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Search Results (2,402)

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Keywords = dynamic geometry

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19 pages, 9016 KiB  
Article
The Effect of Contraction–Expansion Nozzle on High-Temperature Shock Tube Flow
by Junmou Shen, Dapeng Yao, Zhongjie Shao, Feng Ji, Xing Chen, Wei Chen and Jianwei Li
Aerospace 2025, 12(2), 120; https://doi.org/10.3390/aerospace12020120 - 4 Feb 2025
Viewed by 96
Abstract
To achieve higher enthalpy and pressure, the technique of variable cross-section drive is effectively combined with the heating of light gas to enhance the intensity of the incident shock wave. A study was conducted to predict the impact of variable cross-sections on the [...] Read more.
To achieve higher enthalpy and pressure, the technique of variable cross-section drive is effectively combined with the heating of light gas to enhance the intensity of the incident shock wave. A study was conducted to predict the impact of variable cross-sections on the performance of high-temperature shock tube flow using a shock tube with a 2.6:1 diameter ratio between the driver and driven sections. The driver section was filled with a helium–argon gas mixture (mass ratio of 1:9), while the driven section contained dry air. Under total pressure conditions of 14.5 MPa and total temperature of 3404 K, as well as total pressure of 45 MPa and total temperature of 4845 K in the driver section, corresponding to driven section pressures of 10 kPa and 80 kPa, the results of chemical non-equilibrium numerical simulations were compared to experimental measurements of the incident shock Mach number and total pressure. The results indicated the following: First, after adding the contraction–expansion nozzle, the incident shock accelerated through the contraction section and reflected within the contraction section. Strong oscillations occurred during the flow, with increasing intensity as the throat size decreased. Second, without the nozzle, the shock velocity increased and then decreased. However, with the nozzle, the Mach number was highest near the nozzle exit and gradually decreased thereafter. Third, the presence of the nozzle led to the formation of a distinct fan-shaped wavefront, accompanied by significant variations in flow variables such as pressure, temperature, and Mach number in the region. This phenomenon was attributed to the interaction between the shock wave and the nozzle geometry, which altered the flow dynamics. Finally, as the throat size decreased, the intensity of the incident shock also decreased. After reflecting at the end of the shock tube, the total pressure in the driven section also decreased. The numerical simulations employed a multi-component, multi-temperature chemical non-equilibrium model, validated against experimental data, to accurately capture the complex flow behavior and wave interactions within the shock tube. Full article
(This article belongs to the Special Issue Recent Advances in Applied Aerodynamics)
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22 pages, 2532 KiB  
Article
Magnetic Pulse Powder Compaction
by Viktors Mironovs, Jekaterina Nikitina, Matthias Kolbe, Irina Boiko and Yulia Usherenko
Metals 2025, 15(2), 155; https://doi.org/10.3390/met15020155 - 4 Feb 2025
Viewed by 100
Abstract
Powder metallurgy (PM) offers several advantages over conventional melt metallurgy, including improved homogeneity, fine grain size, and pseudo-alloying capabilities. Transitioning from conventional methods to PM can result in significant enhancements in material properties and production efficiency by eliminating unnecessary process steps. Dynamic compaction [...] Read more.
Powder metallurgy (PM) offers several advantages over conventional melt metallurgy, including improved homogeneity, fine grain size, and pseudo-alloying capabilities. Transitioning from conventional methods to PM can result in significant enhancements in material properties and production efficiency by eliminating unnecessary process steps. Dynamic compaction techniques, such as impulse and explosive compaction, aim to achieve higher powder density without requiring sintering, further improving PM efficiency. Among these techniques, magnetic pulse compaction (MPC) has gained notable interest due to its unique process mechanics and distinct advantages. MPC utilizes the rapid discharge of energy stored in capacitors to generate a pulsed electromagnetic field, which accelerates a tool to compress the powder. This high-speed process is particularly well-suited for compacting complex geometries and finds extensive application in industries such as powder metallurgy, welding, die forging, and advanced material manufacturing. This paper provides an overview of recent advancements and applications of MPC technology, highlighting its capabilities and potential for broader integration into modern manufacturing processes. Full article
(This article belongs to the Special Issue Powder Metallurgy of Metallic Materials)
16 pages, 3786 KiB  
Article
Dynamic 3D Measurement Based on Camera-Pixel Mismatch Correction and Hilbert Transform
by Xingfan Chen, Qican Zhang and Yajun Wang
Sensors 2025, 25(3), 924; https://doi.org/10.3390/s25030924 - 3 Feb 2025
Viewed by 246
Abstract
In three-dimensional (3D) measurement, the motion of objects inevitably introduces errors, posing significant challenges to high-precision 3D reconstruction. Most existing algorithms for compensating motion-induced phase errors are tailored for object motion along the camera’s principal axis (Z direction), limiting their applicability in real-world [...] Read more.
In three-dimensional (3D) measurement, the motion of objects inevitably introduces errors, posing significant challenges to high-precision 3D reconstruction. Most existing algorithms for compensating motion-induced phase errors are tailored for object motion along the camera’s principal axis (Z direction), limiting their applicability in real-world scenarios where objects often experience complex combined motions in the X/Y and Z directions. To address these challenges, we propose a universal motion error compensation algorithm that effectively corrects both pixel mismatch and phase-shift errors, ensuring accurate 3D measurements under dynamic conditions. The method involves two key steps: first, pixel mismatch errors in the camera subsystem are corrected using adjacent coarse 3D point cloud data, aligning the captured data with the actual spatial geometry. Subsequently, motion-induced phase errors, observed as sinusoidal waveforms with a frequency twice that of the projection fringe pattern, are eliminated by applying the Hilbert transform to shift the fringes by π/2. Unlike conventional approaches that address these errors separately, our method provides a systematic solution by simultaneously compensating for camera-pixel mismatch and phase-shift errors within the 3D coordinate space. This integrated approach enhances the reliability and precision of 3D reconstruction, particularly in scenarios with dynamic and multidirectional object motions. The algorithm has been experimentally validated, demonstrating its robustness and broad applicability in fields such as industrial inspection, biomedical imaging, and real-time robotics. By addressing longstanding challenges in dynamic 3D measurement, our method represents a significant advancement in achieving high-accuracy reconstructions under complex motion environments. Full article
(This article belongs to the Special Issue 3D Reconstruction with RGB-D Cameras and Multi-sensors)
14 pages, 6126 KiB  
Article
Investigating Hemodynamics in Intracranial Aneurysms with Irregular Morphologies: A Multiphase CFD Approach
by Dimitrios S. Lampropoulos and Maria Hadjinicolaou
Mathematics 2025, 13(3), 505; https://doi.org/10.3390/math13030505 - 3 Feb 2025
Viewed by 313
Abstract
Unruptured intracranial aneurysms, affecting 2–5% of the population, are characterized by localized wall weakening and irregular morphologies, including features such as blebs, lobulations, or asymmetries, which are significant predictors of rupture risk. Although up to 57% of ruptured intracranial aneurysms exhibit irregular dome [...] Read more.
Unruptured intracranial aneurysms, affecting 2–5% of the population, are characterized by localized wall weakening and irregular morphologies, including features such as blebs, lobulations, or asymmetries, which are significant predictors of rupture risk. Although up to 57% of ruptured intracranial aneurysms exhibit irregular dome geometry, its influence on aneurysm stability remains underexplored. Irregular geometries are associated with adverse hemodynamic forces, such as increased wall shear stress (WSS), amplifying wall stress at specific regions, and promoting flow disturbances, which may increase aneurysm vulnerability. This study investigates the influence of aneurysm dome morphology, particularly in IAs with irregular domes that may include daughter blebs, using Computational Fluid Dynamics (CFD). Unlike prior CFD studies that modeled blood as Newtonian or non-Newtonian, this work employs a three-phase blood flow model, representing plasma and red blood cells (RBCs) as distinct phases. Numerical simulations, conducted via the Finite Volume Method, solve the Navier–Stokes equations to capture complex flow dynamics within cerebral vasculature. Key hemodynamic metrics, such as Wall Shear Stress (WSS), Wall Shear Stress Gradient (WSSG), and Viscous Dissipation Rate, are analyzed to assess the interplay between dome morphology and hemodynamic stressors. Full article
(This article belongs to the Special Issue Computational Fluid Dynamics with Applications)
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20 pages, 6345 KiB  
Article
Application of a Coupled Eulerian-Lagrangian Approach to the Shape and Force of Scientific Balloons
by Lingsen Kong, Yanchu Yang, Rong Cai, Hangyue Zhang and Weihao Lyu
Appl. Sci. 2025, 15(3), 1517; https://doi.org/10.3390/app15031517 - 2 Feb 2025
Viewed by 341
Abstract
Scientific balloons provide an inexpensive and reliable platform for near-space scientific experiments. The analysis of the balloon geometry and forces has always been a major concern for balloon designers. Most previous studies have focused solely on the fully inflated shapes and forces of [...] Read more.
Scientific balloons provide an inexpensive and reliable platform for near-space scientific experiments. The analysis of the balloon geometry and forces has always been a major concern for balloon designers. Most previous studies have focused solely on the fully inflated shapes and forces of balloons, analyzing only the membrane structure and simplifying the effects of internal and external gases into a gradient pressure difference. This approach lacks consideration of the fluid–structure interaction (FSI) of scientific balloons. This paper utilizes the Coupled Eulerian–Lagrangian (CEL) method in the Abaqus/Explicit simulation environment to analyze the FSI effects of scientific balloons under the influence of internal helium and external air. Three typical working conditions of scientific balloons are selected for simulation analysis. First, a three-dimensional spherical balloon is simulated during the ascent process to verify the correctness of the CEL simulation framework. This also demonstrates the membrane folding characteristics during balloon ascent, which could not be calculated in previous two-dimensional axisymmetric simulations. Next, the study explores balloon shapes that deviate from quasi-static pressure distributions due to the motion of internal helium. These include the “mushroom” shape observed during the dynamic launching of the balloon on the ground and the “sail” shape caused by lateral airflow. The mushroom shape arises from the sudden loss of the bottom constraint, causing the internal helium to move upward while being resisted by the air at the balloon’s top. The simulation successfully replicates the rapid waist transition and the downward concavity at the top due to air resistance, while also providing the corresponding force distribution. For the sail-shaped condition, the simulation analyzes the balloon’s tilt angle and the characteristic upturn of its windward surface. By a comparison with no-wind conditions, this study quantifies the impact of wind on the forces acting on the balloon, offering practical guidance for balloon launching. The CEL simulation framework established in this study not only provides a new tool for the FSI analysis of scientific balloons but also enriches the mechanical analysis results of these balloons. Full article
(This article belongs to the Section Aerospace Science and Engineering)
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19 pages, 8550 KiB  
Article
An Analysis of Rock Bolt Dynamic Responses to Evaluate the Anchoring Degree of Fixation
by Alberto Godio, Claudio Oggeri and Jacopo Seccatore
Appl. Sci. 2025, 15(3), 1513; https://doi.org/10.3390/app15031513 - 2 Feb 2025
Viewed by 272
Abstract
Rock bolting in underground environments is used for different fundamental reasons, including suspending potentially loosened blocks, clamping small wedges together, inducing a protective pressure arch along the contour of excavated voids to improve the self-supporting capacity of the ground, and providing passive pressure [...] Read more.
Rock bolting in underground environments is used for different fundamental reasons, including suspending potentially loosened blocks, clamping small wedges together, inducing a protective pressure arch along the contour of excavated voids to improve the self-supporting capacity of the ground, and providing passive pressure in integrated support systems. In this study, we describe a testing procedure that was developed to investigate the grouted annulus of a rock bolt using a low-cost investigation method. This diagnostic technique was based on the dynamic response of the system, where mechanical vibrations were induced within the rock bolt and the response was recorded by using geophones/accelerometers on the protruding element of the bolt (the collar and head). The collected signal was then processed to estimate the spectral response, and the amplitude spectrum was analyzed to detect the resonance frequencies. A 3D finite element model of the rock bolt and grouting was established to simulate the quality of the coupling by varying the mechanical properties of the grouting. The model’s response for the studied geometry of the rock bolt suggested that a poor quality of grouting was usually associated with flexural modes of vibration with a low resonance frequency. Good-quality grouting was associated with a frequency higher than 1400 Hz, where the axial vibration was mainly excited. Our analyses referred to short rock bolts, which are usually adopted in small tunnels. The interpretation of the experimental measurements assumed that the spectral response was significantly affected by the quality of the grouting, as demonstrated by the modeling procedure. The resonant frequency was compared with the results of the model simulation. The method was used to test the quality of rock bolts in a small experimental tunnel carved from andesite rock in Chile. Low-cost shock sensors (piezoelectric geophones) with low sensitivity but a wide frequency band were used. The main research outcome was the development of a reliable method to model the dynamic response of rock bolts in mines or for experimental applications in tunnels. Albeit limited to the current specific geometries, the modeling and testing will be adapted to other anchor/bolt options. Full article
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11 pages, 4074 KiB  
Article
Finite Element Analysis and Electrohydrodynamic Multiphysics Modeling of a Corona-Streamer Discharge in a Two-Phase Flow Medium
by Myung-Ki Baek and Ho-Young Lee
Energies 2025, 18(3), 680; https://doi.org/10.3390/en18030680 - 1 Feb 2025
Viewed by 455
Abstract
This study proposes an electrohydrodynamic multiphysics modeling and finite element analysis technique to accurately simulate corona-streamer discharges in a two-phase flow medium. The discharge phenomenon is modeled as a multiphysics system, coupling the Poisson equation for the electric field with a charge dynamics [...] Read more.
This study proposes an electrohydrodynamic multiphysics modeling and finite element analysis technique to accurately simulate corona-streamer discharges in a two-phase flow medium. The discharge phenomenon is modeled as a multiphysics system, coupling the Poisson equation for the electric field with a charge dynamics model based on fluid methods and a thermofluid field for temperature effects. To optimize the numerical simulation, the tip-flat plate electrode model was simplified to two-dimensional axisymmetry, and an unordered lattice network was used to reduce computational time while maintaining high resolution in the region of interest. A high DC voltage was applied to the model to generate a local non-uniform electric field exceeding 10 MV/m, allowing the numerical simulations of ionization, recombination, and charge attachment in the streamer channel. The numerical results were compared with voltage and current measurements from full-scale experiments under identical geometry and initial conditions to verify the effectiveness of the proposed method. The results of this study enhance the understanding of the multiphysical mechanisms behind electrical discharge phenomena and can enable the prediction of insulation failure through simple simulations, eliminating insulation experiments on devices. Full article
(This article belongs to the Section F: Electrical Engineering)
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18 pages, 854 KiB  
Article
Non-Keplerian Charged Accretion Disk Orbiting a Black Hole Pulsar
by Audrey Trova and Eva Hackmann
Universe 2025, 11(2), 45; https://doi.org/10.3390/universe11020045 - 1 Feb 2025
Viewed by 190
Abstract
Recent studies have focused on how spinning black holes (BHs) within a binary system containing a strongly magnetized neutron star, then immersed in external magnetic fields, can acquire charge through mechanisms like the Wald process and how this charge could power pulsar-like electromagnetic [...] Read more.
Recent studies have focused on how spinning black holes (BHs) within a binary system containing a strongly magnetized neutron star, then immersed in external magnetic fields, can acquire charge through mechanisms like the Wald process and how this charge could power pulsar-like electromagnetic radiation. Those objects called “Black hole pulsar” mimic the behaviour of a traditional pulsar, and they can generate electromagnetic fields, such as magnetic dipoles. Charged particles within an accretion disk around the black hole would then be influenced not only by the gravitational forces but also by electromagnetic forces, leading to different geometries and dynamics. In this context, we focus here on the interplay of the magnetic dipole and the accretion disk. We construct the equilibrium structures of non-conducting charged perfect fluids orbiting Kerr black holes under the influence of a dipole magnetic field aligned with the rotation axis of the BH. The dynamics of the accretion disk in such a system are shaped by a complex interplay between the non-uniform, non-Keplerian angular momentum distribution, the black hole’s induced magnetic dipole, and the fluid’s charge. We show how these factors jointly influence key properties of the disk, such as its geometry, aspect ratio, size, and rest mass density. Full article
(This article belongs to the Special Issue Universe: Feature Papers 2024 – Compact Objects)
30 pages, 2359 KiB  
Article
Assessing the Impact of Sand-Induced Ballast Fouling on Track Stiffness and Settlement
by Mohammed A. Alzhrani, Joseph W. Palese and Allan M. Zarembski 
Geotechnics 2025, 5(1), 8; https://doi.org/10.3390/geotechnics5010008 - 31 Jan 2025
Viewed by 224
Abstract
This study investigates the impact of sand-induced ballast fouling on railway track performance, focusing on track stiffness (modulus), settlement, and overall degradation. The research utilized an 18-cubic-foot ballast box designed to replicate real-world track conditions under controlled laboratory settings. A key focus was [...] Read more.
This study investigates the impact of sand-induced ballast fouling on railway track performance, focusing on track stiffness (modulus), settlement, and overall degradation. The research utilized an 18-cubic-foot ballast box designed to replicate real-world track conditions under controlled laboratory settings. A key focus was quantifying voids within clean ballast to establish baseline characteristics, which provided a foundation for evaluating the effects of sand fouling. Two distinct test series were conducted to comprehensively analyze track behavior. The first series investigated pre-existing fouling by thoroughly mixing sand into the ballast to achieve uniform fouling levels. The second series simulated natural fouling processes by progressively adding sand from the top of the ballast layer, mimicking real-world conditions such as those in sandy environments. These methodologies allowed for detailed analysis of changes in track stiffness, deflection, and settlement under varying fouling levels. The findings demonstrate a direct correlation between increasing sand fouling levels and heightened track stiffness and settlement. Dynamic load testing revealed that as void spaces were filled with sand, the track’s flexibility and drainage capacity was significantly compromised, leading to accelerated degradation of track geometry. Settlement patterns and deflection data provided critical insights into how fouling adversely affects track performance. These results contribute significantly to understanding the broader implications of sand-induced fouling on track degradation, offering valuable insights for railway maintenance and design improvements. By integrating void analysis, test series data, and load-deflection relationships, this study provides actionable recommendations for enhancing railway infrastructure resilience and optimizing maintenance strategies in sandy terrains. Full article
40 pages, 1622 KiB  
Article
A Novel Time-Frame Regional Collision Risk Model Based on Dynamic Time Warping
by Zihao Liu and Peijun Yu
J. Mar. Sci. Eng. 2025, 13(2), 263; https://doi.org/10.3390/jmse13020263 - 30 Jan 2025
Viewed by 344
Abstract
The quantification of collision risk in the water area is crucial for marine traffic safety. However, most existing studies primarily adopt a statistical perspective or only consider collision risks at discrete time points, neglecting the dynamic nature and temporal characteristics of collision risk. [...] Read more.
The quantification of collision risk in the water area is crucial for marine traffic safety. However, most existing studies primarily adopt a statistical perspective or only consider collision risks at discrete time points, neglecting the dynamic nature and temporal characteristics of collision risk. To overcome the problem, this paper proposed a novel time-frame regional collision risk model based on dynamic time warping (DTW). The time series of the ships in the water area were generated by modeling the collision risk from the perspectives of geometric encounters and traffic situation pressure. Dynamic time warping was used to mine the eigenvalue of each sequence in representing collision risk. The time-frame regional collision risk can be obtained by synthesizing the collision risk eigenvalues through considering the contribution of each ship to the entire collision risk. To validate the proposed model, some experiments were carried out by using the real AIS data in the Bohai Strait. The results show the capability of the proposed model in reasonably and effectively identifying the time-frame regional collision risk and prove its merits compared with the traditional methods. Therefore, it can better assist the supervision and analysis of regional collision risk so as to further enhance marine traffic safety. Full article
(This article belongs to the Special Issue Maritime Security and Risk Assessments—2nd Edition)
63 pages, 14085 KiB  
Review
Insights from the Last Decade in Computational Fluid Dynamics (CFD) Design and Performance Enhancement of Darrieus Wind Turbines
by Saïf ed-Dîn Fertahi, Shafiqur Rehman, Ernesto Benini, Khadija Lahrech, Abderrahim Samaouali, Asmae Arbaoui, Imad Kadiri and Rachid Agounoun
Processes 2025, 13(2), 370; https://doi.org/10.3390/pr13020370 - 28 Jan 2025
Viewed by 405
Abstract
This review provides an analysis of advancements in the design and performance assessment of Darrieus wind turbines over the past decade, with a focus on the contributions of computational fluid dynamics (CFD) to this field. The primary objective is to present insights from [...] Read more.
This review provides an analysis of advancements in the design and performance assessment of Darrieus wind turbines over the past decade, with a focus on the contributions of computational fluid dynamics (CFD) to this field. The primary objective is to present insights from studies conducted between 2014 and 2024, emphasizing the enhancement of Darrieus wind turbine performance through various technological innovations. The research methodology employed for this review includes a critical analysis of published articles related to Darrieus turbines. The focus on the period from 2014 to 2024 was considered to highlight recent parametric CFD studies on Darrieus turbines, avoiding overlap with previously published reviews and maintaining originality relative to existing review works in the literature. By synthesizing a collection of articles, the review discusses a wide range of recent investigations utilizing CFD modeling techniques, including both 2D and 3D simulations. These studies predominantly utilize the “Ansys-Fluent” V12.0 and “STAR CCM+” V9.02 solvers to evaluate the aerodynamic performance of Darrieus rotors. Technological advancements focus on modifying the geometry of Darrieus, including alterations to blade profiles, chord length, rotor diameter, number of blades, turbine height, rotor solidity, and the integration of multiple rotors in various configurations. Additionally, the incorporation of flow deflectors, the use of advanced blade shapes, such as V-shaped or twisted blades, and the application of an opening ratio on the blades are explored to enhance rotor efficiency. The review highlights the significant impact of these geometric modifications on key performance metrics, particularly the moment and power coefficients. A dedicated section presents CFD-derived visualizations, including vorticity fields, turbulence contours illustrated through the Q-criterion, velocity vectors, and dynamic pressure contours. These visualizations provide a description of the flow structures around the modified Darrieus rotors. Moreover, the review includes an analysis of the dynamic performance curves of Darrieus, which show improvements resulting from the modifications of the baseline design. This analysis covers the evolution of pressure coefficients, moment coefficients, and the increased power output of Darrieus. Full article
(This article belongs to the Special Issue Turbulence Models for Turbomachinery)
19 pages, 8086 KiB  
Article
Numerical Simulation of Turbulent Fountains with Negative Buoyancy
by Muhammad Ahsan Khan, Fabio Addona, Luca Chiapponi, Nicolò Merli and Renata Archetti
Modelling 2025, 6(1), 10; https://doi.org/10.3390/modelling6010010 - 28 Jan 2025
Viewed by 426
Abstract
This paper investigates the flow dynamics of a turbulent fountain with negative buoyancy using a Computational Fluid Dynamics (CFD) model, developed using OpenFOAM® and calibrated against laboratory experiments. The simulations effectively replicate the geometry and buoyancy fluxes of the fountain, showing a [...] Read more.
This paper investigates the flow dynamics of a turbulent fountain with negative buoyancy using a Computational Fluid Dynamics (CFD) model, developed using OpenFOAM® and calibrated against laboratory experiments. The simulations effectively replicate the geometry and buoyancy fluxes of the fountain, showing a fairly good agreement between the numerical and experimental velocity fields. These simulations are then used to investigate momentum and buoyancy fluxes for various source fluid densities. We find a dominant out-upward momentum transfer in the body of the fountain, while it is mainly out-downward below the inlet section. Furthermore, the vertical flux is almost twice the radial flux, while the tangential components are negligible on the inner side of the fountain. For small density differences between the fountain and the surrounding environment, we find a greater diffusion of the source fluid, while both the vertical and radial salt fluxes increase with increasing density of the fountain. The data generated serve as a significant resource for the development of future CFD models. Full article
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16 pages, 6463 KiB  
Article
Complex Dynamics in Circular and Deformed Bilayer Graphene-Inspired Billiards with Anisotropy and Strain
by Lukas Seemann, Jana Lukin, Max Häßler, Sibylle Gemming and Martina Hentschel
Symmetry 2025, 17(2), 202; https://doi.org/10.3390/sym17020202 - 28 Jan 2025
Viewed by 305
Abstract
While billiard systems of various shapes have been used as paradigmatic model systems in the fields of nonlinear dynamics and quantum chaos, few studies have investigated anisotropic billiards. Motivated by the tremendous advances in using and controlling electronic and optical mesoscopic systems with [...] Read more.
While billiard systems of various shapes have been used as paradigmatic model systems in the fields of nonlinear dynamics and quantum chaos, few studies have investigated anisotropic billiards. Motivated by the tremendous advances in using and controlling electronic and optical mesoscopic systems with bilayer graphene (BLG), representing an easily accessible anisotropic material for electrons when trigonal warping is present, we investigate billiards of various anisotropies and geometries using a trajectory-tracing approach founded on the concept of ray–wave correspondence. We find that the presence of anisotropy can change the billiards’ dynamics dramatically from its isotropic counterpart. It may induce chaotic and mixed dynamics in otherwise integrable systems and may stabilize originally unstable trajectories. We characterize the dynamics of anisotropic billiards in real and phase space using Lyapunov exponents and the Poincaré surface of section as phase space representation. Full article
(This article belongs to the Section Physics)
24 pages, 14006 KiB  
Article
The Study of the Common Rail Pipe Geometrical Parameters on Fuel Flow and Fuel Pressure Characteristics
by Ruichuan Li, Lanzheng Chen, Zhengyu Li, Wentao Yuan and Jikang Xu
Processes 2025, 13(2), 343; https://doi.org/10.3390/pr13020343 - 26 Jan 2025
Viewed by 395
Abstract
The influence of the geometric parameters of the common rail pipe on the in-rail fuel flow and pressure is a key issue in the study of high-pressure common rail systems. In this study, based on the principle of fluid dynamics, the effects of [...] Read more.
The influence of the geometric parameters of the common rail pipe on the in-rail fuel flow and pressure is a key issue in the study of high-pressure common rail systems. In this study, based on the principle of fluid dynamics, the effects of the geometric parameters of the common rail pipe inlet on the fuel flow characteristics and pressure distribution in the common rail pipe are analyzed using a combination of numerical simulation and experiment. It was found that the best pressure stabilization was achieved when the fuel inlet was conical with an angle of 120°, which indicates that both the geometry and angle of the fuel inlet have a significant effect on the fuel flow in the common rail pipe. The optimized design in this study has reduced the rail pressure fluctuation value by 3.3 MPa compared to the initial geometry parameters. It is expected to play a role in improving fuel efficiency as well as enhancing system reliability. Full article
(This article belongs to the Section Automation Control Systems)
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19 pages, 4752 KiB  
Article
Computational-Fluid-Dynamics-Based Optimization of Wavy-Slit Fin Geometry in Indoor Units of Air Conditioners Using Low-Global-Warming-Potential Refrigerants
by Jaewon Roh, Youngseo Kim and Joon Ahn
Appl. Sci. 2025, 15(3), 1196; https://doi.org/10.3390/app15031196 - 24 Jan 2025
Viewed by 374
Abstract
This study explores the optimization of wavy-slit fins in the indoor units of air conditioners that use low-global-warming-potential refrigerants, with a focus on the interactions between slit length, width, and height. A response surface method was employed to analyze the trade-offs between thermal [...] Read more.
This study explores the optimization of wavy-slit fins in the indoor units of air conditioners that use low-global-warming-potential refrigerants, with a focus on the interactions between slit length, width, and height. A response surface method was employed to analyze the trade-offs between thermal performance and pressure loss, and numerical optimization was performed using two objective functions: pumping power and volume goodness factor (Gv). The results demonstrated that optimizing the slits’ geometry significantly enhanced overall performance. For pumping power, a minimum point was observed near the design boundaries, which underscores the critical role of geometric interactions. The flow and temperature field analysis under fixed heat-duty conditions revealed substantial flow separation caused by the slits, enhanced mixing between the upper and lower surfaces, and a reduction of up to 2.05% in pumping power. In contrast, the Gv optimization model exhibited a more uniform flow, reducing flow separation beyond the pipe and improving the Gv by 1.85%, although it led to an increase in pumping power. These findings highlight the potential that tailored slit fin designs have to achieve a balanced enhancement in heat transfer and aerodynamic performance, offering valuable insights for the development of efficient, low-environmental-impact air conditioning systems. Full article
(This article belongs to the Section Fluid Science and Technology)
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