Recent years have highlighted that the necessity of ocean data in time and space for the predictions of environmental changes on Earth. As one method of acquiring data, we propose a virtual mooring system using an underwater vehicle. We have developed a disk-type underwater glider. Using the glider, oceanographic observations were conducted in the East China Sea in July, 2016. The details were presented at ISOPE2017. As described in this paper, results of model tests related to course control conducted to improve the performance of virtual mooring are presented. Then the influence of a vertical tail wing on motion control is discussed.
In recent years, predictions of environmental changes on Earth and studies of ecodevelopment have become increasingly important. Such predictions necessitate the continuous collection of ocean data in time and space. However, construction of a conventional mooring system is laborious and expensive. Profiling floats such as Argo floats (Roemmich et al., 2009), because they float in the current, cannot remain at a specific point where continuous and long-term observations are needed. To resolve these difficulties and to collect the necessary data, we propose a virtual mooring system using an underwater glider. Construction of a prototype vehicle was begun at the Research Institute for Applied Mechanics (RIAM), Kyushu University in April 2010 (Koterayama et al., 2012). Some practical underwater gliders are already in use throughout the world (Eriksen et al., 2001; Sherman et al., 2001; Webb et al., 2001). However, they are cruising-type gliders, with a shape resembling that of a conventional airplane. The disk type underwater glider that we are developing has an appropriate form for virtual mooring and loading of an Acoustic Doppler Current Profiler (ADCP). Using this disk-type underwater glider, the BOOMERANG, oceanographic observations were made in the west sea-area of Japan's Kami-Goto islands in July, 2015 and in the East China Sea in July, 2016 yielding interesting data (Nakamura et al., 2017). Since those observations, research to improve the virtual mooring performance has continued. For this purpose, it is thought that a feedback control of the vehicle heading angle is desirable. Many researches on motion control of a vehicle have been carried out (Tran et al., 2014; Roy et al., 2015; Li et al., 2015; Wang et al., 2016; Zhang et al., 2017). However, there is little research on motion control of a disk-type underwater glider.