弹性支承块轨道结构落轴冲击动力性能分析

将轮轨接触边界条件用罚函数法释放,采用点面接触单元导出轮轨接触有限元控制方程,建立轨道结构落轴冲击动力有限元方程。分析落轴冲击对轨道结构产生的动态响应,比较弹性支承块及短轨枕埋入式整体道床轨道结构的动力性能,并用现场实测数据进行验证。结果表明:弹性支承块轨道结构与普通短轨枕结构相比,其轨下及块下刚度易于调整,可进行双层弹性的合理匹配,从而有效吸收轮轨冲击,提高列车运行平稳性,具有减振降噪与延缓轮轨磨损等优越性能。建议其块下刚度稍大于轨下刚度,增幅值控制在20%以内。     

An approach to estimating the hull girder response of a ship due to springing

This article describes an estimation method for the hull girder response of a ship due to springing. The linear and nonlinear springing effects on the hull girder are evaluated. Previous studies on the springing response focused mainly on the symmetric response, or vertical response. In this article, however, the springing analysis is extended to asymmetric responses, or horizontal and torsional responses. The Timoshenko beam model was used to calculate the hull girder response and the quadratic strip method was employed to calculate hydrodynamic forces and moments on the hull. To remove irregular frequencies, a rigid lid was adopted on the hull free surface level and hydrodynamic coefficients were interpolated for asymptotic values. Applications to two ships for the symmetric and asymmetric responses were carried out and the effect of springing responses is also discussed.     

溢油应急培训现状与思考

分析了溢油应急培训现状及存在的实际问题,并在此基础上提出了加强溢油应急培训的意见和建议。     

基于模态参数的工程结构损伤识别方法

介绍了结构故障诊断的技术手段以及应用振动诊断进行结构损伤识别的研究现状。应用有限元程序进行模态分析和频响分析,得到在不同损伤度的条件下轮对局部模态频率和振幅幅值的变化趋势。提出基于频率移动和模态振型变化来判断结构损伤。     

分数阶系统极点分布与时间响应

与传统线性定常控制系统相比,分数阶线性定常系统极点分布与时间响应关系有所不同.本文通过分析多值函数特性在黎曼平面中的表达以及s-平面与w-平面的映射关系,给出了分数阶线性定常系统极点分布与时域响应的定性关系.对位于第二黎曼平面的极点更加远离s-平面的右半平面给出了形象化解释,并称其对应的时间响应为“超阻尼”响应.最后介绍了一种分数阶线性定常系统的稳定性判据.     

不同阻尼计算模式对斜拉桥地震响应分析的影响

大跨度斜拉桥阻尼组成复杂,各阶振型的阻尼差别较大。为了研究阻尼计算模式对斜拉桥地震响应分析结果的影响,以主跨448 m的杭州湾跨海大桥北航道桥为对象,对应用考虑结构阻尼分布影响的振型应变能比例阻尼理论、常数阻尼、Rayleigh阻尼理论的适用性进行分析。结果表明,地震响应结果与所用的阻尼理论有关,常数阻尼不能很好反映结构的阻尼特性,而Rayleigh阻尼模式的计算结果取决于选取的参考振型,在较大的频率范围内存在过大或过小估计结构阻尼的问题,具有很大的随意性。相比之下,振型应变能比例阻尼理论能够考虑斜拉桥阻尼的分布特性,比较合理。     

环境随机激励下高速客车的工作模态分析

根据线性系统在环境激励下各输出点响应之间的相关函数与脉冲响应函数具有相类似的数学表达式,得出了互相关函数理论可同多种经典时域模态分析方法(如:多参考点LSCE法)相结合进行环境激励下模态参数识别的方法。在试验台上以白噪声激励模拟环境激励,对新试制的300km/h高速铰接式试验客车进行了工作状态下的模态试验和分析,并与传统的模态识别法(FRF)进行了对比和分析。试验结果显示,二种方法对模态频率和阻尼比的识别误差分别不超过5.4%和9.9%。这表明,利用环境激励法进行系统工作状态下的模态参数识别是行之有效的,该法可推广应用于在实际线路上运行的各类车辆的模态试验和分析。     

分层圆弧峡谷SV波地震差动模拟理论与桥梁破坏模式

为了探究局部地形及场地分层因素对地下多点地震动的影响，建立了分层圆弧峡谷模型，并进行了目标场地多点地震动模拟程序的开发和验证。在此基础上，对一跨越该场地的刚构桥进行了考虑多点激励作用下的地震反应分析。具体内容包括：首先，在推导得到SV波入射层状圆弧峡谷地震反应频域解基础上，依据规范谱确定矩阵的峡谷各位置自谱（绝对值），联合自谱和峡谷相干函数得到互谱，进而与自谱共同构造出功率谱矩阵。由此同时体现了峡谷局部场地三大典型物理效应：散射、相干和分层效应，奠定了SV波入射下层状峡谷多点地震动模拟的基础，填补了由于竖向边界条件难以满足而大多受限于SH波入射理论解研究的空白。其次，基于上述结果，编制代码和可视化开发，实现理论方法程序化，并验证其可行性和可靠性。最后，为研究SV波输入下分层和峡谷效应多点激励对结构的影响，针对一峡谷桥梁进行模型建立、修正、多点地震反应计算以及分析比较。结果表明：①分层效应对结构反应影响明显，传统均匀介质的假定所带来的影响不容忽视；②采用传统适用于平整场地多点地震动作为激励，会导致与峡谷地形多点地震反应差别明显，且会低估结构反应；③SV波斜入射多点激励下所产生地震动的空间变异性，会使得地震反应计算结果幅值出现明显增大现象。该理论方法、程序开发可供类似工程场地分析参考。     

Microbial food web responses to light and nutrients beneath the coastal Arctic Ocean sea ice during the winter–spring transition

We measured the abundance and biomass of phototrophic and heterotrophic microbes in the upper mixed layer of the water column in ice-covered Franklin Bay, Beaufort Sea, Canada, from December 2003 to May 2004, and evaluated the influence of light and nutrients on these communities by way of a shipboard enrichment experiment. Bacterial cell concentrations showed no consistent trends throughout the sampling period, averaging (± SD) 2.4 (0.9) × 10⁸ cells L^− 1; integrated bacterial biomass for the upper mixed layer ranged from 1.33 mg C m^− 3 to 3.60 mg C m^− 3. Small cells numerically dominated the heterotrophic protist community in both winter and spring, but in terms of biomass, protists with a diameter > 10 µm generally dominated the standing stocks. Heterotrophic protist biomass integrated over the upper mixed layer ranged from 1.23 mg C m^− 3 to 6.56 mg C m^− 3. Phytoplankton biomass was low and variable, but persisted during the winter period. The standing stock of pigment-containing protists ranged from a minimum value of 0.38 mg C m^− 3 in winter to a maximal value of 6.09 mg C m^− 3 in spring and the most abundant taxa were Micromonas-like cells. These picoprasinophytes began to increase under the ice in February and their population size was positively correlated with surface irradiance. Despite the continuing presence of sea ice, phytoplankton biomass rose by more than an order of magnitude in the upper mixed layer by May. The shipboard experiment in April showed that this phototrophic increase in the community was not responsive to pulsed nutrient enrichment, with all treatments showing a strong growth response to improved irradiance conditions. Molecular (DGGE) and microscopic analyses indicated that most components of the eukaryotic community responded positively to the light treatment. These results show the persistence of a phototrophic inoculum throughout winter darkness, and the strong seasonal response by arctic microbial food webs to sub-ice irradiance in early spring.     

Ship appearance optimal design on RCS reduction using response surface method and genetic algorithms

Radar cross section (RCS) reduction technologies are very important in survivability of the militarynaval vessels. Ship appearance shaping as an effective countermeasure of RCS reduction redirects the scatteredenergy from one angular region of interest in space to another region of little interest. To decrease the scatteringelectromagnetic signals from ship scientifically, optimization methods should be introduced in shaping design.Based on the assumption of the characteristic section design method, mathematical formulations for optimalshaping design were established. Because of the computation-intensive analysis and singularity in shapingoptimization, the response surface method (RSM) combined genetic algorithm (GA) was proposed. The poly-nomial response surface method was adopted in model approximation. Then genetic algorithms were employedto solve the surrogate optimization problem. By comparison RCS of the conventional and the optimal design,the superiority and effectiveness of proposed design methodology were verified.Ky words: radar cross section (RCS); characteristic section design method; response surface method; genetic algorithm (GA) was proposed. The polynomial response surface method was adopted in model approximation. Then genetic algorithms were employed to solve the surrogate optimization problem. By comparison RCS of the conventional and the optimal design, the superiority and effectiveness of proposed design methodology were verified.