Physico-chemical and mineralogical studies on cochin marine clays

Large deposits of marine clays are encountered all along the Indian coastal belt. These clays are pleistocene to recent in origin, are considered to be young, and were deposited in a salt or brackish environment. These clays are very soft in consistency with low in-situ strength and high compressibility. The properties of these soil deposits depend mainly on the clay minerals present. In the present investigation, the mineralogical studies of some Cochin marine clays were carried out using XRD technique. The physical and chemical properties of these deposits were also reported. The test results were compared with some earlier reported works on marine clays.     

A prospective thermomagnetic temperature transducer

The possibilities of measuring the temperature of seawater as a continuous medium are analysed. It is shown that contemporary thin-film platinum resistance thermometers are inadequate for seawater temperature measurements because of their lag and resolution. The following shortcomings of these thermometers are indicated: heat dissipation by the terminals and the need for them to be hermetically sealed. A prospective improved design is suggested for a thermomagnetic temperature transducer, which provides for the minimal possible lag for the required resolution.Translated by V. Puchkin.     

Coupled dynamics of tethered buoy systems

The three-dimensional coupled behavior during the interaction of buoys with their mooring systems is numerically analyzed. A time-domain model was developed to predict the response of a tethered buoy subject to hydrodynamic loadings. External loadings include hydrodynamic forces, tethers tensions, wind loadings and weight. System nonlinearities include large rotational and translational motions, and non-conservative fluid loadings. The mooring problem is formulated as a combined nonlinear initial-value and two-point-boundary-value problem which is directly integrated both in time and space. Buoy equations of motion are derived using small Eulerian angles. Coupling between rotational and translational degrees of freedom is included and coupling between the buoy and cable is effected by adopting the buoy equations of motion as boundary conditions at one end for the mooring problem. Numerical examples are provided to validate the formulation and solution technique; predicted responses of three types of buoy (sphere, spar, and disc) are compared with experimental results.     

The formation and evolution of East Australian current warm-core eddies

Data on East Australian Current (EAC) warm-core eddies were obtained over the period 1976–1978 by the Department of Defence and the Commonwealth Scientific and Industrial Research Organization (CSIRO). In that time we have learned that warm eddies form by pinch-off of poleward EAC meanders, can coalesce with the EAC and appear generally similar to Gulf Stream, Kuroshio and other current system eddies. Two eddies were tracked over 1977–1978 with satellite buoys and one (eddy B) was repeatedly studied over eleven months. A deep winter core formed by winter convective cooling and the following summer a new surface mixed layer formed on top of the core. The seasonal changes have been analysed for heat content and changes in dynamic relief. The eddy decayed with a time constant of 650 ± 150 days, due to upwelling below the seasonal thermocline. Surface cooling had little effect on eddy lifetime. The eddy contracted horizontally, possibly after some interaction with the EAC, giving rise to eddy spin-up with increasing age. Surface currents increased after eleven months to 2.0 m s^?1. The dynamic relief during summer was also apparently boosted by contact with the EAC. Eddy B was observed to coalesce with a new meander of the EAC rather than drift away to the south. It is proposed that the formation of these eddies is governed by the westward propagation of the baroclinic Rossby wave known as the Tasman Front. Pinch-off of eddies adjacent to the coast and the variable flow of the EAC may be caused by the baroclinic wave ‘breaking’ on the coast. The eddy formation rate is about two per year and most eddies coalesce with the EAC and do not escape to the south. Eddies coalesce and re-separate, creating many subsurface isothermal layers from old cores south of 34°S.     

Prediction of ocean waves based on the single-parameter growth equation of wind waves

A method for the prediction of ocean waves was developed on the basis of the single-parameter growth equation of wind waves, proposed byToba (1978) on the basis of similarity in growing wind waves. The applicability of the method to actual problems was tested by hindcasting the wave characteristics with the method, for two cases with differing time and space scales, one in Kii Channel Approach, Japan, and the other in the North Atlantic Ocean. The results showed that the present method can predict waves within an error of 1.3 m in wave heights, which ranged from 3 to 12 m.     

Turbulent structure of the subsurface layer of the sea according to the data of the <Emphasis Type="Italic">Sigma-1</Emphasis> measuring complex

We present the results of experimental investigations of the characteristics of turbulence in the layer of wave-induced mixing. The data on the fluctuations of velocity, temperature, and conductivity are obtained with the help of a Sigma-1 measuring complex. The computed values of the dissipation rate of turbulent energy are compared with different models proposed for the subsurface layer. It is shown that the available models fail to guarantee satisfactory agreement of the numerical results with the experimental data for the layer of active wave action and, in particular, in the presence of swell. This leads us to the conclusion concerning the necessity of parametrization and assimilation of more complete data on the state of the sea surface, the structure of currents, and the surface layer of the atmosphere in the models. __________ Translated from Morskoi Gidrofizicheskii Zhurnal, No. 2, pp. 15–28, March–April, 2007.     

Regeneration of sand waves after dredging

Sand waves are large bed waves on the seabed, being a few metres high and lying hundreds of metres apart. In some cases, these sand waves occur in navigation channels. If these sand waves reduce the water depth to an unacceptable level and hinder navigation, they need to be dredged. It has been observed in the Bisanseto Channel in Japan that the sand waves tend to regain their shape after dredging. In this paper, we address modelling of this regeneration of sand waves, aiming to predict this process. For this purpose, we combine a very simple, yet effective, amplitude-evolution model based on the Landau equation, with measurements in the Bisanseto Channel. The model parameters are tuned to the measured data using a genetic algorithm, a stochastic optimization routine. The results are good. The tuned model accurately reproduces the measured growth of the sand waves. The differences between the measured weave heights and the model results are smaller than the measurement noise. Furthermore, the resulting parameters are surprisingly consistent, given the large variations in the sediment characteristics, the water depth and the flow field. This approach was tested on its predictive capacity using a synthetic test case. The model was tuned based on constructed predredging data and the amplitude evolution as measured for over 2 years. After tuning, the predictions were accurate for about 10 years. Thus, it is shown that the approach could be a useful tool in the optimization of dredging strategies in case of dredging of sand waves.     

Investigation of the electromagnetic fields induced by sea wave motion

This paper discusses a theoretical model of the electromagnetic field induced by internal waves of baric origin. Comparison of thein situ data on the differences between the horizontal electrical field potentials conditioned by internal waves in some Black Sea and tropical Atlantic areas and of the results of calculations of the model electrical field's intensity in those areas shows their good agreement. The dependences of the electromagnetic field component amplitudes on the internal waves parameters and sea-bed rock conductivity are considered. Translated by Vladimir A. Puchkin.