脉冲末修弹落点预测导引方法研究

在分析剩余射程影响因素的基础上,以弹道特征参数弹道高y及速度矢量分量Vx和Vy为解释变量,以回归分析方法为数学工具,建立脉冲末修弹剩余射程预测模型。以目标点与弹丸预测落点之间的差值为广义弹道偏差,结合数值仿真,对落点预测导引进行深入研究,验证了回归分析模型的可行性。     

液压水锤效应引起液体喷溅特性及其影响因素试验研究

为研究液压水锤效应引起的液体喷溅特性及其影响因素,进行了高速破片撞击充液容器的试验,测试了液体内的空腔振荡特性、压力分布特性和容器外的液体喷溅特性。试验结果表明:液压水锤效应引起的液体喷溅有两个不同的阶段。第一个阶段发生在空腔生长到最大体积后的400~700 μs内,喷溅液体的头部呈箭状;在第二个阶段出现多次形状相似的脉动喷溅,且单次脉动均发生在每次空腔溃灭之后,喷溅液体具有伞状头部与线状尾部。液体内的压力和侵彻孔的形态共同影响液体的喷溅速度,相对喷溅速度与破片的撞击速度成反比。喷溅液体在运动过程中存在速度波动,且随着喷溅次数的增加,液体喷溅速度逐渐下降,速度拐点出现的位置逐渐接近侵彻孔。     

Damage mechanics and energy absorption capabilities of naturalfiber reinforced elastomeric based bio composite for sacrificial structural applications

The present study deals with the experimental, finite element (FE) and analytical assessment of low ballistic impact response of proposedflexible'green' composite make use of naturally available jute and rubber as the constituents of the composite with stacking sequences namely jute/rubber/jute (JRJ), jute/rubber/rubber/jute (JRRJ) and jute/rubber/jute/rubber/jute (JRJRJ). Ballistic impact tests were carried out by firing a conical projectile using a gas gun apparatus at lower range of ballistic impact regime. The ballistic impact response of the proposed flexible composites are assesses based on energy absorption and damage mechanism. Results revealed that inclusion of natural rubber aids in better energy ab-sorption and mitigating the failure of the proposed composite. Among the three different stacking se-quences of flexible composites considered, JRJRJ provides better ballistic performance compared to its counterparts. The damage study reveals that the main mechanism of failure involved in flexible com-posites is matrix tearing as opposed to matrix cracking in stiff composites indicating that the proposedflexible composites are free from catastrophic failure. Results obtained from experimental, FE and analytical approach pertaining to energy absorption and damage mechanism agree well with each other. The proposed flexible composites due to their exhibited energy absorption capabilities and damage mechanism are best suited as claddings for structural application subjected to impact with an aim of protecting the main structural component from being failed catastrophically.     

一类差分方程的三点边值问题的正解

研究了一类离散型三点边值问题:Δ2y(k-1) a(k)f(k,y(k))=0,k∈N={1,2,…,T},Δy(0)=0,y(T 1)=βy(l),式中:f是变号的,l∈N1={2,3,…,T-1},T∈{3,4,…}。应用双锥上的不动点定理,得到了至少存在两个正解的充分条件,并给出了上述边值问题的Green函数。     

破片模拟弹侵彻钢板的有限元分析

根据破片模拟弹侵彻钢板的实验研究,采用MSC.Dytran对破片模拟弹侵彻钢板的侵彻过程、侵彻特性、钢板的破坏模式以及弹体的侵彻速度、靶板的侵彻阻力进行了有限元分析,并将分析结果与实验结果进行了比较.分析结果表明,破片模拟弹冲击钢装甲的侵彻过程可大致分为初始接触、弹体侵入、剪切冲塞和穿甲破坏4个阶段.有限元分析的破片模拟弹侵彻特性及靶板破坏模式与实验观测结果有较好的一致性,在靶板破口的正面,与弹体平面凸缘两端接触的部分,变形以剪切为主,而与切削面接触的部分,以挤压变形为主;靶板破口背面为剪切冲塞破坏;有限元模拟的弹体剩余速度与实验结果吻合较好,弹体侵彻过程中弹靶作用界面的速度和侵彻速度近似呈线性变化.有限元分析结果还表明,采用适当的模型,有限元法能较好地模拟破片模拟弹侵彻钢板的侵彻过程、侵彻特性以及钢板的破坏模式.     

预定相遇态势的潜射鱼雷射击及其技术方法

为发挥鱼雷的作战效能,提出潜射鱼雷有利相遇态势的概念,指出当一次转角射击不能满足鱼雷以有利相遇态势接近并发现目标时,各种自导方式的鱼雷均需要二次转角射击。在给出二次转角射击时机、解算模型的基础上,着重对预定相遇态势射击的关键----二次转向点的选择问题进行了系统研究,引入基于鱼雷自导探测距离的二次转向点与预定相遇点之间距离的选择方法,使得二次转向点的选择更具合理性和针对性,且适用于包括直航鱼雷在内的各种鱼雷。     

基于结构加权的海面编队预定目标选择方法

海面目标运动和编队阵型的约束特性,使得通过对装订阵型和末制导探测阵型进行点集匹配来选择预定目标成为一种有效途径。但当编队目标释放干扰时,会引起阵型结构发生局部变化,导致目标选择性能恶化。本文基于反舰导弹目标选择需求,分析了传感器导航和探测误差、装订信息误差、编队目标运动和释放干扰等因素所引起的位置点集变形,通过利用阵型中未污染的结构信息,提出了基于几何散列法和结构加权平均Hausdorff距离的编队预定目标选择方法。理论分析和实验结果表明,该方法不受传感器导航误差和编队目标整体运动的影响,在编队存在冲淡干扰时能有效提高目标选择能力。     

Demand forecasting by temporal aggregation

Demand forecasting performance is subject to the uncertainty underlying the time series an organization is dealing with. There are many approaches that may be used to reduce uncertainty and thus to improve forecasting performance. One intuitively appealing such approach is to aggregate demand in lower‐frequency “time buckets.” The approach under concern is termed to as temporal aggregation, and in this article, we investigate its impact on forecasting performance. We assume that the nonaggregated demand follows either a moving average process of order one or a first‐order autoregressive process and a single exponential smoothing (SES) procedure is used to forecast demand. These demand processes are often encountered in practice and SES is one of the standard estimators used in industry. Theoretical mean‐squared error expressions are derived for the aggregated and nonaggregated demand to contrast the relevant forecasting performances. The theoretical analysis is supported by an extensive numerical investigation and experimentation with an empirical dataset. The results indicate that performance improvements achieved through the aggregation approach are a function of the aggregation level, the smoothing constant, and the process parameters. Valuable insights are offered to practitioners and the article closes with an agenda for further research in this area. © 2013 Wiley Periodicals, Inc. Naval Research Logistics 60: 479–498, 2013     

超高速碰撞形成一次碎片云特性

对超高速碰撞数值模拟方法进行了讨论.采用ANSYS/AUTODYN程序的SPH方法,对球形弹丸超高速撞击时弹丸的破碎、碎片云的形成及扩展过程进行数值模拟,其结果与实验结果进行比较,并验证了计算方法和模型参数的正确性.在此基础上采用数值模拟方法,对钨合金、轧制均质装甲及LY12铝三种材料的球形弹丸超高速撞击靶板之后形成的一次碎片云形貌及演化规律进行了研究,并基于量纲分析方法得出了碎片云特征参数(碎片云头部速度、径向最大膨胀速度及膨胀角)随初始撞击条件的变化规律。     

月壤参数对月面着陆气囊缓冲性能的影响

为研究月壤参数对气囊缓冲性能的影响,根据“嫦娥三号”的着陆工况设计了月面着陆气囊,并基于可压溃泡沫模型建立了考虑月壤特性的气囊缓冲动力学模型。对不同月壤下气囊的缓冲过程进行分析,发现月壤越软有效载荷冲击加速度越小,但气囊会陷入月壤中,不利于对外排气,影响其缓冲效果。因此,采用气囊峰值压力、有效载荷最大加速度和最大下落高度3个指标对气囊缓冲性能进行综合评价,定量研究了月壤参数的影响规律。结果表明:月壤密度、剪切模量及屈服参数a₀和a₁对缓冲性能的影响较大,且对前两个指标为正影响,对后一个指标为负影响。进一步研究发现,这4个月壤参数与3个缓冲性能指标之间〖BHDWG8,WK10YQ,DK1*2,WK1*2D〗〖XCZX.TIF;%129%129〗听语音 聊科研与作者互动 均为指数函数关系。