有源滤波器改进控制方法的仿真研究

有源滤波器通常采用常规的三角载波调制PWM控制方法，具有开关频率固定、输出波形谐波分量较少的优点，但响应速度比较慢、精度低。通过增加输入电压补偿来改进三角载波调制的PWM控制方法，可以提高有源滤波器的补偿精度和实时性，减少开关损耗。MATLAB/Simulink仿真验证了改进方案的可行性。     

基于BP神经网络的主成分分析法在效能评估中的应用

针对侦察效能评估中,指标因素的多样性和因素间的复杂关系,依据主成分分析的评估思路,运用BP神经网络对侦察效能进行评估.结合BP神经网络的逼近非线性函数的映射能力和并行处理的特点,解决数据样本的分类问题.通过对侦察效能的评估,验证了BP神经网络对效能评估的可行性,其方法和成果可供其它武器装备效能评估借鉴和参考.     

基于结构特征曲线的软岩隧道钢拱架力学效应研究

针对传统锚喷支护难以适应软岩隧道大变形的问题,文章通过把钢拱架和喷射混凝土同时工作分为钢拱架单独工作和联合工作两个阶段,利用SAP2000有限元程序研究了实腹式型钢拱架和空间钢桁架拱的力学特征及其单独工作的力学效应;考虑材料非线性与几何非线性,研究了钢拱架在不同支撑条件下的极限承载力和极限变形能力。结果表明:(1)将钢拱架单独工作作为支护的一个阶段是可行的;(2)侧向支撑及拱脚的约束情况对实腹式型钢拱架的作用效应有决定性影响;(3)空间钢桁架拱的整体刚度大于实腹式钢架拱,受侧向支撑影响小;(4)提出了提高钢拱架承载能力和变形能力的方法,为喷射混凝土及其它支护措施的实施提供了更多的时间和空间选择。     

海上设备材料腐蚀加速试验研究

开展了盐雾试验的严酷度对试验结果的加速性影响研究,通过采用不同材料的试样：铁板、铝板、不锈钢等。调节试验NaCl溶液的浓度、盐雾沉降量、试验温度、连续喷雾和间歇喷雾4个参数,在每个参数的不同严酷度下针对每个种类的样品进行盐雾腐蚀试验,分析试验后的腐蚀结果和程度并根据拟合分析得到不同严酷度对于每种样品的试验结果的加速影响效果。     

钳工技能实训课程教学设计

钳工技能实训是工科类专业开设的一门必修实践课,是高职院校培养技能人才不可缺少的教学环节。通过设置实践教学环节,以知识和技能为载体,主要培养学生个人综合素质、运用知识能力、善于发现问题并解决问题的能力,只有高质量的实训课程才能满足人才培养需求。从内容分析、学情分析、教学目标、教学重难点、教学策略和课程思政六个方面对钳工技能实训课程进行教学设计,对比教学效果,发现学生动手能力、学习兴趣和满意度都有很大提升。     

不同方法对南黄海重现波高计算值的影响

采用SWAN波浪模型对江苏南黄海地区1979~2018年共40 a的波况进行模拟及验证,将模拟结果与实测资料进行比对,吻合良好。百年重现波高分布通过基于年极值和月极值的广义极值分布函数(GEV)和超阈值取值方法(POT)的广义帕累托分布模型(GP)计算得出。计算结果表明,不同方法的计算结果在辐射沙洲北部地区差别最大,采用月极值所得重现波高偏小,采用年极值计算的重现波高在辐射沙洲南北外围地区最大,其余地区则以POT方法为大值。在分别采用不同数据长度计算重现波高的试验中得出,取月极值的GEV分布计算结果对时间跨度的改变不敏感,而取年极值受之影响最大,POT方法介于两者之间。     

交通管控措施对市域新冠疫情传播的阻断效果分析

面对局部暴发的新冠肺炎（COVID-19）疫情，进行城市交通管控是阻断疫情传播、控制疫情发展的重要途径。为了揭示不同交通管控措施对COVID-19传播的阻断效果，以不同阶段暴发疫情的荆州、孝感、荆门和石家庄4个行政市为研究区域，统计分析了市内道路封闭、客运交通停运和小区人口流动控制等3种典型交通管控措施实施前后的市域疫情传播趋势。基于经典的传染病动力学理论，考虑潜伏者传染性、人口迁徙、市内小区人口流动建立了市域COVID-19疫情传播SEIR优化模型，对比分析了4个行政市有/无交通管控措施以及不同交通管控措施对于疫情发展的阻断效果。研究结果表明：4个行政市的日发病率均与14 d前的迁入指数紧密相关；3种交通管控措施对阻断疫情传播效果明显，使荆州、孝感、荆门、石家庄无交通管控措施时的感染者峰值人数分别下降61.29%、53.71%、66.16%、66.33%；3种管控措施的阻断效果表现出一定的差异性，市内道路封闭措施的阻断效果最为明显，其不同实施节点可使市域潜伏者人数和感染者人数分别下降40.54%~70.88%和49.11%~64.34%。通过及时、全面地实施3种交通管控措施可以有效阻断疫情传播、控制市域疫情发展。考虑潜伏期特性的改进SEIR模型能够准确预测疫情发展趋势，可为疫情流行期间城市交通管控方案的制定提供技术参考。     

Does emission control area policy reduce sulfur dioxides concentration in Shanghai?

As an important measure to abate ship-source air emissions, the establishment of Emission Control Area (ECA) has been adopted not only at international level, but also at national and regional level. However, there exists a research gap of employing econometric models to enrich the ECA policy evaluation research by testing the effectiveness of an ECA policy based on the empirical data. This paper focuses on the effectiveness of the ECA policy in shanghai port by adopting regression discontinuity (RD) approach. The RD design is considered as a wonderful substitution for the randomized control trial, which usually serves as a conventional and effective tool to address endogeneity. The causal effect of the ECA policy on the SO₂ concentration reduction can be detected by the RD approach. According to the estimated results, there is a discontinuity around the ECA policy cutoff point, and it is indicated that the SO₂ concentration in Shanghai decreased by at least 0.229 μg/m³ daily on average due to the implementation of the ECA policy. The positive role that the ECA policy plays in reducing SO₂ concentration in Shanghai is well demonstrated. This paper also puts forward an agenda for the future studies in the domain of the ECA policy evaluation.     

Low-cycle fatigue assessment of offshore mooring chains under service loading

The integrity of mooring chains is essential to the safety of a range of offshore platforms. However, mooring line failures are occurring earlier than their design lives, with a high number of these failures occurring due to fatigue. Early in the fatigue life of the component fatigue initiation processes occur, where the fatigue hotspot is sensitive to the mean load and there is plastic strain accumulation from the multiaxial stress-strain responses of the material, leading to cyclic plastic damage accumulation. The traditional SN approach suggested by mooring standards does not consider these effects, and it is proposed that this lack of consideration under low-cycle fatigue conditions is the reason for the current non-conservative fatigue assessments of mooring chains. This paper aims to develop a fatigue approach based on a critical plane multiaxial fatigue criterion for mooring chains that can consider the damage-induced by the cyclic plasticity and the mean load effect, to investigate the importance of incorporating low-cycle fatigue into the mooring chain life prediction. To develop the critical plane approach, the multiaxial stress-strain states are extracted for the critical plane at the fatigue hotspot from a finite element model of a mooring chain. This is then correlated with a fatigue life prediction provided by conventional fatigue design data. It uses a simulation of an FPSO as a case study to demonstrate the importance of low cycle fatigue, which shows that the mean load effect is significant in reducing the fatigue life for mooring chain applications, while the effect of fatigue damage-induced cyclic plasticity is limited. The fatigue damage accumulation predicted by the critical plane approach is significantly higher than that of the traditional SN approach and should be accounted for in mooring line design.     

基础设施公私合营模式融资影响因素及空间溢出效应研究

在城市层面，影响基础设施PPP(公私合营模式)项目融资额的因素具有多样性。本文基于 2015—2017年我国地级市面板数据，采用空间回归模型对地级市基础设施PPP项目融资额的影 响因素进行实证分析，并验证了PPP项目融资额在空间层面具有溢出效应。研究结果表明：空间 误差模型相比混合OLS回归模型，对于分析PPP项目融资额影响因素的拟合效果更好；PPP项目 融资额在城市层面上具有显著的正向空间溢出效应，即一个城市PPP项目融资额更容易受到相 邻城市PPP项目融资额的影响。地方政府财政缺口、地区生产总值、固定资产投资额、人口密度 对PPP项目融资额虽然都具有显著相关关系，但在不同地区间影响的差异性较大。地方政府财 政缺口在中东部城市与PPP项目融资额呈现显著正相关，即地方政府财政缺口越大，城市越倾向 于采用PPP模式进行基础设施投融资；而在西部城市，两者间这种相关关系则不显著。