ORCID Profile
0000-0002-9176-3702
Current Organisation
University of Western Australia
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Ocean Engineering | Ship and Platform Hydrodynamics | Maritime Engineering
Publisher: Elsevier BV
Date: 07-2022
Publisher: Elsevier BV
Date: 09-2022
Publisher: Elsevier BV
Date: 07-2021
Publisher: American Society of Mechanical Engineers
Date: 11-06-2023
Publisher: European Wave and Tidal Energy Conference
Date: 02-09-2023
Publisher: Cambridge University Press (CUP)
Date: 28-12-2016
DOI: 10.1017/JFM.2016.811
Abstract: A floating air bag, ballasted in water, expands and contracts as it heaves under wave action. Connecting the bag to a secondary volume via a turbine transforms the bag into a device capable of generating useful energy from the waves. Small-scale measurements of the device reveal some interesting properties, which are successfully predicted numerically. Owing to its compressibility, the device can have a heave resonance period longer than that of a rigid device of the same shape and size, without any phase control. Furthermore, varying the amount of air in the bag is found to change its shape and hence its dynamic response, while varying the turbine d ing or the air volume ratio changes the dynamic response without changing the shape.
Publisher: European Wave and Tidal Energy Conference
Date: 02-09-2023
Publisher: Springer Science and Business Media LLC
Date: 19-07-2008
Publisher: WORLD SCIENTIFIC
Date: 08-2009
Publisher: The Royal Society
Date: 08-12-2014
Abstract: We present an analysis of wave energy devices with air-filled compressible submerged volumes, where variability of volume is achieved by means of a horizontal surface free to move up and down relative to the body. An analysis of bodies without power take-off (PTO) systems is first presented to demonstrate the positive effects a compressible volume could have on the body response. Subsequently, two compressible device variations are analysed. In the first variation, the compressible volume is connected to a fixed volume via an air turbine for PTO. In the second variation, a water column separates the compressible volume from another volume, which is fitted with an air turbine open to the atmosphere. Both floating and bottom-fixed, axisymmetric, configurations are considered, and linear analysis is employed throughout. Advantages and disadvantages of each device are examined in detail. Some configurations with displaced volumes less than 2000 m 3 and with constant turbine coefficients are shown to be capable of achieving 80% of the theoretical maximum absorbed power over a wave period range of about 4 s.
Publisher: Institution of Engineering and Technology (IET)
Date: 07-06-2021
DOI: 10.1049/RPG2.12229
Publisher: The Royal Society
Date: 04-2017
Abstract: A new wave energy device features a submerged ballasted air bag connected at the top to a rigid float. Under wave action, the bag expands and contracts, creating a reciprocating air flow through a turbine between the bag and another volume housed within the float. Laboratory measurements are generally in good agreement with numerical predictions. Both show that the trajectory of possible combinations of pressure and elevation at which the device is in static equilibrium takes the shape of an S. This means that statically the device can have three different draughts, and correspondingly three different bag shapes, for the same pressure. The behaviour in waves depends on where the mean pressure-elevation condition is on the static trajectory. The captured power is highest for a mean condition on the middle section.
Publisher: Elsevier BV
Date: 05-2012
Publisher: American Society of Mechanical Engineers
Date: 05-06-2022
Abstract: Accurate and reliable phase-resolved prediction of ocean surface waves is crucial for many offshore operations in ocean engineering and marine science. One important application is in optimal control of a power take-off in a wave energy converter, leading to significantly higher power production. Our interest is the forecasting of wave fields based on measurements obtained from multiple upwave locations in moderate seas with small directional spreading angles, such as is prevalent along the south coast of Australia. The prediction model, based on FFTs and propagation of waves according to the linear dispersion relation, is applied to both wave groups and irregular wave fields generated in a wave basin and, additionally, to ocean waves measured with drifting wave buoys. To account for spreading, the model numerically advances linear, plane (i.e. long-crested) waves in space at an optimum offset angle equal to the underlying sea-state root-mean-square spreading angle. Averaging predictions based on a few slightly separated measurement locations, each weighted according to the estimated variance of the in idual prediction, is shown to be more accurate than that from any single location. We also assess in detail the effect of drifting-buoy measurements in both long-crested and short-crested seas using synthetic wave records and show that it is possible to satisfactorily reconstruct the signal at fixed points based on the Doppler shift felt by the drifting buoy. The reconstructed signals give much better predictions compared to those completely neglecting the effect of even rather slow drift.
Publisher: MDPI AG
Date: 25-10-2019
DOI: 10.3390/JMSE7110379
Abstract: The International Energy Agency Technology Collaboration Programme for Ocean Energy Systems (OES) initiated the OES Wave Energy Conversion Modelling Task, which focused on the verification and validation of numerical models for simulating wave energy converters (WECs). The long-term goal is to assess the accuracy of and establish confidence in the use of numerical models used in design as well as power performance assessment of WECs. To establish this confidence, the authors used different existing computational modelling tools to simulate given tasks to identify uncertainties related to simulation methodologies: (i) linear potential flow methods (ii) weakly nonlinear Froude–Krylov methods and (iii) fully nonlinear methods (fully nonlinear potential flow and Navier–Stokes models). This article summarizes the code-to-code task and code-to-experiment task that have been performed so far in this project, with a focus on investigating the impact of different levels of nonlinearities in the numerical models. Two different WECs were studied and simulated. The first was a heaving semi-submerged sphere, where free-decay tests and both regular and irregular wave cases were investigated in a code-to-code comparison. The second case was a heaving float corresponding to a physical model tested in a wave tank. We considered radiation, diffraction, and regular wave cases and compared quantities, such as the WEC motion, power output and hydrodynamic loading.
Publisher: Institution of Engineering and Technology (IET)
Date: 31-10-2016
Publisher: Elsevier BV
Date: 2023
Publisher: ASMEDC
Date: 2011
Abstract: In this study, a selection of Wave Energy Converters (WECs) with different working principle is considered. It comprises a heaving device reacting against the seabed, a heaving self-reacting two-bodies device, a pitching device, and a floating OWC device. They are inspired by concepts which are currently under development. For each of these concepts, a numerical Wave To Wire (W2W) model is derived. Numerical estimates of the energy delivery which one can expect are derived using these numerical models on a selection of wave site along the European coast. This selection of wave site is thought to be representative with levels of mean annual wave power from 15 to 88 kW/m. Using these results, the performance of each WEC is assessed not only in terms of yearly energy output, but also in terms of yearly absorbed energy/displacement, yearly absorbed energy/wetted surface, and yearly absorbed energy per unit significant Power Take Off force. By comparing these criteria, one gets a better idea of the advantages and drawbacks of each of the studied concepts.
Publisher: American Society of Civil Engineers (ASCE)
Date: 2021
Publisher: Elsevier BV
Date: 02-2015
Publisher: Elsevier BV
Date: 2012
Publisher: Elsevier BV
Date: 05-2022
Publisher: Cambridge University Press
Date: 12-05-2020
Publisher: The Royal Society
Date: 03-2015
DOI: 10.1098/RSOS.140305
Abstract: The time-average wave power that is absorbed from an incident wave by means of a wave-energy conversion (WEC) unit, or by an array of WEC units—i.e. oscillating immersed bodies and/or oscillating water columns (OWCs)—may be mathematically expressed in terms of the WEC units' complex oscillation litudes, or in terms of the generated outgoing (diffracted plus radiated) waves, or alternatively, in terms of the radiated waves alone. Following recent controversy, the corresponding three optional expressions are derived, compared and discussed in this paper. They all provide the correct time-average absorbed power. However, only the first-mentioned expression is applicable to quantify the instantaneous absorbed wave power and the associated reactive power. In this connection, new formulae are derived that relate the ‘added-mass’ matrix, as well as a couple of additional reactive radiation-parameter matrices, to the difference between kinetic energy and potential energy in the water surrounding the immersed oscillating WEC array. Further, a complex collective oscillation litude is introduced, which makes it possible to derive, by a very simple algebraic method, various simple expressions for the maximum time-average wave power that may be absorbed by the WEC array. The real-valued time-average absorbed power is illustrated as an axisymmetric paraboloid defined on the complex collective- litude plane. This is a simple illustration of the so-called ‘fundamental theorem for wave power’. Finally, the paper also presents a new derivation that extends a recently published result on the direction-average maximum absorbed wave power to cases where the WEC array's radiation d ing matrix may be singular and where the WEC array may contain OWCs in addition to oscillating bodies.
Publisher: American Meteorological Society
Date: 08-2022
DOI: 10.1175/JTECH-D-21-0108.1
Abstract: An apparent giant wave event having a maximum trough-to-crest height of 21 m and a maximum zero-upcrossing period of 27 s was recorded by a wave buoy at a nearshore location off the southwestern coast of Australia. It appears as a group of waves that are significantly larger both in height and in period than the waves preceding and following them. This paper reports a multifaceted analysis into the plausibility of the event. We first examine the statistics of the event in relation to the rest of the record, where we look at quantities such as maximum-to-significant wave height ratios, ordered crest–trough statistics, and average wave profiles. We then investigate the kinematics of the buoy, where we look at the relationship between the horizontal and vertical displacements of the buoy, and also attempt to numerically reconstruct the giant event using Boussinesq and nonlinear shallow water equations. Additional analyses are performed on other sea states where at least one of the buoy’s accelerometers reached its maximum limit. Our analysis reveals incompatibilities of the event with known behavior of real waves, leading us to conclude that it was not a real wave event. Wave events similar to the one reported in our study have been reported elsewhere and have sometimes been accepted as real occurrences. Our methods of forensically analyzing the giant wave event should be potentially useful for identifying false rogue wave events in these cases.
Publisher: European Wave and Tidal Energy Conference
Date: 02-09-2023
Publisher: Elsevier BV
Date: 05-2023
Publisher: ASMEDC
Date: 2011
Abstract: This article describes the computation of hydrodynamic parameters, modelling, and simulation of a floating oscillating water column wave energy device. The frequency-domain hydrodynamic parameters are computed using a three-dimensional panel method. Parameters related to wave radiation due to applied air pressure inside the air chamber are evaluated from reciprocity relations, without having to solve explicitly for the radiation potential due to the applied pressure. The dynamics of the whole system, including nonlinear air compressibility and relief valve characteristics, is modelled using bond graph as a tool. Both time- and linear frequency-domain models are described and selected simulation results, especially the converted power, are presented.
Publisher: World Scientific Publishing Company
Date: 09-2009
Publisher: Informa UK Limited
Date: 28-03-2019
Publisher: ASMEDC
Date: 2009
Abstract: This paper examines the effects of viscous d ing on the prediction of air gap demand for semi-submersibles. This is illustrated by a case study of a typical six-column, double pontoon semi-submersible in irregular waves. Linear responses of the platform and free-surface elevations at selected locations are computed using WAMIT, in which viscous d ing effects are included through the use of a linear d ing matrix. The spectra of the platform’s response and of the relative free-surface elevation at the selected locations, as well as the probability distributions of air gap minima obtained using different d ing matrices are compared. It is demonstrated that correct modelling of viscous d ing is important for an accurate prediction of air gap demand of a floating platform, especially if the peak frequency of the wave spectrum is close to the heave, roll, and pitch natural frequencies of the platform.
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 2013
Publisher: American Society of Mechanical Engineers
Date: 30-10-2022
Abstract: We present a computationally efficient time-domain model capable of simulating parametric resonances in a floating body in waves. The model assumes all wave forces to be linear, but the inertia and restoring forces acting on the body are expanded to second order in body motions. The simulation speed on a standard computer is approximately 40 times faster than real time. The model is applied to a soft-moored floating axisymmetric body which absorbs energy through heave, but is otherwise free to move in six degrees of freedom. Under certain conditions, we show that the body undergoes parametric resonance with large litudes not only in surge and pitch, but also in sway, roll, and yaw, provided it is given some small initial displacement in one of these out-of-plane modes. The predictions are confirmed by simulations using state-of-the-art nonlinear Froude-Krylov and computational fluid dynamics models.
Publisher: Elsevier BV
Date: 02-2012
Publisher: ASME International
Date: 26-12-2022
DOI: 10.1115/1.4056422
Abstract: Accurate and reliable phase-resolved prediction of ocean surface waves is crucial for many offshore operations in ocean engineering and marine science. One important application is in optimal control of a power take-off in a wave energy converter, leading to significantly higher power production. Our interest is forecasting wave fields based on measurements obtained from multiple upwave locations in moderate seas with small directional spreading angles, as occurs along the south coast of Australia. The prediction model, based on FFTs and propagation of waves according to the linear dispersion relation, is applied to both wave groups and irregular wave fields generated in a wave basin and, additionally, to ocean waves measured with drifting wave buoys. To account for spreading, the model numerically advances linear, plane (i.e., long-crested) waves in space at an optimum offset angle equal to the underlying sea-state root mean square spreading angle. Averaging predictions from a few slightly separated measurement locations, each weighted according to its estimated variance, results in more accurate predictions than from any single location. We also assess in detail the effect of drifting buoy measurements in both long-crested and short-crested seas using synthetic wave records and show that it is possible to satisfactorily reconstruct the signal at fixed points based on the Doppler shift felt by the drifting buoy. The reconstructed signals give much better predictions compared to those completely neglecting the effect of even rather slow drift due to current.
Publisher: American Society of Mechanical Engineers
Date: 11-06-2023
Location: United Kingdom of Great Britain and Northern Ireland
Start Date: 04-2022
End Date: 04-2024
Amount: $280,000.00
Funder: Australian Research Council
View Funded Activity