• Document: Dynamics modeling of a semi-submersible autonomous underwater vehicle with a towfish towed by a cable
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Int. J. Nav. Archit. Ocean Eng. (2015) 7:409~425 http://dx.doi.org/10.1515/ijnaoe-2015-0029 ⓒ SNAK, 2015 pISSN: 2092-6782, eISSN: 2092-6790 Dynamics modeling of a semi-submersible autonomous underwater vehicle with a towfish towed by a cable Jinmo Park and Nakwan Kim Department of Naval Architecture and Ocean Engineering, Seoul National University ABSTRACT: In this paper, we employ a dynamics modeling method for investigating a multi-body dynamics system of semi-submersible autonomous underwater vehicles consisting of a towing vehicle operated near the water surface, a tow cable, and a towfish. The towfish, which is towed by a marine cable for the purposes of exploration or mine hunting, is modeled with a Six-Degree-of-Freedom (6-DOF) equation of motion that reflects its hydrodynamics characteristics. The towing cable, which can experience large displacements and deformations, is modeled using an absolute nodal coordinate formulation. To reflect the hydrodynamic characteristics of the cable during motion, the hydrodynamic force due to added mass and the drag force are imposed. To verify the completeness of the modeling, a few simple numerical simulations were conducted, and the results confirm the physical plausibility of the model. KEY WORDS: Absolute nodal coordinate formulation; Flexible cable dynamics; Multi-body dynamics; Large deforma- tion; Semi-submersible AUV; Towed system. INTORODUCTION Because the need for subsea exploration for discovery of subsea resources and for military purposes such as mine hunting is increasing, studies of marine cable motion and the use of towfish have been performed by many researchers. Most previous stu- dies on these subjects were focused on a system that consisted of a surface vessel, a marine cable, and a towfish (Grosenbaugh, 2007; Huang, 1994; Park et al., 2003; Vaz and Patel, 1995). Because a marine cable exhibits highly nonlinear characteristics under water, analysis of marine cable dynamics has typically relied on numerical methods. In addition, the highly nonlinear motion of a marine cable can cause coupled motion of the towfish, add to the towfish’s own nonlinear motion. A few studies have examined ways to control the motion of towfish, using devices such as a nonlinear adaptive controller (Curado et al., 2010). For analysis of the motion of marine cables, the lumped mass approximation method (Buckham et al., 2003; Kamman and Nguyen, 1990; Kamman and Huston, 2001) and classical cable theory based on the finite element method (Park et al., 2003; Wu and Chwang, 2001; Yuan et al., 2013) have usually been employed. The lumped mass approximation method assumes that the mass is concentrated at a nodal point and that the cable segment is a bar element. The great advantage of this method is its ease of implementation. The disadvantage of this method is that it cannot take into consideration bending deformation of the cable element. To address this limitation of the lumped mass approximation method, classical cable theory based on the finite element method can be applied. This approach can reveal a cable during motion. However, this approach requires dividing the cable into many segments to obtain accurate simulation result (Park et al., 2003). Another method for modeling cable dynamics Corresponding author: Nakwan Kim, e-mail: nwkim@snu.ac.kr This is an Open-Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. Unauthenticated Download Date | 6/30/17 2:40 PM 410 Int. J. Nav. Archit. Ocean Eng. (2015) 7:409~425 is the Absolute Nodal Coordinate Formulation (ANCF) method (Berzeri and Shabana, 2000; Gerstmayr and Shabana, 2006; Gerstmayr et al., 2013; Shabana and Yakoub, 2001; Shabana et al., 1998). Only a few studies have applied this method to the analysis of underwater cable dynamics (Kim et al., 2012; Takehara et al., 2011). This method was first proposed by Shabana et al (1998) and has since been developed further by other researchers (Yakoub and Shabana, 1999; 2001). The great advantage of the ANCF method is that it uses a constant mass matrix in the equation formulation. Furthermore, it can produce accurate results with fewer cable segments than can be produced using classical cable theory (Berzeri and Shabana, 2000). However, in

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