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1

Method for ship’s rolling period prediction with regard to non-linearity of GZ curve

Wawrzyński W., Krata P.

Journal of Theoretical and Applied Mechanics

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2016

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Vol. 54 nr 4

1329--1343

EN

The paper deals with the problem of prediction of the rolling period. A special emphasis is put on the practical application of the new method for rolling period prediction with regard to non-linearity of the GZ curve. The one degree-of-freedom rolling equation is applied with using the non-linear stiffness moment and linear damping moment formulas. A number of ships are considered to research the discrepancies between the pending GM-based IMO- -recommended method and the results of conducted numerical simulations performed for a wide range of operational loading conditions. Since the research shows some drawbacks of the IMO formula for the ship rolling period, a new formula is worked out and proposed instead.

2

3D CDF modeling of ship's heeling moment due to liquid sloshing in tanks - a case study

Krata P., Jachowski J.

Journal of KONES

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2010

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Vol. 17, No. 4

245-251

EN

Modeling of liquid sloshing inside partly filled ships' tanks can be carried out by a variety of methods. The simplest and perhaps the less reliable is a quasi-static approach which is, however, recommended in the Intact Stability Code by the International Maritime Organization. Hence the only advantage of the static estimation of liquid sloshing is simplicity of calculations, the research into the application of CFD (Computational Fluid Dynamics) was performed in Department of Ship Operation at Gdynia Maritime University. The paper presents results of numerical simulations o f a liquid sloshing phenomenon performed by means of a code Fluent. The research was focused on a computation of the heeling moment affecting stability of a vessel, especially on the dynamic effects, which are omitted in obligatory intact ship's stability regulations nowadays. The computed distributions of dynamic pressures on tank walls were carried out for large oscillation amplitude which is characteristic for stormy sea conditions. Ali the simulations were computed in 3D mode and they provide high accuracy results. A case study described in the paper enables realistic comparison of the results of CFD liquid sloshing simulations and the simple statics based computations. The study reveals some weaknesses of the contemporary quasi-static approach towards the free surface effect and it might be the contribution to the more sophisticated estimation of the ship's stability than it is achieved nowadays.

3

Ship's heeling moment due to liquid sloshing in tanks - 3D attitude

Jachowski J., Krata P.

Journal of KONES

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2009

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Vol. 16, No. 2

191-197

EN

The matter of the paper refers to the dynamic stability of a vessel as an important factor affecting her safety at seaway. Ship 's seakeeping behaviour, which comprises the notion of her stability, is one of the researched key issues leading to the increase in understanding of the safety qualifying factors. Liquid sloshing phenomenon is a result of partly filled tank motions. As a tank moves, it supplies the energy to induce and sustain the fluid motion. The dynamic behaviour of a vessel at seaway is considerably affected by the dynamics of free liquid surfaces, therefore the influence of fluid movement taking place in partly filled tanks on the safety of ship 's exploitation process is emphasized. The paper presents the results of the experimental research and the numerical simulation of the sloshing phenomenon. The research was focused on the computation of the heeling moment affecting the stability of a vessel, especially dynamic effects, which are omitted in obligatory intact ship 's stability regulations nowadays. The experiment performed in the course of the research was carried out in Department of Ship Operation at Gdynia Maritime University. The unique test apparatus was designed and built. It enables to measure dynamic pressures on model tank walls for large oscillation amplitudes, which are characteristic for stormy sea conditions. The numerical simulations of liquid sloshing phenomenon, took into account the viscosity of liquid and the turbulence of considered flows. All the simulations were computed in 3D mode and they provide high accuracy results. The spatial distribution of dynamic pressures on model tank walls enables computation of heeling moment due to liquid sloshing which affects ship 's stability. Further analysis of obtained moments was carried out. The study may be the contribution to the more sophisticated estimation of the ship's stability than it is achieved nowadays.