Critical stress and load conditions for pitting calculations of involute spur and helical gear teeth

Calculation methods of spur and helical gear drives for preliminary designs or standardization purposes available in technical literature, use the Hertz equation to evaluate the contact stress, assuming the load to be uniformly distributed along the line of contact. However, this model presents some discrepancies with experimental results because the changing rigidity of the pair of teeth along the path of contact produces a non-uniform load distribution, which implies that some load distribution factors are required to compute the contact stress. In this paper, a non-uniform model of load distribution along the line of contact, recently developed, obtained from the minimum elastic potential criterion, has been used. This model combined with the Hertz equation yields more accurate values of the contact stress. As the load per unit of length at any point of the line of contact and any position of the meshing cycle has been described by a very simple analytic equation, a complete study of the location and value of the critical contact stress has been carried out. From this study, a recommendation for the calculation of the pitting load capacity of spur and helical gears is proposed.     

水下粉细砂土体在超高频机械振动荷载作用下液化特性的试验研究

为了量化高频机械振动对土壤液化的具体效果,在试验室泥槽中对不同性质的水下粉细砂沉积物开展了诸如不同振动作用时间及不同工况下的液化试验,利用静力触探仪测量了振动作用前后其承载力变化情况,基于试验数据分析讨论了振动作用时间、振动作用距离、振动频率对于液化效果的影响.     

气密性混凝土在松卜岭高瓦斯隧道衬砌中的应用

松卜岭隧道穿越煤岩层,为高瓦斯隧道。为保证隧道的运行安全,在隧道瓦斯设防段须采用气密性混凝土对坑道进行全断面封闭式复合衬砌。通过对隧道穿越的地质环境条件、设计标准、气密性混凝土材料以及合理配合比的选择分析,采用室内试件测定方法对混凝土试件的透气量进行测定,计算得出透气系数。对不同衬砌形式的混凝土的气密性进行了评价,结果表明：气密性混凝土在隧道衬砌中具有明显的抗气性。不仅能在瓦斯隧道衬砌中应用,也可应用于其他有较高防潮、防渗要求的工程中。     

坝下箱涵环向裂缝与纵向抗裂验算

分析了坝下箱涵产生环向裂缝的机理成因,建立了变温与土压力、管身自重及管内水重联合作用下的坝下箱涵伸缩缝间距与纵向抗裂验算计算方法,给出了相应计算公式,具有工程应用价值.     

某资料档案库楼板裂缝成因分析及加固处理

通过对某资料档案库楼板裂缝展布规律、缝宽及实际承受荷载的实测和分析,采用PKPM软件对结构在设计荷载和实际使用荷载两种工况下的安全性进行验算,找出楼板裂缝产生的原因,评价了结构的安全性。为保证结构的安全性和耐久性．提出了楼板裂缝处理的工程措施。     

基于改进串联合闸电阻的变压器励磁涌流抑制研究

在利用合闸电阻抑制变压器轻载或空载合闸时产生励磁涌流的基础上,提出一种在合闸电阻上串联适当电容器的改进方法。该方法在原有的合闸电阻上串联电容,通过适当选取电容的容值,以减少励磁涌流的大小,加快励磁涌流的衰减速度。将该方法与分相合闸技术相结合,可最大程度实现变压器励磁涌流的抑制。仿真实验结果验证了该方法的可行性。     

黄河龙口水利枢纽工程设计过程回顾

黄河龙口水利枢纽工程为河床式水电站工程。设计和建设过程中,随着对客观自然条件认识的逐步加深、外部条件的不断变化和工程技术的发展,对枢纽布置、基础处理、施工导流方案、接入系统等方面,不断调整、完善和优化,取得了良好的效果。     

Spectral‐ALS data fusion for different roughness parameterizations of forested floodplains

Natural river floodplains and adjacent wetlands grow typically a diverse and heterogeneous combination of herbs, shrubs and trees, which play an essential role in determining the total flow resistance. Hydrodynamic effects of trees in forested floodplains can provide the majority of flow resistance during flood events. Nevertheless, ground‐based techniques to acquire vegetation parameters are expensive and difficult to apply over long reaches. This paper presents a novel method of automated roughness parameterization of riparian woody vegetation by fusion of Quickbird multi‐spectral image with airborne laser scanning (ALS) data. The data fusion approach includes: individual tree detection and estimation of vegetation metrics from light detection and ranging (LiDAR) data, assessment of predictive models for the vegetation parameters and spatial mapping of the vegetation parameters for the forest plants in the riparian corridor. The proposed method focuses on estimation of plant density (d), crown diameters (D_C), tree height (h), stem diameter (D_S), crown base height (cbh) and leaf area index (LAI). The procedure is tested along a 14‐km reach of the Sieve River (Tuscany, Italy) characterized by high woody plant density. Due to the complex study area, the data fusion approach explains with variable reliability the local vegetation properties (R²(D_C) = 0.14, R²(h) = 0.84, R²(D_S) = 0.25, R²(cbh) = 0.66). The generated structural parameter maps represent spatially explicit data layers that can be used as inputs to hydrodynamic models used to analyse flow resistance effects in different submergence conditions of vegetation. A simple flow resistance model was applied over a test area comparing the results of the proposed method and a traditional ground‐based approach. The modelling results showed that the new method is able to provide accurate output data to describe the interaction between water levels and bio‐mechanical characteristics of vegetation. The proposed methodology provides a fast, repeatable and accurate way of obtaining floodplain roughness, which enables regular updating of vegetation characteristics. Copyright © 2010 John Wiley & Sons, Ltd.     

大体积混凝土原材料、配合比与混凝土温升及防裂性能之间的关系

岩寨电站大坝工程对混凝土工程使用的水泥、粉煤灰、粗细骨料、外加剂及水等进行了有效的监控,并重点对混凝土原材料在混凝土水化热温升方面的影响和特种混凝土在坝体温控防裂方面的效果进行了研究.为进一步了解不同的水泥品种和混凝土水化热温升之间的关系,采用了掺低热水泥混凝土施工.