Multigrain sedimentation/erosion model based on cross-shore equilibrium sediment distribution: Application to nourishment design

In the light of global warming and sea level rise there are many coastal beaches that suffer from erosion. Beach nourishment has become a common practice to maintain the sediment balance on a shore-face. In this paper, a three-dimensional numerical model for evaluating long-term impact of beach nourishment projects has been developed. The model addresses the longstanding complex issue of coastal morphology and sediment grain size distribution from an unconventional angle, which exploits the strong links between grain size distribution and the prevailing transport direction of each sediment constituent under ‘average’ wave and storm action. The present model predicts the redistribution of nourished sediment according to the subtle clues implied by equilibrium distribution curves and latest coastal wave transformation theories. After verification against recent field observations in Terschelling, The Netherlands, the model was used to predict long-term effects of different beach nourishment strategies. It was found that: (a) given the source sediment available in Terschelling the tactics of large volume and less frequent implementation are better than otherwise; and (b) from a pure engineering point of view, waterline nourishment outperforms offshore trough nourishment.The model offers an additional tool for coastal engineers to evaluate the feasibility, effectiveness and the optimization of dumping locations for beach nourishment projects. It is also a useful tool for stratigraphic modelling of shallow-marine sedimentation in conjunction with sea level changes.     

Kinematic response of single piles to vertically incident P‐waves

Dynamic response of single piles to seismic waves is fundamentally different from the free‐field motion because of the interaction between the pile and the surrounding soil. Considering soil–pile interaction, this paper presents a new displacement model for the steady‐state kinematic response of single piles to vertically incident P‐waves on the basis of a continuum model. The governing equations and boundary conditions of the two undetermined functions in the model are obtained to be coupled by using Hamilton's principle. Then, the two unknown functions are decoupled and solved by an iterative algorithm numerically. A parametric study is performed to investigate the effects of the properties of the soil–pile system on the kinematic response of single piles. It is shown that the effects of the pile–soil modulus ratio, the slenderness ratio of the pile, and the frequency of the incident excitations are very significant. By contrast, the influence of soil damping on the kinematics of the system is slight and can be neglected. Copyright © 2013 John Wiley & Sons, Ltd.     

2007年6—7月西太平洋副热带高压的异常特征及其成因分析

采用NCEP资料以及NOAA卫星观测的OLR场资料,分析了2007年6—7月淮河流域暴雨及江南、华南异常高温期间西太平洋副热带高压的异常特征,其表现为强度强且南北位置相对稳定,东西方向进退明显于南北方向的移动。通过分析经圈平面上的垂直环流及风矢量场的特征表明,副高南北两侧都存在一定强度的上升气流,北侧上升气流对西太平洋副高中心区700 hPa以上高度的下沉运动有激发作用,而南侧上升气流对西太平洋副高中心区的下沉运动作用不大。中高纬度阻塞高压双阻型的建立,有利于西太平洋副高的加强和发展。强劲而稳定少动的中纬度西风急流和热带地区异常活跃的对流均有利于西太平洋副高的相对稳定。     

New hα survey of chromospherically active binaries

We had observed the high-resolution H profiles of fourteen chromospherically active binaries which are And, 3 Cam, 4 UMi, ² Sgr, Sgr, HR 7333, 33 Psc, UMi, And, UMa, 12 Cam, And, Aur and Dra from August 1990 to August 1991. The H emission and absorption equivalent widths, and the half widths and the radial velocities of these systems were determined. These data have a good supply for the information of the catalog of chromospherically active binary stars. The H profiles of HR 7333, 12 Cam, 4 UMi, UMi and And show marked emission filling in core, but 33 Psc, Sgr, Sgr and And systems show the H as the stronger absorption lines. The observed fourteen binaries presented very different activity levels.     

基于岩性-结构的煤层底板突水危险性评价

煤层顶底板突水危险性预测与评价是煤矿突水灾害防治的基础和依据。针对煤层底板隔水介质条件,分析了煤系岩石力学性质,煤层底板突水的岩性、结构和厚度特征,建立了煤层底板突水危险性评价理论和方法。研究表明:煤层底板隔水介质条件取决于隔水层岩性和断裂构造,随着底板泥岩含量增加,煤层底板隔水性能增高,但抗水压能力降低;随着断裂发育程度的增加,底板隔水层由完整结构、块裂结构到碎裂结构和松散结构,煤层底板抗水压能力和隔水性能均降低,突水危险性增大。煤层底板抗水压能力与煤层底板隔水层厚度密切相关,统计表明,煤层底板受的极限水压p与底板隔水层厚度h之间为2次幂函数关系。在传统突水系数的基础上考虑了隔水层的岩性和结构特征,提出了煤层底板突水危险评价分类;进一步根据水压P_w与岩体破裂压力P_c关系和水压P_w与最小主应力σ_hmin关系判断是否突水。      

大采深倾斜薄煤层底板采动破坏形态的连续探测

利用多回路钻孔注(放)水连续探测系统,结合断裂力学分析,研究了大采深倾斜薄煤层底板采动破坏特征与形态,结果表明底板破坏形态为一匙形,与厚煤层开采所形成的破坏形态相比其破坏特征的差异在于,底板采动裂隙主要是原生节理裂隙的扩展,而工作面推过压实后,绝大部分裂隙又趋于闭合。