With the rapid development of offshore renewable energy technologies, open source solvers for hydrodynamic analysis can become beneficial to meet the numerical challenges within the field, particularly when they are both accurate and computationally efficient. Hydrodynamic Analysis of Marine Structures (HAMS), a recently developed open source Boundary Integral Equation Method (BIEM) frequency domain solver has been shown to be a reliable, robust and computationally efficient for analysing single floating structures. This research enhances the capabilities of HAMS further by developing and incorporating a multiple body interaction formulation (henceforth referred as HAMS-MREL), which allows the solution of the diffraction and the radiation problem for multiple floating structures, taking into account their interaction. To evaluate proper performance of this new multi-body solver, comparisons are performed with semi-analytical solutions, as well as with the commercial solver WAMIT in terms of the hydrodynamic coefficients and exciting forces. The excellent comparison with semi-analytical solutions demonstrates the validity of the enhanced multi-body version of HAMS. In addition, the computational comparison considering lower order panels between HAMS-MREL and WAMIT (no symmetry) show that for deep water cases, HAMS-MREL is generally faster than WAMIT, while for the finite depth cases, it is slower. Finally, the functionality to utilize OpenMP parallelization within the multi-body formulation has been added, aiming to reduce the analysis time significantly for the finite depth cases, offering an expected improvement for the future.

@en

Wave energy has immense potential and can provide at least twice as much electricity as globally produced now due to its high energy density. Apart from the vast accessibility of the resource, waves are more predictable and available throughout the year when compared to other forms of renewable energies. This makes the development and utilization of wave energy tech-nologies immensely important, in order to meet the renewable energy targets, an example of which is the 40GW by 2050 set as the offshore energy strategy of the European Commission. For wave energy to become a commercially viable power source, in-dividual wave energy converters (WECs) need to be deployed in large numbers similar to what can be seen in the wind in-dustry. Therefore, numerical tools simulating multiple inter-acting devices becomes highly relevant. This research utilizes the new open-source Boundary Element Method (BEM) based solver HAMS-MREL to analyse the hydrodynamic interactions of mono-array farms of point absorbers inspired by the state-of-the-art Corpower C4 point absorber device in various configurations subjected to waves in different directions. The obtained responses are used to estimate the power absorbed by the arrays in different configurations to obtain the Array Power Matrices, which can be used to study the variability of the q-factors in different sea states and different directions. Furthermore, the obtained Array Power Matrices are used to estimate the power absorbed by the array configurations in the North Sea. This can be a powerful tool for the analysis of the best wave energy farm configurations as it employs a computationally efficient frequency domain-based solver.@en

The Oscillating Water Column (OWC) wave energy converter has been shown to have high potential, thus rendering extensive development in recent years. In order to further accelerate its development, highly accurate yet computationally efficient tools are necessary particularly when studying the interaction of multiple OWC devices. This paper proposes a new framework for fixed OWC devices with an orifice, that uses the input from a high fidelity non-linear numerical model to improve the accuracy of a low fidelity linear numerical model keeping computational costs low. This is done by accounting for the non-linearities in the pressure-flow of an orifice in the input to the linear numerical model. Experimental data is used to validate the framework, thus providing an accurate and computationally efficient linear numerical model, that can be used for the preliminary analysis of fixed OWC devices.@en

One of the key aspects to consider before large scale de-ployments of wave energy converters (WEC), is to optimize the devices’ characteristics to improve wave power absorption. Typi-cally, devices with passive control are designed to have the highest efficiency in wave power absorption/production in the range of the most frequent wave conditions. In general, there is an intrinsic “trade-off” between the range of wave conditions where a WEC can operate and the operation efficiency which, in the end, is linked to the energy production yield. Outside the most frequent wave conditions, there is still a non-negligible percentage of oc-currences of more energetic sea states carrying high energy flux values. Given the specific design characteristics of a WEC de-vice, lower operation efficiency is expected during these stronger sea states, which is translated as a lower production compared to the available (usable) resource. In the present study, a multi-size point absorber WEC array, using passive internal control, is pro-posed to optimize wave power production at the array level. The main aim of this work is to verify the combined use of devices de-signed to work in the most frequent wave conditions, with WECs which mass and dimensions are defined to improve their response during stronger sea states. A comparison of the mean produced power is performed between a proposed multi-array and a single size one. This is done using 30 years of spectral wave data ob-tained from an implementation of the WAVEWATCH III model, while response of the wave energy converters array is simulated with the boundary element model HAMS-MREL. Preliminary results, using 10-devices arrays, show a promising increase in production from 60 to 140% when larger WECs are included.@en

Wave energy has immense potential and can provide at least twice as much electricity as globally produced now due to its high energy density. Apart from the vast accessibility of the resource, waves are more predictable and available throughout the year when compared to other forms of renewable energies. This makes the development and utilization of wave energy technologies immensely important, in order to meet the renewable energy targets, an example of which is the 40GW by 2050 set as the offshore energy strategy of the European Commission. For wave energy to become a commercially viable power source, individual wave energy converters (WECs) need to be deployed in large numbers similar to what can be seen in the wind industry. Therefore, numerical tools simulating multiple interacting devices becomes highly relevant. This research utilizes the new open-source Boundary Element Method (BEM) based solver HAMS-MREL to analyse the hydrodynamic interactions of mono-array farms of point absorbers inspired by the state-of-the-art Corpower C4 point absorber device in various configurations subjected to waves in different directions. The obtained responses are used to estimate the power absorbed by the arrays in different configurations to obtain the Array Power Matrices, which can be used to study the variability of the q-factors in different sea states and different directions. Furthermore, the obtained Array Power Matrices are used to estimate the power absorbed by the array configurations in the North Sea. This can be a powerful tool for the analysis of the best wave energy farm configurations as it employs a computationally efficient frequency domain-based solver.

@en

Ocean wave energy has immense potential and can provide at least twice as much electricity as globally produced now due to its high energy density. In order to efficiently extract this energy and make this commercially viable, Wave Energy Converters (WECs) need to interact with the resource in an optimized way for the expanse of sea states. This interaction is critical to power production by these devices and hence an accurate modelling of this is paramount. The Boundary element method (BEM) based on the linear potential flow theory has yielded accurate results at low computational costs when compared to complex Computational Fluid Dynamics methods. Hydrodynamic Analysis of Marine Structures (HAMS) and Capytaine are recently developed open-source BEM frequency domain solvers, originally created for large marine structures. These solvers have since been utilized for studying wave energy converters, though, for very few converter geometries. Owing to the implementation of parallelization in both HAMS and Capytaine, both these solvers could be capable for significantly lower computational costs as compared to the traditional BEM solvers such as Nemoh. This research aims to compare hydrodynamic coefficients and computational costs in Nemoh, HAMS and Capytaine for various WEC geometries.@en

With the rapid development of offshore renewable energy technologies, open source solvers for hydrodynamic analysis can become beneficial to meet the numerical challenges within the field, particularly when they are both accurate and computationally efficient. Hydrodynamic Analysis of Marine Structures (HAMS), a recently developed open source Boundary Integral Equation Method (BIEM) frequency domain solver has been shown to be a reliable, robust and computationally efficient for analysing single floating structures. This research enhances the capabilities of HAMS further by developing and incorporating a multiple body interaction formulation (henceforth referred as HAMS-MREL), which allows the solution of the diffraction and the radiation problem for multiple floating structures, taking into account their interaction. To evaluate proper performance of this new multi-body solver, comparisons are performed with semi-analytical solutions, as well as with the commercial solver WAMIT in terms of the hydrodynamic coefficients and exciting forces. The excellent comparison with semi-analytical solutions demonstrates the validity of the enhanced multi-body version of HAMS. In addition, the computational comparison considering lower order panels between HAMS-MREL and WAMIT (no symmetry) show that for deep water cases, HAMS-MREL is generally faster than WAMIT, while for the finite depth cases, it is slower. Finally, the functionality to utilize OpenMP parallelization within the multi-body formulation has been added, aiming to reduce the analysis time significantly for the finite depth cases, offering an expected improvement for the future.@en

The Boundary Element Method (BEM) based on the linear potential flow theory has shown to produce accurate results at low computational costs in numerical modelling of the hydrodynamics of Wave Energy Converters (WECs). WAMIT, Nemoh and Capytaine are some of the most popular frequency domain BEM solvers used in the response analysis of various WECs. Hydrodynamic Analysis of Marine Structures (HAMS), another open-source BEM solver gaining traction, has been applied to the analysis of single WECs considering rigid body motions providing highly accurate solutions at lower computational costs as compared to other solvers. This research extends its current capabilities to model structures with constraints by applying the generalized modes approach. Results presented include of a cross-model validation with commercial solver WAMIT, of the hydrodynamic coefficients and exciting forces considering flap converter. Furthermore, a comparison is shown with popular open-source solver Capytaine for the same case, since it has parallelization.

@en

One of the key aspects to consider before large scale deployments of wave energy converters (WEC), is to optimize the devices’ characteristics to improve wave power absorption. Typically, devices with passive control are designed to have the highest efficiency in wave power absorption/production in the range of the most frequent wave conditions. In general, there is an intrinsic “trade-off” between the range of wave conditions where a WEC can operate and the operation efficiency which, in the end, is linked to the energy production yield. Outside the most frequent wave conditions, there is still a non-negligible percentage of occurrences of more energetic sea states carrying high energy flux values. Given the specific design characteristics of a WEC device, lower operation efficiency is expected during these stronger sea states, which is translated as a lower production compared to the available (usable) resource. In the present study, a multi-size point absorber WEC array, using passive internal control, is proposed to optimize wave power production at the array level. The main aim of this work is to verify the combined use of devices designed to work in the most frequent wave conditions, with WECs which mass and dimensions are defined to improve their response during stronger sea states. A comparison of the mean produced power is performed between a proposed multi-array and a single size one. This is done using 30 years of spectral wave data obtained from an implementation of the WAVEWATCH III model, while response of the wave energy converters array is simulated with the boundary element model HAMS-MREL. Preliminary results, using 10-devices arrays, show a promising increase in production from 60 to 140% when larger WECs are included.

@en

Utilization of Boundary Element Method (BEM) based on linear potential flow for modelling Oscillating Water Column (OWC) devices has gained popularity in the last two decades. The commercial BEM solver WAMIT has been used widely for modelling OWCs and validated using experimental modelling. Literature has shown that when using the thin disk approach for modelling the imaginary piston in OWCs in BEM solver Nemoh, the results have been poor since the solver fails to provide good results when the source and field points are very close. In this research, the two-body interaction problem has been adopted in modelling a box-type and bottom-detached OWC device in Nemoh, where the first modelled body is the OWC hull (fixed) and the second body is an imaginary piston modelled to the same length as the internal water column. An average linear damping coefficient relating pressure and discharge is used within a frequency domain model and the obtained response is compared with experimental data. A direct comparison is also conducted with the numerical method of Computational Fluid Dynamics (CFD), which has shown to be accurate for modelling OWC devices, however it does require significantly higher computational resources. A two-dimensional CFD numerical wave tank which allows for wave generation and absorption has been implemented within the open-source package OpenFOAM® and is used for comparative purposes. Results show that while CFD matches well with the experimental results, the BEM model under-estimates the response. To further improve this, an instantaneous frequency dependent damping coefficient relating pressure and discharge is derived, which then provides very close results to both the experiments and CFD model.

@en

To date there is a wide range of wave reanalysis and hindcasts available to the scientific and engineering community which are commonly used for different applications, including downscaling or the estimation of the wave energy resource. These long datasets have been created using different combinations of forcing fields, physical parameterizations, and numerical choices (like spatial and spectral resolution). All these elements have a direct effect on the accuracy of the wave models’ output and thus, they are one of the main reasons for the differences between these products. In the present study we analyze the significant wave heights and peak periods characteristics from a selection of global datasets. We additionally include results from a hindcast created using the WAVEWATCH III model, with adjustments specially aimed to reduce uncertainties of the wave energy resource along the Atlantic coasts of Europe. Models’ output is compared with buoys and altimeter data from the latest ESA (European Space Agency) CCI Sea State V3 product. Preliminary validation of the hindcast we have generated for the North Atlantic already show an important bias reduction for wave heights in the 2.5 to 11.5 range compared to ERA5 wave product. Using the relevant wave parameters, we estimate the power density and quantify the differences between databases. Then, based on scatter diagrams obtained from the joint distributions of significant wave height and peak period, the differences in the power captured by a point absorber wave energy converter (WEC) related to different wave data sources will be quantified.

@en

Wave Energy Converters (WECs) are expected to significantly contribute to the energy transition; however, this depends on their interactions with the resource. Calculating the power generated by WECs depends heavily on the accurate modelling of wave-structure interactions. The Boundary Element Method (BEM) based on the potential flow theory has yielded accurate results at low computational costs when compared to complex Computational Fluid Dynamics (CFD) methods. Hydrodynamic Analysis of Marine Structures (HAMS), a recently developed open-source BEM frequency domain solver, originally was created for large marine structures. To date it has only been applied to single WECs with spherical/cylindrical geometries. HAMS offers unique advantages through its efficient removal of irregular frequencies and lower computational costs. This paper aims to compare hydrodynamic coefficients, exciting forces, Response Amplitude Operators (RAOs) and computational costs between HAMS,WAMIT, and NEMOH for a cylindrical point absorber and an oscillating surge WEC, extending the currently limited WECs application in HAMS.@en