抑制涡激振动的螺旋列板设计参数研究

基于水池模型实验结果和工程设计经验,结合国内外试验数据,着重分析用于抑制海洋立管涡激振动的螺旋列板几何参数(鳍高和螺距)及覆盖率对立管涡激振动的影响;并对水动力直径和水动力系数的选取对预报涡激振动的影响进行了分析,进而提出了适合于海洋立管工程应用的螺旋列板几何和设计参数选取的建议,为螺旋列板工程应用、海洋立管强度和疲劳设计提供参考。     

涡流发生器对潮流能水轮机翼型水动力学特性影响的数值模拟

为了改善潮流能水轮机叶片表面流动分离问题,提高其升阻比,本文通过在潮流能水轮机叶片表面加装涡流发生器,来研究涡流发生器对潮流能水轮机水动力学性能的影响。本文以NACA4418翼型为研究对象,分别建立了含VGs和不含VGs的三维模型,利用CFD方法研究了VGs的高度、长度以及相邻一对VGs之间的间距等多个方面对该翼型性能的影响。结果表明:VGs可以有效地提高翼型的最大升力系数;相邻VGs间距的增加对流动分离的抑制有积极影响。此外,通过对尾迹区流线和旋涡的分析,进一步揭示了尾迹区的流场特征。     

自重湿陷性黄土地区桩基设计探讨

根据自重湿陷性黄土的特点、《湿陷性黄土地区建筑规范》（GB50025—2004）和《建筑桩基技术规范》（JGJ94—94）中关于桩基设计的对比分析，通过自重湿陷性黄土场地工程实例分析计算，依据负摩擦产生的机理——中性点理论，论述了自重湿陷性黄土场地中桩基设计应考虑中性点，而不应全部计入负摩阻的观点。     

皖中泥质岩工程性质探讨

历来对半胶结泥质岩风化等级划分都带有许多主观性,从而影响提承载力,有的规范要求可不对半胶结岩石进行风化程度划分,但有时要对这些岩石进行工程地质细分,从而准确确定各分层的承载力与摩阻力。统计了合肥、六安、淮南、安庆地区等大量实践资料,用标准贯入击数、重型圆锥触探实验击数等原位测试手段来划分泥质岩风化等级,并对泥质岩的承载力与摩阻力等工程地质性质做出了评价。     

玛湖-盆1井西复合含油气系统二叠系地下水动力场的形成与演化

油气运聚及分布和地下水动力场的形成与演化密切相关,随着盆地的演化,地下水动力场也经历了形成、发展和消亡的过程.对水化学、水动力分布特征研究表明,玛湖-盆1井西复合含油气系统二叠系的现今水动力场由于达巴松凸起而呈现分割性,形成玛湖和盆1井西2个独立的水动力体系,欠压实的存在使凹陷内仍然保持离心流特征,而盆地西北缘则是大气水下渗向心流区.研究区二叠系的水动力场演化具有南移特征.     

动三轴试验机轴向摩擦解决的研究

介绍了20 kN动三轴试验机机械工作原理,分析了该仪器轴向摩擦力的产生原因,提出了解决办法并加以具体实施.     

Determining short-term changes in the hydraulic properties of a sandy-loam soil by a three-run infiltration experiment

ABSTRACT

Soil structure-dependent parameters can vary rapidly as a consequence of perturbing events such as intense rainfall. Investigating their short-term changes is therefore essential to understand the general behaviour of a porous medium. The aim of this study is to gain insight into the effects of wetting, perturbation and recovery processes through different sequences of Beerkan infiltration experiments performed on a sandy-loam soil. Two different three-run infiltration experiments (LHL and LLL) were carried out by pouring water at low (L, non-perturbing) and high (H, perturbing) heights above the soil surface and at short time intervals (hours, days). The results demonstrate that the proposed method allows one to capture short-term variations in soil structure-dependent parameters. The developed methodology is expected to simplify the parameterization of hydrological models with temporally variable soil hydraulic properties.     

Dynamic loading tests and seismic response analysis of a stud-type damper composed of multiple friction units with disc springs

This paper presents an experimental study on the performance of a shear-sliding stud-type damper composed of multiple friction units with high-tension bolts and disc springs. A numerical evaluation of the response reduction effects achieved by the stud-type damper is also presented. In dynamic loading tests, the behavior of stud-type multiunit friction damper specimens was investigated. Three different full-scale damper specimens, which were composed of five, six, or seven friction units with two or four sliding surfaces, were incorporated into loading devices for testing. The stud-type friction dampers demonstrated stable rigid-plastic hysteresis loops without any remarkable decrease in the sliding force even when subjected to repetitive loading, in addition to showing no unstable behavior such as lateral buckling. The damper produced a total sliding force approximately proportional to the number of sliding surfaces and friction units. The total sliding force of the stud-type damper can thus be estimated by summing the contributions of each friction unit. In an earthquake response simulation, the control effects achieved by stud-type dampers incorporated into an analytical high-rise building model under various input waves, including long-period, long-duration and pulse-like ground motions, were evaluated. A satisfactory response reduction was obtained by installing the developed stud-type dampers into the main frame without negatively impacting usability and convenience in terms of building planning.     

Failure time variation derived from R–S relation: the role of the static stress perturbation

In general, earthquake cycle related to earthquake faulting could include four major processes which could be described by (1) fault locking, (2) self-acceleration or nucleation (possible foreshocks), (3) coseismic slip, and (4) post-stress relaxation and afterslip. A sudden static stress change/perturbation in the surrounding crust can advance/delay the fault instability or failure time and modify earthquake rates. Based on a simple one-dimensional spring-slider block model with the combination of rate-and-state-dependent friction relation, in this study, we have approximately derived the simple analytical solutions of clock advance/delay of fault failures caused by a sudden static Coulomb stress change applied in the different temporal evolution periods during an earthquake faulting. The results have been used in the physics-based explanation of delayed characteristic earthquake in Parkfield region, California, in which the next characteristic earthquake of M 6.0 after 1966 occurred in 2004 instead of around 1988 according to its characteristic return period of 22 years. At the same time, the analytical solutions also indicate that the time advance/delay in Coulomb stress change derived by the dislocation model has a certain limitation and fundamental flaw. Furthermore, we discussed the essential difference between rate- and state-variable constitutive (R–S) model and Coulomb stress model used commonly in current earthquake triggering study, and demonstrated that, in fact, the Coulomb stress model could be involved in the R–S model. The results, we have obtained in this study, could be used in the development of time-dependent fault interaction model and the probability calculation related to the time-dependent and renewal earthquake prediction model.     

A new friction law for sliding rigid blocks under cyclic loading

A rigid block sliding down an inclined plane under the action of gravity was monitored with accelerometers and an LVDT to investigate how the transition from static to kinetic friction develops. Once the transition patterns were identified, experiments were carried out to study the response of a dynamically excited rigid block sliding down the inclined plane of a shaking table. Harmonic time series were used as input motions. The laboratory results allowed the definition of a continuous friction law to model the continuous variation of the friction from its static to kinetic condition. This law was implemented into the commercial 3D distinct element code 3DEC to numerically reproduce the experiments carried out, thus validating the friction law. Afterwards, the friction law was used to evaluate the sliding due to the kinetics of the block. Three cases were analyzed: constant friction coefficient, Coulomb friction law and the proposed friction law. These computations were compared to laboratory measurements. It is found that permanent displacements computed by considering the new law are in better agreement with laboratory measurements.