Investigation and Modification of Frequency Response Function Using Digital Fourier Analysis for High Speed Dynamic Testing Facility

2009 ◽  
Author(s):  
Chandrashekhar K. Thorbole ◽  
Keshavanarayana S. Raju
Keyword(s):  
Frequency Response ◽  
Frequency Domain ◽  
Response Function ◽  
Time Domain ◽  
Frequency Response Function ◽  
Detection System ◽  
Structural Response ◽  
Wave Form ◽  
Data Set ◽  
Load Detection

The increasing application of composites in the aviation and automobile industry demands a better understanding of composite material behavior under high loading rate. This shall provide a better insight of actual loads on occupants while preserving livable crashworthy structure. In this study, a high stroke rate MTS servo-hydraulic testing machine is used to characterize the behavior of composite materials at high strain rates. At higher stroke rates, the output of the load detection system acquired by the load cell deviates from the true load-time wave form of the specimen. This is due to the convolution of the structural response of the detection system with the true characteristic of the specimen. To identify the true nature of the specimen load-time behavior, the de-convolution of the detection system response is necessary to restore the specimen characteristic wave form closer to its true behavior. The convolution of data set in the time domain is a time consuming process which explains the benefit of using the frequency domain; as the convolution in time domain corresponds to multiplication in the frequency domain. This process requires the transformation of the time domain data to frequency domain data via Fast Fourier Transform (FFT). In the frequency domain the complex division of the Fourier transfer of the detection system output with frequency response function of the detection system shall provide the true complex input characteristic. This paper elaborates the methodology utilized for obtaining the Frequency Response Function (FRF) of the load detection system using digital Fourier analysis with a single input/output data set. This also emphasizes precautions and guidelines for improving results with FFT to obtain true FRF measurements of the load detection system. The FRF obtained is successfully used to identify the actual specimen wave form characteristic. This is achieved by extracting the structural response of the load detection system from the load cell output.

scholarly journals Parameter Identification of Weakly Nonlinear Vibration System in Frequency Domain

2004 ◽  
Vol 11 (5-6) ◽  
pp. 685-692 ◽  
Author(s):  
Jiehua Peng ◽  
Jiashi Tang ◽  
Zili Chen
Keyword(s):  
Parameter Identification ◽  
Frequency Response ◽  
Nonlinear Vibration ◽  
Frequency Domain ◽  
Response Function ◽  
Frequency Response Function ◽  
Physical Parameters ◽  
Vibration System ◽  
Weakly Nonlinear ◽  
Nonlinear Vibration System

A new method of identifying parameters of nonlinearly vibrating system in frequency domain is presented in this paper. The problems of parameter identification of the nonlinear dynamic system with nonlinear elastic force or nonlinear damping force are discussed. In the method, the mathematic model of parameter identification is frequency response function. Firstly, by means of perturbation method the frequency response function of weakly nonlinear vibration system is derived. Next, a parameter transformation is made and the frequency response function becomes a linear function of the new parameters. Then, based on this function and with the least square method, physical parameters of the system are identified. Finally, the applicability of the proposed technique is confirmed by numerical simulation.

scholarly journals The Researches on Damage Detection Method for Truss Structures

2018 ◽  
Vol 38 ◽  
pp. 03030
Author(s):  
Meng Hong Wang ◽  
Xiao Nan Cao
Keyword(s):  
Numerical Simulation ◽  
Frequency Response ◽  
Response Function ◽  
Time Domain ◽  
Experimental Analysis ◽  
Frequency Response Function ◽  
Principal Component ◽  
Truss Structures ◽  
Time Domain Signal ◽  
The Time Domain

This paper presents an effective method to detect damage in truss structures. Numerical simulation and experimental analysis were carried out on a damaged truss structure under instantaneous excitation. The ideal excitation point and appropriate hammering method were determined to extract time domain signals under two working conditions. The frequency response function and principal component analysis were used for data processing, and the angle between the frequency response function vectors was selected as a damage index to ascertain the location of a damaged bar in the truss structure. In the numerical simulation, the time domain signal of all nodes was extracted to determine the location of the damaged bar. In the experimental analysis, the time domain signal of a portion of the nodes was extracted on the basis of an optimal sensor placement method based on the node strain energy coefficient. The results of the numerical simulation and experimental analysis showed that the damage detection method based on the frequency response function and principal component analysis could locate the damaged bar accurately.

scholarly journals Non-linear joint parameter identification using the frequency response function of the linear substructure

2004 ◽  
Vol 218 (9) ◽  
pp. 947-955 ◽  
Author(s):  
W-J Kim ◽  
B-Y Lee ◽  
Y-S Park
Keyword(s):  
Parameter Identification ◽  
Frequency Response ◽  
Frequency Domain ◽  
Response Function ◽  
Frequency Response Function ◽  
Excitation Amplitude ◽  
The Finite Element Method ◽  
Unknown Parameters ◽  
Identification Process ◽  
Non Linear

A method based on frequency domain approaches is presented for the non-linear parameter identification of a structure having non-linear joints. The frequency response function (FRF) of the linear substructure, which can be calculated from the finite element method or measured by an experimental method, is used to calculate its FRFs needed in the parameter identification process. This method is easily applicable to a complex real structure having non-linear joints since it uses the FRF of the substructure. Since this method is performed in the frequency domain, the number of equations can be easily increased to as many as required to identify unknown parameters, not only by just varying the excitation amplitude but also by selecting the excitation frequencies. The validity of this method was tested numerically and experimentally with a cantilever beam having a non-linear element. It was verified through examples that the proposed method is useful to identify the non-linear joint parameters of a structure having arbitrary boundaries.

Frequency Response-Based Indirect Load Identification Using Optimum Placement of Strain Gages and Accelerometers

2019 ◽  
Vol 141 (3) ◽  
Author(s):  
Hana'a M. Alqam ◽  
Anoop K. Dhingra
Keyword(s):  
Frequency Response ◽  
Response Function ◽  
Frequency Response Function ◽  
Structural Response ◽  
Mode Shapes ◽  
Load Identification ◽  
Strain Gages ◽  
Design Algorithm ◽  
Displacement Mode ◽  
Optimum Sensor

This paper presents an approach for indirect identification of dynamic loads acting on a structure through measurement of structural response at a finite number of optimally selected locations. Using the concept of frequency response function (FRF), the structure itself is considered as a load transducer. Two different types of sensors are investigated to measure the structural response. These include a use of accelerometers that leads to the identification of the displacement mode shapes. The second measurement approach involves a use of strain gages since strain measurements are directly related to imposed loads. A use of mixed strain-acceleration measurements is also considered in this work. Optimum sensor locations are determined herein using the D-optimal design algorithm that provides most precise load estimates. The concepts of indirect load identification, strain frequency response function (SFRF), displacement frequency response function (DFRF), along with the optimal locations for sensors are used in this paper. The fundamental theory for strain-based modal analysis is applied to help estimate imposed harmonic loads. The similarities and differences between acceleration-based load identification and strain-based load identification are discussed through numerical examples.

scholarly journals Influence Of Damping On FRF Of Vehicle Computing Model

2015 ◽  
Vol 15 (2) ◽  
Author(s):  
Jozef Melcer
Keyword(s):  
Dynamic System ◽  
Frequency Response ◽  
Frequency Domain ◽  
Response Function ◽  
Frequency Response Function ◽  
Natural Frequencies ◽  
Spectral Lines ◽  
Response Factors ◽  
Computing Model ◽  
Power Response

Abstract Frequency Response Function (FRF) characterizes the response of dynamic system in frequency domain. Its shape is dependent on the property of analyzed system, especially on damping. The damping neglecting during the calculation of frequency response causes that the Power Response Factors have the character of discrete spectral lines at points of natural frequencies of the vehicle computing model.

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