جستجوی مقالات مرتبط با کلیدواژه "آنالیز مودال" در نشریات گروه "عمران"

Operational modal analysis typically requires the physical attachment of a sensor to measure the structure vibration. As a non-contact method, digital cameras are relatively inexpensive, fast, and providing high spatial resolution results. The aim of this study is to identify the dynamic parameters of structures (frequency and damping ratio) by using video measurement (output only) based on the phase. For this purpose, it was only used mobile smartphones to identify modal parameters. The accelerometer sensor in the 3 attached smartphones was used to extract vibrational information. Video recorded by another mobile smartphone simultaneously identifies the dynamic parameters. In video measurement, the steerable pyramid transform is applied to frames that were extracted from the video to identify the local phases encoded in the image. After that, blind source separation (complexity pursuit) and single value decomposition techniques were applied to the image phase. Frequencies and damping ratios are extracted by the Fourier transform and logarithmic reduction technique. Thus, to validate the proposed method, two samples of 3D wall sandwiches panel, including a concrete sample and a straw sample that were already loaded and their stiffness was reduced by an average of 90%, were used. The results showed that the proposed method was able to extract the frequencies and damping ratios of the panels with an error of less than 2%.

Damage to structures is inevitable. Besides, the accumulation and spread of local damage can be a source of global damage; hence, the significance and necessity of monitoring the health of the structure. Wavelet analysis of structural responses is a method of damage detection with optimal performance in the time-frequency domain, which yields more information from the analyzed response of the structure in both time and frequency domains. As beams and columns are among the most fundamental structural elements and, expectably, the last elements to be damaged, it bears greater importance to identify damage in them than in other structural elements. This paper draws on modal analysis data of steel beams modeled in Abacus and a proposal of the wavelet analytical method to track different positions of damage along the beam, where the damages are defined as a decrease in the elastic modal. A decreasing shift in frequency values occurred in all modes due to damage. To detect the damage, the mode shape signal was defined as the damage mode shape and the differentiation between the healthy and the damage mode shapes as the wavelet transform input signal. The output signals from the wavelet analysis of the input signal indicated maximum and minimum relative fluctuations in different situations of damage so that the centers of damage were identified with zero error. The results also revealed that with increasing the severity of the damage, only the irregularity of the wavelet coefficients of that damage position increases.

Nowadays, maintenance and health monitoring of structures and infrastructures of the country are the top priority of engineers. Therefore, acceleration sensors, which are installed on the bridge are used to extract the bridge's modal response, and even the latest studies have shown that sensors that have been attached to the car's chassis can record the bridge's response to vibration. Thus, it is important to use an accurate method, which is based on the output-only, to measure frequency, damping ratio, and mode shape. As a result, practical modal analysis is used for that purpose. In this paper, a new method of blind source separation, called complexity pursuit (CP), is investigated which is able to measure and extract dynamic characteristics in the time domain. Complexity pursuit is a well-known method, that is able to recover hidden sources (independent responses of every degree of freedom) and it can calculate the mixing matrix from measured mixed output data only. Some various conditions are considered in this paper to verify complexity pursuit (3 degrees of freedom mass-spring with various damping ratios, in white Gaussian noise conditions, in non-diagonal damping matrix, close modes, and for 12 degrees of freedom mass-spring system). Comparison of the CP results and modal analysis under all the conditions showed that the proposed method is able to detect, measure and extract the modal characteristics with an error of less than 3% and in most cases less than 1%.

Regarding the importance of bridges as one of the most critical infrastructures, their maintenance, and health monitoring is of high priority. Interaction between the moving vehicles and bridges is amongst the fields of study that have been investigated in depth by numerous researchers in the field of bridge engineering. Among different proposed methods of structural health monitoring of bridges, the indirect methods that do not need the healthy structure response are of high interest because of their ease and low maintenance costs.
The response of a moving mass passing through a bridge can be analyzed for the indirect prediction of the beamchr(chr('39')39chr('39'))s mechanical properties. This can lead to the detection of possible damages or degradations in the structure. By mounting high precision accelerometers on the moving vehicle and recording the corresponding signals, it is possible to capture the sudden change of mechanical properties pertaining to the existence of damage in the bridge.
In the current study, an FE code is developed in order to analyze the moving vehicle response. In this code, the bridge is modeled as an Euler-Bernoulli beam, and a complete model comprising stiffness and damping of the suspension system of moving vehicle is built. In order to verify the results of the code, comparisons are made with the outcomes of modal analysis. The sensitivity of the FE results with respect to the number of elements is examined. These comparisons clearly show that both methods reach the same values for a sufficiently high number of elements for the moving vehicle response.
Following verification of the code, a brief review of the concepts underlying the variational mode decomposition (VMD) method is given for a self-contained representation. The VMD can be used to decompose a signal into a number of signals with limited bandwidth. Although it has found many applications in different signal processing cases (e.g. in the field of electronics, mechanical vibrations of machines, or even in the analysis of economic and financial time series), extending its application to the field of structural health monitoring is entirely a recent and ongoing topic of research.
After the introduction of the VMD, damage in the beams is implemented by using fracture mechanics concepts. Different damage scenarios are applied in order to check the reliability and robustness of using VMD as a damage detection method. These include different damage locations (single, dual) and damage severity represented in terms of crack depth. By having a reliable means for the analysis, the novel variational mode decomposition (VMD) is applied to analyze the signals recorded from the vehiclechr(chr('39')39chr('39'))s back axel in search of any possible irregularity in the signal properties. By monitoring results attained for several damage cases, the following conclusions can be given:• The variational mode decomposition (VMD) can highlight the presence of irregularities in mechanical properties that can be reached directly from decomposed signals.
• The location of these signal irregularities coincides with the presumed location(s) of the crack(s).
• The severity of the signal irregularity and corresponding instantaneous energy is proportional to the degree of damage imposed on the beam. 
• The moving vehiclechr(chr('39')39chr('39'))s natural frequency plays an essential role in the bridgeschr(chr('39')39chr('39')) structural health monitoring. The signal processing results exhibit amplified abrupt changes for the vehicles with the natural frequencies close to the beamchr(chr('39')39chr('39'))s fundamental frequencies.  
Regarding the above conclusions, analyzing moving mass response with the VMD can be a reliable damage detection technique.

In this study, to investigate and compare the performance of the single mass damper in the maximum modal displacement (roof) and multiple mass dampers vertically distributed in the height of the structure, based on the modal analysis, two linear and nonlinear models of a 40-story structure were selected. The structure has been modeled in OpenSees software using seven acceleration time histories. The analysis results for applied earthquakes under the maximum acceleration of 1.0g show that the control of the linear structure by multiple tuned mass dampers (MTMDs) tuned to the first and second modes have more appropriate behavior than others, and the average reduction of the maximum displacement of the Roof applying this type of dampers is 14.5%, which is about 2 times more than reduction of the STMD tuned to the first mode and the MTMDs tuned to the first or second modes, systems. However, due to the assumption of tuning the design parameters of the dampers corresponding to their elastic behavior, the performance of single and multiple mass dampers slightly decreases in a nonlinear model of the structure while structural responses are still controlled. Also, for the 10% error caused by misadjusting of the dampers, the behavior of MTMDs is more appropriate.

Localized singularities caused by changes in the stiffness or mass of the damaged region cannot be simply visible through smooth mode shape curves. However, the wavelet transform of input signal can identify the location of defects by sudden changes in the spatial variation of transformed response. The aim of this study is to present a new method for damage detection in a squarely damaged plate with element of reduced thickness with damage ratio 3% and to decrease the possible random noises that are come from different sources such as numerical solutions or physical situation. In this approach, the value of each point of mode shape data is subtracted from or is added with its symmetric point with respect to the plate’s point of symmetry (point O). The obtained value is located at its first point, again. The result of this process is a symmetrical mode shape matrix of the damaged plate, which is utilized as the input signal function in wavelet analysis.The results demonstrated that using reconstructed modal data is superior to the original modal data and they provide a better crack indicator than the result of the DWT of the original mode shape data. The effects of crack location and sampling interval are examined. The simulated results show that this approach is more effective in damage detection of plate-like structures, as the method requires the knowledge of only the response of the damaged plate as a baseline for crack detection.

The retrofitting of concrete columns by using FRP fiber for strength and ductility is taken into consideration. Recent studies have shown that confined concrete with FRP shows different behavior comparing when confined with steel; therefore, the need for research on concrete columns reinforced with FRP is clear. In this study, finite element analysis and modeling by using finite element software are used to investigate the behavior of columns reinforced with GFRP fibers. Model verification is performed by using the results of laboratory study, and the good agreement between test results and finite element modeling is observed. The next step is to examine the parameters of compressive strength of concrete and column shapes in behavior of reinforced column with FRP. The results in terms of vertical displacement-force Graphs and buckling, are extracted and compared.The deterioration of the nation's infrastructure has been well documented and publicized FRP composites have emerged as a potential solution to the problems associated with the infrastructure. An economic application of FRP materials is in the form of composite construction with concrete, such that FRP can act as a load-carrying partner and protective measure for the structural members. One such application has been demonstrated in fiber jacketing technique, which is now considered as an effective retrofitting tool for the existing columns. By using the principles of fiber-wrapping and steel-jacketing practice, classic steel-concrete composite columns, FRP pressure vessels, and steel-encased plastic piles, a novel type of composite column is proposed that consists of a reinforced concrete core confined in a FRP tubular jacket. The main advantage of FRP-concrete composite construction is the optimal use of materials based on their mechanical properties and resistance to corrosive composite members with pseudo ductile characteristics and high stiffness and strength properties.The composite shell may be a multi-layer FRP tube that consists of at least two plies: an inner ply of longitudinal fibers and an outer ply of circumferential fibers. The longitudinal fibers are inhibited from outward buckling by the outer circumferentially oriented fiber ply and from inward buckling by the concrete core. Similar tubes have been made with a center ply of longitudinal fibers sandwiched between two plies of circumferential fibers.

Natural occurrences, such as earthquake and wind, cause damages to structures (e.g., buildings and bridges) through enforcing extreme loads. Consequently, they might result in catastrophic structural collapse and failures. Most importantly, this brings the necessity of safety assessment of the structures, especially of the large concrete dams affecting the lives of many on the downstream of a dam. Hence, it is required to develop a damage detection system able to recognize the cracks or discontinuity on the dam before they start to propagate. To this end, the Structural Health Mentoring (SHM) process should be adopted to control and keep the structures safe. This safety system will provide with the possibility to detect the damages quickly so that the engineers will be more capable of doing safety operation in terms of maintenance and repairing of structures. Wavelet transform was introduced as an efficient SHM process to achieve the objective of damage detection. This approach can extract hidden information from the obtained results of structural analysis. In this research, using wavelet transform, the static and model analysis of the Koyna gravity dam was done, and the supposed cracks were identified. The obtained results showed that during the damage detection process based on the static data, factors such as vicinity of the crack to the location of sample points were found to be affecting the wavelet coefficients. On the contrary, the modal analysis indicated that the aforementioned relation would not be revealed, and the damage could be properly detected over the regions with high expectation of failures. It was observed that the height of the dam reservoir in the static analysis was not affected to accurately identify damages by the wavelet transform. In addition, the results including the effect of damages under higher modes and multiple cracks during the damage detection process were thoroughly explained and clarified.

O‌v‌e‌r t‌h‌e p‌a‌s‌t f‌e‌w d‌e‌c‌a‌d‌e‌s, t‌h‌e m‌e‌t‌h‌o‌d‌s o‌f d‌a‌m‌a‌g‌e d‌e‌t‌e‌c‌t‌i‌o‌n i‌n c‌i‌v‌i‌l a‌n‌d m‌e‌c‌h‌a‌n‌i‌c‌a‌l s‌t‌r‌u‌c‌t‌u‌r‌e‌s h‌a‌v‌e d‌r‌a‌w‌n m‌u‌c‌h a‌t‌t‌e‌n‌t‌i‌o‌n f‌r‌o‌m v‌a‌r‌i‌o‌u‌s f‌i‌e‌l‌d‌s i‌n s‌t‌r‌u‌c‌t‌u‌r‌a‌l h‌e‌a‌l‌t‌h m‌o‌n‌i‌t‌o‌r‌i‌n‌g (S‌H‌M) s‌y‌s‌t‌e‌m‌s. S‌t‌r‌u‌c‌t‌u‌r‌a‌l h‌e‌a‌l‌t‌h m‌o‌n‌i‌t‌o‌r‌i‌n‌g (S‌H‌M) i‌s r‌e‌l‌a‌t‌e‌d t‌o d‌a‌m‌a‌g‌e m‌o‌n‌i‌t‌o‌r‌i‌n‌g, w‌i‌t‌h o‌p‌e‌r‌a‌t‌i‌o‌n‌a‌l l‌o‌a‌d‌s p‌l‌a‌y‌i‌n‌g a s‌i‌g‌n‌i‌f‌i‌c‌a‌n‌t r‌o‌l‌e i‌n t‌e‌r‌m‌s o‌f f‌a‌t‌i‌g‌u‌e l‌i‌f‌e a‌n‌d d‌a‌m‌a‌g‌e a‌c‌c‌u‌m‌u‌l‌a‌t‌i‌o‌n p‌r‌o‌g‌n‌o‌s‌t‌i‌c‌s. M‌a‌n‌y d‌i‌f‌f‌e‌r‌e‌n‌t t‌e‌c‌h‌n‌i‌q‌u‌e‌s, l‌i‌k‌e a‌c‌o‌u‌s‌t‌i‌c e‌m‌i‌s‌s‌i‌o‌n, u‌l‌t‌r‌a‌s‌o‌n‌i‌c, a‌c‌o‌u‌s‌t‌o-u‌l‌t‌r‌a‌s‌o‌n‌i‌c, g‌u‌i‌d‌e‌d u‌l‌t‌r‌a‌s‌o‌n‌i‌c w‌a‌v‌e‌s o‌r L‌a‌m‌b w‌a‌v‌e‌s, a‌r‌e n‌o‌w‌a‌d‌a‌y‌s i‌n‌v‌e‌s‌t‌i‌g‌a‌t‌e‌d i‌n t‌e‌r‌m‌s o‌f e‌f‌f‌i‌c‌i‌e‌n‌t a‌n‌d u‌s‌e‌r-f‌r‌i‌e‌n‌d‌l‌y d‌a‌m‌a‌g‌e i‌d‌e‌n‌t‌i‌f‌i‌c‌a‌t‌i‌o‌n s‌y‌s‌t‌e‌m‌s. T‌h‌i‌s p‌a‌p‌e‌r p‌r‌o‌p‌o‌s‌e‌s a n‌e‌w a‌p‌p‌r‌o‌a‌c‌h f‌o‌r d‌a‌m‌a‌g‌e d‌e‌t‌e‌c‌t‌i‌o‌n i‌n s‌t‌r‌u‌c‌t‌u‌r‌e‌s w‌i‌t‌h m‌i‌n‌o‌r d‌a‌m‌a‌g‌e i‌n t‌h‌e e‌a‌r‌l‌y g‌r‌o‌w‌t‌h s‌t‌a‌g‌e‌s. W‌a‌v‌e‌l‌e‌t a‌n‌a‌l‌y‌s‌i‌s, a r‌e‌l‌a‌t‌i‌v‌e‌l‌y n‌e‌w m‌a‌t‌h‌e‌m‌a‌t‌i‌c‌a‌l t‌o‌o‌l, h‌a‌s b‌e‌e‌n u‌s‌e‌d i‌n‌c‌r‌e‌a‌s‌i‌n‌g‌l‌y i‌n r‌e‌c‌e‌n‌t y‌e‌a‌r‌s. T‌h‌i‌s r‌a‌t‌h‌e‌r n‌e‌w m‌e‌t‌h‌o‌d h‌a‌s b‌e‌e‌n a‌p‌p‌l‌i‌e‌d t‌o v‌a‌r‌i‌o‌u‌s f‌i‌e‌l‌d‌s i‌n‌c‌l‌u‌d‌i‌n‌g c‌i‌v‌i‌l, m‌e‌c‌h‌a‌n‌i‌c‌a‌l a‌n‌d ‌e‌r‌o‌s‌p‌a‌c‌ee‌n‌g‌i‌n‌e‌e‌r‌i‌n‌g. D‌a‌m‌a‌g‌e d‌e‌t‌e‌c‌t‌i‌o‌n i‌n e‌a‌r‌l‌y s‌t‌a‌g‌e‌s i‌s v‌e‌r‌y c‌r‌u‌c‌i‌a‌l i‌n e‌n‌g‌i‌n‌e‌e‌r‌i‌n‌g s‌t‌r‌u‌c‌t‌u‌r‌e‌s. A‌l‌m‌o‌s‌t a‌l‌l p‌r‌o‌p‌o‌s‌e‌d m‌e‌t‌h‌o‌d‌s, s‌o f‌a‌r, r‌e‌l‌y m‌e‌r‌e‌l‌y o‌n c‌o‌m‌p‌a‌r‌i‌s‌o‌n o‌f t‌h‌e s‌t‌r‌u‌c‌t‌u‌r‌a‌l b‌e‌h‌a‌v‌i‌o‌r o‌f t‌h‌e p‌r‌e‌s‌e‌n‌t s‌t‌r‌u‌c‌t‌u‌r‌e w‌i‌t‌h t‌h‌a‌t o‌f t‌h‌e o‌r‌i‌g‌i‌n‌a‌l i‌n‌t‌a‌c‌t s‌t‌r‌u‌c‌t‌u‌r‌e. H‌o‌w‌e‌v‌e‌r, t‌h‌i‌s m‌e‌t‌h‌o‌d i‌s n‌o‌t a‌l‌w‌a‌y‌s a‌p‌p‌l‌i‌c‌a‌b‌l‌e, a‌s e‌i‌t‌h‌e‌r t‌h‌e b‌e‌h‌a‌v‌i‌o‌r o‌f t‌h‌e o‌r‌i‌g‌i‌n‌a‌l s‌t‌r‌u‌c‌t‌u‌r‌e i‌s n‌o‌t a‌v‌a‌i‌l‌a‌b‌l‌e, i‌n m‌o‌s‌t c‌a‌s‌e‌s, o‌r t‌h‌e i‌m‌p‌a‌c‌t o‌f d‌a‌m‌a‌g‌e i‌s t‌o‌o n‌e‌g‌l‌i‌g‌i‌b‌l‌e i‌n t‌h‌e e‌a‌r‌l‌y s‌t‌a‌g‌e‌s t‌o b‌e i‌d‌e‌n‌t‌i‌f‌i‌e‌d. T‌h‌e n‌e‌w‌l‌y i‌n‌t‌r‌o‌d‌u‌c‌e‌d m‌e‌t‌h‌o‌d o‌f W‌a‌v‌e‌l‌e‌t A‌n‌a‌l‌y‌s‌i‌s h‌a‌s o‌v‌e‌r‌c‌o‌m‌e t‌h‌e‌s‌e p‌r‌o‌b‌l‌e‌m‌s, a‌s i‌t d‌o‌e‌s n‌o‌t r‌e‌q‌u‌i‌r‌e d‌a‌t‌a o‌f t‌h‌e i‌n‌t‌a‌c‌t s‌t‌r‌u‌c‌t‌u‌r‌e. T‌h‌e m‌e‌t‌h‌o‌d u‌t‌i‌l‌i‌z‌e‌s e‌x‌p‌e‌r‌i‌m‌e‌n‌t‌a‌l m‌o‌d‌e s‌h‌a‌p‌e‌s o‌b‌t‌a‌i‌n‌e‌d f‌r‌o‌m d‌a‌t‌a a‌c‌q‌u‌i‌s‌i‌t‌i‌o‌n s‌y‌s‌t‌e‌m‌s. T‌h‌e‌n, w‌i‌t‌h a m‌a‌t‌h‌e‌m‌a‌t‌i‌c‌a‌l t‌r‌a‌n‌s‌f‌o‌r‌m‌a‌t‌i‌o‌n, t‌h‌e d‌i‌s‌c‌o‌n‌t‌i‌n‌u‌i‌t‌i‌e‌s o‌f t‌h‌e m‌o‌d‌e s‌h‌a‌p‌e‌s, w‌h‌i‌c‌h a‌r‌e n‌o‌r‌m‌a‌l‌l‌y v‌e‌r‌y n‌e‌g‌l‌i‌g‌i‌b‌l‌e, a‌r‌e h‌i‌g‌h‌l‌i‌g‌h‌t‌e‌d a‌n‌d, t‌h‌e‌r‌e‌f‌o‌r‌e, e‌a‌s‌i‌l‌y i‌d‌e‌n‌t‌i‌f‌i‌e‌d. T‌h‌r‌o‌u‌g‌h‌o‌u‌t t‌h‌e p‌r‌e‌s‌e‌n‌t s‌t‌u‌d‌y, t‌h‌e a‌p‌p‌l‌i‌c‌a‌b‌i‌l‌i‌t‌y o‌f t‌h‌e m‌e‌t‌h‌o‌d f‌o‌r t‌h‌r‌e‌e t‌y‌p‌e‌s o‌f s‌t‌r‌u‌c‌t‌u‌r‌e, i‌n‌c‌l‌u‌d‌i‌n‌g a s‌i‌m‌p‌l‌e b‌e‌a‌m, a f‌r‌a‌m‌e a‌n‌d a s‌u‌s‌p‌e‌n‌d‌e‌d c‌a‌b‌l‌e b‌r‌i‌d‌g‌e, i‌s v‌e‌r‌i‌f‌i‌e‌d. T‌h‌e o‌b‌t‌a‌i‌n‌e‌d r‌e‌s‌u‌l‌t‌s s‌h‌o‌w t‌h‌e g‌r‌e‌a‌t p‌o‌t‌e‌n‌t‌i‌a‌l o‌f t‌h‌e m‌e‌t‌h‌o‌d i‌n d‌i‌s‌c‌e‌r‌n‌m‌e‌n‌t o‌f d‌a‌m‌a‌g‌e l‌o‌c‌a‌t‌i‌o‌n w‌i‌t‌h g‌r‌e‌a‌t a‌c‌c‌u‌r‌a‌c‌y.

Modal analysis, a recognized subject in civil engineering and mechanics and its applications in other engineering disciplines are developing every day. Modal analysis primarily is used to assess and measure vibrations in structures. It has a diverse applications including detection of damage in structures, monitoring structural health, evaluation of bearing capacity of structures and etc. In this paper, the evolution of empirical modal analysis of evolution and its application in road structures, (especially bridges) are presented. Also, the principal methods of identifying modal input - output and output techniques are introduced. This paper reviewed several reports and experiences of researchers in the laboratory of vibrations and structures’ monitoring in the University of Porto (Portugal).

Most structural failures are because of break in consisting materials. These breaks are initiated with crack extension, which is a serious threat to the behavior of structure, so different methods have been developed for distinguishing and showing such cracks. Meanwhile, the new methods based on original wavelet transform are efficient and very important in the subject of signals. The main aim of this paper is to fin the methods capable of distinguishing the specifications of cracks practically. first a modal analysis of the structure was For this purpose, performed using ANSYS software, Then the structure was analyzed as original wavelet using the wavelet toolbox of MATLAB software the results are shown in two dimensional charts of coefficient-position.

Determining the responses of floating structures the sea are the most important concerns in shipbuilding industry. In physical and dynamical principles a ship can be analyzed as a free elastic beam floating in sea without any supports. The analysis of corresponding dynamic equations are difficult and time-consuming, thus investigation on the behavior of floating structures can be done numerically using specific software. In this research, instead of using expensive specific software, ANSYS 5.5 as a typical finite element software is used for investigating the effect of various parameters on an assumed floating structure. In this way, after structural modal analysis, modeling and analysis of the structure with variation on its properties under different sea environment have been done and the responses are illustrated Amid-ship moment is one of the most important and effective parameters in ship design. In this paper, due to different ship speed and stiffness of cross section, amid-ship moment beside the shear force of various cross section along the ship are considered and the critical shear cross section is determined.