流体电子学时代的气动技术

气动技术正经历一个与之并行的电子控制一体化的过程,但是对这种发展的宣传却少于对液压电子一体化的宣传。自从射流技术出现以来,在气动技术领域中从没有出现过如此令人兴奋的事。虽然气动没有因为液压电子一体化的出现而被忽视,但至今为止大家的注意力主要还是集中在液压电子技术上。这其中的一个原因可能是在美国电子液压控制最初是作为一种代替车辆用大功率液压阀的液—液先导阀的技术而开发的。另一个更基本的原因则是:液压技术采用不可压缩的流体(液体)作为能量传递介质,而气动却采用了可压缩的流体(气体)作介质。在历史上。

Numerical simulation on magnetohydrodynamic power generation channel of scramjet

The reverse magnetohydrodynamic(MHD)energy bypass technology is a promising energy redis⁃tribution technology in the scramjet system,in augmented with a power generation equipment to supply the neces⁃sary long-distance flight airframe power.In this paper,a computational model of the scramjet magnetohydrody⁃namic channel is developed and verified by using the commercial software Fluent.It is found that when the mag⁃netic induction intensity is 1,2,3,4 T,the power generation efficiency is 22.5%,22.3%,22.0%,21.5%,and decreases with the increase of the magnetic induction intensity,and the enthalpy extraction rate is 0.026%,0.1%,0.21%,0.34%,and increases with the increase of the magnetic induction intensity.The deceleration ef⁃fect of electromagnetic action on the airflow in the power channel increases with the increase of magnetic induc⁃tion intensity.The stronger the magnetic field intensity,the more obvious the decreasing effect of fluid Mach num⁃ber in the channel.The power generation efficiency decreases as the magnetic induction intensity increases and the enthalpy extraction rate is reversed.As the local currents gathering at inlet and outlet of the power generation area,total temperature and enthalpy along the flow direction do not vary linearly,and there are maximum and minimum values at inlet and outlet.Increasing the number of electrodes can effectively regulate the percentage of Joule heat dissipation,which can improve the power generation efficiency.

A comparison among optical emission spectroscopic methods of determining electron temperature in low pressure argon plasmas

In this article, four kinds of optical emission spectroscopic methods of determining electron temperature are used to investigate the relationship between electron temperature and pressure in the cylindrical plasmas of dc glow discharges at low pressures in laboratory by measuring the relative intensities of ArI lines at various pressures. These methods are developed respectively on the basis of the Fermi-Dirac model, corona model, and two kinds of electron collision cross section models according to the kinetic analysis. Their theoretical bases and the conditions to which they are applicable are reviewed, and their calculation results and fitting errors are compared with each other. The investigation has indicated that the electron temperatures obtained by the four methods become consistent with each other when the pressure increases in the low pressure argon plasmas.

Numerical analysis of thermal fluid transport behavior during electron beam welding of 2219 aluminum alloy plate

A two-dimensional mathematical model based on volume-of-fluid method is proposed to investigate the heat transfer,fluidflow and keyhole dynamics during electron beam welding(EBW)on20mm-thick2219aluminum alloy plate.In the model,anadaptive heat source model tracking keyhole depth is employed to simulate the heating process of electron beam.Heat and masstransport of different vortexes induced by surface tension,thermo-capillary force,recoil pressure,hydrostatic pressure and thermalbuoyancy is coupled with keyhole evolution.A series of physical phenomena involving keyhole drilling,collapse,reopening,quasi-stability,backfilling and the coupled thermal field are analyzed systematically.The results indicate that the decreased heat fluxof beam in depth can decelerate the keyholing velocity of recoil pressure and promote the quasi-steady state.Before and close to thisstate,the keyhole collapses and complicates the fluid transport of vortexes.Finally,all simulation results are validated againstexperiments.

How Does the Diffusion Dynamics Reconnect the Magnetic Field？

We clarify how magnetic reconnection can be derived from magnetohydrodynamics （MHD） equations in a way that is easily understandable to university students. The essential mechanism governing the time evolution of the magnetic field is diffusion dynamics. The magnetic field is represented by two components. It is clarified that the diffusion of a component causes agene ration of another component that is initially zero and, accordingly, that the magnetic force lines are reconnected. For this reconnection to occur correctly, the initial magnetic field must be directed oppositely in the two regions, e.g., y 〉 0 and y 〈 O; must be concave （convex） for y 〉 0 （y 〈 0）; and must be saturated foryfar from the x axis, which would indicate the existence of the current sheet. It will be clear that our comprehension based on diffusion runs parallel to the common qualitative explanation about the magnetic reconnection.

Molecular Thermodynamics of Charged Hard-Dumbbell Fluids

Chemical potentials of charged hard-dumbbell fluids are obtained by Monte Carlo simulations using Widom's test-particle method, corresponding compressibility factors are achieved by integration of chemical potentials at different densities. A molecular thermodynamic model is also developed for these charged hard-dumbbell fluids where the residual Helmholtz function is composed of two terms: a reference term responsible for the charged hard spheres and a bonding contribution measuring the sticky interactions between positive and negative hard ions.Model predictions are in good agreement with simulation results.

Analysis on the Application of Electrical New Technology of in Electromechanical Integration

The electrical new technology is a new frontier science.This kind of technology, with the development and progress of society, makes the continuous development and innovation.It is the future development trend of electrical engineering system,which plays a very important role in technological innovation.The principle and theoretical support for the development of electrical new technology includes Bio- electro magnetics, plasma physics, electromagnetic fluid mechanics and gas discharge physics etc.In addition, under the application of permanent magnetic materials and other new materials, the electrical new technology and obtained further development also promote the development and application of electronic power supply, strong magnetic field technology, solar photovoltaic power generation, and superconducting power technology.This paper mainly analyzes the application of electrical new technology in electromechanical integration.

Ab initio simulation of the sum-frequency generation response of optically active liquids in the presence of a dc electric field —determination of the absolute molecular configuration

Quantum chemical computations have been performed to evaluate the first and second hyperpolarizability quantities of the interference term, linear in the external static electric field, that appear in the electric field-induced sum-frequency generation signal of chiral liquids. These are performed at the time-dependent Hartree-Fock level on the prototypical 1,1′-bi-2-naphtol chiral species.