Magnetohydrodynamic(MHD)radiative chemically reactive mixed convection flow of a hybrid nanofluid(Al_(2)O_(3)–Cu/H_(2)O)across an inclined,porous,and stretched sheet is examined in this study,along with its unsteady ...Magnetohydrodynamic(MHD)radiative chemically reactive mixed convection flow of a hybrid nanofluid(Al_(2)O_(3)–Cu/H_(2)O)across an inclined,porous,and stretched sheet is examined in this study,along with its unsteady heat and mass transport properties.The hybrid nanofluid’s enhanced heat transfer efficiency is a major benefit in high-performance engineering applications.It is composed of two separate nanoparticles suspended in a base fluid and is chosen for its improved thermal properties.Thermal radiation,chemical reactions,a transverse magnetic field,surface stretching with time,injection or suction through the porous medium,and the effect of inclination,which introduces gravity-induced buoyancy forces,are all important physical phenomena that are taken into account in the analysis.A system of nonlinear ordinary differential equations(ODEs)is derived from the governing partial differential equations for mass,momentum,and energy by applying suitable similarity transformations.This simplifies the modeling procedure.The bvp4c solver in MATLAB is then used to numerically solve these equations.Different governing parameters modify temperature,concentration,and velocity profiles in graphs and tables.These factors include radiation intensity,chemical reaction rate,magnetic field strength,unsteadiness,suction/injection velocity,inclination angle,and nanoparticle concentration.A complex relationship between buoyancy and magnetic factors makes hybrid nanofluids better at heat transmission than regular ones.Thermal systems including cooling technologies,thermal coatings,and electronic heat management benefit from these findings.展开更多
The Dst index has been commonly used to measure the geomagnetic effectiveness of magnetic storm events for several decades.Based on Burton’s empirical Dst model and the global magneto-hydrodynamic(MHD)simulation of E...The Dst index has been commonly used to measure the geomagnetic effectiveness of magnetic storm events for several decades.Based on Burton’s empirical Dst model and the global magneto-hydrodynamic(MHD)simulation of Earth’s magnetosphere,here we proposed a semi-empirical model to forecast the Dst index during geomagnetic storms.In this model,the ring current contribution to the Dst index is derived from Burton’s model,while the contributions from other current systems are obtained from the global MHD simulation.In order to verify the model accuracy,a number of recent magnetic storm events are tested and the simulated Dst index is compared with the observation through the correlation coefficient(CC),prediction efficiency(PE),root mean square error(RMSE)and central root mean square error(CRMSE).The results indicate that,in the context of moderate and intense geomagnetic storm events,the semi-empirical model performs well in global MHD simulations,showing relatively higher CC and PE,and lower RMSE and CRMSE compared to those from the empirical model.Compared with the physics-based ring current models,this model inherits the advantage of fast processing from the empirical model,and easy implementation in a global MHD model of Earth’s magnetosphere.Therefore,it is suitable for the Dst estimation under a context of a global MHD simulation.展开更多
The work comparing the Yamada-Ota and Xue models for nanoparticle flow across a stretching surface has benefits in nanotechnology,medicinal treatments,environmental engineering,renewable energy,and heat exchangers.Mos...The work comparing the Yamada-Ota and Xue models for nanoparticle flow across a stretching surface has benefits in nanotechnology,medicinal treatments,environmental engineering,renewable energy,and heat exchangers.Most published nanofluid flow models assumed constant thermal conductivity and viscosity.With such great physiognomies in mind,the novelty of this work focuses on comparing the performance of the nanofluid models,Xue,and Yamada-Ota models on a stretched sheet with variable thickness under the influence of a magnetic field and quadratic thermal radiation.The altered boundary layer equations for momentum and temperature,subject to adequate boundary conditions,are numerically solved using an optimized,efficient,and extensive bvp-4c approach.The effects of non-dimensional constraints such as magnetic field,power index of velocity,wall thickness parameter,and quadratic radiation parameter on momentum and temperature profile in the boundary layer area are analyzed thoroughly and outcomes were illustrated graphically.Additionally,the consequences of certain distinctive parameters over engineering factors are also examined and results were presented in tabular form.From the outcomes,it is seen that fluid velocity slows down in the presence of a magnetic field but the opposite nature is observed in the case of temperature profile.With a higher index of velocity,the velocity profile decreases and the temperature field elevates.It has been found that the presence of quadratic convection improves the temperature field.The outcomes of the two models are compared.The Yamada-Ota model performed far better than the Xue model in the heat transfer analysis.展开更多
This study employs two-dimensional axisymmetric relativistic magnetohydrodynamic simulations to investigate the evolution of supernova remnant(SNR) and pulsar wind nebula(PWN) composite systems in two distinct interst...This study employs two-dimensional axisymmetric relativistic magnetohydrodynamic simulations to investigate the evolution of supernova remnant(SNR) and pulsar wind nebula(PWN) composite systems in two distinct interstellar medium(ISM) configurations: a uniform density distribution and a medium with a sharp density discontinuity. Compared to the uniform density distribution, the ISM with this density discontinuity better reflects the actual conditions and explains the overall morphological characteristics of specific types of SNR-PWN composite systems. These systems exhibit asymmetries, such as an SNR shell with differing radii or an inner PWN located nearer to the shell on one side. The simulation results suggest that the density discontinuity in the ISM is a contributing factor to both the shell asymmetry and the PWN displacement. Specifically, this density variation directly causes the inconsistency in the forward shock speeds of the SNR between high and low density regions, resulting in discrepancies in the shell layer radii. Furthermore, the asymmetric morphology of the PWN and its positional offset emerge through interactions with the reverse shock. The PWN tends to shift toward the SNR shell on one side. The greater the density jump in the background field, the more pronounced the shell radius differences and PWN offset become.展开更多
This study presents a numerical analysis of the steady-state solution for transient magnetohydrodynamic(MHD)dissipative and radiative fluid flow,incorporating an inducedmagnetic field(IMF)and considering a relatively ...This study presents a numerical analysis of the steady-state solution for transient magnetohydrodynamic(MHD)dissipative and radiative fluid flow,incorporating an inducedmagnetic field(IMF)and considering a relatively high concentration of foreign mass(accounting for Soret and Dufour effects)over a vertically oriented semi-infinite plate.The governing equations were normalized using boundary layer(BL)approximations.The resulting nonlinear system of partial differential equations(PDEs)was discretized and solved using an efficient explicit finite difference method(FDM).Numerical simulations were conducted using MATLAB R2015a,and the developed numerical code was verified through comparison with another code written in FORTRAN 6.6a.To ensure the reliability of the results,both mesh refinement and steady-state time validation tests were performed.Furthermore,a comparison with existing published studies was made to confirm the accuracy of the findings.The dimensionless equations revealed the impacts of several key parameters.The IMF initially intensifies near the plate before gradually diminishing as the magnetic parameter increases.For the range 0≤y≤1.8(where y is the horizontal direction),the IMF decreases with a rise in the magnetic Prandtl number;however,for 1.8≤y≤7(approximately),the magnetic field begins to increase.Beyond this,the profile of the magnetic field becomes somewhat irregular through the remaining part of the BL.展开更多
Before solar eruptions,a short-term slow-rise phase is often observed,during which the pre-eruption structure ascends at speeds much greater than the photospheric motions but much less than those of the eruption phase...Before solar eruptions,a short-term slow-rise phase is often observed,during which the pre-eruption structure ascends at speeds much greater than the photospheric motions but much less than those of the eruption phase.Numerical magnetohydrodynamic (MHD) simulations of the coronal evolution driven by photospheric motions up to eruptions have been used to explain the slow-rise phase,but their bottom driving speeds are much larger than realistic photospheric values.Therefore,it remains an open question how the excessively fast bottom driving impacts the slow-rise phase.Here we modeled the slow-rise phase before eruption initiated from a continuously sheared magnetic arcade.In particular,we performed a series of experiments with the bottom driving speed unprecedentedly approaching the photospheric value of around 1 km s^(-1).The simulations confirmed that the slowrise phase is an ideal MHD process,i.e.,a manifestation of the growing expansion of the sheared arcade in the process of approaching a fully open field state.The overlying field line above the core flux has a slow-rise speed modulated by the driving speed’s magnitude but is always over an order of magnitude larger than the driving speed.The core field also expands with speed much higher than the driving speed but much lower than that of the overlying field.By incrementally reducing the bottom-driving speed to realistic photospheric values,we anticipate better matches between the simulated slow-rise speeds and some observed ones.展开更多
本文研究了正交曲线坐标系中三维不可压MHD系统在大光滑初值条件下的整体适定性。我们针对一类新的光滑大初值,建立了三维不可压粘性MHD系统Cauchy问题在正交曲线坐标系下的整体光滑解的存在性和唯一性。This paper investigates the gl...本文研究了正交曲线坐标系中三维不可压MHD系统在大光滑初值条件下的整体适定性。我们针对一类新的光滑大初值,建立了三维不可压粘性MHD系统Cauchy问题在正交曲线坐标系下的整体光滑解的存在性和唯一性。This paper investigates the global well-posedness of the three-dimensional incompressible MHD system in orthogonal curvilinear coordinates with large smooth initial data. We establish the global existence and uniqueness of the smooth solutions to the Cauchy problem for the three-dimensional incompressible viscous MHD system in orthogonal curvilinear coordinates for a new class of the smooth large initial data.展开更多
文摘Magnetohydrodynamic(MHD)radiative chemically reactive mixed convection flow of a hybrid nanofluid(Al_(2)O_(3)–Cu/H_(2)O)across an inclined,porous,and stretched sheet is examined in this study,along with its unsteady heat and mass transport properties.The hybrid nanofluid’s enhanced heat transfer efficiency is a major benefit in high-performance engineering applications.It is composed of two separate nanoparticles suspended in a base fluid and is chosen for its improved thermal properties.Thermal radiation,chemical reactions,a transverse magnetic field,surface stretching with time,injection or suction through the porous medium,and the effect of inclination,which introduces gravity-induced buoyancy forces,are all important physical phenomena that are taken into account in the analysis.A system of nonlinear ordinary differential equations(ODEs)is derived from the governing partial differential equations for mass,momentum,and energy by applying suitable similarity transformations.This simplifies the modeling procedure.The bvp4c solver in MATLAB is then used to numerically solve these equations.Different governing parameters modify temperature,concentration,and velocity profiles in graphs and tables.These factors include radiation intensity,chemical reaction rate,magnetic field strength,unsteadiness,suction/injection velocity,inclination angle,and nanoparticle concentration.A complex relationship between buoyancy and magnetic factors makes hybrid nanofluids better at heat transmission than regular ones.Thermal systems including cooling technologies,thermal coatings,and electronic heat management benefit from these findings.
基金supported by NNSFC grants 42150101,42188105,42304189National Key R&D program of China No.2021YFA-0718600the Pandeng Program of National Space Science Center,Chinese Academy of Sciences.
文摘The Dst index has been commonly used to measure the geomagnetic effectiveness of magnetic storm events for several decades.Based on Burton’s empirical Dst model and the global magneto-hydrodynamic(MHD)simulation of Earth’s magnetosphere,here we proposed a semi-empirical model to forecast the Dst index during geomagnetic storms.In this model,the ring current contribution to the Dst index is derived from Burton’s model,while the contributions from other current systems are obtained from the global MHD simulation.In order to verify the model accuracy,a number of recent magnetic storm events are tested and the simulated Dst index is compared with the observation through the correlation coefficient(CC),prediction efficiency(PE),root mean square error(RMSE)and central root mean square error(CRMSE).The results indicate that,in the context of moderate and intense geomagnetic storm events,the semi-empirical model performs well in global MHD simulations,showing relatively higher CC and PE,and lower RMSE and CRMSE compared to those from the empirical model.Compared with the physics-based ring current models,this model inherits the advantage of fast processing from the empirical model,and easy implementation in a global MHD model of Earth’s magnetosphere.Therefore,it is suitable for the Dst estimation under a context of a global MHD simulation.
基金supported by the National Research Foundation,Korea(Grant No.NRF2022-R1A2C2002799)support provided by the German Jordanian University,Amman,Jordan,is greatly acknowledged by the authors.Ulavathi Shettar Mahabaleshwar wishes to thank Sang Woo Joo,School of Mechanical Engineering,Yeungnam University,Gyeongsan,Korea,for his hospitality.
文摘The work comparing the Yamada-Ota and Xue models for nanoparticle flow across a stretching surface has benefits in nanotechnology,medicinal treatments,environmental engineering,renewable energy,and heat exchangers.Most published nanofluid flow models assumed constant thermal conductivity and viscosity.With such great physiognomies in mind,the novelty of this work focuses on comparing the performance of the nanofluid models,Xue,and Yamada-Ota models on a stretched sheet with variable thickness under the influence of a magnetic field and quadratic thermal radiation.The altered boundary layer equations for momentum and temperature,subject to adequate boundary conditions,are numerically solved using an optimized,efficient,and extensive bvp-4c approach.The effects of non-dimensional constraints such as magnetic field,power index of velocity,wall thickness parameter,and quadratic radiation parameter on momentum and temperature profile in the boundary layer area are analyzed thoroughly and outcomes were illustrated graphically.Additionally,the consequences of certain distinctive parameters over engineering factors are also examined and results were presented in tabular form.From the outcomes,it is seen that fluid velocity slows down in the presence of a magnetic field but the opposite nature is observed in the case of temperature profile.With a higher index of velocity,the velocity profile decreases and the temperature field elevates.It has been found that the presence of quadratic convection improves the temperature field.The outcomes of the two models are compared.The Yamada-Ota model performed far better than the Xue model in the heat transfer analysis.
基金supported by the National Natural Science Foundation of China(NSFC,grants No.12393852)the Yunnan Fundamental Research Projects(grant No.202501AS070068)the Program of Graduate Research and Innovation Fund Project of Yunnan University(KC-24249493).
文摘This study employs two-dimensional axisymmetric relativistic magnetohydrodynamic simulations to investigate the evolution of supernova remnant(SNR) and pulsar wind nebula(PWN) composite systems in two distinct interstellar medium(ISM) configurations: a uniform density distribution and a medium with a sharp density discontinuity. Compared to the uniform density distribution, the ISM with this density discontinuity better reflects the actual conditions and explains the overall morphological characteristics of specific types of SNR-PWN composite systems. These systems exhibit asymmetries, such as an SNR shell with differing radii or an inner PWN located nearer to the shell on one side. The simulation results suggest that the density discontinuity in the ISM is a contributing factor to both the shell asymmetry and the PWN displacement. Specifically, this density variation directly causes the inconsistency in the forward shock speeds of the SNR between high and low density regions, resulting in discrepancies in the shell layer radii. Furthermore, the asymmetric morphology of the PWN and its positional offset emerge through interactions with the reverse shock. The PWN tends to shift toward the SNR shell on one side. The greater the density jump in the background field, the more pronounced the shell radius differences and PWN offset become.
基金supported by the NST Fellowship under the Ministry of Science and Technology,Government of the People’s Republic of Bangladesh(Session:2019–2020,merit number:334,serial number:714,physical science).
文摘This study presents a numerical analysis of the steady-state solution for transient magnetohydrodynamic(MHD)dissipative and radiative fluid flow,incorporating an inducedmagnetic field(IMF)and considering a relatively high concentration of foreign mass(accounting for Soret and Dufour effects)over a vertically oriented semi-infinite plate.The governing equations were normalized using boundary layer(BL)approximations.The resulting nonlinear system of partial differential equations(PDEs)was discretized and solved using an efficient explicit finite difference method(FDM).Numerical simulations were conducted using MATLAB R2015a,and the developed numerical code was verified through comparison with another code written in FORTRAN 6.6a.To ensure the reliability of the results,both mesh refinement and steady-state time validation tests were performed.Furthermore,a comparison with existing published studies was made to confirm the accuracy of the findings.The dimensionless equations revealed the impacts of several key parameters.The IMF initially intensifies near the plate before gradually diminishing as the magnetic parameter increases.For the range 0≤y≤1.8(where y is the horizontal direction),the IMF decreases with a rise in the magnetic Prandtl number;however,for 1.8≤y≤7(approximately),the magnetic field begins to increase.Beyond this,the profile of the magnetic field becomes somewhat irregular through the remaining part of the BL.
基金supported by the National Natural Science Foundation of China (NSFC,Grant No.42174200)Shenzhen Science and Technology Program (grant No.RCJC20210609104422048)+1 种基金Shenzhen Key Laboratory Launching Project (No.ZDSYS20210702140800001)Guangdong Basic and Applied Basic Research Foundation(2023B1515040021)。
文摘Before solar eruptions,a short-term slow-rise phase is often observed,during which the pre-eruption structure ascends at speeds much greater than the photospheric motions but much less than those of the eruption phase.Numerical magnetohydrodynamic (MHD) simulations of the coronal evolution driven by photospheric motions up to eruptions have been used to explain the slow-rise phase,but their bottom driving speeds are much larger than realistic photospheric values.Therefore,it remains an open question how the excessively fast bottom driving impacts the slow-rise phase.Here we modeled the slow-rise phase before eruption initiated from a continuously sheared magnetic arcade.In particular,we performed a series of experiments with the bottom driving speed unprecedentedly approaching the photospheric value of around 1 km s^(-1).The simulations confirmed that the slowrise phase is an ideal MHD process,i.e.,a manifestation of the growing expansion of the sheared arcade in the process of approaching a fully open field state.The overlying field line above the core flux has a slow-rise speed modulated by the driving speed’s magnitude but is always over an order of magnitude larger than the driving speed.The core field also expands with speed much higher than the driving speed but much lower than that of the overlying field.By incrementally reducing the bottom-driving speed to realistic photospheric values,we anticipate better matches between the simulated slow-rise speeds and some observed ones.
文摘本文研究了正交曲线坐标系中三维不可压MHD系统在大光滑初值条件下的整体适定性。我们针对一类新的光滑大初值,建立了三维不可压粘性MHD系统Cauchy问题在正交曲线坐标系下的整体光滑解的存在性和唯一性。This paper investigates the global well-posedness of the three-dimensional incompressible MHD system in orthogonal curvilinear coordinates with large smooth initial data. We establish the global existence and uniqueness of the smooth solutions to the Cauchy problem for the three-dimensional incompressible viscous MHD system in orthogonal curvilinear coordinates for a new class of the smooth large initial data.
