Vibration Characteristics Of Structure Research Articles

VibroNet: Recurrent neural networks with multi-target learning for image-based vibration frequency measurement

Information on the vibration characteristics of machinery or civil structures is crucial in identifying or diagnosing potential malfunctions or faults. The use of cameras in vibration frequency measurement enables the acquisition of spatially high-density information of a distant measurement target. Cameras can be used for remote monitoring or as contact-less inspection sensors for machinery or civil structures owing to their low cost, high availability, and ease of installation. However, this requires complex image processing and signal processing algorithms to interpret the vibration frequency from image data. This paper proposes an image- and machine-learning-based method to measure the vibration frequency, in which long short-term memory-recurrent neural networks (LSTM-RNNs) and multi-target learning are used to predict the vibration frequency components directly. The results of the proposed method are compared against the results obtained using an accelerometer and eddy current sensor in the frequency domain. The methodology was applied in forced vibration and free vibration laboratory experiments and real-world structure experiments including a membrane structure and a cable bridge. The experimental results show that the proposed method is robust and accurate. Proposals for future applications and research directions of this methodology and limitations and challenges in real-world implementations are presented.

Structural stability and vibrational characteristics of CaB6 under high pressure**Project supported by the National Natural Science Foundation of China (Grant Nos. 51572108, 51632002, 11504127, 11674122, 11574112, 11474127, and 11634004), the 111 Project, China (Grant No. B12011), the Program for Changjiang Scholars and Innovative Research Team in University, China (Grant No. IRT_15R23), and the National Found for Fostering Talents of Basic

In situ Raman spectroscopy and x-ray diffraction measurements are used to explore the structural stability of CaB6 at high pressures and room temperature. The results show no evidence of structural phase transitions up to at least 40 GPa. The obtained equation of state with smooth pressure dependencies yields a zero-pressure isothermal bulk modulus B0 = 170 (5) GPa, which agrees well with the previous measurements. The frequency shifts for A1g, Eg, and T2g vibrational modes of polycrystalline CaB6 are obtained with pressure uploading. As the pressure increases, all the vibration modes have smooth monotonic pressure dependence. The Grüneisen parameter of Eg modes is the largest, indicating its largest dependence on the volume of a crystal lattice.

Research on modal analysis method of CNC machine tool based on operational impact excitation

With the rapid development of modern industry and industrial upgrading, machine tool performances such as high machining speed, high machining accuracy, and high reliability have gradually become the development trend of high-end CNC machine tools. The vibration characteristics of the machine structure become an important factor affecting the machining quality and processing efficiency of the machine tool. Since the movable parts of the CNC machine tool will impact the machine structure itself during the acceleration and deceleration process, by identifying the structural vibration response signal, the modal parameters of the machine tool in the running state can be obtained, called active excitation mode analysis. However, this method still has certain defects in theory and experiment. For example, the excitation principle is not theoretically explained, and the excitation energy and the frequency band of the method are limited. To solve these problems, this paper conducts more comprehensive research on the modal analysis method of CNC machine tools based on operational impact excitation. The main research contents are as follows: considering the rigid body motion of the table and the elastic collision of the screw nut pair, the impact excitation is modeled and analyzed. We have introduced a response-based modal identification algorithm. The influence factors of impact excitation energy and frequency band were studied from both theoretical and experimental aspects. Design three excitation sequences for workbench excitation and spindle excitation, respectively, analyze the vibration response and modal identification of the machine tool structure under different excitation sequences. It is verified that the method does not depend on the specific excitation sequence, as long as it satisfies the random characteristics. Aiming at the problem of insufficient excitation energy of the machine tool structure for single-component impact excitation, a multi-component joint impact excitation method based on the principle of multi-point excitation technology is proposed. The design experiment is carried out to verify the impact excitation method, which shows that the joint excitation has better excitation effect than single-axis excitation.

An optical-based technique to obtain operating deflection shapes of structures with complex geometries

Abstract The dynamic characteristics of structures are conventionally obtained by exciting the structure using an impulse hammer or a mechanical shaker and measuring the response using uniaxial or multi-axial accelerometers. However, contact-based sensors can mass-load the structure and do not provide full-field data. Hence, obtaining the true dynamics of the structure using conventional sensors can be challenging. That makes test engineers seek different non-contact techniques that can provide full-field data without mass-loading the structure. Recently, stereo-photogrammetry and three-dimensional digital image correlation (3D DIC) have been adopted to collect operating data for structural analysis. These non-contact optical techniques provide a wealth of distributed data over the entire structure. However, the stereo-camera system is limited by the field-of-view of the cameras; a single pair of DIC cameras may not be able to provide deformation data for the entire structure. Hence, it is challenging to obtain the vibration characteristics of the entire structure. In the current work, a multi-view 3D DIC approach is used and validated to predict the vibrational characteristics of an automotive muffler with a complex structure. A pair of DIC cameras travels over the entire structure to capture the deformation of each field of view. The measured data includes the geometry and displacement data, which is later mapped into a global coordinate system. The measured data in the time domain for each field-of-view is transformed to the frequency domain to extract the operational deflection shapes and resonant frequencies for each field of view. The obtained deflection shapes are stitched together in the frequency domain to extract the operating deflection shapes and resonant frequencies of the automotive body panel with a complex structure.

Trajectory Dependent Structural Vibration and Its Effects on Surface Generation

The vibration of machine tool plays an important role in surface generation. However, the vibration characteristics is different for different machine tool structures and different machining path. This paper proposed a new method of structural sensitivity analysis to identify trajectory dependent structural vibration and its effect on surface generation in milling. The experimental and theoretical results verify that (i) Multimode low-frequency vibration of the sensitive structures (MLFVSS) directly determines the surface topography in milling; (ii) The sensitivity is different for different structures or the same structure at different modes; (iii) Structural vibration characteristics is related to the machining path, resulting in different influence of the structural vibration on surface generation at different position of the machining path. Finally, a surface topography prediction model was established based on the experimental results. This study is helpful to the optimization of machine tool structures and the selection of machining parameters.

Structural Low-Level Dynamic Response Analysis Using Deviations of Idealized Edge Profiles and Video Acceleration Magnification

The development of high-speed camera systems and image processing techniques has promoted the use of vision-based methods as a practical alternative for the analysis of non-contact structural dynamic responses. In this study, a deviation extraction method is introduced to obtain deviation signals from structural idealized edge profiles. Given that the deviation temporal variations can reflect the structural vibration characteristics, a method based on singular-value decomposition (SVD) is proposed to extract valuable vibration signals from the matrix composed of deviations from all video frames. However, this method exhibits limitations when handling low-level motions that reflect high-frequency vibration components. Hence, a video acceleration magnification algorithm is employed to enhance low-level deviation variations before the extraction. The enhancement of low-level deviation variations is validated by a light-weight cantilever beam experiment and a noise barrier field test. From the extracted waveforms and their spectrums from the original and magnified videos, subtle deviations of the selected straight-line edge profiles are magnified in the reconstructed videos, and low-level high-frequency vibration signals are successfully enhanced in the final extraction results. Vibration characteristics of the test beam and the noise barrier are then analyzed using signals obtained by the proposed method.

Research on multidisciplinary fatigue optimization design method in structural design of high speed train

Aiming at the shortcomings of single-discipline fatigue design and life prediction optimization design method for high-speed trains, considering the characteristics of structural design integrity, a durability analysis method for key structural components based on multi-disciplinary fatigue optimization design is proposed. According to the characteristics of vibration fatigue and structural failure of key structural components of high-speed trains, the multi-disciplinary fatigue design of carbody components is carried out from the perspectives of materials, loads and structural design. In the research process, qualitative and quantitative analysis and comparison of multi-objective optimization analysis (MOO) and multi-disciplinary optimization (MDO) processes were carried out. At the same time, considering the actual example, considering the vibration characteristics of the vehicle structure, the typical load spectrum and the complex material characteristics, the failure characteristics of the structural components are analyzed in detail. The research results are shown that there are certain limitations in single-disciplinary fatigue design and analysis. In order to effectively solve the complex engineering structure failure problem, it is necessary to fully consider the vibration characteristics of the entire vehicle structure. Through the multi-disciplinary fatigue design and optimization method of high-speed train structural components, the safety and structural integrity of key structural components of rail transit can be better guaranteed.

Proposal of Train Operation Control during Earthquakes in Consideration of Vibration Characteristics of Subsurface Ground and Structure

Proposal of Train Operation Control during Earthquakes in Consideration of Vibration Characteristics of Subsurface Ground and Structure

A Semianalytical Approach for Free Vibration Characteristics of Functionally Graded Spherical Shell Based on First‐Order Shear Deformation Theory

This paper describes a unified solution to investigate free vibration solutions of functionally graded (FG) spherical shell with general boundary restraints. The analytical model is established based on the first‐order shear deformation theory, and the material varies uniformly along the thickness of FG spherical shell which is divided into several sections along the meridian direction. The displacement functions along circumferential and axial direction are, respectively, composed by Fourier series and Jacobi polynomial regardless of boundary restraints. The boundary restraints of FG spherical shell can be easily simulated according to penalty method of spring stiffness technique, and the vibration solutions are obtained by Rayleigh–Ritz method. To verify the reliability and accuracy of the present solutions, the convergence and numerical verification have been conducted about different boundary parameters, Jacobi parameter, etc. The results obtained by the present method closely agree with those obtained from the published literatures, experiments, and finite element method (FEM). The impacts of geometric dimensions and boundary conditions on the vibration characteristics of FG spherical shell structure are also presented.

Estimation of vibration characteristics of Kuzuryu River bank and subsurface structures based on microtremor observations

Estimation of vibration characteristics of Kuzuryu River bank and subsurface structures based on microtremor observations

Identification of the Anisotropic Elastic Parameters of NiCrAlY Coating by Combining Nanoindentation and Finite Element Method

For vibration damping, coatings are prepared on surface of the structures (substrates), which constitute the coating‐substrate composite structures. Elastic parameters of the coating are indispensable for the vibration and damping analysis of the composite structure. Due to the small scale of coating thickness and elastic difference compared with the substrate, the identification results are inevitably influenced by the existence of substrate. Moreover, resulting from the preparation process, elastic properties of hard coating often exhibit anisotropic properties. All the above factors bring about the difficulties of accurate identification. In this study, a method for identifying anisotropic elastic parameters of hard coatings considering substrate effect is proposed, by combining nanoindentation and finite element analysis. Based on the identification results, finite element models are established to analyze the vibration characteristics of the coating‐substrate composite structure, which verify the rationality of the anisotropic elastic parameters for vibration analysis. The studies in this paper are significant to more accurately identify the mechanical parameters for establishing the dynamic model. Moreover, they lay the foundation for further optimization design of hard coating damping.

Vibration feature extraction based on the improved variational mode decomposition and singular spectrum analysis combination algorithm

Extraction of the vibration characteristics of a flood discharge structure under the influence of intensive background noise is one of the main challenges in vibration-based damage identification. A novel algorithm called normalized central frequency difference spectrum is proposed to improve the variational mode decomposition algorithm for high-frequency noise filtering. To eliminate the errors caused by end effect, the waveform matching extension algorithm is used to further improve the variational mode decomposition. However, the vibration signal is still coupled in low-frequency noise. Thereupon, the singular spectrum analysis algorithm is applied to filter the low-frequency noise. In this article, a simulated signal and the measured signals from a dam model are analyzed by the proposed algorithm. The results indicate that the proposed algorithm is robust to noise and has high denoising precision. In addition, this algorithm can offer clues for damage identification and localization of a flood discharge structure.

A residual strain energy based damage localisation method for offshore platforms under environmental variations

ABSTRACTVibration-based damage identification methods are committed to detecting structural damage by examining changes in the vibration characteristics of structures. However, these characteristics are not only affected by the structural damage but also subject to the change of environmental condition. A new damage localisation method, termed as residual strain energy (RSE) method, which is capable of locating damage on 3D structures under environmental variations, is presented. This RSE method employs the residual mode shapes to construct the damage localisation indicator, in which the principal component analysis algorithm is introduced to eliminate the influence of environmental variations. Numerical simulations were conducted on a 3D offshore platform structure considering temperature variations. Results indicate that the RSE method can effectively eliminate environmental influences and identify structural damage sites correctly.

Free Vibration Analysis of Fiber Metal Laminated Straight Beam

Abstract In recent years, studies on the development of new and advanced composite materials have been increasing. Among these new technological products, Fiber Metal Laminates (FML), and hybrid structures made of aluminium, carbon, glass or aramid fiber, are preferred especially in the aircraft industry due to their high performance. Therefore, free vibration analysis is necessary for the design process of such structures. In this study, the vibration characteristics of FML for clamped-free boundary conditions were investigated experimentally and numerically. Firstly, numerical results were obtained using Finite Element Method (FEM) and then these results were compared with the experimental results. It was seen that the numerical results were in good agreement with the experimental results. As the theoretical model was justified, the effects of various parameters such as number of layers, fiber orientations, and aluminium layer thickness on the in-plane vibration characteristics of the FML straight beam were analysed using FEM. Thus, most important parameters affecting the vibration characteristics of the hybrid structures were determined.

A Study on Natural Vibration Characteristics of Dome Structure According to Natural Frequency Ratio of Substructure

A Study on Natural Vibration Characteristics of Dome Structure According to Natural Frequency Ratio of Substructure

Numerical simulation of super upper branch of a cylindrical structure with a low mass ratio

SST (shear stress transport) k-ω and Newmark-β methods are used to comprehensively understand vortex-induced vibration (VIV) characteristics of a cylindrical structure with a mass ratio of 2.6 in a range of reduced velocity from 2.0 to 14.0. The details of drag and lift forces, cross-flow and streamwise displacements, vortex pattern, trajectory, and frequency of VIV are presented and compared systematically with the experimental work of Jauvtis and Williamson that first captured the super upper branch in VIV with the maximum value of 1.5 D (diameter). In this study, the numerical simulation results successfully captured the initial branch, the lower branch, and the super upper branch. Very few research studies have successfully simulated the super upper branch by numerical methods. The vibration amplitude corresponding to the super upper branch is stable and the maximum value of the super upper branch is 1.46 D, which is fairly consistent with the results of the Jauvtis and Williamson experiment. This research also successfully captured the law of trajectory under different reduced velocities. With the reduced velocity increasing, the trajectories switch from an irregular shape to a regular "Figure 8″ shape and then enter into an irregular movement, finally again into a regular movement of a Figure 8 shape or crescent. In the range of the super upper branch, the vibration trajectories gradually change from a Figure 8 shape to a crescent shape with the increase of the transverse vibration amplitude. This work has successfully captured the different vortex patterns corresponding to each branch under different reduced velocities, and found the transitional forms of 2S to 2T, 2T to 2P, and 2P to 2S, respectively.

액체가 채워진 원통형 구조물의 진동 특성 규명을 위한 모달 시험 방법 연구

액체 추진 발사체는 발사 후 추진제 소모로 인하여 고유진동수가 변화하는데, 이에 대한 영향을 규명하기 위해서는 모달 시험이 필수적이다. 그러나 액체 추진 발사체는 액체 추진제에 의한 액체의 영향과 발사체 구조의 영향이 복합적으로 작용하여, 이를 규명하는 것은 매우 어렵다. 또한 모달 시험에만 의존하여 복합된 특성을 규명하는 경우, 시험에 소요되는 시간이 과도하게 증가하고 특정 모드와 특정 주파수의 판별 및 확인이 쉽지 않다. 본 논문에서는 이러한 단점을 보완하기 위해 유한요소 해석 결과를 이용한 모달 시험 방법을 제안하였다. 액체가 채워진 원통형 구조물을 연구 모델로 선정하여 모달 시험과 유한요소 해석을 수행하였다. 모달 시험은 충격 가진 방식으로 충격망치와 가속도계를 이용하여 수행하였다. 모달 시험과 유한요소 해석 결과 비교를 통해 제안한 유한요소 해석 결과를 이용한 모달 시험 방법의 타당성을 검증하였으며, 액체가 채워진 비율에 따른 원통형 구조물의 자유진동 특성과 그 경향성에 대해 고찰하였다.

Relationship between Arias intensity and the responses of reinforced soil retaining walls subjected to near-field ground motions

A validated dynamic Finite Element procedure was employed to investigate the seismic responses of geosynthetic-reinforced soil retaining walls subjected to various near-field ground motions. The study is focused on the relationship between the ground motion parameters and the reinforcement loads and residual facing displacement. Twenty-five near-field motions from two earthquakes were scaled to a peak acceleration of 0.4 g and employed as the excitation motions. It was found that the maximum reinforcement load in the retaining wall is determined by the vibration characteristic of the earth structure as well as the intensity of the input motion, and the Arias intensity at the top of the reinforced soil zone is well correlated with the maximum reinforcement load. The residual lateral facing displacement is also affected by these two factors, but a very good correlation with the Arias intensity cannot be established.

Operation conditions monitoring of flood discharge structure based on variance dedication rate and permutation entropy

There has been a growing concern on how to monitor the operation conditions of flood discharge structure in recent decades. However, the online monitoring process is always interfered by ambient excitation which leads to inaccurate and uncertain structural characteristic evaluation. To mitigate the interference, a valid operation conditions monitoring method based on variance dedication rate (VDR) and permutation entropy (VDR-PE) is proposed. Firstly, a de-noising method combining wavelet threshold and empirical mode decomposition is used to remove heavy background noises, reducing the interference of ambient excitation to structural characteristic information. Then VDR method is used to realize the dynamic fusion of multi-channel vibration signals, extracting the vibration characteristic of the overall structure in an accurate and comprehensive way. Finally, permutation entropy is used to extract the entropy value of the fused signal. Through evaluating the operation conditions with coefficient of variation, the online monitoring of flood discharge structure can be realized. The effectiveness of permutation entropy algorithm on signal dynamic monitoring is validated by a simulation experiment. Furthermore, VDR-PE method is applied to Three Gorges dam to compare differences between analytical simulation and finite element simulation. The comparison results show that VDR-PE method can be applied to detect the dynamic changes and reveal the vibration characteristic of the overall structure accurately, which provides a new direction for the online monitoring of flood discharge structure.

Development of a wireless measurement system for ship vibration in a sea trial

Due to the convenience of wireless measurement, wireless acceleration sensors have been widely employed to monitor the structural health of mechanical systems. Although wireless sensors for general purpose have been available in the market, a wireless measurement system still needs to be customized for the purpose of its testing condition (measurement distance and time, communication interference and blockage, frequency range, number of sensors installed, etc.). For ships, vibration measurement in a sea trial is required to evaluate the habitability of crews in the accommodation area and study the vibration characteristics of hull structures and shipboard equipment. However, there have been few attempts to utilize wireless sensors in ship vibration measurements due to concerns about a loss of measured signals caused by failures of wireless network. This article presents the wireless measurement system developed to measure ship vibration in a sea trial. System requirements are first defined, and the wireless measurement system is designed and manufactured. Comparative studies between the wireless and wired measurement systems are conducted to confirm applicability of the wireless measurement system in a sea trial. The results in a frequency domain show that both frequency and magnitude match well with each other. Finally, it is concluded that the developed wireless system is reliable as much as the conventional wired system.