Estimation of the Friction Velocity in Stably Stratified Boundary-Layer Flows Over Hills     

José Luis Argaín  Pedro M. A. Miranda  Miguel A. C. Teixeira 《Boundary-Layer Meteorology》2009,130(1):15-28

A method is suggested for the calculation of the friction velocity for stable turbulent boundary-layer flow over hills. The method is tested using a continuous upstream mean velocity profile compatible with the propagation of gravity waves, and is incorporated into the linear model of Hunt, Leibovich and Richards with the modification proposed by Hunt, Richards and Brighton to include the effects of stability, and the reformulated solution of Weng for the near-surface region. Those theoretical results are compared with results from simulations using a non-hydrostatic microscale-mesoscale two-dimensional numerical model, and with field observations for different values of stability. These comparisons show a considerable improvement in the behaviour of the theoretical model when the friction velocity is calculated using the method proposed here, leading to a consistent variation of the boundary-layer structure with stability, and better agreement with observational and numerical data.  相似文献   

A micromechanics-based elastoplastic damage model for quasi-brittle rocks     

N. Xie  Q.Z. Zhu  L.H. Xu  J.F. Shao 《Computers and Geotechnics》2011

This paper presents a micromechanics-based elastoplastic damage model for quasi-brittle rocks under a compressive stress state. The plastic strain is considered to be related to frictional sliding along micro-cracks, and it is coupled inherently with damage evolution. By following a homogenization procedure, we determine the free energy of the matrix-cracks system. The thermodynamic force associated with the inelastic strain contains a back stress, which controls material hardening. Next, in order to determine plastic flow and crack propagation, we propose a Coulomb-type friction criterion, which is used as the plastic yielding function, and a damage criterion based on strain energy release rate. These thermodynamic formulations with a micro–macro scale change allow reducing significantly the number of model parameters, as compared to phenomenological models. Our model is applied to simulate triaxial compression tests on two sets of diabase samples. The first sample set is cored from a fresh diabase rock mass, and the second from a slightly weathered one. Comparisons between numerical predictions and test data are presented.  相似文献   

断层带中假玄武玻璃成因机制及非稳态流变意义     

李文元  曹淑云 《地质论评》2022,68(1):2022010004-2022010004

假玄武玻璃呈玻璃质或隐晶质特性,常常与断层带相伴出现,其形成能有效地降低断层摩擦强度,被认为是古地震快速滑动的化石纪录。因此,对假玄武玻璃的研究对深入了解深部就位的断层变形和地震成因机制等具有重要意义。尽管国内外学者对假玄武玻璃开展了长期的研究,也积累了丰富的资料,然而,由于天然假玄武玻璃非常少见或零星地被报道,再加上其形成环境和过程的复杂性,对假玄武玻璃的构造特征、形成环境和成因机制仍然存在诸多争议及亟待解决的关键科学问题。研究表明,假玄武玻璃可以发育在大陆岩石圈不同深度范围内,即中下地壳乃至上地幔以糜棱岩为主的韧性变形领域（>60 km）,或中上地壳层次以碎裂岩为主的脆性变形域（<12 km）。越来越多证据也显示出在断层带的脆—韧性转换域中形成的假玄武玻璃跟浅源地震活动直接关联,也意味着中上地壳脆性变形和中下地壳塑性变形之间存在着更为复杂的耦合关联,同时对不同深部岩石强度和力学行为提出了挑战。对假玄武玻璃形成机制存在由断层面上的摩擦热导致的摩擦熔融体或仅仅是断层面岩石超碎裂粉碎作用认识的争议。而有研究认为干的环境有利于假玄武玻璃形成,因为流体的存在会降低断层面的有效正应力,不利于热量的积累以及摩擦熔融的进行;然而,另外一种观点认为流体的存在可以降低矿物熔融温度有利于断层摩擦熔融及形成假玄武玻璃。本文从假玄武玻璃的形成机制、形成深度、流体影响、形成后对断层强度的影响、以及保存与破坏机制几方面进行了最新总结,并对假玄武玻璃中非晶态物质的成因、脆—韧性转换带之下岩石的变形机制以及对陆壳强度的影响和非稳态流变意义进行探讨。  相似文献   

锚杆支护在华能大厦基坑中的应用及提高锚杆抗拔力的措施     

陈喜友 《城市地质》2015,(Z2):38-41

本文以华能大厦基坑工程为例,根据场地工程地质条件、水文地质条件,周边环境设施,结合工程条件及施工经验,对华能基坑工程中锚杆施工的钻进工艺、灌浆工艺等方面进行了改进,从而提高锚杆的抗拔力。  相似文献   

Dynamic responses of two blocks under dynamic loading using experimental and numerical studies     

《Applied Ocean Research》2015

Block type quay walls are one of the most generally used type of gravity quay walls however seismic risks of this kind of structures have not already received the proper amount of attention. In this study, stability of block type quay wall which consists of two concrete blocks is investigated experimentally and numerically. 1 g shaking table tests are used for experimental study. Model scale is 1/10 and model is placed on rigid bed to ignore damage due to foundation deformation. Two different granular materials (Soil 1 and Soil 2) which have different nominal diameters are used as backfill materials to understand the effect of nominal diameters on structure's stability. During the experiments accelerations, pore pressures, soil pressures and displacements are measured for two blocks under different cycling loadings. Soil pressure test results are presented in non-fluctuating and fluctuating components to determine the distribution and application point of the fluctuating component on two blocks. By using experiment results, the friction coefficients between the rubble-block and block-block are determined and compared with recommended friction coefficients in standards. PLAXIS V8.2 software program is used for numerical study to determine the material properties.  相似文献   

Incremental plasticity analysis of frictional soils     

J. T. Christian  A. J. Hagmann  W. A. Marr 《国际地质力学数值与分析法杂志》1977,1(4):343-375

Three constitutive models of soil are used in finite element analyses of lateral earth pressure and bearing capacity. The three models are an elasto-plastic formulation derived from the Mohr-Coulomb law, a similar model with the plastic dilatancy removed, and a strain hardening model with a capped yield criterion. Stiffness formulations are described; the non-dilatant model has a non-symmetric stiffness. The results for the retaining walls are in close agreement with classical soil mechanics, but the bearing capacity analyses greatly overestimate the bearing capacity. The patterns of motion are, however, reasonable. Reasons for the discripancies in the bearing capacity case include: (a) the elements are too stiff and do not permit sliding on discrete failure planes; (b) the bearing capacity problem is itself not well settled theoretically; (c) very fine element divisions are necessary in areas of strong stress gradients and (d) rotation of principal stresses is significant.  相似文献   

城市热岛效应的分析     

卢敬华  李国平 《成都信息工程学院学报》1991,(Z1)

本文从大气热力——动力学方程组出发,分析了城市加热作用和摩察作用引起的热岛环流特征,讨论了环流的强度和温度空间分布与背景大气稳定度和平均风速的关系。本文的结果可以解释城市白天的某些气象现象。  相似文献   

A note on the Lade–Duncan failure criterion     

《Geomechanics and Geoengineering》2013,8(4):299-304

  相似文献   

SEDIMENT TRANSPORT EXPERIMENTSIN UNSTEADY FLOWS     

DE SUTTER R.  HUYGENS M.  and VERHOEVEN R. Hydraulics Laboratory  Ghent University  Sint-Pietersnieuwstraat    Ghent  Belgium. 《国际泥沙研究》2001,16(1)

l INTRODUCTIONThe theories and formulas of sediment dynamics were established based on steady and uniform flows.These theories and formulas often fail to aPply in engineering projects because, in nthee, sediment istransported often by unsteady and non-uniform fiows (Wang et al., l997).TWo cases ofnon-stationarity can be distinguished f long-tertn and short-term (Plate, l994). Long-termnon-stationarity tfansport can be defined as a sediment process which can be treated by sequences ofstat…  相似文献   

EXPERIMENTAL STUDY ON EQUILIBRIUM CONCENTRATION OF DEBRIS FLOWS   总被引：1，自引：0，他引：1  

Bin YU Assoc Prof.  Chengdu Institute of Mountain Disaster  Enviromnent  CAS    P.O. Box  P. R. China.E-mail: drbinyu@sc.homeway.com.cn 《国际泥沙研究》2001,16(2)

Discussion open until 2002.EmunmL SwrY ONEQUII.thare CONCENTRATION OF DEBRIS rrOWSBin YU1AaSTsiCTThe paPe PresentS experimntal study of debris flows. The equiMm concentIation of solidparticle in the now is a hahon of the energy slope, density of solid Particle and kinetic ffichonange of paxtiles. The kinhc forhon angle is a funhon of intemal ffichon angle, the cOnCentrationof solid phocles and the mtalmum POssible concewhon. TO deteImin th6 hahon between thekinetic fficho…  相似文献