Transfer Zone Research Articles

Three-Dimensional Lithospheric Electrical Structure beneath the Handan-Xingtai District, North China: Implications for Tectonic Control of Skarn-Iron Mineralization

In this study, we determined the lithospheric electrical structure beneath the Handan-Xingtai district and its adjacent regions using magnetotelluric sounding data. To the west of the Handan-Xingtai district, the crust and upper mantle beneath the Taihang Mountains are mainly characterized by high resistivity (>1000 Ωm, which we interpreted to be the relic cratonic lithosphere. In contrast, the lithosphere beneath the North China Plain to the east shows high-conductivity features (<100 Ωm) overall, which may indicate that it has suffered significant modifications. Additionally, other geological and geophysical studies suggested that this district was located in a significant boundary zone where the lithospheric thickness, temperature and geochemistry properties sharply changed. Combined with our resistivity model, we attributed this to the different degrees of lithospheric modification. Specifically, since the late Mesozoic, the subduction, roll-back and dehydration of the Pacific slab caused an unsteady asthenospheric flow and upwelling; therefore, the deep-derived melts and fluids concentrated within the uppermost mantle had even underplated or intruded into the crust, while this process had a negligible effect on the Taihang Mountains. Small-scale mantle convection and upwelling are likely to occur in this kind of transfer zone of lithospherice properties, leading to mantle-derived melts and fluids transporting upwardly near the surface, which was confirmed by the significantly enhanced conductivity beneath the ore district in our resistivity model. During this process, Fe derived from mantle-source magma or relic Precambrian metamorphic basement beneath the Taihang Mountains was extracted and emplaced along with the Yanshanian magmatism.

Computational analysis on solar air heater with combination of alternate dimple protrusions and intrusions on absorber plate with one rounded corner triangular duct.

This study focuses on improving heat transfer by converting one of the corners of the duct to a rounded structure. To study the effect of dimpled shaped protrusions and intrusions on the rounded corner triangular duct with a constant radius of curvature by varying relative streamwise distance (z/e) with a constant transverse distance x'/e = 10,14 and 18. Steady-state, turbulent flow heat transfer under thermal boundary conditions is to be analyzed by varying different Reynolds numbers (5600 to 21000). The duct with dimple-shaped protrusions and intrusions is compared with a simple triangular duct. Optimization of relative horizontal distance (z'/e) by keeping constant protrusion to protrusion distance as z/e = 28 and relative transverse distance as x/e = 10, 14, and 18. It was noted that there was a significant loss in friction and a rise in heat transfer. The relationship between friction factor and Nusselt number was formulated using operating and roughness parameters, using the data collected from the numerical investigation. The friction factor increases significantly with roughness elements, and it is maximum for x'/e = 20 at a low Reynolds number. Nusselt number increases with roughness elements, and it is maximum for x'/e = 14 for all Reynolds numbers and all the models. Enhancement of Nusselt number is due to increase of local heat transfer because of local vortex neat heat transfer zone. The maximum outlet temperature is obtained at a low Reynolds number. The maximum temperature of the heated surface is obtained for Rc = 0.67h and the minimum for Rc = 0.33h.

Oblique rifting along transfer zones: The structural evolution model revealed by physical modeling

Oblique rifting is a common process that acts during the rupture of continental masses and can evolve to the passive margin stage. The inter-rift (or intra-rift) interaction can occur by transfer zones (TZs). These zones can be formed at the most diverse scales and, on a large scale, can result in the development of oblique rifts. To understand how TZs nucleate and evolve at the plate scale, we simulated, through physical modeling, the development of oblique transfer zones that connect two parallel rifts (with no lateral overlap) developed orthogonally to the extensional direction. Our results showed that obliquity and rheology could play an important role in the structural architecture of rifts that originated in such a structural environment. When the obliquity ranges from low to intermediate (i.e., 20°≤ α ≤ 45°), these rifts can be compartmentalized into two main structural domains - extremity, and central regions - with diachronic evolution and distinct kinematics. Extremity regions are characterized by oblique-slip deformation with intense rotation/tilting of the substrate. The central region is dominated by transcurrent (and oblique-slip) deformation with the presence of marginal plateaus, pull-apart, and oblique basins. Small variations in the obliquity (around 5°) are enough to affect parameters like faults' dip and geometry, and depocenters’ width and depth, thereby promoting changes in the morphology, geometry, architecture, and configuration of TZs. In a more mature stage, and on a continental scale, the TZs evolve into oblique rifts whose margins are composed of oblique and transcurrent fault segments (transfer/transcurrent) that together define a typical zig-zag geometry. The sizes and numbers of these segments depend on the obliquity and the rheology. Transcurrent fault segments are more common when the obliquity is 20° and 25°, in the model with quartz sand only. The modeling data presented here can be compared with the equatorial Atlantic margin of South America, assuming that it may represent an important plate-scale oblique transfer zone (20°) developed between the South and Central Atlantic.

Structural inheritance and style within the Getic Depression, South Carpathians, Romania

The Carpathians are part of the Alpine orogen, and the Getic Depression (or Getic fold belt) is located to the south of the South Carpathian. Underthrust beneath the fold belt is the Moesian Platform lower plate. This foreland depocenter can reach a depth of up to 10 km and evolved in an oblique convergent setting from latest Cretaceous-Paleogene and was shortened during the Badenian-middle Sarmatian (middle to late Miocene, 16–8 Ma) and Pliocene to recent. Thus far, in previous publications, the role of the structural grain of the lower plate was poorly constrained. For the fold belt, contrasting interpretations implied a range of shortening magnitudes and contrasting fault pattern. This contribution shows seven balanced cross sections that rely on seismic reflection and well data. One section, just outside and to the south of the fold belt, gives insights into the fault network of the Moesian Platform. In that section we see 35 km of north westward directed normal sense extension that creates a set of rotated fault blocks. Growth strata within the half grabens attest to Permo-Lower Triassic extension age. The individual normal faults merge at depth into a common detachment that rises monotonously towards the east and forms a domal-shaped, arched detachment. This is the structural grain that we project down plunge towards the north beneath the fold belt. The interpreted six sections that lie in the tectonic transport direction show that structures in the western part of the Getic fold belt are compatible with the inversion on the underlying Permo-Lower Triassic extensional fault. Ubiquitous truncation of Oligocene strata by overlying units suggest inversion started during late Oligocene (intra-Burdigalian). The Badenian-Sarmatian shortening further deforms the pre-existing contractional features and the shortening increases from 5 km on the west to at least 17 km on the east. NW-SE oriented transfer zones with normal faults separate the fold belt domains with diverging displacement vectors and eastward increasing shortening. Two main salt levels within the fold belts’ sediment pile are laterally discontinuous hence they only have local significance in the deformation. The frontal part of the fold belt consists predominantly of Badenian-Sarmatian synkinematic units as the fold belt propagated into the foredeep units, this interpretation requires less shortening in the frontal structures compared to earlier solutions. Due to the lack of characteristic features on the studied sections, we infer that the Getic fold belt did not evolve as a transtensional depocenter during the lower Miocene as suggested by earlier publications.

Insight into hydrodynamics and heat transfer characteristics in a gas–solid spout fluidized bed from a multiple zone view

In this work, the hydrodynamics and heat transfer characteristics within a gas–solid spout fluidized bed were investigated from a multiple-zone view by employing the coupled computational fluid dynamic and discrete element method. Results show that both the axial and radial particle mixing rates are accelerated with the axial particle mixing rate much faster than the radial one when increasing the spouting gas velocity. Besides, the particle-scale and the multiple-zone heat transfer analyses show that the annulus zone makes the major contribution to inter-particle conduction with the particle–particle conduction and the particle–fluid-particle conduction heat fluxes taking up about 64 % and 73 %, followed by the fountain zone taking up about 28 % and 22 %, respectively. As for the particle–fluid convective heat transfer, the spouting and annulus zones make almost the comparative contributions being about 38 %, followed by the fountain zone being less than 24 %. Moreover, the full-bed time-averaged heat transfer analysis shows that the particle–fluid convective heat transfer plays a dominant role in the heat transfer process in the spout fluidized bed with the particle–particle conductive and the particle–fluid-particle conductive heat fluxes being about 0.1 % and 1 % of the particle–fluid convective heat flux. The results of this study can provide an efficient theoretical reference for the gas–solid flow-mixing-heat transfer processes optimization and intensification of spout fluidized beds.

The potential of direct air capture using adsorbents in cold climates.

Global warming threatens the entire planet, and solutions such as direct air capture (DAC) can be used to meet net-zero goals and go beyond. This study investigates using DAC in a 5-step temperature vacuum swing adsorption (TVSA) cycle with adsorbents' Li-X and Na-X, readily available industrial zeolites, to capture and concentrate CO2 from air in cold climates. From this study, we report that Na-X in cold conditions has the highest known CO2 adsorption capacity in air of 2.54mmol/g. This combined with Na-X's low CO2 heat of adsorption, and fast uptake-rate in comparison to other benchmark materials, allowed for Na-X operating in cold conditions to have the lowest reported DAC operating energy of 1.1 MWh/tonCO2. These findings from this study show the promise of this process in cold climates of Canada, Alaska, Greenland, and Antarctica to be part of the solution to global warming.

Strain Partitioning and Localization Due To Detachment Heterogeneities in Fold‐and‐Thrust Belts of Progressive Arcs: Results From Analog Modeling

AbstractAlthough most arcuate orogens are deformed as progressive arcs—curvature is acquired during shortening‐, they have been scarcely simulated by analog modeling. To investigate factors that control the growth of progressive curves in fold‐and‐thrust belts, we developed seven analog models where the backstop shape changed over time, and distinctive geometric heterogeneities were set in the detachment layer. These heterogeneities, often described in natural cases, include diapirs, thickness lateral variations (including pinch‐outs) of the viscous detachment layer as well as frontal pinch‐outs. Our results show that strain was partitioned between shortening structures showing radial transport directions, and both normal and oblique strike‐slip faults that accommodated arc‐lengthening. The location of any heterogeneity conditioned the nucleation of structures and thus, the wedge evolution and its resulting geometry. The presence of both diapirs and frontal silicone pinch‐outs favored the stagnation of the deformation front, and the subsequent wedge thickening up to reach the supercritical angle. Both diapirs and thickness lateral variations of the viscous layer localized arc‐parallel stretching. In addition, their configuration determined the amount and distribution of salients and recesses along the arcuate belt, diapirs and more frictional detachments favoring thicker wedges and less frontal propagation. The differential displacement between salients and recesses was accommodated by strongly partitioned transfer zones, localized by the boundaries between distinctive detachment domains. These results may be useful to investigate geometric and kinematic changes along natural progressive arcs such as the Gibraltar, Sulaiman and Zagros cases.

Regional-residual separation and enhancement methods applied to regional analysis of potential data: Structure of Florianopolis and Rio de Janeiro fracture zones in the western South Atlantic

Topographic, gravimetric and magnetic data has been employed to map regional tectonic elements in the South Atlantic presenting major oceanic tectonic structures which had previously lacked continuity when approaching the continental margin. The creation of such contoured maps has proven that numerical transform methods involving regional/residual separation and derivatives of gravity and magnetics can enhance geophysical signatures and unveil hidden structures, especially in the transition from the continental margins to the oceanic basin. In assessing the tectonic trend of the Florianopolis and Rio de Janeiro fracture zones close to the Brazilian continental margin, the fracture zones change direction from E-W in the oceanic region to NE-SW in the continental margin, probably displaced by the cretaceous hinge line in the northern portion of the Santos Basin. The continental structures associated with possible transcurrent and transfer zones that gave rise to the fracture zones of Rio de Janeiro and Florianopolis, probably played an essential role in the evolution of both the SE margin of the Santos Basin and the African conjugated margin. Analysis demonstrates the magnetic and gravimetric signatures of fracture zones can serve as important constraints for reconstructing continental margins in the rift and post-rift.

Understanding the Caviahue-Copahue volcanic complex through kinematic solutions, paleotensors and analogue modelling

This work aims to study the interaction between two of the most representative structural systems controlling the Caviahue-Copahue volcanic complex. To achieve this objective, a structural analysis based on outcrop-scale fault-slip data field surveys and analogue models were carried out. The deformation regime acting on the studied area was characterized, and the associated paleostresses were obtained from the kinematic data inversion.The performed analysis in Caviahue-Copahue volcanic complex allowed to define two main sets of faults controlling the deformation of the area: NE-SW to ENE-WSW, and WNW-ESE to NW-SE, respectively. The first group comprises high-angle normal faults, resulting in a horst-and-graben setting with along-strike lengths up to 2 km. The second group shows strike-slip kinematics with a minor normal component. These NW-SE faults are related to the Miocene-Pliocene fissure-related volcanism and define the major caldera axis direction. In the geothermal area, the obtained paleostress orientation shows a consistent vertical σ1, denoting a local extensional regime. Regarding the geothermal field, the NE-SW extensional fault system is proposed as the main circulation pathways for hydrothermal fluids rising to the surface. The major NW-SE faults would act as barriers for this circulation.The set of analogous experiments was used to contrast the obtained local structural kinematic results. Two non-coaxial extensional events were established to achieve a local scale approach to the structural configuration observed in the area. Simulations aimed to understand the structural behavior of the superposition of non-coaxial extensive events; they allowed us to assess the role of the different fault sets surveyed in the field within the system. Particularly, our findings support that the NW-SE-oriented structures compartmentalize the subsequent NE-SW-oriented faults, acting on occasions as transfer zones.

The importance of microbiota and terrestrial inflows in controlling seston C:N:P:O:Si:Ca:Mn:Mg:Fe:K:Na:Cl:S:Cu:Zn stoichiometry of a deep coastal fjord

Comprehensive fjord-systems represent major extensions of the coastline and are therefore important transfer zones of materials from land to ocean. Despite increased terrestrial inflows to fjords due to climate changes, we know little about the effects on the ecosystem, especially biogeochemical cycling. We present novel data on spatiotemporal variations of seston multielement stoichiometry in the Sognefjord, the second longest (204 km) and deepest (1308 m) fjord in the world, relative to environmental conditions and microbiota. Concentration of major elements was highest in the upper brackish layer whereas trace metals and minor elements were highest close to the bottom. Seasonally varying microbiota was an important part of the seston in surface waters. None of the seston C:N:P (molar) annual means at specific depths corresponded to the Redfield ratio (106:16:1). At 5 m, annual means of N/P and C/N were 8.4 and 6.5, respectively, while at depth (50–1220 m) N/P were on scale 3 times higher (21–31) and C/N 3 times lower (1.6–2.6), suggesting alternative N-sequestration mechanisms. Overall, correlations between C-Ca and C-S indicate a strong influence from calcite (CaCO3) and organosulfur producing microorganisms, while correlations between particulate Si and Mg–K–Ca–O at depth are consistent with clay and sinking diatom frustules. Mn concentrations increased strongly towards the bottom, likely from resuspension of MnO2 rich sediments and clay particles. Based on seston concentrations, we arrived at the following stoichiometric relationship: C55N16P1Si3.6Ca3.4O16Fe0.74Mn0.51Zn0.33S0.21Cu0.08Cl1.7Na0.68Mg0.71K0.37, although rarely measured, such information is a prerequisite for evaluating environmental impact on coastal ecosystems, biogeochemical cycling, pollution risk analysis and monitoring guidelines.

Retracing the Africa–Eurasia nascent convergent boundary in the western Mediterranean based on earthquake and GNSS data

In the western Mediterranean, following the intervening continent-continent collision, the subduction of the Tethyan ocean has progressively come to an end or almost in large sectors. Compressional deformation connected with the ongoing Africa–Eurasia convergence has therefore progressively resumed mostly along the southern passive margins of the Mediterranean back-arc basins. The aim of this paper is to trace this nascent boundary and constrain its kinematics through geodetic and seismological data recorded between the Ionian Sea and Gulf of Cadiz, and through pre-existing tectonic data. Based on these data, the nascent plate boundary is drawn, kinematically defined, and compared with the previously identified boundaries in the same region. The nascent boundary is weaving and formed by variably oriented inherited structures. It is characterized by a discrepancy between the general motion of Africa with respect to Eurasia and the local contractional/compressive axes deduced from geodetic and seismic data. The oblique convergence along the nascent boundary matches that recorded in other instances of subduction initiation elsewhere; however, the average convergence rate (∼5mm/yr) in the Mediterranean seems currently too small for such a subduction initiation. Based on the assumption of a future northward tectonic vergence (i.e., Eurasian foreland), the Tyrrhenian, Algerian, and Betic salients, the Oran and Fès recesses, and the Ionian, Trans-Alboran, and Gibraltar transfer zones are identified along the nascent boundary. The latter zones connect salients and recesses through strike-slip displacements. The Algerian offshore hosts a long segment of the boundary characterized by locally increased seismic rate and actual northward vergence that would suggest this area being the first nucleus of subduction initiation in the western Mediterranean, as was previously proposed.

Tectonostratigraphic evolution of the Slyne Basin

Abstract. The Slyne Basin, located offshore NW Ireland, is a narrow and elongated basin composed of a series of interconnected grabens and half-grabens, separated by transfer zones coincident with deep crustal structures formed during the Silurian- to Devonian-aged Caledonian Orogeny. The basin is the product of a complex, polyphase structural evolution stretching from the Permian to the Miocene. Initially, relatively low-strain rifting occurred in the Late Permian and again in the latest Triassic to Middle Jurassic, followed by a third phase of high-strain rifting during the Late Jurassic. These extensional events were punctuated by periods of tectonic quiescence during the Early Triassic and Middle Jurassic. Late Jurassic strain was primarily accommodated by several kilometres of slip on the basin-bounding faults, which formed through the breaching of relay ramps between left-stepping fault segments developed during earlier Permian and Early–Middle Jurassic rift phases. Following the cessation of rifting at the end of the Jurassic, the area experienced kilometre-scale uplift and erosion during the Early Cretaceous and a second, less severe phase of denudation during the Palaeocene. These post-rift events formed distinct regional post-rift unconformities and resulted in a reduced post-rift sedimentary section. The structural evolution of the Slyne Basin was influenced by pre-existing Caledonian structures at a high angle to the basinal trend. The basin illustrates a rarely documented style of fault reactivation in which basin-bounding faults are oblique to the earlier structural trend, but the initial fault segments are parallel to this trend. The result is a reversal of the sense of stepping of the initial fault segments generally associated with basement control on basin-bounding faults.

Volcano‐Tectonic Evolution of the Christiana‐Santorini‐Kolumbo Rift Zone

AbstractLocated on the Hellenic Arc, the Christiana‐Santorini‐Kolumbo (CSK) rift zone represents one of the most active and hazardous volcano‐tectonic systems in the Mediterranean. Although this rift zone has been intensively studied, its tectonic evolution and the interplay of volcanism and tectonism are still poorly understood. In this study, we use high‐resolution reflection seismic imagery to reconstruct the opening of the rift basins. For the first time, we relate the activity of individual faults with the activity of specific volcanic centers in space and time. Our analysis shows a pre‐volcanic NNE‐SSW‐oriented paleo basin underneath the CSK volcanoes, representing a transfer zone between Pliocene ESE‐WNW‐oriented basins, which was overprinted by a NE‐SW‐oriented tectonic regime hosting Late Pliocene volcanism that initiated at the Christiana Volcano. All subsequent volcanoes evolved parallel to this trend. Two major Pleistocene tectonic pulses preceded fundamental changes in the volcanism of the CSK rift including the occurrence of widespread small‐scale volcanic centers followed by focusing of activity at Santorini with increasing explosivity. The observed correlation between changes in the tectonic system and the magmatism of the CSK volcanoes suggests a deep‐seated tectonic control of the volcanic plumbing system. In turn, our analysis reveals the absence of large‐scale faults in basin segments affected by volcanism indicating a secondary feedback mechanism on the tectonic system. A comparison with the evolution of the neighboring Kos‐Nisyros‐Yali volcanic field zone and Rhodos highlights concurrent regional volcano‐tectonic changes, suggesting a potential arc‐wide scale of the observed volcano‐tectonic interplay.

Controlling factors in the interferometric coherence derived from Sentinel-1 images: an example from the Río Chubut Lower Valley, Argentina

In this article, controlling factors on radar interferometric coherence (IC) in a region of the Chubut River are analysed, since its variations could indicate potential sediment transfer zones. Studied control factors are vegetation cover, development of the drainage network, rainfall and winds. The results show that the major control over IC loss is given by rainfalls. A secondary control is exerted by the drainage networks development; whereas the limited changes in the vegetation cover and winds regime would not exert significant control. In addition, a permanent IC loss tendency was recognized in channelized areas whereas temporal IC variations were recognized in non-channelized areas. Finally, as different sectors of the study area under the same known conditions (meteorological phenomena, drainage network and vegetation cover) present different IC variations, the existence of at least a third control factor —likely linked to the geology of the landscape—, is deduced from this research.

Reduction of sulphur dioxide emission into the environment by adsorption on enhanced α-hematite surface.

The top priority of the sustainable development goals is to improve the quality of the environment for better living. Sulphur dioxide is considered more hazardous than any other gases that pollute the environment and harm the well-being of organisms. In 2019, India alone accounted for 21% of the world's SO2 emissions. Strict action is required to reduce maximum levels of SO2 emission to the atmosphere to improve the total air quality. To reduce SO2 emissions more effectively, in this study, α-hematite was chemically activated by using 5% NaOH and C2H5OH with the help of a double bed adsorption column. The adsorbent properties of α-hematite were studied by Brunauer-Emmett-Teller isotherm, which revealed a high surface area (539 m2g-1), and pore size (2.3125nm) and high volume in the pore (0.0293432 cm3mg-1). FTIR confirmed that the SO2 particulate on the surface of the adsorbent with an adsorption capacity of 95%. The operating temperature of 40-50°C was optimal for the chemical adsorption. It was found that the inlet concentration (64mgm-3) of SO2 decreases as the adsorption of SO2 increases. Trace SO2 was well-adsorbed by the adsorbent, which resulted in a mass transfer zone. Freundlich's adsorption spectrum was more fit for low concentrated SO2 than Langmuir isotherm. The results indicate that the environmental emission of SO2 can be reduced with chemically enhanced α-hematite.

Design of Unsteady‐State Fixed‐Bed Processes for Heat Regeneration, Ad‐/Desorption, and Gas‐Solid Reactions

AbstractThis review covers all three unsteady‐state fixed‐bed processes important in chemical engineering, namely, heat transfer from a hot gas to a cold fixed bed (heat regenerator), ad‐ and desorption of a gas for a Langmuir and a linear isotherm, and regeneration of a coked catalyst by coke burn‐off as an important example of a transient gas‐solid process. Albeit of inherent differences, the processes have strong analogies. For example, a moving heat or mass transfer zone, spreading or with constant pattern behavior, is formed. For each case, numerical and suitable analytical solutions for process design either selected from literature or developed in this work are derived and compared. Experimental data, if available, are also considered.

Late Jurassic syn-rift deposition in the Flemish Pass basin, offshore Newfoundland: Evidence for Tithonian magmatism and Appalachian-Variscan sediment sources from quantitative mineral and detrital zircon U–Pb-Hf isotope studies of Mizzen discovery strata

Quantitative mineral and detrital zircon U–Pb-Hf isotope studies of syn-rift sandstone units in the Mizzen F-09 delineation well, northern Flemish Pass basin, were conducted to test competing models for Grand Banks paleogeography and Late Jurassic development of the Newfoundland-Iberia magma-poor rift system. Bodhrán formation (informal nomenclature) strata yield ca. 145–155 Ma detrital zircon grain populations that indicate a late Tithonian (146 ± 1 Ma) maximum depositional age for syn-rift fluvial to tide-modulated fluvial strata in Mizzen F-09 and evidence for Grand Banks rift magmatism to have occurred throughout the Late Jurassic. Late Tithonian tectonic subsidence and magmatism in the northern Flemish Pass basin region were coincident with the onset of necking processes and extreme crustal thinning within the Newfoundland-Iberia rift system. The chondritic to superchondritic Hf isotope compositions of Late Jurassic detrital zircon grains indicate repeated partial melting of lithospheric mantle during rift development, perhaps along master detachment faults or transfer zone systems. Bodhrán formation strata have chemically unstable minerals (plagioclase, potassium feldspar, garnet, muscovite, rutile, staurolite) and late Paleozoic to Paleoarchean detrital zircon age populations that together show provenance from Appalachian-Variscan basement and cover assemblages. A positive correlation between the abundance of metamorphic minerals and unique-aged, mid-Permian (ca. 271–280 Ma) detrital zircon grains from post-Variscan igneous rocks indicate Iberian provenance contributions to Bodhrán formation strata. The new results from Mizzen F-09 are consistent with models for WNW-directed fluvial discharge into the northern Flemish Pass basin and sediment derivation from upper Paleozoic foreland basin or cover assemblages located west of Variscan front, some which may have been stripped off Beothuk Knoll, Flemish Cap, or adjacent highlands.

Identifying critical transfer zones to coordinate transit with on-demand services using crowdsourced trajectory data

This study develops a data-driven approach for identifying critical transfer zones in the city to facilitate the coordination of transit and emerging on-demand services. First, the methods convert the trajectories into a 3 D grid with an optimal cube size. Built upon that, we zoom in and study the trajectory density of each mode in a cube and present the results by heatmaps. After that, we zoom out and aggregate those cube information fragments through the clustering algorithms to explore two critical patterns: the ridesharing swarm (RS) zones where many ridesharing trips go through, and the “sandwich pattern” zones where a transit trajectory dominant zone is sandwiched by two ridesharing trajectory dominant zones. Our numerical analysis confirms that these RS zones are well correlated to the promising areas/corridors for integrating transit and on-demand services; the “sandwich patterns” help discover first/last mile (FLM) zones. Last, we further develop a two-channel deep learning network to predict the variation of the FLM gaps so that adaptive services can be planned. A case study based on the field data of the second ring region of Chengdu, China confirms the effectiveness and capability of our analysis approach.

Development and benchmarking of numerical model in OpenFOAM® for the prediction of channel segregation during columnar alloy solidification

• Benchmark sn-5 wt%Pb alloy solidification problem is simulated using OpenFOAM solver. • Mesh sensitivity analysis is performed to resolve the flow in channels segregates. • Effect of microsegregation and mushy zone models on channels formation is studied. • Scheil's model predicts more negative and positive segregation than Lever rule. • Inertial drag in mushy zone significantly affects the channel segregates formation. In the past, most of the numerical studies on the prediction of macrosegregation and mesosegregation (e.g. channel type segregation) were performed using in-house codes and commercial software, both of which have limitations such as huge license costs, non-availability for general public research etc. In this study, a dedicated CFD solver is developed in an open-source platform – OpenFOAM® for the prediction and characterization of channel segregates in castings. The solver accounts for the fluid flow, heat transfer, species transport, multiscale segregation, solidification and mushy zone drag phenomena that occur during alloy solidification. The developed solver is extensively validated with the reported benchmarked experimental and numerical results for the sn-Pb alloy solidification. Direct numerical simulations (DNS) are performed to resolve the flow field in and around the channels (which are of mesoscopic length scale) for the first time. It is observed that mesh size ≤ 2 d 2 (secondary dendritic arm spacing) is required to resolve the flow in channels and accurately predict their morphology and locations. Further, the effect of different microsegregation and mushy zone drag models on the segregation and morphology of channel segregates is thoroughly investigated. The predicted extent of negative and positive segregation is found to be more (negative segregation ∼ 7.7 wt%Pb and positive segregation ∼ 18.7 wt%Pb) in Scheil’s microsegregation model compared to Lever rule. Furthermore, the inertial drag in the mushy zone significantly affects the convective transport of solute and thereby the morphology and the number of channel segregates.

Investigation of mass transfer model of CO2 absorption with Rayleigh convection using multi-relaxation time lattice Boltzmann method

• MRT-LBM is used to simulate CO 2 absorption with Rayleigh convection. • The characteristics of flow and concentration fields are presented. • The gas-liquid interface division results of Rayleigh convection are presented. • A penetration/surface divergence hybrid mass transfer model is proposed. CO 2 absorption into absorbents is a widely used method to reduce carbon emissions, in which the concentration gradient near the gas–liquid interface may induce Rayleigh convection (RC). Once RC occurs, the mass transfer rate will be significantly enhanced. Therefore, it is necessary to explore the mass transfer enhancement mechanism further and develop a penetration/surface divergence hybrid mass transfer model. In this study, we conduct research on the process of CO 2 absorption into ethanol with RC. Firstly, we use a multi-relaxation time lattice Boltzmann method to simulate the absorption process and obtain the flow and concentration fields. And we also verify the reliability of the numerical simulation results by comparing with the experimental results. Then, we analyze the characteristics of non-uniform flow and concentration fields in RC. Moreover, we divide the near-interface region into diffusion-dominated and convection-dominated mass transfer zones by checking whether the horizontal average velocity is greater than 1.0×10 –4 m∙s –1 . Furthermore, based on the differences in mass transfer mechanisms of the aforementioned two zones, we propose a penetration/surface divergence hybrid model to predict the instantaneous mass transfer coefficient. The prediction results demonstrate that the hybrid model can precisely predict the instantaneous mass transfer coefficient of the entire CO 2 absorption process. Our proposed hybrid model provides a promising way to deal with the complex mass transfer problems with non-uniform flow and concentration fields.