Abstracts of papers for

Previous issue vol. 41, no. 3 (2000)

vol. 41, no. 4 (2000)

Next issue vol. 42, no. 1 (2001)

Contents of issue 4, vol. 41

1. G. Szefer: Dynamics of elastic bodies undergoing large motions and unilateral contact
2. E. Włodarczyk: Brisance of the high explosives
3. Z. Dżygadło, I. Nowotarski, A. Olejnik: Nonlinear, regular and chaotic vibrations of a plate in supersonic flow
4. S. Cudziło, K. Jach, M. Mroczkowski, A. Sarzyński, R. Świerczyński, R. Trębiński: Experimental verification of a theoretical model of the shaped charge jet formation process
5. T. J. Hoffmann and B. Niechciałkowska: Strong discontinuity waves in extended phenomenological electrodynamics
6. R. Nawrowski: Air- or SF₆- insulated heavy-current busways
7. Z. Łęgowski: A new formulation of the local reflection theory of an oblique shock wave at a rigid wall
8. F. Ozek: Estimation of the range for free space optical links between mobile terminals
9. R. Dulski: Computer faceted thermal target model
10. W.A. Trzciński, J. Paszula: Confined explosions of high explosives

    Brief Notes

11. J. Cabański: Generalized exact method of analysis of free and forced oscillations in the non-conservative physical system

G. Szefer: Dynamics of elastic bodies undergoing large motions and unilateral contact

In the paper, a general description and analysis of motion of elastic bodies experiencing large displacements and finite strains in terms of unilateral frictional contact will be presented. Displacements are resolved into displacements due to deformation and displacements due to rigid body motion. The paper consists of two main parts: the first one deals with the coupling of rigid body motion and deformation. Using the principles of momentum and angular momentum, the set of the governing equations of the dynamical system will be derived. The second part deals with the statement and with the characteristic features of a general dynamic large displacement contact problem. We end the presentation with some concluding remarks, perspectives and open problems.

Contents

E. Włodarczyk: Brisance of the high explosives

The essential survey of the literature data, concerning the brisance of high explosives (HE) has been made in this paper. It is confirmed that the quantitative criteria of the theoretical estimate of the HE brisance proposed in the scientific literature are based on several assumptions, which are contradictory to the real course of the explosion phenomenon, and therefore they are erroneous. These criteria must not be applicated in the engineering practice. The reflection process of the detonation wave from the inertial rigid partition was used in order to derive the new formula describing the relative brisance of the HE. Moreover, the brisance of numerous commercial explosives and the military ones has been analysed, too. The results, presented in this paper, are confirmed by experimentally gained data.

Contents

Z. Dżygadło, I. Nowotarski, A. Olejnik: Nonlinear, regular and chaotic vibrations of a plate in supersonic flow

Aeroelasticity of surface structures in supersonic flow is a domain which involves various linear and nonlinear vibrations, static and dynamic instabilites and limit cycle motions (cf. [1-4]). Various types of bifurcations and regular or chaotic motions can appear depending on the values of parameters of the system under investigation [3-11]. In this paper, nonlinear bending vibrations of a plate of finite length and infinite width in supersonic flow are considered under the assumption that a nonlinear in-plane compressing force is acting in the plate. The dynamic pressure difference produced by the plate motion in gas stream is determined on the basis of the potential theory of supersonic flow [1, 2]. Finally, we obtain a nonlinear partial integro-differential equation describing the motion of the structure under investigation. The solution of this equation is obtained in the form of a series of normalised eigenfunctions of the self-adjoint boundary-value vibration problem of the same plate in the vacuum. Making use of the Galerkin method, we then obtain a set of nonlinear ordinary differential equations which can be analysed by means of numerical methods. Types of bifurcations occurring in the problem are investigated, limit cycles of self-excited vibrations and regions of regular and chaotic motions can be determined.

Contents

S. Cudziło, K. Jach, M. Mroczkowski, A. Sarzyński, R. Świerczyński, R. Trębiński: Experimental verification of a theoretical model of the shaped charge jet formation process

Experimental verification of a theoretical model of the shaped charge jet formation process has been performed. The model is based on the numerical solution of the equations of mechanics of continuous media. It was described in earlier works of the authors. In the first stage of its experimental verification, flash radiographs of the shape of collapsing liner were taken and then compared with the results of modelling. After that, theoretical and experimental relations between detonation parameters of explosives, case material, wave shaper diameter, liner shape and jet characteristics were investigated. Validity of the theoretical model was assessed on the basis of comparison of the calculated and experimental jet tip velocities.

Contents

T. J. Hoffmann and B. Niechciałkowska: Strong discontinuity waves in extended phenomenological electrodynamics

In the paper the description of discontinuity of the electromagnetic field in the continuum medium in terms of the extended electrodynamics in considered. The classical field theory based on the analytical Lagrange-Hamilton methods has been used as a formal apparatus. The classical theory of discontinuity waves is applied to the description of the discontinuity of the field. Dynamics of the electromagnetic field is expressed in terms of the Lagrange equations of motion in the linear approximation.

Contents

R. Nawrowski: Air- or SF₆- insulated heavy-current busways

In the paper the method of calculation of the eddy current losses, the temperature, the electrodynamics forces, material and energetic optimization of the shape of busways system with air and SF₆ insulation are presented. The method discussed takes into consideration coupling between the electromagnetic field and the thermal field. The method is based on the numerical solution of equations joining the temperature and the eddy-current losses. The method of successive approximations and numerical optimizations are used to solve the equations. In this paper it is assumed that the analyzed system is linear and infinitely long in the direction of the conductors.

Contents

Z. Łęgowski: A new formulation of the local reflection theory of an oblique shock wave at a rigid wall

A complete solution to the local theory of the shock wave reflection at an inclined wall has been obtained for the first time in two particular regions. One is the region near the Mach stem confluence S point with the wall and the other in the vicinity of the triple point T of an irregular shock-wave configuration. The correct lines of regular-irregular transitions have been established for the self-similar reflection problem in shock tubes. The solutions for all shock-fronts geometry have been obtained in the vicinity of the triple point, which are in agreement with the results of experimental measurements. In all the region of interaction the backward-reflected shock waves have been obtained for incident waves of arbitrary intensity. It has been formulated the hypothesis concerning the regular-irregular transition of weak shock waves, as a result of disintegration of an arbitrary discontinuity formed at the terminal stage of regular reflection.

Contents

F. Ozek: Estimation of the range for free space optical links between mobile terminals

The motivation being the modern trend towards mobile communication, the maximum estimated ranges of communication have been numerically evaluated for free space optical links between mobile on-sea terminals, for different bit rates and atmospheric conditions. An analysis of possible sources of noise, by day and night, is given. The advantages of a wide angle elliptic beam of medium power diodes at the transmitter and a four-quadrant detector at the receiver are emphasized. The effect of the size and position of the laser spot formed on the detector is pointed out.

Contents

R. Dulski: Computer faceted thermal target model

The paper proposes a computer Faceted Thermal Target Model (FTTM) describing target's radiative properties in the infrared spectral region. The model is intended for simulation of a target in analyses of the influence of thermal-scene conditions on the possibilities of target detection by a thermodetection system. This is a model describing the target as a set of facets. The set of data for the model requires information on the shape and dimensions of the target as well as on distribution of temperature and emissivity coefficient of its surface. The model enables to determine emission of radiation from the target surface for various directions of detection, which makes it possible to obtain the data necessary to design devices for infrared recognition, with a limited application of costly experimental investigations.

Contents

W.A. Trzciński, J. Paszula: Confined explosions of high explosives

In the present paper, effects of turbulent combustion of the detonation products of high explosives in confined explosions are studied. Explosions of TNT, TNT/RDX and the mixtures of these explosives with Al are investigated in a steel chamber of 150-liter volume. The chamber is filled with nitrogen or air under normal conditions. Overpressure histories are recorded at the chamber wall. The dependence of the mean overpressure on the loading density of TNT is determined. This dependence is used to determine the TNT equivalent of explosives tested for confined explosions. On the basis of the measured overpressure histories and the results of thermochemical calculations, the rate of energy release and final heat effects of combustion of the detonation products in air are also estimated. Finally, the degree of after-burning of the detonation products is calculated for explosive mixtures tested.

Contents

J. Cabański: Generalized exact method of analysis of free and forced oscillations in the non-conservative physical system

In this paper, the fundamental problems in the generalized exact form used for the analysis of oscillations in composite physical systems, are presented. To these generalized problems belong such as: separation of variables in the complex Hilbert space, orthogonality of the eigenvectors of boundary-value problems, influence of the initial conditions and forced oscillations. The generalizations have been presented in the operator forms. In the case of real physical systems, it is necessary to transform the operator forms into suitable scalar ones. The presented approach is an essential extension of the method of separation of variable applied to the linear system of differential equations.

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