Numerical analysis of hydrodynamic behaviors of two net cages with grid mooring system under wave action

Based on rigid kinematics theory and lumped mass method,a mathematical model of the two net cages of grid mooring system under waves is developed.In order to verify the numerical model,a series of physical model tests have been carried out.According to the comparisons between the simulated and the experimental results,it can be found that the simulated and the experimental results agree well in each wave condition.Then,the forces on the mooring lines and the floating collar movement are calculated under different wave conditions.Numerical results show that under the same condition,the forces on the bridle ropes are the largest,followed by forces on the main ropes and the grid ropes.The horizontal and the vertical float collar motion amplitudes increase with the increase of wave height,while the relationship of the horizontal motion amplitude and the wave period is indistinct.The vertical motion amplitude of the two cages is almost the same,while on the respect of horizontal motion amplitude,cage B(behind cage A,as shown in Fig.4) moves much farther than cage A under the same wave condition.The inclination angle of the floating system both in clockwise along y axis and the counter one enlarges a little with the increase of wave height.     

有耗介质探地雷达波传播衰减特性的研究

探地雷达是利用超高频脉冲电磁波探测地下介质分布的一种浅层地球物理勘探方法,探地雷达超高频、宽频带脉冲电磁波在地下有耗介质中的衰减特性是一个十分复杂的过程。本文从电磁波传播的麦克斯韦方程出发,较为系统地研究和分析了雷达脉冲电磁波在有耗介质中传播的衰减特性,对研究雷达脉冲电磁波在地下有耗介质中的传播机制有指导意义。     

结构地震行波效应分析综述

从时域和频域两个方面介绍了行波效应下结构地震响应的各种分析方法及各方法的优缺点和适用范围,后对桥梁结构、大跨空间结构、普通建筑结构、大坝结构、地下结构等各类结构体系在行波效应下的结构地震响应特征作了简要总结,阐述了国内外在行波效应研究中已取得的成果和结论,并对未来研究重点问题提出了自己的见解。     

双系煤层开采相互影响下的覆岩运动与破坏规律分析

以大同矿区同忻煤矿为例,利用关键层理论、物理探测技术和数值模拟,分析双系煤层开采形成的覆岩运动与破坏规律。研究结果表明：（1）石炭二叠系煤层工作面推进至193 m时,覆岩裂隙带发育高度达到最大为174.7 m;（2）物理探测得到3-5^#煤层开采引起的覆岩垮裂带高度约为180 m,综合理论计算与现场实测,确定覆岩裂隙带发育高度与采厚之比为11.7-12.0;（3）侏罗系煤层开采引起的底板破坏及双系间覆岩软弱夹层的缺失为双系煤层采空区联通进一步提供了条件;（4）侏罗系煤层的开采影响石炭二叠系煤层工作面超前支承压力的分布规律,当石炭系煤层工作面位于侏罗系煤层遗留煤柱下方时,超前支撑压力较无采空区时增大12.4%;（5）研究成果揭示了双系开采相互影响关系,为采取安全开采措施、减弱双系开采相互影响程度提供了科学依据。     

发达国家通勤影响个人健康的研究综述与展望

随着社会经济的不断发展,健康问题已经越来越受到大家的关注。通勤作为居民每日的重要出行活动,是时间利用中的重要组成部分。近些年,城市交通状况开始不断恶化,糟糕的通勤形势逐渐对个人的健康状况构成威胁。发达国家较早开始了对于该问题的关注,已取得丰富的研究成果。相较之下,国内关于通勤影响个人健康的文献则相对缺乏。本文主要从个人心理健康、客观健康、健康行为三个维度,对西方发达国家通勤时间、通勤距离、通勤方式等通勤行对个人健康影响的相关文献进行了系统梳理与评述,并对未来研究进行展望,以期能够为我国城市通勤领域的研究提供新的视角与借鉴。     

冻结粉质黏土三轴抗压强度和变形特性试验研究

通过对-6℃冻结粉质黏土在1～9 MPa的围压范围内进行一系列的三轴压缩试验,分析了冻土的变形和强度特性.结果表明：不同围压下,冻结粉质黏土的应力-应变曲线形态基本相似,而软化程度及初始阶段的硬化速率则有所不同.根据摩尔-库仑准则,得到广义黏聚力和广义内摩擦角随围压的变化规律,同时基于包络线理论建立非线性强度准则,以描述冻结粉质黏土强度随围压先增大后减小的变化规律.     

基于农户行为的耕地质量评价指标体系 构建的理论与方法

从农户土地利用目标变化相关理论出发, 依据在不同经济发展阶段下, 农户土地利用目 标的产量最大化、产量与利润最优化和利润最大化三个阶段的变化特征, 创建了基于农户土地利 用目标变化的“压力- 状态- 效应- 响应”逻辑框架模型; 并据不同经济发展阶段下的“压力- 状态- 效应- 响应”的变化特征, 构建了基于农户土地利用目标变化的耕地质量评价指标体系。这一评价 指标体系的建立为我国在不同经济发展阶段下, 从农户尺度上进行耕地质量保护提供政策依据。     

行波效应对大跨度空间结构随机地震响应的影响

深入研究了行波效应对大跨度空间结构随机地震响应的影响,进一步完善了大跨度空间结构随机地震响应分析理论。推导了双支座、单自由度体系地震响应功率谱密度函数的解析表达式,研究了不同频率体系的响应峰值随地面视波速的变化规律,分析了多支撑点、多自由度体系的地震响应功率谱矩阵的特点,发现多自由度体系地震响应随地面视波速的变化规律与单自由度体系相似。数值模拟了某体育馆网壳结构在不同地面视波速情况下的随机地震响应,结果表明,考虑地震动行波效应后,结构地震响应随地面视波速的变化而显著变化,当视波速较低时其变化规律很复杂;且支撑点附近、受拟静力位移影响较大的部分杆件的地震响应明显增大,远离支撑点处、受拟静力位移影响较小的部分杆件的地震响应稍有减小。由此得出结论,对于大跨度空间结构的随机地震响应分析,必须考虑地震动的行波效应,尤其当受拟静力位移影响较大的部分杆件对结构抗震设计起控制作用时;且应对可能出现的地面视波速进行全面分析,作为结构抗震设计依据。     

不同文化群体来华游客认知评价的差异性研究——以六大旅游热点城市为例

基于市场抽样调查的结果数据,按照客源地的地域、文化特征将来华外国游客主要分为4个文化群体:欧洲文化群(主要包括英、法、荷、德、意、西)、东亚文化群(日、韩)、北美文化群(美国、加拿大)和澳洲文化群(澳大利亚、新西兰),通过建立数学模型,运用EXCEL和SPSS统计软件,归纳分析各个文化群体游客的文化表象以及特征,对来华游客的旅游认知评价行为的一般模式进行了理论上的研究;分析了旅游认知评价行为的规律,探讨来华不同文化群体游客的认知评价的差异性.     

Impacts and effects of government regulation on farmers’ responses to drought: A case study of North China Plain

Frequent extreme weather events like drought, etc. in the context of climate change present huge challenges to agricultural production. To find out if farmers have taken measures against them and identify governments’ impact on their response measures are the foundation of and key to further improving relevant policies and farmers’ responsiveness. Taking the North China Plain as an example, the study analyzes farmers’ responses to frequent climate change-induced drought, and assesses the impacts of governments’ early-warning, policy support and other factors on farmers’ responses based on questionnaire survey data and an econometric approach. The results show that: (1) Farmers are responsive to drought, and they are more likely to take measures as the degree of drought deepening. (2) Governments’ regulation affects farmers’ responses, although only part of its regulation measures has remarkable effects. Governments’ early-warning messages can increase the possibility of farmers’ responding to drought, however, only when they get the early-warning in all the processes including before, during, and after disasters can the effects be significant. Currently, as the primary channel through which early-warning information is released, television cannot change farmers’ behaviors significantly. Early-warning is most effective when spread via two or more types of channels. In addition, governments’ (especially town and village level institutions’) policy support has certain impacts on farmers’ responses to drought, yet with less prominent effects in disaster years than in normal years; to provide subsidies, as a regulation measure, can encourage farmers’ initiative a lot in adopting response measures, but most of the farmers haven’t got support from any institutions. Both the structure and strength of government regulation need to be improved. (3) Farmers with different conditions respond differently. Farmer households in irrigation areas, those whose farmland is lower fragmented, and those with numerous agricultural family members tend to take response measures. The study can provide scientific reference to the making of relevant regulation policies under the background of acidifications.