Applied Mechanics and Materials Vol. 821

Abstract: This paper deals with an experimental analysis of hard rubber dynamic tests under finite torsion deformations. The experimental test rig was designed and composed for torsion loading of rubber under defined amplitudes, frequencies and temperatures. The present paper brings an amplitude-temperature analysis of isoprene-butadiene rubber ascertained by the use of the test rig. The mathematical rheological model of rubber was designed for phenomenological description and parametric identification of rubber.

Abstract: Systematic monitoring of rotational vibration (both torsion and swivelling) of guyed mast shafts has been performed in ITAM since 2005. The occurrence of this phenomenon is conditioned by the fact that the guy ropes are attached to the construction of the shaft, i.e. out of its axis. The simple static calculation model serves for making the proof of the occurrence of the torsional moment, affecting the shaft, which is guyed by three ropes. The exact theoretical solution of the real phenomenon assumes the introduction of dynamics of guy ropes, which vibrate in 3D shapes during the shaft’s movement along the orbit and it ́s torsion (swivelling).

Abstract: Unbalance of rotors is one of the principal causes of their lateral vibration. A technological solution frequently used to its suppression consists in placing damping devices to the rotor supports. To achieve their optimum performance their damping effect must be controllable. This is offered by squeeze film dampers utilizing the magnetorheological phenomenon to control the damping force. In mathematical models magnetorheological oils are usually represented by Bingham or Herschel-Bulkley theoretical materials. Here the magnetorheological oil is modeled by bilinear material with the yielding shear stress depending on magnetic induction. Its flow curve is continuous which contributes to reducing nonlinear character of the motion equations. The new mathematical model was applied to investigate several operating regimes of rotating machines.

Abstract: The paper deals with the upper and lower limits estimation of the friction work and fretting wear in the contact of nuclear fuel rods with fuel assembly (FA) spacer grid cells. The friction work is deciding factor for the prediction of the fuel rod cladding abrasion caused by FA vibration. Design and operational parameters of the FA components are understood as random variables defined by mean values and standard deviations. The gradient and three sigma criterion approach is applied to the calculation of the upper and lower limits of the friction work and fretting wear in particular contact surfaces between the fuel rod cladding and some of spacer grid cells. The fuel assembly vibration is excited by pressure pulsations of the cooling liquid generated by main circulation pumps in the coolant loops of the NPP primary circuit. The method is applied for hexagonal type nuclear fuel assembly in the VVER type reactors.

Abstract: This article provides information about in-flight measurement of a small sport aircraft. The strain gauges were used as sensors for load monitoring on the nose landing gear structure. To obtain overall forces it was necessary to do the calibration procedure. After the calculation of strain gauge coefficients the equations for calculating of total force, total force direction and individual force components were determined. During test flights the data acquisition system was installed into the aircraft. The data from strain gauges were collected together with other flight parameters like speed, altitude and data from inertial measurement unit which determined the exact movements of the aircraft before landing. The data recorded during fifty-six flights were analysed to obtain loads acting in the aircraft structure. These results were compared with calculated values.

Abstract: This paper introduces a procedure for parallel computing with the Dynamic Relaxation method (DR) on a Graphic Processing Unit (GPU).This method facilitates the consideration of a variety of nonlinearities in an easy and explicit manner.Because of the presence of inertial forces, a static problem leads to a transient dynamic problem where the Central Difference Method is usedas a method for direct integration of equations of motion which arise from the Finite Element model.The natural characteristic of this explicit method is that the scheme can be easily parallelized. The assembly of a global stiffness matrix is not required.Due to slow convergence with this method, the high performance which GPUs provide is strongly suitable for this kind of computation.NVIDIA's CUDA is used for general-purpose computing on graphics processing units (GPGPU) for NVIDIA's GPUs with CUDA capability.

Abstract: Recent developments in computer hardware bring in new opportunities in numerical mod-elling. Traditional simulation codes run sequentially on computers with a single processing unit,where only one instruction can be processed at any moment in time. The performance of single pro-cessing units is reaching the physical limits, given by transmission delays and heat build-up on thesilicon chips. The current trend in technology is parallel processing, relying on the simultaneous useof multiple processing units to solve given problem. The efficient utilization of parallel computingresources requires development of new algorithms and techniques allowing to decompose the giventask into pieces of work that can be processed simultaneously.This contribution focuses on parallelization of vector assembly operation, which is one of thecritical operations in any finite element software. The aim of presented work is to propose differentapproaches to parallelization of this operation and to evaluate their efficiency. In this contribution,we focus on shared memory programming model, where individual processes/tasks share a commonaddress space, which they read and write to asynchronously. Open Multi-Processing (OpenMP) andPortable Operating System Interface (POSIX) Threads programming models are used to implementdifferent variants of parallel assembly operations. The efficiency of implemented approaches is eval-uated on a selected benchmark problem, comparing computation times and obtained speed-ups.

Abstract: A novel type of hybrid cell composite structure has been developed and used for many practical applications. Typical macroscopic sub-cells in the cross section structure are formed by the stamping process of partially cured and axially-oriented high modulus carbon fibre bundles. Each bundle is wrapped around by a thin layer of high strength fibres. Main goal of this paper is the simulation of damage of this new composite structure. Modified hierarchy homogenization method (Non-uniform Transformation Field Analysis) was proposed for simulation of damage progress. Modification is based on introducing damage modes. The method is based on assumption that field of in-elastic strain describing damage in each constituents can be decomposed on finite set of fields, called damage modes. Modified NTFA method was incorporated into FEM code and verified in several four-point bending tests.

Abstract: The detailed topometry optimization of the critical part of an aircraft wing is presented in this article. The integral lower wing structural panel of aircraft in the Commuter category of the CS-23 regulation standard is selected for optimization. The first case demonstrates significant weight savings using modern Finite Element (FE) optimization methods for determined structural constraints. A practical aircraft operation and additional regulation requirements affect optimization constraints in the second case. This detailed optimization also consists of FE model validation, stress analyses and complex load capacity analyses, which are necessary for designed structural modifications with an optimal stress distribution.

Abstract: Finite element modeling (FEM) was used for numerical simulations of mechanical performance of aperiodic silicon-carbide scaffold manufactured by robocasting. The FEM approach enabled reliable calculation of theeffective anisotropic elastic properties of the scaffold at the macro-scale, as well as of the acoustic band structureindicating the metamaterial-like behavior of the material at the micro-scale. In addition, the micromechanics of thescaffold was discussed based on the outputs of the model: the mechanisms of the extremely soft shearing modes wereidentified and the corresponding stress concentrations arising at the contact points in the scaffold were analyzedwith respect to the possible failure modes of the robocast structure.