Measurement of Very-Low-Frequency Waves Generated by a Heaving Sphere Based on a Vector Hydrophone

It has long been recognized that underwater vehicles can be detected via gravity waves generated during motion. Therefore, this study aimed to investigate a direct measurement method for surface gravity waves generated by oscillating spheres based on a vector hydrophone. First, based on the principles of linear potential flow theory, the amplitude of the free surface displacement (AFSD) generated by an oscillating sphere in a finite depth fluid is studied. According to the multipole expansion method, the free surface wave characteristics caused by spherical oscillations are numerically analyzed. The surface wave was then tested in a pool. The sensitivity of the very-low-frequency (VLF) vector hydrophone was measured in a water tank, and the AFSD of the VLF gravity surface wave was measured in a pool. The results show that the measured results are larger than the simulation results because of the existence of reflected waves and the influence of the walking mechanism; however, they are of the same order of magnitude. The pool test proved that the vector hydrophone can be used to measure gravity waves and obtain more information than a pressure sensor.