Energy potential of a tidal fence deployed near a coastal headland

Enhanced tidal streams close to coastal headlands appear to present ideal locations for the deployment of tidal energy devices. In this paper, the power potential of tidal streams near an idealized coastal headland with a sloping seabed is investigated using a near-field approximation to represent a tidal fence, i.e. a row of tidal devices, in a two-dimensional depth-averaged numerical model. Simulations indicate that the power extracted by the tidal fence is limited because the flow will bypass the fence, predominantly on the ocean side, as the thrust applied by the devices increases. For the dynamic conditions, fence placements and headland aspect ratios considered, the maximum power extracted at the fence is not related in any obvious way to the local undisturbed kinetic flux or the natural rate of energy dissipation due to bed friction (although both of these have been used in the past to predict the amount of power that may be extracted). The available power (equal to the extracted power net of vertical mixing losses in the immediate wake of devices) is optimized for devices with large area and small centre-to-centre spacing within the fence. The influence of energy extraction on the natural flow field is assessed relative to changes in the M2 component of elevation and velocity, and residual bed shear stress and tidal dispersion

Modelling tidal energy extraction in a depth-averaged coastal domain

An extension of actuator disc theory is used to describe the properties of a tidal energy device, or row of tidal energy devices, within a depth-averaged numerical model. This approach allows a direct link to be made between an actual tidal device and its equivalent momentum sink in a depth-averaged domain. Extended actuator disc theory also leads to a measure of efficiency for an energy device in a tidal stream of finite Froude number, where efficiency is defined as the ratio of power extracted by one or more tidal devices to the total power removed from the tidal stream. To demonstrate the use of actuator disc theory in a depth-averaged model, tidal flow in a simple channel is approximated using the shallow water equations and the results are compared with the published analytical solutions. © 2010 © The Institution of Engineering and Technology

Investigation of granular batch sedimentation via DEM–CFD coupling

This paper presents three dimensional numerical investigations of batch sedimentation of spherical particles in water, by analyses performed by the discrete element method (DEM) coupled with computational fluid dynamics (CFD). By employing this model, the features of both mechanical and hydraulic behaviour of the fluid-solid mixture system are captured. Firstly, the DEM–CFD model is validated by the simulation of the sedimentation of a single spherical particle, for which an analytical solution is available. The numerical model can replicate accurately the settling behaviour of particles as long as the mesh size ratio (Dmesh/d) and model size ratio (W/Dmesh) are both larger than a given threshold. During granular batch sedimentation, segregation of particles is observed at different locations in the model. Coarse grains continuously accumulate at the bottom, leaving the finer grains deposited in the upper part of the granular assembly. During this process, the excess pore water pressure initially increases rapidly to a peak value, and then dissipates gradually to zero. Meanwhile, the compressibility of the sediments decreases slowly as a soil layer builds up at the bottom. Consolidation of the deposited layer is caused by the self-weight of grains, while the compressibility of the sample decreases progressively

A method for calibration of the Hyperplastic Accelerated Ratcheting Model (HARM)

This paper presents an analytical methodology for calibration of the Hyperplastic Accelerated Ratcheting Model (HARM) [3], based on a closed-form expression for the accumulation of ratcheting strain with cyclic history. The proposed method requires the fit of one test response and of a few continuous cyclic tests. The initial motivation for this work is the calibration of models for the design of piles subjected to long-term cyclic lateral loading, and the test results from Abadie, Byrne [1], [2] are used for calibration and proofing of the model. Nevertheless, the method is applicable to other problems of similar behaviour