The scope of the present study is to investigate the effects of various geometrical hull features, such as tunnels, spray rails and whiskers on the hydrodynamic performance of a high-speed planing hull. The criteria being tested to emphasize the boat performance are the total drag, sinkage and trim angle. In addition, the decomposition of the resistance into viscous and wave-making resistance are taken into consideration. The study starts with a validation test against experimental data in order to accentuate the capability of the Computational Fluid Dynamics CFD simulation to accurately predict the total drag and trim angle of the initial form. This is later followed by a verification study based on the Richardson Extrapolation method with a grid- and time-step-convergence test in order to predict the numerical errors during the simulation. After establishing the simulation parameters regarding the proper grid size and time step, the comparative study takes place for five hull shapes and two whisker configurations while the boat is sailing at eight different speeds. The assessment of the hydrodynamic flow parameters is evaluated compared to the initial form in order to investigate the influence of the geometry change on the hydrodynamic performances of the boat. Validation of the numerical results showed the reliability of the CFD simulation to accurately predict the drag and trim angle of the boat, while the comparative study revealed that the total drag can be reduced by up to 9%, especially at higher speeds.
In the last decade, the main concerns of the maritime industry are the reduction of fuel and carbon emissions. IMO (International Maritime Organization) has introduced relevant conventions and improvements in fuel economy standards for ships. Thus, different research projects have been developed to improve the energy efficiency of ships, reducing fuel consumption and carbon dioxide emissions. The flow around the catamarans is a complex hydrodynamic phenomenon due to the interference effects that occur on the free surface between the bodies of the catamaran. The flow around the ship hull has a wide variety of physical fenomena, many of which are relevant for the study of resistance. The two important aspects of the interference effects associated with the catamarans with direct influence on the hydrodynamic performances are: the viscous interference due to the asymmetric flow around the bodies with direct effect on the development of the boundary layer and the wave interference generated at the free surface from the interactions between the wave systems generated by each hull. First set of towing tank tests have been performed to evaluate the ship resistance of the catamaran hull, interference between wave system of the hulls and to analyse the hydrodynamic parameters of the flow. To evaluate the effect of the central bulb positioned between the hull bodies on the ship resistance, six different sets of experiments were carried out for seven speeds corresponding to Froude numbers between 0.20 and 0.80. Six different configurations of the bulb considering three different depth and two position along the hull (bow and stern) have been considered. The calculations revealed that residual resistance can be reduced by using a central bulb between the catamaran hulls by up to 10%. This happens when the bulb is positioned at the bow and the stern and for Froude numbers 0.4-0.6.
The purpose of this study was to determine the total resistance and investigate the flow around a full-scale kayak. Utilizing Computational Fluid Dynamics(CFD), it was deter-mined how the presence of a rudder affects the kayak hydrodynamic performance. To an-alyse the flow, computational fluid dynamics based on the RANS-VOF solver was em-ployed. The fluid volume approach and the k-ω turbulence model were used in two-phase steady flow simulations around the kayak hulls.
The availability of the robust commercial computational fluid dynamics (CFD) software and the increasing power of high-performance computers (HPC) boosts the use of CFD techniques for numerical investigations of ship hydrodynamimcs performaces. Nowadays, CFD tools provide a rather accurate solution for complex physical phenomena, such as wave braking, turbulence, flow detachment and overturning. Consequently, the ability to capture this fenomena allows a detailed insight into the flow mechanism that trigger and sustain them. The paper focuses on a numerical investigation of flow around hull a fully appended ONR Tumblehome model 5613. Due to special operation conditions, naval ships are equipted with a large number of appendages such as sonar domes, brackets, twin propeller shafts and twin rudders. Position and alignment of these appendages are essential in order to avoid the increased resistance, decreased propulsive efficiency and cavitation. NUMECA/FineMarine commercial code has been used to evaluate the flow field around ONRT (Office of Naval Research Tumblehome) hull and to estimate the effect of the appendages on ship hydrodynamics performances. Comparison with experimental towing tank results showed good agreement with a difference of up to 2%.
Traditionally, ship hydrodynamic performances are predicted by extrapolating the model scale measurements or numerical results to full scale. Recently, scientific publications have highlighted the importance of ship scale numerical simulation and its validation. CFD may be used to determine the main reasons for the poor performance of vessels in operation and to evaluate the efficiency of energy-saving solutions that enhance the vessel's hydrodynamics and aerodynamics. Lloyd’s Register (LR) held the world's first workshop dedicated to ship full-scale hydrodynamic performance predictions, where the industry has published comprehensive measurements obtained during the sea trials to offer the community the chance to validate the CFD solvers for full-scale computations. This paper focuses on the numerical investigation of the full-scale general cargo vessel REGAL. NUMECA/Fine Marine commercial code based on the RANS-VOF solver has been used to evaluate the flow field around the hull. Four speeds were considered for this investigation: 8, 10, 12, and 14 knots, and the simulation conditions, identical to the sea trials records, were also taken into consideration. The simulation results were compared to the data provided by LR in 2015 in the workshop proceeding.
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