四阶非线性方程两点边值问题解的存在性

利用上下解理论研究了两类四阶非线性方程两点边值问题解的存在性。     

基于中频化的船舶电力系统研究

为了解决现代船舶由于设计复杂造成的电力系统质量过大,空间及电站容量不足等缺点,给出了解决方案.阐述了基于400 Hz中频化船舶电力系统在节约质量、空间等方面问题的分析和研究.     

西门子小型PLC系统中的PPI通讯网络

运用西门子PLC中的PPI(点对点)通信协议,构成以西门子s7-200PLC为核心的水处理系统中主从式通讯网络.以其中部分站点为例,详细介绍了PPI通讯物理层的制作和连接方法,同时给出了参数设置选择及软件设计方法.     

焊接热输入量对E36高强度钢接头金相组织及机械性能的影响

针对E36高强度钢,通过对不同焊接参数下焊接接头金相组织的变化和机械性能的影响进行分析研究,结果发现若焊接参数选择不当,焊接过程过大的热输入会造成焊接接头金相组织的变化,碳化物在晶界聚集偏析,从而极大降低了接头的冲击性能,导致冲击值极低,而抗拉强度和弯曲无明显影响.     

Changes in the design and operational wind due to climate change at the Indian offshore sites

The increasing global warming is most likely to affect the magnitude and pattern of wind at a regional level and such an effect may or not follow the trend predicted at the global scale. Regional level exercises are therefore necessary while making decisions related to engineering infrastructure. In this paper an attempt is made to know the extent of change in design as well as operational wind conditions at two offshore locations along the west coast of India. The design wind speeds with return periods of 10, 50 and 100 years derived for two 30-year time slices in the past and future are compared. In two separate exercises the past and future wind at the local level is simulated by empirical downscaling as well as by interpolation of the general circulation model (GCM) output. Both sets of past and future data are fitted to the Generalized Pareto as well as Weibull distributions using the peak over threshold method to extract long term wind speeds with a specified return. It is noticed that at the given locations the operational and design wind may undergo an increase of around 11%–14% when no downscaling is adopted and 14%–17% when the GCM data are downscaled. Although these figures may suffer from a certain level of statistical uncertainty the study points out to take a relook into the safety margins kept in the design and operation of ocean structures in the light of global warming.     

城市轨道交通工程重大变动环境影响评价管理初探

对2011—2014年环保部审批的31个城市轨道交通变更环评项目进行系统梳理,总结其主要变更情况。结合最新的变更环评管理要求,从性质、规模、地点、采用的生产工艺以及环保措施等5个方面对城市轨道交通主要变更情况进行分类,并提出其重大变动的界定条件。分析总结城市轨道交通变更环评的重点评价内容。最后,从国家和地方2个层面提出对策措施,并建议强化环境监理和出台相关指导性文件,以期提高城市轨道交通环境管理水平。     

有偏好的多属性灰色关联路径选择模型

路径选择模型是动态交通诱导的核心问题.针对出行者不同偏好及路径属性不 完全确定条件下,提出了一种路径属性为区间值的有偏好路径选择模型.建立了以交通拥 挤程度、行程时间、行程距离和行程时间可靠性为属性的路径选择指标体系,给定路径属 性的区间值及出行者偏好值,计算每条路径客观信息与主观偏好的灰色关联系数.为了减 少主观偏好与客观信息的偏差,构建了单目标最优化模型,得到路径属性的权重值,进而 求得各路径主观偏好与客观信息的关联度,并根据关联度大小进行排序.最后以福州三坊 七巷交通网络为例,给出路径选择实例.结果表明该方法简单有效.     

Wave impact underneath horizontal decks

The problem of water impact on a fixed horizontal platform deck from regular incident waves was studied. Two-dimensional potential flow was assumed, and the resulting boundary-value problem was solved by three alternative numerical methods, a method based on a generalization of the impact theory by Wagner, and two different nonlinear boundary-element methods. The Wagner-based method used a von Karman approach during the water exit phase, i.e., when the wetted surface decreases. Experiments of the impact on an idealized platform deck have been performed to validate the theory. Comparisons show that the Wagner-based method yields good results for the water entry phase, when the wetted deck area increases, but poor results when the wetted area diminishes. The boundary-element methods compare well with experiments for the entire impact process. A Kutta condition is necessary at the aft body–free surface intersection during water exit and when the flow separates from the aft edge. Gravity effects matter for the water exit phase.     

高速铁路环境振动控制限值

现行标准GB10070—1988《城市区域环境振动标准》中,对铁路干线两侧的限值规定是在20世纪80年代根据当时既有普速铁路制订的,没有考虑高速铁路的特点,不适合评价高速铁路。根据国外的有关标准和我国研究成果,笔者认为高速铁路环境振动评价宜采用86 dB作为控制限值。     

大气颗粒物对人体健康影响研究进展

近年来,越来越多的流行病学研究表明,大气颗粒物浓度水平与健康效应终点呈正相关关系。本文对大气颗粒物污染对健康影响的急性和慢性作用的研究进展进行了综述,并分别对颗粒物阈值、质量浓度和计数浓度对人体健康影响以及贫困在颗粒物污染健康影响中的作用这3个热点问题进行了讨论,最后提出了今后的研究方向。