International Shipbuilding Progress - Volume 50, issue 3

Authors: Garme, K. | Rosén, A.

Article Type: Research Article

Abstract: A time-domain simulation model for prediction of global response of planing craft in waves is presented. The simulation model is based on 2-dimensional potential theory, and by updating the hydrodynamic coefficients at each time step, taking the momentary section draught into account, the solution is non-linear. For evaluation captive model tests and full-scale trials that have been performed. Characteristic results from the full-scale trials are reviewed and discussed. The simulations are also validated with …published model experiments. The agreement between simulations and experiments is generally good except for discrepancies in pitch moment and motion. The 2-dimensional approach is attractive from a computational cost point of view and it is believed that an adequate simulation model could be developed from the presented model by better modelling of the pressure at transom. Show more

Citation: International Shipbuilding Progress, vol. 50, no. 3, pp. 177-208, 2003

Authors: Sharma, R. | Sha, O.P.

Article Type: Research Article

Abstract: Surface discretization is an essential part of any analytical tool for effective and accurate geometric representation. Triangular element generation is important because it allows topological simplicity, which enables local mesh adaptivity, and it also provides a unique informative database. Most of the existing techniques deal with generation of flat rectangular or triangular elements, using tessellation over Bspline or NURBS surfaces defined over a rectangular domain, and thus may suffer from geometric and topological …inconsistencies in the case of triangular domains. This work explores the possibility of the application of surface discretization that deals with topologically continuous, smooth and fair triangular elements using piecewise polynomial parametric surfaces which interpolate prescribed R^3 scattered data using spaces of parametric splines defined on R^2 triangulations in the case of ship surfaces. The method is based upon minimizing a certain physics based natural energy expression (i.e. as a fairness norm) over the parametric surface. As for topological continuities between two triangular patches, C^0 or C^1 continuity or both have been imposed as required. Approximate C^2 continuity can also be achieved with the addition of a penalty term, and this has also been considered as a smoothness norm. The geometry is defined as a set of stitched triangles prior to the triangular element generation, and it's selection is based upon the distribution of aspect ratio of the triangular domain over the complete point set, and also the flatness of the geometry. The surface discretization is analyzed using intersection curves with three-dimensional planes for topological continuity, smoothness and fairness. The problems involving triangular element generation for ship surfaces with single or hybrid continuities have been considered. Show more

Keywords: Cubic rational triangular patches, cubic spline, minimal energy surfaces, parametric splines, surface discretization

Citation: International Shipbuilding Progress, vol. 50, no. 3, pp. 209-237, 2003

Authors: Koelman, Herbert J. | Pinkster, Jakob

Article Type: Research Article

Abstract: An introduction is given concerning the probabilistic damage stability method as presently used in daily shipbuilding practice. In this respect some problem areas are described which may lead to difficulties in applying the method, both in actual point design and in design optimisation. These problem areas primarily relate to the bookkeeping at multicompartment damages in combination with both longitudinal and horizontal subdivision (i.e. limited penetration problem). Secondly, ambiguities that arise through naming …conventions are discussed. After a detailed description and analysis of these problems, suggestions are formulated regarding possible solutions. In case where a real solution is lacking, workarounds are put forward as being (for the time being) makeshifts. These solutions or workarounds fully fit within the theoretical background of the present regulations as laid down in the SOLAS convention; they affect mainly interpretations and definitions. Numerical examples applied to two existing new building container vessels are given and the results using the conventional method are compared with those using the various proposed solutions. In these examples it appears that the sum of all probabilities of damage do not tend to reach to the expected value of unity, a phenomenon which indicates a theoretically incorrect behaviour. Finally, conclusions are made regarding these results and recommendations related to the probabilistic damage stability calculation method and statistical approach used therein are made. Furthermore a possible method is brought forward that may be used in combination with tools for optimisation of the subdivision of a newbuilding design with respect to probabilistic damage stability characteristics. Show more

Keywords: damage stability, probabilistic

Citation: International Shipbuilding Progress, vol. 50, no. 3, pp. 239-253, 2003

Authors: Li, Tingqiu

Article Type: Research Article

Abstract: This paper outlines the effects of grid refinements and turbulence models on shipgenerated waves in modelling of turbulent free-surface flows around modern transom stern ships. The computation is performed in a numerical water tank based on the FINFLO-RANS code developed at Helsinki University of Technology. Using a moving mesh, a free surface can be tracked, in which the free-surface boundary conditions are given on the actual location of the free surface. A cell-centered finitevolume multigrid scheme …is implemented. Three grid levels with a grid refinement ratio of 2 are constructed. Two turbulence models, such as Baldwin-Lomax's model and Chien's low Reynolds number k-ε model, are selected. Test case is the KCS model from the KRISO container ship (Korea). This is one of three benchmark test cases recommended by the Gothenburg 2000 Workshop in ship hydrodynamics on CFD. The calculated results are presented in terms of ship resistance, wave patterns, and turbulent flow. Furthermore, the convergence performances at the different grids are studied, and the influences of the grid density and turbulence models on the wave systems of a ship are discussed. Show more

Citation: International Shipbuilding Progress, vol. 50, no. 3, pp. 255-272, 2003