An improved series expansion method of frequency response function under medium and high frequency excitations

2010 ◽  
Vol 6 (1) ◽  
pp. 11-15 ◽  
Author(s):  
Wei Ning ◽  
Jun Wang ◽  
Jing-Hui Zhang
Keyword(s):  
Frequency Response ◽  
Series Expansion ◽  
Response Function ◽  
High Frequency ◽  
Frequency Response Function ◽  
Expansion Method ◽  
Series Expansion Method

An Analysis of the Quadratic Frequency Response for Lateral Drifting Force and Moment

1981 ◽  
Vol 25 (02) ◽  
pp. 117-129
Author(s):  
C. H. Kim ◽  
J. F. Dalzell
Keyword(s):  
Frequency Response ◽  
Response Function ◽  
High Frequency ◽  
Frequency Response Function ◽  
Near Field ◽  
Three Dimensional ◽  
Quadratic Term ◽  
Wave Elevation ◽  
The Mean ◽  
Close Fit

Results of calculations are given for lateral drifting forces acting on a cylinder and a Series 60 hull derived by a new procedure involving application of the quadratic frequency response function (QFRF) and the close-fit method for flows induced by hull sections in the near field. The near-field solutions are required by the QFRF in order to obtain the nonlinear (second order) interaction effects in the presence of dual waves. This method yields the mean drifting force consisting of four components of which the relative wave-elevation term is dominant, whereas the Bernoulli quadratic term is secondary. A mathematical discontinuity of the drifting force in the neighborhood of a high frequency is investigated by applying a modified Green's function. Mean drifting forces for two forms have been calculated and the results compared with available analysis and model data. A fairly complete quadratic frequency response function for lateral drifting forces in the bifrequency domain was computed for the Series 60, CB = 0.6 ship at 60-deg heading. The computed results are presented in a three-dimensional view accompanied by a detailed discussion of the characteristic behavior.

Estimating Rotational Frequency Response Function Using Mode Expansion and Frequency Response Function Synthesis Method

2021 ◽  
Vol 18 (2) ◽  
Author(s):  
W.I.I. Wan Iskandar Mirza ◽  
Muhamad Norhisham Bin Abdul Rani ◽  
M.A. Yunus ◽  
D. Stancioiu ◽  
V. Shripathi
Keyword(s):  
Frequency Response ◽  
Response Function ◽  
Frequency Response Function ◽  
Synthesis Method ◽  
Expansion Method ◽  
Rotational Frequency ◽  
Attractive Alternative ◽  
Fe Model ◽  
System Reduction ◽  
Modal Model

The rotational frequency response function (RFRF) plays a crucial role in increasing the accuracy of the calculated results of the frequency-based substructuring method. However, RFRFs are often omitted due to the difficulties in the measurement process and limitations of the equipment. This paper presents a scheme of estimating the rotational FRF of an irregular plate structure using the FE model reduction and expansion method. The reduced FE model was introduced using the improved reduction system (IRS) and expanded to the experimental modal model (EMA model) using the system reduction and the expansion (SEREP) method. The FRF expanded method was then employed to derive the translational and rotational FRFs from the expanded EMA model. The accuracy of the expanded FRFs was evaluated with the EMA model of the irregular plate. It was found that the translational and rotational FRFs estimated from the proposed scheme were in good agreement with the EMA counterparts. Furthermore, the patterns of the estimated RFRFs were well correlated with the EMA RFRFs. This work shows that the proposed scheme may offer an attractive alternative way of accurately determining the RFRs of complex structures or structural components.

An electrodynamic shaker with an integral force gauge for high-frequency measurements on lightweight structures

2000 ◽  
Vol 214 (10) ◽  
pp. 1285-1297 ◽  
Author(s):  
R M Grice ◽  
R J Pinnington
Keyword(s):  
Frequency Response ◽  
Piezoelectric Material ◽  
Response Function ◽  
High Frequency ◽  
Frequency Response Function ◽  
Dynamic Behaviour ◽  
High Frequencies ◽  
Lightweight Structures ◽  
Electrodynamic Shaker ◽  
Design Construction

The design, construction and calibration of a purpose-built electrodynamic shaker for making frequency response function measurements on lightweight structures at high frequencies (i.e. many kHz) are described. The shaker uses a conventional wire-wound coil onto which is assembled a force gauge. The force gauge is constructed using little more than just a miniature piece of piezoelectric material. The dimensions of the components used to manufacture the shaker are determined by comparing their estimated dynamic behaviour with the estimated mobility of a lightweight perspex test structure. Although such an electrodynamic shaker is not entirely novel, it demonstrates how careful use of basic materials can produce a device that overcomes some limitations of commercial devices at very little cost.

scholarly journals Road Roughness Estimation Based on the Vehicle Frequency Response Function

Actuators ◽  
2021 ◽  
Vol 10 (5) ◽  
pp. 89
Author(s):  
Qingxia Zhang ◽  
Jilin Hou ◽  
Zhongdong Duan ◽  
Łukasz Jankowski ◽  
Xiaoyang Hu
Keyword(s):  
Frequency Response ◽  
Response Function ◽  
Frequency Response Function ◽  
Gaussian White Noise ◽  
Estimation Method ◽  
Time Shift ◽  
Ride Quality ◽  
The Road ◽  
Road Roughness ◽  
Measured Response

Road roughness is an important factor in road network maintenance and ride quality. This paper proposes a road-roughness estimation method using the frequency response function (FRF) of a vehicle. First, based on the motion equation of the vehicle and the time shift property of the Fourier transform, the vehicle FRF with respect to the displacements of vehicle–road contact points, which describes the relationship between the measured response and road roughness, is deduced and simplified. The key to road roughness estimation is the vehicle FRF, which can be estimated directly using the measured response and the designed shape of the road based on the least-squares method. To eliminate the singular data in the estimated FRF, the shape function method was employed to improve the local curve of the FRF. Moreover, the road roughness can be estimated online by combining the estimated roughness in the overlapping time periods. Finally, a half-car model was used to numerically validate the proposed methods of road roughness estimation. Driving tests of a vehicle passing over a known-sized hump were designed to estimate the vehicle FRF, and the simulated vehicle accelerations were taken as the measured responses considering a 5% Gaussian white noise. Based on the directly estimated vehicle FRF and updated FRF, the road roughness estimation, which considers the influence of the sensors and quantity of measured data at different vehicle speeds, is discussed and compared. The results show that road roughness can be estimated using the proposed method with acceptable accuracy and robustness.

scholarly journals Predicting Dam Flood Discharge Induced Ground Vibration with Modified Frequency Response Function

Water ◽  
2021 ◽  
Vol 13 (2) ◽  
pp. 144
Author(s):  
Yan Zhang ◽  
Jijian Lian ◽  
Songhui Li ◽  
Yanbing Zhao ◽  
Guoxin Zhang ◽  
...  
Keyword(s):  
Frequency Response ◽  
Frequency Distribution ◽  
Response Function ◽  
Frequency Response Function ◽  
Ground Vibration ◽  
Vibration Source ◽  
Ground Vibrations ◽  
High Energies ◽  
Flood Discharge ◽  
Opening Method

Ground vibrations induced by large flood discharge from a dam can damage surrounding buildings and impact the quality of life of local residents. If ground vibrations could be predicted during flood discharge, the ground vibration intensity could be mitigated by controlling or tuning the discharge conditions by, for example, changing the flow rate, changing the opening method of the orifice, and changing the upstream or downstream water level, thereby effectively preventing damage. This study proposes a prediction method with a modified frequency response function (FRF) and applies it to the in situ measured data of Xiangjiaba Dam. A multiple averaged power spectrum FRF (MP-FRF) is derived by analyzing four major factors when the FRF is used: noise, system nonlinearity, spectral leakages, and signal latency. The effects of the two types of vibration source as input are quantified. The impact of noise on the predicted amplitude is corrected based on the characteristics of the measured signal. The proposed method involves four steps: signal denoising, MP-FRF estimation, vibration prediction, and noise correction. The results show that when the vibration source and ground vibrations are broadband signals and two or more bands with relative high energies, the frequency distribution of ground vibration can be predicted with MP-FRF by filtering both the input and output. The amplitude prediction loss caused by filtering can be corrected by adding a constructed white noise signal to the prediction result. Compared with using the signal at multiple vibration sources after superimposed as input, using the main source as input improves the accuracy of the predicted frequency distribution. The proposed method can predict the dominant frequency and the frequency bands with relative high energies of the ground vibration downstream of Xiangjiaba Dam. The predicted amplitude error is 9.26%.

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