Flow Development Research Articles

Dynamic mode decomposition for the tip unsteady flow analysis in a counter-rotating axial compressor

Counter-rotating axial compressor (CRAC) is a promising potential technology to improve the thrust-to-weight ratio of aero-engines, but its special aerodynamic layout usually causes more pronounced flow unsteadiness. Understanding the unsteady flow features and mechanism in the CRAC contributes to the aerodynamic optimization design and flow control strategy organization. A data-driven dynamic mode decomposition method is introduced to investigate the tip flow unsteadiness in a CRAC, and the unsteady features of the tip flow at the design point (DP) and near-stall point (NSP) conditions are revealed. The results show that the 1.0 times blade passage frequency (BPF) and its multi-order harmonic frequency are the dominant frequencies for both rotors at the DP condition. At the NSP condition, the 1.0 BPF is no longer the dominant frequency causing the tip flow unsteadiness, and the low frequency fluctuation of the tip leakage flow becomes the dominant frequency to induce the flow unsteadiness. In the front rotor R1, the unsteady dominant frequency is 1.0 BPF, whereas in the rear rotor R2, the frequency (0.801 BPF and 0.803 BPF) of the tip leakage flow is the dominant frequency. By reconstructing the flow field under the NSP condition, the spatiotemporal evolution of the tip flow during the unsteady stable manifests that the interference effect between the rotors is an important source of the tip flow unsteadiness. The increase in flow unsteadiness leads to an increase in the reconstruction error, indicating that more modes are required to obtain a more accurate reconstruction flow field.

Stable Isotopes and Water Level Monitoring Integrated to Characterize Groundwater Recharge in the Pra Basin, Ghana

In the Pra Basin of Ghana, groundwater is increasingly becoming the alternative water supply due to the continual pollution of surface water resources through illegal mining and indiscriminate waste discharges into rivers. However, our understanding of hydrogeology and the dynamics of groundwater quality remains inadequate, posing challenges for sustainable water resource management. This study aims to characterize groundwater recharge by determining its origin and mechanism of recharge prior to entering the saturated zone and to provide spatial estimates of groundwater recharge using stable isotopes and water level measurements relevant to groundwater management in the basin. Ninety (90) water samples (surface water and groundwater) were collected to determine stable isotope ratios of oxygen (δ18O) and hydrogen (δ2H) and chloride concentration. In addition, ten boreholes were installed with automatic divers to collect time series data on groundwater levels for the 2022 water year. The Chloride Mass Balance (CMB) and the Water Table Fluctuation (WTF) methods were employed to estimate the total amount and spatial distribution of groundwater recharge for the basin. Analysis of the stable isotope data shows that the surface water samples in the Pra Basin have oxygen (δ18O) and hydrogen (δ2H) isotope ratios ranging from −2.8 to 2.2‰ vrs V-SMOW for δ18O and from −9.4 to 12.8‰ vrs V-SMOW for δ2H, with a mean of −0.9‰ vrs V-SMOW and 0.5‰ vrs V-SMOW, respectively. Measures in groundwater ranges from −3.0 to −1.5‰ vrs V-SMOW for δ18O and from −10.4 to −2.4‰ vrs V-SMOW for δ2H, with a mean of −2.3 and −7.0‰ vrs V-SMOW, respectively. The water in the Pra Basin originates from meteoric source. Groundwater has a relatively depleted isotopic signature compared to surface water due to the short residence time of infiltration within the extinction depth of evaporation in the vadose zone. Estimated evaporative losses in the catchment range from 51 to 77%, with a mean of 62% for surface water and from 55 to 61% with a mean of 57% for groundwater, respectively. Analysis of the stable isotope data and water level measurements suggests a potential hydraulic connection between surface water and groundwater. This hypothesis is supported by the fact that the isotopes of groundwater have comparatively lower values than surface water. Furthermore, the observation that the groundwater level remains constant in months with lower rainfall further supports this conclusion. The estimated annual groundwater recharge in the catchment ranges from 9 to 667 mm (average 165 mm) and accounts for 0.6% to 33.5% (average 10.7%) of mean annual precipitation. The total estimated mean recharge for the study catchment is 228 M m3, higher than the estimated total surface water use for the entire Pra Basin of 144 M m3 for 2010, indicating vast groundwater potential. Overall, our study provides a novel insight into the recharge mechanism and spatial quantification of groundwater recharge, which can be used to constrain groundwater flow and hydrogeochemical evolution models, which are crucial for effective groundwater management within the framework of the Pra Basin’s Integrated Water Resources Management Plan.

Application of Cross model for granular flow and impact analysis using three-dimensional B-spline material point method

Granular flow and impact, such as landslides and debris flows, are typical problems involving large deformations of non-Newtonian free surfaces, which are of great interest in geological engineering and also pose challenges for traditional mesh-based numerical methods. As an enhancement of the traditional Material Point Method (MPM), the B-Spline Material Point Method (BSMPM) can not only effectively reduce mesh-crossing and quadrature errors, but also facilitate the tracking and capturing of free surfaces and contact interfaces. In this paper, the non-Newtonian general Cross model, the rheological parameters of which are determined by the Bingham model and the Mohr-Coulomb yield criterion, is introduced into the three-dimensional BSMPM (3D BSMPM) for simulating granular flow and impact problems. Interparticle effects of granular materials are represented by artificial damping forces. Dynamic simulations are carried out on the collapse of sand column and glass beads, the flow of bentonite suspensions, and the impact between granular mass and elastic obstacles. The overall evolution of granular flow and impact behavior are presented and compared with existing experimental and/or original MPM results. It is found that the proposed method well reproduces the overall process of granular flow and impact behavior, including its various stages of formation, acceleration, deceleration, and deposition, as well as the impact pressure. The results show that the granular flow and impact behavior can be well represented by the proposed 3D BSMPM with the Cross rheological model, demonstrating the effectiveness of the proposed method in simulating complicated environmental fluid dynamics.

Diffusion mechanisms of convective instability in liquid and gas mixtures

AbstractA review of publications on stability of mechanical equilibrium of multicomponent mixtures in gases and liquids under non‐isothermal and isothermal conditions is given. Studies where diffusion in binary and multicomponent mixtures led to the occurrence of instability of mechanical equilibrium of the system have been analyzed. The main attention is paid to the description of approaches predicting the areas where there are increasing convective disturbances, as well as the determination of the spectrum of thermophysical parameters where the contribution of convection to heat and mass transfer is negligible. At the same time, the problems determining the role of diffusion, thermodiffusion, and double diffusion mechanisms in the separation of mixture components at the boundary of convective instability were given priority in the description. The results of investigations related to the study of the evolution of flows arising due to instability at the initial stage of mixing were also discussed.

A multi-angular extrusion process for fine-grain magnesium alloy plate

The precise forming process with fine-grain strengthening method of magnesium alloy is a common technical problem that needs to be urgently addressed for lightweight application. In this paper, a multi-angular extrusion process integrating severe plastic deformation (SPD) technique and hot forming process was proposed to manufacture the fine-grain plate of AZ80 magnesium alloy. Shear deformation path was introduced via the variable section and secondary angle of mold cavity. The unified internal state variable (ISV) based finite element (FE) model was established to simulate the multi-angular extrusion process. The interaction of viscoplastic flow and microstructure evolution was embedded into the user defined subroutine of DEFORM-3D software. The inhomogeneous strain distribution and microstructure characteristics during the extrusion process were investigated. The improvement of fine-grain homogeneity via the two-pass angular shear deformation was revealed. A fine-grain magnesium alloy plate with good forming performance and average grain size of 9 μm was manufactured. The yield strength is increased to 259 MPa by 23.3 %, ultimate tensile strength is increased to 338 MPa by 27.5 %, and elongation is increased to 12.9 % by 122.4 %. The developed multi-angular extrusion process can be applied to the integrated manufacturing of shape and performance of fine-grain Mg components.

Cerebral Blood Flow, Brain Injury, and Aortic-Pulmonary Collateral Flow After the Fontan Operation

Patients with a single ventricle develop aortopulmonary collaterals (APCs) whose flow has been shown to be inversely proportional to cerebral blood flow (CBF) in a previous cross-sectional study. Longitudinal CBF and APC flow in patients with Fontan physiology adjusting for brain injury (BI) has never been reported. Decreased CBF and BI may adversely impact neurodevelopment. A prospective longitudinal cohort of 27 patients with Fontan physiology (aged 10 ± 1.9years, 74% male) underwent cardiac and brain magnetic resonance imaging 3 to 9months and 6.0 ± 1.86years after Fontan operation to measure the CBF and APC flow and to reassess the BI (focal BI, generalized insult, and hemorrhage). CBF was measured using jugular venous flow and APC flow was measured by the difference between aortic flow and caval return. Multivariate modeling was used to assess the relation between the change in APC flow and BI. A strong inverse relation was found between CBF/aortic flow change and APC flow/aortic flow and APC flow/body surface area change (R2=0.70 and 0.72 respectively, p <0.02). Overall, the CBF decreased by 9 ± 11% and the APC flow decreased by 0.73 ± 0.67l/min/m2. The evolution of CBF and APC flow were significantly and inversely related when adjusting for time since Fontan operation, gender, and BI on the multivariate modeling. Every unit increase in APC flow change was associated with an 8% decrease in CBF change. In conclusion, CBF and APC flow change are inversely related across serial imaging, adjusting for time from Fontan operation, gender, and BI. CBF and APC aortic flow decrease over a 6-year period. This may adversely impact neurodevelopment. Because APCs can be embolized, this may be a modifiable risk factor. Clinical trials numbers: NCT02135081 and NCT02919956.

A multiphase modeling for investigating temperature history, flow field and solidification microstructure evolution of FeCoNiCrTi coating by laser cladding

In this work, a multiphase numerical model was established to investigate the non-isothermal flow and microstructure evolution during laser cladding. The model considered the beam-powder interaction, temperature dependent material properties, the effect of buoyancy and surface tension on convection. The accuracy of the model was verified comparing the simulated coating geometric morphology with the experimental results. Simulation indicated that the temperature and flow of the molten pool were interactive and mutually causal. On the one hand, the temperature field affected the tension gradient and the liquid flow direction. On the other hand, the velocity field significantly affected the heat transfer in the molten pool. Specifically, the maximum fluid velocity was 9.58 mm/s and the Peclet number (PeT) value was less than 5 at the initial stage, indicating that conduction dominated in heat transfer. Furthermore, the PeT value was greater than 200 when the maximum velocity reached 344 mm/s. The heat transfer in the molten pool was mainly thermal convection. In addition, the distribution diagram of solidification parameters (G and R) was calculated to quantitatively establish the internal correlation between solidification parameters and microstructure combing with experimental observation, and revealed the columnar-to-equiaxed transition (CET). Eventually, the microhardness results showed that HEA coating could improve the Ti6Al4V surface microhardness. Simultaneously, the CET behavior significantly affected the microhardness of the coating.

Analysis of non-uniform laminar flow past a circular cylinder on the flow and sound field evolution using direct numerical simulation approach

Analysis of non-uniform laminar flow past a circular cylinder on the flow and sound field evolution using direct numerical simulation approach

Adaptive wave-particle decomposition in UGKWP method for high-speed flow simulations

With wave-particle decomposition, a unified gas-kinetic wave-particle (UGKWP) method has been developed for multiscale flow simulations. With the variation of the cell Knudsen number, the UGKWP method captures the transport process in all flow regimes without the kinetic solver’s constraint on the numerical mesh size and time step being determined by the kinetic particle mean free path and particle collision time. In the current UGKWP method, the cell Knudsen number, which is defined as the ratio of particle collision time to numerical time step, is used to distribute the components in the wave-particle decomposition. The adaptation of particles in the UGKWP method is mainly for the capturing of the non-equilibrium transport. In this aspect, the cell Knudsen number alone is not enough to identify the non-equilibrium state. For example, in the equilibrium flow regime with a Maxwellian distribution function, even at a large cell Knudsen number, the flow evolution can be still modelled by the Navier-Stokes solver. More specifically, in the near space environment both the hypersonic flow around a space vehicle and the plume flow from a satellite nozzle will encounter a far field rarefied equilibrium flow in a large computational domain. In the background dilute equilibrium region, the large particle collision time and a uniform small numerical time step can result in a large local cell Knudsen number and make the UGKWP method track a huge number of particles for the far field background flow in the original approach. But, in this region the analytical wave representation can be legitimately used in the UGKWP method to capture the nearly equilibrium flow evolution. Therefore, to further improve the efficiency of the UGKWP method for multiscale flow simulations, an adaptive UGKWP (AUGKWP) method is developed with the introduction of an additional local flow variable gradient-dependent Knudsen number. As a result, the wave-particle decomposition in the UGKWP method is determined by both the cell and gradient Knudsen numbers, and the use of particles in the UGKWP method is solely to capture the non-equilibrium flow transport. The current AUGKWP method becomes much more efficient than the previous one with the cell Knudsen number only in the determination of wave-particle composition. Many numerical tests, including Sod shock tube, normal shock structure, hypersonic flow around cylinder, flow around reentry capsule, and an unsteady nozzle plume flow, have been conducted to validate the accuracy and efficiency of the AUGKWP method. Compared with the original UGKWP method, the AUGKWP method achieves the same accuracy, but has advantages in memory reduction and computational efficiency in the simulation for flows with the co-existing of multiple regimes.

Chronologic evolution and prognostic implications of impaired coronary flow after chronic total occlusion angioplasty.

Although vessels have the potential to recover following successful recanalization of chronic total occlusion (CTO), evidence is limited about the clinical significance of slow flow (SF) phenomenon after recanalization. The aim of this study was to evaluate the determinants, development and prognostic impact of SF after percutaneous coronary intervention (PCI) for CTO. This was a retrospective cohort study, 500 patients were consecutively enrolled undergoing CTO PCI and consecutive follow-up angiography in Zhongshan Hospital, Fudan University, between 2015 and 2020. Coronary flow was assessed by corrected Thrombolysis in Myocardial Infarction (TIMI) frame count (CTFC). The association between SF and outcomes of CTO PCI was evaluated by analyzing the clinical, angiographic, and procedural characteristics. SF was observed in 29 (5.8%) patients immediately after CTO PCI. Prior myocardial infraction, right coronary artery (RCA) revascularization and lack of bilateral collaterals were independent predictors of SF. SF was associated with increased risks of periprocedural myocardial infarction (PMI) [adjusted odds ratio (adOR): 4.12; 95% confidence interval (CI): 1.68-10.07; P=0.002] and target lesion restenosis (adOR: 2.50; 95% CI: 1.10-5.72; P=0.030). In patients with baseline left ventricular ejection fraction (LVEF) ≤60%, systolic improvement was compromised in the SF group (LVEF: 55.4%±9.6% in follow up vs. 52.1%±9.4% before CTO PCI, P=0.147) compared with that of the normal group (LVEF: 55.7%±9.3% vs. 51.6%±8.5%, P<0.001). SF has a significant influence on the prognosis of patients undergoing CTO PCI. Achieving normal coronary flow is essential in CTO revascularization.

Thermal‒hydraulic‒mechanical‒chemical coupling analysis of enhanced geothermal systems based on an embedded discrete fracture model

Enhanced geothermal system (EGS) is subject to the comprehensive effects of multiple physical fields during the long-term heat extraction process, including hydraulic (H), thermal (T), mechanical (M) and chemical (C) fields. The embedded discrete fracture model (EDFM) can effectively simulate the variations of flow, temperature, mechanical and concentration fields in fractured reservoirs. At present, however, the thermo-hydro-mechanical-chemical (THMC) coupling model based on EDFM is less researched. In this paper, the THMC coupling model of fractured reservoir is established based on EDFM by considering the changes in reservoir heterogeneity and physical properties as well as water–rock reactions. Then, the spatiotemporal evolution of flow, temperature, displacement and concentration fields in the operation process of EGS is simulated and analyzed. And the following research results are obtained. First, when the permeability of the basement rock is low, the production temperature decrease during exploitation is gradual, allowing EGS to maintain a high exploitation temperature for an extended period. However, lower permeability may result in a decrease in the quality flow rate from production wells, thereby affecting net heat extraction power. Second, when fracture permeability or fracture opening changes, EGS can output higher temperature stably for a certain period and then the temperature decreases at different amplitudes. When the fracture permeability increases to a certain value or the fracture opening decreases to a certain value, the influence of the change in fracture parameters on production temperature gets weak. Third, After 40 years of EGS operation, considering variable property fluids results in a 22 °C lower exploitation temperature compared to using constant property fluids, and considering water–rock reactions results in a 15 °C lower exploitation temperature, with a 12.5 % increase in reservoir average porosity. In conclusion, when researching a long-term operating EGS, it is necessary to comprehensively consider the influences of reservoir rock parameters, physical properties of injected fluid, water–rock reaction and other factors. And in the future, attention shall be paid to the two-way coupling of chemical reaction and mechanical deformation of other mineral compositions in the reservoir to the hydro-thermo-chemical field influence, so as to provide more accurate and reliable prediction for the engineering development and utilization of EGS reservoirs.

Spatiotemporal flow evolution in a rocket-based combined-cycle inlet during ejector-to-ramjet mode transition

The spatiotemporal distribution characteristics and flow stability of a rocket-based combined-cycle (RBCC) inlet during the ejector-to-ramjet mode transition are investigated numerically. The operational pressure of the embedded rocket is adjusted to three different levels, and the time-sequences of the rocket and back pressure regulation are varied. The pressure in feature sections is monitored to reveal the coupling relationship and stability of the internal flowfield. The inlet is more adaptable to severe disturbances under the “throttle-maintaining” regulation and is susceptible under the “direct-shutdown” regulation. The severe fluctuation period is relatively short within “medium throttle-maintaining,” while is lengthy within the “high throttle-maintaining.” The severe fluctuation under the direct-shutdown develops with the propagation of the regulation and decays with its establishment. The ultimate flowfields driven by different time-sequences reach unanimity with the same adjustable parameters of embedded rocket and back pressure; however, the dynamic evolutions show distinct characteristics. During the mode transition, pressure “valleys” are formed in any selected sections with the rocket regulations, and “peaks” are developed in many sections due to the propagation of back pressure or the instability of the rocket jet. For the medium throttle-maintaining regulation, the effect of time-sequence on the flowfield is relatively weak. For the high throttle-maintaining regulation, the pressure disturbance rises abruptly under the rocket priority regulation, with a most severe amplitude of 100.7%. For the direct-shutdown regulation, the maximum pressure disturbance of 125% is observed within the rocket priority regulation, and the minimum disturbance occurs within the back pressure priority regulation.

Numerical simulation of melt pool size and flow evolution for laser powder bed fusion of powder grade Ti6Al4V

The study of molten pool characteristics is a powerful means of determining the quality of laser additive manufacturing forming. In this paper, a three-dimensional transient thermal flow field numerical model of Ti6Al4V powder processed by LPBF is developed based on FLOW-3D software, and the dynamic evolution of the molten pool with fixed process parameters is quantitatively described using dimensionless numbers in computational fluid dynamics. It is shown that the main heat transfer mode of the molten pool is thermal convection; the evaporative back sitting pressure, surface tension and Marangoni shear force are the main driving forces for the evolution of the molten pool. Furthermore, the influence of key process parameters on the heat flow field of the molten pool was analyzed. When the laser power was 300 W, the depression depth and molten pool depth caused by the recoil pressure were significantly larger, and the isothermal density of the solidification region was more intensive; when the scanning speed was increased from 0.4 m/s to 0.8 m/s, the molten pool length was reduced from 524 μm to 410 μm, and the line energy density was reduced making the amount of melted powder decrease. The wettability and fluidity of the molten state metal becomes worse; when the scanning interval increases to 120 μm, a large number of incompletely melted powder tracks cannot lap correctly at the midline of the double track. The results of the above simulations achieve a high degree of agreement with the surface quality of the specimens during the experiments, which provides guidance for quantitative analysis of molten pool evolution and prediction of Ti6Al4V forming quality.

Features and mechanisms of asymmetric wake evolution downstream of two parallel circular cylinders

Uniform flow past side-by-side circular cylinders is a classical fluid dynamic model that triggers rich phenomena, from which asymmetric wakes usually emerge. Such asymmetry arising from a completely symmetric geometric setting is of theoretical interest when exploring the system bifurcations. Using direct numerical simulation, a detailed parametric map of the wakes behind two side-by-side circular cylinders is presented with several asymmetric wake patterns. These include asymmetric anti-phase (AAP), typical and special deflected (DF), and in-phase (IP) flows, for which AAP and special DF flows are discovered for the first time. Additionally, the IP flow is simulated by both two- and three-dimensional grids to explore the effect brought by three-dimensional vortical structures. The evolution of these asymmetric wakes is analyzed in different phases, with the aid of the wavelet transform, Hilbert–Huang transform, and dynamic mode decomposition, to reveal their temporal variations of developing features. Interestingly, although revealing with distinct fully developed flow fields, there are several common dynamics identified among these wake patterns: AP and IP vortex shedding, wake transition, and gap flow oscillation. The vicissitudes of dynamic flow evolution allow us to further differentiate several wake patterns and ultimately contribute to a deeper understanding of asymmetric flows.

Assessment of the impact of foreign capital flows on economic growth in Algeria

Purpose. This study aims to measure and assess the impact of foreign capital flows, including foreign direct investment, external loans, foreign aid, and remittances from migrants, as independent variables on real GDP as a dependent variable in Algeria during the period 1990–2021 using the Autoregressive Distributed Lag (ARDL) time series regression model. Results. The study found the existence of a long-term relationship between the selected economic variables and their impact on real GDP in Algeria, both in the short and long term. Additionally, there is a positive effect of both independent variables representing foreign direct investment and migrant remittances on real GDP. However, there is a negative impact of external loans on real GDP, which can be explained by the misallocation of these loans, with a significant portion directed towards non-productive sectors, negatively affecting the long-term economic growth in Algeria. Scientific novelty. The primary contribution of this study is its comprehensive elucidation of all major forms of foreign capital flows to Algeria and their impact on the Algerian economy, including FDI, foreign aid, external loans, and remittances. This is important because different types of foreign capital flows have different effects on the Algerian economy. In addition, the evolution of foreign capital flows to Algeria over a long period of time, from 1990 to 2021, is studied. This made it possible to identify trends and patterns in foreign capital flows that may not be apparent in short-term studies. Practical value. The results of this study can help policymakers to design policies that maximize the benefits of foreign capital flows while minimizing the risks. And Foreign capital flows can play an important role in helping Algeria to address these challenges and achieve its economic development goals.

Transient dark ribbons at the outer boundaries of sunspot superpenumbrae in the chromosphere

Context. Although the flow of material in sunspot superpenumbrae has been studied intensively, detailed observations about the evolution of material flow at the outer boundaries of sunspot superpenumbrae are rare. Aims. We study the evolution of the flow of material at the outer boundaries of superpenumbrae. Methods. Based on Hα observations from the New Vacuum Solar Telescope, we tracked the evolution of the flow of material at the outer boundaries of superpenumbrae in the chromosphere. Data from the Solar Dynamics Observatory Helioseismic Magnetic Imager were employed to examine the photospheric magnetic field environment relevant to the material flow. Results. We observed transient dark ribbons (TDRs) at the outer boundary of a sunspot superpenumbra in the chromosphere on 2018 May 12. The TDRs are located in the middle of the sunspot and a flocculus, and both of them have negative magnetic fields. While the ratio of the length and width of a TDR is greater than 8, we tracked the TDR from its formation to disappearance, so that six TDRs were studied in detail. Five TDRs were formed by the connection of several small dark sticks from end to end, and the sixth TDR was formed by the merging of two thin sticks. In the later stage of the TDR evolution, five TDRs were broken down into several small dark sticks, and the sixth TDR dissipated with oscillation. During the evolution process, no obvious flow of material along the TDRs is detected. Conclusions. We suggest that these TDRs are an observational representation of the regular aggregation of superpenumbral fibril footpoints and adjacent solar flocculus fibril footpoints at the outer boundaries of the sunspot superpenumbrae.

Irrigación de largo plazo como desencadenante de flujos de tierra en Chenque Malal, Norpatagonia argentina

Because of their social, ecological, and economic impacts, landslides are an issue of global concern. Episodes occurring worldwide have been associated with natural and human causes, although the latter have been poorly explored. Despite recent scientific insight into intensive irrigation as a cause, research remains scarce. This paper focuses on determining the anthropogenic influence on the triggering of earth flows by long-term intensive irrigation, based on temporal and geospatial information. This analysis covers a sector of Northern Patagonia in Argentina, an area of transhumant pastoralism. Our results show that excessive water input creates favorable conditions for the triggering and evolution of earth flows in the region, even under water deficit conditions. As a result, on 22 September 2020, a collapse was recorded which mobilized ~19,000 m³ of earth debris along 360 m and produced economic losses estimated at 168,000 USD. Other landslides are expected to occur in the area if irrigation amounts remain at the same level.

Study on the Trend in Evolution of the Energy Flow in the Axis of Annular Booster Pellets

Study on the Trend in Evolution of the Energy Flow in the Axis of Annular Booster Pellets

Mechanisms of Serrated Flow and Microstructural Evolution in MarBN Steel.

The mechanisms of serrated flow and microstructural evolution in MarBN steel were studied under two strain rates (5 × 10-3 s-1 and 5 × 10-5 s-1) at room temperature and high temperatures (430 °C and 630 °C). The experimental results show that the type-C serrations occurred at all temperatures under a high strain rate of 5 × 10-3 s-1. In contrast, type-B serrations occurred at 430 °C and 630 °C under a low strain rate of 5 × 10-3 s-1, indicating that the type of serrated flow was related to the strain rate. The microstructural results reveal that pinning and unpinning dislocation under both strain rates were responsible for the serrations at both strain rates.

Urban Traffic Flow Congestion Prediction Based on a Data-Driven Model

Intelligent transportation systems need to realize accurate traffic congestion prediction. The spatio-temporal features of traffic flow are essential to analyze and predict congestion. Our study proposes a data-driven model to predict the traffic congested flow. Firstly, the traffic zone/grid method is used to store the local area roads’ average speed of the vehicles. Second, the discrete snapshot set is proposed to characterize traffic flow’s spatial and temporal features over a continuous period. Third, the evolution of traffic congested flow in various time dimensions (weekly days, weekend days, and one week) is examined by transforming the global urban transportation network into traffic zones. Finally, the data-driven model is constructed to predict urban road traffic congestion by using the extracted spatio-temporal characteristics of traffic zones’ traffic flow, the snapshot set of which serves as inputs for this model. The model adopts the convolutional LSTM network to learn the temporal and local spatial features of traffic flow, while utilizing a convolutional neural network to effectively capture the global spatial features inherent in traffic flow. The numerical experiments are conducted on two cities’ transportation networks, and the results demonstrate that the performance of the proposed model outperforms traditional traffic flow prediction models.