A combined FEM-Ritz method for modeling 3D acoustics in CANDU fuel sub-channels

The modeling and analysis of 3D acoustics in CANDU fuel sub-channels are conducted using a combined FEM-Ritz method to reduce the number of acoustic degrees of freedom for higher computational efficiency. The method uses a prism element by extruding an isoparametric six-node triangular element along the z-axis and computing the acoustic displacement by combining isoperimetric triangular shape functions and a polynomial shape function of n-th order. Lagrangian mechanics is utilized to assemble the equations of motion and derive all the system's matrices. The acoustic system consists of a cylindrical pressured pipe with rigid walls filled with fluid. At the inlet, an acoustic wave is generated by a time-harmonic source and, at the outlet, the acoustic wave interacts with a reacting and absorbing material. Numerical results obtained are found to be in excellent agreement with the analytic solution. (author)