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EN
Low Cycle Fatigue (LCF) is one of most common mechanisms behind turbine blade failures. The reason is high stress concentration in notch areas, like fir-tree root groves, which can cause cyclic stress beyond the safe threshold. The stress levels strictly depend on the manufacturing accuracy of the fir-tree lock (for both fitted together: blade root and disk groove). The probabilistic study aimed at determination of stress was performed using Finite Element Method (FEM) simulation on a population of 1000 turbine models (disk + blades +friction dampers), where fir-tree lock dimensions were sampled according to the normal distribution, within limits specified in the documentation. The studies were performed for different manufacturing quality levels: 3-Sigma, 6-Sigma and 3-Sigma with tolerance ranges reduced twice. Based on the results, the probabilistic distributions, probabilities and expected ranges of values could be determined for: material plastification, stress, strain, LCF lifetime, etc. The study has shown how each tooth of the root is loaded and how wide a stress range should be expected in each groove. That gives information on how the definition of tolerances should be modified to make the construction more optimal, more robust, with lower likelihood of damage, taking into account the cost-quality balance. It also shows how the Six Sigma philosophy can improve the safety of the construction, its repeatability and predictability. Additionally, the presented numerical study is a few orders of magnitude more cost- and time-effective than experiment.
EN
Settling of solid particles in a stratifed ambient fuid is a process widely encountered in geophysical fows. A set of experiments demonstrating the settling behaviour (the pattern of trajectory, variation of particle orientation, and settling velocity with depth) of thin disks descending through a nonlinear density transition was performed. The results showed complex hydrodynamic interactions between a particle and a liquid causing settling orientation instabilities and unsteady particle descent in low to moderate Reynolds number regime. Five phases of settling were observed: two phases with stable horizontal, one with stable vertical disk position, and two reorientation phases; moreover, two local minima of settling velocity were identifed. It was demonstrated that thresholds for local minima and the frst reorientation depend on the settling dynamics in an upper layer, stratifcation conditions, and disk geometry. The comparison of settling behaviour of thin disks varying in diameter revealed that settling dynamics is sensitive to particle geometry mainly in the upper part of density transition with a non-obvious result that the frst minimum velocity is smaller for a disk with a larger diameter than for a disk with a smaller diameter. The analysis of settling trajectory showed that two reorientations are accompanied with a horizontal drift, which may be important in the context of interactions between particles settling in a group.
3
Content available remote On the number of zeros of a polynomial in a region
EN
In this paper, we impose restrictions on the complex coefficients of a polynomial in order to give bounds concerning the number of zeros in a specific region of the complex plane. Our results generalize and refine a good number of results in this area of research.
PL
Przedstawiono wyniki obliczeń naprężeń w tarczy poddanej działaniu temperatury otrzymane czterema metodami, z których jedna jest formalnie ścisła. Pokazano, że do tarczy obciążonej temperaturowo można zastosować analogię tarczowo-płytową. Stwierdzono, że metoda różnic skończonych (MRS) jest najkorzystniejszą do rozwiązania postawionego problemu.
EN
The paper concerns calculations of stresses in a disc subjected to the action of temperature. There were presented the results obtained with four methods, in which the one is formally exact. There was proved that the disc-plate analogy can be applied to a disc under a temperature load. From all the methods applied in the paper, the Finite Differences Method was acknowledged as the best to solve the set problem.
5
Content available remote Morphology and characterization of cockloft-like ZnO/morin hybrid
EN
Morin modified multilayer ZnO with a cockloft-like morphology was fabricated in alcohol solution, using hydrothermally synthesized ZnO nanodisks and morin as the precursors. The samples were characterized by field emission scanning electron microscopy, X-ray diffractometry, Fourier transform infrared spectroscopy and fluorescence spectroscopy. The results show that the cockloft-like ZnO hybrid, having hexangular morphology with the diameter of 1.5-2 žm and the thickness of ca. 1 žm, is composed of a multilayer flatform stacked by numerous ZnO nanodisks in its middle and a meshlike muffle made up of countless morin nanoparticles with the diameter of ca. 40 nm. The UV emission of the as-fabricated product is obviously attenuated by morin nanoparticles assembling on the surface of the ZnO nanodisks.
PL
W artykule przedstawiono porównanie parametrów procesu łuszczenia i czasów pełnego otwarcia szyszek sosny zwyczajnej różniących się formami, określonymi na podstawie kształtu zewnętrznej części tarczki łuski. Dla szyszek jednego pochodzenia, różniących się cechami zewnętrznymi, nie stwierdzono istotnych różnic dla wyróżnianych parametrów równania opisujących przebieg procesu.
EN
The paper presents comparison of hulling process parameters and full opening times for Scotch Pine cones, which differ in form, determined on the grounds of the shape of external part of hull disk. No significant differences for distinguished parameters of equation describing the process progress were found for cones of the same origin, which differ in their external features.
EN
In this note, the unsteady flow of a Maxwell fluid produced by non-coaxial rotation while a disk and the fluid at infinity are initially rotating with the same angular velocity about a common axis is considered. Even in the case of a non-Newtonian fluid, it is shown that there is an exact solution for this flow geometry. The velocity field is obtained with the help of the Laplace transform technique.
EN
The model of the tyre disk was created in software Autocad and COSMOS M. There are calculated the first ten eigen frequencies disk in this article with the help of the software COSMOSM.
EN
The flow of an incompressible second order/grade fluid due to non-coaxial rotation of a porous disk and the fluid at infinity with the common angular velocity is studied. It is shown that there are physically acceptable solutions for both suction and blowing cases, depending on the sign of the material modulus 'alpha'1 . It is observed that the elasticity of the fluid causes the boundary layer thickness to increase in the case of suction, whereas it causes the boundary layer thickness to decrease in the case of blowing.
PL
Dokonano analizy teoretycznej tensometrycznego pomiaru odkształcenia na pobocznicy ściskanego nieosiowo krążka. Przedstawiono wyniki badań eksperymentalnych tego zagadnienia. Na tej podstawie określono obszar swobodnej, nie obciążonej siłami zewnętrznymi powierzchni krążka, która może ulec uplastycznieniu; dokonano również oszacowania parametrów siłowych niezbędnych do tego uplastycznienia.
EN
In the paper a theoretical tensometric measurement analysis of a side surface deformation, during eccentric compression of a disk, has been carried out. The results of experimental investigation of this problem have been presented. The area of possible plastic deformation and the unite pressure needed for this were determined.
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