Theoretical and numerical models of rock wing crack subjected to hydraulic pressure and far-field stresses

AbstractWe investigated the design parameters of a compact pot-like ultrasonic sensor which possesses a highly anisotropic beam pattern. As the sensor size is small due to its application constraint, the parameters are thus highly coupled to one another. We analyzed the respective effects of the parameters in the case where there is a vertical beam width reduction. The parameters investigated include resonant frequency, vibrating plate width-expanded angle, and ratio of thickness discontinuity of the vibrating plate. Numerical models developed by combining finite-element analysis and spatial Fourier transforms were adopted to predict the far-field radiating beam pattern of the various design configurations. The displacement distribution of the vibrating plate was measured using a microscopic laser Doppler vibrometer and the far-field pressure beam patterns were measured using a standard microphone in a semianechoic environment. The three configurations we used to validate the simulation model resulted in an H-V ratio of 2.67, 2.68 and 3.13, respectively which all agreed well with the numerical calculations. We found that by increasing the operating resonant frequency from 40kHz to 58kHz, the vertical far-field beam width of an ultrasonic sensor can be reduced by 31.62%. We found that the vertical beam width can be significantly reduced when the ratio of the thickness discontinuity of the vibrating plate decreases from 1 to 0.4 and is incorporated with its optimal width-expanded angle of the vibrating plate. It appears that an ultrasonic sensor with this type of anisotropic beam pattern can be ideally adopted for today's automotive applications.

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Near-source characteristics of two-phase gas–solid outbursts in roadways

International Journal of Coal Science & Technology ◽

10.1007/s40789-020-00362-9 ◽

2020 ◽

Author(s):

Aitao Zhou ◽

Meng Zhang ◽

Kai Wang ◽

Derek Elsworth

Keyword(s):

Shock Waves ◽

Numerical Models ◽

Gas Flows ◽

Far Field ◽

Two Phase ◽

Emergency Rescue ◽

Source Characteristics ◽

Basic Parameters ◽

Significant Attenuation ◽

Coal And Gas Outbursts

Abstract Coal and gas outbursts compromise two-phase gas–solid mixtures as they propagate as shock waves and flows from their sources. Propagation is influenced by the form of the outburst, proximity to source, the structure and form of the transmitting roadways and the influence of obstacles. The following characterizes the propagation of coal and gas outbursts as two-phase gas–solid flows proximal to source where the coupled effects of pulverized coal and gas flows dominate behavior. The characteristics of shock wave propagation and attenuation were systematically examined for varied roadway geometries using experiments and numerical models. The results demonstrate that the geometry of roadway obstructions is significant and may result in partial compression and sometimes secondary overpressurization in blocked and small corner roadways leading to significant attenuation of outburst shock waves. The shock waves attenuate slowly in both straight and abruptly expanding roadways and more significantly in T-shaped roadways. The most significant attenuation appears in small angle corners and bifurcations in roadways with the largest attenuation occurring in blocked roadways. These results provide basic parameters for simplifying transport in complex roadway networks in the far-field, and guidance for the design of coal and gas outburst prevention facilities and emergency rescue.

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Simulated Changes in Northwest U.S. Climate in Response to Amazon Deforestation*

Journal of Climate ◽

10.1175/jcli-d-12-00775.1 ◽

2013 ◽

Vol 26 (22) ◽

pp. 9115-9136 ◽

Cited By ~ 36

Author(s):

David Medvigy ◽

Robert L. Walko ◽

Martin J. Otte ◽

Roni Avissar

Keyword(s):

United States ◽

Sierra Nevada ◽

Numerical Models ◽

Regional Climate ◽

Regional Climate Change ◽

The United States ◽

Far Field ◽

Adequate Model ◽

Thermal Anomalies ◽

The Andes

Abstract Numerical models have long predicted that the deforestation of the Amazon would lead to large regional changes in precipitation and temperature, but the extratropical effects of deforestation have been a matter of controversy. This paper investigates the simulated impacts of deforestation on the northwest United States December–February climate. Integrations are carried out using the Ocean–Land–Atmosphere Model (OLAM), here run as a variable-resolution atmospheric GCM, configured with three alternative horizontal grid meshes: 1) 25-km characteristic length scale (CLS) over the United States, 50-km CLS over the Andes and Amazon, and 200-km CLS in the far-field; 2) 50-km CLS over the United States, 50-km CLS over the Andes and Amazon, and 200-km CLS in the far-field; and 3) 200-km CLS globally. In the high-resolution simulations, deforestation causes a redistribution of precipitation within the Amazon, accompanied by vorticity and thermal anomalies. These anomalies set up Rossby waves that propagate into the extratropics and impact western North America. Ultimately, Amazon deforestation results in 10%–20% precipitation reductions for the coastal northwest United States and the Sierra Nevada. Snowpack in the Sierra Nevada experiences declines of up to 50%. However, in the coarse-resolution simulations, this mechanism is not resolved and precipitation is not reduced in the northwest United States. These results highlight the need for adequate model resolution in modeling the impacts of Amazon deforestation. It is concluded that the deforestation of the Amazon can act as a driver of regional climate change in the extratropics, including areas of the western United States that are agriculturally important.

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Faults and magma reservoirs along the Southern Andes Volcanic zone (SAVZ): linking oservations and numerical models of stress change controlling magmatic and hydrothermal fluid flow

10.5194/egusphere-egu2020-11473 ◽

2020 ◽

Author(s):

Javiera Ruz ◽

Muriel Gerbault ◽

José Cembrano ◽

Pablo Iturrieta ◽

Camila Novoa Lizama ◽

...

Keyword(s):

Fluid Flow ◽

Stress Field ◽

Fault Zone ◽

Numerical Models ◽

Fluid Pressure ◽

Seismic Inversion ◽

Fault Zones ◽

Fault System ◽

Far Field ◽

Trigger Failure

The Chilean margin is amongst the most active seismic and volcanic areas on Earth. It hosts active and fossil geothermal and mineralized systems of economic interest documenting significant geofluid migration through the crust. By comparing numerical models with field and geophysical data,&#160;we aim at pinning when and where fluid migration occurs through porous domains, fault zone conduits, or remains stored at depth awaiting a more appropriate stress field. Dyking and volcanic activity occur within fault zones along the SAVZ, linked with stress field variations in spatial and temporal association with &#8211;short therm- seismicity and -long term- oblique plate convergence. Volcanoes and geothermal domains are mostly located along or at the intersection of margin-oblique fault zones (Andean Transverse Faults), and along margin-parallel strike slip zones, some which may cut the entire lithosphere (Liqui&#241;e-Ofqui fault system). Whereas the big picture displays fluid flow straight to the surface, at close look significant offsets between crustal structures occur. 3D numerical models using conventional elasto-plastic rheology provide insights on the interaction of (i) an inflating magmatic cavity, (ii) a slipping fault zone, and (iii)&#160;regional tectonic stresses. Applying either (i) a magmatic overpressure or (ii) a given fault slip can trigger failure of the intervening rock, and generate either i) fault motion or ii) magmatic reservoir failure, respectively, but only for distances less than the structures' breadth even at low rock strength. However, at greater inter-distances the bedrock domain in between the fault zone and the magmatic cavity undergoes dilatational strain of the order of 1-5x10-5. This dilation opens the bedrock&#8217;s pore space and forms &#171;pocket domains&#187; that may store up-flowing over-pressurized fluids, which may then further chemically interact with the bedrock, for the length of time that these pockets remain open. These porous pockets can reach kilometric size,&#160;questioning their parental link with outcropping plutons along the margin. Moreover, bedrock permeability may also increase as fluid flow diminishes effective bedrock friction and cohesion. Comparison with rock experiments indicates that such stress and fluid pressure changes may eventually trigger failure at the intermediate timescale (repeated slip or repeated inflation). Finally, incorporating far field compression (iii) loads the bedrock to a state of stress at the verge of failure. Then, failure around the magmatic reservoir or at the fault zone occurs for lower loading. Permanent tectonic loading on the one hand, far field episodic seismic inversion of the stress field on the other, and localized failure all together promote a transient stress field, thus explaining the occurrence of transient fluid pathways on seemingly independent timescales. These synthetic models are then discussed with regards to specific cases along the SVZ, particularly the Tatara-San Pedro area (~36&#176;S), where magnetotelluric profiles document conductive volumes at different depths underneath active faults, volcanic edifices and geothermal vents. We discuss the mechanical link between these deep sources and surface structures.

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The Wing Crack Growth Processes of Rock Induced by Hydraulic Pressure

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.405-408.611 ◽

2013 ◽

Vol 405-408 ◽

pp. 611-616

Author(s):

Shi Bin Tang ◽

Zheng Zhao Liang ◽

Hong Li ◽

Chu Nan Tang

Keyword(s):

Fluid Flow ◽

Crack Growth ◽

Hydraulic Pressure ◽

Flow Properties ◽

Wing Crack ◽

Growth Processes ◽

Mechanical Coupling ◽

Crack Tips ◽

Crack Growth Mechanism ◽

Crack Growth Path

The pre-existing fractures in rock can close, open and growth as it subjected to mechanical or environment loading, which can in turn change the structure of the rock and alter its fluid flow properties. In order to study the crack growth processes of pre-existing fracture in rock under the condition of hydraulic and mechanical coupling, a numerical tool, named F-RFPA2D which takes into account the growth of existing fractures and the formation of new fractures, is used for this purpose. By considering the effect of hydraulic pressure filling into the wing crack, the behavior of fluid flow, damage evolution and their coupling action in the pre-existing and the newly formed fractures are studied in detail. The modeling results suggest that the hydraulic pressure in the crack enhanced the tensile stresses at the crack tips, resulting in crack growth path is different from that without hydraulic pressure loading. The wing crack growth mechanism under the coupling of hydraulic and mechanical is discussed, which provides a good reference for studying on the hydraulic fracturing in rock masses.

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Near-source characteristics of two-phase gas-solid outbursts in roadways

10.21203/rs.3.rs-25899/v1 ◽

2020 ◽

Author(s):

Aitao Zhou ◽

Meng Zhang ◽

Kai Wang ◽

Derek Elsworth

Keyword(s):

Shock Wave ◽

Shock Waves ◽

Numerical Models ◽

Gas Flows ◽

Far Field ◽

Two Phase ◽

Source Characteristics ◽

Basic Parameters ◽

Significant Attenuation ◽

Coal And Gas Outbursts

Abstract Coal and gas outbursts compromise two-phase gas-solid mixtures as they propagate as shock waves and flows from their sources. Propagation is influenced by the form of the outburst, proximity to source, the structure and form of the transmitting roadways and the influence of obstacles. The following characterizes the propagation of coal and gas outbursts as two-phase gas-solid flows proximal to source where the coupled effects of pulverized coal and gas flows dominate behavior. The characteristics of shock wave propagation and attenuation are systematically examined for varied roadway geometries using experiments and numerical models. The results demonstrate that the geometry of roadway obstructions is significant and may result in partial compression and sometimes secondary overpressurization in blocked and small corner roadways leading to significant attenuation of outburst shock waves. The shock waves attenuate slowly in both straight and abruptly expanding roadways and more significantly in T-shaped roadways. The most significant attenuation appears in small angle corners and bifurcations in roadways with the largest attenuation occurring in blocked roadways. These results provide basic parameters for simplifying transport in complex roadway networks in the far-field, and guidance for the design of coal and gas outburst prevention facilities and disaster ventilation.

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Design of a Lightweight Multilayered Composite for DC to 20 GHz Electromagnetic Shielding

Electronics ◽

10.3390/electronics10243144 ◽

2021 ◽

Vol 10 (24) ◽

pp. 3144

Author(s):

Paul Clérico ◽

Lionel Pichon ◽

Xavier Mininger ◽

Olivier Dubrunfaut ◽

Chadi Gannouni ◽

...

Keyword(s):

Numerical Models ◽

Near Field ◽

Magnetic Layer ◽

Single Layer ◽

Homogenization Method ◽

Electromagnetic Shielding ◽

Far Field ◽

Shielding Effectiveness ◽

Frequency Range ◽

Large Frequency

The work aims to design a trilayer composite dedicated to electromagnetic shielding over a large frequency range, from 1 Hz to 20 GHz. Analytical and numerical models are used to determine the shielding effectiveness (SE) of this composite in the case of a planar shield. The shield is constituted of a support layer, a magnetic layer, and a conductive layer. Two possible designs are considered. To simplify the numerical calculation, a homogenization method and the Artificial Material Single Layer (AMSL) method are used. The proposed composite shows a good shielding capacity over the whole studied frequency range, with shielding effectiveness higher than 17 dB and 75 dB, respectively, in the near-field (1 Hz–1 MHz) and far-field (1 MHz–20 GHz). Both homogenization and AMSL methods show good suitability in near-field and allow one to greatly reduce the calculation time.

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Experimental observation and numerical investigation on propagation and coalescence process of multiple flaws in rock-like materials subjected to hydraulic pressure and far-field stress

Theoretical and Applied Fracture Mechanics ◽

10.1016/j.tafmec.2020.102603 ◽

2020 ◽

Vol 108 ◽

pp. 102603 ◽

Cited By ~ 2

Author(s):

Chao Wei ◽

Yong Li ◽

Weishen Zhu ◽

Shucai Li ◽

Shugang Wang ◽

...

Keyword(s):

Numerical Investigation ◽

Experimental Observation ◽

Hydraulic Pressure ◽

Far Field ◽

Coalescence Process ◽

Field Stress ◽

Far Field Stress

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Approximating a far-field blast environment in an advanced blast simulator for explosion resistance testing

International Journal of Protective Structures ◽

10.1177/2041419620911133 ◽

2020 ◽

Vol 11 (4) ◽

pp. 468-493 ◽

Cited By ~ 1

Author(s):

Edward Chern Jinn Gan ◽

Alex Remennikov ◽

David Ritzel ◽

Brian Uy

Keyword(s):

Fluid Dynamics ◽

Computational Fluid Dynamics ◽

Numerical Models ◽

Experimental Testing ◽

Free Field ◽

Experimental Studies ◽

Gaseous Detonation ◽

Resistance Testing ◽

Far Field ◽

Shock Tubes

While the current state of blast-resistant design methods is based largely on empirical observations of actual explosive testing or numerical simulations, experimental testing remains the ultimate method for validating blast protection technologies. Field trials for performing systematic experimental studies are exceedingly expensive and inefficient. Conventional blast simulators (shock tubes) enable blast testing to be performed in a safe and controlled laboratory environment but are significantly deficient. The Australian National Facility of Physical Blast Simulation based on the ‘Advanced Blast Simulator’ concept was established to address the shortcomings of conventional blast simulators (shock tubes). The blast simulator at the National Facility of Physical Blast Simulation is a state-of-the-art design having a test section of 1.5 × 2.0 m with dual-mode driver able of operating with either compressed gas or gaseous detonation modes. The simulator is capable of a range of blast-test configurations such as full-reflection wall targets and diffraction model targets. This article aims to demonstrate the ability of the Advanced Blast Simulator in accurately generating a far-field blast environment suitable for high-precision and repeatable explosion testing of various building components. Blast pressure-time histories generated with the Advanced Blast Simulator are validated against equivalent TNT free-field curves reproduced with Conventional Weapons Effects Program. Numerical models based on Computational Fluid Dynamics were developed in ANSYS FLUENT to accurately characterise and visualise the internal flow environment of the National Facility of Physical Blast Simulation Advanced Blast Simulator. The Computational Fluid Dynamics model was also used to explain experimental observations and to determine density and dynamic pressure information for comparisons with free-field explosion conditions.

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