Virtual Mooring Research Articles

Optimal experimental design for identification of hydrodynamic loading models

Abstract Hydrodynamic model-scale experiments are an intrinsic part of the design of marine structures, as they enable validating and calibrating the involved hydrodynamic numerical models. Such seakeeping experiments are generally conducted using a simple spring-based mooring system, with fixed properties throughout the tests. In the context of cyber-physical testing, the marine structure is kept in position in the laboratory by a virtual mooring system, the properties of which can be adjusted on the fly. This paper provides an algorithmic approach for maximizing the information gain from the test by optimizing the mooring stifness and damping parameters that define the experiment. The method is verified with synthetic data generated for the INO Windmoor 12MW floater, and is shown to be robust to noise and unmodeled effects.

Research on ocean-current-prediction-based virtual mooring strategy for the portable underwater profilers

The Argo Global Ocean Observing Network has remained the preeminent ocean observation network worldwide. Since the Argo buoys lack freedom of lateral movement, their wave-following working characteristics prevent them from completing the long-term observations in the designated sea area. Long-term monitoring of designated waters is often required, for example, to study the impacts of seabed mining on the marine environment in the surrounding sea area. To solve this problem, a portable underwater profiler (PUP) that combines the functionalities of profiling buoys and underwater gliders was devised. The PUP employs a center of gravity adjustment mechanism utilizing the double-weight block approach, enabling the pitch angle adjustment within -90° to 0°. Remarkably, the PUP weighs only 11.25 kg, meeting the requirements for rapid deployment. Furthermore, the prediction method of the ocean current velocity was optimized by employing the full-depth-averaged ocean current velocity instead of the depth-averaged ocean current velocity. To ensure continuous observation operations of the PUP within designated sea areas, a horizontal displacement correction strategy (HDCS) based on the virtual mooring concept is proposed. The effectiveness of the HDCS has been preliminarily validated through simulations and further confirmed through lake trials conducted in Qiandao Lake.

Dynamics Modeling and Analysis of an Underwater Glider with Dual-Eccentric Attitude Regulating Mechanism Using Dual Quaternions

The underwater glider has difficulty accessing the complex and narrow hadal trench for observation, which is affected by its limited regulation capability of pitch angle (−45°~45°). In this study, a compact attitude regulating mechanism is proposed to extend the regulation range of pitch angle from −90°to 90° and to install it on the hadal-class underwater glider Petrel-XPLUS. Subsequently, the dynamics model of Petrel-XPLUS is established using dual quaternions to solve the “gimbal lock” problem caused by the increased pitch angle range. Within the extended pitch range, the motion modes of the glider are enriched into long-range, virtual mooring, and Lagrangian float modes for long-range, small-area, and current-following observation missions, respectively, and are analyzed using the established dynamics model. Moreover, a ballast method was used to modify the pitch angle range and initial equilibrium state of a constructed underwater glider. Finally, Petrel-XPLUS achieved a pitch angle regulation range of −90°~90° in a water pool experiment and completed three consecutive profiles in a sea trial in the Challenger Deep, Mariana Trench, with all depths over 10,000 m, of which the maximum depth was 10,619 m. The proposed mechanism and methods can also be applied to other submersibles to facilitate ocean observations.

Between escape and return: Rethinking daily life and travel in selective unplugging

Selective unplugging refers to being partially connected or disconnected from information and communication technologies (ICTs) during travel. This study explores the processes of escape and return (i.e., linking with the everyday life domain) in selective unplugging and rethinks the relationship between daily life and travel. Based on the analysis of user-generated content and semi-structured interviews, findings show that: (1) tourists disconnect to reestablish the boundaries between daily life and travel blurred by ICTs; (2) tourists might reconnect to contact with the everyday environment driven by social obligations and inner needs; (3) even if the digital connection is cut off, tourists do not completely leave everyday life behind and would experience a special ideal home. Overall, the relationship between daily life and travel appears to show these two elements are interlaced. This study echoes the mobility turn and further discusses the dialectic of virtual mobility and virtual mooring.

Regional Ocean Current Field Construction based on an Empirical Bayesian Kriging Algorithm using Multiple Underwater Gliders

Zhang, R.; Yang, S.; Wang, Y., and Yin, Y., 2020. Regional ocean current field construction based on an empirical Bayesian kriging algorithm using multiple underwater gliders. In: Zheng, C.W.; Wang, Q.; Zhan, C., and Yang, S.B. (eds.), Air-Sea Interaction and Coastal Environments of the Maritime and Polar Silk Roads. Journal of Coastal Research, Special Issue No. 99, pp. 41-47. Coconut Creek (Florida), ISSN 0749-0208.The ocean current is an important component of the complex marine environment. Ocean current forecasting data mainly come from computational simulation, which merges satellite remote sensing data and in situ data measured from marine vehicles. Having a deep understanding of ocean currents is essential for ocean observation and path guidance of ships or other marine vehicles. In this paper, the regional depth-averaged flow is deduced according to the motion characteristics of underwater glider. Through virtual mooring observations of three underwater gliders in the northern South China Sea, sea trial data from June 25th to July 11th 2019 are obtained. After denoising and filtering, the depth-averaged flow data are used to construct the depth-averaged flow field with the spatial interpolation method. Then, the inverse distance weight (IDW) method, radial basis interpolation (RBI) method and empirical Bayesian kriging (EBK) method are adopted to construct the depth-averaged flow field. Thus, the results from the three constructed methods are compared with the real flow field data, demonstrating that the EBK method shows a better balance in interpolation accuracy and performance than the other methods. More specifically, for the EBK method, the mean error value is 0.00441, and the root-mean-square of error is 0.14977, which are lower than those of the other two methods. Furthermore, the evaluation results thoroughly verify the validity of the EBK method and prove that an underwater glider is a useful tool for observing ocean currents.

Adaptive robust sliding mode control of autonomous underwater glider with input constraints for persistent virtual mooring

Bottom-resting capability will enable an autonomous underwater glider (AUG) to perform long-duration virtual mooring. However, the tracking control of AUG soft landing on the seabed faces a number of challenges. It is crucial that the controller is able to incorporate many important factors, e.g., model uncertainty, environmental disturbances and limited dynamic range of actuators. This study first formulates the soft landing tracking control problem of AUG for persistent virtual mooring. An adaptive robust control scheme based on sliding mode control with a nonlinear disturbance observer is proposed that can effectively solve the challenges aroused by parametric uncertainty and unknown time-varying external disturbances. Moreover, the effect of input constraints of the AUG system is analyzed for the first time and is damped through a dynamic auxiliary compensator. Finally, simulation results demonstrate the superiority and inherent robustness of the proposed control scheme, in comparison with other techniques.

Development of Underwater Glider for Virtual Mooring that can be Used in Shallow Water

In recent years, predictions of environmental changes on Earth and studies of ecodevelopment have become increasingly important. Although oceanographic data in deep sea had attracted attention until now, these days, the importance of data in shallow water is increasing. Then, we aim at development of an underwater glider for virtual mooring that can be used in shallow water. In order to improve a motion control performance, a vertical tail wing and thruster are attached to the disk-type underwater glider already developed. In this paper, results of model tank test for motion control performance verification are shown.

Development of Underwater Shuttle Glider for Virtual Mooring

A prototype of a 3000m-class underwater glider for virtual mooring is being developed by JAMSTEC (Japan Agency for Marine-Earth Science and Technology) with RIAM (Research Institute for Applied Mechanics) of Kyushu University. The vehicle houses observation equipment and glides back and forth between the sea surface and the seabed collecting ocean data in a specific area (virtual mooring area). The motions of the vehicle are controlled by moving its center of gravity using mounted weight-shifters.

Dynamic modeling and three-dimensional motion simulation of a disk type underwater glider

Disk type underwater gliders are a new type of underwater gliders and they could glide in various directions by adjusting the internal structures, making a turnaround like conventional gliders unnecessary. This characteristic of disk type underwater gliders makes them have great potential application in virtual mooring. Considering dynamic models of conventional underwater gliders could not adequately satisfy the motion characteristic of disk type underwater gliders, a nonlinear dynamic model for the motion simulation of disk type underwater glider is developed in this paper. In the model, the effect of internal masses movement is taken into consideration and a viscous hydrodynamic calculation method satisfying the motion characteristic of disk type underwater gliders is proposed. Through simulating typical motions of a disk type underwater glider, the feasibility of the dynamic model is validated and the disk type underwater glider shows good maneuverability.

Planning and Control of Marine Floats in the Presence of Dynamic, Uncertain Currents

We address the control of a vertically profiling float using ocean-model-based predictions of future currents. While these problems are in reality continuous control problems, we solve them by searching a discrete space of future actions. Additionally, while the environment is a continuous space, the ocean model we use is a discrete cell-based model. We show that even with an imperfect model of ocean currents, planning in the ocean current model can significantly improve results for a specific problem of controlling a vertically profiling float when a trade-off between remaining at the same location as a virtual mooring and collecting more data with more profiles is available. We also present anecdotal data from an April 2015 deployment of EM-APEX floats.

Virtual Mooring Buoy “ABA” for Multiple Autonomous Underwater Vehicles Operation

[abstFig src='/00280001/09.jpg' width=""300"" text='Virtual Mooring Buoy ""ABA""' ]We developed a virtual mooring buoy, called an autonomous buoy “ABA” for AUV, which navigates the sea using thrusters in 2014. Its purpose was to deploy autonomous underwater vehicles (AUVs) effectively in seafloor exploration. The ABA tracks and positions AUVs operating underwater using onboard acoustic positioning. We have deployed the ABA with two type AUVs in seafloor exploration. That conducted in February 2015 used the ABA with one AUV to survey and inventory mineral deposits, demonstrating the ABA’s capability of positioning an AUV navigating at 1,370–1,550 m depths at a standard deviation of 100 m or less and tracking it while maintaining a horizontal distance of 50 m or less. The ABA navigated the AUV within a position error of about 10 m.

バーチャルモアリング用円盤型水中グライダーの開発

In recent years it has become evident that ocean data in time and space is required to make predictions of environmental changes on earth. As one method of acquiring data, we propose a virtual mooring system using an underwater glider, and have developed a prototype vehicle called “BOOMERANG” which can glide back and forth between the sea surface and the seabed collecting ocean data. In order to carry out oceanographic observations, the performance of the vehicle was re-improved. This paper presents details of re-modifications of the vehicle, and oceanographic observations carried out at the west sea-area of the Goto islands in Nagasaki Prefecture and in the East China Sea.

バーチャルモアリング用シャトル型水中グライダーの開発

A prototype of a 3000m-class underwater shuttle glider for virtual mooring is being developed by JAMSTEC (Japan Agency for Marine-Earth Science and Technology) with RIAM (Research Institute for Applied Mechanics) of Kyushu University. The vehicle houses an observation equipment and glides back and forth between the sea surface and the seabed collecting ocean data in a specific area (virtual mooring area). In this paper simulated results of the gliding are compared with the field experimental results, and the accuracy of the motion simulator is discussed.

バーチャルモアリング用シャトルグライダー「ツクヨミ」の開発

A prototype of a 3000m-class underwater glider for virtual mooring is being developed by JAMSTEC (Japan Agency for Marine-Earth Science and Technology) with RIAM (Research Institute for Applied Mechanics) of Kyushu University. The vehicle houses an observation equipment and glides back and forth between the sea surface and the seabed collecting ocean data in a specific area (virtual mooring area) for more than one year. This paper summarizes our restudy on the hydrodynamic coefficients of the vehicle by constant acceleration tests and the simulated results of gliding angle control are compared with the experimental results carried out in a towing tank.

The Social Affordances of Flashpacking: Exploring the Mobility Nexus of Travel and Communication

The proliferation of digital devices and online social media and networking technologies has altered the backpacking landscape in recent years. Thanks to the ready availability of online communication, travelers are now able to stay in continuous touch with friends, family and other travelers while on the move. This paper introduces the practice of ‘flashpacking’ to describe this emerging trend and interrogates the patterns of connection and disconnection that become possible as corporeal travel and social technologies converge. Drawing on the concepts of ‘assemblages’ and ‘affordances,’ we outline several aspects of this new sociality: virtual mooring, following, collaborating, and (dis)connecting. The conclusion situates this discussion alongside broader questions about the shifting nature of social life in an increasingly mobile and mediated world and suggests directions for future research at the intersection of tourism and technology.

Hydrodynamic Coefficients and Motion Simulations of Underwater Glider for Virtual Mooring

We are now developing a prototype of a 3000-m class underwater glider for virtual mooring. The vehicle glides back and forth between the sea surface and the seabed collecting ocean data at a specific point. Hydrodynamic forces acting on the half-size model were measured to determine the optimal wing shape. Next, to obtain the dynamical-hydrodynamic coefficients, forced oscillation tests were carried out using the optimally shaped model. Finally, the motions of the glider were simulated using the hydrodynamic coefficients obtained from these model experiments. The experimental and calculated results are shown in this paper.

バーチャルモアリング用シャトルグライダー「ツクヨミ」の開発

A prototype of a 3000m-class underwater glider for virtual mooring is being developed by JAMSTEC (Japan Agency for Marine-Earth Science and Technology) with RIAM (Research Institute for Applied Mechanics) of Kyushu University. The vehicle houses an observation equipment and glides back and forth between the sea surface and the seabed collecting ocean data in a specific area (virtual mooring area) for more than one year.This paper summarizes the design concept and an outline of the glider and shows the results of the gliding tests in a towing tank.

バーチャルモアリング用円盤型水中グライダーの開発

In recent years it has become evident that ocean data in time and space is required to make predictions of environmental changes on earth. As one method of acquiring data, we propose a virtual mooring system using an underwater vehicle, and have developed a test-bed vehicle called "BOOMERANG" which can glide back and forth between the sea surface and the seabed collecting ocean data.Since the results of field experiment in March 2010 were satisfactory, construction on a prototype vehicle for practical use was begun in April 2010. In order to improve reliability and to enable prolonged use, the performance of various pieces of loading pparatus of the vehicle was improved. This paper presents details of the construction of the prototype vehicle for practical use and results of the field experiment.

バーチャルモアリング用円盤型水中グライダーの開発 ‐その２ 実証機の建造と実海域試験‐

An underwater vehicle for virtual mooring was constructed at the Research Institute for Applied Mechanics (RIAM), Kyushu University. The disk type vehicle that houses various pieces of observation equipment glides back and forth between the sea surface and the seabed collecting ocean data. If the position is outside the sea area of virtual mooring because of currents etc., the vehicle is controlled so that it returns the previous area during its next dive. Horizontal movement of the vehicle is done with gliding and without thrusters. The gliding ratio and the course of the vehicle are controlled by moving the position of the built-in weight.This paper presents the developed test-bed vehicle and its field experiment.

バーチャルモアリング用円盤型水中グライダーの開発

In recent years, predictions of changes in the environment on earth and studies on ecodevelopment have become important. For this research on going ocean data in time and space is required, and has been obtainable using by mooring systems. However, a conventional mooring system can observe only discrete data in perpendicular space and moreover, construction of such a system requires a manpower and great expense.To solve this problem, an underwater vehicle for virtual mooring is developing at Research Institute for Applied Mechanics (RIAM). This paper describes the testbed vehicle "LUNA" that was designed to develop a virtual mooring system, and the control algorithm is discussed.