Wyniki wyszukiwania - BazTech

1

Experimental study and numerical simulation of the water entry of a ship-like symmetry section with an obvious bulbous bow

Wang Qiang, Yu Pengyao, Zhang Boran, Li Guangzhao

Polish Maritime Research

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2021

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nr 3

16--34

EN

A bulbous bow is a typical ship structure. Due to the influence of the bulbous bow, complex flow separation and gas capture phenomena may appear during the water entry of ship-like sections. In this paper, experimental and numerical studies on the water entry of a ship-like section with an obvious bulbous bow are carried out. Two thin plates are installed at both ends of the test model to ensure that the flow field during the impact process is approximately twodimensional. The free-fall drop test is carried out in the test rig equipped with guide rails. By changing drop heights, impact pressure on the model surface with different initial impact velocities is measured. A numerical model for simulating the water entry of the ship-like section is established by using the Computational Fluid Dynamics (CFD) method, based on the Navier-Stokes equations. Reasonable time steps and mesh size are determined by convergence analysis. Four different flow models are used in the numerical analysis. It is found that the K-Epsilon turbulence model can present the most reasonable numerical prediction by comparing numerical results with the experimental data. Furthermore, the influence of the bulbous bow on the impact loads is numerically studied by using the validated numerical model. It suggests that the bulbous bow has little effect on the impact force acting on the bow-flared area but, in the position near the bulbous bow, the pressure will be affected by the second slamming and the air cushion.

2

Water entry of a wedge into waves in three degrees of freedom

Sun Shi Yan, Chen Hai Long, Xu Gang

Polish Maritime Research

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2019

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nr 1

117--124

EN

The hydrodynamic problem of a two-dimensional wedge entering into a nonlinear wave in three degrees of freedom is investigated based on the incompressible velocity potential theory. The problem is solved through the boundary element method in the time domain. To avoid numerical difficulties due to an extremely small contact area at the initial stage, a stretched coordinate system is used based on the ratio of the Cartesian system in the physical space to the distance travelled by the wedge in the vertical direction. The mutual dependence of body motion and wave loading is decoupled by using the auxiliary function method. Detailed results about body accelerations, velocities and displacements at different Froude numbers or different waves are provided, and the mutual effect between body motion and wave loading is analysed in depth.

3

Numerical simulation of cushioning problem for blunt bodies using boundary element method

Barjasteh M., Zeraatgar H.

Polish Maritime Research

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2018

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S 1

85--93

EN

Induced air pressure and resulting free surface profile due to air cushioning layer is studied. The study is mainly focused on 2D blunt circular bodies with constant downward speed. The problem is first solved for the air flow between the body and the free surface of the water. Then the results are employed to solve the problem for the water problem, numerically. Both air and water problem are assumed to be governed by Laplace potential equation. Depending on the induced pressure and velocity of the escaping air flow from cushioning layer, compressibility of the air is also included in the modeling. Gravitational acceleration is also included in the model. An iterative boundary element method is used for numerical solution of both air and water problems. Instantaneous pressure distribution and free surface profile are evaluated for different bodies. The results of calculation for large blunt bodies show that inviscid potential method can fairly approximate the problem for large blunt bodies. Additionally, the behavior of the air pressure for the very blunt body is impulsive and the magnitude of the peak pressure is in order of impact pressure of water entry. The obtained results are compared with analytical method. The comparison shows that as the bluntness of a body increases, the better agreement is concluded.

4

Analysis of the process of water entry of an amphibious vehicle

Burciu Z., Kraskowski M., Gerigk M.

Archiwum Motoryzacji

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2012

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Nr 2

5-13

EN

The paper presents a method of computational and experimental analysis of the process of water entry of an amphibious vehicle. The computational method is based on the Reynolds Averaged Navier-Stokes Equations (RANSE) solver and the experiment was carried out in the towing tank at Ship Design and Research Centre S.A. with the use of a scale model. The analysis was focused on the safety of water entry, i.e. the maximum pitch and roll angles, the maximum acceleration, as well as the occurrence and degree of flooding of bonnet and windscreen. Both the computations and the experiment have revealed that in the case of free water entry, i.e. without braking, the water covers the windscreen even at a moderate slope of the beach (10 [degrees]); however, if braking of the wheels during the water entry process were possible, the flooding of the bonnet and windscreen could be avoided even at a steep slope (30 [degrees]).

PL

Artykuł przedstawia obliczeniową oraz eksperymentalną metodę analizy wodowania amfibii. Metoda obliczeniowa oparta jest na programie wykorzystującym model przepływu RANSE (Reynolds Averaged Navier-Stokes Equations), natomiast eksperyment przeprowadzony został w basenie holowniczym Centrum Techniki okrętowej S.A. z użyciem modelu. Analiza skupiona była na bezpieczeństwie wodowania, tzn. na maksymalnych katach przechyłu wzdłużnego i bocznego, maksymalnych przyspieszeniach oraz stopniu zalewania maski silnika i przedniej szyby, Zarówno obliczenia jak i eksperyment wykazały, że w przypadku swobodnego wjazdu do wody, tzn. bez hamowania kół, woda zalewa przednią szybę nawet przy umiarkowanych kątach spadku nabrzeża (10 stopni), jednakże, jeżeli możliwe jest hamowanie kół podczas wjazdu, możliwe jest uniknięcie zalewania maski i przedniej szyby nawet przy dużych kątach spadku nabrzeża (30 stopni).