Unsteady Open Channel Flow Research Papers (original) (raw)

"The effective structuring of knowledge bases is most important for knowledge-based expert-system design, whilst the reliable evaluation of these knowledge bases is the key point for the acceptance of artificial intelligence technology.... more

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- Evaluation, expert System, Knowledge Bases, Structuring

This paper presents settings and results of laboratory experiments on bed load transport. Experiments were performed for unsteady hydrographs and for steady flow conditions. Continuous measurements of transported mass and flow rate reveals a clockwise hysteresis of bed load rate vs. flow rate. The comparison between bed load rate in unsteady and steady flow shows that it depends to large extent on sediment supply. The results are discussed in the light of variable sediment supply, and suggestions for procedure of further experiments are presented.

The unsteady flow can be analysed by Saint-Venant equations. These equations can be solved by characteristics and finite difference methods. The Saint-Venant equations are changed into four complete differential equations in characteristics method and these equations are solved by drawing two characteristics lines. The Saint-Venant equations are changed into set nonlinear equations and are solved using Preissman scheme in finite difference method. This set of equation is changed into linear equation using Newton-Rafson method and can be solved using Sparce method. In this research, the results of the two method were compared and this was shown that: 1) these two methods can draw the surface profiles and flow hydrograph as well; 2) the finite difference method is more accurate than that one; 3) the mesh size in finite difference method can be larger than that one; 4) the difference between two methods are increased by increasing the time and distance.. He is interested in the topics of: groundwater hydrology, irrigation and drainage engineering, sustainable development and environmental assessment, climate and integrated and sustainable water resource management, artificial neural network, and genetic algorithm. He has contributed to more than 80 publications in journals, books, or as technical reports. Currently, he is as a

Knowledge acquisition and representation has been characterised as the major bottleneck in the development of expert systems , especially in problem domains of high complexity. Financial analysis is one of the most complicated practical problems, where the expert systems technology is highly applicable, mainly because of its symbolic reasoning and its explanation capabilities. The aim of this paper is to present a complete methodology for knowledge acquisition and representation for expert systems development in the field of financial analysis. This methodology has been implemented in the development of the FINEVA multicriteria knowledge-based decision support system for the assessment of corporate performance and viability. The application of this methodology in the development of the FINEVA system is presented.

- by Michael Doumpos and +1
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- Information Systems, Mechanical Engineering, Cognitive Science, Machine Learning

An example of carrying out unit hydrograph convolution in order to get the full Hydrograph of a catchment for a given hyetograph is explained in steps. Matrix manipulation using Excel is used for this regard and a simple user defined function is developed to facilitate building the Precipitation Matrix. Using the developed function, it becomes easy to just drag and create the full P matrix in an automated way.

The problem of sudden flame acceleration in narrow channels and subsequent Deflagration to Detonation Transition (DDT) is revisited. The hydrogen-oxygen combustion system is considered both experimentally and numerically. The flame is initiated at one open end of a square narrow channel of different widths (4, 8, 10 and 20 mm) and propagates to another open end. Experimental results show a high sensitivity to the mixture composition: for higher mixture reactivity, an abrupt flame acceleration is reported. In 4 × 4 mm 2 channel, when the mixture composition is close to stoichiometry (2:1), the DDT is observed without any evidence of shock waves prior to the detonation transition. Two complementary sub-models are combined to account for the effect of walls on flow and on flame front geometry. A pseudo-spectral numerical scheme is used to integrate the system of equations both in time and in space. The simulation results show how the suggested model reproduces main features of the phenomenon. A simple criterion is suggested for the onset of the flame self-acceleration. There exists a critical flame folding factor for the DDT, which is an invariant of the system. The reported critical folding factor is compared to the theoretical estimation introduced by Gordon et al (2020).

- by Mike Kuznetsov, PhD
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- Hydrogen, Combustion modelling, DDT, Unsteady Open Channel Flow

- by Chiang-An Hsu and +1
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- Computational Fluid Dynamics (CFD) modelling and simulation, Open Channel Flow, Unsteady Open Channel Flow

The performance graph (PG) hydraulic routing method has been shown to be accurate, numerically efficient, and robust for unsteady flow routing. However, up to present, the performance graphs are constructed using one-dimensional (1D) steady flow models only, which are often questioned when simulating flows through complex bathymetries. This paper investigates whether the PG method can still be used when utilizing two-dimensional (2D) models for the construction of PGs. The test case is a stretch around an island in the Fraser River in British Columbia. The results show that the PG method is still applicable when utilizing a 2D steady flow model. The results also show that once the PGs are constructed, the PG routing method (1D and 2D) is computationally more efficient than the unsteady HEC-RAS model and can be several orders of magnitude faster than TELEMAC-2D.

- by Arturo S Leon
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- Hydraulics, Rivers, Two-dimensional, Unsteady Open Channel Flow

This paper presents an evaluation and analysis of resistance parameters: friction slope, friction velocity and Manning coefficient in unsteady flow. The methodology to enhance the evaluation of resistance by relations derived from flow equations is proposed. The main points of the methodology are (1) to choose a resistance relation with regard to a shape of a channel and (2) type of wave, (3) to choose an appropriate method to evaluate slope of water depth, and (4) to assess the uncertainty of result. In addition to a critical analysis of existing methods, new approaches are presented: formulae for resistance parameters for a trapezoidal channel, and a translation method instead of Jones' formula to evaluate the gradient of flow depth. Measurements obtained from artificial dam-break flood waves in a small lowland watercourse have made it possible to apply the method and to analyse to what extent resistance parameters vary in unsteady flow. The study demonstrates that results of friction slope and friction velocity are more sensitive to applying simplified formulae than the Manning coefficient (n). n is adequate as a flood routing parameter but may be misleading when information on trend of resistance with flow rate is crucial. Then friction slope or friction velocity seems to be better choice.

- by Magdalena Mrokowska and +1
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- Hydrology, Unsteady Flow and Transient Flow, Unsteady flow, Unsteady Open Channel Flow

Using numerical models for the purpose of channel-routing calculation has been well accepted in engineering practice. However, most traditional models fail to predict the transcritical flows because of numerical instability. This paper presents two high-resolution, shock-capturing schemes for the simulation of 1D, rapidly varied open-channel flows. The present schemes incorporate the method of characteristics to deal with the unsteady boundary conditions. Also, the Strang-type splitting operator is used to include the effects of bottom slope and friction terms. To assess the performance of the proposed algorithms, several steady and unsteady problems are simulated to verify the accuracy and robustness in capturing strong shocks in open-channel flows. Furthermore, the results of dynamic flood routing and steady routing are compared to demonstrate the risk of using steady routing for flood mitigation.

- by 朱佳仁老師
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- Hydraulics, Hydraulic Engineering, Open Channel Flow, Hydraulic

This paper addresses the application of C languages in developing hydraulic engineering software and depicts the implementation and the rigorous verification of a generally applicable finite difference numerical model, tailored for use on the IBM PC/XT or PC/AT personal computers, for simulation of unsteady open channel flow. The program is written in the C language, compiling and executing under the integrated program environment TURBO C version 2.0. The various advantages and limitations of employing the TURBO C environment in developing hydraulic engineering software are also presented thoroughly. In the development of the mathematical model, apart from the simplified channel tests where analytical results are available, its effectiveness has also been investigated in a real prototype case, Delaware Estuary, where some field data are available. The program's successful application provides confidence for its capability as a predictive tool in situations involving complex bathymetry and/or nonlinear bottom frictional effects.

- by K.W. Chau
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- Open Channel Flow, Numerical Model, Unsteady Open Channel Flow

A three-dimensional computational code has been developed for the investigation of unsteady laminar flow past single and two inline circular tubes cross-confined in a channel. The developed code is based on the SIMPLE algorithm using finite volume technique to solve the governing equations. A body-fitted, multi-block structured grid has been generated for discretization of the incompressible form of conservation equations of mass, momentum and energy. The computational results correspond to a fixed Reynolds number of 400 based on tube diameter. The instantaneous flow and heat transfer characteristics for single and two inline tubes have been compared using streamline plots, temperature contours, vorticity contours, span-averaged pressure and span-averaged Nusselt number.

- by Jayavel SJV
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- Unsteady Open Channel Flow, Channel Confinement, Circular Tubes

This paper is about the free surface instabilities of granular flows, usually called roll waves. A shallow layer of shear-thickening fluid (τ = a(∂ u/∂ y)n with n = 2) is considered to study finite-amplitude permanent roll waves down a slope, simplified by Karman’s momentum integral approach. The existence of conditions of a periodic discontinuous solution is derived, as smooth profiles with depth increasing monotonically between periodic shocks. Energy dissipation in the body of the stream and in the discontinuity is analysed and discussed. Two conditions are derived. The first is related to the physically acceptable shape of the smooth profiles, and the second is related to positive energy loss across the shock. These conditions can be converted into a limiting discharge, viewed in the fixed frame, and in a limiting flow thickness (or limiting Froude number), for the permanent periodic roll wave to exist without further conditions. A minimum-length roll wave (MLRW) is defined as the periodic permanent roll waves with zero energy dissipation in the shock. The MLRW also requires a limiting value of the Froude number to exist.

This paper describes an attempt to identify catchments within Australia that have similar stream flow signatures. The stream flow from a catchment represents the integrated effect of the catchment’s physical characteristics, such as topogra- phy, soil and vegetation to external impacts such as climate. Therefore, stream flow represents the response of a catchment to these variables and has been called the signature of the catchment in this paper.
Characteristic features of a catchment’s signature are identified using the wavelet transform. Unlike other traditional frequency decomposition methods, the wavelet transformation represents a step by step decomposition of the data signal by time and scale. Therefore, a wavelet decomposition often reveals structures that are obscured in stream flow records.
Integration of the wavelet signals over time yields the wavelet energy contained at a particular time scale. Plotting the wavelet energy for all time scales produces the energy spectra distribution. The energy spectra distribution summarizes the variability present in the stream flow series at a range of time scales. These can be used to categorize the response of catchments by grouping catchments with similar wavelet energy spectra distributions.
Wavelet energy spectra distributions were obtained for years of synthe- sized daily stream flow records at rivers throughout Australia. These were grouped using -means analysis where twelve distinct signatures have been iden- tified. While more work is needed to establish the role of wavelets in the regional- ization of catchments, our preliminary results suggest that classifying daily stream flow using the energy of the wavelet spectrum may be an effective method to clas- sify the behaviour of catchments to climatic and physical catchment parameters.

This paper reports a ®nite dierence predictor±corrector TVD (total variation diminishing) scheme for the computation of unsteady one-dimensional dam-break ¯ows. The algorithm modi®ed the widely used MacCormack scheme by implementing a conservative dissipation step to avoid any unphysical oscillation in the vicinity of strong gradients in the numerical solution. A general treatment for satisfying the entropy inequality condition is incorporated. The accuracy and robustness of the numerical scheme are veri®ed with an analytic solution and experimental data. Furthermore, a sensitivity study is carried out to investigate the accuracy of four dierent versions of the predictor±corrector schemes. It is found that the numerical scheme will have less computational error and higher eciency when the direction of the predictor±corrector step is the same as the direction of the shock wave propagation.

- by 朱佳仁老師
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- Hydraulics, Open Channel Flow, Hydraulic, Unsteady Open Channel Flow

The modelling of unsteady open channel flow, which is an important area in fluvial engineering, involves a complicated heuristic decision-making process. Numerical modelling is an economical and powerful technique being widely used nowadays. However, engineers usually face many obstacles in the application of conventional numerical software, due to the complex process of the task definition, model calibration and result evaluation involved. Expert system, an active subject of artificial intelligence, is suitable to treat the above engineering problem. This paper describes the methodology of knowledge acquisition and representation for fluvial hydrodynamics, which play a key role in the development of a practical knowledge based system. The experience gained through the knowledge acquisition process in this project is discussed. The construction of the knowledge bases for the development of a microcomputer-based expert system for unsteady open channel flow in a river network is also presented.

Intakes are widely used for flow diversion and its control in the open channels. Circular intakes with bellmouth transitions are used to enhance the discharging capacity of the intakes. Analytical and experimental studies for flow through lateral circular intakes with and without bellmouth in open channels are presented in this paper. This study indicates that the coefficient of discharge for the lateral intake under uniform flow is dependent on the Froude number of the approach flow in the main channel and the ratio of width of the orifice to the width of the main channel. Collected data in this study are used to develop regression equation for the coefficient of discharge. The computed discharges using the proposed equations in this study are within ±10% and ±7% of the observed ones for intake with and without bellmouth, respectively. The discharging capacity of an intake with bellmouth is higher than the intake without transition. Sensitivity analysis indicates that the discharge...

- by Kaveh Ostad-Ali-Askari and +1
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- Flow Cytometry, Multiphase Flow, Two Phase Flow, Fluid flow in porous media