https://etalpykla.vilniustech.lt/handle/123456789/156026 Sat, 04 Apr 2026 13:56:21 GMT 2026-04-04T13:56:21Z https://etalpykla.vilniustech.lt/handle/123456789/156926 Phase trajectories of non-linear oscillations of a tower structure with an attached damper in a uniform wind flow Volkova, Viktorija; Pakrastinsh, Leonids; Gaile, Liga This paper is devoted to the study of the dynamic behaviour of a tower structure with an attached damper. Two dampers are attached to the upper end of the rod in two mutually perpendicular planes. The oscillation damper is a mass attached to the rod by elastic coupling and a viscous friction. The mathematical model of the object being under consideration includes a system of two non-linear differential equations. The numerical simulation was used to study the dynamic behavior of a dissipative system with limited excitation, containing a pendulum vibration damper. The characteristics of the system amplitude − the speed of the wind flow is obtained. It is shown that the pendulum vibration damper can significantly reduce the amplitudes of resonant oscillations of the cantilever rod. It is also shown that the choice of system parameters makes it possible to avoid the establishing of resonant oscillations of the system. at the first resonance zone where the amplitudes of oscillations achieved the greatest values. Tue, 01 Jan 2019 00:00:00 GMT https://etalpykla.vilniustech.lt/handle/123456789/156926 2019-01-01T00:00:00Z https://etalpykla.vilniustech.lt/handle/123456789/156925 Application of equivalent cylindrical inhomogeneity to modeling of CNT and analysis of influence of CNT distributions on response of functionally graded structural elements Nazarenko, Lidiia; Chirkov, Aleksandr; Stolarski, Henryk; Altenbach, Holm A mathematical model based on the concept of the energy-equivalent inhomogeneity combined with the method of conditional moments (MCM) has been applied to analyze Carbon Nanotube (CNT)-reinforced materials. The idea of the energy-equivalent inhomogeneity is to replace the inhomogeneity and its interphase by a single equivalent inhomogeneity. It is evaluated for cylindrical inhomogeneity with Gurtin-Murdoch surface model and spring layer model of interphases. Inclusion of multiple mechanisms in the description of interphases is applied to the CNT-reinforced materials. The CNT is modeled as a cylindrical high-stiffness surface. A weak zone surrounding the CNT can be modeled by a spring layer. In this case, one Gurtin-Murdoch and one spring layer models would need to be combined. To evaluate the effective properties of CNT-reinforced materials a statistical method, the MCM, has been employed which describes random distribution of CNT’s. Closed-form formulas for the components of the effective stiffness tensor of such composites have been developed. A composite plate weakened by a hole under different types of loading is considered. It is assumed, that the plate made of the polymer with randomly distributed and disoriented CNT’s. Analysis of how various special distributions of CNT concentration affect the response of this plate is performed. Tue, 01 Jan 2019 00:00:00 GMT https://etalpykla.vilniustech.lt/handle/123456789/156925 2019-01-01T00:00:00Z https://etalpykla.vilniustech.lt/handle/123456789/156924 A community detection method for network structure analysis of force chains in granular medium in a rotating drum Navakas, Robertas; Džiugys, Algis We analyze the motion of granular matter in a partially filled drum rotating around the horizontal axis. The motion of granular medium is simulated using the discrete element model (DEM). As the drum rotates, the free surface sloping angle changes periodically as it attains the limit repose angle leading to an avalanche, after which its value is reduced to below the repose angle. Systems of this type are of interest from both theoretical and application viewpoints: similar setups are used in industry, such as rotary kilns and mixers; besides, dynamics of granular matter leads to macroscopic effects, such as segregation and emergence of patterns. Observable macroscopic effects depend largely on the underlying structure of force chains arising from pairwise mechanical contacts between the particles. Discrete element simulations produce the data for each individual particle: position, translational and rotational velocity, force vector between the interacting particle pairs. These data about the microscopic state must be processed to obtain the observable macroscopic states. Particle configurations at each time moment available from DEM simulations can be represented as graphs: each particle is represented as a graph vertex, the vertex pairs are connected by edges if the respective particle pairs are in contact, and the edge weights are proportional to the interaction force. After the graph for a particle state is created, the algorithms of the graph analysis can be applied to analyze the corresponding state of granular matter. Among such algorithms, we use the community detection algorithms to analyse the emergence of force groups among the particles, i.e., the groups of particles that have stronger mechanical forces among the particles in the group than the forces with particles that do not belong to the given group. Such groups are structures of larger scale than the usual force chains. Distribution of group sizes (number of particles belonging to the group) and their positions depend on the rotation velocities of the drum; in turn, they influence the variation of the repose angle and the process of the avalanches. We report the relations between the characteristics of the detected force groups and the observable effects in the granular matter obtained by DEM simulations. Tue, 01 Jan 2019 00:00:00 GMT https://etalpykla.vilniustech.lt/handle/123456789/156924 2019-01-01T00:00:00Z https://etalpykla.vilniustech.lt/handle/123456789/156922 Direct Metal Laser Sintering of stainless steel alloy: microstructure and mechanical properties Mordas, Genrik; Steponavičiūtė, Ada; Selskienė, Aušra; Tretjakovas, Jurijus; Borodinas, Sergejus Additive manufacturing (AM) is a type of manufacturing technologies whereby the material is added a layer upon layer to produce a 3D object. Produced 3D parts are applied in such industry sectors as space, aviation, automotive, building and has excellent future promises. Ourdays, the commercialy promised technique for metal manufacturing is Direct Metal Laser Sintering (DMLS). Our study concentrated on the investigation of the mechanical properties of produced17-4H (stainless steel) parts using DMLS. The effect of the DMLS process parameters (laser power, scanning speed and energy density) on the ultimate strength, yield strength and Young’s modulus was determined. We showed an evolution of the microstructure. The detected defects were classified. This study allowed to determine the optimal regimes of DMLS for SS 17-4H and describe mechanical properties of the produced parts as well as helped to show future possibilities of DMLS development. Tue, 01 Jan 2019 00:00:00 GMT https://etalpykla.vilniustech.lt/handle/123456789/156922 2019-01-01T00:00:00Z