• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2013.10a
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• pp.862-867
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• 2013

Torsional interaction between electrical network phenomena and turbine-generator shaft cause torsional stress on turbine-generator shaft and torsional fatigue fracture on vulnerable component, but the prediction of the torsional stress is difficult because the torsional stress is occurred instantly and randomly. Therefore continuous monitoring of the torsional stress on turbine-generator shaft is necessary to predict the torsional fatigue, but installing the sensors on the surface of the shaft directly to monitor the stress is impossible practically. In this study torsional vibration was measured using magnetic sensor at a point of turbine-generator rotor kit, the torsional stress of whole train of rotor kit was calculated using rotor kit's stress model and the calculated results were verified in comparison with the measured results using strain gauge at several point of turbine-generator rotor kit. It is expected that these experiment results will be used effectively to calculate the torsional stress of whole train of turbine-generator rotor in power plants.

• Wind and Structures
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• v.32 no.1
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• pp.11-17
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• 2021

In recent years, there has been a tendency towards renewable energy sources considering the damages caused by non-renewable energy resources to nature and humans. One of the renewable energy sources is wind and energy is obtained with the help of wind turbines. To determine the behavior of wind turbines under earthquake loads, dynamic characteristics are required. In this study, the differential transformation method is proposed to determine the free vibration analysis of wind turbines with a variable cross-section. The wind turbine is modeled as an equivalent variable continuous flexural beam and blade weight is considered as a point mass at the top of the structures. The differential equation representing the free vibration of the wind turbine is transformed into an algebraic equation with the help of differential transformation method and the angular frequencies and the mode shapes of the wind turbine are obtained by the help of the differential transformation method. In the study, a sample taken from the literature was solved with the presented method and the suitability of the method was investigated. The same wind turbine example also modeled by finite element modelling software, ABAQUS. Results of the finite element model and differential transformation method are compared with each other and the results are in good agreement.

• Journal of the Microelectronics and Packaging Society
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• v.31 no.2
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• pp.45-53
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• 2024

The maintenance of semiconductor equipment is crucial for the continuous growth of the semiconductor market. System management is imperative given the anticipated increase in the capacity and complexity of industrial equipment. Ensuring optimal operation of manufacturing processes is essential to maintaining a steady supply of numerous parts. Particularly, monitoring the status of substrate transfer robots, which play a central role in these processes, is crucial. Diagnosing failures of their major components is vital for preventive maintenance. Fault diagnosis methods can be broadly categorized into physics-based and data-driven approaches. This study focuses on data-driven fault diagnosis methods due to the limitations of physics-based approaches. We propose a methodology for data acquisition and preprocessing for robot fault diagnosis. Data is gathered from vibration sensors, and the data preprocessing method is applied to the vibration signals. Subsequently, the dataset is trained using Gradient Tree-based XGBoost machine learning classification algorithms. The effectiveness of the proposed model is validated through performance evaluation metrics, including accuracy, F1 score, and confusion matrix. The XGBoost classifiers achieve an accuracy of approximately 92.76% and an equivalent F1 score. ROC curves indicate exceptional performance in class discrimination, with 100% discrimination for the normal class and 98% discrimination for abnormal classes.

• Journal of KSNVE
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• v.7 no.2
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• pp.231-238
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• 1997

An automated scanning laser Doppler vibrometer (LDV) has been designed, and built to measure in-plane vibration fields over structures. Use of optical fibers allows the compact design of a laser probe head which can be scanned over the vibrating structures. An algorithm for automated self-alignment of the laser probe is developed. The system is completely automated for scanning over the structures, focusing two laser beams at each data point until the detected vibration signal is stable, and for recording and transferring the data to a system computer. The automated system allows one to get extensive data of the vibration field over the structures. The system is tested by scanning a piezoelectric cylindrical shell and a plate excited by a continuous signal and by a pulse signal, respectively. Results show that the automated scanning LDV system can be a useful tool to measure the in-plane vibration field and to detect the elastic waves propagating on the vibrating structures.

• Structural Engineering and Mechanics
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• v.72 no.2
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• pp.169-180
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• 2019

The underlying mechanism of the wind-induced vibration of the hangers of the suspension bridges is still not fully understood at present and hence is comprehensively examined in this study. More specifically, a series of field measurements on the No. 2 hanger of the Xihoumen Bridge was first carefully conducted. Large amplitude vibrations of the hanger were found and the oscillation amplitude of the leeward cable was obviously larger than that of the windward cables. Furthermore, the trajectory of the leeward cable was close to an ellipse, which agreed well with the major characteristics of wake-induced vibration. Then, a theoretical model for the wake-induced vibration based on a 3-D continuous cable was established. To obtain the responses of the leeward cable, the finite difference method (FDM) was adopted to numerically solve the established motion equation. Finally, numerical simulations by using the structural parameters of the No. 2 hanger of the Xihoumen Bridge were carried out within the spatial range of $4{\leq}X{\leq}10$ and $0{\leq}Y{\leq}4$ with a uniform interval of ${\Delta}X={\Delta}Y=0.25$. The results obtained from numerical simulations agreed well with the main features obtained from the field observations on the Xihoumen Bridge. This observation indicates that the wake-induced vibration might be one of the reasons for the hanger oscillation of the suspension bridge. In addition, the effects of damping ratio and windward cable movement on the wake-induced vibration of the leeward cable were numerically investigated.

• Journal of Korean Society of Water and Wastewater
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• v.35 no.5
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• pp.335-349
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• 2021

As the frequency of seismic disasters in Korea has increased rapidly since 2016, interest in systematic maintenance and crisis response technologies for structures has been increasing. A data-based leading management system of Lifeline facilities is important for rapid disaster response. In particular, the water supply network, one of the major Lifeline facilities, must be operated by a systematic maintenance and emergency response system for stable water supply. As one of the methods for this, the importance of the structural health monitoring(SHM) technology has emerged as the recent continuous development of sensor and signal processing technology. Among the various types of SHM, because all machines generate vibration, research and application on the efficiency of a vibration-based SHM are expanding. This paper reviews a vibration-based pipeline SHM system for seismic disaster response of water supply pipelines including types of vibration sensors, the current status of vibration signal processing technology and domestic major research on structural pipeline health monitoring, additionally with application plan for existing pipeline operation system.

• Structural Engineering and Mechanics
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• v.71 no.4
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• pp.391-405
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• 2019

Compared to the ambient vibration test mainly identifying the structural modal parameters, such as frequency, damping and mode shapes, the impact testing, which benefits from measuring both impacting forces and structural responses, has the merit to identify not only the structural modal parameters but also more detailed structural parameters, in particular flexibility. However, in traditional impact tests, an impacting hammer or artificial excitation device is employed, which restricts the efficiency of tests on various bridge structures. To resolve this problem, we propose a new method whereby a moving vehicle is taken as a continuous exciter and develop a corresponding flexibility identification theory, in which the continuous wheel forces induced by the moving vehicle is considered as structural input and the acceleration response of the bridge as the output, thus a structural flexibility matrix can be identified and then structural deflections of the bridge under arbitrary static loads can be predicted. The proposed method is more convenient, time-saving and cost-effective compared with traditional impact tests. However, because the proposed test produces a spatially continuous force while classical impact forces are spatially discrete, a new flexibility identification theory is required, and a novel structural identification method involving with equivalent load distribution, the enhanced Frequency Response Function (eFRFs) construction and modal scaling factor identification is proposed to make use of the continuous excitation force to identify the basic modal parameters as well as the structural flexibility. Laboratory and numerical examples are given, which validate the effectiveness of the proposed method. Furthermore, parametric analysis including road roughness, vehicle speed, vehicle weight, vehicle's stiffness and damping are conducted and the results obtained demonstrate that the developed method has strong robustness except that the relative error increases with the increase of measurement noise.

• Tunnel and Underground Space
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• v.28 no.5
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• pp.457-475
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• 2018

For increase of reality in numerical analysis, a blasting vibration waveform obtained from field blast operations has been directly used for input parameters of dynamic analysis in the form of vibration velocity. A numerical model was built considering the geological characteristics of underground limestone opening as well as the mining stages in this opening, and the effect of blast operations on stability of underground limestone opening was investigated by dynamic numerical analysis. The adequacy of applying the real vibration waveform to dynamic analysis has been approved from the preliminary analysis, and the dynamic numerical analysis results show that the continuous mining operation can cause the collapse of roof in openings and the active yield zone around openings. Therefore, the additional reinforcements should be applied for ensuring the stability of underground limestone openings.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.42 no.4
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• pp.1-7
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• 2019

The customer of massage chair is expanding day by day from middle age to all ages. In 2018, the market size was 700 billion KRW, an increase of 30 times over 10 years. However, most related SMEs suffer from excessive competition by the market monopoly of some major companies. In this situation, in order for a related company to survive, it is necessary to steadily research and develop new products. Founded in 2009, company L produces massage chairs for health and relaxation of customers. L's products use a sound wave vibration module that is favorable for human body, unlike other products that use vibration motor type. However, frequent breakdowns of massage chair due to the vulnerability of plate (leaf) springs, which play an important role in sound wave vibration modules, made sap its competitiveness. In this paper, we propose a method to design desirable plate spring structure by sequentially experimenting with five different plate springs. The results of this study are expected to contribute to improve the quality of plate spring and the reliability of sound wave vibration module. In the future, it is necessary to find a way to use it in the development of foot massage or scalp management device as well as continuous research to find optimal plate spring structure through various analysis.

• Wind and Structures
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• v.19 no.4
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• pp.443-465
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• 2014

Hyperbolic thin-shell cooling towers have complicated vibration modes, and are very sensitive to the effects of group towers and wind-induced vibrations. Traditional aero-elastic models of cooling towers are usually designed based on the method of stiffness simulation by continuous medium thin shell materials. However, the method has some shortages in actual engineering applications, so the so-called "equivalent beam-net design method" of aero-elastic models of cooling towers is proposed in the paper and an aero-elastic model with a proportion of 1: 200 based on the method above with integrated pressure measurements and vibration measurements has been designed and carried out in TJ-3 wind tunnel of Tongji university. According to the wind tunnel test, this paper discusses the impacts of self-excited force effect on the surface wind pressure of a large-scale cooling tower and the results show that the impact of self-excited force on the distribution characteristics of average surface wind pressure is very small, but the impact on the form of distribution and numerical value of fluctuating wind pressure is relatively large. Combing with the Complete Quadratic Combination method (hereafter referred to as CQC method), the paper further studies the numerical sizes and distribution characteristics of background components, resonant components, cross-term components and total fluctuating wind-induced vibration responses of some typical nodes which indicate that the resonance response is dominant in the fluctuating wind-induced vibration response and cross-term components are not negligible for wind-induced vibration responses of super-large cooling towers.