Shear Speed Research Articles

The Erosional and Depositional Potential of Holocene Tibetan Megafloods Through the Yarlung Tsangpo Gorge, Eastern Himalaya: Insights From 2D Hydraulic Simulations

AbstractProfound effects of episodic megafloods (≥106 m3/s) have been observed on Earth and Mars. Quaternary megafloods sourced from valley‐blocking glaciers on the Tibetan Plateau likely play an important role in the geomorphic evolution of the Yarlung‐Tsangpo Gorge and mountain landscape of the eastern Himalaya. We use the first 2D numerical simulation of a megaflood sourced from a reconstructed 81 km3 Tibetan lake to analyze flood hydraulics and examine the erosional and depositional potential of megafloods in mountain landscapes. The simulated flood has a duration >60 hr and a peak discharge of 3.1 × 106 m3/s. We find that the extent of inundated features like terraces, narrow valley sections, tight meander bends, and overtopped ridges influences locations of observed maximum depth (370 m), speed (76 m/s), and bed shear stress (>100 kPa), creating dynamic patterns of erosive potential. Consequently, it is difficult to predict local (≤1 km) patterns of megaflood erosional potential from either unit stream power or flood power from smaller magnitude outburst floods. However, both are useful when predicting regional (≥25 km) order‐of‐magnitude shifts in megaflood flood power. Portions of the flood domain downstream of the Gorge experience lower bed shear stresses and flood power <5 kW/m2, indicating potential for significant deposition. We suggest widespread deposition of boulders within the modern channel and fine‐grained particles on hillslopes during a megaflood likely impedes subsequent erosion and affects channel width and longitudinal form throughout the flood pathway. Our findings show the legacy of megaflooding in mountainous terrain includes both extensive erosion and deposition.

Characterizing coastal wind energy resources based on sodar and microwave radiometer observations

Wind energy is a mature and cost-effective solution to greenhouse gas emission reduction and climate change mitigation. Wind resource assessment is the most pivotal activity before wind farm development since it determines the bankability of the wind project. Based on the joint use of a Doppler wind sodar (sonic detection and ranging) system and a microwave radiometer, this paper investigates the wind and thermal characteristics and wind energy resources in a coastal region of Hong Kong. First, wind climatology and variability, as well as their correlation with large-scale and local meteorological and geographical conditions, are analyzed and discussed. Then, statistical distributions of wind speed are evaluated, and the goodness-of-fit of the Weibull, Kappa, Wakeby, Normal-Weibull mixture, and Weibull-Weibull mixture distributions is assessed. Subsequently, the probability distribution and variation of atmospheric stability are examined, and their effects on vertical wind shear, wind profile, and wind speed at turbine hub height are revealed. Lastly, the spatiotemporal variation of wind power density is investigated with attention paid to air density. The results presented in this paper are expected to offer insights into coastal wind and thermal characteristics, provide references for vertical extrapolation of wind speed and wind turbine load evaluation, and facilitate wind farm development in coastal regions.

Atmospheric Conditions within Big Telescope Alt-Azimuthal Region and Possibilities of Astronomical Observations

The paper presents the results of analysis of astroclimatic conditions in the Big Telescope Alt-azimuthal (BTA) region (40°N–50°N; 35°E–55°E). Using data from the European center for medium-range weather forecast ReAnalysis (ERA-5), we estimated the averaged spatial distributions in total cloud cover, vertical integral of mean kinetic energy, vertical component of wind speed, and wind speed shears, as well as inverse values of Richardson number 1/Ri. An extensive region with the development of atmospheric flows is formed south and southeast of BTA in winter. High inverse values of the Richardson number, spatial heterogeneities in vertical wind speed, and significant wind speed shears in the lower atmosphere are observed in this region. In terms of turbulence development over BTA, the best time for astronomical observations falls in summer, when vertical shears of wind speed are weakened in the lower atmospheric layers. The situation is opposite in the upper troposphere. In winter, BTA is in the region of moderate vertical wind shears. In summer, a region with increased vertical wind speed shears is formed. Taking into account that the intensity of optical turbulence decreases rapidly with height, better image quality can be expected in summer. Such structure of the atmosphere does not allow one to directly apply atmospheric models in order to describe turbulence based on the turbulence strength as function of its ground values, or to use the classical model describing the turbulence velocity as function of air flow velocity at the height corresponding to the 200 hPa level.

Rayleigh wave and super-shear evanescent wave excited by laser-induced shock at a soft solid–liquid interface observed by photoelasticity imaging technique

We investigated laser-induced shock excitation of elastic surface waves at a free surface and a soft solid–liquid interface using a custom-designed photoelasticity imaging technique. Epoxy-resin and pure water were selected as the solid and liquid media. The elastic surface waves were excited via a shock process induced by focusing a single nanosecond laser pulse on the solid surface. To confirm the experimental observations, the roots of the Rayleigh and Stoneley equations were calculated. For a free surface, we present an entire-field observation of elastic surface waves, which includes a super-shear evanescent wave (SEW) that propagates faster than the shear wave but slower than the longitudinal wave. For a soft solid–liquid interface, we demonstrate the presence of a non-leaky Rayleigh wave that corresponds to a real root of the Stoneley equation. We also evidence the existence of a SEW that propagates 1.7 times faster than the shear speed in the solid and corresponds to a complex conjugate root of the Stoneley equation. These results correct the previously accepted notion that the Scholte wave is the only surface wave that can be generated at a soft solid–liquid interface.

Experimental and Statistical Study of the Fracture Mechanism of Sn96.5Ag3Cu0.5 Solder Joints via Ball Shear Test.

Ball shear testing is an efficient approach to investigate the mechanical reliability of solder joints at the structural level. In the present study, a series of low-speed ball shear tests were conducted to study the deformation and fracture characteristics of Sn96.5Ag3Cu0.5 solder joints at continuous speeds from 10 μm/s to 200 μm/s. In order to account for randomness, the quantity of tests was repeated for each shear rate. The relationship between mechanical properties and shear speeds was calculated in detail via effective statistical analysis. In addition, by utilizing SEM imaging and ingredient analysis the interfacial effect and fracture mechanism of solder balls were obtained and their fracture mode classified into two types, viz., bulk fracture and interface fracture. Furthermore, by means of statistical analysis and approximate calculation it was proven that bulk fracture balls have greater adhesive powers and reliability compared with interface fracture balls.

Nonparametric copula modeling of wind speed-wind shear for the assessment of height-dependent wind energy in China

The joint probability density function can quantitatively describe the statistical characteristics and correlation features between wind speed and shear; this forms the theoretical basis for assessing height-dependent wind energy. Here, a nonparametric copula-based joint probability model of wind speed-wind shear is developed to assess height-dependent wind energy in China. Utilizing the transformation method and optimal bandwidth algorithms, a nonparametric copula model for wind speed/wind shear correlation analysis is proposed. Joint probability density models of wind speed and wind shear are then constructed. Various copula and marginal density models (including single parametric, mixture parametric, and kernel density estimation models) are evaluated at the regional scale. The nonparametric copula model exhibits remarkable superiority and is therefore deemed to be more suitable for wind speed/wind shear correlation analysis and joint probability modeling. When assessing height-dependent wind energy, the average distributions of wind turbine power output and capacity factor are obtained across mainland China. Additionally, this model could accurately analyze variations in wind power density with respect to hub height. These results can effectively facilitate accurate micro-site selection, thereby economically benefiting wind farms.

Analysis of the Effect of Smear Zone on Consolidation Decline in the Tebing Tinggi-Kisaran Toll Road Project (Phase 1) Tebing Tinggi – Indrapura STA 102+700 Toll Road Project with 3D PLAXIS Modeling

Repairing of soft clay Embankment loading method with PVD is a soil improvement system consisting of Embankment loading work, installation PVD, installation PHD, and geotechnical instruments. Preload serves to compress the subgrade. PVD serves to speed up the process of soil compaction. Horizontal drains serves to drain pore water taken from the PVD in a horizontal direction to the outside of the location that improved. Geotechnical instruments function to monitor and record the process and determine the performance of the result improving soil that have been carried out. Embankment loading and PVD (Prefabricated Vertical Drain) are technologies that are often used in the construction world to increase shear strength and speed up consolidation time of soft soils. However, during the installation of PVD using a mandrel it can affected the surrounding soil, causing the soil to become disturbed. The disturbed area is called by Smearzone. Due to the presence of a smear area, analysis and calculations are needed to obtain a consolidation time that is in accordance with field conditions. This analysis aims to compare the decrease of displacement in the settlement plate (SP-124) with modeling in PLAXIS 3D considering using with or without taking into account the effect of the smearzone. The method used in this thesis is the analytical method using Terzaghi theory and the finite element method using PLAXIS 3D. From the results obtained analytically the magnitude of the decrease is 15.252 cm while the results from the PLAXIS 3D analysis without the effect of the smear zone is 15.15 cm and with the effect of the smear zone being, 2 times the dimensions of the mandrel the results obtained are 15.131 cm, 15.133 cm and 15.134 cm, with 3 times the dimensions of the mandrel the results obtained are 15,142 cm, 15,141 cm and 15,14 cm and with 4 times the dimensions of the mandrel the results obtained are 15,144 cm, 15,143 cm and 15,143 cm. The decrease that occurs in the settlement plate 124 in the field is 15.10 cm. So it can be concluded that the calculation of consolidation decrease using analytical theory is relatively close to the decrease in actual results in the field with a percentage difference of 1% decrease. There are differences in settlement due to laboratory data not representing the entire soil layer. Due to the decrease that occurred 15.10 cm, the result of the effect of the smear effect 2 times the mandrel dimension and half of the coefficient of permeability of the original soil with a reduction ratio of 0.2% is the result that is closest to the results of field observations compared to without a smear effect of 0.331%.

Experimental study on the effect of particle size on the shear characteristics of large-displacement soil exposed to heat treatment: Shear fluctuation and heat degradation

The shear characteristics of soil on the basal face of a landslide body have important implications on landslide dynamics. In this study, ring-shear tests were carried out on quartz sand to study the shear characteristics of soil particle materials on the basal facies. Quartz sand samples of different particle sizes (0.25–1 mm) were treated at high temperature (20–800 °C) to determine the influence of temperature and particle size distribution (PSD) on their shear characteristics at different shear speeds. The shear characteristics of the samples were analyzed, including the shear stress, shear stress fluctuation, density variation, and degree of fragmentation. The results show that the amplitude of shear stress fluctuation increases with increasing shear velocity. It can be determined that the smaller the particle size, the greater the residual shear strength. Elevated temperature has a certain influence on the quartz sand and the shear characteristics (e.g., shear stress) exhibit a low degree of deterioration. The dilatancy and compaction mechanism of the samples under large displacement shearing is further discussed.

LiDAR Measurements of Wind Shear Exponents and Turbulence Intensity Offshore the Northeast United States

AbstractThis paper presents wind speed shear exponents and turbulence intensity (TI) measurements collected from light imaging, detection, and ranging instruments (LiDARs) measuring wind speeds from 40 m to 200 m above sea level and provides comparisons to industry design guidelines. The high-altitude wind speed data are unique and represent some of the first measurements made offshore in this part of the country, which is actively being developed for offshore wind. The data are used to support the New England Aqua Ventus I Floating Offshore Wind Farm to be located 17 km offshore the Northeast United States. Multiple LiDAR measurements were made using a DeepCLiDAR floating buoy and LiDARs located on a nearby island. The measured wind speed shear exponents are compared against industry standard mesoscale model outputs and offshore design codes including the American Bureau of Shipping, American Petroleum Institute, and Det Norske Veritas-Germanischer Lloyd guides. Significant variation in the vertical wind speed profile occurs throughout the year which is not addressed in design standards. Additionally, TI measurements made from the LiDAR, although not widely accepted in the scientific community, are presented and compared against industry guidelines.

Properties of Sn-3 wt%Ag-5 wt%Cu alloys with Cu6Sn5 intermetallics grain refined by Mg

This paper investigates the influence of Mg additions on the microstructure, thermal properties, electrical properties, and joint strength of bulk and ball grid array (BGA) reflowed Sn-3 wt%Ag-5 wt%Cu solder alloy and the joint intermetallics (IMCs). The cross-sectional microstructure analysis revealed that the addition of Mg effectively triggered the grain refinement of primary Cu6Sn5 IMCs in the bulk solder alloys. In addition, the thickness of the interfacial Cu6Sn5 IMCs layer was suppressed. The optimal addition for refinement is in the vicinity of 0.10 wt%Mg. Furthermore, synchrotron tomography three-dimensional reconstructed imaging reveals that the grain refinement of primary Cu6Sn5 IMCs is also effective even in BGA scale solder joint at normal reflow conditions. These primary Cu6Sn5 IMCs showed a non-faceted morphology. 0.10 wt%Mg addition reduced the number and size of the Cu6Sn5 IMCs. The grain refinement of primary Cu6Sn5 IMCs could be attributed to the presence of Mg, Mg2Sn, and MgO phases that potentially serve as heterogenous nucleation sites. The thermal analysis showed that the degree of undercooling values was significantly reduced to the minimum with 0.10 wt%Mg addition, which increased when the amount of Mg increased to 0.15 wt%. The mechanical properties showed that the ductility of the solder joint at high shear speed was improved.

Pressure-induced phase transitions and mechanical properties of insensitive high explosive 1,1-diamino-2,2-dinitroethylene

Abstract The structural and mechanical properties of an insensitive high-explosive 1,1-diamino-2,2-dinitroethylene (FOX-7) polymorphs were studied using dispersion-corrected density functional theory calculations. The predicted lattice parameters of FOX-7 polymorphs agree well with the available single-crystal X-ray diffraction data. From our elastic modulus calculations, we found that the ε phase has the highest shear modulus G, Young’s modulus E, longitudinal speed C L, and shear speed C S, respectively. Moreover, both α and α′ phase are brittle, ε phase is ductile nature. The results of Hirshfeld surfaces and fingerprint plots indicate that the α and α′ phase possess similar molecular packing modes. Meanwhile, the ε phase is found to have the strongest π…π interactions because of the nearly planer molecules formed a planar layer in the crystal. The pressure effects on the α and α′ phase presented an obvious anisotropy, a pressure-induced phase transition from phase α′ (P21/n) to ε phase (P1) was studied. And we also analyze the influence of pressure on the electronic structure.

Characteristics of the atmospheric boundary layer's structure and heating (cooling) rate in summer over the Northern Tibetan Plateau

The atmospheric boundary layer (ABL) is one of the most fundamental yet complex components of the Earth's atmosphere. Hence, studying the ABL has important theoretical value and practical significance. In this paper, the structural characteristics and heating (cooling) rate of the ABL in summer over the Northern Tibetan Plateau (NTP) were analysed using radiosonde observation data from the Amdo and Nagqu regions. The results indicate that the summertime ABL height over the NTP exhibited obvious diurnal variations, with the ABL height during the dry season being greater than that during the rainy season. The maximum convective boundary layer (CBL) height during the daytime reached 3200 m and 2500 m in the dry and rainy seasons, respectively, and the mean maximum CBL height was approximately 2500 m; the maximum stable boundary layer (SBL) height at night reached 900 m, and the mean maximum SBL height was approximately 500 m. The wind speed dominated by westerly wind in the dry season was greater than that dominated by easterly wind in the rainy season, and the zonal (meridional) wind speed (shear) on sunny days was greater than that on cloudy days. The inverse humidity phenomenon occurred in both Amdo and Nagqu, and the strong humidity inversion occurred mainly at midnight on sunny days and at noon on cloudy days. The heating (cooling) rate of the ABL displayed obvious diurnal variations, with the rates being greater on sunny days and lower on cloudy and rainy days. Furthermore, the mean values of the daytime heating rate and nighttime cooling rate of the ABL were relatively equal, indicating that the atmospheric energy budget was, for the most part, balanced.

The Brettenham storm of 25 July 2021

The <scp>Brettenham</scp> storm of 25 <scp>July</scp> 2021

Inversion for Parameters of Mud as a Porous Medium

In this article, the seven input parameters of a porous medium model for mud are defined and inverted for the New England Mud Patch. One distinguishing feature is that the skeletal frame may contain adsorbed water, and the pore water may contain suspended solid material. This means that the effective properties of the skeletal frame and pore water are different from that of the pure solid and pure seawater, and the effective porosity is not the same as the bulk water fraction. The model contains two loss mechanisms: creep and viscous loss due to relative motion between skeletal frame and pore water. It is demonstrated that the input parameters could be inverted from the wave speeds, attenuations, and reflection. The inversion from reflection loss exclusively is more difficult due to the relative insensitivity to shear properties. A partial solution is obtained by using a regression relationship to constrain the shear speed. A connection between the assumed shear speed and the inverted compressional wave attenuation is consistent with a recent finding by Godin. Regarding reflection loss from a half-space, for frequencies less than about 10&#x00A0;kHz, a homogeneous medium model is indistinguishable from a porous medium model, and for shear speeds less than 50&#x00A0;m/s, a fluid model would be adequate. The porous medium model does not suffer from these restrictions.

Characterization of Local Clay for Drilling Mud Production

Oil companies’dealing with drilling operations in Nigeria often spends millions of dollars in importation of bentonite for its operations as a result of its importance and high demand. As a result of this, attempt to source for local substitute has been initiated, which if successful would save the nation from this huge capital flight. In this study, a sample of Umuna local clay deposit was evaluated for drilling fluid application. The viscosity and filtration loss was analyzed and it’s far below that of the imported bentonite. The properties of the local clay was improved by addingmaterials such as HV-CMC, Drispac polymer and bentonite extenders to the formulated mud to enhance its viscosity and filtration loss Also the shearing speed was increased, but the used speed is limited to practical shearing speed. Theclay yield and characterization of the beneficiated samples show that the treated local clay is slightly comparable to the imported bentonite. The Calcium Exchange Capacity (CEC) result for the clay samples fall within the 70 – 150 Meq/100g. This result further suggests that the analyzed clay is of montimorillonite family, with traces of illite which is good for drilling mud production. The obtained results from this study indicates that the filtration loss and plastic viscosity for the analyzed clay samples were generally far from comparing with the imported bentonite, but through beneficiation, they were able to compare with the imported bentonite.

Wind Turbulence over Misaligned Surface Waves and Air–Sea Momentum Flux. Part II: Waves in Oblique Wind

AbstractThe coupled dynamics of turbulent airflow and a spectrum of waves are known to modify air–sea momentum and scalar fluxes. Waves traveling at oblique angles to the wind are common in the open ocean, and their effects may be especially relevant when constraining fluxes in storm and tropical cyclone conditions. In this study, we employ large-eddy simulation for airflow over steep, strongly forced waves following and opposing oblique wind to elucidate its impacts on the wind speed magnitude and direction, drag coefficient, and wave growth/decay rate. We find that oblique wind maintains a signature of airflow separation while introducing a cross-wave component strongly modified by the waves. The directions of mean wind speed and mean wind shear vary significantly with height and are misaligned from the wind stress direction, particularly toward the surface. As the oblique angle increases, the wave form drag remains positive, but the wave impact on the equivalent surface roughness (drag coefficient) rapidly decreases and becomes negative at large angles. Our findings have significant implications for how the sea-state-dependent drag coefficient is parameterized in forecast models. Our results also suggest that wind speed and wind stress measurements performed on a wave-following platform can be strongly contaminated by the platform motion if the instrument is inside the wave boundary layer of dominant waves.Significance StatementSurface waves increase friction at the sea surface and modify how wind forces upper-ocean currents and turbulence. Therefore, it is important to include effects of different wave conditions in weather and climate forecasts. We aim to inform more accurate forecasts by investigating wind blowing over waves propagating in oblique directions using large-eddy simulation. We find that waves traveling at a 45° angle or larger to the wind grow as expected, but do not increase or even decrease the surface friction felt by the wind—a surprising result that has significant implications for how oblique wind-waves are represented as a source of surface friction in forecast models.

Characterization of Water Droplets Size Distribution in Aviation Turbine Fuel: Ultrasonic Homogeniser vs. High Shear Speed Mixer

Characterization of Water Droplets Size Distribution in Aviation Turbine Fuel: Ultrasonic Homogeniser vs. High Shear Speed Mixer

Controllable Angle Shear Wavefront Reconstruction Based on Image Fusion Method for Shear Wave Elasticity Imaging.

The generation and measurement of shear waves are critical in ultrasonic elasticity imaging. Generally, the resulting wavefront direction is very important for accurately measuring the shear speed and estimating the medium elasticity. In this article, the proposed method can generate a compound shear wavefront with the same direction as speed reconstruction and zero angles between the wavefront and the focus direction, which can improve the estimation accuracy of shear wave velocity. Also, this method, called time-division multipoint excitation image fusion (TDMPEIF), can reconstruct the shear wave propagation images acquired at different depths of a medium according to the frame sequence to produce the shear waves front with a regulable angle. Moreover, the shear wave speed and the elasticity of a medium can be mapped quantitatively with this method. The results demonstrate that the TDMPEIF can improve the quality of the shear wave velocity images, which has wide application value and good promotion prospects for quantitative evaluation of tissue elasticity.

Impact of injection limitations on the contact resistance and the carrier mobility of organic field effect transistors

The contact resistance as well as the mobility have developed to key performance indicators for benchmarking organic field-effect transistors. Typically, conventional methods for silicon transistors are employed for their extraction thereby ignoring the peculiarities of organic transistors. This work outlines the required conditions for using conventional extraction techniques for the contact resistance and the mobility based on TCAD simulations and experimental data. Our experimental data contain both staggered and coplanar structures fabricated by exploiting different optimization techniques like SAM treated electrodes, different shearing speeds, PS blending and silicon oxide functionalization. In addition, the work clarifies how injection limited current–voltage characteristics can affect high-performance organic field-effect transistors. Finally, we introduce a semi-physical model for the contact resistance to accurately interpret extracted benchmark parameters by means of the transfer length method (TLM). Guidelines to use conventional extraction techniques with special emphasis on TLM are also provided. • Injection limited IV characteristics are frequent in current OFET technologies. • Criteria are given to identify injection and bulk limitations in IV curves of OFETs. • Contact resistance and mobility should be extracted from bulk limited IV curves. • Contact parameters are extracted from TLM line intersection and not interception. • Architecture-dependent injection optimization is derived from current crowding model.

Optimisation Of Nano-ZnO And Nano-SiO2 Mixing Time For Bitumen Modification

Nanotechnologies have gradually penetrated to the field of bitumen modification especially where durable asphalt mixtures have to be designed. Longer mixing time, higher temperatures or/and higher rotation (shearing) speeds are needed to increase the dispersion of nanoparticles in bitumen. However, this is not necessarily beneficial to the physical and mechanical properties of the final material. As a result, in this study nano-zinc oxide (nano-ZnO) and nano-silica (nano-SiO2) mixing time for bitumen modification was optimized considering the physical and mechanical properties of the final bitumen. For this purpose bitumen PMB 25/55-60 was modified with nanoparticles at 180 °C using a laboratory high-shear mixer at a rotation speed of 4000 rpm for different modification time selected on the basis of literature review (60 and 90 minutes). Penetration, softening point, viscosity at 135 °C, recovery and non-recoverable creep compliance (multiple stress creep and recovery test) at 60 °C were measured in order to determine the optimal mixing time. The results showed that 60 minutes ensures the dispersion of nano-ZnO and nano-SiO2 in the bitumen PMB 25/55-60 and longer mixing time do not have a significant effect on the properties of nano-ZnO and nano-SiO2 modified bitumen (the difference was less than 7%).