Development of surface discharge along a dielectric with large dielectric constant in gas in the nanosecond range

The discharge from a metallic edge along the surface of a dielectric with dielectric constant of the order of 100 or larger is investigated. The dependences of the rate of expansion of the discharge, the time lag, and the volt-ampere characteristics are obtained for exposure times of the order of 10^–9 sec for plates made of barium titanate, titanium dioxide, and steatite ceramicwith thickness of the order of 1 mm or less at voltages up to 1.5 kV of different polarity. The average rate of expansion of the figure of luminosity after a time of 3 nsec is equal to 10⁶ cm/sec in order of magnitude. It is shown that from a negative point the discharge is initiated by the self-electron emission current, while from a positive point it is initiated by the self-ionization current. The basic equations are given for a commutator utilizing surface discharge from a large number of points.Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 1, pp. 48–55, January, 1973.     

Numerical method for obtaining the scattering matrix of a microwave two-port from standing wave measurements

A numerical procedure is presented for obtaining the scattering matrix of a passive reciprocal two-port from eight standing wave measurements with the aid of an image circle in the Smith chart. The optimum circle through more than three points is defined. Furthermore, an averaging method is applied using the fact that theoretically after a certain transformation the experimental points should be distributed regularly on the circle. The procedure is programmed for a computer.     

Parallel computation of incompressible flows with complex geometries

We present our numerical methods for the solution of large-scale incompressible flow applications with complex geometries. These methods include a stabilized finite element formulation of the Navier–Stokes equations, implementation of this formulation on parallel architectures such as the Thinking Machines CM-5 and the CRAY T3D, and automatic 3D mesh generation techniques based on Delaunay–Voronoi methods for the discretization of complex domains. All three of these methods are required for the numerical simulation of most engineering applications involving fluid flow. We apply these methods to the simulation of airflow past an automobile and fluid–particle interactions. The simulation of airflow past an automobile is of very large scale with a high level of detail and yielded many interesting airflow patterns which help in understanding the aerodynamic characteristics of such vehicles. © 1997 John Wiley & Sons, Ltd.     

On a novel expression of the field scattered by an arbitrary constant impedance plane

The electromagnetic field scattered by an impedance plane is generally given by its plane wave expansion (Fourier representation). Here we derive an alternative expression which is more suitable for point source illumination. For this, we consider an original expression of the Hertz potentials for the incident field and express the scattered potentials in a novel form. A special function then involved can be expressed in an integral which is in turn expanded in a convergent series. The expression presented also permits us to express complete asymptotics. Our development considers an arbitrary impedance, passive or active.     

Electromechanical phase transition of a dielectric elastomer tube under internal pressure of constant mass

The electromechanical phase transition for a dielectric elastomer(DE) tube has been demonstrated in recent experiments, where it is found that the unbulged phase gradually changed into bulged phase.Previous theoretical works only studied the transition process under pressure control condition, which is not consistent with the real experimental condition. This paper focuses on more complex features of the electromechanical phase transition under internal pressure of constant mass. We derive the equilibrium equations and the condition for coexistent states for a DE tube under an internal pressure, a voltage through the thickness and an axial force. We find that under mass control condition the voltage needed to maintain the phase transition increases as the process proceeds. We analyze the entire process of electromechanical phase transition and find that the evolution of configurations is also different from that for pressure control condition.     

The computation of the dynamics of the martensitic transformation

We present numerical computations for the dynamics of the development of twinned martensitic microstructure and for the propagation of the austeniticfinely twinned martensitic interface. Our computations approximated a threedimensional model for the dynamics of the In-20.7 at% T1 alloy which used the stress tensor derived from the Ericksen-James energy density.     

Dependence of electrical strength of pressed crystalline powders on filling factor and dielectric constant of crystals

Experimental results of determination of the dependence of the electrical strength of several pressed crystalline powders, differing considerably in dielectric constant, on the filling factor are given. The obtained data are attributed to the distribution of the electric field within a two-phase dielectric.     

Numerical computation of unsteady incompressible flow in complex geometry using a composite multigrid technique

This paper presents a composite multigrid method and its application to a geometrically complex flow. The treatment of the interior boundary conditions within a composite multigrid strategy is described in detail for a 1D model equation. For the Navier-Stokes equations a staggered grid technique is adopted for spatial discretization and a fractional step method is used for the time advance. Lid-driven cavity flows are used to demonstrate the effectiveness of the method.     

Fundamental limits to the measurements of the gravitational constant G

An analysis is given of the limits set by the thermal noise to the accuracy of the measurements ofG with a torsion balance. The results are applied to measurements published recently. This shows that the uncertainty in modern measurements approaches the noise limit.     

An impedance probe for the measurements of liquid hold-up and mixing time in two/three-phase stirred tank reactors

A new probe based on the measurement of the electrical impedance has been developed to measure liquid hold-up in gas/liquid, solid/liquid and gas/solid/liquid stirred tank reactors. It allows measurements of liquid hold-up and mixing time to be made in stirred tanks. The main advantage of the new probe is that it is absolutely non-intrusive, because it uses the shaft and the baffles' support as electrodes, and that it can be used both for laboratory scale reactors as well as for industrial stirred tank reactors. The relation between impedance and liquid hold-up under loading conditions closely follows the predictions made by means of the Bruggeman model. Therefore, the new probe does not need any calibration, in that the liquid hold-up can be theoretically computed by the measurement of impedance. Received: 1 January 2000/Accepted: 8 March 2001     

The flow of a dielectric liquid

The nature of the forces acting on a dielectric liquid in an electric field in the presence of a temperature gradient is investigated. It is shown that the electrical forces produced by nonuniformity in the electrical conductivity of the medium can give rise to a hydrodynamic flow.Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 6, pp. 136–137, November–December, 1973.     

The transient electromagnetic field from an antenna near the plane boundary between two dielectric halfspaces

Summary In a preceding publication of the present author expressions were derived to describe the pulse field from a vertical electric antenna placed near the plane boundary of two semi-infinite diëlectrics. These expressions appeared to be integrals on a finite range in the complex plane and were derived for the field in both media. The analysis of the field also gave information about the time of arrival of the several pulse-fronts.In the present paper the field is studied in more detail, and with the aid of suitable approximations more specific results are obtained, such as logarithmic field singularities.Also a discussion of the pulse analogon to the Zenneck wave in the time harmonic case has been included.     

Three-dimensional magnetic resonance velocimetry measurements of turbulence quantities in complex flow

A magnetic resonance velocimetry (MRV) experimental technique based on magnetic resonance imaging and capable of measuring the turbulent Reynolds stresses in a 3D flow domain is described. Results are presented in backward facing step flow in a square channel with a Reynolds number of 48,000 based on step height and freestream velocity at the step. MRV results are compared to particle image velocimetry (PIV) measurements in the centerplane containing the streamwise and cross-stream axes. MRV and PIV mean velocity measurements show excellent agreement. MRV measurements for Reynolds normal stresses compare to within ±20% of the PIV results while results for the turbulent shear are less accurate.     

The attitudes of constant angular velocity motions

A rotation can be represented by a tensor which in turn can be parameterized by an angle of rotation and an axis of rotation. This paper presents the first systematic study of the class of rotation tensors which possess constant angular velocities. In addition to the expected rotations featuring constant axes of rotation and constant angular rates, the existence of two other types of rotation are shown. For these rotations, the time variation of the angle and axis of rotation are coupled by an integrable dynamical system. Although the temporal behavior of the axis and angle of rotation can be complex, it also demonstrated how the rotations can be considered as motions about the angular velocity vector. One of the methods used to show this result is based on an analogue to the geometry of a circular helix. The presence of the class of rotations in rigid body dynamics and twistless helical deformations of rods is also discussed.     

The computation of dynamical moduli of solids under pressure

On the basis of the theory of finite strains, expressions are obtained in general form for the effective adiabatic second order elastic constants of crystals of any symmetry in terms of the isothermal elastic constants of second, third, and higher orders in the free energy decomposition. These expressions are used in the case of crystals of cubic symmetry under hydrostatic conditions to find the elastic wave velocities in mono- and polycrystals, and their pressure dependences. The polycrystal was considered as an isotropic body consisting of a large number of cubic monocrystals. The isotropic elastic constants were calculated from theoretical and experimental results for monocrystals in the Voigt-Reuss-Hill approximation. A method of applying this approximation to thermodynamic effective second order elastic constants is proposed. The results of a computation are compared with data of experiments to measure the sound velocity in polycrystalline NaCl and CsCl specimens under pressures to 100 kbar. The results of this comparison are discussed.Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 4, pp. 162–170, July–August, 1972.     

The computation of stress intensity factors in dissimilar materials

A reciprocal work contour integral method for calculating stress intensity factors is extended to treat the problem of two bonded dissimilar materials containing a crack along the bond. The method is based on Betti's Reciprocal work theorem from which the singular stress intensities at the crack tip may be evaluated in terms of an integral involving tractions and displacements on a contour remote from the crack tip.