implementation of mass matrix and stiffness matrix in abaqus using external subroutine

 Hi,

I am working on a coupled fluid structure problem , precisley on the elasto-acoustic mode, and i want to make sure that abaqus work with my matrix (stiffness and mass matrix) that i have made by fortran and at the same time i continu using abaqus element to mesh my model,

Any suggestion would be very appreciated

Thanks in advance

Regards

Lamia