In autonomous underwater vehicles(AUVs) the onboard power used to complete missions is limited.To solve this problem,a landing AUV has been designed,which conserves energy by sitting on the seafloor while monitoring the ocean.In order to study the dynamic behaviors for better control of the AUV,the dynamic analysis of the landing AUV is presented in this paper.Based on the momentum theorem and the angular momentum theorem,the dynamic model of the landing AUV is derived.The simulations of rectilinear motion,rotary motion and helix motion indicate the dynamic behaviors of the AUV.The ocean experiments validate the dynamic model presented in this paper.The experiments also verify that the landing AUV can work for a longer time than common AUVs.
In this paper,the hydrodynamically generated noise by the flow over an open cavity is studied.First,aeroacoustic theories and computational aeroacoustic(CAA) methodologies are reviewed in light of hydrodynamic acoustics,based on which,a hybrid method is presented.In the coupling procedure,the unsteady cavity flow field is computed using large-eddy simulation(LES) ,while the radiated sound is calculated by the Ffowcs Williams-Hawkings(FW-H) acoustic analogy with acoustic source terms extracted from the time-dependent solutions of the unsteady flow.The hybrid LES-FW-H acoustic analogy method is tested with an open cavity flow at Mach number of 0.006 and Reynolds number of 105 .Following the reflection theorem of Powell,the contributions from different source terms are quantified,and the terms involving wall-pressure fluctuations are found to account for most of the radiated intensity.The radiation field is investigated in the frequency domain.For the longitudinal direction,the sound propagates with a dominant radiation downstream the cavity in the near-field and a flatter directivity in the far-field,while for the spanwise direction,the acoustic waves have a similar propagation along+z and-z directions,with no visible directivity.
