Comparative study of slamming loads on cylindrical structures
Vepa, K.S.; Van Nuffel, D.; Van Paepegem, W.; Degroote, J.; Vierendeels, J. (2011). Comparative study of slamming loads on cylindrical structures, in: OMAE2011: Proceedings of the ASME 30th international conference on ocean, offshore and arctic engineering, Volume 7: CFD and VIV; Offshore Geotechnics. pp. 279-286. http://dx.doi.org/10.1115/OMAE2011-49408
In: (2011). OMAE2011: Proceedings of the ASME 30th international conference on ocean, offshore and arctic engineering, Volume 7: CFD and VIV; Offshore Geotechnics. ASME: Rotterdam. ISBN 978-0-7918-4439-7.
Wave impact or slamming is a phenomenon characterized by large local pressures (10 bar or more) for very short durations (order of milliseconds). Slamming loads can cause severe damage to the structure [1]. Different numerical approximation methods are available for simulating the fluid structure interaction problems. Traditional mesh techniques use nodes and elements for approximating the continuum equations whereas particle methods like smoothed particle hydrodynamics (SPH) approximates the continuum equations using the kernel approximation technique and hence can be used for a wide range of fluid dynamics problems [2]. Since composite materials are finding increased application in the ship building industry because of their low weight and high strength properties, it is important to understand the effect of slamming loads on composite structures [3]. Normally, composite structures are made quasi-rigid to resist slamming loads, but inducing some deformability helps in reducing the incident pressures and at the same time reduces the overall weight of the structure and in turn the material cost. On the other side, inducing deformability effects the durability of the structure. In this paper, the effect of slamming on two-dimensional cylindrical structures is studied using three solvers i.e., 1) SPH solver, 2) Explicit solver and 3) Implicit solver. In the case of SPH solver, water is modelled using SPH particles and cylinder is modelled using finite elements (FE), in this case shell elements. A coupling between the SPH and FE solvers is made to simulate the fluid-structure interactions. Contact is modelled using the contact algorithms. In the case of the explicit solver, water is modelled using hexahedron or brick elements with one element in the thickness direction since symmetry is applicable along the thickness of the cylinder. Shell elements are used for modelling the cylinder and contact is handled using node to surface contact algorithm. In the case of the implicit solver, water is represented by pure two-dimensional elements. Quadratic elements are used to represent the continuum around the cylinder and triangular elements are used to represent the far off field and also to control the mesh movement. Line elements are used to represent the cylinder in this case. Two models are tested in all the three solvers: 1) rigid cylinder and 2) deformable cylinder. A comparative study of these three solvers shows that the implicit solver needed more calculation time compared to other solvers. The SPH method required less particles than the number of nodes in the other two methods to converge on the peak pressure. All three solvers show reduction of peak pressure in case of the deformable cylinder.
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