Application of double bounded probability density function for analysis of ocean waves     

V. Sundar 《Ocean Engineering》1989,16(2)

Ocean waves and forces induced by them on offshore structures are random in nature. Experience has shown that short term statistics of wave heights can be described by the Rayleigh distribution for narrow band spectra (Longuet-Higgins, 1952) and that the long term statistics or the evaluation of design wave is based on certain well known extreme value distribution such as mixed Frechet distribution (Thom, 1973a, b).This paper presents a new application of the double bounded probability density function to describe the ocean wave statistics. The prime importance is to estimate the most probable maximum wave height for offshore structural designs.  相似文献   

Wave climate in a groin field     

V. Sundar  H. Noethel  K. P. Holz 《Ocean Engineering》1992,19(5)

Wave records at seven different locations within a groin field have been analysed by both statistical and spectral approaches to study the general wave climate. The wave heights and periods from the wave records were obtained by both upcross and downcross methods for the statistical approach. The variation of different wave height and wave period parameters with respect to the time of measurement at a particular location and its variation at different locations within the groin field at a particular instant of time are presented and discussed in detail in this paper. It is generally found that the wave heights follow the Weibull distribution.  相似文献   

Detection of major geological structures in the Eastern offshore of India using Geosat altimeter data     

T. J. Majumdar  K. K. Mohanty  A. K. Srivastava 《Journal of Earth System Science》1997,106(1-2):27-32

Satellite altimetry can be used to infer subsurface geological structures analogous to gravity anomaly maps generated through ship-borne survey. The Eastern offshore was taken up for analysis using Geosat Exact Repeat Mission (ERM) altimeter data. A methodology is developed to use altimeter data as an aid to offshore hydrocarbon exploration. Processing of altimeter data involves corrections for various atmospheric and oceanographic effects, stacking and averaging of repeat passes, cross-over correction, removal of deeper earth and bathymetric effects, spectral analysis and conversion into free-air gravity anomaly. The final processed results were derived for Eastern offshore in the form of prospecting geoid and gravity anomaly maps and their spectral components. The highs and lows observed in those maps were derived in terms of a number of prominent megastructures e.g., gravity linears, 85°E and 90°E ridges, the Andaman trench complex etc. Satellite-derived gravity profiles along 12°N latitude match well with the existing structures.  相似文献   

Three-dimensional forward and backward modelling of diapirism: numerical approach and its applicability to the evolution of salt structures in the Pricaspian basin     

Alik Ismail-Zadeh  Igor Tsepelev  Chistopher Talbot  Alexander Korotkii   《Tectonophysics》2004,387(1-4):81-103

Numerical studies of ductile deformations induced by salt movements have, until now, been restricted to two-dimensional (2D) modelling of diapirism. This paper suggests a numerical approach to model the evolution of three-dimensional (3D) salt structures toward increasing maturity. This approach is also used here to restore the evolution of salt structures through successive earlier stages. The numerical methodology is applied to study several model examples. We analyse a model of salt diapirs that develop from an initial random perturbation of the interface between salt and its overburden and restore the evolved salt diapirs to their initial stages. We show that the average restoration errors are less than 1%. An evolutionary model of a 2D salt wall loaded by a 2D pile of sediments predicts a decomposition of the salt wall into 3D diapiric structures when the overburden of salt is supplied by 3D synkinematic wedge of sediments. We model salt extrusion feeding a gravity current over the depositional surface and estimate an average rate of extrusion and horizontal velocity of salt spreading. Faulting of the overburden to salt overhangs initiates new secondary diapirs, and we analyse the growth of these secondary diapirs. We also study how lateral flow effects the evolution of salt diapirs. The shape of a salt diapir can be very different if the rate of horizontal flow is much greater than the initial rate of diapiric growth solely due to gravity. We discuss the applicability of the results of the models to the evolution of Late Permian salt structures in the Pricaspian basin (Russia and Kazakhstan). These structures are distinguishable into a variety of styles representing different stages of growth: salt pillows, diapirs, giant salt massifs, 2D diapiric walls and 3D stocks complicated by large overhangs. The different sizes, shapes and maturities of salt structures in different parts of the Pricaspian basin reflect areal differences in salt thickness and loading history. Our results suggest that the numerical methodology can be employed to analyse the evolution of all salt structures that have upbuilt through younger ductile overburdens.  相似文献   

Hydrography of the eastern Arabian Sea during summer monsoon 2002     

D. Shankar  S. S. C. Shenoi  R. K. Nayak  P. N. Vinayachandran  G. Nampoothiri  A. M. Almeida  G. S. Michael  M. R. Ramesh Kumar  D. Sundar  O. P. Sreejith 《Journal of Earth System Science》2005,114(5):459-474

Hydrographic observations in the eastern Arabian Sea (EAS) during summer monsoon 2002 (during the first phase of the Arabian Sea Monsoon Experiment (ARMEX)) include two approximately fortnight-long CTD time series. A barrier layer was observed occasionally during the two time series. These ephemeral barrier layers were caused byin situ rainfall, and by advection of low-salinity (high-salinity) waters at the surface (below the surface mixed layer). These barrier layers were advected away from the source region by the West India Coastal Current and had no discernible effect on the sea surface temperature. The three high-salinity water masses, the Arabian Sea High Salinity Water (ASHSW), Persian Gulf Water (PGW), and Red Sea Water (RSW), and the Arabian Sea Salinity Minimum also exhibited intermittency: they appeared and disappeared during the time series. The concentration of the ASHSW, PGW, and RSW decreased equatorward, and that of the RSW also decreased offshore. The observations suggest that the RSW is advected equatorward along the continental slope off the Indian west coast.  相似文献   

Analysis of anomalies in ADS-B and its GPS data     

Busyairah Syd Ali  Wolfgang Schuster  Washington Ochieng  Arnab Majumdar 《GPS Solutions》2016,20(3):429-438

Traditionally, the surveillance component of the air traffic management system has been based on radar, which consists of two separate systems: primary radar and secondary radar, which both enable the measurement of the aircraft range and bearing to the radar station. Primary radar is based on signals emitted by a ground station simply being reflected off an object and detected by a ground-based receiver. Secondary radar also emits signals, but relies upon a transponder onboard the aircraft to emit a signal itself, modulated among others by a four-digit aircraft identity (Mode A), aircraft altitude (Mode C) and/or 24-bit unique address (Mode S). Typical accuracies of secondary radar are of the order of 0.03 NM in range and 0.07° in azimuth. However, no position integrity report is provided. Air traffic density is expected to significantly increase in the future. In order to maintain or enhance air travel efficiency, while maintaining safety, more accurate surveillance systems, with the required integrity, will be required. Automatic dependent surveillance–broadcast (ADS-B) is a new aviation surveillance system, envisioned to overcome the limitations of radar and to enhance surveillance performance and thereby increase airspace capacity. However, its high dependence on external systems such as onboard navigation and communication systems also increases the number of potential points of failure. It is important to understand and mitigate these failure modes before the system can reliably be implemented. The present study emerged as an exploratory research as part of a safety assessment framework development for the ADS-B system. It reviews the ADS-B failure modes, data collection and analysis of ADS-B and its corresponding onboard GPS data. The study identifies a set of failures common to certain aircraft models, with consistent error patterns. A key failure mode was found to be associated with the navigation data from the onboard GPS. We discuss the identified failure modes and investigate the nature and causes of these failures. The findings highlight some of the deficiencies of the current ADS-B system, which will need to be addressed before the ADS-B system can reliably be implemented.  相似文献   

A survey instrument to isolate effectiveness of a novel risk communication intervention     

Anne M. Sanquini  Sundar M. Thapaliya  Michele M. Wood 《Natural Hazards》2016,82(1):59-72

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Spatio-temporal variations of respirable particles at residential areas located in the vicinity of opencast coal projects,India: a case study     

Satya Prakash Sahu  Manish Yadav  Dhruti Sundar Pradhan  Neha Rani  Arka Jyoti Das 《Arabian Journal of Geosciences》2018,11(10):241

The objective of the study is to investigate spatio-temporal variations of PM₁₀, PM_2.5, and PM₁ concentrations at seven residential sites, located in the vicinity of opencast coal projects, Basundhara Garjanbahal Area (BGA), India. Meteorological parameters such as wind speed, wind direction, relative humidity, and temperature were collected simultaneously with PM concentrations. Mean concentrations of PM₁₀ in the range 215 ± 169–526 ± 412 μg m^?3, PM_2.5 in the range of 91 ± 79–297 ± 107 μg m^?3, PM₁ in the range of 68 ± 60–247 ± 84 μg m^?3 were obtained. Coarse fractions (PM_2.5–10) varied from 27 to 58% whereas fine fractions (PM_1–2.5 and PM₁) varied in the range of 51–73%. PM_2.5 concentration was 41–74% of PM₁₀ concentration, PM₁ concentration was 31–62% of PM₁₀ concentration, and PM₁ concentration was 73–83% of PM_2.5 concentration. Role of meteorology on PM concentrations was assessed using correlation analysis. Linear relationships were established among PM concentrations using least square regression analysis. With the aid of principal component analysis, two components were drawn out of eight variables, which represent more than 75% of variance. The results indicated that major sources of air pollutants (PM₁₀, PM_2.5, PM₁, CO, CO₂) at the residential sites are road dust raised by vehicular movement, spillage of coal generated during transportation, spontaneous combustion of coal, and biomass burning in village area.  相似文献   

Hydrodynamic performance of a dual cylindrical caisson breakwater     

K. Sankarbabu  S.A. SannasirajV. Sundar 《Coastal Engineering》2008

The hydrodynamic performance of a dual cylindrical caisson breakwater (DCBW) formed by a row of caissons each of which consisting of a porous outer cylinder circumscribing an impermeable inner cylinder has been theoretically investigated. The theoretical formulation is based on the eigenfunction expansion method proposed by Spring and Monkmeyer (1974) which was further modified by Linton and Evans [Linton, C.M., Evans, D.V., 1990. The interaction of waves with arrays of vertical circular cylinders. Journal of Fluid Mechanics 215, 549–569] for an array of impermeable cylinders. The present formulation is an extension of the work of Wang and Ren [Wang, K.H., Ren, X., 1994. Wave interaction with a concentric porous cylinder system. Ocean Engineering 21(4), 343–360], wherein; the interaction of linear waves with a single concentric porous cylinder system was studied. In the present study, the formulation has been extended to the case of a group of porous dual cylinder system. Parametric studies are carried out to study the influence of porosity (G₀) on the outer caisson, width of the doughnut chamber (a/b) and the angle of wave incidence on the variation in the hydrodynamic loading, wave run-up, free-surface elevation in its vicinity as well as the transmission on its lee-side. The importance of the presence of the inner cylinder in achieving the required hydrodynamic performance in terms of either protection or providing tranquility on its lee side keeping higher stability for the breakwater system is highlighted.  相似文献   

Some studies on induced polarization     

R. K. Majumdar  S. H. Rao 《Pure and Applied Geophysics》1973,109(1):1789-1795

Summary Laboratory induced polarization (IP) or overvoltage measurements over a spherical body at different depths is discussed. Some nomograms are also designed to calculate rapidly induced polarization parameters such as frequency effect, polarization factor and chargeability in the field or laboratory.  相似文献