A Preliminary Assessment of the Use of a Large Semi-Submersible Platform As a Motion-Based Wave Sensor

2017 ◽  
Author(s):  
J. Mas-Soler ◽  
Alexandre N. Simos ◽  
Pedro C. de Mello ◽  
Eduardo A. Tannuri ◽  
Felipe L. Souza
Keyword(s):  
Irregular Waves ◽  
Scale Model ◽  
Extreme Wave ◽  
Promising Alternative ◽  
Norwegian Sea ◽  
Experimental Campaign ◽  
Wave Basin ◽  
Extensive Test ◽  
Directional Wave ◽  
Wave Conditions

A well-known drawback of conventional wave monitoring systems, such as wave buoys, is that they experience a loss of accuracy in extreme wave conditions. Also, most of them require important initial investment and/or high maintenance costs. Over the last few years, directional wave inference obtained from the record of vessel motions is a technique that has significantly grown as complement to traditional methods. This article presents a feasibility study on the use of the motions of a semi-submersible platform for performing wave inference. Experiments were carried out at the USP wave basin (CH-TPN) using a 1:120 scale model of a large semi-submersible platform in operational condition and five different headings. In order to provide an extensive test matrix, the experimental campaign included a set of 32 different irregular waves (sea conditions) for each heading, selected from the scatter diagram of the Norwegian sea and covering many of the sea states of interest for this research. Moreover, each sea condition was obtained using the most appropriate type of energy spectrum (JONSWAP or Torsethaugen). Bayesian inference motion-based method was adapted for the semi-submersible platform by the proper adjustment of the hyper-parameters. The estimations obtained with the Bayesian wave inference method, using the semi-submersible recorded motions, were confronted with the directional wave spectra measured during the calibration process from an array of wave probes. The results attested that the method was able to capture all of the wave conditions tested during the experimental campaign with reasonable accuracy, even the more extreme cases. They suggest that the semisubmersible platform may indeed be a promising alternative for inferring severe sea conditions.

3-D Scale Model Study of Wave Run-Up, Overtopping and Damage in a Rubble-Mound Breakwater Subject to Oblique Extreme Wave Conditions

2019 ◽  
Vol 396 ◽  
pp. 32-41 ◽  
Author(s):  
João Alfredo Santos ◽  
Francisco Pedro ◽  
Mário Coimbra ◽  
Andrés Figuero ◽  
Conceição Juana E.M. Fortes ◽  
...  
Keyword(s):  
Laser Scanning ◽  
Wave Structure ◽  
Scale Model ◽  
Wave Steepness ◽  
Extreme Wave ◽  
Empirical Formulas ◽  
Wave Basin ◽  
Rubble Mound ◽  
Wave Conditions ◽  
Run Up

A set of scale-model tests carried out to enlarge the range of wave steepness values analysed in run-up, overtopping and armour layer stability studies, focusing on oblique extreme wave conditions and on their effects on a gentler slope breakwater’s trunk armour and roundhead, is presented in this paper. A stretch of a rubble mound breakwater (head and part of the adjoining trunk, with a slope of 1(V):2(H)) was built in a wave basin at the Leibniz University Hannover to assess, under extreme wave conditions (wave steepness of 0.055) with different incident wave angles (from 40º to 90º), the structure behaviour in what concerns wave run-up, wave overtopping and damage progression of the armour layer. Two types of armour elements (rock and Antifer cubes) were tested. Non-intrusive methodologies including a new application of laser scanning technique for the assessment of both armour layer damage and wave run-up and overtopping were used. It is expected that such work will contribute also with data to improve empirical formulas as well as to validate complex numerical model for wave-structure interaction.

Simulation of Hurricane Seas in a Multidirectional Wave Basin

1991 ◽  
Vol 113 (3) ◽  
pp. 219-227 ◽  
Author(s):  
A. Cornett ◽  
M. D. Miles
Keyword(s):  
Ocean Waves ◽  
Entropy Method ◽  
Wave Spectra ◽  
Single Wave ◽  
Wave Condition ◽  
Wave Basin ◽  
Wide Range ◽  
Directional Wave ◽  
Wave Conditions ◽  
Multidirectional Wave

This paper describes the generation and verification of four realistic sea states in a multidirectional wave basin, each representing a different storm wave condition in the Gulf of Mexico. In all cases, the degree of wave spreading and the mean direction of wave propagation are strongly dependent on frequency. Two of these sea states represent generic design wave conditions typical of hurricanes and winter storms and are defined by JONSWAP wave spectra and parametric spreading functions. Two additional sea states, representing the specific wave activity during hurricanes Betsy and Carmen, are defined by tabulated hindcast estimates of the directional wave energy spectrum. The Maximum Entropy Method (MEM) of directional wave analysis paired with a single-wave probe/ bi-directional current meter sensor is found to be the most satisfactory method to measure multidirectional seas in a wave basin over a wide range of wave conditions. The accuracy of the wave generation and analysis process is verified using residual directional spectra and numerically synthesized signals to supplement those measured in the basin. Reasons for discrepancy between the measured and target directional wave spectra are explored. By attempting to reproduce such challenging sea states, much has been learned about the limitations of simulating real ocean waves in a multidirectional wave basin, and about techniques which can be used to minimize the associated distortions to the directional spectrum.

Experimental Assessment of the Performance of CECO Wave Energy Converter in Irregular Waves

2018 ◽  
Author(s):  
Claudio A. Rodríguez ◽  
F. Taveira-Pinto ◽  
P. Rosa-Santos
Keyword(s):  
Wave Energy ◽  
Transfer Functions ◽  
Nonlinear Effects ◽  
Model Tests ◽  
Experimental Results ◽  
Irregular Waves ◽  
Scale Model ◽  
Experimental Assessment ◽  
Simplified Approach ◽  
Wave Basin

A new concept of wave energy device (CECO) has been proposed and developed at the Hydraulics, Water Resources and Environment Division of the Faculty of Engineering of the University of Porto (FEUP). In a first stage, the proof of concept was performed through physical model tests at the wave basin (Rosa-Santos et al., 2015). These experimental results demonstrated the feasibility of the concept to harness wave energy and provided a preliminary assessment of its performance. Later, an extensive experimental campaign was conducted with an enhanced 1:20 scale model of CECO under regular and irregular long and short-crested waves (Marinheiro et al., 2015). An electric PTO system with adjustable damping levels was also installed on CECO as a mechanism of quantification of the WEC power. The results of regular waves tests have been used to validate a numerical model to gain insight into different potential configurations of CECO and its performance (López et al., 2017a,b). This paper presents the results and analyses of the model tests in irregular waves. A simplified approach based on spectral analyses of the WEC motions is presented as a means of experimental assessment of the damping level of the PTO mechanism and its effect on the WEC power absorption. Transfer functions are also computed to identify nonlinear effects associated to higher waves and to characterize the range of periods where wave absorption is maximized. Furthermore, based on the comparison of the present experimental results with those corresponding to a linear numerical potential model, some discussions are addressed regarding viscous and other nonlinear effects on CECO performance.

Freak Wave Generation in a Wave Basin With HOSM-WG Method

2015 ◽  
Author(s):  
Hidetaka Houtani ◽  
Takuji Waseda ◽  
Wataru Fujimoto ◽  
Keiji Kiyomatsu ◽  
Katsuji Tanizawa
Keyword(s):  
Control Method ◽  
Irregular Waves ◽  
Frequency Bandwidth ◽  
Freak Waves ◽  
Freak Wave ◽  
Wave Basin ◽  
Wave Trains ◽  
Directional Wave ◽  
Wave Maker ◽  
The Difference

A method to produce freak waves with arbitrary spectrum in a fully directional wave basin is presented here. This is an extension of Waseda, Houtani and Tanizawa at OMAE 2013[1], which used “HOSM-WG” based on the higher-order spectral method (HOSM). We used the following three methods to improve the HOSM-WG in [1]: “separation of free waves from bound waves,” “using Biesel’s transfer function in wavenumber space” and “using Schaffer’s 2nd-order wave maker control method.” Modulational wave trains, freak waves in unidirectional irregular waves and freak waves in short-crested irregular waves were generated in a wave basin. The experimental results using the improved HOSM-WG were compared to the HOSM simulation, and good agreements were found. The effectiveness of the improved HOSM-WG was ascertained. We showed that the difference between HOSM-WG and HOSM simulations became larger as wave steepness, frequency bandwidth of the spectrum or directional spreading became larger.

Experimental Validation for Motion of a SPAR-Type Floating Offshore Wind Turbine Using 1/22.5 Scale Model

2009 ◽  
Author(s):  
Tomoaki Utsunomiya ◽  
Tomoki Sato ◽  
Hidekazu Matsukuma ◽  
Kiyokazu Yago
Keyword(s):  
Wind Turbine ◽  
Simulation Method ◽  
Offshore Wind ◽  
Irregular Waves ◽  
Scale Model ◽  
Offshore Wind Turbine ◽  
Floating Offshore Wind Turbine ◽  
Wave Basin ◽  
Tank Experiment ◽  
Made In

In this paper, motion of a SPAR-type floating offshore wind turbine (FOWT) subjected to wave loadings is examined. The proposed prototype FOWT mounts a 2MW wind turbine of down-wind type, whose rotor diameter is 80m and hub-height 55m. The SPAR-type floating foundation measures 60m in draft, having circular sections whose diameter is 12m at the lower part, 8.4m at the middle (main) part and 4.8m at the upper part. The FOWT is to be moored by a conventional anchor-chain system. In order to design such a FOWT system, it is essential to predict the motion of the FOWT subjected to environmental loadings such as irregular waves, turbulent winds, currents, etc. In this paper, the motion of the FOWT subjected to regular and irregular waves is examined together with the application of steady horizontal force corresponding to steady wind. The wave-tank experiment is made in the deep sea wave-basin at NMRI (National Maritime Research Institute), using a 1/22.5 scale model of the prototype FOWT. The experimental results are compared with the numerical simulation results for validation of the simulation method.

Model Tests With an FPSO in Design Environmental Conditions

2004 ◽  
Author(s):  
Jesper Skourup ◽  
Martin J. Sterndorff ◽  
Susan F. Smith ◽  
Xiaoming Cheng ◽  
R. V. Ahilan ◽  
...  
Keyword(s):  
Model Test ◽  
Environmental Conditions ◽  
Transfer Functions ◽  
Model Tests ◽  
Irregular Waves ◽  
Wind Condition ◽  
Test Programme ◽  
Wave Basin ◽  
Wide Range ◽  
Wave Conditions

An extensive model test programme has been carried out with a turret moored FPSO model in design environmental conditions. The model tests were carried out in the 3D offshore wave basin at DHI Water & Environment at a scale of 1:80. The objectives of the model tests were two-fold: 1. To determine quadratic transfer functions for the slow-drift forces. 2. To determine the turret moored FPSO response in design environmental conditions with wave spreading. The model tests were made with a wide range of monochromatic and bi-chromatic wave conditions and also with long- and short-crested irregular wave conditions. For the tests in design conditions the irregular waves were combined with the corresponding wind condition. The model (which was segmented into two parts) was equipped with instruments to measure forces in mooring lines and turret, 6 dof motions of the FPSO, bending moments on the FPSO hull and wave run-up on the FPSO model. The present paper describes the details of the experimental work and the measurements made in the tests. Comparisons between model test results themselves to demonstrate the effects of wave spreading on the responses and comparisons to numerical results are given. The model test programme is part of the REBASDO project, funded by the European Union, and involving companies and institutions from several European Countries. The overall objective with the REBASDO project is to develop met-ocean and hydrodynamic models, which will capture the significant features of directional wave effects on FPSO design so that relevant enhancements in the design process can be incorporated in the future.

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

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.

Numerical and Experimental Analysis of a Novel Wave Energy Converter

2010 ◽  
Author(s):  
Ken Rhinefrank ◽  
Al Schacher ◽  
Joe Prudell ◽  
Joao Cruz ◽  
Nuno Jorge ◽  
...  
Keyword(s):  
Wave Energy ◽  
Wave Energy Converter ◽  
Irregular Waves ◽  
Numerical Code ◽  
Scale Model ◽  
Energy Converter ◽  
Modeling Tools ◽  
Physical Experiments ◽  
Wave Basin ◽  
Wave Research

A novel point absorber wave energy converter (WEC) is being developed by Columbia Power Technologies, LLC (CPT). Numerical and physical experiments have been performed by Columbia Power, Garrad Hassan and Partners (GH) and Oregon State University (OSU). Three hydrodynamic modeling tools including WAMIT, GH WaveFarmer, and OrcaFlex are used to evaluate the performance of the WEC. GH WaveFarmer is a specialized numerical code being developed specifically for the wave energy industry. Performance and mooring estimates at full scale were initially evaluated and optimized, which were then followed by the development of a 1/33rd scale physical model to obtain comparable datasets, aiming to validate the predictions and reduce the uncertainty associated with other numerical model results. The tests of the 1/33rd scale model of the CPT WEC were recently carried out at the multi-directional wave basin of the O.H. Hinsdale Wave Research Laboratory (HWRL), in conjunction with the Northwest National Marine Renewable Energy Center (NNMREC) at OSU. This paper presents details of the modeling program and progress to date. Emphasis is given to the coupling of WAMIT with GH WaveFarmer for performance estimates and the coupling of WAMIT with the OrcaFlex model for mooring load estimates. An overview of the novel 3-body WEC, including operation and mooring system, is also presented. The 1/33rd scale model functionality is described including an overview of the experimental setup at the basin. Comparisons between the numerical and experimental results are shown for both regular and irregular waves and for several wave headings and dominant directions using a number of spreading functions. The paper concludes with an overview of the next steps for the modeling program and future experimental test plans.

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

2018 ◽  
Vol 140 (4) ◽  
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.

scholarly journals Future behavior of wind wave extremes due to climate change

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Hector Lobeto ◽  
Melisa Menendez ◽  
Iñigo J. Losada
Keyword(s):  
Climate Change ◽  
Wave Climate ◽  
Climate Change Scenarios ◽  
Return Periods ◽  
Extreme Wave ◽  
Future Behavior ◽  
Climate Simulations ◽  
Wave Conditions ◽  
Ne Pacific ◽  
Change In Mean

AbstractExtreme waves will undergo changes in the future when exposed to different climate change scenarios. These changes are evaluated through the analysis of significant wave height (Hs) return values and are also compared with annual mean Hs projections. Hourly time series are analyzed through a seven-member ensemble of wave climate simulations and changes are estimated in Hs for return periods from 5 to 100 years by the end of the century under RCP4.5 and RCP8.5 scenarios. Despite the underlying uncertainty that characterizes extremes, we obtain robust changes in extreme Hs over more than approximately 25% of the ocean surface. The results obtained conclude that increases cover wider areas and are larger in magnitude than decreases for higher return periods. The Southern Ocean is the region where the most robust increase in extreme Hs is projected, showing local increases of over 2 m regardless the analyzed return period under RCP8.5 scenario. On the contrary, the tropical north Pacific shows the most robust decrease in extreme Hs, with local decreases of over 1.5 m. Relevant divergences are found in several ocean regions between the projected behavior of mean and extreme wave conditions. For example, an increase in Hs return values and a decrease in annual mean Hs is found in the SE Indian, NW Atlantic and NE Pacific. Therefore, an extrapolation of the expected change in mean wave conditions to extremes in regions presenting such divergences should be adopted with caution, since it may lead to misinterpretation when used for the design of marine structures or in the evaluation of coastal flooding and erosion.

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