Numerical and experimental investigations into the application of response conditioned waves for long-term nonlinear analyses

Drummen, Ingo; Wu, Mian; Moan, Torgeir

doi:10.1016/j.marstruc.2008.12.002

Cited by 22 publications

(6 citation statements)

References 9 publications

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“…The MLER method was applied successfully in this study; however, this type of equivalent design wave method has been shown to be less accurate when the load response depends heavily on the instantaneous wave train, vessel position, and its deformation, unless a random background wave was used [7]. Ultimately, these methods may work well for some responses of interest but not for others, depending on the WEC design and working principle.…”

Section: Discussionmentioning

confidence: 99%

“…The equivalent design waves represent the sea state at which the extreme loads are most likely to occur. Several methods have been used for numerical and experimental naval architecture studies, including the most likely wave (MLW), most likely extreme response (MLER), most likely response wave (MLRW), conditional random response wave (CRRW) [6,7], and design load generator [8] approaches. These methods assume the nonlinear response of a floating vessel can be approximated by a linearized response, and the nonlinear response is a small perturbation from the linear solution.…”

Section: Omae2016-54751mentioning

confidence: 99%

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Application of the Most Likely Extreme Response Method for Wave Energy Converters

Quon

Platt

et al. 2016

Volume 6: Ocean Space Utilization; Ocean Renewable Energy

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Extreme loads are often a key cost driver for wave energy converters (WECs). As an alternative to exhaustive Monte Carlo or long-term simulations, the most likely extreme response (MLER) method allows mid- and high-fidelity simulations to be used more efficiently in evaluating WEC response to events at the edges of the design envelope, and is therefore applicable to system design analysis. The study discussed in this paper applies the MLER method to investigate the maximum heave, pitch, and surge force of a point absorber WEC. Most likely extreme waves were obtained from a set of wave statistics data based on spectral analysis and the response amplitude operators (RAOs) of the floating body; the RAOs were computed from a simple radiation-and-diffraction-theory-based numerical model. A weakly nonlinear numerical method and a computational fluid dynamics (CFD) method were then applied to compute the short-term response to the MLER wave. Effects of nonlinear wave and floating body interaction on the WEC under the anticipated 100-year waves were examined by comparing the results from the linearly superimposed RAOs, the weakly nonlinear model, and CFD simulations. Overall, the MLER method was successfully applied. In particular, when coupled to a high-fidelity CFD analysis, the nonlinear fluid dynamics can be readily captured.

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Section: Discussionmentioning

confidence: 99%

Section: Omae2016-54751mentioning

confidence: 99%

Application of the Most Likely Extreme Response Method for Wave Energy Converters

Quon

Platt

et al. 2016

Volume 6: Ocean Space Utilization; Ocean Renewable Energy

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“…The natural progression from CNW is an analogous method that embeds the MLER rather than NW. This approach is often referred to as the Conditional Random Response Wave (CRRW), originally developed by Dietz (2005) and has been previously demonstrated for extreme events for ships dynamics (Drummen et al, 2009;Seyffert et al, 2020), concluding that the responses are in-line with those in irregular sea states. The results from these studies are promising but further investigations are necessary, with emphasis on floating ORE devices in particular, before constrained SDWs can become established tools within ORE recommended design practices.…”

Section: Introductionmentioning

confidence: 99%

Laboratory investigation on short design wave extreme responses for floating hinged-raft wave energy converters

et al. 2022

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In offshore renewable energy design procedures, accurate predictions of extreme responses are required in order to design for survivability whilst minimising associated costs. At present, the established method for predicting extreme responses is to conduct a large number of long-duration simulations, which is practical only in cases where the structural behaviour is captured by a computationally efficient linear approach. Many applications, however, will require a nonlinear approach, which significantly increases the computational cost, and hence the time required to analyse a problem. Should high-fidelity numerical approaches be the appropriate analysis tool, the long-duration simulations are likely to be impractical and in many cases infeasible. Laboratory testing can be utilised to address this to some extent, but this still time-consuming and expensive from a financial perspective. Consequently, there has been considerable interest in the use of short design waves as an alternative method for speeding up the design process. Currently, standards advise that short design waves can be utilised in the design of fixed offshore structures, but application to floating offshore structures needs verification before it becomes an established procedure. This study considers application of single and constrained short design waves to a floating hinged-raft wave energy converter using a 1:50 scale physical modelling approach, and compares with equivalent irregular sea states. The single wave approaches considered here are “NewWave” and the “Most Likely Extreme Response” wave, which are derived from the frequency content of the wave spectrum and response spectrum, respectively. The constrained approach considered in this study is the “Conditional Random Response Wave,” where the Most Likely Extreme Response wave is embedded within a random short irregular background. Results show that the single wave approaches under-estimate the extreme loading for the hinge-angle and mooring system compared with the irregular and constrained approaches. The discrepancy between single and constrained waves implies that memory effects are non-negligible, and hence it is critical that they are accounted for when utilising short design waves for floating applications.

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“…Given these computational constraints, the use of a 'design wave', or focused wave, to predict extreme loads for offshore structures, such as WECs, is becoming increasingly common (Coe et al, 2019;Quon et al, 2016;Ransley et al, 2017;van Rij et al, 2019a). Several formulations for designing focused waves for a given spectral sea state have been developed, including the NewWave (Tromans et al, 1991), the most likely wave, the most likely extreme response and conditional random response wave (Dietz, 2004;Drummen et al, 2009). The widely used NewWave theory, as applied in this study, generates a first-order focused wave for a given wave spectrum based on a linear sum of waves focused at a specified position and time.…”

Section: Introductionmentioning

confidence: 99%

Validation of simulated wave energy converter responses to focused waves

Rij

Tran

2021

Proceedings of the Institution of Civil Engineers - Engineering

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Numerical and experimental investigations into the application of response conditioned waves for long-term nonlinear analyses

Cited by 22 publications

References 9 publications

Application of the Most Likely Extreme Response Method for Wave Energy Converters

Application of the Most Likely Extreme Response Method for Wave Energy Converters

Laboratory investigation on short design wave extreme responses for floating hinged-raft wave energy converters

Validation of simulated wave energy converter responses to focused waves

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