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Within the field of elastic metamaterials, topological metamaterials have recently received much attention due to their ability to host topologically robust edge states. Introducing local resonators to these metamaterials also opens the door for many applications such as energy harvesting and reconfigurable metamaterials. However, the interactions between phenomena from local resonance and modulation patterning are currently unknown. This work fills that gap by studying multiple cases of spatially modulated metamaterials with local resonators to reveal the mechanisms behind bandgap formation. Their dispersion relations are determined analytically for infinite chains and validated numerically using eigenvalue analysis. The inverse method is used to determine the imaginary wavenumber components from which each bandgap is characterized by its formation mechanism. The topological nature of the bandgaps is also explored through calculating the Chern number and integrated density of states. The band structures are obtained for various sources of modulation as well as multiple resonator parameters to illustrate how both local resonance and modulation patterning interact together to influence the band structure. Other unique features of these metamaterials are further demonstrated through the mode shapes obtained using the eigenvectors. The results reveal a complex band structure that is highly tunable, and the observations given here can be used to guide designers in choosing resonator parameters and patterning to fit a variety of applications. [ABSTRACT FROM AUTHOR]

In this paper, a new Stroh formalism for gradient electro-mechanics is derived for the first time, which is both mathematically concise and numerically powerful, applicable to generally coupled anisotropic material systems. Based on this new formalism, the complicated Lamb wave in flexoelectric and piezoelectric plates is investigated. The dispersion equation is obtained by solving the eigenvalue problem along with the unconditionally stable dual-variable and position method. From the obtained dispersion equation, the dispersion curves and mode shapes of the Lamb wave are calculated by the 1D form of the multidimensional moduli ratio convergence method. Two important and interesting features are observed from our analysis: One is the difference in the mode shape symmetry between the piezoelectric and flexoelectric cases, and the other is the size-dependent property of the flexoelectric effect as observed by nondimensionalization. These features are further illustrated by comparing the dispersion curves and wave-mode shapes among the three different material models (purely piezoelectric, purely flexoelectric, and flexoelectric and piezoelectric coupled). The newly derived Stroh formalism offers a robust, concise, and unified approach for dealing with strain gradient electro-mechanic materials with crystal systems of general anisotropy. The present work also explains the physical mechanism of symmetry breaking observed, as induced by flexoelectric coupling in piezoelectric materials. [ABSTRACT FROM AUTHOR]

The vibrations of rotating joined conical–conical shells with classical supported conditions have been studied extensively. As a matter of fact, in some cases, these classical boundary conditions cannot exactly model actual situations. Moreover, theoretical frameworks on them are still limited. This research aims to investigate the fundamental frequencies and dynamic mode shapes of the traveling wave of the rotating porous metal material joined conical–conical thin shells (PJCS) with elastic supports. By utilizing artificial spring technology, arbitrary elastic supported boundary conditions and classical boundary conditions are achieved efficiently. A new dynamic model has been formulated with the help of the first-order shear deformation theory (FSDT) and Hamilton's principle. By employing the generalized differential quadrature (GDQ) method along with stress boundary conditions and generalized eigenvalues, various factors such as porosity, semi-vertex angles and stiffness are analyzed for their impact on the fundamental frequencies of forward wave (FW), backward wave (BW) and mode shapes. The presented results are validated through the convergence and comparison studies from literatures. The interesting and novel results indicate that the in-plane displacement constraints have the most significant impact on the critical speed, while the lateral displacement constraint has the least effect. The vibrations are more easily excited for the part with a larger half vertex angle. Rotating PJCS with Type 1 has the biggest critical rotating speed. [ABSTRACT FROM AUTHOR]

In this study, experimental natural frequencies and mid-span deflections were used to assess the tested composite floors against vibration serviceability limit states adopted by different standards such as AS3623. It was found that existing design criteria have predicted inconsistent results. Further, the finite element (FE) model was created, updated, and validated against the experimental modal parameters. The validated numerical model examined how various design parameters, such as material properties, cross-section geometry, and achieved a degree of composite action, have influenced the vibration properties such as natural frequencies and mode shapes. It was shown that as the added mass became more dominant than the stiffness enhancement, the fundamental natural frequency of the floor system dropped. This was evident from the results of the plywood slab thickness and the added permanent load parameters. On the other hand, the fundamental natural frequency increased with thicker and deeper joist sections since they made the floor system stiffer. [ABSTRACT FROM AUTHOR]

The present work intends to use higher-order zigzag theory to analyze double- and cross-helicoidal laminated sandwich plates under buckling conditions. Geometry and boundary effects on buckling and mode shapes are examined. The behavior of helicoidal sandwich plates is compared with the cross-ply and quasi-isotropic lamination schemes. In the case of plates with free edges, the bio-inspired laminated sandwich plates outperform the more traditional cross-ply and quasi-isotropic laminated schemes. Numerous more findings are provided as well, all of which may be used as a standard by which to measure the success of comparable future research efforts. [ABSTRACT FROM AUTHOR]

The ballistic resistance behavior of double-layer steel plates incorporated with different materials is experimentally and numerically investigated by using blunt- and ogive-nosed projectiles of middle strength. These materials are Q235 steel (low strength and high ductility) and 45 steel (high strength and low ductility). Experimental results showed that the ballistic resistance is better for the double-layer plates with the front layer of low ductility and high strength and the back layer of high ductility and low strength material than that of the opposite layer order impacted by ogive-nosed projectiles, but the situation is opposite for blunt-nosed projectiles. The ballistic limit of H + A (753.85 m/s) is increased by 29.5% when compared to that of A + H (582.19 m/s) for ogive-nosed projectiles of 45 steel. In the case of blunt projectiles, a 2.8% decrease in the ballistic limit of middle-strength projectile. Ogive-nosed projectiles are more sensitive than blunt-nosed projectiles when it comes to the effect of the layer order of the double-layer plates. Moreover, the ballistic limit velocities of blunt-nosed projectiles are obviously bigger than that of ogive-nosed projectiles for the double-layer plates of the front layer of low strength, while the situation is opposite for the double-layer plates of the front layer of high strength. Furthermore, the projectiles lose some mass and length after impact. The deformation of projectiles is also concerning the nose shape and velocity of projectiles, as well as the layer order of the double-layer plates. Finally, numerical simulation results are obtained and compared using the ABAQUS subroutine VUMAT-modified Johnson-Cook material model. And these results fairly agree with the experiment. [ABSTRACT FROM AUTHOR]

Sandwich structures have been a subject of intense scrutiny and utilization in engineering applications. However, there has been a limited understanding of the mechanical behaviors of novel sandwich structures composed of auxetic metamaterials. This study aims to contribute to the body of knowledge by examining the buckling responses of sandwich beams or wide plates with an orthotropic anti-tetra chiral lattice (ATCL) aluminum cores and symmetric angle-ply carbon-fiber/epoxy face sheets, both of which can exhibit highly negative Poisson's ratios or extreme auxeticity. The linear stability analysis of the sandwich structures under axial compression is conducted by applying the minimum potential energy principle and solving the eigenvalue problem using a numerical method. To achieve an accurate representation of arbitrary two-dimensional buckling morphologies, the first- and fifth-order shear and normal deformation models are employed to simulate the transverse kinematics of the face sheets and cores, while the finite-element model is utilized to discretize the longitudinal displacement of all constituents. The investigation reveals new insights into the interrelationship between global buckling, facial wrinkling, and shear crimping in conventional sandwich structures. The effects of material auxeticity on buckling responses are analyzed across an extensive range of geometrical configurations for the first time, unveiling five unprecedented buckling mode shapes, sophisticated buckling mode landscapes, and Poisson's ratio-sensitive buckling criteria. These findings lay a crucial foundation for designing and optimizing auxetic sandwich structures, bringing diverse possibilities in lightweight constructions, acoustic insulation, energy absorption, and dynamic and shock mitigation. [ABSTRACT FROM AUTHOR]

This paper presents free-vibration analysis of a rim-driven rotating composite plate. Based on higher-order shear deformation theory (HSDT) and the isogeometric approach (IGA), the formulations are developed. The effects of Coriolis and centrifugal forces due to rotation are considered. The present formulation results are compared and validated with the existing results for the hub-driven rotating plate, non-rotating plate, etc. A parametric study is conducted to investigate effect of the lamination sequence, pitch angle, material anisotropy, thickness ratio, and aspect ratio on natural frequency, critical buckling speed, and resonance speed. Natural frequency crossing and mode shape interchange are observed. [ABSTRACT FROM AUTHOR]

In recent years, there has been extensive research on detecting damage or identifying changes in stiffness in structures by analyzing their dynamic properties or responses. The fundamental idea is that damage or loss of integrity in a structural system can affect its response to dynamic forces, leading to changes in properties like eigenfrequencies, modal damping ratios, mode shape, and transfer functions. In Vietnam and some other countries in the Southeast Asia region, the prevailing climate conditions, slow economic development, and geographical location have resulted in the construction of predominantly short-span bridges with a limited number of spans. This is primarily because these bridges connect small channels and waterways. This characteristic provides a basis for developing and applying research findings specifically for this group of bridges, as they are seldom encountered and researched in other countries worldwide. This paper presents a damage identification technique for short-span bridges based on changes in the representative power spectral density (RPSD) and the static moment of area (SSM). The proposed method is applied to experimental data obtained from various bridge models, including prestressed concrete, reinforced concrete, and composite steel bridges. It is important to note that changes in RPSD and SSM are independent of traffic conditions on the bridge but instead rely on the structural and material properties of the bridge spans. By utilizing RPSD and SSM, new advancements can be made in assessing the structural condition of bridges using vibration signals. [ABSTRACT FROM AUTHOR]

The primary requirement for vibration-based structural damage identification is to develop the damage index with higher damage sensitivity. Although it is believed that higher order mode means more sensitivity to damage, what is the quantitative relationship between damage sensitivity of different orders and how to carry out multi-mode fusion lack theoretical guidance. This paper implements the comparison study of the location-related damage sensitivity for different mode shape curvatures and then proposes a structural damage index with sensitivity enhancement for beam structure. First, the damage sensitivity of the mode shape curvature of beam structures at different orders is compared in theory. It reveals that the damage sensitivity is location-dependent, and the second-order mode in the even 16.6% region is more sensitive than the third-order mode in the simply supported beam. Second, a structural damage index with sensitivity enhancement for beam structure is proposed according to the relationship between the damage sensitivity of mode shape curvature at different orders and locations. Third, a simply supported beam model and a steel stringer bridge model with multiple main girders are both investigated to illustrate the comparison results of the damage sensitivity at different orders and the advantages of the proposed structural damage index. It shows that the confused damage sensitivities are very common between different mode orders, the sensitivity-enhanced damage index that considers the damage location always shows certain degree of improvement of damage indication ability in different damage areas. Finally, the effectiveness and accessibility of the proposed method are verified by a simply supported beam experiment. [ABSTRACT FROM AUTHOR]

L-shaped moderately thick plates have widespread applications in diverse engineering structures. Exploring the benchmark analytic solutions for the free vibration of L-shaped moderately thick plates is important in order to accurately analyze and efficiently design structures. Nevertheless, analytical solutions, which serve as the benchmarks, have been rarely documented in previous literature due to the challenge of finding suitable solutions that satisfy both the governing higher-order partial differential equations (PDEs) and the boundary conditions of the plates. The symplectic superposition method was employed in our recently published study to present the benchmark vibration solutions of clamped rectangular moderately thick plates. In this study, we expand upon this method to solve the free vibration problem of L-shaped moderately thick plates. By employing domain decomposition, we construct an irregular domain by combining multiple rectangular domains. First, the construction of the superposition system is carried out, followed by the import of the sub-problems into the Hamiltonian system, utilizing the fundamental governing equations of the plate. Then, the sub-problems are resolved through the application of the symplectic geometry methodology in an analytical manner. Ultimately, the analytical solutions for frequencies and mode shapes are derived through ensuring the equivalence between the initial problem and the combination of sub-problems. The finite element method is used to validate and present a comprehensive analysis of the natural frequencies and mode shapes obtained from this method. This method possesses the benefits of rapid convergence and accurate precision, rendering it well suited for the analytic modeling of a broader range of plate-related problems. [ABSTRACT FROM AUTHOR]

Functionally graded materials represent advanced composites with typically two materials that exhibit gradual variations in their mechanical properties throughout the structure's thickness in general, as determined by a presumed mathematical model. The current investigation focuses on analyzing free vibrations of functionally graded material plate structures with two efficient isoparametric quadrilateral finite elements (Lagrange and Serendipity) together for the first time and different material combinations based on first-order shear deformation theory. The analysis was carried out on relatively thin as well as medium thick functionally graded plates with varying power law indices and at varied boundary conditions. The framework equation was formed with Hamilton's principle, and solutions were done with finite element method, considering a shear correction factor for the behavioral study of varying material properties. The findings align well with the information presented in prior literature. After validating the present model, parametric analysis was conveyed to show the impact of length-to-thickness ratio, aspect ratio, volume fractions, and skew angles for two novel materials on the fundamental frequencies and mode shapes. The results thus obtained with the two quadrilateral elements have a significant effect on the changes in these parameters. Also, the natural frequencies of different functionally graded plates, including two novel materials, were compared and discussed. [ABSTRACT FROM AUTHOR]

Shredder machines are essential for recycling plastic waste. They are used to shred plastic materials into smaller pieces, which can then be processed into new products. The shaft and rotary blades of the plastic shredder are its most crucial parts since they directly influence how effectively the machine shreds or recycles material. The shredder's rotor is optimized based on the design of experiments and the response surface method. The natural frequencies and mode shapes are identified by modal analysis, and the critical natural frequencies that must be avoided during operation are identified through harmonic response analysis. The shredder's rotor is optimized by determining its critical areas through a transient structural analysis. The optimization goals are attained by using the response surface method and experiment design in the ANSYS WORKBENCH DESIGN EXPLORATION module. The rotor of the optimized shredder is investigated, and its results are contrasted with the nominal design. The study of the optimum structure leads to a slight increase in mass of 2.43% in addition to reductions in equivalent stress and total deformation by about 9.84% and 42.86% respectively, as well as a 21.4%, 4.35%, and 4.48% increase in the first three natural frequencies, respectively. [ABSTRACT FROM AUTHOR]

Nature-built structures effectively sustain higher loads without failing, even though they are made of weak organic materials. The laminated construction mode in various fish scales provides them toughness and flexibility. The present manuscript aims to carry out the free vibration analysis of double- and cross-helicoidal laminated composite plates inspired by the scales of fish. The study has been carried out using the recently proposed finite element-based higher-order zigzag theory. The influence of aspect ratio, side-to-thickness ratio, skew angle, and end conditions on the free vibration behavior of double- and cross-helicoidal plates is depicted. The mode shapes of the plates are studied in detail. The free vibration behavior of skew plates is also studied for the first time. An improved performance of the helicoidal plate compared to the conventional lamination scheme has been obtained. HIGHLIGHTS: Free vibration behavior of cross- and double-helicoidal plates is studied. The study has been carried out in the framework of HOZT. Cross-helicoidal plates exhibit either stiff behavior or similar to quasi-isotropic plates. Increasing the pitch angle increases the stiffness of the helicoidal plate. [ABSTRACT FROM AUTHOR]

Structural modal identification is generally implemented within a dynamic framework, requiring multidisciplinary knowledge and adequate operational experience. This preliminary study attempts to explore an easy-to-handle quasi-static alternative method for dynamics-based modal identification of beam-type structures. Acceleration time-history data are replaced by quasi-static deflections induced by slow moving loads. A concept of quasi-static deflection influence surface is proposed based on the theory of influence lines and the principle of virtual work. Its analytical expression is simplified into a deflection matrix by choosing specific points on the surface according to deflection measurement coordinates. The matrix form is divided by external loads to obtain a generalised quasi-static flexibility matrix, which is used to replace the inversion of the global stiffness matrix in the modal eigenvalue equation. The lumped-mass method is also employed to establish the mass matrix. Subsequently, the eigenvalue equation is analytically solved seeking for modal frequencies and mode shapeswithout performing modal tests. The feasibility of the proposed method has been successfully verified against three experimental examples including a continuous box girder with variable cross sections. It was observed that the modal frequencies and mode shapes estimated by the proposed method were very close to those given by the dynamically modal tests. [ABSTRACT FROM AUTHOR]

To solve the problems with the existing methods for detecting hollowing defects, such as inconvenient operation, low efficiency and intense subjectivity, and to improve the efficiency of the acoustic-optic fusion method for detecting hollowing defects, in this paper the vibration characteristics of hollowing defects are measured and analyzed using a laser self-mixing interferometer. The ceramic tile above the hollowing defect is equivalent to a thin circular plate with peripheral fixed support. According to Kirchhoff's classical circular plate theory and the circular plate displacement function based on the improved Fourier series, a theoretical model of a circular plate is established. By solving the characteristic equation, the theoretical modal parameters of hollowing defects are obtained. Subsequently, an experimental system based on a laser self-mixing interferometer is built, and modal experiments are carried out using the hammering method. The experimental modal parameters are obtained with a professional modal analysis software. Through comparative analysis between the theoretical and experimental modal parameters, the error of the natural frequency results is found to be tiny and the mode shapes are consistent. These results provide theoretical guidance for a practical non-destructive acoustic-optic fusion method for detecting hollowing defects. [ABSTRACT FROM AUTHOR]

Stress wave propagation and free vibration response of functionally graded graphene platelet (FG-GPL)-reinforced porous joined truncated conical–cylindrical-conical shell are investigated in this paper. The shell is constructed of a metallic matrix reinforced by three types of distribution of GPLs in open-cell interior pores. The modified Halpin–Tsai estimation and the generalized rule of the mixture are employed to calculate the effective mechanical properties of the structure. Three different distributions for porosity are assumed along with the shell thickness: two kinds of symmetric FG distributions and uniform distribution of porosity. The Rayleigh-Ritz energy method, accompanied by the Finite element method, has been used to solve 2D-axisymmetric elasticity equations. Furthermore, the Newmark direct integration method is applied to obtain time responses and stress wave propagation of shells subjected to an internal impulse loading. A comparative and detailed investigation is also conducted to indicate the effects of different boundary conditions, geometries, the weight fraction of GPLs, porosity coefficient, distribution of porosity and dispersion pattern of GPLs on the natural frequencies, mode shapes and time histories of displacement and stresses of the shell. [ABSTRACT FROM AUTHOR]

Cross-laminated timber (CLT) is a mass timber product that has been used increasingly as a sustainable and cost-effective alternative to conventional construction materials such as concrete and steel. Understanding the seismic performance of CLT buildings is vital in the design process for engineers as the use of CLT has increased toward mid- and high-rise buildings. In this study, the experimental dynamic behavior of three full-scale two-story platform CLT shear wall mock-ups were investigated under quasi-static reversed cyclic and interval impact hammer modal tests. The mock-ups differed in the tension splice between the two stories, the level of dead load, and the installation of an acoustic insulation layer between stories. The impact hammer modal tests were conducted during different steps of the reversed cyclic tests to extract modal characteristics such as natural frequencies, damping ratios, and mode shapes in the defined drifts of frequent, medium, and rare seismic hazard levels. The mock-up's experimental first period was in good agreement with the results predicted by the empirical equation in the National Building Code of Canada (NBCC). The stiffness degradation during the reversed cyclic tests was related to frequency reductions representing an index of damage. The presence of an acoustic layer increased the damping ratio and stiffness in the first three measured modes. However, further investigations are needed to see the extent of the effect of acoustic layers between the walls and floors on the lateral performance of timber buildings equipped with CLT shear walls and floors. [ABSTRACT FROM AUTHOR]

This article presents the results of the numerical simulations of a dynamic experimental campaign on the shaking table. The specimen is a full-scale masonry cross vault without and with the textile-reinforced mortar used as a strengthening solution. The specimen was tested in the scope of the European project SERA.ta 07 "Seismic Response of Masonry Cross Vaults: Shaking table tests and numerical validations". The specimen replicates a generic cross-section of a central bay located in the lateral nave of a three-nave church, where the recurrent in-plane shear mechanism is induced. Finite element model (FEM) and discrete element model (DEM) were built and calibrated based on the experimental frequencies and mode shapes. Then, a unidirectional seismic action was applied to the numerical model in order to develop shear damage in the shell of the vault. A detailed description of the two simulations and their main outcomes are presented. The response was evaluated based on the displacements, damage, collapse mechanisms and hysteretic behaviour. [ABSTRACT FROM AUTHOR]

This paper presents the numerical evaluation of the seismic response of a masonry cross vault using the Discrete Macro-Element Method (DMEM). The case study corresponded to a full-scale unstrengthened cross vault that was experimentally investigated within the scope of the SERA Project — Seismic Response of Masonry Cross Vaults: Shaking table tests and numerical validations. The cross vault was subjected to repeated shaking table and dynamic identification tests until reaching significant damage. The numerical simulations involved the calibration of the Young's modulus of the masonry material aiming at reproducing the cross vault's experimental natural frequencies and mode shapes. The comparison of frequencies was carried out by estimating the difference between experimental and numerical results, whereas the correspondence between mode shapes was studied using the Modal Assurance Criterion. Subsequently, a sensitivity analysis was performed to identify the influence of nonlinear properties on the seismic response of the cross vault (displacement and acceleration time histories and failure mechanism). The accuracy of the numerical time histories was evaluated by estimating magnitude and phase discrepancies. The results aimed at demonstrating the applicability of the DMEM for assessing the seismic response of masonry cross vaults with an acceptable degree of accuracy and low computational cost. [ABSTRACT FROM AUTHOR]

This paper uncovers the frequency variation in plate-type bridges under moving vehicles, highlighting the transverse characteristics stemming from the bridge’s spatial configuration. First, the mode shapes are determined for plates with two opposite sides simply supported and the other two free (S-F-S-F bridge) by Levy’s method. Then, analytical solutions are derived for the frequencies of the vehicle-plate system subjected to a moving vehicle. Through numerical analysis, it is demonstrated that the frequencies of the vehicle-plate system exhibit spatiotemporal variations, contingent upon both the transverse spatial path and longitudinal time-varying distance of the plate traveled by the vehicle. The “edging effect” was identified wherein maximum frequency variation will occur when the vehicle traverses along one side edge of the plate. Moreover, the transverse variation ratio of the plate-type bridge frequency increases with the decrease in the bridge’s span/width ratio. These findings underscore the significance of the bridge’s transverse characteristics when using the moving vehicle to measure the frequencies of plate-type bridges, particularly for short-span bridges. [ABSTRACT FROM AUTHOR]

The indirect method for bridge modal identification based on the response of moving vehicles has attracted widespread attention in recent years. However, most existing studies only focus on the simply supported bridge, while continuous girder bridges are widely used in practical engineering. Therefore, this study proposes an indirect frequency identification method for continuous girder bridges. First, the mode shape formula of the equal-span continuous beam is deduced using the three-moment equations, and the analytical solution of the vehicle vibration response is deduced via the vehicle–bridge coupled vibration theory. Second, the derived analytical solution is verified through numerical analysis results and field test results. Finally, the effects of bridge and vehicle parameters on the frequency identification accuracy are analyzed. The results show that a reasonable frequency of the trailer should be selected to avoid the resonance between the vehicle and the bridge for better performance. The research findings can provide a reference for the indirect identification of continuous girder bridges based on the response of moving vehicles. [ABSTRACT FROM AUTHOR]

This paper presents a combined numerical and experimental investigation into the vibroacoustic behavior of a traditional oud. An experimental modal analysis was conducted using impact hammer testing to determine the oud’s soundboard’s dynamic characteristics and frequency response function for up to 400 Hz. Finite element analysis was used to model the oud, incorporating its precise geometry, the wood’s orthotropic material properties, and its interaction with the surrounding air. Validation was performed by matching the numerical and experimental mode shapes and the natural frequencies. Harmonic acoustic analysis examined the oud’s sound pressure level radiation and cavity resonance. Structural–acoustic optimizations were conducted systematically, varying the soundhole’s size, the soundboard’s thickness, and the dimensions of the internal bracing to maximize the acoustics properties while minimizing the structural stress. The effects of these geometric factors on the instrument’s tonal characteristics were quantified. The results provide physical insights into the relationship between the oud’s construction and sound production. The methodology demonstrates a rigorous approach combining simulations and experimentation to comprehensively evaluate and optimize the vibroacoustic behavior of a musical instrument. This fundamental understanding could guide future improvements in the design of ouds. [ABSTRACT FROM AUTHOR]

Intimacy suggests familiar, close-up knowing, resulting in emotional attachment to another. Such affective encounters occur between domestic gardeners and their plants, but what about commercial horticulture? Anna Tsing suggests not, characterizing plantationocene agribusiness as production without the love (2012). Relations between commercial growers and plants have scarcely been considered, but horticulture complicates multispecies ethics as plants are to be eaten, and tackling human exploitation might have precedence. Applying a care ethic to agriculture therefore must question care work’s outcomes and motivations. In research with UK commercial growers I trace plant intimacies as how growers relate to their plants, and how globalized food systems touch plant and human bodies in horticultural fields, asking: can following plant intimacies signal how more just food production could love human and plant labourers? Intimacies are shown to be shaped by time, scale and labour, as global food regimes press into intimate plant work, whilst specific modes of plantiness shape labour regimes. Tracing plant intimacies reveals that power to gain intimate plant knowledge is unequally distributed, whilst harmful intimacy concentrates with the most marginalized workers. Rather than questioning whether growers love or care for plants, it may be more important to ask who owns the crops, and who/what benefits. [ABSTRACT FROM AUTHOR]

This study developed a rigid-flexible coupling vibration model for a rotating functionally graded geometrically imperfect microbeam, integrating refined shear deformation theory (RSDT), the von Kármán nonlinear assumption, and modified couple stress theory. The material properties are described by a power-law distribution along the thickness. Utilizing RSDT, deformation was characterized by axial tensile, chordwise bending, and shear variables. The energy of the microbeam was discretized through assumed modal functions that satisfy cantilever beam boundary conditions, and the governing equations were derived using the Lagrange equation, subsequently solved with the complex modal space method. After validating the model, the effects of shear and geometric imperfections on dimensionless natural frequencies and mode shapes were analyzed, taking into account dynamic stiffening, gradient index, and size effects. Key findings include: (i) shear and imperfections reduced the rotational speed, gradient index, and material length scale required for frequency locus veering; (ii) dynamic stiffening and size effects suppressed the influence of shear and imperfections; (iii) larger imperfections initially increased, then decreased, their impact on chordwise deformation modes as the gradient index increases; (iv) coupling between chordwise and axial motions leads to mode transition with increasing imperfection amplitude. This work provided theoretical guidance for addressing the disorder problem of system parameters in micro-electromechanical systems-based devices. [ABSTRACT FROM AUTHOR]

This article develops the mode shape area difference (MSAD) method for detecting sparse damage in beam‐like structures under serviceability conditions. MSAD enhances the static deformation area difference (DAD) damage detection method by extending its application to the modal domain. MSAD leverages the sensitivity of mode shapes to the damage, enabling damage detection and localization through the quantification of area differences between functions of modal displacements and their derivatives. To test the applicability of the method to real modal data that is affected by measurement noise resulting in different accuracies on which the modal displacements are estimated, method is evaluated under different levels of artificial noise added to the theoretical mode shapes derived from numerical model of a simply supported reinforced concrete beam. The noise level is defined by a maximum noise amplitude representing the maximal permutation in each component of normalized mode shape. Additionally, the threshold value of noise level from within the reliable estimation of damage based on MSAD method is determined. It is confirmed that MSAD method requires mode shapes with exceptionally low noise levels and demands precise estimation of all mode shape components, thereby reducing its applicability to real experimental data. [ABSTRACT FROM AUTHOR]

This paper focuses on the magneto-aeroelastic dynamic buckling and flutter generated by traveling waves of rotating conductive disks under air-film loading. A distributed time-variable aerodynamic model is derived by using the Navier–Stokes (NS) equation and the lubrication theory. The electromagnetic force on the disk is modeled by using the electromagnetic theory. Based on Kirchhoff’s theory and considering the rotating centrifugal effect, the dynamic equations for magnetic-aeroelastic coupling are established by using the Hamiltonian principle. Bessel functions are assumed for the mode shapes, and the steady-state properties of the aerodynamic equations are presented that allow for the derivation and decoupling of the coupling differential equations in the Galerkin approach of Hilbert space. The effects of the magnetic field intensity, rotational speed, and aerodynamic parameters on the magneto-aeroelastic buckling instability and flutter characteristics generated by backward traveling wave instability are investigated, respectively. The numerical calculations show the damping effect of the magnetic field, which increases magnetic field intensity and suppresses buckling instability and flutter. Moreover, the sensitivity of the system with respect to magnetic field intensity demonstrated that, for high-order mode instability, a critical instability region (CIR) emerges with changes in the magnetic field intensity, whereby a distribution with a very small frequency may induce dynamical buckling instability of the system. Additionally, the rotational speed escalates to reach either the critical speed or flutter speed, the system may experience dynamic buckling or flutter instability characterized by divergent response or equal-amplitude vibration, respectively. [ABSTRACT FROM AUTHOR]

AbstractIn this article, for the first time, the free vibration and modal shapes of sandwich folded plate with honeycomb core are studied. The current article investigates the free vibrational mode shapes and frequencies of sandwich folded plate made of auxetic honeycomb core and graphene platelet-reinforced functionally graded composite (FG-GPLRC) coating layers which standing on the normal-shear folded supports. The structures are supported by normal-shear folded supports. The negative Poisson’s ratio exhibited by honeycomb materials results in distinct physical and mechanical properties, profoundly impacting the behavior of structures constructed from this material. While structures with basic shapes like rectangular, circular, and spherical configurations find limited applications across various industries, the versatility of folded structures makes them highly suitable for a wide range of industrial applications, given their more complex geometries. Dynamic equations are formulated within the framework of the first-order shear deformation theory (FSDT) for each flat section of the folded plate. The continuous equality conditions for displacements, rotations, and stresses at the junction edges of the two flat sections are rigorously satisfied. To effectively solve these equations, a robust numerical technique known as the generalized differential quadrature method (GDQM) is employed specifically tailored for the 2D analysis of folded plates. Furthermore, the study investigates the influence of various parameters, including material properties and geometry, on the frequencies and mode shapes of the folded structures, shedding light on the intricate interplay between these factors in shaping the dynamic response of the structures. [ABSTRACT FROM AUTHOR]

A conventional vortex-induced vibration (VIV)-based energy harvester is typically restricted to capturing wind energy from a very limited range of wind directions, making it inefficient in varying wind conditions. This Letter proposes a tri-section beam configuration for VIV-based piezoelectric energy harvester to enable harnessing wind energy from varying incident angle with different vibration modes being triggered. The finite element analysis investigates the tri-section beam harvester's mode shapes and natural frequencies. A wind tunnel experiment is conducted for a comparative study of the energy output performance of the harvesters with straight and tri-section beams. The findings show that the proposed harvester with the tri-section beam can efficiently capture wind energy from a much wider range of incident angles, as opposed to the specific limited directions of its counterpart with the straight beam. The proposed harvester can also widen the lock-in speed range with a higher bending mode being triggered and achieve the optimal output power of 1.388 mW when the proposed harvester works in the second mode at a higher natural frequency, superior to that of its counterpart (0.386 mW) that can only work in the first mode. The proposed configuration sheds light on developing multi-directional and multi-modal VIV-based energy harvesters adapted to wind conditions in natural environments. [ABSTRACT FROM AUTHOR]

Structural components with curved edges are common in many engineering designs. Fatigue cracks, corrosion and other types of defects and mechanical damage often initiate from (or are located close to) edges. Damage and defect detection in the presence of complex geometry represents a significant challenge for non-destructive testing (NDT). To address this challenge, this paper investigates the fundamental mode of the quasi-symmetric edge-guided wave ( Q E S 0 ) propagating along a curved edge, as well as its scattering characteristics in the presence of different types of edge defects. The finite element (FE) approach is used to investigate the propagation and mode shapes of the Q E S 0 . It was found that the wave attenuation dramatically increases when the radius-to-thickness ratio is less than 20. Moreover, the mode shapes are significantly affected by the waveguide curvature as well as the excitation frequency. Additionally, to evaluate the sensitivity of Q E S 0 to edge defects, different sizes of edge defects were investigated with the FE model, which validated against experimental results. The validated FE model was further employed to quantify the dependence of the amplitude of scattered waves for different types of edge defects. These studies indicate that the amplitude of scattered wave is very sensitive to the presence of edge defects. The main outcome of this work is the demonstrated ability of the Q E S 0 wave mode to propagate over long distances and a high sensitivity of this mode to different types of edge defects, which manifest its great potential for detecting and characterising damage near the curved edges of structural components. [ABSTRACT FROM AUTHOR]

This paper presents a comparative study focused on a modal parameters estimation of specimens manufactured by the FDM technique using a fixed embedded vibrometer based on the laser Doppler principle and roving hammer-impact method. Part of this paper is devoted to testing a fixed circular plate with a honeycomb infill pattern while varying the number of excitation points (DOFs), the number of analysis lines of fast Fourier transformation (FFT), and the locations or numbers of reference degrees of freedom (REFs). Although these parameters did not significantly affect the values found for the natural frequencies of the structure, there were changes in the estimates of the mode shapes (affected by the low number of DOFs), in the height and sharpness of the peaks of the CMIF functions (caused by the increased number of FFT lines), and in the number of identified modes (influenced by the chosen location(s) of REFs), respectively. Subsequently, the authors compared the results of experimental modal analyses carried out under the same conditions on three circular plates with honeycomb, star, and concentric infill patterns made of PLA. The results confirm that specimens with honeycomb or star infill patterns have a higher stiffness than those with concentric infill patterns. The low values of the damping ratios obtained for each structure indicate a strong response to excitation at or near their natural frequencies. [ABSTRACT FROM AUTHOR]

Featured Application: This research proposed a novel response reconstruction method to localize potential damage with multiple inclinometers. This is a data-driven method and can be easily applied to bridge online monitoring. Damage detection is a critical aspect of bridge health monitoring. While data reconstruction has been posited as a promising method for damage detection, its effectiveness in this context has rarely been empirically validated. In this study, we introduce a novel approach to pinpoint potential bridge damage by reconstructing bridge inclination data. For an intact bridge, we selected reference cross-sections and trained multiple Backpropagation Artificial Neural Networks (BP-ANNs) to simulate transfer matrices for inclination between these base sections and other sections of the bridge. These BP-ANNs were then employed to reconstruct inclination data at the same cross-sections on a bridge with artificial damage. We demonstrated that damage localization is feasible through a comparison of the reconstructed and actual measured responses. The theoretical underpinnings of the transfer matrix and the damage localization method were initially elucidated through an analysis of the dynamics of a simplified vehicle–bridge interaction (VBI) system. A series of finite element models were constructed to substantiate the theoretical basis of the damage localization method. Additionally, a large-scale laboratory experiment was carried out to assess the practical effectiveness of the proposed method. The proposed method has been demonstrated to effectively pinpoint the location of potential structural damage. It successfully differentiates between areas in close proximity to the damage and those that are more distant. Compared to existing research, our method does not necessitate prior knowledge of factors such as mode shape functions, traffic conditions, or the constraint of inspecting with a single vehicle. This approach is anticipated to be more convenient for engineering applications, particularly in the development of online monitoring systems, due to its streamlined requirements and robust performance in identifying damage localization. [ABSTRACT FROM AUTHOR]

The article highlights the importance of analytical computational models of torsionally oscillating systems and their simulation for estimating the lowest resonance frequencies. It also identifies the pitfalls of the application of these models in terms of the accuracy of their outputs. The aim of the paper is to control the dangerous vibration of a mechanical system actuator using a pneumatic elastic coupling using different approaches such as analytical calculations, experimental measurement results, and simulation models. Based on the known mechanical properties of the laboratory system, its dynamic model in the form of a twelve-mass chain torsionally oscillating mechanical system is developed. Subsequently, the model is reduced to a two-mass system using the method of partial frequencies according to Rivin. The total load torque of the piston compressor under fault-free and fault conditions is simulated to obtain the amplitudes and phases of the harmonic components of the dynamic torque. After calculating the natural frequency and the natural shape of the oscillation, the Campbell diagram is processed to determine the critical revolutions. There is a pneumatic flexible coupling between the rotating masses, which changes the dynamic torsional stiffness. The dynamic torque curves transmitted by the coupling are compared with different dynamic torsional stiffnesses during steady-state operation and one cylinder failure. The monitored values are the position of the critical revolutions, the natural frequency, the natural shape of the oscillation, and the RMS of the dynamic load torque. The experimental model is verified by the simulation model. The accuracy of the developed simulation model with the experimental data are apparently very good (even more than 99% of the critical revolutions value obtained by calculation); however, it depends on the dynamic stiffness of the coupling. In this study, a detailed, comprehensive approach combining analytical procedures with simulation models is presented. Experimental data are verified with simulation results, which show a good agreement in the case of 700 kPa coupling pressure. The inaccuracy of some of the experiments (at 300 and 500 kPa pressures) is due to the interaction of the coupling's apparent stiffness and the level of the damped vibration energy in the coupling, which is manifested by its different heating. Based on further experiments, a solution to these problems will be proposed by introducing this phenomenon effectively into the simulation model. [ABSTRACT FROM AUTHOR]

The existing models based on Bayesian inference and ${L_1}$L1 regularisation provide a feasible scheme to the uncertainty problem in structural damage identification. However, ${L_1}$L1 regularisation cannot accurately describe the sparsity of damage due to excessive punishment of large damage parameters, and the mode shape data used by such models are insensitive to the damage. This compromises the accuracy of damage identification. Compared with ${L_1}$L1 regularisation, the fraction function regularisation avoids excessive punishment for larger elements in the damage parameters, resulting in a more accurate sparse solution. The mode shape curvature is more sensitive to damage because it can be viewed as the differential form of the mode shape. Inspired by this, a fraction function regularisation model based on natural frequency and mode shape curvature data is proposed in this paper to further improve the accuracy of Bayesian damage identification. In addition, an improved cuckoo search algorithm is proposed to solve the model by introducing a ranking-based mutation strategy. The results obtained from both the numerical investigation and the experimental study consistently indicate that the proposed method can provide accurate and reliable identification results. [ABSTRACT FROM AUTHOR]

Crises transform the temporal orientation of political decision‐making. They demand immediate and decisive action and thus convert time into a means of political control. In these circumstances, assessing the long‐term consequences of proposed policies with respect to welfare, sustainability or justice also becomes demanding. Yet crisis conditions may also contain of elements that can enable positive postcrisis societal changes. Crises can offer opportunities for new developmental measures and building a better future—something political leaders may capitalise on in their agenda‐setting. By analysing the programmes of the post‐2014 Finnish and Swedish governments, this paper seeks to make sense of how the current crisis mode has shaped these countries' politics in terms of their temporal horizons. The analysis focuses on three main perspectives or forms of articulation—innovative stabilisation, long‐termism and synchronisation—by way of which these governments seek to navigate through crises‐afflicted times and offer a desirable future direction for their respective societies. The analysis offers important insights into the (unused) potential of crises to achieve something substantially novel in the Nordic and European political landscape, ultimately advancing the conditions for a future‐regarding democratic system. [ABSTRACT FROM AUTHOR]

Sandwich panels are key components of many lightweight structures. They are often subjected to time-varying loads, which can cause various types of vibrations that adversely affect the functionality of the structure. That is why it is of such importance to predict the dynamic properties of both the panels and the structures made of them at the design stage. This paper presents finite element modeling of the dynamic properties (i.e., natural frequencies, mode shapes, and frequency response functions) of sandwich panels made of glass fabric impregnated with phenolic resin. The model reproducing the details of the panel structure was built using two-dimensional, quadrilateral, isoparametric plane elements. Afterwards, the model was subjected to an updating procedure based on experimentally determined frequency response functions. As a result, the average relative error for natural frequencies achieved numerically was 5.0%. Finally, a cabinet model consisting of the analyzed panels was built and experimentally verified. The relative error between the numerically and experimentally obtained natural frequencies was on average 5.9%. [ABSTRACT FROM AUTHOR]

The presented work is devoted to studying the dynamics of cantilever trapezoidal plates with non-uniform thickness and enriched with either carbon nanotubes (CNTs) or graphene nanoplatelets (GNPs). It is assumed that the volume fractions of nanofillers (CNTs or GNPs) and thickness of the plate vary in one direction from the clamped edge of the plate to the outer free edge. The mathematical modeling of the plate is performed according to the first-order shear deformation theory (FSDT), and the density and the effective values of elastic constants of the plate are calculated utilizing the rule of mixture (ROM), the Halpin-Tsai model, and the Eshelby-Mori-Tanaka scheme. Hamilton's principle is employed to derive the governing equations and boundary conditions at a clamped edge and three free edges of the plate. An approximate solution is provided via the differential quadrature method (DQM) to estimate the natural frequencies of the plate and achieve the corresponding mode shapes. It is concluded that to attain higher natural frequencies in the low vibrational modes, it is more effective to distribute most of the nanofillers as close as to the clamped edge and reduce their volume fraction from the clamped edge to the outer free edge. [ABSTRACT FROM AUTHOR]

This paper proposes a novel framework for the random vibration fatigue assessment of thin‐walled plate with multiple holes based on the fatigue damage response spectrum method. Compared with other frequency‐domain evaluation methods, this framework fully exploits the dynamic characteristics of complex structures, decoupling the external excitation characteristics from the spatial characteristics of the structural response. This approach significantly enhances evaluation efficiency by avoiding the complex calculations associated with stress response spectral moments. The proposed method is employed to evaluate the contribution of each mode to the overall damage, additionally, the stress mode shapes are used to identify and refine the mesh around fatigue hotspots. Modal damage contribution factors are proposed to identify the key modes. By leveraging both structural dimension reduction and modal reduction techniques, the proposed framework can swiftly and accurately locate fatigue hotspots within complex structures and conduct precise fatigue assessments using the Absolute Sum ‐ Square Root of the Sum of Squares hybrid method. Finite element simulation analysis is conducted on a single‐lap structure containing numerous circular openings, validating the accuracy and efficiency of the proposed stochastic vibration fatigue assessment. Highlights: A framework for assessing random vibration fatigue of thin‐walled plate with localized featuresEmploy stress modes to pinpoint the locations of critical fatigue holesUtilize modal damage contribution factors to identify key modesImplement damage combination considering the identified key modes [ABSTRACT FROM AUTHOR]

Disturbance observer-based sliding mode control (SMC) on the active vertical suspension (AVS) is developed to suppress the car body's rigid and flexible vibration to improve ride comfort for a high-speed rail vehicle. A vertical-dynamics-intended vehicle model is foremost built with the bounce, pitch, and bending mode of the car body involved. Two sliding surfaces and disturbance observers are then designed for SMC, which only require the car body states, obviating the bogies' states. The observer is successful in estimating the effect of unknown track irregularities perturbation as well as externally straightforwardly excitations on the car body with good accuracy. Control efficacy is verified through comparison with passive cases and sky-hook controls. With modal damping below 2% in passive cases, the mode shape function, especially with large displacement at the suspension support, would enlarge the car body acceleration. Moreover, the longitudinal traction rod can significantly multiply the flexible vibration at certain speeds. Comparative studies indicate that SMC provides satisfactory outcomes in the rigid and bending vibration suppression when all the car body's three modes are considered in the sliding surface. However, it requires a high-frequency response actuator and allows a tighter tolerance of the control time delay than the sky-hook control. [ABSTRACT FROM AUTHOR]

In practical applications of wavelet transform, engineers and practitioners encounter challenges that arise due to the disparity between wavelet theory, which deals with continuous functions, and the digital nature of signals in engineering contexts. In particular, wavelet transform theory does not consider the effect of changes in digital signals on the result of the wavelet transform. This paper emphasizes the influence of the type of digital signals on the accuracy of wavelet transform in engineering applications and proposes an efficient wavelet function based on the derivative of the signal for better damage detection in beam structures. For this purpose, the obtained signals from the mode shapes of the steel beam are used to examine the efficiency of the proposed derivative-based wavelet transform. The effects of changes in boundary conditions, location of damage, and level of damage on the performance of the proposed method, are evaluated. Findings show that when we use the derivate of the signal in the wavelet transform, the location of damage in all damage scenarios is detected with high accuracy. This research demonstrates the importance of the type of signal used in the wavelet transform for enhancing the precision of fault and damage detection in signals. [ABSTRACT FROM AUTHOR]

In this paper, a state-space method for double-beam systems with variable cross sections is developed, making it possible to calculate the transverse vibration of the double-beams accurately and effectively. Due to the variability in the double-beam cross sections with the viscoelastic interlayer in between, the governing equations of vibration for the systems become highly coupled partial differential equations, making the problem difficult to solve. A basic double-beam system is introduced to modify the original governing equations to two inhomogeneous differential equations. Given the separation of variables, several mode-shape coefficients and a state variable are defined to construct the state-space equations. The coupling terms and variables are transferred into the constant coefficient matrix of the state-space equations, decoupling them. Numerical procedures are presented to solve the state-space equations to obtain homogenous and inhomogeneous solutions, including the natural frequencies and mode shapes in free vibration and the dynamic responses in forced vibration, respectively. The method has substantial advantages in decoupling high-order partial differential equations and can be further extended to solve complex structural systems. Numerical results also demonstrate that the method is accurate and efficient. Finally, an engineering application with a rail-bridge with a floating slab track is discussed in detail with the method. [ABSTRACT FROM AUTHOR]

As a material screening equipment, vibrating screen is widely used in metallurgy industries due to their simple structure and low production cost. Nevertheless, the traditional vibrating screen box is prone to structural resonance due to low natural frequency and close to the system excitation frequency, which has a serious impact on the service life of the vibrating screen. In order to enhance the natural frequency of the vibrating screen box to avoid resonance, an optimization study of frequency of the vibrating screen was conducted using the response surface analysis method based on a genetic aggregation algorithm. The finite element model of the vibrating screen was established, and a comprehensive analysis of is modal frequency and mode shapes was performed through modal simulation and experimental testing to validate the accuracy of the model and simulation results. Additionally, structural optimization design was implemented using a reinforcement method with ribs, and the response surface method was employed to systematically investigate the influence patterns of rib width and thickness on the modal frequency. Various reinforcement schemes with different rib configurations were designed, and the impact of reinforcement positions on the enhancement of modal frequency was studied. The results indicate that adding ribs at the beams significantly increases the modal frequency of the vibrating screen box. Specifically, the sensitivity of modal frequency to rib thickness is relatively low, while the sensitivity to rib width is higher. The most significant enhancement in modal frequency was observed when reinforcing the intermediate layer of the screen box. By adding reinforced panels to the middle and lower three layers above, the natural frequency of the first four stages of the screen box can be increased by more than 60%, and the optimization effect is good. Through the optimization of the modal frequency, the natural frequency of the vibrating screen can be far away from the exiting frequency, which can effectively solve the structural resonance problem. The aforementioned research findings provide valuable insights and references for the optimization design of the strength and stiffness of vibrating screen boxes. [ABSTRACT FROM AUTHOR]

This study aims to address the challenges of achieving a high harvesting rate and low flower bud damage rate during the harvesting of camellia fruits. To this end, a dynamic model of the camellia osmantha tree and a self-developed shaker-type harvesting machine were used as research subjects. The first 24 natural frequencies and mode shapes of the camellia tree were solved using the finite element method, and the effects of vibration frequency, excitation position, and vibration duration on the harvesting rate and flower bud damage rate were quantitatively analyzed through an orthogonal experiment. The numerical analysis results indicate that the camellia tree exhibits good response characteristics at vibration frequencies of 10–15.5 Hz and 38.5 Hz. The three-factors orthogonal experiment figured out that the optimal operational parameters for shaker-type harvesting were determined to be a vibration duration of 30 s, a motor output frequency of 12.5 Hz, and a gripping position height of 50 to 60 cm above the ground. Meanwhile, under these operational parameters, the harvesting efficiency reached 96.97%, while the flower bud damage rate was only 6%. [ABSTRACT FROM AUTHOR]

In situ dynamic testing is conducted to study the dynamic characteristics of the wooden structure of the North House main hall. The velocity response signals on the measurement points are obtained and analyzed using the self-interaction spectral method and stochastic subspace method, yielding natural frequencies, mode shapes, and damping ratios. This study reveals that the natural frequencies and damping ratios are highly consistent between the two methods. Therefore, to eliminate errors, the average of the results from both modal identification methods is taken as the final measured modal parameters of the structure. The natural frequencies of the first and second order in the X direction were 2.097 Hz and 3.845 Hz and in the Y direction were 3.955 Hz and 5.701 Hz. The modal frequency in the Y direction of the structure exceeds that in the X direction. Concurrently, a three-dimensional finite element model was established using ANSYS 2021R1, considering the semi-rigid properties of mortise–tenon connections, and validated based on in situ dynamic testing. The sensitivity analysis indicates adjustments to parameters such as beam–column elastic modulus, tenon–mortise joint stiffness, and roof mass for finite element model refinement. Modal parameter calculations from the corrected finite element model closely approximate the measured modal results, with maximum errors of 9.41% for the first two frequencies, both within 10% of the measured resonant frequencies. The adjusted finite element model closely matches the experimental results, serving as a benchmark model for the wooden structure of North House main hall. The validation confirms the rationality of the benchmark finite element model, providing valuable insights into ancient timber structures along transportation routes. [ABSTRACT FROM AUTHOR]

Based on the Bayesian framework, a time domain method is proposed for the uncertain quantification of structural modal identification. First, a theoretical prediction model is constructed from the state space model in modal space and then transformed into physical space using the modal basis. Second, taking into account the uncertainty of the identification results caused by measurement noise and modeling errors, the negative log-likelihood function is constructed using time domain measurement data and a theoretical prediction model based on the Bayesian system identification framework. Finally, an unconstrained quadratic function for the identification parameters is derived through matrix vectorization, and, by mathematically transforming the optimization problem, only the dynamic spectral parameters (the natural frequencies and damping ratios) need to be identified, while the spatial parameters (the mode shapes and modal contribution factors) can be analytically calculated from the spectral parameters, which greatly reduces the dimensionality of the identification parameters. In numerical examples, the identification of the modal parameters for a spring–mass system and high-speed pantograph was studied, and the identified modal parameters based on the simulation response's data were in good agreement with the theoretical values. Moreover, the modal parameters of the actual structure of the pantograph were identified based on the experimental data, and the identifying uncertainties were quantified by the coefficient of variation. [ABSTRACT FROM AUTHOR]

Continuous scanning laser Doppler vibrometry (CSLDV) enables fast and full-field vibration measurement in an intact area of a structure. This paper further proposes a novel adaptive CSLDV method that can obtain the operational deflection shapes (ODS) and mode shape of structures with holes. Firstly, an adaptive path planning method is applied to the surface of the tested structure, which can automatically adapt to the size and position of round and square holes, as well as the resolution requirements for the measurement. Secondly, based on the symmetry and other characteristics of the planned path, the time domain signal is processed by delay optimization and demodulation to obtain the ODS of each vibration mode. Finally, a modal test is conducted on a flat structure with a square and circular holes as an example. A validation experiment is also performed using SLDV. The results show that the mode shapes obtained from both methods are consistent and the modal assurance criterion between them are all above 0.96. The method can realize CSLDV of flat plate structures with arbitrary square and round holes, and has the advantages of high efficiency and dense measurement points, which enhances its engineering applicability. [ABSTRACT FROM AUTHOR]

A novel image-based long-range tracking continuously scanning laser Doppler vibrometer (CSLDV) is developed to measure vibration of a rotating structure with a complex background. The image-based long-range tracking CSLDV can track and scan the rotating structure by processing its images captured by a camera in the image-based long-range tracking CSLDV. A novel image-processing method with a background averaging technique is developed to extract the rotating structure from the background in captured images and determine its location. A one-dimensional scan scheme is used to scan along a straight line along the rotating structure. An improved demodulation method is used to process measurements of the image-based long-range tracking CSLDV to estimate modal parameters of the rotating structure, including damped natural frequencies and undamped mode shapes. Experiments of tracking and scanning a rotating blade are conducted to validate vibration measurement of a rotating blade using the image-based long-range tracking CSLDV. Measured responses of the rotating blade are processed to estimate its speeds and modal parameters. The first three damped natural frequencies of out-of-plane vibration of the rotating blade and the first three undamped mode shapes of the rotating blade along its middle line are successfully estimated and compared with results from the finite element model of the corresponding stationary blade. [ABSTRACT FROM AUTHOR]

High frequency and large bandwidth are growing trends in communication radio-frequency devices. The LiNbO3 thin film material is expected to become the preferred piezoelectric material for high coupling resonators in the 5G frequency band due to its ultra-high piezoelectric coefficient and low loss characteristics. The main mode of laterally excited bulk acoustic wave resonators (XBAR) have an ultra-high sound velocity, which enables high-frequency applications. However, the interference of spurious modes is one of the main reasons hindering the widespread application of XBAR. In this paper, a Z-cut LiNbO3 thin film-based XBAR with arc-shaped electrodes is presented. We investigate the electric field distribution of the XBAR, while the irregular boundary of the arc-shaped electrodes affects the electric field between the existing interdigital transducers (IDTs). The mode shapes and impedance response of the XBAR with arc-shaped electrodes and the XBARs with traditional IDTs are compared in this work. The fabricated XBAR on a 350 nm Z-cut LiNbO3 thin film with arc-shaped electrodes operating at over 5 GHz achieves a high effective electromechanical coupling coefficient of 29.8% and the spurious modes are well suppressed. This work promotes an XBAR with an optimized electrode design to further achieve the desired performance. [ABSTRACT FROM AUTHOR]

Composite hollow–core slab floor with reinforced concrete topping (i.e. CHFT) is relatively new, which can be applied to various long-span structures. However, these systems are typically lightweight and exhibit low damping, posing potential serviceability concerns related to human vibrations. This paper presents a comprehensive vibration test on a 9m-long CHFT system. Natural frequencies, damping ratios, and mode shapes of the floor system were obtained through modal tests. The peak acceleration, root–mean–square acceleration, maximum transient vibration value, and perception factor of the floor under heel-drop excitation were obtained through the perceived vibration test and were checked against the available design codes and standards. Sensitivity studies using the finite element method were made to investigate the vibration performance of the CHFT system. Analytical formulas for the fundamental frequency and peak acceleration were derived, which are therefore suggested for practical use. Additionally, an approach for evaluating the vibration serviceability of CHFTs is described. [ABSTRACT FROM AUTHOR]

Structural dynamic properties like frequencies and mode shapes have been widely adopted for bridge condition assessment and damage identification. One of the main challenges lies in environmental factors, particularly the varying temperature, which significantly influences the bridge’s natural frequencies. In some cases, the effect of temperature changes can be comparable to, or even exceed, the effect caused by damage, rendering the damage identification methods ineffective. This study investigates the influence of the cross-sectional non-uniform temperature distribution, as a result of surrounding environmental factors, on the frequency of concrete girder bridges. A theoretical analysis is conducted to derive the bridge’s frequencies considering the cross-sectional non-uniform temperature distribution. The upper and lower bounds of the frequencies are developed by using only the environmental temperature and the largest temperature gradient defined by codes. More importantly, the damage to the bridge can be detected if the frequencies exceed the bounds for a certain period. This approach is convenient and practical in real applications without embedding thermocouples in the main girder. Numerical simulations, laboratory experimental tests, and field measurements are carried out to validate the derived frequency considering the cross-sectional non-uniform temperature distribution as well as the upper and lower bounds of the frequency. In particular, the results of the Z24 bridge show that when the bridge is damaged, the measured frequency exceeds the bound continuously, verifying the capability of the developed upper and lower bounds to evaluate bridge conditions. [ABSTRACT FROM AUTHOR]