Simulating the Escaping Atmosphere of GJ 436 b with Two-fluid Magnetohydrodynamic Models

Observations of transmission spectra reveal that hot Jupiters and Neptunes are likely to possess escaping atmospheres driven by stellar radiation.Numerous models predict that magnetic fields may exert significant influences on the atmospheres of hot planets.Generally,the escaping atmospheres are not entirely ionized,and magnetic fields only directly affect the escape of ionized components within them.Considering the chemical reactions between ionized components and neutral atoms,as well as collision processes,magnetic fields indirectly impact the escape of neutral atoms,thereby influencing the detection signals of planetary atmospheres in transmission spectra.In order to simulate this process,we developed a magnetohydrodynamic multi-fluid model based on MHD code PLUTO.As an initial exploration,we investigated the impact of magnetic fields on the decoupling of H^(+)and H in the escaping atmosphere of the hot Neptune GJ436b.Due to the strong resonant interactions between H and H^(+),the coupling between them is tight even if the magnetic field is strong.Of course,alternatively,our work also suggests that merging H and H^(+)into a single flow can be a reasonable assumption in MHD simulations of escaping atmospheres.However,our simulation results indicate that under the influence of magnetic fields,there are noticeable regional differences in the decoupling of H^(+)and H.With the increase of magnetic field strength,the degree of decoupling also increases.For heavier particles such as O,the decoupling between O and H^(+)is more pronounced.Our findings provide important insights for future studies on the decoupling processes of heavy atoms in the escaping atmospheres of hot Jupiters and hot Neptunes under the influence of magnetic fields.

Artificial Intelligence-Driven FVM-ANNModel for Entropy Analysis ofMHD Natural Bioconvection in Nanofluid-Filled Porous Cavities

The research examines fluid behavior in a porous box-shaped enclosure.The fluid contains nanoscale particles and swimming microbes and is subject to magnetic forces at an angle.Natural circulation driven by biological factors is investigated.The analysis combines a traditional numerical approach with machine learning techniques.Mathematical equations describing the system are transformed into a dimensionless form and then solved using computational methods.The artificial neural network(ANN)model,trained with the Levenberg-Marquardt method,accurately predicts(Nu)values,showing high correlation(R=1),low mean squared error(MSE),and minimal error clustering.Parametric analysis reveals significant effects of parameters,length and location of source(B),(D),heat generation/absorption coefficient(Q),and porosity parameter(ε).Increasing the cooling area length(B)reduces streamline intensity and local Nusselt and Sherwood numbers,while decreasing isotherms,isoconcentrations,and micro-rotation.The Bejan number(Be+)decreases with increasing(B),whereas(Be+++),and global entropy(e+++)increase.Variations in(Q)slightly affect streamlines but reduce isotherm intensity and average Nusselt numbers.Higher(D)significantly impacts isotherms,iso-concentrations,andmicro-rotation,altering streamline contours and local Bejan number distribution.Increased(ε)enhances streamline strength and local Nusselt number profiles but has mixed effects on average Nusselt numbers.These findings highlight the complex interactions between cooling area length,fluid flow,and heat transfer properties.By combining finite volume method(FVM)with machine learning technique,this study provides valuable insights into the complex interactions between key parameters and heat transfer,contributing to the development of more efficient designs in applications such as cooling systems,energy storage,and bioengineering.

Heat Transfer in MHD Flow of Maxwell Fluid via Fractional Cattaneo-Friedrich Model:A Finite Difference Approach

The idea of fractional derivatives is applied to several problems of viscoelastic fluid.However,most of these problems(fluid problems),were studied analytically using different integral transform techniques,as most of these problems are linear.The idea of the above fractional derivatives is rarely applied to fluid problems governed by nonlinear partial differential equations.Most importantly,in the nonlinear problems,either the fractional models are developed by artificial replacement of the classical derivatives with fractional derivatives or simple classical problems(without developing the fractional model even using artificial replacement)are solved.These problems were mostly solved for steady-state fluid problems.In the present article,studied unsteady nonlinear non-Newtonian fluid problem(Cattaneo-Friedrich Maxwell(CFM)model)and the fractional model are developed starting from the fractional constitutive equations to the fractional governing equations;in other words,the artificial replacement of the classical derivatives with fractional derivatives is not done,but in details,the fractional problem is modeled from the fractional constitutive equations.More exactly two-dimensional magnetic resistive flow in a porous medium of fractional Maxwell fluid(FMF)over an inclined plate with variable velocity and the temperature is studied.The Caputo time-fractional derivative model(CFM)is used in the governing equations.The proposed model is numerically solved via finite difference method(FDM)along with L1-scheme for discretization.The numerical results are presented in various figures.These results indicated that the fractional parameters significantly affect the temperature and velocity fields.It is noticed that the temperature field increased with an increase in the fractional parameter.Whereas,the effect of fractional parameters is opposite on the velocity field near the plate.However,this trend became like that of the temperature profile,away from the plate.Moreover,the velocity field retarded with strengthening in the magnetic parameter due to enhancement in Lorentz force.However,this effect reverses in the case of the temperature profile.

Soret and Dufour effects on magnetohydrodynamic (MHD) flow of Casson fluid

This article studies the Soret and Dufour effects on the magnetohydrody- namic （MHD） flow of the Casson fluid over a stretched surface. The relevant equations are first derived, and the series solution is constructed by the homotopic procedure. The results for velocities, temperature, and concentration fields are displayed and discussed. Numerical values of the skin friction coefficient, the Nusselt number, and the Sherwood number for different values of physical parameters are constructed and analyzed. The convergence of the series solutions is examined.

Modeling the Jovian magnetosphere under an antiparallel interplanetary magnetic field from a global MHD simulation

We present preliminary results of a new global Magnetohydrodynamics(MHD) simulation model of the Jovian magnetosphere.The model incorporates mass loading from Jupiter's satellite Io, the planet's fast corotation, and electrostatic coupling between its magnetosphere and ionosphere(M-I coupling). The basic configuration of the Jovian magnetosphere including the equatorial plasma flow pattern, the corotation enforcement current system, and the field aligned currents(FACs) in the ionosphere are presented under an antiparallel interplanetary magnetic field(IMF) condition. The simulation model results for equatorial density and pressure profiles are consistent with results from data-based empirical models. It is also found that there are similarities between the FACs distribution in the ionosphere and the observed aurora features, showing the potential application of the simple ionospheric model to the complicated M-I coupling. This model will help deepen our understanding of the global dynamics of the Jovian magnetosphere.

Hall Current Effects on Unsteady MHD Flow in a Rotating Parallel Plate Channel Bound-ed by Porous Bed on the Lower Half—Darcy Lapwood Model

We discussed the unsteady flow of an incompressible viscous fluid in a rotating parallel plate channel bounded on one side by a porous bed under the influence of a uniform transverse magnetic field taking hall current into account. The perturbations are created by a constant pressure gradient along the plates in addition to the non-torsional oscillations of the upper plate. The flow in the clean fluid region is governed by Navier-Stoke’s equations while in the porous bed the equations are based on Darcy-Lapwood model. The exact solutions of velocity in the clean fluid and the porous medium consist of steady state and transient state. The time required for the transient state to decay is evaluated in detail and ultimate quasi-steady state solution has been derived analytically and also its behaviour is computationally discussed with reference to different flow parameters. The shear stresses on the boundaries and the mass flux are also obtained analytically and their behaviour is computationally discussed.

Analysis of Pulsatile Magnetohydrodynamic (MHD) Third Grade Blood Flow in a Stenosed Artery

In this research, we modeled MHD third grade blood flow in a stenosed artery. The blood viscosity and the density have been modeled into the shear thinning/thickening parameters, the most important rheological properties of blood. We used regular perturbation method and obtained the flow characteristics such as the flow velocity, the volume flow rate, the shear stress and the resistance to the flow considering a single layered stenosed artery. The results however showed that there is significant increase in volume flow rate and the velocity with increase in the magnetic field intensity H and the shear thinning Λ and reduces with increase in the shear thickening Ω.

垂直上升通道内气泡–液态金属MHD流动与传热的数值研究

在聚变堆的冷却系统中,由于强磁场的影响,液态金属流动受到抑制,通过掺入气泡到液态金属中可减小磁流体力学(Magnetohydrodynamic,MHD)效应,提升传热速率。该文基于VOF多相流模型,在不同的磁场强度(0~1.3 T)和不同的气泡雷诺数(1.3×10^(4)~6.76×10^(4))范围内,对横向磁场作用下垂直上升通道中气泡-液态金属两相流动传热特性进行数值研究。结果表明,无磁场时气体呈柱状流,而在磁场作用下,由于MHD箍缩效应的影响,气柱破裂、分离,形成了气泡流;随着磁场增大,其分离点由入口逐渐向上移动,且气泡运动速度随之增加。与液态金属单相流相比,气泡-液态金属两相流动的平均换热系数随磁场强度和气泡雷诺数增加均呈下降趋势,但因两相流动显著减小由MHD效应引起的压降,从而提升通道内综合换热因子,且在磁场较小时,提升效果更好。

Assessing the performance of magnetopause models based on THEMIS data

The magnetopause is the boundary between the Earth’s magnetic field and the interplanetary magnetic field(IMF),located where the supersonic solar wind and magnetospheric pressure are in balance.Although empirical models and global magnetohydrodynamic simulations have been used to define the magnetopause,each of these has limitations.In this work,we use 15 years of magnetopause crossing data from the THEMIS(Time History of Events and Macroscale Interactions during Substorms)spacecraft and their corresponding solar wind parameters to investigate under which solar wind conditions these models predict more accurately.We analyze the pattern of large errors in the extensively used magnetopause model and show the specific solar wind parameters,such as components of the IMF,density,velocity,temperature,and others that produce these errors.It is shown that(1)the model error increases notably with increasing solar wind velocity,decreasing proton density,and increasing temperature;(2)when the cone angle becomes smaller or|Bx|is larger,the Shue98 model errors increase,which might be caused by the magnetic reconnection on the dayside magnetopause;(3)when|By|is large,the error of the model is large,which may be caused by the east-west asymmetry of the magnetopause due to magnetic reconnection;(4)when Bz is southward,the error of the model is larger;and(5)the error is larger for positive dipole tilt than for negative dipole tilt and increases with an increasing dipole tilt angle.However,the global simulation model by Liu ZQ et al.(2015)shows a substantial improvement in prediction accuracy when IMF Bx,By,or the dipole tilt cannot be ignored.This result can help us choose a more accurate model for forecasting the magnetopause under different solar wind conditions.

Cross-Diffusion Effects on an MHD Williamson Nanofluid Flow Past a Nonlinear Stretching Sheet Immersed in a Permeable Medium

The primary aim of this research endeavor is to examine the characteristics of magnetohydrodynamicWilliamson nanofluid flow past a nonlinear stretching surface that is immersed in a permeable medium.In the current analysis,the impacts of Soret and Dufour(cross-diffusion effects)have been attentively taken into consideration.Using appropriate similarity variable transformations,the governing nonlinear partial differential equations were altered into nonlinear ordinary differential equations and then solved numerically using the Runge Kutta Fehlberg-45 method along with the shooting technique.Numerical simulations were then perceived to show the consequence of various physical parameters on the plots of velocity,temperature,and concentration of the nanofluid flow.Boosting the magnetic,Williamson,porosity,and stretching sheet index parameters,the velocity of the fluid flow decreases.The temperature is enhanced as theWilliamson and Brownian motion parameters upsurge,but it decreases as the Prandtl,thermophoresis,stretching sheet index,and Dufour parameters escalate.The concentration distribution decreases as the thermophoresis andmagnetic parameters upsurge,but it escalates as the Soret,Schmidt,Brownian motion,and stretching sheet index parameters increase.Skin friction coefficient boosted as the stretching sheet index and magnetic parameters enhanced against the Williamson parameter.The findings from this study have been contrasted with earlier findings on local Nusselt numbers,which show substantial support and endorse the existing approach’s validity.The numerical values of the local Sherwood number gradually increase as the Schmidt,Soret,stretching sheet index,and thermophoresis parameters are upsurged.

Effects of Viscous Dissipation and Periodic Heat Flux on MHD Free Convection Channel FlowwithHeat Generation

This study investigates the influence of periodic heat flux and viscous dissipation on magnetohydrodynamic(MHD)flow through a vertical channel with heat generation.A theoretical approach is employed.The channel is exposed to a perpendicular magnetic field,while one side experiences a periodic heat flow,and the other side undergoes a periodic temperature variation.Numerical solutions for the governing partial differential equations are obtained using a finite difference approach,complemented by an eigenfunction expansion method for analytical solutions.Visualizations and discussions illustrate how different variables affect the flow velocity and temperature fields.This offers comprehensive insights into MHD flow behavior and its interactions with the magnetic field,heat flux,viscous dissipation,and heat generation.The findings hold significance for engineering applications concerning fluid dynamics and heat transfer,offering valuable knowledge in this field.The study concludes that the transient velocity and temperature profiles exhibit periodic patterns under periodic heat flow conditions.A temperature reduction is observed with an increase in the wall temperature phase angle.In contrast,an increase in the heat flux phase angle values raises the temperature values.

Mixed convectional and chemical reactive flow of nanofluid with slanted MHD on moving permeable stretching/shrinking sheet through nonlinear radiation,energy omission

Hybrid nanofluids are remarkable functioning liquids that are intended to reduce the energy loss while maximizing the heat transmission.In the involvement of suction and nonlinear thermal radiation effects,this study attempted to explore the energy transmission features of the inclined magnetohydrodynamic(MHD)stagnation flow of CNTs-hybrid nanofluid across the nonlinear permeable stretching or shrinking sheet.This work also included some noteworthy features like chemical reactions,variable molecular diffusivity,quadratic convection,viscous dissipation,velocity slip and heat omission assessment.Employing appropriate similarity components,the model equations were modified to ODEs and computed by using the HAM technique.The impact of various relevant flow characteristics on movement,heat and concentration profiles was investigated and plotted on a graph.Considering various model factors,the significance of drag friction,heat and mass transfer rate were also computed in tabular and graphical form.This leads to the conclusion that such factors have a considerable impact on the dynamics of fluid as well as other engineering measurements of interest.Furthermore,viscous forces are dominated by increasing the values ofλ_(p),δ_(m)andδ_(q),and as a result,F(ξ)accelerates while the opposite trend is observed for M andφ.The drag friction is boosted by the augmentation M,λ_(p)andφ,but the rate of heat transfer declined.According to our findings,hybrid nanoliquid effects dominate that of ordinary nanofluid in terms of F(ξ),Θ(ξ)andφ(ξ)profiles.The HAM and the numerical technique(shooting method)were found to be in good agreement.

Utilization of Logistical Regression to the Modified Sine-Gordon Model in the MST Experiment

In this paper, a logistical regression statistical analysis (LR) is presented for a set of variables used in experimental measurements in reversed field pinch (RFP) machines, commonly known as “slinky mode” (SM), observed to travel around the torus in Madison Symmetric Torus (MST). The LR analysis is used to utilize the modified Sine-Gordon dynamic equation model to predict with high confidence whether the slinky mode will lock or not lock when compared to the experimentally measured motion of the slinky mode. It is observed that under certain conditions, the slinky mode “locks” at or near the intersection of poloidal and/or toroidal gaps in MST. However, locked mode cease to travel around the torus;while unlocked mode keeps traveling without a change in the energy, making it hard to determine an exact set of conditions to predict locking/unlocking behaviour. The significant key model parameters determined by LR analysis are shown to improve the Sine-Gordon model’s ability to determine the locking/unlocking of magnetohydrodyamic (MHD) modes. The LR analysis of measured variables provides high confidence in anticipating locking versus unlocking of slinky mode proven by relational comparisons between simulations and the experimentally measured motion of the slinky mode in MST.

喷口电弧二维磁流体动力学(MHD)数学模型

为了揭示电弧在开断过程中的复杂物理现象，建立的喷口电弧二维磁流体动力学数学模型，强调了电弧、气流、电磁场三者的相互作用，消除了因忽略Ｌｏｒｅｎｔｚ力和电流密度径向分量引起的物理意义失真．应用有限元法对模型中Ｎ－Ｓ（ＮａｖｉｅｒＳｔｏｋｅｓ）方程和二维电磁场方程进行数值求解．数值计算结果反映了Ｌｏｒｅｎｔｚ力以及电流密度径向分量对电弧特性的影响，同时揭示了电弧热边界区的存在．

MHD能量旁路超燃冲压发动机可行性分析

使用准一维模型对磁流体能量旁路超燃冲压发动机MPCE(Magneto-Plasma-Chem ical Engine)进行了性能计算.考察了理想和非理想的超燃冲压发动机应用磁流体MHD(magnetohydrodynam ics)能量旁路的效果,对于理想的超燃冲压发动机应用MHD反而会使发动机的性能降低;对于非理想的超燃冲压发动机,MHD的作用使发动机的比冲增加.考虑发动机工作的工程限制条件对超燃冲压发动机和MPCE的性能进行了比较,结果表明应用MHD可以扩大超燃冲压发动机的工作范围,在非设计马赫数下提高发动机的性能.计算了负载系数、通道压力系数等重要的设计参数对MPCE性能的影响,结果显示优化参数设置可以使发动机比冲增加,但是同时又会受到工程条件的限制.

日冕物质抛射的理想MHD模型研究

概括了日冕物质抛射的一些观测结果和它们与其它太阳活动现象的相关性。简要回顾了较早期日冕物质抛射的理论研究，着重介绍了最近研究得较多的理论机制，即能量储存机制，以及其中的磁通量绳突变模型与其它理论模型的MHD数值和解析研究以及相应的重要应用．

MHD控制微电离等离子体射流

为了研究磁流体动力学(MHD)控制低温微电离等离子体射流,实现推力矢量的可行性,提出了一种基于MHD控制等离子体流动理论的试验方法,建立了种子(碱金属盐)诱导燃气电离的MHD流动控制试验台,研究了不同温度和不同磁场方向条件下射流偏转向量角,并用用户自定义函数(UDF)加载MHD模型求解三维N-S方程,探究了数值研究MHD控制的可行性.结果表明:向燃烧室内注入低电离能种子能够诱导燃气电离,形成磁流体,在磁场作用下实现推力矢量控制;等离子体射流偏转的数值模拟结果与试验结果在一定程度上是一致的,说明数值模拟MHD流动控制具有一定的可信度.

基于MHD的小间隙真空电弧仿真研究

真空开关电弧电流过零前的电弧等离子体状态对真空开关能否顺利开断具有十分重要的影响。本文在建立小间隙真空电弧磁流体动力学(MHD)模型的基础上,采用通用计算流体力学仿真软件对电弧电流过零前0.5 ms时的电弧等离子体的特性进行数值仿真研究。计算得到了真空电弧等离子体压力、等离子体密度、离子纵向速度、阳极表面纵向电流密度和电弧电压等的空间分布。仿真结果表明:从阴极到阳极,真空电弧等离子体压力和密度逐渐增大,而等离子体速度逐渐减小;阳极表面电流密度存在较大径向梯度,最大值低于形成阳极斑点的极限收缩电流,阳极仍不活跃。仿真得到的等离子体密度分布与高速摄像机拍摄得到的CMOS图像光强基本吻合,计算得到的电弧电压与测得的电弧电压是一致的,从而验证了本模型的可行性。

Al_2O_3-Si_3N_4-ZrO_2多相复合材料在燃煤MHD发电中的应用

采用Ａｌ２Ｏ３基料，添加第二相（ＺｒＯ２，Ｓｉ３Ｎ４）和纤维相（ＺｒＯ２，（ｆ），以热压法制成Ａｌ２Ｏ３－Ｓｉ３Ｎ４－ＺｒＯ２多相复合材料。研究表明，新材料在青静态和动态试验中表现出良好的综合性能：１０７３Ｋ时的高温电阴率ｐ＝１．２４×１７＾７Ω．ｃｍ；静态熔渣最大腐蚀速率Ｖｓ＝０．１６μｍ／ｈ；动态最大腐蚀速率Ｖｄ＝０．４４９μｍ／ｈ。与Ａｌ２Ｏ３陶瓷相比，室温抗弯强度提高９３％，抗热震临界...

MHD燃烧室煤粉喷嘴的冷态试验研究

对浓相输送条件下ＭＨＤ燃烧室的钝体型煤粉喷嘴进行了冷态试验研究，用极板电容棵针测量了钝体不同张角、不同轴向位置、不同宽径比下ＭＨＤ燃烧室内煤粉颗粒相对浓度分布，分析了上述因素对浓度场的影响。