Laboratory observations of frictional stability and fault zone evolution under heterogeneous friction, rheology, and stress conditions

2020 ◽  
Author(s):  
Chun-Yu Ke ◽  
Sara Beth Leach Cebry ◽  
Srisharan Shreedharan ◽  
Chris Marone ◽  
David S. Kammer ◽  
...  
Keyword(s):  
Numerical Simulations ◽  
Laboratory Experiments ◽  
Patch Size ◽  
Numerical Models ◽  
Seismic Stability ◽  
Heterogeneous Environment ◽  
Normal Stresses ◽  
State Dependent ◽  
Earthquake Ruptures ◽  
Fault Gouges

<p>Natural faults experience a variety of frictional, rheological, and stress heterogeneities. To investigate the effects of these heterogeneities on seismic stability and the mode of fault slip behavior, laboratory experiments were conducted using a biaxial shearing apparatus with a 0.76 m by 0.076 m simulated fault where 2.5 to 5 mm thick gouge layers were sheared at applied normal stresses of 7 to 12 MPa for 25 mm of cumulative slip. Laboratory faults consisted of uniform layers of gouge, homogeneous mixtures, and/or heterogeneous patches of talc, quartz, and gypsum minerals. Experiments with a uniform layer of velocity weakening fault gouge revealed the development of two asperities at the highly stressed ends of the fault that could fail independently, and creep fronts that facilitated interaction between asperities. This behavior was also reproduced with simple numerical simulations that employ rate- and state-dependent friction. In other experiments, the fault consisted of patches of alternating velocity strengthening and velocity weakening fault gouges. Patch size and location were varied to understand how earthquake ruptures accelerate or decelerate in this heterogeneous environment. These experiments revealed that a velocity weakening fault patch was more likely to remain stable if located next to a velocity strengthening fault patch. However, stability was dependent on the patch sizes and location relative to where the load is applied. In certain cases, some sections of the fault slipped unstably while others slid stably. These experiments, and matching numerical models, highlight the complexity that can arise on natural faults due to frictional, rheological, and stress heterogeneities.</p>

scholarly journals Roughness of Fracture Surfaces in Numerical Models and Laboratory Experiments

2021 ◽  
Author(s):  
Steffen Abe ◽  
Hagen Deckert
Keyword(s):  
Numerical Simulations ◽  
Laboratory Experiments ◽  
Numerical Models ◽  
Stress Conditions ◽  
Roughness Coefficient ◽  
Confining Stress ◽  
Rock Samples ◽  
Fracture Surfaces ◽  
Wide Range ◽  
Hurst Exponents

Abstract. We investigate the influence of stress conditions during fracture formation on the geometry and roughness of fracture surfaces. Rough fracture surfaces have been generated in numerical simulations of triaxial deformation experiments using the Discrete Element Method and in laboratory experiments on limestone and sandstone samples. Digital surface models of the rock samples fractured in the laboratory experiments were produced using high resolution photogrammetry. The roughness of the surfaces was analyzed in terms of absolute roughness measures such as an estimated joint roughness coefficient (JRC) and in terms of its scaling properties. The results show that all analyzed surfaces are self-affine, but with different Hurst exponents between the numerical models and the real rock samples. Results from numerical simulations using a wide range of stress conditions to generate the fracture surfaces show a weak decrease of the Hurst exponents with increasing confining stress and a larger absolute roughness for transversely isotropic stress conditions compared to true triaxial conditions. Other than that, our results suggest that stress conditions have little influence on the surface roughness of newly formed fractures.

scholarly journals Roughness of fracture surfaces in numerical models and laboratory experiments

Solid Earth ◽  
2021 ◽  
Vol 12 (10) ◽  
pp. 2407-2424
Author(s):  
Steffen Abe ◽  
Hagen Deckert
Keyword(s):  
Numerical Simulations ◽  
Laboratory Experiments ◽  
Numerical Models ◽  
Stress Conditions ◽  
Roughness Coefficient ◽  
Confining Stress ◽  
Rock Samples ◽  
Fracture Surfaces ◽  
Wide Range ◽  
Hurst Exponents

Abstract. We investigate the influence of stress conditions during fracture formation on the geometry and roughness of fracture surfaces. Rough fracture surfaces have been generated in numerical simulations of triaxial deformation experiments using the discrete element method and in a small number of laboratory experiments on limestone and sandstone samples. Digital surface models of the rock samples fractured in the laboratory experiments were produced using high-resolution photogrammetry. The roughness of the surfaces was analyzed in terms of absolute roughness measures such as an estimated joint roughness coefficient (JRC) and in terms of its scaling properties. The results show that all analyzed surfaces are self-affine but with different Hurst exponents between the numerical models and the real rock samples. Results from numerical simulations using a wide range of stress conditions to generate the fracture surfaces show a weak decrease of the Hurst exponents with increasing confining stress and a larger absolute roughness for transversely isotropic stress conditions compared to true triaxial conditions. Other than that, our results suggest that stress conditions have little influence on the surface roughness of newly formed fractures.

scholarly journals Preliminary Results on the Dynamics of a Pile-Moored Fish Cage with Elastic Net in Currents and Waves

2020 ◽  
Vol 9 (1) ◽  
pp. 14
Author(s):  
Gianluca Zitti ◽  
Nico Novelli ◽  
Maurizio Brocchini
Keyword(s):  
Numerical Model ◽  
Laboratory Experiments ◽  
Numerical Models ◽  
Offshore Structures ◽  
Fish Farm ◽  
Maximum Displacement ◽  
Drag Forces ◽  
Real Size ◽  
Lift And Drag ◽  
Mesh Grid

Over the last decades, the aquaculture sector increased significantly and constantly, moving fish-farm plants further from the coast, and exposing them to increasingly high forces due to currents and waves. The performances of cages in currents and waves have been widely studied in literature, by means of laboratory experiments and numerical models, but virtually all the research is focused on the global performances of the system, i.e., on the maximum displacement, the volume reduction or the mooring tension. In this work we propose a numerical model, derived from the net-truss model of Kristiansen and Faltinsen (2012), to study the dynamics of fish farm cages in current and waves. In this model the net is modeled with straight trusses connecting nodes, where the mass of the net is concentrated at the nodes. The deformation of the net is evaluated solving the equation of motion of the nodes, subjected to gravity, buoyancy, lift, and drag forces. With respect to the original model, the elasticity of the net is included. In this work the real size of the net is used for the computation mesh grid, this allowing the numerical model to reproduce the exact dynamics of the cage. The numerical model is used to simulate a cage with fixed rings, based on the concept of mooring the cage to the foundation of no longer functioning offshore structures. The deformations of the system subjected to currents and waves are studied.

scholarly journals rpe v5: An emulator for reduced floating-point precision in large numerical simulations

2016 ◽  
Author(s):  
Andrew Dawson ◽  
Peter Düben
Keyword(s):  
Numerical Simulations ◽  
Climate Models ◽  
Numerical Models ◽  
Computational Cost ◽  
Floating Point ◽  
Climate Modelling ◽  
Acceptable Quality ◽  
Weather And Climate ◽  
Code Changes ◽  
Numerical Precision

Abstract. This paper describes the rpe library which has the capability to emulate the use of arbitrary reduced floating-point precision within large numerical models written in Fortran. The rpe software allows model developers to test how reduced floating-point precision affects the result of their simulations without having to make extensive code changes or port the model onto specialised hardware. The software can be used to identify parts of a program that are problematic for numerical precision and to guide changes to the program to allow a stronger reduction in precision. The development of rpe was motivated by the strong demand for more computing power. If numerical precision can be reduced for an application under consideration while still achieving results of acceptable quality, computational cost can be reduced, since a reduction in numerical precision may allow an increase in performance or a reduction in power consumption. For simulations with weather and climate models, savings due to a reduction in precision could be reinvested to allow model simulations at higher spatial resolution or complexity, or to increase the number of ensemble members to improve predictions. rpe was developed with particular focus on the community of weather and climate modelling, but the software could be used with numerical simulations from other domains.

scholarly journals Combined numerical and experimental study of microstructure and permeability in porous granular media

2020 ◽  
Author(s):  
Philipp Eichheimer ◽  
Marcel Thielmann ◽  
Wakana Fujita ◽  
Gregor J. Golabek ◽  
Michihiko Nakamura ◽  
...  
Keyword(s):  
Fluid Flow ◽  
Numerical Simulations ◽  
Granular Media ◽  
Large Scale ◽  
Earth Science ◽  
Numerical Models ◽  
Effective Porosity ◽  
Flow Properties ◽  
Wide Range ◽  
Flow Through

Abstract. Fluid flow on different scales is of interest for several Earth science disciplines like petrophysics, hydrogeology and volcanology. To parameterize fluid flow in large-scale numerical simulations (e.g. groundwater and volcanic systems), flow properties on the microscale need to be considered. For this purpose experimental and numerical investigations of flow through porous media over a wide range of porosities are necessary. In the present study we sinter glass bead media with various porosities. The microstructure, namely effective porosity and effective specific surface, is investigated using image processing. We determine flow properties like hydraulic tortuosity and permeability using both experimental measurements and numerical simulations. By fitting microstructural and flow properties to porosity, we obtain a modified Kozeny-Carman equation for isotropic low-porosity media, that can be used to simulate permeability in large-scale numerical models. To verify the modified Kozeny-Carman equation we compare it to the computed and measured permeability values.

DYNAMICS OF A PREY-DEPENDENT DIGESTIVE MODEL WITH STATE-DEPENDENT IMPULSIVE CONTROL

2012 ◽  
Vol 22 (04) ◽  
pp. 1250092 ◽  
Author(s):  
LINNING QIAN ◽  
QISHAO LU ◽  
JIARU BAI ◽  
ZHAOSHENG FENG
Keyword(s):  
Numerical Simulations ◽  
Analytical Method ◽  
Impulsive Control ◽  
Dynamical Behavior ◽  
Sufficient Conditions ◽  
Period Doubling ◽  
Lambert W Function ◽  
Impulsive Effect ◽  
State Dependent ◽  
Theoretical Results

In this paper, we study the dynamical behavior of a prey-dependent digestive model with a state-dependent impulsive effect. Using the Poincaré map and the Lambert W-function, we find the analytical expression of discrete mapping. Sufficient conditions are established for transcritical bifurcation and period-doubling bifurcation through an analytical method. Exact locations of these bifurcations are explored. Numerical simulations of an example are illustrated which agree well with our theoretical results.

PC-Based Computer Modeling of Combustion Processes

1999 ◽  
Author(s):  
Greg W. Gmurczyk ◽  
Ashwani K. Gupta
Keyword(s):  
Numerical Simulations ◽  
Computer Modeling ◽  
Numerical Experiments ◽  
Laboratory Experiments ◽  
Combustion Process ◽  
Numerical Algorithms ◽  
Computer Hardware ◽  
Simplifying Assumptions ◽  
High Level ◽  
Analytical Approaches

Abstract Constant and significant progress in both computer hardware and numerical algorithms, in recent years, have made it possible to investigate complex phenomena in engineering systems using computer modeling and simulations. Advanced numerical simulations can be treated as an extension of traditional analytical-theoretical analyses. In such cases, some of the simplifying assumptions can usually be dropped and the nonlinear interactions between various processes can be captured. One of the most complex engineering processes encountered in industry is a combustion process utilized either for power/thrust generation or incineration. However, even nowadays, because of the high level of complexity of the general problem of a combustion process in practical systems, it is not currently possible to simulate directly all the length and time scales of interest. Simplifying assumptions still need to be made, but they can be less drastic than in analytical approaches. Therefore, another view of numerical simulations is as a tool to simulate idealized systems and conduct numerical experiments. Such numerical experiments can be complementary to laboratory experiments and can also provide more detailed, nonintrusive diagnostics. Therefore, simulations, along with theory and laboratory experiments, can provide a more complete picture and better understanding of a combustion process. As an example of computer modeling of industrial combustion systems, an enclosed spray flame was considered. Such a flame can frequently be encountered in power generation units, turbine engines, and incinerators. Both the physical and mathematical models were formulated based on data from earlier laboratory studies and results obtained for open air spray flames. The purpose of this study was to use those data as model input to predict the characteristics of a confined flame and provide a means of optimizing the system design with a PC computer.

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