scholarly journals Spectral subtraction-based filter for experimental modal analysis under harmonics excitation force

2021 ◽  
Vol 15 (4) ◽  
pp. 8480-8489
Author(s):  
Che Ku Eddy Nizwan Che Ku Husin ◽  
Mohd Fairusham Ghazali ◽  
Ahmad Razlan Yusoff
Keyword(s):  
Transfer Function ◽  
Modal Analysis ◽  
Spectral Subtraction ◽  
Gain Function ◽  
Operating Condition ◽  
Filtering Algorithm ◽  
Input Force ◽  
Analysis Measurement ◽  
Function Calculation ◽  
Excitation Force

In modal analysis, measurement of input force and vibration response are crucial to accurately measure the transfer function of the structure. However, under operating condition, the force induced by operating machinery is impossible to be measured due to the sensor placement issue. In this case, the ambient response induced by the operating force should be suppressed to minimize the error in the Frequency Response Function (FRF) calculation. This paper presents the utilization of a modified spectral subtraction filter for ambient suppression. The introduction of effective ambient magnitude in gain function calculation has increased the efficiency of spectral subtraction filter. This parameter is calculated based on the phase information of the reconstructed artificial ambient response. The measurement using EMA was carried out on a motor-driven structure to verify the proposed technique. Two sets of data under shutdown and running condition were recorded to observe the effect of ambient operating force. Under the operating condition, the measured FRF show the non-identical features at operating frequencies as compared to the baseline data. The utilization of filtering process shows the ambient features contained in the transfer function was effectively suppressed. The output of filtering algorithm could provide an alternative option to perform EMA procedure under running condition.

Modal Analysis of Machine Tool Structures Based on Experimental Data

1983 ◽  
Vol 105 (4) ◽  
pp. 282-287 ◽  
Author(s):  
K. F. Eman ◽  
K. J. Kim
Keyword(s):  
Transfer Function ◽  
Machine Tool ◽  
Modal Analysis ◽  
Moving Average ◽  
Parametric Representation ◽  
Modeling Procedure ◽  
Fitting Procedure ◽  
Machine Tool Structures ◽  
Computer Based ◽  
Three Degree Of Freedom

The basic problem in modal analysis of machine tool structures is the extraction of modal parameters from the measured transfer function data. Conventionally this task is performed in two steps. The transfer function is determined using a Digital Fourier Analyzer followed by a suitable curve fitting procedure. In order to avoid the inherent problems associated with these procedures a new approach for modal analysis is proposed in this paper. Anticipating the stochastic nature of the systems excitation and response Modified Autoregressive Moving Average Vector models (MARMAV) are proposed. The modeling procedure yields a parametric representation of the structural behavior allowing the extraction of the modal information in one step, directly, rather than in two as in the conventional approaches. The mathematical foundation for the approach is given along with its application to a simulated three-degree-of-freedom system and a knee type milling machine. The newly proposed procedure is commensurate to the existing ones in light of the computational efforts involved; however, it eliminates the subjective judgment of the analyst since the modeling procedure is based on rigorous statistical adequacy checks. Finally, the proposed approach is amenable for implementation in a computer-based machine tool structural dynamics analyzer.

Study on the Method of Modified Random Decrement for Transfer Function

2003 ◽  
Author(s):  
Zhenzhong Zhang ◽  
Shijian Zhu
Keyword(s):  
Transfer Function ◽  
Steady State Response ◽  
Vibration System ◽  
State Response ◽  
Modified Method ◽  
Conventional Process ◽  
Random Decrement ◽  
Initial Excitation ◽  
Function Calculation ◽  
Random Decrement Method

This paper presents a modified random decrement method to obtain the steady-state response of vibration system. The expressions are deduced. Two numerical simulations and verification are given. The efficiencies of the modified method and the conventional process are compared. It is shown that the method is more efficient than the conventional process to diminish the influence of the initial excitation on the transfer function calculation of the vibration system.

Operational Modal Analysis of Lateral Rotordynamic Modes of Rotating Machinery

2014 ◽  
Author(s):  
Eoin Peter Carden ◽  
Stefano Morosi
Keyword(s):  
Modal Analysis ◽  
Rotating Machinery ◽  
Operational Modal Analysis ◽  
Modal Testing ◽  
Normal Operation ◽  
Stability Margins ◽  
Normal Production ◽  
Testing Techniques ◽  
Excitation Force ◽  
Operational Range

The lateral rotordynamic response of turbomachinery is typically speed dependent due to hydrodynamic lubricated bearings, seals, gyroscopic and centrifugal effects, etc. Rotordynamic tools are used to predict the behavior of the machine during operation, however validating these results is challenging. Traditional experimental modal testing techniques rely on controlled and measured excitation together with measured responses. However, during operation this is unpractical, as the actual excitation force is rarely known. Operational modal analysis (OMA) can identify the modal parameters of a system over its entire operational range from measurement of response due to some (unknown) excitation. OMA has proven successful on non-rotating structures, but has seldom been applied to rotating machinery. Three case studies are presented demonstrating the use of OMA in identifying lateral rotors modes based on measurements from existing radial proximity probes during normal production undertaken as part of commissioning campaigns. Challenges encountered in using and interpreting OMA results are discussed. The results show that proximity probe data acquired during normal operation may be used as input to OMA for the assessment of stability margins of rotating machinery, to produce experimentally derived Campbell diagrams and to identify backwards as well as forwards whirling modes.

ASSESSMENT OF TRANSFER FUNCTION MODELLING IN AN ADAPTIVE STEAM FLOW CONTROL SYSTEM

2019 ◽  
Author(s):  
Fedor Venediktov ◽  
N. Koryakovskaya
Keyword(s):  
Control System ◽  
Transfer Function ◽  
Flow Control ◽  
Approximation Error ◽  
Steam Flow ◽  
Regulation System ◽  
System Quality ◽  
Function Modelling ◽  
Function Calculation ◽  
Flow Control System

The article shows the transfer function calculation for an adaptive steam flow control system with the use of 1st and 2nd order aperiodic link model and experimental data. The approximation error at the control points was used for evaluating the results of modelling. The indicators of the regulation system quality with constructed models are obtained. The conclusions of using such models in corrective algorithms are formulated.

New Analytical Line Spread Function Fitting Model for Modulation Transfer Function Calculation

2010 ◽  
Vol 30 (12) ◽  
pp. 3454-3459
Author(s):  
李铁成 Li Tiecheng ◽  
冯华君 Feng Huajun ◽  
徐之海 Xu Zhihai ◽  
李晓彤 Li Xiaotong
Keyword(s):  
Transfer Function ◽  
Modulation Transfer Function ◽  
Analytical Line ◽  
Modulation Transfer ◽  
Line Spread Function ◽  
Function Fitting ◽  
Spread Function ◽  
Function Calculation ◽  
Fitting Model ◽  
Line Spread

Transient Vibration Analysis of Impact Ripper

2014 ◽  
Vol 551 ◽  
pp. 150-157
Author(s):  
Ge Ning Xu ◽  
Meng He ◽  
Jian Feng Wu
Keyword(s):  
Finite Element ◽  
Modal Analysis ◽  
Impact Load ◽  
Negative Influence ◽  
Superposition Method ◽  
Vibration Source ◽  
Transient Vibration ◽  
Finite Element Software ◽  
Excitation Force ◽  
The Impact

In view of the vibration problem of impact ripper working under the excitation force of hydraulic ripper, finite element method is adopted for transition analysis of the structure. The impact ripper operating process is divided into two stages. Analyze the producing process of main vibration source for the structure. Establish the model of impact ripper by the finite element software SolidWorks, and its modal analysis is based on Simulation. The modal analysis gives the former eight natural frequencies and their corresponding vibration modes. Then use modal superposition method for transient analysis, calculate the dynamic response of impact ripper under the excitation force. Results show that the excitation force of hydraulic hummer significantly influences on the displacement response of structure (increasing about 145%). Continuous impact load leads to fatigue failure of structure easily, so the vibration design should be done to reduce the negative influence caused by impact vibration.

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