Wave generation and absorption using force-feedback control

Imperial Users onl

Composite modelling of subaerial landslide-tsunamis in different water body geometries and novel insight into slide and wave kinematics

This article addresses subaerial landslide-tsunamis with a composite (experimental-numerical) modelling approach. A shortcoming of generic empirical equations used for hazard assessment is that they are commonly based on the two idealised water body geometries of a wave channel (2D) or a wave basin (3D). A recent systematic comparison of 2D and 3D physical block model tests revealed wave amplitude differences of up to a factor of 17. The present article investigates two of these recently presented 2D-3D test pairs in detail, involving a solitary-like wave (scenario 1) and Stokes-like waves (scenario 2). Results discussed include slide and water particle kinematics and novel pressure measurements on the slide front. Instantaneous slide-water interaction power graphs are derived and potential and kinetic wave energies are analysed. Solitary wave theory is found most appropriate to describe the wave kinematics associated with scenario 1, whereas Stokes theory accurately describes the tsunami in scenario 2. The data of both scenarios are further used to calibrate the smoothed particle hydrodynamics (SPH) code DualSPHysics v3.1, which includes a discrete element method (DEM)-based model to simulate the slide-ramp interaction. Five intermediate geometries, lying between the ideal 2D and 3D cases, are then investigated purely numerically. For a “channel” geometry with a diverging side wall angle of 7.5°, the wave amplitudes along the slide axes were found to lie approximately halfway between the values observed in 2D and 3D. At 45°, the amplitudes are practically identical to those in 3D. The study finally discusses the implications of the findings for engineering applications and illustrates the potential and current limitations of DualSPHysics for landslide-tsunami hazard assessment

Investigation into wave basin calibration based on a focused wave approach

The purpose of this paper is to present a detailed numerical investigation concerning the calibration of force controlled wave generation facilities. The methodology is presented for a 2-dimensional calibration; the findings being equally applicable to the calibration of 3-dimensional wave basins. State-of-the-art force controlled wavemaking facilities comprise sophisticated hardware, software and control systems, commonly incorporating active absorption mechanisms. Such facilities have the potential to reproduce ocean wave of exceptional quality, but poor understanding of accurate calibration processes often hinders full exploitation. A technique based upon the generation of focused wave events may oer a very accurate and time-efficient calibration. However, such a methodology may lead to erroneous results if not employed correctly. The theoretical and statistical analysis presented herein investigates the sensitivity of such method to a number of important parameters. The results obtained are directly applicable to a large number of hydrodynamic facilities

On the effect of the water body geometry on landslide–tsunamis: physical insight from laboratory tests and 2D to 3D wave parameter transformation

Preliminary landslide–tsunami hazard assessment is commonly based on empirical equations derived from wave channel (2D) or wave basin (3D) experiments. The far-field wave in 2D can easily be an order of magnitude larger than in 3D. The present study systematically investigates the effect of the water body geometry on the wave characteristics in the near- and far-field. Subaerial landslide–tsunami tests were conducted relying upon both a 2D and a 3D physical model, undertaken with identical boundary conditions. The test parameters included two water depths, three rigid slides, as well as various slide release positions. Empirical equations for 3D offshore and laterally onshore wave properties are presented and compared with previous work. A direct comparison of the wave features reveals that the waves decay in 2D, 3D onshore and 3D offshore with x− 0.30, r− 0.67 and r− 1.0, where x (2D) and r (3D) describe the distance from the impact zone. In 2D four wave types are observed, whereas only the two least non-linear types were observed in 3D. This finding is further analysed with wavelet spectra. For a large slide Froude number F, relative slide thickness S and relative slide mass M, the 3D wave heights in the slide impact zone can be as large as in 2D. However, for small F, S and M, the 3D waves are considerably smaller both in the near- and far-field. A novel method is presented and validated to transform data from 2D studies to 3D. This method may have favourable implications on preliminary landslide–tsunami hazard assessment

Wave generation and absorption using force-feedback control

EThOS - Electronic Theses Online ServiceGBUnited Kingdo

A Review of Numerical Modelling of Wave Energy Converter Arrays

Large-scale commercial exploitation of wave energy is certain to require the deployment of wave energy converters (WECs) in arrays, creating 'WEC farms'. An understanding of the hydrodynamic interactions in such arrays is essential for determining optimum layouts of 'WECs, as well as calculating the area of ocean that the farms will require. It is equally important to consider the potential impact of wave farms on the local and distal wave climates and coastal processes; a poor understanding of the resulting environmental impact may hamper progress, as it would make planning consents more difficult to obtain. It is therefore clear that an understanding the interactions between WECs within a farm is vital for the continued development of the wave energy industry. To support WEC farm design, a range of different numerical models have been developed, with both wave phase-resolving and wave phase-averaging models now available. Phase-resolving methods are primarily based on potential flow models and include semi-analytical techniques, boundary element methods and methods involving the mild-slope equations. Phase-averaging methods are all based around spectral wave models, with supra-grid and sub-grid wave farm models available as alternative implementations. The aims, underlying principles, strengths, weaknesses and obtained results of the main numerical methods currently used for modelling wave energy converter arrays are described in this paper, using a common framework. This allows a qualitative comparative analysis of the different methods to be performed at the end of the paper. This includes consideration of the conditions under which the models may be applied, the output of the models and the relationship between array size and computational effort. Guidance for developers is also presented on the most suitable numerical method to use for given aspects of WEC farm design. For instance, certain models are more suitable for studying near-field effects, whilst others are preferable for investigating far-field effects of the WEC farms. Furthermore, the analysis presented in this paper identifies areas in which the numerical modelling of WEC arrays is relatively weak and thus highlights those in which future developments are required