scholarly journals Vibration Analysis of Cylindrical Sandwich Aluminum Shell with Viscoelastic Damping Treatment

2013 ◽  
Vol 2013 ◽  
pp. 1-7 ◽  
Author(s):  
Tai-Hong Cheng ◽  
Zhen-Zhe Li ◽  
Yun-De Shen
Keyword(s):  
Frequency Response ◽  
Frequency Response Function ◽  
Natural Frequencies ◽  
Damping Ratio ◽  
Viscoelastic Damping ◽  
Viscoelastic Layer ◽  
Response Functions ◽  
Out Of Plane ◽  
Displacement Theory ◽  
Damping Treatments

This paper has applied the constrained viscoelastic layer damping treatments to a cylindrical aluminum shell using layerwise displacement theory. The transverse shear, the normal strains, and the curved geometry are exactly taken into account in the present layerwise shell model, which can depict the zig-zag in-plane and out-of-plane displacements. The damped natural frequencies, modal loss factors, and frequency response functions of cylindrical viscoelastic aluminum shells are compared with those of the base thick aluminum panel without a viscoelastic layer. The thickness and damping ratio of the viscoelastic damping layer, the curvature of proposed cylindrical aluminum structure, and placement of damping layer of the aluminum panel were investigated using frequency response function. The presented results show that the sandwiched viscoelastic damping layer can effectively suppress vibration of cylindrical aluminum structure.

Experimental and Finite Element Analysis of Stand-Off Layer Damping Treatments for Beams

2007 ◽  
Author(s):  
Jessica M. H. Yellin ◽  
I. Y. Shen ◽  
Per G. Reinhall
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Frequency Response ◽  
Viscoelastic Layer ◽  
Constrained Layer Damping ◽  
Response Functions ◽  
Element Analysis ◽  
Frequency Response Functions ◽  
Damping Treatments ◽  
Passive Constrained Layer Damping

Passive stand-off layer (PSOL) and slotted stand-off layer (SSOL) damping treatments are presently being implemented in many commercial and defense designs. In a PSOL damping treatment, a stand-off or spacer layer is added to a conventional passive constrained layer damping treatment. In an SSOL damping treatment, slots are included in the stand-off layer. A set of experiments using PSOL and SSOL beams in which the geometric properties of the stand-off layer were varied was conducted to analyze the contribution of the stand-off layer to the overall system damping. This set of experiments measured the frequency response functions for a series of beams in which the total slotted area of the stand-off layer was held constant while the number of slots in the stand-off layer was increased for a constant stand-off layer material. Finite element analysis models were developed in ANSYS to compare the predicted frequency response functions with the experimentally measured frequency response functions for the beams treated with PSOL and SSOL damping treatments. In these beams, the bonding layers used to fabricate these treatments were found to have a measurable and significant effect on the frequency response of the structure. The finite element model presented here thus included an epoxy layer between the base beam and the stand-off layer, a contact cement layer between the stand-off layer and the viscoelastic layer, and a method for modeling delamination.

Identification of Rotating Asymmetry in Rotating Machines by Using Reverse dFRF

1999 ◽  
Author(s):  
Chong-Won Lee ◽  
Kye-Si Kwon
Keyword(s):  
Frequency Response ◽  
Response Function ◽  
Frequency Response Function ◽  
Modal Testing ◽  
Vibration Sensor ◽  
Response Functions ◽  
Physical Realization ◽  
Simple Method ◽  
Testing Method ◽  
Asymmetric Rotor

Abstract A quick and easy but comprehensive identification method for asymmetry in an asymmetric rotor is proposed based on complex modal testing method. In this work, it is shown that the reverse directional frequency response function (reverse dFRF), which indicates the degree of asymmetry, can be identified with a simple method requiring only one vibration sensor and one exciter. To clarify physical realization associated with estimation of the reverse dFRF, its relation to the conventional frequency response functions, which are defined by the real input (exciter) and output (vibration sensor), are extensively discussed.

Detection of Damage Extension in Cantilever Beams Using Change Ratio of Frequency Response Functions

2011 ◽  
Vol 50-51 ◽  
pp. 875-879
Author(s):  
Hai Lei Jia ◽  
Yin Zhao
Keyword(s):  
Frequency Response ◽  
Natural Frequencies ◽  
Dynamic Properties ◽  
Damage Index ◽  
High Sensitivity ◽  
Cantilever Beams ◽  
Response Functions ◽  
Full Spectrum ◽  
Structural Dynamic ◽  
Low Dimensional

Frequency response function (FRF) is a fundamental dynamic index, which is capable of reflecting structural dynamic properties using full-spectrum information. In spite of distinct merits over conventional modal parameters, the FRF has an observable drawback of multi-dimensionality, unsuited for damage characterization. Such a situation motivates an interesting subject, i.e., extracting low-dimensional, high-sensitivity damage index from the FRF. This study focuses on developing a valid damage index, called FRF change ratio, to detect extension of damage. An experiment towards cantilever beams is systemically conducted. The results show that the FRF change ratio can effectively reflects damage extension, and it is more sensitive than conventional natural frequencies. This new damage index holds promise for practical damage detection in beam-like structures.

scholarly journals Fault Diagnosis of Nonlinear Analog Circuit Based on Generalized Frequency Response Function and LSSVM Classifier Fusion

2020 ◽  
Vol 2020 ◽  
pp. 1-11
Author(s):  
Jialiang Zhang
Keyword(s):  
Support Vector Machine ◽  
Fault Diagnosis ◽  
Frequency Response ◽  
Frequency Response Function ◽  
Analog Circuit ◽  
Least Square ◽  
Classifier Fusion ◽  
Support Vector ◽  
Response Functions ◽  
Nonlinear Analog

For fault diagnosis of nonlinear analog circuit, a novel method based on generalized frequency response function (GFRF) and least square support vector machine (LSSVM) classifier fusion is presented. The sinusoidal signal is used as the input of analog circuit, and then, the generalized frequency response functions are estimated directly by the time-domain formulations. The discrete Fourier transform of measurement data is avoided. After obtaining the generalized frequency response functions, the amplitudes of the GFRFs are chosen as the fault feature parameters. A classifier fusion algorithm based on least square support vector machine (LSSVM) is used for fault identification. Two LSSVM multifault classifiers with different kernel functions are constructed as subclassifiers. Fault diagnosis experiments of resistor-capacitance (RC) circuit and Sallen Key filter are carried out, respectively. The results show that the estimated GFRFs of the circuit are accurate, and the fault diagnosis method can get high recognition rate.

scholarly journals Vibrational Analysis of Composite Beam Embedded with Nitinol Shape Memory Alloy Wires

2018 ◽  
Vol 7 (3.4) ◽  
pp. 143
Author(s):  
Omer Muwafaq Mohmmed Ali ◽  
Rawaa Hamid Mohammed Al-Kalali ◽  
Ethar Mohamed Mahdi Mubarak
Keyword(s):  
Shape Memory Alloy ◽  
Shape Memory ◽  
Frequency Response ◽  
Response Curve ◽  
Natural Frequencies ◽  
Damping Ratio ◽  
Vibrational Analysis ◽  
Laminated Composite ◽  
Vibration Modes ◽  
Frequency Response Curve

In this paper, laminated composite materials were hybridized with fibers (E-glass) and shape memory alloy wires which considered a smart material. The effect of changing frequency on the (acceleration- frequency) response curve, the damping ratio of the vibration modes, the natural frequencies of the vibration mode, the effect of shape memory alloy wires number on the damping characteristics were studied. Hand lay-up technique was used to prepare the specimens, epoxy resin type was used as a matrix reinforced by fiber, E-glass. The specimens were manufactured by stacking 2 layers of fibers. Shape memory alloy, type Nitinol (nickel-titanium) having a diameter (1 and 2mm), was used to manufacture the specimens by embedding (1,2 and 3) wires into epoxy. Experimentally, the acceleration- frequency response curve was plotted for the vibration modes, this curve was used to measure the natural frequencies of the vibration modes and calculate the damping ratio of the vibration modes. ANSYS 15- APDL was used to determine the mode shape and find the natural frequencies of the vibration modes then compared with the experimental results. The results illustrated that, for all specimens increasing the natural frequency leads to decreasing the damping ratio. Increasing the number of shape memory alloy wires leads to increase the values of the damping ratio of the vibration modes and the natural frequencies of the vibration modes at room temperature. 

Use of dFRFs for Identification of Travelling Wave Modes in Rotating Disks

1998 ◽  
Vol 120 (3) ◽  
pp. 719-726 ◽  
Author(s):  
Myeong-Eop Kim ◽  
Chong-Won Lee
Keyword(s):  
Frequency Response ◽  
Frequency Response Function ◽  
Rotating Disk ◽  
Travelling Wave ◽  
Weighted Sum ◽  
Response Functions ◽  
Rotating Disks ◽  
Complex Wave ◽  
Wave Coordinates ◽  
Wave Modes

Use of the wave directional frequency response function (dFRF), which is composed of conventional frequency response functions, is proposed for identification of the forward and backward travelling wave modes of isotropic rotating disks. The driving point dFRF, which is a weighted sum of complex wave dFRFs defined in the complex wave coordinates, is also derived for separation of the forward and backward travelling wave modes in the frequency domain. Numerical examples of rotating disks are treated to demonstrate the analytical developments. Experiments with a laboratory rotating disk are also performed to verify the theoretical findings.

Model updating–based damage detection of a concrete beam utilizing experimental damped frequency response functions

2018 ◽  
Vol 22 (4) ◽  
pp. 935-947 ◽  
Author(s):  
Qianhui Pu ◽  
Yu Hong ◽  
Liangjun Chen ◽  
Shili Yang ◽  
Xikun Xu
Keyword(s):  
Damage Detection ◽  
Frequency Response ◽  
Frequency Response Function ◽  
Concrete Beam ◽  
Model Updating ◽  
Response Functions ◽  
Experimental Frequency ◽  
Frequency Response Functions ◽  
Function Formulation ◽  
Analytical Frequency

This article evaluates the use of experimental frequency response functions for damage detection and quantification of a concrete beam with the help of model updating theory. The approach is formulated as an optimization problem that intends to adjust the analytical frequency response functions from a benchmark finite element model to match with the experimental frequency response functions from the damaged structure. Neither model expansion nor reduction is needed because the individual analytical frequency response function formulation is derived. Unlike the commonly used approaches that assume zero damping or viscous damping for simplicity, a more realistic hysteretic damping model is considered in the analytical frequency response function formulation. The accuracy and anti-noise ability of the proposed approach are first verified by the numerical simulations. Next, a laboratory reinforced concrete beam with different levels of damage is utilized to investigate the applicability in an actual test. The results show successful damage quantification and damping updating of the beam by matching the analytical frequency response functions with the experimental frequency response functions in each damage scenario.

Change of modal parameters due to crack growth in a tripod tower platform

1993 ◽  
Vol 20 (5) ◽  
pp. 801-813 ◽  
Author(s):  
Yin Chen ◽  
A. S. J. Swamidas
Keyword(s):  
Finite Element ◽  
Frequency Response ◽  
Response Function ◽  
Frequency Response Function ◽  
Experimental Results ◽  
Modal Testing ◽  
Modal Parameters ◽  
Response Functions ◽  
Frequency Response Functions ◽  
Strain Frequency

Strain gauges, along with an accelerometer and a linear variable displacement transducer, were used in the modal testing to detect a crack in a tripod tower platform structure model. The experimental results showed that the frequency response function of the strain gauge located near the crack had the most sensitivity to cracking. It was observed that the amplitude of the strain frequency response function at resonant points had large changes (around 60% when the crack became a through-thickness crack) when the crack grew in size. By monitoring the change of modal parameters, especially the amplitude of the strain frequency response function near the critical area, it would be very easy to detect the damage that occurs in offshore structures. A numerical computation of the frequency response functions using finite element method was also performed and compared with the experimental results. A good consistency between these two sets of results has been found. All the calculations required for the experimental modal parameters and the finite element analysis were carried out using the computer program SDRC-IDEAS. Key words: modal testing, cracking, strain–displacement–acceleration frequency response functions, frequency–damping–amplitude changes.

Sign in / Sign up

Export Citation Format

Share Document