CHARACTERISTICS OF DIRECTIONAL WAVE SPECTRA ESTIMATED BY A HIGH PRECISION ESTIMATION METHOD OF DIRECTIONAL WAVE SPECTRUM

A parametric estimation of the directional wave spectrum based on ship motions is presented. The estimation of the sea- state parameters is essential to have an updated data base of the main characteristics of the sea-state, which are useful for several applications on open-sea such as offshore platforms installations and safe ship navigation. The sea-state parameters at a fixed position can be obtained using a traditional waverider buoy. The analogy between the ship and the buoy is clear thus, it is possible to obtain an estimate of the wave spectrum at the location of an advancing ship by processing its wave-induced responses similarly to the traditional waverider buoy. In the parametric procedure the estimated wave spectrum is a-priori assumed to be composed of one parameterized spectrum or by the summation of several parameterized spectra, e.g. the generalized JONSWAP spectrum. Genetic algorithms are applied to found the best estimation of wave parameters. The wave estimation method is validated against numerical simulations and full scale tests in a patrol ship.

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Bayesian Estimation of Directional Wave-Spectrum Using Vessel Movements and Wave-Probes: Proposal and Preliminary Experimental Validation

Volume 1: Offshore Technology ◽

10.1115/omae2017-61241 ◽

2017 ◽

Author(s):

Felipe Lopes de Souza ◽

Eduardo Aoun Tannuri ◽

Pedro Cardozo de Mello ◽

Guilherme Franzini ◽

Jordi Mas-Soler ◽

...

Keyword(s):

Linear Model ◽

Wave Spectrum ◽

Estimation Method ◽

Scale Model ◽

Spectral Energy ◽

Peak Period ◽

Directional Wave Spectrum ◽

Wave Basin ◽

Directional Wave ◽

Probe Response

The measurement of the directional wave spectrum in oceans has been done by different approaches, mainly wave-buoys, satellite imagery and radar technologies; these methods, however, present some inherent drawbacks, e.g., difficult maintenance, low-resolution around areas of interest and high-cost. In order to overcome those problems, recent works in the area proposed a motion-based estimation procedure using the vessel, or the floating facility, as a wave sensor, what was called wave-buoy analogy. Despite of solving the issues, the solution is still incomplete, since it suffers from low estimation capabilities of the spectral energy below the cut-off period of the systems, around eight seconds, a frequency range that is responsible for the drift effects, that are critical for operation planning and dynamic positioning. This work studies the usage of wave-probes installed on the hull of a moored vessel to enhance the estimation capabilities of the motion-based strategy, using a high-order estimation method based on Bayesian statistics. The proposal is founded on the asymptotical response of the oceanic systems facing low period waves, which starts to behave like a wall, reflecting all the incoming energy, i.e., the worst the motion-based estimation is, the better the wave-elevation based estimation should be. Firstly, the measurements from the wave-probes are incorporated to the dynamic system of the vessel as new degrees-of-freedom, using a linear model extension, thus the Bayesian method can be expanded without additional reasoning. Secondly, the linear model hypothesis and the possible improvements are validated by experiments conducted in a wave-basin with a scale model of a moored FPSO-VLCC, concluding that the approach is able to improve not only the estimation of spectra with low peak period, but also the estimation in the entire range of expected spectra, mainly the significant height and the peak period properties. Lastly, some drawbacks are discussed, as the effect of the non-linear roll movement, which must be taken in account when calculating the wave-probe response; and the poor mean-direction estimation capability in some particular wave directions and low peak periods, in which even the vessel motions allied with the wave-probe response are not able to provide the proper direction discrimination.

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Bayesian Estimation of Directional Wave-Spectrum Using Vessel Motions and Wave-Probes: Proposal and Preliminary Experimental Validation

Journal of Offshore Mechanics and Arctic Engineering ◽

10.1115/1.4039263 ◽

2018 ◽

Vol 140 (4) ◽

Cited By ~ 5

Author(s):

Felipe Lopes de Souza ◽

Eduardo Aoun Tannuri ◽

Pedro Cardozo de Mello ◽

Guilherme Franzini ◽

Jordi Mas-Soler ◽

...

Keyword(s):

Degrees Of Freedom ◽

Wave Spectrum ◽

Estimation Method ◽

Estimation Procedure ◽

Scale Model ◽

Spectral Energy ◽

Peak Period ◽

Directional Wave Spectrum ◽

Wave Basin ◽

Directional Wave

The measurement of the directional wave spectrum in oceans has been done by different approaches, mainly wave-buoys, satellite imagery and radar technologies; these methods, however, present some inherent drawbacks, e.g., difficult maintenance, low resolution around areas of interest and high cost. In order to overcome those problems, recent works proposed a motion-based estimation procedure using the vessel as a wave sensor; nevertheless, this strategy suffers from low-estimation capabilities of the spectral energy coming from periods lower than the cutoff period of the systems, which are important for the drift effect predictions. This work studies the usage of wave-probes installed on the hull of a moored vessel to enhance the estimation capabilities of the motion-based strategy, using a high-order estimation method based on Bayesian statistics. First, the measurements from the wave-probes are incorporated to the dynamic system of the vessel as new degrees-of-freedom (DOF); thus, the Bayesian method can be expanded without additional reasoning. Second, the proposal is validated by experiments conducted in a wave-basin with a scale model, concluding that the approach is able to improve not only the estimation of spectra with low peak period but also the estimation in the entire range of expected spectra. Finally, some drawbacks are discussed, as the effect of the nonlinear roll motion, which must be taken in account when calculating the wave-probe response; and the poor mean-direction estimation capability in some particular wave directions and low peak periods.

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

Coastal Engineering Proceedings ◽

10.9753/icce.v21.3 ◽

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.

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The Influence Evaluation of the Noise for the Directional Wave Spectrum Estimated from HF Radar Received Signal

Ocean Wave Measurement and Analysis (2001) ◽

10.1061/40604(273)22 ◽

2002 ◽

Author(s):

Shoichiro Kojima ◽

Noriaki Hashimoto ◽

Yuji Sato

Keyword(s):

Wave Spectrum ◽

Hf Radar ◽

Directional Wave Spectrum ◽

Directional Wave

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

Volume 4: Ocean Engineering; Offshore Renewable Energy ◽

10.1115/omae2008-57431 ◽

2008 ◽

Cited By ~ 2

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.

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HF Radar Directional Spectra Validation With Buoy and Model Data

Volume 4: Ocean Engineering; Offshore Renewable Energy ◽

10.1115/omae2008-57742 ◽

2008 ◽

Author(s):

L. R. Wyatt ◽

J. J. Green ◽

A. Middleditch ◽

J. C. Waters

Keyword(s):

Wave Spectrum ◽

Hf Radar ◽

Model Data ◽

Work In Progress ◽

Directional Wave Spectrum ◽

Directional Wave ◽

Good Agreement

Examples of the measurement of the directional wave spectrum using HF radars are presented. These are compared with both buoy and model data and good agreement is demonstrated. Work in progress on partitioning these spectra for more detailed comparisons and for assimilation into models is discussed.

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Dynamic Selection of Ship Responses for Estimation of On-Site Directional Wave Spectra

Volume 5: Ocean Engineering; CFD and VIV ◽

10.1115/omae2012-83206 ◽

2012 ◽

Author(s):

Ingrid Marie Vincent Andersen ◽

Gaute Storhaug

Keyword(s):

Transfer Functions ◽

Response Spectrum ◽

Wave Spectrum ◽

Selection Procedure ◽

Selection Method ◽

Parametric Modelling ◽

Dynamic Selection ◽

Directional Wave Spectrum ◽

Reliability Method ◽

Directional Wave

Knowledge of the wave environment in which a ship is operating is crucial for most on-board decision support systems. Previous research has shown that the directional wave spectrum can be estimated by the use of measured global ship responses and a set of transfer functions determined for the specific ship. The approach can either be based on parametric or Bayesian (non-parametric) modelling, and in both cases a set of three ship responses usually provides the best estimation. The optimal response combination of three responses at any time depends on the environmental conditions and the operation of the ship. Since measurements of more than three responses are usually available, a quick, dynamic selection procedure of the three signals best suited for the wave spectrum estimation procedure is essential. In the present paper the concept of a selection method based on a simple pre-estimate of the wave spectrum is suggested. The selection method needs to be robust for what reason a parameterised uni-directional, two-parameter wave spectrum is treated. The parameters included are the zero up-crossing period, the significant wave height and the main wave direction relative to the ship’s heading. The procedure basically seeks to minimise the difference between a set of spectral moments derived from a measured response spectrum and the corresponding response spectrum calculated from the parameterised wave spectrum and the transfer function for any given response. Subsequently, the three responses with the best overall agreement are selected for the actual estimation of the directional wave spectrum. The transfer functions for the ship responses can be determined using different computational methods such as striptheory, 3D panel codes, closed form expressions or model tests. The uncertainty associated with transfer functions depends on the computational method used, relative heading, frequency and type of response. This uncertainty is conceptually taken into account in the selection procedure using the First Order Reliability Method (FORM). However, specific assessment of the uncertainties has not been carried out, but is subject to later studies.

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