复合材料帽型加筋层合梁刚度的理论计算研究

根据层合板理论,首先利用三维应力、应变转换关系,推导出复合材料帽型加筋层合梁的总体刚度矩阵公式,建立了复合材料帽型加筋层合梁的拉伸刚度和弯曲刚度理论计算式;然后,计算了轴向或横向荷载作用下,复合材料帽型加筋悬臂层合梁的拉伸和弯曲变形,并和ANSYS有限元计算结果进行了对比;最后,计算分析了腹板倾斜角度对结构刚度的影响。计算结果表明:腹板倾斜角度为60°时,帽型加筋结构的刚度和所需材料的比值达到最优值;拉伸和弯曲刚度的理论解和ANSYS有限元计算结果吻合较好,说明上述方法以及推导的计算公式是准确、可靠的。     

弹性支座阶梯形连续梁弯曲计算的普遍方程

本文借助奇异函数,用阶梯函数表示阶梯形梁的抗弯刚度的倒数,在考虑支座沉陷影响的情况下,推导出了阶梯形连续梁在弹性支座支承下的弯曲计算普遍方程,给出了支座反力计算的矩阵方程。     

弯管结构模态柔度曲率差法损伤识别

对弯管结构进行损伤识别,采用模态柔度比结构的频率或位移模态更灵敏,且模态柔度仅需结构的低阶频率和振型就可准确地计算。采用有限元方法,以一弯管为仿真算例,以结构模型的单元刚度的下降来模拟损伤。结果表明:弯管结构的模态柔度具有方向性,弯管所在平面x、y方向柔度求解的模态柔度曲率差不能对弯管进行频率损伤识别,垂直弯管所在平面z方向柔度不仅可以对弯管进行单处、多处的损伤定位,而且可以对同一位置的损伤程度进行定量分析。     

粗糙模糊C均值融合聚类

提出一种新的粗糙模糊C均值融合聚类算法,该算法通过粗糙集上、下近似的引入改变了模糊C均值算法中隶属度函数的分布情况,修正了类心的更新公式和模糊隶属度计算公式,降低了计算复杂度,在改变模糊隶属度分布的同时,通过使得每一类总的隶属度变化保持最小,进一步提出了边界调节参数的自适应选择算法,实验结果表明,粗糙模糊C均值融合算法...     

高柔悬臂结构的弯曲型集中质量模型研究

基于质量集中和刚度等效的原则,提出了一种将高柔悬臂结构简化为弯曲型集中质量模型的新方法。首先,根据集中质量法确定简化模型节点处的集中质量。然后,基于振动特征方程和悬臂结构柔度矩阵中各元素与抗弯刚度的倒数之间具有线性关系的特点,推导出固有频率与层间等效抗弯刚度之间的非线性关系式;通过有限元软件对结构进行模态分析,提取其固有频率,将提取的固有频率代入关系式即可计算出等效抗弯刚度。最后,用数值算例对比验证了该模型简化方法的有效性和精确性。     

复合材料帽形加筋梁强度及刚度实用计算与试验

利用变形协调方程,推导了复合材料帽形加筋梁的等效弯曲刚度公式,建立了复合材料帽形加筋梁的应力、挠度计算公式.计算了均布荷载作用下,不同边界条件下复合材料帽形加筋梁的应力和挠度,并进行了帽形加筋梁的三点弯曲强度试验.对比分析了数值计算结果和试验结果,结果表明:理论计算结果和试验结果吻合较好,说明该方法以及推导的计算公式是可靠的,易于在复合材料船体初步设计阶段中使用.     

机电二阶振荡平滑装置设计与计算

本文推导出二阶振荡平滑装置的各函数公式和系统参数同性能指标间的关系,并总结出参数计算表。根据观察时间T_4和超调量⊿_2,用此表可很简便地计算出平滑装置的各个参数,进而计算出各函数的数值,并举了实例。在实例中还介绍了转值、电比例尺和速比的计算方法。     

斜梁的内力计算

对斜梁的内力进行了全面分析,并给出了计算方法,考虑了斜梁的拉力和压力。     

BFRP筋无粘结预应力混凝土梁受弯性能理论分析

在试验研究的基础上进行了理论分析.详细分析了BFRP筋无粘结预应力梁张拉、加载过程中应力变化;分析了BFRP筋无粘结预应力混凝土梁破坏模式及极限承载力计算方法;提出计算BFRP筋无粘结部分预应力梁开裂后短期刚度的"等受拉刚度代换法",及计算平均裂缝宽度的"两步等效法",计算值与试验值符合较好;BFRP筋无粘结预应力梁耗能能力随预应力度的提高而降低,根据试验结果提出耗能比例系数计算公式.     

弹性支承梁固有频率影响因素研究

通过将折叠舵简化为梁模型来研究一种典型结构折叠舵频率的影响因素。对于梁内出现的弹性支承情形,采用了以分段表示的运动微分方程、简支和自由边界条件以及弹性支承处连续性条件来描述。根据梁的振动的基本方程,推导出弹性支承弯曲振动梁的频率方程的解析表达式,并利用数值方法计算出在不同条件下弯曲振动梁的频率,研究弹簧刚度,有效比刚度,以及支承点位置对固有频率的影响。     

Convex/stochastic programming and multilocation inventory problems

This paper examines a convex programming problem that arises in several contexts. In particular, the formulation was motivated by a generalization of the stochastic multilocation problem of inventory theory. The formulation also subsumes some “active” models of stochastic programming. A qualititative analysis of the problem is presented and it is shown that optimal policies have a certain geometric form. Properties of the optimal policy and of the optimal value function are described.     

不卸载时侧贴碳纤维布加固连续梁试验研究

为研究不同初始荷载作用下侧贴碳纤维布加固连续梁的受力与变形特性,以及初始荷载对加固效果的影响,对4根钢筋混凝土两跨连续梁（其中1根为未加固连续梁,其余3根为在不同初始荷载下侧贴碳纤维布加固连续梁）进行了试验研究。结果表明：侧贴碳纤维布加固连续梁不仅能提高加固梁的承载力,提高幅度达16%以上;还能提高加固梁的刚度,减少其挠度和裂缝宽度;加固效果受初始荷载影响,初始荷载越小,加固效果越好。     

A robust queueing network analyzer based on indices of dispersion

We develop a robust queueing network analyzer algorithm to approximate the steady-state performance of a single-class open queueing network of single-server queues with Markovian routing. The algorithm allows nonrenewal external arrival processes, general service-time distributions and customer feedback. The algorithm is based on a decomposition approximation, where each flow is partially characterized by its rate and a continuous function that measures the stochastic variability over time. This function is a scaled version of the variance-time curve, called the index of dispersion for counts (IDC). The required IDC functions for the external arrival processes can be calculated from the model primitives or estimated from data. Approximations for the IDC functions of the internal flows are calculated by solving a set of linear equations. The theoretical basis is provided by heavy-traffic limits for the flows established in our previous papers. A robust queueing technique is used to generate approximations of the mean steady-state performance at each queue from the IDC of the total arrival flow and the service specification at that queue. The algorithm's effectiveness is supported by extensive simulation studies.     

Strategic capacity decision‐making in a stochastic manufacturing environment using real‐time approximate dynamic programming

In this study, we illustrate a real‐time approximate dynamic programming (RTADP) method for solving multistage capacity decision problems in a stochastic manufacturing environment, by using an exemplary three‐stage manufacturing system with recycle. The system is a moderate size queuing network, which experiences stochastic variations in demand and product yield. The dynamic capacity decision problem is formulated as a Markov decision process (MDP). The proposed RTADP method starts with a set of heuristics and learns a superior quality solution by interacting with the stochastic system via simulation. The curse‐of‐dimensionality associated with DP methods is alleviated by the adoption of several notions including “evolving set of relevant states,” for which the value function table is built and updated, “adaptive action set” for keeping track of attractive action candidates, and “nonparametric k nearest neighbor averager” for value function approximation. The performance of the learned solution is evaluated against (1) an “ideal” solution derived using a mixed integer programming (MIP) formulation, which assumes full knowledge of future realized values of the stochastic variables (2) a myopic heuristic solution, and (3) a sample path based rolling horizon MIP solution. The policy learned through the RTADP method turned out to be superior to polices of 2 and 3. © 2010 Wiley Periodicals, Inc. Naval Research Logistics 2010     

Properties of a mean residual life function arising from renewal theory

The present article discusses the properties of the mean residual life function in a renewal process. We examine the relationship this function has with the failure rate function and the conventional mean, variance and coefficient of variation of residual life. We also discuss some monotonicity properties of the mean residual life function. A partial order based on the renewal mean residual function is introduced along with its interrelationship with some existing stochastic orders. © 2010 Wiley Periodicals, Inc. Naval Research Logistics, 2010     

黏弹性基底上阻尼碳纳米管的动力学特性

采用欧拉梁模型建立了有阻尼碳纳米管在黏弹性基底上的动力学问题分析模型。通过引入非局部理论、广义Maxwell黏弹性模型、速度相依的外阻尼模型及黏弹性基底模型推导出碳纳米管动力学分析的欧拉梁振动控制方程。在Kelvin-Voigt黏弹性模型基础上,分别给出无基底和全基底支撑时碳纳米管固有频率的一般解析表达式,并分析讨论全基底时的多种典型情况。然后利用传递函数方法求解出一般边界条件下振动控制方程的封闭解。以某单壁碳纳米管为例,得到不同边界条件下该单壁碳纳米管的前四阶固有频率,并分析了碳纳米管非局部参数、黏弹性参数、基底刚度及长度等影响因素对固有频率和阻尼因子的影响情况。结果表明,文中所建的动力学分析模型及计算方法对解决碳纳米管在黏弹性基底上的动力学问题准确有效。     

A stochastic air combat logistics decision model for Blue versus Red opposition

Technologically advanced aircraft rely on robust and responsive logistics systems to ensure a high state of operational readiness. This paper fills a critical gap in the literature for combat models by closely relating effectiveness of the logistics system to determinants of success in combat. We present a stochastic diffusion model of an aerial battle between Blue and Red forces. The number of aircraft of Blue forces aloft and ready to be aloft on combat missions is limited by the maximum number of assigned aircraft, the reliability of aircraft subsystems, and the logistic system's ability to repair and replenish those subsystems. Our parsimonious model can illustrate important trade‐offs between logistics decision variables and operational success.     

Robust capacity planning in semiconductor manufacturing

We present a stochastic programming approach to capacity planning under demand uncertainty in semiconductor manufacturing. Given multiple demand scenarios together with associated probabilities, our aim is to identify a set of tools that is a good compromise for all these scenarios. More precisely, we formulate a mixed‐integer program in which expected value of the unmet demand is minimized subject to capacity and budget constraints. This is a difficult two‐stage stochastic mixed‐integer program which cannot be solved to optimality in a reasonable amount of time. We instead propose a heuristic that can produce near‐optimal solutions. Our heuristic strengthens the linear programming relaxation of the formulation with cutting planes and performs limited enumeration. Analyses of the results in some real‐life situations are also presented. © 2005 Wiley Periodicals, Inc. Naval Research Logistics, 2005.     

A stochastic approximation algorithm to compute bid prices for joint capacity allocation and overbooking over an airline network

In this article, we develop a stochastic approximation algorithm to find good bid price policies for the joint capacity allocation and overbooking problem over an airline network. Our approach is based on visualizing the total expected profit as a function of the bid prices and searching for a good set of bid prices by using the stochastic gradients of the total expected profit function. We show that the total expected profit function that we use is differentiable with respect to the bid prices and derive a simple expression that can be used to compute its stochastic gradients. We show that the iterates of our stochastic approximation algorithm converge to a stationary point of the total expected profit function with probability 1. Our computational experiments indicate that the bid prices computed by our approach perform significantly better than those computed by standard benchmark strategies and the performance of our approach is relatively insensitive to the frequency with which we recompute the bid prices over the planning horizon. © 2011 Wiley Periodicals, Inc. Naval Research Logistics, 2011     

脆性材料中的裂纹对组合梁剪切件滑移的影响

组合梁的承载能力受多种因素的影响,工程中通常采用强度条件进行设计,这种方法的实质是假定剪切联接件具有无限大的滑移能力。实际上,剪切联接件的超量滑移会引起梁的破坏。假设组合梁由脆性材料和韧性材料组合而成,在考虑脆性材料产生拉伸裂纹的情况下,用等效刚度法计算了剪切件的滑移量,进而得出组合梁的极限弯矩。