Dynamics of Remotely Operated Underwater Vehicle Systems
MetadataShow full item record
- Institutt for marin teknikk 
The dynamics of typical remotely operated vehicle (ROV) systems are considered, and the subject is divided into three topics. Topic 1 considers the dynamics of single-body and multi-body ROVs, topic 2 considers the dynamics of ROV-cable systems, and topic 3 considers the dynamics of the manipulators used by the ROVs to perform intervention work. By combining the three topics, a complete representation of the ROV system dynamics is obtained. In topic 1, the problem of modeling the ROV hydrodynamic properties is investigated. A novel methodology to estimate the most important hydrodynamic forces and moments acting on the ROV is developed. The methodology is verified numerically against numerical results obtained using boundary element method (BEM) and computational fluid dynamics (CFD) software and experimentally by a simple procedure performed using a planar motion mechanism (PMM). The results show that despite the simple nature of the methodology, the hydrodynamic forces and moments can be estimated with accuracy equivalent to that of advanced numerical solvers (CFD). The methodology therefore presents a practical and accurate approach for estimating the hydrodynamic forces and moments using basic properties of the vehicle. The methodology is then extended to multi-body ROV systems consisting of two or more ROVs operating under kinematic constraints. The multi-body formulation utilizes the Udwadia-Kalaba formulation to represent the constraints between the ROVs, and the single-vehicle dynamics of each ROV are estimated based on the proposed methodology. The multi-body formulation is tested experimentally and is shown to be able to capture the most important dynamic effects related to the ROV-system response. Topic 2 considers the dynamic response of the ROV and cable system. The cable connecting the ROV to the surface ship produces significant forces and moments on the ROV and can dominate the overall response of the system. Therefore, accurate knowledge of how the cable behaves and how this behavior impacts and is impacted by the ROV is crucial. A novel ROV-cable model is presented and tested both numerically and experimentally. The model has the benefit of being applicable to a wide range of ROV systems and scenarios and is therefore not limited by constraints typically found in ROV-cable models. From the numerical studies performed using the presented model, it is observed that cable forces are significant even for short cables and limited environmental disturbances and that cable forces quickly become critical as the cable length and magnitude of the environmental disturbances increases. When compared with experimental results obtained in laboratory tests, it is observed that the presented model is able to capture the most important characteristics of the cable. The model is furthermore applied in two different applications demonstrating the versatility and the potential for use in practical applications. The model is used as a state observer for the response of a tether management system (TMS) and shows that by using basic measurements from the surface ship, it can simulate the TMS response accurately. Furthermore, a novel methodology for cable selection considerations is presented. By analyzing the electrical and mechanical properties of typical underwater cables, a systematic approach for determining which cable to use for a given system is developed. In this methodology, the mechanical considerations are based on results obtained from the presented cable model, hence showing another potential for use in practical applications. As no standards for selection of cables used on underwater vehicles are available today, the presented methodology represents a novel framework for cable selection. Topic 3 considers the dynamics of manipulators mounted on ROVs. Manipulators are the hands of the ROV and are therefore a critical component as they perform the majority of intervention tasks required by the ROV and as the industry shifts toward autonomous operations, the need for the development of tools and equipment that can facilitate this shift is crucial. A novel design of a fully electric underwater manipulator for use on observation-class ROVs is presented. The manipulator solves several existing problems regarding small-scale underwater electric manipulators, such as weight, torque, control, and cost. Experimental functionality testing of the manipulator is performed and proves that the novel design can be used on small ROV systems both for commercial and recreational use. A dynamic model for the underwater manipulator is furthermore presented. The model is tested experimentally using the presented manipulator and the results show that the model is able to capture the most important characteristics of the manipulator accurately. The results also show that the modeling of the hydrodynamic forces (added mass and drag) have equivalent accuracy to that of the rigid body forces (inertia and gravity) and friction. Overall topics 1 to 3 cover the most important elements for modeling the dynamics of ROV systems. The presented methods, models, and designs have been extensively tested both experimentally and numerically and it has been proven that they are able to capture the most important dynamics related to an ROV system. The work therefore presents a complete framework for modeling the dynamics of remotely operated underwater vehicle systems.