Evaluating the stress intensity factors of anisotropic bimaterials using boundary element method

This paper presents a boundary element method (BEM) procedure for a linear elastic fracture mechanics analysis in two‐dimensional anisotropic bimaterials. In this formulation, a displacement integral equation is only collocated on the uncracked boundary, and a traction integral equation is only collocated on one side of the crack surface. A fundamental solution (Green's function) for anisotropic bimaterials is also derived and implemented into the boundary integral formulation so that except for the interfacial crack part, the discretization along the interface can be avoided. A special crack‐tip element is introduced to capture the exact crack‐tip behavior. A computer program using FORTRAN has been developed to effectively calculate the stress intensity factors of an anisotropic bimaterial. This BEM program has been verified to have a good accuracy with previous studies. In addition, a central cracked bimaterial Brazilian specimen constituting cement and gypsum is prepared to conduct the Brazilian test under diametral loading. The result shows that the numerical analysis can predict relatively well the direction of crack initiation and the path of crack propagation. Copyright © 2007 John Wiley & Sons, Ltd.     

Study on Effects of Building Morphology on Urban Boundary Layer Using an Urban Canopy Model

An urban canopy model is incorporated into the Nanjing University Regional Boundary Layer Model. Temperature simulated by the urban canopy model is in better agreement with the observation, especially in the night time, than that simulated by the traditional slab model. The coupled model is used to study the effects of building morphology on urban boundary layer and meteorological environment by changing urban area, building height, and building density. It is found that when the urban area is expanded, the urban boundary layer heat flux, thermal turbu- lence, and the turbulent momentum flux and kinetic energy all increase or enhance, causing the surface air temperature to rise up. The stability of urban atmospheric stratiˉcation is a?ected to diffierent extent at diffierent times of the day. When the building height goes up, the aerodynamic roughness height, zero plane displacement height of urban area, and ratio of building height to street width all increase. Therefore, the increase in building height results in the decrease of the surface heat flux, urban surface temperature, mean wind speed, and turbulent kinetic energy in daytime. While at night, as more heat storage is released by higher buildings,thermal turbulence is more active and surface heat flux increases, leading to a higher urban temperature. As the building density increases, the aerodynamic roughness height of urban area decreases, and the effect of urban canopy on radiation strengthens. The increase of building density results in the decrease in urban surface heat flux, momentum flux, and air temperature, the increase in mean wind speed, and the weakening of turbulence in the daytime. While at night, the urban temperature increases due to the release of more heat storage.     

雨滴谱的变化对降水估计的影响

针对雨滴谱的变化对降水估计的影响,提出根据激光雨滴谱仪上方雷达回波的结构特征将降水过程划分为对流云降水和层状云降水交替分布5个部分,通过基于2种降水类型的第1种分类Z-R关系、基于5个部分的第Ⅱ种分类Z-R关系和基于整个降水过程的总体Z-R关系分析雨滴谱的变化对降水估计的影响.结果表明:当对流云降水向层状云降水过渡时,指数谱从无到有、多峰谱比例减小,Nw减小、μ增大、Dm变化不大;Mw与R变化相似,当Z增大时μ和Dm分别是递减和递增的;Z-R关系(Z=aRb)中a值变化范围较大、系数b在1～2波动且与层状云阶段相比,对流云阶段的a和b值较小;利用第Ⅱ种分类Z-R关系反演的雨强与基于雨滴谱仪观测数据计算的雨强最接近;雨滴谱仪在层状云阶段的反演效果明显强于对流云阶段,这与对流云降水中雨滴谱信息变化大且快等因素有关.     

西沙群岛生物碳酸盐的成因和沉积:来自活体仙掌藻的证据

A recent island survey reveals that the Xuande Atoll and the Yongle Atoll in the Xisha Islands can be classified into one of two systems: the depleted atoll system and growth atoll system; the survey also indicates that the decreased area of several shoals is an unbearable burden for the Xisha Islands, of which the largest island area is 2.13 km2 and the minimum elevation is 1.4 m. According to a survey on the ecological characteristics of Halimeda in the Laolongtou breaker zone of Shidao Island in the Xisha Islands, the green and white living Halimeda are collected,the isotopic ages of 14 C contained in the Halimeda are shown to be 27 years and 55 years, respectively, and carbonate mainly occurs in five types, i.e., luster, segment, sand, sand grain, and marl in the formation. The Halimeda segments mainly provide the carbonate sediments of long-term biogenic deposits in the reef environment and the annual productivity per area is 60–100 g/m2; the characteristics of the microstructure of the Halimeda are analyzed, the aragonite raphide carbonate is deposited and enriched in the cortexes, medullas and cysts, and the Halimeda generally contain major elements such as C, O, Ca, Cl, Mg, K, Na, S and Al, and are rich in trace elements such as tellurium(Te), rhodium(Rh) and strontium. It is believed that the Halimeda grow slowly,including the biotic community of reef corals in the reef areas, thus they possess an environmental remediation capacity, but it takes much time to remedy the environment, and it is necessary to make the law to protect the diversity and vulnerability of the Xisha marine ecology, the ecology of the reef community and the island environment in a scientific way. As indicated in the survey, under the background of global warming and sea-level rise, the discovery of large amounts of Halimeda in the Laolongtou sea area is significant for the natural increase of the depleted atoll system of the Xuande Atoll, while the Halimeda segments represent the primary form of the fossil Halimeda, of which the species can be identified and preserved in great numbers under geological conditions. The Miocene was discovered in large amounts in the Xichen-1 well, therefore the study on the characteristics and mechanism of Halimeda carbonate sediments plays a pivotal role in the formation and construction of organic reefs in the South China Sea as well as oil and gas exploration.     

MPI环境下基于边界校正方法的海洋模型的并行化

基于区域分解技术,设计了一种针对海洋模型的边界校正方法,该方法不需要对原有海洋模型进行较大改动,只需要利用消息传递接口(message passing interface,MPI)编写子区域间的数据传输模块,即可实现原有海洋模型的并行化。相对于重新开发并行系统,该方法能够较快把原有模型的串行解决方案转化为并行解决方案,并且并行化后的海洋模型能够获得较高的加速比。     

一种CORS站高程序列噪声识别算法

针对能量密度谱判断噪声与信号主导模态分界点性能不稳定的问题,该文提出基于夹角余弦的分界点判断方法。该方法首先利用EEMD对CORS站高程数据进行分解,其次计算原始信号与各阶模态分量的夹角余弦值,最后根据夹角余弦值的首次逆向转折位置判定噪声主导模态和信号主导模态的分界点。以4个CORS基准站近20年原始高程时间序列信号为研究对象,对噪声与信号模态分量分界点进行判定,实验结果表明采用基于夹角余弦的判定方法可以一次判断出噪声和信号模态分量的分界点。该方法应用到CORS站高程信号与噪声序列的识别中性能更加稳定。     

A diagnostic analysis on the effect of the residual layer in convective boundary layer development near Mongolia using 20th century reanalysis data

Although the residual layer has already been noted in the classical diurnal cycle of the atmospheric boundary layer,its effect on the development of the convective boundary layer has not been well studied. In this study, based on 3-hourly20 th century reanalysis data, the residual layer is considered as a common layer capping the convective boundary layer. It is identified daily by investigating the development of the convective boundary layer. The region of interest is bounded by(30°–60° N, 80°–120° E), where a residual layer deeper than 2000 m has been reported using radiosondes. The lapse rate and wind shear within the residual layer are compared with the surface sensible heat flux by investigating their climatological means, interannual variations and daily variations. The lapse rate of the residual layer and the convective boundary layer depth correspond well in their seasonal variations and climatological mean patterns. On the interannual scale, the correlation coefficient between their regional averaged(40°–50°N, 90°–110° E) variations is higher than that between the surface sensible heat flux and convective boundary layer depth. On the daily scale, the correlation between the lapse rate and the convective boundary layer depth in most months is still statistically significant during 1970–2012. Therefore, we suggest that the existence of a deep neutral residual layer is crucial to the formation of a deep convective boundary layer near the Mongolian regions.     

Structures and characteristics of the windy atmospheric boundary layer in the South China Sea region during cold surges

An observational analysis of the structures and characteristics of a windy atmospheric boundary layer during a cold air outbreak in the South China Sea region is reported in this paper. It is found that the main structures and characteristics are the same as during strong wind episodes with cold air outbreaks on land. The high frequency turbulent fluctuations(period<1 min) are nearly random and isotropic with weak coherency, but the gusty wind disturbances(1 min相似文献