A simplified instrumentation for measuring scour in silty clay around a vertical pile     

M. Ram Babu  S. Narasimha Rao  V. Sundar   《Applied Ocean Research》2002,24(6):355-360

The obstruction to flow around a pile placed in an erodible seabed causes scour leading to changes in the bed elevation in the vicinity of the pile. In the present investigation, scour around piles induced by the seabed current has been studied in a wave flume using model piles of diameters 50, 90 and 110 mm embedded in a silty clay soil bed. The particulate movement due to scour is time dependent and in case of sediments with particle sizes ranging upto clay fractions, the measurement of scour becomes extremely difficult. This paper presents a simplified experimental technique for the measurement of scour depth with time around a pile foundation in a silty clay soil.  相似文献   

Stability of breakwater defenced by a seaward submerged reef     

Kiran G. Shirlal  Subba Rao  Venkata Ganesh  Manu 《Ocean Engineering》2006,33(5-6):829-846

The stability of a uniformly sloped conventional rubble mound breakwater defenced by a seaward submerged reef is investigated using physical model studies. Regular waves of wide ranging heights and periods are used. Tests are carried out for different spacings between two rubble mound structures (X/d=2.5–13.33) and for different relative heights (h/d=0.625–0.833) and relative widths (B/d=0.25–1.33) of the reef. It is observed that a reef of width (B/d) of 0.6–0.75 constructed at a seaward distance (X/d) of 6.25–8.33 breaks all the incoming waves and dissipates energy and protects the breakwater optimally.  相似文献   

Regional gravity and magnetic studies over the continental margin of the central west coast of India     

L. V. Subba Raju  K. A. Kamesh Raju  V. Subrahmanyam  D. Gopala Rao 《Geo-Marine Letters》1990,10(1):31-36

Gravity studies over the continental margin of the central west coast of India show a sediment thickness of 2–3 km on the shelf associated with deeper horst and graben structures, of 6 km in the shelf margin basin, and about 1 km in the deep sea. The upward trend in free-air gravity anomaly toward the deep sea region is interpreted as crustal thinning. Model studies indicate a 25-km-thick crust in the shelf region and a minimum of 18 km in the more offshore region. An abrupt magnetic signature change suggests differential basement depths in the shelf region. Major faulting in the region is confirmed in water depths of approximately 100–200 m.  相似文献   

Cementation in cold-water bryozoan sand, Tasmania, Australia     

C.Prasada Rao 《Marine Geology》1981,40(3-4):M23-M33

Cold-water (<3–11°C) carbonate is the predominant sediment on the Tasmanian shelf. Calcitic skeletal grains (bryozoa, foraminifera, echinoderms, etc.) predominate over aragonitic (gastropods, etc.) ones. Non-skeletal grains are mostly micritic intraclasts with some pellets.

Fibrous spherulitic and rhombohedral calcite submarine cements range up to 90% in the bryozoan sand. X-ray analyses show that the bryozoan sand is characterized by a spectrum of calcites (low to high magnesian) and some aragonite.

A uniform spread of Mg concentrations from 0.06 to 2.48 wt.% indicates <3–10°C ambient water temperatures. The Mn (10–360 ppm) and Fe (176–2499 ppm) concentrations increase with increasing Mg values due to the formation of impure CaCO₃ phases. The Sr content in bryozoan sand (bryozoa = 3200 ppm Sr) decreases with increasing rhombohedral calcite cement, as low Mg-calcite precipitating from 3° C sea water would have 1350 ppm Sr. The bryozoan sand grains with fibrous spherulitic calcite cements have high Sr concentrations (4470–7000 ppm), in the same range as in aragonitic (detected only by X-ray analyses) bryozoan sand grains. The spherulitic calcite cements are either pseudomorphs after original aragonite cements or these calcite cements and aragonite were inverted from fibrous spherulitic vaterite, a predominant CaCO₃ polymorph at temperatures <10°C.  相似文献   

Factors affecting seasonality of lithogenic and biogenic particle flux in a large estuarine ecosystem     

B.T. Hargrave  G.L. Bugden  E.J.H. Head  B. Petrie  G.A. Phillips  D.V. Subba Rao  P.A. Yeats 《Estuarine, Coastal and Shelf Science》2007,73(3-4):379-398

Seasonal patterns of vertical flux over two years (2001–2003) at two stations in the Bras d'Or Lakes, a large estuary in Cape Breton Island, Nova Scotia, were determined using aluminum and organic carbon in settled particles collected in moored traps to calculate lithogenic (terrigenous) and marine biogenic fractions. On an annual basis, lithogenic material comprised 53% and 81% of dry weight and 48% and 66% of organic carbon in settled particles at the deep- (128 m) and shallow-water (41 m) locations, respectively. Peaks in runoff, inferred from rain and snowfall precipitation, ice cover and possible horizontal transport of resuspended sediment coincided with maximum sedimentation rates of lithogenic material during unstratified periods between October and March. Biological factors correlated with phytoplankton and ice algal primary production and seasonal changes in zooplankton grazing inferred from phaeopigments controlled biogenic particle fluxes under stratified conditions between June and September and during winter. Year-to-year variations in deposition of lithogenic and marine biogenic material depended on seasonal differences in stratification, precipitation, freeze/melt conditions and the extent of ice cover.  相似文献   

Lime injection technique to improve the behaviour of soft marine clays     

S. Narasimha Rao  G. Rajasekaran 《Ocean Engineering》1994,21(1)

Soft marine clay deposits pose several foundation problems and such weak clay deposits have been found both along seacoasts and in offshore areas spread over many parts of the world. We suggest using some chemical injection techniques to improve the engineering behaviour of soft underwater marine clays. A test programme was carried out by injecting lime into a soft marine clay in a test tank. The penetration of lime into the soil was established by taking a number of pH measurements and calcium oxide estimation from samples taken at various radial distances. The improvement in the plasticity characteristics of the soil has been verified by indices tests. Test results indicated the improvement in the strength and reduction in the compressibility of the soil with time. The beneficial changes that occurred in the soil have been attributed to the formation of cementation compounds and these compounds have been identified by using X-ray Diffraction Technique (XRD). The test results show good promise for the use of lime grouting in the treatment of weak marine clayey deposits.  相似文献   

Behaviour of rigid piles in marine clays under lateral cyclic loading   总被引：1，自引：0，他引：1  

S. Narasimha Rao  K. Mallikarjuna Rao 《Ocean Engineering》1993,20(3)

In the field of ocean engineering, pile foundations are extensively used in supporting several structures. In many cases, piles are subjected to significant lateral loads. The environment prevalent in the ocean necessitates the piles to be designed for cyclic wave loading. In this investigation, the behaviour of rigid piles under cyclic lateral loading has been studied through an experimental programme carried out on model piles embedded in a soft marine clay. Static tests were also conducted on piles embedded in a clay bed prepared at different consistencies suitable to field situations. Cyclic load was applied by using a specially designed pneumatic controlled loading system. Tests were conducted on model piles made of mild steel (MS), aluminium and PVC with wide variation in pile soil relative stiffness. For cyclic load levels less than 50% of static lateral capacity, the deflections are observed to increase with number of cycles and cyclic load level and stabilise after a certain number of cycles. For cyclic load levels greater than 50% of static lateral capacity, the deflections are observed to increase enormously with number of cycles. The results of post-cyclic load tests indicate that the behaviour under static load can improve for cyclic load levels less than 40% of the static lateral capacity. The variations in the load capacity due to cyclic loading are explained in terms of the changes in strength behaviour of soil.  相似文献   

Growth and photosynthetic rates of Chlamydomonas plethora and Nitzschia frustula cultures isolated from Kuwait Bay, Arabian Gulf, and their potential as live algal food for tropical mariculture     

Durvasula Venkata Subba Rao  Youlian Pan  & Faiza Al-Yamani 《Marine Ecology》2005,26(1):63-71

With a view to utilize local algae as food organisms in mariculture, the green alga Chlamydomonas plethora and the diatom Nitzschia frustula were isolated and studied from the unique coastal waters arid zone off Kuwait. Batch cultures of C. plethora and N. frustula had maximum division rates (μ_max) of 2.5 and 3.4 day^?1, respectively. Cultures grown for 36 h yielded comparable growth rates. Photosynthesis‐irradiance relationships in cultures harvested at various phases of growth showed that cultures attained log phase after 1‐day growth and yielded the highest assimilation numbers (P: μg C [μg Chl a]^?1 h^?1): 22.8 for C. plethora and 18.1 for N. frustula. Their initial slopes (α^B: ng C [μg Chl a]^?1 h^?1 [μmol m^?2 s^?1]^?1 were also the highest observed so far: 79.5 for C. plethora and 39.6 for N. frustula. Photoinhibition was low. Compared with these, assimilation numbers in senescent cultures of 20‐day growth were <8% of the maximum for both species, and the initial slope decreased to 17 and 13% in C. plethora and N. frustula, respectively. Two polyunsaturated fatty acids (20:5n‐3 eicosapentaenoic acid and 22:6n‐3 docosahexaenoic acid) that are essential in many marine animal diets constituted up to 24% and 1.9% of the total fatty acids, respectively. Of the two algae, N. frustula contained higher levels of 16:1n‐7, 20:5n‐3 and comparatively low levels of 22:6n‐3 fatty acids. Due to its rapid growth, high photosynthetic rate and presence of the amino acids leucine, lysine, glutamic acid and arginine N. frustula has good potential as a feed organism in mariculture applications. The capacity of these algae to produce a wide range of size groups (nano and net plankton) is an additional bonus for mariculture operations.  相似文献   

Satellite and In Situ Observations of a Phytoplankton Bloom from Coastal Bay of Bengal: Role in pCO<Subscript>2</Subscript> Modulation     

Rajdeep Roy  K. H. Rao  T. Preethi Latha  Vinay Kumar Dadhwal  V. V. S. S. Sarma  P. V. Nagamani  S. B. Choudhury  Seetharam Pondala 《Journal of the Indian Society of Remote Sensing》2017,45(3):513-524

A phytoplankton bloom was monitored in coastal waters of Bay of Bengal and its influence in water column properties was investigated. Significant draw down of CO₂ was noted within the vicinity of the bloom associated with high chlorophyll biomass. Microscopic analysis revealed diatoms as the dominant population. Skeletonema costatum a diatom, reached cell density of 36,898 cells l^?1 within the bloom. The lowest surface pCO₂ observed was 287 µatm at the southern end of the transect covarying with surface chlorophyll of 1.090 µg l^?1. At the northern end the surface pCO₂ went as low as 313 µatm. The pCO₂ levels below the mixed layer increased twice of that of surface value (~600 µatm). The chlorophyll values observed by Ocean Colour Monitor-2 were modestly related with the in situ measurements. The primary productivity derived from growth rate, assimilation number and maximum surface chlorophyll was 160.6 mg C m^?2 day^?1 leading to a modest sequestration ~of 0.08 Gg of carbon per day by the surface waters. Our observations reflects the potential role of diatom blooms on coastal carbon dynamics therefore should be carefully monitored in realm of anthropogenic changes.  相似文献   

Local Contrast Based Adaptive SAR Speckle Filter     

Sanjay Shitole  Mayank Sharma  Shaunak De  Avik Bhattacharya  Y. S. Rao  B. Krishna Mohan 《Journal of the Indian Society of Remote Sensing》2017,45(3):451-462

In this paper, we propose an adaptive filtering technique for Synthetic Aperture Radar (SAR) images. A new windowing technique is introduced where the total window is divided into five equal sized overlapping sub-windows. The pixel to be filtered is a part of each of these sub-windows. A weighted mean of all sub-windows is computed for the pixel under consideration. The weights are accounted from a measure of heterogeneity calculated for each sub-windows. The filter is able to adapt automatically and adjust the speckle suppression strength based on local statistics. This allows the filter to preserve edges while strongly suppressing speckle over homogeneous areas. The proposed filter was compared with some well known SAR filtering techniques in terms of speckle suppression and edge preservation ability. Several experiments were performed on datasets acquired from both air-borne and space-borne SAR platforms. Some well known indices were used for quantitative comparison with other filters. Among the filters compared, the proposed filter shows good speckle suppression ability while still exhibiting reasonable edge preservation ability.  相似文献