Wave runup on a concentric twin perforated circular cylinder

The regular wave interaction with a twin concentric porous circular cylinder system consisting of an inner impermeable cylinder and an outer perforated cylinder was studied through physical model and numerical model studies. The experiments were carried out on the twin concentric cylinder model in a wave flume to study the wave runup and rundown at the leading and trailing edges of the perforated cylinder. It was found that the maximum wave runup on the perforated cylinder is almost same as the incident wave height. The experimental results were used to develop the predictive formulae for the wave runup and rundown on the perforated cylinder, which can be easily used for design applications. The wave runup profiles around the perforated cylinder for different values of ka and porosities were studied numerically using Green's Identity Method. The results of the numerical study are presented and compared with the experimental measurements.     

The flow of viscoelastic non-Newtonian fluid in the Ekman layer

In this paper the unsteady flow in the Ekman layer of a visco-elastic non-Newtonian fluid near a flat plate is discussed. Laplace transform technique has been employed to show the basic differential equations. Expressions for velocity profile, the skin friction have been calculated. It is shown that the time to attain the steady state increases with the elastic parameter. It is shown that normally the ultimate steady state is reached through a decay of inertial oscillations whose frequency decreases with increase in the elastic parameter. In the present study we examine the following unsteady problem in non-Newtonian fluid. Consider an infinite plate coinciding with the platez=0 and rotating in unison with elasticoviscous liquid occupying the regionz>0 with a uniform angular velocity about thez-axis for timet<-0. At timet>0, the plate starts moving with a uniform velocityU _o along thex-axis relative to the rotating frame of reference. The horizontal homogeneity of the problem demands that conditions depend onz andt only. The equation of continuity together with the no slip condition at the plate then shows that thez-component of the velocity vanishes everywhere.     

Hydrogen photoproduction ofA. Variabilis incorporated in a photobioreactor

H₂ photoproduction and nitrogenase activities in two strains ofAnabaena variabilis marked wild type ATCC 29413 and mutant PK84 exposed to thermal stress (temperature higher than the normal incubation temperature of 30°C) were studied. Cultures of both strains collected from any interval of logarithmic growth phase exhibited high H₂ photoproduction and nitrogenase activities when exposed to limited time heat shock during the assay process. In contrast, the algal H₂ photoproduction rate of both strains fluctuated with long term thermal stress caused by increasing the growth temperature from 30°C to 36°C.

The changes of nitrogenase (the key H₂ photobiosynthetic enzyme) activities in the mutant PK84 showed variation tendency similar to that of H₂ photoproduction during exposure to thermal stress, indicating that fluctuation of H₂ photoproduction in the mutant was mainly due to the variation of nitrogenase activities. A temporary maximal H₂ photoproduction in the mutant PK84 (wild type ATCC29413) was observed when cells grew at 36°C for 14 (6) days. However, the responses of nitrogenase activities in the wild type to thermal stress were not completely similar to those in the mutant in spite of similar variations of H₂ photoproduction in both strains. The data obtained in these studies suggested that the activities of other enzymes (in the wild strain) involved in H₂ photoproduction were affected by thermal stress since H₂ photoproduction maximized or dropped to 0 without variation tendency similar to that of nitrogenase activities.

Furthermore, an enhancement of H₂ photoproduction speed of the mutant strain cultured in a 4.4 L laboratory photobioreactor was also observed when it was subjected to short time continuous charge of argon, and temperature rise.

All these results indicated that high temperature plays an important role in the photo-autotrophic H₂ photoproduction, and that long term thermal stress is unfavourable for net H₂ photoproduction in both strains ofA. variabilis though short-time heat shock is conducive to H₂ photoproduction.

     

Sound velocity,density, and related properties along a transect across the Bay of Bengal

Physical properties, sound velocity and density of 95 core samples from ten locations along a transect (parallel to 15°N latitude) across the Bay of Bengal were measured. Results indicate that sound velocities range from 1,482 to 1,679 m/s (av: 1,583 m/s) and densities from 1,338 to 1,757 kg/m³ (av: 1,527 kg/m³). It has been observed that dark colored clays and sandy clays show higher values of sound velocity and density than the average values. A comparative study of the same with that of the sediment cores collected from the Norwegian basin, Mediterranean Sea, and Hatteras, Nares Abyssal plains, western North Atlantic Ocean was done.     

Magnetic studies over the northern extension of the Prathap Ridge complex,eastern Arabian Sea

The northern parts of the Prathap and Laccadive Ridge system, eastern Arabian Sea, consist of three parallel basement ridge peaks at varied depths. The topographic highs are associated with either well-developed or subdued magnetic signatures. Model studies, constrained by seismic results, determine the varied nature and depth to the top of the causative basement bodies. Similarities of the geophysical signatures of the ridges and their structural resemblance perhaps point to their common origin. Hence we propose that the Prathap Ridge complex may be a part of the Chagos-Laccadive Ridge system and formed because of the Reunion hotspot activity.     

Seaward dipping reflectors along the SW continental margin of India: Evidence for volcanic passive margin

Multi-channel seismic reflection profiles across the southwest continental margin of India (SWCMI) show presence of westerly dipping seismic reflectors beneath sedimentary strata along the western flank of the Laccadive Ridge — northernmost part of the Chagos-Laccadive Ridge system. Velocity structure, seismic character, 2D gravity model and geographic locations of the dipping reflectors suggest that these reflectors are volcanic in origin, which are interpreted as Seaward Dipping Reflectors (SDRs).     

Modelling and inversion of single-ended refraction data from the shot gathers of multifold deep seismic reflection profiling—an approach for deriving the shallow velocity structure

A multifold crustal-scale deep seismic near-vertical reflection profile generates a large number of single-ended shot gathers, which provide redundant data sets because of overlapping coverage of the shallow refractors. We present an approach for deriving the shallow velocity structure by modelling and inversion of single-ended seismic refraction first arrival traveltime data. We apply this method to a data set acquired with a 12-km long spread with 100 m spacing of shots and receivers, of the Neoproterozoic Marwar basin in the NW Indian shield. The approach is shown to be quite successful for delineating the shallow refractor depths, steep dips and velocities, even in the absence of regular reverse refraction profiles. The study reveals two-layered sedimentary formations, Malani volcanics and a complicated basement configuration of the Marwar basin, and provides a measure of resolution and uncertainty of the estimated model parameters. A seismic section of the near-trace gather is found to be qualitatively consistent with the derived structural features of the basin. The relative highs and lows, observed in the Bouguer gravity profile, further corroborate the derived velocity model. The present approach can be especially useful in offshore areas and elsewhere, where the single-ended multifold seismic profiles are the only available data sets.