Wyniki wyszukiwania - BazTech

1

Forced motion CFD simulation and load refinement evaluation of floating vertical-axis tidal current turbines

Zhang Wanchao, Zhou Yujie, Wang Kai, Zhou Xiaoguo

Polish Maritime Research

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2020

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nr 3

40--49

EN

Simulation of the hydrodynamic performance of a floating current turbine in a combined wave and flow environment is important. In this paper, ANSYS-CFX software is used to analyse the hydrodynamic performance of a vertical-axis turbine with various influence factors such as tip speed ratio, pitching frequency and amplitude. Time-varying curves for thrust and lateral forces are fitted with the least squares method; the added mass and damping coefficients are refined to analyse the influence of the former factors. The simulation results demonstrate that, compared with nonpitching and rotating turbines under constant inflow, the time-varying load of rotating turbines with pitching exhibits an additional fluctuation. The pitching motion of the turbine has a positive effect on the power output. The fluctuation amplitudes of thrust and lateral force envelope curves have a positive correlation with the frequency and amplitude of the pitching motion and tip speed ratio, which is harmful to the turbine’s structural strength. The mean values of the forces are slightly affected by pitching frequencies and amplitudes, but positively proportional to the tip speed ratio of the turbine. Based upon the least squares method, the thrust and lateral force coefficients can be divided into three components, uniform load coefficient, added mass and damping coefficients, the middle one being significantly smaller than the other two. Damping force plays a more important role in the fluctuation of loads induced by pitching motion. These results can facilitate study of the motion response of floating vertical-axis tidal current turbine systems in waves.

2

Determination of the internal resistance of a hammer drill chisel

Nikolov N., Sinapov P.

Journal of Theoretical and Applied Mechanics

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2018

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Vol. 56 nr 1

169--178

EN

The present work examines damped oscillations of a chisel, represented as a distributed parameters system. The system is discretized with the finite element method. Rayleigh’s law is used for the modelling of the resistance. The internal resistance of the mechanical system has been determined by an experiment, then enshrined in the numerical model. Comparison and analysis of the results have been made.

3

Numeryczne wyznaczanie liniowych i nieliniowych współczynników sztywności i tłumienia poprzecznych łożysk hydrodynamicznych

Breńkacz Ł., Żywica G.

Mechanik

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2016

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R. 89, nr 7

648--649

PL

W artykule przedstawiono numeryczne obliczenia współczynników sztywności i tłumienia hydrodynamicznych poprzecznych łożysk ślizgowych. Oprócz liniowych i nieliniowych obliczeń wykonano badania eksperymentalne, podczas których zmierzono przemieszczenia czopów łożyskowych dla wirnika pracującego w szerokim zakresie prędkości obrotowych. Trajektorie drgań zmierzone eksperymentalnie zostały porównane z wynikami obliczeń numerycznych.

EN

The article presents numerical calculations of stiffness and damping coefficients of hydrodynamic journal bearings. In addition to linear and nonlinear calculations, the experimental studies were performed in which the displacements of bearing journals were measured for a wide range of rotational speeds. The trajectories were compared with the results from numerical calculations.

4

Application of the correlation function for determination of damping during in-flight flutter tests

Lenort F., Niepokólczycki A.

Prace Instytutu Lotnictwa

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2005

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Nr 4 (183)

61-64

EN

The paper presents a method for determination of damping during in-flight flutter tests. The method is based on a new estimate of the correlation function. Actually, the necessity has emerged of a new estimator of the autocorrelation function which, when applied to finite unsteady signals of short duration, does not change the values and signs of damping coefficients. The paper provides theoretical backgrounds of the proposed method. The new correlation function was applied to the AND AT procedure [4,5,6] for flutter analysis. The procedure was verified based on both simulation data and in-flight vibration measurements.

PL

Artykuł prezentuje metodę wyznaczania tłumienia w czasie prób flatterowych w locie. Metoda oparta jest o nową estymację funkcji korelacji. Prezentowany estymator funkcji autokorelacji, zastosowany do skończonych, niestacjonarnych, krótkich sygnałów nie zmienia wartości i znaków wyznaczonych współczynników tłumienia. Artykuł przedstawia teoretyczne podstawy proponowanej metody. Metoda ta zastosowana została w procedurze analizy flatterowej ANDAT. Testowano ją stosując sygnały symulowane oraz zarejestrowane w czasie prób w locie. Praca zrealizowana została w ramach programu EUREKA E!2419 "FLITE".

5

Współczynniki sztywności i tłumienia łożyska ślizgowego z panewką pływającą.

Mazurkow A.

Zagadnienia Eksploatacji Maszyn

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2002

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Vol. 37, nr 4

27-46

PL

Rozwój szybkoobrotowych maszyn wirnikowych wymaga uwzględnienia w fazie projektowania właściwości dynamicznych węzłów łożyskowych. W pracy przedstawiono trzy metody oceny właściwości dynamicznych łożyska ślizgowego z panewką pływającą: metodę analityczną, linearyzacji siły nośnej, linearyzacji ciśnienia w otoczeniu położenia równowagi dynamicznej. Wyznaczono współczynniki sztywności i tłumienia filmu olejowego oraz dokonano porównania wyżej przedstawionych modeli.

EN

The basic unit of a turbo-blower, which has the decisive influence on its quality is a rotating unit. The unit is composed of a shaft, a rotor, journal and axial bearings and seals. One of the most significant reasons of rotating unit non-stable operation is vibrations generated in a bearing system. The type of a bearing usually used in the system is a floating ring bearing. A floating ring bearing is one in which a bush - called a floating ring - is allowed to float freely in the lubricating fluid between the shaft and the fixed bearing bush. The development of high speed turbo-blowers requires new, accurate methods of bearing system design. In the process of vibration and stability analysis of a rotating unit, it is necessary to know exactly stiffness and dumping coefficients, which allow to obtain dynamic characteristics of oil films. In the coordinate system (OXYZ), the following coefficients may be determined: kxy, bxy - stiffness and dumping coefficients determined for the displacements in OYZ plane under the action of forces in OXZ plane. kxx, bxx - stiffness and dumping coefficients determined for the displacements in OXZ plane under the action of forces in OXZ plane. kyx, byx - stiffness and dumping coefficients determined for the displacements in OXZ plane under the action of forces in OYZ plane. kyy, byy - stiffness and dumping coefficients determined for the displacements in OYZ plane under the action of forces in OYZ plane. The above mentioned coefficients can be determined using one of the following methods: - analytical method, - carrying load linearization method in the state of stable static equilibrium, - method of pressure linearization in the vicinity of the static equilibrium position. Procedures for determination of stiffness and dumping coefficients using each of the methods have been presented in the paper. Considering various simplifying assumptions applied, the analytical method can be used mainly at the preliminary stage of design (calculations). For verification calculations, however, models which more exactly represent real conditions of bearing operation should be employed. Such a model is an adiabatic model of the bearing. Considering the problem, that at each regarded position of equilibrium, linearity condition must be checked, the dynamic, adiabatic model utilizing the method of pressure linearization in the vicinity of the static equilibrium position has been found more convenient to be used.