Numerical simulation of the spatial structure of a moving arc discharge

Results are given of the calculation of the structure of an arc discharge moving on parallel electrodes in air under the effect of a transverse magnetic field (0.086 T) at a current strength of 320 A. The numerical simulation is performed within an unsteady-state three-dimensional mathematical model of radiation magnetogasdynamics. The calculations reveal that fluctuations of values of physical parameters and of spatial shape of arc arise in the arc, which are caused by the gas flow past the discharge column and by unsteady-state processes in the electrode regions. Comparison is made with the available experimental data.     

Formation of Structures of Multieddy Natural Convection in a Horizontal Layer Heated from Below

The Galerkin finite-element method is used to investigate the structures of supercritical thermogravitational convection in an elongated plane horizontal layer of a liquid with the Prandtl number Pr = 10. The solution of the problem with a constant heat-flux density preassigned at the lower boundary is compared to the solution of the problem for the case of boundaries at constant temperature. The results of comparative analysis of convective modes arising under different conditions at the boundaries of the layer and under different initial thermal conditions are given. The mathematical model is provided by two-dimensional unsteady-state equations for natural thermal convection in the Boussinesq approximation that are written in terms of the variables of speed eddy, stream function, and temperature.     

Lag in the temperature measurement system in performing fractional distillation of petroleum products

We carried out mathematical simulation of the temperature measurement system in performing fractional distillation of petroleum products (FDPP). To evaluate the actual lag in measuring the temperature in the process of FDPP, a special experiment was run on the basis of the mathematical model developed. It is shown that under unsteady-state conditions the error of a glass thermometer due to the phenomenon of thermal response may attain 15–25°C or more.     

The simulation of ultraviolet radiation under conditions of re-entry of space vehicle from near-earth orbit

Numerical simulation is performed of nonequilibrium radiation spectrum in near ultraviolet in the range of 230–280 nm from the high-temperature shock layer on the frontal surface of a sphere with a radius of 2.2 m moving in the Earth atmosphere at hypersonic velocity of the order of orbital velocity. Radiation is considered in seven systems of bands originating from electron transitions in diatomic molecules, which may give an appreciable contribution in the given spectral range. The flow field is determined using the numerical solution of two-dimensional Navier-Stokes equations for a nonequilibrium mixture of chemically reacting gases, which are complemented with conservation equations for electronic states of molecules. The calculations are performed for the conditions of trajectory of re-entry of the Soyuz-TMA space vehicle (SV) into the Earth atmosphere in the altitude range from 70 to 90 km. Adequate agreement is observed with full-scale experiment involving the observation of radiation during the descent of Soyuz-TMA SV from aboard the international space station.     

Effect of thermal processes on the accuracy of precision fiber-optic inertial sensors

A mathematical model of thermal processes and temperature errors is constructed for a promising sensor to determine the angular position and angular velocity of moving objects—a fiber-optic gyroscope (FOG). Methodological, algorithmic, and program supports are developed making it possible to carry out an automatic investigation of the functioning of an FOG exposed to temperature effects. Computational experiments and computer analysis of thermal processes and thermal drift are performed for specific design versions of the FOG, and recommendations for decrease in the temperature errors of the FOG are developed.Branch of the A. A. Blagonravov Institute of Mechanical Engineering, Saratov. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 66, No. 1, pp. 61–68, January, 1994.     

Modeling in Thermal Behavior of Charring Materials

Physical and mathematical models are the key to analyze thermal behavior of charring materials in the thermal protection system of reentry vehicles subjected to aerodynamic heating. To explore the thermal behavior of charring ablator, we developed and compared two models (pyrolysis interface model and pyrolysis layer model) with pyrolysis and surface recession. Taking AVCOAT composites as an example, its nonlinear thermal behavior, which are caused by temperature dependent thermal properties, moving interfaces and moving boundary, were simulated using the calculation codes written respectively on the basis of the pyrolysis layer model and the pyrolysis interface model. Numerical results indicate that the nonlinear calculation is easier by the pyrolysis interface model than by the pyrolysis layer model; on the other hand, the selection of the pyrolysis interface temperature is complicated but significant in the calculation on thermal behavior of charring materials. This study will be helpful for the design of the thermal protection system in reentry vehicles.     

Nonlinear correlation for estimating the motion of multiple objects in image sequences

A nonlinear correlation algorithm is proposed for estimating the motion of objects from an image pair. This algorithm requires no a priori information on the number, size, or shape of the moving objects and does not require feature extraction or segmentation of either image. The algorithm directly yields information on the number of moving objects, the motion of the objects, and the size of the objects. Additional processing can be performed to yield the centroid of the objects in either frame. The utility of the resulting algorithm is demonstrated by application to a pair of example image sequences.     

Generalized numerical modelling of unsteady heat transfer during cooling and freezing using an improved enthalpy method and quasi-one-dimensional formulation

A numerical solution of a generalized Stefan problem is presented. It covers a great variety of unsteady heat conduction cases accompanied by phase transformations. A mathematical model is developed for determination of the unsteady-state temperature and enthalpy fields (as well as the space-time evolution of the phase content) and of the cooling and freezing (heating and thawing) times of food materials and other bodies of various configuration (representing multicomponent two-phase systems having one freezable component). An improved enthalpy method is proposed by which all non-linearities, caused by the temperature dependence of the thermophysical coefficients, are introduced in a functional relationship between the volumetric specific enthalpy and the Kirchhoff function. Thus the non-linearities are eliminated as a factor making the solution difficult. The applied approach possesses great adaptivity and flexibility in solving complicated moving boundary problems: it is suitable for both isothermal and non-isothermal phase change, reaches a high degree of correspondence between the real physical phenomenon and its mathematical formalization, uses uniform and easy fixed-grid computational techniques, makes it possible to avoid complications and to eliminate possible errors caused by ‘jumping’ of the equivalent specific heat capacity peak at the maximum of the latent heat effect, etc. Efficient procedures and algorithms for computer simulation of complex refrigerating technological processes are created. Experimental verification demonstrating the applicability and accuracy of the model is carried out.     

Trajectory optimization of nonholonomic mobile manipulators departing to a moving target amidst moving obstacles

How to plan the optimal trajectory of nonholonomic mobile manipulators in dynamic environments is a significant and challenging task, especially in the system with a moving target. This paper presents trajectory optimization of a nonholonomic mobile manipulator in dynamic environment pursuing a moving target. Full nonlinear dynamic equations of the system considering the nonholonomic constraints of wheels are presented. Then, dynamic motion planning of the system is formulated as an optimal control problem considering moving obstacle avoidance conditions. Accordingly, a new formulation of dynamic potential function was proposed based on the dynamic distance between colliding objects. In addition, an appropriate boundary value for a moving target was defined, and the resulted boundary value problem was solved to optimize the trajectory of the system. To solve the problem, an indirect solution of optimal control was applied which leads to transform the optimal control problem into a set of coupled differential equations. To demonstrate the efficiency and applicability of the method a number of simulations and experiments was performed for a spatial nonholonomic mobile manipulator.     

Investigation of Pyrolysis of Methane under Conditions of Filtering through a Heated Porous Medium

An unsteady-state one-dimensional mathematical model is used to perform a theoretical analysis of the process of thermal decomposition of methane under conditions of filtering through a heated porous medium formed by granules of commercial-grade carbon. A scheme of the process kinetics is developed. The effect of the basic characteristics of commercial-grade carbon and of the operating conditions on the efficiency of the process is treated. Laboratory experiments are performed in support of the commercial-scale technology of production of granular pyrocarbon. A comparison of the calculation results with experimental data demonstrates their good agreement.