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This paper presents a new method for locating and quantifying damage in beam-like structures based on the modal constant curvatures and natural frequency extracted from the measurements of the Frequency Response Function (FRF). The modal constant curvature is very effective for localising the damage due to the discontinuity created near the damaged zone. However, in classical vibrational measurement techniques, the discontinuity is confounded by measurement noise. To overcome these limitations, a new index is developed by normalising the curvature of the first fourth vibration mode. The new index gives a value of 1 in the damage location with the elimination of all the values that can distort the results. In order to make the index sensitive for damage depth, quantification charts are developed based on natural frequency ratios. Numerical simulations on a cantilever beam demonstrated the high sensitivity of the proposed method, with errors of under 0.4%. Experimental tests on a cantilever beam confirmed its reliability, with errors of under 3.6%. The method’s low sensitivity to disturbance makes it a robust method for locating and quantifying damage in mechanical structures. [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]

Modelling the dynamic interaction between equipment and the bogie of a railway vehicle is crucial for the vibration and fatigue analysis of equipment. Current methods such as finite element and rigid-flexible coupling techniques are cumbersome. In this study, an efficient modelling approach is proposed to obtain the dynamic properties of coupled equipment. First, the vehicle and equipment are treated as independent modules, and further coupled using the frequency response function (FRF)-based substructuring method (FBSM). The FBSM is then developed from the finite element method to derive the FRF for the force to stress of equipment. Validation against experimental data and existing methods for a metro vehicle demonstrates the efficacy of our approach. The results indicate that the proposed approach models the vehicle and equipment as independent modules, eliminating the interdependent modeling steps of the previous approach and requiring less computation. The coupled small-mass equipment has a negligible influence on the dynamic properties of the vehicle bogie, but its dynamic properties are sensitive to vehicle and connection stiffness. Moreover, the vibration fatigue of equipment caused by the wheel/rail roughness can also be analyzed with the proposed approach. [ABSTRACT FROM AUTHOR]

To efficiently attenuate flexural waves at low-frequency range (0–100 Hz) in the complex vibration environment, a metamaterial plate consists of steel, magnetorheological elastomer and cement-based piezoelectric composite (CPC) is proposed in this paper. The propagation of flexural waves in binary and ternary periodic material plate are studied by the plane wave expansion method (PWE) which combined with the Mindlin plate theory, and the frequency response functions are calculated by the finite element method (FEM). The dispersion curves under open and shorted electrical boundary conditions are considered, the regulation effect of bias magnetic field on the band gap is explored. The results show that material and geometric parameters significantly influence the band gap. Although the effect of electrical boundary conditions on the band gap can be ignored, the introduction of the CPC widens the width of band gap by 130%. The location and width of the band gap can be adjusted by varying magnetic field intensity, as magnetic field intensity H intensifies from 0 A / m to 8 × 10 5 A / m , the band gap has a 25% increase. The proposed metamaterial plate has certain stiffness and strength, and it is suitable to be used in engineering. The results may provide an alternative avenue for understanding and optimizing the design of metamaterial plates with wide tunable band gaps. [ABSTRACT FROM AUTHOR]

AbstractThis study aims to: (1) apply computer-aided engineering to automotive design, (2) investigate the dynamic load transmission lines causing vibrations in the truck cabin, and (3) analyze and compare vibration characteristics on different road types. A model of a light truck was numerically examined. A frequency response function and a dynamic simulation were used to study how the road surface’s excitation force affects structure vibration. The Multi-body Dynamics simulation was performed to estimate the external force acting on the vehicle. In the case of a flat road at a speed of 60 km/h, the counterforce values almost remain constant, corresponding to 1 G. In the case of a vehicle crossing a hole, at a speed of 30 km/h, the counterforce is about 3.57 and 5.67 G at the front and rear axles, respectively. On a bumpy road, at 30 km/h, the counterforce is about 3.3 G on the front axle and 7.2 G on the rear axle. The FRF analysis shows that the truck cabin’s resonant frequency is 29 to 32 Hz. [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 6 m 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]

Optimal sensor placement (OSP) is one of the essential factors affecting the accuracy of health management, particularly in health monitoring driven by mode information. A novel OSP method based on active learning is proposed to effectively capture modal shapes for Structural Health Monitoring (SHM). First, the optimal Latin Hypercube Sampling is carried out to generate initial sensor positions, and the corresponding amplitudes of modal shapes at these positions are obtained by a frequency response function. Subsequently, data-driven models are built to be treated as virtual sensors to reconstruct the integrated modal shapes of the structure, and the accuracies of the results are calculated. Then, considering the distribution of the input sensor position, an improved reliability-based expectation improvement function (IREIF2) is applied to find the optimal sensor positions by optimizing the parameters of the probability density function in IREIF2. Finally, the position and response of the optimal sensor are used to update the data-driven models for more accurate modal shape reconstruction, and the accuracies are calculated to determine whether the OSP process continues. Once the accuracies meet the desired criteria, the optimal sensor positions are also obtained. The superiority of the proposed method is verified by the comparisons with other OSP methods, and different case studies are also used to prove the proposed method can realize OSP for SHM. [ABSTRACT FROM AUTHOR]

Turbulence excitation is an unavoidable form of excitation in flutter flight tests, and it is also a necessary and effective excitation method in high-speed flights, dives, other high-risk test, and high-frequency modal information mining. However, because the turbulence excitation signals are unmeasurable in the time domain, although the turbulence response contains rich and valuable flutter test information, the randomness and low quality of the data often cause difficulties in modal analysis. Therefore, an improved frequency domain decomposition algorithm for turbulence response processing is proposed in this paper. First, due to the irrelevancy of the atmospheric excitation, the power spectral density function matrix of the multi-channel turbulence response is subjected to singular value decomposition. There is a mathematical relationship between the maximum singular value curve and the system frequency response function. Second, the modal assurance criteria are used to calculate the maximum singular value of a single-degree-of-freedom system. Finally, an orthogonal polynomial method is applied to fit the maximum singular value curve, and the system identification is performed directly in the frequency domain. The simulated data and a certain type of aircraft flutter flight test data are used to verify the proposed method, and the results confirm the effectiveness and engineering applicability of the method developed in this work. [ABSTRACT FROM AUTHOR]

Due to increasing demands regarding higher manufacturing accuracy and the machining of high-strength materials, the stiffness and load-carrying capacity of main spindles must be enhanced. One approach is to replace the conventionally used angular contact ball bearings, so called spindle bearings, with tapered roller bearings of the same size, which have a higher stiffness and load carrying capacity due to their larger rolling contact. In case the speed requirement is below a speed parameter n · d m = 0.9 × 10 6 mm/min, the poorer speed parameter of tapered roller bearings can be compensated by a sufficiently high lubrication quantity. However, the stiffness increase by using this bearing type in main spindles has not yet been quantified in field tests. Therefore, the aim of this paper is to demonstrate the stiffness advantage of a spindle with an elastically arranged tapered roller bearing compared to a conventional spindle with angular contact ball bearings by machining tests. First, the radial load displacement characteristic of the newly developed tapered roller bearing spindle is tested in advance on an isolated test rig. In machine cutting tests, full slots are milled in an aluminum block. During the tests, the axial and radial displacements of the spindle shaft relative to the housing are measured and evaluated in radial and axial direction. These tests are repeated and compared with the conventional spindle. By varying the process parameters such as cutting depth, feed rate or rotational speed, the increased stiffness of the tapered roller bearing spindle compared to the conventional spindle is illustrated based on the measured displacements. Moreover, frequency response measurements at different speeds underpin the improved damping of the tapered roller bearing spindle. Assuming that the speed requirements are not too high and the tapered roller bearing is sufficiently lubricated, the use of this type of bearing can significantly increase the stiffness and thus the manufacturing precision in the long term for main spindles. [ABSTRACT FROM AUTHOR]

This paper presents frequency response function (FRF) expansion techniques that minimize the difference between the analytical and predicted FRF matrices to satisfy the FRF constraints. The measured FRF relationships at a small number of locations were used as constraints. The expansion method is useful for estimating the rotational FRFs that are difficult to measure or apply using frequency-based substructuring (FBS) techniques. The validity of the proposed method, including the effects of external noise, was confirmed using numerical examples. An FBS algorithm was also derived by incorporating the FRFs of each substructure, and the compatibility conditions were transformed into FRFs with pseudomasses at the joint nodes. A discrepancy between the FRFs of the synthesized system estimated using the proposed method and the analysis results of the entire system was observed in the numerical example, and the reasons for the discrepancy were investigated and discussed. It is estimated that the proposed FBS method can be enhanced by combining it with other dynamic substructuring techniques and supplementing additional information, such as measured FRFs. [ABSTRACT FROM AUTHOR]

Damage location vector (DLV) method is a model-based structural health monitoring approach that needs the frequency response–function response of the structure. A review of the literature indicates that although the DLV method accurately identifies the damage location in the single-damage structures, it does not work properly for the multi-damage. Accordingly, the aim of this research is to advance the DLV approach to increase its accuracy to detect the damage locations and severities in the multi-damage structures. In this regard, experimental and numerical studies were performed on the two-fixed ends steel beam having multiple damages with different intensities. During laboratory tests, the vibration response of steel beam specimens with multiple defects stimulated by hammer impact was measured. Different sensor locations were considered in the tests. A finite-element model of the steel beam was developed to calculate the dynamic response of undamaged beam under impact loading. Based on the fundamentals of hypothesis testing and data fusion, a threshold was derived to advance the DLV approach to detect the multiple damages. Moreover, the effect of sensor position on the performance of the DLV approach was investigated. The proposed method was also applied to a long-span box-shaped bridge to investigate its accuracy and efficiency for detecting damages in realistic complex structures. Moreover, the results obtained from the advanced DLV method were compared with other conventional methods, considering the effect of noise and different damage scenarios. The findings reveal that the advanced DLV approach proposed in this study accurately detects the defect locations and severities in the structures having multiple damages. [ABSTRACT FROM AUTHOR]

This work is concerned with the kernel-based approximation of a complex-valued function from data, where the response function of a partial differential equation in the frequency domain is of particular interest. In this setting, kernel methods are employed more and more frequently; however, standard kernels do not perform well. Moreover, the role and mathematical implications of the underlying pair of kernels, which arise naturally in the complex-valued case, remain to be addressed. We introduce new reproducing kernel Hilbert spaces of complex-valued functions and formulate the problem of complex-valued interpolation with a kernel pair as minimum-norm interpolation in these spaces. Moreover, we combine the interpolant with a low-order rational function, where the order is adaptively selected based on a new model selection criterion. Numerical results on examples from different fields, including electromagnetics and acoustics examples, illustrate the performance of the method in comparison to available rational approximation methods. [ABSTRACT FROM AUTHOR]

The use of digital image correlation for modal analysis is becoming an appealing option thanks to its non-contact and full-field measurement process. However, frequency response function (FRF) estimation can be challenging due to the limited number of time domain data and heavy measurement noise. Thereby, the present work aims to propose a method which improves the estimation accuracy of point-wise FRFs. Firstly, a Gaussian-process-based spatial-frequency model is proposed, which makes use of the intrinsic properties of the FRF and the local spatial information of field measurements. Then, a Bayesian solution is developed, which is enforced by a stable and efficient numerical procedure. Finally, the effectiveness of the proposed method is verified by making a comparison with the spectral estimator through the use of simulated data, and it is further validated based on an experimental application. [ABSTRACT FROM AUTHOR]

The vibrational characteristics of the Hybrid III and NOCSAE headforms are not well understood. It is hypothesized that they may perform differently in certain loading environments due to their structural differences; their frequency responses may differ depending on the impact characteristics. Short-duration impacts excite a wider range of headform frequencies than longer-duration (padded) impacts. While headforms generally perform similarly during padded head impacts where resonant frequencies are avoided, excitation of resonant frequencies during short-duration impacts can result in differences in kinematic measurements between headforms for the matched impacts. This study aimed to identify the natural frequencies of each headform through experimental modal analysis techniques. An impulse hammer was used to excite various locations on both the Hybrid III and NOCSAE headforms. The resulting frequency response functions were analyzed to determine the first natural frequencies. The average first natural frequency of the NOCSAE headform was 812 Hz. The Hybrid III headform did not exhibit any natural frequencies below 1000 Hz. Comparisons of our results with previous studies of the human head suggest that the NOCSAE headform's vibrational response aligns more closely with that of the human head, as it exhibits lower natural frequencies. This insight is particularly relevant for assessing head injury risk in short-duration impact scenarios, where resonant frequencies can influence the injury outcome. [ABSTRACT FROM AUTHOR]

Accurate information on vehicle parameters is essential for vehicle design, vehicle-bridge interaction analysis, and road maintenance. Currently, most vehicle parameters identification (VPI) methods are deterministic and rely on strict experimental conditions. This paper proposes a simple method based on Bayesian framework to identify uncertain vehicle parameters, which only requires the vibration response of the vehicle under arbitrary excitation. First, the dynamics of the vehicle is analyzed and the link between excitation and response is established using the vehicle frequency response function. Subsequently, the likelihood function is formulated based on the difference function between the measured responses and the expected responses of updated model. Notably, this method introduces a creative probabilistic form of the frequency-domain response assurance criterion. Furthermore, a numerical simulation of the vehicle driving over bumps is performed to assess the influence factors on VPI, such as noise pollution and the excitation correlation between the front and rear wheel. At last, the parameters of a van are identified through field test and the reliability of the results is demonstrated. [ABSTRACT FROM AUTHOR]

Resonance frequencies of a mechanical system are the most important parameters that determine the dynamic characteristics of the system. When the frequencies of the harmonic forces under the influence of the system coincide with the resonance (natural) frequencies of the system, a resonance situation occurs and the mechanical system vibrates with high amplitudes. This can cause serious damage to the system by causing effects such as break, fatigue, impact, noise on the bearings, connections and elements in the system. It is possible to eliminate some resonance frequencies of mechanical systems in an examined frequency range using pole-zero cancellation methods by shifting a resonance frequency of the system to an anti-resonance frequency or an anti-resonance frequency to a resonance frequency. Thus, a solution can be obtained for some vibration problems. In this study, a new method using the Sherman-Morrison formula is presented to eliminate some of the resonance frequencies for some FRFs (Frequency Response Functions) of mechanical systems with pole-zero cancellation. In order to eliminate a selected resonance frequency of the system in any FRF determined using the presented method, a mass (kg) and a grounded spring (N/m) modification are made and the required modification values for this are calculated by solving the obtained non-linear equation set numerically. With the proposed method, it is aimed to contribute to the literature by presenting an alternative approach for the solution of vibration problems by cancelling some selected resonance frequencies. The main highlight of the method is there is no need of a matrix inversion for calculating the required modification values. This provides a very fast solution. In addition, the proposed method uses directly the FRFs of the active coordinates (response, excitation and modification) only, which makes the method very useful for practical engineering applications. [ABSTRACT FROM AUTHOR]

Damages to various building structures often occur over their service life and can occasionally lead to severe structural failures, threatening the lives of its residents. In recent years, special attention has been paid to investigating various damages in buildings at the early stage to avoid failures and thereby minimize maintenance. Structural health monitoring can be used as a tool for damage quantification using vibration measurements. The application of various sensors for measuring accelerations, velocity and displacement in civil infrastructure monitoring has a long history in vibration-based approaches. These types of sensors reveal dynamic characteristics which are global in nature and ineffective in case of minor damage identification. In a practical application, the available damage detection approaches are not fully capable of quickly sensing and accurately identifying the realistic damage in structures. Research on damage identification from strain data is an interesting topic in recent days. Some work on the cross-correlation approach is now a centre of attraction and strictly confined to bridge or symmetric structures. The present paper uses strain data to validate the cross-correlation approach for detecting damage to building structures. The effectiveness of the methodology has been illustrated firstly on a simply supported beam, then on a 5-storey steel frame and a 6-storey scaled-down reinforced concrete shear building and lastly on a frame structure with moving load as a special case. The results show that this approach has the potential to identify damages in different kinds of civil infrastructure. [ABSTRACT FROM AUTHOR]

Multi-segment shell typical of underwater vehicles is currently important underwater equipment. Stealth performance is a key indicator to improve the working capacity of underwater vehicles. Low-noise design is an important means to improve stealthy performance. Accurate and effective identification of its structure Frequency Response Function (FRF) is the premise of low-noise design. However, the multi-section shell joint interface has many connection points, complex transmission path and typical nonlinear characteristics, which challenges the acquisition of its structural FRF. The Receptance Coupling Substructure Analysis (RCSA) is used to segment the multi-stage shell, which can realize the integration of finite element method and experimental method, and provide an effective way to obtain the FRF of multi-segment shell. At the same time, the multi-segment shell is a typical thin-wall structure, and its actual buckling process under impact is a nonlinear (large deformation) process. Therefore, the nonlinear joint interface is constructed based on linear connection, and the RCSA for nonlinear joint interface is studied. On the basis of accurately obtaining the FRF, it is of theoretical and application significance to study the low noise design of shell. [ABSTRACT FROM AUTHOR]

The substructure method based on the frequency response function is an effective method to solve the frequency response function of locally variable structure, which is especially suitable for the design of vibration absorber parameters in the inertial navigation vibration reduction system. In this paper, one inertial navigation vibration reduction system was taken as an example, and its random dynamic response model was established by using the substructure method based on the frequency response function. Then the influence of the variation of the stiffness and damping parameters of the vibration absorber on the random vibration response of the system was analyzed. The results showed that: (1) it is difficult to effectively reduce the vibration response of inertial navigation vibration reduction system by simply changing the axial stiffness of the vibration absorber, but probably increasing the response in other directions; (2) the vibration response of the inertial navigation vibration reduction system will decrease with the increase of damping, which indicates that the response of the inertial vibration reduction system mainly includes medium and low frequency. The numerical example shows that the proposed method is suitable for the optimization of vibration absorber parameters in the inertial navigation system.

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 spindle tool is an important module of the machine tool. Its dynamic characteristics directly affect the machining performance, but it could also be affected by thermal deformation and bearing preload. However, it is difficult to detect the change in the bearing preload through sensory instruments. Therefore, this study aimed to establish a digital thermal–mechanical model to investigate the thermal-induced effects on the spindle tool system. The technologies involved include the following: Run-in experiments of the milling spindle at different speeds, the establishment of the thermal–mechanical model, identification of the thermal parameters, and prediction of the thermal-induced preload of bearings in the spindle. The speed-dependent thermal parameters were identified from thermal analysis through comparisons with transient temperature history, which were further used to model the thermal effects on the bearing preload and dynamic compliance of the milling spindle under different operating speeds. Current results of thermal–mechanical analysis also indicate that the internal temperature of the bearing can reach 40 °C, and the thermal elongation of the spindle tool is about 27 µm. At the steady state temperature of 15,000 rpm, the bearing preload is reduced by 40%, which yields a decrease in the bearing rigidity by approximately 16%. This, in turn, increases the dynamic compliance of the spindle tool by 22%. Comparisons of the experimental measurements and modeling data show that the variation in bearing preload substantially affects the modal frequency and stiffness of the spindle. These findings demonstrated that the proposed digital spindle model accurately mirrors real spindle characteristics, offering a foundation for monitoring performance changes and refining design, especially in bearing configuration and cooling systems. [ABSTRACT FROM AUTHOR]

Because robotic milling has become an important means for machining significant large parts, obtaining the structural frequency response function (FRF) of a milling robot is an important basis for machining process optimization. However, because of its articulated serial structure, a milling robot has an enormous number of operating postures, and its dynamics are affected by the motion state. To accurately obtain the FRF in the operating state of a milling robot, this paper proposes a method based on the structural modification concept. Unlike the traditional excitation method, the proposed method uses robot joint motion excitation instead of hammering excitation to realize automation. To address the problem of the lack of information brought by motion excitation, which leads to inaccurate FRF amplitudes, this paper derives the milling robot regularization theory based on the sensitivity of structural modification, establishes the modal regularization factor, and calibrates the FRF amplitude. Compared to the commonly used manual hammering experiments, the proposed method has high accuracy and reliability when the milling robot is in different postures. Because the measurement can be performed directly and automatically in the operation state, and the problem of inaccurate amplitudes is solved, the proposed method provides a basis for optimizing the machining posture of a milling robot and improving machining efficiency. [ABSTRACT FROM AUTHOR]

The paper presents a method for determining the dynamic response of systems containing viscoelastic damping elements with uncertain design parameters. A viscoelastic material is characterized using classical and fractional rheological models. The assumption is made that the lower and upper bounds of the uncertain parameters are known and represented as interval values, which are then subjected to interval arithmetic operations. The equations of motion are transformed into the frequency domain using Laplace transformation. To evaluate the uncertain dynamic response, the frequency response function is determined by transforming the equations of motion into a system of linear interval equations. Nevertheless, direct interval arithmetic often leads to significant overestimation. To address this issue, this paper employs the element-by-element technique along with a specific transformation to minimize redundancy. The system of interval equations obtained is solved iteratively using the fixed-point iteration method. As demonstrated in the examples, this method, which combines the iterative solving of interval equations with the proposed technique of equation formulation, enables a solution to be found rapidly and significantly reduces overestimation. Notably, this approach has been applied to systems containing viscoelastic elements for the first time. Additionally, the proposed notation accommodates both parallel and series configurations of damping elements and springs within rheological models. [ABSTRACT FROM AUTHOR]

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]

Purpose: In many engineering structures, undesirable harmonics can occur due to changes in operating conditions. The effects of these unwanted harmonics can be eliminated by assigning the zeros of point or cross Frequency Response Functions (FRFs) of the structure to the frequencies of the unwanted harmonics. In this study, a method is proposed for assigning the zeros of point or cross FRFs to particular frequencies. Methods: The method is based on Sherman–Morrison (SM) formula known in matrix theory. The inverse structural modification problem was investigated by making spring modifications on a structure to assign zeros. Results: The required modifications are calculated by solving the set of equations containing nonlinear combinations of the spring coefficients. Conclusion: There is no need for a physical or modal model of the structure because FRFs are used directly in the method. Therefore, it is quite practical in applications. The accuracy and efficiency of the presented method are illustrated by different numerical simulations and successful results are obtained. [ABSTRACT FROM AUTHOR]

The dynamic substructuring design describes the dynamic responses in the modal, frequency and physical domains using coupling methods at joint nodes. This paper presents dynamic structuring methods to modify existing substructuring methods by merging the concept of interfacial forces in the satisfaction of compatibility conditions at joint nodes. The algorithms correspond to a type of model reduction approaches that use a few modes of substructures with the assumption of pseudo-masses at the joint nodes of the substructures. It was verified through numerical examples that the pseudo-masses rarely affected the dynamic responses of the synthesized structure. A frequency response function-based substructuring method was derived by applying interface forces at joint nodes to frequency response function (FRF). The proposed dynamic substructuring methods are expressed in explicit forms for synthesizing substructures without any numerical schemes. The validity of the proposed method was illustrated using two numerical examples. The limitations of this study are evaluated using numerical examples.

The use of digital image correlation for modal analysis is becoming an appealing option thanks to its non-contact and full-field measurement process. However, frequency response function (FRF) estimation can be challenging due to the limited number of time domain data and heavy measurement noise. Thereby, the present work aims to propose a method which improves the estimation accuracy of point-wise FRFs. Firstly, a Gaussian-process-based spatial-frequency model is proposed, which makes use of the intrinsic properties of the FRF and the local spatial information of field measurements. Then, a Bayesian solution is developed, which is enforced by a stable and efficient numerical procedure. Finally, the effectiveness of the proposed method is verified by making a comparison with the spectral estimator through the use of simulated data, and it is further validated based on an experimental application.

Abstract Composite materials have attracted researchers in vibration and noise control applications due to their significant dynamic characteristics such as high strength and high damping level. In this paper, a Glass Fiber Reinforced Composite material (GFRC) is presented as a vibration isolation system to control vibration levels in industry. In addition, the impact of integration of a mechatronic control system to improve the machining process and increase the control of vibration nature. A prototype of an industrial cam–follower machine is motorized, and the Frequency Response Function (FRF) is recorded using a B&K data acquisition analyzer at five rotational speeds. The transmitted vibrations to the machine foundation are estimated without any isolation system. Then, two optimized GFRC plates of optimum stacking sequences are used as an isolation system to reduce the transmitted vibration. The displacement transmissibility is calculated theoretically and experimentally. The results show that the use of GFRC plates as an isolator reduces the vibration level of the system by 98.46% and 98.5% for [90/90/90/0/0]s and [90/ ± 45/ ± 35/90/ ± 35]s GFRC configurations respectively.

Purpose: This study presents a nonlinear transformation-based data augmentation approach to diagnose delaminations such as interlaminar, through-hole and buckle, in relatively complex composites. The approach uses tailored vibration signals of relatively simplified composites and employs a convolutional neural network (CNN). Methods: The present study involves modeling several composite structures with and without interlaminar, through-hole and buckle delaminations using finite-element method (FEM)-based simulation. A vibration experiment is also conducted for the case of interlaminar delamination. In our method, it is assumed that all vibration signals of simplified composites and healthy condition of complex real composites are obtained that paves the way to investigate the delamination conditions of real composites. Then, the present approach adopts the nonlinear transformation method mapping the signals of complex healthy composites and simplified healthy composites. The difference between the transformed signals of complex real composites and the reference signals of simplified composites is utilized for the virtual spectrogram computed by the short-time Fourier Transform (STFT). These virtual spectrograms fed into a CNN-based diagnosis system to diagnose the types and locations of delaminations. Results: For interlaminar cases, the simulation and experimental vibration signals are diagnosed with 100 and 92.5%, respectively. Through-hole and buckle cases are both diagnosed with an accuracy of 100%. Using nonlinear transformation to classify vibration signals prior to diagnosis has been shown to be highly advantageous for delamination diagnosis. Conclusion: The results allow the diagnosis of three cases of complex composites with simplified composites using the delamination diagnosis system. [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]

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]