Changes In Vibration Characteristics Research Articles

Comparison of CFBP, FFBP, and RBF Networks in the Field of Crack Detection

The issue of crack detection and its diagnosis has gained a wide spread of industrial interest. The crack/damage affects the industrial economic growth. So early crack detection is an important aspect in the point of view of any industrial growth. In this paper a design tool ANSYS is used to monitor various changes in vibrational characteristics of thin transverse cracks on a cantilever beam for detecting the crack position and depth and was compared using artificial intelligence techniques. The usage of neural networks is the key point of development in this paper. The three neural networks used are cascade forward back propagation (CFBP) network, feed forward back propagation (FFBP) network, and radial basis function (RBF) network. In the first phase of this paper theoretical analysis has been made and then the finite element analysis has been carried out using commercial software, ANSYS. In the second phase of this paper the neural networks are trained using the values obtained from a simulated model of the actual cantilever beam using ANSYS. At the last phase a comparative study has been made between the data obtained from neural network technique and finite element analysis.

Numerical investigation on vibration characteristics of a micro-speaker diaphragm considering thermoforming effects

Micro-speaker diaphragms play an important role in generating desired sound responses, and are designed to have thin membrane shapes for flexibility in the axial direction. The micro-speaker diaphragms are formed from thin polymer film through the thermoforming process, in which local thickness reductions occur due to strain localization. This thickness reduction results in a change in vibration characteristics of the diaphragm and different sound responses from that of the original design. In this study, the effect of this thickness change in the diaphragm on its vibration characteristics is numerically investigated by coupling thermoforming simulation, structural analysis and modal analysis. Thus, the thickness change in the diaphragm is calculated from the thermoforming simulation, and reflected in the further structural and modal analyses in order to estimate the relevant stiffness and vibration modes. Comparing these simulation results with those from a diaphragm with the uniform thickness, it is found that a local thickness reduction results in the stiffness reduction and the relevant change in the natural frequencies and the corresponding vibration modes.

Experimental Investigations on Effect of Damage on Vibration Characteristics of a Reinforced Concrete Beam

Need for developing efficient non-destructive damage assessment procedures for civil engineering structures is growing rapidly towards structural health assessment and management of existing structures. Damage assessment of structures by monitoring changes in the dynamic properties or response of the structure has received considerable attention in recent years. In the present study, damage assessment studies have been carried out on a reinforced concrete beam by evaluating the changes in vibration characteristics with the changes in damage levels. Structural damage is introduced by static load applied through a hydraulic jack. After each stage of damage, vibration testing is performed and system parameters were evaluated from the measured acceleration and displacement responses. Reduction in fundamental frequencies in first three modes is observed for different levels of damage. It is found that a consistent decrease in fundamental frequency with increase in damage magnitude is noted. The beam is numerically simulated and found that the vibration characteristics obtained from the measured data are in close agreement with the numerical data.

Comparative kinetic model of fluorescence enhancement in selective binding of monochlorobimane to glutathione

The highly specific binding of fluorescent label monochlorobimane (MCB) to thiols has been investigated using a tripeptide thiol, glutathione (GSH), a biomolecule protecting cells against oxidative stress and damaging radicals. Due to the reported uneven distribution of MCB in living cells and compartmentalization of GSH in cells, we have explored binding of MCB to GSH in a higher concentration range than normally applied in fluorimetric analysis. Since at higher concentrations, a concentration quenching may interfere with the analysis and because MCB binding to GSH is controlled by kinetics, a special comparative kinetic model of the binding reaction has been developed and utilized in fluorimetric determinations of GSH and in an independent non-optical isothermal reaction-heat measurement. The rate constants: k 1 = 0.274 ± 0.012 and 0.315 ± 0.004 s −1 M −1, have been obtained from fluorescence and microcalorimetric methods, respectively. The molar enthalpy of binding, Δ H = −48.46 ± 0.61 kJ/mol, has been determined. The low value of k 1 obtained from fluorimetric measurements precludes concentration quenching for MCB concentrations up to 330 μM and GSH concentrations up to 5 mM. The DFT quantum mechanical calculations have been performed to elucidate changes in vibrational characteristics of bimane fused rings upon GSH binding. The predicted relaxing of rings vibrational modes has been confirmed in Raman scattering spectra and is consistent with the increased fluorescence emission of the adduct. Plausible elucidation of the mechanism of this process is discussed.

Crack identification in curvilinear beams by using ANN and ANFIS based on natural frequencies and frequency response functions

This paper presents different artificial intelligence (AI) techniques for crack identification in curvilinear beams based on changes in vibration characteristics. Vibration analysis has been performed by applying the finite element method (FEM) to compute natural frequencies and frequency response functions (FRFs) for intact and damaged beams. The analysis reveals the changes in natural frequencies and amplitudes of FRFs of the beams for cracks of different sizes at different locations. These changes are used as input data for single and multiple artificial neural networks (ANN) and multiple adaptive neuro-fuzzy inference systems (ANFIS) in order to predict the size of the crack and its location. To avoid large models, the principal component analysis (PCA) approach has been carried out to reduce the computed FRFs data. The analysis of different techniques shows that the average prediction errors in the multiple ANN models is less than those in the single ANN model and in the multiple ANFIS. It is shown that the cracks longer than 5 mm can be located with satisfactory accuracy, even if the input data are corrupted with various level of noise. Multiple ANFIS is adopted to construct a more reliable and less sensitive model for noise excitation.

Dynamic simulation of spur gear with tooth root crack propagating along tooth width and crack depth

Gear tooth crack will cause changes in vibration characteristics of gear system, based on which, operating condition of the gear system is always monitored to prevent a presence of serious damage. However, it is also a unsolved puzzle to establish the relationship between tooth crack propagation and vibration features during gear operating process. In this study, an analytical model is proposed to investigate the effect of gear tooth crack on the gear mesh stiffness. Both the tooth crack propagations along tooth width and crack depth are incorporated in this model to simulate gear tooth root crack, especially when it is at very early stage. With this analytical formulation, the mesh stiffness of a spur gear pair with different crack length and depth can be obtained. Afterwards, the effects of gear tooth root crack size on the gear dynamics are simulated and the corresponding changes in statistical indicators – RMS and kurtosis are investigated. The results show that both RMS and kurtosis increase with the growth of tooth crack size for propagation whatever along tooth width and crack length. Frequency spectrum analysis is also carried out to examine the effects of tooth crack. The results show that sidebands caused by the tooth crack are more sensitive than the mesh frequency and its harmonics. The developed analytical model can predict the change of gear mesh stiffness with presence of a gear tooth crack and the corresponding dynamic responses could supply some guidance to the gear condition monitoring and fault diagnosis, especially for the gear tooth crack at early stage.

Damage Identification in Timber Bridges Utilising the Damage Index Method and Neural Network Ensembles

Many of Australia’s timber bridges are in aged and decayed conditions. In order to ensure the reliability of these structures and the safety of the public, condition assessment, damage detection and safety evaluation is necessary. This paper presents a damage identification procedure, which is based on global change of vibration characteristics of a structure. The developed method utilises the damage index (DI) method in combination with neural network techniques to identify damage in numerical and experimental timber beam structures. The neural network ensemble approach is utilised in order to respect important diversities of different modes and to integrate individual characteristics of vibrational mode separated damage features. The method considers field testing issues associated with measurement noise, limited number of sensor arrays and environmental fluctuations. The results of damage detection using the proposed approach demonstrate its ability to determine the location and severity of all present damage cases. The outcomes show that the developed damage detection method is effective, robust and reliable.

The Stuttgart TV Tower — displacement of the top caused by the effects of sun and wind

The monitoring of static, quasi-static and dynamic deformations of long-period structures is now possible using Global Positioning System (GPS) technology. This paper describes the way in which the Stuttgart TV Tower was monitored using static and kinematic GPS modes. The displacements of the tower were caused by two factors. Quasi-static displacements were caused by the combined influence of solar radiation and daily air temperature variation during different weather seasons and conditions. Dynamic displacements were caused by wind. The results clearly demonstrate that the procedure using GPS measurements allows us to collect displacement data which could be used to determine the displacement thresholds of the tower and/or to examine the changes of vibration characteristics. This data was valuable for the assessment of the integrity and reliability of the tower.

Dynamic Effect on Vibration Signatures of Cracks in Railway Prestressed Concrete Sleepers

In general, cracks in structural members indicate a level of serviceability of the engineering structures. Usually a hairline crack can be detected by visual inspection, crack gauge, fibre optical sensor, or laser sensor. Recently, an attempt to develop a non-destructive tool for health monitoring of prestressed concrete sleepers in railway tracks using the vibration responses has been established at the University of Wollongong, Australia. However, the fundamental understanding of the dynamic effect due to the cracks in sleepers is insufficient. This paper investigates the dynamic effect of the cracks on the vibration signatures of the railway prestressed concrete sleepers. The modal analysis has been used to evaluate the modal changes in vibration characteristics of the prestressed concrete sleepers in the frequency band between 0 and 1,600 Hz. The sample cracks have been initiated by the impulsive forces attributed to the high capacity drop impact testing machine. Comparison of the modal parameters of the intact and cracked sleepers has been highlighted in terms of natural frequencies and modal damping. This understanding will lead to further development of the economical technology to evaluate the structural integrity of railway track and its components.

Development of a System to Control Noise Transmitted Through Interior Panels of Railway Vehicles (1st Report, Study on a Method of Controlling Noise Transmitted Through a Panel Using a Module-Type Noise Control System)

In considering the application of an active noise control system to interior noise reduction of railway vehicles, the control system must respond to changes in the vibration characteristics of the interior panels during train running. We propose a new module-type noise control system, in which small noise control devices are arranged on a plane, to act against the noise transmitted through the interior panel that becomes dominant in tunnels. This noise control system controls the noise incidence to the interior panel, therefore, it is unnecessary to identify the vibration characteristics of the interior panel or noise transmitted through it, and a certain level of noise reduction is ensured irrespective of the change of vibration characteristics of the interior panel during train running. As fundamental work, we carried out a study on the application to the noise transmitted through a flat plate equivalent to an interior panel. This paper first presents an outline of the noise control system and modeling. Furthermore, the overall behavior of the system is examined by numerical analysis, and finally experimental results of the control effect are shown.

Damage Assessment in Advanced Composite Structures Using Embedded Fibre Bragg Grating Sensors

Three methodologies for damage assessment in glass fibre reinforced composite structures using embedded fibre Bragg grating (FBG) sensors are introduced in this paper. These are static strain, vibration-based and ultrasonic wave approaches. For the static strain method, the embedded FBG sensors are used to investigate the response of the reflection spectrum from the sensors due to delamination. Composite beams with various delamination locations along their thickness-wise direction are studied. Quantitative damage detection is demonstrated by using the FBG sensors to measure the change of vibration characteristics of composite beams. The correlation of the vibration characteristics and the corresponding delamination size and location is established by a theoretical model. Both delamination size and location can be identified based on the change of the vibration characteristics with genetic algorithm (GA), simultaneously. The ultrasonic wave sensing ability of embedded and surface bonded FBG sensors in the...

836 歩道橋の振動特性評価手法に関する研究

It is desirable to investigate changes in vibration characteristics of pedestrian bridges to evaluate the seismic performance of old pedestrian bridges. This paper presents an experimental and analytical study on methods for evaluation of the vibration characteristics of pedestrian bridges. First, measurement system and methods of vibration tests are proposed to examine natural frequencies and damping ratios of these bridges. Vibration measurements and vibration characteristic evaluation of the pedestrian bridge in Fujisawa city were performed using the proposed measurement system. Next, Eigen value analysis using a multi-mass beam model of the pedestrian bridge was performed, and the analytical results were compared with the measured results.

Identification of damage in an aeroelastic system based on attractor deformations

Vibration-based damage detection is a powerful method of structural health monitoring, which is based on the identification of changes in vibration characteristics due to changes in material and/or stiffness properties of structures. Current such techniques are based mostly on linear approaches, whereas nonlinear methods still have certain difficulties in detecting the level and location of damage, especially in the case of high dimensional systems. One of the main reasons for these difficulties is the low sensitivity of current methods to small parametric variations. In this paper, we increase this sensitivity by exploiting nonlinearities. To explore the potential offered by nonlinearities in increasing sensitivity, results are presented for a two dimensional panel subjected to supersonic flows. The nonlinearity resulting from the coupling of stretching and bending of the panel is considered in the structural model. The damage in the panel is modeled as a local loss of bending stiffness (along the panel) and at the mounting points. The basis for the development of a method for detecting multiple simultaneous damages is presented. This method is based on probability density functions of sampled attractors of the dynamics. Exploiting nonlinear dynamics is shown to be powerful in detecting different damage levels and locations.

Dynamic characteristics of a damaged plate

It is very important to well understand the dynamic characteristics of damaged structures to successfully develop or to choose a most appropriate structural damage identification method (SDIM) as the means of non-destructive testing. In this paper, the dynamic equation of motion for damaged plates is derived by introducing a damage distribution function, which may characterize the effective state of structural damages. It is found that structural damages may induce the coupling between modal coordinates. The effects of damages on the vibration characteristics of a plate depending on their locations, sizes, and magnitudes are numerically investigated in a systematic way. The numerical investigations are also given to the effects of damage-induced modal coupling on the changes in vibration characteristics and to the minimum number of natural modes required to predict sufficiently accurate vibration characteristics of damaged plates.

QUANTIFICATION OF CHANGE OF VIBRATION CHARACTERISTICS CAUSED BY UNCERTAINTY AND ITS APPLICATION TO SIGNIFICANCE TESTING

振動特性の変化から構造物の損傷を推定する際には, 損傷による振動特性の変化と不確実性に起因するその変化との有意性を明確にしなければならない. 本研究では, 計測データから同定される振動特性を確率変動するものとして捉え, その確率分布の信頼区間を Bootstrap 法により算出し, 不確実性に起因する振動特性の変化を定量化する手法を構築した. さらに, そのときに得られる Bootstrap 分布に基づいてその変化の有意性を検定する一手法を提案した. 実際に, 免震橋の地震時における振動計測結果およびRC構造物の常時微動計測結果に対して適用し, 前者においては地震振幅の違いにより有意な振動特性の変化が生じていることを, 後者においては震度4程度の地震前後では振動特性の変化は有意なものではないことを統計的に明らかにした.

Vibrational analysis of the cantilever in non-contact scanning force microscopy

In this paper the basic principles of non-contact scanning force microscopy (SFM) are explained. The major long-range forces acting between a tip and a sample, and consequently the changes of vibration characteristics with the tip–sample distance, are discussed. To estimate the resolution limits of the non-contact method, the motion of a vibrating silicon cantilever above testing silicon nanostructure models was simulated numerically. This was done both in the mode of constant height and of constant force. To simulate the real behaviour of the tip in the mode of constant force, we included into our calculations the feedback loop. It was shown that by using long-range van der Waals forces an atomic lattice periodicity and individual adatoms can be recognized by non-contact SFM only when the equilibrium tip–surface distance is ∼1.0 nm. Copyright © 2000 John Wiley & Sons, Ltd.

An overview of vibration-based damage detection research at Los Alamos National Laboratory

The ability to monitor the structural health of our aging infrastructure is becoming increasingly important. A wide variety of highly effective local nondestructive evaluation tools are available. However, damage identification based upon changes in vibration characteristics is one of the few methods that monitors changes in the structure on a global basis. The material presented herein will summarize the structural health monitoring research that has been conducted at Los Alamos National Laboratory over the last 8 years. First, the process of vibration-based damage detection will be described as a problem in statistical pattern recognition. This process has three portions: (1) data acquisition and cleansing; (2) feature selection and data compression; and (3) statistical model development. Current research regarding feature selection and statistical model development will be emphasized with the application of this technology to large-scale, in situ bridge structures and to bridge columns that were tested in a laboratory. In particular, the ability to quantify uncertainties in measured dynamic properties caused by variable environmental and operational conditions is addressed. The paper will conclude by summarizing some of the underlying technical issues associated with vibration-based global damage detection that continues to make this area of technology a challenging research topic.

A free vibration analysis of sound-structure interaction plate having a small cut-out

In order to investigate the characteristics of sound-structure interaction plate having a cut-out, we modeled a rectangular cavity and the flexible plate of the cavity. Because the particle velocity of air is the same as that of plate on the plate, we could easily redefine vibration equation using the velocity potential. We calculated the natural frequencies of plate using orthogonal polynomial functions which satisfy the boundary conditions in the Rayleigh-Ritz method. For the change of vibration characteristics, the effect of sound-structure interaction is more dominant than that of cut-out size.

Discrimination of munition fill types by k-nearest neighbour classification tree analysis of acoustic resonance signatures

We have developed a noncontacting, long-standoff inspection system for munition fill type identification. The inspection system, based on using a laser vibrometer to measure the response of containers to acoustic excitation, is capable of detecting subtle changes in vibration characteristics due to variations in the physical properties of different fill materials. Determination of fill type is achieved by applying a k-nearest neighbour classification tree analysis to the resulting acoustic resonance data. Application of the method to field trial measurements of chemical weapons shows the inspection system to be a practical and reliable means for discriminating between munitions with a variety of chemical fills.

Simulation experiments of loose parts and abnormal vibration of core internals

The drifting and impact phenomena of loose parts in the reactor coolant loop and also the change of vibration characteristics of the core internals due to their looseness or defects were studied by means of simulation experiments employing reduced scale model. The model loop on the scale of one fifth consisted of a reactor vessel (R/V), core internals (C/I) and the water chamber of a steam generator (S/G) which were constructed to simulate the flow and vibration characteristics of the actual components according to similality law. The experiments were performed in two stages. In the first stage or a loose parts simulation test, simulated loose parts of different shapes scaled down to the model were thrown into the loop to study the drifting and impact characteristics by means of accelerometers installed on the surface of R/V and S/G. In the second stage, the core internals were intentionally subjected to abnormal conditions to examine changes in vibration characteristics of the core internals and study the possibility of monitoring abnormal vibration from outside R/V. On the basis of the model test results and data accumulated in actual plant operation, a loose parts monitoring system was developed that allows estimation of impact location and impact energy on-line real time.