Calculation of transverse hydrodynamic coefficients using computational fluid dynamic approach   总被引：1，自引：0，他引：1  

Amit Tyagi  Debabrata Sen 《Ocean Engineering》2006,33(5-6):798-809

Computational Fluid Dynamic (CFD) based on Reynolds Averaged Navier–Stokes equation is used for determining the transverse hydrodynamic damping force and moment coefficients that are needed in the maneuverability study of marine vehicles. Computations are performed for two geometrical shapes representing typical AUVs presently in use. Results are compared with available data on similar geometries and from some of the available semi-empirical relations. It is found that the CFD predictions compares reasonable well with these results. In particular, the CFD predictions of forces and moments are found to be nonlinear with respect to the transverse velocity, and therefore both linear and nonlinear coefficients can be derived. A discussion on the sources of the component forces reveal that the total force and moment variations should in fact be nonlinear.  相似文献   

An analysis of mechanisms for submesoscale vertical motion at ocean fronts   总被引：8，自引：1，他引：8  

Amala Mahadevan  Amit Tandon 《Ocean Modelling》2006,14(3-4):241-256

We analyze model simulations of a wind-forced upper ocean front to understand the generation of near-surface submesoscale, O(1 km), structures with intense vertical motion. The largest vertical velocities are in the downward direction; their maxima are situated at approximately 25 m depth and magnitudes exceed 1 mm/s or 100 m/day. They are correlated with high rates of lateral strain, large relative vorticity and the loss of geostrophic balance. We examine several mechanisms for the formation of submesoscale structure and vertical velocity in the upper ocean. These include: (i) frontogenesis, (ii) frictional effects at fronts, (iii) mixed layer instabilities, (iv) ageostrophic anticyclonic instability, and (v) nonlinear Ekman effects. We assess the role of these mechanisms in generating vertical motion within the nonlinear, three-dimensionally evolving flow field of the nonhydrostatic model. We find that the strong submesoscale down-welling in the model is explained by nonlinear Ekman pumping and is also consistent with the potential vorticity arguments that analogize down-front winds to buoyancy-forcing. Conditions also support the formation of ageostrophic anticyclonic instabilities, but the contribution of these is difficult to assess because the decomposition of the flow into balanced and unbalanced components via semigeostrophic analysis breaks down at O(1) Rossby numbers. Mixed layer instabilities do not dominate the structure, but shear and frontogenesis contribute to the relative vorticity and strain fields that generate ageostrophy.  相似文献   

Comment on “Deconvolving the δO-seawater component from subseasonal coral δO and Sr/Ca at Rarotonga in the southwestern subtropical Pacific for the period 1726 to 1997,” by L. Ren, B. K. Linsley, G. M. Wellington, D. P. Schrag, and O Hoegh-Guldberg (2003)     

Amit Huppert  Andrew R Solow 《Geochimica et cosmochimica acta》2004,68(14):3137-3138

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Analysis of temperature variability over north-west part of India for the period 1970–2000     

Monika Punia  Suman Nain  Amit Kumar  Bhupendra Pratap Singh  Amit Prakash  Krishan Kumar  V. K. Jain 《Natural Hazards》2015,75(1):935-952

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Coralline algae and benthic foraminifera from the long formation (middle Miocene) of the Little Andaman Island,India: Biofacies analysis,systematics and palaeoenvironmental implications     

Suman Sarkar  Amit K. Ghosh  G. M. Narasimha Rao 《Journal of the Geological Society of India》2016,87(1):69-84

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Coal fire mapping of East Basuria Colliery,Jharia coalfield using vertical derivative technique of magnetic data     

S K PAL  JITENDRA VAISH  SAHADEV KUMAR  ABHAY KUMAR BHARTI 《Journal of Earth System Science》2016,125(1):165-178

The present study deals with the coal fire mapping of East Basuria Colliery, Jharia coalfield, India, using the magnetic method. It is based on the fact that rise in temperature would result significant changes in magnetic susceptibility and thermo-remanent magnetization (TRM) of the overlying rocks. Magnetism increases slowly with the rise of temperature until the Curie temperature. Generally, rock/ overburden loses magnetization and becomes paramagnetic due to heating to Curie temperature, which results with significant reduction in magnetic susceptibility. However, magnetism increases significantly after cooling below the Curie temperature. Several data processing methods such as diurnal correction, reduction to pole (RTP), first and second vertical derivatives have been used for analysis of magnetic data and their interpretation. It is observed that the total magnetic field intensity anomaly of the area varies approximately from 44850 to 47460 nT and the residual magnetic anomaly varies approximately from ?1323 to 1253 nT. The range of the magnetic anomaly after RTP is approximately 1050–1450 nT. About 20 low magnetic anomaly zones have been identified associated with active coal fire regions and 11 high magnetic anomaly zones have been identified associated with non-coal fire regions using vertical derivative techniques.  相似文献   

Investigation of azimuthal variation in S-wave velocity in the western part of the Himalayas-Tibet Indo-Gangetic plains region using surface waves     

Sagarika Mukhopadhyay  Amit Kumar  Naresh Kumar 《《地质学报》英文版》2018,92(Z1):53-53

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Tectonometamorphic Evolution of Jutulsessen,Gjelsvikfjella, cDML,East Antarctica     

Amit Dharwadkar  Prakash K. Shrivastava  Hari B. Srivastava 《Journal of the Geological Society of India》2018,92(3):265-280

The Jutulsessen area, can provide a vital clue to the supercontinent assembly of Gondwana Land as it is situated within the Circum East Antarctic Mobile Belt just east of the Penksockett rift marking the divide between the central Dronning Maud Land from the Western Dronning Maud Land. This landmass is dominated by migmatitic quartzo-feldspathic rocks intruded by syn to post-tectonic granites. The work highlights the data from western part cDML area with a view to arrive at a more comprehensive model for the cDML and subsequently to the super continent assembly. Granitic and migmatitic gneisses comprising of amphibolitic and biotite rich enclaves. The gneisses show variations from quartzo-felspathic gneiss to amphibolitic gneiss. The area has witnessed complex geological history involving at different deformational episodes with concomitant metamorphism. The pervasive dominant foliation trends NW-SE with shallow to medium dips towards SW. In the Stabben area, a nonfoliated intrusive syenite-gabbro pluton limits the gneissic exposures. Compositionally, the orthogneisses plot in the monzogranitegranodiorite field where as the mafic dykes/enclaves plot in the basalt-andesite-rhyodacite field. The bulk geochemical characteristics suggest significant crustal contamination. Garnet-biotite Fe-Mg exchange thermometry gives peak metamorphic temperature of 483° C for the gneisses and 628° C for the dioritic enclave within gneisses. A peak metamorphic grade of upper amphibolite to granulite facies is deduced from the mineral assemblages. Widespread anatexis has led to extensive occurrence of migmatites in the area. Recent geochronological studies assign an age of 1170 Ma to 970 Ma for the migmatites/gneisses and an emplacement age of 501 Ma for the Stabben gabbro and syenite. The discriminant plots of the Jutulsessen rocks indicate diverse origin ranging from pre-plate collision to post-collision orogenic tectonic setting. The mafic enclaves/dykes show ocean island arc to MORB affinities. Voluminous addition of juvenile crust during the Pan-African orogeny strongly overprints earlier structures.  相似文献   

The effect of vulnerability on climate change mitigation policies     

Amit Tubi  Itay Fischhendler  Eran Feitelson 《Global Environmental Change》2012,22(2):472-482

Climate change is likely to adversely affect many countries throughout the world, but the responses of different countries to this threat vary widely. Attempts to explain the differences in countries’ mitigative policies have been largely deficient. This study seeks to assess the degree to which vulnerability may improve the level of explanation of adopted mitigation policies, studying over 90 countries between 1990 and 2011. Vulnerability is defined to be comprised of two basic factors: impacts (expected damages due to climate change) and adaptive capacity (the ability to adjust to these damages). As there may be a gap between declared and implemented policies, these components of mitigation policy are examined separately. In addition, other variables which mediate between these ‘extreme ends’ of mitigation policies are tested.The effect of vulnerability on climate change mitigation policies is examined by multiple regressions, incorporating a wide range of control variables. The results indicate that climate impacts do not affect mitigation policies. Adaptive capacity has a positive effect on the level of declared policy, but this effect becomes insignificant once implemented policy is examined. However, other tests suggest a possible transition from declarations to actions by high adaptive capacity countries. This finding suggests that high adaptive capacity countries do not view mitigation and adaptation as substitutes. Further analyses indicate that the insignificancy of impacts is caused by the uncertainty in their assessment.  相似文献   

Erratum to: Uplift Capacity of Single Bent Pile and Pile Group Considering Arching Effects in Sand     

Amit Shelke  P. Basha  P. K. Basudhar  N. R. Patra  Sudib Mishra 《Geotechnical and Geological Engineering》2010,28(4):349-349

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