Field Characteristics Research Articles

Simulation and analysis of the over-expanded flow field in asymmetric nozzles with lateral expansion

Abstract Numerical simulations of a three-dimensional asymmetric nozzle with lateral expansion were carried out, focusing on the characteristics of the three-dimensional flow field in the over-expanded state and the influence of the sidewall surface profiles on the over-expanded flow field. The results show that the sidewall profiles cause the separation zones inside the nozzle to exhibit different shapes. The center separation bubble and the corner zone separation bubble are independent of each other in the lower wall surface confined shock wave separation mode. In the upper wall-constrained shock wave separation mode, the center separation bubble, the corner zone separation bubble, and the sidewall surface separation bubble are interconnected. Under the same drop pressure ratio, changes in the sidewall profile affect the shape and size of the separation zones, and the convex wall can slow the occurrence of separation to a certain extent.

Feature selectivity and invariance in marsupial primary visual cortex.

A fundamental question in sensory neuroscience revolves around how neurons represent complex visual stimuli. In mammalian primary visual cortex (V1), neurons decode intricate visual features to identify objects, with most being selective for edge orientation, but with half of those also developing invariance to edge position within their receptive fields. Position invariance allows cells to continue to code an edge even when it moves around. Combining feature selectivity and invariance is integral to successful object recognition. Considering the marsupial-eutherian divergence 160million years ago, we explored whether feature selectivity and invariance was similar in marsupials and eutherians. We recovered the spatial filters and non-linear processing characteristics of the receptive fields of neurons in wallaby V1 and compared them with previous results from cat cortex. We stimulated the neurons in V1 with white Gaussian noise and analysed responses using the non-linear input model. Wallabies exhibit the same high percentage of orientation selective neurons as cats. However, in wallabies we observed a notably higher prevalence of neurons with three or more filters compared to cats. We show that having three or more filters substantially increases phase invariance in the V1s of both species, but that wallaby V1 accentuates this feature, suggesting that the species condenses more processing into the earliest cortical stage. These findings suggest that evolution has led to more than one solution to the problem of creating complex visual processing strategies. KEY POINTS: Previous studies have shown that the primary visual cortex (V1) in mammals is essential for processing complex visual stimuli, with neurons displaying selectivity for edge orientation and position. This research explores whether the visual processing mechanisms in marsupials, such as wallabies, are similar to those in eutherian mammals (e.g. cats). The study found that wallabies have a higher prevalence of neurons with multiple spatial filters in V1, indicating more complex visual processing. Using a non-linear input model, we demonstrated that neurons with three or more filters increase phase invariance. These findings suggest that marsupials and eutherian mammals have evolved similar strategies for visual processing, but marsupials have condensed more capacity to build phase invariance into the first step in the cortical pathway.

RESEARCH STATUS, HOTSPOTS AND EVOLUTİON İN THE FİELD OF ONLİNE MUSİC EDUCATİON: A BİBLİOMETRİC REVİEW

ABSTRACT In the contemporary era of swift informational advancement, the rapid progression of digital technology has become especially significant, profoundly reshaping numerous fields. Globally, the demand for personalized learning, an emerging educational model, is increasing day by day, while the discussion and pursuit of unified educational standards are also gradually strengthening. This parallel pursuit of educational diversity and standardization reflects society's expectations and demands for high-quality education. Against this backdrop, we have witnessed the transformation of educational models, particularly the widely recognized and valued importance of collaborative learning and the sharing of educational resources. This trend is not only evident in traditional educational practices but also significantly manifested and developed in the field of online education. In this wave of educational change, the online music education sector has attracted widespread attention with its unique charm and potential. Music education, as an artistic form rich in creativity and emotional expression, has provided learners with brand-new learning experiences and possibilities through its online trend. However, despite the rapid development of online music education, existing research lags, particularly in the quantitative and empirical analysis of bibliometric indicators such as influential authors, popular topics, and evolutionary trends. To fill this gap, our research utilizes abundant data from the globally authoritative Web of Science (WOS) database. Through systematic literature review and analysis, we aim to reveal the core content and characteristics of the online music education field. In this process, we employ VOSviewer, a powerful analytical tool, which helps us gain a deep understanding of multiple dimensions within this field, including the distribution of authors, geographical contributions, key journals, co-occurring keywords, and co-cited references. Through this series of in-depth analyses, we not only clearly depict the current status of the online music education field but also reveal its frontier hotspots and future evolution trends. The insights from this study aim to provide scholars and educators in this field with a comprehensive and multidimensional perspective, serving as a strong reference and guidance for their future research and work.

Non-monotonically changes in double Schottky barrier of MnCO3–doped ZnO varistors during DC aging

Abstract ZnO varistors play a crucial role as core component in metal oxide arresters due to their excellent nonlinear current density-electrical field (J–E) characteristics. After long-term operation under DC stress (DC aging), the J–E curves of ZnO varistors invented in the last decade cross with the original curve. Unexpectedly, the ‘crossover’ phenomenon cannot be explained by the vastly-accepted ion migration mechanism by which the barrier height monotonically declines after DC aging. In the present study, aging and recovery experiments were carried out on MnCO3-doped ZnO varistors. The symmetry of J–E characteristics in the same direction as and the opposite direction to the DC stress was compared, parameters of double Schottky barrier were analyzed, and evolution of point defects was deduced using dielectric spectra. It was found that, in addition to ion migrations, there are electrons ionized by zinc interstitials filling the interface states in the early stage of aging. Because these processes are dominant in different stages, the barrier height changes non-monotonically. MnCO3 can suppress the formation of zinc interstitials, so it simultaneously inhibits ion migrations and filling of the interface states by electrons. When 0.38 mol% MnCO3 is doped, J–E characteristics and the Schottky barrier of ZnO varistors show the smallest deviations during aging and recovery. The findings are helpful in updating criteria for the long-term stability of ZnO varistors and suggest that modifications to their formulae targeting the suppression of the filling the interface states by electrons are also expected to bolster the stability.

VOF-based modeling study of surface oscillation behavior and gas–liquid stirring dynamics in the bottom-blown reactors

Gas bottom-blown reactors are widely employed in the chemical, metallurgical, and biochemical industries due to their superior mixing capabilities. This study numerically investigates the gas–liquid flow hydrodynamics and bubble dynamics in a bottom-blown system with a circular boundary using the volume of fluid approach. Following the experimental validation of the mathematical model, the study evaluates the effects of gas flow rates, liquid heights, and fluid medium properties on both the dynamics of the bubble swarm and the mixing characteristics of the flow field. The results indicate that: (1) Rising bubbles disturb the fluid, generating numerous vortices that facilitate momentum transfer for effective gas stirring; (2) The height of the liquid surface oscillation during the bottom-blown process exhibits significant temporal variation, with the peak showing clear lateral swings; (3) Due to the nonlinear interactions involving bubble coalescence and breakup during their ascent, along with constructive and destructive interference between liquid surface waves, the liquid surface can exhibit violent fluctuations at certain moments; (4) Bubble size and aspect ratio significantly influence liquid surface oscillations; (5) The bubble rising path displays instability due to vortex shedding, with some vortices forming at locations where the bubble shape changes abruptly. A bubble velocity prediction equation is proposed: uc=σ5.2737Lcρc4.2737/16156μl9.5475.

Research on transparency of coal mine geological conditions based on distributed fiber‐optic sensing technology

AbstractCoal mining induces changes in the nature of rock and soil bodies, as well as hydrogeological conditions, which can easily trigger the occurrence of geological disasters such as water inrush, movement of the coal seam roof and floor, and rock burst. Transparency in coal mine geological conditions provides technical support for intelligent coal mining and geological disaster prevention. In this sense, it is of great significance to address the requirements for informatizing coal mine geological conditions, dynamically adjust sensing parameters, and accurately identify disaster characteristics so as to prevent and control coal mine geological disasters. This paper examines the various action fields associated with geological disasters in mining faces and scrutinizes the types and sensing parameters of geological disasters resulting from coal seam mining. On this basis, it summarizes a distributed fiber‐optic sensing technology framework for transparent geology in coal mines. Combined with the multi‐field monitoring characteristics of the strain field, the temperature field, and the vibration field of distributed optical fiber sensing technology, parameters such as the strain increment ratio, the aquifer temperature gradient, and the acoustic wave amplitude are extracted as eigenvalues for identifying rock breaking, aquifer water level, and water cut range, and a multi‐field sensing method is established for identifying the characteristics of mining‐induced rock mass disasters. The development direction of transparent geology based on optical fiber sensing technology is proposed in terms of the aspects of sensing optical fiber structure for large deformation monitoring, identification accuracy of optical fiber acoustic signals, multi‐parameter monitoring, and early warning methods.

Sloshing-induced evolution of self-cleaning performance and flow characteristics within a tank installed on an offshore aquaculture vessel

In this study, a six-degree-of-freedom (6-DOF) motion platform is utilized to simulate the transverse rolling motion of aquaculture tanks aboard deep-sea aquaculture vessels. It examines the effects of different inlet configurations (single and four-pipe inlet), rolling motions (amplitude Θ and period T), and inlet pipe jet angles α (the acute angle between the jet direction of the inlet pipe and the inclined wall to which it is connected) on the self-cleaning capabilities and flow field characteristics of the aquaculture tank. The findings indicate that the waste collection time in the tank is affected by the combined influences of rolling amplitude and period. In the single-pipe inlet configuration, waste collection time increases with the rolling period and initially increases, then decreases with the rolling amplitude. In the four-pipe inlet configuration, waste collection time increases with the rolling period and decreases with the rolling amplitude. Optimal waste collection performance is achieved at α = 45° in both configurations. Regarding flow field characteristics, variations in rolling period and amplitude significantly alter the flow field within the aquaculture tank. In both configurations, as the period decreases and the amplitude increases, the high-velocity regions and the central vortex area within the tank expand, and the average flow velocity of the water also rises. This corresponds to a reduction in waste collection time and an increase in the waste collection rate. In both configurations, the Flow field is most uniform at α = 45°, which corresponds to the highest waste collection capabilities among all jet angles. The results indicate that while decreasing the rolling period and increasing the amplitude can enhance the self-cleaning capabilities, they also lead to excessively rapid water flow velocities. In practical applications, it is important to select appropriate farming areas based on fish suitability and to choose the correct inlet jet angles for different numbers of inlets. The findings can provide theoretical support and a scientific basis for optimizing the flow characteristics and self-cleaning performance of aquaculture vessels under rolling motion and contribute positively to the advancement of deep-sea aquaculture technology.

Rotating machinery flow field prediction based on hybrid neural network

ABSTRACT The flow phenomena in fluid machinery such as pumps, wind turbines and turbines are complex. For large-scale engineering problems, the computational resources required to solve the Navier-Stokes(N-S) equation are large. In order to solve this problem, a fast and accurate solution method based on hybrid neural network (Convolutional Neural Network – Long Short-Term Memory) is proposed. The nonlinear mapping relationship between the flow field characteristics of rotating machinery and the eddy viscosity coefficient is constructed. The deep learning model is used to replace the RANS standard k-ϵ model, and the eddy viscosity coefficient distribution cloud diagram of rotating machinery is obtained. The results show that the predicted value of the eddy viscosity coefficient of the hybrid neural network model on different slices is in good agreement with the original value and the error is small. Compared with traditional machine learning models such as random forest model, hybrid neural network model takes up only 11.4% of memory, and the accuracy is much better than the random forest model. The hybrid neural network model proposed in this paper has great potential in the prediction of the flow field of rotating machinery.

Heat transfer and fluid flow analysis in circular tubes with multi-delta-winglets vortex generators

In this work, the positive projection plane of self-join winglet vortex generator is modified into a non-circular design, aiming to provide novel insights into optimizing vortex interaction in tubes equipped with winglets. The experimental and numerical investigation of heat transfer and fluid flows in circular tubes equipped with multi-delta-winglets vortex generators is conducted. The influence of three structural parameters (included angle (α), blockage ratio (BR), winglet pairs number (PN)) on the thermal performance of the enhanced tube are explored across a Reynolds number range of 7577 to 27,276. It is found that the vortex pairs near the tube wall contribute to enhancing the mixing uniformity of fluid flows in tubes. Furthermore, the dissipation intensity of the vortex pairs near the tube wall is increased with increasing α. The Nusselt number and friction factor are increased by 1.90–2.32 and 2.23–5.10 times, respectively, compared with the smooth tube. The maximum thermal enhancement factor reaches 1.63 when BR = 0.10, PN = 4, and α = 90°. Optimization strategies are performed through similarity analysis, and the similarity equations between structural parameters and flow field characteristics are obtained. These findings offer valuable theoretical insights for the design of winglet structures and the optimization of flow fields.

Causal Effect of Leading-Edge Sawtooth Configuration on Flow Field Characteristics and Aerodynamic Losses in the Supersonic Compressor Cascade

Causal Effect of Leading-Edge Sawtooth Configuration on Flow Field Characteristics and Aerodynamic Losses in the Supersonic Compressor Cascade

Investigation on the integrated characteristics of n-decane/air rotating detonation combustor and supersonic turbine

In this study, the two-dimensional numerical simulations are conducted to study the flow field characteristics, turbine performance and loss mechanism of integrated system of rotating detonation combustor and supersonic turbine under two different directions of detonation wave propagation. The results indicate that the propagation direction of RDW affects the incident angle between OSW and guide vanes, resulting in different operating modes for aligned and unaligned modes. OSW in the turbine cascade undergoes the leading-edge shock, blade surface reflection and trailing edge diffraction. The backward-propagating rake-type shock envelope is formed due to leading-edge shock of the rotor. In misaligned mode, the stator has higher damping of both pressure and temperature. The stator significantly improves the circumferential uniformity of both velocity and pressure, particularly when operating in aligned mode. The total pressure loss in aligned mode is less, therefore the turbine achieves higher rim work and efficiency. The viscosity is one of the main sources of loss in the flow field. The reflected shock waves at the leading edge of the rotor and in the stator cascade are the primary factors contributing to the leading-edge vortices on the stator vanes.

Numerical Simulation of Hydrodynamic Properties of Perforated Corrugated Sheet Materials

Packings are widely used as important materials in the chemical industry, but their internal structure is complex and the study of their internal fluid dynamics is still challenging. The hydrodynamic properties inside a Perforated corrugated sheet packing are simulated. The flow field characteristics of the packings with different pore sizes and the main mechanisms causing changes in the dry pressure drop were analyzed. It was found that the drag coefficient gradually converges to a constant as the Reynolds number increases. The factors affecting the variation of dry pressure drop varied with the Reynolds number. Under low Reynolds number conditions, the drag coefficient is the main influencing factor, while with the increase in Reynolds number, the role of the drag coefficient gradually decreases and the void fraction becomes the main influencing factor. The conclusions obtained can be used as a reference for the optimal design of packing.

Experimental study on aeration characteristics of plunging wave impact on a vertical cylinder

The impact force exerted by plunging breakers on structures is most pronounced, with the impact pressure being most sensitive to the changes in air entrainment, posing a threat to the structural safety of offshore wind turbines. However, the current explanations of the high impact force mechanisms in plunging waves are relatively superficial, and the relationship between the air entrainment motion and pressure oscillations remains unclear. According to the experimentally obtained pressure characteristics and the formation of entrapped air, this paper systematically divides the process of plunging wave impact on a vertical cylinder into three stages: breaking wave crest impact, entrained air cavity impact, and plume impact. Employing a bubble image velocimetry platform to visualize flow field characteristics and quantify turbulence intensity, we investigated the connection between gas motion and impact loads. The results indicate that the conversion of gas energy is closely related to the load characteristics, with the maximum impact force occurring near the peak of the energy gradient. The gas movement significantly influences pressure oscillations, which are positively correlated with the gas's physical compression and expansion characteristics. This study has uncovered new insights into the phenomenon of plunging waves impacting wind turbine towers and has enhanced the understanding of its load characteristics.

Experimental investigation to analyze the electromagnetic radiation exposure from wireless communication devices

Recent advancements in wireless communication technologies have led to the existence of a higher amount of electromagnetic radiation (EMR) in the atmosphere. The intensity of these exposed radiation depends upon the frequency of operation from these communication devices. The paper presents a scientific study on assessing the intensity of electromagnetic waves emitted by different wireless communication devices with human beings based on analyzing the electric field, magnetic field and power density generated from various electronic gadgets and wireless communication devices like smartwatch, laptop, mobile phone, nano-station, headset and mobile towers using an electro-smog meter (Electromagnetic Field (EMF) Meter - PCE-EM 29). The interaction is being studied by placing different wireless communication equipment near to human body. Based on the study, it is identified that a portion of the EMR is absorbed by nearby human beings and is identified by differentiating the field characteristics with and without its presence and is tested in near or far away from the devices. From the test results, it is identified that a portion of the EMR is absorbed by the body parts of the human beings near to the wireless device. This result could act as scientific evidence providing the effects of EMR interactions like electromagnetic hypersensitivity symptoms on humans. Similarly, most of the field exposures from the radiating devices are highly influenced by all the biotic community including human beings based on its interaction. All these field exposures to radiation from various wireless communication devices are direct indications of the Specific Absorption Rate (SAR).

A Numerical Study on Cloud Structure of Typical Summer Precipitation Process over Liupan Mountain Area

Using Weather Research and Forecasting model (WRF), four microphysical schemes (Lin, Goddard, WSM6 and Thompson) were applied for precipitation simulations over southern Ningxia on July 21st, 2024. The simulated results are used to analyze the impact of different microphysical schemes on summertime precipitation processes. The sensitivity experiments show the precipitation process simulated by WSM6 and Thompson schemes are closer to observed precipitation than Lin and Goddard schemes in Southern Ningxia mountainous areas. The evolution characteristics of the dynamic field, water vapor field, and microphysical structures of cloud structures are analyzed. In vertical direction, the cloud system in mountainous areas generally displays a structure of "catalysis-supply". The structure of water condensation in each layer of cloud is different, leading to differences in the contribution of various microphysical processes to precipitation. The super-cooled cloud water is the main source for rain water production. When cloud system grows upward, the abundant cloud water layer simultaneously enhances the microphysical processes within clouds. On the windward slope (eastern part) of the mountain, deep warm cloud layer will contribute to the development of warm cloud precipitation process, which leads to enhanced precipitation under the combined action of cold and warm clouds.

A comprehensive analysis of the tail-dependent structure of wind loads and its engineering applications

Wind load field characteristics on the roof surface of low-rise buildings based on field measurements have crucial engineering guidance value. In the background, tail-dependence structure from measured wind loads can assist in modeling the joint tail distribution of multivariate wind loads. In this study, the non-parameter estimation method, multi-copula function model and multivariate peak over threshold model are applied to estimate its precise value. The upper tail dependence coefficient's value is around 0.20 when the quantile for p(y) = 0.75. When p(y) = 0.95, the Gumbel copula overestimates the tail-dependence value slightly. Additionally, the lower tail-dependence values estimated by the Clayton copula are around 0.19 at 0.25 quantile. For extreme tail-dependence coefficients, little difference exists in the estimated results by the non-parameter estimation method and the peak over threshold model, in which its value varies from 0.80 to 0.90. Under roof pitch = 5°, its value exhibits some dispersion at different locations. An area weight function is applied to estimate the extreme tail-dependence value between critical regions. Then, the expectation function of tail dependence reaches the peak value in p(x) = 0.50, p(y) = 0.50 and it has different gradients for different variables and tail regions. Additionally, the lower tail dependence structure is significantly stronger than the upper tail dependence for wind loads with negative skewness. For application in wind engineering, potential applications in risk analysis for roof structures, extreme value estimation for local region block wind load, and wind load forecast for unmonitored locations are proposed.

Experimental study on the effect of wall proximity on the flow around a cylinder under an axial magnetic field

Investigations are conducted on the effect of wall proximity on the flow around a cylinder under an axial magnetic field, using the electrical potential probe technology to measure the velocity of liquid metal flow. The study focused on the impact of the inlet velocity of the fluid, the magnetic field and wall proximity on the characteristics of velocity fields, particularly on the vortex-shedding mode. Based on different magnitudes of the magnetic field and the distance from the cylinder to the duct wall, three types of vortex-shedding modes are identified, (I) shear layer oscillation state, (II) quasi-two-dimensional vortex-shedding states and (III) transition of the magnetohydrodynamic to hydrodynamic Kármán street. The transitions between these modes are analysed in detail. The experimental results show that the weak wall-proximity effect leads to the formation of the Kármán vortex street, while a reverse Kármán vortex street and secondary vortices emerge under a strong wall-proximity effect. It is noticed that the Kelvin–Helmholtz instability drives vortex shedding under regime I, leading to an increase in the Strouhal number (St) with stronger magnetic fields. Additionally, under a strong axial magnetic field, the wall-proximity effect (‘Shercliff layer effect’) promotes the instability of shear layers on both sides of the cylinder. These unique coupling effects are validated by variations in modal coefficients and energy proportions under different vortex-shedding regimes using the proper orthogonal decomposition method.

Microwave field vector detector based on the off-resonant spin rectification effect

Normal microwave (MW) electromagnetic field detectors convert microwave power into voltages, which results in loss of the vector characteristics of the microwave field. In this work, we developed a MW magnetic field (h-field) vector detector based on the off-resonant spin rectification effect. By measuring and analyzing the angle dependence of the rectification voltages under off-resonant conditions, we can extract the three components of the h-field. As an initial test of this method, we obtained the h-field distributions at 5.4 GHz generated by a coplanar waveguide with sub-wavelength resolution. Compared to methods using ferromagnetic resonance, this technique offers a faster and more convenient way to determine the spatial distribution of the h-field, which can be used for MW integrated circuit optimization and fault diagnosis.

Analysis of the Effect of Structural Parameters on the Internal Flow Field of Composite Curved Inlet Body Hydrocyclone

Analysis of the Effect of Structural Parameters on the Internal Flow Field of Composite Curved Inlet Body Hydrocyclone

Transient flow field characteristics of scraper pump based on viscosity wall strategy

This study presents an innovative scraper pump design. The design utilizes the synchronized movement of the upper and lower scrapers of the rotor to adjust the cavity volumes on either side, facilitating efficient fluid transfer. Unlike previous studies, scraper pumps face the challenge of dynamic contact between the scraper and the rotor due to their unique structure. A viscous wall strategy was employed to address hydrodynamic challenges at the point of contact, significantly improving performance prediction accuracy. The experimental data verified the accuracy of the simulation model, and the mass flow rate deviation between the simulation results and the experimental results was maintained within 10% when the viscosity at the contact point was set to 40 times the original medium viscosity. In addition, the study examined the effect of different operating speeds and load pressures on the pump performance. The results indicated that the outlet flow rate decreased by 22% when the pressure was increased from 2 MPa to 10 MPa and increased by 88.24% when the speed was increased from 900 r/min to 2200 r/min. These quantitative analyses provided valuable insights into optimizing scraper pump design and offered clear guidance for improving hydraulic performance and operational efficiency.