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For the drag and heat flux reduction of hypersonic blunt body, a novel combinational spike-aerodisk and channel concept has been proposed. The high pressure air behind the bow shock flows into the channel at the head of the aerodisk, and then sprays out through the lateral jet in the middle of the spike. The Reynolds-averaged Navier-Stokes (RANS) equations coupled with the shear stress transport (SST) k - ω turbulence model have been employed to simulate the flow field. The numerical results reveal that compared with the spike-aerodisk, with the application of the channel, the lateral jet pushes the separated shock wave away from the spike. The range of the recirculation zone between the shear layer and the spike is increased, and the intensity of the reattached shock wave is significantly weakened, so the drag and heat flux reduction properties of the combinational configuration are significantly improved. The influences of the channel convergent half angle and lateral jet location on the flow field, drag and heat flux reduction properties are investigated thoroughly. When the channel convergent half angle is appropriate and the location of the lateral jet is close to the middle of the spike, the drag and heat flux reduction effect becomes better. Besides, with the increase of the Mach number and the decrease of the flying height, the drag and heat flux reduction performance become more significant. In the research range, the combinational configuration in which the convergent half angle is 60° and the lateral jet is located in the middle of the spike has a better overall effect of drag and heat flux reduction, and the effect reaches the best when the Mach number is 6 and the flying height is 20 km. Compared with the spike-aerodisk, the total drag coefficient of the configuration is reduced by 12.95%, and the peak value of Stanton number along the blunt body surface is reduced by 35.19%. • A novel combinational spike-aerodisk and channel concept was numerically investigated. • The combinational concept has better performance in both drag and heat flux reduction. • Effects of channel convergent half angle and lateral jet location on drag and heat flux reduction were studied. • Variation laws of drag and heat flux reduction under different Mach numbers and flight altitudes were analyzed. [ABSTRACT FROM AUTHOR]

Over the years, it has become obvious that simultaneous backfill grouting is of great significance to the design of the tunnel lining and process control of shield construction. It is essential to know the grout pressure distribution around the tunnel lining. The purpose of this study is to seek an alternative method to simulate the grout diffusion process and obtain pressure distribution of different time during simultaneous backfill grouting of tunnel construction. A lattice Boltzmann method (LBM) based free surface flow model is introduced and modified, and a Smagorinsky large-eddy simulation model serves to deal with the small-scale turbulent problem, which is a challenge for LBM to simulate the large-scale real-world engineering. The simulation results obtain the grout filling state with time and pressure distribution around the tunnel lining. Additionally, the grout pressures on site are measured at a ring in line 8 of Chengdu Rail tunnel, and the measurement results are also compared with ones taken from numerical simulation, it is showed that the numerical results are consistent with that of measurement on the whole. Through simulating different grouting strategies, it is concluded that for four-holes grouting schemes, the grouting pressures of upper holes are significant for the grout pressure distribution and should be paid most attention in construction. [ABSTRACT FROM AUTHOR]

On July 20, 2013, a landslide-induced debris flow occurred in Dujiangyan city, China. Eleven houses were destroyed with more than 166 fatalities. Previous literature indicated that the 2008 Ms 8.0 earthquake and a long period of heavy rain contributed to this landslide. The rock slide was initiated and 21% of the rupture mass fell from the cliff. These rocks fragmented when impacting the ground and then entrained the base soil. Subsequently, the volume of rockfall increased by 28%. In an area of flow convergence, a short-lived blockage occurred, and the following outburst triggered a debris flow. Previous field investigations have shown that both topography and bed entrainment affect the landslide-debris flow transformation. However, the dynamic process has not been quantified. In this study, the discrete element method (DEM) considering the dragging and rolling effects was used to perform a back numerical analysis to capture the dynamic processes. The computational results indicate two different entrainment scenarios, plowing and shearing. The former occurred when the rock slide detached from the cliff, and the latter occurred when debris material moved above the colluvium. The landslide transformed into a debris flow during a short-term blockage that occurred in the gradually narrowing channel. During flow convergence, the inertial shearing stress developed due to the inter-particle collision. [ABSTRACT FROM AUTHOR]

Shock drag and aeroheating are major problems faced by hypersonic vehicles. This study proposes a novel three-dimensional model combining spike-aerodisk with a bleed air channel featuring multiple lateral nozzles for drag and aeroheating reduction. The high-temperature and high-pressure air at the stagnation point of the aerodisk is introduced into the channel and ejected laterally through multiple nozzles to modify the flow field structure and reduce drag and aeroheating. In contrast to previous research employing a two-dimensional axisymmetric assumption, our innovation considers the structure of the exit nozzles and the spacing between nozzles. Due to multiple lateral nozzles, the connection thickness between nozzles can lead to asymmetric flow phenomena. Three-dimensional flow field simulation has been employed with the Reynolds-averaged Navier-Stokes (RANS) equations coupled with the shear stress transport (SST) k-ω turbulence model. The effects of the convergence half-angle of the channel inlet, the divergent angle of the nozzle, and the nozzle position on modifying the characteristics of the flow field are studied. Increasing the convergence half-angle of the channel inlet can further push away the reattachment shock, but when it exceeds 60°, the drag reduction performance degrades. Reducing the divergent angle of the nozzle and increasing the number of nozzles can reduce the drag coefficient and the peak value of the Stanton number. However, when the divergent angle is reduced to 10°, the performance of reducing drag and aeroheating is weakened. In the range of research parameters, when the convergence half-angle is 60°, the divergent angle is 15°, and the nozzles are located in the middle of the spike, compared with the plain spike-aerodisk model, the drag coefficient and peak Stanton number of the combined model are further reduced by 17.8 % and 34.8 %, respectively. Our findings confirm that a multi-nozzle can effectively reduce drag and aeroheating while the channel structure is viable in practice. • A new model of lateral jet without gas source is studied by 3-D numerical simulation. • The gas for the lateral jet is coupled with the outside flow. • A distribution form of multiple lateral nozzles is proposed. • A realistic 3-D simulation is conducted, enhancing its practical applicability. [ABSTRACT FROM AUTHOR]

A long-span stadium roof has always been a wind load sensitive system, given its usual complex curved surface. However, there is no definite method for calculating the wind load shape factor of the complex building in the code. Based on this, the standard k − ε model was applied to the computational fluid dynamics numerical simulation of a long-span stadium roof at the wind attack angles of 0°–180°. The pressure distribution on the top and bottom surfaces of the stadium roof and the wind load shape factor were obtained by numerical simulation. The results show that the negative pressure was dominant on the top surface of the roof and the positive pressure was dominant on the bottom surface of the stadium at the wind attack angle of 0°. The ring-shaped curtain wall made the wind field environment more complicated, mainly under the wind attack angles of 45° and 180°. Because of the dip angles at both ends of the roof, the wind pressure distribution at both ends of the roof was opposite to the main region. The maximum wind load shape factors of each region were negative. In addition, the maximum wind load shape factor was at 45°, which was −1.1. The maximum wind load shape factors in regions of R13–R19 were larger, which should be paid attention in design stage. In general, the wind load shape factors were large in the central region and small at both ends. The wind load shape factors of the roof were bounded by 90°, showing an anti-symmetric trend. [ABSTRACT FROM AUTHOR]

Abstract Contact dynamic models for active debris capturing using a net are presented and analyzed using numerical simulations. The contact dynamics are based on two methods: the penalty-based method and the impulse-based method. Both methods apply contact detection algorithms based on the Axis-Aligned Bounding Box. The impulse-based method is, for the first time, being used in a net capturing scenario. Strengths and weaknesses of both models are compared and discussed. Moreover, the results from numerical simulations of target capturing are presented and analyzed to evaluate the effectiveness of the contact dynamic models. It is found that the average difference of bullet trajectories obtained by two models can be restricted within 6% when it compares with the dimension of the net. Highlights • The impulse-based method is proposed for contact dynamics modeling of a net capturing scenario. • The impulse-based method is compared with the penalty-based method using numerical simulations. • The impulse-based method is found suitable by avoiding penetration and a stiff equation system. [ABSTRACT FROM AUTHOR]

This paper investigates the influence of heterogeneity on mechanical and acoustic emission (AE) behaviours of stratified rock specimens under uniaxial compression using a digital image processing (DIP)-based finite difference method (FDM). In the DIP, a developed image segmentation algorithm based on seeded region growing (SRG) is proposed to fully acquire the mesostructure of stratified rock specimens, instead of the traditional threshold value method. To sufficiently capture the heterogeneity of stratified rock, Weibull statistical manner is adopted to describe mechanical properties of each material component. Three schemes are adopted to study the effect of heterogeneity with different homogeneity index and different mesostructure under two compression loading conditions. The results show that heterogeneity has a great influence on the mechanical and AE behaviours of stratified rock. As the homogeneity of material components increases, the peak strength and brittleness of rocks increase, and the macro elastic modulus improves as well. Simultaneously, the AE modes change from swarm shock to main shock. Under the same component content, the macro-property is better while the component distribution is concentrative relatively, especially to the property of strength. For the coupling effect of mesostructure and heterogeneity arising from material components, mesostructure is considered to cause the visible increase of AE counts. And the numerical results agree well with the previously numerical results and experimental data. [ABSTRACT FROM AUTHOR]

By slotting an inlet at the head of the aerodisk, a channel through the spike, and the lateral jet outlet at the middle of the spike, the blunt body with spike-aerodisk can further reduce its aeroheating and drag. In this paper, the numerical simulation method was used to analyze the flow field structure of this spike-aerodisk-channel, the effects of the spike length, the aerodisk diameter, and the channel diameter on the drag and aeroheating performance of this spike-aerodisk-channel configuration were studied. In general, the lateral jet introduced by the channel from the stagnation region of the aerodisk leads to the shear layer separation in advance, pushes the separation shock away from the spike, enlarges the recirculation zone near the blunt body, avoids the interaction between the separation shock and the reattachment shock, increases the distance from the reattachment shock to the surface of the blunt body. The reattachment shock strength of the blunt body is weakened. With increased spike length and channel diameter, drag and aeroheating reduction are improved. With the increase of the diameter of the aerodisk, the aeroheating performance is improved, but the drag reduction performance continues to decline. Compared with the plain spike-aerodisk, the spike-aerodisk-channel is generally conducive to further drag and aeroheating reduction. In the range of research parameters, considering the effect of drag and aeroheating reduction and the structural feasibility, the spike-aerodisk-channel has the best drag and aeroheating reduction performance when the spike length is twice the blunt-body diameter, the ratio of the aerodisk diameter to the blunt-body diameter is 0.3, and the ratio of the channel diameter to the blunt-body diameter is 0.075. Compared with the plain spike-aerodisk of the same size, the aeroheating reduction efficiency is increased by 37.9%, and the drag reduction efficiency is increased by 16.0%. • Drag and aeroheating reduction mechanism of the spike-aerodisk and channel concept under hypersonic conditions was investigated by the numerical simulation. • Three influence factors were analyzed and compared comprehensively. • Combined spike-aerodisk and channel concept is a promising drag and aeroheating reduction technique. [ABSTRACT FROM AUTHOR]

The Sichuan-Tibet Railway traverses the Qinghai-Tibet Plateau in China, where giant landslides occur frequently and densely. Accurately assessing the velocity, runout distance, and influenced area of the potential landslides is one of the nonnegligible scientific and technical issues. This study establishes a dynamic model for the landslide runout assessment along the Sichuan-Tibet Railway. The proposed model is based on the shallow water theory and takes into account the mechanism that the friction is weakening with the increase of velocity, the finite difference method is used to solve the governing equations, and the ideal one-dimensional dam break experiment was used to verify the shock-capturing capacity of the numerical methods. The Lagang ancient landslide, only 500 m away from the Jiacha Station of the Sichuan-Tibet Railway, represents the typical environment and development pattern of landslides in this region. Therefore, the proposed model is applied to discuss its effects on the landslide dynamic process and deposit patterns. Besides, 75 sets of numerical experiments were further carried out to explore the sensibility of the three parameters including peak friction coefficient μ p , steady friction coefficient μ s , and critical velocity V c in this model. The results indicate that μ s determine the lower limit of the friction coefficient, which significantly impacts the landslide runout distance; μ p is mainly acting at the initial and final stage and has less influence on the landslide dynamic. By contrast, V c is the most significant. When the V c is small, the landslide can quickly reach the threshold velocity after the initial, and the dynamic process has a small correlation with the μ p ; when the V c is large, the landslide is difficult to reach the threshold, and the mobility will be limited. It should be noted that the materials, lithology, strength, and micro-cracks of landslides mass formed under the special geological, geomorphic, and climatic conditions in this region may affect the input values when using the friction weakening model on landslides risk assessment. • Established a numerical method for landslide risk assessment in the Sichuan-Tibet railway area • The parameters sensitivity of the resistance weakening model was discussed based numerical tests • Provides a calibration basis and range for the parameters required to apply the model [ABSTRACT FROM AUTHOR]

The two-equation thermal model could be an effective method for the simulation of thermal-hydrodynamic process in industry-scale EGS heat reservoirs. The conventional way of computing the heat transfer rate between rock and fluid in the two-equation model is using Newton’s law of cooling with a constant equivalent solid-fluid heat transfer coefficient. However, the present work reveals that this method is unable to precisely simulate EGS heat extraction, in which the thermal resistance of solid plays an important role and the temperature of fluid is in rapid changing. Instead, we propose an analytical method to determine the heat transfer rate between rock and fluid, in which variations of fluid and rock temperatures are adequately considered. Simulation cases with different meshes or using different thermal models corroborate that the proposed method improves the prediction accuracy of the two-equation model and makes the model to be more applicable for industrial-scale EGS simulations as a larger mesh size is allowed to be used in the simulation. [ABSTRACT FROM AUTHOR]

Bed entrainment changes the rheology of the sliding mass and the topography of the sliding surface, finally influencing the propagation of flow-like landslides. In previous studies, both empirical methods and physically based methods have been used to simulate bed entrainment. However, the influences of bed entrainment on the rheology and topography of flow-like landslides were not deeply explored. In this paper, the physically based model proposed by Fraccarollo and Capart (J Fluid Mech 461:183–228, 2002) is adopted to calculate the bed entrainment rate, and a new method is proposed to consider the rheology change associated with bed entrainment in flow-like landslides. The new rheology change method and the Fraccarollo and Capart model are incorporated into a quasi-3D finite difference code to analyze an ideal case and two typical flow-like landslides. The two real landslides are the Dabaozi landslide and the Dagou landslide in the Chinese Loess Plateau. They represent two different bed entrainment scenarios: the erodible mass is relatively thick in the Dabaozi landslide, while that of the Dagou landslide is relatively thin. The results show that both the topography and rheology changes have a significant influence on the propagation of flow-like landslides: (1) the rheology change mainly influences the run-out distance of a landslide, while the topography change mainly impacts the lateral spreading; (2) entraining soft materials can significantly increase the run-out distance of a flow-like landslide; (3) the topography change can obviously constrain the lateral spreading of those landslides when the erodible mass is relatively thick. In addition, it shows that the rheology change and topography change influence each other in the propagation of a flow-like landslide, and the proposed rheology change method in this paper can properly reflect this interactive process. [ABSTRACT FROM AUTHOR]

In this paper, a modified finite difference model is proposed to simulate the propagation of flowslides. Modifications of the new model are conducted by calculating the lateral pressure coefficient k in the sliding mass and the entrainment and centrifugal effect during the transport process. The strength parameters are modified based on the size of the entrainment to consider the change in the landslide strength due to material mixing. Two dam break problems are simulated to test the accuracy and stability of the numerical scheme, and the results show good agreement with the analytical solutions and the measured data. Then, the model is used to analyze a typical flowslide: the Dagou landslide in Gansu Province, China. The model can accurately predict the details of the motion of the landslide, especially behaviors such as turning along the meandering gully and thrusting on the gully slopes due to centrifugal force. [ABSTRACT FROM AUTHOR]

Forecasting the rapid intensification of tropical cyclones over offshore areas remains difficult. In this article, the Weather Research and Forecast (WRF) model was used to study the rapid intensification of Typhoon Haikui (1211) off the shore of China. After successful simulation of the intensity change and track of the typhoon, the model output was further analyzed to determine the mechanism of the rapid change in intensity. The results indicated that a remarkable increase in low-level moisture transportation toward the inner core, favorable large-scale background field with low-level convergence, and high-level divergence played key roles in the rapid intensification of Typhoon Haikui in which high-level divergence could be used as an indicator for the rapid intensity change of Typhoon Haikui approximately 6 h in advance. An analysis of the typhoon structure revealed that Typhoon Haikui was structurally symmetric during the rapid intensification and the range of the eyewall was small in the low level but extended outward in the high level. In addition, the vertically ascending motion, the radial and tangential along wind speeds increased with increasing typhoon intensity, especially during the process of rapid intensification. Furthermore, the intensity of the warm core of the typhoon increased during the intensification process with the warm core extending outward and toward the lower layer. All of the above structural changes contributed to the maintenance and development of typhoon intensity. [ABSTRACT FROM AUTHOR]

• PEMFC of zigzagged flow field configuration with contrary arrangement is simulated. • Detailed characteristics of the flow field configuration are investigated. • The PEMFC performance is significantly improved in high current density regions. • Quantitative analysis reveals the flow field configuration improves oxygen transport. • Uniformity index analyses find the flow field makes key quantities more uniform. Flow field configuration of a proton exchange membrane fuel cell (PEMFC) is crucial to its performance enhancement because it determines the distribution of reactants and reaction products. This paper numerically investigates a zigzag flow field with a contrary anode/cathode arrangement (ZFFCA). First, a three-dimensional numerical model is developed and validated against the published experimental data of a PEMFC that operates under low-humidity conditions. Then, the behavior of the contrary arrangement design is analyzed and compared with the zigzag parallel flow field (ZPFF) and straight parallel flow field (SPFF) designs. The model predictions show that the ZFFCA and ZPFF flow field designs provide more uniform distributions of oxygen, water content, temperature, and current density compared to the SPFF design, while the ZFFCA configuration is found to exhibit the most uniform distributions. More importantly, besides the enhanced transport along the flow direction in-between the underneath-land and underneath-channel regions in zigzag-shaped channels, the ZFFCA configuration is found to further reduce the mass transport resistance of reactants and boost up the heat/mass transfer rates. Additionally, the findings show that the positive effects of the ZFFCA configuration can further increase under higher relative humidity and larger operating pressure conditions, indicating that the ZFFCA design might be a more advanced option for the PEMFC stacks. [ABSTRACT FROM AUTHOR]

Many flow-like landslides entrain material from their paths during motion. At the flow front and along the lateral margins the sliding mass can plow into the path material pushing or entraining the existing soil. Although plowing can be a dominant mechanism for landslide mobility, little attention has been paid to this phenomenon in comparison with other entraining mechanism such as basal scouring. Therefore, establishing a suitable mathematical description is still a challenge. In this paper, a two-layer finite difference model is proposed to simulate frontal plowing. The frontal erodible mass and the sliding mass are simplified as two separate layers based on the assumption that they are immiscible in their propagation processes. The interaction (i.e., thrusting and shear) between the two layers is simulated by the normal force and shear force acting on the two-layer interface. The governing equations for the two-layer model are deduced from the mass and momentum conservations of a soil column and transformed into a finite difference form for numerical solving. Then the proposed model is tested in the back analysis of the Ximiaodian landslide which is a typical loess flow-like landslide located at the south bank of the Jing River, China. The modeling results show that frontal plowing has significant influence on the propagation of this landslide, especially on the final topography of the deposit. Without considering this effect, the thickness of the final deposit tends to be underestimated, while the propagation duration, area and distance are likely to be overestimated. The proposed model can provide more accurate and reliable simulations for rapid flow-like landslides with frontal plowing phenomenon. • A mathematical model was proposed for depicting frontal plowing in flow-like landslides. • The run-out and frontal plowing processes of the Ximiaodian landslide were analyzed by the model. • Frontal plowing impeded the motion of this landslide, but it also caused the rapid lateral spreading of the terrace. • The modeling results indicate that the proposed model performs well in simulating frontal plowing. [ABSTRACT FROM AUTHOR]