Influence of anisotropy in sediment mechanical properties on CH4 bubble growth topology and migration pattern in muddy aquatic sediments

2021 ◽  
Author(s):  
Abhishek Painuly ◽  
Regina Katsman
Keyword(s):  
Bubble Growth ◽  
Mechanical Response ◽  
Vertical Direction ◽  
Water Bodies ◽  
Small Scale ◽  
Muddy Sediment ◽  
Atmospheric Methane ◽  
Aquatic Sediments ◽  
Vertical Orientation ◽  
Muddy Sediments

<p>Gas-charged sediments of shallow water bodies are significant sources of atmospheric methane, an important greenhouse gas. Past accounts of gas bubbles developed in shallow aquatic sediments (and in their surrogates) have reported a controversial occurrence of vertical as well as horizontal bubbles topologies. Within the framework of tensile fracturing of muddy sediment produced by the growing bubbles, the vertical orientation of bubbles is well understood, however factors controlling horizontal bubble growth are largely unclear. This study is conducted by employing a mechanical/reaction–transport numerical model, which couples diffusion-led expansion of gas bubble and elastic-fracture mechanical response of sediment to its growth. Muddy sediment is assumed to exhibit a transverse anisotropy in fracture toughness (a property describing an easiness of breaking the inter particle bonds), attributed to partial or full alignment of plate-like clay particles. Our results demonstrate that bubbles growing in isotropic sediment develop a vertically oriented topology and start their ascent once reaching their mature sizes. Under an increasing measure of anisotropy, the bubbles grow horizontally at the initial stages, however at later stages they start evolving in vertical direction as well, under influence of gravity, and eventually initiate their vertical ascent as well. Our results suggest an explanation of apparent conundrum about preferred orientations of bubbles in muddy sediments. Laterally growing bubbles produced in anisotropic sediment are able to coalesce with neighboring ones and form interconnected permeable horizontal gas networks, as observed in some lab experiments. For the first time, our results reveal that anisotropy-led initial lateral bubble growth can also play a crucial role in accumulating gas reserve from long distances around large and small scale seeps and outlets, at continental margins and inland water bodies sediments. Additionally, horizontal bubbles tend to be stationary (in contrast to the vertical bubbles) thus being responsible for high gas storage (or retention) capability of aquatic sediments.</p>

scholarly journals Analysis of Non-Stationarity for 5.9 GHz Channel in Multiple Vehicle-to-Vehicle Scenarios

Sensors ◽  
2021 ◽  
Vol 21 (11) ◽  
pp. 3626
Author(s):  
Fang Li ◽  
Wei Chen ◽  
Yishui Shui
Keyword(s):  
Transmission Rate ◽  
Radio Channel ◽  
Vertical Direction ◽  
Statistical Characteristics ◽  
Small Scale ◽  
Delay Spread ◽  
Important Indicator ◽  
Power Delay Profile ◽  
Channel Characteristics ◽  
Vehicle To Vehicle

The vehicle-to-vehicle (V2V) radio channel is non-stationary due to the rapid movement of vehicles. However, the stationarity of the V2V channels is an important indicator of the V2V channel characteristics. Therefore, we analyzed the non-stationarity of V2V radio channels using the local region of stationarity (LRS). We selected seven scenarios, including three directions of travel, i.e., in the same, vertical, and opposite directions, and different speeds and environments in a similar driving direction. The power delay profile (PDP) and LRS were estimated from the measured channel impulse responses. The results show that the most important influences on the stationary times are the direction and the speed of the vehicles. The average stationary times for driving in the same direction range from 0.3207 to 1.9419 s, the average stationary times for driving in the vertical direction are 0.0359–0.1348 s, and those for driving in the opposite direction are 0.0041–0.0103 s. These results are meaningful for the analysis of the statistical characteristics of the V2V channel, such as the delay spread and Doppler spread. Small-scale fading based on the stationary times affects the quality of signals transmitted in the V2V channel, including the information transmission rate and the information error code rate.

scholarly journals Nonlinear magneto-thermo-elastic vibration of mass sensor armchair carbon nanotube resting on an elastic substrate

2020 ◽  
Vol 7 (1) ◽  
pp. 153-165
Author(s):  
Rajendran Selvamani ◽  
M. Mahaveer Sree Jayan ◽  
Rossana Dimitri ◽  
Francesco Tornabene ◽  
Farzad Ebrahimi
Keyword(s):  
Carbon Nanotube ◽  
Mechanical Response ◽  
Scale Effects ◽  
Nonlocal Elasticity Theory ◽  
Wave Dispersion ◽  
Elastic Vibration ◽  
Ultrasonic Waves ◽  
Small Scale ◽  
Dimensionless Frequency ◽  
Mass Sensors

AbstractThe present paper aims at studying the nonlinear ultrasonic waves in a magneto-thermo-elastic armchair single-walled (SW) carbon nanotube (CNT) with mass sensors resting on a polymer substrate. The analytical formulation accounts for small scale effects based on the Eringen’s nonlocal elasticity theory. The mathematical model and its differential equations are solved theoretically in terms of dimensionless frequencies while assuming a nonlinear Winkler-Pasternak-type foundation. The solution is obtained by means of ultrasonic wave dispersion relations. A parametric work is carried out to check for the effect of the nonlocal scaling parameter, together with the magneto-mechanical loadings, the foundation parameters, the attached mass, boundary conditions and geometries, on the dimensionless frequency of nanotubes. The sensitivity of the mechanical response of nanotubes investigated herein, could be of great interest for design purposes in nano-engineering systems and devices.

scholarly journals Low-Level Wind Shear Identification along the Glide Path at BCIA by the Pulsed Coherent Doppler Lidar

Atmosphere ◽  
2020 ◽  
Vol 12 (1) ◽  
pp. 50
Author(s):  
Hongwei Zhang ◽  
Xiaoying Liu ◽  
Qichao Wang ◽  
Jianjun Zhang ◽  
Zhiqiang He ◽  
...  
Keyword(s):  
Wind Shear ◽  
Vertical Direction ◽  
Small Scale ◽  
Observation Data ◽  
Doppler Lidar ◽  
Low Level ◽  
Glide Path ◽  
Coherent Doppler Lidar ◽  
Scanning Strategies ◽  
Meteorological Phenomenon

Low-level wind shear is usually to be a rapidly changing meteorological phenomenon that cannot be ignored in aviation security service by affecting the air speed of landing and take-off aircrafts. The lidar team in Ocean University of China (OUC) carried out the long term particular researches on the low-level wind shear identification and regional wind shear inducement search at Beijing Capital International Airport (BCIA) from 2015 to 2020 by operating several pulsed coherent Doppler lidar (PCDL) systems. On account of the improved glide path scanning strategy and virtual multiple wind anemometers based on the rang height indicator (RHI) modes, the small-scale meteorological phenomenon along the glide path and/or runway center line direction can be captured. In this paper, the device configuration, scanning strategies, and results of the observation data are proposed. The algorithms to identify the low-level wind shear based on the reconstructed headwind profiles data have been tested and proved based on the lidar data obtained from December 2018 to January 2019. High spatial resolution observation data at vertical direction are utilized to study the regional wind shear inducement at the 36L end of BCIA under strong northwest wind conditions.

Exploring the variation in ecosystem scale methane fluxes and its drivers within a boreal mire complex

2021 ◽  
Author(s):  
Koffi Dodji Noumonvi ◽  
Joshua L. Ratcliffe ◽  
Mats Öquist ◽  
Mats B. Nilsson ◽  
Matthias Peichl
Keyword(s):  
Eddy Covariance ◽  
Land Surface ◽  
Chemical Properties ◽  
Growing Season ◽  
Small Scale ◽  
Atmospheric Methane ◽  
Flux Footprint ◽  
Growing Season Length ◽  
Methane Fluxes ◽  
Northern Peatlands

<p>Northern peatlands cover a small fraction of the earth’s land surface, and yet they are one of the most important natural sources of atmospheric methane. With climate change causing rising temperatures, changes in water balance and increased growing season length, peatland contribution to atmospheric methane concentration is likely to increase, justifying the increased attention given to northern peatland methane dynamics. Northern peatlands often occur as heterogeneous complexes characterized by hydromorphologically distinct features from < 1 m² to tens of km², with differing physical, hydrological and chemical properties. The more commonly understood small-scale variation between hummocks, lawns and hollows has been well explored using chamber measurements. Single tower eddy covariance measurements, with a typical 95% flux footprint of < 0.5 km², have been used to assess the ecosystem scale methane exchange. However, how representative single tower flux measurements are of an entire mire complex is not well understood. To address this knowledge gap, the present study takes advantage of a network of four eddy covariance towers located less than 3 km apart at four mires within a typical boreal mire complex in northern Sweden. The variation of methane fluxes and its drivers between the four sites will be explored at different temporal scales, i.e. half-hourly, daily and at a growing-season scale.</p>

Double-Sided Microchannel Cooling of a Power Electronics Module Using Power Overlay

2009 ◽  
Author(s):  
Adam G. Pautsch ◽  
Arun Gowda ◽  
Ljubisa Stevanovic ◽  
Rich Beaupre
Keyword(s):  
Power Electronics ◽  
High Performance ◽  
Mechanical Response ◽  
Thermal Contact ◽  
Small Scale ◽  
Micro Channel ◽  
Performance Technology ◽  
Actual Performance ◽  
Low Performance ◽  
Microchannel Cooling

In the continuing effort to alleviate the increasing thermal loads for power electronics devices, numerous aggressive solutions have been developed, such as small-scale micro-channel heat exchangers. Although these methods can improve overall surface heat transfer to the order of 500 W cm−2, they are limited to single-sided cooling due to the typical wire-bonded electrical connections of the devices. Power overlay (POL) technology provides a stable planar structure for electrical connection, as well as attachment of an additional top-side heat exchanger. This study presents an analysis of double-sided microchannel cooling of a power electronics module. Two optimized, integral micro-channel heat sinks were attached above and below silicon power devices, with more traditional attachment on one side and a POL interface on the other. A compliant TIM was selected for low thermal resistance and good mechanical response, which allowed top-side connection to the POL surface. A theoretical model is presented that predicts the benefit of double-sided cooling based on the known performance of a single-sided heat sink and given addition thermal contact resistance for the top side. For microchannels with water, an enhancement of 26% was predicted. An experiment was also carried out to measure the actual performance benefit seen with double-sided cooling. An enhancement of over 30% was measured for a particular design. As the theory predicts, the benefit of double-sided cooling is limited for high performance designs. However, double-sided cooling could lead to high levels of thermal performance using low-performance technology.

scholarly journals Vertically localised equilibrium solutions in large-eddy simulations of homogeneous shear flow

2017 ◽  
Vol 827 ◽  
pp. 225-249 ◽  
Author(s):  
Atsushi Sekimoto ◽  
Javier Jiménez
Keyword(s):  
Shear Flow ◽  
Vertical Direction ◽  
Large Eddy Simulations ◽  
Small Scale ◽  
Box Dimension ◽  
Equilibrium Solutions ◽  
Vortical Structures ◽  
Homogeneous Shear ◽  
Large Eddy ◽  
Homogeneous Shear Flow

Unstable equilibrium solutions in a homogeneous shear flow with sinuous (streamwise-shift-reflection and spanwise-shift-rotation) symmetry are numerically found in large-eddy simulations (LES) with no kinetic viscosity. The small-scale properties are determined by the mixing length scale $l_{S}$ used to define eddy viscosity, and the large-scale motion is induced by the mean shear at the integral scale, which is limited by the spanwise box dimension $L_{z}$. The fraction $R_{S}=L_{z}/l_{S}$, which plays the role of a Reynolds number, is used as a numerical continuation parameter. It is shown that equilibrium solutions appear by a saddle-node bifurcation as $R_{S}$ increases, and that the flow structures resemble those in plane Couette flow with the same sinuous symmetry. The vortical structures of both lower- and upper-branch solutions become spontaneously localised in the vertical direction. The lower-branch solution is an edge state at low $R_{S}$, and takes the form of a thin critical layer as $R_{S}$ increases, as in the asymptotic theory of generic shear flow at high Reynolds numbers. On the other hand, the upper-branch solutions are characterised by a tall velocity streak with multiscale multiple vortical structures. At the higher end of $R_{S}$, an incipient multiscale structure is found. The LES turbulence occasionally visits vertically localised states whose vortical structure resembles the present vertically localised LES equilibria.

scholarly journals Quantifying methane point sources from fine-scale (GHGSat) satellite observations of atmospheric methane plumes

2018 ◽  
Author(s):  
Daniel J. Varon ◽  
Daniel J. Jacob ◽  
Jason McKeever ◽  
Dylan Jervis ◽  
Berke O. A. Durak ◽  
...  
Keyword(s):  
Wind Speed ◽  
Methane Emissions ◽  
Point Sources ◽  
Small Scale ◽  
Atmospheric Methane ◽  
Flux Method ◽  
Pixel Resolution ◽  
Cross Sectional ◽  
Source Rate ◽  
The Cross

Abstract. Anthropogenic methane emissions originate from a large number of relatively small point sources. The planned GHGSat satellite fleet aims to quantify emissions from individual point sources by measuring methane column plumes over selected ~ 10 × 10 km2 domains with ≤ 50 × 50 m2 pixel resolution and 1–5 % measurement precision. Here we develop algorithms for retrieving point source rates from such measurements. We simulate a large ensemble of instantaneous methane column plumes at 50 × 50 m2 pixel resolution for a range of atmospheric conditions using the Weather Research and Forecasting model (WRF) in large eddy simulation (LES) mode and adding instrument noise. We show that standard methods to infer source rates by Gaussian plume inversion or source pixel mass balance are prone to large errors because the turbulence cannot be properly parameterized on the small scale of instantaneous methane plumes. The integrated mass enhancement (IME) method, which relates total plume mass to source rate, and the cross-sectional flux method, which infers source rate from fluxes across plume transects, are better adapted to the problem. We show that the IME method with local measurements of the 10-m wind speed can infer source rates with error of 0.07–0.17 t h−1 + 5–12 % depending on instrument precision (1–5 %). The cross-sectional flux method has slightly larger errors (0.07–0.26 t h−1 + 8–12 %) but a simpler physical basis. For comparison, point sources larger than 0.5 t h−1 contribute more than 75 % of methane emissions reported to the U.S. Greenhouse Gas Reporting Program. Additional error applies if local wind speed measurements are not available, and may dominate the overall error at low wind speeds. Low winds are beneficial for source detection but not for source quantification.

Mechanical Response and Incomplete Filling in Compression Molding With Microscale Double-Punch Sets

2019 ◽  
Author(s):  
Bin Zhang ◽  
M. Dodaran ◽  
S. Shao ◽  
W. J. Meng
Keyword(s):  
Mechanical Response ◽  
Ion Beam ◽  
Compression Molding ◽  
Molding Pressure ◽  
Small Scale ◽  
Width Ratio ◽  
Significant Dependence ◽  
Incomplete Filling ◽  
Surface Patterns ◽  
Scale Surface

Abstract Forming nano-/micro-scale surface patterns on metal surfaces by direct compression molding is an important means for achieving small scale surface features with potential usage in wide ranging technological applications. Geometric fidelity of molded features and the corresponding molding response are of critical importance in determining the usefulness of the molding replication technique. In this paper, two series of microscale punches made of tool steels were fabricated using Ga+ focused ion beam (FIB). In one series, the punch consists of a single protruding rectangular strip of different width, w (dubbed the “single punch”). In the other series, the punch consists of two rectangular strips of identical dimensions separated by a spacing in between, s (dubbed the “double punch”). These so-fabricated punches were used to mold elemental single crystal Al. The mechanical response during compression molding was measured and analyzed. For the double-punch experiments, measured characteristic molding pressure exhibited a significant dependence on the spacing to punch width ratio, λ = s/w, as well as a significant dependence on s when λ was fixed. The molded features were examined and the phenomenon of incomplete filling was observed to occur at λ < 0.5.

scholarly journals Investigation of thermo-mechanical response of a geothermal pile through a small-scale physical modelling

2020 ◽  
Vol 205 ◽  
pp. 05016
Author(s):  
Hussein Hashemi Senejani ◽  
Omid Ghasemi-Fare ◽  
Davood Yazdani Cherati ◽  
Fardin Jafarzadeh
Keyword(s):  
Mechanical Response ◽  
Thermal Response ◽  
Physical Modelling ◽  
Elastic Response ◽  
Small Scale ◽  
Thermal Cycles ◽  
Prolonged Heating ◽  
Excessive Heat ◽  
Head Displacement ◽  
Bed Changes

Energy piles have been used around the world to harvest geothermal energy to heat and cool residential and commercial buildings. In order to design energy geo-structures, thermo-mechanical response of the geothermal pile must be carefully understood. In this paper, a small scale physical model is designed and a series of heating thermal cycles with various vertical mechanical loads are performed. The instrumented pile is installed inside a dry sand bed. Changes in pile head displacement, shaft strains and pile and sand temperatures are monitored using an LVDT, strain gauges and thermocouples, respectively. Prolonged heating cycles, which would continue until boundary temperature changes, would allow the investigation of excessive heat injection when service loads are active on the pile. The thermal response is discussed including confirmation of a temperature influence zone around the pile, the increase in soil temperature, and minimum vertical heat dispersion in the soil. The mechanical response includes plastic settlements when the vertical load passes 20% of ultimate capacity. Plastic settlements have been observed at the half of the capacity reported for the shorter thermal cycles in similar models. The decrease in the capacity indicates a reduction in elastic response of the soil during longer thermal cycles.

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