Josh Davidson

• PhD
• Research Fellow at Basque Center for Applied Mathematics

Simulating the free decay motion and wave radiation from a heaving semi-submerged sphere poses significant computational challenges due to its three-dimensional complexity. By leveraging axisymmetry, we reduce the problem to a two-dimensional simulation, significantly decreasing computational demands while maintaining accuracy. In this paper, we ex...

In ocean engineering, accurate and efficient numerical simulations are crucial. Leveraging axisymmetry vastly enhances the efficiency of a simulation, reducing a three-dimensional scenario to a two-dimensional simulation. Exploiting axisymmetry enables a significant reduction in computational demand while maintaining simulation fidelity. In this pa...

This review considers the dynamic phenomenon of parametric resonance (PR) within marine renewable energy, specifically in wave systems and offshore wind. It consolidates literature on the observation, suppression, exploitation, and modeling of PR in wave energy conversion and offshore wind turbines. Insights from other offshore industries are integ...

Parametric resonance in floating bodies presents a complex nonlinear dynamic problem with significant implications for offshore engineering, wave energy systems, and naval architecture. Addressing the computational challenges inherent in modelling such phenomena, this paper introduces an innovative analytical model that incorporates position depend...

The modelling of wave-structure interaction (WSI) has significant applications in understanding natural processes as well as securing the safety and efficiency of marine engineering. Based on the technique of Computational Fluid Dynamics (CFD) and the open-source simulation framework - OpenFOAM, this paper provides a state-of-the-art review of WSI...

The modelling of wave-structure interaction (WSI) has significant applications in understanding natural processes as well as securing the safety and efficiency of marine engineering. Based on the technique of Computational Fluid Dynamics (CFD) and the open-source simulation framework - OpenFOAM, this paper provides a state-of-the-art review of WSI...

Parametric excitation in the pitch/roll degrees of freedom (DoFs) can induce dynamic instability in floating cylinder-type structures such as spar buoys, floating offshore wind or wave energy converters. At certain frequency and amplitude ranges of the input waves, parametric coupling between the heave and pitch/roll DoFs results in undesirable lar...

This study pertains to analysing the dynamical behaviour of a floating body undergoing parametric resonances. A simple vertical cylinder, representing a classical spar-buoy, is considered, limiting its motion to heave and pitch degrees of freedom. Its geometry and mass distribution are chosen such that a 2:1 ratio of heave to pitch/roll natural fre...

Exploiting parametric resonance may enable increased performance for wave energy converters (WECs). By designing the geometry of a heaving WEC, it is possible to introduce a heave-to-heave Mathieu instability that can trigger parametric resonance. To evaluate the potential of such a WEC, a mathematical model is introduced in this paper for a heavin...

Scaled model tests are an important step during the research and development of wave energy converters (WECs). While such scaled model tests in physical wave tanks are prone to undesired scaling effects due to e.g. mechanical artefacts and/or fluid effects, numerical wave tanks (NWTs) provide excellent tools for the analysis of WECs across a range...

The oscillating-water-column (OWC) spar-buoy is a type of wave energy converter that may exhibit undesirable large roll and pitch amplitudes caused by a dynamic instability induced by parametric resonance. The occurrence of this phenomenon not only reduces the power extraction but significantly increases the structural loads on the buoy, the turbin...

This document aims to disseminate the results of the 3rd UCL OpenFOAM Workshop, which was held during 24-26 February 2021. It gives a summary of the event and presents links to all recorded videos. The author list is organisers and then speakers in the order of presenting. Keynote Speeches: (1) Bayesian Optimisation with OpenFOAM (2) The finite vo...

Highly accurate and precise heave decay tests on a sphere with a diameter of 300 mm were completed in a meticulously designed test setup in the wave basin in the Ocean and Coastal Engineering Laboratory at Aalborg University, Denmark. The tests were dedicated to providing a rigorous benchmark dataset for numerical model validation. The sphere was b...

Reviewing the literature of CFD-based numerical wave tanks for wave energy applications, it can be observed that different flow conditions and different turbulence models are applied during numerical wave energy converter (WEC) experiments. No single turbulence model can be identified as an ‘industry standard’ for WEC modeling. The complexity of th...

Parametric resonance is a dynamic instability due to the internal transfer of energy between degrees of freedom. Parametric resonance is known to cause large unstable pitch and/or roll motions in floating bodies, and has been observed in wave energy converters (WECs). The occurrence of parametric resonance can be highly detrimental to the performan...

The modelling of ocean waves is an integral part of coastal and offshore engineering. Both theoretical and experimental modelling methods are available and are commonly used in support of each other. In particular, due to the difficulty in measuring the velocity throughout the water column, the wave kinematics are often derived, by means of wave th...

The paper presents results from the Collaborative Computational Project in Wave Structure Interaction (CCP-WSI) Blind Test Series 2. Without prior access to the physical data, participants, with numerical methods ranging from low-fidelity linear models to fully nonlinear Navier-Stokes (NS) solvers, simulate the interaction between focused wave even...

An active control method, to suppress the onset of pitch/roll parametric resonance on an oscillating water column (OWC) spar buoy, is proposed in this paper, which utilises a pressure relief valve at the top of the OWC air chamber. The paper examines the hypothesis that by opening the relief valve, to reduce the air chamber pressure difference and...

The vast majority of numerical wave tank applications are solved using finite volume-based, volume of fluid methods. One popular numerical modelling framework is OpenFOAM and its two phase solvers, interFoam and interIsoFoam, enabling the simulation of a broad range of marine hydrodynamic phenomena. However, in many applications, certain aspects of...

Numerical wave tanks (NWTs) provide efficient test beds for the numerical analysis at various stages during the development of wave energy converters (WECs). To ensure the acquisition of accurate, high-fidelity data sets, validation of NWTs is a crucial step. However, using experimental data as reference during model validation, exact knowledge of...

Mathematical models are essential for the design and control of offshore systems, to simulate the fluid–structure interactions and predict the motions and the structural loads. In the development and derivation of the models, simplifying assumptions are normally required, usually implying linear kinematics and hydrodynamics. However, while the assu...

Measurement uncertainties are inevitable during physical wave tank tests. Therefore, when validating a numerical wave tank against experiments, knowledge of the uncertainties in the physical experiments, and the sensitivity of the body dynamics to such uncertainties, is crucial. Specifically, the inertial properties, as well as the location of the...

Results from the CCP-WSI Blind Test Series 3 are presented. Participants, with numerical methods, ranging from low-fidelity linear models to high-fidelity Navier–Stokes (NS) solvers, simulate the interaction between focused waves and floating structures without prior access to the physical data. The waves are crest-focused New Waves with various cr...

Computational fluid dynamics (CFD)-based numerical wave tanks are valuable tools for the development and evaluation of energy maximising control systems for wave energy converters (WECs). However, the exaggerated body motion amplitude, which can be induced by the energy maximising control system, challenges the commonly applied mesh morphing method...

During the development and optimisation of wave energy converters, numerical wave tanks are useful tools, providing detailed insight into the hydrodynamic performance of devices. Specifically, computational fluid dynamics (CFD)-based numerical wave tanks (CNWTs) can deliver high-fidelity, high-resolution results for a wide range of test conditions....

This review focuses on the most suitable form of hydrodynamic modeling for the next generation wave energy converter (WEC) design tools. To design and optimize a WEC, it is estimated that several million hours of operation must be simulated, perhaps one million hours of WEC simulation per year of the R&D program. This level of coverage is possible...

Computational fluid dynamics (CFD)-based numerical wave tanks are valuable tools for the development and evaluation of energy maximising control systems for wave energy converters (WECs). However, the exaggerated body motion amplitude, which can be induced by the energy maximising control system, challenges the commonly applied mesh morphing method...

Free Surface Effects Turbines like the ORPC RivGen cross-flow turbine, but also conventional horizontal axis turbines deployed in surface proximity, will be affected by the deformation of the free surface. For industrial design and development , those effects must be taken into account. Fully non-linear volume of fluid methods increase the computat...

The implementation of energy-maximizing control systems (EMCSs) can significantly increase the efficiency and economic viability of resonant wave-energy converters (WECs). To achieve optimal control and drive the WEC into resonance with the incoming wave field, knowledge of the wave excitation force is required. In operational conditions, this quan...

Computational fluid dynamics (CFD) based numerical wave tanks (NWTs) can provide valuable insight into the hydrodynamic performance of wave energy converters (WECs). Being able to capture hydro-dynamic non-linearities, CFD-based NWTs (CNWTs) allow the analysis of WECs over a wide range of test conditions, such as sea states, power takeoff control s...

During the development and optimisation of wave energy converters, numerical wave tanks are useful tools, providing detailed insight into the hydrodynamic performance of devices. Specifically, computational fluid dynamics based numerical wave tanks can deliver high-fidelity, high resolution, results for a wide range of test conditions. However, CFD...

For the economical operation of wave energy converts (WECs), energy maximising control systems (EMCSs) are included in the device design, introducing large structural motions. During the numerical modelling of WECs in CFD-based numerical wave tanks (NWTs), the structural motions must be explicitly accommodated in the finite volume domain. Using wel...

CFD-based numerical wave tank (CNWT) models, are a useful tool for the analysis of wave energy converters (WECs). During the development of a CNWT, model validation is vital, to prove the accuracy of the numerical solution. This paper presents an extensive validation study of a CNWT model for the 1:5 scale Wavestar point-absorber device. The previo...

Numerical wave tanks (NWTs) are an essential tool for wave energy converter (WEC) development. Due to it's opensource nature and wide user base, OpenFOAM is proving to be an eective software platform for implementing NWTs for WEC experiments. Indeed, in a recent review of Computational Fluid Dynamics based NWTs (CNWTs) for WECs, OpenFOAM was the mo...

This paper addresses the issue of hydrodynamic model identification from recorded tank test data, for a prototype wave energy device. The study focusses on nonlinear Kolmogorov–Gabor polynomial models, with linear models also used as a baseline reference. Six different experimental data sets are employed for model identification and validation, all...

Computational Fluid Dynamics (CFD) simulations, based on Reynolds-Averaged Navier–Stokes (RANS) models, are a useful tool for a wide range of coastal and offshore applications, providing a high fidelity representation of the underlying hydrodynamic processes. Generating input waves in the CFD simulation is performed by a Numerical Wavemaker (NWM),...

A fully non-linear numerical wave tank (NWT), based on Computational Fluid Dynamics (CFD), provides a useful tool for the analysis of coastal and offshore engineering problems. To generate and absorb free surface waves within a NWT, a variety of numerical wave maker (NWM) methodologies have been suggested in the literature. Therefore, when setting...

Computational Fluid Dynamics (CFD) simulations, based on Reynolds Averaged Navier Stokes (RANS) models, are a useful tool for a wide range of coastal and offshore applications, providing a high fidelity representation of the underlying hydrodynamic processes. Generating input waves in the CFD simulation is performed by a numerical wavemaker (NWM),...

Wave energy conversion is an active field of research, aiming to harness the vast amounts of energy present in ocean waves. An essential development trajectory towards an economically competitive wave energy converter (WEC) requires early device experimentation and refinement using numerical tools. OpenFOAM\(^{\textregistered }\) is proving to be a...

CFD-based numerical wave tank (CNWT) models, are a useful tool for the analysis of wave energy converters (WECs). During the development of a CNWT, model validation is important, to prove the accuracy of the numerical solution. This paper presents a validation study of a CNWT model for the 1:10 scale Wavestar point-absorber device. The previous stu...

Performing rigorous technical and commercial assessment of wave energy converters (WECs) numerically, before engaging in expensive wave tank and open ocean tests, is vital for the economically successful development of prototypes. To that end, this paper presents a high-fidelity wave-to-wire simulation platform (the HiFiWEC), where a Computational...

For the research and development (R&D) of wave energy converters (WECs), numerical wave tanks (NWTs) provide an excellent numerical tool, enabling a cost-effective testbed for WEC experimentation, analysis and optimisation. Different methods for simulating the fluid dynamics and fluid structure interaction (FSI) within the NWT have been developed o...

To maximise the energy output of wave energy converters (WECs), large structural motions are desired. When simulating WEC performance in Computational Fluid Dynamics (CFD) based numerical wave tanks, these motions must be explicitly accommodated in the computational domain. Using well established mesh morphing (MM) methods, this explicit accommodat...

The analysis of wave-current interaction (WCI) in numerical wave tanks (NWTs) requires the simultaneous generation of a current velocity profile and free surface waves. This paper presents a novel approach to simulate the WCI using an impulse-source-based methodology together with a numerical beach implementation. Three additional terms are added t...

European Research Community On Fluids, Turbulence and Combustion

The concept of resonance is well known in the study of wave energy converters (WECs), with the natural fre- quency of WECs typically designed to resonate with the external excitation provided by the input wave field. Para- metric resonance, on the other hand, has received very little attention, likely due to the complexity of the mod- els required...

Wave energy conversion is an active field of research, aiming to harness the vast amounts of energy present in ocean waves. An essential development tra-jectory towards an economically competitive wave energy converter (WEC) requires early device experimentation and refinement using numerical tools. OpenFOAM is proving to be a useful numerical tool...

Energy maximising controllers, for wave energy converters (WECs),based on linear models, are attractive in terms of simplicity and computation. However, such models are normally built around the still water level as an equilibrium point and assume small movement, leading to poor model validity for realistic WEC motions, especially for the large amp...

A numerical wave tank (NWT) based on Computational Fluid Dynamics (CFD) provides a useful tool for the analysis of offshore renewable energy (ORE) systems, such as wave energy converters (WECs). NWT experiments, of WEC operation, rely on accurate wave generation and absorption at the NWT boundaries. To tackle this problem, different method-ologies,...

Energy maximising controllers (EMCs), for wave energy converters (WECs), based on linear models are attractive in terms of simplicity and computation. However, such (Cummins equation) models are normally built around the still water level as an equilibrium point and assume small movement, leading to poor model validity for realistic WEC motions, es...

Turbulence Modelling for Ocean Wave Energy Systems

Mathematical analysis is an essential tool for the successful development and operation of wave energy converters (WECs). Mathematical models of moorings systems are therefore a requisite in the overall techno-economic design and operation of floating WECs. Mooring models (MMs) can be applied to a range of areas, such as WEC simulation, performance...

The modelling approach presented in this chapter is that of system identification, where models are determined from input/output data measured from the system under study. Models identified from recorded wave energy converter (WEC) data can accurately describe WEC behaviour, provided the data is of a sufficiently high quality. The chapter details g...

In this paper and its companion [1], the identification of mathematical models describing the behaviour of wave energy devices (WECs) in the ocean is investigated through the use of numerical wave tank (NWT) experiments. This paper deals with the identification tests used to produce the data for the model identification. NWTs, implemented using com...

In this paper and its companion [1], the identification of mathematical models describing the behaviour of wave energy devices (WECs) in the ocean is investigated through the use of numerical wave tank experiments. When the wave amplitude and the WEC displacement are not negligible with respect to the WEC dimensions, nonlinear hydrodynamic effects...

This work examines powering marine based sensors (MBSs) by harvesting energy from their local environment. MBSs intrinsically operate in remote locations, traditionally requiring expensive aintenance expeditions for battery replacement and data download. Nowadays, modern wireless communication allows real-time data access, but adds a significant en...

A numerical wave tank (NWT) can be a useful tool for wave energy experiments. This paper outlines the implementation of a NWT using the open-source computational fluid dynamics (CFD) software, OpenFOAM. In particular, the paper focusses on an NWT designed for experiments involving rigid-body type wave energy converters (WECs), using OpenFOAM versio...

This paper addresses the mathematical modelling of the relationship between the free surface elevation (FSE) and the excitation force for wave energy devices (excitation force model). While most studies focus on the model relating the FSE to the device motion, the excitation force model is required to complete the mathematical wave energy system de...

Mathematical modelling of wave energy devices has many uses, including power production assessment, simulation of device motion and as a basis for model-based control design. Apart from computationally heavy approaches, such as those based on computational fluid dynamics (CFD) and smooth particle hydrodynamics (SPH), the vast majority of models emp...

While linear and nonlinear system identification is a well established field in the control system sciences, it is rarely used in wave energy applications. System identification allows the dynamics of the system to be quantified from measurements of the system inputs and outputs, without significant recourse to first principles modelling. One signi...

Innovative research and development, supported by creative, enthusiastic and collaborative researchers, is vital to advancement of the offshore renewable energy (ORE) sector. The innovation system concept stresses that the flow of technology and information between people, enterprises and institutions is key to innovation. R&D, engineering and proj...

To facilitate commercially relevant numerical design optimization in wave energy conversion accurate and validated simulations of wave body interactions are necessary. Wave energy, more so than almost any other industry, can benefit from such numerical optimization because of the high cost and long period of design iteration in experimental and fie...

Hydrodynamic models are important for the design and control of wave energy converters. Traditionally they have been obtained using velocity potential/boundary element type methods, however associated assumptions of inviscid fluid, ir-rotational flow, small waves and small body motions are a major limitation of this modelling approach, since WECs a...

Size and power requirements of wireless sensor nodes are gradually decreasing and this has allowed data collection across a range of spatial and temporal ranges. These nodes have power requirements that often necessitate batteries as an energy source. As the power requirements decrease for these sensors, alternative energy sources become more attra...

Over the last decade, wireless computing and mobile devices have decreased in size and power requirements. These devices traditionally had significant power requirements that necessitated the use of batteries as their power source. However, as the power requirements are reducing, with wireless sensor nodes rarely exceeding 75mW, alternative means o...

Seventy percent of the Earth's surface is covered by water and all living things are dependent upon this resource. As such there are many applications for monitoring environmental data in and around aquatic environments. Wireless sensor networks are poised to revolutionise this process as the reduction in size and power consumption of electronics a...

Reduction in size and power consumption of consumer electronics has opened up many opportunities for low power wireless sensor networks. One of the major challenges is in supporting battery operated devices as the number of nodes in a network grows. The two main alternatives are to utilize higher energy density sources of stored energy, or to gener...

By harvesting energy from their local environment, sensor networks can achieve much greater run-times, years not months, with potentially lower cost and weight. At Australia??s Commonwealth Scientific and Industrial Research Organisation (CSIRO), we are developing tools to help sensor network designers power sensor networks for prolonged periods of...

By scavenging energy from their local environment, portable electronic devices such as mobile phones, radios and wireless sensors can achieve greater run-times with potentially lower weight. Vibration energy harvesting is one such approach where energy from parasitic vibrations can be converted into electrical energy, through the use of piezoelectr...