Effects of the terms associated with ϕzz in free surface condition on the attitudes and resistance of different ships

Abstract

Citation: Li, Y., Gong, J., Ma, Q. ORCID: 0000-0001-5579-6454 and Yan, S. ORCID: 0000-0001- 8968-6616 (2018). Effects of the terms associated with phi(zz) in free surface condition on the attitudes and resistance of different ships. Engineering Analysis with Boundary Elements, 95, pp. 266-285. Abstract:One of approaches for numerical simulation of a ship moving in a still water is based on the composition of double-body flow and wavy flow solved by a boundary element method. There are several terms related to the second order derivative ( of double-body flow velocity potential with respect to the vertical coordinate in the free surface conditions. Understanding of the effects of the terms is very limited so far. In many cases, they are just ignored even for ships with a high forward speed, particularly in the cases associated with multihull ships, for which no investigations on their effects have been found. This paper will present a study on the effects of the terms on the numerical prediction of the attitudes and resistance of different ships in various situations, including monohull, catamaran and trimaran with different parameters and at different Froude numbers. The results will demonstrate that the effects of the terms are significant in many cases and that considering this term may lead to the results similar to those obtained by fully nonlinear models at high Froude numbers.

A new phenomenon in interference effect on catamaran dynamic response

“…The reasons behind this selection for the range of separation ratios were covering that of previous research into interference effects as well as some considerations in experiments. For instance, Zaghi, Broglia and Di Mascio [25] chose separation ratios between the two extremes of 0.167 and 0.3 whereas in some other cases separation ratios s/L of 0.226-0.470 [26], 0.15-0.81 [18], 0.2-0.5 [38], 0.2-1.0 [19,31], 0.12-0.39 [21], 0.2-0.4 [23], 0.17-0.23 [32], 0.2-0.8 [62], 0.2-0.5 [63], 0.2-0.4 [34], 0.226-0.4696 [28], 0.2-0.6 [29], and 0.09-0.5 [36] were investigated.…”

“…Or even when there is a relative motion between two neighboring bodies, the slower one experiences stronger hydrodynamic loads as well as greater trim and sinkage due to the interaction [35]. In order to better capture the variations of trim and sinkage due to interference effect, Li, Gong, Ma and Yan [36] developed a fully nonlinear model of free surface based on boundary element method. Their findings showed that the smaller the separation ratio is, the more pronounced is the nonlinearity of the free surface.…”

A Potential Flow Theory and Boundary Layer Theory Based Hybrid Method for Waterjet Propulsion

“…The numerical research of hydrodynamics of marine structures mainly adopts the potential flow CFD [16,17] and the viscous flow CFD method [18], which captures more details of the flow field. However, the computational efficiency of viscous flow CFD still needs to be improved, and a rapid thrust prediction method is required in the preliminary design stage for the waterjet ship.…”