Natural frequencies of arch dam reservoir system—by a mapping finite element method     

B. Nath 《地震工程与结构动力学》1982,10(5):719-734

A simple mapping finite element method is used to calculate the coupled natural frequencies and mode shapes of realistic arch dam reservoir systems in which the dam is circular cylindrical with non-uniform cross-section. This method, in which both the dam and the reservoir domains are mapped into geometrically simpler shapes using cylindrical-polar transformations, is found to give accurate results, achieved simply and economically. Results of analysis show that hydrodynamic interaction has a substantial effect on the coupled natural frequencies and mode shapes; also that the effect of water compressibility in the type of dams considered can be ignored without significant loss of accuracy. A simple method is also presented for predicting the water compressibility effect before undertaking detailed response analysis.  相似文献   

A novel spherical polar finite element for the solution of the steady-state scalar wave equation in three-dimensions     

B. Nath 《地震工程与结构动力学》1981,9(1):33-51

A novel method has been proposed for the finite element solution of the steady-state scalar wave equation in three-dimensions. In this the governing equation and the prescribed boundary conditions in the physical space are transformed into a spherical polar space in which the radial direction is logarithmically condensed; the physical problem domain is also mapped into the new space. The transformed equation is then solved in the mapped domain using conventional finite elements. Because physical dimensions of the problem are logarithmically condensed in the proposed spherical polar space, the method is particularly suitable for solving truly three-dimensional problems in which the aspect ratio(s) is large or very large. A number of illustrative examples considered show that the proposed method is capable of a high degree of accuracy, achieved efficiently and economically. A hybrid scheme has also been proposed for dealing with awkward-shaped domains.  相似文献   

Hydrodynamic pressure on arch dams—by a mapping finite element method     

B. Nath 《地震工程与结构动力学》1981,9(2):117-131

A novel Finite Element Method (FEM) is proposed for the analysis of the uncoupled hydrodynamic pressures generated on arch dams due to a steady-state ground acceleration. In this method the equation governing hydrodynamic pressures and also the prescribed boundary conditions are all transformed from the Cartesian space to a logarithmically condensed cylindrical polar space; in this process the physical configuration of the reservoir-dam is also mapped into an ‘image’ domain. The transformed governing equation is then solved in the image domain, subject to the transformed boundary conditions, using standard finite elements. Because physical dimensions are logarithmically condensed in the image space, the proposed method is particularly suitable for dealing with large or very large aspect-ratio reservoir-dam systems, economically and efficiently. The high degree of accuracy which the proposed method is capable of, and also the simple way in which it can be applied to complex reservoir-dam shapes, have been demonstrated by means of examples. The method has also been applied to study the uncoupled hydrodynamic pressures on the upstream face of a cylindrical arch dam, generated by a steady-state vertical ground acceleration.  相似文献   

Leadership and Trade-Offs Between Social–Ecological Outcomes in Community-Governed Forests     

Sanchayan Nath 《社会与自然资源》2018,31(7):790-806

I explore the effect of leadership on the trade-off between social and ecological outcomes of community driven efforts in governing forests globally. I do so by using logistic regression and QCA (qualitative comparative analysis) for the analysis of cross-sectional data from the International Forestry Resources and Institutions (IFRI) research program. While the net effect of leadership on the trade-off in forestry outcomes is significant, there are multiple causal paths via which various factors influence the trade-off in forestry outcomes. Some of these paths take place in the presence of leadership, while the presence or the absence of leadership is irrelevant for the rest of the paths. This finding indicates that leaders often play an important role in the decisionmaking process during the governance of forests, especially when hard decisions need to be taken.  相似文献   

Planetary wave reflection and its impact on tropospheric cold weather over Asia during January 2008   总被引：3，自引：0，他引：3  

DebashisNATH  CHEN Wen  WANG Lin  MA Yin 《大气科学进展》2014,31(4):851-862

Reflection of stratospheric planetary waves and its impact on tropospheric cold weather over Asia during January 2008 were investigated by applying two dimensional Eliassen-Palm （EP） flux and three-dimensional Plumb wave activity fluxes.The planetary wave propagation can clearly be seen in the longitude-height and latitude-height sections of the Plumb wave activity flux and EP flux,respectively,when the stratospheric basic state is partially reflective.Primarily,a wave packet emanating from Baffin Island/coast of Labrador propagated eastward,equatorward and was reflected over Central Eurasia and parts of China,which in turn triggered the advection of cold wind from the northern part of the boreal forest regions and Siberia to the subtropics.The wide region of Central Eurasia and China experienced extreme cold weather during the second ten days of January 2008,whereas the extraordinary persistence of the event might have occurred due to an anomalous blocking high in the Urals-Siberia region.  相似文献   

Parametric study of factors affecting fluid flow through a fracture     

Kunwar Mrityunjai Sharma  Debanjan Guha Roy  Praksh Kumar Singh  Lakshmi Kant Sharma  Trilok Nath Singh 《Arabian Journal of Geosciences》2017,10(16):362

Understanding the flow behavior through fractures is critically important in a wide variety of applications. In many situations, the fluid flow can be highly irregular and non-linear in nature. Numerical simulation can be employed to simulate such conditions which are difficult to replicate in laboratory experiments. Therefore, a parametric study has been conducted on the fluid flow through micro-fracture over a large range of inlet pressure, fluid density, fluid viscosity, temperature, joint roughness coefficient (JRC), and fracture using finite element analysis. Irregular fracture profiles were created using Barton’s joint roughness coefficient. The Navier-Stokes (NS) equation was used to simulate the flow of water in those micro-fractures. The result showed that the fracture, fluid, and ambient conditions have a wide and varied effect on the fluid flow behavior. The interrelationship between these parameters was also studied. The model simulation provided result in the form of velocity and pressure drop profile, which can be used to determine the behavior of flow under different condition. The volumetric flow was calculated for each condition and has been plotted against the corresponding parameter to study the interrelationship.  相似文献   

Seismic source zoning and maximum credible earthquake prognosis of the Greater Kashmir Territory,NW Himalaya     

Hamid Sana  Sankar Kumar Nath 《Journal of Seismology》2017,21(2):411-424

We present the seismic source zoning of the tectonically active Greater Kashmir territory of the Northwestern Himalaya and seismicity analysis (Gutenberg-Richter parameters) and maximum credible earthquake (m _max) estimation of each zone. The earthquake catalogue used in the analysis is an extensive one compiled from various sources which spans from 1907 to 2012. Five seismogenic zones were delineated, viz. Hazara-Kashmir Syntaxis, Karakorum Seismic Zone, Kohistan Seismic Zone, Nanga Parbat Syntaxis, and SE-Kashmir Seismic Zone. Then, the seismicity analysis and maximum credible earthquake estimation were carried out for each zone. The low b value (<1.0) indicates a higher stress regime in all the zones except Nanga Parbat Syntaxis Seismic Zone and SE-Kashmir Seismic Zone. The m _max was estimated following three different methodologies, the fault parameter approach, convergence rates using geodetic measurements, and the probabilistic approach using the earthquake catalogue and is estimated to be M _w 7.7, M _w 8.5, and M _w 8.1, respectively. The maximum credible earthquake (m _max) estimated for each zone shows that Hazara Kashmir Syntaxis Seismic Zone has the highest m _max of M _w 8.1 (±0.36), which is espoused by the historical 1555 Kashmir earthquake of M _w 7.6 as well as the recent 8 October 2005 Kashmir earthquake of M _w 7.6. The variation in the estimated m _max by the above discussed methodologies is obvious, as the definition and interpretation of the m _max change with the method. Interestingly, historical archives (～900 years) do not speak of a great earthquake in this region, which is attributed to the complex and unique tectonic and geologic setup of the Kashmir Himalaya. The convergence is this part of the Himalaya is distributed not only along the main boundary faults but also along the various active out-of-sequence faults as compared to the Central Himalaya, where it is mainly adjusted along the main boundary fault.  相似文献