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Title CFD analysis of stepped planing vessels
URL
Publication Date
Discipline/Department Mechanics
University/Publisher KTH
Abstract High speed planing hulls are currently widely used for example in recreational and emergency vessel applications. However, very little CFD research has been done for planing vessels, especially for those with stepped hulls. A validated CFD method for planing stepped hulls could be a valuable improvement for the design phase of such hulls. In this thesis, a CFD method for stepped hulls, with a primary focus on two-step hulls, is developed using STAR-CCM+. As a secondary objective, porpoising instability of two-step hulls is investigated. The simulations are divided into two parts: In the first part a method is developed and validated with existing experimental and numerical data for a simple model scale planing hull with one step. In the second part the method is applied for two two-step hulls provided with Hydrolift AS. A maximum two degrees of freedom, trim and heave, are used, as well as RANS based k-w SST turbulence model and Volume of Fluid (VOF) as a free surface model. The results for the one-step hull mostly corresponded well with the validation data. For the two-step hulls, validation data did not exists and they were first simulated with a fixed trim and sinkage and compered between each other. In the simulations with free trim and heave both hulls experienced unstable porpoising behavior.
Subjects/Keywords Computational Fluid Dynamics (CFD); Ship hydrodynamics; Planing hull; Stepped hull; STAR-CCM+; Overset mesh; Volume of fluid (VOF); Reynolds averaged Navier-Stokes equations (RANS); Dynamic instabilities; Engineering and Technology; Teknik och teknologier
Language en
Country of Publication se
Record ID oai:DiVA.org:kth-250023
Repository diva
Date Indexed 2020-01-03

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…Blount and Codega [1] from 1992 focuses on the instability issues of planing hulls. Furthermore, a thesis by Mancini [2] gives an introduction to the common problems faced when simulating planing hulls numerically. Planing hull

…addition, it is investigated if capturing the porpoising instability of a two-step hull is possible. The long term goal would be to develop a simplified CFD method for investigating the stability and performance of a stepped planing hull. STAR-CCM+ is a…

…of local low pressure areas more than less curved buttocks when the pressure distribution on the hull changes for example due to a change in trim or heel angle. Therefore, planing hulls have relatively straight buttock lines aft of the bow. Flow…

…separation at the transom and along the sides of a planing hull is important in order to avoid low pressures. This is achieved by using a hard chine. [1] [5] A study which includes several full-scale tests performed by Codega and Lewis…

…Spray rails and steps are common modifications used in planing hulls to increase the lift and reduce the friction on the hull. A planing vessel is mostly supported by the lift generated by hydrodynamic forces. Therefore, a flat bottom hull with zero…

…forces on the hull. More about numerical ventilation later in section 3.6. [2] Stepped hull simulations lack validated guidelines and recommendations. The setup for basic planing hulls developed by David Frisk and Linda Tegehall in their…

…flows, such as those around a planing hull, the boundary layer is turbulent. Resolving or modelling a turbulent boundary layer accurately is often essential due to larger shear stresses on the wall than when dealing with laminar boundary layers. [12…

…stable at low speeds might suddenly experience unstable motions when the speed is increased. These motions are called dynamic instabilities and they occur at high speeds when the vessel is planing. In the worst case dynamic instabilities might lead to…

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