Transition Section Research Articles

Preliminary design and analysis of an afterburner module

In this study, design calculations and calculations of afterburner used in jet engines are presented by evaluating the results of analytical and computational analysis. Afterburner inlet values of 1050 K temperature, 300 kPa pressure and 3.6 kg/s mass flow rate are taken as the design conditions. Maximum length and diameter are 500 mm and 200 mm, respectively, for the sections to be designed as length constraints within the scope of the conceptual design. The two-ring vee-gutter has 1.33 cm in diameter and 4.25 cm high. Jet A fuel is assumed to be injected into the core flow (90 degrees) from the spray bars. The spray is mounted in line with the vee-gutter to optimize the mixing of the flow. Analyses are performed for 4 cm between the spray bar and the vee-gutter. For the study, the GE J79 engine was examined from the literature and taken as a basis for the aerodynamic transition section design. Within the scope of TEKNOFEST 2023 Jet Engine Design Competition, a preliminary design of an afterburner module that can produce 700 pounds of thrust and has a life capacity of 25 hours should be realized in line with the design requirements and constraints. In the light of geometric constraints, one-dimensional combustion calculations of the module are made, and the parts are modelled using the relevant SolidWorks CAD program and these modelled parts are then transferred to ANSYS™ environment and the results and analyses are verified. The afterburner module flow analysis software program ANSYS™ is used to analyse the afterburner operation in both cold operating ranges (i.e. without combustion) using compressible, viscous and standard k-epsilon turbulence model. As a result, the effect of afterburner length on combustion performance is found to be significant. As a result of the calculations, afterburner length is found as 28.14 cm. It is found that the combustion efficiency is 81.5% and the temperature can be increased from 1050 K to 2044 K. The total pressure loss is 14.96% as pressure drop due to the geometric parameters and heat addition. The blockage ratio calculated due to the use of vee-gutter geometry is the most important parameter in the pressure drop. It is found that the jet engine producing 670 lbs (2981 N) of thrust when the afterburner is not working whereas it can provide a significant amount of power increment at the expense of a 50% increase in specific fuel consumption when the afterburner is active as well as providing a 738 lbs (3238 N) with a 10.1% thrust increase. The reason of the enhancement is mainly coming from the mixing effect of the vee-gutter on the flow structure.

ÇİFT-BANT İRİS POLARİZÖR TASARIM VE OPTİMİZASYONU

The structure that transforms a linear polarized signal into right-hand or left-hand circularly polarized signals is called a polarizer. In this study, a dual-band waveguide polarizer used in satellite communications is presented. The waveguide polarizer is designed using iris structures on a square waveguide. The purpose of the polarizer is to transmit the ±45° tilted linearly polarized signal at its input to the output as a right-hand or left-hand circularly polarized wave, and vice versa. At the input of the polarizer, a transition is designed between the WR42 waveguide and the square waveguide. At the output stage, a transition from square waveguide to circular waveguide is designed. In this paper, the design steps of both the polarizer and the transition sections, the optimization parameters, and simulation results are presented in full detail. The simulations are performed with a commercial electromagnetic simulation software, CST Studio Suite. The design operates within the Ka-band, specifically at 17.2 – 21.2 GHz and 27.5 – 31 GHz frequency bands. The insertion loss of the iris polarizer is 23 dB, and the phase difference is less than 15° around 90° for both bands.

Spatial-temporal characteristics of the transient flow field around high-speed trains transiting the subgrade-cutting transition section under crosswinds

High-speed trains (HSTs) transiting subgrade-cutting transition sections in crosswinds have become a common operating scenario. This paper utilizes the Improved Delayed Detached Eddy Simulation (IDDES) turbulence model, considers air compressibility, and establishes a three-dimensional coupled train-subgrade-wind dynamics model. The aerodynamic load (AL) variation rules of trains and discrepancies in the flow field mechanisms when HSTs transit various types of subgrade-cutting transition sections [half cutting and half flat (HCHF), double side cutting (DC), and half cutting and half embankment (HCHE)] under crosswind conditions are revealed using this model. The results indicate the following. (1) The aerodynamic performance deteriorates when trains transit three subgrade-cutting transition sections under crosswinds. (2) As trains enter the transition section from a flat approach, the head car’s AL power spectrum density (PSD) is the largest when operating in the DC case. (3) After the train drives into the subsequent operating scenario, the average of the AL in the DC case is the lowest. (4) In the DC case, a slope of 1:0.75 should be taken as the basis for the design of the corresponding cutting parameters. (5) After the train enters the cutting, the winding flow speed and number of vortex structures surrounding the trains increase significantly.

Modeling of contact thermal resistance in lateral capillary tube-suction line heat exchangers with experimental validation and investigation

This paper studied the lateral capillary tube-suction line heat exchanger (CTSLHX) with different contact types and different geometries. An improved one-dimensional model of the CTSLHX was established, using the CFD model to derive the contact thermal resistance between the capillary tube and the suction tube. An experimental bench was built to test the steady-state heat transfer and flow performance. It was found that the model predicted 87.6 % and 98.9 % of the measured mass flow rate within the error band of ± 10 % and ± 15 %. The prediction error of the CTSLHX heat transfer effectiveness was within ± 10 %. Parametric effects of different operating conditions and structural parameters on the performance of CTSLHX were investigated. Furthermore, experiments were carried out to study the temperature distribution along the transition section between the exit of the capillary tube and the evaporator. The unique temperature increase reveals that it is beneficial for reducing noise by wrapping a layer of rubber around the second increaser fitting.

The Impact of Anisotropic Properties of the Rail Track Superstructure on the Parameters of Dynamic Settlement of Bridge Approaches

Numerous artificial structures, bridges, overpasses, tubes, channels, chutes are operated on railway networks. Artificial structures are considered to have a longer life cycle and thus will need during it overhaul and reconstruction with the use of modern technology. Currently, there is an increase in axial load and traffic speed, the makes even more relevant the solution of tasks referring to dynamic impact of trains on artificial structures and superstructure. See the features of construction and maintenance of rail track sections at the approaches to bridges, the respective problems merit special consideration.The research which results are presented in the article was dedicated to the impact of the anisotropy of the track superstructure on the parameters of the dynamic settlement of sections of transitional stiffness located at the approaches to bridges and built using bottomless box culverts.The research proposed to model the railway track within the transitional section as a set of flat elements of constant thickness, while each of them is regarded as a anisotropic plate supported by deformable foundation with its own deformability rates. By setting boundary conditions for individual fragments of the track structure and varying the anisotropy coefficients that determine the ratio of mechanical characteristics in different directions of anisotropy, it is possible to select necessary rail track stiffness rates for a section at bridge approaches, that paves the way to further research on structural features of designing and arrangement of those structures.

Aerodynamic impact of wind-sand flow on moving trains in tunnel-embankment transition section: from field testing to CFD modeling

The acceleration of land desertification has led to an increasingly serious threat to the operation safety of tunnel entrance in the Gobi and desert regions by wind-sand flow, and it is urgent to study and enhance the running safety of train. Firstly, an ultrasonic anemometer is used to collect the characteristics of wind-sand flow at a tunnel entrance site in Xinjiang, China. Then, based on the Euler multiphase flow and the SST k-w model, the variation difference law of the train running at the tunnel entrance is revealed under the four inflow conditions of constant crosswind, constant wind-sand flow, pulsating crosswind and pulsating wind-sand flow respectively. Finally, the disturbance law of the solid wind barrier at the tunnel entrance on the wind-sand flow and the influence mechanism on the train’s flow field structure and pressure are revealed. The results show that compared with other cases, the pulsating wind-sand flow has the most significant effect on the moving trains’ aerodynamic loads (ALs), and the sand particles carried in the air cause the trains’ ALs to fluctuate within 9.09%. The solid wind barrier has a significant disturbing effect on the wind-sand flow, and the lightweight sand particles follow the air flow over the top of the wind barrier and are not deposited on the embankment during a short period, and the wind-sand flow’s impact on the HSTs is dramatically reduced. The wind barrier changes the HST’s flow field, and the AL fluctuation of the train is sharply reduced. The maximum values of the head train’s AL coefficients are reduced by 46.53–85.75%.

In Situ Investigation of the Dynamic Response and Settlement in the Expressway Culvert–Subgrade Transition Section Using a Vibration Exciter

During the operational phase of the expressway, a significant challenge arises concerning substantial differential settlement in the transition zone connecting the culvert and the general subgrade, affecting its smoothness. In order to address the issue of abrupt stiffness variations within the transition section and to mitigate the occurrence of differential settlement, a gradient pile–reinforced-concrete slab composite foundation was implemented for the first time within an expressway culvert–subgrade transition section. At the same time, an in situ vibration test was conducted through the SBZ30 vibration exciter to comprehensively understand the vertical dynamic responses in the culvert–subgrade transition section under various axle loads and speed conditions. Furthermore, continuous monitoring was conducted to track the long-term settlement of the roadbed. The findings indicate that the utilization of gradient pile–reinforced-concrete slab composite foundations can significantly mitigate the amplitude of the dynamic response parameters. Moreover, dynamic parameters and attenuation coefficients exhibit a gradual reduction as the depth increases. Dynamic stresses, acceleration, and displacements on the roadbed surface exhibited positive correlations with both the axle weight and vehicle speed. However, at deeper depths, the load weight exerted a more pronounced influence. As the speed rose, acceleration decayed faster, affecting a shallower depth. Conversely, the increased load slowed the acceleration decay. The cumulative deformation of the roadbed and the number of excitations followed exponential function characteristics. Settlement values progressively increased while the settlement rate gradually diminished, eventually reaching a stable state, ultimately stabilizing within 4.7 mm. These research outcomes offer valuable guidance and serve as a reference for the implementation of gradient pile–reinforced-concrete slab composite foundations within the culvert–subgrade transition section.

Optimization analysis of thermal–hydraulic features of the 2.5 MW LBE spallation target of CiADS

In an Accelerator Driven System (ADS), the spallation target typically has a power of several megawatts or above. As high-power targets are challenging to design, the targets studied in the past generally had a power of 2 MW or less. For the China initiative Accelerator Driven System (CiADS) under construction, a 2.5 MW lead–bismuth eutectic (LBE) target is planned. In this paper, thermal–hydraulic and structural analyses were performed to optimize the design of the LBE spallation target. As a first step, given other conditions being fixed, the influence of a single parameter on the target performances, i.e., the outlet size, the diameter of the guide tube, the angle of the transition section, and the vertical distance from the origin of the beam window (BW) hemisphere to the upper end of the transition section, were investigated. Subsequently, the multi-factor analysis was conducted by adopting a four-factor and four-level orthogonal test. Results indicated that the target optimized by the multi-factor analysis, performed much better than the original design and that obtained by the single-factor analysis, providing a new approach for the parameter optimization of spallation target. Moreover, detailed analyses showed that the improved target met the thermal–hydraulic and mechanical design requirements.

Computer Modelling of Yarn Winding on Conical Bobbins

The article presents the results of the computer modelling of yarn winding on conical bobbins based on the analytical method of constructing tubular-shaped surfaces as a partial case of channel surfaces using the vector algebra apparatus. It is stated that the guide line takes the shape of a conical spiral line along which the forming moves (in the form of a circle with a diameter equal to the average diameter of the yarn), and is set using the moving Frenet basis. The obtained mathematical models facilitate the building, in MathCAD 3D visualization graphics, of a tubular-shaped surface, which represents the layers of yarn winding on a conical cartridge, and the reinforced yarn, which comprise the core component and the wrapping component, as well as the determination of both the lengths of individual layers of winding and the total length of winding (not including the transition sections). Well-known methods of forming geometric objects and computer modelling were also used in the work. The theoretical studies are based on the basic principles of textile production technology.

Variation and dynamics of soil properties of ordinary chernozem in the Saratov region

Based on data from an agrochemical survey using GIS technologies at test site No. 2 in 2009-2016 within the framework of the general scheme of soil-ecological monitoring of the Saratov region, an assessment was made of the dynamics and spatial variation of soil properties of ordinary chernozem, depending on the steepness and exposure of the slope. Soil and agrochemical characteristics in conditions of a pronounced relief demonstrate a certain dependence on the location and are very variable over time. Soil sampling on an area of more than 2000 hectares using navigation equipment made it possible to obtain agrochemical cartograms in GIS and analyze them using zonal statistics, taking into account a digital elevation model. The spatial variability of soil properties is often lower in leveled areas or short transition sections of the slope, while the maximum variability is noted on steeper slopes. The highest values of indicators are typical for flat watershed surfaces, which are the most fertile, however, the closest relationship between humus and other agrochemical indicators was noted just on steeper slopes. The variability of fertility indicators on differently directed slopes was within 28–36 % for P2O5, 20 % for K2O, and 4–6 % for pH. The greatest differences in the variability of the polar slopes along the survey tours are noted for the content of humus in the soil. In 2009, the coefficient of variation was 19 and 30 %, and in 2016, 11 and 24 % on the slope of the northern and southern exposure, respectively. A retrospective analysis showed that the highest rates of decline were noted for the content of humus in the soil and the reaction of the environment on gently sloping slopes (by 2 and 1.5 times, respectively) relative to the average change in the massif. For mobile forms of phosphorus and potassium, the maximum decrease was noted on gentle slopes.

Evolution Characteristics of Long Time Series of Secondary Perched River in Typical Reaches of the Lower Yellow River

Secondary perched rivers are extensively distributed in the lower section of the Yellow River, and their condition is grave, representing a significant peril to the flood control safety of this region. Consequently, conducting an analysis of their evolution characteristics holds immense engineering importance for ensuring the flood control safety of the lower reaches of the Yellow River. This study focuses on the downstream section of the Yellow River, specifically from Dongbatou-Taochengpu. This research is based on extensive data, including topographic measurements of large cross-sections and water and sand data from Huayuankou spanning from 1960 to 2022. The transverse slope of the beach, which indicates the level of development of the secondary perched rivers, was chosen as the calculation index. To analyze the trend and mutation of the transverse slope, statistical methods such as the Theil–Sen slope estimation, Mann–Kendall test, Pettitt test, and double cumulative curve method were employed. The findings indicate that the average transverse slope along the wandering section (Dongbatou-Gaocun) is 5.81‱, is significantly lower compared to the transitional section (Gaocun-Taochengpu), with an average transverse slope of 8.89‱. Furthermore, the range of fluctuation in the variation in the transverse slope along the wandering section (3.19–8.18‱) is considerably narrower than that observed in the transitional section (2.94–19.51‱). Prior to the implementation of Xiaolangdi, there was a significant increase in the transverse slope. Notably, the transitional section experienced a sudden change in 1975, while the wandering section experienced a sudden change in 1990. The abrupt alteration in the transitional section can be attributed to the substantial variation in the water and sand conditions. Conversely, the sudden change in the wandering section resulted from the insufficient flow rate of the flat beach. However, following the implementation of Xiaolangdi, the rapid increase in the transverse slope was effectively mitigated.

Settlement trend of embankment–bridge transition section reinforced with thermosyphons in permafrost regions

Differential settlement of embankment–bridge transition section (EBTS) is easy to occur in permafrost regions, so it is necessary to carry out a long-term dynamic investigation, maintenance, and reinforcement on EBTS. In this study, settlement characteristics of two EBTSs reinforced by thermosyphons along the Qinghai–Tibet Railway (QTR) in 2010 were analyzed. In addition, the Pettitt test method was used to analyze the time when the thermosyphons showed a significant cooling effect after reinforcement, and the Verhulst model and exponential curve method were used to analyze the long-term settlement trend of an EBTS in the next 10 years. The results indicate that the accumulated settlements and settlement rates of monitoring EBTSs after reinforcement were obviously lower than the requirements of the design code for railway embankments in China. The fifth year after the completion of thermosyphon is the abrupt change point of the settlement data. The maximum difference between the change rate of the settlement rate before and after the abrupt change point is 78.5%. Thermosyphon will make the EBTSs close to the deformation stability after reinforcement for 10 years. Finally, according to the settlement evolution results, the accumulated settlements of the abutment of monitoring sites will be less than 50 mm in the 10 years after 2020. In general, thermosyphon, as a reinforcement measure, can significantly and rapidly slow down the settlement trend of the EBTSs and maintain its long-term stability. This study aims to deepen the understanding of the effect of EBTS reinforcement measures and provide a scientific basis for EBTS reinforcement in permafrost regions.

Effect of process parameters on interface microstructure and performance in laser welding of steel-ZrO2 ceramic

The laser was used to weld the stainless steel and the ZrO2 ceramic. By adding a AgCuTi filler layer for the laser welding. The formation of the reaction products is affected by the mutual diffusion of Fe, Ti and Cu between the base metal and the filler during the welding process, and the diffusion behavior between the atoms is closely related to the heat input during welding. Therefore, the heat input during welding has a direct impact on the Fe–Ti and Fe–Cu metallic compounds in the joint. Referred to the advantages and disadvantages of the above welding methods, and proposed a design scheme of ceramic/steel hybrid joints with transition section. In this study, it was found that although the ceramic side was the fracture area, the overall refinement of the grains in the joint interface was beneficial to the increase of the joint strength. In the welding process, the heat reaching the filler interface is mainly controlled by the process parameters such as laser power, welding speed and laser offset. In this study, the required laser welding parameters were determined by the cross-sectional state of the joint, the microstructure of the interface and the mechanical properties, and then the coupling control of the welding parameters (power, welding speed, offset) with the interface temperature and microstructure was realized. The connection between steel and ceramic was parametrically optimized and the ceramic side was analyzed by interface thermal and mechanical simulation, and the mechanism of the connection was explained.

Investigating the Mutual Feedback between Wind–Sand Fields and a Running Train on the Bridge–Road Transition Section of a Railway

Strong wind–sand flow exerts great potential safety hazards for high-speed train operations. In this paper, we investigate the aerodynamic characteristics of high-speed trains passing through the bridge–road transition section under a wind-blown sand environment. In particular, we adopt the sliding grid method to simulate the changes in aerodynamic pressure on the train surface when the train passes the bridge transition at different speeds and bridge heights. The variation in the aerodynamic lateral force borne by the vehicle body at various times is then obtained. The results reveal that in the wind–sand environment, when a train drives from the bridge to the embankment, the pressure values on both the windward and leeward sides of the train change abruptly, with the most obvious increase in the lateral force of the head car. Moreover, the abrupt change in pressure increases with the speed of the lateral wind–sand flow. The differential pressure force of the train on the embankment is larger where the differential pressure force on both sides of the head train is the largest. When the train is running in the opposite direction, the differential pressure force on both sides of the train decreases. Compared with the lateral wind condition, the lateral force at different positions of the train under the wind–sand condition exceeds that under the non-sand condition. The average increases in the train body are approximately 17.6% (10 m/s), 10.5% (20 m/s) and 9.5% (30 m/s), which will cause passengers to experience an obvious “shaking” phenomenon.

Microbial community diversity and potential functionality in response to dam construction along the Three Gorge Reservoir, China.

River and reservoir bacterial communities are the most basic part of river biomes and ecosystem structure, and play an important role in river biological processes. Yet, it remains unclear how highly regulated dam reservoirs affect both soil and sediment bacterial communities. A temporal distribution pattern of bacterial communities was investigated using Illumina MiSeq sequencing in a transition section of the Three Gorges Reservoir (TGR). In total, 106,682 features belong to the bacteria kingdom, encompassing 95 phyla, 228 classes, 514 orders, 871 families, 1959 genera, and 3,053 species. With water level regulation, Shannon diversity index, and observed species differed significantly, with no significant difference in Simpson evenness. Both in the high water level period (October) and the low water level period (June), Proteobacteria, Acidobacteri, and Chloroflexi were the most abundant phyla. Whereas, based on PCA plots and Circos plot, the microbial community structure has changed significantly. LEfSe method was used to identify the classified bacterial taxa with significant abundance differences between the low water level and high water level periods. KOs (KEGG Orthology) pathway enrichment analysis were conducted to investigate functional and related metabolic pathways in groups. To some extent, it can be inferred that water level regulation affects community growth by affecting the metabolism of the microbial community.

Study of the Design and Mechanical Properties of the Mix Proportion for Desulfurization Gypsum–Fly Ash Flowable Lightweight Soil

In order to solve the global problem of bridge head jumping caused by the insufficient compaction of the roadbed in the transition section of highways and bridges, a desulfurization gypsum–fly ash flowable lightweight soil without vibration, capable of self-compaction, low bulk density, and economic and environmental protection, has been developed. This study selected low-grade cement, industrial waste (fly ash and desulfurization gypsum), and Yellow River silt as the raw materials for the design of the mix ratio of a desulfurization gypsum–fly ash flow-state lightweight soil mix. Through multiple indoor experiments, the influence of cement content, silt content, and the fly ash/desulfurization gypsum quality ratio on its fluidity and mechanical properties was systematically studied. The stress–strain relationship under uniaxial compression was analyzed and the strength formation mechanism was revealed through scanning electron microscopy (SEM). The results show that the mechanical properties of the prepared desulfurization gypsum–fly ash flowable lightweight soil meet the engineering requirements. Increasing both the cement and fly ash content results in the decreased fluidity of the desulfurization gypsum and fluidized fly ash. However, as the mass ratio of fly ash to desulfurization gypsum increases, the fluidity reaches its maximum when the mass ratio of fly ash to desulfurization gypsum is 2:1. Based on the stress–strain relationship test results, a uniaxial compressive constitutive model of the desulfurization gypsum–fly ash flowable lightweight soil was proposed. The model was fitted and analyzed with the test results, and the correlation was greater than 0.96. The high degree of agreement showed that desulfurization gypsum can promote the disintegration of fly ash, thereby increasing the specific surface area. This provides more contact points, promotes the hardening process, and enhances the interlocking force between particles and the formation of cementitious substances, further enhancing strength.

Forming method and cross-section deformation of transition section of finned special-shaped tubes in 3D free bending technology

In 3D free-bending technology, the bending forming of the tube consists of the transition section and the stable forming section. However, because of the continuous movement of the bending die and tube in the transition section, the forming mechanism of the tube in the transition zone is relatively complex and still unclear. In addition, due to the complexity of the cross-section deformation of the finned special-shaped tube (FSST), its application in the heat dissipation pipeline of aerospace vehicles is severely hindered. To address the above issues, in this paper, a 3D free-bending forming process method, which can effectively coordinate the movement of FSST and the bending die in the transition section, was proposed. Meanwhile, an analytical model of FSST bending forming was established, which can effectively characterize the elastic-plastic evolution of the FSST cross-section and match the bending radius with the cross-sectional bending moment effectively. Then, the effectiveness of the process method and analytical model was verified by finite element model (FEM), and experiments. Further, FEM and experiments were used to investigate the influence of the process parameters of the transition section on the forming radius and cross-section deformation of FSST after springback. The results from this study show that reasonable coordination of the rotation speed of the bending die and the advancing speed of FSST in the transition zone can improve the forming quality of FSST.

Field Investigation of the Dynamic Response of Culvert-Embankment-Culvert Transitions in a High-Speed Railway.

The stiffnesses of embankments and culverts differ in the transition sections of high-speed railways (HSRs) due to their different supporting conditions. The dynamic irregularity caused by the different stiffnesses makes this transition area the weakest part of high-speed railways. Graded crushed stone combined with 5% cement is typically used to fill the subgrade in these transition areas. Thus, three different particle size ratios of crushed stone were matched and tested regarding the construction parameters to explore the most suitable materials to fill the roadbed in a transition section. Then, field dynamic tests were carried out on the culvert-embankment-culvert transition area where trains run at speeds of 5-360 km/h. A time-domain analysis of the test data was performed to obtain the laws of variation that cause the dynamic characteristics to change with the railway line and roadbed layer and the changes induced by a train's running speed, operating direction, and axle weight. The results indicate that (i) it is feasible to fill transition section roadbeds with well-graded crushed stone combined with 5% cement with optimal water contents; (ii) extreme dynamic responses in some special sections are observed, suggesting the value of taking special measures at the transition section. For example, the sections 14.5 m and 30 m from the 679 culvert and the bed layer should be specially stabilized; (iii) the train's axle load and driving direction show a great effect on corresponding sections and layers but present a small effect on the sections and layers nearby; and (iv) 260 km/h is a critical speed.

A polygenetic origin for the Sikhoran ultramafic-mafic complex in South Iran

The nature and geodynamic setting of the Sikhoran ultramafic–mafic complex, southwest Iran, is debated, with multiple competing theories having been proposed in recent years. The Sikhoran ultramafic–mafic complex is located in the southern part of the Sanandaj-Sirjan metamorphic-magmatic zone (SSMMZ) and is comprised of porphyroclastic, transitional and layered ultramafic-mafic sequences of Carboniferous age. These units are cut by isotropic gabbros, diabasic and pegmatoid gabbroic dikes with ages ranging from Permian to the Cretaceous. These bodies also intrude into Upper Paleozoic metamorphic rocks, where they induced high-temperature contact metamorphism during the Late Carboniferous. Here we present new textural descriptions, mineral and whole-rock geochemical analyses, and the results of zircon UPb dating of magmatic mafic rocks and metamorphic host rocks from this region in order to reconstruct the petrogenesis of the Sikhoran ultramafic–mafic complex. Zircon UPb ages from layered gabbros indicate Late Carboniferous (320.8 ± 6.4 Ma) crystallization, which is similar to the age of the Upper Paleozoic host gneisses (334.6 ± 4.9 Ma). By contrast, isotropic gabbros that cross-cut the complex have a crystallization age of 178.3 ± 2.3 Ma, and anatectic quartz diorite/plagiogranite produced from partial melting of hosting amphibolite in contact with the gabbros yielded Late Triassic-Early Jurassic ages (187.2 ± 2.6 Ma). These data suggest a polygenetic origin and a range of tectonic settings for various parts of the ultramafic-mafic complex. Geochemical modeling shows that mantle plume-related melting (∼5–40%) of metasomatized mantle could have formed the ultramafic-mafic layered cumulate complex during the Late Carboniferous. A geochemical transition from island arc tholeiite (IAT) isotropic gabbros to cross-cutting enriched mid-ocean ridge basalts (E-MORB)–diabasic dikes occurred between the Late Triassic-Early Jurassic to the Late Cretaceous. The mantle-derived ultramafic parts of the Sikhoran ultramafic-mafic complex have similarities with other known ultramafic-mafic mantle plumes (e.g., Tinaqulllo, Lherz, and Ronda), and its layered ultramafic-mafic segment has similarity with layered intrusions (e.g., Pulur complex in Turkey). The highest observed crystallization temperature in porphyroclastic, transitional and layered ultramafic mantle sections of ∼1140 °C is considered as the mantle potential temperature, since the highest crystallization temperatures are observed in the most forsteritic olivine crystals. Based on amphibole chemistry, the crystallization conditions of transitional to layered ultramafic rocks at 900–1005 °C occurred at high H2O contents in a melt between nickel–nickel oxide (NNO) −8.5 and NNO −9.0, which lies along the NNO−2 buffer. These results are consistent with a model in which the opening of the Zagros Neotethys Oceanic basin in the Esfandagheh region initiated in the Late Carboniferous, alongside the formation of an extensional environment that allowed ascent of a subcontinental mantle plume. Subduction initiation of oceanic lithosphere began during the Late Triassic-Early Jurassic and ended in the Late Cretaceous.

Evolution of flow field around high-speed trains meeting at the tunnel entrance under strong wind-rain environments

Tropical storms pose a great threat to the traffic safety of tunnel-embankment transition sections in coastal areas, especially when two trains are meeting. A series of 3D computational fluid dynamics numerical simulations of wind-rain-tunnel-embankment-train are established using the Eulerian multiphase and the Shear-Stress Transport k-ω models. The numerical model's reliability is verified by wind tunnel tests using rainfall simulation technology. The differences in the train's aerodynamic performance before and during the meeting under different wind-rain conditions are analyzed. The rain phase's impact mechanism on the flow field is revealed. Results show that: Before the meeting, the rain phase will worsen the train's aerodynamic performance. When the wind speed and rainfall intensity is 20 m/s and 400 mm/h, the head train's average lift force (C‾y), yawing and pitching moments (C‾mz) increase by 6.25%, 9.68% and 10.31%, respectively. The rain phase increases the wind-rain load amplitude during the meeting, and the head train's pitching moment increases by 10.7%. The moment is more worthy of attention than that of force under a rainy day, and the change rate of C‾mz is 4.9 times of that of C‾y. The amplification effect of rain on wind-rain loads may endanger the driving safety of trains at the tunnel entrance.