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Location : Centre for Marine Science and Technology, Curtin University of Technology
Results 1 - 5 of 9
A combined strip theory and Smoothed Particle Hydrodynamics approach for estimating slamming loads on a ship in head seas
Smoothed Particle Hydrodynamics (SPH) is a mesh-free Lagrangian numerical method suited to modelling fluids with a freely deforming surface. A two-dimensional SPH algorithm has been developed and applied to the problem of ship keel and bow-flare slamming. Freely decelerating drop tests of a model flared hull section were used as a basis for an initial validation of the SPH model. Relative vertical velocity profiles measured during tow tank experiments were then imposed on two-dimensional SPH models and reasonable agreement between the experimental and numerical slamming pressures was found. Finally, relative vertical velocity profiles calculated using SEAWAY software were implemented in the SPH algorithm, so as to simulate slamming on a typical V-form hull model.
A 2D Smoothed Particle Hydrodynamics Theory for Calculating Slamming Loads on Ship Hull Sections
Current methods for assessing slamming of ships in head seas are generally based on constant-velocity wedge impact results for each hull section. A 2D Smoothed Particle Hydrodynamics (SPH) method is described for calculating slamming loads on realistic hull section shapes and impact velocity profiles. SPH is a particle-based method that is mesh-free and is therefore able to accurately simulate large free surface deformations such as jets and splashes, which are an important factor in slamming events. It is shown that large slamming pressures are predicted on wedge shaped hull sections and the concave part of flared monohull sections. Similarly, cross-deck slamming of catam aran hulls can produce large slamming pressures at the top of the arches. The nature of relative vertical velocity profiles during slam events is also discussed. Hull sections with varying velocity profiles are modelled using SPH to show the effect on slamming pressures as compared to the commonly used constant velocity profile.
Aero-Hydrodynamics of an RS:X Olympic Racing Sailboard
The RS:X Olympic sailboard is an all-round board designed to be raced in 4 to 25 knots of wind, and is an example of the current state-of-the-art in sailboard design. This board has been chosen as the specific example for an overview of sailboard aero-hydrodynamics. The current article brings together previous research on sailboard sail and fin lift, and applies it to the case of the RS:X sailboard. Measured sail camber and twist, as well as mast stiffness and deflection, are described for realistic upwind racing settings. The three-dimensional force and moment balance of an RS:X sailing upwind is investigated, in order to determine the limits on righting moment, sail lift and fin lift for different wind strengths. Finally a planing analysis is performed on the RS:X sailboard to calculate trim, wetted length and resistance.
Have you ever wondered how accurate the section of a keel or rudder has to be? I have, so I did some background reading to find out. It all started a couple of years ago when my 10 m sailing yacht showed a tendency to turn to port and had an appalling tacking angle of nearly 100 degrees. That’s the subject of a long and slightly different story — suffice to say that I had narrowed it down to a hydrodynamic cause. So I set to making templates for the fin keel and spade rudder to rectify the problem. Before doing this I had to satisfy myself that I could fair the keel to the required accuracy, which begs the question: what is the required accuracy? I am not talking about surface roughness (that is a well-understood effect), but larger-scale undulations — waviness, lumps and hollows.
A Smoothed Particle Hydrodynamics Study of Ship Bow Slamming in Ocean Waves
Smoothed Particle Hydrodynamics (SPH) is a mesh-free Lagrangian computational method suited to modelling fluids with a freely deforming surface. This thesis describes the development, validation and application of a two-dimensional Smoothed Particle Hydrodynamics algorithm to the problem of ship bow slamming in regular ocean waves. Slam events often occur in rough seas and have the potential to cause significant structural and payload damage due to the loads and subsequent whipping experienced by the ship. SPH is well suited to modelling ship bow slamming because the interaction between the bow of the ship and the water surface is of a freely deforming transient nature. The developed SPH algorithm was subjected to an extensive validation using both analytical and experimental data as a basis for comparison. The influence of each numerical correction – necessary for SPH stability – was evaluated using two theoretical problems free from the influence of external forces: the evolution of initially circular and square patches of fluid. Solid boundaries treated by the ghost particle technique were introduced and evaluated by way of the hydrostatic tank and the two-dimensional dam break. Still water impacts of two-dimensional wedges and hull cross-sections were simulated using the SPH algorithm and the results were compared with the experimental data of Aarsnes (1996), Whelan (2004) and Breder (2005). The complexity of the slamming problem was then increased by imposing the relative vertical velocity profile (between the hull and the water surface) measured during the ocean wave basin experiments of Hermundstad and Moan (2005) on a hull cross-section. Reasonable agreement between the simulated and experimental slamming pressures confirmed that the two-dimensional SPH algorithm could be applied to a three-dimensional problem through the use of a relative vertical velocity profile. Finally, the commercial ship motion prediction software SEAWAY and the validated SPH algorithm were combined in a 2D + t method to simulate bow slamming of a slender hull. The relative motion between the bow and the free water surface was extracted from the ship motion data and then imposed on a cross-section of a given hull form. Satisfactory agreement with the peak pressures measured on a model V-form hull in regular waves (Ochi, 1958) demonstrated that the developed two-dimensional SPH code is capable of modelling three-dimensional ship bow slamming.
