Long-term Vibration Research Articles

Active Arc Suppression Algorithm for Generator Stator Winding Ground Fault in the Floating Nuclear Power Plant

Electrical equipment of the floating nuclear power plant operates in a long-term vibration environment. Ground faults occur frequently and are often accompanied by arc, a reliable arc suppression algorithm for the generator stator winding is necessary. In this paper, an active arc suppression method is proposed by connecting a controllable voltage source to the generator neutral point. Through regulating the neutral point voltage to be equal in amplitude and opposite in phase to the fault potential, the fault point voltage can be clamped to a low level to achieve arc suppression. Since the generator's phase potential contains certain harmonic components, the controllable voltage source includes fundamental and third-order harmonic components. To accurately calculate the output voltage, online calculation methods for the fault location, fault potential and grounding capacitance are proposed. The accuracy of the fault location method is verified by simulation and dynamic test. And simulation results based on PSCAD/EMTDC software show that the proposed method can achieve effective arc suppression at different ground fault conditions.

Attenuation and propagation characteristics of railway load-induced vibration in a loess area

The long-term vibration caused by the operation of high-speed trains not only reduces the strength and stability of a roadbed but also affects infrastructure such as buildings along the line, resulting in a series of engineering–environmental problems. In this study, field tests were conducted to examine the ground vibrations caused by the operation of the Datong-Xi’an high-speed railway; three different line forms––viaducts, embankments, and embankment culverts––were considered. First, the propagation law and attenuation characteristics of environmental vibration caused by high-speed railways in typical loess areas were analyzed using time-domain and frequency-domain features. Second, based on the Bornitz model and combined with the measured data, the geometric attenuation coefficient and damping attenuation coefficient of the formula are discussed, and the optimized Bornitz model is used to predict the ground vibration caused by high-speed trains in a loess area. The results showed the following: (1) The ground vibration caused by high-speed train operation is a periodic excitation, and there is an obvious superimposition effect at the bogie of the train. The vertical vibration acceleration of the ground surface decays continuously as the distance from the vibration source increases. The dominant frequency also decreased with an increase in distance. (2) The geometric attenuation coefficient of the bridge and embankment sections decrease with an increase in the distance from the vibration source, and the overall attenuation is a power function. Different distances should be regarded as different types of vibration sources, and the damping attenuation coefficient differs at different measurement points. (3) The improved Bornitz model was used to predict ground vibrations caused by the operation of high-speed trains. A comparison with the measured data showed good agreement, explaining the amplification effect in the attenuation of ground vibration.

A feasibility study on piezoelectric energy harvesting from the operational vibration of a highway bridge

Vibration-based energy harvesting represents a clean power technology that can be of interest for application in civil engineering structures. This study focuses on energy harvesting using cantilever piezoelectric devices excited by operational and ambient bridge vibration. The optimal design and analysis of energy harvesters is usually performed using the mean and standard deviation of a response quantity of interest (i.e. voltage) under broadband Gaussian white noise excitation. In this paper, a novel holistic approach to the problem is proposed through the statistics of the voltage of piezoelectric energy harvesters under real measured bridge vibration base excitation. A new semi-analytic expression of the expected power is developed. The solution is based on the closed-form of the frequency response function between the harvester output voltage and the base excitation, and the experimentally measured spectral density of the latter. A study on the influence of the electromechanical coupling of the problem equations is first conducted. Then, a sensitivity analysis of the piezoelectric energy harvester parameters is performed. The critical analysis is developed through a case study of the measured long-term vibrations of a bowstring-arch highway bridge. Both operational and ambient vibration records are considered in the feasibility study. The results show the potential of the semi-analytic expression to evaluate the harvested power of piezoelectric harvesters under operational structural vibration. This is a promising approach to confidently develop future analyses on the power requirements of wireless sensor networks for SHM.

Hybrid feature selection method for SVM classification and its application for fault diagnosis of wear and peeling in journal bearing with a little muddy water using long-term real data

Rotating machines are widely used as components of various industries around the world, and its normal operation of rotating machines is important. Thus, condition monitoring and fault diagnosis of rotating machines have considerable attention in recent years. Industrial statistics illustrate that 40% of total large machine breakdowns happened due to broken bearings, while for small machines, the analogous number reaches up to 90%. This study aimed at researching fault diagnosis of journal bearings using the support vector machine (SVM) method. The experimental systems of vertical and horizontal rotating shafts were developed. There was no adding any initial artificial failure in the bearing, and a little muddy water was used, and long-term vibration data in both systems were obtained in the normal operation of the machines until bearing damages occurred in the journal bearing (3-hour tests were conducted repeatedly and total 128 datasets for vertical shaft and 24 datasets for horizontal shaft were obtained). A feature selection method is focused, and a hybrid feature selection method by combining Fisher score (FS) and a sequential forward selection (SFS) method was proposed. Its accuracy and efficiency was proved experimentally with 97.14% and 100% for vertical shaft and 100% for horizontal shaft. Furthermore, as a result of the SVM model and hybrid feature selection method, the most important feature for journal bearing of horizontal rotor system was clarified as mean value of RMS, and only this feature can give good diagnosis result. It is useful suggestion in selecting the features for the fault diagnosis of horizontal rotating machines.

Research on vibration of the reactor for HVDC thyristor protection

As the key equipment to protect the thyristor of HVDC converter valve, the vibration problem of anode saturable reactor (ASR) is very prominent. Its long-term vibration will even cause the failure of the whole converter valve system. From the perspective of multi-physical field coupling, this paper establishes the solid model of ASR, considers the influence of Maxwell electro-magnetic field and magnetostrictive effect, numerically calculates the magnetic field and vibration of iron core, analyzes the contribution of two forces to vibration, and expounds the vibration phenomenon of iron core at different positions. In order to evaluate the effectiveness of the simulation, a single iron core vibration experiment is designed and compared with the single iron core simulation. This study can predict the vibration level of ASR core and provide theoretical basis and calculation method for vibration reduction in ASR design stage.

Experimental models of vibration disease (literature review)

Introduction. Long-term vibration exposure to the human body is a risk factor for the development of occupational diseases and comorbid conditions causing, first of all, the pathology of the nervous system, as well as the cardiovascular, gastrointestinal tract and musculoskeletal systems. Pathogenetic aspects of vibration exposure at the molecular level remain open and require the search for adequate experimental animal models. The review describes experimental methods for studying vibration disease. A literature search was conducted in the databases MedLine, PubMed, Web of Science, Scopus, Google Scholar, CyberLeninka and RSCI. The results of experimental studies differ due to the difference in frequencies and duration of vibration exposure. Sanitary and hygienic characteristics of workplaces of coal-mining enterprises in Kuzbass. Data are given at the levels of local and whole-body vibration at the workplaces of an underground sinker, a stope miner, and a mining machine operator. Experimental modelling of local and whole-body vibration. Experimental methods of vibration exposure to laboratory rats, mice and rabbits at the local and whole-body levels are described. The presented experimental models are as close as possible to real vibration effects in production conditions. Vibration at frequencies above 4 Hz has been shown to cause changes in the structure and functions of peripheral vessels and nerves, along with hypoxic damage of the brain, heart, kidneys, liver, and skeletal muscles. Conclusion. Experimental modelling of vibration disease makes it possible to study the organ-specific molecular mechanisms of damaging vibration exposure to the body and develop effective preventive and therapeutic measures.

Contact parameters evolution of bolted joint interface under transversal random vibrations

Bolt connection plays an important role in assembly structures. Under long-term vibrations, bolted joint interface will change due to fretting-induced friction and wear behavior. This leads to changes in the dynamic characteristics of assembly structures, which increases the difficulty of control of the structure. In this paper, a new random fretting test method was developed to reproduce realistic vibration situations as much as possible and to study the evolution of contact parameters (friction coefficient and contact stiffness) of bolted joint interfaces with increasing wear. A recently developed test rig was used to perform the fretting wear tests under random oscillation. During the tests, interface hysteresis response and bolt preload were recorded. A model-based parameter estimation method was developed to estimate the friction coefficient and tangential contact stiffness. The evolution curves of contact parameters were obtained, and the effects of initial bolt preload, excitation level, and surface roughness were discussed. To the authors' knowledge, no studies on the fretting behavior of bolted joint interfaces under random vibration have been published. This research can promote a better understanding of the fretting wear behavior of bolted joints and provide a basis for the dynamic analysis of joint-dominated structures.

An Optimal Design of a Fire Pump with Protection Function

At present, the existing power mechanical gasoline engine fire pump is prone to large vibration during operation. Due to the lack of protection structure, long-term vibration will shorten the service life of the fire pump. Meanwhile, the upper end of the fire pump body is usually not set up with a protective structure, which is easily damaged by the extrusion and impact of objects. Therefore, a new type of protection device is designed in this paper, which plays a protective role by setting a relevant absorber at the lower end of the fire pump body, and at the same time, a buffer pad is arranged at the upper end of the cover to have the effect of buffering and shock absorption. To this end, this device has the function of reducing the damage to the fire pump body caused by the impact of heavy objects, improving the performance of the existing fire pump, and prolonging its service life.

Effects of Long-Term Vibration on Cellulose Degradation in an Oil-Impregnated Pressboard under Simultaneous Thermal–Electrical–Mechanical Stress Aging

Due to the complex operation conditions in a power transformer, an oil-impregnated pressboard (OIP) simultaneously suffers from thermal, electrical, and mechanical stress. Since most research studies have paid much attention to thermal or electrical aging of OIPs, this paper analyzes the effects of long-term mechanical vibrations on cellulose degradation in OIPs under simultaneous multi-stress. The aging experiments were firstly conducted at 130 °C, with a DC electric voltage of +6 kV, vibration amplitude of 10–50 μm, and vibration frequency of 100–300 Hz. The finite element analysis (FEA) of the pressboard vibration model was then performed on Abaqus to investigate the time–frequency domain characteristic parameters of compressive stress on the pressboard under varied vibration frequencies and amplitudes. The FEA results reveal that compressive stress on the pressboard in a multi-stress aging experiment coincided with the axial compressive stress on the insulation spacers in an SZ-50000/110 transformer. Moreover, combined with the degree of polymerization (DP) of cellulose, the effects of long-term vibration on cellulose degradation are reflected in two ways: the increase in compressive stress on the pressboard generates more links available for degradation, while more high frequency harmonic components in compressive stress accelerate the reaction rate in cellulose degradation.

Experimental investigation on the impact resistance of rubber self-compacting concrete

Stiffness degradation and micro-cracks are commonly observed in the self-compacting concrete subjected to long-term vibration and impact loading. Adding rubber particles to the concrete is a universal approach to improve impact resistance. Exploiting the dynamic mechanical properties of the rubber self-compacting concrete under impact loading is of great significance. Herein, a comprehensive investigation of rubber self-compacting concrete under impact loading was carried out using a split Hopkinson pressure bar. The influence of rubber replacement rate, rubber particle size, and strain rate on impact resistance was considered. 108 rubber self-compacting concrete specimens along with 36 ordinary self-compacting concrete ones were designed. As a result, the dynamic stress–strain relationship of rubber self-compacting concrete was proposed. The results show that rubber self-compacting concrete's dynamic peak strain and peak stress were higher than ordinary self-compacting concrete with similar static compressive strength. The dynamic compressive strength and DIF-σ and DIF-ε of rubber self-compacting concrete can be increased with strain rate. The sensitivity of growth rates of DIF-σ and DIF-ε to strain rate decreases with the strain rate. DIF-σ and DIF-ε showed a positive linear correlation with rubber content. The increase of rubber content reduces the dynamic compressive strength of rubber self-compacting concrete. Compared with other sizes, the dynamic compressive strength and DIF-σ and DIF-ε of 12 mesh (1 ∼ 2 mm) rubber particles are generally higher.

Investigation of a seat suspension installed with compact variable stiffness and damping rotary magnetorheological dampers

Long-term vibration poses a threat to drivers’ health and affects their ride performance. Furthermore, large-magnitude vibration and sudden shocks may even result in end-stop impacts, raising the drivers’ injury risk. To reduce the vibration and avoid end-top impacts, this paper presents an innovative seat suspension installed with variable stiffness and variable damping (VSVD) rotary magnetorheological (MR) dampers. At first, a novel compact VSVD rotary MR damper was designed and prototyped for the suspension, making the suspension’s stiffness and damping controllable. Then, with two identical VSVD MR dampers were installed, the prototyped seat suspension was characterised by an MTS test frame to verify its capabilities of variable stiffness and damping. A control strategy consisting of a nonlinear stiffness control and a no-jerk skyhook damping control was also designed. Finally, the vibration attenuation performance of the seat suspension was numerically and experimentally evaluated under three vibration excitations, i.e., harmonic excitation, bump excitation, and random excitation. Both numerical and experimental results indicate that the vibration control performance of the seat suspension can be significantly improved by the VSVD rotary MR dampers.

Coupling Vibration Model of Submerged Floating Tunnel in Space

Submerged floating tunnel is a new type of traffic building structure under water surface which can span various water courses. The structure has the characteristics of high flexibility and low damping so that vibration problems would be caused by hydrodynamic excitation. Long-term vibration problems could affect the safety and durability of the structure. Therefore, it is necessary to accurately understand the dynamic behavior of the floating tunnel under hydrodynamic excitation. This paper proposes a simplified three-dimensional model to study vibration of the structure for the excitation. Based on the Galerkin method and the mode superposition method with the boundary conditions, the dynamic differential equations of the structure were established in Generalized coordinate system. The Newmark - beta method is used to solve the equations. Then, adopting FEA (Finite Element Analysis) method to establish the finite element model of the submerged floating tunnel. The result verified the accuracy of the present model. Based on the present model for parameter analysis, the following conclusions are: displacement coordination at the connection position affects the cables’ dynamic behavior greatly compared to tube. Current and horizontal component of wave have significant impact on dynamic response of tube. While the vertical wave component influences cable greatly.

Novel Gaussian Acceleration Profile for Smooth Jerk-Bounded Trajectories

Industrial machines regularly work at their limits causing excessive long-term vibrations that deteriorate their movement, stability, and precision. In this sense, reference profiles are able to reduce the detrimental vibration effects by manipulating the machine motion dynamics using predefined movement trajectories. Most of the approaches for lessening damages due to long-term machine vibrations are based on polynomial functions with high computational complexity and high resources demand. Hence, in this work, an innovative acceleration outline based on a Gaussian function is proposed for machine motion trajectories. The introduced strategy simplifies the position-profile estimation that works as reference for restraining the machine movements through the parameters that define its motion dynamics; thus, a smooth and continuous jerk contour is produced, which reduces vibrations and improves the machine stability. Exhaustive computer-based and real-time experimental comparisons of the introduced scheme produces a significantly lower maximum jerk value than any of the others. The assessment of the presented approach was performed utilizing the software Matlab (R2020a) on a PC with an Intel Core i7-6500U microprocessor at 2.5 GHz, with 16 GB in RAM and a 64-bit operating system.

Assessment of passenger long-term vibration discomfort: a field study in high-speed train environments

This study revealed the mechanism of long-term passenger vibration discomfort in high-speed trains and proposed a novel evaluation model to assess it, while the most popular international standard ISO 2631-1 is unsuitable. Here, a field test was conducted to investigate the long-term passenger vibration comfort in high-speed trains under different operation environments by the measurement of the whole-body vibration (WBV) and the subjective ratings of passenger comfort. During the whole sitting period of high-speed train passengers, the phenomena ‘compensatory degradation’ and ‘discomfort accumulation’ were found, which meant that the brief termination of vibration cannot fundamentally alleviate passenger vibration comfort. And the vibration comfort can be evaluated by the product of exposure time and the novel vibration acceleration index we proposed. Meanwhile, high-speed trains with higher velocities or running in tunnel environments have higher frequency-weighted WBV amplitude than open-air and lower velocities, which caused more vibration discomfort of passengers. Practitioner Summary: This field study provided data support for ensuring the occupational health of train drivers whose work routes involve a large number of tunnels and improving passenger vibration comfort. Meanwhile, a novel idea was provided for evaluating the vibration comfort of passengers who prolonged exposure to low-amplitude environments.

The modal and harmonic response analysis of final superheater based on workbench

In order to avoid pipe failures affecting the operation of thermal power plants, the modal and harmonic response analysis method were carried out through the finite element software ANSYS Workbench to solve the long-term vibration of the final superheater at high temperature. Modal analysis can predict the natural frequencies of each stage of the structure and provide the frequency range for the harmonic response analysis. Then the response curve of stress to the frequency under the forced vibration was obtained on the base of harmonic response analysis, and observed the stress corresponding to the peak frequency. Furthermore, the fatigue life of the system was analyzed by the fatigue tool module in ANSYS Workbench. The results show that the fatigue safety factor of the final superheater pipe is greater than the allowed safety factor, and the fatigue life could meet the requirements for safe operation. The research results have certain reference value for further research on vibration fatigue of superheater pipelines.

Long-term vibration laboratory tests of sandy soils

The presented work examines the features of testing at the laboratory of the Moscow State University of Civil Engineering “Research and Education Center” Geotechnics “on a triaxial device with the ability to create dynamic loads (vibration stabilometer). Information on the course of cyclic tests of sandy soils is given, their analysis is carried out and formulated the main conclusions about the effect of the duration of vibration loading on the final stress-strain state of the soil mass.

Change in Dynamic Characteristics of Base-Isolated Buildings with Irregular Shape Based on Long-Term Vibration Records

Change in Dynamic Characteristics of Base-Isolated Buildings with Irregular Shape Based on Long-Term Vibration Records

Passive vibration reduction of a squeeze film damper for a rotor system with fit looseness between outer ring and housing

Clearances between bearing outer ring and sleeve can generally be maintained to provide a margin for the thermal expansion of the bearings. However, temperature variation, improper assembly and long-term vibration can enlarge the clearances and accelerate mechanical wear, leading to what is known as the fit looseness fault. Therefore, it is important to study a fit looseness fault model and investigate how to control the vibration coming from the fit looseness fault. In this paper, a Jeffcott rotor system with three disks was modeled as a single unit. A fit looseness model was applied in the whole rotor model to study the contact problems and response characteristics using a numerical integration method. Then, a squeeze film damper model was applied to assess the vibration reduction effects on the whole rotor system with the fit looseness fault. By comparing the results of the fit looseness fault without squeeze film damper and with squeeze film damper, it is found that the squeeze film damper can reduce nonlinear vibration responses effectively generated by the fit looseness fault for the nonlinear contact. This research work contributes to understanding the mechanism of fit looseness fault and controlling strong nonlinear vibration responses due to the fit clearances.

Study on Wind-Induced Vibration of Tension String Shielding Ring for UHVDC Transmission Lines Based on Modal Test

Under the action of natural wind, the shielding ring of tension string of UHVDC transmission line is prone to low frequency vibration, and the long-term vibration may lead to the fatigue damage of the shielding ring, threatening the safe operation of the line. In this paper, the modal test of the shielding ring of the tension string of UHVDC transmission line is carried out by using hammering method, and the natural frequencies and vibration mode shapes of the shielding ring are mastered. Combined with the analysis of the wind speed and wind direction in the engineering site, it is shown that the vortex induced vibration of the shielding ring is caused by the low-speed continuous stable wind along the line.

Vibration suppression of tunnel boring machines using non-resonance approach

Tunnel boring machines (TBM) are efficient tunnel excavation equipment, and the number of TBM in many countries is increasing rapidly. TBM works in a harsh geological environment and long-term vibration will cause tremendous damages, including loosening the pipeline and damaging the mechanical system on the main frame of TBM. In this paper, a variable stiffness magnetorheological elastomer (MRE) isolator is installed under the main frame in order to control its resonance frequency to avoid the vibration resonance to reduce the high-level vibration of TBM, this is called non-resonance control approach. A multi-degree-of-freedom dynamics model of the TBM is established as the first step. The performance of the MRE isolator on vibration control of TBM is numerically evaluated. Then a scaled TBM is built for experimental evaluation and a laminated MRE isolator is designed, prototyped according to the requirement of the scaled TBM; its properties are tested by a shaking table, including its current-dependency, frequency-dependency, and amplitude-dependency features. In the end, the MRE is installed on the scaled TBM platform to evaluate its vibration reduction effectiveness. The experimental test results demonstrate that the displacement amplitude of the TBM vibration could be reduced by up to 20.18% and 14.52% under harmonic sweep excitation and nonsynchronous excitation, respectively.