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By
Ashok Jaswal, India Meteorological Department, On May 22, 2011
Abstract
Climate normals are used to describe the average climatic conditions of a particular place and are computed by National Meteorological Services of all countries. The World Meteorological Organization (WMO) recommends that all countries prepare climate normals for the 30-year periods ending in 1930, 1960, 1990 and so on, for which the WMO World Climate Normals are published. Recently, Climatological Normals for the period 1961-1990 have been prepared by India Meteorological Department (IMD) which will change the baseline of comparison from 1951-1980. In this paper, preparation of the 30-year Climatological Normals of India for the period 1961 to 1990 and spatial patterns of differences of annual means of temperatures , relative humidity, clouds, rainfall and wind speed from the previous normals (1951-1980) are documented.
The changes from earlier climatological normals indicate increase in annual means of maximum temperature , relative humidity and decrease in annual means of minimum temperature , cloud amount, rainfall, rainy days and wind speed over large parts of the country during 1961-1990. The spatial patterns of changes in dry bulb temperatures and relative humidity are complementary over most parts of the country. Compared with 1951-1980 climatology, there are large scale decreases in annual mean rainfall, rainy days and wind speed over most parts of the country during 1961-1990. The decrease in wind speed may be partly due to changes in exposure conditions of observatories due to urbanization.
Electrically operated high temperature furnaces and reactors are used in many industrial manufacturing processes such as sintering or single crystal growth in order to allow for the required process conditions. In view of their outstanding characteristics refractory metals are ideally suited as materials for the resistive heating elements. Nevertheless, significant and lifetime- limiting irreversible deformations of these elements can be frequently observed which are assumed to be caused by a combination of temperature expansion, electromagnetic forces, and high temperature creep effects. In order to study this undesired behavior, a multi-physics model of a particular three-phase AC heating element of a sintering furnace is formulated and implemented within Abaqus. It accounts for the primary involved coupled physical mechanisms such as the harmonic electrical field problem, the thermal problem governed by Joule's law, thermal expansion, high temperature creep and harmonic forces caused by the electromagnetic field along with field dependent constitutive behavior. Since in general solving the fully coupled problem on a 3D domain is computationally demanding and Abaqus lacks functionality in the field of electromagnetism, a semi-analytical approach for consideration of time-harmonic electromagnetic forces within mechanical analysis is developed in the present work. The model implemented as a userdefined extension for Abaqus is computationally very attractive since it avoids discretization of the medium surrounding the heater. Furthermore, some aspects of modeling coupled physical problems of different characteristic time-scale are briefly discussed. Results from application of the model are in good qualitative agreement with in-situ observations and confirm the relevance of considering electromagnetic forces within analysis of high temperature furnaces.
