Flexible support of a pile embedded in unsaturated soil under Rayleigh waves     

Zijian Yang  Wenbing Wu  Hao Liu  Yunpeng Zhang  Rongzhu Liang 《地震工程与结构动力学》2023,52(1):226-247

Under the action of Rayleigh waves, pile head is easy to rotate with a concrete pile cap, and pure fixed-head condition is rarely achieved, which is a common phenomenon for it usually occurs on the precast piles with insufficient anchorage. In addition, the propagation characteristics of Rayleigh wave have been changed significantly due to the existence of capillary pressure and the coupling between phases in unsaturated soil, which significantly affects the pile-soil interaction. In order to study the above problems, a coupled vibration model of unsaturated soil–pile system subjected to Rayleigh waves is established on the basis that the pile cap is equivalent to a rigid mass block. Meanwhile, the soil constitution is simplified to linear-elastic and small deformations are assumed to occur during the vibration phase of soil–pile system. Then, the horizontal dynamic response of a homogeneous free-field unsaturated soil caused by propagating Rayleigh waves is obtained by using operator decomposition theory and variable separation method. The dynamic equilibrium equation of a pile is established by using the dynamic Winkler model and the Timoshenko beam theory, and the analytical solutions of the horizontal displacement, rotation angle, bending moment and shear force of pile body are derived according to the boundary conditions of flexible constraint of pile top. Based on the present solutions, the rationality of the proposed model is verified by comparing with the previous research results. Through parametric study, the influence of rotational stiffness and yield bending moment of pile top on the horizontal dynamic characteristics of Rayleigh waves induced pile is investigated in detailed. The analysis results can be utilized for the seismic design of pile foundation under Rayleigh waves.  相似文献   

柔性仿金枪鱼月牙形尾鳍水动力分析     

成巍苏玉民  秦再白徐玉如 《海洋工程》2004,22(4):73-79

为研究鱼类高速游动机理,以金枪鱼月牙形尾鳍为对象,采用面元法计算分析了其非定常水动力性能。假设尾鳍在横移和摇摆的同时,以某一匀速向前运动,并假设其在弦向和展向以某一给定规律发生变形,以模仿柔性变形。探讨了前进速度、横移和摇摆的幅度、频率及其相位差对柔性尾鳍推进性能的影响,并与做相应运动的刚性尾鳍进行了对比。  相似文献   

In-plane floor flexibility effects on torsionally unbalanced systems     

J. De-La-Colina 《地震工程与结构动力学》1999,28(12):1705-1715

This paper presents the results of an analytical work addressed to understand the effects of in-plane floor flexibility on torsionally unbalanced (TU) systems subjected to bidirectional firm-soil earthquake records. The study uses a structural system consisting of a linear-elastic diaphragm supported by non-linear frames oriented along two orthogonal directions. The diaphragm is modelled with plane-stress finite elements and frames with stiffness-degrading flexural elements. Results indicate that an increase of in-plane diaphragm flexibility leads to a reduction of frame displacements for systems with initial lateral period of vibration T>0·4 s. For systems with T⩽0·4 s, in-plane floor flexibility can lead to significant frame displacement increments (50 per cent higher). Results show that these variations on displacements decrease for increasing values of both the seismic-force reduction factor and the system initial lateral period. Copyright © 1999 John Wiley & Sons Ltd.  相似文献   

海油陆采平台护底方案优化研究——以胜利油田垦东12区块3号平台为例     

王顺华  刘波  魏光虎 《海岸工程》2008,27(4):70-76

胜利油田垦东12区块3号海油陆采平台位于进海路端头，防护非常重要。通过建立潮流数学模型及理论计算确定护底宽度，进而对护底结构进行了优化研究。经过经济技术对比，优选出砼联锁块软体排＋局部抛石结构为3号平台的护底结构方案，该方案具有现场施工效率高，后期维护工作量少的优点。  相似文献   

Step-wise Land-class Elimination Approach for extracting mixed-type built-up areas of Kolkata megacity     

Ansar Khan  Soumendu Chatterjee  Hashem Akbari  Saad Saleem Bhatti  Apurba Dinda  Chandana Mitra 《国际地球制图》2019,34(5):504-527

The extraction of urban built-up areas is an important aspect of urban planning and understanding the complex drivers and biophysical mechanism of urban climate processes. However, built-up area extraction using Landsat data is a challenging task due to spatio-temporal dynamics and spatially intermixed nature of Land Use and Land Cover (LULC) in the cities of the developing countries, particularly in tropics. In the light of advantages and drawbacks of the Normalized Difference Built-up Index (NDBI) and Built-up Area Extraction Method (BAEM), a new and simple method i.e. Step-wise Land-class Elimination Approach (SLEA) is proposed for rapid and accurate mapping of urban built-up areas without depending exclusively on the band specific normalized indices, in order to pursue a more generalized approach. It combines the use of a single band layer, Normalized Difference Vegetation Index (NDVI) image and another binary image obtained through Logit model. Based on the spectral designation of the satellite image in use, a particular band is chosen for identification of water pixels. The Double-window Flexible Pace Search (DFPS) approach is employed for finding the optimum threshold value that segments the selected band image into water and non-water categories. The water pixels are then eliminated from the original image. The vegetation pixels are similarly identified using the NDVI image and eliminated. The residual pixels left after elimination of water and vegetation categories belong either to the built-up areas or to bare land categories. Logit model is used for separation of the built-up areas from bare lands. The effectiveness of this method was tested through the mapping of built-up areas of the Kolkata Metropolitan Area (KMA), India from Thematic Mapper (TM) images of 2000, 2005 and 2010, and Operational Land Imager (OLI) image of 2015. Results of the proposed SLEA were 95.33% accurate on the whole, while those derived by the NDBI and BAEM approaches returned an overall accuracy of 83.67% and 89.33%, respectively. Comparisons of the results obtained using this method with those obtained from NDBI and BAEM approaches demonstrate that the proposed approach is quite reliable. The SLEA generates new patterns of evidence and hypotheses for built-up areas extraction research, providing an integral link with statistical science and encouraging trans-disciplinary collaborations to build robust knowledge and problem solving capacity in urban areas. It also brings landscape architecture, urban and regional planning, landscape and ecological engineering, and other practice-oriented fields to bear together in processes for identifying problems and analyzing, synthesizng, and evaluating desirable alternatives for urban change. This method produced very accurate results in a more efficient manner compared to the earlier built-up area extraction approaches for the landscape and urban planning.  相似文献   

Experimental Investigation on Flow Characteristics at Leeside of Suspended Flexible Curtain for Sedimentation Enhancement     

李艳红  喻国良 《中国海洋工程》2009,23(3):565-576

A new patent registered device-suspended flexible curtain (SFC) for sedimentation enhancement is proposed in this paper, which consists of two parts: a light-weight curtain with sediment-passing windows and a heavy pillar for the device stability. The mechanism of trapping nearbed sediment by the SFC is such that a primary and a secondary circulations with horizontal hubs would be formed at the leeside when it is placed on beds in running flow; the velocities within the sediment-passing windows are locally ...  相似文献   

柔壁渗透仪在防渗工程中的应用          下载免费PDF全文

靖向党  何世鸣  陈鹏  于波 《探矿工程》2012,39(2):53-55

针对防渗工程渗透系数检测的需要,介绍了柔壁渗透仪在测试水泥土固结体试样（钻孔取样）渗透系数中的应用。实践证明,柔壁渗透仪可用于防渗工程质量的检测,对制样要求不高、密封好、测试速度快,采用数字化采集处理系统,不但减少了测量读数等人为影响,提高了测量精度,而且快速便捷,无人值守,提高了工作效率,减轻了劳动强度。  相似文献   

边界问题及其对真空预压的影响     

高志义  冯军 《岩土工程技术》2014,28(5):250-256

给出了真空预压区四周开敞式与封闭式边界定义、两者的不同,分析了开敞式边界加固效果优于封闭式边界的原因并以三个实例说明之,给出如何将封闭式转化为开敞式的方法;柔性与刚性密封膜同样可构成开敞式与封闭式边界,讨论了此时两种边界下差别;给出了密封墙和支挡墙的定义、功能、应用范围;讨论了水泥搅拌与旋喷桩单体墙与格栅墙的定义、功能、应用范围,前者只能作为密封墙,后者既可作密封墙也可作支挡墙.  相似文献   

Combining cap-and-trade with offsets: lessons from the EU-ETS     

Raphael Trotignon 《Climate Policy》2013,13(3):273-287

Linking a cap-and-trade with an offset mechanism has many theoretical advantages: it reduces compliance costs, extends the price signal outside the cap-and-trade, and triggers technology transfer. However, it is feared that such linking will induce outsourcing of emissions reduction at a low price and undermine the price incentive in the cap-and-trade. The EU Emissions Trading Scheme (EU ETS) is the first full-scale example of a cap-and-trade system linked to project-based mechanisms such that offsets have effectively been used by industrial installations. This article is an ex post analysis of EU ETS data for the years 2008 and 2009, and the characteristics of the link and its efficiency are evaluated. Although offsets have been much used, their use is concentrated and not very intense or frequent, which allays the fear that offsets will flood the market. Although the majority of surrendered CERs effectively come from the largest and oldest projects, the credits surrendered are similar to those available on the market. Possible factors that contribute towards inefficiency are the rules for using offsets, transaction costs affecting the participation of small installations, awareness and openness to market-based instruments, and uncertainties regarding CERs offer and demand from other markets. However, the impact on EUA equilibrium price still needs to be quantified.  相似文献   

On the mechanics of contact between a flexible transducer diaphragm located at a rigid boundary and an elastic material     

A. P. S. Selvadurai  S. Labanieh  M. J. Boulon 《国际地质力学数值与分析法杂志》2007,31(7):933-952

In this paper we examine the mechanics of contact between a flexible elastic diaphragm and an isotropic elastic halfspace region where contact is established through the application of a normal stress. It is shown that a convenient solution for the maximum displacement and maximum flexural moment in the flexible diaphragm can be obtained by employing a variational technique. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献