3. Numerical examples
In this section, all the computations are carried out on the same desktop computer with an Intel Core i5-3470 CPU (3.2GHZ) and 4GBmemory. The original FMM is applied in this paper for testing the validity and efficiency of the proposed adaptive expansion technique, although it is seldom used for very low frequency acoustic problems. In addition, the FMM without the adaptive expansion technique is named standard algorithm, and the FMM with the adaptive expansion technique is named adaptive algorithm in this section.
In the numerical examples, the maximum number of the elements in leafs is 60, and p set as 8 in both standard algorithm and in adaptive algorithm. In the GMRES solver, we stop the iteration when the tolerance error in FMM is less than 10^3
The radiation problem on a cylinder domain (Fig. 1) is used to study the performances of the presented adaptive algorithm using the CFMM. The diameter of this cylinder is 2, and the length is 5. The sample point in this example is (0, 5, 0). The pulsating cylinder is formulated by prescribing the normal velocity on a cylinder
surface produced by a pulsating ball with radius a=1, which is shown in Fig. 1. The wave number k=1.0. The pulsating ball is circumscribed by the cylinder.