Large motion analysis of compliant structures using euler parameters

The large motions that a compliant offshore structure experiences were analysed using Euler parameters. Firstly, the equations of motion of a rigid body undergoing large translations and rotations were obtained using the Lagrangian formulation. Secondly, the hydrodynamic forces acting on the structure were calculated using the modified Morison's equation. A tension-leg platform (TLP) subjected to an oblique incident wave was then analysed using the above formulation. This was followed by an analysis of an articulated tower for comparison with the results of other researchers. An example showing the tower undergoing subharmonic oscillations was also included.     

Mapping lithology and assessing recharge characteristics in a granitic hard rock aquifer: Inference from 2D resistivity,induced polarization,tracer and moisture measurements

Two dimensional Electrical Resistivity Tomography (ERT) investigation along with Time Domain Induced Polarization (TDIP) investigation covering 1.6 km line were carried out at 3 natural recharge sites in a overexploited groundwater granite watershed, situated in a semi arid region in the state of Telangana, India. At these sites, shallow and/ or deep moisture influx measurements were also carried out using injected tritium tracer and neutron moisture probe. The watershed is covered by sandy loam to silt loam soil, receives an average annual rainfall of 620 mm with the pre monsoon groundwater level ranging from 8m to 29m bgl. The spot investigations were done to assess and understand the recharge process and groundwater potential in terms of resistivity/conductivity and moisture characteristics of the subsurface rock formation.     

Vertical propagation of baroclinic Kelvin waves along the west coast of India

A linear, continuously stratified ocean model is used to investigate vertical propagation of remotely forced, baroclinic Kelvin waves along the Indian west coast. The extent of vertical propagation over the length of the coast is found to be an increasing function of the forcing frequency. Simulations show that, over the length of the Indian west coast, vertical propagation is limited at annual and semi-annual periods, but significant at periods shorter than about 120 days. This has two major consequences. First, the depth of subsurface currents associated with these frequencies varies substantially along the coast. Second, baroclinic Kelvin waves generated in the Bay of Bengal at periods shorter than about 120 days have negligible influence on surface currents along the north Indian west coast.     

Environmental and social recovery asymmetries to large-scale disturbances in small island communities

Natural Hazards - People’s livelihoods in tropical small-island developing states are greatly dependent on marine ecosystem services. Yet services such as fisheries and coastal buffering are...     

Heave Studies on Fly Ash-Stabilised Expansive Clay Liners

Clay liners or compacted earthen barriers are important barrier materials used for preventing contaminant transport through soils. A low hydraulic conductivity (k) is a significant parameter that governs the design and construction of clay liners. Compacted expansive clays, which are montmorillonite clays, also have a very low hydraulic conductivity (k). When expansive clays are blended with fly ash, an industrial waste, the hydraulic conductivity (k) further reduces as the ash-clay blends result in increased dry densities at increased fly ash contents. Hence, fly ash-stabilised expansive clay can also be proposed as a unique clay liner material. As expansive clays undergo heave when they come into contact with water, it is necessary to study the heave behaviour of fly ash-stabilised expansive clay liners. This paper presents heave studies on fly ash-stabilised expansive clay liners. Fly ash in different contents by dry weight of the expansive clay was added to the clay, and the ash-clay blend was compacted as a liner overlying a natural field soil layer. Compacted lateritic clay was used for simulating the natural field soil into which contaminants migrate. Calcium chloride (CaCl₂) solution of varying concentration (5, 10, 20, 50, 100 and 500 mM) was used as the permeating fluid in the heave studies. The rate of heave and the amount of heave of the fly ash-stabilised expansive clay liners were monitored. Deionised water (DIW) was also used as inundating fluid for comparative study. Heave (mm) decreased with increase in solute concentration for all fly ash contents. For a given solute concentration, heave decreased up to a fly ash content of 20 % and thereafter it increased when the fly ash content was increased to 30 %. Heave of the fly ash-stabilised expansive clay liners was correlated with their permeability, liquid limit (LL) and free swell index (FSI) pertaining to the respective fly ash content and CaCl₂ concentration.     

Influence of spatially random soil on lateral thrust and failure surface in earth retaining walls

The present study investigates the influence of spatial variability of soil properties on the lateral thrust and failure surface of a 6?m high frictionless rigid earth retaining wall in active condition. The drained friction angle of the soil is modelled as a log-normal anisotropic random field in two dimensions, using the Cholesky decomposition technique. The effect of horizontal and vertical scale of fluctuation is observed on the lateral thrust. The failure surface in the backfill is found to be more or less similar for different combinations of spatial variability in vertical and horizontal directions. Monte-Carlo simulation technique is used to compute the probability of failure and to obtain the worst-case spatial variability configuration.     

Mapping of Cropping System for the Indo-Gangetic Plain Using Multi-Date SPOT NDVI-VGT Data

The present study has been carried out to delineate the existing cropping systems in the Indo-Gangetic Plains (IGP) using 10 day composite SPOT VEGETATION (VGT) NDVI data acquired over a crop year (June–May). Results showed that it is feasible to identify the major crops like rice, wheat, sugarcane, potato, and cotton in the dominant growing areas with good accuracy. Double cropping pattern is the most prevalent. Rice-wheat, sugarcane based, cotton-wheat, rice-potato, rice-rice, maize/millet-wheat are some of the major rotations followed. Rice-wheat is the dominant rotation accounting for around 40% of the net sown area. Triple crop rotations was less than 5% of the area and observed in some parts of Uttar Pradesh, Bihar and West Bengal. Single crop rotation of rice-fallow is significant only in West Bengal.     

Antifouling activities of marine bacteria associated with sponge (Sigmadocia sp.)

The present study aimed at assessing the antifouling activity of bacteria associated with marine sponges. A total of eight bacterial strains were isolated from the surface of sponge Sigmadocia sp., of them, SS02, SS05 and SS06 showed inhibitory activity against biofilm-forming bacteria. The extracts of these 3 strains considerably affected the extracellular polymeric substance producing ability and adhesion of biofilm-forming bacterial strains. In addition to disc diffusion assay, microalgal settlement assay was carried out with the extracts mixed with polyurethane wood polish and coated onto stainless steel coupons. The extract of strain SS05 showed strong microalgal settlement inhibitory activity. Strain SS05 was identified as Bacillus cereus based on its 16S rRNA gene. Metabolites of the bacterial strains associated with marine invertebrates promise to be developed into environment-friendly antifouling agents.     

Potential groundwater recharge zones within New Zealand

Water resources in New Zealand are not evenly distributed across the country which makes it difficult to adequately allocate the use of water resources in every basin. Groundwater is a fundamental water resource in New Zealand for agricultural, industrial and domestic use. Detailed knowledge regarding groundwater recharge potential is a pre-requisite for sustainable groundwater management, including the assessment of its vulnerability to contamination by pollutants. In this study, a comprehensive GIS approach was used to map the potential groundwater recharge zones across New Zealand. National data sets of lithology, slope, aspect, land use, soil drainage and drainage density were converted to raster data sets with a spatial resolution of 500 m × 500 m and superimposed to derive groundwater potential zones. The resultant maps demonstrate that the potential is low in urban and mountainous areas, such as the Southern Alps, whereas the highest potential can be found in regions with large lakes and in the lower elevation plains areas, where Quaternary sediments prevail. The resulting maps can be used to identify areas of high nutrient leaching in zones where high groundwater recharge potential exists.