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Operational modal analysis (OMA) is required to maintain large-scale and necessary civil infrastructures. The non-contact method of OMA using digital image correlation and point tracking algorithms requires a speckle pattern placed on the structure. Alternatively, advanced computer vision methods like optical flow and phase-based video motion magnification (PBVMM) techniques are used to measure modal parameters. Despite the importance of PBVMM, the users should know the range of frequencies in which the natural structure frequency lies. A methodology based on an unsupervised machine learning technique is developed to extract the modal parameters blindly from its recorded digital video. The proposed methodology uses complex steerable pyramids and an unsupervised machine learning technique, also known as principal component analysis, and analytical mode decomposition with a random decrement technique to blindly extract the modal parameters of a structure. This study validated the proposed methodology using a multi-degree of freedom (DOF) numerical model. The results are compared with theoretical and estimated values and are in good agreement. Furthermore, it is implemented on a laboratory benchmark SDOF, MDOF, and real-time videos of the London Millennium and Tacoma Narrows bridges for blindly extracting the modal frequencies and damping ratios. [ABSTRACT FROM AUTHOR]

This study employs advanced techniques, namely the improved multi-synchrosqueezing transform (IMSST) and the Fouriersynchrosqueezed transform (FSST), to extract the instantaneous frequency of the Humber Bridge, in the UK, in operational conditions. First, a brief overview of the relevant theories behind the techniques used is provided. These techniques are then applied to track the instantaneous frequencies within the monitored vertical acceleration data of the bridge. The instantaneous frequencies extracted by both techniques are verified against each other. The investigation further encompasses the development of three distinct regression models: a simple regression model, an expanded regression model and a regression model based on principal component analysis (PCA). The efficacy of the PCA-based model is scrutinised by generating and testing datasets that mirror the monitored data, with the Kolmogorov-Smirnov (KS) test confirming theirvalidity. The findings of this research indicate a statistically significant inverse relationship between modal frequency and acceleration intensity. Furthermore, by incorporating wind effect considerations into the regression analysis, the R-squared values in both the expanded and PCA-based models exhibit substantial improvements. This demonstratesthe performance of the enhanced model in capturing the dynamics of the bridge. The robustness of the PCA-based model is furthercorroborated by its performance during testing, proving its potential as a reliable tool in structural health monitoring (SHM). [ABSTRACT FROM AUTHOR]

Copyright of Journal of Railway Science & Engineering is the property of Journal of Railway Science & Engineering Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Chinese Journal of Computational Mechanics / Jisuan Lixue Xuebao is the property of Chinese Journal of Computational Mechanics Editorial Office, Dalian University of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Chinese Journal of Applied Mechanics is the property of Chinese Journal of Applied Mechanics Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The use of tuned liquid dampers (TLDs) as an alternative to reduce the response of flexible structures with a low amount of structural damping is a viable option. The correct characterization of the dynamic properties of the TLD plays an important role in the performance of the TLD-main structure system. This work presents the results of an experimental study to evaluate the dynamic properties of a scaled rectangular TLD using high-speed videos. For the experimental investigation, a scaled rectangular TLD is subjected to lateral displacement of the sinusoidal type with amplitudes that range from 5 to 40 mm and frequency equal to 0.625 Hz. The dynamic properties of the TLD system are identified with the use of high-speed videos with a duration of 28.96 s and recorded at 500 frames per second (fps). The recorded videos are analyzed with the software Tracker to extract time histories of wave elevation at predefined locations. The frequency and damping of the TLD system are identified from the time histories of wave elevation through Fourier analysis and free-vibration decay. The findings of this study revealed that the identified dynamic properties of the TLD by using high-speed videos presented small differences with respect to the target values, with errors that range from 0.93 to 2.9% for frequency and from 1.6 to 8.8% for damping, indicating that the use of high-speed videos can be an alternative to evaluate the dynamic properties of TLD systems. [ABSTRACT FROM AUTHOR]

Purpose: The real-time dynamics of the single-link flexible manipulator is a challenging problem due to its inherent instability and in situ vibration. In order to add the criticalities to these real-time dynamics, run-time vibration does play a pivotal role in designing a robust control system for the flexible robotic manipulator. Methodology: Governing differential equations and the boundary conditions are usually considered exact of the single-link manipulator and the formulation leads to an Eigenvalue problem where the elements of the matrices are in exact form. Double parametric form has been used to solve the fuzzy differential equation. Results and Conclusions: In this paper, a new idea has been introduced in the above problem for a representative single-link robotic manipulator considering the uncertainty in the associated parameter(s) in the governing differential equation, which may mimic the actual scenario of the real environment. The uncertainty has been considered in terms of a novel fuzzy model which agrees with the crisp case model too. [ABSTRACT FROM AUTHOR]

The energy amplification factor transmitted from the excitation source to the response end cannot be identified quickly and accurately using the method of obtaining modal frequency combined with damping through modal frequency resonance. As a result, the above method cannot be used to further evaluate the effect of structural improvement. In this paper, a frequency difference sensitivity method is proposed in order to improve the efficiency of the above identification and evaluation processes while also guaranteeing accuracy. Firstly, a theoretical model suitable for the damping and rigid-body-mode frequency range of the cooling module is established according to the frequency difference between the excitation frequency,.system mode frequency, and vibration response sensitivity. Then, the accuracy and effect of the model are studied from the perspective of a simulation and experiment. The model can be used to identify and evaluate the resonance problem of the vehicle cooling module quickly and accurately. The energy amplification factor of the fan to the passive end of the cooling module can be efficiently predicted using the frequency difference sensitivity method proposed in this paper while ensuring accuracy. The quantized noise-reduction effect of the interior before and after the improvement can be efficiently predicted and evaluated using said model. The literature shows that the resonance of a vehicle cooling module can be identified and evaluated quickly and accurately via the frequency difference sensitivity method, which can overcome the problems that the conventional modal frequency resonance method encounters in identifying and evaluating quickly. [ABSTRACT FROM AUTHOR]

Purpose: Single walled carbon nanotubes (SWCNT) are materials described as nanoscale cylindrically shaped allotropes of carbon possessing high surface area and aspect ratio (length to diameter ratio) which makes them to be modelled as one-dimensional tubes. SWCNTs have superior mechanical properties, which makes them a primary filler in the polymer matrix to enhance its mechanical characteristics. This study aims to examine the longitudinal forced vibration of SWCNT embedded in elastic medium subjected to different types of axial loads such as uniform, linearly varying and sinusoidal. Methods: Formulation is considered based on Hamilton's principle and Eringen's nonlocal elasticity theory. Analytical solution is obtained based on variation of parameters to get modal frequencies, shapes and dynamic displacements within the nanotube. Results: Obtained frequency results are compared with those available in the literature and a high level of accuracy is achieved. Parametric analyses are carried out to examine the influences of elastic medium stiffness, nonlocal parameter and aspect ratio on mode shapes and dynamic displacements. Conclusion: Increase in the elastic medium stiffness leads to increase in the modal frequencies and this increase is greater for nanotubes with clamped-free (C-F) boundary conditions. Dynamic displacement value of the midpoint decreases as stiffness is increased at the same non-dimensional frequency. Change in modal frequency due to the increase in stiffness remains the same for different aspect ratios. The influence of nonlocal parameter on modal frequencies is the highest at smaller aspect ratios, which implies the necessity of the use of nonlocal elasticity theory at nano-scale vibration analysis. [ABSTRACT FROM AUTHOR]

The monitoring of bridges is a crucial operation for their structural health examination and maintenance. GNSS technology is one of the methods which are applied with the main advantage that the direct measurement of the bridge displacement is conducted in an independent global coordinate system. However, the high cost of the GNSS stations, which are consisted of dual-frequency receivers and geodetic GNSS antennas, is the main reason of the limited application of GNSS for bridge monitoring. In this study, we assessed the performance of low-cost multi-GNSS receivers in monitoring dynamic motion, similar to that of bridge response. The performance of the low-cost GNSS receivers was assessed based on controlled experiments of horizontal and vertical motion. For the horizontal motion, controlled experiments of circular motion of various predefined radius between 5 and 50 cm were executed where the low-cost GNSS receivers were assessed against dual-frequency geodetic receivers. For the vertical motion, manually controlled experiments of vertical oscillations of amplitude 8 and 15 mm were executed where the low-cost GNSS receivers were assessed against the Robotic Total Station (RTS). Finally, a low-cost monitoring system formed by two closely spaced low-cost GNSS receivers was applied in dynamic displacement monitoring of the Wilford Suspension Bridge. The analysis of the low-cost GNSS data revealed the beneficial contribution of (i) the multi-constellation on the accuracy and precision of the GNSS solution and (ii) the combination of closely spaced low-cost GNSS receivers, to limit potential cycle slips and the low-cost GNSS noise level and reach accuracy and precision similar to that of geodetic-grade GNSS receivers. This was confirmed in the bridge monitoring application, where the main modal frequency and the response amplitude of the bridge were identified successfully by the low-cost GNSS receivers' data analysis. [ABSTRACT FROM AUTHOR]

Bridge modal frequency is an important parameter reflecting its overall property change and widely used for bridge condition assessment. However, the effects of multiple environmental conditions on the modal frequency will mask the variation induced by structural damage. Traditional single regression models cannot quantify measurable and unmeasurable environmental effects simultaneously, resulting in poor prediction and separation performance. Therefore, a two-stage elimination model (TSEM) integrating regression analysis and trend decomposition technique was developed. Environmental principal components (PCs) sensitive to the single-order modal frequency were extracted based on partial least-squares analysis. To quantify the nonlinear effects of measurable environmental factors, the baseline predictor with respect to modal frequency and environmental PCs was constructed through relevance vector machine technology. An error compensation model based on singular spectrum analysis was established to extract trend-related components and remove the part of residual modal variability unknot considered by the baseline model. On this basis, exponential weighted moving average control chart was established to highlight slight abnormal changes in modal frequency. A cable-stayed bridge case verified its validity and accuracy. The results indicate that the proposed TSEM has better modeling, generalization, and separation performance than the baseline model, and the variation of normalized frequency tends to be more stable. Additionally, the significant differences of damage sensitivity of different orders were determined. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Natural Fibers is the property of Taylor & Francis Ltd and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In the present study, an attempt is made to replace the synthetic glass fiber used in the FRP structures in terms of natural flax fibers without much sacrifice on static and dynamic stability of the structure. Three types of glass/flax hybrid composite laminates were prepared with different fiber volume fraction of glass and flax fibers. For better understanding purpose, a dedicated glass and dedicated flax laminates were also fabricated. All the laminates were fabricated by vacuum bag molding method with uniform laminate thickness. The mechanical properties of the fabricated laminates, such as tensile strength and flexural strength, were evaluated in accordance with ASTM standards. The impulse excitation technique was used to assess the free vibration characteristics of glass/flax laminates such as modal frequency and material damping. Based on experimentally evaluated mechanical and vibration characteristics a suitable fiber volume fraction for the preferred laminate thickness was suggested to achieve optimum static and dynamic stability. [ABSTRACT FROM AUTHOR]

A method to estimate modal frequency based on empirical mode decomposition (EMD) and ensemble empirical mode decomposition (EEMD) is proposed. This method can decrease the difficulties in identifying modal frequency of combine harvesters. First, we used 16 acceleration sensors installed at different test points to collect vibration signals of a corn combine harvester under operating conditions (mass time-varying conditions). Second, we calculated mean value, variance and root mean square (RMS) value of the vibration signals, and analyzed its stationarity of vibration signals. Third, the main frequencies of the 16 points were extracted using the EMD and EEMD methods. Finally, we considered modal frequencies identified by the SSI algorithm as standard, and calculated the fitting degrees of the EMD and EEMD methods. The results show that in different time periods (0~60 s and 60~120 s), the maximum differences of the mean value, variance and RMS value of signals were 0.8633, 171.1629 and 11.3767, and the vibration signal under the operating condition of field harvesting can be regarded as a typical non-stationary random vibration signal. The EMD method had more modal aliasing than EEMD, and when we obtained the fitting equations of EMD, EEMD and SSI methods, the value of the Euler distance between the EMD fitting equation and the SSI fitting equation was 446.7883, while that for EEMD and SSI was 417.2845. The vibration frequencies calculated by the EEMD method is closer to the modal frequencies identified by SSI algorithm. The proposed method provides a reference for modal frequency identification and vibration control in a complex working environment. [ABSTRACT FROM AUTHOR]

Stay cables are crucial components in cable-stayed bridges. The time-varying cable tension is an important indicator for the condition assessment of cables because the variation in tension will cause fatigue damage. This paper proposes an adaptive identification method for time-varying cable tension based on an improved variational mode decomposition (VMD) algorithm. In the proposed method, the cable vibration signal is decomposed by improved VMD to identify the time-varying modal frequencies by the Hilbert transform, and then the time-varying cable tension is calculated by the vibration method. To realize adaptive and accurate identification, the VMD algorithm is improved by optimizing parameters: the number of decomposed modes is determined by the characteristic that frequency differences between the adjacent modal frequencies of the cable vibration signal are equal, and the balancing parameter is optimized by constructing an evaluation index and searching for the minimum of the index. A numerical simulation illustrates that the accuracy of the proposed method is satisfactory. To verify the practicability of the proposed method, the monitoring data of a single tower cable-stayed bridge are used. The results demonstrate that the proposed method is a practical and reliable method to identify the time-varying cable tension. [ABSTRACT FROM AUTHOR]

Structural health monitoring (SHM) has been widely used for the performance assessment of bridges, especially the methods based on dynamic characteristics. Meanwhile, bridge modal frequency is influenced significantly by environmental factors, such as temperature and humidity. Combined with SHM, a reliability assessment of bridges with the temperature and humidity effects eliminated is proposed. Firstly, the bridge deflection verification coefficient is adopted as the evaluation indicator for bridge condition, which is the ratio of deflection-measured value to deflection-calculated value. It is obtained from the relationship between verification coefficient and modal frequency through theoretical derivation. Secondly, a back propagation (BP) neural network is improved by using an artificial bee colony algorithm and employed as a surrogate model to eliminate the effect of temperature and humidity on frequency. Thirdly, a dynamic Bayesian network is applied to establish the reliability analysis model combined with the monitoring results, so that the probability distribution of bridge parameters is updated to improve the accuracy of the reliability analysis. Finally, a simply supported bridge is used as the case study, based on the proposed method in this work. The results indicate that the proposed method can eliminate the temperature and humidity effect on frequency precisely and effectively. With the effect of temperature and humidity on frequency eliminated, the bridge condition assessment can be evaluated accurately through the reliability analysis based on SHM and the dynamic Bayesian network. [ABSTRACT FROM AUTHOR]

In this study, the possibility of using the rail vibration frequency to assess the longitudinal temperature force on the rail of ballasted track was investigated experimentally. An empirical formula was subsequently derived to link the frequency index to multiple factors, including the longitudinal temperature force, under-rail stiffness, and fastener spacing. Further tests were conducted to analyse the applicability and accuracy of the frequency index in continuous longitudinal force measurements under different line conditions (i.e. in the non-expansion zone and expansion zone). A technique for using the frequency index to assess the longitudinal temperature force was finally developed. The main results are as follows. (1) The first-order pinned–pinned modal frequency and peak frequency of the mid-span response are very close, and they both change linearly with the longitudinal temperature force on the rail. The rate of change in the vertical direction is larger than that in the horizontal direction. (2) Even if influenced by multiple factors, the peak frequency of the rail mid-span response is suitable for continuous longitudinal temperature force assessment under appropriate measures, and longitudinal temperature force detection could be realized with proper preparation. (3) Using the mid-span response frequency to detect the temperature force of rail located in the expansion zone causes deviation of the results, and under-rail materials whose stiffnesses are insensitive to temperature help reduce this deviation. [ABSTRACT FROM AUTHOR]

Cylindrical roller bearing is an important component of the airflow root blower of a power generation plant, and its malfunction has been identified as one of the root causes of poor quality demineralized water produced during operation. Hence, there is need to study the dynamic behaviour of a typical cylindrical roller bearing of an airflow root blower. In this study, the dynamic analysis of a cylindrical roller bearing subjected to different rotational speeds was simulated using finite element analysis software, Abaqus. The frequency response of the bearing was determined experimentally and analytically, and the modal frequency results obtained from both analyses were com- pared. The outcome of the dynamic analysis showed that the maximum temperature and Hertzian stress was developed on the outer ring of the bearing during operation, thus making this component most prone to failure. It was observed that the value of the temperature and stress developed increase with an increase in rotational speed. However, at a rotational speed greater than 503 rad/s, a drop in the Hertzian stress was developed due to the stress relaxation the bearing experience at the higher tempera- tures. A good agreement was obtained when the modal frequency of the frequency response obtained numerically was compared with those obtained experimentally. [ABSTRACT FROM AUTHOR]

In this article, a magnetic suspension technique was introduced into the field of vibration absorption. Using the advantage of adjustable control parameters of a magnetic suspension system, a type of a magnetic suspension dynamic vibration absorber that can achieve broadband vibration suppression was designed. First, the theoretical model of a magnetic suspension dynamic vibration absorber was established. Then, the cantilever beam with sinusoidal excitation is seen as the main system of vibration suppression; combined with the fixed point theory (Seto K (2013) Dynamic Vibration Absorber and its Application. Mechanic Industry Press), the specific structure of the magnetic suspension dynamic vibration absorber was designed. Based on that, the simulation study of vibration suppression performance of the magnetic suspension dynamic vibration absorber was carried out. The results indicated that the vibration of the main system at the 1st modal frequency was reduced by 65.38% under the action of the magnetic suspension dynamic vibration absorber, compared with that without the action of the magnetic suspension dynamic vibration absorber. Furthermore, the vibration of the main system can be suppressed in the frequency band of [16 Hz, 32 Hz]. Finally, a vibration test rig of the magnetic suspension dynamic vibration absorber was built up for experimental study. And the results showed that the absorber can decrease the vibration of the main system by 43.03% at the 1st modal frequency compared with that without the action of magnetic suspension dynamic vibration absorber and had a certain suppression effect (decrease varies from 0 to 43.03%) on the vibration of the main system in the frequency band of [20 Hz, 32 Hz]. [ABSTRACT FROM AUTHOR]

Modal frequencies are often used in structural model updating, based on the finite element model, while the metamodel approach is often used in the respective optimization process. In this work, the Kriging model is adopted as the metamodel. First, the influence of different correlation functions of Kriging model is inspected, followed by the investigation of the approximate capability of Kriging model by inspecting the approximate accuracy of nonlinear functions. Next, a model updating procedure is proposed, based on the Kriging model, constructed using samples generated via the method of Optimal Latin Hypercube. Finally, a typical frame structure is taken as a case study, demonstrating the feasibility and efficiency of the proposed approach. The results show that, the Kriging model can match the target functions very well, while the finite element model can achieve accurate frequencies and can reliably predict the frequencies after model updating. [ABSTRACT FROM AUTHOR]

In this paper, the vibration and buckling behavior of a functionally graded piezoelectric porous cylindrical microshell under thermo-electro-mechanical loads are explored on the basis of modified couple stress theory and higher-order shear deformation theory. First, the model of a functionally graded piezoelectric porous cylindrical microshell composed of piezoelectric materials with gradient change in the thickness direction was described. Second, the governing equations of the microshell were derived by Hamilton's principle and Maxwell equation. Third, the modal frequency and buckling equations of the microshell with simply supported ends were obtained on the basis of harmonic trigonometric functions. Finally, the effects of parameters on the modal frequency and buckling behavior were carried out by case studies. The results show that the modal frequency of the microshell can be adjusted by changing the porosity volume fraction, power index, applied voltage, axial load and geometric dimensions. It is also found that the vibration of the microshell is suppressed by positive voltage and axial compression but is strengthened by negative voltage and axial tension, and the material length scale parameter increases stiffness. In addition, the effects of applied voltage and axial load on the buckling behavior are larger than those of temperature. Results can be used to guide the design and application of piezoelectric devices. [ABSTRACT FROM AUTHOR]

Summary: The influence of varying environmental/operational situations on damage‐sensitive properties is a vital problem when the vibration responses are employed for structural damage detection. In this work, singular spectrum analysis (SSA) and the statistical control chart are combined to develop a new damage identification approach for structural damage detection under variable environmental/operational situations. The SSA is utilized to decompose the measured frequency sequence into the sum of independent components, including a tardily changing trend, oscillatory, and noise components. The trend‐related decomposed components can be identified by finding the corresponding slow‐varying eigenvectors. The trend components induced by varying environmental/operational conditions are discarded, while the remaining ones, including oscillatory and noise components, are selected to reconstruct the new frequency sequence. Hence, the impact of variable environmental/operational situations on the original frequency sequence is removed. The reconstructed frequency shift from its reference status (undamaged status) is utilized to construct the damage features, which are employed as the control chart samples. Accordingly, the damage features obtained from the undamaged status are utilized to calculate the control limits. The subsequent damage indices in unknown status are monitored considering the control limits. A considerable number of damage indices out of the control limits range show a system transformation from an undamaged status to a damaged one. The feasibility of the presented approach is analytically and experimentally evaluated through an offshore platform in the presence of a white noise excitation. [ABSTRACT FROM AUTHOR]

The Xihoumen Bridge, with a main span of 1650 m and two side spans of 578 m and 485 m, respectively, is a long-span suspension bridge spanning the Jintang and Cezi islands in Zhejiang Province, China. In order to establish a reference baseline for vibration mitigation and condition assessment of the bridge under typhoons, the wind field properties, vibration energy distribution, and modal parameters of the bridge are identified through in-situ monitoring. Dynamic responses at different locations on main span and wind speeds at 1/2 main span of the bridge under 10 typhoons and under normal wind were collected for this study. Vibration energy distribution is estimated using wavelet packet transform. Modal parameters are identified by the peak-picking (PP) and data-driven stochastic subspace identification (SSI-DATA) methods. The results indicate that in the low-frequency range, the fluctuating wind energy of typhoons changes more significantly than that of normal wind. More than 80% of the vibration energy is concentrated in the frequency band (0–1.5625 Hz) under typhoons, while nearly 90% of the vibration energy under normal winds is evenly distributed in three frequency bands (0–1.5625 Hz, 1.5625–3.125 Hz, and 3.125–4.6875 Hz). When using typhoon-induced dynamic responses as input, the SSI-DATA method performs better than the PP method in the identification of modal parameters. The results obtained in this study can be used as a baseline for future structural condition assessment of the bridge after typhoon events. [ABSTRACT FROM AUTHOR]

The modal frequencies of a functionally graded material (FGM) cylindrical shell with different geometry dimensions and material constituents are studied under eight boundary conditions. The main goal is to reveal the influencing mechanism of different factors on the modal frequencies of the FGM shell. Firstly, the Voigt model is used to describe the properties of FGM. Secondly, the motion equation of the FGM shell is derived using Hamilton's principle. Thirdly, the modal frequency equation of the FGM shell is obtained based on a trigonometric function for the eight boundary conditions. Lastly, the effects of geometry dimension, material constituents, and boundary conditions on the modal frequencies of the FGM shell are analyzed through case studies. Results indicate that the modal frequencies obtained are good agreement with those from previous literature and the finite element method. The geometry dimensions of the FGM shell, the material constituents of the FGM, and the boundary conditions are crucial to the modal frequencies. This work can serve as a reference for the design of FGM and optimization of the structure of FGM shells. [ABSTRACT FROM AUTHOR]

Structural health monitoring represents an efficient way to diagnose the condition of cable-stayed bridges. Most studies assessing the condition of cable-stayed bridges and detecting damage to them have been developed to monitor the longitudinal performance of bridge bearings. However, few studies have aimed to detect the damage to tension pendulums, which are usually tie-down cables that resist girder uplift from auxiliary piers. This study aims to develop an effective method for detecting the damage of tension pendulums in cable-stayed bridges using structural modal frequencies. First, the sensitivity of the bridge frequency to tension pendulum damage is derived according to the Rayleigh method. Then, a finite-element simulation of a cable-stayed bridge is conducted to validate the rationality of the frequency index. Finally, a case study on tension pendulum damage is carried out for the cable-stayed Yonghe Bridge. The results indicate that the frequency change is far more sensitive to the damage of the tension pendulums than to the damage of the stay cables. The failure of tie-down cables will result in a substantial decrease in the bridge frequency, up to approximately 35% for the first vertical bending mode of the bridge. In practice, the damage of tension pendulums can be effectively detected by a sudden decrease in the measured frequency of cable-stayed bridges. [ABSTRACT FROM AUTHOR]

GNSS technology (known especially for GPS satellites) for measurement of deflections has proved very efficient and useful in bridge structural monitoring, even for short stiff bridges, especially after the advent of 100 Hz GNSS sensors. Mode computation from dynamic deflections has been proposed as one of the applications of this technology. Apart from formal modal analyses with GNSS input, and from spectral analysis of controlled free attenuating oscillations, it has been argued that simple spectra of deflections can define more than one modal frequencies. To test this scenario, we analyzed 21 controlled excitation events from a certain bridge monitoring survey, focusing on lateral and vertical deflections, recorded both by GNSS and an accelerometer. These events contain a transient and a following oscillation, and they are preceded and followed by intervals of quiescence and ambient vibrations. Spectra for each event, for the lateral and the vertical axis of the bridge, and for and each instrument (GNSS, accelerometer) were computed, normalized to their maximum value, and printed one over the other, in order to produce a single composite spectrum for each of the four sets. In these four sets, there was also marked the true value of modal frequency, derived from free attenuating oscillations. It was found that for high SNR (signal-to-noise ratio) deflections, spectral peaks in both acceleration and displacement spectra differ by up to 0.3 Hz from the true value. For low SNR, defections spectra do not match the true frequency, but acceleration spectra provide a low-precision estimate of the true frequency. This is because various excitation effects (traffic, wind etc.) contribute with numerous peaks in a wide range of frequencies. Reliable estimates of modal frequencies can hence be derived from deflections spectra only if excitation frequencies (mostly traffic and wind) can be filtered along with most measurement noise, on the basis of additional data. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Aeronautical Materials is the property of Editorial Board of Journal of Aeronautical Materials and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

To improve the simulation efficiency of mistuned blisk, a method called receptance substructure component modal synthesis method (RSCMSM) is proposed to reduce its degrees of freedom (DOFs). The advantage of this method is that only the interface DOFs need to be solved, which observably enhances the computational efficiency. The modal frequencies, maximum modal shape and frequency response function are calculated via RSCMSM. It is seen that the smooth frequency band is governed by blade vibration and the steep frequency band is governed by disk or bladed-disk coupling vibration. In addition, a peak is observed for the tuned blisk but many peaks appear for the mistuned blisk and many small wave crests are observed near the peak. To verify validity of this method, the computational time of RSCMSM is compared with high fidelity finite element method (HFFEM) and classical substructure component modal synthesis method (CSCMSM), which manifests that the computational efficiency increases by 32.19 %–80.82 % than that of HFFEM when the mistuned level is 0 %~5 %. Moreover, computational efficiency of RSCMSM is increased by 0.85 %–7.56 % than that of CSCMSM. The validity of RSCMSM is verified for calculating the complex mechanical structure. [ABSTRACT FROM AUTHOR]

Purpose: When a manipulator captures an unknown space object, inertia parameters of endpoint payload should be timely obtained to handle possible unexpected parameter variations and monitor the system's operating conditions. Therefore, this study aims to present an identification method for estimating the inertia parameter of the payload carried by a flexible two-link space manipulator. Design/methodology/approach: The original nonlinear dynamics model of the manipulator is linearized at a selected working point. Subsequently, the system modal frequencies with and without payload are determined using the subspace identification algorithm, and the difference of these frequencies is computed. Furthermore, by adjusting the structural configuration of the manipulator, multiple sets of frequency differences are obtained. Therefore, the inertia parameters of the payload, i.e. the mass and the moment of inertia, can be derived from the frequency differences by solving a least-squares problem. Findings: The proposed method can effectively estimate the payload parameters and has satisfactory identification accuracy. Practical implications: The approach's implementation provides a practical reference for determining inertia parameters of an unknown space target in the capture process. Originality/value: The study proposes a novel method for identifying the inertia parameters of the payload of a flexible two-link space manipulator using the estimated system frequencies. [ABSTRACT FROM AUTHOR]

Fine grain particles such as sugar, sand, salt etc. form Chladni patterns on the surface of a thin plate subjected to acoustic excitation. This principle has found its relevance in many scientific and engineering applications where the displacement or response of components under the influence of vibration is vital. This study presents an alternative method of determining the modal shapes on vibrating plate in addition to other existing methods like the experimental method by Ernst Chladni. Three (3) finite element solvers namely: CATIA 2017 version, ANSYS R15.0 2017 version and HYPERMESH 2016 version were employed in the modelling process of the 0.40 mm x 0.40 mm plate and simulation of corresponding mode shapes (Chladni patterns) as well as the modal frequencies using Finite Element Method (FEM). Result of modal frequency obtained from the experimental analysis agreed with the FEM simulated, with HYPERMESH generated results being the closest to the experimental values. It was observed that the modal frequencies obtained from the FEM and experimental approach increased as the excitation time increased. ANSYS R15.0 and HYPERMESH software clearly represented the modal lines and mode shapes for each frequency which CATIA software was somewhat limited. This study has shown that FEM is an effective tool that can save time and energy invested in acoustic experiments in determining modal frequencies and patterns. [ABSTRACT FROM AUTHOR]

Dynamic response control of a wind-excited tall building installed with distributed multiple tuned mass dampers (d-MTMDs) is presented. The performance of d-MTMDs is compared with those of single tuned mass damper (STMD) and MTMDs installed at top of the building. The modal frequencies and mode shapes of the building are first determined. Based on the mode shapes of the uncontrolled and controlled building, the most suitable locations are identified for the dampers, in that the TMDs are placed where the modal amplitude of the building is the largest/larger in a particular mode, with each tuned to the modal frequency of the first five modes. The coupled differential equations of motion for the system are derived for the cases with the STMD, MTMDs, and d-MTMDs and solved numerically. Extensive parametric studies are conducted to compare the effectiveness of the three control schemes using STMD, MTMDs, and d-MTMDs by examining the variations in wind-induced responses. The mass ratios, damping ratios of the devices, number of TMDs, and robustness of the TMDs are the parameters of investigation. It is concluded that the MTMDs exhibit improved performance when compared with the STMD. The use of d-MTMDs is most efficient among the three schemes because it can effectively control wind-induced response of the building, while reduced space is required in the installation of the TMDs, as they are placed at various floors. [ABSTRACT FROM AUTHOR]

A modified masking empirical mode decomposition (EMD) for effectively improving the mode separation capability of standard EMD while analysing power system signals with closely spaced modes of frequency is proposed here. A multi‐frequency test signal resembling the dynamic power system signal and the actual data recorded by wide area measurement systems (WAMS) from Northern Grid, India, on 1 June 2010 due to generation loss are analysed by both the existing method and the proposed method. Various components of modal frequency extracted by masking signal base EMD are compared with extracted components by the proposed modified masking EMD. Further, the time–frequency representation of extracted modes by Hilbert spectral analysis is implemented to know mode behaviour with time reference. Simulation results prove that the EMD with proposed modification is capable of separating various modes of frequencies present in the WAMS signal. [ABSTRACT FROM AUTHOR]

Human safety represents the key requirement in physical human-robot interaction (pHRI). However, the majority of current research works focus on the safety evaluation. There is no definite way to design a robot that not only meets the performance but also has inherent safety. A humanoid robot for human joint movement rehabilitation is developed, to fulfill the requirement of both safety and its performance. A nonlinear model of human-robot collision with effective mass and stiffness of robot's end-effecter (EE) is proposed. An important parameter involved in the model is the joint stiffness of the robot, which has an inherent direct effect on the safety. The influence of joint compliance on the modal frequencies is analyzed, and the kinematic performance of the robot is estimated roughly by the lowest order modal frequency. The design method of compliant joint stiffness is put forward, which can balance the safety and kinematics performance requirements. When the compliance is utilized intentionally in joints to improve safety, the question whether or not rigid performance of compliant joint can be achieved or approached by control is arose naturally. Such a challenge is addressed by the cascade control, where outer position loop with link-side position feedback is constructed. Here, restoring torque in the elastic transmission is taken as virtual control that is, in turn, set as the reference command of the inner torque loop. Intuitively, once the virtual control is reproduced as rapidly as possible in the inner torque loop, quasi-rigid performance is exhibited in the outer position loop as if there were no series elasticity in compliant joint. The stability criterion is derived, and the virtual stiffness and dynamic performance are examined. Finally, experiments are performed to validate effectiveness of the suggested control scheme. [ABSTRACT FROM AUTHOR]

Although a detailed finite element (FE) model provides more precise results, a lumped-mass stick (LMS) model is preferred because of its simplicity and rapid computational time. However, the reliability of LMS models has been questioned especially for structures dominated by higher modes and seismic inputs. Normally, the natural frequencies and dynamic responses of a LMS model based on tributary area mass consideration are different from the results of the FE model. This study proposes a basic updating technique to overcome these discrepancies; the technique employs the identical modal response, D(t), to the detailed FE model. The parameter D(t) is a time variable function in the dynamic response composition and it depends on frequency and damping ratio for each mode, independent of the structure's mode shapes. The identical response D(t) for each mode is obtained from the frequency adaptive LMS model; the adaptive LMS model which can provide identical modal frequencies as the detailed FE model. Theoretical backgrounds and formulations of the updating technique are proposed. To validate the updating technique, two types of structures (a symmetric straight column and an unsymmetric T-shaped structure) are considered. From the seismic response results including base shear and base moment, the updating technique considerably improves the seismic response accuracy of the tributary area-based LMS model. [ABSTRACT FROM AUTHOR]

This study investigates the relationship between the temperature and the modal frequencies of bridges through a series of model experiments using a concrete continuous beam bridge model and a steel cable-stayed bridge model in a controlled-temperature chamber. The experimental results show that, for a given boundary condition and in the absence of freezing, a change in temperature affects the structural frequencies of the bridge as it alters the elastic modulus of the bridge materials. The structural frequency tends to linearly decrease with increasing temperature and with the decrease in the frequency of steel bridges smaller than that of concrete bridges. For the particular case of wet concrete bridges, the temperature dependencies of modal frequencies vary dramatically near the freezing point, which is attributable to the freeze–thaw process of concrete pore water. The effect of air humidity on structural frequency is less significant than that of temperature when the boundary conditions remain unchanged. Furthermore, temperature changes may alter the boundary conditions of bridges, thereby affecting the structural frequencies. [ABSTRACT FROM AUTHOR]

This paper aims to develop a new probabilistic monitoring-based framework for damage detection of long-span bridges, by eliminating the temperature effects from the measured modal frequencies, probabilistic modeling of modal frequencies using kernel density estimate, and detection damage using the control chart. A methodology is presented to address the issue of modal frequencies' non-normal distribution, which has been neglected in the past studies using the control chart to detect the modal frequencies' abnormality caused by structural damages. The efficiency of the proposed framework is validated through a case study of long-term monitoring data of a long-span suspension bridge. The results show that after elimination of the temperature effects, the selected modal frequencies are not normally distributed, while the Q statistics transferred from the modal frequencies follow the standard normal distribution. The abnormality of modal frequencies can be detected when the data points of the Q statistics exceed the limits of the control chart. Further, the control chart has sufficient sensitivity and thus can be used to detect minor abnormalities of the prototype bridge's modal frequencies. It is concluded that the proposed probabilistic monitoring-based framework offers an effective technique for structural health monitoring of long-span bridges. [ABSTRACT FROM AUTHOR]

To identify the location and severity of structural damages precisely, a two-stage damage detection method is proposed here. In the first stage, the most probable elements that maybe damaged are determined using the modal strain energy concept of structure. For such purpose, an efficient modal strain energy conversion-based index is proposed. In the second stage, the structural damage identification problem is defined as an optimization problem that to be solved by a modified genetic algorithm. In the optimization problem, the damage extents of structure’s elements which are determined in the previous stage are considered as the variables. An efficient objective function considering the first few modal frequencies of the structure, before and after damage occurrence, is utilized for optimization. The robustness of the proposed method is assessed by several benchmark examples. The numerical results exhibit the effectiveness of the proposed method for precisely determining the location and severity of multiple structural damages. [ABSTRACT FROM AUTHOR]

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High-frequency transverse vibration of stepped beams has attracted increasing attention in various industrial areas. For an n-step Timoshenko beam, the governing differential equations of transverse vibration have been well established in the literature on the basis of assembling classic Timoshenko beam equations for uniform beam segments. However, solving the governing differential equation has not been resolved well to date, manifested by a computational bottleneck: only the first k modes (k ≤ 12) are solvable for i-step (i ≥ 0) Timoshenko beams. This bottleneck diminishes the completeness of stepped Timoshenko beam theory. To address this problem, this study first reveals the root cause of the bottleneck in solving the governing differential equations for high-order modes, and then creates a sophisticated method, based on local coordinate systems, that can overcome the bottleneck to accomplish high-order mode shapes of an n-step Timoshenko beam. The proposed method uses a set of local coordinate systems in place of the conventional global coordinate system to characterize the transverse vibration of an n-step Timoshenko beam. With the method, the local coordinate systems can simplify the frequency equation for the vibration of an n-step Timoshenko beam, making it possible to obtain high-order modes of the beam. The accuracy, capacity, and efficiency of the method based on local coordinate systems in acquiring high-order modes are corroborated using the well-known exact dynamic stiffness method underpinned by the Wittrick-Williams algorithm as a reference. Removal of the bottlenecks in solving the governing differential equations for high-order modes contributes usefully to the completeness of stepped Timoshenko beam theory. [ABSTRACT FROM AUTHOR]

Wind turbine gearbox (WTG), which functions as an accelerator, ensures the performance and service life of wind turbine systems. This paper examines the distinctive modal properties of WTGs through finite element (FE) and experimental modal analyses. The study is performed in two parts. First, a whole system model is developed to investigate the first 10 modal frequencies and mode shapes of WTG using flexible multibody modeling techniques. Given the complex structure and operating conditions of WTG, this study applies spring elements to the model and quantifies how the bearings and gear pair interactions affect the dynamic characteristics of WTGs. Second, the FE modal results are validated through experimental modal analyses of a 1.5 WM WTG using the frequency response function method of single point excitation and multi-point response. The natural frequencies from the FE and experimental modal analyses show favorable agreement and reveal that the characteristic frequency of the studied gearbox avoids its eigenfrequency very well. [ABSTRACT FROM AUTHOR]

A development of the 'first-order storey pseudo-stiffness-based damage index' of high-rise buildings is presented in this article. The proposed damage index is based on identification of an input set of one modal eigenpair, consisting of one modal frequency and the corresponding mode shape, overcoming the need and the difficulties of identifying multiple sets of eigenpairs in operational modal analyses of multistorey buildings. The calculation of first-order storey pseudo-stiffness-based damage index is expressed as a simple numerical procedure for comparison between the dynamic parameters of undamaged and damaged structures. The accuracy of the proposed damage assessment approach has been verified in two different tests - numerical and experimental. The numerical tests are based on the calculation of first-order storey pseudo-stiffness-based damage index in numerical models in which the structural damage is simulated with previously defined storey stiffness degradation. The experimental test consists of first-order storey pseudo-stiffness-based damage index accuracy test on the structure of the Urban Disaster Prevention Research Center, located in Tsukuba, Japan, and comparison to the results obtained by previously proven accurate damage detection method. The test results have shown that the proposed first-order storey pseudo-stiffness-based damage index index, based on the first modal eigenpair, can be applied as an instant damage detection method in structural health monitoring of multistorey buildings, providing the location and severity of structural damage. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Mechanical & Electrical Engineering is the property of Mechanical & Electrical Engineering Magazine and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In the present work, woven fabric glass laminate is modified by interplying high modulus carbon fabric layers for improving the stiffness to weight ratio to enable good performance in dynamic conditions. The glass, carbon, and hybrid of glass/carbon laminates were fabricated with two different stacking sequences by hand layup method and tested for evaluating the mechanical properties with considerable trials. The vibration characteristics of composite beams were experimentally studied by impulse excitation techniques under fixed-free boundary conditions. The stacking sequence of beams influences the mechanical properties and vibration characteristics. The modal response of tested samples are compared and discussed. [ABSTRACT FROM PUBLISHER]

The development of robust damage detection methods for offshore structures is crucial to prevent catastrophes caused by structural failures. In this research, we developed an Improved Modal Strain Energy (IMSE) method for detecting damage in offshore platform structures based on a traditional modal strain energy method (the Stubbs index method). The most significant difference from the Stubbs index method was the application of modal frequencies. The goal was to improve the robustness of the traditional method. To demonstrate the effectiveness and practicality of the proposed IMSE method, both numerical and experimental studies were conducted for different damage scenarios using a jacket platform structure. The results demonstrated the effectiveness of the IMSE method in damage location when only limited, spatially incomplete, and noise-polluted modal data is available. Comparative studies showed that the IMSE index outperformed the Stubbs index and exhibited stronger robustness, confirming the superiority of the proposed approach. [ABSTRACT FROM AUTHOR]

Vibration characteristics of carbon/epoxy composite beams await increased attention in structural industries such as aerospace, automotive, machine tools, marine industries. The objective of the present work is to investigate and analyze the shape effects of carbon/epoxy composite beams on vibration behavior. Specimens were fabricated using woven carbon fabric for basic shapes: I, box, and channel sections by hand layup method. The fabricated beams were subjected to impulse frequency response test under cantilever and fixed-end boundary conditions for free vibration test up to 3.5 kHz. Vibration response was measured using piezoelectric transducer and was recorded using computer-controlled data acquisition system for analyzing its behavior. The vibration characteristic of beams with various shapes shows modified performance under different boundary conditions. The experimental mode shapes and modal frequencies of beams are discussed and compared for successive resonance sets. At a lower frequency range of 3.5 kHz, the experimental modal responses of beam that were compared with modal results of finite element method analysis using software ANSYS V12® exhibited acceptable deviation in error maximum of up to 8.2%. Further, all deformed mode shapes of various shaped beams tested at increased frequency level of 12 kHz using finite element software were also observed and discussed. [ABSTRACT FROM AUTHOR]

To facilitate an effective assessment of stress-related bridge performance and safety, a baseline multiscale finite-element (FE) model and a corresponding model-updating technique are required so that the FE model can best represent the prototype and can be used to well predict both global and local responses. The companion paper demonstrates that considering modal frequencies alone as updating objectives cannot ensure the updated multiscale FE model being able to predict local (stress) responses accurately. This paper presents a new updating method that uses both modal frequencies and multiscale (displacement and stress) static influence lines as updating objectives. The paper first explains the relationship between displacement influence lines and mode shapes and the relationship between strain influence lines and strain mode shapes. The formulation of the multiscale objective functions and the selection of updating parameters are then presented. As a case study, the proposed model-updating method is finally applied to the multiscale FE model of the Stonecutters Bridge. In light of the large number of degrees of freedom of the multiscale model, the response surface method is adopted in the optimization process to reduce computation time. The updated results show that the proposed model-updating technique can reduce the differences not only between measured and computed modal frequencies but also between measured and computed influence lines. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Mechanical & Electrical Engineering is the property of Mechanical & Electrical Engineering Magazine and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Development of efficient model-updating and parameter estimation techniques is of great importance for civil structures. The present paper extends a recently developed cross-model cross-mode (CMCM) method for model updating and parameter estimation, when connectivity flexibility and boundary conditions are incorporated. First, the stiffness matrix of a beam member with semi-rigid joints at both ends is formulated, where the semi-rigid joints enable connections to be modelled as partially restrained. Second, boundary substructure elements are used to capture the stiffness and mass properties of the foundation. Finally, the model updating and parameter estimation of connection flexibility and boundary conditions are incorporated into the CMCM method. To validate the capability and effectiveness of the developed algorithm, numerical studies are conducted on a 2D bridge structure based on data generated from finite-element models. Numerical results demonstrate that the present method is effective for model updating and parameter estimation, when incorporating connectivity flexibility and boundary conditions. [ABSTRACT FROM AUTHOR]

We recorded ongoing EEG and measured mean values of the modal frequency (MF), absolute spectral power (ASP), and relative (normalized) spectral power (RSP) of the delta, theta, alpha rhythms, and beta1 and beta2 subrhythms in 31 children with inborn visual dysfunctions (average intragroup visual acuity of about 0.2) and 49 children with normal vision (age, from 8 to 12 years). Background EEG activity in children with visual dysfunctions was characterized by lower ASPs of all EEG frequency ranges (maximally, of the alpha rhythm), a lower RSP of alpha oscillations against the background of a higher RSP of the delta range (and that of beta2 subrange in boys), and also by higher MFs of slow-wave activity and of beta oscillations (beta2 and beta1 subranges in girls and boys, respectively); the MF of alpha activity in most cortical regions was unchanged. The data obtained are probably indicative of increased activity of the caudal brainstem regions related to the existence of visual dysfunctions; this results in changes in the pattern of interaction between activating and deactivating cerebral systems. Possible compensatory mechanisms influencing integrative activity of the brain under conditions of visual dysfunctions are discussed. [ABSTRACT FROM AUTHOR]