Hydrodynamic oscillations and variable swimming speed in squirmers close to repulsive walls

We present a lattice Boltzmann study of the hydrodynamics of a fully resolved squirmer, radius R, confined in a slab of fluid between two no-slip walls. We show that the coupling between hydrodynamics and short-range repulsive interactions between the swimmer and the surface can lead to hydrodynamic trapping of both pushers and pullers at the wall, and to hydrodynamic oscillations in the case of a pusher. We further show that a pusher moves significantly faster when close to a surface than in the bulk, whereas a puller undergoes a transition between fast motion and a dynamical standstill according to the range of the repulsive interaction. Our results critically require near-field hydrodynamics; they further suggest that it should be possible to control density and speed of squirmers at a surface by tuning the range of steric and electrostatic swimmer-wall interactions.Comment: 5 + 8 pages, 4 + 4 Figure

Behaviour of a concrete structure in a real compartment fire

In July 2006, a full-scale compartment fire was set in an existing block of flats in Dalmarnock, Glasgow, Scotland. Prior to ignition, the structure was instrumented with deflection gauges, thermocouples and strain gauges. The growth of the fire was also carefully monitored. The resulting data provided a unique record of the behaviour of a concrete structure in fire through a heating–cooling cycle. The results show significant variation in structural temperatures within a relatively small compartment, demonstrating that the assumption of uniform temperature at any level within a fire compartment, which is implicit in many simple design fires, is incorrect. The response of the structure showed a corresponding complexity due to the combination of non-uniform spatial and temporal heating and the structural boundary conditions. </jats:p

Optimising Structural Loading and Power Production for Floating Wave Energy Converters

This is the author accepted manuscript. The final version is available from EWTEC via the link in this record.This paper investigates the design trade-off between power production and structural loading for Wave Energy Converters (WECs), based on tank test results for the Albatern 12S floating wave energy array. This work feeds into the design development process, which is currently in the concept design and testing phase. The paper focuses on two methods for reducing structural loading: limiting the power take off (PTO) torque generation capacity (for operational loads), and controlling the PTO damping (for extreme loads). The torque that can be generated by the primary PTO mechanism affects the size (and cost) of the structural components within the device. Increased torque results in a potentially greater power capture, but also greater structural loading. It is therefore important to highlight the target torque limit early in the design process. The aim of this work is to identify the optimum torque limit to refine the design towards the lowest overall Levelised Cost of Energy (LCoE). In addition, a high-level investigation of the impact of PTO damping on extreme loading has been carried out, to help to identify appropriate “operational” and “survival” sea states for the device. The paper calculates an optimum torque limit for the device at the West Harris site and quantifies the trade-off between Annual Energy Production and structural cost, using the LCoE as an optimisation criteria. The approach is in principle applicable to other technologies, if the design drivers are adjusted to the technology’s working principle.Tank testing was funded by Wave Energy Scotland (WES) as part of the Novel Wave Energy Converter Stage 1 (NWEC1) programme. This work has been carried out as part of the IDCORE programme, funded by the Energy Technology Institute and RCUK Energy programme (grant no. EP/J500847/1