Unconfined seepage analysis in earth dams using smoothed fixed grid finite element method     

Farhang Daneshmand 《国际地质力学数值与分析法杂志》2012,36(6):780-797

One major difficulty in seepage analyses is finding the position of phreatic surface which is unknown at the beginning of solution and must be determined in an iterative process. The objective of the present study is to develop a novel non‐boundary‐fitted mesh finite‐element method capable of solving the unconfined seepage problem in domains with arbitrary geometry and continuously varied permeability. A new non‐boundary‐fitted finite element method named as smoothed fixed grid finite element method (SFGFEM) is used to simplify the solution of variable domain problem of unconfined seepage. The gradient smoothing technique, in which the area integrals are transformed into the line integrals around edges of smoothing cells, is used to obtain the element matrices. The solution process starts with an initial guess for the unknown boundary and SFGFEM is used to approximate the field variable. The boundary shape is then modified to eventually satisfy nonlinear boundary condition in an iterative process. Some numerical examples are solved to evaluate the applicability of the proposed method and the results are compared with those available in the literature. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Asymptotic formulae for correcting finite element predicted natural frequencies of gravity and embankment dams     

Chongbin Zhao  G.P. Steven 《Soil Dynamics and Earthquake Engineering》1996,15(3):161-169

Extraction of natural frequencies of a gravity dam or an embankment dam plays an important role in the seismic design of the dam because the seismic response of a dam is dependent largely on the dynamic characteristics of the dam. Owing to the lack of exact solutions and the geometry of a dam, numerical methods such as finite element methods have been often used to extract the natural frequencies of the dam. Since the finite element method is an approximate one, the resulting finite element solution to the natural frequency of a dam cannot be safely used unless its accuracy is evaluated within the acceptable range for the seismic design of the dam. To solve this problem, some asymptotic formulae for correcting the finite element predicted natural frequencies of a gravity dam and an embankment dam have been developed in this paper. Since the present asymptotic formulae are derived from the fact that the finite element solution tends to the exact one if the finite element size used approaches zero, they provide a corrected solution of higher accuracy for the natural frequency of a dam so that the accuracy of a finite element solution can be evaluated against this corrected solution. After the correctness and usefulness of the present formulae are assessed, two practical examples have been given to show how the asymptotic formulae can be used to correct and evaluate the discretization error for the finite element predicted natural frequencies of gravity dams and embankment dams.  相似文献   

Seismic hazard evaluation for dams in northern Colorado, U.S.A.     

Ute R. Vetter  Jon P. Ake  Roland C. Laforge 《Natural Hazards》1996,14(2-3):227-240

A seismic hazard evaluation for three dams in the Rocky Mountains of northern Colorado is based on a study of the historical seismicity. To model earthquake occurrence as a random process utilizing a maximum likelihood method, the catalog must exhibit random space-time characteristics. This was achieved using a declustering procedure and correction for completeness of recording. On the basis of the resulting a- and b-values, probabilistic epicentral distances for a 2 × 10^–5 annual probability were calculated. For a random earthquake of magnitude M _L 6.0–6.5, this distance is 15 km. Suggested ground motion parameters were estimated using a probabilistic seismic hazard analysis. Critical peak horizontal accelerations at the dams are 0.22g if median values are assumed and 0.39g if variable attenuation and seismicity rates are taken into account. For structural analysis of the dams, synthetic acceleration time series were calculated to match the empirical response spectra. In addition, existing horizontal strong motion records from two Mammoth Lakes, California earthquakes were selected and scaled to fit the target horizontal acceleration response spectra.  相似文献   

Impacts of fisheries on plankton community structure   总被引：3，自引：2，他引：3  

Reid  P. C.; Battle  E. J. V.; Batten  S. D.; Brander  K. M. 《ICES Journal of Marine Science》2000,57(3):495-502

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基于分布式光纤传感的堤坝安全监测技术及展望          下载免费PDF全文

冷元宝  朱萍玉  周杨  王送来 《地球物理学进展》2007,22(3):1001-1005

及时、准确地掌握堤坝的性态，是保证堤坝安全运行的基础.因此，需要一种实时监测系统对堤坝进行监测.分析了堤坝健康监测的主要内容，介绍了分布式光纤传感技术的工作原理及使用现状；探讨了分布式光纤传感技术在我国堤坝渗流和形变中的应用；指出了分布式光纤传感技术在土堤坝使用中存在的问题，并给出了新的堤坝长期安全监测系统设计建议，结论有益于指导构建新的基于分布式光纤技术的堤坝安全监测系统.  相似文献   

Seismic fragility assessment of concrete gravity dams     

Paulos B. Tekie  Bruce R. Ellingwood 《地震工程与结构动力学》2003,32(14):2221-2240

Many concrete gravity dams have been in service for over 50 years, and over this period important advances in the methodologies for evaluation of natural phenomena hazards have caused the design‐basis events for these dams to be revised upwards. Older existing dams may fail to meet revised safety criteria and structural rehabilitation to meet such criteria may be costly and difficult. Fragility assessment provides a tool for rational safety evaluation of existing facilities and decision‐making by using a probabilistic framework to model sources of uncertainty that may impact dam performance. This paper presents a methodology for developing fragilities of concrete gravity dams to assess their performance against seismic hazards. The methodology is illustrated using the Bluestone Dam on the New River in West Virginia, which was designed in the late 1930s. The seismic fragility assessment indicated that sliding along the dam–foundation interface is likely if the dam were to be subjected to an earthquake with a magnitude of the maximum credible earthquake (MCE) specified by the U.S. Army Corps of Engineers. Moreover, there will likely be tensile cracking at the neck of the dam at this level of seismic excitation. However, loss of control of the reservoir is unlikely. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

修筑寒区小型水利工程的经验回顾     

Rudolf V. Zhang 《冰川冻土》2004,26(Z1):12-20

The paper provides a review of experience with the construction of hydraulic projects in the permafrost regions. Principles for construction, operation and maintenance of earth dams are refined and formulated. High priority needs for improving the stability of structures are identified.  相似文献   

Continuous ambient‐vibration monitoring of the arch dam of Mauvoisin     

Georges R. Darbre  Jean Proulx 《地震工程与结构动力学》2002,31(2):475-480

This paper presents the experimental programme and results of a continuous ambient vibrations recording programme carried out on the 250 m arch dam of Mauvoisin. This project follows a series of previous measurements completed for seven different water levels. An automated system was set up on the dam and the ambient vibrations were recorded twice daily for a period of 6 months. Frequency shifts were tracked throughout the testing period and the effects of the varying water level were identified. The results confirmed the behaviour observed in previous ambient‐ and forced‐vibration tests. The added‐mass effects are overcome by the stiffening of the dam due to increasing hydrostatic pressure for lower reservoir levels. This trend is then reversed for higher water levels. Any temperature‐related effects were not identified. The experimental techniques are briefly described and the frequency identification process and its limitations are discussed. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

An experimental evaluation of ice cover effects on the dynamic behaviour of a concrete gravity dam     

Patrick Paultre  Jean Proulx  Charles Carbonneau 《地震工程与结构动力学》2002,31(12):2067-2082

An extensive forced‐vibration testing programme has been carried out on an 84‐m concrete gravity dam located in northeastern Québec, Canada. The dam was subjected to a harmonic load on the crest in summer and severe winter conditions with temperatures ranging from ?10°C to ?15°C and a 1.0–1.5m ice cover. Acceleration and hydrodynamic frequency responses were obtained in different locations on the dam and in the reservoir. The main objective of the repeated tests was to investigate the effects of the ice cover on the dynamic behaviour of the dam–reservoir–foundation system, by comparing summer and winter results. Modifications in damping and resonance frequencies were observed, as well as an additional resonance that was attributed to an interaction of the dam with the ice cover. These findings provided a reliable and unique database for the investigations of dam–reservoir–foundation interaction and, in particular, the ice‐cover effects for dams located in northern regions. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

Assessing the TOPKAPI non‐linear reservoir cascade approximation by means of a characteristic lines solution     

Zhiyu Liu  Ezio Todini 《水文研究》2005,19(10):1983-2006

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