Design of Funnel Port Tubular Propellant Grain for Neutral Burning Profile in Rockets

Radial outward burning tubular propellant grain gives progressive burning profile, but trimming port at one end to conical form gives close to neutral burning profile. Though this configuration is easy to realize, but closeform burnback equation for performance prediction of such propellant geometry is not available. In this paper, close-form burnback equation for conically trimmed tubular propellant grain is developed. One propellant grain is also evaluated and performance matching to prediction by developed formulation is realised. Parametric study for different aspect ratio (L/D), diameter ratio (d/D) and slant angle (q) is carried out for a typical configuration and variation is explained. The developed formulation is simple, handy, easy and quick.Defence Science Journal, 2009, 59(5), pp.494-498, DOI:http://dx.doi.org/10.14429/dsj.59.155

Modelling of Burning Surface Regression of Taper Convex Star Propellant Grain

The burn area calc,ulhtion of al propellant, grain with taper convex star Port is discussed and a software developed, usIng a new zoning definition of the star cross-section,is elaborated. The evolution of lengthwise conditions,inclusion of a coupled sustainer mode, real-time calculations andcalculation for sliver burrling part make this software a versatile tool for propellant grain design and parametric studies

Parametric Studies on Star Port Propellant Grain For Ballistic Evaluation

Star port propellant grains have been extensively studied for their operating as well as geometrical parameters. It is observed that reduced tail-off and better neutrality cannot be achieved simultaneously in a configuration. Parametric study is conducted to know the effect of various parameters of star-shaped propellant grains for ballistic evaluation motor. For reduced tail-off, higher characteristic velocity, lower outer diameter of the star, and lower value of angular fraction is preferred. Star angle, burning rate, and throat diameter have negligible effects on the tail-off factor. For better neutrality, higher value of angular  fraction, higher star outer diameter, and star angle near to neutrality, is needed. An alternate configuration is suggested using this parametric study to ascertain least tail-off and enhanced neutrality

Estimation of Pressure Index and Temperature Sensitivity Coefficient of Solid Rocket Propellants by Static Evaluation

Burning rate of a solid rocket propellant depends on pressure and temperature. Conventional strand burner and Crawford bomb test on propellant strands was conducted to assess these dependent parameters. However, behaviour of propellant in rocket motor is different from its behaviour in strand form. To overcome this anomaly, data from static evaluation of rocket motor was directly used for assessment of these burningrate controlling parameters. The conventional empirical power law (r=aoexp[p{T-To}]Pn) was considered and a method was evolved for determination of pressure index (n) and temperature sensitivity coefficient (p) of burning rate for solid rocket propellants from static evaluation data. Effect of pressure index and temperature sensitivity coefficient on firing curve is also depicted. Propellant grain was fired in progressive mode to cover a very wide pressure range of 50 kg/cm2 to 250 kg/cm2 and propellant burning rate index was calculated to be 0.32 in the given pressure range. Propellant grain was fired at +35 °C and 20 °C temperatures and temperature sensitivity coefficient of burning rate was calculated to be 0.27 % per °C. Since both the values were evaluated from realised static evaluation curves, these are more realistic and accurate compared to data generated by conventional methods.Defence Science Journal, 2009, 59(6), pp.666-669, DOI:http://dx.doi.org/10.14429/dsj.59.157

Studies on Stress-Strain Curves of Aged Composite Solid Rocket Propellants

Mechanical property evaluation of composite solid rocket propellants is used as a quick quality control tool for propellant development and production. However, stress-strain curves from uni-axial tensile testing can be utilised to assess the shelf-life of propellants also. Composite propellants (CP) of two varieties cartridge-loaded (CLCP) and case-bonded (CBCP) are utilized in rocket and missile applications. Both classes of propellants were evaluated for mechanical properties namely tensile strength, modulus and percentage elongation using specimens conforming to ASTM D638 type IV at different ageing time. Both classes of propellants show almost identical variation in various mechanical properties with time. Tensile strength increases with time for both classes of propellants and percentage elongation reduces. Initial modulus is also found to decrease with time. Tensile strength is taken as degradation criteria and it is observed that CLCP has slower degradation rate than CBCP. This is because of two facts–(i) higher initial tensile strength of CLCP (1.39 MPa) compared to CBCP (0.665 MPa) and (ii) lower degradation rate of CLCP (0.0014 MPa/day) with respect to CBCP (0.0025 MPa/day). For the studied composite propellants, a degradation criterion in the form of percentage change in tensile strength is evaluated and shelf life for different degradation criteria is tabulated for quick reference.Defence Science Journal, 2012, 62(2), pp.90-94, DOI:http://dx.doi.org/10.14429/dsj.62.77

Peak Strain in Regressing Finocyl Port Propellant Grainsunder Pressure Loading

Finite element analysis (FEM) has been conducted for case-bonded finocyl port propellantcross section under pressure loading conditions during burning. Peak strain is found todecrease in course of burning, hence, analysis of any intermediate configuration in courseof burning is not required for assessing margin of safety in finocyl port propellant grains.The Power Law proposed1 has also been used to predict peak strain. Variation in strainsobtained by FEM and using the Power Law is found to be matching closely with findingsreported in CPIA (Chemical Propulsion Information Agency) publications. Extension indomain of power law to regressing pressurised finocyl port propellant grain eliminates dependenceon time-consuming computer- intensive FEM computations without compromising the accuracyof results

Prediction of Maximum Strain in Finocyl Port Case-bonded Solid Propellants under Pressure Loading

Finite element analysis of case-bonded solid propellants in finocyl port configuration hasbeen carried out using finite element method. The parametric studies have also been conductedfor loading conditions, material properties, and geometrical configurations. The results arepresented in the form of a universal power law, which can be utilised for primary assessmentof peak strain in any finocyl port propellant configuration without using finite element software.This eliminates dependence on finite element software for structural integrity analysis of solidpropellants in finocyl port configuration under port pressurisation. The results obtained by finiteelement analysis and power law are in close agreement

Effect of Temperature on Mechanical Properties of Solid Rocket Propellants

Mechanical properties of solid rocket propellants are dependent on temperature. Any change in temperature brings significant change in the tensile strength, percentage elongation, and elastic modulus of the propellant. Different classes of operational solid rocket propellants namely extruded double-base propellants, composite, extruded composite and nitrarte ester polyester propellants were evaluated at different temperatures in the operating range of the rockets and missiles preferably in the range of –50 oC to +55 oC. It was observed that for each class of propellant, as temperature reduces, propellant becomes hard. This is depicted by increase in elastic modulus and tensile strength of the material. However, trend of percentage elongation is not very uniform. Extruded double-base propellants show less percentage elongation (around 1 per cent) at reduced temperature (–50 oC) probably due to brittleness. So is the trend with case-bonded composite propellants. However, reverse trend is exhibited by cartridge-loaded composite propellants and nitrate ester polyester propellants. Such propellants show higher percentage elongation (6 per cent for CLCP and 35 per cent for NEPE) at reduced temperature (–50 oC). This makes such propellants tough and more area under stress-strain curve at reduced temperature is observed.Defence Science Journal, 2011, 61(6), pp.529-533, DOI:http://dx.doi.org/10.14429/dsj.61.77

Mermera: Non-Coherent Distributed Shared Memory for Parallel Computing

The proliferation of inexpensive workstations and networks has prompted several researchers to use such distributed systems for parallel computing. Attempts have been made to offer a shared-memory programming model on such distributed memory computers. Most systems provide a shared-memory that is coherent in that all processes that use it agree on the order of all memory events. This dissertation explores the possibility of a significant improvement in the performance of some applications when they use non-coherent memory. First, a new formal model to describe existing non-coherent memories is developed. I use this model to prove that certain problems can be solved using asynchronous iterative algorithms on shared-memory in which the coherence constraints are substantially relaxed. In the course of the development of the model I discovered a new type of non-coherent behavior called Local Consistency. Second, a programming model, Mermera, is proposed. It provides programmers with a choice of hierarchically related non-coherent behaviors along with one coherent behavior. Thus, one can trade-off the ease of programming with coherent memory for improved performance with non-coherent memory. As an example, I present a program to solve a linear system of equations using an asynchronous iterative algorithm. This program uses all the behaviors offered by Mermera. Third, I describe the implementation of Mermera on a BBN Butterfly TC2000 and on a network of workstations. The performance of a version of the equation solving program that uses all the behaviors of Mermera is compared with that of a version that uses coherent behavior only. For a system of 1000 equations the former exhibits at least a 5-fold improvement in convergence time over the latter. The version using coherent behavior only does not benefit from employing more than one workstation to solve the problem while the program using non-coherent behavior continues to achieve improved performance as the number of workstations is increased from 1 to 6. This measurement corroborates our belief that non-coherent shared memory can be a performance boon for some applications

R1 Retrotransposons in Drosophila melanogaster are Transcribed by RNA Polymerase I Upon Heat Shock

The ribosomal RNA genes of Drosophila melanogaster reside within centromere-proximal nucleolar organizers on both the X and Y chromosomes. Each locus contains between 200-300 tandem repeat rDNA units that encode 18S, 5.8S, and 28S ribosomal RNAs (rRNAs) for ribosome biogenesis. In arthropods like Drosophila, about 60% of rDNA genes are inserted with R1 and/or R2 retrotransposons at specific sites within the 28S regions; these units likely fail to produce functional 28S rRNA. We showed previously that R2 expression increases upon nucleolar stress caused by the loss of a ribosome assembly factor, the Nucleolar Phosphoprotein of 140 kDa (Nopp140). Here we show that R1 expression is selectively induced by heat shock. Actinomycin D, but not α-amanitin, blocked R1 expression in S2 cells upon heat shock, indicating that R1 is transcribed by Pol I. RT-PCR analysis confirmed read-through transcription by Pol I from the 28S gene region into R1. Using a genome wide precision run-on sequencing (PRO-seq) data set available at NCBI-GEO, we showed that Pol I activity on R1 elements is negligible under the normal non-heat shock condition but increases dramatically upon heat shock. We propose that prior to heat shock, Pol I pauses within ~350 bp of the 5’ end of R1 wherein we find ‘pause button’ like sequence motifs, and that heat shock releases Pol I for read-through transcription into R1