A Strain-Rate Dependent Clay Constitutive Model with Parametric Sensitivity and Uncertainty Quantification

This paper presents a strain-rate dependent plastic constitutive model for clays. Based on the concepts of critical-state soil mechanics and bounding surface plasticity theory, the model reproduces the mechanical response of clays under triaxial and simple shear loading conditions. The model parameters are determined for Boston Blue Clay, London Clay and Kaolin Clay, and the performance of the model in simulating the mechanical response of these clays is demonstrated for low to medium strain rates. The sensitivity of each model parameter is checked by perturbing the calibrated values by ±20 %. Subsequently, a probabilistic analysis using Monte Carlo simulations is performed by treating the model parameters as random variables and the impact of the statistics of the parameters on the undrained shear strength is investigated.     

Estimating peak dynamic response from pushover type analysis using a semi-empirical method

A procedure is developed in this paper that enables modification of the Modal Pushover results to predict the peak dynamic responses. Steps involved in this procedure cannot be strictly derivable from the first principle, but the resulting responses always match with the theoretical results within the elastic regime. A Generalized Single Degree of Freedom system is defined with a displacement profile derived from the maximum (regardless of sign) relative floor displacements and results of which is semi-empirically modified to predict the peak dynamic responses. Three test-beds are considered for assessment of the proposed method: (1) ten-storeyed symmetric building designed and detailed conforming to the Indian seismic code; (2) ten storey plan-asymmetric building designed and detailed per Indian seismic code; and (3) seven-storeyed existing building located in seismic Zone IV of India. Three seismic events recorded at the Large Scale Seismic Testing array in Lotung, Taiwan are used for this purpose. Distribution of the peak absolute floor acceleration and peak relative floor velocity across the height based on the proposed method is found in well agreement with those calculated using the rigorous IDA. The procedure can best be applied to the seismic safety assessment non-structural components (that are acceleration and velocity sensitive) of building adding a little cost to the routine assessment of structural components.     

Simulated Heat Content Variability in the Upper Layers of the Tropical Indian Ocean

Ocean General Circulation Model (OGCM) simulations from 1970–2007 are used to study the upper ocean heat content variability in the Tropical Indian Ocean (TIO). Model computed heat contents up to 50 m (denoted by HC50 m hereafter) representing upper ocean heat content and 300 m (HC300 m) representing heat content up to thermocline depth are first compared with heat contents computed from observations of two buoys in the TIO. It is found that there is good agreement between the model and observations. Fourier analysis of heat content is carried out in different regions of TIO. The amplitudes of semi-annual variability for HC50 m and HC300 m are observed to be greater than those for the annual variability in the Bay of Bengal, while in the Arabian Sea there is a mixed result. Heat content tendency is known to be governed by net surface heat flux and horizontal as well as vertical heat transports. For understanding the relative importance of these processes, a detailed analysis of these terms in the tendency equation is carried out. Rossby wave is observed in the annual mode of heat transport while equatorial jet and Kelvin waves are observed in the semi-annual mode of heart transport. Finally, the correlation between heat content and sea surface temperature (SST) and sea level anomaly (SLA), taken one at a time, is computed. It is found that the correlation improves significantly when both these quantities are together taken into account.     

Output only modal identification and structural damage detection using time frequency ＆ wavelet techniques

The primary objective of this paper is to develop output only modal identifi cation and structural damage detection.Identif ication of multi-degree of freedom(MDOF) linear time invariant(LTI) and linear time variant(LTV—due to damage) systems based on Time-frequency(TF) techniques—such as short-time Fourier transform(STFT),empirical mode decomposition(EMD),and wavelets—is proposed.STFT,EMD,and wavelet methods developed to date are reviewed in detail.In addition a Hilbert transform(HT) approach to determine ...     

Improvement in predictability of waves over the Indian Ocean

Accurate prediction of ocean surface waves is a challenging task with many associated difficulties. Availability of good quality wind and wave information from satellite platforms inspired the scientific community to assimilate such data in various spectral wave models for enhancing the accuracy of prediction. Over the Indian Ocean, which is the region of interest for the present study, wave heights in extreme situation can go up to 12–14 m, thereby increasing the probability of coastal hazards. This region is further governed by the southern ocean swells that propagate thousands of kilometers. These are, in general, not well captured by the spectral wave models. Therefore, assimilation of altimeter data in open ocean wave model WAM has been attempted with the aim of enhancing the quality of prediction of significant wave height. Further, simulated wave spectra have been assimilated in a coastal wave model SWAN. This assimilation has been found to significantly improve the prediction of the height of wind waves as well as swell waves. V. Bhatt and S. Surendran are former students of Meteorology and Oceanography Group, Space Applications Centre, ISRO, Ahmedabad.     

Palaeomagnetic and rock magnetic study of charnockites from Tamil Nadu,India, and the ‘Ur’ protocontinent in Early Palaeoproterozoic times

Palaeomagnetic and magnetomineralogical results are reported from charnockites in basement terrane at the eastern sector of the WSW–ENE granulite belt of South India. Magnetite is the dominant ferromagnet identified by rock magnetic and optical study; it is present in several phases including large homogeneous titanomagnetites and disseminated magnetite in microfractures linked to growth stages ranging from primary charnockite formation to uplift decompression and exhumation within the interval ～2500–2100 Ma. Several components of magnetization are resolved by thermal demagnetization and summarized by four pole positions; in the northern (Pallavaram) sector these are P1 (33°N, 99°E, dp/dm = 8/9°) and P2 (79°N, 170°E, dp/dm = 3/6°), and in the southern (Vandallur) sector they are V1 (23°N, 116°E, dp/dm = 8/9°) and V2 (26°S, 136°E, dp/dm = 5/10°). These magnetizations are linked to uplift cooling of the basement and unblocking temperature spectra suggest acquisition sequences P1 → P2 and V1 → V2 in each case implying movement of the shield from higher to lower palaeolatitudes sometime between 2500 and 2100 Ma. Palaeomagnetic poles from the cratonic nuclei of Africa, Australia and India all identify motion from higher to lower palaeolatitudes in Early Palaeoproterozoic times, and this is dated ～2400 and ～2200 Ma in the former two shields. The corresponding apparent polar wander (APW) segments match the magnetization record within the charnockite basement terranes of southern India to yield a preliminary reconstruction of the ‘Ur’ protocontinent, the oldest surviving continental protolith with origins prior to 3000 Ma. Although subject to later relative movements these nuclei seem to have remained in proximity until the Mesozoic break-up of Gondwana.     

Medium Range Prediction of Summer Monsoon Activities over India vis-a-vis Their Correspondence with the Observational Features

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Sm-Nd Isotopic and Geochemical Study of the Archean Tonalite-Amphibolite association from the eastern Indian Craton

We report the results of a Sm-Nd isotopic, major element and rare earth element (REE) study of the Older Metamorphic Group (OMG) tonalite-amphibolite association of the eastern Indian Craton. The Older Metamorphic Tonalite Gneisses (OMTG) have been previously dated to be 3.8 Ga using Sm-Nd isotope systematies, and 3.2–3.4 Ga by Rb-Sr and Pb-Pb dating. The results of this study indicate that the protoliths of the OMG amphibolites are 3.3 Ga isochron age=3.30±0.06 Ga, _Nd= +0.9 ± 0.7), and therefore, the OMTG, which intrude into the associated amphibolites, cannot be any older than 3.3 Ga. The amphibolites display light REE enrichment ((Ce/Yb)_N=2.2–6.7; La=30–100 x chondrite) and nearly flat heavy REE patterns ((Tb/Lu)_N=1.2–1.9); the basaltic parents of the amphibolites were probably generated by the partial melting of a spinel lherzolite mantle. Strong linear relationships between the amphibolites and tonalites in ¹⁴⁷Sm/¹⁴⁴Nd-¹⁴³Nd/¹⁴⁴Nd space (isochron age =3.29±0.04 Ga, _Nd= +0.8 ± 0.8) imply that they are genetically related. The tonalites display fractionated REE patterns (La=100–300 x chondrite) with moderate heavy REE depletions ((Tb/Lu)_N=1.9–3.4). The isotopic, major element and REE data are consistent with the derivation of the OMTG from partial melting of OMG amphibolites or equivalent rocks at amphibolegarnet stabilization depths. An initial _Nd(t) value of +0.9±0.7 for the amphibolites indicates the presence of a slightly depleted mantle source at 3.3 Ga with ¹⁴⁷Sm/¹⁴⁴Nd. between 0.20 and 0.22. It is suggested that the growth of continental crust in the eastern Indian craton occurred in response to magmatic underplating in a plume setting.     

Chloritization and its bearing on uranium mineralization in Madyalabodu area,Cuddapah district,Andhra Pradesh

Uranium mineralization in Madyalabodu area, Cuddapah district, Andhra Pradesh, is spatially related to chloritized and brecciated quartzite of the Gulcheru Formation in the immediate vicinity of E-W to ESE-WNW trending basic dyke. Chloritization transgresses the lithological boundaries. Whole-rock geochemical data indicate enrichment of MgO and Al₂O₃ coupled with depletion of SiO₂, Na₂O, K₂O, CaO and TiO₂ in the chlorite-rich zone. Fe₂O₃ and FeO do not vary significantly in the altered and the unaltered zones. Electron Probe Microanalysis (EPMA) data reveal that the chlorites in contact with uranium minerals are enriched in MgO and depleted in FeO than in the others. Considering the petrological evidence, geochemical signature and structural constraints, it appears that chlorite acted more as an adsorbent rather than as a reductant in facilitating uranium mineralization. Uraninite crystallized later from the uranium originally adsorbed on chlorites. Chloritization might also have facilitated mineralization through the generation of nascent hydrogen, H₂S and lowering pH of uranium-bearing solution.     

Fixed-bed column study for the adsorptive removal of acid fuchsin using carbon–alumina composite pellet

The carbon–alumina composite pellet was developed for the adsorption of acid fuchsin from its aqueous solution. The composite pellet was characterized using Brunauer–Emmett–Teller method, scanning Electron Microscopy and Fourier Transform Infrared Spectroscopy. The adsorption capacity of commercial alumina, commercial activated carbon and the prepared composite pellet was investigated against acid fuchsin, and the adsorption capacity was found to be increased in the order of alumina < carbon–alumina composite pellet < activated carbon. Although the adsorption capacity of carbon–alumina composite pellets was less than that of activated carbon, the use of the pelletized form of the present adsorbent was proven to be advantageous for the use in the packed-bed column. The experimental data were fitted to Langmuir, Freundlich and Temkin adsorption isotherms, and the equilibrium behavior was well explained by Langmuir isotherm. Besides, the kinetic behavior was well predicted by pseudo-second-order kinetics. The effects of inlet dye concentration (10–20 mg/L), feed flowrate (5–15 mL/min) and bed height (2.54–7.62 cm) on the breakthrough characteristics were investigated using a fixed-bed column. The maximum removal capacity in the column study was found to be 343.87 mg/L with an initial dye concentration and flowrate of 20 and 10 mL/min according to Bohart–Adams model. The breakthrough behavior was also effectively described by the Yoon–Nelson and Clark models.