Guangqian Wang

Tsinghua University, Peping, Beijing, China

Are you Guangqian Wang?

Claim your profile

Publications (79)115.98 Total impact

  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: With the increasing resolution of digital elevation models (DEMs), computational efficiency problems have been encountered when extracting the drainage network of a large river basin at billion-pixel scales. The efficiency of the most time-consuming depression-filling pretreatment has been improved by using the O(NlogN) complexity least-cost path search method, but the complete extraction steps following this method have not been proposed and tested. In this paper, an improved O(NlogN) algorithm was proposed by introducing a size-balanced binary search tree (BST) to improve the efficiency of the depression-filling pretreatment further. The following extraction steps, including the flow direction determination and the upslope area accumulation, were also redesigned to benefit from this improvement. Therefore, an efficient and comprehensive method was developed. The method was tested to extract drainage networks of 31 river basins with areas greater than 500,000 km2 from the 30-m-resolution ASTER GDEM and two sub-basins with areas of approximately 1000 km2 from the 1-m-resolution airborne LiDAR DEM. Complete drainage networks with both vector features and topographic parameters were obtained with time consumptions in O(NlogN) complexity. The results indicate that the developed method can be used to extract entire drainage networks from DEMs with billions of pixels with high efficiency.
    Geomorphology 06/2015; 238. DOI:10.1016/j.geomorph.2015.02.028 · 2.58 Impact Factor
  • Source
    Zi Wu, Xudong Fu, Guangqian Wang
    [Show abstract] [Hide abstract]
    ABSTRACT: Study on contaminant transport in wetland flows is of fundamental importance. Recent investigation on scalar transport in laminar tube flows (Wu, Z., Chen, G.Q., 2014. J. Fluid Mech., 740: 196-213.) indicates that the vertical concentration difference in wetland flows may be remarkable for a very long time, which cannot be captured by the extensively applied one-dimensional Taylor dispersion model. To understand detailed information for the vertical distribution of contaminant in wetland flows, for the first time, the present paper deduces an analytical solution for the multidimensional concentration distribution by the method of mean concentration expansion. The solution is verified by both our analytical and numerical results. Representing the effects of vegetation in wetlands, the unique dimensionless parameter α can cause the longitudinal contraction of the contaminant cloud and the change of the shape of the concentration contours. By these complicated effects, it is shown unexpectedly that the maximum vertical concentration difference remains nearly unaffected, although its longitudinal position may change. Thus the slow-decaying transient effect (Wu, Z., Chen, G.Q., 2014. J. Hydrol., 519: 1974-1984.) is shown also apply to the process of contaminant transport in wetland flows.
    Journal of Hydrology 06/2015; 525:335-344. DOI:10.1016/j.jhydrol.2015.03.058 · 2.69 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Mesoscopic structures form in dense granular materials due to the self-organisation of the constituent particles. These structures have internal structural degrees of freedom in addition to the translational degree of freedom. The resultant granular elasticity, which exhibits intrinsic variations and inevitable relaxation, is a key quantity that accounts for macroscopic solid- or fluid-like properties and the transitions between them. In this work, we propose a potential energy landscape (PEL) with local stable basins and low elastic energy barriers to analyse the nature of granular elasticity. A function for the elastic energy density is proposed for stable states and is further calibrated with ultrasonic measurements. Fluctuations in the elastic energy due to the evolution of internal structures are proposed to describe a so-called configuration temperature T(c) as a counterpart of the classical kinetic granular temperature T(k) that is attributed to the translational degrees of freedom. The two granular temperatures are chosen as the state variables, and a fundamental equation is established to develop non-equilibrium thermodynamics for granular materials. Due to the relatively low elastic energy barrier in the PEL, granular elasticity relaxes more under common mechanical loadings, and a simple model based on mean-field theory is developed to account for this behaviour.
    Scientific Reports 05/2015; 5:9652. DOI:10.1038/srep09652 · 5.08 Impact Factor
  • Source
    Dechao Hu, Deyu Zhong, Hongwu Zhang, Guangqian Wang
    [Show abstract] [Hide abstract]
    ABSTRACT: Parallel solutions of linear systems arising from velocity–pressure coupling in implicit two-dimensional (2D) hydrodynamic models are usually difficult and inefficient. Using domain decomposition, a prediction–correction parallelization method is proposed to solve such systems in parallel. It is proposed as a special method for parallelizing simulations of free-surface flows in alluvial rivers. Rather than solving a large-scale global linear system over the whole domain, the method solves sub linear systems for subdomains in two steps, prediction and correction. For free-surface flows in alluvial rivers, the gravity wave propagation over subdomains is divided into internal and external parts, moving within a subdomain and across its boundaries, respectively. The external part is assumed to be well solved at the prediction step; the whole wave propagation is then solved at the correction step using updated boundary values and initial estimates. A theoretical analysis is conducted to derive the computational errors at the prediction and correction steps of this method, resulting in the condition for its application. The method is tested on five meshes whose numbers of elements are 12,800–819,200. The grid scale, which is equal to or smaller than a common scale of real applications, provides grid-independent results. The method performs well for problems of various computational granularities. In solving linear systems with the different meshes, sequential runs were 41–96 times slower than parallel runs using 64 subdomains and 64 working cores.
    Journal of Hydraulic Engineering 04/2015; DOI:10.1061/(ASCE)HY.1943-7900.0001012 · 1.26 Impact Factor
  • Source
    Dechao Hu, Deyu Zhong, Yonghui Zhu, Guangqian Wang
    [Show abstract] [Hide abstract]
    ABSTRACT: A two-dimensional (2D) hydrodynamic model is developed for the Jing-Dongting river–lake system, with the computation domain (3,900 km 2) covered by a channel-refined grid of 300,000 cells. The model provides good descriptions of the river–lake characteristics (strongly coupled, annular branches, varying flow regimes). In a simulation of a 1-year unsteady flow process, the mean absolute error in simulated water levels is 0.11–0.15 m, and the mean absolute relative error in simulated cross-section discharges is 4.3–8.5%, compared with field data. The accuracy of the 2D model is obviously better than those of existing one-dimensional (1D) and 1D–2D nested models. The prediction–correction parallelization (PCP) method is then tested by simulating the river–lake system using 64 subdomains. The complexities of real rivers are revealed to have almost no negative effects on the quasi-coupled solutions and accuracy of the PCP method. In tests, the mean absolute error in water level is found to be approximately 0.3 cm, and the mean absolute relative error in cross-section discharges is 0.23%, comparing the results of sequential and PCP simulations. In solving linear systems, sequential runs are 40.5 to 76.8 times slower than parallel runs using 64 cores. It takes 6.6 h to complete a simulation of a 1-year unsteady flow process in the river–lake system. The 2D model is then applied to the study of regulations of real river networks.
    Journal of Hydraulic Engineering 04/2015; DOI:10.1061/(ASCE)HY.1943-7900.0001013 · 1.26 Impact Factor
  • Source
    Sha Zhou, Bofu Yu, Yuefei Huang, Guangqian Wang
    [Show abstract] [Hide abstract]
    ABSTRACT: The Budyko hypothesis states that the ratio of the actual evapotranspiration over precipitation (E/P) is fundamentally related to the ratio of the potential evapotranspiration over precipitation (E0/P). A number of Budyko functions have been proposed to describe such a relationship between E0/P and E/P. There is, however, no simple method to generate Budyko functions that meet the water and energy constraints. This study showed analytically that for any Budyko function, the sum of elasticity of evapotranspiration with respect to potential evapotranspiration and that with respect to precipitation equals to unity. This complementary relationship for sensitivity of evapotranspiration has important implications for evaluating hydrologic impact of change in climate and/or catchment characteristics. More importantly, this study found a function that is monotonically increasing with simple limiting properties. This function can be used to generate numerous valid Budyko functions, and can also be used to test the validity of the existing Budyko functions.
    02/2015; 42(6). DOI:10.1002/2015GL063511
  • Source
    Haiyun Shi, Guangqian Wang
    [Show abstract] [Hide abstract]
    ABSTRACT: Due to climate change and its aggravation by human activities (e.g., hydraulic structures) over the past several decades, the hydrological conditions in the middle Yellow River have markedly changed, leading to a sharp decrease in runoff and sediment discharge. This paper focused on the impacts of climate change and hydraulic structures on runoff and sediment discharge, and the study area was located in the 3,246 km2 Huangfuchuan (HFC) River basin. Changes in annual runoff and sediment discharge were initially analysed by using the Mann-Kendall trend test and Pettitt change point test methods. Subsequently, periods of natural and disturbed states were defined. The results showed that both the annual runoff and sediment discharge presented statistically significant decreasing trends. However, compared with the less remarkable decline in annual rainfall, it was inferred that hydraulic structures might be another important cause for the sharp decrease in runoff and sediment discharge in this region. Consequently, sediment-trapping dams (STDs, a type of large-sized check dam used to prevent sediment from entering the Yellow River main stem) were considered in this study. Through evaluating the impacts of the variation in rainfall patterns (i.e., amount and intensity) and the STD construction, a positive correlation between rainfall intensity and current STD construction was found. This paper revealed that future soil and water conservation measures should focus on areas with higher average annual rainfall and more rainstorm hours.
    Hydrological Processes 01/2015; DOI:10.1002/hyp.10439 · 2.70 Impact Factor
  • Source
    Guangqian Wang, Xudong Fu, Haiyun Shi, Tiejian Li
    [Show abstract] [Hide abstract]
    ABSTRACT: Soil erosion is the root cause of environmental and ecological degradation in the Loess Plateau of the Yellow River. Watershed sediment dynamics was fully analyzed here, and a physically based, distributed, and continuous erosion model at the watershed scale, named the Digital Yellow River Integrated Model (DYRIM), was developed. The framework, the key supporting techniques, and the formulation for natural processes were described. The physical processes of sediment yield and transport in the Loess Plateau are divided into three subprocesses, including the water yield and soil erosion on hillslopes, gravitational erosion in gullies, and hyperconcentrated flow routing in channels. For each subprocess, a physically based simulation model was developed and embedded into the whole model system. The model system was applied to simulate the sediment yield and transport in several typical years in different watersheds of the Yellow River, and the simulation results indicated that this model system is capable of simulating the physical processes of sediment yield and transport in a large-scale watershed.
    Advances in Water Resources Engineering, Edited by Chih Ted Yang, Lawrence K. Wang, 01/2015: pages 1-40; Springer International Publishing., ISBN: 978-3-319-11022-6
  • Lubo Liu, Xudong Fu, Guangqian Wang
    Journal of Environmental Engineering 09/2014; 140(9):A5013001. DOI:10.1061/(ASCE)EE.1943-7870.0000745 · 1.22 Impact Factor
  • Source
    Haiyun Shi, Xudong Fu, Ji Chen, Guangqian Wang, Tiejian Li
    [Show abstract] [Hide abstract]
    ABSTRACT: This paper develops an algorithm for computing spatially distributed monthly potential evaporation (PE) over a mountainous region, the Lhasa River basin in China. To develop the algorithm, first, correlation analysis of different meteorological variables was conducted. It is observed that PE is significantly correlated with vapor pressure and temperature differences between the land surface and the atmosphere. Second, Dalton model, which was developed based on mass transfer mechanism, was modified by including the influences of the related meteorological variables. Third, the influences of elevation on monthly temperature, vapor pressure and wind velocity were analyzed, and the functions for extending these meteorological variables to any given altitude were developed. Fourth, the inverse distance weighting method was applied to integrate the extended meteorological variables from five stations adjacent to and within the Lhasa River basin. Finally, using the modified Dalton model and the integrated meteorological variables, we computed the spatially distributed monthly PE. This study indicated that spatially distributed PE can be obtained using data from sparse meteorological stations, even if only one station is available; the result showed that in the Lhasa River basin PE decreases when elevation increases. The new algorithm, including the modified model and the method for spatially extending meteorological variables, developed in this paper can provide the basic inputs for distributed hydrological models.
    Hydrological Sciences Journal/Journal des Sciences Hydrologiques 09/2014; 59(10):1856-1871. DOI:10.1080/02626667.2014.881486 · 1.25 Impact Factor
  • Source
    Sha Zhou, Bofu Yu, Yuefei Huang, Guangqian Wang
    [Show abstract] [Hide abstract]
    ABSTRACT: Water use efficiency is a critical index for describing carbon-water coupling in terrestrial ecosystems. However, the nonlinear effect of vapor pressure deficit (VPD) on carbon-water coupling has not been fully considered. To improve the relationship between gross primary production (GPP) and evapotranspiration (ET) at the sub-daily time scale, we propose a new underlying water use efficiency (uWUE = GPP · VPD0.5/ET) and a hysteresis model to minimize time lags among GPP, ET, and VPD. Half-hourly data were used to validate uWUE for 7 vegetation types from 42 AmeriFlux sites. Correlation analysis shows that the GPP · VPD0.5 and ET relationship (r = 0.844) is better than that between GPP · VPD and ET (r = 0.802). The hysteresis model supports the GPP · VPD0.5 and ET relationship. As uWUE is related to CO2 concentration, its use can improve estimates of GPP and ET, and help understand the effect of CO2 fertilization on carbon storage and water loss.
    07/2014; 41(14). DOI:10.1002/2014GL060741
  • Source
    Sha Zhou, Yuefei Huang, Bofu Yu, Guangqian Wang
    [Show abstract] [Hide abstract]
    ABSTRACT: With rapid socio-economic development over the past three decades in China, adverse effects of human activities on the natural ecosystem are particularly serious in arid regions where landscape ecology is fragile due to limited water resources and considerable interannual climate variability. Data on land use, surface and ground water, climate, gross domestic product (GDP) per capita from the middle Heihe River Basin were used to (i) examine changes in water consumption, land use composition, and vegetation cover; (ii) evaluate the effectiveness of short-term management strategies for environmental protection and improvement, and (iii) apply and extend the environmental Kuznets curve (EKC) framework to describe the relationship between economic development and environmental quality in terms of the normalized difference vegetation index (NDVI). The results showed that with rapid development of agriculture and economy, land use change for the period 1986–2000 was characterized by the expansion of constructed oases, considerable contraction of oasis-desert transitional zone and natural oases. This has led to a decrease in ecosystem stability. Since 2001, effective basin management has brought about improved environment conditions, with a more optimal hierarchical structure of vegetation cover. The original EKC model could not explain most of the observed variation in NDVI (R2 = 0.37). Including additional climate variables, the extended EKC model to explain the observed NDVI was much improved (R2 = 0.78), suggesting that inclusion of biophysical factors is a necessary additional dimension in the relationship between economic development and environmental quality for arid regions with great climate variability. The relationship between GDP per capita and NDVI, with the effect of precipitation and temperature taken into consideration, was adequately described by an N-shaped curve, suggesting that the relationship between society and the environment followed a process of promotion, contradiction, and coordination.
    Ecological Engineering 05/2014; 76. DOI:10.1016/j.ecoleng.2014.04.020 · 3.04 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: This paper develops a parallel dynamic programming algorithm to optimize the joint operation of a multi-reservoir system. First, a multi-dimensional dynamic programming (DP) model is formulated for a multi-reservoir system. Second, the DP algorithm is parallelized using a peer-to-peer parallel paradigm. The parallelization is based on the distributed memory architecture and the message passing interface (MPI) protocol. We consider both the distributed computing and distributed computer memory in the parallelization. The parallel paradigm aims at reducing the computation time as well as alleviating the computer memory requirement associated with running a multi-dimensional DP model. Next, we test the parallel DP algorithm on the classic, benchmark four-reservoir problem on a high-performance computing (HPC) system with up to 350 cores. Results indicate that the parallel DP algorithm exhibits good performance in parallel efficiency; the parallel DP algorithm is scalable and will not be restricted by the number of cores. Finally, the parallel DP algorithm is applied to a real-world, five-reservoir system in China. The results demonstrate the parallel efficiency and practical utility of the proposed methodology.
    Advances in Water Resources 05/2014; 67:1-15. DOI:10.1016/j.advwatres.2014.01.002 · 2.78 Impact Factor
  • Yuanjian Wang, Xudong Fu, Guangqian Wang
    Journal of Applied Mathematics 01/2014; 2014:1-12. DOI:10.1155/2014/852174 · 0.72 Impact Factor
  • Source
    Deyu Zhong, Guangqian Wang, Baosheng Wu
    [Show abstract] [Hide abstract]
    ABSTRACT: The drift velocity, at which sediment disperses relative to the motion of water-sediment mixtures, is a key variable in two-phase mixture equations. A constitutive relation for the drift velocity, expressed as a power series in the particle bulk Stokes number, was obtained by solving the momentum equation for sediment with the perturbation approach. It shows that gravity and turbulent diffusion are the primary dispersion effects on sediment, whereas flow inertia, particle-particle interactions, and other forces such as lift are the first-order particle inertial corrections that also play significant roles in sediment suspension. Analysis proves that studies based on turbulent diffusion theory are the zeroth-order approximations to the present formulation with respect to the particle inertia effect. The vertical concentration and velocity distributions of sediment in simple flows were investigated with the two-phase mixture equations closed by the drift velocity acquired in the research reported in this paper. The calculated concentration profiles agree well with measurements when the first-order particle inertial effect is considered. The calculated velocity of sediment coincides with available experiments that sediment lags behind water in open-channel flows as a result of turbulence-induced drag.
    Journal of Hydraulic Engineering 01/2014; 140(1):35-47. DOI:10.1061/(ASCE)HY.1943-7900.0000798 · 1.26 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: This paper develops a methodology for optimizing the hydro unit commitment (HUC) for the Three Gorges Project (TGP) in China. The TGP is the world's largest and most complex hydropower system in operation. The objective is to minimize the total operational cost. The decision variables are the startup or shutdown of each of the available units in the system and the power releases from the online units. The mathematical formulation must take into account the head variation over the operation periods as the net head changes from hour to hour and affects power generation. Additionally, the formulation must consider the operation of 32 heterogeneous generating units and the nonlinear power generation function of each unit. A three-dimensional interpolation technique is used to accurately represent the nonlinear power generation function of each individual unit, taking into account the time-varying head as well as the non-smooth limitations for power output and power release. With the aid of integer variables that represent the on/off and operation partition statuses of a unit, the developed HUC model for the TGP conforms to a standard mixed integer linear programming (MILP) formulation. We demonstrate the performance and utility of the model by analyzing the results from several scenarios for the TGP.
    IEEE Transactions on Power Systems 11/2013; PP(99):1-10. DOI:10.1109/TPWRS.2013.2288933 · 3.53 Impact Factor
  • Dechao HU, Deyu Zhong, Guangqian Wang, Hongwu Zhang
    [Show abstract] [Hide abstract]
    ABSTRACT: The circulations (secondary flow) at cross sections are common structures of free-surface flows in natural rivers. They play important roles in shaping the flow regime, governing sediment transport and fluvial processes. The extraction and analysis will help improving the understanding of river mechanics. However, the circulation at an arbitrary cross-section may not be well represented by the cross-sectional flow (transverse velocity field). More over, the irregular, multiple-channel, compound cross-section profiles of natural rivers add difficulties to extract circulations. Based on the 3D velocity field produced by a numerical model on the unstructured, sigma grid, a method for extracting large-scale circulations at arbitrary cross sections of natural rivers is proposed and validated. The local spatial helix structure is first extracted from the 3D velocity field, and then circulations at cross sections are obtained by projection. The new method is validated by using the field data of a natural riverbend “Si-Ma River Bend” in lower Yangtze River. The extracted circulations and their intensities agree well with the field data. Through a further illustration, the new scheme is found to be sophisticated enough to catch multiple, opposite circulations at cross sections, and describe the circulation evolution along the river.
    PROCEEDINGS OF THE 35TH IAHR WORLD CONGRESS, Chengdu, PEOPLES R CHINA; 09/2013
  • Source
    Hao Wang, Xudong Fu, Yuanjian Wang, Guangqian Wang
    [Show abstract] [Hide abstract]
    ABSTRACT: The distributed basin model (DBM) has become one of the most effective tools in river basin studies. In order to overcome the efficiency bottleneck of DBM, an effective parallel-computing method, named temporal-spatial discretization method (TSDM), is proposed. In space, TSDM adopts the sub-basin partitioning manner to the river basin. Compared to the existing sub-basin-based parallel methods, more computable units can be supplied, organized and dispatched using TSDM. Through the characteristic of the temporal-spatial dual discretization, TSDM is capable of exploiting the river-basin parallelization degree to the maximum extent and obtaining higher computing performance. A mathematical formula assessing the maximum speedup ratio (MSR) of TSDM is provided as well. TSDM is independent of the implementation of any physical models and is preliminarily tested in the Lhasa River basin with 1-year rainfall-runoff process simulated. The MSR acquired in the existing traditional way is 7.98. Comparatively, the MSR using TSDM equals to 15.04 under the present limited computing resources, which appears to still have potential to keep increasing. The final results demonstrate the effectiveness and applicability of TSDM.
    Computers & Geosciences 08/2013; 58:62–68. DOI:10.1016/j.cageo.2013.04.026 · 1.56 Impact Factor
  • QiHua Ran, DanYang Su, XuDong Fu, GuangQian Wang
    [Show abstract] [Hide abstract]
    ABSTRACT: To conduct a large-scale hydrologic-response and landform evolution simulation at high resolution, a complex physics-based numerical model, the Integrated Hydrology Model (InHM), was revised utilizing cluster parallel computing. The parallelized InHM (ParInHM) divides the simulated area into multiple catchments based on geomorphologic features, and generates boundary-value problems for each catchment to construct simulation tasks, which are then dispatched to different computers to start the simulation. Landform evolution is considered during simulating and implemention in one framework. The dynamical Longest-Processing-Time (LPT) first scheduling algorithm is applied to job management. In addition, a pause-integrate- divide-resume routine method is used to ensure the hydrologic validity during the simulation period. The routine repeats until the entire simulation period is finished. ParInHM has been tested in a computer cluster that uses 16 processors for the calculation, to simulate 100 years’ hydrologic-response and soil erosion for the 117-km2 Kaho’olawe Island in the Hawaiian Islands under two different mesh resolutions. The efficiency of ParInHM was evaluated by comparing the performance of the cluster system utilizing different numbers of processors, as well as the performance of non-parallelized system without domain decomposition. The results of this study show that it is feasible to conduct a regional-scale hydrologic-response and sediment transport simulation at high resolution without demanding significant computing resources.
    Science China Technological Sciences 08/2013; 56(8). DOI:10.1007/s11431-013-5276-4 · 1.11 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: doi: 10.1061/(ASCE)WR.1943-5452.0000379
    Journal of Water Resources Planning and Management 05/2013; 140(6). DOI:10.1061/(ASCE)WR.1943-5452.0000379 · 1.76 Impact Factor