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Cavity flow regime for spillway aerators

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Science China(Technological Sciences) 2013年第4期56卷 818-823页

作者： wu jianhua MA Fei College of Water Conservancy and Hydropower Engineering Hohai University

It is well known that the effect of air entrainment for cavitation damage controls is related not only to the air discharge into aerator devices but also the flow regime of the cavity below *** the basis of the hydraulic characteristics of the flow,the aerator devices were for the first time *** theoretical considerations were performed about the jet length and cavity flow regime with the influencing *** with the behavior of the flow through the aerator of discharge tunnels,the flow regimes of the cavity below spillway aerators were experimentally investigated,and the empirical expressions were presented to identify the conversions of the cavity flow regimes,including fully filled cavity,partially filled cavity,and net air *** issues of the design of the aerator devices were suggested in the present work.

关键词： aerator air entrainment cavity discharge tunnel flow regime spillway

Cavity length below chute aerators

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Science China(Technological Sciences) 2008年第2期51卷 170-178页

作者： wu jianhua RUAN ShiPing College of Water Conservancy and Hydropower Engineering Hohai UniversityNanjing 210098China

It is proved that air entrainment is one of the efficient measures dealing with cavi-tation control for the release works of hydropower projects. There are many factors to be considered in designing a chute aerator. One of the most important factors concerns the cavity length below the aerator,which has outstanding effects on air entrainment against cavitation damage. It is crucial to determine reasonable emergence angle for the calculation of the cavity length. In the present paper the overall effects of structural and hydraulic parameters on the emergence angle of the flow from the aerator were analyzed. Four improved expressions of the emer-gence angle with weight coefficient were investigated through experimental data of 68 points observed from 12 aerators of 6 hydropower projects,of both model and prototype,on the basis of error theory. A method to calculate the cavity length be-low aerators was suggested,which considers overall effects of the above men-tioned parameters. Comparison between the method in this paper and the other five methods of calculating the cavity length showed that the present method is much more reliable than the existing methods while the mean error of the method is less than others.

关键词： aerator air entrainment cavitation damage cavity length emergence angle flow depth transverse fluctua-ting velocity

New image encryption combining fractional DCT via polynomial interpolation with dependent scrambling and diffusion

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The Journal of China Universities of Posts and Telecommunications 2015年第5期22卷 1-9页

作者： Liang Yaru wu jianhua School of Mechatronic Engineering Nanchang University School of Information Engineering Nanchang University

Based on the fractional discrete cosine transform(DCT) via polynomial interpolation(PI-Fr DCT) and the dependent scrambling and diffusion(DSD), an image encryption algorithm is proposed. Under certain conditions, the introduction of PI-Fr DCT reduces computational complexity compared with fractional DCT(Fr DCT). By using a sigmoid function, the encrypted results are limited within a range from 0 to 255. The real-valued output of PI-Fr DCT is beneficial to the storage, display and transmission of the cipher-text. During the stage of confusion and diffusion, the values of all PI-Fr DCT coefficients change simultaneously as their locations are replaced. DSD enhances the scrambling and diffusion level of encrypted images and provides nonlinearity to the encryption system. Simulation results demonstrate that the proposed encryption algorithm is feasible, effective and secure.

关键词： image encryption fractional discrete cosine transf

Hydraulic characteristics of stepped spillway dropshafts

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Science China(Technological Sciences) 2019年第5期62卷 868-874页

作者： SHEN JieYi wu jianhua MA Fei College of Water Conservancy and Hydropower Engineering Hohai University

Nowadays, "Sponge Cities" are being built to provide a valid solution to the glaring drainage problems in the urban areas of China. The hydraulics of a dropshaft, especially discharge capacity, energy dissipation and cavitation damage control, evidently affect its safety and the city's underground tunnel system, due to the high dropshaft and large discharge. The hydraulic characteristics of stepped spillway dropshafts are experimentally investigated for the variable step rotation angles and end sill heights. Flow regimes inside the dropshafts are classified under the different approach flow discharges. The results illustrate that there is high energy dissipation in the present dropshafts with the stepped spillway and the cavitation damage could be effectively avoided thanks to the effect of the air entrainment to the flow.

关键词： dropshaft end sill height hydraulic characteristics step rotation angle stepped spillway

Multiplicity results for the unstirred chemostat model with general response functions

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Science China Mathematics 2013年第10期56卷 2035-2050页

作者： NIE Hua wu jianhua College of Mathematics and Information Science Shaanxi Normal University

We investigate the multiplicity of positive steady state solutions to the unstirred chemostat model with general response functions. It turns out that all positive steady state solutions to this model lie on a single smooth solution curve, whose properties determine the multiplicity of positive steady state solutions. The key point of our analysis is to study the ＂turning points＂ on this positive steady state solution curve, and to prove that any nontrivial solution to the associated linearized problem is one of sign by constructing a suitable test function. The main tools used here include bifurcation theory, monotone method, mountain passing lemma and Sturm comnarison theorem.

关键词： chemostat general response function multiplicity bifurcation theory Sturm comparison theorem

Coexistence states for a cooperative model with saturation

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Chinese Science Bulletin 1998年第14期43卷 1230-1231页

作者： wu, jianhua Department of Mathematics Shaanxi Normal University Xian China

Stability and persistence for prey-predator model with saturation

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Chinese Science Bulletin 1998年第24期43卷 2102-2103页

作者： jianhua wu Department of Mathematics Shaanxi Normal University Xi’an China Xidian University Xi’an China

Emergy footprint evaluation of hydropower projects

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Science China(Technological Sciences) 2013年第9期56卷 2336-2342页

作者： wu jianhua HE ChengLong XU WeiLin College of Water Conservancy and Hydropower Engineering Hohai University State Key Laboratory of Hydraulics and Mountain River Engineering Sichuan University

In the past thirty years, various hydropower projects, some with a dam height of over 300 m, have been planned and constructed within China. It is inevitable that these will have sizable effects on the environment, and it is crucial therefore to reasonably evaluate and control adverse effects. In this paper, the transformities of various items for hydropower projects were systematically analyzed, and an emergy footprint model for the projects was developed based on ecological footprint analyses and emergy theory, so that it can quantitatively evaluate the effects on the environment, both positive and negative, resulting from the whole process of planning, constructing and operating the projects. As an example, the effects of a large-scale hydropower project, the 'LP project', were investigated. The results showed that the hydropower projects have strong positive effects on the environment and can even in the short term balance the emergy footprint appropriation resulting from the construction and operation of the hydropower projects. Finally, suggestions were presented for the design of hydropower projects.

关键词： ecological footprint emergy emergy footprint model environment hydropower project transformity

Effect of air bubble size on cavitation erosion reduction

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Science China(Technological Sciences) 2017年第4期60卷 523-528页

作者： wu jianhua SU KunPeng WANG Yu GOU WenJuan College of Water Conservancy and Hydropower Engineering Hohai University State Key Laboratory of Hydraulic Engineering Simulation and Safety Tianjin University

Over the past 60 years, the air concentration in water has been considered as a control index of cavitation erosion reduction and widely used in the designs of hydraulic structures. However, the mechanism of air entrainment against cavitation erosion has been paid good attention to. In the present work, the effect of air bubble size on cavitation erosion reduction was experimentally investigated. A device with micron-scale orifice diameters(10, 20 and 50 μm in size) was specially designed to introduce air bubbles into water. The experiments about the effect of air bubble size were conducted by means of a vibratory apparatus, including the behavior of formation and movement for single air bubble, the characteristics of cavitation erosion reduction at different air entrainment conditions. The findings demonstrate that high air concentration has significant effects on cavitation erosion ***, a notable problem was that the size of air bubbles is of outstanding effect on cavitation erosion reduction. Small air bubbles support to alleviate cavitation erosion, even at same air concentration.

关键词： air bubble size air entrainment cavitation erosion micron-scale