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The damping of spruce wood is analysed at different moisture content levels for the first three vibration modes of tangentially and radially vibrating samples. Two methods were used to determine the damping. The first was the vibration envelope fitting as an improved version of the well-known logarithmic decrement, and the second was the newer and recently increasingly used wavelet transform. Both methods showed that the damping of spruce wood first decreases and then increases with moisture content, with the damping in the first vibration mode being about 9% higher in the radial direction than in the tangential direction. In the second and third vibration modes, the damping in the tangential direction was higher than in the radial direction by about 10% and 8.8%, respectively. The measured damping factors from the envelope fitting had, on average, 15.9% higher values than those from the wavelet transform. It can be concluded from the results that the wavelet transform is more accurate for determining the damping factor, as it enables the decoupling of multi-degree of freedom systems if mode coupling is present. [ABSTRACT FROM AUTHOR]

The dynamic behavior of the large-pitch screw during turning affects the stability of the cutting process, which in turn impacts the machining quality of the large-pitch screw. The large-pitch screw turning system among the machine tool, cutting tool, and the workpiece is taken as the present research object, and the frequency response function modeling of the large-pitch screw turning process system is carried out. The concept of generalized modal field and generalized stiffness field of large-pitch screw turning process system is introduced. Considering the dynamic change of the whole process system with the change of tool position, the dynamic characteristic information of the processing system is obtained and analyzed and ultimately reflects the inherent properties of the large-pitch screw turning process system and the ability to resist deformation. The cutting stability prediction model based on support vector machines (SVM) is established, and the average prediction error is 5.04%. The artificial bee colony algorithm is used to optimize the cutting parameters, and finally, the optimization method of large-pitch thread cutting stability based on SVM is proposed. This method can reduce the cutting vibration and effectively improve the cutting stability. [ABSTRACT FROM AUTHOR]

It is important but still challenging to detect structural damage with limited instrumentation in the spatially large civil infrastructure. In this paper, a damage detection algorithm is proposed employing a global–local approach with limited sensors for detecting structural damage of spatially large civil engineering structures. The proposed algorithm is based on measuring frequency response functions (FRFs) at convenient yet selective locations on the structure with very limited sensors to localize the region of damage in the structure using the proposed global diagnostic approach. Once the local region of damage is established, local diagnostics are performed in the isolated small region of the structure using high fidelity sensing, still, a limited number of sensors in the small localized region (segment) of the structure, to precisely locate the damage. The principal component analysis combined with fractal dimension theory is employed for local diagnostics. Numerical studies have been conducted on a 6m simply supported beam and a 30-storey framed structure idealized as a shear building. Experimental verification of the proposed global–local damage diagnostic approach is also carried out. Studies presented in this paper indicate that the global–local approach for damage diagnosis of spatially large structures is very promising for precisely locating the damage with very limited sensors. [ABSTRACT FROM AUTHOR]

In many mechanical systems, it is very common to bring together different structural elements or subsystems produced by different producers and create a whole coupled system. It is often not possible to manufacture an entire mechanical system in one place. Although the dynamic properties of each of the subsystems produced by different manufacturers are known, it is a matter that should be known and studied how the dynamic behavior of the new system will be after the creation of a new system by combining these subsystems. In this study, a method for structural coupling of mechanical systems is presented in order to contribute to the solution of structural dynamic problems. It is based on Sherman–Morrison formula known for solving mathematical inverse problems of modified matrices. The method is very useful and practical for real mechanical engineering applications due to only the frequency response functions belong to the coupling coordinates of the subsystems are used. The main highlight of the presented method is there is no need a matrix inversion for calculations. [ABSTRACT FROM AUTHOR]

The paper examines the possibility of using a nonlinear Quasi-Zero-Stiffness (QZS) spring in a vehicle suspension. The response of a Single Degree of Freedom (SDOF) model to harmonic base excitations is obtained which may be unstable and unbounded depending on the excitation level and the damping ratio. This is followed by obtaining the response of the SDOF model to harmonic base excitation with an amplitude that is varying according to a road profile spectrum. Such dependency of the excitation amplitude to the frequency changes the qualitative behaviour of the nonlinear system and the responses would be always bounded. The QZS spring also improves the isolation of the system. Transient responses of a quarter car model with a QZS suspension to a road hump and random road profile are investigated. The maximum acceleration of the vehicle with the QZS suspension passing over the speed hump is considerably lower than a vehicle with a conventional linear suspension. Wb weighted RMS of acceleration (BS 6841-1987) is also lower by as much as 14% for a vehicle with the QZS suspension travelling at 30 km/h on a class E road compared to its linear counterpart. [ABSTRACT FROM AUTHOR]

The vibration isolation and absorption technologies for ship mechanical systems were reviewed, such as the concept, the application background, and the research status of floating raft vibration isolation systems and dynamic vibration absorbers. Meanwhile, the concept and development of passive control and active control were also analyzed. The smart materials and new structural forms were summarized. The concept, the working condition and the development of control components such as the quasi-zero stiffness vibration isolator, the acoustic black hole structure, the intelligent material actuator, and the active and semi-active dynamic vibration absorbers, were considered, and the control strategies of the active control were discussed. Besides, the theoretical and numerical methods for modelling, calculating and testing mechanical damping systems were also surveyed. At last, the development trend of the ship mechanical vibration reduction and isolation system was envisioned and portrayed. [ABSTRACT FROM AUTHOR]

Background: Rubber mounts are widely used to isolate vibrating components. Their complex stiffness characteristics, including dynamic stiffness and loss factors, are highly concerning in terms of vibration analysis and optimization. Rubber mounts show non-linear behavior with preload, leading to difficulty to predict their complex stiffness. Dynamic testing is generally necessary. Objective: An approach to identify the complex stiffness of preloaded rubber mounts in both vertical and horizontal directions simultaneously is developed. Methods: Tested Frequency Response Functions (FRF) of a mass suspended by rubber mounts are transformed to an FRF matrix of the mass center to decouple the Z Degrees of Freedom (DOF) and RZ DOF from other DOFs, which allows complex stiffness to be identified from the two decoupled DOFs. A software tool to implement automatically the FRF transformation and parameter identification is developed. An EPDM rubber mount is tested using the device and its complex stiffness is identified using the software to validate the proposed approach. Results: The driving-point FRFs of the mass center calculated from the identified complex stiffness are very close to the corresponding FRFs determined from the test data. The comparison between the Finite-Element Analysis (FEA) results of the surficial FRFs and the test results shows good consistency as well. Therefore, the proposed approach and its supporting algorithm are validated. Conclusion: the proposed approach allows for swift identification of high-accuracy complex stiffness of preloaded rubber mounts in both vertical and horizontal directions simultaneously. [ABSTRACT FROM AUTHOR]

Inclined pile groups have been adopted in engineering practice (e.g. offshore wind turbines) to withstand strong horizontal environmental loads that are repetitive in nature. Field reactions including the additional stresses and excess pore water pressures are responsible for the cyclic degradation of foundation soil, which may induce the accumulative deformation and fundamental frequency shifting of the marine structure. In this study, a theoretical model incorporating an inclined pile group and a saturated half-space was established, wherein the pile and saturated soil were described by the E–B beam and Biot poroelasticity theories, respectively. The pile and soil were coupled through the receptance matrix, which was established at the pile–soil interaction points in the transform domain. The dynamic impedances of the inclined pile group are first obtained, and then the field responses, including stresses and excess pore water pressure in the saturated ground, are evaluated for different types of loads applied to the pile cap. The frequency response function and spatial distributions of the field responses were obtained for varying rake angle of pile and permeability of soil. It was found that the horizontal force induces the largest responses in the ground when compared to the vertical force and the overturning moment applied to the inclined pile group. It is beneficial to employ an inclined pile group to withstand the horizontal force and overturning moment because the foundation stiffness increases, and the additional stresses in the ground decrease with increasing rake angle. [ABSTRACT FROM AUTHOR]

Anomaly detection and section estimation methods using multiplexed fiber Bragg gratings (FBGs) have been developed to identify propellant supply anomalies rapidly and autonomously in spacecraft propulsion systems. FBGs were used to measure the external strain of the pipe due to internal pressure fluctuations in the pipe during the pressure response caused by a water hammer. The measured strain was substituted into the constructed conversion formula to obtain the differential pressure through the FBGs. As a result, compared with the differential pressure measured by a conventional pressure sensor at the same position, the error was 2% for the maximum pressure of the water hammer and 1% for the natural frequency, indicating high applicability as a differential pressure sensor in piping with FBG simply wrapped around the outside of the pipe. Since the peak intensity and frequency of the measured values in the frequency domain change during flow anomaly and bubble localization, the frequency response function (FRF) between response data of the section to be detected was calculated, and the least-squares error of the FRF was used as the degree of anomaly. As a result, flow anomalies and bubble localization became detectable and sectional estimation was possible. • Multiplexed FBGs enable highly accurate anomaly detection for spacecraft propulsion systems. • Simple and accurate pressure dynamic response measurement method realized by FBGs. • Anomaly evaluation and detection by frequency response function between normal and target data. • Estimation of anomaly occurrence section by round robin comparison of anomaly degree. [ABSTRACT FROM AUTHOR]

Frequency response functions (FRFs) are one of the most useful methods for representing machine tool dynamics under force excitation. FRFs are usually obtained empirically through output measurements, and force excitations are controlled by an external device such as hammers or shakers. This study offers an operational identification method that utilizes the calculation of force applied during the process as an input for FRF identification. Force excitation is provided through the face milling of a thin-walled workpiece, and acceleration measurements are taken during the process. The FRF is calculated at a designated position by sampling workpiece-cutting tool contacts as individual tap tests and substituting a force calculation as input. Force coefficients need to be known for the force calculation. An experimental force coefficient identification method is proposed. In that case, a similar thin-walled workpiece at a point with known FRF and acceleration measurements is utilized. Results are confirmed with FRFs obtained in the same location for both FRF identification and force coefficient identification approaches. [ABSTRACT FROM AUTHOR]

Dynamic load of compressors is of great concern to designers of refrigeration products since pipes and sheet metals are easy to be excited, leading to noise or fatigue failure. The excitation is impossible to measure directly and difficult to calculate according to generation mechanism; thus, dynamic load identification which skips the mechanism is a more practicable way. However, the reported approaches have the problems of inaccuracy and clumsy. Therefore, an easy-to-implement approach is proposed, in which the accelerations and the frequency response functions from test are transformed to an arbitrarily given point based on rigid body dynamics, and then the equivalent six-degrees of freedom dynamic load of this point is calculated. This approach is validated using a motor with eccentric mass, whose centrifugal force is identified with the proposed approach and also calculated in analytical way. Comparison indicates that the error is within 5% except for the rotational speeds close to natural frequencies. Curve fitting or interpolation is recommended to correct the data in order to reduce the influence of natural frequencies. Cases studies with a rotary compressor and a scroll compressor respectively are presented. For the rotary compressor, the force magnitudes in X and Y directions are almost the same and pretty close to their quadratic polynomial fitting curves with zero intercept respectively, conforming to the characteristics of centrifugal force; the RZ component is larger than the RX and RY components as expected, but the latter two are not negligible; and there is a step change at 45 rps due to the removal of torque compensation. For the scroll compressor, the force magnitudes in X and Y directions are different, but very close to their quadratic polynomial fitting curves, respectively; the Z component has a jump in high-speed range; and there is no significant difference of dynamic force in the cooling and the heating modes. [ABSTRACT FROM AUTHOR]

Measuring the Frequency Response Functions (FRF) at the tool-tip is essential for the identification of chatter-free machining conditions. The tool-tip FRF in CNC machines are usually measured by impulse hammer tests in idle conditions, and the measured FRF remain relatively unchanged under operational conditions. This method is not effective in robotic machining, because the robot's vibration response in idle and operational conditions are significantly different. The robot's vibration response is pose-dependent and nonlinear and therefore strongly dependent on the operational conditions. This paper presents new methods for measuring the TCP (tool-tip) FRF of machining robots under operational conditions. In-process FRF are measured by leveraging the milling forces as the excitation source, and two approaches are proposed to achieve broadband, uncorrelated, and sufficiently exciting forces: i) milling of porous materials to generate randomized cutting forces, and ii) milling of a homogeneous material with spindle speed sweep. In the latter approach, the periodic content of cutting forces is used for excitation while in the former approach excitation by the random content is considered. A table dynamometer is used to measure the excitation (milling) forces and accelerometers are used to measure the resulting vibrations. The measured in-process FRF are then used to develop the chatter stability lobes diagram of the process, which determine the chatter-free combinations of the cutting depth and spindle speed for milling. Chatter experiments are conducted to confirm that the stability diagrams are more accurate when the presented in-process FRF measurements are used instead of the FRF measured in idle conditions. [ABSTRACT FROM AUTHOR]

Ultrasonic welding (USW) is recognized as a sustainable and green manufacturing process due to its high energy efficiency, cleanliness, and excellent welding attributes. The performance of USW majorly depends on small end vibration amplitude (SEVA), achieved through a sonotrode, whose design has been the focus of many researchers. A high SEVA is essential for achieving excellent welding attributes, minimizing wastage, and ensuring a clean environment. In this study, a novel USW sonotrode was designed to enhance the output amplitude of the Langevin ultrasonic transducer (LUT). The sonotrode was evaluated for eigenfrequency characterization and harmonic excitation response through finite element analysis. The performance of this novel ultrasonic transducer was evaluated in terms of SEVA and various types of stresses at an operating frequency close to but higher than the LUT's axial modal frequency. Variations in axial displacement and Von Mises (VM), axial, tangential, radial, principal, and shear stresses were examined along the length of the tool for titanium, aluminum, and steel sonotrodes. The SEVA of the aluminum sonotrode was 136.72% and 5.87% higher than that of the titanium and steel sonotrodes, respectively. The equivalent VM stress in the steel sonotrode was 159.2% and 379.2% greater than their aluminum and titanium counterparts. Selected cases from the present study were compared with prior research, revealing a reasonable agreement. This work provides insights into the performance of sonotrodes in USW, offering potential paths for improving the effectiveness of this sustainable manufacturing process. [ABSTRACT FROM AUTHOR]

The nonlinearities present in engineering structures are generally local in nature. Hence for system identification, it is required first to identify the spatial location and then the nonlinearities are characterized. Once the nonlinearity is characterized, the system identification involves identifying coefficient of nonlinear terms. In the present work, an improved version of traditional conditioned time and frequency domain reverse path method for nonlinear parameter estimation of multiple-degree-of-freedom structures is presented. Both numerical and experimental studies have been carried out to investigate the effectiveness of the proposed improved time and frequency domain parameter estimation techniques over the traditional ones. The comparisons between the time and frequency domain reverse path approaches are also carried out to highlight the strengths and weaknesses of each of these approaches. Numerical and experimental investigations reveal that both the time and frequency domain approaches proposed in this paper overcomes the major limitations of their traditional counterparts and are capable of estimating the nonlinear coefficients of multiple nonlinear attachments either grounded or attached between the masses. [ABSTRACT FROM AUTHOR]

In this study, elastic metamaterial sandwich plates with axially deformed Timoshenko beam cores, considering both the out-of-plane and in-plane deformations of the face plates, are designed and the vibration band-gap properties are explored. The beam cores act as local resonators that can bear axial force, bending moment and shearing force. The finite element method (FEM) and the spectral element method (SEM) are combined to create the finite/spectral element hybrid method (FE-SEHM) for establishing the dynamic model and calculating the frequency response functions (FRFs) of the elastic metamaterial sandwich plate with axially deformed beam cores. It is observed that the metamaterial sandwich plate possesses both the axial and transverse vibration band-gaps of the beams, and the two kinds of band-gaps are independent. Compared with the metamaterial sandwich plates with rod cores, those with axially deformed beam cores have more extensive application ranges for vibration reduction. [ABSTRACT FROM AUTHOR]

This paper provides a chronological review of publications that implement and advance the receptance coupling substructure analysis (RCSA) approach first applied to tool tip receptance (or frequency response function) prediction for milling applications in 2000. The review topics mimic the RCSA approach, where the tool, holder, and spindle-machine receptances are coupled analytically, and include: tool-holder receptance modeling; connection modeling; spindle-machine receptances; and applications. The review paper summarizes contributions from multiple, international authors (198 papers) to these topics. It also provides a comprehensive resource for those beginning an investigation into RCSA. • This paper provides a review of publications that implement and advance the receptance coupling substructure analysis (RCSA) approach. • The review topics include: tool-holder receptance modeling; connection modeling; spindle-machine receptances; and applications. • The review paper summarizes contributions from multiple, international authors to these topics. • The paper provides a comprehensive resource for those beginning an investigation into RCSA. [ABSTRACT FROM AUTHOR]

Resonance and anti-resonance frequencies are important parameters that determine the dynamic behavior of mechanical systems. Changes in these parameters, which depend on the system's physical properties such as mass and stiffness, also affect the system's dynamic behavior. Finding the necessary structural modifications to adjust the resonance and antiresonance frequencies of a system to the desired values is a study area of inverse structural modification. In this study, an inverse structural modification method for one and multi-rank modifications is presented. With the presented method some resonance or anti-resonance frequencies of mechanical systems can be shifted to prescribed values by calculating the necessary modifications. The presented method is based on Sherman-Morrison (SM) formula and uses the frequency response functions (FRF) of the original system directly. For one modification an exact solution is obtained on the other hand for two or more modifications some nonlinear set of equations has to be solved. A meta-heuristic optimization technique known as Grey Wolf Optimizer (GWO) is applied for the solution of the nonlinear equations. The method is applied to a six-degrees-of-freedom mass-spring system. Some resonance and anti-resonance frequencies in the frequency bandwidth of the system are selected as target frequencies. The necessary modification masses are calculated to match these frequencies. After applying the calculated masses to the system the target frequencies are obtained successfully. [ABSTRACT FROM AUTHOR]

The application of oil-bearing joint that is widely used in various mechanical equipment can effectively improve the dynamic characteristics of integrated machineries. A fractal contact model of oil-bearing joint considering the effect of asperity interaction is proposed in this article. The equivalent stiffness and damping of oil-bearing joint are divided into a solid contact portion and a liquid contact portion. On the basis of elastic mechanics and fractal theory, the deformation of a single asperity of solid contact part is deduced. The stiffness and damping model considering the asperity interaction are obtained from the relationship between normal load and deformation. The stiffness and damping expression of the liquid contact part are also deduced based on the generalized Reynolds equation. It is concluded that the equivalent stiffness increases with the increase of the fractal dimension and the decrease of the fractal roughness parameter. At the same time, increasing the hydrodynamic viscosity can demonstrably improve the contact stiffness. Experiment shows that the proposed model is more in line with the actual load-stiffness relationship. The model considers the factor of asperity interaction and provides a theoretical basis for predicting the dynamic characteristics of oil-bearing joint. An accurate theoretical model of the dynamic characteristics for the oil-bearing joint surface was established. Identification of the dynamic properties of the oil-bearing joint surface using frequency response functions. The factors influencing the stiffness of solid portion and liquid portion were studied, respectively. [ABSTRACT FROM AUTHOR]

The frequency response function (FRF) in the frequency domain is a black box used to collect physical information and to indicate the modal characteristics of a dynamic system. Analyzing the collected FRF data through the impact hammer test, dynamic parameters, such as stiffness, mass, and the damping matrix, can be estimated. By extracting and analyzing the FRFs within certain ranges of the lowest few resonance frequencies, this study presents a nondestructive method to estimate the dynamic parameters and the material properties. Updating of the dynamic parameters and material properties is a crucial process for the subsequent design and maintenance. This study presents a method to estimate the physical properties of structural members using measured FRF data and generalized inverse. By extracting and analyzing the FRFs within certain ranges of the lowest few resonance frequencies, the dynamic parameters were predicted. It was observed in numerical experiments that the proposed method could properly estimate the elastic modulus and dynamic parameters of steel beams, although the results were affected by the extracted FRF ranges. The physical properties were close to more accurate values in taking the FRFs at more resonance frequencies, as the member was flexible. The proposed method was also extended to a nondestructive test for an estimation of the compressive strength of concrete. However, it faced difficulty due to the external noise contained in the measured data. It was found sin the nondestructive test that the proposed technique was affected by external noise, unlike a simple steel beam. The concrete strength could be predicted by taking the FRFs in a wide frequency range containing the lowest two resonance frequencies and by averaging the repeated test results. [ABSTRACT FROM AUTHOR]

Viscoelastic material can significantly reduce the vibration energy and radiated noise of a structure, so it is widely used in lightweight sandwich structures. The accurate and efficient determination of the frequency-dependent complex modulus of viscoelastic material is the basis for the correct analysis of the vibro-acoustic behavior of sandwich structures. Based on the behavior of a sandwich beam whose core is a viscoelastic layer, a combined theoretical and experimental study is proposed to characterize the properties of the viscoelastic layer constituting the core. In this method, the viscoelastic layer is bonded between two constraining layers. Then, a genetic algorithm is used to fit the analytical solution of the frequency¬ response function of the free–free constrained beam to the measured result, and then the frequency-dependent complex modulus is estimated for the viscoelastic layer. Moreover, by varying the length of the beams, it is possible to characterize the frequency-dependent complex modulus of the viscoelastic material over a wide frequency range. Finally, the characterized frequency-dependent complex modulus is imported into a finite element model to compute the complex natural frequencies of a sandwich beam, and a comparison of the simulated and measured results displays that the errors in the real parts are within 2.33% and the errors in the imaginary parts are within 3.31%. It is confirmed that the proposed method is feasible, accurate, and reliable. This provides essential technical support for improving the acoustic vibration characteristics of sandwich panels by introducing viscoelastic materials. [ABSTRACT FROM AUTHOR]

The frequency response function (FRF) provides an input-output model that describes the system dynamics. Learning the FRF of a mechanical system can facilitate system identification, adaptive control, and condition-based health monitoring. Traditionally, FRFs can be measured by off-line experimental testing, such as impulse response measurements via impact hammer testing. In this paper, we investigate learning FRFs from operational data with a nonlinear regression approach. A regression model with a learned nonlinear basis is proposed for FRF learning for run-time systems under dynamic steady state. Compared with a classic FRF, the data-driven model accounts for both transient and steady-state responses. With a nonlinear function basis, the FRF model naturally handles nonlinear frequency response analysis. The proposed method is tested and validated for dynamic cutting force estimation of machining spindles under various operating conditions. As shown in the results, instead of being a constant linear ratio, the learned FRF can represent different mapping relationships under different spindle speeds and force levels, which accounts for the nonlinear behavior of the systems. It is shown that the proposed method can predict dynamic cutting forces with high accuracy using measured vibration signals. We also demonstrate that the learned data-driven FRF can be easily applied with the few-shot learning scheme to machine tool spindles with different frequency responses when limited training samples are available. [ABSTRACT FROM AUTHOR]

This paper presents an analytical transfer matrix modeling framework for the forced vibration of a bending-torsional-warping coupling Euler-Bernoulli thin-walled beam carrying an arbitrary number of three degree-of-freedom (DOF) spring-damper-mass (SDM) subsystems. The thin-walled beam is divided into a series of distinct sub-beams whose ends are connected to the SDM subsystems. The transfer matrix for each sub-beam is developed based on the exact shape functions of the bending-torsional-warping coupling Euler-Bernoulli theory. Each SDM system is modelled by a set of effective springs based on the dynamic condensation method. The governing matrix equation is formulated based on the compatibility conditions of the placement and the force at the common interfaces of two adjacent sub-beams. Then, a closed-form expression for the frequency response function of the thin-walled beam system is proposed. The results computed by the proposed method achieve good agreement with those obtained by the conventional finite-element method, which shows the accuracy and reliability of the proposed method. The effects of the system parameters on the vibration transmission and vibration isolation properties of the thin-walled beam system are studied. The presented method can simultaneously consider arbitrary number of SDM subsystems and boundary conditions. Furthermore, none of the associated matrices are larger than 12 × 12, which provides a significant computational advantage. [ABSTRACT FROM AUTHOR]

The present paper discusses a new approach for the experimental determination of modal parameters (resonant frequencies, modal shapes and damping coefficients) based on measured displacement values, using the non-contact optical method of digital image correlation (DIC). The output is a newly developed application module that, based on a three-dimensional displacement matrix from the experimental measurement results, can construct a frequency response function (FRF) for the purpose of experimental and operational modal analysis. From this frequency response function, the modal parameters of interest are able to be determined. The application module has been designed for practical use in Scilab 6.1.0, and its code interfaces directly with the ISTRA4D high-speed camera software. The module was built on measurements of a steel plate excited by an impact hammer to simulate experimental modal analysis. Verification of the correctness of the computational algorithm or the obtained modal parameters of the excited sheet metal plate was performed by simulation in the numerical software Abaqus, whose modal shapes and resonant frequencies showed high agreement with the results of the newly developed application. [ABSTRACT FROM AUTHOR]

This paper proposes a convolutional neural network (CNN)-based method with which to predict bolt clamping force using the frequency response of bolted structures. The dynamic characteristics of the bolted structure change with the bolt clamping force, which is predicted using a CNN trained with massive frequency response data. Big data required for training the CNN is constructed using prestressed frequency response analysis according to the clamping force of individual bolts. The numerical efficiency is increased using the Krylov subspace-based model order reduction (MOR) method. The frequency response for each set of bolt clamping forces calculated from the MOR method is converted into form of the magnitude and shape (MS) similarity spectrum by using the MS similarity function. Finally, an MS similarity map is generated by stacking the MS similarity spectrum at several output points. A CNN that is trained using massive MS similarity maps as training data, is used to predict the clamping force of bolted structures. To validate the efficiency and accuracy of a trained CNN in practical applications, the prediction results of the trained network in terms of computation time and accuracy were compared according to the size of the training input data. [ABSTRACT FROM AUTHOR]

This paper mainly studies the model design of a thin-film heat-flux sensor (TFHFS), and focuses on the comparison of three dynamic calibration methods. The primary motivation for studying this came from the urgent need for heat-flux dynamic measurements in extreme environments, and the one-sidedness of the dynamic performance evaluation of the corresponding TFHFS. The dynamic theoretical model of the TFHFS was originally established on the principle of a temperature gradient on the basis of a thermal radiation boundary. Then, a novel TFHFS sensor was developed, which can be used at temperatures above 880 °C and has a high sensitivity of 2.0 × 10−5 mV/(W/m2). It can function stably for long durations under a heat-flux density of 3 MW/m2. The steady-state, transient, and frequency calibration of a TFHFS were compared to comprehensively analyze the dynamic characteristics of the TFHFS. The steady-state response time measured by the step excitation method was found to be 0.978 s. The QR decomposition method was applied to the steady-state response experimental model construction, and the fitting degree of a second-order transfer function model obtained was 98.61%. Secondly, the transient response time of the TFHFS was 0.31 ms based on the pulse-excitation method. The transient relationship between the surface temperature and the heat flux, and the pulse-width dependence of the TFHFS transient response time were established. Surprisingly, the response frequency of the TFHFS, about 3000 Hz, was efficiently tested using the frequency response function (FRF), which benefitted from the harmonic characteristics of a periodic square-wave excitation signal. Finally, a comprehensive evaluation of the dynamic performance of the TFHFS was realized. [ABSTRACT FROM AUTHOR]

• Propose self-powered sensing of fluid-conveying piezoelectric pipes via energy harvesting. • Employ distributed-parameter electromechanical model to explore the nonlinear dynamics. • Identify the fluid-conveying piezoelectric pipes via output frequency response functions and system transfer functions. • Benefits of voltage OFRF of the transverse vibrations to self-powered sensing. This paper reports on an investigation of nonlinear energy harvesting from fluid-conveying piezoelectric pipes for self-powered sensing. Based on Euler Bernoulli theory, a distributed-parameter electromechanical model was employed to explore the nonlinear dynamics of fluid-conveying piezoelectric pipes. The Galerkin method and harmonic-balance analysis were employed to find output frequency response functions (OFRFs) and system transfer functions of the fluid-conveying piezoelectric pipes. The influences of fluid velocity on energy harvesting are also discussed. With an increase of fluid velocity, the resonance peak moves towards lower frequency, the odd-mode resonant peak amplitudes decrease, and the even mode resonant peak amplitudes increase. The semi-analytical results are supported by a numerical finite-difference method. The results demonstrate that the displacement, voltage, current, and power OFRFs can be increased by increasing the excitation amplitude and reducing the damping coefficient. The results show the advantage of using the voltage OFRF of the transverse vibrations of fluid-conveying piezoelectric pipes for self-powered sensing. [ABSTRACT FROM AUTHOR]

The dynamic stability of reinforced concrete structures in regions of reduced restoring force was theoretically investigated according to the ductility and negative gradient in the skeleton curve of their restoring force - displacement relationship, using the frequency response function derived by Caughey (1960). This method derives the frequency response function, which is a relational expression between input and response, for a single-degree-of-freedom system subjected to a harmonic external force in the form of a cosine wave; it also derives two conditions that make the response solution of a nonlinear one-degree-of-freedom system unstable. The results of the investigation showed that the behavioral range in which the structure was stable in the region of reduced restoring force could be determined using the ductility and negative stiffness indicated by the skeleton curve of the restoring force - displacement relationship. Parametric studies varying the ductility and negative stiffness also suggested the possibility that dynamic stability cannot be ensured in the region of reduced restoring force when the ductility is excessive. • This study investigated the dynamic stability of a structural system under harmonic force. • The object is RC structures, characterized by constant restoring force that later decreases. • The link between ductility and gradient of restoring force drop is crucial for dynamic stability. • This paper presented the application of its theoretical considerations to actual RC columns. [ABSTRACT FROM AUTHOR]

The sensitivity of structural health monitoring systems to environmental and operational conditions poses a significant challenge due to their inherent susceptibility to outliers. This paper proposes an effective model-updating-based optimization algorithm that can alleviate the impact of outliers associated with field and operational fluctuations. The proposed method addresses the influence of uncertainties from sources such as white noise, colored noise, and measurement errors, which can introduce outliers in datasets. The approach comprises a hybrid procedure in which a Gaussian smoothing technique is first employed to smooth out measured data to reduce the impact of irregularities. Next, Johansen cointegration is employed for raw data fusion to further enhance the signature of shared patterns. A novel optimization algorithm based on the Reptile Search Algorithm (RSA), named Improved RSA (IRSA), is proposed to solve the objective function based on the concept of mutual information. This algorithm provides a superior solution with much improved computational speed and accuracy compared to RSA. The new hybrid method was validated by several numerical and experimental damage detection studies. Furthermore, it was compared to other state-of-the-art methods described in the literature. The results clearly demonstrate the superior performance of the newly developed method. • Applying Gaussian smoothing to handle high-frequency noise while preserving more information and maintaining functionality. • Introducing novel application of Johansen cointegration as a data fusion technique, effectively handling outliers in FRF signals. • Proposing a new objective function based on Mutual Information, Johansen cointegration, and Gaussian smoothing. • Proposing a new and robust optimization algorithm based on the concept of the Reptile Search Algorithm (RSA), named Improved RSA (IRSA). • Demonstrating the robustness of the proposed method with numerical and experimental evaluations. [ABSTRACT FROM AUTHOR]

• A pyramid cylinder lattice truss structure with vibration attenuation is developed. • The impact of cell parameter on vibration transmission characteristics is explored. • The effectiveness of vibration attenuation capability is experimentally assessed. In this work, an innovative cylindrical metamaterial inspired by origami was developed. It featured arrays of pyramid units arranged both circumferentially and axially. The vibration transfer characteristics were determined using numerical method (Frequency Domain Frequency Response Solver of COMSOL) and dynamic testing (Scanning Vibrometer System). The results indicate that the structure effectively attenuates vibrations within the 0–6000 Hz range. Adjusting key geometric parameters can widen or shift vibration attenuation bands toward low–frequencies. Increasing the rod diameter weakens the vibration attenuation capability, while an increase in circumferential and axial angles has a positive impact on the frequency band for vibration attenuation. The significance of this work lies in providing an appropriate method to enhance vibration attenuation for the design and optimization of engineering structures. [Display omitted] [ABSTRACT FROM AUTHOR]

The primary focus of this paper is to analyze the impact of the periodic resonators on the wave dispersion phenomenon of a thin-walled asymmetric beam. An analytical framework has been developed to study the triply coupled flexural and torsional wave propagation in an asymmetric metabeam. The resonators are modeled as a beam with a lumped mass at the center and placed eccentrically from the shear center. Their periodicity allows them to generate a subwavelength attenuation band in the beam. The governing equations for the coupled bending-bending-torsion vibration of a metabeam having an asymmetric cross-section are considered for generating the dispersion phenomenon, including the warping effect. Applying the Bloch-Floquet principle, the dispersive characteristics of the asymmetric metabeam are obtained by using the transfer matrix method. The modal characteristics of an asymmetric beam without a resonator are computed using the spectral element method and are validated with previously published results. Subsequently, the attenuation band is investigated due to the presence of a resonator and followed by the transmittance spectrum to verify the suppression of the elastic waves in the attenuation band. The experimental analysis is carried out to validate the analytical framework by obtaining the modal frequencies from the frequency response function. The detailed parametric investigation reveals that the resonator's position and characteristics significantly impact the occurrence of the band gap. A substantially wide attenuation band gap is attained by considering a continuous beam-mass resonator instead of a discrete spring-mass type resonator. This type of novel structure has the potential for the application of vibration control and acoustics. • Triply coupled wave propagation analysis of thin-walled asymmetric metabeam. • Analytical study on coupled bending-bending-torsion wave propagation. • Experimental validation of the modal characteristics of the beams. • Generation of band gap due to periodicity of the beam-mass resonator. [ABSTRACT FROM AUTHOR]

Uncertainty propagation of the frequency response function is crucial for vibration problems such as model calibration, and the probability assessment is another indispensable item in structural optimization. Considering only one of them will inevitably lead to a lack of uncertain knowledge of practical engineering structures. However, it is still challenging to evaluate the system response bounds and probability characteristics simultaneously and maximally reduce the computational cost. This paper focuses on the frequency response function involving correlated uncertainties and proposes a novel uncertainty propagation and probability assessment method. First, a convex model was established to quantify the correlated uncertainty parameters, and then, the Chebyshev polynomial function was developed as the surrogate model to efficiently quantify the uncertainty propagation from uncertainty parameters to system response. Subsequently, the novel normalized and coordinated transformation combined the uncertainty propagation method, making the uncertainty system response easy to assess. Note that the response value at the interpolation point can be employed as the input of probability assessment. One can also estimate the probability characteristics at different frequency positions during the construction of the surrogate model. Finally, two numerical examples were presented to demonstrate the effectiveness and cheaper computation by a discrete system and a continuous system, respectively. Results indicate that the proposed method can be conveniently and accurately applied to assess the bounds and probability characteristics of frequency response function involving correlated uncertainties. [ABSTRACT FROM AUTHOR]

The surging demand for fiberglass pipe materials in the Oil and Gas transportation sectors are driven by their exceptional durability and ease of use. This study combined improved experimental and numerical analyses to assess the behavior of composite pipe and focused on characterizing it, especially in terms of identifying the frequency based on different crack lengths. Various tests, such as impact hammer tests and modal analysis, determine the pipe properties and natural frequencies. The study also investigates the impact of varying fiber volume fractions to refine material properties. To understand crack effects behavior, different crack lengths have been introduced into the pipes and analyzing the modal analysis using frequency and mode shapes. The effect of cracks into frequency based on experimental and developed numerical models is investigated. A predective model is developed based on YUKI-Gradient Boosting algorithms and Deep Artificial Neural Networks. To test the robustness of developed algorithm several tests are provided and the results show the effectiveness of YUKI-Gradient Boosting outperforms YUKI-Deep-ANN in accuracy and consistency. • Improved experimental tests of composite pipe. • Predicting modal analysis using Machine learning. • Advanced numerical analysis. • Characterization using modal analysis. • YUKI-Enhanced Gradient Boosting. [ABSTRACT FROM AUTHOR]

Rail vibration suppression is important to reduce rail noise radiation and ensure vehicle ride comfort. Conventional rail absorbers have been demonstrated to be effective for suppressing rail vibration; however, their effective frequency bandwidth remains limited. Herein, for the first time, we propose a broadband rail absorber, called an acoustic black hole (ABH) absorber, for rail vibration suppression. This novel ABH absorber consists of a variable-thickness cantilever beam with a power-law profile covered by a viscoelastic damping layer. A 3D finite element model of a 12.35-m long full-scale rail with ABH absorber was developed to investigate its performance. The effects of the thickness and loss factor of the damping layer on the rail vibration-suppression performance were investigated via a parametric study. In addition, a full-scale experiment was conducted on an actual rail to investigate the vibration-suppression performance of the ABH absorber. Both numerical and experimental results indicate that the ABH absorber can significantly reduce rail vibration at tuning frequencies and provide broadband vibration suppression within the non-resonance range. The experimental results demonstrate that the ABH absorber increases the track decay rate at frequencies above 100 Hz; in addition, a maximum track decay rate of 5.85 dB/m was achieved. This study may help to develop next-generation rail absorbers, which is important for developing sustainable and eco-friendly urban rail transit. • An acoustic black hole absorber is proposed for broadband rail vibration suppression. • Numerical and experimental results validate its performance. • The ABH absorber can significantly improve the track decay ratio above 100 Hz. [ABSTRACT FROM AUTHOR]

In this study, we present a methodology that combines statistical analysis of measured population FRFs (Frequency Response Functions) of a hardware device (Product A) with the FEM (Finite Element Method) simulated nominal FRF of another, closely related hardware device (Product B) to predict the device-to-device FRF variation of the latter device (Product B). Firstly, measured population FRFs of Product A are acquired in large quantities from high-volume manufacturing builds. Each FRF from the population data of Product A is decomposed into a set of fitted SDOF (Single Degree-of-Freedom) modes using the LSCF (Least-Squares Complex Frequency-domain) estimator. Unsupervised clustering is deployed against the sample of all SDOF modes to assign a "mode shape label" to every mode from every FRF in the population. Next, the clustered SDOF modes are analyzed to select "boundary FRFs", which represent the worst-case FRFs from the population of Product A. Finally, variation from "selected boundary FRFs" of Product A is applied to FEM FRF of Product B to predict its boundary response. We utilize this methodology to predict population boundary FRFs for an HDD (Hard Disk Drive) device. Our methodology would help create a realistic population boundary FRF dataset for HDD servo-control design optimization to ensure that the servo-controller is robust against any possible variations in the high volume of HDDs that are built and shipped. While we predict boundary FRFs for an HDD in this study, the underlying methodology can be utilized to predict device-to-device FRF variation for any Multi-Input Multi-Output device. • Modal parameter estimation of measured population Frequency Response Function (FRF) data. • Unsupervised clustering of FRF modes to assign a mode shape label to every mode. • Selection of boundary FRFs (worst case response) from population data. • Combine statistical analysis of measured FRFs with simulated FRF to predict variation. [Display omitted] [ABSTRACT FROM AUTHOR]

• CT-FEM simulated both the thoracic and internal responses within the 5–100 Hz range. • The state-space model assessed two apparent resonance frequencies at 28 Hz and 41 Hz. • We validated that FRF equals 0.138 m/s2N at the peak frequency of 28 Hz. • The mean displacement and energy density distribution of the thorax were determined. High-frequency chest wall compression (HFCC) therapy by airway clearance devices (ACDs) acts on the rheological properties of bronchial mucus to assist in clearing pulmonary secretions. Investigating low-frequency vibrations on the human thorax through numerical simulations is critical to ensure consistency and repeatability of studies by reducing extreme variability in body measurements across individuals. This study aims to present the numerical investigation of the harmonic acoustic excitation of ACDs on the human chest as a gentle and effective HFCC therapy. Four software programs were sequentially used to visualize medical images, decrease the number of surfaces, generate and repair meshes, and conduct numerical analysis, respectively. The developed methodology supplied the validation of the effect of HFCC through computed tomography-based finite element analysis (CT-FEM) of a human thorax. To illustrate the vibroacoustic characteristics of the HFCC therapy device, a 146-decibel sound pressure level (dB SPL) was applied on the back-chest surface of the model. Frequency response function (FRF) across 5–100 Hz was analyzed to characterize the behaviour of the human thorax with the state-space model. We discovered that FRF pertaining to accelerance equals 0.138 m/s2N at the peak frequency of 28 Hz, which is consistent with two independent experimental airway clearance studies reported in the literature. The state-space model assessed two apparent resonance frequencies at 28 Hz and 41 Hz for the human thorax. The total displacement, kinetic energy density, and elastic strain energy density were furthermore quantified at 1 µm, 5.2 µJ/m3, and 140.7 µJ/m3, respectively, at the resonance frequency. In order to deepen our understanding of the impact on internal organs, the model underwent simulations in both the time domain and frequency domain for a comprehensive analysis. Overall, the present study enabled determining and validating FRF of the human thorax to roll out the inconsistencies, contributing to the health of individuals with investigating gentle but effective HFCC therapy conditions with ACDs. This innovative finding furthermore provides greater clarity and a tangible understanding of the subject by simulating the responses of CT-FEM of the human thorax and internal organs at resonance. [Display omitted] [ABSTRACT FROM AUTHOR]

The main purpose of this article is to monitor the natural frequency of stainless steel (SS304) with and without defect by spray-coated smart graphene nanoplatelet (GNPs)-doped poly (methyl methacrylate) (PMMA) nanocomposite strain sensor and human health by smart Lycra denim textile sensor. Methods such as impact hammer test and NI-daq, finite element method (FEM) simulation by Abaqus 6.12, and fast Fourier transform (FFT) study were applied for frequency monitoring of SS304. For human health monitoring, edema disease inspection, cough, and biceps locomotion were studied by graphene sol–gel textile sensor. We report eight sensors fabricated by scotch tape exfoliation method and their sensitivity was checked in terms of gauge factor (GF). The highest and lowest GF-based sensors were checked for sensitivity in the defect (hole) specimen. These sensors were used to sense the natural frequency of SS304 at three different positions in the cantilever beam. The same quantity of GNPs was used for making Lycra denim textile sensors for human health monitoring. The Lycra denim textile sensor showed a 216% change in resistance in the left calf muscle, which is less than right leg flexibility, indicating good sensitivity. In addition, the textile sensor helped in sensing coughing and biceps monitoring. The ease in fabrication and high sensitivity demonstrate the potential ability of GNPs for futuristic smart material for structural and human health monitoring. [ABSTRACT FROM AUTHOR]

This study presents iterative optimal sensor placement (OSP) techniques using the modal assurance criterion (MAC) and the effective independence (EI) algorithm. The algorithms use the proper orthogonal mode (POM) extracted from the frequency response functions (FRFs) of dynamic systems within a wide range of frequencies. The FRF-based OSP method proposed in this study has the merit of reflecting dynamic characteristics, unlike the mode shape-based method. Evaluating the MAC values and the EI indices at each iteration, the DOFs of low contribution to the objective function of candidate sensor DOFs are deleted from master DOFs and moved to slave DOFs. This process is repeated until the sensor number corresponds with the master DOFs. The validity of the proposed methods is illustrated in an example, the sensor layouts by the proposed methods are compared, and the layout inconsistency between the MAC and the EI techniques is analyzed. [ABSTRACT FROM AUTHOR]

Multipocket thin-walled parts are used extensively in aerospace industry, and their dynamics greatly depend on the structures. Available methods for the prediction of their dynamics are repetitive modeling and computational demanding. This paper presents a generalized equivalent method with high computational efficiency to predict the dynamics of multipocket thin-walled parts. The parts compose of a series of dynamics units, which can be further decomposed into thin plate and adjacent structure. The dynamics model of the thin plate is developed based on the characteristic of the dimension and the vibration in machining. The adjacent structure is regarded as the flexible boundary condition of the thin plate model, which is equivalent as cantilever beam. The cross sections of the beam are parameterized based on subareas, which makes the calculation rapidly. This generalized equivalent method is validated by the frequency response function (FRF) measurement of seven points on the benchmark including different thin plates and adjacent structures. The proposed method reaches a good agreement with the experimental tests; meanwhile, it can avoid reduplicative modeling and is ~ 100 times more computationally efficient than the typical finite element method. [ABSTRACT FROM AUTHOR]

To facilitate climate change adaptations and water management, estimates of precipitation retention time (time required for precipitation to reach a lake) can help to accurately determine a water body's terrestrial water storage capacity and water cycle. Although estimating the precipitation retention time on land is difficult, estimating the lag between precipitation on land and a rise in lake water levels is possible. In this study, the delay times (using a depth metre installed in the mooring system in the northern basin of Lake Biwa from August 2017 to October 2018) were calculated using response functions, and it evaluated the precipitation retention time in the catchment. However, as several delays between the river surface flow (<1 d) and shallow subsurface flow (≈45 d) remained unidentified, the delay times resulting from direct precipitation on the lake as well as from internal seiches were determined. The results suggest that delay times of approximately 20 d correspond to the paddy–waterway system between the river inflow and the subsurface flow, and that this effect corresponds to that of large rivers such as the Ane River. These findings can enhance water management strategies regarding the regulation of river flows, adapting to climate change-induced fluctuations in precipitation. [ABSTRACT FROM AUTHOR]

Increased attention has been given to ground-borne vibrations induced by railway vehicles and to the effects of these vibrations as they propagate through the ground into nearby buildings. Various studies, mainly based on numerical methods as well as physical modelling, have been carried out to investigate this problem. To study the dynamic response of tunnels and the surrounding soil due to train-induced vibration loads, a centrifuge test was conducted with a small-scale model in 1 g and 50 g stress field environments. An aluminum tube was embedded in sand to model the underground tunnel. A small parallel pre-stressed actuator (PPA) was employed to apply vibration loads on the tunnel invert. The model responses were measured using accelerometers. Both time and frequency domain analyzes were performed. The test results demonstrated that electronic noise had a clear impact on the test results and should be eliminated. It also found that the dynamic response of both the tunnel and soil were affected by the stress field. Therefore, it is important to account for the stress field effects when assessing the ground-borne vibration from tunnels. [ABSTRACT FROM AUTHOR]

Considering the frequency dispersion and the scale sensitivity in wave propagation, the central frequency and bandwidth should be carefully selected in Lamb wave-based structural health monitoring. These crucial parameters are hardly determined without the prior knowledge. Therefore, massive trials should be conducted before the formal test. A Fourier spectral Frequency Response Function (FRF) method is proposed to address this problem. As the FRF contains wide-band information on the relationship between excitation and output, the Lamb wave responses in a wide frequency range can be estimated by using an arbitrary virtual input within the frame of single FRF test, being free from the massive experimental works. The theoretical FRF can be obtained from the unit impulse response of a linear system, but this path is impracticable due to the difficulty of exciting the ideal impulse. Considering the integral relationship and Fourier differential properties between step excitation and the ideal impulse, a robust approximation of wave signal by FRF is developed. Synthetic data tests and experiments both verified that the present method can accurately extract the response in isotropic and anisotropic materials for the specifically designed excitation signal in a wide parameter range. [ABSTRACT FROM AUTHOR]

Vibration-based damage detection techniques receive wide attention of the research community in recent years to overcome the limitations of conventional structural health monitoring methods. The modal parameters, namely, natural frequencies, mode shapes, transmissibility, frequency response function (FRF), and other damage sensitive features are usually employed to identify damage in a structure. The main objective of this review is to generate a detailed understanding of FRF-based techniques and to study their performance in terms of advantage, accuracy, and limitations in structural damage detection. This paper also reviews various approaches to develop methodologies in terms of efficiency and computational time. The study observed that excitation frequency, location of application of excitation, type of sensor, number of measurement locations, noise contamination in FRF data, selection of frequency range for simulation, weighting and numerical techniques to solve the over-determined set of equations influence the effectiveness of damage identification procedure. Limitations and future prospects have also been addressed in this paper. The content of this paper aims to guide researchers in developing formulations, updating models, and improving results in the field of FRF-based damage identification. [ABSTRACT FROM AUTHOR]

By introducing disorders in thickness and cross-sectional size, the random behavior of wave propagation in the one-dimensional randomly disordered phononic crystal with finite cells is studied from the statistical point of view. A finite element model of a one-dimensional phononic crystal is established based on the lumped-mass method. Using the proposed model, an analytical solution to the frequency response function is presented, which does not require the large-scale stiffness equation to be solved. Based on 105 samples, the means, standard deviations, and confidence intervals of the random frequency response functions with different degrees of disorder are discussed, which show the wave localization is strengthened in the passband of periodic phononic crystal and weakened in the stopband of periodic phononic crystal. Furthermore, it is found that the considered randomly disordered phononic crystals not only have the wave localization, but also the wave delocalization. When the degree of disorder is small, the wave delocalization is more likely to occur. With increasing of degree of disorder, the probability of wave localization is increasing. [ABSTRACT FROM AUTHOR]

• Innovates wheel polygonal wear (WPW) diagnosis with calibrated wheel-rail FRF. • Cepstral-Bayesian FRF calibration using hybrid numerical-experimental data. • Weighted angle-synchronous moving average (WASMA) filter out rail disturbance. • FRF and WASMA synergy enhances accuracy for WPW quantitative diagnosis. The safety and efficiency of high-speed trains in China are significantly impacted by Wheel Polygonal Wear (WPW). Onboard monitoring methods for WPW currently suffer from reduced precision due to the intrinsic modal characteristics of the wheel-rail system and external disturbances such as rail roughness. To address this issue, this study develops a quantitative diagnostic approach for WPW employing a calibrated Frequency Response Function (FRF). A novel Cepstral-Bayesian calibration method is proposed for calibrating the FRF to precisely represent the real behaviors of the wheel-rail system, which is critical for considering system resonances. This method integrates information from dynamic simulation with sensor measurements. Furthermore, the weighted angle-synchronous moving average preprocessing is combined to reduce disturbances from rail roughness. Both dynamic simulations and field test data validate this technique, demonstrating its superior accuracy in quantifying WPW compared to existing methodologies. This offers a robust solution for both identifying and precisely quantifying WPW. [ABSTRACT FROM AUTHOR]

Vibration-based damage identification techniques have gained popularity immensely in the field of structural health monitoring (SHM). Frequency response function (FRF)-based damage quantification is mainly performed based on iterative model updating techniques. Most of these methods are time-consuming and erroneous in higher modes. Spectral element method (SEM) can overcome some of these limitations and can determine FRF expression directly for a broad class of civil structures. However, a closed-form expression for multiple damage severity is not proposed to date. In this study, an FRF-based formulation for quantifying damage has been proposed with the help of SEM in order to bypass the mode shape extraction for damage identification. To determine the effectiveness of the proposed formulation both numerical and experimental studies have been performed. A numerical simulation has been performed on a 14-storey shear building. Damage has been introduced by reducing the storey stiffness at intermediate and adjacent storeys. It has been perceived that damage severity at any storey can be estimated with only 3 sensors, one at the top storey and two others at the adjacent floors of the desired storey. To verify the effectiveness of the proposed expression, an experimental study has been carried out on a 9-storey miniature model. It has been observed that the first resonating peak amplitudes of the responses recorded simultaneously at desired locations of intact and damaged structures are sufficient to estimate the damage intensity. Thus, the proposed formulation is efficient as an output measurement-based approach. The novelty of this study lies in the proposed closed-form FRF-based multi-damage severity expression involving minimum number of sensors and without any information on the input excitation. The results obtained from both numerical and experimental study showcase the robustness, simplicity and applicability of the proposed formulation. [Display omitted] • FRF-based closed-form expression for damage quantification developed. • The proposed approach detoured mode shape extraction minimizing error and computational time. • The one-shot approach involves only 3 sensors to determine damage severity at a particular storey. • The effortless application of proposed approach with real data sets it apart. • Study novelty involves mathematical development and results within permissible range. [ABSTRACT FROM AUTHOR]

Nonlinear energy sinks (NESs) have emerged as a promising solution to overcome the narrow effective bandwidth of linear dynamic vibration absorbers such as the tuned mass damper (TMD). In particular, track NESs are increasingly attracting attention as they are capable of generating nonlinear restoring forces by the movement of an additional mass on the curved tracks. The present study aims to investigate and explore the versatile characteristics of track NESs in structural vibration control. To this end, three different track profiles are considered, namely the profiles designed by a quartic term only, by combined positive quadratic and quartic terms, and by combined negative quadratic and positive quartic terms. Their profiles and damping coefficients are analytically derived in closed form. The frequency response functions of standalone track NESs are constructed using the Harmonic Balance Method and compared with those obtained by the 4th-order Runge-Kutta method, and the dynamic responses, including the displacements, the phase planes, the nonlinear stiffness forces, and the vibrational frequencies, of the track NESs are presented and discussed under different excitation amplitudes and frequencies. The effectiveness and robustness of using track NESs for structural vibration control are also systematically investigated and compared with TMD under harmonic and white-noise ground excitations. Results show that the closed-form solutions of optimal profile and damping coefficients are sufficiently accurate for lightly damped structures, and the frequency response functions of track NESs can be accurately estimated using the Harmonic Balance Method for low and moderate excitations, although their dynamic responses are sensitive to the excitation amplitudes and frequencies. Furthermore, in comparison to TMD, the track NESs are superior in terms of decreased stiffness and smaller working strokes. In general, the present study demonstrates the potential of using track NESs as an effective and robust alternative for structural vibration control. • Track profiles and damping coefficients of three track nonlinear energy sinks (NESs) are analytically derived. • Frequency responses functions and dynamic responses of three track NESs are constructed and investigated. • Control performances of three track NESs are examined under harmonic and white-noise excitations. [ABSTRACT FROM AUTHOR]

A novel biometric recognition method is presented for future personal devices, utilizing the frequency responses of the human body, especially the fingers, for personal identification. A series of experimental vibration modal analyses were conducted to measure the frequency response functions (FRFs) of individuals' fingers. In addition, a biodynamic lumped system model was constructed for the major components of a finger, including phalanges, joints, and skin. Analytical FRFs were then computed for a comparative study with the measured FRFs. In the person identification process, we employed an effective feature extraction method based on the correlation coefficient between frequency bins of the measured FRFs to extract the most effective set of frequency bins from the entire FRF spectrum. These extracted features were utilized to train a support vector machine for classifying individuals. In a controlled experimental setup, the classification results showed a maximum accuracy of 99%, affirming the feasibility of using the vibration responses of human fingers as a novel biometric method for person recognition. [ABSTRACT FROM AUTHOR]

Model updating of large-scale structures is difficult to carry out when using a frequency response function (FRF) for damage identification, as the solutions for the global system matrices with too many degrees of freedom are required in each iteration. In this paper, a substructure damage identification method is proposed based on the model updating of the acceleration FRF. The original finite element model is divided into several substructures using the improved reduced system (IRS) by the dynamic condensation method, resulting in the simplified substructure model. The final simplified model is composed of the simplified mass matrix and stiffness matrix of the substructure considered. The damage acceleration FRF to be identified is used to iteratively update the simplified model. The locations and extents of the damage elements are obtained by updating the results, which reduces the number of uncertain parameters to be updated and leads to the rapid convergence of the optimization process. In the iteration, L1 norm regularization is introduced to solve the ill-posed problem, which improves the stability of the identification results. A numerical simulation of a six-story steel frame structure under various working conditions was carried out to verify the effectiveness of the proposed method, which was also validated by the experiments. The robustness and performance of the proposed damage identification method based on substructures have been demonstrated. [ABSTRACT FROM AUTHOR]

The tuned mass damper (TMD) has been used in machining processes for reducing forced vibration, suppressing chatter, and improving machined surface quality. In micro-milling process, the tiny size of the cutting tool-tip and the high rotating speed bring challenges in implementing the TMD. Besides, the TMD needs to have two degrees-of-freedom (DOFs) for reducing vibrations of micro-mill in two orthogonal directions. This paper presents the chatter suppression for micro-milling by attaching a two-DOF TMD to the tool shank and rotates with the cutting tool. The frequency response function (FRF) at the tip of the micro-mill clamped by an aerostatic spindle is predicted using receptance coupling analysis. A two-DOF TMD is designed via graphical approach based on the FRF result at the tool-tip. The natural frequencies and damping ratio of the TMD are optimized under different spindle speeds in order to enhance the cutting stability. The chatter stability of micro-milling is predicted considering the gyroscopic and centrifugal effects of the TMD structure. Modal tests and micro-milling experiments are conducted to validate the effect of the TMD on chatter stability. The results show that the TMD is able to improve the critical depth of cut by 13 folds, and satisfy the compact design requirement for micro-milling. • Shank-mounted TMD satisfies the specific geometric requirement in micro-milling. • Design of TMD using graphical approach based on synthesized FRFs of substructures. • The centrifugal and gyroscopic effects of TMD on chatter stability are studied. • Chatter-free axial depth of micro-milling operation is enhanced by 13 folds. [ABSTRACT FROM AUTHOR]

In the framework of vehicle-track interaction, this work puts an emphasis on clarifying the influence of sleeper finite element types on system dynamic responses. Three sleeper element types, namely the rigid-body, extensible Euler-Bernoulli beam and solid element are used respectively in the track system modelling with detail mathematical formulations presented. The rails are modelled as Timoshenko beams. The ballasted track system is subject to a moving vehicle with coupled wheel-rail interactions. From aspects of both frequency- and time- domain analysis in the numerical study, the effectiveness of this model has been validated. The influences of the sleeper finite element type, the sleeper support stiffness and damping coefficient on the system responses have been investigated. [ABSTRACT FROM AUTHOR]