Fan Structure Research Articles

Sympathetic Filament Eruptions within a Fan-spine Magnetic System

Abstract It is unclear whether successive filament eruptions at different sites within a short time interval are physically connected or not. Here, we present the observations of successive eruptions of a small and a large filament in a tripolar magnetic field region whose coronal magnetic field showed as a fan-spine magnetic system. By analyzing the multiwavelength observations taken by the Solar Dynamic Observatory and the extrapolated three-dimensional coronal magnetic field, we find that the two filaments resided respectively in the two lobes that make up the inner fan structure of the fan-spine magnetic system. In addition, a small fan-spine system was also revealed by the squashing factor Q map, which located in the east lobe of the fan structure of the large fan-spine system. The eruption of the small filament was a failed filament eruption, which did not cause any coronal mass ejection (CME) except for three flare ribbons and two post-flare-loop systems connecting the three magnetic polarities. The eruption of the large filament not only caused similar post-flare-loop systems and flare ribbons, as observed in the small filament eruption, but also a large-scale CME. Based on our analysis results, we conclude that the two successive filament eruptions were physically connected, in which the topology change caused by the small filament eruption is thought to be the physical linkage. In addition, the eruption of the small fan-spine structure further accelerated the instability and violent eruption of the large filament.

Localized Acceleration of Energetic Particles by a Weak Shock in the Solar Corona

Abstract Globally propagating shocks in the solar corona have long been studied to quantify their involvement in the acceleration of energetic particles. However, this work has tended to focus on large events associated with strong solar flares and fast coronal mass ejections (CMEs), where the waves are sufficiently fast to easily accelerate particles to high energies. Here we present observations of particle acceleration associated with a global wave event which occurred on 2011 October 1. Using differential emission measure analysis, the global shock wave was found to be incredibly weak, with an Alfvén Mach number of ∼1.008–1.013. Despite this, spatially resolved type iii radio emission was observed by the Nançay RadioHeliograph at distinct locations near the shock front, suggesting localized acceleration of energetic electrons. Further investigation using magnetic field extrapolation identified a fan structure beneath a magnetic null located above the source active region, with the erupting CME contained within this topological feature. We propose that a reconfiguration of the coronal magnetic field driven by the erupting CME enabled the weak shock to accelerate particles along field lines initially contained within the fan and subsequently opening into the heliosphere, producing the observed type iii emission. These results suggest that even weak global shocks in the solar corona can accelerate energetic particles via reconfiguration of the surrounding magnetic field.

Heat Dissipation Structure and Test System Design of a New Piezoelectric Fan

The heat dissipation structure of a new piezoelectric fan is put forward in this paper; the system adopts the piezoelectric fan embedded design, which realizes efficient and stable heat dissipation for the target without increasing the volume of the device. The system adopts the improved piezoelectric fan structure, on the basis of orientation, low power consumption, low cost, and highly efficient heat dissipation, realizes key technologies such as low noise, temperature control, and leakage prevention. This paper introduced composition and characteristics of the new heat dissipation structure in detail and conducted thermal stress simulation, built test platform, carried out temperature test for the physical object, and realized the integrated iterative closed-loop design of thermal design, thermal simulation, and thermal test.

СТРУКТУРА СКЛОНОВОЙ ЛОЖБИННОЙ СЕТИ КРИОЛИТОЗОНЫ В ОКРЕСТНОСТЯХ г. АНАДЫРЯ

Water runoff on the slopes of the permafrost zone passes through a network of hollows of various structures and patterns in plan. This is clearly distinguishable on aerial and satellite images, but often poorly distinguished on the ground. The study is aimed at recognizing the reasons for the difference in the structure of the drainage network, which is necessary for understanding the mechanisms of surface runoff generation and the modern relief formation in the permafrost areas. In the vicinity of Anadyr (Chukotka, Russia), three morphological types of the hollow network were identified. In the areas of distribution of each type of hollow network field observations were made, and the morphometric characteristics of the slopes to which they are associated were obtained from the digital surface model and satellite images. Each type of the hollow network corresponds to definite range of altitude, the type of relief, the slope gradient and profile, the composition of the deposits, and the depth of seasonal thawing. It has been established that although all types of troughs are used by temporary streams, they have different mechanisms of development. The hollows with a fan structure form the densest parallel network with a distance of 10–40 m apart. These are characteristic of concave slopes of interfluves with close bedding of bedrock and are the result of fluvial modeling of irregularities formed as a result of uneven sliding of the slope material (gelifluction). The intertwining troughs are confined to the slopes of the volcanic hills, the steepest of the studied ones. Fresh silty sediments have been observed at their bottoms and their formation is associated with erosional processes. Single hollows located at a considerable (200–300 m) distance from each other are formed in loose quaternary deposits with a developed network of ice-wedge-polygons. The role of thermokarst is significant in their deepening.

Research on the application of on-line monitoring technology for bolt axial force of wind turbine

During wind turbine operation, hub and pitch bearing connection bolts are constantly subject to alternating loads. The axial force of the bolts is an important factor affecting the normal operation of the wind operation. Real-time monitoring of residual axial force can timely feedback the operation of the wind turbine and then the health assessment of the fan structure can be realized. This paper introduces a monitoring system of axial force based on ultrasonic method for measuring bolt axial force. The system can realize the data acquisition of multiple bolts and multiple measuring points in the period. Then, we introduce the engineering application of the system and the corresponding data management system. Through the analysis of the monitoring data, scientific and accurate maintenance of the connection structure is realized, which reduces the operation cost and quality cost. This paper also tests the adaptability of the system to verify its accuracy and reliability at different temperatures.

Modelling foam improved oil recovery: towards a formulation of pressure-driven growth with flow reversal.

The pressure-driven growth model that describes the two-dimensional (2-D) propagation of a foam through an oil reservoir is considered as a model for surfactant-alternating-gas improved oil recovery. The model assumes a region of low mobility, finely textured foam at the foam front where injected gas meets liquid. The net pressure driving the foam is assumed to reduce suddenly at a specific time. Parts of the foam front, deep down near the bottom of the front, must then backtrack, reversing their flow direction. Equations for one-dimensional fractional flow, underlying 2-D pressure-driven growth, are solved via the method of characteristics. In a diagram of position versus time, the backtracking front has a complex double fan structure, with two distinct characteristic fans interacting. One of these characteristic fans is a reflection of a fan already present in forward flow mode. The second fan however only appears upon flow reversal. Both fans contribute to the flow's Darcy pressure drop, the balance of the pressure drop shifting over time from the first fan to the second. The implications for 2-D pressure-driven growth are that the foam front has even lower mobility in reverse flow mode than it had in the original forward flow case.

Multidisciplinary assessment of blade number and manufacturing parameters for the performance of centrifugal fans

This work targets the development of the multidisciplinary design for centrifugal fans, based on the calculation of the fan performance following changes in the fan structure and manufacture. A parametric method that starts from the blade number and manufacturing parameters is first developed to control the shape of fan assembly and its fluid domain. The parametric code, and the aerodynamic and structure analysing codes are then integrated, from the solution of which algorithms are developed to calculate the fan indexes including the flow rate, pressure rise, fan efficiency, fan strength, and the motor power. Validation of the proposed method is performed by the comparison with an experimental test. An orthogonal sampling opens out relevant changes of the fan working performance with respect to the blade number and manufacturing parameters. Results suggest ranges for the blade number and manufacturing parameters that have a sound performance and structure safety when converting the motor power to airflow.

Edge-State Wave Functions from Momentum-Conserving Tunneling Spectroscopy.

We perform momentum-conserving tunneling spectroscopy using a GaAs cleaved-edge overgrowth quantum wire to investigate adjacent quantum Hall edge states. We use the lowest five wire modes with their distinct wave functions to probe each edge state and apply magnetic fields to modify the wave functions and their overlap. This reveals an intricate and rich tunneling conductance fan structure which is succinctly different for each of the wire modes. We self-consistently solve the Poisson-Schrödinger equations to simulate the spectroscopy, reproducing the striking fans in great detail, thus, confirming the calculations. Further, the model predicts hybridization between wire states and Landau levels, which is also confirmed experimentally. This establishes momentum-conserving tunneling spectroscopy as a powerful technique to probe edge state wave functions.

Application of Magnetic Metal 3-D Printing on the Integration of Axial-Flow Impeller Fan Motor Design

This article aims to implement a fan motor design with an airfoil-shaped rotor via the newly developed 3-D printing method. This integrated design is originated from a flux-switching permanent magnet motor, in which the motor rotor can directly produce airflow without any external impellers. Such a design and manufacturing process can effectively enhance the robustness of the fan motor structure and increase its power density. This article adopts 3-D finite element analysis for electromagnetic and fluid field simulation. Moreover, a new metal 3-D printing method with a low core loss feature during high frequency operation is applied. Finally, the experimental results with a prototype are presented to verify the designed performance.

Quantum-limit Chern topological magnetism in TbMn6Sn6.

The quantum-level interplay between geometry, topology and correlation is at the forefront of fundamental physics1-15. Kagome magnets are predicted to support intrinsic Chern quantum phases owing to their unusual lattice geometry and breaking of time-reversal symmetry14,15. However, quantum materials hosting ideal spin-orbit-coupled kagome lattices with strong out-of-plane magnetization are lacking16-21. Here, using scanning tunnelling microscopy, we identify a new topological kagome magnet, TbMn6Sn6, that is close to satisfying these criteria. We visualize its effectively defect-free, purely manganese-based ferromagnetic kagome lattice with atomic resolution. Remarkably, its electronic state shows distinct Landau quantization on application of a magnetic field, and the quantized Landau fan structure features spin-polarized Dirac dispersion with a large Chern gap. We further demonstrate the bulk-boundary correspondence between the Chern gap and the topological edge state, as well as the Berry curvature field correspondence of Chern gapped Dirac fermions. Our results point to the realization of a quantum-limit Chern phase in TbMn6Sn6, and may enable the observation of topological quantum phenomena in the RMn6Sn6 (where Ris a rare earth element) family with a variety of magnetic structures. Our visualization of the magnetic bulk-boundary-Berry correspondence covering real space and momentum space demonstrates a proof-of-principle method for revealing topological magnets.

Analysis and comparison of potential power and thermal management systems for high-speed aircraft with an optimization method

• An advanced PTMS with an indirect regenerative air cycle is analyzed. • A comparison based on minimum fuel weight penalty optimization is proposed. • Optimal matching of the PTMS and flight mission is achieved at Mach 1-4.4. • The PTMS with a ram air bleed mode is suitable for Mach 3.4–4.4 cruise aircraft. Under the dual effects of aerodynamic heating and high-power electronic equipment heating, the heat sink and power demand of advanced high-speed aircraft have been exponentially rising, which seriously restricts the aircraft performance. To improve system cooling and power supply performance and reduce engine performance loss, a power and thermal management system (PTMS) with high performance, low energy consumption, and light weight urgently needs to be developed. In this paper, three modes of a potential PTMS with different heat sinks and bleed air sources are further discussed to analyze and compare the optimal matching with the flight mission at Mach 1–4.4. The equivalent mass method is used to uniformly assess the costs of the fixed weight, bleed, resistance, etc. as a function of the fuel weight penalty, which is chosen as the optimization objective. The optimization variables consist of the compressor outlet temperature, cooling air flow rate, and fan duct heat exchanger structure size. The results show that the intermediate-stage bleed air and fan duct heat sink are more suitable when the Mach number is less than 2, but the ram air bleed is highly suitable for flight missions at a high Mach number. Especially at Mach 3.4–4.4, the ram air bleed mode can respond to the cooling and power demands with a simple architecture.

Geomorphological evolution and sediment stratigraphy of numerically simulated alluvial fans

AbstractWhen a sediment laden river reaches a flat basin area the coarse fraction of their sediment load is deposited in a cone shaped structure called an alluvial fan. In this article we used the State Space Soil Production and Assessment Model (SSSPAM) coupled landform–soilscape evolution model to simulate the development of alluvial fans in two‐ and three‐dimensional landforms. In SSSPAM the physical processes of erosion and armouring, soil weathering and sediment deposition were modelled using state‐space matrices, in both two and three dimensions. The results of the two‐dimensional fan showed that the fan grew vertically and laterally keeping a concave up long profile. It also showed a downstream fining of the sediments along the fan profile. Both of these observations are in agreement with available literature concerning natural and experimental fan formations. Simulations with the three‐dimensional landform produced a fan with a semicircular shape with concave up long profiles and concave down cross profiles which is typical for fans found in nature and ones developed in laboratory conditions. During the simulation the main channel which brings sediment to the fan structure changed its position constantly leading to the semicircular shape of the fan. This behaviour is similar to the autogenic process of ‘fanhead trenching’ which is the major mechanism of sediment redistribution while the fan is developing. The three‐dimensional fan simulation also exhibited the downstream fining of sediments from the fan apex to the peripheries. Further, the simulated fan also developed complex internal sediment stratification which is modelled by SSSPAM. Currently such complex sediment stratification is thought to be a result of allogenic processes. However, this simulation shows that, such complex internal sediment structures can develop through autogenic processes as well. © 2020 John Wiley & Sons, Ltd.

Heating and Eruption of a Solar Circular-ribbon Flare

Abstract We studied a circular-ribbon flare, SOL2014-12-17T04:51, with emphasis on its thermal evolution as determined by the differential emission measure (DEM) inversion analysis of the extreme ultraviolet (EUV) images of the Atmospheric Imaging Assembly instrument on board the Solar Dynamics Observatory. Both temperature and emission measure start to rise much earlier than the flare, along with an eruption and formation of a hot halo over the fan structure. In the main flare phase, another set of ribbons forms inside the circular ribbon, and expands as expected for ribbons at the footpoints of a postflare arcade. An additional heating event further extends the decay phase, which is also characteristic of some eruptive flares. The basic magnetic configuration appears to be a fan–spine topology, rooted in a minority-polarity patch surrounded by majority-polarity flux. We suggest that reconnection at the null point begins well before the impulsive phase, when the null is distorted into a breakout current sheet, and that both flare and breakout reconnection are necessary in order to explain the subsequent local thermal evolution and the eruptive activities in this confined magnetic structure. Using local DEMs, we found a postflare temperature increase inside the fan surface, indicating that the so-called EUV late phase is due to continued heating in the flare loops.

On the inertial wave activity during spin-down in a rapidly rotating penny shaped cylinder: a reduced model

In a previous paper, Oruba et al. (J. Fluid Mech., vol. 818, 2017, pp. 205-240) considered the 'primary' quasi-steady geostrophic (QG) motion of a constant density fluid of viscosity ⌫ that occurs during linear spin-down in a cylindrical container of radius r † = L and height z † = H, rotating rapidly (angular velocity ⌦) about its axis of symmetry subject to mixed rigid and stress-free boundary conditions for the case L = H. Here, Direct numerical simulation at large L = 10H and Ekman numbers E = ⌫/H 2 ⌦ in the range = 10 3-10 7 reveals inertial wave activity on the spin-down time scale E 1/2 ⌦ 1. Our analytic study, based on E ⌧ 1, builds on the results of Greenspan & Howard (J. Fluid Mech., vol. 17, 1963, pp. 385-404) for an infinite plane layer L ! 1. In addition to QG spin-down, they identify a 'secondary' set of quasi-maximum frequency ! † ! 2⌦ (MF) inertial waves, which is a manifestation of the transient Ekman layer, decaying algebraically / 1/ p t †. Here, we acknowledge that the blocking of the meridional parts of both the primary-QG and the secondary-MF spin-down flows by the lateral boundary r † = L provides a trigger for other inertial waves. As we only investigate the response to the primary QG-trigger, we call the model 'reduced' and for that only inertial waves with frequencies ! † < 2⌦ are triggered. We explain the ensuing organised inertial wave structure via an analytic study of the thin disc limit L H restricted to the region L r † = O(H) far from the axis, where we make a Cartesian approximation of the cylindrical geometry. Other than identifying a small scale fan structure emanating from the corner [r † , z † ] = [L, 0], we show that inertial waves, on the gap length scale H, radiated (wave energy flux) away from the outer boundary r † = L (but propagating with a phase velocity towards it) reach a distance determined by the mode with the fastest group velocity.

The Formation of CME from Coupling Fan-spine Magnetic System: A Difficult Journey

Abstract We present the eruption of a mini-filament that caused a large-scale complicated coronal mass ejection (CME) on 2014 March 28, using the high-resolution observations taken by the Solar Dynamic Observatory. Three-dimensional coronal magnetic field extrapolated from the nonlinear force-free field code reveals that the magnetic environment of the eruption source region was a large fan-spine magnetic system that hosted another small fan-spine system under its fan, and the mini-filament was located under the fan structure of the small fan-spine system. Our analysis results suggest that the eruption of the mini-filament underwent three reconnection processes before the formation of the CME. First, the erupting filament triggered the null point reconnection in the small fan-spine system. During this stage, the sudden expansion of the spine field lines also excited a large-scale extreme-ultraviolet wave. Second, the spine field lines of the small fan-spine system were pushed up by the erupting filament and therefore further triggered the null point reconnection in the large fan-spine magnetic system. Third, during the second stage, magnetic reconnection also occurred between the two legs of the stretched confining field lines of the mini-filament. The present study suggests that the formation of the observed CME from the coupling fan-spine magnetic system was more complicated than previously thought, needing to undergo multistage magnetic reconnection processes in the low corona.

Round-trip Slipping Motion of the Circular Flare Ribbon Evidenced in a Fan-spine Jet

Abstract A solar jet that occurred on 2014 July 31, which was accompanied by a GOES C1.3 flare and a mini-filament eruption at the jet base, was studied by using observations taken by the New Vacuum Solar Telescope and the Solar Dynamic Observatory. Magnetic field extrapolation revealed that the jet was confined in a fan-spine magnetic system that hosts a null point at the height of about 9 Mm from the solar surface. An inner flare ribbon surrounded by an outer circular ribbon and a remote ribbon were observed to be associated with the eruption, in which the inner and remote ribbons, respectively located at the footprints of the inner and outer spines, while the circular one manifested the footprint of the fan structure. It is worth noting that the west part of the circular ribbon exhibited an interesting round-trip slipping motion, while the inner ribbon and the circular ribbon’s east part displayed a northward slipping motion. Our analysis results indicate that the slipping motions of the inner and the circular flare ribbons reflected the slipping magnetic reconnection process in the fan’s quasi-separatrix layer, while the remote ribbon was associated with the magnetic reconnection at the null point. In addition, the filament eruption was probably triggered by the magnetic cancellation around its south end, which further drove the slipping reconnection in the fan quasi-separatrix layer and the reconnection at the null point.

Same but different: Socially foraging ants backtrack like individually foraging ants but use different mechanisms

Diverse species may adopt behaviourally identical solutions to similar environmental challenges. However, the underlying mechanisms dictating these responses may be quite different and are often associated with the specific ecology or habitat of these species. Foraging desert ants use multiple strategies in order to successfully navigate. In individually foraging ants, these strategies are largely visually-based; this includes path integration and learned panorama cues, with systematic search and backtracking acting as backup mechanisms. Backtracking is believed to be controlled, at least in solitary foraging species, by three criteria: 1) foragers must have recent exposure to the nest panorama, 2) the path integrator must be near zero, and 3) the ant must be displaced to an unfamiliar location. Instead of searching for the nest, under these conditions, foragers head in the opposite compass direction of the one in which they were recently travelling. Here, we explore backtracking in the socially foraging desert harvester ant (Veromessor pergandei), which exhibits a foraging ecology consisting of a combination of social and individual cues in a column and fan structure. We find that backtracking in V. pergandei, similar to solitary foraging species, is dependent on celestial cues, and in particular on the sun’s position. However, unlike solitary foraging species, backtracking in V. pergandei is not mediated by the same criteria. Instead the expression of this behaviour is dependent on the presence of the social cues of the column and the proportion of the column that foragers have completed prior to displacement.

Analysis of Flow Field Characteristics of Unequal Distance Fans

This paper establishes the simulation model of the unequal-distance fan, obtains the details of the flow field when the fan works by CFD simulation method, and analyses the internal flow field characteristics of the unequal-distance fan from three aspects: streamline trace distribution, pressure distribution and velocity distribution, so as to get the working condition of the fan, which is of great significance for the design and transformation of the fan structure.

Weak shock reflection in channel flows for dense gases

The canonical problem of transonic dense gas flows past two-dimensional compression/expansion ramps has recently been investigated by Kluwick &amp; Cox (J. Fluid Mech., vol. 848, 2018, pp. 756–787). Their results are for unconfined flows and have to be supplemented with solutions of another canonical problem dealing with the reflection of disturbances from an opposing wall to finally provide a realistic picture of flows in confined geometries of practical importance. Shock reflection in dense gases for transonic flows is the problem addressed in this paper. Analytical results are presented in terms of similarity parameters associated with the fundamental derivative of gas dynamics$(\unicode[STIX]{x1D6E4})$, its derivative with respect to the density at constant entropy$(\unicode[STIX]{x1D6EC})$and the Mach number$(M)$of the upstream flow. The richer complexity of flows scenarios possible beyond classical shock reflection is demonstrated. For example: incident shocks close to normal incidence on a reflecting boundary can lead to a compound shock–wave fan reflected flow or a pure wave fan flow as well as classical flow where a compressive reflected shock attached to the reflecting boundary is observed. With incident shock angles sufficiently away from normal incidence regular reflection becomes impossible and so-called irregular reflection occurs involving a detached reflection point where an incident shock, reflected shock and a Mach stem shock which remains connected to the boundary all intersect. This triple point intersection which also includes a wave fan is known as Guderley reflection. This classical result is demonstrated to carry over to the case of dense gases. It is then finally shown that the Mach stem formed may disintegrate into a compound shock–wave fan structure generating an additional secondary upstream shock. The aim of the present study is to provide insight into flows realised, for example, in wind tunnel experiments where evidence for non-classical gas dynamic effects such as rarefaction shocks is looked for. These have been predicted theoretically by the seminal work of Thompson (Phys. Fluids, vol. 14 (9), 1971, pp. 1843–1849) but have withstood experimental detection in shock tubes so far, due to, among others, difficulties to establish purely one-dimensional flows.

Electrical structure of the Kunlun–Qinling fault system, northeastern Tibetan Plateau, inferred from 3-D inversion of magnetotelluric data

Located in the northeastern Tibetan Plateau, the East Kunlun fault is a west–east left-lateral strike-slip fault that branches out into a horsetail-shaped structure known as the Kunlun–Qinling Fault system (KQFS) at its eastern terminus. The 2017 Jiuzhaigou Ms 7.0 earthquake occurred in this horsetail-shaped structure. The electrical structures of four profiles that cross different sections of the KQFS and Jiuzhaigou earthquake region are obtained in this study. Our results reveal key differences among these sections. The East Kunlun fault is the only electrical boundary in the Maqu section, whereas the Tazang, Bailongjiang, and Guanggaishan–Dieshan faults in the Tazang section form an imbricate fan structure that extends from south to north and merges into a high conductivity layer (HCL) in the mid–lower crust. Alternating high and low resistivity bodies below the KQFS revealed by the magnetotelluric method (MT) may be related to the cause of slip rate segmentation from the East Kunlun fault into the KQFS. The hypocenter of the 2017 Ms 7.0 Jiuzhaigou earthquake lies between the high and low resistivity bodies at the northeastern, shallowing edge of the HCL. The northern section of the Huya fault corresponds to a deep crustal electrical boundary. The Huya and Tazang faults form a one-sided imbricate fan structure that merges at depth into the HCL. The HCL is deep in the southwestern part of our study area but shallows to the northeast. This observation suggests that northeast movement of the Tibetan Plateau causes tectonic uplift and the frequent occurrence of strong earthquakes in this region.