scholarly journals Model development for simulating mudslide and the case study of the failure of the gypsum tailings dam in East Texas in 1966

2020 ◽  
Author(s):  
Tso-Ren Wu ◽  
Thi-Hong-Nhi Vuong ◽  
Chun-Yu Wang ◽  
Chia-Ren Chu ◽  
Chun-Wei Lin
Keyword(s):  
Strain Rate ◽  
Field Data ◽  
Stokes Equations ◽  
Slip Surface ◽  
Viscosity Model ◽  
Sensitivity Analyses ◽  
Tailings Dam ◽  
East Texas ◽  
Yield Strain ◽  
Stratification Effect

Abstract. Mudslides, avalanches, and mine dam-breaks can be serious disasters and cause severe damages but the detailed flow field description has not been completed yet. This paper developed a modified Bi-viscosity model (MBM) to solve the mudslide flow by adopting Bingham model (BM) and the conventional Bi-viscosity model (CBM). In both CBM and MBM, a yield strain rate is used to identify the plug and liquefied rheological prosperities. In the MBM, an extremely high plug viscosity adopted to represent the stratification effect. BM, CBM, and MBM are integrated into the Splash3D model, which solves Navier-Stokes equations with PLIC-VOF surface-tracking algorithm. The viscosity term is solved by implicit iteration. The model is carefully validated with theoretical results and laboratory data with good agreements. The Splash3D model is then used to study the failure of the gypsum tailings dam in East Texas in 1966, briefed as FGT66. A series of sensitivity analyses on the yield strain rate and grid resolution is performed. The results show that the predicted flood distance and flood speed by MBM is very close to the field data. The MBM results illustrate the process that the plug zone and liquefied zone is developed. The simulations show the initiation of the mudslide flow, the development of the slip surface, the flooding process, and the velocity ceasing process. The slip surface is developed automatically without empirical equations. By comparing the results of BM, CBM, and MBM to the field data, we conclude that the liquefied tailings are under the effect of stratification, and the stratification effect is presented in the extremely high plug viscosity in the Splash3D model.

scholarly journals Modeling the Slump-Type Landslide Tsunamis Part I: Developing a Three-Dimensional Bingham-Type Landslide Model

2020 ◽  
Vol 10 (18) ◽  
pp. 6501 ◽  
Author(s):  
Tso-Ren Wu ◽  
Thi-Hong-Nhi Vuong ◽  
Chun-Wei Lin ◽  
Chun-Yu Wang ◽  
Chia-Ren Chu
Keyword(s):  
Strain Rate ◽  
Stokes Equations ◽  
Laboratory Data ◽  
Three Dimensional ◽  
Viscosity Model ◽  
Navier Stokes ◽  
Observation Data ◽  
Yield Strain ◽  
Slide Material ◽  
Landslide Tsunamis

This paper incorperates Bingham and bi-viscosity rheology models with the Navier–Stokes solver to simulate the dynamics and kinematics processes of slumps for tsunami generation. The rheology models are integrated into a computational fluid dynamics code, Splash3D, to solve the incompressible Navier–Stokes equations with volume of fluid surface tracking algorithm. The change between un-yield and yield phases of the slide material is controlled by the yield stress and yield strain rate in Bingham and bi-viscosity models, respectively. The integrated model is carefully validated by the theoretical results and laboratory data with good agreements. This validated model is then used to simulate the benchmark problem of the failure of the gypsum tailings dam in East Texas in 1966. The accuracy of predicted flood distances simulated by both models is about 73% of the observation data. To improve the prediction, a fixed large viscosity is introduced to describe the un-yield behavior of tailings material. The yield strain rate is obtained by comparing the simulated inundation boundary to the field data. This modified bi-viscosity model improves not only the accuracy of the spreading distance to about 97% but also the accuracy of the spreading width. The un-yield region in the modified bi-viscosity model is sturdier than that described in the Bingham model. However, once the tailing material yields, the material returns to the Bingham property. This model can be used to simulate landslide tsunamis.

scholarly journals Adjoint-based parametric sensitivity analysis for swirling M-flames

2018 ◽  
Vol 859 ◽  
pp. 516-542 ◽  
Author(s):  
Calum S. Skene ◽  
Peter J. Schmid
Keyword(s):  
Sensitivity Analysis ◽  
Frequency Response ◽  
Stokes Equations ◽  
Numerical Study ◽  
Computational Cost ◽  
Base Flow ◽  
Sensitivity Analyses ◽  
Perturbation Expansions ◽  
Mean Flow ◽  
Adjoint Solutions

A linear numerical study is conducted to quantify the effect of swirl on the response behaviour of premixed lean flames to general harmonic excitation in the inlet, upstream of combustion. This study considers axisymmetric M-flames and is based on the linearised compressible Navier–Stokes equations augmented by a simple one-step irreversible chemical reaction. Optimal frequency response gains for both axisymmetric and non-axisymmetric perturbations are computed via a direct–adjoint methodology and singular value decompositions. The high-dimensional parameter space, containing perturbation and base-flow parameters, is explored by taking advantage of generic sensitivity information gained from the adjoint solutions. This information is then tailored to specific parametric sensitivities by first-order perturbation expansions of the singular triplets about the respective parameters. Valuable flow information, at a negligible computational cost, is gained by simple weighted scalar products between direct and adjoint solutions. We find that for non-swirling flows, a mode with azimuthal wavenumber $m=2$ is the most efficiently driven structure. The structural mechanism underlying the optimal gains is shown to be the Orr mechanism for $m=0$ and a blend of Orr and other mechanisms, such as lift-up, for other azimuthal wavenumbers. Further to this, velocity and pressure perturbations are shown to make up the optimal input and output showing that the thermoacoustic mechanism is crucial in large energy amplifications. For $m=0$ these velocity perturbations are mainly longitudinal, but for higher wavenumbers azimuthal velocity fluctuations become prominent, especially in the non-swirling case. Sensitivity analyses are carried out with respect to the Mach number, Reynolds number and swirl number, and the accuracy of parametric gradients of the frequency response curve is assessed. The sensitivity analysis reveals that increases in Reynolds and Mach numbers yield higher gains, through a decrease in temperature diffusion. A rise in mean-flow swirl is shown to diminish the gain, with increased damping for higher azimuthal wavenumbers. This leads to a reordering of the most effectively amplified mode, with the axisymmetric ($m=0$) mode becoming the dominant structure at moderate swirl numbers.

scholarly journals Longitudinal Stress Gradients and Basal Shear Stress of a Temperate Valley Glacier

1979 ◽  
Vol 24 (90) ◽  
pp. 507-508 ◽  
Author(s):  
Robert Bindschadler
Keyword(s):  
Shear Stress ◽  
Strain Rate ◽  
Field Data ◽  
Numerical Models ◽  
Lateral Strain ◽  
Longitudinal Stress ◽  
Base Shear ◽  
Stress Gradients ◽  
Valley Glacier ◽  
Image Position

AbstractFor the first time field data from a temperate valley glacier, the Variegated Glacier, are used to investigate the behavior of longitudinal stress gradients predicted by the relation(1)whereHis the local depth, andysandybare the surface and bed elevations respectively. This equation is similar to one derived by Budd (1970) for plane strain-rate, to evaluate the importance of longitudinal stress gradients, but a shape factorfis included to account approximately for lateral strain-rate gradients. Predictive numerical models of valley glaciers require the local base shear stress to be known as accurately as possible. It has been argued on theoretical grounds that whenTis averaged over distances of more than five to ten times the depth, this term is negligible. At larger averaging scales, 2Gcan then be considered a correction to the simple geometric expression of base stress due to the presence of longitudinal stress gradients. Field data of velocity and geometry are used to evaluate the terms of Equation (1), whereτband 2Gare estimated asandat intervals of 100 m,Usis the measured surface center-line velocity,Aandnare the flow-law parameters, andis the surface longitudinal strain-rate. The expression for 2Gis an approximation proposed by Budd (1970).

scholarly journals Hydrodynamics of flagellated microswimmers near free-slip interfaces

2016 ◽  
Vol 789 ◽  
pp. 514-533 ◽  
Author(s):  
D. Pimponi ◽  
M. Chinappi ◽  
P. Gualtieri ◽  
C. M. Casciola
Keyword(s):  
Numerical Solutions ◽  
Stokes Equations ◽  
Slip Surface ◽  
Initial Conditions ◽  
Aerobic Bacteria ◽  
Slip Boundary ◽  
Experimental Findings ◽  
Micro Organisms ◽  
Air Interfaces ◽  
Shed Light

The hydrodynamics of a flagellated micro-organism is investigated when swimming close to a planar free-slip surface by means of numerical solutions of the Stokes equations obtained via a boundary element method. Depending on the initial conditions, the swimmer can either escape from the free-slip surface or collide with the boundary. Interestingly, the micro-organism does not exhibit a stable orbit. Independently of escape or attraction to the interface, close to a free-slip surface, the swimmer follows a counter-clockwise trajectory, in agreement with experimental findings (Di Leonardo et al., Phys. Rev. Lett., vol. 106 (3), 2011, 038101). The hydrodynamics is indeed modified by the free surface. In fact, when the same swimmer moves close to a no-slip wall, a set of initial conditions exists which result in stable orbits. Moreover, when moving close to a free-slip or a no-slip boundary, the swimmer assumes a different orientation with respect to its trajectory. Taken together, these results contribute to shed light on the hydrodynamical behaviour of micro-organisms close to liquid–air interfaces which are relevant for the formation of interfacial biofilms of aerobic bacteria.

Subgrid-scale structure and fluxes of turbulence underneath a surface wave

2019 ◽  
Vol 878 ◽  
pp. 768-795
Author(s):  
Kuanyu Chen ◽  
Minping Wan ◽  
Lian-Ping Wang ◽  
Shiyi Chen
Keyword(s):  
Strain Rate ◽  
Eddy Viscosity ◽  
Isotropic Turbulence ◽  
Wave Theory ◽  
Viscosity Model ◽  
Strain Rate Tensor ◽  
Linear Wave ◽  
Subgrid Scale ◽  
Eddy Viscosity Model ◽  
Wave Induced

In this study, the behaviours of subgrid-scale (SGS) turbulence are investigated with direct numerical simulations when an isotropic turbulence is brought to interact with imposed rapid waves. A partition of the velocity field is used to decompose the SGS stress into three parts, namely, the turbulent part $\unicode[STIX]{x1D749}^{T}$, the wave-induced part $\unicode[STIX]{x1D749}^{W}$ and the cross-interaction part $\unicode[STIX]{x1D749}^{C}$. Under strong wave straining, $\unicode[STIX]{x1D749}^{T}$ is found to follow the Kolmogorov scaling $\unicode[STIX]{x1D6E5}_{c}^{2/3}$, where $\unicode[STIX]{x1D6E5}_{c}$ is the filter width. Based on the linear Airy wave theory, $\unicode[STIX]{x1D749}^{W}$ and the filtered strain-rate tensor due to the wave motion, $\tilde{\unicode[STIX]{x1D64E}}^{W}$, are found to have different phases, posing a difficulty in applying the usual eddy-viscosity model. On the other hand, $\unicode[STIX]{x1D749}^{T}$ and the filtered strain-rate tensor due to the turbulent motion, $\tilde{\unicode[STIX]{x1D64E}}^{T}$, are only weakly wave-phase-dependent and could be well related by an eddy-viscosity model. The linear wave theory is also used to describe the vertical distributions of SGS statistics driven by the wave-induced motion. The predictions are in good agreement with the direct numerical simulation results. The budget equation for the turbulent SGS kinetic energy shows that the transport terms related to turbulence are important near the free surface and they compensate the imbalance between the energy flux and the SGS energy dissipation.

Numerical investigation into the effect of ballast properties on buckling of continuously welded rail (CWR)

2020 ◽  
pp. 095440972096579
Author(s):  
Fatemeh Khatibi ◽  
Morteza Esmaeili ◽  
Saeed Mohammadzadeh
Keyword(s):  
Finite Element ◽  
Discrete Element Method ◽  
Finite Element Model ◽  
Field Data ◽  
Friction Angle ◽  
Element Model ◽  
Sensitivity Analyses ◽  
Track Stiffness ◽  
Dem Analysis ◽  
Continuously Welded Rail

In this paper, the effect of ballast properties including ballast depth, shoulder width, shoulder height, inter particle friction angle and ballast porosity on track buckling capacity are investigated numerically using discrete element method (DEM) analysis. First, a Single Tie Push Test (STPT) is simulated using DEM and the results are validated with field data. Then a sensitivity analyses is carried out. To investigate the effect of ballast properties on buckling capacity, the STPT responses according to the DEM analysis are introduced as a lateral track stiffness into a finite element model of continuously welded rail track, and a thermal buckling simulation is performed. The results show a significant effect of ballast porosity on buckling temperature.

Depth and minimal slope for surface flows of cohesive granular materials on inclined channels

2013 ◽  
Vol 727 ◽  
pp. 191-235 ◽  
Author(s):  
Alain de Ryck ◽  
Olivier Louisnard
Keyword(s):  
Friction Coefficient ◽  
Strain Rate ◽  
Stokes Equations ◽  
Surface Flow ◽  
Force Balance ◽  
Channel Width ◽  
Wall Friction ◽  
Incline Angle ◽  
Important Conclusion ◽  
Flowing Material

AbstractWe present analytical predictions of the depth and onset slope of the steady surface flow of a cohesive granular material in an inclined channel. The rheology of Jop, Forterre & Pouliquen (Nature, vol. 441, 2006, pp. 727–730) is used, assuming co-axiality between the stress and strain-rate tensors, and a coefficient of friction dependent on the strain rate through the dimensionless inertial number $I$. This rheological law is augmented by a constant stress representing cohesion. Our analysis does not rely on a precise $\mu (I)$ functional, but only on its asymptotic power law in the limit of vanishing strain rates. Assuming a unidirectional flow, the Navier–Stokes equations can be solved explicitly to yield parametric equations of the iso-velocity lines in the plane perpendicular to the flow. Two types of channel walls are considered: rough and smooth, depicting walls whose friction coefficient is respectively larger or smaller than that of the flowing material. The steady flow starts above a critical onset angle and consists of a sheared zone confined between a surface plug flow and a deep dead zone. The details of the flow are discussed, depending on dimensionless parameters relating the static friction coefficient, cohesion strength of the material, incline angle, wall friction, and channel width. The depths of the flow at the centre of the channel and at the walls are calculated by a force balance on the flowing material. The critical angle for the onset of the flow is also calculated, and is found to be strongly dependent on the channel width, in agreement with experimental results on heap stability and in rotating drums. Our results predict the important conclusion that a cohesive material always starts to flow for an incline angle lower than 90° between smooth walls, whereas in a narrow enough channel with rough walls, it may not flow, even if the channel is inclined vertically.

Two and Three-Dimensional Simulations of Enhanced Heat Transfer in Nuclear Fuel Rod Bundles

2009 ◽  
Author(s):  
Leo A. Carrilho ◽  
Jamil Khan ◽  
Michael E. Conner ◽  
Abdel Mandour ◽  
Milorad B. Dzodzo
Keyword(s):  
Heat Transfer ◽  
Finite Element ◽  
Turbulent Flow ◽  
Stokes Equations ◽  
Three Dimensional ◽  
Element Model ◽  
Sensitivity Analyses ◽  
Artificial Roughness ◽  
Pressurized Water ◽  
Fuel Rod

The effects of artificial roughness for the purpose of thermal performance improvement in pressurized water nuclear reactors are investigated. The artificial roughness consists of two-dimensional ribs parallel to the turbulent flow. The fuel rod bundle subchannel is preliminarily modeled as an annulus using the finite element method in ANSYS/FLOTRAN. The Navier-Stokes equations are solved from the SST (Shear Stress Transport) turbulence model for the simulated annulus thermal-flow. The analyses are performed for ribs dimensions and pitch provided by published previous work. It is found that, heat transfer and differential pressure have similar behavior with highest heat transfer occurring at the reattachment point. The finite element model describes well the characteristics of turbulent flow in smooth and rough rod when compared to previous semi-empirical models. Next paper extends the analysis by comparing numerical results with experimental test data and sensitivity analyses for different roughness configurations.

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