Wyniki wyszukiwania - Biblioteka Nauki

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Shape optimization of a hydrofoil with leadingedge protuberances using full factorial sweep sampling and an RBF surrogate model

100%

Nazemian A. , Ghadimi P.

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tom nr 62 (134)

116--123

EN

This paper investigates improving the leading-edge of a hydrofoil with sinusoidal protuberances based on its hydrodynamic performance. The original hydrofoil geometry was inspired by the leading edge of the flipper of a humpback whale. A multi-step optimization process was performed for a 634-021 hydrofoil. The free-form deformation technique defined the shape parameters as a variable design, and these parameters included the amplitude of the leading-edge protuberances, which ranged from 0 to 20% of the chord length, and the corrugate span, with 3 and 4 crests. The flow characteristics of a parametric hydrofoil were examined using a CFD solver, and the lift, drag, and lift-to-drag ratio (L/D) were computed as responses to the optimization cycle. To accomplish this, two design study methods were sequentially applied at different angles of attack. A full factorial design sweep tool was applied that went through all parameter value combinations, and an RBF-based surrogate model was constructed to investigate the system behavior. The results indicated the existence of an optimum design point, and the highest L/D ratio was determined to be 10.726 at a 12° angle of attack.

2

The effect of the stern wedge length and height on the drag and trim of a chine-planing hull

80%

Ghassemi M. A. , Ghadimi P. , Sajedi S. M.

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tom nr 67 (139)

39--52

EN

This paper examines the effect of the stern wedge length and height on the drag and trim of a chine-planing hull in calm water. To this end, fluid flow was simulated by Star-CCM+ software by applying an overset mesh and k-ε turbulent model. The finite volume method was used to discretize the fluid domain, and the fluid volume was utilized to capture the generated free surface. The considered model is a prismatic planing hull with a deadrise angle of 24°, a mass of 86 kg, a length (L) of 2.64 m, and a beam (B) of 0.55 m. For validation, the numerical results of drag and trim were compared against experimental data, which displayed good compliance. Subsequently, the hydrodynamic performance of the planing hull was investigated, and the wedge effect was assessed. The stern wedge was located at the bottom and near the aft perpendicular to the hull to facilitate a moderate distribution. Various wedge lengths of 0.2B, 0.5B, and B at two different heights of 5 mm and 10 mm were examined to assess the hydrodynamic performance of the hull at various speeds. The trim angle, resistance, water surface elevation, porpoising, roster tail, and the stern and bow were computed and analyzed. Based on the numerical results, it was concluded that when the wedge length increased, the drag and trim were reduced. It was also concluded that the best wedge for a vessel with desirable wake generation is one with a length of 0.2B and a height of 5 mm.

3

Numerical simulation of the seakeeping of a military trimaran hull by a novel overset mesh method in regular and irregular waves

80%

Ghadimi P. , Karami S. , Nazemian A.

Zeszyty Naukowe Akademii Morskiej w Szczecinie

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2021

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tom nr 65 (137)

38--50

EN

The hydrodynamic performance of trimaran hulls has been previously investigated for optimum performance in calm water, but there is still a limited understanding of its motion response; therefore, a CFD-based numerical approach was developed and applied on a trimaran hull in the presence of regular and irregular waves. To validate the CFD method, a comparison was conducted using both experimental and 3D panel method data. In this study, two different turbulence models were surveyed, and the SST Menter k-Omega (k-ω) turbulence model was shown to be a more accurate model than the realizable k-Epsilon (k-ε) model. The different features of the proposed numerical model include the implementation of an overset mesh method, unique mesh plan refinement, and wave-damping region. The discrepancy between the experimental data and the results of other seakeeping calculation methods have always been problematic, especially for low-speed strip theory and 3D panel methods, but good consistency was observed between the proposed CFD model and experimental data. Unlike potential-based or conformal mapping seakeeping analysis methods, the effect of nonlinear waves, hull shape above the waterline, and other ship dynamic phenomena were considered in this CFD application. The proposed CFD method reduces the simulation time and computational efforts for ship motion calculations.