The Effect of Speed and Sea State for Probability of Ships Slamming
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Based on the Seakeeping Standard Series, the effect of speed and sea state for slamming probability of ships is studied in this paper. Five ships with different size were selected as sample ship. The range of relative significant wave height and Fn is 0.015~0.06 and 0.1~0.3 respectively. The results show that the slamming probability at bow of ships increases obviously with the sea state rising and the effect of speed for slamming probability presents different tendency while ship sailing at different sea states. With respect to slamming problem, low, middle and high sea conditions could be bounded by 0.02 and 0.03, which is the ratio of significant wave height and ship length.Keywords:
Slamming
Sea state
Seakeeping
Ship motions
Significant wave height
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This paper presents the forecast method of ships' inserting velocities by considering the relationship between waves and ship motions. It uses two dimension slamming empirical formula to calculate the slamming pressure.
Slamming
Impact pressure
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In this paper, we study the problem of wave slamming on the cross structures of both fast ferry type catamarans and ocean going racing sailing catamarans. The emphasis is given to the prediction of the statistical distributions of slamming occurrence and slamming pressure magnitudes in a random seaway. A partly non-linear high-speed strip theory sea-keeping program is used to calculate the vessel motions and the relative motions between any part of the hull and the sea surface, including slamming impact velocity. Impact velocities are classified in 5 groups, and slamming pressures calculated for each group. To calculate vessel motions of heeled sailing catamarans a strip method for an asymmetric multi-hull is developed; the theory and initial results are presented. An investigation into the effect of sail forces on motions and slamming occurrence is also performed. The sail forces are found to be an important factor in predicting motions of sailing catamarans. The procedure proposed in this paper gives the necessary information to estimate the maximum slamming pressures the vessel is likely to encounter and equally importantly the expected frequency of lighter slams, which is useful for fatigue calculations.
Slamming
Ship motions
Naval architecture
Impact pressure
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Slamming
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We present a numerical procedure to predict impact-related wave-induced (slamming) loads on ships. The procedure was applied to predict slamming loads on two ships that feature a flared bow with a pronounced bulb, hull shapes typical of modern offshore supply vessels. The procedure used a chain of seakeeping codes. First, a linear Green function panel code computed ship responses in unit amplitude regular waves. Wave frequency and wave heading were systematically varied to cover all possible combinations likely to cause slamming. Regular design waves were selected on the basis of maximum magnitudes of relative normal velocity between ship critical areas and wave, averaged over the critical areas. Second, a nonlinear strip theory seakeeping code determined ship motions under design wave conditions, thereby accounting for the ship’s forward speed, the swell-up of water in finite amplitude waves, as well as the ship’s wake that influences the wave elevation around the ship. Third, these nonlinearly computed ship motions constituted part of the input for a Reynolds-averaged Navier-Stokes equations (RANSE) code that was used to obtain slamming loads. Favourable comparison with available model test data validated the procedure and demonstrated its capability to predict slamming loads suitable for design of ship structures.
Slamming
Seakeeping
Ship motions
Swell
Rogue wave
Response amplitude operator
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This paper discusses about flare slamming pressure on a large container ship when it runs at head seas with the direct calculation method.Based on 3-D potential flow theory Rankine Panel Method,the nonlinear motion response of the ship was predicted when it runs at different sea conditions and speed in irregular waves in the time domain with the commercial software,Wasim of DNV.Then,the flare slamming pressure on the bow flare area was calculatedbased with the Wagner impact theory.At last,the slamming probability and the extreme value ofthe slamming pressure in different working conditions were calculated based on the probability and stochastic theory,and the characteristics were analyzed.
Slamming
Ship motions
Degree Rankine
Flare
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Slamming
Ship motions
Bow wave
Impact pressure
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A computational procedure of predicting bottom slamming motion and loads for FPSO is presented.The approach of transition of frequency-time domain is used to determine the occurrence of slamming and the impact loads on hull-bottom for FPSO in which ship hull motions in waves are calculated by using the three-dimensional Green function method and the wave slamming pressure is determined by means of the empirical formula.The effect of the encountered phase-angle between ship hull and incident wave and of design wave period on slamming loads at bow hull-bottom is considered in computation and analysis.This procedure can be used to predict slamming loads for FPSO with the environmental conditions in operative sea area and the occurrence frequency of slamming expediently.The calculating results can be applied as input message for fatigue analysis of hull-bottom of FPSO to predict slamming loads for hull with various loading states under different angles of wave direction.
Slamming
Ship motions
Impact pressure
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This paper discusses a method to estimate slamming characteristics of a ship at an early design stage using the ship lines. The first section of the paper deals with the derivation of a regression equation which yields a coefficient necessary to estimate impact pressure for any given hull form. The second section discusses the procedure of application of the regression equation in conjunction with other computer programs to estimate frequency and severity of slamming for ship design. As an example of the application, the extreme values of impact pressure are computed at several forward stations of the Mariner as a function of ship operation time in various sea states. By assigning an allowable extreme pressure magnitude and tolerable number of slams, it is possible to estimate the limiting sea state or limiting ship speed below which safe navigation without seriously suffering from slamming is anticipated.
Slamming
Naval architecture
Limiting
Response amplitude operator
Impact pressure
Sea state
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Based on the probabilistic method proposed by Ochi,this paper develops a method which could predict slamming pressure directly for the vehicle whose lines plan is unconventional.In this method the ship's motion response is calculated in time domain when it sails in the wave,and the slamming coefficient is calculated through the software Msc.dytran.Then the characteristic of slamming pressure is predicted with Monte Carlo method based on the above results.The effect of relative velocity between the ship and the wave at the time of slamming and wave slope angle on the slamming coefficient is analyzed particularly.Research result shows that there is a great difference in characteristic of slamming pressure between the impact in still water and that in wave.The slamming which occurs at the peak and the trough of a wave will generate higher pressure.The effect of relative velocity between the ship and the wave on the slamming coefficient varies with different waves.
Slamming
Impact pressure
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Slamming against the wetdeck of a high-speed catamaran in head sea waves is studied analytically and numerically. The theoretical slamming model is an asymptotic method valid for small local angles between the undisturbed water surface and the wetdeck. The disturbance of the water surface, the local hydroelastic effects in the slamming area as well as the interaction between the slamming loads and the global heave and pitch motions are accounted for. The slamming model is two-dimensional and nonlinear while the hydrodynamic loads on the ship hulls are based on a linear high-speed frequency domain theory. The linear time domain representation of the hydrodynamic loads on the ship hulls are obtained by an analytical transformation of the frequency domain results in terms of retardation functions. The elastic deflections of the wetdeck are express in terms of dry normal modes. Parameters influencing the slamming level and uncertainties in the slamming model are discussed. it is demonstrated that the local hydroelastic effects of the wetdeck structure can significantly reduce the hydrodynamic impact loads on the wetdeck. This study also shows that it is important to describe the hydrodynamic loading on the wetdeck in terms of analytical functions. This ensures the accuracy of the hydrodynamic loads as well as the numerical stability of the time integration.
Slamming
Ship motions
Hydroelasticity
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