Effect of normal and shear loading on the hydraulic transport properties of calcite bearing faults with customized roughness.

2021 ◽  
Author(s):  
Mateo Acosta ◽  
Robin Maye ◽  
Marie Violay
Keyword(s):  
Fluid Flow ◽  
Large Scale ◽  
Numerical Procedure ◽  
Shear Loading ◽  
Shear Displacement ◽  
Shear Stresses ◽  
Surface Geometry ◽  
Normal Loading ◽  
Normal Contact ◽  
Fault Surface

<p>Understanding fluid flow in rough fractures is of high importance to large scale geologic processes and to most anthropogenic geo-energy activities. Here, we conducted fluid transport experiments on Carrara marble fractures with a novel customized surface topography. Transmissivity measurements were conducted under normal stresses from 20 to 50 MPa and shear stresses from 0 to 30 MPa. An open-source numerical procedure was developed to simulate normal contact and fluid flow through fractures with complex geometries. It was validated towards experiments. Using it, we isolated the effects of roughness parameters on fracture fluid flow. Under normal loading, we find that i) the transmissivity decreases with normal loading and is strongly dependent on fault surface geometry ii) the standard deviation of heights (hrms) and macroscopic wavelength of the surface asperities control fracture transmissivity. Transmissivity evolution is non-monotonic, with more than 4 orders of magnitude difference for small variations of macroscopic wavelength and roughness. Reversible elastic shear loading has little effect on transmissivity, it can increase or decrease depending on contact geometry and overall stress state on the fault. Irreversible shear displacement (up to 1 mm offset) slightly decreases transmissivity and its variation with irreversible shear displacements can be predicted numerically and geometrically at low normal stress only. Finally, irreversible changes in surface roughness (plasticity and wear) due to shear displacement result in a permanent decrease of transmissivity when decreasing differential stress. Generally, reduction of a carbonate fault’s effective stress increases its transmissivity while inducing small shear displacements doesn’t.</p>

scholarly journals Natural Rock Fractures: From Aperture to Fluid Flow

2021 ◽  
Author(s):  
Alejandro Cardona ◽  
Thomas Finkbeiner ◽  
J. Carlos Santamarina
Keyword(s):  
Fluid Flow ◽  
Normal Stress ◽  
Size Distribution ◽  
Power Law ◽  
Preferential Flow ◽  
Shear Displacement ◽  
Shear Direction ◽  
Aperture Size ◽  
Standard Deviation Increase ◽  
Normal Loading

AbstractFractures provide preferential flow paths and establish the internal “plumbing” of the rock mass. Fracture surface roughness and the matedness between surfaces combine to delineate the fracture geometric aperture. New and published measurements show the inherent relation between roughness wavelength and amplitude. In fact, data cluster along a power trend consistent with fractal topography. Synthetic fractal surfaces created using this power law, kinematic constraints and contact mechanics are used to explore the evolution of aperture size distribution during normal loading and shear displacement. Results show that increments in normal stress shift the Gaussian aperture size distribution toward smaller apertures. On the other hand, shear displacements do not affect the aperture size distribution of unmated fractures; however, the aperture mean and standard deviation increase with shear displacement in initially mated fractures. We demonstrate that the cubic law is locally valid when fracture roughness follows the observed power law and allows for efficient numerical analyses of transmissivity. Simulations show that flow trajectories redistribute and flow channeling becomes more pronounced with increasing normal stress. Shear displacement induces early aperture anisotropy in initially mated fractures as contact points detach transversely to the shear direction; however, anisotropy decreases as fractures become unmated after large shear displacements. Radial transmissivity measurements obtained using a torsional ring shear device and data gathered from the literature support the development of robust phenomenological models that satisfy asymptotic trends. A power function accurately captures the evolution of transmissivity with normal stress, while a logistic function represents changes with shear displacement. A complementary hydro-chemo-mechanical study shows that positive feedback during reactive fluid flow heightens channeling.

Finite Element Analysis of Tire/Rim Interface Forces Under Braking and Cornering Loads

1992 ◽  
Vol 20 (2) ◽  
pp. 83-105 ◽  
Author(s):  
J. P. Jeusette ◽  
M. Theves
Keyword(s):  
Finite Element ◽  
Shear Stress ◽  
Contact Pressure ◽  
Element Model ◽  
Shear Stresses ◽  
Detailed Knowledge ◽  
Stress Distributions ◽  
Element Analysis ◽  
Plane Shear ◽  
Normal Contact

Abstract During vehicle braking and cornering, the tire's footprint region may see high normal contact pressures and in-plane shear stresses. The corresponding resultant forces and moments are transferred to the wheel. The optimal design of the tire bead area and the wheel requires a detailed knowledge of the contact pressure and shear stress distributions at the tire/rim interface. In this study, the forces and moments obtained from the simulation of a vehicle in stationary braking/cornering conditions are applied to a quasi-static braking/cornering tire finite element model. Detailed contact pressure and shear stress distributions at the tire/rim interface are computed for heavy braking and cornering maneuvers.

Cyclic Loading of Piles Using the P-Y Method

2019 ◽  
Vol 13 (2) ◽  
Author(s):  
Matt Bristow
Keyword(s):  
Cyclic Loading ◽  
Soil Depth ◽  
Large Diameter ◽  
Reference Conditions ◽  
Numerical Procedure ◽  
New Method ◽  
Shear Stresses ◽  
Applied Loading ◽  
Cyclic Degradation ◽  
Laterally Loaded

A new analytical method is presented to determine the effects of cyclic loading on laterally loaded piles. The method uses a new numerical procedure to quantify the effects of the cyclic loading at each soil depth and convert that to a set of cyclic p-y modifiers. The reduced foundation stiffness associated with the cyclic loading can be determined, including the residual static capacity and an estimate of the accumulated displacement. The new method introduces the concept of cyclic degradation damage, which is defined as sum of the cyclic degradation that is occurring at each soil depth. Cyclic degradation calculations are based on the shear stresses in the soil. Consequently, anything that causes the shear stresses to change (e.g. pile length, pile diameter, applied loading, etc.) will automatically be included in the calculation of cyclic p-y modifiers. The method has been validated by comparing the cyclic p-y curves produced using the new method with established cyclic p-y curves derived from fielding testing. The new method has also been used to investigate what happens to the cyclic p-y modifiers as one moves away from the reference conditions used to determine the established cyclic p-y curves in API RP2A (2000). The new method shows that every application (e.g. combination of cyclic loading, pile properties, and soil characteristics) has its own unique set of cyclic p-y curves, though most p-y curves fit within an upper and lower bound range. Examples are provided for large diameter monopiles.

scholarly journals Trace element catalyses mineral replacement reactions and facilitates ore formation

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Yanlu Xing ◽  
Joël Brugger ◽  
Barbara Etschmann ◽  
Andrew G. Tomkins ◽  
Andrew J. Frierdich ◽  
...  
Keyword(s):  
Mass Transfer ◽  
Trace Elements ◽  
Fluid Flow ◽  
Large Scale ◽  
Metal Accumulation ◽  
Nucleation And Growth ◽  
Reaction Interface ◽  
Ore Formation ◽  
Key Factor ◽  
Mineral Replacement

AbstractReaction-induced porosity is a key factor enabling protracted fluid-rock interactions in the Earth’s crust, promoting large-scale mineralogical changes during diagenesis, metamorphism, and ore formation. Here, we show experimentally that the presence of trace amounts of dissolved cerium increases the porosity of hematite (Fe2O3) formed via fluid-induced, redox-independent replacement of magnetite (Fe3O4), thereby increasing the efficiency of coupled magnetite replacement, fluid flow, and element mass transfer. Cerium acts as a catalyst affecting the nucleation and growth of hematite by modifying the Fe2+(aq)/Fe3+(aq) ratio at the reaction interface. Our results demonstrate that trace elements can enhance fluid-mediated mineral replacement reactions, ultimately controlling the kinetics, texture, and composition of fluid-mineral systems. Applied to some of the world’s most valuable orebodies, these results provide new insights into how early formation of extensive magnetite alteration may have preconditioned these ore systems for later enhanced metal accumulation, contributing to their sizes and metal endowment.

scholarly journals Evolution of Friction and Permeability in a Propped Fracture under Shear

Geofluids ◽  
2017 ◽  
Vol 2017 ◽  
pp. 1-13 ◽  
Author(s):  
Fengshou Zhang ◽  
Yi Fang ◽  
Derek Elsworth ◽  
Chaoyi Wang ◽  
Xiaofeng Yang
Keyword(s):  
Normal Stress ◽  
Shear Loading ◽  
Particle Crushing ◽  
Normal Loading ◽  
Fracture Surfaces ◽  
Frictional Strength ◽  
Transport Response ◽  
Shear Slip ◽  
High Normal Stress ◽  
Proppant Embedment

We explore the evolution of friction and permeability of a propped fracture under shear. We examine the effects of normal stress, proppant thickness, proppant size, and fracture wall texture on the frictional and transport response of proppant packs confined between planar fracture surfaces. The proppant-absent and proppant-filled fractures show different frictional strength. For fractures with proppants, the frictional response is mainly controlled by the normal stress and proppant thickness. The depth of shearing-concurrent striations on fracture surfaces suggests that the magnitude of proppant embedment is controlled by the applied normal stress. Under high normal stress, the reduced friction implies that shear slip is more likely to occur on propped fractures in deeper reservoirs. The increase in the number of proppant layers, from monolayer to triple layers, significantly increases the friction of the propped fracture due to the interlocking of the particles and jamming. Permeability of the propped fracture is mainly controlled by the magnitude of the normal stress, the proppant thickness, and the proppant grain size. Permeability of the propped fracture decreases during shearing due to proppant particle crushing and related clogging. Proppants are prone to crushing if the shear loading evolves concurrently with the normal loading.

Multi-Objective Optimization of a Microturbine Compact Recuperator

2008 ◽  
Vol 130 (3) ◽  
Author(s):  
Diego Micheli ◽  
Valentino Pediroda ◽  
Stefano Pieri
Keyword(s):  
Heat Transfer ◽  
Three Dimensional ◽  
Numerical Procedure ◽  
Design Procedure ◽  
Domain Size ◽  
Multidisciplinary Optimization ◽  
Computational Domain ◽  
Surface Geometry ◽  
Multi Objective ◽  
Flux Boundary Conditions

An automatic approach for the multi-objective shape optimization of microgas turbine heat exchangers is presented. According to the concept of multidisciplinary optimization, the methodology integrates a CAD parametric model of the heat transfer surfaces, a three-dimensional meshing tool, and a CFD solver, all managed by a design optimization platform. The repetitive pattern of the surface geometry has been exploited to reduce the computational domain size, and the constant flux boundary conditions have been imposed to better suit the real operative conditions. A new approach that couples cold and warm fluids in a periodic unitary cell is introduced. The effectiveness of the numerical procedure was verified comparing the numerical results with available literature data. The optimization objectives are maximizing the heat transfer rate and minimizing both friction factor and heat transfer surface. The paper presents the results of the optimization of a 50kWMGT recuperator. The design procedure can be effectively extended and applied to any industrial heat exchanger application.

Mechanics of Composite Layered Rough Medium in Contact

2013 ◽  
Vol 703 ◽  
pp. 200-203
Author(s):  
Shao Biao Cai ◽  
Yong Li Zhao
Keyword(s):  
Material Properties ◽  
Three Dimensional ◽  
Shear Stresses ◽  
Normal Loading ◽  
Layered Coatings ◽  
Pressure Profiles ◽  
Tangential Traction ◽  
Von Mises ◽  
Von Mises Stresses ◽  
Tangential Friction

This study presents a first attempt to develop a numerical three-dimensional multilayered (more than 2 composite layered coatings) elasticperfectly plastic rough solids model to investigate the contact behavior under combined normal loading and tangential traction. Contact analyses are performed to study the effects composite thin film layers. Local contact pressure profiles, von Mises stresses, and shear stresses as a function of material properties and applied normal and tangential friction loads are calculated.

High-frequency ground-motion variability for rough-fault ruptures  

2021 ◽  
Author(s):  
Jagdish Chandra Vyas ◽  
Martin Galis ◽  
Paul Martin Mai
Keyword(s):  
Ground Motion ◽  
Large Scale ◽  
Earthquake Ground Motion ◽  
Small Scale ◽  
Dynamic Rupture ◽  
Roughness Effects ◽  
Ground Shaking ◽  
Fault Surface ◽  
Fault Roughness ◽  
Ground Motion Variability

<p>Geological observations show variations in fault-surface topography not only at large scale (segmentation) but also at small scale (roughness). These geometrical complexities strongly affect the stress distribution and frictional strength of the fault, and therefore control the earthquake rupture process and resulting ground-shaking. Previous studies examined fault-segmentation effects on ground-shaking, but our understanding of fault-roughness effects on seismic wavefield radiation and earthquake ground-motion is still limited.  </p><p>In this study we examine the effects of fault roughness on ground-shaking variability as a function of distance based on 3D dynamic rupture simulations. We consider linear slip-weakening friction, variations of fault-roughness parametrizations, and alternative nucleation positions (unilateral and bilateral ruptures). We use generalized finite difference method to compute synthetic waveforms (max. resolved frequency 5.75 Hz) at numerous surface sites  to carry out statistical analysis.  </p><p>Our simulations reveal that ground-motion variability from unilateral ruptures is almost independent of  distance from the fault, with comparable or higher values than estimates from ground-motion prediction equations (e.g., Boore and Atkinson, 2008; Campbell and Bozornia, 2008). However, ground-motion variability from bilateral ruptures decreases with increasing distance, in contrast to previous studies (e.g., Imtiaz et. al., 2015) who observe an increasing trend with distance. Ground-shaking variability from unilateral ruptures is higher than for bilateral ruptures, a feature due to intricate seismic radiation patterns related to fault roughness and hypocenter location. Moreover, ground-shaking variability for rougher faults is lower than for smoother faults. As fault roughness increases the difference in ground-shaking variabilities between unilateral and bilateral ruptures increases. In summary, our simulations help develop a fundamental understanding of ground-motion variability at high frequencies (~ 6 Hz) due small-scale geometrical fault-surface variations.</p>

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