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Frequency Regulation of Power Systems With a Wind Farm by Sliding-Mode-Based Design

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IEEE/CAA Journal of Automatica Sinica 2022年第11期9卷 1980-1989页

作者： Zhiwen Deng Chang Xu the college of water conservancy and hydropower engineering Hohai UniversityNanjing 210098China

Load frequency regulation is an essential auxiliary service used in dealing with the challenge of frequency stability in power systems that utilize an increasing proportion of wind power.We investigate a load frequency control method for multiarea interconnected power systems integrated with wind farms,aimed to eliminate the frequency deviation in each area and the tie-line power deviation between different areas.The method explores the derivative and integral terminal sliding mode control technology to solve the problem of load frequency regulation.Such technology employs the concept of relative degrees.However,the subsystems of wind-integrated interconnected power systems have different relative degrees,complicating the control design.This study develops the derivative and integral terminal sliding-mode-based controllers for these subsystems,realizing the load frequency regulation.Meanwhile,closed-loop stability is guaranteed with the theory of Lyapunov stability.Moreover,both a thermal power system and a wind power system are applied to provide frequency support in this study.Considering both constant and variable external disturbances,several numerical simulations were carried out in a two-area thermal power system with a wind farm.The results demonstrate the validity and feasibility of the developed method.

关键词： Load frequency control(LFC) power system sliding mode control(SMC) wind farm

An efficient approach for mesoscale fracture modeling of fully-graded hydraulic concrete

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water Science and engineering 2022年第4期15卷 337-347页

作者： Lei Xu Lei Jiang Ye-fei Huang Qing-wen Ren college of water conservancy and hydropower engineering Hohai UniversityNanjing 210098China

Large coarse aggregates used in fully-graded hydraulic concrete necessitate large specimens for numerical modeling.This leads to a high computational cost for mesoscale modeling and thus slows the development of multiscale modeling of hydraulic mass concrete structures.To overcome this obstacle,an efficient approach for mesoscale fracture modeling of fully-graded hydraulic concrete was developed based on the concept of the governing mesostructure.The mesostructure was characterized by a critical aggregate size.Coarse aggregates smaller than the critical size were homogenized into mortar matrices.Key issues in mesostructure generation of fully-graded hydraulic concrete are discussed,as is the development of mesoscale finite element modeling methodology.The basic concept and implementation procedures of the proposed approach are also described in detail.The numerical results indicated that the proposed approach not only significantly improves the compu-tational efficiency of mesoscale modeling but also captures the dominant fracturing mechanism at the mesoscale and reproduces reasonable fracture properties at the macroscale.Therefore,the proposed approach can serve as a basis for multiscale fracture modeling of hydraulic mass concrete structures.

关键词： Fully-graded hydraulic concrete Mesoscale Fracture modeling Governing mesostructure Critical aggregate size

Energy dissipation of slot-type flip buckets

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Journal of Hydrodynamics 2018年第2期30卷 365-368页

作者：吴建华李书芳马飞 college of water conservancy and hydropower engineering Hohai University college of water conservancy and hydropower engineering Hebei University of Engineering

The energy dissipation is a key index in the evaluation of energy dissipation elements.In the present work,a flip bucket with a slot,called the slot-type flip bucket,is theoretically and experimentally investigated by the method of estimating the energy dissipation.The theoretical analysis shows that,in order to have the energy dissipation,it is necessary to determine the sequent flow depth h1 and the flow speed V1 at the corresponding position through the flow depth h2 after the hydraulic jump.The relative flow depth h2/ho is a function of the approach flow Froude numberFro,the relative slot widthb/Bo,and the relative slot angleθ/β.The expression for estimating the energy dissipation is developed,and the maximum error is not larger than 9.21%.

关键词： Energy dissipation hydraulic jump slot-type flip bucket

Numerical models and theoretical analysis of supercritical bend flow

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water Science and engineering 2018年第4期11卷 338-343页

作者： Xi-bin Huang Qing Wang college of water conservancy and hydropower engineering Hohai University

The flow pattern of supercritical flow in bend channels is complicated due to the shock wave phenomenon, which creates difficulties with regard to research and design of bend channels. Using the spillway of an actual project as an example, a three-dimensional numerical investigation was conducted to simulate the flow in a steep-slope bend based on the renormalization group(RNG) k-ε turbulence flow model and the volume of fluid(VOF) method. The validity of the numerical simulation was demonstrated by comparison between the results of numerical simulation and physical model tests. An optimal scheme of setting vertical vanes in the bend channel is presented. The results of numerical simulation and physical model tests are in agreement, which demonstrates the effectiveness of optimization of vertical vanes and the validity of the three-dimensional numerical simulation. water depths along both bend walls were analyzed numerically and theoretically. The formula for calculating supercritical water depth along either bend wall was derived, and the critical condition of flow separation from the inner wall was determined.

关键词： Supercritical flow Bend Shock wave Numerical simulation VOF method

Transient air-water flow patterns in the vent tube in hydropower tailrace system simulated by 1-D-3-D coupling method

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Journal of Hydrodynamics 2018年第4期30卷 715-721页

作者：王希晨张健俞晓东陈胜 college of water conservancy and hydropower engineering Hohai University

The vent tube is commonly used for the water hammer protection in the hydropower tailrace system. In transient processes, with air entering and exiting the vent tube, one sees complex hydraulic phenomena, which threaten the station＇s safe operation. It is necessary to investigate the transient mechanisms in the tailrace system with vent tube. In this paper, a 3-D, two-phase numerical model of a vent tube on the connection of the tailrace tunnel and the diversion tunnel, is developed based on the FLUENT with the volume of fluid（VOF） algorithm to investigate the transient air-water flow patterns and the complex hydraulic phenomena in the vent tube of the tailrace system. A 1-D and 3-D unidirectional adjacent coupling（1-D-3-D-UAC） approach with a linear interpolation method is adopted to adjust the timesteps between the 1-D model and the 3-D model on the tunnel inlet and outlet boundaries through the user defined function（UDF）, to transmit the data from the 1-D model to the 3-D model. The model is verified by comparing the results obtained by using the 1-D model alone and from the experiments in literature. The transient flow processes under the full load rejection consist of four stages： the water level dropping stage, the air entering stage, the air pocket collapsing stage, and the air exiting stage. Detailed hydraulic phenomena in the air pocket collapsing process are also discussed.

关键词： Vent tube tailrace tunnel two phase volume of fluid （VOF） 1-D-3-D coupling

Air entrainment of hydraulic jump aeration basin

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Journal of Hydrodynamics 2018年第5期30卷 962-965页

作者：吴建华周宇马飞 college of water conservancy and hydropower engineering Hohai University

In order to avoid the cavitation damage and the decrease of the energy dissipation of the stepped spillways with a large unit discharge, the air entrainments of the hydraulic jump aeration basin （HJAB） are theoretically and experimentally investigated for the hydraulic-jump-stepped spillway developed by the authors. It is shown that the submerged degree of the hydraulic jump and the air concentration in the measuring section are all functions of the dimensionless discharge, the length and the end sill height of the H JAB. The submerged degree odecreases with the increase of the dimensionless discharge or the dimensionless length of the H JAB, but increases with the increase of the dimensionless height of the end sill of the HJAB. The flow regimes near the critical hydraulic jump, namely, at or= 1.0, have the best effect of the air entrainment for the flow at the measuring section and then that of the stepped spillway.

关键词： Air entrainment hydraulic jump hydraulic jump aeration basin stepped spillway submerged degree

An experimental study on embankment failure induced by prolonged immersion in floodwater

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water Science and engineering 2016年第1期9卷 81-86页

作者： Yu-long Luo Cheng Zhang Min Nie Mei-li Zhan Jin-chang Sheng college of water conservancy and hydropower engineering Hohai University

Prolonged immersion in floodwater is one of the main causes of embankment failure or dam breaks, although failure mechanisms have not been extensively studied. In this study, an embankment model was constructed to investigate the influence of prolonged immersion in floodwater on the failure of an embankment. The results indicate that：（1） the phreatic surface gradually rises and negative pore pressures gradually dissipate with the time of prolonged immersion in floodwater, and, finally, a stable and fully saturated state is reached; （2） observable cracks and a heave phenomenon are found near the downstream toe and in the top stratum of the foundation, which are attributed to the large uplift pressure on the interface between the top stratum and the pervious substratum, the tremendous impact effect induced by the rapid rise in water level, and the reduction of shear strength of heavy silt loam. The present study enhances our in-depth knowledge of the mechanisms of embankment failure induced by floodwater, and provides experimental data for validation of mathematical models of the embankment seepage failure.

关键词： Embankment Floodwater Seepage failure Prolonged immersion Heave phenomenon

Impact of depth ratio on flow structure and turbulence characteristics of compound open channel flows

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water Science and engineering 2022年第3期15卷 265-272页

作者： Shao-wei Ding Cheng Zeng Jie Zhou Ling-ling Wang Chen Chen college of water conservancy and hydropower engineering Hohai UniversityNanjing 210098China college of Mechanics and Materials Hohai UniversityNanjing 211100China

Compound open channel flows appear in most natural rivers are of great importance in river management and flood control.In this study,large eddy simulations were carried out to simulate the compound open channel flows with four different depth ratios(hr=0.10,0.25,0.50,and 0.75).The main flow velocity,secondary flow,Reynolds stress,and bed shear stress were obtained from numerical simulations.The depth-averaged stream wise momentum equation was used to quantify the lateral momentum exchange between the main channel and floodplain.The instantaneous coherent structures were presented by the Q criterion method.The impact of hr on flow structure and turbulence charac-teristics was analyzed.The results showed that with the increase of hr,the high velocity area in the main channel shifted to the floodplain,and the dip phenomenon became more obvious;the Reynolds stress largely contributed to the lateral momentum exchange within the flows near the side walls of floodplain;and the vortex structures were found to significantly increase in the floodplain region.

关键词： Large eddy simulation Compound open channel Depth ratio Flow structure Turbulence characteristics

Erosion probability model of base-soil particle migration into a granular filter under local flow

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International Journal of Sediment Research 2019年第5期34卷 455-460页

作者： Yuan Wei Mei-li Zhan Qing-fu Huang Jin-chang Sheng Yulong Luo Qing Zhou college of water conservancy and hydropower engineering Hohai University

To avoid soil erosion, filters often are installed in the downstream cross section of dams. However, the probability of piping failure and the filter effect both are related to the soil pore network. Previous erosion probability models for a base soil-filter system do not consider the effect of local flow. Therefore, in this study, an improved erosion probability model is established, in which the deviation between the main flow direction of the soil and the local flow direction in the filter was considered based on a previous model. The improved model was validated by numerical simulation. The erosion probability was found to affect the reasonable evaluation of filter effects and the optimal selection of filter thickness. The controlling constriction size in a granular filter was increased to D*c= Dc5 with a filter thickness of 59 Dm.

关键词： Granular filter Pore network Erosion probability Local flow Deviation probability