INTERACTIVE SIMULATION OF SHIP MOTIONS IN RANDOM SEAS BASED ON REAL WAVE SPECTRA

2011 ◽  
Keyword(s):  
Ship Motions ◽  
Wave Spectra ◽  
Interactive Simulation ◽  
Random Seas

scholarly journals Ship Motions in Shallow Water As the Base for a Probabilistic Approach Policy

2008 ◽  
Author(s):  
Marc Vantorre ◽  
Erik Laforce ◽  
Katrien Eloot ◽  
Jan Richter ◽  
Jeroen Verwilligen ◽  
...  
Keyword(s):  
Shallow Water ◽  
Probabilistic Approach ◽  
Ship Motions ◽  
Wave Spectra ◽  
Fluid Mud ◽  
Response Functions ◽  
Regular Waves ◽  
Directional Wave ◽  
Probabilistic Criteria ◽  
Selection Of

A calculation tool has been developed for determining tidal windows for deep-drafted ships approaching and leaving the Belgian harbors according to probabilistic criteria. The calculations are based on a database containing response functions for the vertical motions in waves and squat data for a selection of representative ships. The database contains both results of model tests carried out in the Towing tank for maneuvers in shallow water – co-operation Flanders Hydraulics Research & Ghent University in Antwerp (Belgium), as well as calculated values. During the experiments, draft, trim, under keel clearance (7 to 20% of draft) and speed have been varied. The tests were performed in regular waves with lengths which are small compared to ship length, and in wave spectra that are typical for the Belgian coastal area. For given input data (ship characteristics, speed, tide, directional wave spectra, bottom, trajectory, current, departure time), the tool calculates the probability of bottom touch during the transit, so that a tidal window can be determined. Other restrictions, such as penetration into fluid mud layers and current, are taken into account as well.

On the Effect of Short-Crestedness on Ship Motions

1966 ◽  
Vol 10 (03) ◽  
pp. 192-200
Author(s):  
E. O. Tuck
Keyword(s):  
Transfer Function ◽  
Transfer Functions ◽  
Full Scale ◽  
Slender Body ◽  
Ship Motions ◽  
Forward Speed ◽  
Slender Body Theory ◽  
Random Seas ◽  
Body Theory

A simple mathematical example, using the slender-body theory of ship motions, is given to illustrate the nature of errors due to short-crestedness in estimations of ship transfer functions from full-scale measurements in directionally random seas. As expected physically, any transfer function obtained in this manner is a smoothed estimate of the true transfer function which would be observed in a unidirectional sea. Computations of this "pseudotransfer function" are presented for heave and pitch of an idealized ship at zero speed, and the effects of forward speed are discussed briefly.

Extended Bayesian Estimation of Directional Wave Spectra

2004 ◽  
Author(s):  
Toshio Iseki
Keyword(s):  
Bayesian Estimation ◽  
Wave Spectrum ◽  
Time History ◽  
Ship Motions ◽  
Wave Spectra ◽  
Time Varying ◽  
Bayesian Modelling ◽  
History Data ◽  
Modelling Procedure ◽  
Directional Wave

The Bayesian modelling procedure has been extended to estimate time-varying directional wave spectra. In the proposed method, the hull of a ship is regarded as a wave sensor and the time history data of ship motions is analyzed to evaluate cross spectra. In this concept, a special attention should be paid to changes of the directional wave spectrum because the ship is moving and the location at sea is changing continuously. Therefore, the extended Bayesian estimation is based on the cross spectra evaluated at different times and the fluctuation of wave spectrum is taken into account. In order to examine the reliability of the proposed method, data of onboard experiments were analyzed. Comparisons between the results of the proposed method and visual observations show good agreements.

Ship As a Wave Buoy: Estimating Full Directional Wave Spectra From In-Service Ship Motion Measurements Using Deep Learning

2020 ◽  
Author(s):  
T. P. Scholcz ◽  
B. Mak
Keyword(s):  
Neural Network ◽  
Real Time ◽  
Accurate Estimation ◽  
Ship Motions ◽  
Wave Spectra ◽  
Operational Conditions ◽  
Directional Spectrum ◽  
The Neural Network ◽  
Directional Wave ◽  
Convolutional Encoding

Abstract The ocean wave directional spectrum is an important wave characteristic for maritime safety and navigation. Accurate estimation of directional spectra in real-time is a challenge. In this study we aim to reconstruct the directional spectra from ship motions using a deep convolutional encoding-decoding neural network. In-service measurements of ship motions and wave spectra from a WAMOS II wave scanning radar were used to train the neural network. The data was collected from a frigate type ship for a period of two years. We demonstrate that the deep convolutional encoding-decoding neural network is successful in predicting the directional spectra in real-time. At the same time, we conclude that more data is needed for a better prediction performance, including a more complete coverage of operational conditions.

scholarly journals Influence of the aspect ratio of energy-saving wing elements fitted on the ship bottom upon spectral densities of longitudinal motions in irregular waves

2020 ◽  
pp. 45-51
Author(s):  
З.М. Хтет ◽  
К.В. Рождественский
Keyword(s):  
Aspect Ratio ◽  
Energy Saving ◽  
Calculated Data ◽  
Irregular Waves ◽  
Ship Motions ◽  
Wave Spectra ◽  
Regular Waves ◽  
Spectral Densities ◽  
Strip Theory ◽  
Oscillating Foil

В статье приводятся оценки спектральных плотностей качки судна с энергосберегающими крыльевыми элементами на встречном нерегулярном волнении, а также результаты сравнения расчета и эксперимента для продольной качки судна на регулярном волнении. Метод расчета основан на линейной теории поперечных сечений в частотной области. При этом сначала рассматривается продольная качка на встречном регулярном волнении с учетом демпфирующего и инерционного влияния крыльев посредством привлечения теории Теодорсена колеблющегося крыла. Определение спектральной плотности продольной качки на нерегулярном волнении проводится на основании формулы А.Я. Хинчина. Для расчета спектра волнения используется спектр JONSWAP по рекомендации DNV GL(2018). В ходе расчетов демонстрируется влияние на спектральные плотности удлинения и площади энергосберегающих крыльев, а также на спектральные плотности качки при совместном использовании носового и кормового крыльев по сравнению со случаем использования только одного из этих крыльев. Полученные расчетные данные дают представление о механизме снижения спектральных плотностей при использовании крыльев. The article presents some estimates of spectral densities of longitudinal motions for a ship with energy-saving wing devices in headwind irregular waves, and also comparisons of calculated and experimental data for longitudinal ship motions in headwind regular waves. The calculation method is based on a linear strip theory in frequency domain. Considered first are longitudinal motions of a ship in headwind regular waves with account of inertial and damping influence of the wings through use of Theodorsen oscillating foil theory. Spectral densities of longitudinal motions in irregular waves are determined with use of A.Ya. Khinchin formula and JONSWAP wave spectra as recommended by DNV GL (2018). Demonstrated in the course of calculations is the influence of the wings aspect ratio and area as well as their position with respect to the ship hull (bow wing, stern wing, bow & stern wings). Calculated data gives an idea of the mechanism of spectral densities reduction for motions of a ship with wing elements.

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