Journal of Hydroelectric Engineering

水力发电学报

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2015 Vol. 34, No. 12 Published: 2015-12-25

	1	State-of-the-art literature review on concrete meso-scale mechanics
		ZHANG Chuhan, TANG Xinwei, ZHOU Yuande, JIANG Hui
		DOI: 10.11660/slfdxb.20151201
		As a typical multiphase heterogeneous material, concrete has been widely used in high-rise buildings, bridges, dams, nuclear power stations as well as other industrial and civil structures. The whole process of concrete production, transportation, construction, curing and hardening, and its nonlinear mechanical and deformation response subjected to complex loading environments are generally dominated by the physico-mechanical properties of meso-scale ingredients and fabrics, including aggregates, mortar and their interfaces. This paper presents a literature review on the state-of-the-art concrete meso-scale mechanics, emphasizing the development progress on experimental investigation on meso-scale ingredients, pre-processing modeling approaches, and numerical modeling methods for concrete. An in-depth review is also presented on selected aspects on the forefront of the meso-scale concrete mechanics, including the fracture failure mechanism, size effect, multi-scale coupling and rate effect. Finally, some recommendations for future studies are provided.
		2015 Vol. 34 (12): 1-18 [Abstract] ( 411 ) PDF (1833 KB) ( 1107 )

	19	Study on analysis methods for stiffener ring buckling of embedded steel penstocks under external pressure
		WU Hegao, ZHOU Cairong, FU Shan, SHI Changzheng
		DOI: 10.11660/slfdxb.20151202
		This paper presents a comparison study on the existing common methods for calculation of stiffener ring buckling of embedded steel penstocks under external pressure. The results indicate that the critical external pressure of stiffener ring obtained from equation (B16) in the design codes DL/T 5141—2001 is conservative. Equation (30) in the appendix of the codes is an incorrect expression of Svoisky's method and it may lead to a too large or even wrong estimate for the critical pressure. Moreover, Jacobsen's method not only overcomes the limitation in the adaptation range of Amstutz's method, but avoids the shortage of Svoisky's method that fails to consider the external pressure of shell beyond the equivalent flange. Thus Jacobsen's method is recommended and an effective calculation thought for solving the Jacobsen's formulas is given.
		2015 Vol. 34 (12): 19-23 [Abstract] ( 342 ) PDF (327 KB) ( 431 )

	24	Flexural tensile properties of plastic concrete
		GAO Danying, SONG Shuaiqi
		DOI: 10.11660/slfdxb.20151203
		This paper presents a systematic study of flexural tensile tests on flexural tensile strength, mid-span deflection at peak load, and toughness of plastic concrete, influenced by fiber type, fiber content, fly ash content, and silica fume content. The results indicate that flexural tensile strength and deformation properties could be improved to some extent by adding fibers, fly ash or silica fume into the plastic concrete. With fiber content increasing up to 0.9 kg/m3, all the flexural tensile strength, peak load mid-span deflection, and area under flexural tensile load-deflection curve were increased, while these three parameters decreased when the content exceeded 0.9 kg/m3. The secant modulus at peak load was reduced to different degrees with different fiber contents, and reached the minimum at the content of 0.9 kg/m3. Adding fly ash within some content increased all the three parameters and reduced the secant modulus at peak load. With an increase in silica fume content, all the three parameters were increased, but a pinch phenomenon became obvious in the load-deflection curve . By analysis on the test results, we formulated a new formula for calculation of toughness and an equation of load-deflection curve.
		2015 Vol. 34 (12): 24-32 [Abstract] ( 396 ) PDF (461 KB) ( 488 )

	33	Experimental study on deformation characteristics of rock-fill material under cyclic drying-wetting
		ZHANG Qingzhen, YUAN Huina, ZHANG Qiguang, SUN Xun, HUANGFU Xingjian
		DOI: 10.11660/slfdxb.20151204
		Series of cyclic drying-wetting tests have been performed under isotropic and deviator stress conditions using a medium-size triaxial test apparatus to study the deformation characteristics of rock-fill material under cyclic drying-wetting and the influence of stress state. The experimental results show that in the condition of isotropic stress, the wetting volumetric strain of rock-fill under low confining pressure increases with increasing confining pressure while its variation under high confining pressure does not follow this trend, and such wetting volumetric strain mainly occurs in initial wetting process. In the condition of deviator stress, wetting deformation takes a direction consistent with that of loading deformation at the initial wetting stage, while deformation during drying evidently turns its direction toward that of volumetric shrinkage, consistent with the characteristics of creep deformation. The wetting deformation at the initial stage dominates and the ratio of initial wetting axial strain over total wetting axial strain is about 75% ~ 95%. Under low confining pressure, initial wetting axial strain increases with an increase in confining pressure or stress level; under high confining pressure, its trend of variation with confining pressure is different. During cyclic drying-wetting, the deformation of rock-fill specimens (including volumetric and axial strains) increases gradually with time and tends toward a stable limit value. A hyperbolic model is recommended for description of the relationship of specimen deformation versus the number of cycles.
		2015 Vol. 34 (12): 33-41 [Abstract] ( 150 ) PDF (910 KB) ( 505 )

	42	A modified method for non-stationary hydrological time series forecasting based on empirical mode decomposition
		ZHANG Hongbo, WANG Bin, LAN Tian, CHEN Keyu
		DOI: 10.11660/slfdxb.20151205
		Influenced by global climate change and human activities, the processes of rainfall and runoff show non-stationary characteristics that are increasingly remarkable. To provide necessary and useful decision making information, it is crutial to improve forecasting accuracy of the future changes in hydrological time series using more effective methods. Empirical mode decomposition (EMD) is a key technique of the decomposition-prediction-reconstruction approach. This paper decribes a modified radial basis function (RBF) prediction model that integrates EMD and the RBF neural network. Using this model, we have examined the efficiencies of such an approach in prediction of two non-stationary time series for the Wei River basin, a precipitation series showing weak-trend changes, and a runoff series showing strong-trend changes, and compared our modfied RBF method with the original RBF. In addition, a new measure was adopted to reduce errors in prediction of high-frequency components decomposed by EMD. The results show that for weak-trend precipitation series, RBF gave a satisfactory prediction with a mean relative error of 11% and the modified RBF behaved similar. For strong-trend runoff series, the modified RBF was better, reducing the errors from 54% to 30%. This error can be decreased further by 2% if using error control measures. The comparison shows that the modified RBF method is applicable to non-stationary time series featured with strong-trend changes and it can easily decompose a time series into random, periodic and trend components and extrapolate each of them effectively. But beyond that, error control measures improve the efficiency of a prediction approach and can be used as a general technique for non-stationary time series forecasting.
		2015 Vol. 34 (12): 42-53 [Abstract] ( 256 ) PDF (2811 KB) ( 469 )

	54	Multi-objective operation rules for Danjiangkou Reservoir under future runoff changes
		YANG Guang, GUO Shenglian, LI Liping, HONG Xingjun, WANG Le
		DOI: 10.11660/slfdxb.20151206
		Climate change alters hydrologic cycle and reservoir inflow and brings about conflicts between different objectives in reservoir operation. A significant issue in reservoir management is how to adjust reservoir operation rules accordingly through research considering the possible future changes in runoff and hydrologic cycle. In this study, we have developed a multi-objective optimization model for operation of the Danjiangkou Reservoir considering possible future runoff changes. To predict future runoff in this model, the results of the global climate model (GCM) are downscaled by a statistical downscaling model and then inputted into a calibrated variable infiltration capacity (VIC) model. And multi-objective operation rules can be derived using a non-dominated sorting genetic algorithm II (NSGA-II) method, combining the design operating rule curves with the predicted future inflow series and considering the tradeoff between power generation and water supply. Results show that this reservoir needs to modify its existing operation rules to adapt to the future runoff changes and the multi-objective operating rules so obtained are effective in mitigating the conflict between water supply and power generation and improving comprehensive water utilization. In general, power generation-oriented and water supply-oriented rules will produce different results in the objectives, among which the water supply-oriented rule is able to increase water supply capacity significantly (by 18% in the Danjiangkou case).
		2015 Vol. 34 (12): 54-63 [Abstract] ( 249 ) PDF (1085 KB) ( 475 )

	64	Numerical simulations and analysis on flood merging from ten major tributaries into Yellow River
		JIA Wangqi, ZHONG Deyu, WU Baosheng
		DOI: 10.11660/slfdxb.20151207
		Flood merging into the Yellow River from the Xiliugou river, one of the ten major tributaries, has been simulated and analyzed in this study using a 2-D water and sediment mathematical model. Results show that the merging of hyper-concentrated flood can cause a certain rise in water level in the backwater zone upstream of the merging location along with a decrease followed by an increase in flow velocity. Increasing in flow velocity at different locations is unsynchronized. A high velocity zone occurs near the tributary mouth where riverbed has an abrupt drop, and starting from this zone, flow velocity decreases rapidly and sediment deposits in the Yellow main channel. The recirculation zone created by the merging is narrower and longer than that by low-sediment flood, and the corresponding flow structure is more complex. In the main channel, all the sediment injected from a low-sediment tributary can be transported downstream while one part of the sediment from a hyper-concentration tributary will be transported upstream. Near the tributary mouth, an upper sandbar and lower sandbar develop in the main channel. The upper bar develops from the banks to the center and finally closes up, forming a blockage. The whole lower bar rises continuously at a roughly constant rate on its left side but a gradually decreasing rate on its right side, and at the final stage it extends downstream along the right bank. Generally, velocity field and riverbed deformation around a flood merging confluence should also be closely related to the time process of floods.
		2015 Vol. 34 (12): 64-72 [Abstract] ( 170 ) PDF (2676 KB) ( 341 )

	73	Numerical simulation of dynamic interaction between flow and sediment for dam-break floods with vegetation effect
		XU Yuanyuan, ZHANG Mingliang, QIAO Yang, ZHANG Zhongzhe, WANG Siyuan
		DOI: 10.11660/slfdxb.20151208
		Based on the finite volume method and unstructured triangular mesh, a depth-averaged 2D mathematical model for dam-break flows on erodible beds has been developed by coupling the shallow water equations, sediment transport equation, and bed evolution equation. This model adopts the momentum and continuity equations for turbid water considering vegetation effects, sediment transport and morphological changes, and uses a Roe solver and approximate Riemann solutions to calculate the grid face fluxes, which is able to capture dry-wet moving fronts with second-order accuracy. The hydrostatic pressure and the vegetation resistance are put into the source term of momentum equation. The model was verified against four cases of the laboratory measurements documented in the literature, and the calculations agree well with the measurements. The verification shows that the model is able to simulate the evolvement of dam-break flows and the deformation of bed morphology on a complex computational domain with good accuracy. Simulations of the vegetation cases show that the vegetation on a shoal can reduces the velocity of dam-break flows and the erosion on the downstream bed but it also reduces the local flood discharge capacity, which leads to a certain rise in the upstream water level.
		2015 Vol. 34 (12): 73-83 [Abstract] ( 171 ) PDF (797 KB) ( 340 )

	84	Study on optimal design of trapezoidal labyrinth weirs for efficient and safe utilization of rain and flood
		ZHANG Fengli, WANG Zhengzhong, ZHAO Yanfeng, SHI Jiao, WANG Yi
		DOI: 10.11660/slfdxb.20151209
		Using labyrinth weirs for operating reservoirs at higher than normal stages can expand reservoir capacity and flood storage and improve power generation efficiency, while keeping the same levels of inflow, dam height, weir height, and flood control standards. This study has adopted a nonlinear programming method to examine the relationship of weir height versus sidewall angle of labyrinth weirs at fixed reservoir stages on the basis of weir capacity analysis. We have developed and solved an optimization model, and its objective function is maximizing the weir crest elevation under the constraint of normal discharges that ensure safety and the constraint of stream-wise weir size not longer than spillway control section. The results show that to maintain normal ranges of discharge capacity at fixed reservoir stages, weir height can be reduced if sidewall angle increases. Applying this technique to optimization of weir design, we found out that if dam height is determined by normal water level, the optimized weir is able to lower check water level or design water level and hence improve flood control standard. If dam height is determined by either check water level or design water level, using such weirs can expand reservoir capacity and ensure flood discharge safety.
		2015 Vol. 34 (12): 84-91 [Abstract] ( 235 ) PDF (408 KB) ( 347 )

	92	Experimental study on shapes of stilling basin combined with flaring gate piers
		YIN Jinbu, LIANG Zongxiang, ZHANG Hongqin, HE Wei
		DOI: 10.11660/slfdxb.20151210
		For a stilling basin in combined use with flaring gate piers, the flow velocity near its bottom much depends on its geometrical shape. This paper presents a study of hydraulic model tests to optimize the shape of the Ludila stilling basin, considering several commonly-used existing shapes. Our model tests show that if such a stilling basin is modified with an embedded notch in combination of double arcs and a compound tail sill, the double arcs are able to guide the flow near the bottom so as to reduce the bottom velocity, hence improving the energy dissipation rate. In the stilling basin with the optimized shape, its bottom velocity can be reduced by 15% - 30% on average, and bottom pressure fluctuations also reduced even in the most unfavorable flow conditions.
		2015 Vol. 34 (12): 92-98 [Abstract] ( 153 ) PDF (359 KB) ( 333 )

	99	Flow characteristics and performance of underwater self-excitation inspiration jet device
		LIU Xinyang, GAO Chuanchang, XIE Keyu, HU Yazhou, MA Wenliang
		DOI: 10.11660/slfdxb.20151211
		In this study, we have simulated the water-air flow characteristics of an underwater self-excitation inspiration jet device using an Eulerian two-phase flow model and RNG k-? turbulence model, focusing on the distributions of internal pressure and water-air flow velocity of this device and its water-air mixing process in inspiration and non-inspiration cases. Experimental tests were conducted to examine its performance and the variation trends of its impact power and erosion effect. The results show that relative to the non-inspiration case, inspiration makes the internal pressure closer to atmospheric pressure and brings about longer jet cores and significantly greater velocity at the outlet of the lower nozzle. In the inspiration case, high air concentration occurs in the whirlpool regions outside of the jet core if air is fully mixed with water, and air content increases gradually from the core to whirlpool. And the impact power at the target center and in its vicinity is significantly higher than that of the non-inspiration case, explaining the fact that such a device has a gathering energy effect. Moreover, erosion volume and erosion depth increase dramatically while the area of eroded surface decreases slightly. Calculations of inspiration capacity and pressures at typical locations show good agreement with test results.
		2015 Vol. 34 (12): 99-107 [Abstract] ( 193 ) PDF (1890 KB) ( 305 )

	108	Internal structure and efficiency of energy dissipating fixed cone valve
		YU Zheqin, LI Zhipeng, TONG Chengbiao, JU Wei
		DOI: 10.11660/slfdxb.20151212
		Energy dissipating fixed cone valve is a fluid device commonly used for dissipation of the excessive flow energy in the inflow, and its performance of energy dissipation depends on its internal structure. To improve the performance of its traditional design, we have installed a perforated annular casing and a perforated cone casing behind its valve core and studied how each energy dissipating component inside the valve of this modification affects the performances. A CFD numerical simulation method was adopted to predict and analyze the flows in the valve passages, and three different internal structures were examined and compared. Hydraulic model tests were conducted to verify the simulations. Results show that the cone core is a dominant component in energy dissipation and the total performance of the valve can be improved by installing a perforated annular casing and a perforated cone casing.
		2015 Vol. 34 (12): 108-114 [Abstract] ( 235 ) PDF (943 KB) ( 327 )

	115	Study on bending-torsional coupling vibrations of rub-impact rotor system for hydro turbine generators
		GOU Dongming, SONG Zhiqiang, GUO Pengcheng, LUO Xingqi
		DOI: 10.11660/slfdxb.20151213
		Rub-impact between the stator and rotor of a hydro turbine generator caused by electromechanical coupling oscillations, could excite bending-torsional coupling vibrations and even lead to serious safety accidents. This study has developed a bending-torsional coupling dynamic model of the rub-impact rotor system and made an analysis of the coupling vibration behaviors using numerical method, focusing on the influence of electromagnetic stiffness, mass eccentricity, and damping ratio on the vibration signals in time and frequency domains. Results show that bending and torsional electromagnetic stiffness had a coupling effect that tended to excite and amplify the vibrations, but this effect decayed as the eccentricity was increasing. When mass eccentricity was large, damping ratio had an important role because of the strong effect of bending-torsional coupling. An increase in stator radial stiffness leaded to weaker bending vibrations but stronger torsional vibrations. The results would be useful to the design, control and diagnosis of rotor systems and their economical operation.
		2015 Vol. 34 (12): 115-122 [Abstract] ( 222 ) PDF (966 KB) ( 416 )

	123	Vibration fault diagnosis of hydropower unit by using stochastic resonance and multidimensional permutation entropy
		HE Yangyang, JIA Rong, LI Hui, DONG Kaisong
		DOI: 10.11660/slfdxb.20151214
		Aiming at the issue that the characteristics of hydropower unit vibration faults are difficult to extract under strong background noises, this paper presents a fault diagnosis method using the techniques of stochastic resonance (SR) denoising and multidimensional permutation entropy (MPE) for extraction of the characteristic vectors from vibration signals. This method first denoises a vibration signal using stochastic resonance to enhance its stochastic resonance, then uses MPE to extract its feature vectors. Taking the feature vectors as input, an improved particle swarm algorithm and support vector machine model is able to achieve identification and diagnosis of the signal faults. Our simulations show that the method enables the fault diagnosis of hydropower units with high accuracy.
		2015 Vol. 34 (12): 123-130 [Abstract] ( 261 ) PDF (521 KB) ( 413 )

	131	Power generation pricing mechanism for trans-region power supply of Tibetan green hydroelectricity considering carbon emission reduction benefits
		LIU Yue, HUANG Weibin, MA Guangwen, WANG Jinlong, HU Yanlong, CHEN Shijun
		DOI: 10.11660/slfdxb.20151215
		Most trans-region power supply in China is from north to south and west to east, and Tibetan hydropower will play a key role in west-to-east power transmission from the vision of long-term supply. Although the new electricity price reformation puts forward a project to realize marketization of electricity generation and sale, Tibetan hydropower is unsuitable yet for marketization due to its particularity? integrated plants and network, high construction costs, and very long transmission distance. Without an appropriate supporting pricing mechanism, power supply from Tibet to the outside is facing huge challenges. This paper suggests a new pricing method to promote the development of Tibetan hydropower and its trans-region supply, namely the power generation pricing mechanism for trans-region power supply of Tibetan green hydroelectricity considering carbon emission reduction benefits. This method considers the environmental costs and benefits of hydroelectricity and all the advantages and disadvantages of the existing pricing mechanism, thus providing a new idea of power pricing for power transmission from Tibet to the outside.
		2015 Vol. 34 (12): 131-139 [Abstract] ( 191 ) PDF (328 KB) ( 405 )