Nj(L1,L2,L3))|J(L1,L2,L3)|的形式。然后进而可以求得单元质量矩阵，这是一般等参元的做法。(L1,L2,L3)为体积坐标下的积分点值，H(i,j)为权系数。



我编程就是按照上述过程。但是结果和解析值出现严重的偏差。并且|J全为负。|




解析值为的推导见附件




有没有人遇到过这个方面的问题啊


还是10节点的四面体单元不能够用hammer积分计算？

hillyuan

The value of Jacobian is detremined by two things: shape function and shape of your tetrahedron. That is, it is irrelevent to your integration process! So check out your process of Jacobain calculation at first.

Although in case that tetrahedron is greatly distorted the Jacobian may less than zero, but generally it is a plus value. If your Jacobian of a tetrahedron with same side length is minus value, you are definitly wrong.