The influence of heterogeneity on the strength and stability of faults

2021 ◽  
Author(s):  
Daniel Faulkner ◽  
John Bedford ◽  
Nadia Lapusta ◽  
Valère Lambert
Keyword(s):  
Shear Stress ◽  
Large Scale ◽  
Small Scale ◽  
Dynamic Rupture ◽  
Slip Rates ◽  
Average Shear Stress ◽  
Lower Shear ◽  
Scale Heterogeneity ◽  
Fault Strength ◽  
Average Shear

<div><span>Heterogeneity of fault zones is seen at all scales in nature. It may manifest itself in terms of the variability of material property distribution over the fault, of stress heterogeneity brought about by the history of previous earthquake ruptures, and of fault geometry. In this contribution, we consider the effect on fault strength and stability of small-scale heterogeneity in laboratory experiments and large-scale heterogeneity from numerical dynamic rupture modeling. In model laboratory faults at slow slip rates (0.3 and 3 microns/s), the area occupied by rate-weakening gouge (quartz) versus rate-strengthening gouge (clay) was systematically varied and the results compared with homogenized mixtures of the two gouges. We found that the heterogeneous experimental faults were weaker and less stable than their homogenized counterparts, implying that earthquake nucleation might be promoted by fault zone heterogeneity. In elasto-dynamic numerical simulations of sequences of earthquakes and aseismic slip based on rate and state friction but with enhanced dynamic weakening (EDW) through pore fluid pressurization, uniform material properties on the fault plane are assumed, and heterogeneity spontaneously develops by stress variations along the fault arising from differing histories of motion at points along the fault. In these models, ruptures spontaneously nucleate in favorably prestressed regions. Larger ruptures - that result in greater degrees of EDW - are capable of propagating through areas of lower shear stress that would arrest smaller events. This behavior leads to a relationship between rupture size and the average shear stress over the rupture plane before the earthquake occurs. Faults that host larger events may overall appear to be driven by lower average shear stress and hence appear ‘weaker’. It is clear that the apparent fault strength and stability is difficult to predict from either simple homogeneous gouge experiments, or from scaling up of these results. Heterogeneity at all scales will affect the slip behaviour of faults.</span></div>

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>

scholarly journals Numerical Study of Fluid Dynamics in Suspension Culture of iPS Cells

2019 ◽  
Vol 17 (1) ◽  
pp. 73 ◽  
Author(s):  
Masaki Yano ◽  
Takuya Yamamoto ◽  
Yasunori Okano ◽  
Toshiyuki Kanamori ◽  
Mashiro Kino–oka
Keyword(s):  
Shear Stress ◽  
Suspension Culture ◽  
Numerical Study ◽  
Maximum Shear Stress ◽  
Ips Cells ◽  
Stirred Tanks ◽  
Average Shear Stress ◽  
Average Shear ◽  
Orbital Shaking ◽  
Induced Pluripotent

In a suspension culture of iPS cells, the shear stress generated during mixing is expected to promote differentiation of induced pluripotent stem (iPS) cells. The stress on the cells can be controlled by rotational rate and shape of impeller. However, it is difficult to optimize these operative parameters by experiments. Therefore, we have developed a numerical model to obtain the average and the maximum shear stress in two kinds of stirred tanks and an orbital shaking cylindrical container. The present results showed that the shear stress strongly depended on the type of mixing and lesser extent on the shape of the impeller. The average shear stress is larger in the shaking mode than that in the stirring mode. In contrast, the maximum shear stress is much smaller in the shaking than the stirring. These results suggest that stirring and shaking should be selectively used depending on the application

scholarly journals Effects of Nanoparticle Enhanced Lubricant Films in Thermal Design of Plain Journal Bearings at High Reynolds Numbers

Symmetry ◽  
2019 ◽  
Vol 11 (11) ◽  
pp. 1353 ◽  
Author(s):  
Abdollahzadeh Jamalabadi ◽  
Alamian ◽  
Yan ◽  
Li ◽  
Leveneur ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Shear Stress ◽  
Temperature Rise ◽  
Rotational Speed ◽  
Volume Fraction ◽  
Journal Bearings ◽  
Thermal Design ◽  
Average Shear Stress ◽  
Average Shear ◽  
Dissipation Power

Performance investigation of oil journal bearings is of particular importance given the growing use of them as a support for rotary components in a wide range of industrial machines. Frictional forces and shear stresses, which are proportionate to the velocity of lubricating layers at different points in the bearing space, provide the basis for changing temperature conditions. Various factors such as rotational velocity increase, slip width reduction, and small heat transfer coefficient of lubricant cause intensification of lubricant temperature changes. In the present study, with using computational fluid dynamic (CFD) thermohydrodynamic (THD) numerical simulations, the effect of nanoparticles on the performance features of plain journal bearings is evaluated. Particularly, 3D simulation of a journal bearing is implemented using CFD which considerably improves the accuracy of results, coupled with conjugate heat transfer model for metal parts of bearings. Reynolds equation model is used to calculate the oil-film pressure developed in hydrodynamic journal bearings by applying the nano-based lubricants. The configuration of thrust bearing consists of six pads in this study. In order to reduce the modeling complexity and computational cost and because of the symmetrical geometry of the pads, simulation of a single pad is considered instead of the entire domain. In this study, TiO2 nanoparticle with different volume fraction percentages are used. The parameters that are changed to evaluate the performance of the bearing include volume fraction percentage of the nanoparticle, type of lubricant, and rotational speed. Based on the results, for all different lubricant types, the dissipation power, average shear stress, and temperature rise are increased with augmenting the rotational speed. By increasing the rotational speed from 500 to 1500 rpm, the average shear stress increases by more than 100%, 120%, and 130% for DTE 26, DTE 25, and DTE 24 lubricant types, respectively. Moreover, by increasing the rotational speed from 500 to 1500 rpm, the dissipation power, and temperature rise are increased around 600% and 800%, respectively. Furthermore, increasing nanoparticles volume fraction from 0% to 10%, increases all parameters by approximately 10% for all lubricant types and in all rotational speeds.

Model-Based Shear Stress Gradient in Realistic Vascular Flows and Its Relation to Arterial Macromolecular Permeability

2003 ◽  
Author(s):  
Jeffrey A. LaMack ◽  
Heather A. Himburg ◽  
Xue-Mei Li ◽  
Morton H. Friedman
Keyword(s):  
Shear Stress ◽  
Fluid Dynamic ◽  
Stress Gradient ◽  
Blue Dye ◽  
Infrarenal Aorta ◽  
Flow Measurements ◽  
Average Shear Stress ◽  
Average Shear ◽  
Time Average ◽  
Shear Stress Gradient

Evans blue dye (EBD) was injected into the carotid arteries of three anesthetized pigs and allowed to circulate for 90 minutes. At the conclusion of the 90-minute period, the animals were sacrificed and injection casts of the infrarenal aorta and iliac-femoral arteries were prepared. The casts with their surrounding arteries were removed and immersed in fixative. After fixation, the EBD-stained vessels were separated from the casts, which were used to construct computational meshes for simulation of the flow fields and wall shear stress distributions that had existed in the casted regions during the experiments. The inlet flow waves and flow partitions were based on flow measurements performed during each experiment. Based on a conceptual model of the relation between shear stress nonuniformity and permeability increase, the spatial and angular variation of the gradient of the time-average shear stress at the walls of the external iliac arteries was found from the computational fluid dynamic simulations for each experiment. Using affine transformations, the gradient and time-average shear stress results, and the EBD optical density distributions, were mapped to a common template, allowing pixel-by-pixel correlations of the hemodynamic stress parameters and local permeability. The results suggest that both shear stress gradient and time-average shear play a role in determining vascular permeability to macromolecules.

Analytical and numerical modelling of Newtonian and non-Newtonian liquid in a rotational cross-flow MBR

2012 ◽  
Vol 66 (11) ◽  
pp. 2318-2327 ◽  
Author(s):  
T. R. Bentzen ◽  
N. Ratkovich ◽  
S. Madsen ◽  
J. C. Jensen ◽  
S. N. Bak ◽  
...  
Keyword(s):  
Shear Stress ◽  
Laser Doppler Anemometry ◽  
Membrane Surface ◽  
Empirical Relationship ◽  
Tangential Velocity ◽  
Cross Flow ◽  
Weighted Average ◽  
Newtonian Liquid ◽  
Average Shear Stress ◽  
Average Shear

Fouling is the main bottleneck of the widespread use of MBR systems. One way to decrease and/or control fouling is by process hydrodynamics. This can be achieved by the increase of liquid cross-flow velocity. In rotational cross-flow MBR systems, this is attained by the spinning of, for example, impellers. Validation of the CFD (computational fluid dynamics) model was made against laser Doppler anemometry (LDA) tangential velocity measurements (error less than 8%) using water as a fluid. The shear stress over the membrane surface was inferred from the CFD simulations for water. However, activated sludge (AS) is a non-Newtonian liquid, for which the CFD model was modified incorporating the non-Newtonian behaviour of AS. Shear stress and area-weighted average shear stress relationships were made giving error less that 8% compared with the CFD results. An empirical relationship for the area-weighted average shear stress was developed for water and AS as a function of the angular velocity and the total suspended solids concentration. These relationships can be linked to the energy consumption of this type of systems.

Failure Pressure in Corroded Pipelines Based on Equivalent Solutions for Undamaged Pipe

2010 ◽  
Vol 132 (5) ◽  
Author(s):  
M. Bony ◽  
J. L. Alamilla ◽  
R. Vai ◽  
E. Flores
Keyword(s):  
Shear Stress ◽  
Numerical Simulations ◽  
Wall Thickness ◽  
Yield Criteria ◽  
Failure Pressure ◽  
Average Shear Stress ◽  
Average Shear ◽  
Thin Walled ◽  
Von Mises

Simple and accurate approaches to predict failure pressures in corroded pipelines are outlined in this work. It is shown that failure pressures for corroded pipelines can be predicted from the solution for undamaged pipelines using an equivalent wall thickness. Three different yield criteria (Tresca, ASSY (average shear stress yield), and von Mises) are reviewed in the light of reported experimental burst pressures. At first, failure pressures for cylindrical vessels with an infinitely long groove are studied by means of numerical simulations. The effect of groove size (depth and width) over the pipeline performance is quantified through a model. Finally, the scheme is extended to estimate the failure pressure of thin walled vessels with irregular finite defects.

scholarly journals COMPUTATIONAL STUDY OF GEOMETRIC EFFECTS OF BOTTOM WALL MICROGROOVES ON CELL DOCKING INSIDE MICROFLUIDIC DEVICES

2021 ◽  
pp. 2150017
Author(s):  
SINA AHANDOUST ◽  
MARYAM SAADATMAND
Keyword(s):  
Shear Stress ◽  
Cell Surface ◽  
Drag Force ◽  
Fluid Velocity ◽  
Cell Movement ◽  
Microfluidic Devices ◽  
Cell Detachment ◽  
Average Shear Stress ◽  
Average Shear ◽  
Recirculation Area

Cells docking inside microfluidic devices is effective in studying cell biology, cell-based biosensing, as well as drug screening. Furthermore, single cell and regularly cells docking inside the microstructure of microfluidic systems are advantageous in different analyses of single cells exposed to equal drug concentration and mechanical stimulus. In this study, we investigated bottom wall microgrooves with semicircular and rectangular geometries with different sizes which are suitable for single cell docking along the length of the microgroove in [Formula: see text]-direction and numerous cells docking regularly in one line inside the microgroove in a 3D microchannel. We used computational fluid dynamics to analyze the fluid recirculation area inside different microgrooves. The height of recirculation area in the bottom of microgroove could affect the cell’s attachment, and also materials delivery to attached cells, so the height of recirculation area may have optimum value. In addition, we analyzed the fluid drag force on cell movement toward the microgroove. This parameter was proportional to the fluid velocities in [Formula: see text] and [Formula: see text] directions in different microgrooves geometries. In different microgrooves’ geometries the fluid velocity in [Formula: see text]-direction did not change, but the fluid velocity in [Formula: see text]-direction decreased inside the microgroove. Therefore, the cell movement time inside the microgroove increased, and also the drag force in [Formula: see text]-direction could push the cells toward the bottom due to the lower drag force in [Formula: see text]-direction. The percentages of negative shear stress and average shear stress on the adhered cell surface were also calculated. The lower average shear stress, and negative shear stress around 50% on the cell surface were against cell detachment from the substrate. The results indicated that at the constant fluid inlet velocity and microchannel height, microgroove geometry and ratio of cell size to the microgroove size play pivotal roles in the cell initial adhesion to the substrate as well as the cell detachment.

scholarly journals Endothelial cell responses to atheroprone flow are driven by two separate flow components: low time-average shear stress and fluid flow reversal

2010 ◽  
Vol 298 (2) ◽  
pp. H367-H374 ◽  
Author(s):  
Daniel E. Conway ◽  
Marcie R. Williams ◽  
Suzanne G. Eskin ◽  
Larry V. McIntire
Keyword(s):  
Gene Expression ◽  
Cell Proliferation ◽  
Endothelial Cells ◽  
Shear Stress ◽  
Umbilical Vein ◽  
Steady Shear ◽  
Monocyte Adhesion ◽  
Average Shear Stress ◽  
Average Shear ◽  
Time Average

To simulate the effects of shear stress in regions of the vasculature prone to developing atherosclerosis, we subjected human umbilical vein endothelial cells to reversing shear stress to mimic the hemodynamic conditions at the wall of the carotid sinus, a site of complex, reversing blood flow and commonly observed atherosclerosis. We compared the effects of reversing shear stress (time-average: 1 dyn/cm2, maximum: +11 dyn/cm2, minimum: −11 dyn/cm2, 1 Hz), arterial steady shear stress (15 dyn/cm2), and low steady shear stress (1 dyn/cm2) on gene expression, cell proliferation, and monocyte adhesiveness. Microarray analysis revealed that most differentially expressed genes were similarly regulated by all three shear stress regimens compared with static culture. Comparisons of the three shear stress regimens to each other identified 138 genes regulated by low average shear stress and 22 genes regulated by fluid reversal. Low average shear stress induced increased cell proliferation compared with high shear stress. Only reversing shear stress exposure induced monocyte adhesion. The adhesion of monocytes was partially inhibited by the incubation of endothelial cells with ICAM-1 blocking antibody. Increased heparan sulfate proteoglycan expression was observed on the surface of cells exposed to reversing shear stress. Heparinase III treatment significantly reduced monocyte adhesion. Our results suggest that low steady shear stress is the major impetus for differential gene expression and cell proliferation, whereas reversing flow regulates monocyte adhesion.

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