Yang S.-Q.,University of Wollongong |
Dou G.,Nanjing Hydraulic Research Institute
Journal of Fluid Mechanics | Year: 2010
Friction factor of drag-reducing flow with presence of polymers in a rough pipe has been investigated based on the eddy diffusivity model, which shows that the ratio of effective viscosity caused by polymers to kinematic viscosity of fluid should be proportional to the Reynolds number, i.e. uR/ and the proportionality factor depends on polymer's type and concentration. A formula of flow resistance covering all regions from laminar, transitional and fully turbulent flows has been derived, and it is valid in hydraulically smooth, transitional and fully rough regimes. This new formula has been tested against Nikuradse and Virk's experimental data in both Newtonian and non-Newtonian fluid flows. The agreement between the measured and predicted friction factors is satisfactory, indicating that the addition of polymer into Newtonian fluid flow leads to the non-zero effective viscosity and it also thickens the viscous sublayer, subsequently the drag is reduced. The investigation shows that the effect of polymer also changes the velocity at the top of roughness elements. Both experimental data and theoretical predictions indicate that, if same polymer solution is used, the drag reduction (DR) in roughened pipes becomes smaller relative to smooth pipe flows at the same Reynolds number. © 2010 Cambridge University Press.
Zhu D.,Nanjing Southeast University |
Zhu D.,Nanjing Hydraulic Research Institute
Coastal Engineering | Year: 2011
The present paper extends the impedance analytical method to the study of the interaction of regular plane waves with a row of rectangular piles. The dissipative energy is estimated from the flow resistance for the row of piles. Formulas of wave reflection and transmission coefficients and the wave force for the row of piles are derived. Predictions obtained using the present model agree with experimental data in the literature. © 2011 Elsevier B.V.
Zhan C.-S.,CAS Institute of Geographical Sciences and Natural Resources Research |
Song X.-M.,Nanjing Hydraulic Research Institute |
Xia J.,CAS Institute of Geographical Sciences and Natural Resources Research |
Tong C.,Lawrence Livermore National Laboratory
Environmental Modelling and Software | Year: 2013
Efficient sensitivity analysis, particularly for the global sensitivity analysis (GSA) to identify the most important or sensitive parameters, is crucial for understanding complex hydrological models, e.g., distributed hydrological models. In this paper, we propose an efficient integrated approach that integrates a qualitative screening method (the Morris method) with a quantitative analysis method based on the statistical emulator (variance-based method with the response surface method, named the RSMSobol' method) to reduce the computational burden of GSA for time-consuming models. Using the Huaihe River Basin of China as a case study, the proposed approach is used to analyze the parameter sensitivity of distributed time-variant gain model (DTVGM). First, the Morris screening method is used to qualitatively identify the parameter sensitivity. Subsequently, the statistical emulator using the multivariate adaptive regression spline (MARS) method is chosen as an appropriate surrogate model to quantify the sensitivity indices of the DTVGM. The results reveal that the soil moisture parameter WM is the most sensitive of all the responses of interest. The parameters Kaw and g1 are relatively important for the water balance coefficient (WB) and Nash-Sutcliffe coefficient (NS), while the routing parameter RoughRss is very sensitive for the Nash-Sutcliffe coefficient (NS) and correlation coefficient (RC) response of interest. The results also demonstrate that the proposed approach is much faster than the brute-force approach and is an effective and efficient method due to its low CPU cost and adequate degree of accuracy. © 2012 Elsevier Ltd.
Hu S.,Nanjing Hydraulic Research Institute |
Hu S.,Northwestern University
Applied Clay Science | Year: 2013
When the angular velocity of a circular disk at room temperature is gradually increased the disk first of all behaves elastically, then, at a certain velocity, plastic yielding begins and proceeds, with work-hardening, until all the material of the disk has reached the initial yield point, Further increase in speed causes unrestricted plastic flow to take place. The system is stable as long as an increase in speed is necessary to produce further plastic flow. In the paper, theoretical analysis in polar coordinate of the elastic-plastic interface under rotating status was finished, The calculated results are given out in exact solution. The formula of large deformation analyses of rotating disk were derived out of an equation group which could become into seven independent equations with seven unknowns and can be solved by COLSYS software. Then, some calculated examples were given out. The bursting speed of rotating disk was analyzed. © 2013 Elsevier B.V.
Fu Z.,Nanjing Hydraulic Research Institute |
Chen S.,Chinese Ministry of Water Resources |
Peng C.,Nanjing Hydraulic Research Institute
International Journal of Geomechanics | Year: 2014
Typical triaxial compression experiments were revisited to investigate the essential mechanical behavior of rockfill materials to be reflected in constitutive modeling, such as the nonlinear dependence of the strength and the dilation on the confining pressure and the accumulation of permanent strains during cyclic loading. The mathematical descriptions of the axial stress-strain behavior during initial loading, unloading, and reloading were formulated, respectively, which enables us to represent the hysteresis loops directly without recourse to complex concepts and parameters. The axial stress-strain model was then incorporated into the constitutive framework of generalized plasticity for the modeling of cyclic behavior of rockfill materials. This task was fulfilled by defining the elastic modulus, the plastic flow direction tensor, the loading direction tensor, and the plastic modulus for different loading conditions. In particular, the plastic flow direction tensor was derived based on a stress-dilatancy equation considering the influence of loading direction, and the representation of the plastic modulus was established in terms of the tangential modulus and the elastic modulus by using the special constitutive equations under axisymmetric stress states. The cyclic model proposed in this study has three distinct features. First, the hysteresis behavior and the accumulation of permanent strains were unified and described under the framework of generalized plasticity. Second, all the loading phases were treated as elastoplastic processes so that no purely elastic regions exist in the principal stress space. Third, the introduction of two aging functions for the consideration of the hardening effect facilitates the controlling of the magnitudes of permanent strains. There are in total 13 parameters in the model, all of which can be determined easily from (cyclic) triaxial compression experiments. To check the capabilities of the model in reproducing the monotonic and cyclic behavior, typical triaxial compression experiments were simulated with the constitutive equation. Satisfactory agreement between the experimental results and the corresponding model predictions lent sufficient creditability to the effectiveness of the proposed model, which further motivates us to extend the model for more complex stress paths and apply the model in practical engineering in the future. © 2014 American Society of Civil Engineers.
Liu G.W.,Nanjing Hydraulic Research Institute
Science China Earth Sciences | Year: 2012
This paper investigates the important scientific problem of river regulation strategies in the lower reaches of the Yellow River, and discusses the "geo-basis" of river regulation. The concept of a geo-basis to river regulation in the lower Yellow River was discussed in terms of subsidence and sedimentation features of the river plain; channel features, erosion characteristics of the Loess Plateau and storm-flood features of the middle and lower reaches. The geographic features of the lower Yellow River have gradually changed since the Holocene but there has been no fundamental change. Based on an analysis of the geo-attributes of the lower reaches of the Yellow River, several conclusions on its river regulation were made. The release of sediment should be the first measure of river regulation because of deposition in the lower reaches. The river channels should be provided with adequate space for wandering in the lower reaches. The tail river should be also provided with necessary wandering space because of weak marine dynamics in the estuary area and changes in the delta. Because the erosion environment of the Loess Plateau will not fundamentally change, river harnessing of the middle reaches should focus on improving the plateau morphology, which can be done by reducing the fragmentation of terrain and building a planation surface. Ecoremediation should focus on converting farmland to grassland. There may be extreme floods in the future, as has occurred previously, thus an extreme flood defense system should be considered for the lower reaches. A periodic law for regulation in the Yellow River is discussed. We also discuss how the current use of the lower reaches of the Yellow River is unsustainable and it is urgent to research artificial rechanneling and the creation of new flow paths for the lower reaches. © 2011 Science China Press and Springer-Verlag Berlin Heidelberg.
Shaowei H.,Nanjing Hydraulic Research Institute
Automation in Construction | Year: 2014
At present, there is no design specification for the pre-stressed composite beam. To research the bending mechanical behaviors of pre-stressed steel-concrete composite box beams and provide corresponding design specification and requirements, the tests of ten pre-stressed composite box beams were finished, and the effects on flexural behaviors were given for different initial pre-stress levels, the forms of reinforcement placement and loading method and so on. Design calculation methods under serviceability and bearing capacity limits were mainly discussed. Test results indicated that the pre-stressed composite beam displays a lot of advantages compared with ordinary composite beams. The flexural capacity of the composite beams through using pre-stressed technology was greatly increased. The elastic-plastic analysis of the pre-stressed composite beams was finished; what's more, the equations of deflection and elastic bearing capacity with consideration of interface slip were derived out. Calculating equations for ultimate banding capacity were derived with consideration of pre-stress increments. Finally, the calculated values met precise requirements when compared with the test results. This study provides advisory opinions for the designer to analysis and design of the pre-stressed composite beams. © 2013 Elsevier B.V.
Hu S.,Nanjing Hydraulic Research Institute
Applied Mechanics and Materials | Year: 2011
Rotating discs are used widely as important structural elements in mechanical engineering. In order to obtain an optimal structural design, it is necessary to estimate the angular velocity and the stress distribution of a rotating disc in fully plastic state. So Large deformation and discontinuous yield analysis of rotating disks were analyzed by ABAQUS. Moreover, continuous yield, buckling and bifurcation analysis of rotating disk with discontinuous yield were studied. Then, Minidisk model is analyzed using ABAQUS. © (2011) Trans Tech Publications.
Zhang J.-Y.,Nanjing Hydraulic Research Institute
Shuikexue Jinzhan/Advances in Water Science | Year: 2010
The history of China's hydrological forecasting and technique progresses are reviewed in this paper, which involves the use of empirical correlations, catchment hydrological modeling, and the development of hydrological forecasting systems. The commonly used methods and models for hydrological forecasting are discussed in detail together with the conditions for applications. The current skill of China's hydrological forecasting techniques is assessed objectively. In-depth analysis of the impacts of intense human-induced land-surface changes and global warming on the catchment runoff generation and flow concentrating is provided. Emerging issues and challenges in hydrological forecasting under a changing environment is also analyzed. Finally, the future direction of China's hydrological forecasting development is prospected together with research focuses on the subject. Copyright.
Hu S.,Nanjing Hydraulic Research Institute
Applied Mechanics and Materials | Year: 2012
Rotating discs are used widely as important structural elements in mechanical engineering. In order to obtain an optimal structural design, it is necessary to estimate the angular velocity and the stress distribution of a rotating disc in fully plastic state. So J2 deformation Theory is used for large deformation analysis of axisymmetric rotating disk. The bursting speed of rotating disk, the stress distribution at instability and analysis on the elastic-plastic interface of rotating disk are studies in detail. © (2012) Trans Tech Publications, Switzerland.