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.

scholarly journals OBSERVATION OF DIRECTIONAL WAVE SPECTRA AND REFLECTION COEFFICIENT OF BREAKWATER IN A HARBOR

1988 ◽  
Vol 1 (21) ◽  
pp. 3
Author(s):  
Tetsunori Ohshimo ◽  
Kosuke Kondo ◽  
Tsunehiro Sekimoto
Keyword(s):  
Reflection Coefficient ◽  
Wave Diffraction ◽  
Maximum Likelihood Method ◽  
Wave Spectrum ◽  
Field Investigation ◽  
Likelihood Method ◽  
Electromagnetic Current ◽  
Wave Spectra ◽  
Field Investigations ◽  
Directional Wave

Field investigations were performed in order to show the effect of wave diffraction by breakwaters through directional wave spectra measurements in a harbor, and to estimate the reflection coefficient by resolving the incident and reflected wave energy in front of a composite type breakwater. Combinations of an ultrasonic wave gage (USW) and an electromagnetic current meter (EMC) were used to measure the synchronized data of the water surface elevation and two horizontal velocities. The EMLM (Extended Maximum Likelihood Method) was applied for the calculation of the directional wave spectrum, and the modified EMLM for an incident and reflection wave field was applied for the estimation of the reflection coefficient. Through the estimated directional wave spectra, the effect of wave diffraction by breakwaters were discussed and the reflection coefficient was estimated at about 0.9. As a result, the applicability of the field investigation method and the modified EMLM were verified.

On the Estimation of Directional Wave Spectrum Based on Stationary Vessels 1st Order Motions: A New Set of Experimental Results

2008 ◽  
Author(s):  
Joa˜o V. Sparano ◽  
Eduardo A. Tannuri ◽  
Alexandre N. Simos ◽  
Vini´cius L. F. Matos
Keyword(s):  
Bayesian Inference ◽  
Wave Spectrum ◽  
Small Scale ◽  
Large Set ◽  
Wave Spectra ◽  
Inference Method ◽  
Peak Period ◽  
Wave Basin ◽  
Bayesian Inference Method ◽  
Directional Wave

The practicability of estimating directional wave spectra based on a vessel 1st order response has been recently addressed by several researchers. The interest is justified since on-board estimations would only require only a simple set of accelerometers and rate-gyros connected to an ordinary PC. The on-board wave inference based on 1st order motions is therefore an uncomplicated and inexpensive choice for wave estimation if compared to wave buoys and radar systems. The latest works in the field indicate that it is indeed possible to obtain accurate estimations and a Bayesian inference model seems to be the preferable method adopted for performing this task. Nevertheless, most of the previous analysis has been based exclusively on numerical simulations. At Polytechnic School, an extensive research program supported by Petrobras has been conducted since 2000, aiming to evaluate the possibility of estimating wave spectrum on-board offshore systems, like FPSO platforms. In this context, a series of small-scale tests has been performed at the LabOceano wave basin, comprising long and short crested seas. A possible candidate for on-board wave estimation has been recently studied: a crane barge (BGL) used for launching ducts offshore Brazil. The 1:48 model has been subjected to bow and quartering seas with different wave heights and periods and also different levels of directional spreading. A Bayesian inference method was adopted for evaluating the wave spectra based on the time-series of motions and the results were directly compared to the wave spectra measured in the basin by means of an array of wave probes. Very good estimations of the statistical parameters (significant wave height, peak period and mean wave direction) were obtained and, in most cases, even the directional spreading could be properly predicted. Inversion of the mean direction (180° shift), mentioned by some authors as a possible drawback of the Bayesian inference method, was not observed in any case. Sensitivity analysis on errors in the input parameters, such as the vessel inertial characteristics, has also been performed and attested that the method is robust enough to cope well with practical uncertainties. Overall results once again indicate a good performance of the inference method, providing an important additional validation supported by a large set of model tests.

scholarly journals COMBINED REFRACTION-DIFFRACTION CALCULATIONS WITH DIRECTIONAL WAVE SPECTRA

1984 ◽  
Vol 1 (19) ◽  
pp. 71 ◽  
Author(s):  
P. Gaillard
Keyword(s):  
Water Depth ◽  
Arbitrary Shape ◽  
Wave Spectrum ◽  
Wave Spectra ◽  
Combined Effects ◽  
Random Waves ◽  
Method Of Calculation ◽  
Wave Refraction ◽  
Directional Wave

A method of calculation of the combined effects of wave refraction, diffraction and reflection in harbours of arbitrary shape and non uniform water depth, subject to periodic or random waves is presented. Examples of application are given and practical aspects on the wave spectrum discretisation are considered.

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.

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