توجه: محتویات این صفحه به صورت خودکار پردازش شده و مقاله‌های نویسندگانی با تشابه اسمی، همگی در بخش یکسان نمایش داده می‌شوند.
۱Off–line\On–line Multi Mass–Stiffness Damage Detection by Structural Input–Output Data
نویسنده(ها): ،
اطلاعات انتشار: اولین کنفرانس تمدید و تخمین عمر سازه های هوایی و صنعتی پیر و فرسوده، سال
تعداد صفحات: ۱۸
In this paper, a new technique is proposed to detect and localize multi mass–stiffness damage level in a damaged structure. The identified system digital pulse response (SDPR) matrices of the collocated multi–input\multi–output structure, before and after the presence of the damage, are used to examine how the system mass and stiffness matrices change. The relationship between the change in SDPRs and the change in the mass and stiffness matrices is shown. Because this technique computes only the SDPRs of the structure and does not need any costly computation used by methods in other research papers, this procedure could effectively be used for damage detection and health monitoring of instrumented structures. This method could also be used in on–line monitoring of structures in some recursive forms in order to detect and quantify the damage in a real time. This procedure is verified with some numerical examples in off–line and on–line processing times and encouraging results are reported.<\div>

۲On the Application of Impulsive Loads and Propagation of Waves in Thick FGM Plates
اطلاعات انتشار: بیستمین کنفرانس سالانه مهندسی مکانیک، سال
تعداد صفحات: ۴
This paper presents results of numerical study of impulsive loading types effects on the behaviour of elastic waves in thick functionally graded material plates. It is assumed that the material properties of the FGM plate have a simple power–law distribution function in the thickness direction in terms of the volume fractions of the constituents. Based on Reddy’s third order shear deformation plate theory (TSDT) for FGM plates and using Fourier transform and modal analysis, plate transverse displacement responses are obtained. It is shown that the type of impulse changesthe pattern of transient waveforms in plates, significantly. For this purpose, two common types of impulsive excitations, half and full cycle sine pulses, are applied as the acoustic wave sources and the differences of results are compared illustratively<\div>

۳Wave Propagation in Thick FGM Plates on Elastic Foundations
اطلاعات انتشار: بیستمین کنفرانس سالانه مهندسی مکانیک، سال
تعداد صفحات: ۴
The present paper addresses the propagation of acoustic waves due to point impact loading in thick functionally graded material plates resting on elastic foundations. Material properties are assumed to vary in the thickness direction of the plate and have a simple power–law distribution of the volume fractions of the constituents. The effects of elastic foundations on the propagation of flexural waves in thick FGM plates are studied whilethe governing equations are based on the Reddy’s thirdorder shear deformation plate theory (TSDT). Twoparameter Pasternak foundation is used from which results for one–parameter Winkler foundation are obtained as a limiting case. Spatial Fourier transform and modal analysis are employed to obtain the plate waveforms. It is observed that the foundation plays a major role in changing the behaviour of elastic waves in thick FGM plates.<\div>

۴Free vibration of multidirectional functionally graded circular clamped plate
اطلاعات انتشار: بیستمین کنفرانس سالانه مهندسی مکانیک، سال
تعداد صفحات: ۴
In this paper free vibration of multidirectional functionally graded (FG) circular plates is studied based on three–dimensional elasticity equations. It is assumed that the mechanical properties of this plate vary along the thickness and the radial directions. The vibration problem is solved by a semi–analytical\numerical method. The analytical state–space method is used to solve the problem in thickness direction and the numerical differential quadrature method is applied in radial direction. The results of present study are compared by the results in the literatures. The dimensionless frequencies and corresponding mode shapes are obtained and the influences of different parameters on the natural frequencies are demonstrated<\div>

۵Wave Propagation in Thin FGM Plates on Elastic Foundation
اطلاعات انتشار: نهمین کنگره بین المللی مهندسی عمران، سال
تعداد صفحات: ۸
The present paper investigates the transient wave behaviour in functionally graded plates resting on a two–parameter elastic foundation The elastic wave is due to point impact loading. The plat materialproperties change continuously through the thickness of the plate according to a simple power lawdistribution in terms of the volume fractions of the constituents The Classical and first order shear deformation theories of plates are employed. Therefore, the analysis is limited to thin plates Fouriertransform and modal analysis are used to obtain the dynamic response. The effects of the elastic foundation on the wave motion for FGM plates are studied. In addition, the waveforms are compared with the problem of Winkler foundation as a limiting case<\div>

۶De–noising and compression of SHM signals with wavelet transform
اطلاعات انتشار: دومین کنفرانس بین المللی آکوستیک و ارتعاشات، سال
تعداد صفحات: ۸
Structural Health Monitoring (SHM) signals usually are recorded with noise. Moreover, in some applications, saving the extracted signals is of great importance. Thus de–noising and compression of SHM signals is of great importance. Wavelet transform is one of the most popular tools for de–noising and compression of SHM signals. In this work, de–noising and compression of SHM signals, based on wavelet transform, are studied. A steel beam is used as the experiment structure. A saw–cut slot is created in the middle of the beam as damage. Several signals are captured by means of Piezoelectric Wafer Active Sensors (PWAS) as the experimental signals. Furthermore, simulation signals are computed using Finite Element Method (FEM) simulations. The signals are de–noised with Discrete Wavelet Transform (DWT) by means of different wavelets. Furthermore, simulation and de–noised experimental signals are compressed using Wavelet Packet Transform (WPT) by means of different orthogonal and bi–orthogonal wavelets. In both, de–noising and compression subjects, bi–orthogonal wavelets show better efficiency than the orthogonal ones. The results indicate that in low noisy signals, SNR of the de–noised signal by means of bi–orthogonal wavelets is almost 10–15dB better than SNR of the de–noised signal by means of orthogonal wavelets. Also, with the same retained energy parameter in compressed signals, numbers of coefficients that converted to zero, in compression by means of bi–orthogonal wavelets are almost 0.5–1% more than similar numbers in compression by means of orthogonal wavelets<\div>

۷Damage detection by wavelet packet transform and multiclass SVM in structural health monitoring applications
اطلاعات انتشار: دومین کنفرانس بین المللی آکوستیک و ارتعاشات، سال
تعداد صفحات: ۸
In recent years, guided ultrasonic wave (GUW) technique has been widely used for detecting different damage types in aerospace, mechanical, and civil engineering structures. In this study, a feature extraction and pattern recognition algorithm based on wavelet packet transform (WPT) and multiclass support vector machines (SVM) is proposed to detect existence and severity of damage in a structural beam. A prismatic beam is simulated in healthy and damaged conditions and the corresponding signals are captured from finite element method (FEM) simulations. The damage is a slot having several depths, located in several positions in the beam. The computed signals from FEM simulations are decomposed by WPT. Then, statistical features of the decomposed signals are extracted. A multiclass SVM classifier is used to classify the conditions of simulation signals into four classes: healthy condition, low, medium and high severity damage conditions. By using 43 signals for training the classifier, it can classify 8 test signals into 4 condition classes perfectly. The performance of the SVM classifier is compared with two different artificial neural network (ANN) classifiers. The ANN classifier that has more hidden neurons can classify the damage conditions perfectly; however, another classifier can classify only 6 signals into correct conditions. Moreover, performance of the introduced algorithm is better than some other feature extraction algorithms including: WPT node energies and the statistical features algorithm<\div>

۸Free vibration of undamped Euler–Bernoulli and Timoshenko beams by using spectral finite element method for different boundary conditions
اطلاعات انتشار: اولین کنفرانس سراسری توسعه محوری مهندسی عمران، معماری، برق و مکانیک ایران، سال
تعداد صفحات: ۱۰
This paper describes spectral finite element (SFE) formulation and solution for free vibration of Euler–Bernoulli and Timoshenko beams. Formulation based on SFE method includes partial differential equations of motion, spectral displacement field, dynamic shape functions, and dynamic stiffness matrix. Dynamic shape functions in frequency–domain are derived from the exact solution of governing wave equations. By considering free vibration of Euler–Bernoulli and Timoshenko beams, natural frequencies for different boundary conditions (simply–supported, clamped and cantilever beams) are derived. In the SFE model, whole length of beam is represented by one or two spectral elements and in finite element (FE) model, total number of finite elements is varied in order to improve its solutions. The accuracy of results obtained from SFE formulation is compared with those of FE method and analytical formulations, whenever available. The SFE results display remarkable superiority compared to FE results in reducing number of elements as well as increasing numerical accuracy.<\div>

۹Using spectral finite element method for time domain analysis of Timoshenko beam under concentrated impulse load
اطلاعات انتشار: اولین کنفرانس سراسری توسعه محوری مهندسی عمران، معماری، برق و مکانیک ایران، سال
تعداد صفحات: ۷
In this article, FFT–based spectral finite element (FSFE) is formulated for time domain analysis of Timoshenko beam subjected to a concentrated impulse load. The formulation of FSFE for a structure element is fairly similar to the formulation of the conventional finite element (FE) models. However, the major difference is that in general FSFE formulation begins with transforming the time domain governing partial differential equations of motion into the frequency domain ordinary differential equations by using the FFT. Then, exact dynamic stiffness matrix called the spectral element matrix is finally formulated by using the force–displacement relation method. Global system equation can be obtained after assembling all spectral elements and imposing associated boundary conditions on the assembled set of equations, like FE method. Finally, solution of the assembled global system equation map to time by applying inverse FFT (or IFFT). FSFE method in contrast to FE method can give exact solution without the need to divide the structure member into many finite elements. The high accuracy of FSFE model is then evaluated by comparing its results with those of FE model results.<\div>

۱۰A finite element model for extension and shear modes of piezo–laminated beams based on von Karman's nonlinear displacement–strain relation
اطلاعات انتشار: Journal of Theoretical and Applied Vibration and Acoustics، دوم،شماره۱، Winter & Spring ۲۰۱۶، سال
تعداد صفحات: ۳۰
Piezoelectric actuators and sensors have been broadly used for design of smart structures over the last two decades.Different theoretical assumptions have been considered in order to model these structures by the researchers. In this paper, an enhanced piezolaminated sandwich beam finite element model is presented. The facing layers follow the Euler–Bernoulli assumption while the core layers are modeled with the third–order shear deformation theory (TSDT). To refine the model, the displacement–strain relationships are developed by using von Karman's nonlinear displacement–strain relation. It will be shown that this assumption generates some additional terms on the electric fields and also introduces some electromechanical potential and non–conservative work terms for the extension piezoelectric sub–layers. A variational formulation of the problem is presented. In order to develop an electromechanically coupled finite element model of the extension\shear piezolaminated beam, the electric DoFs as well as the mechanical DoFs are considered. For computing the natural frequencies, the governing equation is linearized around a static equilibrium position. Comparing natural frequencies, the effect of nonlinear terms is studied for some examples.
نمایش نتایج ۱ تا ۱۰ از میان ۱۰ نتیجه