Analysis of pressure blips in aft-finocyl solid rocket motor

Ballistic anomalies have frequently occurred during the firing of several solid rocket motors (SRMs) (Inertial Upper Stage, Space Shuttle Redesigned SRM (RSRM) and Titan IV SRM Upgrade (SRMU)), producing even relevant and unexpected variations of the SRM pressure trace from its nominal profile. This paper has the purpose to provide a numerical analysis of the following possible causes of ballistic anomalies in SRMs: an inert object discharge, a slag ejection, and an unexpected increase in the propellant burning rate or in the combustion surface. The SRM configuration under investigation is an aft-finocyl SRM with a first-stage/small booster design. The numerical simulations are performed with a quasi-one-dimensional (Q1D) unsteady model of the SRM internal ballistics, properly tailored to model each possible cause of the ballistic anomalies. The results have shown that a classification based on the head-end pressure (HEP) signature, relating each other the HEP shape and the ballistic anomaly cause, can be made. For each cause of ballistic anomalies, a deepened discussion of the parameters driving the HEP signatures is provided, as well as qualitative and quantitative assessments of the resultant pressure signals

Load distribution in small world networks

In this paper we introduce a new model of data packet transport, based on a stochastic approach with the aim of characterizing the load distribution on complex networks. Moreover we analyze the load standard deviation as an index of uniformity of the distribution of packets within the network, to characterize the effects of the network topology. We measure such index on the model proposed by Watts and Strogatz as the redirection probability is increased. We find that the uniformity of the load spread is maximized in the intermediate region, at which the small world effect is observed and both global and local efficiency are high. Moreover we analyze the relationship between load centrality and degree centrality as an approximate measure of the load at the edges. Analogous results are obtained for the load variance computed at the edges as well as at the vertices.Comment: 6 pages, 5 figures. Included in conference proceedings International Conference PhysCon 2005 August 24-26, 2005, Saint Petersburg, RUSSI

Bifurcations of piecewise smooth flows:perspectives, methodologies and open problems

In this paper, the theory of bifurcations in piecewise smooth flows is critically surveyed. The focus is on results that hold in arbitrarily (but finitely) many dimensions, highlighting significant areas where a detailed understanding is presently lacking. The clearest results to date concern equilibria undergoing bifurcations at switching boundaries, and limit cycles undergoing grazing and sliding bifurcations. After discussing fundamental concepts, such as topological equivalence of two piecewise smooth systems, discontinuity-induced bifurcations are defined for equilibria and limit cycles. Conditions for equilibria to exist in n-dimensions are given, followed by the conditions under which they generically undergo codimension-one bifurcations. The extent of knowledge of their unfoldings is also summarized. Codimension-one bifurcations of limit cycles and boundary-intersection crossing are described together with techniques for their classification. Codimension-two bifurcations are discussed with suggestions for further study

Complex behavior in switching power converters

Author name used in this publication: Chi K. Tse2001-2002 > Academic research: refereed > Publication in refereed journalVersion of RecordPublishe

OTTIMIZZAZIONE DI GIUNTI IBRIDI HBB A DOPPIA SOVRAPPOSIZIONE GFRP-ALLUMINIO

In order to exploit the advantages of both mechanical joints and adhesively bonded joints, in the last year a noticeable research activity has addressed to the so called hybrid joints (Hybrid Bonded Bolted joint, HBB) that consist in combining a classical mechanical joint (bolted, riveted joint, etc..) to a traditional bonded joint or a co-cured joint. The present work shows the results of experimental and numerical analyses of double-lap HBB joints, carried out to detect the geometric configuration that permits to distribute the applied load between the two coexisting junctions and then to optimize their mechanical performance. The studied joint consists of an internal adherent made by GFRP and external adherents made by aluminum type 2024-T6, connected by using an adhesive bonding and a M6 bolt. The optimization is detected by varying various influence parameters such as the geometry of the lip and the shape of the washer, which influences the distribution of the bolt preload. After the experimental tests, various numerical analyses are carried out to obtain a better understanding of the static behavior of the joint, as well as to define reliable criteria for the strength prediction under various operating conditions