Thermal internal boundary layer and its effects on air pollutants during summer in a coastal city in North China

The thermal internal boundary layer(TIBL) is associated with coastal pollution dispersion,which can result in high concentrations of air pollutants near the surface of the Earth. In this study, boundary layer height data which were obtained using a ceilometer were used to assess the effect of the TIBL on atmospheric pollutants in Qinhuangdao, a coastal city in North China.A TIBL formed on 33% of summer days. When a TIBL formed, the sunshine duration was 2.4 hr longer, the wind speed was higher, the wind direction reflected a typical sea breeze, and the boundary layer height was lower from 9:00 LT to 20:00 LT compared to days without a TIBL. If no TIBL formed, the average concentrations of PM_(2.5) and PM_(10) decreased with increasing boundary layer height. However, when a TIBL was observed, the average concentrations of PM_(2.5) and PM_(10) increased with increasing boundary layer height. Because the air from the sea is clean, PM_(2.5) and PM_(10) concentrations reached minimums in the daytime at 16:00 LT. After16:00 LT, the PM_(2.5) and PM_(10) concentrations increased rapidly on days when a TIBL formed,which indicated that the TIBL leads to the rapid accumulation of atmospheric pollutants in the evening. Therefore, the maximum concentrations of particulate matters were larger when a TIBL formed compared to when no TIBL was present during the night. These results indicate that it is suitable for outdoor activities in the daytime on days with a TIBL in coastal cities.     

飞机结构腐蚀数值仿真模拟的研究进展

系统介绍了飞机结构腐蚀数值仿真模拟中应用较为广泛的元胞自动机方法、有限元方法、边界元方法,尤其是它们在点蚀、电偶腐蚀、缝隙腐蚀、晶间腐蚀仿真的研究现状,并对各自方法的优点和缺点与适用的范围进行了阐述,以期对该领域的研究者提供一定的导向作用。     

Near Field Dispersion in the Urban Environment - A Hydraulic Flume Study

The dispersion of material released from a point source immediately upwind of an obstacle array has been examined in a hydraulic flume with a low level of background turbulence. The main purpose of the experiments was to examine the interaction of the plume and the internal boundary layer (IBL) created over the obstacle array. The obstacle array consisted of 11 rows of cubes at 16% packing density in a staggered arrangement. Plume dispersion was measured using flow visualization with Rhodamine dye and also with a thermal tracer technique. During the experiments the source release height was varied between z = 0 and z = 4H, where H is the obstacle height. For the low-level releases, the upper boundary of the plume followed the growth of the IBL over the array. For higher level releases (z/H 2) the rate of plume growth was much reduced until the point downstream where it descended into the IBL, after which it experienced the intense turbulent mixing within the array. This suggests that the urban lateral spread parameter _y should be a strong function of height in situations where the turbulence level in the ambient approach flow is low. These results highlight the importance of the ambient turbulence even in strongly obstacle-affected dispersion.     

广东冬季寒害的时空分布规律

用广东省22个分布较均匀的代表站1957-2001年冬季(12月至次年2月)逐日平均气温和最低气温资料,研究了广东冬季寒害的时空分布规律,计算了广东冬季综合寒害指数.对广东22个代表站上述44年的综合寒害指数进行了自然正交分解,得到了2个有意义的特征向量场.由此发现广东冬季寒害的地域分布主要有2大类型:整体分布型和南北分布型.对广东冬季综合寒害指数和综合寒害指数第一特征向量时间系数、第二特征向量时间系数进行了小波变换.结果表明,广东冬季寒害整体分布型的主要振荡为准8年周期,南北分布型的主要振荡为准22年周期.综合而言,广东冬季寒害除具有准8年振荡的主要周期变化外,还有2～4年及22～24年的周期变化.根据小波变换图分析,预计未来2年广东冬季寒害以偏弱为主,尔后进入转换期.     

竖向断裂缝对场地地震动的影响分析

断裂缝在工程场地十分常见,研究其对场地地震动的影响很有必要.基于应用局部人工边界条件模拟辐射阻尼影响的二维显式有限元方法,分别对垂直入射和斜入射地震波情形下具有不同深度的竖向断裂缝场地地震动进行了数值模拟,并与地表水平的均匀半空间场地地震动进行了对比,结果表明,断裂缝对其附近场地地震动的影响显著,但随着离开裂缝的距离变大,其影响迅速减小.     

历史洪水在洪水序列隐含周期分析中的应用

历史洪水调查是洪水序列的重要组成部分,对揭示洪水序列的周期,论证周期的稳定性和可靠性具有重要的作用.本文提出具有历史洪水调查的不连序序列三种周期分析模型,理论分析和实例计算结果表明,文中提出的模型是合理和可行的.     

单侧接触埋置结构与瞬态SH波的动力相互作用——时域边界元分析

应用时域边界元法 ,研究了单侧接触埋置结构与瞬态SH液 (剪切横波 )的动力相互作用 ,当入射SH波足够强时 ,界面会出现局部滑移并假设摩擦遵守库仓定理。笔者从实际情况出发 ,提出了新的数学模型和计算方法 ,计算了埋置矩形结构与瞬态SH波的动力相互作用问题 ,由于对此类问题的深入研究 ,为评估和预测埋置结构在动荷载下的安全性及疲劳寿命提供了重要的理论价值     

企业投入的安全经济效用及边际效用

企业投入一般具有安全的经济效益和社会效益等多属性,如何以有限的安全投入做最为合理的配置以获得最大的安全经济效用,需要采用效用尺度来研究其变化规律及均衡条件     

宁镇地区石炭二叠系界线

将宁镇地区上石炭统船山组Sphaeroschwagerina带与二叠系栖霞组底部碎屑岩段之间的灰黑,深灰色中至厚层石灰岩、炭质石灰岩单独划出,称之为镇江组(新义)。石炭二叠系界线放在船山组Sphaeroschwagerina带之顶,镇江组(新义)之底。     

华南二叠纪末缺氧海水中的有毒气体与生物集群绝灭

对华南P/T界线地层有机碳同位素和碳酸盐岩碳氧同位素和沉积特征进行研究表明 :二叠纪末海洋中发生了大规模海水缺氧事件 ,持续时间约 6～ 10万年 ;海洋底层存在大量的CO、CO2 、H2 S和CH4等水溶性有毒气体 ,在剧烈的火山爆发事件及相伴的温室效应影响下 ,这些气水化合物由海底及陆架沉积中快速分离释放 ,导致生物集群绝灭 ,最终造成灰岩的δ13 C值发生强烈的负漂移