Adaptive Expanding Ring Search Based Per Hop Behavior Rendition of Routing in MANETs

Routing protocols in Mobile Ad Hoc Networks(MANETs)operate with Expanding Ring Search(ERS)mechanism to avoid ooding in the network while tracing step.ERS mechanism searches the network with discerning Time to Live(TTL)values described by respective routing protocol that save both energy and time.This work exploits the relation between the TTL value of a packet,trafc on a node and ERS mechanism for routing in MANETs and achieves an Adaptive ERS based Per Hop Behavior(AERSPHB)rendition of requests handling.Each search request is classied based on ERS attributes and then processed for routing while monitoring the node trafc.Two algorithms are designed and examined for performance under exhaustive parametric setup and employed on adaptive premises to enhance the performance of the network.The network is tested under congestion scenario that is based on buffer utilization at node level and link utilization via back-off stage of Carrier Sense Multiple Access with Collision Avoidance(CSMA/CA).Both the link and node level congestion is handled through retransmission and rerouting the packets based on ERS parameters.The aim is to drop the packets that are exhausting the network energy whereas forward the packets nearer to the destination with priority.Extensive simulations are carried out for network scalability,node speed and network terrain size.Our results show that the proposed models attain evident performance enhancement.

Expanding the bandwidth of planar MNG materials with co-directional split-ring resonators

An effective approach to expand the bandwidth of negative permeability of small-sized planax materials is proposed. Based on qualitative analysis of equivalent circuit models, the fractional bandwidth of an μ-negative （MNG） material is expanded from 3.53% up to 12.87% by adding split-ring resonators （SRRs） and arranging them by proposed steps. Moreover, the experimental results validate the effectiveness of bandwidth-expanding methods, which is promising for the extensive application of metamaterials in the microwave field.

An Energy Efficient Random Walk Based Expanding Ring Search Method for Wireless Networks

Wireless networks generate large amount of data. It is important to design energy efficient data search method since power of wireless nodes is finite. Expanding Ring Search (ERS) is a data search technique exploring for targets progressively, which is widely used to locate destinations or information in wireless networks. The existing studies on improving the energy efficiency of ERS cannot work without positioning systems. In this paper, we combine the technique of random walk with ERS, and propose a random walk based expanding ring search method (RWERS) for large-scale wireless networks. RWERS can work without using positioning systems, and improve the energy efficiency of ERS by preventing each node from transmitting the same request more than once using the technique of random walk. We compare RWERS with the optimal ERS strategy and CERS in networks with various shapes of terrains. The simulation results show that RWERS decreases the energy cost by 50% without decreasing in success rate compared with ERS, and has twice the success rate of CERS when the network is sparse. RWERS can be applied to various shapes of terrains better compared with CERS.

Strain rate dependency and fragmentation pattern of expanding warheads

For 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 flyer plate impact testing produces the uniform stress and strain rates but the testing is expensive. The Taylor test is relatively inexpensive but produces non-uniform stress and strain fields, and the results are not so easily inferred for 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 fragments. The experimental results are compared with the numerical simulations using the hydrocodes AUTODYN, IMPETUS Afea and a regularized smooth particle(RSPH) software. The number of fragments increases with the increase in the expansion velocity of the rings. The number of fragments is similar to the experimental results. The RSPH software shows much the same results as the AUTODYN where the Lagrangian solver is used for the ring. The IMPETUS Afea solver shows a somewhat different fragmentation characteristic due to the node splitting algorithm that induces pronounced tensile splitting.

Simulation of natural fragmentation of rings cut from warheads

Natural fragmentation of warheads that detonates causes the casing of the warhead to split into various sized fragments through shear or radial fractures depending on the toughness,density,and grain size of the material.The best known formula for the prediction of the size distribution is the Mott formulae,which is further examined by Grady and Kipp by investigating more carefully the statistical most random way of portioning a given area into a number of entities.We examine the fragmentation behavior of radially expanding steel rings cut from a 25 mm warhead by using an in house smooth particle hydrodynamic(SPH) simulation code called REGULUS.Experimental results were compared with numerical results applying varying particle size and stochastic fracture strain.The numerically obtained number of fragments was consistent with experimental results.Increasing expansion velocity of the rings increases the number of fragments.Statistical variation of the material parameters influences the fragment characteristics,especially for low expansion velocities.A least square regression fit to the cumulative number of fragments by applying a generalized Mott distribution shows that the shape parameter is around 4 for the rings,which is in contrast to the Mott distribution with a shape parameter of 1/2.For initially polar distributed particles,we see signs of a bimodal cumulative fragment distribution.Adding statistical variation in material parameters of the fracture model causes the velocity numerical solutions to become less sensitive to changes in resolution for Cartesian distributed particles.

RESEARCH ON HOT FORMING PROCESS OF A RETAINING RING OF HIGH-NITROGEN STEEL

Mn18Cr18N, the high-nitrogen steel, is the 2nd generation material for manufacturing the retaining ring of firepower generators. In this paper, the hot deformation behavior of the material was investigated by thermo-mechanical modeling tests. And the flow stress curves of the steel were obtained for various combinations of the temperature and strain rate. Based on the results of the tests, the complex forming process of a retaining ring including punching, expanding and extrusion with an enclosure was put forward and simulated by means of numerical simulation method. The results indicate that the process is a novel and force-saved practical technology for manufacturing heavy retaining rings.

Research on the expanding deformation of ring radius in cold profiled ring rolling process

Cold profiled ring rolling is an advanced local plastic deformation technology widely used to precisely manufacture various complex seamless ring parts.It plays an important role in many industrial fields such as aeronautics,astronautics,automobile,bearings,etc.In the cold ring rolling process,the ring radius expands gradually with the increase of the feeding amount(i.e.rolling reduction),and the expanding deformation of the ring radius is closely related to the rolling reduction.It is very important to investigate the expanding deformation of ring radius for the precise control of ring dimensions and the design of feeding movement.In this paper,the relation between the expanding deformation of the ring radius and the rolling reduction in the stepped ring rolling process,a typical profiled ring rolling process,is analyzed by using analytical method.The results show that the growth amount of the filling depth of groove can't exceed the rolling reduction,that in the inner stepped ring rolling process,the curves of the outer radius and big inner radius with the rolling reduction are monotonous,ascending and concave,i.e.,the outer radius and big inner radius expand faster and faster with the increase of the rolling reduction,and that in the outer stepped ring rolling process,the curves of the inner radius and small outer radius with the rolling reduction are also monotonous,ascending and concave,i.e.,the inner radius and small outer radius expand faster and faster with the increase of the roll reduction.

环氧化天然橡胶的合成与表征

采用过氧化氢在甲酸存在条件下对天然橡胶胶乳进行环氧化反应 .实验表明 ,较适当的反应条件为 :反应温度 30℃ ,初始干胶含量为 30 % ,初始 pH值为 2 .0 ,H2 O2 ,HCOOH与NR干胶之摩尔比为1∶0 .5 5∶1.分别采用了红外光谱 (IR)、核磁共振 (1HNMR)和化学滴定等手段对天然橡胶的环氧化含量进行了表征 .

爆炸膨胀环的截面尺寸效应

利用爆炸膨胀环实验数据修正了无氧铜的J-C本构模型参数,计算获得的速度历史与实验测试结果吻合。通过数值模拟研究了膨胀环宽度对速度历史、应力状态的影响,发现:对厚度1mm的膨胀环,加载速度峰值随着膨胀环宽度的增加而增加,当宽度超过8mm后速度峰值不再变化;膨胀环宽度不超过2mm时,能较好满足1维应力状态的假定。膨胀环的应力状态在一定范围内具有明显的尺寸效应,可为爆炸膨胀环的试样尺寸设计提供参考。

爆炸膨胀环实验数据处理方法讨论

采用线性关系式及多项式对爆炸膨胀环速度曲线上不同长度的数据窗口进行拟合,获得了应力应变关系,结果表明数据窗口的选取是膨胀环实验数据处理的基础;同时发现当拟合关系式高于2次时,获得的应力应变关系从形式上偏离了物理规律。对数据进行高阶光滑后采用差分方法直接处理,可以更好地反映膨胀环速度历史与瞬时应力之间的关系,澄清了2次以上关系式拟合处理得到的应力应变关系偏离物理规律并不是由数据处理方法造成的,而是由速度点测试的不确定性造成的。

实现材料高应变率拉伸加载的爆炸膨胀环技术

设计了新型的爆炸膨胀环实验加载装置,加载装置中采用爆炸丝线起爆方式,避免了传统装置中对碰爆轰波加载时的应力不均匀性。利用新型的爆炸膨胀环实验技术研究了无氧铜材料的动态性能,利用激光位移干涉仪测量了试样环的径向速度历史,处理数据获得了无氧铜材料的流动应力-塑性应变-应变率的关系,为进一步利用爆炸膨胀环实验技术研究材料在高应变率拉伸加载时的本构关系奠定了基础。

韧性金属圆环高速膨胀碎裂过程的有限元模拟

用数值方法模拟了韧性金属圆环的自由膨胀碎裂过程.采用Johnson-Cook热黏塑性本构模型描述材料的动态变形和热软化特性,采用包含内聚力失稳断裂准则的Johnson-Cook型损伤断裂模型描述材料的破坏和分离过程,采用结合单元消去技术的A.BAQUS/Explicit程序进行分析.在特定膨胀速度下对多个圆环进行碎裂数值实验,获得碎片样本集合.研究证实,Grady-Kipp基于塑性卸载波传播机制的韧性碎片尺寸公式可以较好地预测碎片的平均长度.模拟再现了圆环碎裂过程中塑性卸载波的传播,揭示了Grady-Kipp公式合理性的物理基础.

护环扩挤复合成形新工艺的模拟研究

针对护环锻造成形中存在的问题，提出了一种扩挤复合成形新工艺。运用刚塑性有限元数值模拟与物理模拟相结合的方法，分析研究了环坯复合成形过程的变形规律，对模具几何结构参数和扩孔与挤压变形的匹配关系进行了优化，有限元模拟与试验结果一致。研究表明，该新工艺具有轴对称变形均匀、剪切变形量大及压缩与剪切复合变形等特点，能够改善现用成形工艺，因而可以在生产中应用。

一种基于SHPB的冲击膨胀环实验技术

设计了一种基于分离式Hopkinson压杆(SHPB)的冲击膨胀环实验装置,实验装置包括一个液压腔,一侧为驱动活塞,另一侧为圆环试件封闭。对活塞施加轴向冲击,利用液体体积近似不可压缩的特性,通过液压腔截面积的大比例缩小,将较低速度的对活塞冲击转化为圆环试件沿径向的高速膨胀,驱动试件发生拉伸变形直至断(碎)裂。使用这种冲击膨胀装置,获得了LY12铝环在不同撞击速度下碎裂过程的初步结果。实验结果显示,随着撞击速度增大,圆环试件碎裂产生的碎片的尺度减小,试件的表观断裂应变增加。这为研究材料的动态拉伸碎裂问题提供了一种加载方式。

电磁膨胀环实验设计的关键因素

为了更好地研究电磁膨胀环实验加载技术,利用带有电磁模块的LS-DYNA三维动力学有限元程序对电磁膨胀环加载过程进行三维数值模拟。分析了螺线圈绕法、加载电流波形、膨胀环截面尺寸和轴向位移对电磁膨胀环实验结果的影响。计算结果表明,连接带缺口螺线圈的圆圈绕线方法优于均匀过渡绕法,加载电流峰值与膨胀环径向速度峰值近似成线性关系,适当增加膨胀环截面轴向的宽度可提高膨胀环运动稳定性,双螺线圈模型可有效减小膨胀环轴向位移。

爆炸与电磁加载下无氧铜环、柱壳的断裂模式转变

考虑断面收缩率、局域断裂应变以及平均断裂应变,并基于电磁膨胀环、爆炸膨胀环(柱壳)实验平台,研究了高纯无氧铜(TU1)环及柱壳在高应变率载荷下的膨胀断裂行为。采用高速摄影技术拍摄柱壳外壁的膨胀断裂形貌演化过程,用于确定柱壳平均断裂应变;利用激光干涉测速技术获得样品径向膨胀速度历史,用于确定加载应变率;利用样品的全回收测量及微观表征,确定了无氧铜环、柱壳的局域断裂应变及断裂模式。实验表明,随着应变率的增加,TU1材料的平均断裂应变增加,断面的收缩程度加剧,并在应变率约为1.0×10~4s^(-1)附近会出现明显的断裂模式转变,断面收缩率出现量级上的跳跃,从10~0变化至约10~3,局域断裂应变呈现明显的分区现象。

爆炸丝线起爆装置研制及应用

为实现低密度粉末炸药的线同步起爆,研制了一种爆炸丝线起爆系统。储能装置采用3个低感电容并联,总容量为12μF;采用200kV/100kA场畸变开关作为放电开关;触发器产生1.5kV脉冲经过高压脉冲变压器输出幅度大于40kV的高压脉冲触发开关。在储能电容器充电40kV下,电爆炸丝负载上获得了73kA的脉冲电流。采用高速分幅相机观测了爆炸丝爆炸过程图像,结果表明爆炸丝膨胀过程的同步性较好。该线起爆系统已成功应用于爆炸膨胀环实验。

护环热锻新技术

针对目前护环质量及其热锻工艺中存在的问题 ,通过对热成形技术的分析 ,提出了护环扩挤复合成形新工艺。并经过理论分析 (FEM)和模拟试验 ,证明了新工艺的先进性和可行性.

爆炸膨胀环一维应力假定的分析与讨论

对爆炸膨胀环的运动过程和应力状态进行了理论分析,指出膨胀环在径向变形过程中其厚度减小将引起内外壁的速度差,对膨胀环内外壁的速度差进行了分析。由于膨胀环内外壁速度差的存在必然造成复杂应力状态,无法满足一维应力假定,由此推断出实验中利用外壁速度计算出的应力要略大于膨胀环内的平均应力。利用LS-DYNA三维动力学有限元程序验证了理论分析结果,利用膨胀环外壁速度计算出的应力比数值模拟给出的膨胀环内平均应力大1%左右。

韧性材料冲击拉伸碎裂中的碎片尺寸分布规律

利用有限元方法模拟韧性金属圆环高速膨胀过程中的碎裂过程,获得不同初始膨胀速度下碎片的样本集合.通过对碎片的尺寸进行统计分析发现:(1)无论初始膨胀速度如何,碎片的归一化尺寸分布具有相似性,可以用一个具有初始阈值的Weibull分布描述,近似地,这个分布还可以简化为Rayleigh分布;(2)碎片尺寸的累积分布曲线呈现阶梯特性,表现出较明显的"量子化"特性.在上述发现基础上,建立一个Monte-Carlo模型:碎裂点来自于颈缩点,颈缩之间的间距满足某种连续的Weibull分布,而碎片的尺寸为随机的若干个颈缩间距之和.概率模拟表明:除非早期的颈缩间距分布很宽,否则选择的离散性必然导致碎片尺寸分布呈现某种量子化特性.采用L04工业纯铝和无氧铜试件进行了爆炸膨胀碎裂实验,回收得到的碎片尺寸分布结果与理论分析基本一致.