Experimental investigations of a breadboard model of Hall thruster

Various breadboard models of Hall thrusters are analyzed with a view to optimizing the output parameters which characterize the degree of processing of the working medium and the energy efficiency of the device. It is demonstrated that the channel geometry with the magnetic field uniform along the channel affects only slightly the efficiency of acceleration of ion flow. In a number of working modes, the formation of accelerated ion flow is accompanied by the emergence of pulsations of discharge current, this leading to destructive processes of acceleration and formation of ion flow. The development of a breadboard model with a nonuniform magnetic field along the channel significantly decreasing in the direction of anode with cylindrical space makes possible the elimination of discharge current pulsations in a wide range of parameters. The increase in the density of the flow of working medium by a factor of 1.7 results in a 30% increase in the energy efficiency and provides for the working medium utilization factor of the order of 1.2.     

High-Temperature Physicochemical Mechanics of Materials

We propose to regard investigations in the field of high-temperature strength of structural metals and alloys interacting with corrosive media as high-temperature physicochemical mechanics of materials (HTPCMM). The most important feature of HTPCMM is the principle of correlation between deformation processes and physicochemical phenomena, which allows one to describe the features and regularities of changes in the properties of materials under service conditions most completely and correctly. We emphasize the most important role of diffusion as a controlling factor in a metal–medium system at high temperatures. Results of analytical investigations aimed at the development and investigation of physicomathematical models of elastic and elastoviscous multicomponent solid solutions with inherent degradation processes (accumulation of damage) are presented. The fact that, as a rule, these models are constructed within the framework of continuum mechanics on the basis of principles of nonequilibrium mechanics is noted Experimental data obtained, in particular, on refractory metals and titanium interacting actively with components of a vacuum or an inert atmosphere testify to the intensification of saturation of metals by interstitial impurities under conditions of long-term loading and to significant changes in the character of their creep, namely, under the influence of oxygen diffusion the creep rate decreases as stresses increase.     

Non-Gaussian models for stochastic mechanics

Memoryless transformations of Gaussian processes and transformations with memory of the Brownian and Lévy processes are used to represent general non-Gaussian processes. The transformations with memory are solutions of stochastic differential equations driven by Gaussian and Lévy white noises. The processes obtained by these transformations are referred to as non-Gaussian models. Methods are developed for calibrating these models to records or partial probabilistic characteristics of non-Gaussian processes. The solution of the model calibration problem is not unique. There are different non-Gaussian models that are equivalent in the sense that they are consistent with the available information on a non-Gaussian process. The response analysis of linear and non-linear oscillators subjected to equivalent non-Gaussian models shows that some response statistics are sensitive to the particular equivalent non-Gaussian model used to represent the input. This observation is relevant for applications because the choice of a particular non-Gaussian input model can result in inaccurate predictions of system performance.     

Mechanics op porous two-phase visco-deformed medium and its geophysical applications

The paper presents the thermodynamic analysis of a saturated cracked porous medium with visco-deformed skeleton and phase transitions between the skeleton and its liquid content. Supposition on viscous skeleton deformations originates from the study of tectonic processes. The bulk viscosity originates naturally within framework of the two-phase visco-deformed medium. The seafloor spreading and crust formation processes correspond to the bulk extension of cracked porous medium in the considered case of slow geological movements. Some geophysical applications of the model are given.     

Transport Phenomena in Zeolites in View of Graph Theory and Pseudo‐Phase Transition

Transport phenomena play an essential role in catalysis. While zeolite catalysis is widely applied in industrial chemical processes, its efficiency is often limited by the transport rate in the micropores of the zeolite. Experimental and theoretical methods are useful for understanding the transport phenomena on multiscale levels. Traditional diffusion models usually use a linear driving force and an isotropic continuum medium, such that transport in a hierarchical catalyst structure and the occurrence of nonlinear deactivation cannot be well understood. Due to the presence of spatial confinement and an ordered structure, some aspects of the transport in a zeolite cannot be regarded as continuum phenomena and discrete models are being developed to explain these. Graph theory and small‐world networks are powerful tools that have allowed pseudo‐phase transition phenomena and other nontrivial relationships to be clearly revealed. Discrete models that include graph theory can build a bridge between microscopic quantum physics and macroscopic catalyst engineering in both the space and time scales. For a fuller understanding of transport phenomena in diverse fields, several theoretical methods need to be combined for a comprehensive multiscale analysis.     

Wirtschaftliche Anwendung von Mikrowellen‐Plasmen vom mittleren bis Atmosphärendruck. Economic utilisation of microwave excited plasma in medium to atmospheric pressure

An overview on the potential of medium to atmospheric pressure processes will be given and discussed in context to production applications. The introduction of the medium to atmospheric pressure plasma source is a huge progress and a valuable, attractive tool. The plasma source bases on the concept of cy lindrical r esonator with annu lar s lots (CYRANNUS®). High process speed and reliability are the most important facts for technical applications. Parameters as gas/flow dynamic can be controlled and lead to further improvements of equipment and process design. The CYRANNUS® plasma is used in down‐stream configuration for several applications such as glass films on polymer substrate to reduce oxygen permeation, protective coatings against corrosion or wear and hydrophilic or hydrophobic surface properties. Also etching or cleaning can be done easily because of arbitrary process gas in the plasma source. The advantage of medium pressure is higher supply of reactive species and improved transportation of reaction products. Various processes with plasma surface interaction are discussed from physical and technical viewpoint as plasma enhanced CVD, plasma polymerisation on metal or polymer substrates. Using the advantages of medium pressure plasma processes consequently leads to new design of equipment and material flow. In‐line/on‐line treatment of 3‐D material becomes most efficient and enables competitive plasma processes for mass productions. For diamond deposition a larger size of the plasma at high pressure processes are essential for a device with best economics.     

Correction to the Beer-Lambert-Bouguer law for optical absorption

The Beer-Lambert-Bouguer absorption law, known as Beer's law for absorption in an optical medium, is precise only at power densities lower than a few kW. At higher power densities this law fails because it neglects the processes of stimulated emission and spontaneous emission. In previous models that considered those processes, an analytical expression for the absorption law could not be obtained. We show here that by utilizing the Lambert W-function, the two-level energy rate equation model is solved analytically, and this leads into a general absorption law that is exact because it accounts for absorption as well as stimulated and spontaneous emission. The general absorption law reduces to Beer's law at low power densities. A criterion for its application is given along with experimental examples.     

Stochastic process models for earthquake ground motion

In this paper we present a review of stochastic process models proposed for the simulation of seismic ground motion. The models reviewed include those based on filtered white noise processes, filtered Poisson processes, spectral representation of stochastic processes, and finally those based on stochastic wave theory. Mathematical expressions are provided for all models along with comments on their usefulness, advantages and disadvantages.Together with the review of auto-regressive moving-average models by F. Kozin in this PEM review series on earthquake engineering (June issue), this paper represents an overview of stochastic models of earthquake ground motion, which is hopefully of some use to researchers as well as practitioners.     

A simulation method for stationary Gaussian random functions based on the sampling theorem

A unified method is developed for simulating realizations of real-valued stationary Gaussian processes, vector processes, fields, and vector fields. The method is based on parametric random models consisting of superpositions of deterministic functions of time or space with random amplitudes. The parametric models are based on the sampling theorem for random processes and generalizations of it for vector processes and random fields. The proposed simulation method is efficient and uses algorithms for generating realizations of random processes and fields that are similar to simulation techniques based on ARMA models. Several examples are presented to demonstrate the proposed simulation method and evaluate its efficiency and accuracy.     

接近爆炸作用下板状介质破坏数值模拟

利用有限元计算软件LS-DYNA建立板状介质破坏的三维模型,并用LS-DYNA970软件的求解器和后处理器对板状介质在爆炸作用下的破坏过程进行了数值模拟。通过数值模拟,再现了炸药爆炸后,冲击波的传播过程以及冲击波作用下板状介质的变形过程;并对爆破动载作用下板状介质破坏情况进行了相应的理论分析。     

“Equivalent” permeability and flow in compliant porous media

Resin flow modeling for liquid composite molding processes is generally based on assumptions of rigid porous media. This is invalid for process variations utilizing compliant mold. Yet the models built on rigid porous media assumption are used with some success in analyzing such infusions.Previous work showed that for certain porous media the one dimensional flow patterns are similar to those in rigid porous media and the deformation effects can be included in a scaling factor for permeability.This note analyzes the one-dimensional linear and radial flows in porous media with generic constitutive relations between resin pressure, thickness and permeability. It shows that as long as the deformation remains moderate, the effect of deforming porous medium may be incorporated in a single scaling factor for material permeability. This scaling factor depends on material and applied injection pressure, but does not change with time, flow-front position or type of infusion (linear or radial).     

Heat Transfer in Straight Channels with Two‐Dimensional Cross‐Sectional Profiles under Conditions of Nonisothermal Stabilized Flow of a Fluid

Heat transfer in stabilized regimes of nonisothermal flows in a round tube and in channels with twodimensional convex cross sections is investigated with allowance for the velocity profile of a heating or cooling flow of a fluid. Mathematical models of unsteady processes of cooling by convection and radiation in pulling of rods and plane sheets at a constant velocity and of heat transfer (mass transfer) in a thin runningdown layer of a medium (fluid) are solved.     

球形装药浅层水中水底爆炸冲击波压力测试及分析

介绍了四个球形装药浅层水中水底裸爆时冲击波荷载的测试技术 ,包括实验方案、测试系统、波形分析及数据处理 ,并总结出部分相关结论和经验公式     

Construction of a Mechanism of Physicochemical Processes Behind a Shock Wave Propagating in the Atmospheres of Planets

The problems of construction of a kinetic model of a medium (gas, plasma) based on the choice of the most important physicochemical processes are considered. The optimum kinetic mechanisms of a medium that describe the main nonequilibrium processes behind the shockwave front are constructed with the example of the problem of propagation of a direct shock wave in the atmosphere of planets of the solar system. The investigations have been carried out using an automated system described earlier.     

Correspondence between heat-transfer coefficients in steady and unsteady processes

An experimental study is made of the unsteady flow of heat through an element of a heat-exchanger wall for various flow conditions of the heat-carrying medium. These processes are compared with the processes occurring in the simple heating of the element (i.e., with one end thermally insulated to prevent through-flow of heat). The comparison is made for the same flow conditions of the heat-carrying medium. The conclusions of the thought experiment described in [1] are confirmed.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 25, No. 5, pp. 792–799, November, 1973.     

Identification of parametric models for ultrasonic wave propagation in the presence of absorption and dispersion

Acoustic wave propagation in an absorptive and dispersive medium is usually described using models derived from a nearly local form of the Kramers-Kronig relationship, e.g., Q- and relaxation models. A modeling approach based on rational transfer function models for the generalized Hooke's law is presented. The assumptions and restrictions of models based on the nearly local absorption-dispersion relations and rational transfer function models are discussed. Using identification techniques, it is experimentally shown that the rational transfer function models explain the ultrasonic wave propagation in an absorptive-dispersive medium much better than the classical Q-models.     

液化流程中氧液化器的流程组织和相关参数确定

简介了中压循环液化和低压循环液化两种主要的液化流程,对两种流程进行了比较;分析了在中压循环液化流程中单独设置氧液化器的必要性;探讨了在低压氧液化和中压氧液化时不同的氧液化器流程组织形式;提出了低压氧液化时合理的流程组织方案和相关参数。     

CFD model of ITER CICC. Part VI: Heat and mass transfer between cable region and central channel

Dual-channel cable-in-conduit conductors (CICC) are used in the superconducting magnets for the International Thermonuclear Experimental Reactor (ITER). As the CICC axial/transverse size ratio is typically ∼1000, 1D axial models are customarily used for the CICC, but they require constitutive relations for the transverse fluxes. A novel approach, based on Computational Fluid Dynamics (CFD), was recently proposed by these authors to understand the complex transverse thermal-hydraulic processes in an ITER CICC from first principles. Multidimensional (2D, 3D) Reynolds-Averaged Navier-Stokes models implemented in the commercial CFD code FLUENT were validated against compact heat exchanger and ITER-relevant experimental data, and applied to compute the friction factor and the heat transfer coefficient in fully turbulent spiral rib-roughened pipes, mimicking the central channel of an ITER CICC. That analysis is extended here to the problem of heat and mass transfer through the perforated spiral separating the central channel from the cable bundle region, by combining the previously developed central channel model with a porous medium model for the cable region. The resulting 2D model is used to analyze several key features of the transport processes occurring between the two regions including the relation between transverse mass transfer and transverse pressure drop, the influence of transverse mass transfer on axial pressure drop, and the heat transfer coefficient between central channel and annular cable bundle region.     

Effects of stochastic parametrization on conceptual climate models

Conceptual climate models are very simple mathematical representations of climate processes, which are especially useful because their workings can be readily understood. The usual procedure of representing effects of unresolved processes in such models using functions of the prognostic variables (parametrizations) that include no randomness generally results in these models exhibiting substantially less variability than do the phenomena they are intended to simulate. A viable yet still simple alternative is to replace the conventional deterministic parametrizations with stochastic parametrizations, which can be justified theoretically through the central limit theorem. The result is that the model equations are stochastic differential equations. In addition to greatly increasing the magnitude of variability exhibited by these models, and their qualitative fidelity to the corresponding real climate system, representation of unresolved influences by random processes can allow these models to exhibit surprisingly rich new behaviours of which their deterministic counterparts are incapable.