scholarly journals Predicting discharge capacity of vegetated compound channels: uncertainty and identifiability of one-dimensional process-based models

2020 ◽  
Vol 24 (8) ◽  
pp. 4135-4167
Author(s):  
Adam Kiczko ◽  
Kaisa Västilä ◽  
Adam Kozioł ◽  
Janusz Kubrak ◽  
Elżbieta Kubrak ◽  
...  
Keyword(s):  
Discharge Capacity ◽  
Probabilistic Approach ◽  
River Channels ◽  
Compound Channels ◽  
One Dimensional ◽  
Practical Applications ◽  
Rigid Vegetation ◽  
Output Uncertainty ◽  
Hydraulic Conditions ◽  
Flexible Vegetation

Abstract. Despite the development of advanced process-based methods for estimating the discharge capacity of vegetated river channels, most of the practical one-dimensional modeling is based on a relatively simple divided channel method (DCM) with the Manning flow resistance formula. This study is motivated by the need to improve the reliability of modeling in practical applications while acknowledging the limitations on the availability of data on vegetation properties and related parameters required by the process-based methods. We investigate whether the advanced methods can be applied to modeling of vegetated compound channels by identifying the missing characteristics as parameters through the formulation of an inverse problem. Six models of channel discharge capacity are compared in respect of their uncertainty using a probabilistic approach. The model with the lowest estimated uncertainty in explaining differences between computed and observed values is considered the most favorable. Calculations were performed for flume and field settings varying in floodplain vegetation submergence, density, and flexibility, and in hydraulic conditions. The output uncertainty, estimated on the basis of a Bayes approach, was analyzed for a varying number of observation points, demonstrating the significance of the parameter equifinality. The results showed that very reliable predictions with low uncertainties can be obtained for process-based methods with a large number of parameters. The equifinality affects the parameter identification but not the uncertainty of a model. The best performance for sparse, emergent, rigid vegetation was obtained with the Mertens method and for dense, flexible vegetation with a simplified two-layer method, while a generalized two-layer model with a description of the plant flexibility was the most universally applicable to different vegetative conditions. In many cases, the Manning-based DCM performed satisfactorily but could not be reliably extrapolated to higher flows.

scholarly journals Predicting discharge capacity of vegetated compound channels: uncertainty and identifiability of 1D process-based models

2020 ◽  
Author(s):  
Adam Kiczko ◽  
Kaisa Västilä ◽  
Adam Kozioł ◽  
Janusz Kubrak ◽  
Elżbieta Kubrak ◽  
...  
Keyword(s):  
Discharge Capacity ◽  
Probabilistic Approach ◽  
River Channels ◽  
Compound Channels ◽  
Practical Applications ◽  
Rigid Vegetation ◽  
Dimensional Modeling ◽  
Output Uncertainty ◽  
Hydraulic Conditions ◽  
Flexible Vegetation

Abstract. Despite the development of advanced process-based methods for estimating the discharge capacity of vegetated river channels, most of the practical one-dimensional modeling is based on a relatively simple divided channel method (DCM) with the Manning's flow resistance formula. This study is motivated by the need to improve the reliability of modeling in practical applications while acknowledging the limitations on the availability of data on vegetation distributions and densities required by the process-based methods. We investigate whether the advanced methods can be applied to modeling vegetated compound channels by identifying the missing characteristics as parameters through the formulation of an inverse problem. We developed a new probabilistic approach for comparing six models of channel discharge capacity in respect of their uncertainty, with the model with the lowest uncertainty considered the most favorable. Calculations were performed for flume and field settings varying in floodplain vegetation submergence, density, and flexibility, and in hydraulic conditions. The output uncertainty, estimated on the basis of a quasi-Bayes approach, was analyzed for a varying number of observation points, demonstrating the significance of the parameter equifinality. The results showed that very reliable predictions with low uncertainties can be obtained for process-based methods with a large number of parameters. The equifinality affects the parameter identification but not the uncertainty of a model. The best performance for sparse, unsubmerged, rigid vegetation was obtained with the Mertens method and for dense, flexible vegetation with the generalized two-layer method combined with a description of the flexibility-induced reconfiguration. We found that the process-based methods are superior when applied for vegetative conditions they were developed for while the Manning based DCM seems to be the most flexible technique.

A comparison of one-dimensional methods for estimating discharge capacity of straight compound channels

2004 ◽  
Vol 31 (4) ◽  
pp. 619-631 ◽  
Author(s):  
Galip Seckin
Keyword(s):  
Discharge Capacity ◽  
Single Channel ◽  
Scale Effects ◽  
Compound Channels ◽  
One Dimensional ◽  
Mobile Bed ◽  
Series Of Experiments ◽  
And Performance ◽  
Discharge Estimation ◽  
Fixed Boundaries

A series of experiments was carried out in a two-stage flume having a smooth main channel and smooth or rough floodplains to investigate the reliability and performance of four different one-dimensional methods for computing the discharge capacity of compound channels, namely, the single-channel method (SCM), the divided-channel method (DCM), the exchange discharge method (EDM), and the Ackers method (AM). Additional data from fixed- and mobile-bed compound laboratory channels with smooth and roughened floodplains and of a prototype compound river channel were also used in the computations. The boundary roughness and scale effects associated with the performance of the four methods are also examined. The results show that the EDM and the AM are able to simulate the measured discharge values more accurately than those of the traditional methods, namely, the DCM and the SCM. Although the error in discharge estimation produced by both the AM and the EDM was generally lower than 10% for both smooth and fixed boundaries, it increased up to 20% for mobile boundaries. Overall, the average relative error in discharge estimations using the AM and the EDM was about 5.4% and 7.1%, respectively, with a standard deviation of 6.7% and 6.8%, respectively. Key words: compound channel flow, stage-discharge relationship, one-dimensional methods.

Fabrication of Mesoporous Graphene@Ag@TiO2 Composite Nanofibers Via Electrospinning as Anode Materials for High-Performance Li-Ion Batteries

NANO ◽  
2021 ◽  
pp. 2150119
Author(s):  
M. M. Xia ◽  
J. Li ◽  
Y. Y. Zhang ◽  
D. N. Kang ◽  
Y. L. Zhang
Keyword(s):  
Anode Material ◽  
Discharge Capacity ◽  
Anode Materials ◽  
High Performance ◽  
Composite Nanofibers ◽  
Electrochemical Impedance ◽  
Electronic Conductivity ◽  
Lithium Ion ◽  
One Dimensional ◽  
Practical Applications

Nanosized TiO2 has been actively developed as a low-cost and environment-friendly anode material for lithium-ion batteries (LIBs), but its poor electronic conductivity seriously restricts its practical applications. This drawback is addressed in this work by the fabrication of one-dimensional mesoporous graphene@Ag@TiO2 composite nanofibers as anode materials for high-performance LIBs. The materials were prepared via electrospinning combined with annealing treatment, and the effects of graphene addition on the microstructure and electrochemical performance of the resulting mesoporous graphene@Ag@TiO2 nanofibers were investigated in detail. Ag@TiO2 nanofibers with the optimal amount of graphene displayed a maximum initial discharge capacity of [Formula: see text] at [Formula: see text] and retained a discharge capacity of [Formula: see text] at [Formula: see text] after 100 cycles. These results reflect the excellent cycling stability of the material. The average specific discharge capacity of the nanofibers ([Formula: see text] at [Formula: see text] was two-fold higher than that of samples without graphene, and their discharge capacity returned to [Formula: see text] (approximately [Formula: see text] for other nanofibers) when the current density was recovered to the initial value ([Formula: see text]. Electrochemical impedance spectroscopic measurements confirmed that the conductivity of the electrode was [Formula: see text], which is higher than that of bare mesoporous Ag@TiO2 ([Formula: see text]). Thus, one-dimensional mesoporous graphene@Ag@TiO2 nanofibers can be regarded as a promising anode material for LIBs.

Analysis of One-Dimensional Modelling for Flood Routing in Compound Channels

2011 ◽  
Vol 26 (5) ◽  
pp. 1065-1087 ◽  
Author(s):  
Pierfranco Costabile ◽  
Francesco Macchione
Keyword(s):  
Flood Routing ◽  
Compound Channels ◽  
One Dimensional

scholarly journals Flume experiments on vegetated alternate bars

2018 ◽  
Vol 40 ◽  
pp. 02034 ◽  
Author(s):  
Giulio Calvani ◽  
Simona Francalanci ◽  
Luca Solari
Keyword(s):  
Hydrological Regime ◽  
Spatial Arrangement ◽  
Flume Experiments ◽  
Rigid Vegetation ◽  
Hydraulic Conditions ◽  
Laboratory Flume ◽  
Alternate Bars ◽  
River Reach ◽  
Bed Slope ◽  
And Migration

The planform morphology of a river reach is the result of the combined actions of sediment motion (erosion, transport and deposition), hydrological regime, development and growth of vegetation. However, the interactions among these processes are still poorly understood and rarely investigated in laboratory flume experiments. In these experiments and also in numerical modelling, vegetation is usually represented by rigid cylinders, although it is widely recognized that this schematization cannot reproduce the effects of root stabilization and binding on riverbed sediment. In this work, we focus on the effects of added vegetation on morphological dynamics of alternate bars in a straight channel by means of flume experiments. We performed laboratory experiments reproducing hydraulic conditions that are typical of gravel bed rivers, in terms of water depth, bed slope and bed load; these conditions led to the formation of freely migrating alternate bars. We then employed rigid vegetation that was deployed on the reproduced alternate bars according to field observations. Various vegetation scenarios, in terms of density and spatial arrangement, were deployed in the flume experiments such to mimic different maintenance strategies. Results show the effects of rigid vegetation on the alternate bar configuration on the overall topographic pattern, the main alternate bar characteristics (such as amplitude and wavelength) and migration rate.

scholarly journals Estimation of peak discharges of historical floods

2014 ◽  
Vol 11 (5) ◽  
pp. 5463-5485 ◽  
Author(s):  
J. Herget ◽  
T. Roggenkamp ◽  
M. Krell
Keyword(s):  
Flood Frequency ◽  
River Channels ◽  
Sources Of Information ◽  
Mean Flow ◽  
General Outline ◽  
One Dimensional ◽  
Flood Level ◽  
Alternative Approaches ◽  
The Mean ◽  
Generalized Statement

Abstract. There is no doubt, that the hazard assessment of future floods especially under consideration of the recent environmental change can be significantly improved by the consideration of historic flood events. While flood frequency inventories on local, regional and even European scale are already developed and published, the estimation of their magnitudes indicated by discharges is still challenging. Such data are required due to significant human impact on river channels and floodplains though historic flood levels cannot be related to recent ones or recent discharges. Based on own experiences from single local key studies the general outline of an approach to estimate the discharge of the previous flood based on handed down flood level and topographic data is presented. The model for one-dimensional steady flow is based on the empirical Manning equation for the mean flow velocity. Background and potential sources of information, acceptable simplifications and data transformation for each element of the model-equation are explained and discussed. Preliminary experiences on the accuracy of ±10% are documented and potential approaches for the validation of individual estimations given. A brief discussion on benefits and limitations including a generalized statement on alternative approaches closes the review presentation of the approach.

scholarly journals Numerical Simulation of Effects of River Reconstruction on Flooding: A Case Study of the Ba River, China

2021 ◽  
Vol 2021 ◽  
pp. 1-10
Author(s):  
Haixiao Jing ◽  
Yongbiao Lang ◽  
Xinhong Wang ◽  
Mingyang Yang ◽  
Zongxiao Zhang
Keyword(s):  
Flow Velocity ◽  
Eddy Currents ◽  
Human Life ◽  
River Channel ◽  
Computational Domain ◽  
River Channels ◽  
One Dimensional ◽  
Local Reconstruction ◽  
Before And After ◽  
Flood Flow

The local reconstruction of river channels may pose obstacles of flood flow, local eddy currents, or high flow velocity which pose potential threats to human life and infrastructures nearby. In the design of such projects, the effects of local reconstruction of the river channel on flooding are often evaluated by the one-dimensional method, which is based on the formula of one-dimensional nonuniform flow. In this study, a two-dimensional hydrodynamic model based on shallow water equations is employed to investigate the impacts of river reconstruction on flooding in the Ba River, China. The finite volume method and an unstructured triangular mesh are used to solve the governing equations numerically. The numerical model is validated by comparison with the results of a physical model of 1 : 120 scale. The backwater effects and impacts of flood flow fields under two flood frequencies are analyzed by comparing the numerical results before and after local reconstruction. The results show that the backwater length under both 10-year and 100-year floods can be reached up to the upstream boundary of the computational domain. However, the maximum water level rises are limited, and the levees in this river channel are safe enough. The flow velocity fields under both floods are changed obviously after local reconstruction in the Ba River. Areas with the potential for scour and deposition of the river bed are also pointed out. The findings of this study are helpful for the evaluation of flood risks of the river.

Combined enhanced redox kinetics and physiochemical confinement in three-dimensionally ordered macro/mesoporous TiN for highly stable lithium-sulfur batteries

2021 ◽  
Author(s):  
Jiabing Liu ◽  
Chenchen Hu ◽  
Wanjie Gao ◽  
Haipeng Li ◽  
Yan Zhao
Keyword(s):  
Discharge Capacity ◽  
Active Sites ◽  
Surface Region ◽  
Cycling Performance ◽  
Great Promise ◽  
Energy Storage Devices ◽  
Shuttle Effect ◽  
Practical Applications ◽  
Redox Kinetics ◽  
Lithium Sulfur

Abstract Lithium-sulfur (Li-S) batteries with tremendous energy density possess great promise for the next-generation energy storage devices. Even though, the shuttle effect and sluggish redox kinetics of lithium polysulfides (LiPSs) seriously restrict practical applications of Li-S batteries. Herein, a three-dimensionally ordered macro/mesoporous TiN (3DOM TiN) nanostructure is established via using poly (methyl methacrylate) PMMA spheres as template. The interconnected macro/mesoporous channels are constructed to effectively alleviate the stacking of composite materials and render a large portion of inherent active sites exposed on the surface region. Moreover, TiN exhibits high electrical conductivity, which efficiently enhances charge transfer kinetics and guarantees the favorable electrochemical performance of sulfur cathode. More importantly, the as-prepared 3DOM TiN suppresses the shuttle effect and improves the redox kinetics significantly due to strong affinity toward LiPSs. Attributed to these unique features, the S/3DOM TiN electrode achieves an ultrahigh initial discharge capacity of 1187 mAh g-1 at 0.2 C, and stable cycling performance of 552 mAh g-1 over 500 cycles at 1 C. Meanwhile, the discharge capacity retention of 701 mAh g-1 (3.5 mAh cm-2) can be endowed for the S/3DOM TiN electrode under high sulfur loading of 5 mg cm-2 after 100 cycles at 0.1 C. Therefore, the 3DOM TiN nanostructure electrocatalyst provides a promising path for developing practically useable Li-S batteries.

scholarly journals Synthesis of One-Dimensional Mesoporous Ag Nanoparticles-Modified TiO2 Nanofibers by Electrospinning for Lithium Ion Batteries

Materials ◽  
2019 ◽  
Vol 12 (16) ◽  
pp. 2630 ◽  
Author(s):  
Yuyao Zhang ◽  
Jun Li ◽  
Wenyao Li ◽  
Danning Kang
Keyword(s):  
Electron Microscopy ◽  
Electrochemical Performance ◽  
Discharge Capacity ◽  
Ag Nanoparticles ◽  
Electronic Conductivity ◽  
Lithium Ion ◽  
Initial Value ◽  
Tio2 Nanofibers ◽  
One Dimensional ◽  
Pristine Tio2

TiO2 is regarded as a prospective electrode material owing to its excellent electrochemical properties such as the excellent cycling stability and the high safety. However, its low capacity and low electronic conductivity greatly restrict the further improvement in electrochemical performance. A new strategy was put forward to solve the above defects involved in TiO2 in which the low capacity was enhanced by nanomerization and porosity of TiO2, and the low electronic conductivity was improved by introducing Ag with a high conductivity. One-dimensional mesoporous Ag nanoparticles-embedded TiO2 nanofibers (Ag@TiO2 nanofibers) were successfully synthesized via a one-step electrospinning process combined with subsequent annealing treatment in this study. The microstructure and morphology of mesoporous TiO2@Ag nanofibers were confirmed by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and nitrogen adsorption–desorption. TiO2 nanofibers mainly consisted of a large amount of anatase TiO2, accompanied with traces of rutile TiO2. Ag nanoparticles were uniformly distributed throughout TiO2 nanofibers and promoted the transformation of TiO2 from the anatase to the rutile. The corresponding electrochemical performances are measured by galvanostatic charge-discharge, cycle stability, rate performance, cycle voltammetry, and electrochemical impedance spectroscopy measurements in this research, with pristine TiO2 nanofibers as the reference. The results indicated that the introduction of Ag nanoparticles into TiO2 nanofibers significantly improved the diffusion coefficient of Li ions (5.42 × 10−9 cm2⋅s−1 for pristine TiO2, 1.96 × 10−8 cm2⋅s−1 for Ag@TiO2), and the electronic conductivity of TiO2 (1.69 × 10−5 S⋅cm−1 for pristine TiO2, and 1.99 × 10−5 S⋅cm−1 for Ag@TiO2), based on which the comprehensive electrochemical performance were greatly enhanced. The coulombic efficiency of the Ag@TiO2 nanofibers electrode at the first three cycles was about 56%, 93%, and 96%, which was higher than that without Ag (48%, 66%, and 79%). The Ag@TiO2 nanofibers electrode exhibited a higher specific discharge capacity of about 128.23 mAh⋅g−1 when compared with that without Ag (72.76 mAh·g−1) after 100 cycles at 100 mA·g−1. With the current density sharply increased from 40 mA·g−1 to 1000 mA·g−1, the higher average discharge capacity of 56.35 mAh·g−1 was remained in the electrode with Ag, when compared with the electrode without Ag (average discharge capacity of about 12.14 mAh·g−1). When the current density was returned to 40 mA·g−1, 80.36% of the initial value was returned (about 162.25 mAh·g−1) in the electrode with Ag, which was evidently superior to that without Ag (about 86.50 mAh·g−1, only 55.42% of the initial value). One-dimensional mesoporous Ag@TiO2 nanofibers can be regarded as a potential and promising candidate as anode materials for lithium ion batteries.

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