等、变深度舰船水压场的理论计算

在浅水、薄船、无限宽水域的条件下,舰船以亚临界速度(F_H<1)运动时,利用E.O.Tuck提出的渐近匹配展开法,可以得到定深度扰动速度势的摄动方程。对水深缓慢变化的海底,舰船的绕流不再是定常的,根据A.Plotkin所采用的多重尺度法,可以得到变深度浅水舰船扰动速度势的摄动方程。如果仅考虑扰动速度势的一阶摄动方程,则可得到考虑了线性兴波影响的舰船水压场的计算公式。     

Choosing arrival process models for service systems: Tests of a nonhomogeneous Poisson process

Service systems such as call centers and hospital emergency rooms typically have strongly time‐varying arrival rates. Thus, a nonhomogeneous Poisson process (NHPP) is a natural model for the arrival process in a queueing model for performance analysis. Nevertheless, it is important to perform statistical tests with service system data to confirm that an NHPP is actually appropriate, as emphasized by Brown et al. [8]. They suggested a specific statistical test based on the Kolmogorov–Smirnov (KS) statistic after exploiting the conditional‐uniform (CU) property to transform the NHPP into a sequence of i.i.d. random variables uniformly distributed on [0,1] and then performing a logarithmic transformation of the data. We investigate why it is important to perform the final data transformation and consider what form it should take. We conduct extensive simulation experiments to study the power of these alternative statistical tests. We conclude that the general approach of Brown et al. [8] is excellent, but that an alternative data transformation proposed by Lewis [22], drawing upon Durbin [10], produces a test of an NHPP test with consistently greater power. We also conclude that the KS test after the CU transformation, without any additional data transformation, tends to be best to test against alternative hypotheses that primarily differ from an NHPP only through stochastic and time dependence. © 2014 Wiley Periodicals, Inc. Naval Research Logistics 61: 66–90, 2014     

Optimal pricing for a short life‐cycle product when customer price‐sensitivity varies over time

Technology products often experience a life‐cycle demand pattern that resembles a diffusion process, with weak demand in the beginning and the end of the life cycle and high demand intensity in between. The customer price‐sensitivity also changes over the life cycle of the product. We study the prespecified pricing decision for a product that exhibits such demand characteristics. In particular, we determine the optimal set of discrete prices and the times to switch from one price to another, when a limited number of price changes are allowed. Our study shows that the optimal prices and switching times show interesting patterns that depend on the product's demand pattern and the change in the customers' price sensitivity over the life cycle of the product. © 2012 Wiley Periodicals, Inc. Naval Research Logistics, 2012     

The building evacuation problem with shared information

In this article, the Building Evacuation Problem with Shared Information (BEPSI) is formulated as a mixed integer linear program, where the objective is to determine the set of routes along which to send evacuees (supply) from multiple locations throughout a building (sources) to the exits (sinks) such that the total time until all evacuees reach the exits is minimized. The formulation explicitly incorporates the constraints of shared information in providing online instructions to evacuees, ensuring that evacuees departing from an intermediate or source location at a mutual point in time receive common instructions. Arc travel time and capacity, as well as supply at the nodes, are permitted to vary with time and capacity is assumed to be recaptured over time. The BEPSI is shown to be NP‐hard. An exact technique based on Benders decomposition is proposed for its solution. Computational results from numerical experiments on a real‐world network representing a four‐story building are given. Results of experiments employing Benders cuts generated in solving a given problem instance as initial cuts in addressing an updated problem instance are also provided. © 2008 Wiley Periodicals, Inc. Naval Research Logistics, 2008     

Many‐server loss models with non‐poisson time‐varying arrivals

This article proposes an approximation for the blocking probability in a many‐server loss model with a non‐Poisson time‐varying arrival process and flexible staffing (number of servers) and shows that it can be used to set staffing levels to stabilize the time‐varying blocking probability at a target level. Because the blocking probabilities necessarily change dramatically after each staffing change, we randomize the time of each staffing change about the planned time. We apply simulation to show that (i) the blocking probabilities cannot be stabilized without some form of randomization, (ii) the new staffing algorithm with randomiation can stabilize blocking probabilities at target levels and (iii) the required staffing can be quite different when the Poisson assumption is dropped. © 2017 Wiley Periodicals, Inc. Naval Research Logistics 64: 177–202, 2017     

Military expenditure,economic growth and structural instability: a case study of South Africa

This paper contributes to the growing literature on the milex-growth nexus, by providing a case study of South Africa and considering the possibility of structural breaks by applying newly developed econometric methods. Using full sample bootstrap Granger non-causality tests, no Granger causal link is found between military expenditure and GDP for 1951–2010, but parameter instability tests show the estimated VARs to be unstable. Using a bootstrap rolling window estimation procedure, however, finds evidence of bidirectional Granger causality in various subsamples. This implies standard Granger non-causality tests, which neither account for structural breaks nor time variation may be invalid.     

反舰导弹大空域变轨的三维扩展比例导引律

为了使大空域变轨弹道的理论研究更符合反舰导弹的实际运动状态,建立了反舰导弹追踪虚拟目标的三维空间相对运动模型。同时,为了保证反舰导弹大空域变轨弹道的四段弹道平滑过渡,在导引律设计时同时考虑了脱靶量要求和末端落角要求。应用Lyapunov稳定性理论求解出满足要求的三维扩展比例导引律,对大空域变轨弹道的四段弹道设计了相应的过载控制指令,并进行了仿真研究。仿真结果表明:所提出的三维扩展比例导引律可以使反舰导弹顺利完成大空域飞行任务,而且保证了反舰导弹的所有性能指标均满足要求。     

高速艇自由变深水动力试验研究

通过模型试验,研究了高速艇从压载半潜状态自由变深到高速滑行状态的水动力现象.结果表明,当容积傅氏数大于1.25时,与舷外相通的水能完全自动排出.高速艇自由变深主要有以下5个原因:惯性作用、压载水逐渐排出导致的艇体上抬作用、艇艉由于负压形成的空穴对压载水的吸附作用、艇体动升力导致的艇体上抬作用、有利的艉倾作用.其中对具有较快加速运动的情形,惯性作用起重要地位,艇体动升力在排出流道水方面所发挥的作用相对较小,但在保持流道水排空方面发挥主导作用.     

速变信号的小波分析应用研究

遥测速变参数处理方法大多基于经典分析方法,文中采用现代时频分析方法对遥测动态环境参数进行分析,对比算法在瞬态信号成分检测方面的优势,小波变换比傅立叶变换更适合分析非平稳信号,尤其是含瞬态或突变成分的信号.     

极值指数之推广矩估计量的渐近正态性

首先将推广矩估计量代换为一种新的估计量,然后研究由该估计量引起的一种与尾经验过程有关的函数的弱收敛问题,最后得到与推广矩估计量有关的一随机过程的弱收敛函数,同时也就得到了推广矩估计量的渐近分布,因而证明了推广估计量的渐近正态性.