scholarly journals On the applicability of minimum channel length criterion for roll-waves in mud-flows

2013 ◽  
Vol 61 (4) ◽  
pp. 286-292 ◽  
Author(s):  
Cristiana Di Cristo ◽  
Michele Iervolino ◽  
Andrea Vacca
Keyword(s):  
Flow Model ◽  
Laboratory Data ◽  
Channel Length ◽  
Clear Water ◽  
Spatial Growth ◽  
Roll Waves

Abstract The paper addresses the prediction of roll-waves occurrence in mud-flows. The spatial growth of a point-wise disturbance is analytically described, based on the linearized flow model of a Herschel and Bulkley fluid, in the neighborhood of an initial uniform base condition. The theoretical achievements allow to generalize to mud-flows the minimum channel criterion commonly used for the prediction of roll-waves in clear-water. The applicability of the criterion is discussed through the comparison with literature laboratory data concerning unstable flows without rollwaves.

The front runner in roll waves produced by local disturbances

2021 ◽  
Vol 932 ◽  
Author(s):  
Boyuan Yu ◽  
Vincent H. Chu
Keyword(s):  
Shock Waves ◽  
Numerical Scheme ◽  
Wave Amplitude ◽  
Laboratory Data ◽  
Periodic Waves ◽  
Wave Group ◽  
Clear Water ◽  
Roll Waves ◽  
Simulation Results ◽  
The Waves

Roll waves produced by a local disturbance comprise a group of shock waves with steep fronts. We used a robust and accurate numerical scheme to capture the steep fronts in a shallow-water hydraulic model of the waves. Our simulations of the waves in clear water revealed the existence of a front runner with an exceedingly large amplitude – much greater than those of all other shock waves in the wave group. The trailing waves at the back remained periodic. Waves were produced continuously within the group due to nonlinear instability. The celerity depended on the wave amplitude. Over time, the instability produced an increasing number of shock waves in an ever-expanding wave group. We conducted simulations for three types of local disturbances of very different duration over a range of amplitudes. We interpreted the simulation results for the front runner and the trailing waves, guided by an analytical solution and the laboratory data available for the smaller waves in the trailing end of the wave group.

Clear-water local scour at wide piers in shallow-water flow

2014 ◽  
Vol 9 (3) ◽  
pp. 331-343 ◽  
Author(s):  
N. Ahmad ◽  
T. Mohamed ◽  
F. H. Ali ◽  
B. Yusuf
Keyword(s):  
Laboratory Data ◽  
Local Scour ◽  
The Other ◽  
Scour Depth ◽  
Temporal Development ◽  
Clear Water ◽  
Shallow Water Flow ◽  
Equilibrium Time ◽  
Sediment Size ◽  
Flow Intensity

Laboratory data for local scour depth regarding the size of wide piers are presented. Clear water scour tests were performed for various pier widths (0.06, 0.076, 0.102, 0.14 and 0.165 m), two types of pier shapes (circular and rectangular) and two types of uniform cohesionless bed sediment (d50 = 0.23 and d50 = 0.80 mm). New data are presented and used to demonstrate the effects of pier width, pier shape and sediment size on scour depth. The influence of equilibrium time (te) on scouring processes is also discussed. Equilibrium scour depths were found to decrease with increasing values of b/d50. The temporal development of equilibrium local scour depth with new laboratory data is demonstrated for flow intensity V/Vc = 0.95. On the other hand, the results of scour mechanism have shown a significant relationship between normalized volume of scoured and deposited with pier width, b. The experimental data obtained in this study and data available from the literature for wide piers are used to evaluate predictions of existing methods.

scholarly journals Inlet effects on roll-wave development in shallow turbulent open-channel flows

2016 ◽  
Vol 64 (1) ◽  
pp. 45-55 ◽  
Author(s):  
Francesca Campomaggiore ◽  
Cristiana Di Cristo ◽  
Michele Iervolino ◽  
Andrea Vacca
Keyword(s):  
Statistical Characteristics ◽  
Finite Volume Scheme ◽  
Flow Profile ◽  
Spatial Evolution ◽  
Inlet Condition ◽  
Spatial Growth ◽  
Roll Waves ◽  
Saint Venant Equations ◽  
Wave Development ◽  
Wave Trains

Abstract The present work investigates the effect of the flow profile induced by an inlet condition on the roll-wave evolution in turbulent clear-water flows. The study employs theoretical and numerical analyses. Firstly, the influence of the inlet condition on the spatial evolution of a single perturbation in a hypercritical flow is examined through the expansion near a wavefront analysis. The results show that an accelerated unperturbed profile reduces the disturbance spatial growth. A decelerated profile causes an increase. The effect of the flow profile on the spatial evolution of roll-wave trains is then numerically investigated solving the Saint Venant equations with a second-order Runge-Kutta Total Variation Diminishing (TVD) Finite Volume scheme. The numerical simulations comply with the analytical results for the initial and transition phases of the roll-wave development. The unperturbed profile influences even the roll-waves statistical characteristics in the final stage, with a more evident effect in case of accelerated profiles. The influence of the flow profile should be therefore accounted for in the formulation of predictive criteria for roll-waves appearance based on the estimation of the disturbance spatial growth rate.

scholarly journals A Numerical Study on Oscillatory Flow-Induced Sediment Motion over Vortex Ripples

2015 ◽  
Vol 45 (1) ◽  
pp. 228-246 ◽  
Author(s):  
Xin Chen ◽  
Xiping Yu
Keyword(s):  
Turbulence Model ◽  
Oscillatory Flow ◽  
Flow Model ◽  
Two Phase Flow ◽  
Numerical Study ◽  
Laboratory Data ◽  
Phase Flow ◽  
Mass Force ◽  
Two Phase ◽  
Reference Concentration

AbstractA two-dimensional, two-phase flow model is applied to the study of sediment motion over vortex ripples under oscillatory flow conditions. The Reynolds-averaged continuity equations and momentum equations for both the fluid and sediment phases, which include the drag force, the added mass force, the lift force for interphase coupling, and the standard k–ε turbulence model as well as the Henze–Tchen particle turbulence model for closure, are numerically solved with a finite-volume method. The model is effective over the whole depth from the undisturbed sandy bed to the low concentration region above the ripples. Neither a reference concentration nor a pickup function is required over the ripple bed as in a conventional advection–diffusion model. There is also no need to identify the bed load and the suspended load. The study focuses on the effects of erodible ripples on the intrawave flow and sediment motion over the ripples. The computational results show reasonable agreement with the available laboratory data. It is demonstrated that the formation–ejection process of vortices and the trapping–lifting process of sediment over vortex ripples can be well described by the two-phase flow model. The numerical model can also accurately predict the vertical distribution of the mean sediment concentration.

Clear-Water Abutment Scour Prediction for Simple and Complex Channels

2002 ◽  
Vol 1797 (1) ◽  
pp. 23-30
Author(s):  
J.R. Richardson ◽  
Robert Trivino
Keyword(s):  
Laboratory Data ◽  
Power Transformation ◽  
Data Sets ◽  
Predictive Equation ◽  
Clear Water ◽  
Predictive Equations ◽  
Momentum Ratio ◽  
Independent Variables ◽  
Transformation Procedure ◽  
Abutment Scour

One hundred and sixty-one laboratory and one field clear-water abutment scour data sets were regressed using a Box-Tidwell power transformation procedure. The predictive equation was verified using additional laboratory data for compound channels. A momentum ratio term was used to account for flow redistribution, differences in overbank geometries, and scale sizes. The regression identified the most applicable and dominant independent variables that affect the magnitude of clear-water abutment scour. The resulting equation has a significantly lower standard error of estimate than previously published equations. This formulation is more robust and accurately predicted abutment scour depth at both laboratory and prototype scale. With additional refinement, improved abutment scour predictive equations can be realized by using alternative regression procedures and including the momentum ratio to buffer the effect of abutment length at large prototype scales.

scholarly journals Low Pressure Experimental Validation of Low-Dimensional Analytical Model for Air–Water Two-Phase Transient Flow in Horizontal Pipelines

Fluids ◽  
2021 ◽  
Vol 6 (6) ◽  
pp. 220
Author(s):  
Hamdi Mnasri ◽  
Amine Meziou ◽  
Matthew A. Franchek ◽  
Wai Lam Loh ◽  
Thiam Teik Wan ◽  
...  
Keyword(s):  
Multiphase Flow ◽  
Experimental Validation ◽  
Flow Model ◽  
Transient Flow ◽  
Volume Fraction ◽  
Laboratory Data ◽  
Low Pressure ◽  
Two Phase ◽  
Fluid Properties ◽  
Low Dimensional

This paper presents a low-pressure experimental validation of a two-phase transient pipeline flow model. Measured pressure and flow rate data are collected for slug and froth flow patterns at the low pressure of 6 bar at the National University of Singapore Multiphase Flow Loop facility. The analyzed low-dimensional model proposed in comprises a steady-state multiphase flow model in series with a linear dynamic model capturing the flow transients. The model is based on a dissipative distributed parameter model for transient flow in transmission lines employing equivalent fluid properties. These parameters are based solely on the flowing conditions, fluid properties and pipeline geometry. OLGA simulations are employed as an independent method to validate the low-dimension model. Both low-dimensional and OLGA models are evaluated based on the estimated two-phase pressure transients for varying gas volume fraction (GVF). Both models estimated the two-phase flow transient pressure within 5% mean absolute percent error of the laboratory data. Additionally, an unavoidable presence of entrained air within a pipeline is confirmed for the case of 0% GVF as evidenced by the pressure transient estimation. Thus, dampened oscillations in the simulated 0% GVF case exists owing to an increase in the fluid compressibility.

scholarly journals On the convective nature of roll waves instability

2005 ◽  
Vol 2005 (3) ◽  
pp. 259-271 ◽  
Author(s):  
C. Di Cristo ◽  
A. Vacca
Keyword(s):  
Flow Model ◽  
Theoretical Foundation ◽  
Wave Number ◽  
Branch Points ◽  
Periodic Disturbance ◽  
One Dimensional ◽  
Dimensional Flow ◽  
Roll Waves ◽  
The One ◽  
Time Periodic

A theoretical analysis of the Saint-Venant one-dimensional flow model is performed in order to define the nature of its instability. Following the Brigg criterion, the investigation is carried out by examining the branch points singularities of dispersion relation in the complexωandkplanes, whereωandkare the complex pulsation and wave number of the disturbance, respectively. The nature of the linearly unstable conditions of flow is shown to be of convective type, independently of the Froude number value. Starting from this result a linear spatial stability analysis of the one-dimensional flow model is performed, in terms of time asymptotic response to a pointwise time periodic disturbance. The study reveals an influence of the disturbance frequency on the perturbation spatial growth rate, which constitutes the theoretical foundation of semiempirical criteria commonly employed for predicting roll waves occurrence.

scholarly journals A shallow-flow model for the propagation of tsunamis over complex geometries and mobile beds

2013 ◽  
Vol 13 (10) ◽  
pp. 2533-2542 ◽  
Author(s):  
D. A. S. Conde ◽  
M. A. V. Baptista ◽  
C. Sousa Oliveira ◽  
R. M. L. Ferreira
Keyword(s):  
Flow Model ◽  
Source Term ◽  
Laboratory Data ◽  
Riemann Solver ◽  
Tsunami Propagation ◽  
Major City ◽  
Splitting Technique ◽  
The Past ◽  
Volume Method ◽  
Shallow Flow Model

Abstract. A distinguishable feature of overland tsunami propagation is the incorporation of solids within the flow column, either sediment from the natural environment or remains from built infrastructure. This article describes a 2DH (two-dimensional horizontal) mathematical model particularly suited for tsunami propagation over complex and dynamic geometries, such as river and estuarine mobile beds. The discretization scheme is based on a finite-volume method using a flux-splitting technique featuring a reviewed Roe–Riemann solver, with appropriate source-term formulations to ensure full conservativeness. The model is validated with laboratory data and paleo-tsunami evidence. As a forecasting application, it is applied to a tsunami scenario in the Tagus estuary, an effort justified by the numerous catastrophic tsunamis that are known to have struck this location over the past two millennia. The obtained results show that, despite the significant differences in Lisbon's layout and morphology, a 1755-like tsunami would still inflict a devastating impact on this major city.

scholarly journals Characteristics of elastic wave dispersion and attenuation induced by microcracks in complex anisotropic media

2021 ◽  
Vol 18 (5) ◽  
pp. 788-807
Author(s):  
Xiaobin Li ◽  
Jianguo Yan ◽  
Qiaomu Qi ◽  
Rui Xie
Keyword(s):  
Flow Model ◽  
Fractured Reservoirs ◽  
Laboratory Data ◽  
Low Frequency ◽  
Transversely Isotropic ◽  
Wave Dispersion ◽  
Azimuthal Anisotropy ◽  
Inherent Anisotropy ◽  
Porous Sandstone ◽  
Dispersion And Attenuation

Abstract The mechanism of dispersion and attenuation induced by fluid flow among pores and microcracks in rocks is an important research topic in geophysical domain. A generalised frequency-dependent fourth-rank tensor is proposed and derived herein by combining Sayers's discontinuity tensor formula and Gurevich's squirt flow model. Furthermore, a proposed method for establishing a cracked model with cracks embedded in a transversely isotropic (TI) background medium is developed. Based on the new formulation, we investigate the characteristics of dispersion, attenuation and azimuthal anisotropy of three commonly encountered vertical crack distributions, including aligned cracks, monoclinic cracks and cracks with partial random orientations. We validate the developed model by comparing its predictions with those of the classic anisotropic squirt flow model for an aligned crack. The numerical analyses indicate that the azimuth is independent of frequency when the maximum attenuation is observed for all three crack distributions. In a low-frequency range in the case of an anisotropic background, the attenuation of the qP-wave is inversely proportional to velocity, whereas the attenuation of the qSV-wave is proportional to velocity. In addition, the inherent anisotropy of the rock does not significantly affect the dispersion and attenuation owing to squirt flow. Finally, to investigate the applicability of the theory, we model laboratory data of a synthetic porous sandstone with aligned cracks. Overall, the models agree well with laboratory data. The complex characteristics determined through this study may be useful for the seismic characterisation of fractured reservoirs.

Sign in / Sign up

Export Citation Format

Share Document