FRICTION SLOPE MODELS FOR M2 PROFILES1

ABSTRACT: Results of studies which have considered the relative merit of various friction slope averaging equations previously used in water surface profile computations are described. Limitations of the most accurate equation known for the M2 profile have indicated that a new equation which gives more emphasis to the upstream energy gradient is desirable. Based upon friction slope curves developed for M2 water surface profiles two new equations, one a parabolic and the other an elliptical approximation, are presented. The behavior of the new equations and of the previously most recommended equation is described by test calculations. The elliptical equation performed more satisfactorily than the harmonic method commonly recommended for M2 profile computations. Insertion of an additional cross-section about 50 feet upstream from a critical depth section was found to reduce computational errors for any energy gradient averaging method.     

粘性泥石流体应力本构关系的试验研究

为了能直接测定含有粗颗粒砾石的粘性泥石流体原样的流变特性，专门研制了大型泥石流流变仪，利用该仪器测试的结果分析研究了粘性泥石流体的应力本构关系。分析研究表明：粘性泥石流体在低速率区启动初始段，颗粒间的作用以接触挤压和滑动摩擦为主，其应力本构关系可用剪切稀化的幂定理方程来描述；在剪切速率区流动剪切段的应力本构关系，包含滑动摩擦作用的零次项和反映惯性碰撞的平方项，具有屈服应力和剪切膨胀的流变特征。     

城区道路交通噪声污染危害及控制方法

道路交通噪声来源于地面、车轮与地面摩擦噪声、机动车辆发动机噪声、车体带动空气形成的气流噪声、喇叭噪声等,其流动性大,影响面广。随着社会经济的发展,交通运输工具成倍增长,道路交通噪声污染也随之增加。     

空气负离子浓度分布特征及其与环境因子的关系

大气离子是由许多自然和人为的原因产生,并且它们的浓度在不同环境场所下差别很大。选取我国南部沿海某省份作为研究区域,挑选近10处具有代表性的环境场所进行实测研究,收集了空气正、负离子浓度、风速、空气温度、相对湿度、材料和植物负离子浓度等数据。实测数据表明：地面上的空气负离子浓度随着地理环境因素（瀑布、海边、峡谷、乡村田野、郊区旷野、县城等）不同差别很大,其中瀑布〉海边〉峡谷〉溪流〉县城;同时空气负离子浓度与风速、水、植物、相对湿度等有较为密切的关系。通过对实测数据进行分析得出以下结论,1）空气的摩擦可以有效显著地增加空气中负离子的浓度,两者呈现出一定的正相关关系。2）水体在撞击和喷射过程能加快正负电荷的分离,水速流动地越快,相应摩擦产生的电离能越大,周边环境的空气负离子浓度就越高;同时随着距离的衰减,环境中的空气负离子浓度也在不断地降低。3）空气负离子浓度与植物群落的种类结构和配置相关,其中高处复层结构植物〉低处复层结构植物〉低处单层结构植物。4）相对湿度与空气负离子具有良好的相关性。5）温度与空气负离子的关系有待进一步明确。6）适宜的温度、湿度以及风速能使人感到舒服,有益于人体的健康。7）自然生态环境整体而言,空气负离子浓度大,空气清洁度均为A级最清洁。通过结果和分析给城市生态环境建设方面以重要的启示,因此作者从城市规划层面进一步提出以下建议：1）以自然环境的空气负离子浓度值为参考标准研究城市环境的空气负离子浓度和空气清洁度,进行符合气候和生态资源运行状态的设计,对于优化城市生态环境和城乡规划建设的水平有着重要的意义。2）加强自然通风、增加水体景观设计以及扩大绿地并减少不必要的硬质广?     

西北地区戈壁和绿洲风蚀起沙(尘)的研究

利用敦煌地区戈壁和绿洲的观测资料,分析了两种地表下春季的风蚀起沙(尘)情况.研究表明,在自然状态下,由于地表土壤的粒子尺度分布特征、植被覆盖度及地表土壤水分含量等下垫面特征不同,绿洲地表风蚀起沙的临界摩擦速度要大于戈壁地表,其垂直尘粒通量(风蚀起沙率)比戈壁地表小将近一个数量级;但考虑人为的翻耕作用时,绿洲地表风蚀起沙的临界摩擦速度可能会减小一半以上,其垂直尘粒通量也将增加大约一个数量级,甚至比戈壁地表还要大.     

Heat transfer augmentation and flow characteristics in ribbed triangular duct solar air heater: An experimental analysis

An experimental study has been carried out to analyze the effect of inclined ribs used as roughness element on heat transfer along its friction characteristics. The roughness parameters include relative roughness pitch (P/e) ranges from 4–16, relative roughness height (e/D_h) ranges from 0.021–0.043 and angle of attack (α) ranges from 30° to 75°. The Reynolds number (Re) lies in the range of 4500–28000. The heat transfer and friction factor data obtained from the experiment and it is compared with the data obtained from smooth duct under the same conditions. Considerable augmentation was observed in heat transfer and friction over the smooth duct. Correlation was also developed for Nusselt number (Nu) and friction factor (f) as a function of roughness and flow parameter.     

基于吸引力-摩擦力分析的入境旅游市场研究——以大连市为例

以2008年大连市夏季调查问卷为基础,运用因子分析从吸引力和摩擦力两个方面分析大连入境游客的潜在特征,确立了3个吸引力因子和3个摩擦力因子,并在此基础上利用方差分析法进一步研究吸引力和摩擦力在不同人口统计学特征群体间的差异,为大连旅游目的地的开发和旅游市场开拓提供有益参考。     

An analytic study of the effect of saltation on wind profiles

An analytic study of wind profiles above the saltation layer, in which the motion of uniform saltating grains of sand or snow occurs, is conducted. In this study, analytic solutions of the Ekman layer equation that governs the motion of air in a barotropic, neutral atmosphere are obtained in order to investigate the effects of the saltation on the airflow at large distance from a smooth surface. Solutions are derived subject to expressions of the eddy viscosity K(z) defined above the saltation layer up to the Ekman layer. The wind profiles and boundary layer interactions with the saltation process are discussed. With the assumptions that the eddy viscosity varies smoothly from the surface layer to the Ekman layer and K=0.4u _* z(1–z/h), the solutions are found to be consistent with bottom boundary conditions, specified by the velocity profile law outside the saltation layer. These solutions can be either used as an alternative to predict the saltation or used to test the sensitivities of the parameterization scheme designed to simulate dust emissions in a climate or general circulation model (GCM).     

Human walks carefully when the ground dynamic coefficient of friction drops below 0.41

This study investigated the available and utilized friction during non-slip gait in level walking, and determined the limit which human starts to walk carefully to adapt to slippery surface. Sixteen floor–footwear-contaminant conditions with different slipperiness (dynamic coefficient of friction, DCOF, from 0.11 to 1.06) were employed. Fifteen harnessed Chinese male performed ten self-paced walking trials in each condition without slips. The utilized friction (COF_u) was obtained from the maximum value of shear to normal ground reaction force ratio during the first 25% stance. ANOVA and Tukey tests showed three subsets with similar COF_u, and confirmed the hypothesis that the utilized friction drops gradually when the available friction drops below a certain critical limit. Non-linear regression models were applied to the data to determine the COF_u to be 0.20 and the limit of available ground friction which human starts to walk carefully to adapt to slippery surface (DCOF_limit) to be 0.41.     

高耐磨化学复合镀层的研究

为了改善化学镀Ni-P合金镀层的耐磨性能,提高化学镀Ni-P合金镀层的使用寿命,实验中分别在化学镀液中加入了硬质相SiC粒子、Al2O3粒子以及具有自润滑性能的PTFE粒子,使它们与Ni-P合金一起共沉积,从而制备出具有特殊功效的高耐磨复合镀层.实验结果表明:化学镀Ni-P-SiC以及Ni-P-Al2O3复合镀层由于硬质粒子的加入使镀层的耐磨性比Ni-P镀层提高了6倍左右;Ni-P-PTFE复合镀层的摩擦系数可达0.063,远小于Ni-P镀层0.2的摩擦系数,同时耐磨性能也比Ni-P合金镀层有了较为明显的提高.