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.

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.

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 Determination of Water Motions Inside a Moonpool

2017 ◽  
Author(s):  
Bastien Abeil
Keyword(s):  
Experimental Determination ◽  
Transfer Functions ◽  
Side Wall ◽  
Model Tests ◽  
Irregular Waves ◽  
Video Recordings ◽  
Non Linear ◽  
Relative Water ◽  
Water Elevation

Model tests of a drillship with a rectangular moonpool opening were conducted in regular and irregular waves from the bow and bow-quarter. Most tests were conducted at zero speed, the rest was performed with the model towed to a speed of 10 kn. From the video-recordings and transfer functions of the measured relative water elevation inside the moonpool, the typical piston and first sloshing modes are well captured, for wave frequencies that agree relatively well with relevant formulations. A few tests conducted at varying wave amplitudes show that the water elevation is non-linear by nature, while repeat tests conducted with the moonpool fitted with two layers of side wall flanges shows that these can reduce the water motions by nearly 40 %.

The Behaviour of Tugs in Waves Assisting LNG Carriers During Berthing Along Offshore LNG Terminals

2005 ◽  
Author(s):  
Bas Buchner ◽  
Pieter Dierx ◽  
Olaf Waals
Keyword(s):  
Model Test ◽  
Weather Conditions ◽  
Model Tests ◽  
Design And Development ◽  
Test Study ◽  
Wave Conditions

For future offshore LNG terminals tugs are planned to assist LNG carriers during berthing and offloading operations. A model test study was carried out to better understand the tug behaviour in waves and to make a first step in the quantification of the related weather limits. Scale 1:35 model tests were performed in the two important ‘modes’ of a tug during this type of operation: the ‘push’ mode and the ‘pull’ mode. Realistic weather conditions were used and the tugs were working at the unshielded and shielded sides of the LNG carrier. Based on the results presented in this paper, it can be concluded that the motions of tugs in waves are significant, even in wave conditions that are considered to be mild for the berthing and offloading LNG carriers. The resulting push or pull loads may hamper these tug operations significantly. Special measures are necessary to take this behaviour into account in tug design, LNG carrier design and development of operational procedures and equipment. The paper gives insight in the typical tug behaviour in different weather conditions. One should be careful, however, to generalize the present results: with an optimised tug design and operation the tugs can be used in more severe conditions.

Slowly Varying Wave Drift Forces Analyzed From Model Test Data on a Moored Ship in Shallow Water

2009 ◽  
Author(s):  
Carl Trygve Stansberg ◽  
Csaba Paˆkozdi
Keyword(s):  
Noise Reduction ◽  
Shallow Water ◽  
Model Test ◽  
Transfer Functions ◽  
Numerical Study ◽  
Wave Frequency ◽  
Irregular Waves ◽  
Spectral Peak ◽  
Frequency Range ◽  
Wave Drift

Model test estimation of quadratic transfer functions (QTFs) is investigated for slowly varying wave drift excitation on a large moored ship in shallow water. Cross-bi-spectral analysis in irregular waves is used. A numerical study is run first, with a known, synthetical QTF model characterized by a strong off-diagonal variation, combined with a very lightly damped linear slow-drift dynamical system. The purpose is to check the accuracy of the analysis. For this simple model, a good accuracy is obtained in the estimated QTF. This is because of a refined noise reduction method which works well in this case. The wave frequency range of valid estimates is where the wave spectrum S(f) is higher than 7% of the spectral peak. Without the refinement, the useful range is reduced to where S(f) is higher than 15% of the spectral peak, based on a 3-hour sea state simulation. The method is then applied on experimental surge motion records from 1:50 scaled model tests carried out in an offshore basin, simulating 15m water depth. It is found that the QTF estimation procedure works reasonably well, but the accuracy is lower than that in the numerical study because the refined noise reduction could not be used due to the particular characteristics of the QTF. Therefore a basic version without the refinement had to be used. Still, results appear to be fairly reliable in the reduced wave frequency range with S(f) > 15% of the spectral peak, i.e. from 0.07Hz to 0.10Hz in this case.

Ship Movements’ Analysis in a Physical Scale Model

2017 ◽  
Vol 372 ◽  
pp. 132-141
Author(s):  
Liliana Pinheiro ◽  
Joana Simão ◽  
João Alfredo Santos ◽  
Conceição Juana Fortes
Keyword(s):  
Physical Model ◽  
Fiber Optic ◽  
Transfer Functions ◽  
Model Tests ◽  
Scale Model ◽  
Physical Model Tests ◽  
Physical Scale ◽  
Wave Heights ◽  
Wave Conditions ◽  
The Waves

A set of physical model tests was run in to characterize the ship’s response to different wave conditions going from frequently-occurring conditions up to extreme ones. Several wave heights, periods and directions were generated. The waves around the ship were measured with probes and the movements of the ship were measured with a fiber-optic gyrocompass. Transfer functions are established and compared with numerical ones obtained with the WAMIT model.

scholarly journals Validation of Numerical Wave Tank Simulations Using REEF3D With JONSWAP Spectra in Intermediate Water Depth

2020 ◽  
Author(s):  
Csaba Pakozdi ◽  
Sebastien Fouques ◽  
Maxime Thys ◽  
Arun Kamath ◽  
Weizhi Wang ◽  
...  
Keyword(s):  
Test Data ◽  
Model Test ◽  
Water Depth ◽  
Model Tests ◽  
Irregular Waves ◽  
Wave Crest ◽  
Intermediate Water ◽  
Numerical Wave Tank ◽  
Wave Tank ◽  
Numerical Wave

Abstract As offshore wind turbines increase in size and output, the support structures are also growing. More sophisticated assessment of the hydrodynamic loads is needed, particularly for the ultimate limit state design. For higher-order phenomena related to rare steep wave events such as ringing, a better understanding of the stochastic loads is needed. As an innovative step forward to reduce the cost of extensive model tests with irregular waves, a larger number of investigations can be carried out using high-performance high-fidelity numerical simulations after an initial stochastic validation with model test data. In this paper, the open-source hydrodynamic model REEF3D::FNPF (Fully Nonlinear Potential Flow) is used to carry out three-hour long simulations with the JONSWAP spectrum in intermediate water depth conditions. Statistical properties of the free surface elevation in the numerical wave tank are validated using the available data from model tests carried out at SINTEF Ocean/NTNU. The spectral shape, significant wave height, peak period, skewness, kurtosis, and wave crest height statistics are compared. The results are analyzed and it is found that the numerical model provides reasonably good agreement with the model test data.

Green Water on FPSO Predicted by a Practical Engineering Method and Validated Against Model Test Data for Irregular Waves

2014 ◽  
Author(s):  
Rafael Vergara Schiller ◽  
Csaba Pâkozdi ◽  
Carl Trygve Stansberg ◽  
Douglas Gustavo Takashi Yuba ◽  
Daniel Fonseca de Carvalho e Silva
Keyword(s):  
Model Test ◽  
Model Tests ◽  
Irregular Waves ◽  
Green Water ◽  
Wave Impact ◽  
Irregular Wave ◽  
Beam Seas ◽  
Practical Engineering ◽  
The University ◽  
Wave Induced

This paper presents a series of numerical analyses performed with the potential theory-based Green Water engineer tool KINEMA3. KINEMA3 was designed to predict wave-induced impact loads on FPSOs in steep irregular waves, and for use in design load analysis. The purpose of the study presented herein is to validate KINEMA3 green water (deck overtopping) predictions in nonlinear irregular waves with results from model tests performed at the TPN (Tanque de Provas Numérico) laboratory at the University of São Paulo, Brazil. Comparisons are made for a selection of irregular wave cases, for two choices of anchoring conditions (free floating vessel and fixed vessel) and for three wave headings (180°, 225° and 270°: head, quartering and beam seas, respectively). KINEMA3 statistical green water predictions present a general good agreement with observations from the TPN model tests for all wave cases, headings and mooring conditions. Overall, observed trends for occurrence of green water and standard deviation/maximum of relative wave height are successfully reproduced by KINEMA3. In agreement with model test results, it is predicted that green water occurs more frequently for a free floating vessel and for beam seas. Additional comparisons between KINEMA3 predictions using different FPSO panel models (low-order and high-order models) present negligible differences with respect to green water estimates. The results presented herein demonstrate the robustness of the tool towards the prediction of green water for variable wave headings and sea states, and highlight the capability of KINEMA3 to be employed as an engineering-like tool for fast and multiple estimates of green water in early design studies. This work is a part of the research project “Green Water and Wave Impact on FPSO” carried out for and in cooperation with PETROBRAS.

On the Validity of CFD for Simulating Extreme Green Water Loads on Ocean-Going Vessels

2020 ◽  
Author(s):  
Henry Bandringa ◽  
Joop A. Helder ◽  
Sanne van Essen
Keyword(s):  
Model Test ◽  
Natural Extension ◽  
Model Tests ◽  
Water Dynamics ◽  
Green Water ◽  
Forward Speed ◽  
Maritime Industry ◽  
Cooperative Research ◽  
Wave Basin ◽  
Non Linear

Abstract The amount of green water and the associated loads that an ocean-going vessel may encounter during its service life are important aspects to consider in the vessel’s design and classification. As green water is typically a highly non-linear phenomenon, commonly the maritime industry relies on model tests to predict green water loads and their occurrence. In recent years, however, a lot of progress with Computation Fluid Dynamics (CFD) has been made in predicting non-linear flows and associated loads at a high level of accuracy. Especially in the field of wave impacts on (moored) offshore structures at zero speed, significant progress has been made and documented using CFD. A natural extension of this progress is to expand the obtained confidence in the applicability of CFD for simulating extreme wave events to applications involving vessels at forward speed. To that end, this paper presents a validation study towards the prediction of green water loading on a (typical) container vessel at forward speed by CFD. For validation, two extreme green water events were selected from a model test campaign carried out at MARIN within the context of the CRS (Cooperative Research Ships) working group ‘green water dynamics’. In these tests a KRISO Container Ship (KCS) is sailing in head seas when encountering severe green water. As CFD tool, the Cartesian-grid based Volume-of-Fluid CFD solver ComFLOW was selected. Furthermore, a deterministic approach is taken for the validation, by reconstructing the non-linear incoming wave in a high amount of detail and imposing the 6 degrees of motion of the vessel using the wave basin measurements. Time traces of the green water flow on deck and local- and global impact loads on the breakwater are presented and compared against the experimental data. Detailed visualizations of the CFD results are presented to further illustrate the obtained match with the model test results and emphasize the additional value of complementing model tests with deterministic CFD analysis.

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.

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