Vibration Acceleration Response Research Articles

Experimental investigation on seismic performance of a super high-rise mega frame-double core tube composite structure

Increasing population density and urbanization have intensified the need for high-rise buildings in recent years. The seismic resistance of high-rise buildings should be carefully concerned in seismic regions, especially for super high-rise buildings which are most vulnerable to long-period earthquakes. This paper introduced the model design of a 499 m super high-rise mega frame-double core tube composite structure and presented the shaking table test results of the 1/50 scaled structural model. This super high-rise building possesses many conducive merits to resist seismic hazard, including steel reinforced concrete members, high-strength concrete and double core tube. In the test, there were three groups of long-period earthquakes and four incremental seismic intensity levels considered. The test phenomena indicated that the coupling beams of exterior tube were the first line of defense to resist seismic actions. The existence of inner tube improved the shear resistance of this building and there was no observed shear damage on the walls. Based on the instrumented data, the vibration characteristics, acceleration, displacement and strain responses of the structure were reported. The seismic performance of this super high-rise building meets the requirements of design specifications and its collapse resistance capacity is physically proved under severe earthquakes. However, the whiplash effect of acceleration is serious on the roof due to the reduction of mass and constraint for the mega column end. Furthermore, the inter-story drifts and strain responses of trusses in the top region are significantly larger. For the seismic measurement, great attentions should be paid to the exterior coupling beams and structural members in the top region of this super high-rise building. The presented work provides well experimental confirmation and reference for super high-rise buildings with mega frame-double core tube composite system.

Field study on vibration characteristics of geocell-reinforced aeolian sand subgrades

Constructing highways in deserts is expensive due to the difficulty of acquiring materials; utilizing aeolian sand effectively has become a problem, especially in the Xinjiang region, where the desert widely occurs. This paper aims to investigate the vibration response of a geocell-reinforced aeolian sand subgrade under traffic loading based on field tests of highways in deserts. The vibration acceleration response of geocell-reinforced aeolian sand and gravelly soil upper roadbed structures is tested. The field test results illustrate the effects of dynamic loading on geocell-reinforced aeolian sand roadbeds, and the thickness substitution ratio between geocell-reinforced aeolian sand roadbeds and conventional gravelly soil roadbeds is determined and verified based on the vibration acceleration monitoring values. The results show that the vibration response induced by the test vehicle is concentrated within the 30 Hz frequency band, and the higher the vibration frequency, the faster the vertical decay in the road. The vibration damping capacity of the reinforced aeolian sand roadbed is better than that of the gravelly soil roadbed; when replacing the gravelly soil roadbed with the reinforced aeolian sand roadbed, the substitution ratio is 0.31–0.42. It is verified that half thickness of gravel soil on roadbeds can be replaced by geocell-reinforced aeolian sand under different working conditions. The results of this study can provide reference data for the design of highway subgrades in deserts.

Research on vibration response distorted similitude of cylindrical shells under modal distribution disorder

Similitude theory enables local-scale models to reflect the dynamic characteristics of full-scale models and is widely employed in engineering experimentation. However, shell structures, constrained by wall thickness, cannot undergo experiments through proportional downsizing. Existing similitude studies with retained wall thickness exhibit only minimal distortion, and accurate prediction of vibration responses is hindered by modal distribution disorder. To address these challenges, a method based on modified frequency response functions of natural frequencies and mode shapes is proposed. Scaling laws for natural frequencies and mode shapes of cylindrical shells with retained wall thickness are established. This method yields a maximum prediction error of 4.29 % for prototype natural frequencies, compared to 50.57 % for existing methods. Predicted prototype vibration acceleration responses correspond well with theoretical calculations in both frequency and amplitude, while existing methods fail entirely. The phenomenon of modal distribution disorder and the effectiveness of the proposed method in mitigating it are verified by modal experiments and response tests. Research reveals that the sensitivity of different modal frequencies to the wall thickness scaling factor varies, serving as the cause of modal distribution disorder. The modal distribution with the same circumferential wave number is unaffected by wall thickness. Modes above the bending frequency, with axial half-wavelength consistent with bending modes, are prone to disorder due to wall thickness distortion. During wall thickness distortion, a mode originally with the lowest frequency is surpassed towards lower frequency by the mode with larger circumferential wave number and the same axial half-wave number, leading to disorder. The proposed method addresses the challenge of minimal distortion in structural vibration response and poor performance, advancing the development of distorted similitude.

Simplified Tunnel–Soil Model Based on Thin-Layer Method–Volume Method–Perfectly Matched Layer Method

In order to analyze the ground vibration responses induced by the dynamic loads in a tunnel, this paper proposes a new simplified tunnel–soil model. Specifically, based on the basic theory of the thin-layer method (TLM), the basic solution of three-dimensional layered foundation soil displacement was derived in the cylindrical coordinate system. The perfectly matched layer (PML) boundary condition was applied to the TLM. Subsequently, a tunnel–soil dynamic interaction analysis model was established using the volume method (VM) in conjunction with the TLM-PML method. The displacement frequency response function of the foundation soil around the tunnel foundation was derived. Finally, a ground vibration test under an impact load in a tunnel was carried out. The test and calculated results were compared. The comparison results show that the ground vibration acceleration response values within 25 m from the load are similar. Compared with the test results, the theoretical calculation results exhibit a decreasing trend in the range of 40–80 Hz between 25 and 60 m, with the maximum reduction being approximately one order of magnitude. In addition, the experimental comparison demonstrates that the model can be used to analyze the ground vibrations caused by underground loads.

One data-driven vibration acceleration prediction method for offshore wind turbine structures based on extreme gradient boosting

With the development of offshore wind power towards large-scale and deep-sea, the safety risks and the difficulty of intelligent operation and maintenance of offshore wind turbine (OWT) during operation periods have increased significantly. Structural vibration response is an important factor affecting the safety and stability of OWT. Accurate prediction on vibration through environmental conditions and operational factors can identify the safety risks of OWT in advance, and reduce harmful vibration through appropriate operation strategy regulation. Therefore, a vibration acceleration prediction method of OWT structures was proposed in this research based on Harris hawks optimization (HHO) and extreme gradient boosting (XGBoost). Firstly, approximately two months of monitoring data from a 3 MW OWT were extracted to establish the database for training the machine learning models. Then, the key hyperparameters of XGBoost were optimized by the HHO algorithm and compared with other typical algorithms. Finally, the trained prediction model was applied to the regularity analysis of different conditions and long time series data. The analysis results demonstrate that the proposed method can effectively predict the vibration acceleration response of OWT structures using operational and environmental characteristics, and has higher accuracy and stability than other methods, with R2 of 0.9715 and mean absolute percentage error (MAPE) of 6.55%. Simultaneously, it also shows acceptable accuracy on the long-term measured data because the MAPE of chosen summer, autumn, and winter samples were calculated as 9.60%, 11.76%, and 7.21%, respectively. The establishment of the HHO-XGBoost vibration prediction model can be applied in the subsequent prediction of the vibration trend, which provides a guarantee for the safe and stable operation of OWT.

Shaking table test of a dry-connection fully precast frame structure system

In view of the construction difficulties and ecological environment sensitivity of building construction in extremely cold and high seismic intensity areas, a new type of dry-connection fully precast frame structure system was proposed. The connections of the structure are easy to assemble, which can greatly improve the construction efficiency and provide convenience for the upgrading and replacement of components during service. In order to provide essential insights into the seismic performance of the dry-connection precast structure, a three-story precast frame structure specimen with a scale ratio of 1/2 was designed, constructed, and tested on a shaking table subjected to a series of ground motions with increasing seismic intensities. The connections of the specimen structure include beam-column joint, beam-floor joint and column-foundation joint, precast components were processed in the factory and assembled in the laboratory. The vibration characteristics, damage development, acceleration response and displacement response of the structure were investigated. The experimental results illustrated the excellent seismic performance of the structure with sufficient strength and relatively confined damage. The gradually decreasing frequency and increasing damping ratio were attributed to the slippage and plastic deformation of the connectors and the cracking of beam concrete. And the maximum story drift under rare earthquake of intensity 8 was within the design limit, indicated that the precast frame structure could achieve the performance target of no collapse under severe earthquakes. The data of this test provided support for further study on the design methods and numerical modeling of dry-connection fully precast frame structure systems.

Dynamic measurements to assess stress levels on buried hydraulic structures

ABSTRACT Old masonry structures have a very special nature that require periodical inspection and evaluation programs. The problem becomes more sophisticated when dealing with vital buried hydraulic structures under continuous functional operation while bearing additional loads from running public services such as railways. This could add extra challenges for determining their structural performance and engineering characteristics if conventional methods are used. Moreover, traditional methods are sometimes costly, time consuming, and can lead to some damage to the structure. The importance of the current research is therefore providing a rapid methodology for evaluating these structures to confirm their current ability to resist operating loads safely, especially when subjected to aging. In this study, the evaluation depends mainly on analyzing the vibration acceleration response of a structure under dynamic loads. Insight into system identification using formal modal analysis was also conducted. Simultaneously, calibrated numerical model was then adopted to predict the expected level of internal stresses. An old masonry irrigation intake buried culvert underneath the main railway lines was selected for examination. The structure was firstly plugged from both sides and emptied, site inspection as well as core sampling of construction materials were conducted. Vibration time history was recorded due to train passage with different speeds. The filed measurements along with mathematical model were used to estimate the level of stresses among the structure. The results showed the ability of the proposed method to evaluate structures in an easy and rapid fashion compared to traditional methods without stopping serviceability of the structure.

Vibration behavior of innovative discretely connected precast concrete sandwich floors

This paper investigates the vertical vibration behavior of an innovative discretely connected precast concrete sandwich floor (DCPCF) in orthogonal slab laying direction (OSLD). An experimental program included the full-scale tests of seven DCPCF specimens and two cast-in-situ floor (CISF) specimens was conducted. In order to evaluate the vertical vibration behavior of the DCPCF, the parameters considered the number of slabs, the number of connectors, the position of slab joints and loading condition were studied according to the vibration mode, fundamental frequency, damping ratio and acceleration response. The test results indicated that the first two vibration modes of DCPCF specimens and CISF specimens were basically the same. The fundamental frequency of the DCPCF was negatively correlated with the number of slab joints and overlying loads, and positively correlated with the number of connectors and the distance of slab joints to the mid-span. The damping ratio of the DCPCF decreased with the decrease of the number of slab joints, the increase of the number of connectors and the distance of slab joints to the mid-span. The vibration response of DCPCF specimens was slightly larger than those of CISF specimens under the same excitation. The peak acceleration increased with the increase of the loading frequency and the number of pedestrians. The closer the loading distribution was to the mid-span, the greater the peak acceleration would be. Based on the vertical vibration theory of elastic thin slab, the calculation methods for predicting the first mode natural frequency and peak acceleration of the DCPCF in OSLD were proposed. The calculated results obtained by the proposed formula showed good agreement with the experiment results.

Earthquake wonders: High school investigation in mortise tenon structures

Frequent global earthquakes lead to catastrophic property damage and casualties due to building collapses. However, the 1976 Tangshan Earthquake showcased an exception: the Forbidden City, constructed with wooden materials and featuring mortise-tenon structures, remained unscathed among surrounding destruction. This study investigates the earthquake-resilient attributes of wooden mortise-tenon joints utilizing economical high school equipment. An innovative low-cost sensor system, featuring custom instrumented hammer, is developed and validated. Calibration of the hammer's impact force employs correlation with acceleration data from a standardized scale weight during impact. The system's reliability is tested by comparing resonance frequencies from Finite Element modal analysis and experimental data for a cantilever beam. Impact hammer tests assess frequency response and damping across buildings with various joint configurations. Mortise-tenon joints display augmented frictional damping due to internal displacement. Through simulated vibration acceleration responses, a crucial finding emerges---integration of mortise-tenon joints translates to an impressive 11.0% reduction in earthquake vibrations. This research underscores the potential of accessible high school devices in advancing seismic engineering insights.

Monitoring and analysis of railway-induced vibration and structure-borne noise in a transit oriented development project

With the rapid development of modern cities, the construction of over-track buildings and buildings along the subway line are increasing gradually. In order to evaluate the influence of rail transit on these buildings, the railway-induced vibration and structure-borne noise of subway stations and buildings in a Transit Oriented Development (TOD) project are monitored and analyzed in this paper. The vibration monitoring data in the subway station shows that the vibration acceleration response of the measuring point in the station caused by the train entering and leaving the station is the largest in the vertical direction, followed by the along-track direction, and the vertical-track direction is the smallest. The corresponding predominant frequency of vibration is usually in the range of 100 Hz-200 Hz. The vibration monitoring data of the building foundation along the subway line shows that the railway-induced vibration of the building foundation along the track near the subway station decreases with the reduction of the distance from the subway station. The monitoring vibration results of the over-track building on the metro depot are different from the buildings near the main line. The predominant frequency of the vibration at the measuring point is in the range of 30 Hz-40 Hz. The small vertical vibration acceleration response of the measuring point corresponds to a high vibration level. In addition, the amplitude of railway-induced vibration in some building rooms near the metro depot is basically consistent with the amplitude of background vibration, but the monitoring value of the structure-borne noise is obviously higher than the background noise. The research results of this paper show the influence of railway-induced vibration on the over-track buildings and the buildings along the subway line, which has important reference value for the comprehensive development of rail transit.

Vibration Analysis of Low Height-to-Span Ratio Pedestrian Bridge under Human-Induced Excitation

Driven by the aesthetic pursuit of the urban landscape, pedestrian bridges become longer, lighter, and slender, which may be susceptible to unacceptable vibrations induced by human activities. This paper presented on-site vibration tests of a pedestrian bridge with a very low height-to-span ratio (1/60). The vibration characteristics and dynamic responses were analyzed using environmental, heel-drop, and walking tests. Then, a verified finite model was established to investigate the effect of the height-to-span ratio and the concrete filling ranges of tree-like steel piers on the vibration characteristics and acceleration responses of this kind of pedestrian bridges. Moreover, the relationship between different peak accelerations under heel-drop and walking at various frequencies by the same person was detailed and studied experimentally and by computer simulation, after which the ratios of the peak acceleration during walking and the one under heel-drop were recommended. Finally, a method that demonstrates the feasibility of predicting the peak acceleration of pedestrian bridges of a small height-to-span ratio across a range of walking frequencies was proposed based on a simplified heel-drop load model developed according to 60 time-history records.

Influence of the Electromagnetic Characteristics in Air Region on High‐Speed Permanent Magnet Generator Based on Multi‐Physical Field

The cooling performance of the machine with the closed liquid cooling system is excellent. However, the electromagnetic characteristics of the oil separator which sealing the cooling oil in the stator side can have a significant impact on the performance of the machine. In this paper, a liquid cooling structure with the magnetic oil separator is proposed. Taking the 20 000 rpm high‐speed permanent magnet generator as an example, the influence of the electromagnetic parameters of the magnetic oil separator on the generator output performance is studied by the analytical calculation and the finite element method, and the mechanism of the nonlinear variation of the generator output performance with the permeability of the oil separator is obtained. The influence of the oil separator on the air‐gap magnetic field and electromagnetic force is analyzed, and the reduction mechanism of the different permeability of the oil separator on the harmonic magnetic field and radial force is revealed. The vibration acceleration response of the generator stator is obtained through the modal and harmonic response analysis, it is confirmed that the magnetic oil separator has the effect of reducing vibration. In addition, the 3‐D temperature field calculation model of the generator is established, the influence of the thermal parameters of the oil separator on the internal heat exchange of the generator is studied, and the temperature distribution is obtained. Finally, experiments on the electromagnetic performance and temperature rise of the prototype are carried out to verify the correctness of the theoretical analysis. © 2023 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC.

Experimental study on impact response of seaborne rocket launch platform

This paper presents a novel test method for evaluating the impact response of a seaborne launch platform. By simulating and analyzing the platform's impact response to develop a test plan, designing an assistive test device to enhance data accuracy, and conducting a shipboard test, we analyzed the launch platform's impact response during cold launch. Results show that during the ejection stage, the platform experiences a sudden acceleration peak that quickly attenuates. During ignition, the vibration acceleration response oscillates and fluctuates. The maximum structural impact response occurs below the launcher, gradually attenuating to the bow, stern, and sides of the ship, and propagating slowly along the captain's direction. The vibration acceleration response varies along different directions, with the highest response in the vertical direction and the lowest in the longitudinal direction. FE numerical analysis confirms the experimental results. This study provides reference data for the structural anti-impact design of seaborne launch systems.

Vibration Influence on Structural Perspectives According to Pedestrian Traffic Type of Pedestrian Bridge

The vibration acceleration response and excellent frequency generated by pedestrian’s walking type of the steel composite wooden bridge were measured and analyzed. Based on the modified Reiher-Meister vibration curve, vibration influence evaluation on the structural perspectives of the pedestrian bridge was performed. The pedestrian’s walking types were divided into walking, running, rolling, and shaking, and eight experimental cases were set up by combining them with the number of users and moving direction. A total of 37 measurements were made. To evaluate the vibration serviceability of pedestrian bridges, the pedestrian’s walking type must be considered, and a standardized study on the pedestrian’s walking type will be necessary in the future.

Dynamic modelling and vibration characteristics of a marine compound gear transmission system

The vibration level is the key index to measure the performance of marine gear transmission device. The compound gear transmission system, which is composed of a helical gear pair and a spur star gear train, is widely used in marine gear transmission device. This paper presents a multi-node dynamic model for a marine compound gear transmission system, investigating the modal properties and dynamic responses of the system. The mesh stiffness and transmission error for each gear pair are determined using the loaded tooth contact analysis (LTCA) model. The theoretical and experimental vibration acceleration responses of the gearbox housing are contrastively analysed. The results show that some vibration modes are very similar to those of a single planetary gear train, but other modes are multi-node and multi-degree of freedom coupling modes. The vibration coupling and transferring phenomenon between two stages can be observed remarkably, but those show obvious differences under different working conditions. The torsional stiffness of the elastic connecting shaft has significant influence on the vibration coupling and transferring phenomenon. The results can provide useful guidance for the low vibration and noise design of the marine compound gear transmission system.

Damping Characteristics of Cantilever Beam with Obstacle Grid Particle Dampers

In order to understand the damping effect and energy dissipation mechanism of the obstacle grid particle dampers, we conduct experimental and simulated studies. In this paper, the obstacle grid particle dampers are applied to the cantilever beam structure. The effect of filling ratio, particle size, particle material and excitation amplitude of the obstacle grid particle damper on the vibration characteristics of the cantilever beam is studied experimentally and compared with the conventional particle damper for damping effect. A simulation model of the particle damper was developed and experimentally validated using the discrete element method. The experimental results show that the vibration acceleration response of the obstacle grid particle damper decreases by 10.4 dB compared with the conventional particle damper at 90% filling ratio. The obstacle grid particle damper increases the area of energy transfer between the external vibration energy and the particles. It makes the particles, which originally have almost no contribution to the energy dissipation, produce violent motion and participate in the energy dissipation process, thus effectively improving the damping performance of the particle dampers.

Design of a 2 m Primary Mirror Assembly Considering Fatigue Characteristics

The design requirements of a 2 m mirror assembly installed on a large space optical remote sensor are investigated in this study. The mirror body and rigid connectors are designed using topology and size optimization methods. The initial design scheme of flexible supports is then proposed through an in-depth exploration of fatigue failure mechanism caused by impacts of size parameters, thermal–mechanical vibration, and surface abrasion. The comprehensive analysis mode of the flexible support structure is established with the help of finite element and fatigue analysis software programs. The designed mirror surface error under composited force is 5.6 nm, first natural vibration mode is 119.16 Hz, and fatigue life synthesizing thermal–mechanical vibration is about 21,790,000 cycles, thereby meeting the design requirements. The first natural vibration mode, acceleration response, and stress responses of sine and random vibration are verified with experiments, and the findings are compared with the theoretical analysis results. The analysis mode can successfully and significantly improve the reliability of the mirror assembly and help optimize the design of flexible supports.

Research on the Identification Method of Overhead Transmission Line Breeze Vibration Broken Strands Based on VMD−SSA−SVM

For the problem of overhead line broken strand identification, a VMD−SSA−SVM-based overhead transmission line broken strand identification method is proposed. First, the vibration acceleration response signal of overhead transmission line under breeze environment was simulated by Ansys simulation software. Then the variable modal decomposition of the vibration acceleration response of the transmission line is performed to obtain the intrinsic mode function corresponding to the vibration behavior of the transmission line. The Hilbert transform is used to analyze the intrinsic mode functions of each order, and the Hilbert spectrum and marginal spectrum of the intrinsic mode functions of each order are studied to extract the first six order intrinsic frequencies. Each set of intrinsic frequencies is input as a feature vector into a support vector machine optimized by the sparrow search algorithm for training to achieve the identification of broken strands in overhead transmission lines. This paper studies the inherent frequency changes and identification results of overhead transmission lines under two states of normal operation and broken 5 strands operation, and the test results show that the identification method based on VMD-SSA-SVM has good identification effect on broken strands of overhead lines.

Research on system identification method of buffer system based on experimental signal pre-processing

In order to obtain the theoretical model of a gun buffer system, the dynamic vibration characteristics of the buffer system were studied by force hammer experiments, and the vibration acceleration response curves of the buffer system after being excited by the impact load were obtained. The acquired signals were processed by noise reduction, detrending, data smoothing and frequency domain integration, and the second-order free vibration model was used to identify the stiffness, damping and other parameters of the system, and compared with the experimental results. The deviation between the calculated results of the identification model and the experimental results is less than 4%, which compared with the general direct identification method, the error is reduced by about 10%. This method can provide a simple and fast technical way for the accurate identification of vibration system models.

Switch Semi-Active Control of the Floating Raft Vibration Isolation System

Switch semi-active control is introduced to improve the performance of the floating raft vibration isolation system on isolating vibration in the vicinity of the resonance frequency. A switch-controllable linear damper based on the electromagnetic damping principle is developed, whose characteristic parameters are obtained by experiment. The dynamic model of a semi-active control floating raft vibration isolation system is established, and two switch control algorithms are proposed. Algorithm 1 aims to minimize the kinetic energy of the raft, and Algorithm 2 balances minimizing the kinetic energy of the raft and minimizing the input energy of the system. The simulations of the original system, the system with the controllable damper, and the system with the damper controlled by the algorithms are carried out. The vibration acceleration responses of the foundation of the systems are used to evaluate the vibration isolation effect. The results show that the switching semi-active control using Algorithms 1 and 2 can significantly suppress the vibration of the system near the resonance frequency. Finally, the test platform of the switch’s semi-active controlled floating raft vibration isolation system is built, and the simulation results are verified by the experimental result.