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Taking the nonlocal effect into account, the vibration governing differential equation and boundary conditions of a magnetostrictive composite cantilever resonator were established based on the Euler magnetoelastic beam theory. The frequency equation and vibration mode function of the composite cantilever were obtained by means of the separation of variables method and the analytic solution of ordinary differential equations. The lateral deflection, vibration governing equations, and boundary conditions were nondimensionalized. Furthermore, the natural frequency and modal function of the composite beam were quantitatively analyzed with different nonlocal parameters and transverse geometry dimensions using numerical examples. Compared with the results without considering the nonlocal effect, the influence of the nonlocal effect on the vibration characteristics was analyzed. The numerical results show that the frequency shift and frequency band narrowing of the magnetostrictive cantilever resonator are induced by nonlocal effects. In particular, the high-frequency vibration characteristics, such as vibration amplitude and modal node of the composite beam, are significantly affected. These analysis results can provide a reference for the functional design and optimization of magnetostrictive resonators. [ABSTRACT FROM AUTHOR]

As a complex load-bearing system, high-speed tracked vehicles not only need to have certain protective capabilities, but also need to be able to withstand the effects of various excitation sources. With the emergence of lightweight design requirements for vehicle bodies, research on the design of such high-speed tracked vehicles is gradually deepening. The modal analysis of vehicles is related to the reliability design of the vehicle bodies. However, current research on the modal characteristics of lightweight high-speed tracked vehicles is mainly based on experimental methods, which cannot conduct extensive research on the dynamic response of vehicle bodies under different application conditions. Modal calculation and analysis were conducted on the vehicle body model of a lightweight high-speed tracked vehicle based on the finite element method, and the model was modified combined the experimental modal test results. And, the suggestions were made for optimizing the design of the vehicle body. The modified vehicle body model and modal characteristics were contributed scholars to analyze the rationality of relevant vehicle structural design, thereby avoiding resonance during vehicle movement. Moreover, the research results are expected to be applied to analyze the dynamic characteristics of the vehicles under different working conditions, and provide reference and guidance for the design and modification of the lightweight highspeed tracked vehicles. [ABSTRACT FROM AUTHOR]

In this article, the design process of a novel vibrating tool is presented to improve some key aspects of Single Point Incremental Sheet Forming (SPISF). The overall effect of a vibration assistance is an improvement of the process by decreasing certain constraints occurring during manufacturing (e.g., high forming forces, poor roughness and elastic springback). For developing such assistance, the objective of this study is to present the design methodology and characterization of an innovative tool. The horn-shape design of the tool is optimized to resonate at its natural frequencies in the 4–16 kHz frequency bandwidth. A frequency decoupling of the tool modes is obtained by a successful desymmetrization of the tool design to precisely control the vibration direction, focusing on axial, radial or coupled vibrating motion of the tool tip. Then, the unidirectional vibrating force generated by a piezoelectric actuator is transformed into a controlled multidirectional vibrating motion of the tool tip depending on the frequency and the amplitude of the actuator input signal. The core contribution of the paper is the design methodology itself of the forming tool, which encompasses a novel approach focused on the tool/sheet contact coupling analysis and its effect on the vibrating behavior of the tool during SPIF process conditions. All steps of the design methodology are described: from the design specifications to the prototype validation, including a finite element analysis and an experimental characterization of its modal behavior in free-end tool conditions as well as in different tool/sheet contact conditions through a simple indentation forming test inside an AA5086 metal sheet. Experimental results highlight the importance of considering process boundary conditions for modal identification and the influence of the vibration direction on the force reduction in forming conditions. A forming force reduction up to 26% is obtained exciting the 2 nd bending mode of vibration of the presented forming tool identified in tool/sheet contact configuration, while reduction is less significant for the 1 st and 3 rd bending modes. [ABSTRACT FROM AUTHOR]

Aiming to address the vibration noise problems on ships, we constructed a piezoelectric phononic crystal (PC) plate structure model, solved the governing equations of the structure using the partial differential equations module (PDE) in the finite element softwareCOMSOL6.1, and obtained the corresponding energy band structure, transmission curves, and vibration modal diagrams. The application of this method to probe the structural properties of two-dimensional piezoelectric PCs is described in detail. The calculation results obtained using this method were compared with the structures obtained using the traditional plane wave expansion method (PWE) and the finite element method (FE). The results were found to be in perfect agreement, which verified the feasibility of this method. To safely and effectively adjust the bandgap within a reasonable voltage range, this paper explored the order of magnitude of the plate thickness, the influence of the voltage on the bandgap, and the dependence between them. It was found that the smaller the order of magnitude of the plate thickness, the smaller the order of magnitude of the band in which the bandgap was located. The magnitude of the driving voltage that made the bandgap change became smaller accordingly. The new idea of attaching the PC plate to the conventional plate structure to achieve a vibration damping effect is also briefly introduced. Finally, the effects of lattice constant, plate width, and thickness on the bandgap were investigated. [ABSTRACT FROM AUTHOR]

Flexible vibration has a great impact on flexible spacecraft attitude control, which will reduce the pointing accuracy of the spacecraft platform and bring severe challenges to the design of a high-precision attitude control system for flexible spacecraft. Aiming at the problem of attitude and vibration coupling control of flexible spacecraft, an anti-unwinding attitude coupling controller using the positive position feedback (PPF) control is proposed in this paper. The model compensation control term is constructed based on the prior information to improve the tracking performance. The proposed attitude coupling control method can effectively suppress the flexible vibration while achieving more accurate attitude control. The obtained closed-loop system under the proposed control scheme is asymptotically stable, which is proved by the Lyapunov stability theory. The numerical simulation illustrates that the proposed method can effectively improve the attitude control accuracy of the flexible spacecraft and is capable of large-angle attitude maneuver control because of its prominent performance in attitude tracking and its unwinding-free performance. • Coupling control for flexible spacecraft. • Active vibration control using positive position feedback. • Model compensation control term is constructed to improve the dynamic performance. • The obtained closed-loop system achieves the asymptotic stability and anti-unwinding performance. [ABSTRACT FROM AUTHOR]

Aims: To find the prevalence of tactile hallucinations of phone vibrations among individuals aged 18 years-22 years. To find whether the hallucinations are bothersome. Background: Overuse of phones can lead to physiological health hazards. Repeated use of vibration mode leads to fake perception of device being vibrating when it is not. Tactile hallucination of phone vibration is a prevalent phenomenon among young individuals. Theories explaining the possibility of the phenomenon are proven through researchers. Design: Cross sectional survey. Participants: 204 individuals responded to the questionnaire. Materials and Methods: An electronic survey consisting of 12 questions bases on demographic, mobile usage hours, frequency of phantom vibrations experienced. An online questionnaire was used for the study. It is known as the phantom vibration scale or phantom vibration questionnaire which was taken from an article. Results: 204 responses were received. Out of that 68% experienced tactile hallucinations. Among those who had hallucination different factors were viewed in association with it. 88% possessed a smart phone for more than a year. Respondents were asked about the phone usage hours and majority used it for 3 hours-5 hours daily. Social media is a known addiction of phone and the survey showed that 55% of the respondents used phones to scroll social media. The next factor that is vibration mode of phone, was used by 17% of the people always. 29% used it for most of the time. About the placement while carrying of phone it showed that 69% always carried phone in their jean front pocket. Also, 42% of the participants found those vibrations to be bothersome. 21% had the hallucinations so severe that they felt it when the phone was switched off. Conclusions: More than half of the people on this planet carry smartphone and most use it on vibration mode. Even if one third of them experience the hallucinations, a planned treatment is required for this. [ABSTRACT FROM AUTHOR]

The diagnosis of structural damage usually belongs to a mathematical inverse problem. This work presents a novel frequency-shift flexibility sensitivity algorithm for structural damage assessment using only the first-order vibration mode to achieve the goal of successfully identifying structural damage with fewer modal parameters. The core idea of the proposed method is to make the first-order vibration mode contribute the most to a structural flexibility matrix through the frequency-shift operation. A high-precision flexibility matrix can be obtained after the frequency-shift operation, which only needs the first mode of structural free vibration. Through this special advantage, structural damage coefficients can be accurately calculated by the frequency-shift flexibility sensitivity equation. Thus, a reliable identification result can be obtained according to the values of the calculated damage coefficients. In some engineering applications, another advantage of the proposed method is that it does not require a complete finite element modeling process, as long as a few lower-frequency vibration modes of the intact structure are measured. A truss structure and a beam structure are used as two numerical examples to demonstrate the proposed approach. The results show that the proposed method has higher calculation accuracy than the ordinary flexibility sensitivity method by using only the first-order vibration mode. The proposed method can overcome possible misdiagnosis of the ordinary flexibility sensitivity method. It also has been shown that the proposed method may have the potential to identify minor damage in a structure. Using the experimental data of a steel frame structure, the effectiveness and reliability of the proposed method have been further verified. The proposed method provides a simple way for structural damage identification with only a few vibration modal data. [ABSTRACT FROM AUTHOR]

Here, we report the distinct behaviors of 4‐azidobenzoic acid (C7H5N3O2, 4‐ABA) in diamond anvil cells with the pressure up to ∼18 GPa at room temperature by in situ Raman scattering and synchrotron angle‐dispersive X‐ray diffraction (ADXRD) measurements. The analyses of Raman spectra revealed that 4‐ABA underwent a phase transition in the pressure range of 0.8–1.3 GPa and a conformational change at 6.3 GPa, which were supported by XRD results. The phase transition is attributed to the distortion of the benzene ring, and the change of hydrogen bonds results in the conformational change. Above 11.2 GPa, the (112) Bragg peak moved toward a low angle, indicating the increase of the interplanar distance of 4‐ABA. Upon compression to 18.0 GPa, 4‐ABA transformed into amorphous phase that the low amorphization pressure is helpful for nitrogen polymerization. This study provides an effective route for understanding the evolution of the azide group under high pressure, which is beneficial to studying the mechanism of forming polymeric nitrogen. [ABSTRACT FROM AUTHOR]

Multilayer piezoelectric ceramics have wide application prospects in the fields of precision driving and intelligent sensing owing to their low driving voltages and large strains. However, high sintering temperatures and expensive noble metal electrodes limit their application as multilayer piezoelectric ceramic actuators (MLAs) in conventional devices. In this study, a modified piezoelectric ceramic powder and Ag inner electrode were used to prepare a low-cost MLA with a low sintering temperature of 900 °C. The MLA showed superior piezoelectric properties with d 33 = 3015 pC/N and a large electric-field-induced strain of 0.13% at 22.2 kV/cm. Moreover, the stator of the ultrasonic motor composed of this MLA produced the ideal vibration mode, and the maximum rotation speed of the ultrasonic motor was 192 r/min under a 50 g load, which verifies the applicability of this component in practical minimised devices. These results demonstrate a strategy for fabricating low-cost and high-precision micro-actuators for precision driving. [ABSTRACT FROM AUTHOR]

The structure of DNA double helix is stabilized by water molecules and metal counterions that form the ion-hydration shell around the macromolecule. Understanding the role of the ion-hydration shell in the physical mechanisms of the biological functioning of DNA requires detailed studies of its structure and dynamics at the atomistic level. In the present work, the study of collective vibrations of water molecules around the DNA double helix was performed within the framework of classical all-atom molecular dynamics methods. Calculating the vibrational density of states, the vibrations of water molecules in the low-frequency spectra ranged from ∼ 30 to ∼ 300 cm - 1 were analyzed for the case of different regions of the DNA double helix (minor groove, major groove, and phosphate groups). The analysis revealed significant differences in the collective vibrations behavior of water molecules in the DNA hydration shell, compared to the vibrations of bulk water. All low-frequency modes of the DNA ion-hydration shell are shifted by about 15–20 cm - 1 towards higher frequencies, which is more significant for water molecules in the minor groove region of the double helix. The interactions of water molecules with the atoms of the macromolecule induce intensity decrease of the mode of hydrogen-bond symmetrical stretching near 150 cm - 1 , leading to the disappearance of this mode in the DNA spectra. The obtained results can provide an interpretation of the experimental data for DNA low-frequency spectra and may be important for the understanding of the processes of indirect protein–nucleic recognition. [ABSTRACT FROM AUTHOR]

Purpose: This study aims to provide a reliable and effective algorithm that is suitable for addressing the problems of continuous orders of frequencies and modes under different boundary conditions, circumferential wave numbers and thickness-to-length ratios of moderately thick circular cylindrical shells. The theory of free vibration of rotating cylindrical shells is of utmost importance in fields such as structural engineering, rock engineering and aerospace engineering. The finite element method is commonly used to study the theory of free vibration of rotating cylindrical shells. The proposed adaptive finite element method can achieve a considerably more reliable high-precision solution than the conventional finite element method. Design/methodology/approach: On a given finite element mesh, the solutions of the frequency mode of the moderately thick circular cylindrical shell were obtained using the conventional finite element method. Subsequently, the superconvergent patch recovery displacement method and high-order shape function interpolation techniques were introduced to obtain the superconvergent solution of the mode (displacement), while the superconvergent solution of the frequency was obtained using the Rayleigh quotient computation. Finally, the superconvergent solution of the mode was used to estimate the errors of the finite element solutions in the energy norm, and the mesh was subdivided to generate a new mesh in accordance with the errors. Findings: In this study, a high-precision and reliable superconvergent patch recovery solution for the vibration modes of variable geometrical rotating cylindrical shells was developed. Compared with conventional finite element method, under the challenging varying geometrical circumferential wave numbers, and thickness–length ratios, the optimised finite element meshes and high-precision solutions satisfying the preset error limits were obtained successfully to solve the frequency and mode of continuous orders of rotating cylindrical shells with multiple boundary conditions such as simple and fixed supports, demonstrating good solution efficiency. The existing problem on the difficulty of adapting a set of meshes to the changes in vibration modes of different orders is finally overcome by applying the adaptive optimisation. Originality/value: The approach developed in this study can accurately obtain the superconvergent patch recovery solution of the vibration mode of rotating cylindrical shells. It can potentially be extended to fine numerical models and high-precision computations of vibration modes (displacement field) and solid stress (displacement derivative field) for general structural special value problems, which can be extensively applied in the field of engineering computations in the future. Furthermore, the proposed method has the potential for adaptive analyses of shell structures and three-dimensional structures with crack damage. Compared with conventional finite element methods, significant advantages can be achieved by solving the eigenvalues of structures with high precision and stability. [ABSTRACT FROM AUTHOR]

Purpose: In this paper, a superconvergent patch recovery method is proposed for superconvergent solutions of modes in the finite element post-processing stage of variable geometrical Timoshenko beams. The proposed superconvergent patch recovery method improves the solution speed and accuracy of the finite element analysis of a curved beam. The free vibration and natural frequency of the beam were considered for studying forced vibrations and structural resonance. Beam vibration mode analysis was performed for high-precision vibration mode solutions and frequency values. The proposed method can be used to compute beam vibration modes of beams with different shapes and boundary conditions as well as variable cross sections and curvatures. The purpose of this paper is to address these issues. Design/methodology/approach: An adaptive method was proposed to analyse the in-plane and out-of-plane free vibrations of the variable geometrical Timoshenko beams. In the post-processing stage of the displacement-based finite element method, the superconvergent patch recovery method and high-order shape function interpolation technique were used to obtain the superconvergent solution of mode (displacement). The superconvergent solution of mode was used to estimate the error of the finite element solution of mode in the energy form under the current mesh. Furthermore, an adaptive mesh refinement was proposed by mesh subdivision to derive an optimised mesh and accurate finite element solution to meet the preset error tolerance. Findings: The results computed using the proposed algorithm were in good agreement with those computed using other high-precision algorithms, thus validating the accuracy of the proposed algorithm for beam analysis. The numerical analysis of parabolic curved beams, beams with variable cross sections and curvatures, elliptically curved beams and circularly curved beams helped verify that the solutions of frequencies were consistent with the results obtained using other specially developed methods. The proposed method is well suited for the mesh refinement analysis of a curved beam structure for analysing the changes in high-order vibration mode. The parts where the vibration mode changed significantly were locally densified; a relatively fine mesh division was adopted that validated the reliability of the mesh optimisation processing of the proposed algorithm. Originality/value: The proposed algorithm can obtain high-precision vibration solutions of variable geometrical Timoshenko beams based on more optimized and reasonable meshes than the conventional finite element method. Furthermore, it can be used for vibration problems of parabolic curved beams, beams with variable cross sections and curvatures, elliptically curved beams and circularly curved beams. The proposed algorithm can be extended for application in superconvergent computation and adaptive analysis of finite element solutions of general structures and solid deformation fields and used for adaptive analysis of more complex plates, shells and three-dimensional structures. Additionally, this method can analyse the vibration and stability of curved members with crack damage to obtain high-precision vibration modes and instability modes under damage defects. [ABSTRACT FROM AUTHOR]

Rotational acoustic manipulation technology offers precise control of particle motion, making it advantageous for applications in microfluidics, biomedicine, materials research, and so on. Current advanced techniques that use acoustic waves to rotate particles include microstructure vibration, microbubble oscillation, and acoustic holography. Although these methods have achieved some success in rotational acoustic manipulation, they face challenges such as limited types of particles, complex device fabrication, and single-mode manipulation. To address these issues, this study proposes a novel rotational acoustic manipulation device based on traveling wave acoustic fields. The traveling wave acoustic field is achieved by planning the vibration modes of the vibrational source. In this study, a ring-shaped piezoelectric ceramic with four-quadrant dual polarization is designed to excite two orthogonal B 11 bending vibration modes of the vibrator. By adjusting the phase difference of the excitation signals, these two B 11 bending vibration modes can be coupled into either clockwise or counterclockwise traveling wave vibration modes, thereby establishing unidirectional rotating traveling waves in the water within the PDMS ring. The PDMS ring features an open structure, meeting the requirements for manipulating both floating and submerged particles. The performance of the proposed acoustic manipulation device is validated and analyzed through experiments with hollow glass particles, hollow polystyrene particles, and solid polystyrene particles. The results demonstrate that the proposed acoustic manipulation device can achieve precise fixed-point self-rotation and regional revolution manipulation of particles, regardless of their floating, submerged, hydrophilic, or hydrophobic properties. This indicates the high universality and robustness of the device, making it applicable for the manipulation of various types of particles. Overall, this study introduces a novel acoustic manipulation method for particle rotation, providing strong support for the development and application of acoustic manipulation devices in diverse fields. [Display omitted] • A novel piezoelectric device is proposed for manipulating the self-rotation and revolution of particles. • The rotating acoustic field and acoustic streaming field are established in water by planning the vibration modes. • The proposed manipulation device is effective regardless of whether particles are floating or submerged. • Both hydrophilic and hydrophobic particles can undergo self-rotation and revolution within the proposed device. [ABSTRACT FROM AUTHOR]

The bolt joint is the key component connecting the rigid moving base body and the flexible manipulator. The dynamic characteristics of the flexible manipulator under the elastic constraint of the joint are analyzed, and the action mechanism of the elastic constraint of the bolt joint on the frequency and vibration mode is revealed. Considering the effects of line constraint and torsion constraint, the elastic constraint model of the joint is established. Based on the principle of virtual work, the boundary constraints of the joint end and the free end are established, and the analytical equation of frequency and the expression of vibration mode function are derived. The first three frequencies and vibration mode characteristics of the flexible manipulator under elastic constraints are analyzed numerically. The sensitivity method is used to analyze the effect of linear constraints and torsional constraints on the frequency, and the elastic constraint region is established to characterize the functional relationship between the binding stiffness and the natural frequency. It is found that under elastic constraints, the influence of torsional stiffness of bolt joint is mainly concentrated in the low-order modal frequency, while the linear stiffness has a great influence on each order modal frequency of the manipulator; With the decrease of elastic constraint stiffness, its influence on modal shapes gradually increases, especially on highorder modal shapes. The research results prove the internal mechanism of the influence of elastic constraints on vibration characteristics, which provide a theoretical basis for improving the dynamic characteristics of flexible manipulator. [ABSTRACT FROM AUTHOR]

In this paper, the bandgap characteristics of a missing rib lattice structure composed of beam elements are investigated by using the Floquet-Bloch theorem. The tuning of the width and position of the bandgap is achieved by changing the local structural parameters, i.e., the rotation angle, the short beam length, and the beam thickness. In order to expand the regulation of the bandgap, the influence of the material parameters of the crossed long beams inside the structure on the bandgap is analyzed. The results show that the mass density and stiffness of the structure have significant effects on the bandgap, while Poisson's ratio has no effect on the bandgap. By analyzing the first ten bands of the reference unit cell, it can be found that the missing rib lattice structure generates multiple local resonance bandgaps for vibration reduction, and these bandgap widths are wider. The modal analysis reveals that the formation of the bandgap is due to the dipole resonance of the lattice structure, and this dipole resonance originates from the coupling of the bending deformation of the beam elements. In the band structure, the vibrational mode of the 9th band with a negative slope corresponds to a rotational resonance, which is different from that with the conventional negative slope formed by the coupling of two resonance modes. This study can provide a theoretical reference for the design of simple and lightweight elastic metamaterials, as well as for the regulation of bandgaps and the suppression of elastic waves. [ABSTRACT FROM AUTHOR]

Viscous dampers enhance the seismic performance of buildings by increasing the capacity for damping. It remains a challenge to decide on the optimum placement for the added dampers and it has been a continuing subject of research. In this paper, Element Exchange Method and energy-based distribution methods are proposed. The proposed methods are compared against currently available methods through case studies. The case studies are based on a two-dimensional ten-story shear building adopting different nonlinearity of viscous dampers and a three-dimensional steel moment-resisting-frame (MRF) building with varying plan asymmetry. The methods then automatically develop damper placement schemes, and subsequently, the buildings are evaluated for their maximum peak inter-story drift against a suite of ground motions. The result shows that Element Exchange methods and energy-based distribution methods can successfully reduce maximum peak inter-story drift over all case studies. [ABSTRACT FROM AUTHOR]

Identifying relatively weak areas is of great significance for improving the seismic reliability of structures. In this paper, a modal strain energy decomposition method is proposed, which can realize the decoupling of the comprehensive modal strain energy of a planar structure into three basic modal strain energies. According to the decomposition results, the modal strain energy decomposition diagram and the modal strain energy cloud diagram can be drawn so as to realize the quantitative and visual analysis of the vibration modes. The method is independent of load cases and can identify relatively weak areas of a structure from the perspective of inherent characteristics. The comparison with the shaking table test results of the two-story shear wall shows that the modal strain energy decomposition method can effectively identify the type of the relatively weak area of a structure and locate the position of the relatively weak area. Finally, the 6-story shear wall is analyzed by the modal strain energy decomposition method, and the relatively weak areas under the first two vibration modes are identified. [ABSTRACT FROM AUTHOR]

• The optical fiber coil with spool (OFCS) is a crucial tool for precise physics measurements. • To improve the seismic resistance of OFCSs in space applications, the vibration modes are thoroughly investigated through dynamic analysis, simulations, and experiments. • We establish a dynamic model of the OFCS based on the vibration transmission mechanism to characterize its vibration modes. • The vibration eigenfrequency and shapes are calculated under various conditions. • The experimental results validate the feasibility of the dynamic model and simulation, meanwhile, the discrepancies between the simulations and experiments are analyzed. • This study is the first of its kind to develop a comprehensive dynamic model for an OFCS, with simulations and experiments confirming its effectiveness. The optical fiber coil with spool (OFCS) is a crucial tool for precise physics measurements. To improve the seismic resistance of OFCSs in space applications, the vibration modes are thoroughly investigated through dynamic analysis, simulations, and experiments. We establish a dynamic model of the OFCS based on the vibration transmission mechanism to characterize its vibration modes. The vibration eigenfrequency and shapes are calculated and simulated under various conditions. The experimental results validate the feasibility of the dynamic model and simulation, meanwhile, the discrepancies between the simulations and experiments are analyzed. This study is the first of its kind to develop a comprehensive dynamic model for an OFCS, with simulations and experiments confirming its effectiveness. [ABSTRACT FROM AUTHOR]

Purpose: This study presents a novel hp-version adaptive finite element method (FEM) to investigate the high-precision eigensolutions of the free vibration of moderately thick circular cylindrical shells, involving the issues of variable geometrical factors, such as the thickness, circumferential wave number, radius and length. Design/methodology/approach: An hp-version adaptive finite element (FE) algorithm is proposed for determining the eigensolutions of the free vibration of moderately thick circular cylindrical shells via error homogenisation and higher-order interpolation. This algorithm first develops the established h-version mesh refinement method for detecting the non-uniform distributed optimised meshes, where the error estimation and element subdivision approaches based on the superconvergent patch recovery displacement method are introduced to obtain high-precision solutions. The errors in the vibration mode solutions in the global space domain are homogenised and approximately the same. Subsequently, on the refined meshes, the algorithm uses higher-order shape functions for the interpolation of trial displacement functions to reduce the errors quickly, until the solution meets a pre-specified error tolerance condition. In this algorithm, the non-uniform mesh generation and higher-order interpolation of shape functions are suitable for addressing the problem of complex frequencies and modes caused by variable structural geometries. Findings: Numerical results are presented for moderately thick circular cylindrical shells with different geometrical factors (circumferential wave number, thickness-to-radius ratio, thickness-to-length ratio) to demonstrate the effectiveness, accuracy and reliability of the proposed method. The hp-version refinement uses fewer optimised meshes than h-version mesh refinement, and only one-step interpolation of the higher-order shape function yields the eigensolutions satisfying the accuracy requirement. Originality/value: The proposed combination of methodologies provides a complete hp-version adaptive FEM for analysing the free vibration of moderately thick circular cylindrical shells. This algorithm can be extended to general eigenproblems and geometric forms of structures to solve for the frequency and mode quickly and efficiently. [ABSTRACT FROM AUTHOR]

A special vibration mode called intrinsic localized mode (ILM) in a dispersed multi mass point-nonlinear spring system has been actively studied in solid-state physics and has a high application potential in engineering. Previous studies have only considered parameter-invariant systems; hence, active control of the excited ILM is not possible. Therefore, even though the phenomena are very interesting, there are no applications to devices. In this article, we propose a new paradigm of ILM by designing a dynamic nonlinear vibration system that can treat nonlinear spring properties in a variable manner depending on the applied current. By using variable spring characteristics, the localized vibration energy of the ILM can be freely transferred in unconventional way than before. The spring properties of the variable spring structure with applied current are investigated using finite element analysis. Then, numerical simulations in MATLAB show that the active control of the ILM is possible in a dynamic vibration system with variable spring characteristics. [ABSTRACT FROM AUTHOR]

Intrinsic localized mode (ILM) can be generated in multiple mass‐spring systems using nonlinear springs, and ILM has attracted a lot of attention due to its special vibration modes that are not found in linear systems. However, the difficulty of creating nonlinearity remains a barrier to ILM research. In this paper, we propose a rotating magnetic spring based on magnetic nonlinearity. The nonlinear restoring properties of the proposed magnetic spring are confirmed by finite element method (FEA). Finally, using the restoring properties obtained from FEA, it is shown that ILM can be excited by MATLAB numerical analysis. © 2021 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC. [ABSTRACT FROM AUTHOR]

Poor understanding of the fluid–structure interaction of a wind turbine blade is a well-known bottleneck in the development of the wind power industry. The degree to which different blade vibration modes influence the fluid fluctuation intensity and the manner of its variation with working conditions remain unknown, which restricts the understanding of fluid–structure interaction and the development of corresponding decoupling methods. To this end, an experiment for synchronously monitoring blade vibration parameters, near-wake flow parameters, and generator output parameters was conducted in the present study. To prevent impacting the characteristics of blade structure and wake flow, an indirect test for identifying the dynamic frequencies was developed. To validate this method, a small wind turbine was utilized to experimentally investigate the influence of different blade vibration modes on the fluid fluctuation in the tip vortex region. The results revealed that the blade vibrations have significant influences on the wake flow fluctuation. They also indicated the differences in the intensities of four types of low-frequency vibrations under static and dynamic conditions. Eventually, the relationship between the intensities of blade vibration modes and those of fluid fluctuation with varying blade rotation speeds was also analyzed. [ABSTRACT FROM AUTHOR]

• The analytical solution for free vibration of constrained arches is proposed. • The arches with lateral translational and/or rotational braces are considered. • Closed-form solutions are obtained for the maximum fundamental frequency. • The threshold bracing stiffness or stiffness requirements is investigated herein. • The influences of the lateral braces on free vibration of arch are discovered. Discrete lateral braces are commonly employed to enhance the out-of-plane stability of arches. However, these braces generate coupling effects among vibration modes, which significantly impact the vibration characteristics of the arches. This paper presents an analytical solution for the free vibration analysis of two-hinged arches with equally-spaced lateral translational and/or rotational braces. A simplified method of evaluating the fundamental frequency for the out-of-plane vibration of arches with equally-spaced lateral braces is introduced. The method relies on the conventional approach of representing arch braces through elastic springs, but here the out-of-plane deflection of the braced arch is constructed by adding related coupled sinusoidal functions to that of the unbraced arch, satisfying both the boundary and kinematic conditions. Subsequently, the fundamental frequency and threshold bracing stiffness or stiffness requirement are derived using the Rayleigh–Ritz method. Finite element analysis (FEA) is applied to investigate the flexural-torsional vibration mode and fundamental frequency of arches with discrete braces, and the results from FEA closely match the theoretical predictions. The effects of number of lateral translational and/or rotational brace, out-of-plane slenderness, included angle, bracing stiffness and bracing position on the fundamental frequency are comprehensively analyzed. It is found that when the fundamental frequency of the braced arch increases due to changes in bracing stiffness, the mode shape displays more intricate behavior, rather than following a straightforward low-to-high mode growth pattern. Furthermore, it is observed that in some cases, the addition of rotational bracing stiffness can markedly enhance the maximum fundamental frequency of the arch with both translational and rotational braces. [ABSTRACT FROM AUTHOR]

• A novel method for pressure prediction and cavitation evaluation of water jacket in engines is proposed. • The pressure amplification factor for a thin liquid layer under modal vibration is derived. • The nonlinear relationship between liner vibration and coolant pressure is investigated to reveal the mechanism of vibration-induced cavitation. • Effects of acoustic parameters and liner modal parameters on cavitation are discussed. • The correctness and rationality of the method is verified by experiment. Vibrations of the cylinder liner in internal combustion engines cause coolant cavitation, inducing cavitation erosion. Owing to the lack of a comprehensive understanding of vibration-induced cavitation, the cavitation erosion has been long an unresolved problem influencing engine lifetime and reliability and concerned more in recent years due to lightweight designs. This study proposes a novel pressure prediction method that considers the dynamic properties of a cylinder liner and the pressure amplification effect of a thin water jacket. A pressure amplification factor for a thin water jacket, defined as the ratio of the acoustic pressure to the plane progressive wave pressure generated by the same liner vibration, was derived for the first time. The pressure amplification mechanism in the thin water jackets was revealed. The cavitation risk area on the cylinder liner was predicted, and the effects of acoustic parameters and liner modal properties on cavitation were analysed. The theoretical analyses agreed with the experimental results, proving the accuracy of the proposed method. Moreover, it has found that the thin-layer configuration of the water jacket significantly reduced the vibration threshold for triggering cavitation. Vibration-induced cavitation in cylinder liners is closely related to the liner constraint modes and acoustic properties of the water jackets. The research results enrich the theoretical understanding of vibration-induced cavitation and provide theoretical support for the prediction and mitigation of cavitation erosion in internal combustion engines. [Display omitted] [ABSTRACT FROM AUTHOR]

The aim of the study is to propose a diagnostics method based on blade's vibration model in frequency domain. Amplitude spectrum A(ω) and phase spectrum φ(ω) have been experimentally identified which define transfer function G(jω) = P(ω) + jQ(ω) and their real P(ω) and imaginary Q(ω) parts. Transfer function G(jω) and resulting frequency, amplitude, phase characteristics and real P(ω) and imaginary Q(ω) parts are parts of blade's diagnostics model. Changes in those characteristics are directly related to changes in the technical condition of the blades. It has been noticed that small changes in the technical condition cause large changes in frequency characteristics, which proves their usefulness in the diagnosis process. [ABSTRACT FROM AUTHOR]

Manual harvesting of large area fruits is inefficient, which consumes manpower and resources. Mechanized harvesting is the inevitable trend of fruit harvest. Vibration harvesting is one of the important forms in terms of fruit mechanized harvesting. According to the different striking parts of fruit trees, the vibration modes were classified as trunk, crown, and branch types. The harvesting efficiency of fruit is an important index to measure the quality of all fruit harvesting machines. The reduction of fruit damage is considered in the harvesting of vulnerable fruits. In this study, the development of vibration harvesting technologies were studied in terms of vibration mode. The development of fruit damage, harvesting efficiency, and fruit tree modeling were discussed. Finally, the development direction of fruit vibration mechanized harvesting was looked forward. Machinery instead of manpower, fully mechanized harvesting is the inevitable development direction of fruit harvesting. [ABSTRACT FROM AUTHOR]

• The classification of saturated, supersaturated and undersaturated cavitation clouds was proposed. • The vibration mode of the radiation surface of transducer is investigated experimentally. • The characteristics and formation mechanism of supersaturated cavitation cloud structure were investigated. • A new approach is proposed to measure the vibration mode of transducer operating at high power and large amplitude in real time. The vibration mode of the radiation surface of transducer (or structure of supersaturated cavitation cloud in thin liquid) is investigated experimentally by high-speed photography. The classification of saturated, supersaturated and undersaturated cavitation clouds was proposed, and a comparison was made between saturated and supersaturated cavitation cloud structures in liquid thin layers. The characteristics and formation mechanism of supersaturated cavitation cloud structure were investigated. Based on the close correspondence and rapid response between the distribution of supersaturated cavitation clouds and vibration modes of radiation surface, a new approach is proposed to measure the vibration mode of transducer operating at high power and large amplitude in real time. [ABSTRACT FROM AUTHOR]

• The subdiced transducer (SDT) was fabricated and its performance was studied. • For lower frequency, SDT can achieve a smaller size and shorter transmission pulse. • SDT may have great potential for miniaturization and close-range imaging. Structure design of medical ultrasonic transducers is of prime importance, as it not only affects the transducer's imaging performance, but also limits its application scene and scope. In this paper, a single element transducer with subdicing is fabricated and its performance is studied using finite element method. In addition, the comparison transducers (CPTs) are fabricated as well as single element transducers with and without subdicing the element. The experimental results show that by subdicing the element with cut width 120 μm and cut depth 500 μm of the single transducer with a center frequency of 8 MHz and dimension of 2 mm × 0.9 mm × 1.2 mm, the center frequency reduced by up to 58.3 %, the −6 dB bandwidth increased by up to 48.7 %, but the echo signal amplitude reduced by 52.4 %. Compared to CPT-5, the volume of the subdicing transducer reduced by 94.6 %, the center frequency reduced by 4.3 %, the −6 dB bandwidth increased by 1.26 times, the transmitted pulse signal length decreased by 50 %, and the echo signal amplitude achieved 28 % of CPT-5. Therefore, the proposed subdicing transducer may have great potential for miniaturization and close-range imaging. [ABSTRACT FROM AUTHOR]

In this paper, a closed-form solution is presented for the free vibration response of a 2-DOF parametric system by a technique with special trigonometric series. The technique extends the concept of modulation feedback to the problem of multiple degrees of freedom (M-DOF) parametric system using an equivalent dynamic system. The characteristic equation is derived by the harmonic balance in a parametric equation with the principal oscillation frequencies computed. The computation of modes and splitting modes is carried out by operation on a mixed matrix. The arbitrary constants in the general solution are determined by the initial conditions. A real-life example of a coupled inverted-pendulum system is provided to illustrate the applicability of the proposed approach. An approaching error is adopted to assess the computational errors both using the proposed technique and the Runge–Kutta algorithm. Of interest is that the time-periodic coefficient results in the changeability of the mode in the 2-DOF parametric system, while exciting the splitting mode in the harmonic combination resonance. The proposed technique is numerically demonstrated to possess not only high approaching accuracy, but is also capable of revealing some new phenomena in the parametric system, such as characteristics of mode and slitting mode, etc. It proves to be useful for future research and engineering applications of parametric systems. [ABSTRACT FROM AUTHOR]

The paper presents the results of simulations and experimental investigations on natural frequencies and oscillation modes of pairwise-shrouded cooled turbine blades and their rings with allowance for a possible frequency mistuning and the assured contact of mating surfaces of the root and shroud platform halves. As the research object, the high-pressure turbine wheel of an aircraft bypass turbojet engine has been selected. 3D finite element models of the turbine wheel blades/ period were developed as a system with structural rotational symmetry. The contact interaction between blades over the mating surfaces was modeled on basis of solving the stationary problem. The calculation-and-experimental investigations were performed for two operating conditions of the engine – the non-running engine and the steady-state maximum take-off condition. Results have been cited for individual, isolated blades. The results show a good agreement between calculated and experimental data. The frequency mistuning of those blades is found to be considerably dependent on oscillation mode number, but the mistuning value is practically not affected by the operating condition of the engine. It is confirmed that two oscillation modes are excited in the blade pair as a regular system in the presence of the mistuning of their frequencies, which are close to the inphase and antiphase frequencies. The ratio of natural frequencies of those oscillation modes is dependent on oscillation mode of isolated blades. It is shown that the frequency mistuning of paired blades due to excitation of two oscillation (inphase and antiphase) modes causes doubling of the number of resonant states of the turbine wheel what must be considered when developing methods to ensure their vibrational reliability. [ABSTRACT FROM AUTHOR]

As a sub-process of flotation, the bubble-particle detachment plays a critical role in final flotation recovery. In this short communication, the effect of vibration mode, i.e., sine wave, triangle wave and square wave, on the detachment of low-rank coal particle from oscillating bubble was investigated using a home-made bubble-particle detachment measurement system. The critical detachment amplitude was used to evaluate the stability of bubble-particle aggregate. Three coal size fractions, i.e., 0.25–0.5, 0.5–1, and 1–1.5 mm, were used as the experimental samples, respectively. The results show that the critical amplitude decreased as particle size increased under different vibration modes due to the increased inertia. The critical amplitude at three different size fractions always decreased in the following order: sine wave, triangle wave and square wave, indicating the bubble-particle aggregate was the most stable under sine wave vibration. Square wave vibration has the most dramatic movement path changes, causing a highest instantaneous impulse and detachment force. Unlabelled Image • Effect of vibration mode on detachment of low-rank coal was studied. • The critical amplitude decreased with increasing particle size. • The critical amplitude decreased as follows: sine, triangle and square wave. [ABSTRACT FROM AUTHOR]

• Flow induced vibration of four-span tube is tested. • FEI critical velocity for tube with AVB is obtained. • FEI critical velocity for tube with TSP is obtained. • Five correlations for predicting onset of FEI are evaluated. Flow induced vibrations in steam generator and other heat exchangers can result in tube failure and lead to large economic losses. Tube supports such as tube support plates (TSP) or anti-vibration bars (AVB) are commonly used to suppress the flow induced vibration. Knowledge on the tube dynamic characteristics and instability phenomena under these support conditions is therefore essential, when fluid flows across the multi-span tubes. In this paper, flow induced vibration of a four-span rotated triangular tube array with a pitch-to-diameter ratio of 1.4 under three sets of AVB or TSP supports is experimentally studied. Part of the middle segment of the tube is subjected to cross flow. The vibration displacements and frequency spectra of a tube on first row are analyzed. It was found that the vibration mode for four-span tube bundle with TSP is different from that of the tube supported by AVB when fluid elastic instability (FEI) happens. The effective FEI critical velocities for the tube with TSP and that with AVB is 6.8 m/s and 3.0 m/s, respectively. Five correlations for predicting the onset of FEI of the tube bundle tested are compared with experimental results. Weaver and El-Kashlan correlation (1981b) is best. The effective FEI critical velocities predicted by Weaver and El-Kashlan correlation (1981b) are 15% and 27% higher than the experimental results for tube with TSP and tube with AVB, respectively. The vortex shedding responses are analyzed for the two tube-support structures. The Strouhal number for non-resonant vortex shedding response is calculated and compared with expectations from literature. The turbulent buffeting response for tube under different supports are compared with each other and discussed. [ABSTRACT FROM AUTHOR]

Electrocatalysis provides a powerful means to selectively transform molecules, but a serious impediment in making rapid progress is the lack of a molecular-based understanding of the reactive mechanisms or intermediates at the electrode-electrolyte interface (EEI). Recent experimental techniques have been developed for operando identification of reaction intermediates using surface infrared (IR) and Raman spectroscopy. However, large noises in the experimental spectrum pose great challenges in resolving the atomistic structures of reactive intermediates. To provide an interpretation of these experimental studies and target for additional studies, we report the results from quantum mechanics molecular dynamics (QM-MD) with explicit consideration of solvent, electrode-electrolyte interface, and applied potential at 298 K, which conceptually resemble the operando experimental condition, leading to a prototype of operandoQM-MD(o-QM-MD). With o-QM-MD, we characterize 22 possible reactive intermediates in carbon dioxide reduction reactions (CO2RRs). Furthermore, we report the vibrational density of states (v-DoSs) of these intermediates from two-phase thermodynamic (2PT) analysis. Accordingly, we identify important intermediates such as chemisorbed CO2 (b-CO2), *HOC-COH, *C-CH, and *C-COH in our o-QM-MD likely to explain the experimental spectrum. Indeed, weassign the experimentalpeakat 1,191cm-1 to themodeofC-Ostretch in*HOC-COH predicted at 1,189 cm-1 and the experimental peak at 1,584 cm-1 to the mode of C-C stretch in *C-COD predicted at 1,581 cm-1. Interestingly, we find that surface ketene (*C=C=O), arising from *HOC-COH dehydration, also shows signals at around 1,584 cm-1, which indicates a nonelectrochemical pathway of hydrocarbon formation at low overpotential and high pH conditions. [ABSTRACT FROM AUTHOR]

In this paper, vibration modal analysis of a horizontal axis micro wind turbine blade of different rotational speeds was carried out by using the finite element analysis software COSMOSWorks. The dynamic stiffening phenomenon and its effect on the vibration mode of the wind turbine blade were taken into account. Numerical results were analyzed and compared. The analysis can help not only to ensure the reliability of system operation but also to improve the structural performance. [ABSTRACT FROM AUTHOR]

Torque ripple of permanent magnet synchronous motor (PMSM) will result in the distortion of current waveform and the load flexibility of spiral torsion spring (STS) will affect the control performance of driving system. This study focuses on a new control problem of simultaneous suppression of PMSM's torque ripple and flexible load's vibration. First, the Lagrange equation is used to establish the dynamic model of STS to describe its vibration mode. The overall model of STS directly derived by PMSM under stator current vector orientation is built. Then, based on the magnetic co‐energy model of electromagnetic torque of PMSM, the constraint relation of optimal stator harmonic current under the condition of torque ripple minimisation is derived, and the controller based on stator current oriented closed‐loop I/f control to suppress load vibration and torque ripple simultaneously is presented through backstepping control. A wide speed range identification method based on the least‐square algorithm with a forgetting factor is also designed. The simulation and experiment show that the speed identification algorithm can estimate the speed accurately in a wide range. The proposed control scenario improves control performance, smoothes current waveform and inhibits torque ripple and load vibration effectively. [ABSTRACT FROM AUTHOR]

Abstract This study investigates the vibration mode structure of general cyclically symmetric systems with central components vibrating as three-dimensional rigid bodies. This work does not rely on the assumptions of the system matrix symmetries; asymmetric inertia matrix, damping, gyroscopic, and circulatory terms can be present. In the equation of motion of a general cyclically symmetric system, the matrix operators are proved to have properties related to the cyclic symmetry. These symmetry-related properties are used to prove the modal properties of general cyclically symmetric systems. Only three types of modes can exist: substructure modes, translational-tilting modes, and rotational-axial modes. Each mode type is characterized by specific central component modal deflections and substructure phase relations. Instead of solving the full eigenvalue problem, all vibration modes and natural frequencies can be obtained by solving smaller eigenvalue problems associated with each type. This computational advantage is dramatic for systems with many substructures or many degrees of freedom per substructure. [ABSTRACT FROM AUTHOR]

This paper presents the detail analysis of the radial force and bending moment responsible for vibration in the stator permanent magnet synchronous motors (PMSMs). The vibration characteristics, especially vibration mode, of stator PMSM are studied. First, the air-gap flux density distribution and radial force density distribution are derived in detail. Then, two types of vibration modes, called pulsating and bending modes, and their reasons as pulsating force and bending moment are analyzed and elaborated which are not analyzed and verified before. In addition, the relationships between these two vibration shapes and pole width, pole number, and slot number are analyzed. To confirm the analysis and theory, the multi-probe mode-included test method of vibration acceleration is used to obtain the vibration mode information of motors, and the experimental results on a 6-pole/36-slot stator PMSM match well with the simulation results. [ABSTRACT FROM AUTHOR]

The vibration mode of electric machines is an important characteristic of vibration, which is useful for finding the vibration sources with different frequencies, but has always been neglected before. In this paper, the vibration characteristics, especially the vibration mode, of permanent magnet (PM) brush DC motors are studied. First, the air gap flux density distribution and radial force density distribution are derived in detail and compared with the results of the finite-element method. Then, two types of vibration modes, called pulsating and bending modes, and their reasons as pulsating force and bending moment are analyzed and elaborated, which have not been analyzed and verified sufficiently before. In addition, the relationships between these two vibrations and pole width, pole number, and slot number are analyzed. The main modal shapes and their frequencies are acquired from the modal test. To confirm the analysis and theory, the multiprobe mode-included test method of vibration acceleration is proposed and emphasized to obtain the vibration mode information of motors, and the experimental results on a PM brush DC motor match well with the simulation results. [ABSTRACT FROM AUTHOR]

An attempt is conducted to explore the relationship between the macroscopic global damage and the local damage of shear-type RC frames. A story damage index, which can be expressed as multi-variate functions of modal parameters, is deduced based on the tridiagonal matrix of the shear-type frame. The global damage model is also originated from structural modal parameters. Due to the connection of modal damage indexes, the relationship between the macroscopic global damage and the local story damage is reasonably established. In order to validate the derivation, a case study is carried out via an 8-story shear-type frame. The sensitivities of modal damage indexes to the location and severity of local story damages are studied. The evolution of the global damage is investigated as well. Results show that the global damage is sensitive to the degree of story damage, but it's not sensitive to its location. As the number of the damaged stories increases, more and more modes will be involved. Meanwhile, the global damage evolution curve changes from the concave shape to the S-type and then finally transforms into the convex shape. Through the proposed story damage, modal damage and global damage model, a multi-level damage assessment method is established. [ABSTRACT FROM AUTHOR]

Spinning-type membrane space structures easily deform because they have no supporting structure. This may lead to an unexpected change in the effect of solar radiation pressure (SRP) on the membranes. Since SRP is a dominant factor of the dynamics of membrane space structures, especially for solar sails, knowledge of deformation is vital. However, it is almost impossible to precisely predict and design the actual deformation of membranes. This study provides a method to actively control the deformation of spinning membrane space structures. A completely fuel-free solar sailing technique is also shown as one application of the shape-control method developed. [ABSTRACT FROM AUTHOR]

The mass and surface stress loadings in microcantilever-based sensors, caused by surface adsorption of target analytes/biomolecules, change their resonance behavior. Despite numerous efforts, the mechanisms of surface stress impact on the resonance behavior of microcantilevers are not fully understood. This results in substantial discrepancies between theoretically predicted and experimentally measured resonance frequency shifts in wide microcantilevers with aspect ratios (width-to-thickness) larger than 10, commonly found in chemical and biological sensing applications. This also impedes the proper decoupling of the effects of mass and surface stress loading and hinders the development of accurate microcantilever-based sensors. In this work, we attempt to decrease the discrepancy found between theoretical models and experiments by introducing a new mechanism that correlates the nonlinear geometric effects associated with surface stress-induced variation of microcantilever biaxial curvature to its frequency and modal responses, with a correlation intensity that strongly depends on the microcantilever aspect ratio. A new comprehensive analytical model combining the new mechanism with currently available theoretical models is proposed and used to study the resonance behavior of microcantilevers with different deformations and sizes. Using the new model, it is shown that in wide microcantilevers, the theoretically predicted resonance frequency shifts agree with experimental and finite element simulations results within 30% whereas the predictions by other currently available theoretical models are off by more than one order of magnitude. The new model is also used to investigate the modal response of microcantilevers where it anticipates the bending-extensional mode coupling associated with the flexural vibration modes of microcantilevers with a coupling strength that depends on the microcantilever curvature. The presented model is expected to provide a new tool to decouple the effects of mass and surface stress loadings on the resonance behavior of microcantilevers used in chemical and biological sensors. [ABSTRACT FROM AUTHOR]

For large-scale offshore wind turbine blades, ANSYS and UG were respectively used to complete the solid modeling and the calculation of vibration modes, and the influences of the rotating speed on each order vibration mode and their main reasons were analyzed. Furthermore, the effects of material categories, the deviations of physical parameters in the process of material manufacture and structural parameters on the natural frequencies of rotating blades were respectively compared. Numerical results show that the dynamic stiffening effect of rotating blades is obvious, and the stress stiffness and the geometric stiffness play a dominant role on the natural frequencies from the first to the sixth order and from the seventh to the tenth order respectively. The influences of material categories on natural frequencies of the blades are significantly higher than those of physical parameter deviations and chord length changes. The effects of the equal amplitude increase of elasticity modulus or the chord length and the equal amplitude decrease of density on the tenth order frequency for the torsional vibration are less than those of them on the first nine orders' frequencies for the shimmy and flapping vibration, making that the increase amplitude of the blade natural frequencies first increases and then decreases with the increase of the order number. In addition, the results in this work can provide technical references for the optimization design and the further analysis of vibration characteristics of wind turbine blades. [ABSTRACT FROM AUTHOR]

Numerous papers deal with the Equivalent Plate Model (EPM) for corrugated panels. Comparison of published formulas for the four relevant equivalent bending stiffnesses D 11 eq , D 22 eq , D 66 eq , and D 12 eq revealed ambiguities: Three different formulas were found for D 22 eq , which describes the bending of the ridges and troughs; for D 66 eq two ‘competing’ formulas emerged. Expressions not converging to the flat-plate values in the limit of vanishing corrugation height were discarded. All discussed formulas are written in a uniform notation for general one-dimensionally periodic shapes. Formulas derived for isotropic panel materials were generalized to the orthotropic case. In order to resolve the ambiguities and assess the EPM with regard to its range of applicability, vibration modes of six rectangular corrugated panels were measured. While agreement with numerical results obtained with COMSOL was fair, the EPM predictions of natural frequencies were satisfactory only for low-order modes. Finally, equivalent bending stiffnesses were determined numerically from COMSOL results for a few low-order modes by inverse methods. Thus the ambiguities with regard to D 22 eq and D 66 eq could be resolved. However, the D 12 eq values determined numerically came out significantly larger than the EPM prediction, in particular for stronger corrugations. Even though this discrepancy had little effect on the natural frequencies tested in the present paper, it remains a theoretical challenge. [ABSTRACT FROM AUTHOR]

This study has presented a method to estimate the damage location in the concrete gravity dam monolith. The first four vibration mode of the highest monolith of the Koyna dam was estimated and analyzed by the combined discrete and continuous wavelet transform. The position of the damage scenarios was identified by using bior 3.9 wavelet in the spatial variation of the data response. The sensitivity of wavelet to random signal noise was investigated by using noise to displacement response of cracked monolith. Three noise levels were introduced in the model and the capacity of this method to detect damage from noisy data was discussed. [ABSTRACT FROM AUTHOR]

Non-linear static procedure (NSP) has been considered as a popular method to predict seismic force and deformation demands for performance evaluation of the structures, in recent years. However, this evaluation tool is restricted to low-rise and regular buildings in which the fundamental vibration mode dominates the structural behavior. Recently, some advanced procedures have been presented to oversee these conventional procedure deficiencies. In the current study, a new nonlinear static procedure considering the effects of higher modes in structural responses is presented. This approach assigns a contribution factor for each mode based on modal shear distribution. The offered contribution factor can be applied for determining the importance of each mode in lateral load pattern formation. In order to verify the results, some other types of pushover-based analysis are also performed and the responses obtained from each NSP are compared with those of rigorous non-linear response history analysis (NL-RHA). Results demonstrated the efficiency of the proposed method in accurate prediction of the seismic demands of high-rise buildings. [ABSTRACT FROM AUTHOR]

In this work, a novel technique is proposed for generating desired transient vibrations in a structure. Cantilevered plate structure is instrumented with one piezoelectric sensor patch and one piezoelectric actuator patch. Quadrilateral plate finite element having three degrees of freedom at each node is employed to divide the plate into finite elements. Thereafter, Hamilton's principle is used to derive equations of motion of the smart plate. Finite-element model is reduced to first three modes using orthonormal modal truncation and subsequently, the reduced finite-element model is converted into a state-space model. Optimal tracking control is then applied to the state-space model of the smart plate. Using this optimal controller, cantilevered plate is made to vibrate as per desired decay curves of first three modes. Simulation results show that presented optimal control strategy is very effective in simultaneously tracking first three vibration modes of the smart plate. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel integral dynamic model of retaining clips on pipes is established. • The necessity of the integral pipe model is illustrated by comparing with the half pipe model. • Effects of the clip parameters on the natural vibration of the pipe are presented. • The clip width and thickness have a noticeable effect on the vibration of the pipe. As an indispensable accessory, retaining clips on pipes are usually modeled as simply supported or fixed end boundaries. In this paper, a dynamic model of a pipe without fluid, with fixed–fixed ends and restrained by a middle clip is established. Different from the previous modeling that ignores the width of a clip, the clip is modeled as a rigid body with a certain width, which is elastically connected to the base. The effects of clip width, thickness, material parameters, and connection stiffness on the natural vibration of the pipe are presented. Moreover, to illustrate the necessity of the proposed model, a dynamic model of a half pipe is extracted with a clip as one end boundary. According to the two models, the natural frequencies and modes of the pipe are calculated and compared. Some meaningful results are obtained. The clip parameters influence the natural frequencies of the pipe nonlinearly. When calculating the natural frequencies of the pipe, ignoring the clip width or modeling the clip as a boundary will cause a noticeable error. The symmetry of the modes and the numbers and locations of modal nodes change as the clip stiffness changes. Furthermore, modal shapes of the symmetric modes change noticeably as the clip thickness or width increases. The locations of the maximum modal displacements may change as the clip width varies. In summary, a novel and valuable dynamic model of the retaining clip is proposed in this study. The vibration of a pipe restrained by a clip can be more accurately described. Influence laws of clip parameters can be used to guide the design and vibration measurement of pipes with clips. [ABSTRACT FROM AUTHOR]

A new dynamic model for double-helical star gearing system is proposed in this research. The dynamic model can used to analysis double-helical star gearing system in any condition. A equivalent meshing error analysis on different types of gear errors in the external and internal meshing line for star gearing system respectively. Axial, transverse, torsional and rotational motions of gears are included in the dynamic model. Establishes a refined new dynamic model for vibration and natural characteristic analysis of double-helical star gearing system. A type of gearing system for aero-engine was researched and calculated to demonstrate the validity of the dynamic model, obtained the values and the vibration mode for different order. It is revealed that the vibration characters for left side and right side of double-helical star gears have a nice distinction, which can provide scientific theory evidence for dynamic design and vibration control for precision double-helical star gearing system. [ABSTRACT FROM AUTHOR]

A novel technique is presented for exciting desired transient vibrations in a structure. A cantilevered plate instrumented with piezoelectric sensor and actuator is used as a test-structure. Finite element model of the test-plate is developed using Hamilton's principle. Finite element model is reduced to first two modes using orthonormal modal truncation and then this reduced model is converted into a state-space model. Tracking optimal control is then employed to obtain desired transient curves simultaneously, of first two modes of vibration. Theoretical findings are verified by conducting experiments, for experimentation, Kalman observer is used to estimate first two modes and Labview software is used for interfacing. Presented strategy can be used to do dynamic vibration testing of a product by forcing the product to experience same transient vibrations that it is expected to experience in field. [ABSTRACT FROM PUBLISHER]