A large number of over‐track buildings have been designed in metropolis during the recent decades for adapting to rapid urbanization and saving land resources. However, the over‐track buildings are ...potentially affected by train‐induced vibration that may cause discomfort or health problem for residents, which in turn needs to be carefully evaluated. In this study, the responses of a high‐rise over‐track building with three different transfer types have been investigated using the recorded three‐dimensional accelerations from in‐situ tests. By performing time history analyses, the vibration responses of the fixed structure, traditional rubber bearing (TrRB) isolated, and thick‐layer rubber bearing (ThRB) isolated structures are analyzed and evaluated, respectively. The results show that the most evident vibration is in the vertical direction with vibration energy mainly concentrated among the high frequencies. Thereafter, the effects of vibration control by using different isolation technologies are compared. It is demonstrated that the abilities to isolate vertical train‐induced vibration could be enhanced by using ThRB while the horizontal isolation performance is still guaranteed. Then the reason for the variation of vibration amplitude along the building height is discussed. This research enriches the train‐induced vibration database and exemplifies the vibration mitigation control and design for over‐track buildings.
In order to explore the propagation law of blasting vibration velocity in strata and reduce the damage caused by blasting vibration to buildings, a series of blasting vibration tests were carried out ...in this paper based on the Dizong tunnel project. The affected area of tunnel blasting was divided into four areas according to observed data, respectively, the dangerous zone, the warning zone, the blasting control zone, and the safe zone. The power spectral, wavelet-energy, wavelet packet energy analysis, and other signal processing were programmed with the help of MATLAB to analyze the propagation law of blasting vibration of super-large section shallow tunnel in the stratum. The results show that the maximum particle vibration velocity at the ground surface decreased with distance. The particle vibration velocity in the z-direction was larger than that in the horizontal direction. The energy of blasting vibration mainly came from the explosion in the first cut blasting. Based on the monitoring data and vibration signal analysis, a blasting vibration reduction scheme was put forward. The maximum particle vibration velocity caused by this scheme was controlled at 1.12 cm/s, and the main frequency of blasting vibration was much higher than the natural vibration frequency of the building. The blasting vibration reduction scheme could control the delayed release of blasting energy and realize the vibration missing peak of blasting vibration, which could provide a reference for similar engineering construction in the future.
•The affected area of tunnel blasting was divided into four areas according to observed data.•The energy of blasting vibration mainly came from the explosion in the first cut blasting.•A blasting vibration reduction scheme was put forward.
Herein, the dynamics and flow fields of an inverted flag are studied using hydrogen bubble flow visualization and particle image velocimetry technologies at different height-to-length ratios and flow ...velocities in a water tunnel. Results show that the height-to-length ratio of the inverted flag at which the critical flow velocity remains nearly constant is approximately 1.4. Moreover, a nonperiodic flapping phenomenon is observed under various height-to-length ratios. This phenomenon may be attributed to the existence of multiple equilibrium solutions to the self-excited vibration system, thus engendering chaos in the system comprising an inverted flag and surrounding fluid. Other indications that the system has entered chaos include multiple frequencies, nonoverlapping phase diagram, and positive Lyapunov exponent. Further discussion of the flow fields around the inverted flag reveals that the large-amplitude oscillation is due to the flow separation, while the flapping instability is a static divergence instability. In the large flapping mode, the starting leading-edge vortex (LEV) is wrapped by Kelvin-Helmholtz instabilities, which are arranged at almost uniform spacing along a circular path. In addition, the variation in position, circulation, and radius of the starting LEV are discussed in detail. inverted flag, modes, aperiodic flapping, LEV PACS number(s): 47.20.Ky, 47.32.cd, 47.52.+j
•Vibration of fluid-conveying pipes is isolated by quasi-zero stiffness systems.•Nonlinear solution is obtained via Galerkin method and the finite difference.•The fluid flow can deteriorate the ...performance of vibration isolation.
Fluid-conveying pipes are always subjected to various excitations to cause unwanted vibrations. A quasi-zero stiffness system consisting of three linear springs is adopted as the nonlinear isolator to attenuate the transverse vibrations of fluid-conveying pipes induced by foundation excitations. A dynamic model of nonlinear forced vibration of the fluid-conveying pipe coupled with two nonlinear isolators is established for the nonlinear continuous system and validated by using two methods, Galerkin method and the finite difference method. The influence of the quasi-zero stiffness isolators on the vibration characteristics and vibration transmission of the pipe is investigated by analyzing the natural frequency, vibration mode, and nonlinear vibration response. The effects of flow speed of the fluid and the system parameters of the isolator are studied to evaluate the isolation performance. It is found that the quasi-zero stiffness isolator and fluid flow can shift several natural frequencies of vibration of the pipeline to the low-frequency region. When the linear stiffness of the vibration isolation is zero in the vertical direction, the first two modes of the bending vibration of the fluid-conveying pipe tend to become rigid mode. While achieving high-efficiency vibration isolation in the high-frequency region, the vibration in the low-frequency region is complicated. The flow speed of the fluid can deteriorate the performance of vibration isolation.
•Suggests a new signal analysis method to investigate structural vibration signals.•Decomposes the structural vibration signal into simple components.•Determines the linear (sine) and the nonlinear ...oscillations of the motion.•Can determine the frequencies of the above oscillations.•Is able to reconstruct a signal as a sum of simple oscillations.
This study aims to demonstrate some capabilities of singular spectrum analysis (SSA) for the purposes of analysis of vibrating/dynamic structures. SSA is a powerful method for time series analysis, which encompasses elements of classical time series analysis, multivariate statistics, principal component analysis, dynamical systems and signal processing. This paper introduces the application of SSA for vibration response time series and investigates the decomposition of the structural vibrations into harmonics, trend and noise components and their reconstruction.
After an introduction to SSA and its application for structural vibration signals, the paper investigates a simple model of a dynamic system and attempts to analyse it using classical methods of structural dynamics and SSA. The results and the capabilities of the two methods are then compared and discussed. Furthermore, the paper considers an experimental case of a layered GFRP composite plate which is subjected to free vibration and the recorded signals are analysed using conventional structural dynamics methods and SSA. The results demonstrate that SSA can be used as a powerful tool for analysis of the vibratory behaviour especially for structures with more complex and/or nonlinear dynamic behaviour. It is capable of extracting the vibratory/oscillation patterns even in the case of nonlinear oscillations.
This paper proposes a new tool for the selection of optimal elementary shunts connected to piezoelectric patches, which are bonded on thin structures to control the multi-resonant flexural vibration ...produced by broadband stochastic excitations. More specifically, the study introduces a procedure for the identification of simple shunt architectures composed by a small-number of low-value RLC elements, which yet produce significant multi-resonant vibration control effects. The challenge to identify beneficial elementary shunts lies in the fact that numerous candidate circuits exist, and this number grows exponentially with the increase of allowed electrical components. To this end, a design optimisation procedure is proposed, which enables the characterisation of all candidate shunt networks with a pre-defined number of elements having a given range of values. The paper refers to a practical model-problem, which encompasses a thin plate equipped with five piezoelectric patches connected to shunts. A trial design study is illustrated, where the tool is used to find suitable simple shunts to control the resonant responses of 6 flexural modes of the plate in a frequency band comprised between 20 and 150 Hz. The full set of shunt circuits composed by 4 elements is systematically searched and two simple shunts are identified. The physics and control performance of these two shunts are contrasted with those of classical single-resonant and multi-resonant shunts. The study shows that these elementary shunts generate 6 to 16 dB reductions of the target resonant responses, which are comparable to those that would be produced by a classical six-branches multi-resonant shunt encompassing 18 elements. Moreover, it shows that the two shunts produce combined absorption and damping effects such that they can provide beneficial vibration control in presence of significant variations of the flexural response of the structure too.
To exploit its advantages in passive vibration isolation, an X-shaped structure is integrated into a two-stage vibration isolation system so as to realize the broadband vibration isolation ...capability. The Lagrange equation is employed to establish the nonlinear equation of motion of the proposed X-shaped two-stage vibration isolator, which takes into account both rotational and vertical displacements. The incremental harmonic balance method is used to examine the effects of the key parameters of the system on the frequency response characteristics and vibration isolation frequency bands. The correctness and feasibility of the present analytical approach are validated by comparing with the numerical simulation and the experimental results. The investigation results indicate that the vibration isolation frequency of the designed system can be as low as 2–5 Hz, and the performance of low-frequency vibration isolation can be improved considerably by softening nonlinearity. Additionally, systematic revelations behind the occurrence of softening-hardening, softening, and hardening nonlinear behaviors are made. To assess the effectiveness of the system in vibration isolation, random vibration tests are also conducted. In conclusion, the designed X-shaped two-stage mechanism offers a novel point of view on low-frequency vibration isolation.
Winding condition assessment is an essential task for operating transformers, and the vibration method provides a low-cost and non-intrusive approach. In this paper, a novel feature extraction method ...based on vibration analysis is proposed, which converts the vibration monitoring data with load information into a vibration image. Then, a deep learning approach based on convolutional neural network (CNN) is used to classify the images belong to different classes. In the laboratory experiment, free vibration tests are performed on an on-load winding model, which are used to verify the relationship between the natural frequency and the electromagnetic force under different clamping forces. During the field experiment, transformers are divided into three categories, including normal, degraded and anomalous, and the proposed scheme is trained and tested by using the vibration samples acquired from more than 100 operating transformers. The performance of the CNN classifier under different input sizes is investigated, which achieves 98.3% overall accuracy. Besides, the confusion matrices obtained by other methods are compared, such as artificial neural network (ANN), support vector machine (SVM) and naive Bayes classifier (NBC). The results show that the proposed scheme including the vibration image extraction method and the CNN classifier offers superior performance in winding fault diagnosis.
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