Determination of the natural frequencies and natural modes of a rod using the dual BEM in conjunction with the domain partition technique

In this paper, the dual BEM in conjunction with the domain partition technique is employed to solve both natural frequencies and natural modes of a rod. In this new approach, there exists no spurious eigenvalue using the complex-valued singular or hypersingular equation alone. In the derivation of the singular and hypersingular integral equations, if only the real parts of the kernel functions are chosen, the resulting eigenequations have spurious eigenvalues. Such spurious eigenvalues stem from adding the dummy links into the interior structures considered. Although the spurious eigenvalues exist in this approach which uses the real-valued kernel functions, the possible indeterminacy of eigenmodes using the conventional real-valued singular or real-valued hypersingular equations disappears when the domain partition technique is adopted. The conventional real-valued multiple reciprocity BEM results in spurious eigenvalues for the mixed boundary conditions and indeterminacy of eigenmodes owing to insufficient rank of the leading coefficient matrix for the Dirichlet and Neumann boundary conditions. Such problems can be solved by combining the singular and hypersingular equations together; however, they also can be treated by using the real-valued singular or hypersingular equation alone if the domain partition technique is adopted. Three examples including the Dirichlet, Neumann and mixed type boundary conditions are investigated to show the validity of current approach.