Rijswijk, Netherlands
Rijswijk, Netherlands

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Zhang J.-M.,Tsinghua University | Wang G.,Ertan Hydropower Development Company
Acta Geotechnica | Year: 2012

This paper presents a theoretical framework for predicting the post-liquefaction deformation of saturated sand under undrained cyclic loading with emphasis on the mechanical laws, physical mechanism, constitutive model and numerical algorithm as well as practical applicability. The revealing mechanism behind the complex behavior in the post-liquefaction regime can be appreciated by decomposing the volumetric strain into three components with distinctive physical background. The interplay among these three components governs the post-liquefaction shear deformation and characterizes three physical states alternating in the liquefaction process. This assumption sheds some light on the intricate transition from small pre-liquefaction deformation to large post-liquefaction deformation and provides a rational explanation to the triggering of unstable flow slide and the post-liquefaction reconsolidation. Based on this assumption, a constitutive model is developed within the framework of bounding surface plasticity. This model is capable of reproducing small to large deformation in the pre- to post-liquefaction regime. The model performance is confirmed by simulating laboratory tests. The constitutive model is implemented in a finite element code together with a robust numerical algorithm to circumvent numerical instability in the vicinity of vanishing effective stress. This numerical model is validated by fully coupled numerical analyses of two well-instrumented dynamic centrifuge model tests. Finally, numerical simulation of liquefaction-related site response is performed for the Daikai subway station damaged during the 1995 Hyogoken-Nambu earthquake in Japan. © 2012 Springer-Verlag.

Wu Y.,Tsinghua University | Liu S.,Tsinghua University | Zhang L.,Ertan Hydropower Development Company
Engineering with Computers | Year: 2011

This paper reports the simulation results for the unsteady cavitating turbulent flow in a Francis turbine using the mixture model for cavity-liquid two-phase flows. The RNG k-ε turbulence model is employed in the Reynolds averaged Navier-Stokes equations in this study. In the mixture model, an improved expression for the mass transfer is employed which is based on evaporation and condensation mechanisms with considering the effects of the non-dissolved gas, the turbulence, the tension of interface at cavity and the effect of phase change rate and so on. The computing domain includes the guide vanes, the runner, and the draft tube, which is discretized with a full three-dimensional mesh system of unstructured tetrahedral shapes. The finite volume method is used to solve the governing equations of the mixture model and a full coupled method is combined into the algorithm to accelerate the solution. The computing results with the mixture model have been compared with those by the single-phase flow model as well as the experimental data. The simulation results show that the cavitating flow computation based on the improved mixture model agrees much better with experimental data than that by the single-phase flow calculation, in terms of the amplitude and dominated frequency of the pressure fluctuation. It is also observed from the present simulations that the amplitude of the pressure fluctuation at small flow rate is larger than that at large flow rate, which accords with the experimental data. © 2010 Springer-Verlag London Limited.

Wang G.,Ertan Hydropower Development Company | Zhang J.-M.,Tsinghua University | Wei X.,Southwest Jiaotong University
Yantu Gongcheng Xuebao/Chinese Journal of Geotechnical Engineering | Year: 2011

Soil-structure dynamic response analysis in liquefiable soil is a difficult problem due to the difficulty of modeling the post-liquefaction behavior and the instability of numerical calculation. A cyclic elasto-plasticity model developed by the authors, which can describe the large strain behavior during an entire liquefaction process, has been implemented in a fully coupled finite element program. The seismic response of Daikai subway station subjected to the 1995 Hyogoken-Nambu Earthquake is investigated to illustrate the philosophy of soil-structure dynamic response analysis with emphasis on soil liquefaction and also to validate its effectiveness. The calculated stress-strain curves and effective stress paths of typical soil elements are given to reveal the relationship of the large lateral deformation of the station and surrounding soil with the liquefaction extent of sandy stratum. It is found that liquefaction-induced large deformation may be the main reason causing serious damage to the Daikai station during the earthquake.

Zhu L.,Deyang Electrical Power Bureau | Wei C.,Ertan Hydropower Development Company | Yu Y.,North China Electrical Power University
Dianli Xitong Baohu yu Kongzhi/Power System Protection and Control | Year: 2010

DC bias will lead to half-cycle distortion of exciting currents. Then large quantity of even and odd harmonics will be produced. In order to research the effect of DC bias on single transformer and its protection, this paper uses PSCAD/EMTDC to create a simulation model. It simulates exciting current of a practical 750 kV single-phase transformer in variant cases under DC bias. It studies the relationship between the DC bias and distortion of exciting current, harmonic distribution, as well as the peak value of the exciting current. Meanwhile, the performance of transformer protection in this harmonic environment is analyzed. The loss made by exciting current's distortion and the elevated temperature of the core tie-plate are quantitatively calculated.

Yu Y.,North China Electrical Power University | Wei C.,Ertan Hydropower Development Company | Zhu L.,Deyang Electrical Power Bureau
Dianli Xitong Baohu yu Kongzhi/Power System Protection and Control | Year: 2010

The paper adopts PSCAD/EMTDC software to establish the system model and simulates the impact of DC ground electrode current on transformers of different structures including group transformer, three-phase three pole transformer, and three-phase fineplole transformer, etc. The results show that because of the independent magnetic flux circuit and small reluctance, group-type transformer is most influenced by DC bias; three-phase three-pole transformer which has no DC circuit and has larger reluctance is least-affected by DC bias; three-phase five-pole transformer in which area of iron core is smaller than that of single-phase transformer is impacted between the former two even though having DC circuit.

Xu J.,University of Sichuan | Zheng H.,University of Sichuan | Zheng H.,Chongqing University | Zeng Z.,University of Sichuan | And 2 more authors.
International Journal of Project Management | Year: 2012

This paper presents a discrete time-cost-environment trade-off problem for large-scale construction systems with multiple modes under fuzzy uncertainty. A multi-objective decision making model is established in which the total project duration is regarded as a fuzzy variable. To deal with the uncertainty, the fuzzy numbers in the model are defuzzified by using an expected value operator with an optimistic-pessimistic index. The objective functions are to minimize the total project cost, project duration, crashing cost, and environmental impact. Furthermore, a fuzzy-based adaptive-hybrid genetic algorithm is developed to find feasible solutions. The one-point crossover and repairing strategy for mutations are designed to avoid infeasible solutions. Finally, the Jinping-II Hydroelectric Project is used as a practical example to demonstrate the practicality and efficiency of the model. Results and a sensitivity analysis are presented to highlight the performance of the optimization method, which proves to be very effective and efficient compared to other algorithms. © 2012.

Cheng L.-M.,University of Sichuan | Li X.-Y.,University of Sichuan | Liu J.,Ertan Hydropower Development Company
Gaodianya Jishu/High Voltage Engineering | Year: 2011

The imbalance between electromagnetic torque and mechanical torque of each synchronous machine is the main factor which affects transient stability in the AC/DC transmission systems, and the DC power can be regulated rapidly. Thereby, combining the control of valve opening and DC power modulation, we proposed a coordinated control strategy to improve transient stability. According to the characteristic of system model, namely, a nonlinear system with multi-input and multi-output, the control strategy was designed based on feedback linearization of nonlinear system theory and optimal control theory of linear system. The validity of the coordinated control method was verified in a typical AC/DC parallel hybrid transmission system.

Zeng Z.,Chengdu University of Technology | Xu J.,Chengdu University of Technology | Wu S.,Ertan Hydropower Development Company | Shen M.,Ertan Hydropower Development Company
Computer-Aided Civil and Infrastructure Engineering | Year: 2014

The aim of this article is to develop an antithetic method-based particle swarm optimization to solve a queuing network problem with fuzzy data for concrete transportation systems. The concrete transportation system at the Jinping-I Hydropower Project is considered the prototype and is extended to a generalized queuing network problem. The decision maker needs to allocate a limited number of vehicles and unloading equipment in multiple stages to the different queuing network transportation paths to improve construction efficiency by minimizing both the total operational costs and the construction duration. A multiple objective decision-making model is established which takes into account the constraints and the fuzzy data. To deal with the fuzzy variables in the model, a fuzzy expected value operator, which uses an optimistic-pessimistic index, is introduced to reflect the decision maker's attitude. The particular nature of this model requires the development of an antithetic method-based particle swarm optimization algorithm. Instead of using a traditional updating method, an antithetic particle-updating mechanism is designed to automatically control the particle-updating in the feasible solution space. Results and a sensitivity analysis for the Jinping-I Hydropower Project are presented to demonstrate the performance of our optimization method, which was proved to be very effective and efficient compared to the actual data from the project and other metaheuristic algorithms. © 2014 Computer-Aided Civil and Infrastructure Engineering.

Xue Y.F.,Ertan Hydropower Development Company
Applied Mechanics and Materials | Year: 2013

Pre-estimate of hydropower project investment risks is of much importance because of the huge economic loss caused by the negative effects of the risk factors. Components of cash flow of hydropower project investment and finance evaluation are presented to study the effect of investment risk variables on hydropower project based on the structure of hydropower project investment and benefits. The project investment risk and index are evaluated by the simulation technique, which provides a basis for scientific decision-making of the project. © (2013) Trans Tech Publications, Switzerland.

Deng H.-F.,China Three Gorges University | Li J.-L.,China Three Gorges University | Wang L.-H.,China Three Gorges University | Zhou J.-F.,Ertan Hydropower Development Company | Deng C.-J.,China Three Gorges University
Yantu Lixue/Rock and Soil Mechanics | Year: 2010

The genetic mechanism and evolvement process of the reservoir bank landslide were discussed detailedly based on engineering exploration and analyzing environmental geological conditions. And some main factors effecting stability of the landslide were analyzed emphatically. Through building a 3D FEM model of landslide, the stable situations of the landslide under various situations were considered based on the strength reduction method. The result shows that the landslide is steady under the natural situation. The front edge of the landslide will be drowned out when the reservoir retains water normally; the safety factor reduces and can't meet the requirements of norms. The landslide tends to be more dangerous under rainfall infiltration and rapid drawdown of the reservoir water level. And the landslide will be instable when water storage situation and earthquake situation were considered at the same time. According to the preceding analysis, the treatment measures of cutting slope and reducing load were presented. The landslide is steady under various conditions after being controlled. The relevant conclusions and methods proposed take a good effect in landslide treatment.

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