Minvydas Ragulskis

Plotting isoclinics for hybrid photoelasticity and finite element analysis

Displacement-based finite element method formulations are coupled with stress-based photoelasticity analysis. As the stress field is discontinuous at the interelement boundaries, the introduced smoothing procedure enables the generation of high-quality digital images acceptable for hybird experimental-numerical techniques. The proposed methods are applicable for the analysis of static and dynamic results of experimental photoelasticity.

Applicability of Attractor Control Techniques for a Particle Conveyed by a Propagating Wave

The governing equations of motion describing the dynamics of a conveyed particle by a propagating surface wave are derived. Although the problem may look rather primitive, it holds considerable complications first of all due to the fact that the shape of the surface cannot be described explicitly Special forward and reverse time marching numerical techniques, incorporating the solution of nonlinear algebraic equations in every time step, are developed for time integration of derived differential equations. It is shown that the described system possesses numerous nonlinear features such as sensitivity to initial conditions. cocxistint, attractors. This fact builds the foundation for the potential applicability of attractor control techniques based on small external impulses.

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.

Development of smart piezoceramic transducers for detection of solidification in composite materials

An engineering solution for development of smart composite materials is proposed. It is based on the implanting of piezoelectric sensors into the composite material during its manufacturing. Sweeping of sensors input alternating voltage frequency enables tracking of sensors resonance. The resonance spectrum changes due to the changes of sensors boundary conditions during cure of the composite material. Those changes are related to the degree of composite cure. Moreover, such design of composite constructions with implanted sensors enables monitoring of structural defects during explotation of those constructions. Numerical as well as experimental investigations validated the applicability of the described solidification monitoring methodology.

Investigation of the effect of self-resonance of vibration excitation systems

Eccentric type dis-balance type vibration excitation systems are analyzed in the paper. It is assumed that the dis-balance has an additional degree of freedom. It is shown that resonance vibrations in such systems can occur in the regime of self-resonance which is understood as a mode of motion when the driving shafts angular frequency is high, but the generated vibration frequency is relatively low. Experimental investigations of the effect of self-resonance enabled to define the zones of existence of such motion modes. Such principle of vibration excitation can be successfully exploited in different areas of engineering as it eliminated the necessity of complex and expensive vibration control and stabilization equipment.

Adaptive structural vibration control of acoustic deflector

Vehicle interior acoustics became an important design criterion. Both legal restrictions and the growing demand for comfort, force car manufacturers to optimize the vibro-acoustic behavior of their products. The main source of noise is, of course, the engine, but sometimes some ill-designed cover or other shell structure inside the car resonates and makes unpredicted noise. To avoid this, we must learn the genesis mechanism of such vibrations, having as subject complex 3D shells. The swift development of computer technologies opens the possibility to numerically predict and optimize the vibrations and noises.

Hybrid numerical-experimental holographic fluid interferometry

Fluid holography enables effective analysis of high speed flow problems, high frequency vibrations of micro-scale components and fluids in dosing and contacting units, high speed processes taking place in biological and chemical microsystems. The investigation of the high frequency vibrations of the fluid is an important problem in the design of various devices. Though the production stage of the interferograms is technically not extremely complicated, the interpretation of the produced fringes faces a number of mathematical and numerical problems. That is related with the complex geometry of the phase-shifting media. Under such circumstances the density can change along the line of sight, and the density is no longer proportional to phase. Therefore, development of hybrid numerical-experimental fluid holographic methods is important both for the interpretation of experimental results and for the analysis of systems in the virtual environments by generating realistic interferograms. In this paper the method of holographic interferometry is used for the analysis of the two-dimensional fluid problem. FEM analysis techniques are based on the approximation of nodal displacements (not the volumetric strains) via the shape functions. Conventional FEM would require unacceptably dense meshing for producing sufficiently smooth images. Therefore the technique for smoothing of the generated images representing the distribution of the volumetric strains and calculated from the displacement distribution is developed. The smoothing technique is based on conjugate approximation used for the calculation of nodal values of stresses and enables to obtain the images of better quality on a coarse mesh by using the displacement formulation for the calculation of the eigenmodes.