IR-UWB系统几种新型调制技术

IR-UWB(Impulse Radio-Ultra wide Bandwidth,冲激无线电-超宽带技术)是短距离无线通信中一个非常有前景的技术.该文介绍了几种有关IR-UWB信号的比较新型的调制技术,例如伪混沌编码跳时调制、脉冲位置幅度调制、自适应调制等,分析了其调制方法的基本原理,并给出了误码率分析.     

基于卷积神经网络的低截获概率雷达信号检测算法

为了解决雷达截获接收机对低截获概率(LPI)雷达信号检测效果不理想的问题,针对截获信号中有效信号脉宽长度来定义信号和噪声,该文提出一种基于卷积神经网络(CNN)的LPI雷达信号检测方法,利用卷积核与匹配滤波器结构上的相似性,在低信噪比下能够提高信号的检测准确率。利用大量的基于4种典型LPI雷达信号(线性调频信号(LFM)、非线性调频信号(NLFM)、二相编码信号(BPSK)、COSTAS频率编码信号)和白噪声信号的模拟数据集进行CNN模型训练,同时增加少量实测信号(LFM, BPSK)作为验证集进行适配,更好地拟合实测信号的检测模型。最终利用实际信号进行测试,实验结果表明：该文算法在低信噪比的情况下具有较好的检测效果,对多种调制方式、不同信噪比下的LPI雷达信号具有泛化能力。     

计划评审技术工序综合重要度分析方法

针对如何识别影响整个项目进度的关键工序的问题,提出了面向计划评审技术(PERT)的工序综合重要度分析方法.首先将PERT中工序按照时序关系划分为始工序节点、终工序节点、紧前工序节点和紧后工序节点,并给出了对应工序时间的概率分布计算方法.然后,基于PERT中不同工序对项目整体进度的影响程度,提出了工序综合重要度分析方法,并研究了基于工序综合重要度的PERT关键工序识别方法.最后,以神舟飞船研制过程甘特图为例说明了基于工序综合重要度的关键工序识别过程,验证了工序综合重要度与工序持续时间之间的关联关系.     

Time-Dependent Reliability of PSC Box-Girder Bridge Considering Creep, Shrinkage, and Corrosion

Bridge performance undergoes time-varying changes when exposed to aggressive environments. While much work has been done on bridge reliability under corrosion, little is known about the effects of creep and shrinkage on the reliability of concrete bridges. In this paper, the CEB-FIP model for creep and shrinkage is applied by using finite-element (FE) analysis in conjunction with probabilistic considerations. Verification is made by comparing the analytical findings with existing test data. More specifically, a time-dependent reliability assessment is made for a composite prestressed concrete (PSC) box-girder bridge exposed to a chloride environment. This realized via an advanced probabilistic FE method. The postcracking behavior of the thin-walled box girder is described using composite degenerated shell elements, and importance sampling is used to improve the efficiency of the reliability analyses. It is shown that concrete creep and shrinkage dominate during the early stages of bridge structure deterioration. This is accompanied by a decrease in reliability owing to the combined action of creep, shrinkage, and corrosion. The reliability indexes for the serviceability and the tendon yielding limit state fall below the target levels prior to the expected service life. Therefore, early maintenance and/or repair measures are required.     

概率法在页岩气未开发最终可采量评估中的应用——以北美某成熟页岩气区块为例

中国实现页岩气规模开发的时间不长,页岩气最终可采量(EUR)评估方法研究尚处于不断积累和完善的阶段,尤其是评估准确度较高的概率法应用还不普遍。为此,在分析评价页岩气EUR评估方法的基础上,应用改进双曲递减模型预测了北美某成熟页岩气区块内在产井的EUR并建立其概率分布,基于上述结果应用概率法模拟新井的未开发EUR,并分4种情形(目标概率、项目风险、项目对比、更合理的EUR评估)对概率法的合理使用及其应用效果进行了详细阐述。研究结果表明:(1)随着页岩气开发项目的推进,生产井数的增加、开采技术的成熟,概率法所需的具有合理置信度水平的类比井组可以建立起来,为应用概率法评估未开发EUR奠定了基础;(2)页岩气项目未开发EUR在部分程度上受总井数的影响,未来钻井数量减少会增加未开发EUR的不确定性,相反钻井数量增加则可以减少未开发EUR的不确定性;(3)概率法具备定量描述不同级别未开发EUR的可能性,定量反映项目存在的不确定性和风险,通过对不同项目的不确定性及风险进行对比,可以为项目的鉴别和决策提供依据。结论认为,随着页岩气生产井数的增加和开采技术的成熟,采用概率法对页岩气项目未开发EUR进行评估是更为合理可靠的选择。     

基于狼群算法的概率积分法模型参数反演方法研究

概率积分法模型属于典型的多元复杂非线性函数,且部分参数存在相关性,使得概率积分法模型参数反演一直是开采沉陷数据处理的热点问题和难点问题。WPA(狼群算法)作为一种新群体智能算法,已在多维背包求解问题、水电站水库优化调度以及旅行商等复杂非线性最优化问题中得到成功应用,但在开采沉陷数据处理领域尚未见文献报道。鉴于此,本文首次将WPA引入概率积分法模型参数反演中,构建了基于WPA的概率积分法模型参数反演方法。研究结果表明:WPA反演概率积分法模型参数具有较高的准确度、较好的精度、良好的稳健性,且满足工程应用标准。本文研究成果对概率积分法模型参数精准反演具有重要参考价值。     

Comparison of interwell connectivity predictions using percolation, geometrical, and Monte Carlo models

Reservoir connectivity is often an important consideration for reservoir management. For example, connectivity controls waterflood sweep efficiency and it affects decisions concerning well placement and spacing. The uncertainty of sandbody distributions, however, can make interwell connectivity prediction extremely difficult. Percolation models are a useful tool to simulate sandbody connectivity behavior to estimate interwell connectivity.This study applies a percolation method to estimate interwell connectivity. Using results derived by Andrade, King, and others for fluid travel time between locations in a percolation model, we develop a method to estimate interwell connectivity. Four parameters are needed to use this approach: the net-to-gross ratio p_sand, the typical sandbody size, reservoir length and well spacing. To evaluate this new percolation method, the results are compared to results from geometrical models, Monte Carlo, and reservoir simulation.These methods were applied to estimate interwell connectivity for three non-communicating stratigraphic intervals in Monument Butte oil field, Utah. The results suggest that the percolation method can estimate the probability of interwell connectivity reliably for thin intervals for any values of p_sand, well spacing, and reservoir length. The geometrical model also performs well, but can only be applied in fields where the well spacing is less than one-half of the sandbody size.The proposed method requires that the reservoir interval for evaluation be sufficiently thin so that 2D percolation results can be applied. For thick intervals or heterogeneous sandbody distributions, the percolation method developed here is not suitable because it assumes thin layers. Future percolation research will be needed to adapt this new method to 3D cases.     

Life Expectancy Evaluation of the Wood Poles Which Support the Hellenic Electrical Distribution Network

The Hellenic electrical distribution lines have been basically supported with the use of wood poles. Outages due to aging, degradation, or broken wood poles may infer significant costs due to repair and loss of energy to consumers. Lifetime estimation of wood poles is significant for maintenance and replacement decisions at the power utility. The paper presents a methodology, based on a statistical analysis, for the evaluation of the life expectancy and the production of a survival curve of a typical Hellenic distribution wood pole in-service. The proposed methodology intends to minimize the life-cycle cost of inspection and refurbishment of wood poles in the distribution network of Hellas, something that is really important in the new competitive and liberating Hellenic electrical energy market.     

Assessment of odorous VOCs released from a main MSW landfill site in Istanbul-Turkey via a modelling approach

An air pollution modeling study was conducted to investigate the odorous effects of volatile organic compounds (VOCs) emissions from a sanitary landfill area on ambient air quality. The atmospheric dispersion of hydrogen sulfide (H₂S) and 22 VOCs was modeled. Industrial Source Complex v3 Short Term (ISCST3) model was used to estimate hourly concentrations of odorous VOCs over the nearest residential area. Odor thresholds of VOCs of interest were also found in the literature. Results showed that short-term averages of three odorous VOCs, namely ethyl mercaptan, methyl mercaptan and hydrogen sulfide, exceeded their odor thresholds, which are reported to be 0.022, 0.138 and 11.1 μg/m³, respectively, at several points within the domain. Their highest concentrations within Gokturk County were estimated to be 0.09387 μg/m³ for ethyl mercaptan, 0.07934 μg/m³ for methyl mercaptan and 6.315 μg/m³ for hydrogen sulfide. Short-term model results revealed the occasional odor problems being reported for Gokturk County. Hourly concentrations were used to obtain frequencies of odor episodes in Gokturk County via a probability analysis. The results showed that ethyl mercaptan concentrations did not exceed its odor threshold during more than 8.84% of the time. Similarly, the maximum odor episode frequencies for methyl mercaptan and hydrogen sulfide were 0.98% and 0.34% of the time, respectively.     

Water Treatment Units Residence-Time Distributions as Probabilistic Functions

A probabilistic approach to obtain theoretical residence-time distribution (RTD) functions for series of reactors with possible stagnation, bypassing, and recycle is presented. It is shown that most known RTD functions can be obtained from probability arguments alone, thus avoiding abstract Laplace transform mathematical techniques and providing additional physical insight. Several new RTD models for reactors in series are derived, based exclusively on using the binomial probability distribution to describe the passage of a particle through the treatment train with bypassing and stagnation possible at each individual reactor. The proposed RTD models are validated with travel time computer simulation of a large number of particles through the series of reactors. A MSExcel based computer procedure was programmed to obtain the nonideal flow parameters by minimizing the squared sum of the differences between tracer test data and the derived unit’s RTD function. The least squares parameter estimation procedure was used to fit theoretical RTDs to tracer data collected from real water treatment units with different hydraulic behavior at two locations in Mexico.