Free surface,current profile and buoyancy effects upon internal wave energy flux profiles in sill regions

A non-hydrostatic ocean circulation model is used to determine the distribution of the horizontal energy flux terms due to internal waves in sill regions. Calculations show that although the linear energy flux term is significant, the contribution from the non-linear terms is appreciable. In addition, unlike as is often assumed in deep ocean situations, the free surface contribution to the energy flux distribution often dominates. The magnitude and relative importance of the energy flux terms are influenced by how the fluctuating velocity due to internal waves is computed. In addition changes in vertical stratification affects the relative contribution of the energy flux terms although the free surface term still dominates.     

WAKE SHIELDING EFFECTS OF THREE CYLINDERS IN CURRENTS

A large amount of experimental work has been carried out in the past to understand mean and fluctuating forces on a single circular cylinder in cross flows. In comparison substantially less work can be found on the interference between multiple cylinders and the number of publications available becomes drastically smaller as the number of cylinders involved increases. The current experimental work systematically examines the wake shielding effects of three cylinders in a towing tank. Though staggered, the three cylinders are arranged mainly along the flow direction with the downstream cylinders situating in the wakes of the upstream cylinders.The tests are mainly carried out in the sub-critical Reynolds number regime with the upper end close to the critical Reynolds number regime. Significant drag reduction on downstream cylinders is identified.     

Comparative studies of phytotoxicity and chemical composition of aqueous oil solutions affected by evaporation, illumination and extraction

Aqueous stock solutions of Ekofisk crude oil were prepared in darkness and under illumination, and fractions of both types of stock solutions were further treated by controlled evaporation, illumination, extraction with hexane and dichloromethane and phytoplankton cultivation. Chemical analysis of all fractions were combined with toxicity testing based on the marine diatom Skeletonema costatum.Removal of the readily water-soluble aromatic hydrocarbons did not reduce the phytotoxicity of the solutions. Illumination led to a dramatic increase in both toxicity and the total amount of dissolved material. In no case did the hydrocarbon content exceed 5% of the total dissolved material, and the traditional analytical values referred to as “total hydrocarbon content” are therefore considered highly misleading. The toxicity of these aqueous oil solutions must apparently be ascribed to a multitude of slightly polar, oxidized compounds originating from the oil.     

Load control of a wind-hydrogen stand-alone power system

A new generation of load controllers enable stand-alone power systems (SAPS) to use one or many standard (grid connected) wind turbines. The controllers use fuzzy logic software algorithms. The strategy is to use the control loads to balance the flow of active power in the system and hence control system frequency. The dynamic supply of reactive power by a synchronous compensator maintains the system voltage within the limits specified in EN50160. The resistive controller loads produce a certain amount of heat that is exchanged down to the end user (hot water). It was decided to investigate the implementation of a hydrogen subsystem into the SAPS that can work in parallel with the Distributed Intelligent Load Controller (DILC). The hydrogen subsystem can then function as energy storage on long-term basis and an active load controller on short-term basis.