A Forecast Method of Slamming Pressure on Ship Surface
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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.Keywords:
Slamming
Impact pressure
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The analysis of slamming effect has been mainly discussed about the local strength assessment and the global longitudinal strength assessment under slamming loads. The former is to forecast the local design pressure and access the local structural strength. To achieve the strength assessment of local structure of the ship bow, the slamming design pressure results of bow bottom and bow flare areas have been selected, so as to show the calculation results of relative velocity extreme values and design slamming pressure. And then according to the slamming loads and strength assessment, the direct strength assessments have been used to check key areas. The latter is to forecast the global vertical design moment and access the global longitudinal strength through three dimension finite model.
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In rough seas, actual behaviours of a ship may not be estimated by the linear strip theory, because of Nonlinearities due to the hull shape, bottom slamming and bottom and/or bow-flare slamming. In case of slamming, impulsive hydrodynamic pressure occurs on the fore body surface of the ship, resulting hull vibration called whipping, by which the ship may suffer from serious structural damages and the impact pressure, depends critically on the relative velocity at re-entry. In this paper, the Time history of impact froce at each station, the longitudinal distribution of impact force at critical time, the Time history of acceleration at F.P. and the Time history of Bending moment at midship are illustrated. That is, authors analyzed Dynamic response of container ship to be subjected slamming impact force.
Slamming
Keel
Impact
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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.
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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 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.
Slamming
Sea state
Seakeeping
Ship motions
Significant wave height
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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
Offshore geotechnical engineering
Flare
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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.
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Ship motions
Hydroelasticity
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