The study of unsteady combustion modes and, in particular, the deflagration-to-detonation transition, is of particular importance for the aerospace industry. Knowledge of the basic mechanisms, as ...well as the criteria for the development of detonation, helps to control this process in the framework of its applications for novel propulsion devices and safety issues. In this paper, a series of calculations are carried out in order to distinguish the role of channel geometry (planar or circular) in the flame dynamics at all the stages of acceleration prior to the deflagration-to-detonation transition. The combustion of a stoichiometric acetylene-oxygen mixture diluted with nitrogen is considered. It is established that in channels with a circular cross-section, the flame front is stretched and the combustion process evolves up to the transition to detonation, in accordance with the experiment. At the same time, in planar channels (slits), the primary flame acceleration leads to the establishment of a quasi-stationary mode. The peculiarities of the compression and rarefaction waves evolution in the cylindrical and planar geometry are responsible for such a difference between the flame dynamics in channels of different geometry. The detonation onset takes place via the formation of a “chocked flame” structure characterized by permanent joint compression and acceleration of the combustion. As well as in experiments the deflagration-to-detonation transition occurs exactly at the flame front.
•Numerical study of flame acceleration in C2H2/O2/N2 mixtures using reduced chemistry.•The effect of the channel geometry on the flame acceleration is demonstrated.•Flame dynamics in planar and circular channels is described.•Detailed analysis of deflagration-to-detonation transition is provided.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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•A single family of star-shaped poly(ethylene glycol)-poly(lactide) photopolymers is proposed to yield biocompatible degradable hydration-based actuators.•Dual-materials ...microstructures are designed and easily printed from two photopolymers resins by stereolitographic digital-light processing.•Modelled actuation is experimentally validated confirming the concept of actuators designed from degradable photopolymers of same nature but distinct swellings.•The similar nature of the two photopolymers ensures a cohesive interface for a rapid actuation in less than a minute.
Actuators are largely used in biomedical applications in the presence of sensitive live cells or biomolecules, which makes actuators triggered by water uptake highly appealing. Dual-material printing and hydration driven expansion is a method of choice to produce such actuators, but mostly rely of non-degradable polymers or on the combination of polymers of different nature that may lead to interface incompatibilities. To overcome this challenge, we report here on two photocrosslinkable resins based on a single family of degradable hydrophilic or hydrophobic star-shaped poly(ethylene glycol)-poly(lactide) copolymers. The two materials are first printed individually and characterized to ensure that their properties enable the printing of dual material objects by stereolithographic digital-light processing. Dual-materials actuators are then printed by sequential switching of the hydrophobic and hydrophilic resin baths. Objects of simple and complex shapes are easily obtained and exhibit rapid actuation (<60 s) upon hydration. The swelling-induced shape changes are accurately reproduced by numerical modeling of the printed geometries using the obtained material swelling properties. This set of results offers new perspectives to develop 4D-printed temporary medical devices.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
This study examines the dynamic system response of a liquefiable deposit retained by a sheet-pile wall, with emphasis on the roles of pre- and post-liquefaction stages of soil response. A recently ...developed constitutive model, SANISAND-MSf, is utilized to simulate the pre- and post-liquefaction cyclic response of sands. The model is a stress-ratio controlled, critical state compatible, bounding surface plasticity model, which incorporates the concepts of memory surface and semifluidized state. The model’s performance is validated using a combination of cyclic simple shear tests and dynamic centrifuge tests from the LEAP-2020 project. A sensitivity analysis is then conducted by varying the base input motion intensity and duration. The results reveal that the amplitude of equivalent uniform base acceleration in pre-liquefaction correlates well with the timing of liquefaction triggering, and the cumulative absolute velocity of the base acceleration during the post-liquefaction stage correlates well with the post-liquefaction displacements. The study highlights the importance of accurately simulating response in the pre-liquefaction stage for the extent and timing of occurrence of liquefaction, which regulates the remaining intensity and duration of shaking, and in turn, affects the post-liquefaction permanent deformations at the system level.
•SANISAND-MSf accurately simulates pre- and post-liquefaction cyclic response of sand•Model validated with extensive element-level and centrifuge tests from LEAP-2020•Validated model used for sensitivity analysis on base motion’s max acceleration and duration•Pre-liquefaction response controls liquefaction triggering extent/timing, post-liquefaction controls permanent displacements•āpre and CAVpost of base acceleration correlate with liquefaction timing and post-liquefaction displacements, respectively
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Overbreak and underbreak are the crucial problems during the blasting excavation of underground tunnels owing to their effects on the construction costs and operational safety. A critical challenge ...facing overbreak and underbreak control is the difficulty in developing guidelines with respect to various and complex engineering conditions. In this study, a series of field measurements of overbreak and underbreak using the FocusS 150 laser scanner were performed in a deep roadway of the Kaiyang phosphate mine, China. The distribution and extent of the overbreak and underbreak surrounding the roadway contour were accurately analyzed in accordance with the collected point cloud data. Subsequently, a simplified three-dimensional model was established to simulate the blasting excavation of pre-stressed roadway using the explicit dynamic analysis code LS-DYNA. A comparison of numerical and measurement results revealed that the proposed model was a reliable tool to simulate the overbreak and underbreak induced by blasting excavation. Thereafter, the influences of uncontrollable geological factors such as in situ stress conditions and controllable blasting factors including contour hole spacing (S), charge concentration (β) and decoupled coefficient (ζ) as well as stemming were further numerically investigated. The simulation results indicated that the lateral pressure coefficient significantly affected the distribution pattern of the overbreak and underbreak, while the stress magnitude contributed to their extents. Moreover, a comparison of the simulation findings and the field measurement data indicated that the minimal extents of the overbreak and underbreak corresponding the optimal contour blasting results were obtained at S = 0.70 m, β = 0.9 kg/m and ζ = 2.5, respectively. Furthermore, the contour blastholes stemmed with sand created smaller damage to the periphery rock mass of roadway and enhanced the utilization efficiency of explosive energy. The research findings of this study provide important implications for similar blasting excavation projects.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
A coupled surface water and variably-saturated groundwater model is developed for a coastal salt marsh (Nueces Delta, Texas USA). To evaluate the relative impacts of common model simplifications, the ...new model is compared against a prior salinity transport model that neglects evaporation and groundwater coupling. Both marsh-scale (at coarse grid resolution) and bank-scale (at fine grid resolution) simulations are used to examine the flux mechanisms in the intertidal zone where soil-moisture evaporation and groundwater fluxes contribute to hypersalinity. New numerical methods provide the groundwater–surface water coupling mechanisms necessary for practical marsh-scale simulations using the two-dimensional (2D) Shallow Water Equations for surface water and the density-dependent 3D Richards equation for groundwater. An asynchronous surface–subsurface coupling scheme is shown to significantly reduce the computational cost of marsh-scale simulations. Comparison of marsh-scale and bank-scale results indicates that a coarse model grid can represent the mechanisms of surface/subsurface salinity flux in the intertidal zone, but likely misrepresents the inundation effects of topography smaller than the model grid. Due to relatively weak tidal amplitudes at the study site, surface-water evaporation is a stronger driver of hypersalinity than surface–subsurface exchange induced by soil-moisture evaporation. The combination of evaporation and groundwater exchange creates small hypersalinity “hot spots” that do not appear in the simulations neglecting these processes. However, including these processes has only a marginal impact on comparisons with field data previously collected in the marsh. Both types of simulations have good agreement for surface-water volumetric transport (as evidenced by water surface levels), but the remaining model-field disagreement in salinity appears to be dominated by biases in salinity transport for oscillatory (tidal, wind-driven) fluxes through narrow channels.
•A 2D surface – 3D subsurface flow model is developed for marsh salinity evolution.•An asynchronous coupling scheme is analyzed to evaluate coupling error.•Surface-water evaporation strongly affects marsh-scale salinity evolution.•Surface–subsurface exchange has a minor role because of weak tidal amplitude.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Plowing refers to the phenomenon by which a landslide displaces and pushes the path material forward. Despite its importance in shaping the dynamics of many rapid flow-like loess landslides, the ...mechanism of plowing is not fully understood. Therefore, this paper presents an improved numerical model based on the material point method (MPM). This model takes into account the interactions between the landslide mass and the path material. The reliability of this model was validated by simulating two granular column collapse experiments involving interaction with an erodible mass. The model was then applied to analyze the plowing dynamics of the Ximiaodian loess landslide in Jingyang County, Shaanxi Province, China. A series of well-designed simulations were conducted to investigate this specific landslide event, contributing to a deeper understanding of the plowing phenomenon in loess landslides. The simulation results show that our model can satisfactorily simulate the plowing process of the Ximiaodian landslide. The plowing process of a rapid-flow loess landslide is proposed to consist of four distinct stages: 1) the collision stage, when the landslide strikes the terrace, resulting in the bending of its strata; 2) the shear failure stage, characterized by significant plastic shear deformation within the bent strata, resulting in the formation of multiple shear failure planes; 3) the steady plowing stage, during which the deformation structure in the affected terrace stabilizes and plowing continues in a steady pattern; and 4) the stopping stage, when the propagation of the disturbed terrace gradually stops. Furthermore, the disturbed terrace zone exhibits three distinct deformation structures. In the rear part, a stable zone develops where the terrace layers are compressed. However, due to the compressive forces exerted by the overlying loess, no significant shear deformation is observed. The middle part is the shear failure zone, characterized by the formation of multiple shear failure planes. The front part is the upheaval zone, where the terrace layers are slightly bent and tilted.
•An improved MPM model is proposed to simulate the plowing process of rapid flow-like landslides.•The plowing mechanism of a real loess landslide is analyzed by the MPM model for the first time.•The plowing process of a rapid flow-like loess landslide consists of four stages.•Three distinct deformation structures are formed in the disturbed terrace zone during the plowing process.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Several mechanisms have been suggested for the formation of flat slabs including buoyant features on the subducting plate, trenchward motion and thermal or cratonic structure of the overriding plate. ...Analysis of episodes of flat subduction indicate that not all flat slabs can be attributed to only one of these mechanisms and it is likely that multiple mechanisms work together to create the necessary conditions for flat slab subduction. In this study we examine the role of localized regions of cratonic lithosphere in the overriding plate in the formation and evolution of flat slabs. We explicitly build on previous models, by using time‐dependent simulations with three‐dimensional variation in overriding plate structure. We find that there are two modes of flat subduction: permanent underplating occurs when the slab is more buoyant (shorter or younger), while transient flattening occurs when there is more negative buoyancy (longer or older slabs). Our models show how regions of the slab adjacent to the subcratonic flat portion continue to pull the slab into the mantle leading to highly contorted slab shapes with apparent slab gaps beneath the craton. These results show how the interpretation of seismic images of subduction zones can be complicated by the occurrence of either permanent or transient flattening of the slab, and how the signature of a recent flat slab episode may persist as the slab resumes normal subduction. Our models suggest that permanent underplating of slabs may preferentially occur below thick and cold lithosphere providing a built‐in mechanism for regeneration of cratons.
Key Points:
Two modes of flat subduction: permanent underplating and transient flattening
Cratonic lithosphere in the overriding plate produces highly contorted slab shapes
Permanent underplating provides a built‐in mechanism for regeneration of cratons
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Co-gasification technology provides a promising solution for the energetic valorization of various biomass feedstocks, especially those not directly applicable for gasification owing to their ...low-calorific values or high ash content, but the complexity of co-gasification technology has put forward challenges to model formulation when using numerical methods to evaluate the performance of the gasifier. In the present work, the Multiple Thermally Thick Particle (MTTP) model is developed and validated for fixed-bed co-gasification process. The sub-phase treatment that extends the conventional Eulerian-Eulerian framework allows calculating the inhomogeneity in the solid phase, and the intra- and inter-particle heat and mass transfer sub-models enable quantitative evaluation of the conversion of different solid fuels with nonnegligible intraparticle gradients. Parametric analyses of moisture content and particle size were performed to evaluate how the degree of difference between each fuel would influence the reaction processes, gasification performances and steady-state operating conditions. Upon changing the moisture content of the fuel mixtures (biomass and MSW) from both 9.0 wt% to 9.0 wt% for MSW and 27.0 wt% for biomass, the maximum temperature difference between the solid particle surfaces of different fuels was nearly 150 K, and the regions of different conversion processes became highly overlapped. When increasing the moisture content of biomass from 9.0 wt% to 27.0 wt% under 1:1 mixing ratio, the cold gas efficiency, volume fraction of H2 and higher heating value of syngas increased from 65.26%, 12.03%, and 6.29 MJ/Nm3 to 68.39%, 15.62%, and 6.44 MJ/Nm3, respectively. Therefore, the quality and efficiency can be improved when increasing the moisture content in a certain range although the overall capacity of the gasifier will decrease. The intraparticle temperature profiles calculated by the MTTP model also revealed that decreasing the particle size from centimeter- to millimeter-level will significantly reduce the temperature difference between the surface and center of the fuel particles, thus accelerating the in-bed reaction rates and increasing the overall capacity of the gasifier. The MTTP model is flexible for various working conditions and solid fuel mixtures, which is a versatile and convenient tool to optimize the complicated co-gasification process.
•A CFD model for co-gasification of thermally thick fuel particles is developed.•The sub-phase treatment allows calculating the inhomogeneity in the solid phase.•Intra- and inter-particle sub-models enable evaluating conversion of different fuels.•Impacts of difference in moisture content and particle size were assessed.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Spectral variations of gravity and topography data show nonisostatic compensation of elevation in the Southeast Carpathians that is consistent with our new residual topography calculations. ...Multidimensional thermomechanical models are created to consider a possible mantle flow component of the surface topography with varying temperature models and crustal configurations. The temperature anomalies derived from large‐scale P wave velocity anomalies and combined temperature model are estimated as input for the parametric numerical modeling experiments. Model results show that a surface uplift (up to ~1 km) develops in the southeastern Carpathians due to the rising hot upper mantle beneath the region. The upwelling flow is also in concordance with observations such as volcanism and enhanced surface heat flow in the region. Subsidence in the eastern part (0.5–1 km over the Vrancea zone and the Focsani Basin) forms in relation to the downgoing Vrancea slab. The findings indicate the significant role of upper mantle structures on the present‐day anomalous topography related to proposed postcollisional tectonics in the Southeast Carpathians.
Key Points
Present‐day upper mantle flows drive the surface subsidence and uplift in the Southeast Carpathians
Spectral analyses of gravity data show nonisostatic compensation of the elevation that is consistent with residual topography calculations
Thermomechanical numerical models satisfy geophysical and geological observations in the region
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
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