Simulating the propagation of 3D ultrasonic waves in a nonlinear medium is a demanding task. It requires the solution of time-dependent and nonlinear partial differential equations (PDEs). For such nonlinear PDEs, we have to use an implicit numerical method that is very CPU-intensive. Parallel simulation is therefore essential for studying those ultrasonic waves with satisfactory accuracy. We present in this paper the parallelization of an ultra-sonic wave simulator and report some numerical experiments that have been run on a 24-node Linux cluster. Our CPU-measurements indicate that Linux clusters can deliver satisfactory parallel computing power for the numerical solution of PDEs. For simulating 3D ultrasonic waves in particular, we have found that our Linux cluster, which consists of 48 Pentium-III 500MHz processors inter-connected with a 100Mbit/s ethernet network, is fully comparable with an SGI Origin 2000 machine.