Extreme Wave Conditions Research Articles

Nonlinear Bragg resonance of focused wave groups by periodic seabed topography

Bragg resonance induced by periodic bottoms has potential applications for coastal protection. Under extreme wave conditions, nonlinearity may play a critical role in the wave-topography interactions. It is important to understand the nonlinear effects in Bragg resonance of periodic bottoms subject to a nonlinear focused wave group, as a representation of an extreme transient event. An efficient fully nonlinear numerical model using the conformal mapping method is developed to simulate wave-topography interaction problems. Validation of this model is performed against theoretical predictions and experimental data in the literature. It is then employed to study Bragg reflection triggered by nonlinear focused wave groups. The nonlinear analysis finds that increased wave group amplitudes slightly weaken the Bragg reflection and shift the value of the corresponding relative wavelength 2S/LP, as a result of the free surface nonlinear effect. The three bottom configurations tested include ripples, rectified cosinoidal bars, and steps. A second order Bragg reflection is observed at 2S/LP=2.0, with reflection coefficients potentially exceeding the fundamental reflection coefficients by up to 20% at greater bar heights. This study provides new insights into the nonlinear Bragg Resonance of free surfaces and periodic seabed topography under extreme wave conditions.

Understanding Decadal-Scale Dynamics in the Bering Sea: Investigating Trends and Variability in Sea Ice, Winds, and Waves

Abstract Despite the societal and economic importance of the Bering Sea, recent rapid changes in surface ocean conditions are not well documented. We address this gap by characterizing the Bering Sea winter ice–wind–wave climate using satellite observations and reanalysis data. Nine of the last 10 years (2014–23) have experienced anomalously low sea ice extent relative to the 1980–2023 mean. Between 2003 and 2023, gale force wind speeds have become more common and satellite altimeter observations show significant wave height (SWH) has increased ≥6 m, and has increased by 1 m between 2003 and 2023, while 20 days yr−1 exhibit SWH > 9 m. Winters between 2018 and 2023 were the six stormiest since 2003, and the sea ice season decreases by 1–4 days yr−1. Should ice loss in the Bering Sea continue to decline, we hypothesize that the frequency of extreme waves over the Bering Sea shelf would increase, severely impacting coastal communities. In September 2022, extratropical cyclone Merbok caused unprecedented SWH (>15 m) over the shelf which were uncharacteristic for the season, and caused widespread coastal inundation and property damage. Such anomalous wave conditions exemplify the emerging threat storms pose in a future where sea ice is absent more frequently in winter, when severe storms are most common. Satellite altimeters have improved the observation of surface ocean conditions in the Bering Sea during the most intense storms, and we demonstrate that a suite of five or more altimeters is required to capture regional events adequately. Significance Statement Although the Bering Sea region has recently endured rapid sea ice loss and the decline of several species important for subsistence and commercial fishing, it has relatively few resources to monitor and mitigate changing climatic conditions. In this article, we show that extreme wind and wave conditions in the Bering Sea have strongly increased in recent years, as sea ice has declined. This points to a need for reliable and continued monitoring, and with only two wave buoys providing year-round observations, an adequate constellation of ocean remote sensing instruments is required to capture extreme ocean–ice–atmosphere events in an isolated and challenging environment.

Real scale experiments on the wave-induced burial and mobilization of Unexploded Ordnance on the seafloor

As a result of armed conflicts, huge amounts of Unexploded Ordnance devices (UXO) and Discarded Munition Material (DMM) are expected to be located on the seafloor, especially in coastal regions. During Offshore Construction, strategical site monitoring and systematic remediation activities, the behavior of such objects in waves and currents is of huge interest as potential mobilization of objects after a survey or clearance activity could change the situational picture again. From findings and reports it often is assumed that UXO and DMM tend to migrate over the seafloor for long distances. Here, anthropogenic effects like fishing or dredging activities are underestimated. More scientific approaches clearly show that mobilization and migration of UXO over long distances does not occur. However, theoretical analysis remain theories until they are proven by experiments. For this reason, three large representative objects were investigated under real scale wave conditions in the Delta Flume of Deltares. The objects represent real scale models of UXO found in the North Sea as well as academically shaped objects. All objects as well as the Flume Tank were intensively instrumented to measure the full environmental conditions as well as the behavior of the objects. The sediment represents typical sand as found in the North Sea and the seabed morphology and soil conditions were closely monitored during the experiments. The experiments support the theoretical models that predict burial but no mobilization also under extreme wave conditions.

Understanding bimodal seas, shingle beach response and flood risk at Hayling Island, UK

Beach management through nourishment and annual recycling has been applied for over 37 years to manage flood and coastal erosion risk to 1700 properties at Eastoke, Hayling Island, UK. This form of natural flood risk management has proved successful in avoiding the annual flooding that blighted this area previously. However, there have been unexpected storm events that have caused beach erosion and localised flooding. Using long-term nearshore wave datasets and state-of-the-art statistical methods, new multi-variate extreme wave conditions were derived and applied to assess beach performance. Eastoke beach was found to meet its original design criteria of a 0.5% AEP standard of protection for unimodal wave conditions. However, it experiences greater rollback erosion, wave overwash and therefore flood inundation under certain (but not all) bimodal wave conditions, causing uncertainty around the future standard of protection. Communicating these inconsistencies to practitioners and a non-specialist audience is challenging as we tend to oversimplify, despite every beach and storm being unique. Better understanding of mixed beaches, both in situ and through parametric and numerical models, would reduce uncertainty to ensure communities are resilient to climate change.

High-resolution atlas of extreme wave height and relative risk ratio for US coastal regions

Interest in marine energy development has motivated numerous studies on extreme wave conditions to characterize wave loads and project risks. Metrics on extreme wave conditions, including extreme wave height, are limited in nearshore regions by insufficient spatiotemporal coverage and resolution of wave data. This study estimates 1-, 5- and 50-year return period significant wave heights, and relative-risk-ratios computed by non-dimensionalizing these extreme wave heights with their mean values, for US nearshore regions using 32-year regional SWAN wave hindcasts with spatial resolutions of 200–300 m. The model-derived extreme wave height estimates are systematically biased lower than buoy-derived estimates, but are well correlated enabling simple bias correction to buoy-observations. As wave heights at shallow nearshore sites are physically limited by depth-induced wave breaking, model-derived extreme wave height estimates are replaced with estimates using common empirical models based on breaking depth limits. The corrected high-resolution extreme wave height and relative risk ratio atlas generated herein provides important metrics that support resource characterization for the marine energy industry, including resource and site assessment, and the establishment of upper design limits for device type classification and certification to streamline product line development.

Mooring line materials for mini-TLP platforms

Abstract The present paper aims to compare the different types of mooring lines and materials with respect to motions and performance of a mini-Tension-Leg Platform. FloatMast®, that has been deployed in the Aegean Sea and completed a 1-year successful offshore site assessment, is a mini TLP and its structural model was used to evaluate the different mooring systems. Synthetic ropes, as alternative to wire ropes, have been introduced recently for mini TLPs, and their performance in these types of offshore platforms is of notable interest, both performance and marketwise. The simulations were conducted using DNV’s software SESAM suite and address operational as well as extreme wave conditions. The results present, for all materials, the performance of each mooring line in terms of axial tension and platform movement.

Numerical modeling of an offshore shellfish farm exposed to extreme wave conditions

Shellfish cultivation is a sustainable method of providing human food and can help remove large amounts of CO2 from the atmosphere. Over the last two decades, longline-based structures have dominated farming systems. So far, the innovative technologies for open-ocean shellfish farming remain stagnant and need to be developed. As such, this paper preliminarily studies the operation and survivability abilities of an innovative shellfish farm under extreme wave conditions. To that end, an efficient numerical scheme with a robust implicit finite element method is established. First, the numerical modeling of a single module of the shellfish farm is conducted and the numerical results are verified against physical model tests. Then, the numerical modeling is implemented in a full-scale shellfish farm containing nine floating rafts with suspended lantern nets in a 3×3 configuration exposed to extreme wave conditions. Different angles of wave attack and shellfish rafts with and without lantern nets are fully considered, allowing an assessment of the operation and survivability abilities of the shellfish farm under extreme wave conditions in various situations. The results highlight that the angle of wave attack significantly affected the energy absorption of the mooring system. Moreover, non-linear instability such as subharmonics, which existed in the motion dynamics, can be manipulated to avoid resonant motions. This study provides insights into the evaluation of the safety design of a shellfish farm at both operational and survivability levels. The numerical method can also model other advanced offshore marine structures with multi-modules, such as floating bridges, airports, and even floating energy islands.

Design considerations for a continuous mussel farm in New England Offshore waters. Part I: Development of environmental conditions for engineering design

Sustainable aquaculture in nearshore waters faces challenges such as stakeholder conflicts, environmental pollution, and spatial constraints. Offshore aquaculture offers a promising solution but requires robust engineering design to withstand extreme weather conditions. This study develops the environmental conditions essential for engineering the design of a continuous mussel dropper system in New England offshore waters. A potential farm location was identified using criteria including water depth, federal boundaries, seafloor suitability, farm size, and proximity to ports, based on bathymetric and sedimentary maps. Historical data from five wave monitoring stations and two current velocity stations were analyzed to model extreme environmental conditions, as waves and currents pose primary threats. The extreme wave and current conditions are modeled using the Weibull distribution, on the annual maximum hourly significant wave height data and the largest 0.3 % of current speeds. A newly proposed method combining Spalding’s wall function with a fourth-order polynomial is used to enhance the current profile analysis. Additionally, a joint probability density function was developed for wave height and current velocity at a specific depth, providing insights into wave height, period, and wavelength for various return periods such as 10, 25, 50, and 100 years. The results suggest a 10-yr wave of 8 m significant wave height and a current speed of 1.68 m/s, while a 50-yr values are 9.4 m and 1.96 m/s respectively. These findings offer critical data on extreme wave and current conditions in New England’s offshore waters, providing practical guidance for the engineering design of offshore mussel farms. This research advances offshore mussel farming and benefits the development of all types of offshore aquaculture systems.

Longshore Sediment Transport Across a Tombolo Determined by Two Adjacent Circulation Cells

AbstractLongshore sediment transport (LST) is essential for shaping sandy shorelines. Many shorelines are complex and indented, containing headlands, offshore islands and tombolos. Tombolos often form between islands and the mainland; however, the conditions for LST across tombolos are unclear. This question is important because tombolos are often reinforced with anthropogenic infrastructure, potentially causing sediment starvation of downdrift beaches. Along many shorelines, the return to a tombolo's natural condition has been proposed to promote sediment connectivity and counteract erosion. Nevertheless, the implications of such restorations remain uncertain. In this study, we employ the Delft3D wave‐current model to investigate hydrodynamics and sediment dynamics across a tombolo, examining its role as a connector between adjacent beaches. Contrary to expectations, our simulations show only diminutive longshore currents from the updrift beach across the tombolo unless offshore wave heights exceed 8 m. Instead, predominant currents crossing the tombolo originate from offshore of the island, driven by storm‐induced water level differences and circulation cells on both sides of the tombolo. The offshore island shelters the downdrift domain, resulting in higher wave energy and dissipation updrift of the tombolo. Further, increasing wave height or wave approach angle not only intensifies water level differences but also relocates circulation cells, enhancing total sediment transport from the updrift beach across the tombolo. However, in general, the deposition of sediment from the updrift side of the domain does not compensate for the sediment loss on the downdrift beach. We conclude that LST across tombolos is limited and occurs only under extreme wave conditions.

Hydrodynamic analysis of sea-crossing bridge piers subjected to freak waves

Coastal areas are witnessing a surge in critical infrastructure development, such as sea-crossing bridges, to support growing populations and economic activities. However, these structures face ongoing challenges in harsh marine environments. Therefore, understanding the hydrodynamics of bridge structures under extreme freak wave conditions is imperative for designing effective countermeasures. This study investigates pier hydrodynamics using a three-dimensional numerical flume simulated by OpenFOAM, focusing on loading characteristics and wave climb differences under freak and linear waves. Results show that freak waves induce larger surges and forces compared to linear waves, with a notable “bell vibration” effect near the wave surface. Moreover, peak forces and bending moments increase nonlinearly with the wave height-to-significant wave height ratio. For double-column piers, transverse alignment concentrates wave climb on the rear side of the front pier, with forces increasing with spacing, while those on the rear pier decrease. Conversely, longitudinal arrangements show amplified loading effects. These findings provide valuable insights into the hydrodynamic behaviour of bridge piers under freak wave conditions, offering practical implications for the design and protection of sea-crossing bridges.

Joint probabilistic modeling of extreme wind-wave conditions under typhoon impact and applications to extreme response analysis of floating offshore wind turbines

The joint probabilistic modeling of extreme wind and wave conditions under typhoon impact is a critical task for extreme response analysis of floating offshore wind turbines (FOWTs) deployed in typhoon-prone areas. However, wind and wave observations under typhoon impact are quite limited, which poses great challenges to the probabilistic modeling task. Although some sophisticated programs can be employed to simulate typhoon-induced wave fields, they suffer from unbearable computational burdens. To improve the accuracy and efficiency of joint probabilistic modeling of extreme wind and wave conditions under typhoon impact, an approach that synthesizes the typhoon hazard analysis method and copula-based conditional modeling method is proposed in the present study. The proposed joint distribution model is expressed as the product of the distribution of extreme wind speed and the conditional distribution of significant wave height. The distribution of extreme wind speed is estimated through the typhoon hazard analysis method, and the conditional distribution of significant wave height is modeled by the copula-based method. The effectiveness of the proposed method is verified by comparing with observation data. Applications of the proposed method to extreme response analysis of FOWTs are illustrated as well.

Soliton groups and extreme wave occurrence in simulated directional sea waves

The evolution of nonlinear wave groups that can be associated with long-lived soliton-type structures is analyzed, based on the data of numerical simulation of irregular deep-water gravity waves with spectra typical to the ocean and different directional spreading. A procedure of the windowed Inverse Scattering Transform, which reveals wave sequences related to envelope solitons of the nonlinear Schrödinger equation, is proposed and applied to the simulated two-dimensional surfaces. The soliton content of waves with different directional spreading is studied in order to estimate its dynamical role, including characteristic lifetimes. Statistical features of the solitonic part of the water surface are analyzed and compared with the wave field on average. It is shown that intense wave patterns that persist for tens of wave periods can emerge in stochastic fields of relatively long-crested waves. They correspond to regions of locally enhanced on average waves with reduced kurtosis. This eventually leads to realization of locally extreme wave conditions compared to the general background. Although intense soliton-like groups may be detected in short-crested irregular waves as well, they possess much shorter lateral sizes, quickly disperse, and do not influence the local statistical wave properties.

Coastal bridges with a box-girder superstructure under the action of solitary waves: Study on the optimization of bearings, dynamic characteristics and failure mechanism

Coastal bridges featuring a box-girder design are instrumental in advancing coastal transport and economic development. However, numerous coastal bridges with limited clearance above sea level are prone to the impact of the extreme waves. In order to enhance the survivability of superstructures of the bridge in the face of severe wave conditions, the present study implemented measures such as adding steel fasteners to conventional laminated rubber bearings and incorporating fluid viscous dampers to the box-girder superstructure. A three-dimensional fluid-structure coupling model, including a three-dimensional numerical flume, adjacent structures, and a box-girder superstructure supported by various bearings, is developed to explore the failure mechanisms and dynamic properties of the superstructure when subjected to extreme solitary wave conditions. Then, the effects of the implemented measures on the disaster resistance of bridge superstructures are comprehensively examined. The results indicate that: (1) After subjected to extreme solitary wave actions, the box-girder superstructure is at a high risk of failure due to sliding, unseating, and overturning. (2) Adding steel fasteners to conventional laminated rubber bearings can effectively alleviate overturning failure of the box-girder superstructure. (3) The addition of fluid viscous dampers into the box-girder superstructure can effectively decrease its maximum displacement. (4) Bridges with box-girder superstructures typically undergo bearing vertical and deformation failure during their failure process.

Neural network survivability approach of a wave energy converter considering uncertainties in the prediction of future knowledge

To tune the wave energy converter (WEC) controller parameters such as damping to reduce the line force during extreme wave conditions, future knowledge of the line force is required. To achieve this, the incoming wave and system state should be predicted for a few seconds in the future. It is rather an arduous task to predict the future knowledge of waves and the system’s dynamic when dealing with breaking and steep waves, and the system is subject to various nonlinear forces. The classical model-based control strategies often rely on linear assumptions to estimate the WEC dynamics for the sake of simplicity. Unlike the model-based, the data-driven approaches are free from modeling errors and the algorithms are trained over the true and noisy data to predict non-linear system behaviors. Using data-driven approaches, we are able to model nonlinear dynamics. However, new questions emerge on the accuracy of the future wave and system state predictions, and how this uncertainty propagates into the final prediction of the line force. As incorrect damping may lead to excessive line force and detrimental damage to the system, these are the knowledge gaps that need to be addressed. The main purpose of this paper is to answer these questions through a survivability strategy for wave energy converters by providing a realistic perspective on the implementation of the neural network approaches by accounting for the errors in the input data. For this purpose, a series of neural networks is designed that first predicts the surface elevation for 0.36 s ahead, i.e. corresponding to 2 s in the full-scale WEC. This future knowledge of the wave elevation is then used to predict the system state (i.e. power take-off (PTO) translator position) for the same prediction horizon based on the PTO damping. This information is then fed to a convolutional neural network (CNN) that predicts the peak line force 0.36 s ahead. This paper also evaluates the predictive capabilities of neural network (NN) models, comparing them to classical autoregressive (AR) and Kalman filter methods. While the AR model exhibits slightly higher accuracy in fixed PTO system configurations, it falters in providing real-time predictions when system parameters undergo variations. In contrast, the NN prediction model excels by establishing a robust relationship between system configuration and output signals. Especially noteworthy is its ability to outperform classical methods with minimal training on a selective set of system configurations. Then, the sensitivity of the peak line force prediction to the uncertainties in the input data from NN models and the prediction horizon is analyzed. The neural network models are trained over the experimental data subjected to extreme sea states for a point absorber wave energy converter. The results suggest that the accuracy of the surface elevation prediction has an insignificant direct effect on the peak force prediction model. However, these uncertainties are reflected in the PTO translator position prediction, and the model is considerably sensitive to the accuracy of this prediction. This sensitivity nonetheless is less notable for higher PTO damping values.

The Evaluation of Explicit Parameters on Eulerian-Lagrangian Simulation of Wave Impact on Coastal Bridges

Simply supported bridges along the United States Gulf Coast are highly vulnerable to extreme wave conditions and water elevations. A better understanding of the loading demands on the bridges under these extreme events will lead to improved designs and enhanced resiliency. Nonetheless, analyses through numerical models pose difficulties in terms of reliability and computational burden. On the other hand, experimental models for large-scale bridge superstructures are subject to limited space allocation and related scaling challenges. Hence, optimized Finite Element (FE) models that can simulate Wave-Superstructure Interaction (WSI) are a preferred viable solution to estimate loads experienced by these bridge superstructures. Nonetheless, the results of the FE simulations are highly dependent on the numerical parameters and configurations implemented in the model; thus, the implications of parameter selection must be assessed to help scholars and engineers develop reliable FE models. In this paper, an experimental scaled model was used to calibrate numerical models following the Coupled Eulerian-Lagrangian (CEL) technique in ABAQUS. This explicit approach solves the Navier-Stokes (NS) equations to simulate fluid flow, and the dynamics response of the structure depends on analysis parameters (mass scaling factor, damping hourglass control, displacement hourglass scaling factor, and bulk viscosity scaling factors) and configurations (mesh size). The results provide a platform to compare numerical outputs and find the best parameters that suit WSI models. Moreover, the force signals applied to the superstructure experience high oscillations due to WSI. Different digital filter designs have been used to remove unwanted oscillations and provide researchers with recommendations on generating models that deliver optimal results.

Optimal strategy of the asymmetric wave energy converter survival in extreme waves

Enhancing the survival performance of wave energy converters (WECs) in extreme wave conditions is crucial, and reducing wave loads is a key aspect of this. Placing the device underwater has been recognized as a beneficial strategy, yet the determination of the optimal submerged depth and the effects of varying wave conditions remain ambiguous. To address this, the study numerically analyzes the total forces in both horizontal and vertical directions, along with their harmonic components, across different wave configurations. A computational fluid dynamics method is employed to investigate a triangular-baffle bottom-shaped oscillating floater, which is known for its high energy conversion efficiency. The findings indicate that submerging the device to a depth equivalent to half the actual focused amplitude (1/2Ab) is the most effective strategy in the given sea state, offering superior wave force reduction vertically and robust performance horizontally. The analysis of harmonics reveals the significant contribution of high-order components to the total wave forces. Additionally, the study examines the impact of focused wave amplitudes and peak frequencies, showing that although force reductions are lessened in more extreme conditions, the optimal submerged depth of 1/2Ab still yields near 30% reduction in total vertical force and 22% in total horizontal force. This research provides theoretical insight that can guide the enhancement of WECs' survival capabilities in practical engineering applications.

The Expected Dynamics for the Extreme Wind and Wave Conditions at the Mouths of the Danube River in Connection with the Navigation Hazards

The entrance in the Sulina channel in the Black Sea is the target area of this study. This represents the southern gate of the seventh Pan-European transport corridor, and it is usually subjected to high navigation traffic. The main objective of the work is to provide a more comprehensive picture concerning the past and future expected dynamics of the environmental matrix in this coastal area, including especially the extreme wind and wave conditions in connection with the possible navigation risks. The methodology considered assumes analyses performed at three different levels. First, an analysis of some in situ measurements at the zero-kilometer point of the Danube is carried out for the 15-year period of 2009–2023. Together with the maximum wind speed and the maximum value of the wind gusts, the water level variation was analyzed at this point. As a second step, the analysis is based on wind speed data provided by regional climate models. Two periods, each spanning 30 years, are considered. These are the recent past (1976–2005), when comparisons with ERA5 reanalysis data were also performed, and the near future (2041–2070), when two different models and three climate scenarios were considered. The focus was on the extreme wind speed values, performing comparisons between the past and future expected extreme winds. Finally, the third analysis is related to the wave conditions. Thus, using as a forcing factor each of the wind fields that was previously analyzed, simulations employing a spectral wave model were carried out. The wave modeling system was focused using three different computational domains with increasing resolution towards the target area, and the nearshore wave conditions were evaluated. The results show that both the extreme wind and wave conditions are expected to slightly increase in the future. Especially in the wintertime, strong wind fields are often expected in this area, with wind gusts exceeding more than 70% of the hourly average wind velocity. With regard to the waves, due to the complex nearshore phenomena, considerable enhancements in terms of significant wave heights are induced, and there is also an elevated risk of the occurrence of rogue waves. This work is still ongoing, and taking into account the high navigation risks highlighted, the next step would be to elaborate the risk assessment of severe shipping conditions, particularly related to the likelihood or probability of adverse conditions with the potential of generating hazardous situations in this coastal environment.

A National‐Scale Coastal Flood Hazard Assessment for the Atoll Nation of Tuvalu

AbstractAtoll nations such as Tuvalu are considered to be amongst those most vulnerable to the effects of climate change. Here we present a national‐scale coastal flood hazard assessment for Tuvalu based on high‐resolution Light Detection and Ranging (LiDAR) topography and bathymetry. We follow a fully probabilistic approach, considering sea level anomalies, tides, and extreme wave conditions from a mixed climate (i.e., from distant extra‐tropical storms and local tropical cyclones). Nearshore processes such as wave setup and runup are also accounted for. Hazard maps were calculated for the present sea level, as well as for sea level rise projections corresponding to different shared socioeconomic pathways (SSP2 4.5 and SSP5 8.5) and time horizons (2060 and 2100). With a mean elevation of 1.55 m above mean sea level (1.37 m above mean high water spring) >25% of land area is inundated once every 5 years and >50% of land area floods once every 100 years nationally. Results indicate that present day 1‐in‐50 years floods (>45% of land area flooded) will occur more than once every 5 years by 2060 (annual exceedance probability >20%), even under the moderate SSP2 4.5 sea level rise projections. Results of this study highlight the pressing need for ambitious and large‐scale adaptation solutions which are commensurate with projected sea level rise and marine hazard impacts. The methodologies presented in this paper can easily be applied to other low‐lying islands in the tropical Pacific, where mixed climates (i.e., regular and TC conditions) and non‐linear nearshore processes dominate extreme water levels and flooding.

General formulation for floating body with elastic mooring in irregular waves: A hybrid linear and nonlinear framework and validation

In the present study, an advanced computational platform has been developed for offshore renewable energy converter systems, considering nonlinear wave input, body dynamics, mooring line dynamics, and kinematic and mechanical constraints. In particular, a hybrid linear and nonlinear hydrodynamic model is formulated through coupling with a numerical wave tank generated by OceanWave3D. A novel nodal position finite element model considering geometrical and material nonlinearities is developed to simulate the nonlinear behaviour of the mooring dynamics. Then, an implicit solver with an iteration process solves the dynamics of the rigid body, the dynamics of the mooring lines, and kinematic and mechanical constraints simultaneously. Therefore, the developed platform is capable of studying the wave body interaction with mooring lines in extreme wave conditions. Wave basin model tests of a single float on a nonlinear mooring line are carried out under a series of irregular waves for comparison. The developed model was also validated against commercial software under identical conditions for idealised cases. In steep wave conditions, the hybrid nonlinear/linear hydrodynamics give improved predictions over the linear hydrodynamic method.

CFD analysis of wave loading on a 10 MW TLP-type offshore floating wind turbine in regular waves

This paper aims to study the higher-harmonics wave-induced surge force on the CENTEC-TLP platform in regular head waves with non-breaking assumptions, using a CFD-based numerical wave tank model, which is a useful tool for the analysis of the nonlinear interaction of waves and structures. Moreover, the influence of change in the wave diffraction and the incident wave angle on the surge force subject to operational and extreme wave conditions is investigated. The numerical analysis is conducted using the CFD toolbox OpenFOAM. The link between Secondary Load Cycle and the wave scattering Type2 is apparent and it is concluded that they are all inertia-driven and that 2nd harmonics play an important role.