Experimental and numerical investigation of the hydrodynamic characteristics of Autonomous Underwater Vehicles over sea-beds with complex topography

Abstract

Improved designs for Autonomous Underwater Vehicles (AUV) are becoming increasingly important due to their utility in academic and industrial applications. However, a majority of such testing and design is carried out under conditions that may not reflect the operating environment of shallow water AUVs. This may lead to imprecise estimations of the AUV's performance and sub-optimal designs. This article presents experimental and numerical studies carried out in conjunction, to investigate the hydrodynamic characteristics of AUV hulls at different Reynolds numbers over sloped channel-beds. We carry out experiments to measure the velocity field and turbulent statistics around the AUV with quantified uncertainty. These are contrasted against corresponding flat bed experiments to gauge the effect of test bed topography on AUV performance.The experimental data was used to validate Reynolds Stress Model predictions. Hydrodynamic parameters such as drag, pressure and skin friction coefficients were predicted from the RSM simulations at different test bed slopes, angles of attack and drift angles of the AUV hull, to analyze the hydrodynamic performance of the AUV. The results presented in this article offer avenues for design improvement of AUVs operating in shallow environments, such as the continental slope and estuaries.The exploration of ocean and to interpret its underwater behavior is of importance in todays world. To examine the ocean bed, convenient accessories are required to minimize the presence of human operators underneath of ocean. Autonomous Underwater Vehicles (AUV) are automated vehicles that are capable of underwater locomotion. These have applications in a variety of fields. For example, in the commercial field, oil and sub-sea drilling companies use AUVs for the purpose of checking the appropriate oceanic area where drilling may be optimally beneficial. For research and exploration, AUVs are used to track reefs and other life-forms that exist underwater. Additionally, AUVs have found applications in military and academic fields as well, besides others[1].The initial AUV designs were just modifications on existing designs of submersible torpedoes [2]. However, with the new found applications of these vehicles, focused investigation into their optimal design have become more critical. For instance, there is a demand for AUVs that can execute missions of the order of weeks and months. This requires that the AUV design be as optimal as possible, necessitating a careful analysis of the hydrodynamic performance of the AUV structure. Several experimental and numerical studies are available in the literature to analyze the hydrodynamic parameters around AUVs [3,4,5,6,7,8,9,10,11,12,13,14,15].Mansoorzadeh and Javanmard [3] have studied the effect of free surface on drag and lift coefficients of AUV at different submergence depths and compared the experimental data with the computational fluid dynamics (CFD) simulations. It was observed that hydrodynamic coefficients were very much responsive to the submergence...

A review on the hydrodynamic characteristics of autonomous underwater vehicles

“…AUV often operates in complex flow fields like near moving submarines, near ships, or sea-beds with complex topography. 38 AUV works near the surface ship, another AUV or a submersible will experience hydrodynamic interaction due to the presence of different vehicles. The relative motion between AUV with another nearby marine vehicle will affect the operation and objective of AUV.…”

Turbulence anisotropy with higher-order moments in flow through passive grid under rigid boundary influence

“…This time is sufficient for the estimation of statistically significant turbulence characteristics. 28 The ADV velocity data was sampled only when the signal-to-noise ratio (SNR) was greater than 15 dB, and the signal correlation was greater than 70% similar to the literature 29–31 for acquisition of good quality data free from spikes in the signal.…”

Role of rigid boundary on the decay of turbulence generated by passive-grid for free surface flow

“…18 The detailed description of ADV, the data acquisition, post-processing of the samples are detailed in literature. 19–21 The uncertainty analysis (i.e., 95% confidence limit) was executed by collecting 15 sets of ADV data sampled at 40 Hz for a duration of 5 min at z / h = 0.04 from the bottom boundary for the without grid case similar to the method suggested in earlier studies. 22,23 For the uncertainty analyses, the time-averaged mean velocities (u¯ and w¯) and turbulent intensities (ur.m.s and wr.ms) are calculated as follows 24,25 where N is the total number of sample collected during experiment, u i and w i are the instantaneous velocity components and u ′ and w ′ are the corresponding velocity fluctuation in x and z direction, respectively.…”