A numerical and experimental study on tank wall influences in drag estimation

This study has been undertaken to quantify the tank wall effects on resistance estimation of ship models. Given the finite width of a tank, the flow around a ship model has been numerically modelled and the pressure and pressure related drag have been estimated.Since the model runs at speeds essentially in the laminar and transient speed range, an inviscid model has been chosen for obtaining the pressure drag component in the numerical studies. Grid dependency study has been done to optimize the mesh in the control volume for the numerical studies. An unstructured grid consisting of hexahedral cells has been used in the volume of fluid (VOF) model. The model chosen is a medium speed, ocean going barge and the residuary resistance has been obtained for different tank width conditions. The tank width has been defined using a non-dimensionalized parameter W/B (tank width W, model width B) ratio. The study shows that the residuary resistance obtained at W/B=5.0 is free from tank wall influence for the chosen model. The findings of the study have been compared by testing two geosim models under the same tank width conditions. The residuary resistance values have been compared with numerical results. The combined numerical experimental approach provides interesting results of consistency for comparison. The tank wall influences suggested by the numerical study are well quantified in the experimental study and give useful guideline for limiting wall influences.     

Heavy metals distribution in the sediments of ganges and Brahmaputra rivers

Bed sediments were collected from the entire region of the Ganges basin and some parts of the Brahmaputra. In addition, selected stations were sampled for suspended sediments as well. The samples were analysed for a number of heavy metals (Fe, Mn, Ni, Cr, Cu, and Zn) by the thin-film energy dispersive X-ray fluorescence technique. There are pronounced temporal and spatial variations in the heavy metals distributions. Suspended sediments are 5–10 times richer than the bed sediments. None of the tributaries contribute significant heavy metal load, but around urban areas in Yamuna (tributary of Ganges), very high levels due to the distribution from the drainage network are observed. Compared to the Brahmaputra, the distribution and fractionation of heavy metals in the Ganges sediments are more erratic and highly variable. All the metals considered show high correlation among themselves. Given the high flux of suspended sediments from the Himalayan rivers (nearly 20% of the global flux), the worldwide budget for heavy metal transport may need to be suitably revised.     

Persistent organochlorine residues in green mussels from coastal waters of South India

Green mussels (Perna viridis) collected from nine locations along the South Indian coast were used as bioindicator to assess the organochlorine contamination (HCHs, DDTs, and PCBs) in the coastal environment of South India. Concentrations of ΣHCH and ΣDDT were found to be similar, ranging from 3 to 39 ng g⁻¹ on wet wt basis. On the other hand, PCB levels were apparently lower, varying from <1.0 to 7.1 ng g⁻¹ wet wt. The residue pattern of organochlorines in mussels are principally similar to those in Indian human samples, reported earlier. The coastal marine pollution by HCH in India ranks among the highly contaminated areas in the world.     

Phosphorus,silicon, and some trace contaminants in the Ganges Estuary

Dissolved silica and phosphorous show a highly nonconservative behavior in the Ganges Estuary. In addition, phosphorous also shows seasonal variations, with winter levels higher than the levels in the monsoon. Mineral composition inducates enrichment of coarse quartz grains due to selective removal of finer clays in the estuary, either due to flocculation or due to dredging effects of the Port of Calcutta. Particulate P and Si show strong opposite trends, possibly indicating the presence of P in predominently nondetrial fractions in the sediments. Certain trace contaminants, such as Fe, Mn, Cu, Pb and Zn, show seasonal variability as well as enrichment in suspended particulate material relative to bed sediments. Levels of all these contaminents are still well below those reported for rivers such as the Rhine and other highly man-influenced systems.     

Geochemistry of the Cauvery Estuary,East Coast of India

Major ion chemistry of water and elemental geochemistry of suspended and surficial sediments collected from the Cauvery Estuary were studied to understand the geochemical processes in this tropical estuarine system. Specific conductance (EC), total dissolved solids (TDS), and total suspended matter (TSM) increased conservatively with increasing chlorinity. In general, SO₄ ^2?, Na, K, Ca, and Mg showed an increasing trend while H₄SiO₄ and PO₄ ^3? showed a decreasing trend toward the sea. Additional removal mechanisms operating for these ions in the Cauvery Estuary have been identified based on observed concentrations. Factor analysis pointed out the sources contributing to the observed trends in estuarine water chemistry. POC and PON decreased toward the high chlorinity zone. TSM in the Cauvery Estuary were mostly of inorganic nature. Stable carbon isotope values showed that the carbon was equally of marine and terrestrial origin and helped to delineate the contribution of river water and seawater. The ? mean size (a logarithmic grain size scale commonly used by sedimentologists) indicated that the surficial sediments were primarily comprised of coarse and silt, whereas suspended sediments were principally silt and clay. Suspended sediments were enriched in clays compared to surficial sediments. Quartz and feldspar were abundant among detritals while chlorite, kaolinite, and montmorillonite were dominant among clays. Silicon was the most abundant element in the sediments followed by Al, Ca, Na, K, Fe, Mn, and P. Heavy metals were enriched in the suspended sediments compared to the surficial bottom sediments as follows: Fe = 3.5, Mn = 7.4, Pb = 1.1, Zn = 15.2, Cu = 7.4, and Cr = 4.0. The levels of Cd, Cr, Zn, and Fe increased up the middle reaches and then decreased toward the sea due to urban effluent and fertilizer input. Size fractionation studies indicated that the metal concentration in the finer fraction was 50% higher by mass than the coarse silt and fine silt fractions. Chemical fractionation studies showed that the abundance of metals were in the order of residual > organic/sulfide > carbonate > Fe/Mn oxide > exchangeable fractions.     

Heavy metal distribution in the Godavari River basin

Suspended and bed sediments collected from the entire region of the Godavari River basin were analyzed for Fe, Mn, Cr, Cu, Ni, and Zn. There are pronounced temporal and spatial variations in the heavy metal distributions. The concentrations of heavy metals in the suspended sediments are significantly higher than the bed sediments.Throughout the basin heavy metals are enriched in the finer fractions (<2 µm) of the bed sediments. The average heavymetal composition of the sediments is higher when compared to the average Indian river sediments. Heavy-metal concentration in the two shallow cores collected shows, to some extent, the influence of urbanization. When compared to the other tropical Indian rivers such as the Krishna, the Godavari appears to be a significant contributor of heavy metals to the Bay of Bengal. Considering the enormous sediment load of the Godavari River—170 million tons/yr, the heavy metal fluxes to the Bay of Bengal is very significant. Except for the Pranhita, other tributaries of the Godavari do not contribute significant loads of heavy metals. All the metals show high correlation among themselves and the correlation is more pronounced in suspended sediments than in the bed sediments. The heavy-metal distribution, fractionation, and its relationship with total suspended sediments and depth in various parts of the basin are discussed in detail.     

Coastal geomorphology and sediment distribution mapping using Landsat—TM digital data —A study in Coastal area of parts of Orissa,India

An area of about 1100 sq.km forming a part of east coast of India was taken for digital analysis using the VAX 11/780 image analysis computer system. The data used for the analysis is Thematic mapper data of Landsat 5. By using the maximum likelihood algorithm and the existing ground truth, the area was classified geomorphologicall.. In addition a qualitative mapping of suspended sediments of coastal waters in Bay of Bengal around the estuary of Dhamra river in Orissa has been carried out. In seventeen classes, eleven correspond to geomorphic units and six belongs to different categories of sediments concentration in Coastal waters.     

Silica and alumina transfer in supercritical aqueous fluids and growing of topaz monocrystals in them

Silica and alumina transfer during the dissolution and growth of quartz, corundum, and topaz in supercritical aqueous fluids have been experimentally studied under a direct temperature gradient, and the possibility for growing of topaz monocrystals in them have been determined. It was demonstrated that the directions of silica and alumina transfer shows no unambiguous correlation with the composition, PT conditions, pH, and density of the fluids, and, in some cases, can be opposite. This defines simultaneous spatially associated or separated growth of quartz and topaz, as is often observed in camera pegmatites. Our experimental data made it possible to develop a reproducible seed growth of topaz monocrystals and to study their structure, morphology, and physical properties.