Journal of Hydroelectric Engineering

水力发电学报

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2018 Vol. 37, No. 9 Published: 2018-09-25

	1	Vegetation effects on open channel flows and sediment transport
		CHENG Niansheng
		DOI: 10.11660/slfdxb.20180901
		In recent decades, many studies have been conducted to investigate open channel flows subject to vegetation. In contrast, little knowledge is available in literature concerning vegetation effects on sediment transport. This paper discusses how vegetation may affect the characteristic length scale of open channel flow, bed roughness height, scaling of velocity profile, incipient sediment motion, bedload transport and suspended sediment concentration.
		2018 Vol. 37 (9): 1-7 [Abstract] ( 166 ) PDF (811 KB) ( 562 )

	8	Lake control on surface runoff causing urban flood inundation
		QI Wenchao, HOU Jingming, LIU Jiahong, HAN Hao, GUO Kaihua, MA Yue
		DOI: 10.11660/slfdxb.20180902
		This work applies a hydrodynamic model to simulations of urban rainfall-runoff process to examine the effect of a lake in controlling urban flood inundation, focusing on peak volumes of inundation and severely inundated areas under the conditions of different rainfalls, different lake areas, and different lake locations. The results indicate that as the lake area centered at the same location is reduced from 0.502 km2 to 0.00785 km2, the peak inundation volume is increased by 12.7% - 18.2%, and the severely inundated area increased by 11.7% - 25.7%. Lake location plays an important role in determining flood inundation. This is demonstrated by the typical condition of a storm of 100 year return period and a lake area of 0.5024 km2, in which the severely inundated areas are 0.173 km2, 0.169 km2 and 0.163 km2 in the three cases of the lake located in the river’s upper, middle and lower reaches respectively, indicating more effective control of a downstream lake on the surface runoff that causes urban inundation.
		2018 Vol. 37 (9): 8-18 [Abstract] ( 102 ) PDF (3628 KB) ( 393 )

	19	Optimization on joint flood forecast and control operation modes for parallel reservoir groups
		ZHOU Rurui, LU Di
		DOI: 10.11660/slfdxb.20180903
		Joint flood forecast and control operation modes of reservoir groups are a key measure to river basin flood control and city flood control and also to the reasonable and optimized allocation of water resources. Joint operation of reservoirs needs to consider not only the constraints and forecast of each reservoir, but also reservoir compensation relationship. Previous trial calculation methods depend too much on empirical factors to obtain true global optimal solutions to such operation problems. This work integrates the optimization technique with a planning flood forecast-based operation, formulates a general form and solution procedure of the forecast operation rules considering forecast errors, and develops an optimal operation model for a reservoir group. This model can solve for the optimized flood control operation rules of each reservoir and its dynamic flood control stages. A case study of the Qinghe and Chaihe reservoirs shows that the joint operation schemes can raise the flood control stages of the two reservoirs by 0.4 m and 0.3 m, respectively, hence increasing the total flood water storage by 62 million m3. The results lay a basis for further studies on flood forecast and control operation of reservoir groups.
		2018 Vol. 37 (9): 19-28 [Abstract] ( 172 ) PDF (481 KB) ( 470 )

	29	Precipitation bias-correction methods for Yellow River basin upstream of Tangnaihai
		GAO Chao, LIU Li, WANG Zixia, XU Yueping
		DOI: 10.11660/slfdxb.20180904
		To improve the accuracy of climate models in precipitation simulation, we collect the monthly precipitation at 12 meteorological stations over the Yellow River basin upstream of Tangnaihai, and correct the deviation in precipitation simulated by 18 global climate models (GCMs) using three methods, i.e., single gamma (SG), separated double gamma (SDG), and separated triple gamma (STG) distributions. The effects of these bias-correction methods are evaluated and compared in terms of three indexes: bias-correction effective index C, Nash-Sutcliffe (NS) efficiency coefficient, and relative bias index (PBIAS). The results indicate that all the three methods are able to effectively remove the deviation in simulated precipitations from the observed ones. After correction, 69.4%, 82% and 88.4% of index C values exceed 0.85 for SG, SDG and STG, respectively; 69%, 70.8% and 71.3% of NS values exceed 0.4; 65.7%, 67.6% and 69.9% of index PBIAS values are -1.3% to 2.3%, a range close to zero. In summary, STG is the best in precipitation bias correction and SG is the worst.
		2018 Vol. 37 (9): 29-39 [Abstract] ( 95 ) PDF (2162 KB) ( 324 )

	40	Analysis on the relationship between swirling flow at outlet of a Francis turbine runner and vortex rope inside draft tube
		ZHONG Lintao, LAI Xide, LIAO Gonglei, ZHANG Xiang
		DOI: 10.11660/slfdxb.20180905
		In order to predict the vortex rope during the design process for hydro turbine, the relationship between the runner outlet’s swirling flow of Francis turbine and the vortex rope inside the draft tube was analyzed. A 180-meter head Francis turbine is numerically simulated under three typical operating conditions by using the Reynolds-averaged Navier-Stokes (RANS) equations. The shape of vortex rope visualizations was compared with the results of the model test for verifying the correctness of simulation. Then, the swirl number, the velocity profile of runner outlet and the swirl number along the centerline of draft tube cone was analyzed to explain vortex rope formation under typical conditions. The results show that the swirl number at outlet of runner increase with the decrease of operating flow rate. When the swirl number at the outlet of the runner is greater than the critical value, the helical vortex rope, the low velocity zone and the backflow are formed in the draft tube. Meanwhile, when the swirl number is less than the critical value, there is no obvious vortex rope forming in the draft tube.
		2018 Vol. 37 (9): 40-46 [Abstract] ( 262 ) PDF (863 KB) ( 444 )

	47	Modeling supersonic gas cavity flows with open-channel water flows
		ZHANG Jinsong, TAN Lei, LIU Jun, HAN Yadong, LIU Minjiang
		DOI: 10.11660/slfdxb.20180906
		This study derives formulas of the similarity between compressible gas flows and open-channel water flows through calculus transformation based on the basic relationships of thermodynamics and hydrodynamics, and obtains mapping relationships between similarity parameters, their application scope, and the limiting factors. We design a specific nozzle based on the method of characteristics, construct an open-channel flow test stand, and conduct tests on cavity flows in the open channel, using a high speed camera and fluctuating pressure sensors for measurements. The experimental results verify the similarity between compressible gas flows and open channel flows, and show that the cavity flow has a dominant pressure fluctuating frequency of 2.09 Hz when its Froude number is 2.0 and flow rate 11 m3/h. Thus, this study would help model supersonic gas cavity flows experimentally using a more convenient open-channel flow approach.
		2018 Vol. 37 (9): 47-53 [Abstract] ( 116 ) PDF (1159 KB) ( 243 )

	54	Condition-based maintenance of hydroelectric generating sets based on Bayesian network
		CHENG Jiangzhou, ZHU Cai, FU Wenlong, WANG Canxia
		DOI: 10.11660/slfdxb.20180907
		A Bayesian network model is adopted in the maintenance of hydroelectric generating sets to provide maintenance personnel with a better tool in decision making of auxiliary maintenance. Based on the sensor diagnosis strategy and a Bayesian network model, we design a condition-based maintenance method that uses the strategy to handle the cases of false alarm, redundant alarm, and potential fault diagnosis on sensor monitoring signals. We apply the Bayesian network model to effective diagnosis of transmission faults, and carry out risk assessment via combining fault probability and fault risk. The results of risk assessment provide reasonable information for the maintenance personnel to set up a procedure for failure checking during maintenance. Finally, we use accuracy analysis to analyze the method and its practical operation, and verify the calibration curve by comparing the modeled results with field data, showing that the operating accuracy of the system is 80%.
		2018 Vol. 37 (9): 54-64 [Abstract] ( 76 ) PDF (895 KB) ( 278 )

	65	Methods comparison for calculating peak-to-peak amplitudes of vibrations and pressure pulsations in hydropower units
		ZHANG Fei, LIU Shiqi, XUE Xiaobing, DENG Lei
		DOI: 10.11660/slfdxb.20180908
		Collecting accurate data of stability parameters is a key to monitoring and fault diagnosis of hydropower units, particularly the core stability parameters: peak-to-peak amplitudes of vibrations and pressure pulsations. First, this paper examines different methods for calculating peak-to-peak values specified in different standards and discusses the concept of confidence interval from the two viewpoints of statistics and engineering application. Then, considering signal collection in a complicated field environment, we verify each method using both numerically simulated signals with normally distributed noises and field measurements. Results show that for low frequency dominated signals, the ±1.96σ method produces large errors and thus is not applicable, while for signals with high frequency components, different methods often result in great differences. This study recommends the method of 95% confidence interval for calculation of peak-to-peak values of the signals, which is conservative but robust and insensitive to noises. These results would help the revision of GB/T 17189, IEC 60994 and other related ISO specifications.
		2018 Vol. 37 (9): 65-73 [Abstract] ( 188 ) PDF (738 KB) ( 353 )

	74	Acceleration-based approach to calculation of safety factors of slopes
		JIE Yuxin, GUO Zhenghao
		DOI: 10.11660/slfdxb.20180909
		Slope stability analysis is a classic topic in soil mechanics, and many methods have been developed to calculate the safety factors of slopes. Theoretically, the finite element method can obtain the stress at any point in the computational domain, and thus it is more advantageous in stability analysis than the conventional limit equilibrium method which requires rigid body assumption. However, there still exist several shortcomings in how to use the finite element results to calculate the safety factor of a slope. In this paper, we introduce the concept of acceleration and develop a new acceleration-based approach to calculation of the safety factors of slopes. That is, among different strength reduction factors, the one that minimizes modulus of acceleration is thought to be the corresponding safety factor. This idea is more rigorous and more applicable, and examples show that it can give satisfactory results in calculating the safety factor of slopes.
		2018 Vol. 37 (9): 74-83 [Abstract] ( 120 ) PDF (602 KB) ( 375 )

	84	Temporal-spatial global surrogate model for structural inversion
		HU Yu, LIANG Guohe, LIU Chang, LI Qingbin
		DOI: 10.11660/slfdxb.20180910
		This paper presents a temporal-spatial global surrogate model that can be used for reverse analysis as a substitute for the complicated FEM. It extracts the representative base vectors of space and time for a response field through two-layer proper orthogonal decomposition, and expresses this field as a linear combination of the base states. Then, theoretical equations are derived to obtain the basis state combination coefficients of sample response fields. And for any parameters, the corresponding combination coefficients can be calculated via a nonlinear parameter-coefficient relationship that is established forehand using a radial basis function interpolation model. This method can be used to model the temporal-spatial response fields of any degree of freedom and achieve real time outputs, keeping the same number of outputs as that of a FEM model.
		2018 Vol. 37 (9): 84-92 [Abstract] ( 265 ) PDF (1031 KB) ( 472 )

	93	Determination of equivalent loads on downsized rollers in DEM simulation of rock-fill dams
		LIU Donghai, MA Hongyan, SUN Longfei
		DOI: 10.11660/slfdxb.20180911
		In discrete element method (DEM) simulation of rock-fill dam compaction, the sizes of the work area and the roller are usually reduced for lower computational cost, and applying a load on the roller equivalent to its real value is the premise of numerical simulation. This equivalent load depends on the roller size, and hence an accurate calculation of it is crucial to simulation accuracy. This paper develops a method of determining the equivalent load on downsized rollers considering the same porosity of dam material to be compacted. First, we use the particle flow code (PFC) to construct a 2D model and a 3D model that describe the features of rock-fill materials: aggregate gradation, particle shape, contact characteristics, etc., and establish a quantitative relationship between the modeled porosity and the real one. Then, we derive a formula for determining the equivalent load on downsized rollers based on the same compaction ability coefficients, and modify it by matching the modeled porosity with the real one, therefore establishing a relationship of the equivalent roller load versus the roller size. A case study shows that the equivalent load calculated by our method leads to the same compaction effect compared to that of the real roller, thus laying a basis for numerical simulation of downsized roller compaction.
		2018 Vol. 37 (9): 93-102 [Abstract] ( 126 ) PDF (2309 KB) ( 331 )

	103	Experimental study on fracture energy of fiber and nano-particle reinforced concrete
		ZHANG Peng, LI Qingfu, HAN Juhong, ZHANG Tianhang
		DOI: 10.11660/slfdxb.20180912
		Experimental tests on three-point bending fracture of steel fiber and nano-particle reinforced concrete is conducted to study the effect of nano-particles, steel fibers and relative notch depth on its fracture toughness, focusing on the measurements of fracture energy and fracture process. The test results indicate that adding appropriate contents of nano-SiO2 and steel fibers to the concrete can improve its fracture energy significantly. As the nano-SiO2 content is increasing, fracture energy is increased gradually up to a peak content of 5% and then decreased gradually. And with the increasing steel fiber content, it manifests a similar tendency and has a peak value at the content of 2%. The depth of a relative notch on a beam specimen has great effect on its fracture energy that is decreased gradually with the increasing depth.
		2018 Vol. 37 (9): 103-110 [Abstract] ( 132 ) PDF (742 KB) ( 348 )

	111	Effect of recycled coarse aggregate properties on tensile constitutive relation of concrete
		WANG Xuefang, FANG Jinjie, LUO Surong, ZHANG Ming
		DOI: 10.11660/slfdxb.20180913
		Properties of coarse aggregate, interface and mortar are main factors in the tensile constitutive relation of concrete. The surface of recycled coarse aggregate is usually covered by an old mortar layer, making it much different in properties from natural aggregate. The paper describes a five phase meso-scale numerical model of recycled coarse aggregate concrete (RCAC) that is based on the random aggregate model, and verifies its reliability using our test results. For this concrete, we also examine the trend in damage development and the effect of strength and thickness of the old mortar layer on its tensile properties, and construct its tensile constitutive relation based on our analytical results. The results show that the tensile damage to RCAC under uniaxial tension loads starts at the transition zone on an aggregate-mortar interface and then expands to the old and new mortar layers until cutting through the section of structure. When the old mortar layer is thin or its strength is greater than that of new mortar, RCAC has little change in tensile properties as the thickness or strength of old mortar layer is varied. Otherwise, its tensile stress, elastic modulus, and peak deformation modulus are all increased with an increase in the strength or a decrease in the thickness of old mortar layer. And the peak tensile strain of RCAC increase proportionally with the strength and thickness of old mortar layer.
		2018 Vol. 37 (9): 111-120 [Abstract] ( 114 ) PDF (3450 KB) ( 383 )