Algimantas Fedaravicius

Estimation of the Drag Coefficient of Mine Imitator in Longitudinal Air Flow Using Numerical Methods

Abstract One of the most important measures to reduce the cost of preparing mortar units is the use of mortar shooting trainers operating according to the ‘shell in shell’ principle that best meets the needs of military forces. When increasing the efficiency of using equipment for mortar shooting training and seeking to reduce their production costs, further research on external ballistics is strictly necessary in order to improve the structural parameters of mine imitators. With the help of finite element modelling techniques, this article investigates air flow over mortar mine imitators. In order to achieve the aim, a package of Mechanical Desktop Software was used for creating a dimensional model of mine imitator the model of which was imported into ANSYS CFX and a finite element numerical model was generated. Considering the literary sources of experimental studies, SST turbulence model generating the results closest to those of experimental research was selected. After modelling, air drag force influ...

Applicability of time-average fluid holography for analysis of propagating waves

Numerical procedures for construction of digital patterns of fringes mimicking fluid holograms are developed. Because conventional finite-element fluid analysis techniques are based on the approximation of nodal displacements, conjugate smoothing of the values of volumetric strain is performed in order to obtain realistic holographic images. Two-dimensional fluid oscillations are analyzed using the developed techniques. It is shown that though time-average fluid holography is a powerful optical experimental method for analysis of short-term transient processes and harmonic vibrations, it has rather limited applicability to studying propagating waves.

Development of Laser Rifle Trainer with Full Shot Imitation

Laser trainers are effective tools for shot and sportsmen training. However, the majority of trainers have neither realistic recoil nor sound imitation systems. The objective of the development of laser rifle trainer with full shot imitation was to investigate and simulate the recoil of combat weapons under single and serial shooting regimes so that the training weapons could simulate complete recoil and sound imitation. Theoretical and experimental investigations lead to the development of shot training systems which were successfully implemented in Lithuanian Army combat training facilities. The laser trainers are also equipped with interactive software interface which does not only control and register the process of shooting but also can reproduce the whole set of statistical data, including psychological impact on the rifleman and detection of his training problems. The incorporation of multimedia advances the system up to interactive laser shot trainer in virtual combat reality.

Modal and flutter analysis of the sailplane LAK-17B using numerical methods

AbstractThe objective of current work is to determine the V–g and V–f diagrams for the sailplanes LAK-17B empennage using numerical methods. The article considers the following problems: development of finite element model of the sailplane LAK-17B; normal modes calculation using created finite element model; flutter analysis of sailplane LAK- 17B using doublet lattice method.

Near-Optimal Moire Grating for Chaotic Dynamic Visual Cryptography

Image hiding based on chaotic oscillations and near-optimal moire gratings is presented in this paper. The secret image is embedded into a single cover image. The encrypted secret image appears in a form of time-averaged moire fringes when the cover image is oscillated in a predefined direction, according to a chaotic law of motion. The criterion of the optimality of a moire grating is based on the absolute difference between the standard deviation of time-averaged images of near-optimal moire gratings in the background and in the zones associated to the secret image. Genetic algorithms are used for the identification of a nearoptimal set of moire gratings for image hiding applications. Numerical experiments are used to illustrate the functionality of the method.

Development of Mortar Simulator with Shell-In-Shell System – Problem of External Ballistics

The shell-in-shell system used in the mortar simulator raises a number of non-standard technical and computational problems starting from the requirement to distribute the propelling blast energy between the warhead and the ballistic barrel, finishing with the requirement that the length of warheads flight path must be scaled to combat shell firing tables. The design problem of the simulator is split into two parts – the problem of external ballistics where the initial velocities of the warhead must be determined, and the problem of internal ballistics – where the design of the cartridge and the ballistic barrel must be performed.

External Ballistics Simplified Model of the “RT – 400” Rocket Aerial Target

1. This work was supported by the Research Council of Lithuania, grant No. S-MIP-17-94 “Experimental Rocket: Research and Development”.

Analysis of Aerodynamic Characteristics of the Rocket-Target for the „Stinger” System

This paper presents an analysis of aerodynamic characteristics of the rockettarget for the final training of shooting at aerial targets by the „Stinger” system service staff. The governing equations of fluid dynamics are presented and the computational model of airflow around the rocket is developed. ANSYS CFX computational fluid dynamics software is used to compute airflow velocities, pressure, the drag force and the drag coefficient. A practical implementation of the research is presented. Taking into account the simulation results, the rocket-target was designed and manufactured.

Design, Research and Practical Implementation of the Laser Shooting Simulation System for 5.56 mm G-36, 7.62 mm FN MAG and 84 mm Carl Gustaf

This paper is based on the work presented at the 10th International Armament Conference on „Scientific Aspects of Armament and Safety Technology”, Ryn, Poland, September 15-18, 2014.

Cryptographic Hash Algorithms Based on Time Averaging Techniques

An algorithm for the construction of hash function based on optical time averaging techniques is proposed in this paper. Algebraic structures of grayscale color functions and time average operators are constructed. Properties of time average operators and effects of digital image representation are explored. The fact that the inverse problem of identification of the original grayscale color function from its time averaged image is an ill‐posed problem helps to construct an efficient algorithm for the construction of a new class of one‐way collision free hash functions. The algorithm can be generalized to 2D or even 3D problem.