Steven Czitrom

A tidal mixing front in an area influenced by land runoff

Abstract A potential energy model of stratification, adequate for thermal fronts, is extended to incorporate the added buoyancy input of river fresh water discharge. The model is discussed in the light of CTD data taken at a section in the southern German Bight which was repeatedly sampled throughout the year. A front observed in this area exhibits similarities with surface heat input induced fronts in the United Kingdom shelf despite the dominating contribution of salinity to the density field.

Hydrodynamics of an oscillating water column seawater pump: Part I: theoretical aspects

A wave-driven seawater pump, composed of a resonant and an exhaust duct joined by a variable-volume air compression chamber, is studied. The time dependent form of Bernoullis equation, adapted to incorporate losses due to friction, vortex formation at the mouths and radiation damping, describes the pump behaviour. A dimensional analysis of the pump equations shows that a proposed scale-model will perform similar to a full-scale seawater pump. Fluid oscillations in the ducts perform similar to a damped, two-mass spring system, excited by the waves. A resonant condition can be maintained, for different wave frequencies, by varying the volume of air in the compression chamber. The dimensional analysis shows that the basic behaviour of the pump is linear and that its performance can be significantly increased by optimising the design of the duct mouths. Linear estimates of the resonant air chamber volume and flow rate through the pump are derived.

The effect of river discharge on the residual circulation in the Eastern Irish Sea

Abstract A method is described for measuring horizontal density gradients using data from a current meter mooring which permits the density driven component to be isolated from the observed residual currents. An estuarine-like residual circulation, towards the coast near the bottom and to the right of the offshore direction near the surface, is a result of the river discharge induced horizontal density gradients near the centre of the Eastern Irish Sea. This indicates an intermediate situation between an estuary where friction is large and the open sea where the geostrophic effect is dominant. The above method may provide more appropriate values against which to compare theoretical and numerical models of the density driven residual circulation than the charts used up to now. In these charts, the density driven component is inextricably intermingled with the effects of other driving forces. The adjustment of complex numerical models that take account of several driving forces could also be considerably simplified.

Hydrodynamics of an oscillating water column seawater pump. Part II: tuning to monochromatic waves

Flume experiments with a scale-model of a wave driven seawater pump in monochromatic waves are described. A tuning mechanism optimises the pump performance by keeping it at resonance with the waves. The pumping process itself was found to de-tune the system because of the reduced gravity restoring force due to spilling in the compression chamber. A perturbation analysis of the pump equations shows that performance of the system can be increased by optimising the shape of the pump intake to minimise losses due to vortex formation. An algorithm is derived, using a numerical model of the pump, which accurately determines the required volume of air in the compression chamber to induce resonance given variations in the wave frequency, the wave height and the tides. A sustainable development project to use a seawater pump to manage fisheries at a coastal lagoon in Mexico is described.

Innovative uses of wave power: Environmental management of the port of Ensenada, Mexico

Over the past century, the water and sediments of the port of Ensenada, Mexico, have accumulated a lot of pollution from human activities. Although present day restrictive measures inhibit any further accumulation, the existing aggregation in the sediments is sufficient to maintain high levels of contamination throughout the port, despite the flushing action of the tides. A SIBEO (SIBEO is an acronym for the Spanish SIstema de Bombeo por Energia de Oleaje) wave-driven seawater pump recently developed at the National University of Mexico is proposed to inject clean and oxygen rich seawater from outside the port to promote flushing in the more stagnant sections of the harbour. Results from a numerical model of the port hydrodynamics shed light on why the tides cannot on their own adequately flush the system, and how the wave-driven seawater pump will help to promote ventilation. Over the next 4 years, a cluster of SIBEO pumps is proposed to be installed on the Ensenada breakwater to inject unpolluted seawater at various locations in the port. A programme will be carried out to study the effects on the water column and sediments, in this first full-scale application of the SIBEO.

Water quality of a port in NW Mexico and its rehabilitation with swell energy

Ensenada Harbor is one of the most important ports of Mexico. Anthropogenic activities have affected the area over several decades, leading to the accumulation of contaminants in its sediments, which eventually are re-suspended into the water column. In spite of water treatment of the tributaries that discharge into the Ensenada Harbor, the water circulation patterns of the harbor, which consist of closed eddies in the northern and southeastern sector, favor the accumulation of those contaminants and hinder exchange with adjacent seawater. Samples collected in October of 2005 registered 63 microM total inorganic nitrogen and 280 mg/L of COD, confirming that this is a highly contaminated environment when compared with other water bodies of North America. Such concentrations can be lowered up to 80% by using a wave energy pumping system that demonstrates the possibility to gradually dilute these contaminants and rehabilitate the Ensenada Harbor.

Wave energy-driven resonant sea-water pump

A wave-driven sea-water pump which operates by resonance is described. Oscillations in the resonant and exhaust ducts perform similar to two mass-spring systems coupled by a third spring acting for the compression chamber. Performance of the pump is optimized by means of a variable volume air compression chamber (patents pending) which tunes the system to the incoming wave frequency. Wave tank experiments with an instrumented, 1:20-scale model of the pump are described. Performance was studied under various wave and tuning conditions and compared to a numerical model which was found to describe the system accurately. Successful sea trials at an energetic coastline provide evidence of the system`s viability under demanding conditions.

On the tuning of a wave-energy driven oscillating-water-column seawater pump to polychromatic waves

Performance of wave-energy devices of the oscillating water column (OWC) type is greatly enhanced when a resonant condition with the forcing waves is maintained. The natural frequency of such systems can in general be tuned to resonate with a given wave forcing frequency. In this paper we address the tuning of an OWC sea-water pump to polychromatic waves. We report results of wave tank experiments, which were conducted with a scale model of the pump. Also, a numerical solution for the pump equations, which were proven in previous work to successfully describe its behavior when driven by monochromatic waves, is tested with various polychromatic wave spectra. Results of the numerical model forced by the wave trains measured in the wave tank experiments are used to develop a tuning criterion for the sea-water pump.

Three-Dimensional Modeling of a Wave-Driven Seawater Pump Inflow to the Port of Ensenada, Mexico

Abstract Like most harbors, the Port of Ensenada, Mexico, is vulnerable to the accumulation of pollutants. A wave-driven seawater pump (Sistema de Bombeo por Energía de Oleaje [SIBEO]) is proposed to inject clean and oxygen-rich water from outside the Port to promote flushing in its more stagnant areas. Three-dimensional, numerical simulations with the Estuary and Lake Computer Model (ELCOM) were used to investigate the behavior, extent, and effect of the SIBEO inflow. Conservative tracer experiments indicate that the effect of the pump would spread through the pycnocline and become noticeable throughout the harbor within a month. The tracer method yields a bulk estimate of the flushing time for the port of approximately 4 days, although the spatial variability of the flushing is significant. The least-flushed areas of the harbor are its NE and SE corners, where greater concentrations of pollutants have been observed.