Multi-standby system with repair and replacement policy

This paper investigates the mathematical model of a system composed of (m + 1) non-identical units—one functioning and m standbys. Each unit of the system has four possible states—normal, partial failure, total failure and repair facility—the last one meaning that the totally failed unit is being attended to at the repair facility where it might be either repaired or eventually rejected and replaced. The normal and partial failure states are up states while the other two are down states. The system breaks down when the (m + 1)th unit after total failure is finally rejected and no standby remains to replace it. Several reliability characteristics of interest to system designers as well as operations managers have been computed. Results obtained earlier are verified as particular cases.     

Bonded wedges with an interface crack under anti-plane shear loading

The primary aim of this paper is to describe an analytical technique which may be used in connection with the general problem of bonded wedges containing radial cracks. The technique consists of the reduction of the related dual integral equations of the problem to a singular integral equation in a systematic manner, and is described by applying it to a relatively simple anti-plane shear problem. The paper also presents the results of various numerical examples and the closed form solution for the special case of two bonded wedges with equal angles and an interface crack.

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Résumé L'objet principal du mémoire est de décrire une technique d'analyse utilisable dans le cas du problème général de secteurs jointifs comportant des fissures radiales. La technique consiste à réduire de manière systématique à une équation intégrale singulière les équations intégrales décrivant le problème; un exemple d'application est donné dans le cas d'un problème relativement simple de cisaillement antiplanaire. L'article présente également les résultats de divers exemples numériques, et la solution de forme fermée que l'on trouve dans le cas particulier de deux secteurs collés ayant un angle au centre égal et une fissure dans leur surface de séparation.

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This work was supported by the National Science Foundation under the Grant GK-11977.     

A dynamic analysis of necking phenomena

A new approach, based on the phenomena of stress wave propagation, is presented to analyse necking in the uniaxial tension test. The initiation of necking has been associated in this analysis with a stage, wherein the stress level at any section of the specimen acquires an instability stress value, and the stress wave velocity becomes zero at the section concerned. A method to compute the gradual development of the neck as a function of time with the aid of successive strain hardening curves has been developed. Experimental profiles were obtained by testing specimens of aluminium, copper, brass and low carbon steel under tension at two different velocities—one being hundred times that of the other—and unloading them after reaching different stages of necking. These compare well with theoretically obtained profiles.     

Model for optical density of films with grain clustering

In photographic emulsions, grains have been reported to be clustered. A model for the observed optical density in the presence of grain clustering has been developed.     

Effect of jammer power on the performance of adaptive arrays

The effect of jammer power on the performance of adaptive arrays is studied. It is shown that the output signal-to-interference-plus-noise ratio (SINR) of an adaptive array is a function of jammer power. In the presence of a wide-band jammer, the output SINR of the array decreases with an increase in jammer power and eventually goes to zero. Unlike continuous wave (CW) jammers, a wide-band jammer does not go through power inversion. Instead, as the jammer power is increased, the interference-to-noise ratio (INR) at the array output shows oscillations. For large jammer power, the output INR increases with an increase in jammer power.     

A ferrous chloride-oxygen leach process for nickel-copper sulphide concentrations

This paper describes a ferrous chloride-oxygen leach process for recovery of nickel and copper values from sulphide concentrates available in India. The sulphide concentrates aareleached with a stirred solution of ferrous chloride in a glass-lined reactor operated at various temperatures and oxygen pressures. In this single step process, copper and nickel are converted into their water soluble chloride forms, whereas iron is rejected as hydrated iron oxide with simultaneous generation of sulphur in the non-polluting elemental form. The influence of various parameters such as (i) amount of ferrous chloride (60–100% stoichiometric), (ii) oxygen pressure (0.308–0.515 MPa), (iii) leaching temperature (90–120°C) and (iv) duration of leaching (2–10 h) on the leaching process has been examined. It has been possible to recover 94–99% nickel and 98% copper with low iron contamination by using optinum conditions, such as a stoichiometric amount of ferrous chloride, a temperature of 110°C, an oxygen pressure of 0.377 MPa and a duration of 8 h.     

The thermal control system

This paper presents the design, analysis and performance of the thermal control system ofAryabhata. A passive thermal control system, using flat absorber-AK-512 black paint for the outer surface of the satellite and a combination of solar reflector-AK-512 white paint and mechanical polishing for the inner surfaces, was employed to maintain the temperature of all the electronics subsystems onboard the satellite within the specified limits of 0°C and 40°C during the operational life of the satellite. The in-flight temperature data obtained from sixteen temperature sensors onboard the satellite was compared with the theoretically predicted temperature values and the agreement was good for all electronic subsystems housed within the framework of the satellite. The observed deviations in temperature for the tape recorder, proportional counter package and gas bottles of the spin-up system are attributed to the assumptions made for the mathematical model. It has been found that by improving these approximations, the deviations could be reduced to negligible values.     

On a numerical solution of the plastic buckling problem of structures

An automated digital computer procedure is presented for the accurate and efficient solution of the plastic buckling problem of structures. This is achieved by a Sturm sequence method employing a bisection strategy, which eliminates the need for having to solve the buckling eigenvalue problem at each incremental (decremental) loading stage that is associated with the usual solution techniques. The plastic bucking mode shape is determined by a simple inverse iteration process, once the buckling load has been established. Numerical results are presented for plate problems with various edge conditions. The resulting computer program written in FORTRAN for the JPL UNIVAC 1108 machine proves to be most economical in comparison with other existing methods of such analysis.     

A test rig for testing radial diffusers

A simple test rig for investigating the performance of vaneless diffusers with diverging walls for centrifugal compressors has been designed, fabricated and satisfactorily tested. The test rig was designed to give values of area ratio from 1·5 to 6 for an included angle of 10°. A uniform flow at the entry of the diffuser had been achieved by the use of a centre body and suction on both the walls. The swirl was zero in all the tests.A maximum Reynolds' number of 2·8 × 10⁵ can be obtained during the tests. Experimental values of the coefficients for losses, the pressure recovery and efficiency were obtained from the measurements of static and stagnation pressures.