scholarly journals Control of pre-existing fabric in fracture formation, reactivation and vein emplacement under variable fluid pressure conditions: An example from Archean Greenstone belt, India

2020 ◽  
Author(s):  
Sreyashi Bhowmick ◽  
Tridib Kumar Mondal
Keyword(s):  
Pressure Ratio ◽  
Fluid Pressure ◽  
Tectonic Stress ◽  
Fault Slip ◽  
Magnetic Fabric ◽  
Pressure Condition ◽  
Crustal Fluid ◽  
Wide Range ◽  
Riedel Shear ◽  
Archean Greenstone Belt

Abstract. Most of the upper crustal fluid flows are strongly influenced by the pre-existing fractures/foliations in the rocks under a certain state of tectonic stress and fluid pressure condition. In the present study, we analyze a wide range of crosscutting fractures that are filled with quartz veins of variable orientations and thicknesses, from the gold bearing massive metabasalts (supracrustal) of the Chitradurga Schist Belt adjacent to the Chitradurga Shear Zone (CSZ), western Dharwar craton, south India. The study involves the following steps: 1) analyzing the internal magnetic fabric using anisotropy of magnetic susceptibility (AMS) studies, and strength of the host metabasalts, 2) quantifying the fluid pressure condition through lower hemisphere equal area projection of pole to veins by determining the driving pressure ratio (R'), stress ratio (ϕ), and susceptibility to fracturing, and 3) deciphering the paleostress condition using fault slip analysis. We interpret that the NNW-SSE to NW-SE (mean 337°/69° NE) oriented magnetic fabric in the rocks of the region developed during regional D1/D2 deformation on account of NE-SW shortening. However, D3 deformation manifested by NW-SE to E-W shortening led to the sinistral movement along CSZ. As a consequence of this sinistral shearing, fractures with prominent orientations formed riedel shear components, with CSZ as the shear boundary. Subsequently, all the pre-existing fabrics along with the riedel shear components were reactivated and vein emplacement took place through episodic fluid pressure fluctuation from high to low Pf at shallow depth (~ 2.4 km). However, NNW-SSE orientations were susceptible for reactivation under both high and low Pf conditions leading to a much greater thickness along the same. The deduced paleostress from fault-slip analysis, along with the kinematics of the fractures and veins are in good agreement with the previously revealed regional tectonics. Thus, integrating multiple domains of studies, help in the logical interpretation of fluid flow condition and vein emplacement mechanism in the study area that has not been ventured before.

scholarly journals Control of pre-existing fabric in fracture formation, reactivation and vein emplacement under variable fluid pressure conditions: an example from Archean greenstone belt, India

Solid Earth ◽  
2020 ◽  
Vol 11 (4) ◽  
pp. 1227-1246
Author(s):  
Sreyashi Bhowmick ◽  
Tridib Kumar Mondal
Keyword(s):  
Pressure Ratio ◽  
Fluid Pressure ◽  
Tectonic Stress ◽  
Fault Slip ◽  
Magnetic Fabric ◽  
Pressure Condition ◽  
Crustal Fluid ◽  
Wide Range ◽  
Riedel Shear ◽  
Archean Greenstone Belt

Abstract. Most of the upper crustal fluid flows are strongly influenced by the pre-existing fractures/foliations in the rocks under a certain state of tectonic stress and fluid pressure condition. In the present study, we analyzed a wide range of crosscutting fractures that are filled with quartz veins of variable orientations and thicknesses, from the gold-bearing massive metabasalts (supracrustals) of the Chitradurga Schist Belt adjacent to the Chitradurga Shear Zone (CSZ), Western Dharwar Craton, southern India. The study involves the following steps: (1) analyzing the internal magnetic fabric, using anisotropy of magnetic susceptibility (AMS) studies, and determining strength of the host metabasalts, (2) quantifying the fluid pressure condition through lower hemisphere equal area projection of pole to veins by determining the driving pressure ratio (R′), stress ratio (ϕ), and susceptibility to fracturing, and (3) deciphering the paleostress condition using fault-slip analysis. We interpret the NNW–SSE to NW–SE (mean 337/69∘ NE) oriented magnetic fabric in the rocks of the region as having developed during regional D1/D2 deformation on account of NE–SW shortening. However, D3 deformation manifested by NW–SE to E–W shortening led to the sinistral movement along CSZ. As a consequence of this sinistral shearing, fractures with prominent orientations formed riedel shear components, with CSZ as the shear boundary. Subsequently, all the pre-existing fabrics along with the riedel shear components were reactivated and vein emplacement took place through episodic fluid pressure fluctuation from high to low Pf at shallow depth (∼ 2.4 km). However, NNW–SSE orientations were prone to reactivate under both high- and low-Pf conditions, thereby attaining maximum vein thickness along these orientations. The deduced paleostress from fault-slip analysis along with the kinematics of the fractures and veins are in good agreement with previously estimated regional tectonics. Thus, integrating multiple domains of studies helps in the logical interpretation of fluid flow conditions and vein emplacement mechanisms in the study area that has not been ventured before.

Mechanisms for Pore Fluid Stabilization of Fault Propagation and Slip

2020 ◽  
Author(s):  
Wen-lu Zhu ◽  
Tiange Xing ◽  
Takamasa Kanaya ◽  
Zachary Zega ◽  
Melodie French
Keyword(s):  
Fluid Pressure ◽  
Fault Slip ◽  
Pore Fluid ◽  
Initial Porosity ◽  
Effective Pressure ◽  
Strain Accumulation ◽  
Fault Propagation ◽  
Pore Fluid Pressure ◽  
Wide Range ◽  
Fault Growth

<p>Sudden motions of fault (i.e., fault propagation and slip) cause earthquakes. Understanding the mechanics of earthquakes requires quantitative knowledge of fault propagation and slip instability, which has long been a focus of experimental rock mechanics. In a classic framework based on the elastic rebound theory, the earthquake cycle includes the interseismic period of strain accumulation and the coseismic period of sudden strain release along a tectonic fault.</p><p>Geophysical observations reveal diverse behaviorsof fault motions resulted from strain accumulation and release, from aseismic creep to slow slip events (SSEs) to regular earthquakes. Discovery of SSEs during the interseismic period provides a new means to assess the mechanical states of a seismogenic fault between earthquakes. Most seismic studies link SSEs to high pore fluid pressure. Yet, the mechanical link between slow fault slip and high pore fluid pressure is not well understood. We conduct experimental investigation to elucidate the mechanisms responsible for pore fluid stabilization of fault propagation and slip.</p><p>Our experimental results show that slip events along gouge bearing faults can transform from fast to slow with increasing pore fluid pressures while keeping the effective pressure (i.e., confining pressure minus pore fluid pressure) constant. In these experiments, a layer of fine-grained quartz gouge was placed between the saw-cut surfaces in porous sandstone samples. The saw-cut samples were subject to conventional triaxial loading under a constant effective pressure using various combinations of confining and pore fluid pressures. Different slip events, from dynamic, audible stick-slip to slow, silent  slip, with a range of slip rates and stress drops were produced along the gauge-filled saw-cut surface. These results suggest that on the same fault, varying pore fluid pressure alone could result in a range of fault slip behaviors from dynamic to creep.</p><p>Experimental data further demonstrate that under the same effective pressure, high pore fluid pressure conditions stabilize fault propagation in a wide range of intact rocks including granite, serpentine, and sandstones. In  compact rocks (initial porosity <5%) the stabilization effect can be explained by dilatant hardening. When dilatancy occurs faster than fluid diffusion along a propagating fracture, the resultant increase in effective normal stress impedes further fracture growth. In porous sandstones (initial porosity >10%), however, dilatancy hardening alone could not adequately explain the stable  post-peak fault growth observed at slow loading rates where drained conditions are achieved. Based on the quantitative microstructural analysis of the deformed samples, we propose that the stable fault growth in highly permeable sandstones manifests stable cracking due to stress corrosion. These results elucidate the important controls of pore fluid on rock strength and fault slip beyond the effective stress law. The results provide a mechanic link between the spatially correlated SSEs and high pore fluid pressure conditions.</p>

The Effects of Ambient Conditions on Gas Turbine Emissions—Generalized Correction Factors

1978 ◽  
Vol 100 (4) ◽  
pp. 640-646 ◽  
Author(s):  
P. Donovan ◽  
T. Cackette
Keyword(s):  
Gas Turbine ◽  
Pressure Ratio ◽  
Turbine Engines ◽  
Inlet Temperature ◽  
Gas Turbine Engines ◽  
Correction Factors ◽  
Oxides Of Nitrogen ◽  
Ambient Conditions ◽  
Nitrogen Emission ◽  
Wide Range

A set of factors which reduces the variability due to ambient conditions of the hydrocarbon, carbon monoxide, and oxides of nitrogen emission indices has been developed. These factors can be used to correct an emission index to reference day ambient conditions. The correction factors, which vary with engine rated pressure ratio for NOx and idle pressure ratio for HC and CO, can be applied to a wide range of current technology gas turbine engines. The factors are a function of only the combustor inlet temperature and ambient humidity.

scholarly journals The Design and Evaluation of a High Pressure Ratio Radial Turbine

1992 ◽  
Author(s):  
K. R. Pullen ◽  
N. C. Baines ◽  
S. H. Hill
Keyword(s):  
High Pressure ◽  
High Speed ◽  
Pressure Ratio ◽  
Performance Measurements ◽  
Turbine Engine ◽  
High Pressure Ratio ◽  
Turbine Efficiency ◽  
Wide Range ◽  
Dimensional Parameters ◽  
Very High

A single stage, high speed, high pressure ratio radial inflow turbine was designed for a single shaft gas turbine engine in the 200 kW power range. A model turbine has been tested in a cold rig facility with correct simulation of the important non-dimensional parameters. Performance measurements over a wide range of operation were made, together with extensive volute and exhaust traverses, so that gas velocities and incidence and deviation angles could be deduced. The turbine efficiency was lower than expected at all but the lowest speed. The rotor incidence and exit swirl angles, as obtained from the rig test data, were very similar to the design assumptions. However, evidence was found of a region of separation in the nozzle vane passages, presumably caused by a very high curvature in the endwall just upstream of the vane leading edges. The effects of such a separation are shown to be consistent with the observed performance.

Estimation of driving pressure ratio and paleostresses from veins in the Pelling-Munsiari shear zone, Sikkim Himalayan Fold Thrust Belt

2021 ◽  
Author(s):  
Deblina Ray ◽  
Kathakali Bhattacharyya
Keyword(s):  
Crustal Deformation ◽  
Pressure Ratio ◽  
Fluid Pressure ◽  
Driving Pressure ◽  
Field Analysis ◽  
Stress Axis ◽  
High Angle ◽  
Mylonitic Foliation ◽  
Angle Fracture ◽  
Dominant Sets

<p>We analyze veins from the deepest exposure of the regionally folded Pelling-Munsiari thrust (PT), the roof thrust of the Lesser Himalayan duplex, in the Sikkim Himalaya. The PT is exposed as a discontinuous, ~970 m thick quartz-mica mylonite zone near Mangan (27°29′ N, 88°31′ E), and records progressive deformation path where shallow crustal deformation features overprint deeper crustal deformation structures. The mean mylonitic foliation is north easterly oriented in the studied location (mean ~31°, 042°).  Based on the angular relationship with respect to the mylonitic foliation, we recognize three different fracture- and associated vein-sets at the outcrop scale. These are low-angle set (<30° with respect to the mylonitic foliation), moderate-angle (30°-60°) and high-angle set (>60°).The high-angle fracture set overprints the mylonitic foliation and is the youngest set. These are also the most dominant fracture set (~58 %), followed by the moderate-angle (~32%) and low-angle (~10%) sets. Interestingly, the low-angle vein set (mean orientation ~ 29°, 054°) is the most  dominant set (~61%), followed by the moderate-angle set (~26%; mean orientation  ~ 19°,  055°),  and the high-angle set (~13% ; mean ~23°, 340°).Field analysis indicates that ~95% of low-angle, ~71% of moderate-angle and ~ 40% of high-angle fracture-sets form veins. Some of the low- and moderate-angle veins are locally folded along with the mylonitic foliation. The co-efficient of variation (C<sub>v</sub>) of spacing of both the fracture and vein sets are less than 1, indicating that these follow anti-clustered distribution. The poles to the veins indicate two distinct patterns. The low- and moderate-angle veins define girdle distribution, implying pore fluid pressure (P<sub>f</sub>) exceeded intermediate principal stress axis (σ<sub>2</sub>), whereas the high-angle set shows a clustered distribution indicating σ<sub>2</sub> exceeded P<sub>f</sub>. A preliminary study reveals presence of blocky texture in the low- and moderate-angle veins with quartz growing at high angles with respect to the vein walls. The average thickness of the low-angle, moderate-angle, and high-angle veins, measured along appropriate scan-lines are ~ 0.92 cm, ~1.03 cm and ~0.64 cm respectively. As the low- and moderate-angle vein-sets are the most dominant sets and both show girdle distribution, we estimated a driving pressure ratio (R' ~0.35-0.6) and stress ratio (ɸ~0.251) for these veins.  The estimated paleostresses from these veins are σ<sub>1</sub> (28°, 058°), σ<sub>2</sub> (2°, 327°), σ<sub>3</sub> (62°, 233°).</p>

scholarly journals Initial effective stress controls the nature of earthquakes

2020 ◽  
Vol 11 (1) ◽  
Author(s):  
François X. Passelègue ◽  
Michelle Almakari ◽  
Pierre Dublanchet ◽  
Fabian Barras ◽  
Jérôme Fortin ◽  
...  
Keyword(s):  
Effective Stress ◽  
Physical Mechanism ◽  
Fluid Pressure ◽  
Fault Slip ◽  
Rupture Velocity ◽  
Complete Spectrum ◽  
Available Energy ◽  
Different Types ◽  
Theoretical Predictions ◽  
Shallow Part

Abstract Modern geophysics highlights that the slip behaviour response of faults is variable in space and time and can result in slow or fast ruptures. However, the origin of this variation of the rupture velocity in nature as well as the physics behind it is still debated. Here, we first highlight how the different types of fault slip observed in nature appear to stem from the same physical mechanism. Second, we reproduce at the scale of the laboratory the complete spectrum of rupture velocities observed in nature. Our results show that the rupture velocity can range from a few millimetres to kilometres per second, depending on the available energy at the onset of slip, in agreement with theoretical predictions. This combined set of observations bring a new explanation of the dominance of slow rupture fronts in the shallow part of the crust or in areas suspected to present large fluid pressure.

Theory Versus Experiment for the Effects of Pressure Ratio on the Performance of an Orifice-Compensated Hybrid Bearing

1998 ◽  
Vol 120 (4) ◽  
pp. 930-936 ◽  
Author(s):  
P. Mosher ◽  
D. W. Childs
Keyword(s):  
High Speed ◽  
Stokes Equations ◽  
Load Capacity ◽  
Dynamic Stiffness ◽  
Pressure Ratio ◽  
Navier Stokes ◽  
Rotordynamic Coefficients ◽  
Wide Range ◽  
Bearing Load ◽  
Hybrid Bearing

This research investigates the effect of varying the concentric recess pressure ratio of hybrid (combination hydrostatic and hydrodynamic) bearings to be used in high-speed, high-pressure applications. Bearing flowrate, load capacity, torque, rotordynamic coefficients, and whirl frequency ratio are examined to determine the concentric, recess-pressure ratio which yields optimum bearing load capacity and dynamic stiffness. An analytical model, using two-dimensional bulk-flow Navier-Stokes equations and anchored by experimental test results, is used to examine bearing performance over a wide range of concentric recess pressure ratios. Typically, a concentric recess pressure ratio of 0.50 is used to obtain maximum bearing load capacity. This analysis reveals that theoretical optimum bearing performance occurs for a pressure ratio near 0.40, while experimental results indicate the optimum value to he somewhat higher than 0.45. This research demonstrates the ability to analytically investigate hybrid bearings and shows the need for more hybrid-bearing experimental data.

A New Approach to Maximize the Potential of Reciprocating Engines Operating on Bio-Fuel Energy

2011 ◽  
Author(s):  
Henry Lam ◽  
Mark Richter ◽  
Geoff Ashton
Keyword(s):  
Combustion Engine ◽  
Pressure Ratio ◽  
Waste Water Treatment ◽  
Pressure Sensors ◽  
Bulk Temperature ◽  
Lean Burn ◽  
Fuel Gas ◽  
Heating Value ◽  
Combustion Performance ◽  
Wide Range

Since the Industrial Revolution one of the oldest and “greenest” bio-fuel energy sources has been the byproduct of sewage and landfill. These biogases also known as Land Fill Gas or Digester Gas can be used as a fuel in an internal combustion engine, the clear choice for their efficiency in heat recovery and utility as a prime mover. The problem with bio-fuels is their unpredictable and varying fuel heating values which creates a challenge for maintaining air fuel ratio (AFR). If AFR is not controlled this can lead to engine instability and an increase in NOx, CO and THC emissions. With today’s ever increasing scrutiny of combustion pollutants this could spell the end of these types of fuels in combustion engines. AETC has embraced this challenge to provide a system that addresses the seasonal fuel gas quality, Low Heating Value (LHV) fluctuation to operate engines at best achievable emissions. This case study focuses on two Caterpillar 3516 Generator Engines rated 1000VA, at 1200 rpm, lean burn gas and turbocharged, running on renewable energy source supplementing power to a waste water treatment facility in California. The engines operate on wide range of fuel mixture including landfill, digester gas and air blended natural gas over a heating value range from 350–650 BTU. The fuel gas LHV constantly varies depending on fuel availability controlled by pressure switches within the individual fuel headers. Determining fuel heating values by using a gas calorimeter is not a viable option due to its high cost and poor reliability when operating in the environment of unfiltered Digester and landfill gas. AETC installed their Advanced Monitoring System (AMS) to utilize the engine as a calorimeter and to determine the fuels LHV. As part of the AMS functionality, the system acquired all the existing AFRC parameters such as kilo-Watt, RPM, Fuel Flow, Air Manifold Pressure and Temperature to determine the combustion performance. This simple approach offers surprisingly good performance while tying together basic thermodynamics, combustion performance and emissions. The system can also be used to parametrically determine engine emissions, based on the calculated combustion pressure without installing pressure sensors. The AMS monitors and determines emissions based on Trapped Equivalence Ratio, Effective Bulk Temperature or Pressure Ratio on single or multiple fuels providing a green/red light as an indicator of in/out of compliance accurately meeting today’s most stringent regulatory conditions.

Demonstration of a Dynamic Clearance Seal in a Rotating Steam Test Facility

2019 ◽  
Author(s):  
Andrew Messenger ◽  
Richard Williams ◽  
Grant Ingram ◽  
Simon Hogg ◽  
Philip Reggentin
Keyword(s):  
High Temperature ◽  
Pressure Ratio ◽  
Load Condition ◽  
Rotating Machinery ◽  
Design Tool ◽  
Test Facility ◽  
Design System ◽  
Working Fluid ◽  
Wide Range ◽  
High Temperature Steam

Abstract This paper reports on the latest phase of the development of a new rotating machinery sealing technology, which was a successful seal test in a high temperature steam test facility at TU Brauschweig in Germany. The “Aerostatic Seal” is a dynamic clearance seal that is capable of maintaining very small clearances with a rotor and has the potential for a wide range of rotating machinery applications. It has been developed in recent years at Durham University, UK, in collaboration with a major OEM, with a focus on steam turbine sealing, and has previously been reported on in a number of ASME Turbo Expo papers. Previous work has reported on the design tool, and two air test facilities; testing in steam addressed the effect of high temperature components and the working fluid, and was an opportunity to verify the design system. The seal is a development of a retractable gland seal and so in a low load condition it is retracted from the rotor with a large rotor clearance and then when the pressure ratio is sufficient moves to an operational small clearance. At its operational clearance the seal is capable of moving with rotor vibrations which means the design clearance can be smaller than any expected rotor movement. The benefits include a significant reduction in leakage when compared to conventional sealing technologies and also the ability to react to large transients or thermal growths caused by rapid changes in machine loads and speeds. The seal is shown to operate well in this environment and this work moves the technology closer to deployment in industry.

scholarly journals Short communication: A semi-automated method for rapid fault slip analysis from topographic scarp profiles

2019 ◽  
Author(s):  
Franklin D. Wolfe ◽  
Timothy A. Stahl ◽  
Pilar Villamor ◽  
Biljana Lukovic
Keyword(s):  
Monte Carlo ◽  
High Resolution ◽  
Open Source ◽  
Hanging Wall ◽  
Temporal Analysis ◽  
Fault Scarp ◽  
Fault Slip ◽  
Source Characterization ◽  
Automated Method ◽  
Wide Range

Abstract. Here, we introduce an open source, semi-automated, Python-based graphical user interface (GUI) called the Monte Carlo Slip Statistics Toolkit (MCSST) for estimating dip slip on individual or bulk fault datasets. Using this toolkit, profiles are defined across fault scarps in high-resolution digital elevation models (DEMs) and then relevant fault scarp components are interactively identified (e.g., footwall, hanging wall, and scarp). Displacement statistics are calculated automatically using Monte Carlo simulation and can be conveniently visualized in Geographic Information Systems (GIS) for spatial analysis. Fault slip rates can also be calculated when ages of footwall and hanging wall surfaces are known, allowing for temporal analysis. This method allows for rapid analysis of tens to hundreds of faults in rapid succession within GIS and a Python coding environment. Application of this method may contribute to a wide range of regional and local earthquake geology studies with adequate high-resolution DEM coverage, both regional fault source characterization for seismic hazard and/or estimating geologic slip and strain rates, including creating long-term deformation maps. ArcGIS versions of these functions are available, as well ones that utilize free, open source Quantum GIS (QGIS) and Jupyter Notebook Python software.

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