Vibration Response Of Structure Research Articles

Nonstationary random vibration analysis of structures with uncertain parameters based on a polynomial dimensional decomposition

AbstractBased on polynomial dimensional decomposition (PDD), a novel method for analysing nonstationary random vibration of structures with uncertain parameters is proposed in this paper. The uncertain structural parameters are assumed to be independent random variables, with certain types of probability distributions; thus, the nonstationary random vibration responses of the structures become stochastic functions of these uncertain parameters. A dimensional decomposition and Fourier expansion were applied to calculate the statistical characteristics of the nonstationary random vibration responses of the structures. To calculate the conditional power spectral density (CPSD) and conditional standard deviation (CSD) of the nonstationary random vibration responses, CPSD and CSD were explicitly expressed using expansion coefficients and polynomial basis. Subsequently, the probability distributions of the structural responses can be effectively calculated in terms of these explicit expressions. Dimension‐reduction integration and Gauss numerical integration were applied to calculate expansion coefficients. The validity of the proposed method was verified by numerical examples, including a single‐degree‐of‐freedom system and a multi‐degree‐of‐freedom system (reinforced concrete shear wall). The results indicate that the proposed method is as accurate as Monte Carlo simulation (MCS), whereas the proposed method requires considerably smaller number of nonstationary random vibration analyses than MCS. Moreover, the nonstationary random vibration analysis of a long‐span cable‐stayed bridge demonstrates that the proposed method is feasible for quantifying the uncertainties of the nonstationary random vibration responses of complex engineering structures with uncertain parameters.

Working Mode Identification Method for High Arch Dam Discharge Structure Based on Improved Wavelet Threshold–EMD and RDT Algorithm

Prototype vibration response data of high arch dam discharge structures inevitably mix various noises under the discharge excitation, which adversely affects the accuracy of the working modal identification of the structure. To effectively filter noise and reduce modal aliasing for better identification accuracy, this study proposes an improved modal threshold identification method based on an improved wavelet threshold–empirical mode decomposition (EMD) and random decrement technique (RDT) algorithm for high arch dam discharge structures. On the basis of the measured vibration response data of the dam, the wavelet threshold is adopted to filter out most of the high-frequency white noise and to reduce the boundary accumulation effect of EMD decomposition. Detrended fluctuation analysis (DFA) is utilized to filter white noise and low-frequency flow noise after EMD decomposition. The natural frequency and damping ratio of the structure system are obtained by the improved RDT algorithm. The engineering examples show that the proposed method can accurately filter the measured vibration response signal noise of the discharge structure, retain the signal characteristic information, improve the accuracy of working modal recognition of the structural vibration response, avoid the complex ordering process of the system, and ease the working modal parameter identification of high arch dam discharge structures. This method can be applied to the mode identification of other large structures, as well.

A Study on Wind Pressure Characteristics of a Large-Span Membrane Structure under the Fluctuating Wind in a Vertical Direction Based on a Large Eddy Simulation

This paper reports the wind pressure characteristics on long-span roofs under fluctuating wind in a vertical direction based on a large eddy simulation (LES). Three types of roofs, i.e., saddle, wavy, and continuous arch roofs, are tested. First, the membrane structure canopy is measured, and the model is established for numerical simulation. The computational models and methods are verified by comparing the obtained wind pressure distributions on the roof with the measured results and numerical simulation results under other methods. Next, a numerical simulation is performed to understand not only the wind pressure and the wind speed time series but also the wind vibration responses and fluid-solid coupling. The effects of lateral fluctuating wind at different wind speeds on the wind-induced vibration response and wind pressure distribution of different membrane structures are studied. Based on the results, the wind pressure zones of the roofs are discussed. Furthermore, the original structures are optimized and numerically simulated considering the streamlined design concept to study the influence mechanism of fluctuating wind on the roof in more detail.

A High-Accurate Time Integration Method for Solving Structural Vibration Responses

A time integration method for the equations of motion is developed based on the Gauss implicit Runge-Kutta method to high-accurate solving the responses in structural vibration. The present method possesses the features of unconditional stability and self-starting and can achieve fourth-order accuracy in displacement, velocity, and acceleration simultaneously. The algorithm is a matrix form and no need to iterate in the calculation. The convergent accuracy is verified by a numerical example, and the effectiveness is also verified by solving the dynamic responses of a vibration isolation system and the vibration responses of a pylon structure with cyclic loads and earthquake loads.

Study on noise reduction method of main noise transmission path of axial piston pump with new damping material

Axial piston pump is complex fluid machinery with mechanical fluid coupling, and it has the characteristics of multiple noise sources. In order to solve the high noise problem of axial piston pump, this paper proposes a noise reduction method by identifying the main noise sources of axial piston pump and laying new damping materials to reduce noise. It breaks through the existing method of optimizing the parameters of piston pump shell and valve plate structure. A multi-parameter trajectory sensitivity identification and noise reduction method for vibration transmission path of axial piston pump is proposed in this paper. First, the lumped parameter method is used to establish the mathematical model of vibration transmission path of axial piston pump. The sensitivity of structural vibration response to transmission path multi-parameters are analyzed based on trajectory sensitivity method. The most sensitive parameters in the main noise transmission path are determined. Then, the experimental study of radiated noise transmission path of axial piston pump is carried out. A new type of viscous damping material is proposed to reduce the noise on the transmission path of the main noise source. The experimental results show that the noise of piston pump is reduced by 2.32 dB. The research results provide a new method and way for the design and manufacture of low noise piston pump.

A Two-Stage Structural Damage Detection Method Based on 1D-CNN and SVM

Deep learning has been applied to structural damage detection and achieved great success in recent years, such as the popular structural damage detection methods based on structural vibration response and convolutional neural networks (CNN). However, due to the limited number of vibration response samples that can be acquired in practice for damage detection, the CNN-based models may not be fully trained; thus, their performance for identifying different damage severity as well as the damage locations may be reduced. To solve this issue, in this paper, we follow the strategy of "divide-and-conquer" and propose a two-stage structural damage detection method. Specifically, in the first stage, a 1D-CNN model is constructed to extract the damage features automatically and identify the damage locations. In the second stage, a support vector machine (SVM) model and wavelet packet decomposition technique are combined to further quantify the damage. Experiments are conducted on an eight-level steel frame structure, and the accuracy of the experimental results is greater than 99%, which demonstrates the superiority of the proposed method compared to the state-of-the-art approaches.

Investigations on Nonlinear Dynamic Modeling and Vibration Responses of T-Shaped Beam Structures

A novel nonlinear dynamic modeling approach is proposed for the T-shaped beam structures widely used in the field of aerospace. All of the geometrical nonlinearities including the terms in the deformation of the beams, the terms at the connections, and the free ends of beams are considered in the dynamic modeling process. The global mode method is employed to determine the natural frequencies and global mode shapes of the linearized system. The validity and accuracy of the derived model are verified by comparing the natural frequencies obtained with those calculated from FEM. Adopting the Galerkin truncation procedure, a set of reduced-order nonlinear ODEs is obtained for the structure. A study on the variation of dynamic responses taking the different numbers of global modes into account is performed to determine the number of modes taken in nonlinear vibration analysis. A comparison between the responses of the system with linear or nonlinear matching and boundary conditions is given to evaluate the importance of neglecting and reserving the nonlinear terms in matching and boundary conditions. It is shown that ignoring the nonlinear terms in both matching and boundary conditions may significantly alter the responses while developing the discretized governing ODEs of the structure.

Experimental and mathematical model of a novel viscoelastic bio-inspired multi-dimensional vibration isolation device

The earthquake usually causes multi-dimensional vibration for the large span grid structure, how to effectively isolate and mitigate the vibration response of structure is an important problem in engineering. In this paper, a novel viscoelastic bio-inspired multi-dimensional vibration isolation (VBM-VI) device is proposed under the inspiration of bionic design of the bird legs, which possesses multi-dimensional vibration isolation performance by constituting of viscoelastic core pad and VE-LLS device together. The property experiment of the VBM-VI device is performed to explore the mechanical performance at vertical and horizonal directions, the hysteretic curves and characteristic parameters are discussed to reveal the influence of the excitation frequency and amplitude on the mechanical properties of the VBM-VI device, the experimental results show that the mechanical properties express significant frequency and amplitude dependence at vertical and horizontal directions. To further describe the mechanical proprieties of the VBM-VI device, the mathematical models are established at vertical and horizontal directions respectively, and the comparison analysis between experimental and theoretical results indicates that the established mathematical models can precisely describe mechanical performance of the VBM-VI device.

Application of the Lagrange Equation for Intelligent Sensor Vibration Control for Power Network Monitoring

Objective. In order to control the vibration of the beam structure more effectively and improve the safety and availability of the beam structure, an application study of the Lagrange equation for vibration control of smart sensors for power grid monitoring is proposed. The vibration of the beam structure, the displacement of the beam structure under the excitation of seismic acceleration, the response analytical electrical formula, and the displacement response formula of the beam structure under the action of the kinematic force are deduced. The optimal parameters of the beam-TMDI system are given, and the parameter sensitivity analysis is carried out. Then, the control effect of the TMDI system is studied by numerical analysis, and the vibration reduction effect of the TMDI system and the tuned mass damper (TMD) system is compared. Experimental results show that when the mass ratio μ of the TMDI system and the TMD system are both set to a fixed value of 0.005, and the parameter β of the TMDI system is set to 0, namely β = b = 0 , at this time, the TMDI system degenerates into a TMD system. The TMD natural frequency is 14.179 rad/s and the damping ratio is 0.0432 by the DH optimization method, while the TMD natural frequency is 14.1812 rad/s, and the damping ratio is 0.0436 by the augmented Lagrangian optimization algorithm. Conclusion. The vibration displacement response spectrum of a beam structure obtained by the frequency domain method can effectively reflect electricity in the displacement response of a beam structure. The parameters that minimize the vibration response of the beam structure can be accurately obtained by using the augmented Lagrangian parameter optimization method. The sensitivity of the TMDI system is controlled by the inertial device, and the inertial device has a significant impact on its robustness. The vibration reduction performance of the TMDI system is obviously better than in the conventional TMD systems.

Bandgap manipulation of single and multi-frequency smart metastructures with random impedance disorder

Metamaterials and metastructures usually exhibit some form of periodicity that is broken due to randomness in the media, affecting the vibration and elastic wave propagation performance. Disorder in the periodicity caused by the variability in properties or geometry may lead to interesting physical phenomena such as trapping and scattering waves, wave reflection, and energy localisation. While the randomness may be attributed to manufacturing irregularities and quantifying its effect is crucial for ensuring adequate performance of a range of smart systems, and these effects can also be exploited for manipulating the wave properties. Here we investigate a smart metastructure in the form of a beam integrated with piezoelectric transducers coupled to a resonant shunt circuit. The piezoelectric shunt in a periodical arrangement can induce locally resonant bandgaps that can be employed in wave (and vibration) manipulation and control. This paper quantifies the uncertainty associated with electrical circuit components that affect the circuit impedance influencing wave and vibration control features. The smart unimorph meta-beam is formulated by spectral element method based on the Hamiltonian principle, and dispersion curves are estimated using the spectral transfer matrix method that relies on the Bloch-Floquet theorem. The first and second statistical moments are obtained from the stochastic simulations ( realizations) that could be realized efficiently due to the current development of spectral element approach for analysing the disordered system. Further experimental validation and exploration of shunt circuit confirms the need to include the stochastic information on the numerical model used to design the metastructure. Numerical results of the unimorph meta-beam with single and multi-frequency shunt configuration show that the bandgap behaviour is sensitive to the random disorder associated with circuit impedance parameters. Such disorder can be exploited for enhanced functionalities of the meta-beam based on optimal RL shunt circuits for controlling structural vibration response along with wave propagation and attenuation.

Experimental study on the nonlinear dynamic characteristics of a kind of hinged connection structure

The hinged connections are widely used in mechanical structures, such as the expandable structures and truss structures in spacecraft and the three-point hitch device in agricultural machinery. The hinged connections allow relative rotations between the connected members so that the positions of mechanical structures can be adjusted. Thus, the hinged connections are always subject to large and complex forces during working operation, and these will lead to complicated nonlinear vibrations which have a significant impact on the working performance and fatigue lifespan of the mechanical structures. Therefore, the nonlinear dynamics characteristics of the hinged connection are studied. Firstly, the experimental platform of a typical hinged connection is established according to the mechanical structure characteristics and loading features of the hinged connection structure. Then the vibration experiments of the hinged connection structure are carried out respectively under different working conditions. Finally, the effect of hinge clearances and excitation frequencies on the nonlinear dynamics of the hinge connection structure is studied by the vibration response of the hinge connection structure under different working conditions. The results of this study can provide a reference for the optimal design of the hinged connection structure.

Comparison study of the dynamic behavior of a generally restrained beam structure attached with two types of nonlinear vibration absorbers

Beam structures with nonlinear vibration absorbers (NVAs) are attracting great research attention. Nonlinear vibration absorbers can more effectively suppress the vibration response of beam structures over the traditional vibration absorbers. The existing studies mainly focus on the dynamic behavior of beam structures with NVAs and boundary rotational restraints of beam structures are typically ignored. Additionally, it is difficult to adjust the stiffness of NVAs, limiting their engineering applications. Motivated by such limitations, the dynamic model of a generally restrained beam attached with two types of NVAs is established. Stiffness coefficients of NVAs can be adjusted by changing the initial length of horizontal springs. Dynamic behavior of the beam structure is predicted via the Galerkin truncated method (GTM). Results calculated by the GTM are verified by the harmonic balance method. Based on this, the influence of these two types of NVAs on dynamic behavior and vibration suppression of the beam structure is investigated. Appropriate parameters of the NVA beneficially affect the vibration suppression of the beam structure. With the same varying range of parameters belonging to NVAs, dynamic responses of the beam structure are more sensitive to the type-A NVA.

Nonlinear vibration analysis of FGM sandwich structure under thermal loadings

The geometrically nonlinear thermal frequencies of the functionally graded (FG) sandwich structures are predicted numerically in the current work considering the variable temperature distributions (linear and nonlinear). For numerical analysis of the FG sandwich structure, an in-house finite element code has been developed in MATLAB using the higher-order shear deformation theory (HSDT) and Green–Lagrange nonlinear strain kinematics. The governing equation of motion for the graded sandwich structure is obtained using Hamilton’s principles, and the direct iterative method is used to predict the nonlinear vibration response of the sandwich structure. The temperature distributions along the thickness of the sandwich structure are considered. Temperature dependent material properties are considered in the present work for computation of frequency responses under thermal environment. The material properties are described in accordance with the power-law distribution. The current models are initially validated with the published results. The influence of various input parameters, i.e. the curvature ratio (CRO), thickness ratio (TRO), aspect ratio (ARO), boundary conditions, and power-law indices on the nonlinear vibration behaviours of FG sandwich structure have been studied.

Numerical Simulation and Wind Tunnel Test on the Wind-Induced Response of Three Typical Types of Greenhouse Main Structures

Investigating the wind-induced vibration response of the greenhouse structure, and the wind pressure distribution on its surface takes on a critical significance when the main structure is under large wind loads. A computational fluid dynamics-based study was conducted, and wind tunnel tests were performed to study the wind pressure distribution on the surface of the greenhouse structure. First, three types of greenhouses, including Venlo, Round-arch, and Saw-tooth type greenhouses, were selected as the design models for the study. In addition, the double-span, four-room structure model was built to explore the wind pressure distribution and the extreme wind pressure coefficient on the greenhouse surface for 13 (0°–180°, every 15°) directions of the wind direction to obtain the wind load characteristics in the greenhouse surface under different conditions. The results of the wind tunnel tests were consistent with those of the simulations, with the maximum wind pressure in the X-direction occurring at 30°-wind and the maximum wind pressure in the Y-direction at 75°-wind. The maximum negative wind pressure acting locally on the roof of the greenhouse was twice the maximum positive pressure acting on the windward side of the greenhouse. Accordingly, it is necessary to strengthen the structure in regions sensitive to wind direction with significant response to wind.

Study on fluid-structure interaction vibration characteristics of absorber feed tank based on micro vibration monitoring

Absorber feed tank (AFT tower) is a kind of reinforced concrete structure supported steel tank. It is a composite structure used for desulfurization and cleaning in power industry. A large amount of slurry is sumped in the steel tank, and oxidation air is blown into the tank through a pipe to impact the slurry surface, then the agitator vibrates and disturbs the slurry in the tank. The structure has obvious vibration in daily operation, which is not conducive to the safety of the structure, but also brings greater psychological burden to the staff. Therefore, field monitoring and numerical simulation analysis are carried out for the AFT tower. The field investigation of AFT tower is also carried out. The video monitoring and local monitoring are used to monitor the AFT tower, and the corresponding laws of vibration are explored. A simplified simulation method for this kind of structure is proposed. The model is established with the aid of the fluid structure coupling function of ADINA finite element analysis software to study the vibration characteristics of AFT tower. The results show that the motion trajectory of AFT tower can be determined quickly by video monitoring. The local monitoring can demonstrate that the effect of mixer is the main factor of structural vibration, and the blowing in of oxidation wind intensifies the structural vibration response, resulting in different degrees of damage to the infilled wall between the columns of the structure. By comparing the numerical simulation results with the monitoring results, the reliability of the simplified model is verified, which provides a reference for analyzing the vibration response, damage mechanism and reinforcement design of this kind of structure.

Dynamic characteristic analysis of acoustic black hole in typical raft structure

Abstract As a hot content of research in recent years, acoustic black holes have bright application prospects in the field of vibration and noise reduction. In this article, based on the acoustic black hole theory, we carry out a study on the dynamic characteristics of a typical raft structure. The manuscript gives the simplified method of the acoustic black hole model, verifies the validity of the method by the structure natural frequency and vibration response, and discusses the influence of the main parameters such as acoustic black hole tip cutoff ratio and damping thickness ratio on the vibration characteristics of the raft frame structure. The better values of the parameters were applied to the raft structure on this basis, and the results showed that the peak value of some frequency points decreased by about 10 dB after the acoustic black hole was laid in the raft structure, which improved the vibration isolation performance of the raft.

Clean Vibes: Hand Washing Monitoring Using Structural Vibration Sensing

We present a passive and non-intrusive sensing system for monitoring hand washing activity using structural vibration sensing. Proper hand washing is one of the most effective ways to limit the spread and transmission of disease, and has been especially critical during the COVID-19 pandemic. Prior approaches include direct observation and sensing-based approaches, but are limited in non-clinical settings due to operational restrictions and privacy concerns in sensitive areas such as restrooms. Our work introduces a new sensing modality for hand washing monitoring, which measures hand washing activity-induced vibration responses of sink structures, and uses those responses to monitor the presence and duration of hand washing. Primary research challenges are that vibration responses are similar for different activities, occur on different surfaces/structures, and tend to overlap/coincide. We overcome these challenges by extracting information about signal periodicity for similar activities through cepstrum-based features, leveraging hierarchical learning to differentiate activities on different surfaces, and denoting “primary/secondary” activities based on their relative frequency and importance. We evaluate our approach using real-world hand washing data across four different sink structures/locations, and achieve an average F1-score for hand washing activities of 0.95, which represents an 8.8X and 10.2X reduction in error over two different baseline approaches.

Downburst-Induced Vibration Coefficient of Long-Span Roof Structures

Long-span roof structures are vulnerable to being damaged by downbursts due to the sensitivity of such structures to wind loads. However, there is still no simple and practical method for the downburst-resistant design of such structures to date. Inspired by the wind-induced vibration coefficient (WVC) frequently used by engineers, this paper proposes a downburst-induced vibration coefficient (DVC) to evaluate the response of a roof structure subjected to downbursts. The proposed DVC is defined as the ratio of the total response to the mean response of the structure due to the action of downburst wind loads. The influences of different parameters on the downburst-induced vibration response of a long-span single-layer spherical reticulated structure are first analyzed in detail. Then, using a statistical approach, a design DVC, which can be practically adopted for civil engineers to evaluate the total structural response, is proposed to facilitate the structural downburst-resistant design. With the influences of different structural parameters fully taken into consideration, the design DVCs of displacement and internal force are studied through orthogonal analysis. Finally, regression models of the design DVCs are presented, and their reliability is verified via the application to a case study. The verification results indicate that the proposed regression models of the design DVCs are reliable and can be utilized to simply calculate the structural downburst-induced vibration response. The results obtained can serve as a reference for the downburst-resistant design of long-span roof structures.

Seismic Response Study of L-Shaped Frame Structure with Magnetorheological Dampers

To analyze the multi-dimensional seismic mitigation performance and the torsional vibration characteristic of an L-shaped frame structure with a magnetorheological damper (MRD). Firstly, the mechanical property of the MRD is experimentally studied. Then, the calculation models of the L-shaped frame structure without and with MRDs are found through theoretical analysis, and the programs of the calculation models are compiled. Finally, the time history responses of the calculation models are calculated during the excitation of bi-directional seismic wave; the responses of displacement, acceleration, story drift ratio, shear force and bending moment and torsional vibration are then compared and analyzed. The results show that by adjusting the current, the damping force provided by the MRD can be adjusted continuously in the range of 3.1 to 120 kN. The compiled calculation model programs of the L-shaped frame structure without and with MRDs can effectively simulate the multi-dimensional seismic response of the structure. Reasonable arrangement of MR dampers can effectively reduce the displacement, acceleration, shear force, bending moment, multi-dimensional vibration, and torsional vibration response of L-shaped frame structures.

Identification of Abnormal Vibration Signal of Subway Track Bed Based on Ultra-Weak FBG Sensing Array Combined with Unsupervised Learning Network

The performance of the passing train and the structural state of the track bed are the concerns regarding the safe operation of subways. Monitoring the vibration response of the track bed structure and identifying abnormal signals within it will help address both of these concerns. Given that it is difficult to collect abnormal samples that are symmetric to those of the normal state of the structure in actual engineering, this paper proposes an unsupervised learning-based methodology for identifying the abnormal signals of the track beds detected by the ultra-weak fiber optic Bragg grating sensing array. For an actual subway tunnel monitoring system, an unsupervised learning network was trained by using a sufficient amount of vibration signals of the track bed collected when trains passed under normal conditions, which was used to quantify the deviations caused by anomalies. An experiment to validate the proposed procedures was designed and implemented according to the obtained normal and abnormal samples. The abnormal vibration samples of the track beds in the experiment came from two parts and were defined as three levels. One part of it stemmed from the vibration responses under the worn wheels of a train detected during system operation. The remaining abnormal samples were simulated by superimposing perturbations in the normal samples. The experimental results demonstrated that the established unsupervised learning network and the selected metric for quantifying error sequences can serve the threshold selection well based on the receiver operating characteristic curve. Moreover, the discussion results of the comparative tests also illustrated that the average results of accuracy and F1-score of the proposed network were at least 11% and 13% higher than those of the comparison networks, respectively.