Applied Mechanics and Materials Vol. 821

Abstract: Experimental facility situated in the test section of the wind tunnel suction type was adjusted both in the total construction and in the construction of the fluttering body, the methodology of the measurement and evaluation of the flow and dynamic parameters during flutter were also changed. Preserved was the conception of the NACA0015 profile with two degrees of freedom, rotational and translational. Torque elasticity was now realized by the coil spring and changed by different length of this spring or by different diameter of the spring wire. The pitch angle of the profile was now measured by the magnetic rotary encoder. The translational position was indicated by the magnetic linear encoder and was centered by plane springs situated on both ends of the shiftable frame. With this model the testing measurement was realized by its self-excited vibration of flutter type in the range of Mach numbers M=0.20-0.215 and Reynolds numbers 263 000 – 283 000. Results obtained with M=0.21 and Re=276 000 are presented.

Abstract: One of the most effective methods for descaling hot-rolled steel products is performed using highpressure flat jet nozzles. These descaling nozzles are arranged in rows in hot rolling mills and areset in such a way that each adjoining pair of nozzles creates an overlapping area of water jet streams.Good homogeneity of the pressure distribution over the width of the hot-rolled plate is often used as anindicator of quality of the homogeneity of descaling. The presented laboratory measurements examineone pair of adjoining nozzles with a particular focus on the pressure distribution in the overlappingarea. This paper deals with one particular setting of a pair of descaling nozzles with zero offset anglesfor the jet streams. A measured pressure distribution and an outcome of an erosion test on an aluminumplate are presented and discussed. The erosion test shows that spots with higher pressures do notnecessarily result in a higher amount of removed material during an erosion test. The erosion test differs from the expected outcome in such a way that a detailed discussion of this phenomenon is outlined with possible explanations.

Abstract: This article describes a complex and generally applicable computational model for solving the frictional losses of directionally oriented and non-oriented sliding surfaces working under mixed lubrication regime. In the primary phase of this paper are described ways to get characteristics data describing rough surfaces together with the formula for determination of surface pattern directional dependence. Furthermore, formulae describing used contact model are listed and also the structure of the whole powertrain dynamics solution is briefly explained. In the closing section of this paper are shown and discussed results of several types of slide bearing analysis.

Abstract: The continuously tightening regulations limiting the amount of exhaust gas components of internal combustion engines force the manufacturers to further increase the effectivity of their power units. Due to the already relatively highly-developed state of engines result in the need of research and development of even smaller engine parts – e.g. piston rings. The main aim of this project was to develop a tool for the computer simulation of the behavior of the piston ring pack, which could aid the optimization process of the piston ring pack towards lowered friction losses.

Abstract: Long-span cable-supported bridges, characterized with low natural frequencies and mechanical damping, are very sensitive to wind effects. Therefore, investigation of the aeroelastic behaviour of bridges is particularly important when designing these complex engineering structures. The focus is on evaluation of dimensionless aeroelastic coefficients, i.e. flutter derivatives, which are considered as indicators of the aeroelastic stability of bridges. A comprehensive experimental study on dynamic wind-induced behaviour of the Kao-Pin Hsi Bridge in Taiwan is carried out in the Climatic Wind Tunnel of the Centre of Excellence Telč (CET), Czech Republic. The bridge-deck section is tested at a multipurpose experimental setup originally developed in the CET. Flutter derivatives are obtained by the means of the free-vibration technique for the double-degree-of-freedom (DDOF) system. The results are compared to those of a thin flat plate with large width to height ratio, which previously proved to be stable with respect to the flutter phenomenon. While the torsional instability is observed for the Kao-Pin Hsi bridge-deck section, the flat plate proves to be aeroelastically stable.

Abstract: Presented paper deals with modelling of a twisted blade with rhombic shroud as one-dimensional continuum by means of Rayleigh beam finite elements with varying cross-sectional parameters along the finite elements. The blade is clamped into a rotating rigid disk and the shroud is considered to be a rigid body. Since the finite element models based on the Rayleigh beam theory tend to slightly overestimate natural frequencies and underestimate deflections in comparison with finite element models including shear deformation effects, parameter tuning of the blade is performed.

Abstract: The paper is focused on the design and development of the system simulating nonlinear attachment of the aileron actuation on the aeroelastic demonstrator. The system is based on the concept of the digitally controlled additional stiffness, activated by the real time control law system, controlling the required ratio of the force and deformation. The solution is based on the electromagnetic exciter. The nonlinear force is simulated by means of the system of the exciter and the deformation sensor. The active control system is independent of the excitation system. It adds the force ensuring the required characteristics and it allows to simulate the additional stiffness, damping or mass. Doing this, it is possible to adjust the selected vibration mode by controlling the force and obtain the required nonlinear characteristics. In the second order, there is also a constant influence of the exciter mass, stiffness and damping. The simulation of the linear, quadratic and cubic additional stiffness were verified.

Abstract: Development of internal combustion engine’s components is based on the use of advanced computational models in order to compare and verify the individual design proposals. Connecting rod, which performs a general planar motion, is exposed to the gas pressure forces, inertia, contacts, and hydrodynamic pressure during the engine operation cycle. To incorporate all these aspects, Finite Element Method (FEM) is extended by Finite Difference Method (FDM) simulating a slide bearing of connecting rod’s end. It includes different properties of lubricating oil (pressure and temperature dependent viscosity and density) and elastic deformations, so the pressure distribution in an oil film can be evaluated. The computational process concludes with an estimation of the endurance safety factor of the connecting rod. The four-cylinder inverted aircraft engine is used as an example.

Abstract: The paper deals with nonlinear phenomena that occurs during vibration of nuclear fuel rod (FR). The FR is considered as a system consisting of two impact-interacting subsystems FR cladding (zircalloy tube) and fuel pellets stack placed inside FR cladding. Between both subsystems, there is a small radial clearance. The FR is bottom-end-fixed, and at eight equidistant levels, the FR cladding is supported by spacer grids (SG). Both subsystems are modelled by means of finite element method for one-dimensional Euler-Bernoulli continua. During fuel assembly (FA) motion caused by pressure pulsations of the coolant, the FR vibrates and impacts can possibly occur between FR cladding and fuel pellets stack. The paper focuses on qualitative change of vibration with change of bifurcation parameters clearance between FR cladding and fuel pellets stack and stiffness of spacer grids cells. The change of vibration quality is shown by extremes of relative radial displacements of both continua in discretization nodes and by phase trajectories. Dependence of impact motion on modal properties of both subsystems is shown.

Abstract: The light high-speed transmission systems with minimum dimensions and weights may show a wide spectrum of properties extending from the regular - periodic solutions to irregular ones of chaotic character. The method of transformation of differential boundary value problems to equivalent nonlinear integro-differential equations with solving kernels of Green’s type and the method of successive approximations are applied for analytical analysis of dynamic phenomena. The paper contains the concise summary of the long-term studies in the given area of basic research.