地震作用下车辆-公路桥梁耦合作用的能量机理

由于地震作用下车辆和公路桥梁相互耦合作用的复杂性,目前对其相互作用机理的研究较少,导致各国现行公路桥梁抗震设计规范关于桥梁在地震作用时是否需要考虑活载作用仍然存在分歧.现有研究表明,车辆既可能对桥梁的地震响应产生有利影响,也可能产生不利的影响.本文在已有的研究基础上,对车桥耦合接触行为进行简化模拟,采用能量法对车辆-公路桥梁耦合作用机理进行分析.结果表明：车桥耦合作用对输入到桥梁水平方向能量的影响可以忽略不计,但会导致输入到桥梁竖向总能量的减小,因而使桥梁的竖向地震响应减小,而输入到车辆竖向的能量则主要来自桥面振动;此外,车辆质量越小,桥梁振动产生的对车辆水平方向的能量输入越大.     

钢纤维及预应力对BTRC板抗弯性能的影响

采用三点弯曲试验研究了玄武岩纤维编织网增强混凝土(BTRC)抗弯性能.试验考虑了编织网层数、编织网上预拉力水平和钢纤维掺量3个影响因素.试验结果表明:随着编织网层数的增加,BTRC板的抗弯强度和韧性增大.随编织网上预拉力水平的提高,BTRC板的开裂应力和开裂后抗弯刚度均增大,极限挠度减小,而抗弯强度变化不明显.钢纤维有助于提升BTRC板的开裂应力、抗弯强度和韧性;对编织网施加预拉力使钢纤维掺量对BTRC板的抗弯强度影响更显著.编织网层数和钢纤维的增加使BTRC板上的裂缝形态更均匀细密,但对编织网施加预拉力使板上裂缝数目减少且裂缝间距增大.     

基于CR全量非线性梁柱理论的平面剪切梁元

基于CR全量非线性计算模式,结合考虑梁元剪切效应的Timoshenko梁理论,采用梁柱理论(稳定函数格式)建立精细高效的综合考虑单元轴力、弯矩、剪力及其耦合效应的平面梁元分析理论.采用梁柱理论,结合CR坐标法,完善高精度目标下的平面梁元几何非线性问题快速求解方法;以二阶梁柱理论为基础,推导考虑剪切效应的转角位移方程具体格式,获得刚度系数的精确稳定函数表达式,在保证数值精度及计算过程稳定性的前提下,将上述稳定函数幂级数化且提出对应的截断准则,随后推导了剪切变形影响下考虑梁元弓弦效应的单元节点计算表达式;编写程序对本文提出的方法与经典算例进行对比检验,并结合实际工程进行分析.研究结果表明:对一般的多跨连续梁结构,利用本文计算理论能获得与经典算例一致精度的计算结果;对发生大位移的类如肘型刚架结构,利用本文理论可获得其考虑剪切效应的荷载-位移全过程变形曲线,其跃越屈曲第一及第二临界点亦与经典文献符合;对不同主梁形式的特大跨度斜拉桥结构,利用本文理论亦可得到合理的整体变形特征,同时明显提高分析效率.     

An optimized short-term wind power interval prediction method considering NWP accuracy

In recent years, the accuracy of the wind power prediction has been urgently studied and improved to satisfy the requirements of power system operation. In this paper, the relevance vector machine(RVM)-based models are established to predict the wind power and its interval for a given confidence level. An NWP improvement module is presented considering the characteristic of NWP error. Moreover, two parameter optimization algorithms are applied to further improve the prediction model and to compare each performance. To take three wind farms in China as examples, the performance of two RVM-based models optimized, respectively, by genetic algorithm(GA)and particle swarm optimization(PSO) are compared with predictions based on a genetic algorithm–artificial neural network(GA–ANN) and support vector machine. Results show that the proposed models have better prediction accuracy with GA–RVM model and more efficient calculation with PSO–RVM.     

燃料电池车用超高速空压机永磁体结构强度研究

针对大功率燃料电池系统高速空压机转子永磁体离心拉应力破坏,采用解析法计算了额定转速时护套与永磁体间过盈量的大小及应力,采用有限元方法建立二维轴对称模型,计算了永磁体和护套内的应力分布,对比解析法与有限元方法的准确性.基于有限元法研究了温升和护套材料对永磁体应力的影响,结果表明,解析法和有限元法计算的各应力的相对误差不超过2.5％,而影响因素中转速和温升均会造成永磁体应力的显著提升,需要增大过盈量对转子永磁体保护.碳纤维护套相比合金护套可以至少降低42.1％的永磁体应力,且在高温工况下的效果更为显著.降低转速、增大装配过盈量以及改善转子冷却均能有效优化结构强度,而复合材料护套相比钢护套更适用于保护永磁体.     

Influence factor of diesel soot formation in diesel engine combustion predicted by multistep soot model with highlight in soot surface activity

As more strict regulations on soot emission with increasing emphasis on the emitted soot particle size have been imposed, diesel engine partially premixed combustion had been proven to achieve ultra-low NOx and soot emissions with high thermal efficiency simulta- neously, by synergy control of mixing and chemical parameters. It calls for further study in the effect of com- bustion boundaries on soot formation. In this study, soot formation characteristic was investigated by CFD code coupled with reduced n-heptane model and improved multistep soot model. History of acetylene, which is taken as the main species of PAH formation and soot surface growth, plays more important roles on soot prediction. The revised parameter of fraction of active sites αCH was introduced as the indicator of soot surface activity in diesel soot formation. The effects of combustion boundaries on soot surface activity and soot surface growth were explored in this study. When the mixture was quite homogeneous, lowered combustion temperature was the main factor for reduced soot formation due to the lowered specific surface growth rate RCH, in spite of ec/4 increasing slightly due to the slowed decay rate of surface activity. As the inhomo- geneity of the mixture was increased, more unburned hydrocarbons were produced, promoting the formation of acetylene and soot surface activity. It was the dominated reason for higher soot surface growth rate, resulted wors- ened engine-out soot. In addition, residual of CO in later combustion phase impeded the re-oxidation of soot.     

丙氨酸在紫外/氯工艺中生成挥发性DBPs的潜能

采用紫外/氯(UV/chlorine)组合工艺对原水中代表性氨基酸-丙氨酸(Ala)进行处理,并对该过程中产生的挥发性消毒副产物(三卤甲烷和卤乙腈)进行测定和分析.研究了不同投氯量、pH、紫外照射时间、溴离子和氨氮浓度对消毒副产物(DBPs)生成潜能的影响.结果表明,丙氨酸经紫外/氯工艺处理后会产生三氯甲烷(TCM)和二氯乙腈(DCAN)两种消毒副产物,且TCM、DCAN的质量浓度在处理15 min时达到最高的20.37μg/L和34.17μg/L,在较低的[Ala]/[Cl2]、较长的紫外照射时间以及中性的pH条件下有利于减少TCM和DCAN的产生,本试验得出的最佳工况为[Ala]/[Cl2]=1∶2,紫外照射2 h,溶液pH=7.此外,水中存在的溴离子使得UV/chlorine消毒后产生了溴氯乙腈(BCAN),增加了消毒副产物的种类和毒性;而氨氮的存在则会减少相应的消毒副产物的产生.还对不同工艺进行了对比,单独紫外照射时没有产生消毒副产物,单独使用氯时TCM产率小于UV/chlorine的产率,但DCAN的产率大于UV/chlorine的产率.最后,提出了UV/chlorine处理丙氨酸生成消毒副产物的可能途径:先是进攻丙氨酸氮原子上的氢,接着是脱羧基和脱氨基作用,生成乙醛和乙腈,再经过一系列取代和水解反应生成二氯乙腈和三氯甲烷.以上试验结果可以为紫外/氯组合工艺的应用和推广提供理论依据.     

00 g干重之间;主要成分反式茴香脑的相对含量

d Component of Fennel from Seven Different AreasREN An-xiang~1,HE Jin-ming~1,GUO Yuan~2,WANG Yu-mei~(1,2)(1.College of Yingdong Bioengineer Shaoguan University,Shaoguan,Guangdong 512005,China;2.Agriculture College of Inner Mongolia Agricul愎?对科技型中小企业无形资产价值的评估提出了展望。     

基于纹理特性的能量差调制视频水印算法

针对现有视频水印算法复杂度高、鲁棒性差的问题,提出一种基于残差纹理特征的能量差调制视频水印算法. 该算法首先利用视频编码过程得到的残差DCT系数进行区域纹理强度建模,然后依据纹理强度对DCT中高频系数的能量进行自适应调制实现水印的嵌入. 算法在不引入额外复杂计算过程的条件下,针对不同区域自适应地嵌入不同强度的水印信息,保证视频质量的同时提高水印的鲁棒性. 算法以H.264/AVC视频编解码器为测试实例,实验结果表明,本文提出的水印算法在保证视频质量和编码码率的情况下,对重编码、滤波和噪声等攻击具有很好的鲁棒性,水印提取过程满足盲检测应用需求.     

Structural metamaterials with negative mechanical/thermomechanical indices: A review

Structural metamaterials presenting negative values of one or more mechanical and thermomechanical indices–namely the Poisson’s ratio, the linear compressibility, and the coefficient of thermal expansion – are the promising candidates to the applications in many fields, ranging from precision mechanics to biomedical devices or energy absorption. Although scattered mentions may be found in the literature since the late eighties of 20th century, the systematic research efforts concerning these mat...