Modelling of flexible spacecraft and their stabilization†

The paper deals with the problem of rigorous modelling of flexible spacecraft and their stabilization. The attitude dynamics of the satellite bus and the equations for vibration of a flexible beam attached to it are derived. The complete system dynamics are given by a coupled set of ordinary and partial differential equations. The effects of controls applied on the. bus and/or on the flexible beam are investigated. It is shown that stabilization of the flexible spacecraft can be achieved by use of simple feedback controls.     

Urban growth trend analysis using GIS techniques—a case study of the Bombay metropolitan region

Abstract

Towns and cities in India are facing complex problems regarding the provision and maintenance of services and infrastructure in the face of the rapid growth of pupulation, caused both by natural increase and migration. In order to meet such challenges a planner needs to have fairly accurate and up-to-date information, especially about physical structures and related land parameters. A study of their trends generally helps in the understanding of the emerging growth pattern and in formulating policies to guide or redirect it. Recent advances in the field of remote sensing technology and computer based Geographical Information Systems (GIS) provide very useful tools in undertaking such analysis. The results from a study about growth trends of the urban areas in the Bombay Metropolitan Region using multi-date remote sensing data and ARC/INFO GIS package are described here. The period under consideration is from 1968 to 1989. It should be noted that the major growth in the region is confined to Greater Bombay between 1968 to 1975. After the year 1975, a distinct outward growth along the rail corridors is visible. Growth after 1975 is mainly in the Kalyan, Bhiwandi, New Bombay and Panvel areas and in the area around Manori creek (Charkop area). The growth rate is found to be higher after the year 1975 compared to the prior growth rate. The spatial growth trends are examined in relation to the population and the population density has been computed for different periods. Based upon these densities, the extent of land required for urban development for the year 2001 has been calculated. Suitability of land for urbanisation has been carried out based upon physical characteristics of the land and environmental parameters. The priority areas of urban development to meet the additional requirement in 2001 have been identified on the basis of this suitability analysis. A map on a 1:250000 scale has been prepared to show the areas for urbanisation which will meet the demands for the year 2001. This study demonstrates the potential offered by the integration of the tools of remote sensing and GIS for urban and regional planning.     

A new semi-empirical sea spectrum for estimating the scattering coefficient

A large data base comprising SEASAT A satellite scatterometer measurements and quasi-concurrent high quality sea wind data, as represented by Britt and Schroeder (1984) in the form of a multivariate regression, has been used to tune the overall magnitude of the assumed sea spectrum by inverting the two scale scattering theory. Scattering coefficient values computed for the derived spectrum have been compared with those computed for the spectrum suggested by earlier authors, and an improvement is found in the surface wind-scattering coefficient relationship as verified by comparison with the independent AAFE RADSCAT data set.     

Synergism between NOAA-AVHRR and Meteosat data for studying vegetation development in semi-arid West Africa

Abstract

Rainfall estimates, based on cold cloud duration estimated from Meteosat data, are compared with vegetation development depicted by data of the normalized difference vegetation index (NDVI) from the National Oceanic and Atmospheric Administration's (NOAA) advanced very high resolution radiometer (AVHRR) for part of the Sahel. Decadal data from the 1985 and 1986 growing seasons are examined to determine the synergism of the datasets for rangeland monitoring. There is a general correspondence between the two datasets with a marked lag between rainfall and NDVI of between 10 and 20 days. This time lag is particularly noticeable at the beginning of the rainy season and in the more northern areas where rainfall is the limiting factor for growth. Principal component analysis was used to examine deviations from the general relationship between rainfall and the NDVI. Areas of low NDVI values for a given input of rainfall were identified: at a regional scale, they give an indication of areas of low production potential and possible degradation of ecosystems. This study demonstrates in a preliminary way the synergism of such datasets derived from satellite--borne sensors with coarse spatial resolution, which may provide new information for the improved management of the Sahelian grasslands.     

BUBBLE TEMPERATURE MEASUREMENTS ON THE BINARY MIXTURES OF 1,4-DIMETHYLBENZENE WITH ISO -, SEC -, AND TERT - BUTANOLS AT 95 kPa

Bubble temperatures at 95 kPa over the entire composition range were measured for the three binary systems formed by 1,4-dimethylbenzene with iso-, sec-, and tert- butanols. A Swietoslawski-type ebulliometer was used for the measurements. The composition versus temperature measurements are well represented by the Wilson model.     

Quasi-static crack tip fields in rate-sensitive FCC single crystals

In this work, the effects of loading rate, material rate sensitivity and constraint level on quasi-static crack tip fields in a FCC single crystal are studied. Finite element simulations are performed within a mode I, plane strain modified boundary layer framework by prescribing the two term (K − T) elastic crack tip field as remote boundary conditions. The material is assumed to obey a rate-dependent crystal plasticity theory. The orientation of the single crystal is chosen so that the crack surface coincides with the crystallographic (010) plane and the crack front lies along [10[`1]][10\overline 1] direction. Solutions corresponding to different stress intensity rates [(K)\dot]\dot{{K}}, T-stress values and strain rate exponents m are obtained. The results show that the stress levels ahead of the crack tip increase with [(K)\dot]\dot{{K}} which is accompanied by gradual shrinking of the plastic zone size. However, the nature of the shear band patterns around the crack tip is not affected by the loading rate. Further, it is found that while positive T-stress enhances the opening and hydrostatic stress levels ahead of crack tip, they are considerably reduced with imposition of negative T-stress. Also, negative T-stress promotes formation of shear bands in the forward sector ahead of the crack tip and suppresses them behind the tip.     

ANALYSIS OF LAMINATE METAL MATRIX COMPOSITES

This article describes an integrated micro/ macro mechanical study of the thermo-elastic-uiscoplastic behavior of unidirectional metal matrix composites. The microme-chanical analysis of the elastic moduli are based on the representative unit cell approach with comparisons also drawn with the composite cylinder assemblage model. These “ homogenization ” results are later incorporated into the vanishing fiber diameter model develop the macroscopic stress-strain relations. The finite element method is employed for the analysis in conjunction with the Bodner and Partom thermoviscoplas-tic constitutive model for the associated macroscopic analysis and a “ smeared” element approach. Comparisons are made against experimental and analytical results available in the literature whenever feasible.     

Letter to the editor: Design of FIR notch filters by using Bernstein polynomials

In this paper, Bernstein polynomials have been used to derive an explicit formula for the coefficients of linear phase FIR notch filters which are maximally flat at ω=0 and π. The approach is relatively simple and enables us to design the filter for a specific notch frequency and bandwidth. © 1997 by John Wiley & Sons, Ltd.