随机模型估算分期设计洪水的初探

本文尝试将随机模型用于估算分期设计洪水,提出了一种具体方法。该法的主要优点在于能充分利用样本信息,成果使用方便。文中举例说明了建议方法的应用,并和传统方法作了比较。     

随机过程的均方连续性

全面探讨了随机过程均方连续的若干性质，并应用这些性质，研究了平稳随机过程、泊松过程、维纳过程的均方连续性。     

泊松过程的随机模拟及参数估计

研究了泊松过程的随机模拟，给出泊松过程的最大后验密度可信区间，借助Matlab软件对此展开探讨并给出了模拟程序。     

基于非齐次泊松过程的软件可靠性增长模型

非齐次泊松过程软件可靠性增长模型是评测软机可靠性的重要工具,影响软件可靠性的2个重要参数是软件中初始的故障数和故障检测率.通过对软件错误分布进行定义,建立了非齐次泊松过程软件可靠性模型,并对不同参数下的模型进行了分析和比较.讨论了非齐次泊松过程模型的使用条件,对模型初始的故障数和故障检测率参数进行了推导,并给出了评估方法.     

复合泊松分布和泊松过程的可加性

在泊松分布可加性基础上,应用特征函数,证明了与泊松分布有着紧密联系,分别在精算数学和随机过程领域中有着广泛应用的复合泊松分布和泊松过程也具有类似的可加性.     

泊松过程中到达时刻条件分布的推广

将泊松过程到达时刻W1,W2,…,Wn,当Wn=μ时的条件分布从两个方面进行了推广,一是将它推广到Wk=μ(k=1,2,…,n)时的条件分布情形,二是将它推广到非齐次泊松过程到达时刻的条件分布情形.     

非平稳随机振动中首次越界问题的随机游动法

给出了计算机随机振动中首次越界概率的简便快速的数值解法，该方法依赖于振幅响应过程Ａ（ｔ）的Ｍａｒｋｏｖ性以及它所满足的Ｆｏｋｋｅｒ－Ｐｌａｎｃｋ方程，通过建立了一扩散过程的随机游动模型，Ｆｏｋｋｅｒ－Ｐｌａｎｃｋ方程的数值解被极大的简化。     

泊松过程在用户上下线模型中的应用

提出了基于非齐次泊松过程的宽带拨号上网(ADSL)用户上下线模型.对用户上下线行为进行建模,并基于现网真实数据,使用模型计算用户24 h内的每时刻退出登录的平均概率,将模型的预测值与现网实测数据进行对比,分析了不同用户组退出登录概率一天内的变化和持续在线平均概率的变化.分析结果表明,提出的ADSL宽带用户上下线模型可以有效、量化地描述用户上下线行为,在ADSL宽带用户上下线行为的异常检测和舆情分析等领域具有较好的工程应用价值.     

保费收取次数为负二项随机序列的复合泊松风险模型的破产概率

在经典的风险模型的基础上，考虑保费收取次数为负二项随机序列且保单的保费为随机变量，而索赔过程为复合Poisson过程时的情形，得到了破产概率以及Lundberg不等式．     

A stochastic model of bubble distribution in gas-solid fluidized beds

On the basis of the Langevin equation and the Fokker-Planck equation, a stochastic model of bubble distribution in a gas-solid fluidized bed was developed. A fluidized bed with a cross section of 0.3 m×0.02 m and a height of 0.8m was used to investigate the bubble distribution with the photographic method. Two distributors were used with orifice diameters of 3 and 6 mm and opening ratios of 6.4% and 6.8%, respectively. The particles were color glass beads with diameters of 0.3, 0.5 and 0.8 mm (Geldart group B particles). The model predictions are reasonable in accordance with the experiment data. The research results indicated that the distribution of bubble concentration was affected by the particle diameter, the fluidizing velocity, and the distributor style. The fluctuation extension of the distribution of bubble concentration narrowed as the particle diameter, fluidizing velocity and opening ratio of the distributor increased. For a given distributor and given particles the distribution was relatively steady along the bed height as the fluidizing velocity changed.     

窄隙自然循环过冷沸腾流道中的温度分布特性

针对一体化反应堆的窄通道和自然循环特点,在常压下,以水为工质,对竖直窄环隙流道进行了自然循环过冷沸腾换热实验研究,通过对流道内温度的测量,考察了入口过冷度、流道间隙和加热负荷对流道内温度分布的影响.结果表明,在中低负荷区,流体的截面温度基本不受加热负荷的影响,入口过冷度使轴向壁温分布呈现非单调性变化,在一定条件下会引起沸腾区壁温的逆向升高,减小流道间隙或增大加热负荷有助于弱化入口过冷度的影响,减小流道间隙还有利于降低壁面温度,但流道间隙也不宜过小.     

水库坝前水温结构日变化规律研究

水库水温结构受来流水温和气象要素的影响,在年内呈现周期性变化,但对其日内变化规律的认识较为缺乏。以龙滩水库为研究对象,于2011年11月～2012年9月分六期对龙滩水库坝前水温进行了原型观测。资料分析结果表明：龙滩水库库区水温除1月外,其余各月均存在分层现象,在7月和9月出现了双温跃层;表层水温年内变化较大,库底水温全年较为稳定;气象要素对坝前水温影响深度与季节有关,夏季影响深度最大;气温越高水温最大值出现的时间越早;水温结构日变化的影响因素主要是气温和太阳辐射,此外坝前水温结构日内变化明显的范围仅为库表20m以内,表层水温的日内变化几乎不对电站发电取水水温构成影响。     

中国气候变化敏感区气温变化对比

近50 a来全球气候变化已经是当今自然科学重大课题之一,中国的区域响应也日渐引人关注.依据黑龙江、新疆、西藏3省区93个国家基准或基本气象站1961—2008年的日气温数据,就年均气温及四季气温变化过程和特征进行了对比分析.3省区增温幅度分别为1.71,1.20,1.15℃,且线性趋势明显;增温过程方面,黑龙江和西藏均为持续增温,而新疆增温、降温过程动荡大;季节对比可知,虽然黑龙江以冬春、新疆和西藏以秋冬增温最强,但冬季的贡献率都最为显著,分别为38.35%,38.73%和36.75%.     

富水砂卵石地层地铁联络横通道人工冻结数值分析

人工地层冻结法作为一种常用的土层加固方法,被广泛应用于煤矿、地铁等地下结构工程中。成都地区的砂卵石地层含水量丰富,渗透系数大,实施冻结法难度更大。以成都地铁10号线某隧道区间为工程依托,研究采用人工冻结法在砂卵石地层中修建联络横通道的问题。对冻结工程进行现场监测,根据冻结管实际布置形式建立考虑冰水相变的非线性三维弹塑性热—力耦合数值模型,通过现场监测和数值模拟两种手段对积极冻结期温度场和位移场的发展及分布规律进行研究。结果表明：数值模拟结果与现场监测数据吻合较好,建立的数值模型比较可靠;冻结壁交圈时间是冻胀变形快速增长的临界时间点,交圈时间约为25 d;冻结43.7 d时冻结壁厚度达到2 m,在37.8 d时冻结壁内平均温度达到-10 ℃,满足后续开挖施工要求。     

U型通风采场的温度场相似实验模型

为了预测采动影响下采场温度分布状态,建立了U型通风采场的温度场实验台以模拟采场中的热输运现象.基于采场内流场与温度场数学模型,提出了选取α2rxr/u2r=α3rd2nr/ur=xr/pfr和xr/urTr=1/qr作为模型的相似关系式,确定了模型中独立变量的合理取值,论证了为使温度场相同而应满足的热源项的比例关系.模拟U型通风采场的氧化带局部区域自热工况的实验结果表明:采场温度场分布趋势与数值模拟及现场实测结果吻合较好,均呈现由进风口到回风口先上升再下降的分布规律,并在采空区倾向中心线偏回风口20～30m处出现温度峰值,实验台能够合理再现实际采场的热交换过程.     

摩擦制动器接触表面温度计算模型

应用局部热流和整体热流的概念,将接触表面的温升划分为名义表面温升和局部温升,从而建立了摩擦制动器接触表面的温度计算模型．建立模型中考虑了制动盘的有限尺寸和摩擦产生的摩擦热在制动过程中沿制动盘同一摩擦半径重复的实际情况,使该模型更接近于实际制动工况．     

热轧带钢精轧过程的混合温度模型

结合现场数据采集系统的实测数据,应用差分法替换精轧温度设定系统中计算误差较大的轧制传导温度模型,根据带钢各层温度的分布特点提出变长和变厚度网格划分的方法;对原精轧温度设定系统中空冷温降模型的辐射系数进行离线的钢种和厚度等级修正,并建立新的指数水冷温降模型,在线调整对流换热系数.由此构建的混合温度模型在保证计算速度的同时大幅度提高了预测精度.为满足现场生产精度和稳定性的需要,采用“接力式”初始化训练方法,建立了神经网络自学习系统.结果表明,改造后精轧温度设定系统的预测精度比原系统高,并且在变钢种、变规格轧制时误差波动小.     

Spatio-temporal variation and propagation direction of coal fire in Jharia Coalfield,India by satellite-based multi-temporal night-time land surface temperature imaging

In this paper, the spatio-temporal variation and propagation direction of coal fire were studied in the Jharia Coalfield(JCF), India during 2006–2015 through satellite-based night-time land surface temperature(LST) imaging. The LST was retrieved from Advanced Spaceborne Thermal Emission and Reflection Radiometer(ASTER) night-time thermal-infrared data by a robust split-window algorithm based on scene-specific regression coefficients, band-specific hybrid emissivity, and night-time atmospheric transmittance. The LST-profile-based coal fire detection algorithm was formulated through statistical analysis of the LST values along multiple transects across diverse coal fire locations in the JCF in order to compute date-specific threshold temperatures for separating thermally-anomalous and background pixels. This algorithm efficiently separates surface fire, subsurface fire, and thermally-anomalous transitional pixels.During the observation period, it was noticed that the coal fire area increased significantly, which resulted from new coal fire at many places owing to extensive opencast-mining operations. It was observed that the fire propagation occurred primarily along the dip direction of the coal seams. At places,lateral-propagation of limited spatial extent was also observed along the strike direction possibly due to spatial continuity of the coal seams along strike. Moreover, the opencast-mining activities carried out during 2009–2015 and the structurally weak planes facilitated the fire propagation.     

Two-stage numerical simulation for temperature profile in furnace of tangentially fired pulverized coal boiler

Considering the fact that the temperature distribution in furnace of a tangential fired pulverized coal boiler is difficult to be measured and monitored, two-stage numerical simulation method was put forward. First, multifield coupling simulation in typical work conditions was carried out off-line with the software CFX-4.3, and then the expression of temperature profile varying with operating parameter was obtained. According to real-time operating parameters, the temperature at arbitrary point of the furnace can be calculated by using this expression. Thus the temperature profile can be shown on-line and monitoring for combustion state in the furnace is realized. The simulation model was checked by the parameters measured in an operating boiler, DO130-9. 8/540. The maximum of relative error is less than 12% and the absolute error is less than 120℃, which shows that the proposed two-stage simulation method is reliable and able to satisfy the requirement of industrial application.