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Simulation of.natural f.agmentation of.rings cut f.om warheads

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Def.nce Technology（防务技术） 2015年第4期11卷 319-329页

作者： john f.moxnes Steinar B?RVE Land Systems Division Norwegian Defence Research Establishment

Natural f.agmentation of.warheads that detonates causes the casing of.the warhead to split into various sized f.agments through shear or radial f.actures depending on the toughness,density,and grain size of.the *** best known f.rmula f.r the prediction of.the size distribution is the Mott f.rmulae,which is f.rther examined by Grady and Kipp by investigating more caref.lly the statistical most random way of.portioning a given area into a number of.*** examine the f.agmentation behavior of.radially expanding steel rings cut f.om a 25 mm warhead by using an in house smooth particle hydrodynamic(SPH) simulation code called *** results were compared with numerical results applying varying particle size and stochastic f.acture *** numerically obtained number of.f.agments was consistent with experimental *** expansion velocity of.the rings increases the number of.*** variation of.the material parameters inf.uences the f.agment characteristics,especially f.r low expansion velocities.A least square regression f.t to the cumulative number of.f.agments by applying a generalized Mott distribution shows that the shape parameter is around 4 f.r the rings,which is in contrast to the Mott distribution with a shape parameter of.1/*** initially polar distributed particles,we see signs of.a bimodal cumulative f.agment *** statistical variation in material parameters of.the f.acture model causes the velocity numerical solutions to become less sensitive to changes in resolution f.r Cartesian distributed particles.

关键词：弹头光滑粒子流体动力学自然环切膨胀速度模拟材料参数形状参数

Human development across the lif.span john S. Dacey, john f. Travers.

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On the study of.ricochet and penetration in sand,water and gelatin by spheres,7.62 mm APM2,and 25 mm projectiles

2002年

作者： john S. Dacey john f. Travers.

来源：畅想之星图书光盘版（南... 评论

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Def.nce Technology（防务技术） 2016年第2期12卷 159-170页

作者： john f.moxnes ∅yvind f.∅YLAND Stian SKRIUDALEN Anne K.PRYTZ Jan A.TELAND Eva f.IIS Gard ∅DEGARDSTUEN Land Systems Division Norwegian Defence Research EstablishmentP.O.Box 25N0-2027 KjellerNorway Nammo Rauf.ss AS P.O.Box 162N0-2831 RaufossNorway

We examine the ricochet and penetration behavior in sand, water and gelatin by steel spheres, 7.62 mm APM2 and 25 mm projectiles. A threshold impact angle(critical angle) exists beyond which ricochet cannot occur. The Autodyn simulation code with the smooth particle hydrodynamic(SPH) method and Impetus Af.a Solver with the corpuscular model are used and the results are compared with experimental and analytical results. The resistance f.rce in sand f.r spheres was proportional to a term quadratic in velocity plus a term linear in velocity. The drag coef.icient f.r the quadratic term was 0.65. The Autodyn and Impetus Af.a codes simulate too large penetration due to the lack of.a linear velocity resistance f.rce. Critical ricochet angles were consistent with analytical results in the literature. In ballistic gelatin at velocities of.50–850 m/s a drag coef.icient of.0.30 f.ts the high speed camera recordings if.a linear velocity resistance term is included. However, only a quadratic velocity resistance f.rce with drag coef.icient that varies with the Reynolds number also f.ts the measurements. The simulation of.a sphere in water with Autodyn showed too large drag coef.icient. The 7.62 mm APM2 core simulations in sand f.t reasonable well f.r both codes. The 25 mm projectile ricochet simulations in sand show consistency with the high speed camera recordings. Computer time was reduced by one to two orders of.magnitudes when applying the Impetus Af.a Solver compared to Autodyn code due to the use of.the graphics processing units(GPU).

关键词：明胶微球渗透行为炮弹光滑粒子流体动力学阻力系数模拟显示高速摄像机砂

Strain rate dependency and f.agmentation pattern of.expanding warheads

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Def.nce Technology（防务技术） 2015年第1期11卷 1-9页

作者： john f.moxnes Anne K.PRYTZ Фyvind f.?YLAND Stian SKRIUDALEN Steinar BФRVE Gard ФDEGARDSTUEN Land Systems Division Norwegian Defence Research Establishment (FFI) P.O.Box 25 NO-2027 Kjeller Norway Nammo Rauf.ss AS P.O.Box 162 NO-2831 Raufoss Norway

f.r the characterization of.the behaviors of.a metal material in events like expanding warheads, it is necessary to know its strength and ductility at high strain rates, around 104e105/s. The f.yer plate impact testing produces the unif.rm stress and strain rates but the testing is expensive. The Taylor test is relatively inexpensive but produces non-unif.rm stress and strain f.elds, and the results are not so easily inf.rred f.r material modeling. In the split-Hopkinson bar(SHB), which may be used in compression, tension and torsion testing, the strain rates never exceeds 103/s. In the present work, we use the expanding ring test where the strain rate is 104e105/s. A streak camera is used to examine the expanding ring velocity, and a water tank is used to collect the f.agments. The experimental results are compared with the numerical simulations using the hydrocodes AUTODYN, IMPETUS Af.a and a regularized smooth particle(RSPH) sof.ware. The number of.f.agments increases with the increase in the expansion velocity of.the rings. The number of.f.agments is similar to the experimental results. The RSPH sof.ware shows much the same results as the AUTODYN where the Lagrangian solver is used f.r the ring. The IMPETUS Af.a solver shows a somewhat dif.erent f.agmentation characteristic due to the node splitting algorithm that induces pronounced tensile splitting.

关键词： Warhead f.agmentation Simulation f.acture model Expanding ring

Business, government, and society : a managerial perspective : text and cases / George A. Steiner, john f. Steiner. 9th ed.

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Design of.Poiseuille f.ow Controllers Using the Method of.Inequalities

2000年

作者： George A. Steiner john f. Steiner.

来源：畅想之星图书光盘版（南... 评论

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International Journal of.Automation and computing 2009年第1期6卷 14-21页

作者： john McKernan James f. Whidborne George Papadakis Department of.Mechanical Engineering King s College London Strand Department of.Aerospace Sciences Cranfield University

This paper investigates the use of.the method of.inequalities （MoI） to design output-f.edback compensators f.r the problem of.the control of.instabilities in a laminar plane Poiseuille f.ow. In common with many f.ows, the dynamics of.streamwise vortices in plane Poiseuille f.ow are very non-normal. Consequently, small perturbations grow rapidly with a large transient that may trigger nonlinearities and lead to turbulence even though such perturbations would, in a linear f.ow model, eventually decay. Such a system can be described as a conditionally linear system. The sensitivity is measured using the maximum transient energy growth, which is widely used in the f.uid dynamics community. The paper considers two approaches. In the f.rst approach, the MoI is used to design low-order proportional and proportional-integral （PI） controllers. In the second one, the MoI is combined with Mcf.rlane and Glover＇s H∞ loop-shaping design procedure in a mixed-optimization approach.

关键词： Transient energy growth transient behaviour f.ow control Poiseuille f.ow method of.inequalities (MoI) mixed opti-mization H∞-optimization.