Fluid-structure interaction effects for offshore structures     

A. S. Veletsos  A. M. Prasad  G. Hahn 《地震工程与结构动力学》1988,16(5):631-652

Comprehensive analyses are made of the differences in the responses of simple models of offshore structures computed by the standard and extended versions of Morison's equation for the hydrodynamic forces, and of the effects and relative importance of the numerous parameters involved. The responses also are evaluated by the equivalent linearization technique and Penzien's decoupling technique, and the interrelationship and accuracy of these approaches are elucidated. The results are displayed graphically in the form of response spectra for absolute maximum displacement employing dimensionless parameters that are easy to interpret and use. In addition, the decoupling technique is generalized to include consideration of a current of constant velocity, and a simple modification is proposed which improves the accuracy of this approach. A particularly simple approximation is included for the hydrodynamic modal damping values of multi-degree-of-freedom, stick-like systems.  相似文献   

Late-Quaternary miliolite (biogenic carbonate) deposits and their implications for sea-level fluctuations and climatic variability     

A. Durga Prasad  Falguni Bhattacharya  Gaurav Chauhan  D. Balaji  M.G. Thakkar  Y. Srinivasa Rao 《地球表面变化过程与地形》2021,46(5):921-941

The western coast of India (Kachchh) has ubiquitous preservations of Quaternary carbonate deposits popularly known as “miliolites”. Field-based detail documentation of the nature and distribution of miliolites supported by sedimentology and scanning electron microscopy (SEM) microtextural studies indicates that the miliolites were primarily deposited by wind as aeolinites and are termed “primary miliolites (PM)”. These were subsequently fluvially eroded and deposited and such deposits are termed “secondary miliolites (SM)”. The PM are dated between 28 ka to 16 ka largely clustering around the Last Glacial Maxima (LGM). In comparison, the fluvially reworked SM occurs as valley-fill deposits and were deposited episodically during 23 ka to 10 ka before present. Climatically, the deposition of PMs suggests enhanced aridity whereas SMs represent episodic strengthening of the Indian Summer Monsoon (ISM). The bedding attitudes of the PMs indicate that they were deposited predominantly by the northeasterly winds whereas the presence of the deflation lag deposits suggests downwind migration of sands during the equilibrium condition (reduced sediment supply). The aeolian parameters (based on the grain size and wind velocities) for PMs indicate high shear velocity (~23 to 48 cm⁻¹) and high transport rate (< 0.1 to 0.2 g/cm s). The short average flying distance implies that the biogenic sands were transported in multiple pulses (from coast to inland) at rates varying from ~200 m/h to ~1 km/h. Comparing our data with related occurrences along the biologically productive coasts in the mid-latitudinal belt indicates that the regional/global aridity during the lowered sea level was responsible for inland occurrences of aeolinites, particularly during the LGM. The strengthened northeast monsoon winds during the LGM was conducive to upwelling and production of biogenic carbonates along the coasts. The subsequent reworking of the aeolinites were mainly the results of local variability in precipitation.  相似文献   

Site classification of Pondicherry using shear-wave velocity and horizontal-to-vertical spectral ratio     

S. Trupti  K. Goverdhan  K. N. S. S. S. Srinivas  P. Prabhakar Prasad  T. Seshunarayana 《Natural Hazards》2013,69(1):953-964

Site classification studies play a vital role in earthquake hazard assessment since in situ ground conditions substantially affect the characteristics of incoming seismic waves during earthquakes. Flat areas along the coast and rivers generally consist of thick layers of soft clay and sand. Such deposits amplify certain frequencies of ground motion, thereby attributing to an increase in the damage due to an earthquake. Hence, site classification studies have been carried out using shear-wave velocity, ground response, and corresponding amplification at 83 locations in Pondicherry, a coastal city in India. The present study is aimed at estimating the shear-wave velocity through multichannel analysis of surface waves and to compute the average shear-wave velocity (V _S ³⁰ ), stiffness, and N values using empirical relations. Further, site-response studies (horizontal-to-vertical spectral ratio) were conducted to estimate the ground-response frequencies and corresponding amplifications through Nakamura technique. From the results, the study area was classified into three types, i.e., C-class: with V _S ³⁰ in the range of 360–760 m/s, D-class: with V _S ³⁰ in the range of 180–360 m/s, and E-class: with V _S ³⁰  < 180 m/s following the National Earthquake Hazard Reduction Programme norms (BSSC in NEHRP recommended provisions for seismic regulations for new buildings and other structures (FEMA 450), part 1: provisions. Building Seismic Safety Council for the Federal Emergency Management Agency, Washington, 2003). Finally, a site classification map for Pondicherry region has been prepared, which can be used in urban planning and strengthening of existing structures against future earthquakes.  相似文献   

News and notes     

P. Krishnamurthy  K. S. Godhavari  Manish A. Mamtani  Swati Dixit  Md. Firoze Quamar  Ratan Kar  Sita Bora  Quazi A. Rasool  K. V. Subbarao  S. D. Mukherji  C. V. R. K. Prasad  Kakani Nageswara Rao 《Journal of the Geological Society of India》2013,81(6):849-864

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Strong ground motion simulation during the November 1759 Earthquake along Serghaya Fault in the metropolitan of Damascus, Syria     

Hussam Eldein Zaineh  Hiroaki Yamanaka  Yadab Prasad Dhakal  Rawaa Dakkak  Mohamad Daoud 《Journal of Seismology》2013,17(4):1295-1319

The seismic hazard potential for metropolitan of Damascus, Syria is mainly controlled by earthquakes along Serghaya Fault which is a branch of Dead Sea Fault System. In this study, strong ground motion due to the November 1759 Earthquake along the fault of Serghaya was estimated with a numerical simulation technique. In the simulation, the Kostrov-like slip-velocity function was used as an input to the discrete wave number method to simulate the strong ground motions in a broadband frequency range. In order to model the incoherent rupture propagation which can excite large high-frequency waves, random numbers are added to arrival time of circular rupture front. MMI intensities calculated from the synthetic ground motions are compared with the observed values by Ambraseys and Barazangi (J Geophys Res 94:4007-4013, 1989). The calculated intensities are in good agreement with the observed ones at the most sites that validate appropriateness of the proposed source model. The PGA and PGV in the eastern region of Damascus city are higher than those in the western region due to the effects of local site amplification. The simulated high-frequency (1.0–6.0 Hz) ground motions for the sites in the Damascus city are higher than the design requirements defined by the Syrian building code. Furthermore, the simulated high-frequency ground motions for sites in the focal region are bigger than the design requirements in the case of the near-fault factors and are not considered. That demonstrates the appropriateness of considering the near-fault factors for a site near the focal region as introduced by the new building code.  相似文献   

Foliar Applied Nickel on Buckwheat (Fagopyrum esculentum) Induced Phenolic Compounds as Potential Antioxidants     

Oksana Sytar  Marian Brestic  Abhay Kumar  M. N. V. Prasad  Nataliya Taran  Iryna Smetanska 《洁净——土壤、空气、水》2013,41(11):1129-1137

In this study, Fagopyrum esculentum (common buckwheat) sprayed with nickel (Ni) (0, 0.5, 1.0, 3.0, and 5.0 mM) for different duration has been investigated for Ni accumulation, malondialdehyde (MDA), total phenolics, and phenolic acids. Ni accumulation significantly increased in dose‐dependent manner. Plants exposed for 72 h, showed visible damages as chlorosis and irreversible necrosis. The MDA and total phenolic contents increased at 24 h of Ni treatments. HPLC data revealed that phenolic acids are in good correlation with concentration and durations of treatments. After 24 and 48 h the contents of chlorogenic, p‐hydroxybenzoic, hesperetic, p‐anisic, and caffeic acids increased in Ni treated leaves. On the other hand, p‐hydroxybenzoic, hesperetic, p‐anisic, p‐coumaric, caffeic acids contents decreased after 72 h of Ni exposure. Vanillic and cinnamic acid followed same pattern and increased significantly at 3.0 and 5.0 mM after 48 h of Ni exposure. It may suggest that buckwheat can be possible hyperaccumulators of Ni, because of high Ni accumulation in tissues through foliar treatment. Furthermore, the analyzed phenolic acids have potential role as antioxidants, which provide tolerance to buckwheat against Ni treatment.  相似文献   

Effects of the size of cosmological N-body simulations on physical quantities – I. Mass function     

J. S. Bagla  Jayanti Prasad 《Monthly notices of the Royal Astronomical Society》2006,370(2):993-1002

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Simultaneous Stokes-V diagnostic of a Sunspot using Mg b and Fe I lines     

Gosain  Sanjay  Prasad Choudhary  Debi 《Solar physics》2003,217(1):119-132

Simultaneous observations of Stokes profiles in photospheric Fei (630.15 nm and 630.25 nm) and chromospheric Mgi b ₁ and b ₂ (518.4 nm and 517.3 nm) lines over a sunspot are presented. Observations were carried out using the Advanced Stokes Polarimeter of HAO/NSO, VTT, SacPeak, U.S.A. The Stokes-V amplitude asymmetries for these lines are analyzed. The values of amplitude asymmetry in Mgb lines are negative in disk-center-side penumbra while they are positive in limb-side penumbra. This trend is similar in nature to photospheric Fei line observations. Further, the spatial distribution of Stokes-V asymmetry is analyzed using Net Circular Polarization (NCP) maps. The chromospheric and photospheric NCP maps are different in many aspects. These observations with longitudinal magnetic field, estimated using weak field approximation, are discussed in this paper.  相似文献   

Angular momentum transport in quasi-Keplerian accretion disks     

Prasad Subramanian  B. S. Pujari  Peter A. Becker 《Journal of Astrophysics and Astronomy》2004,25(1-2):81-91

We reexamine arguments advanced by Hayashi & Matsuda (2001), who claim that several simple, physically motivated derivations based on mean free path theory for calculating the viscous torque in a quasi-Keplerian accretion disk yield results that are inconsistent with the generally accepted model. If correct, the ideas proposed by Hayashi & Matsuda would radically alter our understanding of the nature of the angular momentum transport in the disk, which is a central feature of accretion disk theory. However, in this paper we point out several fallacies in their arguments and show that there indeed exists a simple derivation based on mean free path theory that yields an expression for the viscous torque that is proportional to the radial derivative of the angular velocity in the accretion disk, as expected. The derivation is based on the analysis of the epicyclic motion of gas parcels in adjacent eddies in the disk.  相似文献   

Effects of the size of cosmological N-body simulations on physical quantities — II: Halo formation and destruction rate     

Jayanti Prasad 《Journal of Astrophysics and Astronomy》2007,28(2-3):117-131

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