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1

Diagnostics of turbine blades, based on estimation of frequency response function

Kotkowski Jerzy, Rokicki Edward, Lindstedt Paweł, Spychała Jarosław, Perczyński Jerzy, Karbowiak Hieronim

Journal of KONBiN

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2021

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Vol. 51, iss. 2

63--78

EN

The aim of the study is to propose a diagnostics method based on blade’s vibration model in frequency domain. Amplitude spectrum A(ω) and phase spectrum φ(ω) have been experimentally identified which define transfer function G(jω) = P(ω) + jQ(ω) and their real P(ω) and imaginary Q(ω) parts. Transfer function G(jω) and resulting frequency, amplitude, phase characteristics and real P(ω) and imaginary Q(ω) parts are parts of blade’s diagnostics model. Changes in those characteristics are directly related to changes in the technical condition of the blades. It has been noticed that small changes in the technical condition cause large changes in frequency characteristics, which proves their usefulness in the diagnosis process.

PL

Celem badania jest zaproponowanie metody diagnostycznej opartej na modelu drgań łopatek w dziedzinie częstotliwości. Zidentyfikowano eksperymentalnie widma ampli-tudowe A(ω) i fazowe φ(ω), które definiują transmitancję operatorową G(jω) = P(ω) + jQ(ω) oraz jej rzeczywiste P(ω) oraz urojone Q(ω) części. Transmitancja operatorowa G(jω) i wynikająca z niej częstotliwość, amplituda, charakterystyka fazowa oraz rzeczywiste P(ω) i urojone Q(ω) części są częściami modelu diagnostycznego łopatki. Zmiany w tych charakterystykach są bezpośrednio związane ze zmianami w stanie technicznym łopatek. Zauważono, że małe zmiany w stanie technicznym powodują duże zmiany w charakterystykach częstotliwościowych, co świadczy o ich przydatności w procesie diagnostycznym.

2

Damage identification using 2-D discrete wavelet transform on extended operational mode shapes

Makki Alamdar M., Li J., Samali B.

Archives of Civil and Mechanical Engineering

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2015

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Vol. 15, no. 3

698--710

EN

In this paper a new scheme of damage detection and localisation is presented by implementing frequency response functions (FRFs) of damaged structure only. First damage sensitive shape signals are generated by taking the second order derivatives of the operational mode shapes at each frequency coordinate and then the anti-symmetric extension of each shape signal at the beginning and at the end of the signal is created to avoid boundary distortion phenomenon. In order to highlight the damage influence on shape signals, the shape signals are normalised with respect to the maximum value to adjust the amplitude difference between shape signals at different frequencies. It is illustrated that normalisation of shape signals significantly improves the damage localisation results. After normalising the shape signals, a two-dimensional (2-D) map of all shape signals is created and then is analysed by employing 2-D discrete wavelet transform (DWT). By performing 2-D DWT, three sets of horizontal, vertical and diagonal detailed wavelet coefficients will be obtained. It is demonstrated that amongst these three sets, horizontal detail coefficients are the most sensitive ones to any perturbation in the shape signals due to damage occurrence and, thus, are utilised to localise damage in this study.

3

Modal analysis of honeycomb panels and the influence of boundary conditions on the calculation

Vlach J., Pomp N.

Journal of Achievements in Materials and Manufacturing Engineering

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2014

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Vol. 66, nr 2

81--86

EN

Purpose: In this work we investigate the elastic properties of sandwich beams manufactured by using the LF Technology. Design/methodology/approach: The investigation of the behaviour of rectangular shaped sandwich specimens is focused on the modal analysis and the experimental determination of the samples damping properties. Panels are made by unique technique of dry lamination patented by Czech company 5M s.r.o. The Hexagonal cell honeycomb core is made of aluminium as well as the facesheets. The influence of the main directions of anisotropy and the different panel’s thicknesses on the natural frequencies are investigated. Findings: The results of experiments are compared with the theoretical calculations and finite element method(FEM)simulation results. Theories used for the calculations are the First-order shear deformation theory (FSDT) and the Reddy’s third-order shear deformation theory (TSDT). FEM model had mapped mesh with 20-nodes brick elements. Research limitations/implications: The results obtained from FEA were closest to the experimentally measured data, but still with a deviation. The main reason of different results are geometrical irregularities. While FEM model was too much idealistic, the specimens prepared for measurement were not precisely planar. The specimens with small thickness were more twisted and therefore we got bigger error in the measured data and consequently the bigger deviation in results. In the future, we would like to do further measurements to transfer the real specimen geometry with all irregularities to a FEM model and to do new computations. Originality/value: Originality of this work is modal analysis of honeycomb panels and the influence of boundary conditions on the calculation.

4

Impact tests of micromilling tool mounted in micromilling machine spindle introduction

Matuszak M.

Management Systems in Production Engineering

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2012

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nr 3 (7)

34-37

EN

Method of performing impact test of tool mounted in micromilling machine spindle is presented. Due to very small tool dimensions performing impact test in classical way is impossible. Accelerometer cannot be used for impulse response measurement. For measurement of tool displacement laser vibrometer is used. Frequency response function was measured in two directions in seven points of micromilling tool. Additionally frequency response function in three points of machine spindle is measured. Resonant frequencies and their amplitude for points on tool and on machine spindle are compared. Results of performed impact tests are shown. Conclusions arising from performed impact tests are presented.

PL

Zaprezentowano sposób przeprowadzenia testu impulsowego narzędzia zamocowanego we wrzecionie mikrofrezarki. Bardzo małe wymiary freza uniemożliwiają przeprowadzenie testu impulsowego w sposób klasyczny z wykorzystaniem akcelerometru do pomiaru odpowiedzi impulsowej narzędzia. Do pomiaru odpowiedzi impulsowej wykorzystano wibrometr laserowy. Pomiaru odpowiedzi impulsowej dokonano w dwóch kierunkach i siedmiu punktach narzędzia. Dodatkowo wyznaczono odpowiedź impulsową w trzech punktach wrzeciona obrabiarki. Dokonano porównania otrzymanych częstotliwości rezonansowych dla punktów pomiarowych na narzędziu oraz wrzecionie mikroobrabiarki. Przedstawiono wyniki przeprowadzonych testów impulsowych oraz wynikające z nich wnioski.