Collapse Characteristics Research Articles

Investigation of contact mechanism and gate electrostatic control in multi-channel AlGaN/GaN high electron mobility transistors with deep recessed ohmic contact

In this paper, the ohmic contact mechanism and gate electrostatic control of a deep-recessed ohmic contact structure for multi-channel Al0.3Ga0.7N/GaN high electron mobility transistors (HEMTs) is investigated. A transmission electron microscope and an energy dispersive spectrum are utilized to investigate the ohmic contact interface mechanism. Due to a reduction of source/drain parasitic resistances and simultaneous connection of five channels by using deep-recessed ohmic contact, a large maximum drain current density and a distinct five hump feature of ultra-wider trans-conductance are achieved. More importantly, it is revealed that the downward expansion of the gate potential for the deep-recessed ohmic contact structure is much deeper than that for conventional devices. This characteristic leads to a remarkable reduction in subthreshold swing (SS) and off-state leakage, indicating an ultra-wide and high trans-conductance profile. The fabricated devices show a lower off-state drain leakage, a lower SS, and a wider gate voltage swing (40 V). Due to an enhancement of gate electrostatic control, the current collapse and electrical reliability characteristics of multi-channel Al0.3Ga0.7N/GaN HEMTs with deep-recessed ohmic contact also improve. The results presented here indicate that the multi-channel device has great potential for high current and wide bandwidth applications.

Three-dimensional Stability Analysis of Slurry Trench Based on Mohr-Coulomb Nonlinear Failure Criterion

In accordance with the collapse characteristic of trench wall during underground diaphragm wall construction, a modified three-dimensional (3D) failure mechanism of trench wall is established. By introducing nonlinear characteristic and the nonhomogeneity of soil into the theoretical calculation, the objective function of the safety factor (Fs) of the trench wall in the limit condition is derived, and the upper bound solution of the Fs of the slurry trench is derived by employing the optimization computation. To prove the validity of the presented approach, the solutions derived from the presented method are compared with those previous solutions and the comparing results show a good agreement. Moreover, the parametric analysis is conducted to study the effect of various parameters on the stability of trench wall. The results of parametric analysis show that nonlinear and the nonhomogeneous parameters have significant influence on the safety factors, and the nonlinear failure characteristic of the nonhomogeneity of soil cannot be ignored in the practical engineering.

Effect of Time History on Long-Term Deformation of Gypseous Soils

Abstract The time-dependent behavior of three gypseous soils was investigated. The soils had gypsum content of 66%, 44%, and 14.8%. The mineralogical and chemical properties of the soils were determined. Two series of tests were performed. In the first, collapsibility characteristics were investigated for a long period (60 days) by conducting single and double oedometer tests. In the second series, the effect of relative density on collapse with time was investigated. The samples were compacted to 40%, 50%, and 60% relative density and then tested. The results of collapse tests showed that the relationship between the strain and logarithm of effective stress has two vertical lines. The first one represents the collapse settlement taking place within 24 h, while the second one represents the long-term collapse. The collapse potential (CP) in both single and double oedometer tests increases when the gypsum content increases from 14.8% to 66% and when the initial void ratio increases. The CP–logarithm of time relationship for soaked samples prepared at different relative densities under 800 kPa indicated that the CP increased with time for the soil sample compacted at 60% relative density and the increase was higher than those compacted at 40% and 50% relative density. The curves started with a straight line and then a concave downward curve was observed with a high strain. For samples compacted at 40% and 50% relative densities, the curves were interrupted by little soil collapses, while the third curve exhibited smooth relation following the collapse.

Fluid–structure interactions between a near-field underwater explosion bubble and a suspended plate

During near-field underwater explosions, the structural response induced by the shock wave and bubble load significantly affects the bubble collapse and jet characteristics. The effect of fluid–structure interaction (FSI) may increase the damage potential of the structure. In this study, we conduct experiments examining the interaction between small-charge underwater explosion bubbles and a suspended plate under different initial detonation distances. The morphological evolution of the bubble and the structural response are recorded using a high-speed camera and strain gauges, respectively. In addition, the bubble dynamic behaviors are simulated using the finite volume method, and an FSI model is established based on the overset mesh technology. The model is verified by comparisons between the experimental and numerical results. The physical mechanism affecting the bubble collapse pattern is revealed. The influence of the distance parameter γ between the bubble and the plate on the jet pattern and structure load is systematically studied. The findings presented in this study provide a reference for bubble-related fields and transient gas–liquid–structure interactions.

Ultimate strength characteristics and assessment of laser-welded web-core sandwich plates under combined biaxial compression and lateral pressure

The ultimate strength and the collapse characteristics of laser-welded web-core sandwich plates subjected to the combined biaxial compression and lateral pressure are investigated by the finite element method. The finite T-joint rotation stiffness is considered, which is derived from the published experimental data. The results show that the finite T-joint rotation stiffness will result in a maximum of 23% decrease in the transverse ultimate strength, much larger than that in the longitudinal ultimate strength. The decrease of the transverse shear stiffness accounts for the reduction of the load-carrying capacity. The lateral pressure reduces the ultimate strength of the sandwich plates, and the reduction in the ultimate strength dominated by the longitudinal compressive collapse is more significant than that in the ultimate strength dominated by the transverse compressive collapse. The applied compressive stress ratios determine the collapse modes of the sandwich plates, which explains the difference in the degree to which the lateral pressure reduces the ultimate strength under the biaxial compression. Based on the numerical results, a preliminary formula is proposed in this paper to assess the load-carrying capacity of the laser-welded web-core sandwich plate subjected to the combined biaxial compression and lateral pressure.

Bubble dynamics near a locally curved region of a plane rigid wall

The dynamics of a bubble near a local axisymmetric convexity or concavity, cosine-like in the axial section, on a plane rigid wall is studied under conditions of formation of a cumulative liquid jet directed to the wall. The study is performed by the boundary element method. Our main attention is focused on the bubble collapse characteristics at the moment tc when the jet impacts on the bubble surface part near the wall, namely, on the jet tip velocity and radius, the internal bubble pressure, the distance between the bubble and the uneven region of the wall, and so on. These characteristics are of interest since they, to a large extent, determine the destructive potential of cavitation. The dependences of these characteristics on the radius of the non-plane region of the wall, the depth of the concave region, the height of the convex region, and the local character of the wall unevenness have been investigated. To estimate the effect of the local character of the wall unevenness, the cases of completely concave and convex walls in the form of blunt conical surfaces are used for comparison. It has been found, in particular, that with changing radius of the convex region of the wall, the bubble shape at the moment tc varies significantly: the shape diversity includes the profiles with a gas microcavity in front of the impacting jet tip, an emerging second oppositely directed jet, and a relatively large area of the jet tip impact at its beginning.

Mitigation of collapse characteristics of gypseous soils by activated carbon, sodium metasilicate, and cement dust: An experimental study

AbstractThis study includes adding chemicals to gypseous soil to improve its collapse characteristics. The collapse behavior of gypseous soil brought from the north of Iraq (Salah El-Deen governorate) with a gypsum content of 59% was investigated using five types of additions (cement dust, powder sodium meta-silicate, powder activated carbon, sodium silicate solution, and granular activated carbon). The soil was mixed by weight with cement dust (10, 20, and 30%), powder sodium meta-silicate (6%), powder activated carbon (10%), sodium silicate solution (3, 6, and 9%), and granular activated carbon (5, 10, and 15%). The collapse potential is reduced by 86, 71, 43, 37, and 35% when 30% cement dust, 6% powder sodium meta-silicate, 10% powder activated carbon, 6% sodium silicate solution, and 10% granular activated carbon are used, respectively.

Study on the Regularity of Surface Collapse in Goaf using UAV Remote Sensing Technology

UAV remote sensing technology is used to analyze the characteristics of surface collapse and evaluate the degree of damage in the mining area, and the regularity of surface collapse in the mining area is studied. The distribution and variation characteristics of surface collapse pits and surface cracks and surface deformation characteristics are obtained from UAV images. Taking the area of collapse pits, the depth of collapse pits, the width of cracks, the drop of cracks, the density of cracks, surface subsidence and surface inclination as the evaluation factors, the fuzzy opinion centralized decision-making of the classical fuzzy comprehensive evaluation method is introduced into the combined weighting method, and the fuzzy comprehensive evaluation model based on AHP-CRITIC method is established. The results show that: (1) From August 2020 to June 2021, 125 surface cracks have increased; Three new collapse pits are generated, with a maximum area of about 323m2 and a maximum depth of about 21m; The surface deformation in the south of the mining area is obvious, forming a settlement funnel. (2) The severe damage degree of surface collapse is mainly distributed near the surface collapse pits, the moderate damage degree is mainly distributed in the central and southern part of the study area, and the mild and slight damage degree is mainly distributed in the periphery of the ore body.

충격압궤 실험에 의한 경량화용 차체 구조부재의 개발

The most important requirement in the initial design stage of vehicles is that the structural members of a vehicle body adequately absorb impact energy and secure a safe space during collision. Furthermore, it is the development of materials for weight reduction. Therefore, the collapse characteristics caused by the collision of the structural member having the largest collision energy absorption must be accurately understood when designing a vehicle in consideration of a safe and lightweight design. In this study, the impact collapse experiments were conducted after designing, manufacturing, and molding single hat and double-hat cross-section members of steel and carbon fiber reinforced plastic(CFRP)/epoxy materials. By examining the resulting energy absorption characteristics, accurate design data could be obtained to develop the side structural members for optimal lightweight vehicles.

Collapse and recovery of seafood wholesale prices in time of COVID-19.

The COVID‐19 pandemic has spread around the world, disrupting economies, societies and daily life. Early research anticipated significant negative impacts for the globalized seafood supply network. Here, we explore the impact of the COVID‐19 pandemic on wholesale prices from five major seafood markets around the world. An anomalies analysis was used to establish a 5‐year baseline price for each commodity. Daily price data from 2020 were compared to the baseline to identify collapses (>1.96 SE from baseline) and analyse collapse characteristics (timing, duration and magnitude). Non‐uniform price collapses were observed across, and within, the markets analysed. Toyosu (Tokyo) Market experienced price collapses to 51% of commodities, Rungis (Paris) 36%, Mercamadrid (Madrid) 19%, Mercado La Nueva Viga (Mexico City) 35% and the Portland Fish Exchange (Portland, Maine) 32%. Collapse magnitude varied from 11% to 79% of the 5‐year average price. Average collapse duration ranged from 13 to 24 weeks with some commodities (4%–22%) remaining collapsed at the end of 2020. For markets where volume data were available, collapses were also noted (59% of commodities in Toyosu, 10% in Mercamadrid and 19% in Portland Fish Exchange); in these cases, the volume collapse was more severe than the related price collapse. To better detect, anticipate and respond to future shocks, we recommend that relevant government agencies conduct comprehensive economic reviews of the COVID‐19 pandemic throughout the seafood supply chain, including the outcomes of emergency measures, short‐ and long‐term implications of market volatility and identify areas of supply and labour vulnerabilities.

Molecular dynamics simulations of the distance between the cavitation bubble and benzamide wall impacting collapse characteristics

The cavitation process has become a promising wastewater treatment technology. The use of bubble collapse can effectively degrade the benzamide in wastewater. However, the mechanisms of bubble collapse and pollutant wall cannot be explained accurately. In this study, models with different distances (d) from the cavitation bubble to the benzamide wall are established to understand the relationship between the distance from the cavitation bubble to the wall and the collapse characteristics. The TIP4P-FB water model and the ReaxFF are selected to study the dynamic characteristics and pressure field variation rule of bubble collapse, and compares it with R–P equation derivation. The results show that the bubble in the middle of the parallel walls has the largest change rate of the volume during the initial stage of the collapse. In the acceleration stage, the closer the bubble is to the wall, the higher the change rate of the bubble volume is. The longer the time in the maximum pressure field is, the greater the maximum pressure is. The shape of the bubble far from the wall is relatively smooth, and the spherical bubble gradually develops into an irregular ellipsoid shape. When d < 1.59 R0, the wall is in the maximum pressure field released through bubble collapse. The change rate of the volume and the change of the maximum releasing pressure in the simulation are consistent with the rule of the derivation of the R–P equation. The simulation results are fully verified.

Gravitational collapse involving electric charge in the decoupling limit of the dilatonic Gauss–Bonnet gravity

The paper discusses gravitational collapse of an electrically charged scalar field in the decoupling limit of the dilatonic Gauss–Bonnet gravity. The emerging spacetimes contained Schwarzschild black holes for sufficiently big scalar fields self-interaction strengths. Dependencies of the collapse characteristics on the dilatonic and Gauss–Bonnet parameters turned out to be similar in the case of black hole masses and radii as well as their time of formation in terms of retarded time. In the cases of masses and radii minima were observed, while in the remaining case a maximum existed. The electric charge of the emerging black holes possessed a maximum when measured versus the dilatonic coupling constant and was strictly decreasing with the Gauss–Bonnet coupling. The times of formation and charges of black holes decreased, while masses and radii increased with the self-interaction strengths of the dynamical fields. Values of the energy density, radial pressure, pressure anisotropy and the collapsing scalar fields were the biggest along the hypersurface of propagation of the scalar fields initial peaks. For big values of the Gauss–Bonnet coupling constant, an increase in their values was also observed in the vicinity of the central singularity within the whole range of advanced time. Non-zero values of the dilaton field outside the black hole event horizon may indicate a formation of a hairy black hole. The local temperature calculated along the apparent horizon was increasing for late times of the evolution and exhibited extrema in areas, where the dynamics of the gravity–matter system was observed.

Role of wall temperature on cavitation bubble collapse near a wall investigated using thermal lattice Boltzmann method

The thermal lattice Boltzmann method can be adopted to simulate cavitation bubble collapse in heating or cooling systems. The numerical results satisfy Laplace's law and are consistent with temperature solutions derived from the Rayleigh–Plesset equation. In this paper, in order to study the effects of wall temperature on a collapsing bubble, a calculation model for a cavitation bubble near the heated/cooled wall is established. The influence mechanism of the micro-jet and the cavitation bubble itself on the solid-wall heat transfer, and the thermodynamic behavior characteristics of the cavitation bubble collapse near the wall are obtained. Adjusting the wall temperature Tw also affects the thermal effects of cavitation. Furthermore, A dimensionless temperature parameter η is introduced to study the heat transfer intense of the model. The influence of λ, Δp and R0 on the heat transfer intense are studied and analyzed. The results show that the optimal λ, Δp, R0 and Tw values can be used to enhance heat transfer and realize heating or cooling treatment of different surfaces.

Spray collapse characteristics of practical GDI spray for lateral-mounted GDI engines

Spray collapsing and plume merging processes were investigated using a lateral-mounted gasoline direct injection (GDI) injector with a practical 'triangular' spray pattern. High-speed diffusive back illumination extinction imaging followed by computed tomography reconstruction was applied to understand the spatiotemporal plume dynamics under engine-like conditions. The spray chamber and injector conditions include (1) cold, subcooled standard temperature and pressure (STP) used by the injector manufacturer, (2) practical gasoline fuels with full-range distillation, (3) flash-boiling with fuel temperature and vacuum gas pressure, and (4) high gas pressure and temperature typical of injection during compression. The novel experiments permit tracking of plume merging at different times and axial distances downstream of the nozzle. A triangular 6-hole pattern, which is widely used in lateral-mounted GDI engines, was found to be prone to having the centrally located plumes move close to each other thus leading to spray collapse with these plumes at all practical test conditions (2)–(4). Variations of air entrainment and local pressure with different conditions were identified as dominant factors for the timing and position of spray collapse.

Characteristics and Evolution of Tunnel Collapse in Fully-Weathered Coastal Red Sandstone Strata

Xu, H.; Shao, Z.; Chen, C.; Wang, Z.; Cai, L.; Li, Z., and Huang, C., 2022. Characteristics and evolution of tunnel collapse in fully-weathered coastal red sandstone strata. Journal of Coastal Research, 38(2), 289–301. Coconut Creek (Florida), ISSN 0749-0208. Understanding characteristics of tunnel collapse and its evolution is the premise of effective prevention and control. Fully-weathered coastal red sandstone is widely distributed in coastal areas, and the characteristics of tunnel collapse under this stratum are not clear. This paper studies characteristics of tunnel collapse and its evolution by conducting a model test of tunnel excavation in fully-weathered coastal red sandstone with digital image processing, where the whole process of rock mass failure, displacement, and strain variations are studied. The results show that: (1) the instability failure of the fully-weathered coastal red sandstone rock mass is a progressive process under the load. Three major collapses occur consecutively, where the first and the second start at the arch foot and arch waist, respectively; both manifested as cracks developing upward to the middle until the cracks penetrate. The third is mainly manifested as the collapse of rock mass block above the tunnel crown. (2) The displacement and shear strain around the tunnel increase first with the load and then stabilize. The vertical displacement is more significant than the horizontal displacement. Tunnel crown is where the vertical displacement increases the fastest and accumulates the most, which directly threatens the rock mass stability and thus deserves special attention. The arch waist has the most intense change of shear strain. (3) All three collapses end up forming a stable balanced arch. The three collapses show the evolution that the foot of the balanced arch gradually moves horizontally outward, and the height of the balanced arch gradually expands upward. The shape of the balanced arch can be well fitted by a parabolic function. Practical suggestions on tunnel collapse prevention and control of fully-weathered coastal red sandstone are also put forward.

The Effect of Surface Geometry of Solid Wall on the Collapse of a Cavitation Bubble

Abstract The objective of this paper is to reveal the influence of different surface geometric conditions on the dynamic behavior characteristics of a laser-induced bubble collapse. A high-speed camera system was used to record the oscillation process of the laser-induced bubble on plane solid walls with different roughness and a wall containing reentrant cavities full of water or gas. The focus is on the quantitative analysis of the morphological characteristics of the cavitation bubble near the solid wall under different surface forms during the first two oscillation periods. The results show that the dimensionless ratio γ, defined as the distance from the center of the bubble to the wall divided by the maximum radius of the bubble, has a great influence on the change of the cavitation shape in the direction of the vertical wall. Different surface geometries without gas in our cases have no significant effect on the collapse time of cavitation bubbles. While for the surface containing gas, the direction of movement of the bubble accompanying the microjet will greatly change during the collapse of the cavitation bubble, and the collapse time seems to be independent of the dimensionless ratio γ. These achievements shed the light for engineering to avoid the damage of the microjet caused by designing suitable surface geometry.

Analysis of Instability Mechanism and Induced Cause of Urban Pavement in Xining City, China

As a large human gathering place, the city directly causes huge property losses and casualties due to the ground collapse accident every year. In order to explore the causes and damage characteristics of urban ground collapse, taking Xining City, Qinghai Province, as an example, this paper analyzes the accidental factors causing ground collapse through on-site geological exploration and then expounds the deformation characteristics of urban ground collapse by using the numerical simulation method of Fluent and PFC. Using the collapsible balance method, it is obtained that the insufficient thickness of the top plate of the Loess Soil Subgrade in the collapse pit area is the inevitable factor causing the final collapse. The results show the following: (1) The failure of water supply pipe is an accidental factor leading to the formation of underground cavity, and the ground collapse accident is hidden, sudden, and of high risk, and its deformation and failure development process is slow. (2) The critical thickness of the roof above the air raid shelter is about 22 m, and the actual thickness is about 11.6 m, which is prone to deformation and uneven settlement, which is also an inevitable factor causing ground collapse. (3) The numerical simulation study shows that the final formation deformation range is about 16 m. At this time, the height of the formed cavity is about 9 m. The plastic zone tends to develop around, and the maximum settlement position appears above the air raid shelter. (4) The collapse process includes four stages: water supply pipeline leakage, underground cavity formation, collapse critical state, and ground collapse. This research and analysis provides theoretical guidance and scientific basis for the investigation, measurement, detection, and monitoring of various underground pipe networks of urban roads.

Analysis of Characteristics of Roof Fall Collapse of Coal Mine in Qinghai Province, China

This paper presents the roof fall collapse of a coal mine that occurred, causing 20 deaths and 1 injury, in Qinghai Province, China, on 14 August 2021. After the primary investigation of this incident and a brief description of the rescue action undertaken, this report discussed the possible reasons behind this disaster. The fissure water and damaged rock mass are the dominant triggering factors of this incident. Little concern for risk assessment and monitoring systems is one of the main man-made mistakes. Consequently, the reflections and suggestions are put forward to reduce or prevent the occurrence of roof fall incidents in coal mines. The noteworthy actions that are necessary in coal mine projects are conducting risk assessments based on geological condition and building proper support systems for coal mines considering he situation in situ.

The Effects of Particle Gradation on Salinized Soil in Arid and Cold Regions

Particle size grading impacts salt-frost heaving and dissolution collapse events of salinized soil on northwestern China’s arid and cold region highways. However, the influencing mechanisms remain unclear and the impact of varying particle size grading needs further investigation. Hence, this study focused on these effects and the number of freeze–thaw cycles on the characteristic changes in highway salinized soil in arid and cold regions. Three soil columns with different gradations were prepared to explore the gradation and the number of freeze–thaw cycle affects on salinized soil’s salt-frost heaving and dissolution collapse characteristics. The multi-functional physical simulation platform conducted multiple freeze–thaw cyclic tests in the laboratory. Test results confirmed significant and conclusive effects of gradation and the number of freeze–thaw cycles on salinized soil’s salt-frost heaving and dissolution collapse behaviors. Poorly graded salinized soil with high coarse particle content caused repeated freeze and thaw engineering hazards, significantly affecting salinized soil’s displacement and deformation behaviors during freezing. Contrarily, an increased range of fine particles more easily involved the characteristics of salinized soil during thawing. Therefore, the fourth freeze–thaw cycle was a crucial time node. After four freeze–thaw cycles, the displacement and deformation of original salinized soil and B-grade salinized soil samples (poorly graded with high fine particle content) tended to be stable. In contrast, the displacement and deformation of A-grade salinized soil samples (poorly graded with high coarse particle content) increased the growth rate. The present research results contribute to in-depth knowledge of the effects of gradation and freeze–thaw cycles on the characteristics of salinized soil in northwestern China, providing excellent referenced data support for the prevention and control of highway salinized soil failures and other engineering projects in arid and cold regions of northwest China.

Shaking table test of the single-layer aluminum alloy cylindrical reticulated shell

Aluminum alloys have been increasingly used in reticulated shells due to their favorable properties. A single-layer aluminum alloy cylindrical reticulated shell model with a length and width of 3.6 m is designed to study its seismic performance. A shaking table test is carried out to test the natural vibration characteristics of the model. A dynamic response test of the reticulated shell model is conducted under frequent, rare and severe earthquakes. The difference in the stress characteristics of the reticulated shell affected by two horizontal seismic waves is compared. The acceleration, displacement, and strain responses of the model under different horizontal seismic waves are analyzed, and the collapse and failure characteristics of the reticulated shell model are studied. The non-linear code ABAQUS is used for numerical simulation, and the validity of the finite element (FE) model is verified by comparing the simulation and experimental results. The results show that the bending moment controls the stress of the cylindrical reticulated shell members under a horizontal earthquake. Under rare earthquakes, the reticulated shell model remains elastic. After reaching the plastic stage under a severe earthquake, the reticulated shell retains its high bearing capacity, indicating excellent seismic performance. The joints of the reticulated shell exhibit weakness under stress, thus, it should be considered in the seismic design. The test results show that the single-layer cylindrical reticulated shell has the risk of progressive collapse.