I have to compute the mass matrix of a Hexahedral mesh.
There are 3 methods to compute mass matrix. I'm interested in one method which consists of dividing the mass of the element by the number of nodes and attributes this mass at each node for each degree of freedoms.
My problems is that: I don't know how to compute the volume of the element and then multiply it by the density to calculate mass.
In 2D, I have the solution, but not in 3D.
I'm open to any help on this subject due to the fact that I don't know any article on this subject.