Flow Trajectories Research Articles

Proposal of Hazard Connectivity Index for debris flow disaster management

The concept of connectivity and its index have been widely discussed and applied to environmental studies such as ecology, hydrology, geomorphology and hydrosedimentology. Supposing that this concept is very useful also in disaster risk management, we define the hazard connectivity associated to debris flows as the connectivity degree between the debris flow occurrence (trajectory) and the point of interest (location of house, person, and so on). Based on this definition, the Hazard Connectivity Index (HCI) associated to debris flow is proposed as: HCI = L/(x+L), where x is the shortest distance between the debris flow trajectory and the point of interest; and L is the runout distance of the debris flow or just mass movement. The HCI value varies from 0 to 1, being that its higher value indicates larger hazard condition. The HCI application to one case study showed that it can be useful in the analysis of the debris flow related hazard.

A particle morphology characterization system and its method based on particle scattering image recognition

The morphology of particles is usually detected by microscopic imaging methods such as scanning electron microscope (SEM). However, this type of direct observation relies on expensive equipment and requires complex preparations. Inspired by the transit method in astronomy, a characterization system based on the scattering patterns change due to the relative motion between the particle and facula was proposed in this work. The scattering patterns of particles could be recognized and analyzed automatically to detect the particle shape. The flow trajectory was studied by the optical fluid field couple (OFFC) model proposed in this work to calculate the size and specific surface area of the particle. For getting more accurate results, particle surface roughness was measured by image recognition to correct the results of specific surface areas. The accuracy of the classification machine learning (CML) model was about 97%, and the errors of the specific surface area results were lower than 10%. Comparing with the previous work, the proportions of different particles in mix sample could be detected successfully by this system with a maximum error less than 6%. This work can offer a valuable reference for the fields of characterization morphology systems based on scattering.

A Cooperative Trajectory Optimization Algorithm for Connected Vehicles in Merging Zones

Traffic flow optimization and trajectory guidance in merging zones have significant implications for improving capacity and reducing time consumption. The development of V2X communication provides new insights to solve this problem by tackling the information and releasing trajectories schemes. Therefore, this paper aims to discuss the trajectory management in the merging zone for ACC vehicles. A vehicle dispatching and car-following model is proposed to generate steady traffic flow first. An algorithm framework for consecutive traffic flow is presented with the idea of FIFO rules. Then, a two-step method for an individual vehicle is discussed in detail to compute a trajectory. The first step is to select and determine the priority of the optional gaps. The next step is to verify the options’ feasibility, decide on the target gap, and output the trajectories to merge successfully. Numerical experiments validate that the proposed method guarantees safe driving and provides relatively smooth trajectories to the vehicles. Furthermore, increased capacity and higher velocity are observed in a comparative experiment. The cooperative optimization algorithm could be applied efficiently in practice and benefit from its rapid response and low computation complexity.

Unconventional self-similar Hofstadter superconductivity from repulsive interactions

Fractal Hofstadter bands have become widely accessible with the advent of moiré superlattices, opening the door to studies of the effect of interactions in these systems. In this work we employ a renormalization group (RG) analysis to demonstrate that the combination of repulsive interactions with the presence of a tunable manifold of Van Hove singularities provides a new mechanism for driving unconventional superconductivity in Hofstadter bands. Specifically, the number of Van Hove singularities at the Fermi energy can be controlled by varying the flux per unit cell and the electronic filling, leading to instabilities toward nodal superconductivity and chiral topological superconductivity with Chern number {{{{{{{mathcal{C}}}}}}}}=pm 6. The latter is characterized by a self-similar fixed trajectory of the RG flow and an emerging self-similarity symmetry of the order parameter. Our results establish Hofstadter quantum materials such as moiré heterostructures as promising platforms for realizing novel reentrant Hofstadter superconductors.

1005 STROKE VOLUME INDEX AND TRANSVALVULAR FLOW RATE TRAJECTORIES IN SEVERE AORTIC STENOSIS TREATED WITH TAVR

Abstract Aims The prognostic impact of flow trajectories according to stroke volume index (SVi) and transvalvular flow rate (FR) in patients with severe aortic stenosis (AS) undergoing transcatheter aortic valve replacement (TAVR) remains poorly assessed. We evaluated and compared SVi and FR prior and after TAVR for severe AS. Methods and results Patients were categorized according to SVi (<35 ml/m2) and FR (<200 ml/sec). The association of pre- and post-TAVR SVi and FR with all-cause mortality up to 3 years was assessed with multivariable Cox regression models. Among 980 patients with pre-TAVR flow assessment, SVi was reduced in 41.3% and FR in 48.1%. Baseline flow status was not an independent mortality predictor (SVi: HR 1.39, 95%CI 0.81-2.40, FR: HR 0.86, 95%CI 0.51-1.46). Among 731 patients undergoing early (5 days, IQR 2-29) post-TAVR flow assessment, SVi recovered in 40.1% and FR in 49.0% patients with baseline low-flow. Reduced FR following TAVR was an independent predictor of mortality (HR 2.08, 95%CI 1.07-4.04) while SVi was not (HR 0.68, 95%CI 0.34-1.36). Three-year estimated mortality in patients with recovered FR was lower as compared to patients with reduced FR (13.3% vs 37.7% vs, p=0.003) and similar to patients with normal baseline FR (p=0.317). Conclusions Baseline flow status was not an independent predictor of mid-term mortality among all-comers with severe AS undergoing TAVR. Flow recovery early after TAVR was frequent. Post-TAVR FR, but not SVi, was independently associated with mid-term all-cause mortality. By impacting flow status, AV replacement modifies the association of flow status with outcomes.

Motion trajectory mathematical model of burden flow at the top of bell-less blast furnace based on coordinate transformation

The motion trajectory mathematical model of burden flow is the basis for implementing blast furnace (BF) charging operation, which is of great significance for the stable and efficient operation of BFs. To calculate the motion trajectory of the burden flow at the top of the BF, static and dynamic coordinate systems are first established. Then, coordinate transformation and point composite motion methods are proposed and implemented to calculate this motion trajectory. Finally, the motion trajectories of the single-particle, multi-particle, and entire burden flows are analyzed and compared with the simulation results of a 1:8 scale BF discrete element method model. The results indicate that the absolute percentage errors (APEs) of the particle’s radial and Z-axis velocities are 7.89% and 4.65%, respectively, when the particle is at the chute tip in the single-particle flow trajectory. And the APEs of the radial and Z-axis velocities are 8.79% and 4.38%, respectively, when the burden flow is regarded as a particle. The foregoing demonstrates that the proposed mathematical model can effectively calculate the motion trajectory of the burden flow at the top of BF.

Scaling formulation of multiphase flow and droplet trajectories with rime ice accretion on a rotating wind turbine blade

In this paper, scaling and similitude are investigated for ice accretion on a rotating wind turbine blade. Numerical CFD icing simulations are performed using FENSAP ICE software to test the scaling methods and verify the results. A small blade section is scaled six times, and each case is tested at specific flow conditions. Scaled conditions for velocity (streamwise and rotational), droplet size, and icing time are examined. CFD solutions for the flow field (air and droplet) are obtained in terms of the velocity, droplet trajectories, pressure coefficient distributions, ice thickness, and ice shapes, by quantifying the significant parameters involved in the icing process. Recommendations for parameters to be used for rime ice scaling on a rotating blade are presented, and numerical results are reported to support those recommendations. Numerical results and test conditions are obtained at sea level in wind tunnel facilities for experimental investigation. This paper presents the formulation of non-dimensionlized governing equations for scaling of the flow field, droplet trajectories, and ice accretion on a rotating blade model. It derives a set of non-dimensional groups which govern the flow parameters for a rotating blade, including the Strouhal number, Froude number, drag coefficient of droplets and droplet based Reynolds number, droplet inertia parameter, and two other new parameters. The scaling methodology can also be utilized to determine alternative test conditions to predict rime ice conditions on a rotating blade. The study provides valuable insight to predict ice accretion on large wind turbine blade sections in the field based on scaled smaller blade sections tested in a laboratory setting.

Ventilation Simulation in an Underground Ant Nest Structure of Camponotus japonicus Mayr

Ants are ancient animals on the earth and are known as excellent architects in the animal kingdom. The structure and performance of their nests are full of remarkable mysteries. At present, there are only a limited number of studies on the ventilation performance of underground ant nest structures. In this study, the nests of Camponotus japonicus Mayr were collected manually, and a three-dimensional digital model of the ant nest structure was obtained by the method of industrial CT scanning. The ventilation performance of the Camponotus japonicus Mayr nest structure was numerically simulated using the finite element analysis software, FLUENT. By changing the air inlet and outlet of the nest, the pressure changes inside the nest and the trajectory of the air flow inside the nest could be calculated and analysed, in order to explore the ventilation characteristics of the underground nest structure during natural ventilation. It was found that the ventilation environment inside the nest was stable, and that the external air flow had little effect on the life of the ants inside the nest.

CFD simulation and parameter optimization of the internal flow field of a disturbed air cyclone centrifugal classifier

In the present study, a new disturbance structure is designed to improve the performance of classification air cyclones. To this end, numerical simulations and experiments are carried out to analyze the flow field inside the disturbance structure. It is found that the perturbation structure has a great effect on the velocity and pressure distributions, properties of gas and particles, and the classification performance of the cyclonic air centrifugal classifier. The obtained results show that the pressure and velocity profile in different radial sections has W-shaped and Rankin distributions, respectively. The outer layer is quasi vortex-free, while the inner layer is quasi forced vortex, and the forced vortex is the dominant force field that affects the classification performance. The critical speed of the perturbation structure to reach a uniform stability of the graded flow field is 1500 rpm. When the particle motion path is completed and the trajectory of different particle sizes is regular, the helix angle of the gas flow trajectory is 28°, the gas flow has low speed and high density, the effective graded flow field occupies more space, and the vortex flow field is strong, uniform, and stable. It is found that any speed other than the critical speed (1500 rpm) affects the uniformity and stability of the airflow. The obtained results show that for a rotational speed of 1500 rpm, a feed speed of 0.3 kg/s, and an inclination angle of 4°, macroscopic and microscopic classification efficiencies exceed 91 %. The order of significant effects between parameters was determined as Rf > v > β, and the correlation model between classification index and parameter factors was established. This article is expected to provide a reference to study the influence of internal flow field and classification performance of large-scale industrial air classifiers.

Observation of spatter-induced stochastic lack-of-fusion in laser powder bed fusion using in situ process monitoring

Material produced via additive manufacturing (AM) continues to exhibit variable mechanical properties despite apparent optimization of processing parameters, inhibiting qualification efforts and limiting use in critical applications. Stochastic lack-of-fusion flaws may help explain this variability, but the origin of these seemingly random defects has to this point remained unclear. In this work, we show that spatter particles, material ejected from the laser melt pool, are directly responsible for generating stochastic lack-of-fusion in laser-based powder bed fusion components through the application of spatial statistics. A statistically significant, causal relationship between spatter particles and stochastic lack-of-fusion is established, and the spatial and morphological relationships between spatter and internal flaws are investigated. The occurrence of spatter-induced lack-of-fusion in relation to the inert gas flow and laser trajectory direction is also investigated, and recommendations for mitigating the occurrence of spatter are evaluated.

Using Optical Flow Trajectories to Detect Whitecaps in Light-Polluted Videos

Whitecap formation is an important factor in the exchange of momentum, heat, and gas on the ocean surface. The long-term measurement of whitecaps is necessary to deepen our understanding of the mechanisms of ocean surface motion. However, traditional detection methods are highly sensitive to illumination. Under various illumination conditions, significant light pollution may be introduced into images. The poor performance caused by using images degraded with light pollution is not conducive to automated long-term whitecap measurement. In this study, we propose a two-step method for the detection of whitecaps under various illumination conditions. An abnormal detection method based on previous whitecap detection methods for the accurate detection of whitecaps in light-polluted areas is proposed as the first step. Using the detection results, we propose a post-processing method based on optical flow trajectories at two sampling rates to separate actual whitecap components in images containing false positives. Experiments show that the method proposed in this study can more accurately detect whitecaps in images with light pollution when compared to existing methods.

Flux trajectory analysis of Airy-type beams.

Airy beams are solutions to the paraxial Helmholtz equation known for exhibiting shape invariance along their self-accelerated propagation in free space. These two properties are associated with the fact that they are not square integrable, that is, they carry infinite energy. To circumvent this drawback, families of so-called finite-energy Airy-type beams have been proposed in the literature and, in some cases, also implemented in the laboratory. Here an analysis of the propagation of this type of structured light beam is presented from a flux trajectory perspective with the purpose of better understanding the mechanisms that make infinite and finite energy beams exhibit different behaviors. As is shown, while the foremost part of the beam can be clearly and unambiguously associated with the well-known accelerating term, the rear part of the beam corresponds to a nearly homogeneous distribution of flow trajectories, particularly for long propagation distances. This is shown to be related to an effective transfer of trajectories between adjacent lobes (gradually, from the fore part of the beam to its rear part), which leads to smearing out the transverse flow along the rear part of the beam. This is in sharp contrast to the situation found in ideal Airy beams, where trajectories belonging to a given lobe of the intensity distribution remain the same all along the propagation. The analysis is supplemented with an also trajectory-based description of Young's experiment performed with finite-energy Airy beams to provide a dynamical understanding of the autofocusing phenomenon observed with circular Airy beams.

The interaction analysis between liquid-solid two-phase flow and equipment components in a molten salt pump

Latent heat energy storage is an important issue in the solar energy engineering. As energy storage materials, molten salts release some of latent heat and crystallize. The particles of salt crystals probably collide and rub with the contact parts in the process of movement, and the colliding and rubbing leads to the abrasion or damage of the contact parts. In this study, a dimensionless analysis of the solid-liquid two-phase flow transported by molten salt pump (MSP) was carried out by Buckingham's theorem and the similarity criterion, and the numerical model verified by the theory was used to analyze the flow field in the pump. To accurately evaluate the wear-prone position of the MSP, dozens of monitoring points were arranged on the blade and near the volute tongue. The effects of multiple factors such as the solid particle size, pump inlet particle volume fraction (IPVF), span, and flow rate on the internal flow field and stability of the MSP were studied. The results show that the solid particles mainly concentrate at the inlet and outlet ends of the suction surface of the blades, as well as near the volute tongue. Under low flow rate conditions, the IPVF has a significant influence on the flow trajectory with large-sized particles, whereas has little influence on that of the small-sized particles; when the solid particle size is large, the occurrence of vortex and back flow decreases with the increase of IPVF. The IPVF, curvature of the blade and span have a certain impact on the pressure load, and the greatly affected areas are mainly distributed near the blade head and tail. The research results have certain reference value for improving the anti-wear performance and stable operation of MPSs.

Sample geometry transformation for mechanical tests of constructional materials in an FDM structure

The aim was to obtain a rough determination of the dimensions and shape of a sample for an experimental study of the mechanical characteristics of filamentary FDM-printing structures with a low filling at central tension. The sample geometry was designed based on the dimensions and shape provided in the GOST 17370-2017 “Cellular rigid plastics. Tension testing method”. The research methods included the finite element analysis of stress state parameters in an automated environment, elements of the stiffened shell theory and experimental testing of samples. The theory of stiffened shells was used to simplify the geometry of the finite element model for the studied samples. Finite element analysis was carried out in a linear formulation and, based on the results of its combination with the analysis of the technological model of a designed sample, a decision on transforming the sample geometry was made. The samples were produced using a “line” template with an orientation along the longitudinal axis of the sample. According to the results of testing the samples, a conclusion about the success of implied transformation was made. The success criterion involves the destruction of an FDM sample within the limits of the working part. As a result, both external and internal geometries of the prototype sample were transformed. This allowed the main emphasis in the work of the stretchable FDM sample to be shifted to its working part and the trajectory of power flows to be adjusted according to the FDM-printing specifics. Experimental testing of FDM samples with a low “line” template filling showed a consistently satisfactory result: fractures occurred in the working part of test samples. In the course of the studies, the general trend in the dependence of the force flow distribution over the sample volume on the combination of the printing thread trajectory with external and internal geometries of the sample was determined. Future work will focus on a more detailed analysis and formalisation of the obtained results with regard to various printing templates.

Manufacturing of fine-grained structures by multilevel kinking mechanism through a novel periodic undulating compression method: An example 7075 aluminum alloy

Combining the advantages of high strength and excellent plasticity, fine-grained bulk materials have gained superiority and potential to manufacture lightweight components. However, the efficient preparation of large-sized fine-grained materials remains a challenge, which further hinders their industrial applications. In this study, a novel approach named periodic undulating compression (PUC) and a multilevel kinking mechanism based on this approach were proposed for the fabrication of large-sized fine-grained materials. Compared with conventional severe plastic deformation (SPD) approaches, PUC can realize multi-pass deformation of large-sized materials without changing the dies and can homogeneously accumulate relatively high strain in a single pass deformation. Furthermore, large amounts of kinking band are generated at 350 °C, which improves the conversion of dislocations to grain boundaries, and effectively promotes grain refinement. Due to the complex flow trajectories of materials, and matrix refinement during PUC deformation, the texture intensity can be effectively inhibited with increasing deformation passes. Experimental results indicate that multilevel kinking bands are more efficient at inhibiting the texture intensity than continuous dynamic recrystallization (CDRX). Therefore, the production of ultrafine grained materials for industrial applications is possible with PUC.

Water-rock exchange of Sr isotopes evaluated through a reactive transport model: Application to the El Chichón hydrothermal system

The strontium isotope ratio (87Sr/86Sr) is a natural tracer commonly used to determine water sources, water flow trajectories, and mixing relationships. In high-temperature hydrothermal systems, the low solubility of retrograde minerals such as calcite and anhydrite may significantly reduce the dissolved Sr concentration. Further contribution of Sr along the flow path from isotopically distinct sources will alter and potentially mask the original Sr isotopic signature of the fluid, limiting the potential of 87Sr/86Sr data for reconstructing fluid flow patterns. This study investigates the tracing potential of 87Sr/86Sr in terms of fluid circulation within the El Chichón volcano hydrothermal system. Although limestone aquifers are evidenced in the region, the 87Sr/86Sr signature of most thermal fluids from the volcano does not indicate any major Sr contribution from such lithologies, but rather reveals that Sr is inherited from volcanic rocks. An isotope-enabled reactive transport model is performed to investigate under which conditions a connection between the limestone and volcanic aquifers is compatible with chemical and Sr isotopic compositions of the thermal springs. Results indicate that the 87Sr/86Sr signature of a sedimentary fluid with moderate Sr concentration can be completely modified into a magmatic signature after interacting with Sr-rich primary minerals, such as plagioclases, within short period of times (<1 year). Primary minerals release magmatic Sr to the fluid while secondary minerals (such as calcite) progressively precipitate and remove the initial sedimentary Sr. The El Chichón hydrothermal system hence represents a case where the 87Sr/86Sr of most springs does not keep any memory of the circulation through the sedimentary basement, as magmatic Sr dominates the isotopic signature. A certain analogy exists with hydrothermal fluids vented at oceanic spreading centers, whose 87Sr/86Sr signature departs from seawater and reflects Sr inherited from water-basalt interaction.

Motion Video Recognition in Speeded-Up Robust Features Tracking

Motion video recognition has been well explored in applications of computer vision. In this paper, we propose a novel video representation, which enhances motion recognition in videos based on SURF (Speeded-Up Robust Features) and two filters. Firstly, the detector scheme of SURF is used to detect the candidate points of the video because it is an efficient faster local feature detector. Secondly, by using the optical flow field and trajectory, the feature points can be filtered from the candidate points, which enables a robust and efficient extraction of motion feature points. Additionally, we introduce a descriptor, called MoSURF (Motion Speeded-Up Robust Features), based on SURF (Speeded-Up Robust Features), HOG (Histogram of Oriented Gradient), HOF (Histograms of Optical Flow), MBH(Motion Boundary Histograms), and trajectory information, which can effectively describe motion information and are complementary to each other. We evaluate our video representation under action classification on three motion video datasets namely KTH, YouTube, and UCF50. Compared with state-of-the-art methods, the proposed method shows advanced results on all datasets.

Numerical research of lubricant flow behaviors in rolling-slider bearing under the microscopic scale

In order to reveal the fluid flow behaviors of rolling-slider bearing under the microscopic scale, a full-basin fluid-solid coupling model with different slider shapes is established by CFD and multiple mesh technology. The flow trajectory of fluid is monitored by a slip mesh model, and the dynamics performance is also compared. A reasonable model of rolling-slider bearing is derived. Moreover, this paper analyzes the influence of bearing speed, fluid viscosity, and fluid velocity on fluid behavior. The results show that there is a recirculation flow of fluid and vortex shedding in rolling-slider bearing during the process of lubrication. The distribution of maximum pressure on rolling body is in the orientation of bearing rotation. The fluid flow rate near inner ring is greater than that at outer ring. The established model is suitable for simulating the lubricant flow behaviors of rolling-slider bearings under different working conditions. It also provides a new method for designing the parameters of rolling-slider bearings and the function of working conditions.

Experimental Analysis of Dual Inlet Cyclone Separator

Cyclone separators are suitable to remove particles in extreme conditions with high pressure and temperature during the gas-solid separation process. The important performance of cyclone separators is determined by the separation efficiency and pressure drop. The inlet parameters including the number of inlets, inlet geometry and inlet gas velocity affects the performance of cyclone separators. In this paper, the experimental investigation has been conducted to determine the effects of dual inlet to the separation efficiency of cyclone separators. The cyclone separator was fabricated using the acrylic materials to accommodate the flow observation and trajectories inside the chamber. The experiments were conducted at 9, 11 and 13 m/s of inlet velocity using three particle sizes at 277.5, 42.5 and 625 um. Results showed that as the particle sizes increases, the separation efficiency also increases up to 94.5% for 625 um particles. The findings indicate that the dual inlet cyclone separators increases the performance of cyclone separators especially to remove fly ash in the biomass processing plant and other gas-solid process.

Ecosystems impact on aeolian dust emissions in Inner Mongolia from 2001 to 2018

Aeolian dust emission is a major contributing factor to soil degradation and environmental pollution and threatens human well-being. Inner Mongolia, as an ecological barrier in northern China, is a hot spot of Aeolian dust emission, which indicates that the ecosystems act very important roles in preventing mineral dust from being emitted. In this study, utilizing a widely used model, we aim to identify the impacts of local ecosystems in preventing dust emissions and the corresponding trajectories in Inner Mongolia during 2001–2018. We found that the 18 years accumulated potential dust emission was approximately 12634.027 Tg, about ten times higher than the accumulated actual dust emission (approximately 1274.925 Tg); this showed the ecosystems of Inner Mongolia had prevented 11359.102 Tg mineral dust from being emitted. So, the prevention rate of the ecosystems was approximately 0.899. By studying the flow trajectories of ecosystems dust emission prevention (EDEP), we found that the EDEP worked most frequently in Spring and in the central regions of Inner Mongolia. The effects of EDEP mainly flowed to the areas located on the southeast of Inner Mongolia, like Shanxi, Hebei, Liaoning, Jilin, and Heilongjiang Province. We further identified the distributions of the EDEP benefiting areas and the corresponding beneficiary frequency. We found that the EDEP benefiting areas were distributed in most parts of China, and the regions closer to Inner Mongolia had the higher beneficiary frequency, especially the ones located in the eastern areas. This study provides some valuable theoretical foundations for the economic analysis of restoration projects.