Abstract

The authors have been developing an autonomous underwater glider which equips an OBEM (Ocean Bottom Electro-Magnetometer). That is a hopeful instrument for the ocean floor resources explorations. The autonomous vehicle has an ability to achieve a continuous resource exploration autonomously for a long term. The motion control system for landing of the vehicle was investigated in the previous studies. In these reports, hydrodynamic performance of the vehicle in landing is examined by CFD calculations. The bottom effect which affects the lift and drag of the wings of the glider is studied and the characteristics of the blended wing body near a sea bottom is discussed.

On the other hand, the transient motions of the vehicle such as a deployment, the motion when the vehicle changes its buoyancy for cruise are also important problems for the motion control of the vehicle. The control system might be affected by the unpredicted change of the hydrodynamic forces acting on the body and the wing in the transient conditions. Consequently, it may cause deterioration of the performance of the control system.

In this report, these transient motions are investigated based on CFD analysis. The overset mesh approach is used to simulated the sequential maneuvers in the cruising of the underwater vehicle.

Introduction

Development of sea floor resources gathers attention from wide area recently. Ocean floor resources such as sea-floor hydrothermal deposit, methane hydrate and manganese nodule are promising resources in the near future. The seismic exploration, a multi-beam echo sounder and a sub-bottom profiler which are equipped with a survey ship or an underwater vehicle are used for these resource explorations in the ocean (Yoshida, Hyakudome, Ishibashi et al., 2013). The OBEM is one of these devices which measures the slight variation of the electromagnetic field on the sea floor and the structure under the seabed can be analyzed by the gathered data. On the other hand, various types of underwater gliders which have high energy efficiency and long endurance have been developed for ocean observations. These advantages are suitable for offshore resource explorations because they have capability to achieve their mission for a few weeks autonomously. Nakamura, Asakawa, Hyakudome, Kishima and Matsuoka (2013) developed a prototype of a 3,000m class underwater glider for long time virtual mooring.

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