• 한국소음진동공학회논문집
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• 제24권2호
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• pp.131-138
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• 2014

Vibration measurement of rotating shafts by installing sensors such as accelerometers or displacement sensors is costly and dangerous in some cases. As an alternative method, vibration measurement using camera images has been researched because sensor installation is not needed and displacement of a rotating shaft can be directly evaluated. This paper also suggests the enhanced technique applicable to the measurement of vibration of a large-scale rotating shaft. The concurrent methods based on camera images use marks, which are hardly applicable to rotating shafts. The proposed method measures vibration without any marks by evaluating shape errors. The working principle of the method is described and verified by a series of experiments.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2004년도 춘계학술대회논문집
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• pp.912-918
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• 2004

Main vibration problems of a transaxle type forklift truck are caused by the resonance of engine excitation force and natural mode shade of major components such as engine-mount system, mast, and main frame. But, it is well known that the reduction of vibration is very difficult because of the limitation of structural modifications. In this paper, the vibration characteristics of engine-mast system including engine mount were firstly identified by the experimental and simplified numerical methods. And also, the free and forced vibration characteristics of a whole forklift truck were surveyed with modal test and ODS(operation deflection shape) measurement. Based on these results, the reliable finite element model was developed. Finally, various countermeasures were considered and applied to a real forklift truck and then its effects were confirmed.

• Structural Engineering and Mechanics
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• 제53권2호
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• pp.297-309
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• 2015

The purpose of this work is to analyze the effect of structure parameter disturbance on the dynamic characteristics of a hydropower station powerhouse. A vibration model with a head-cover system is established, and then the general disturbance problem analysis methods are discussed. Two new formulae based on two types of disturbances are developed from existing methods. The correctness and feasibility of these two formulae are validated by analyzing the hydropower station powerhouse vibration model. The appropriate calculation method for disturbance of the hydropower station powerhouse vibration dynamic characteristics is derived.

• Structural Engineering and Mechanics
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• 제18권2호
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• pp.231-246
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• 2004

In this paper, a comparison of various random vibration and deterministic dynamic analyses of cable-stayed bridges subjected to asynchronous ground motion is presented. Different random vibration methods are included to determine the dynamic behaviour of a cable-stayed bridge for various ground motion wave velocities. As a numerical example the Jindo Bridge located in South Korea is chosen and a 413 DOF mathematical model is employed for this bridge. The results obtained from a spectral analysis approach are compared with those of two random vibration based response spectrum methods and a deterministic method. The analyses suggest that the structural responses usually show important amplifications depending on the decreasing ground motion wave velocities.

• 한국정밀공학회지
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• 제25권4호
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• pp.39-46
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• 2008

• 터널과지하공간
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• 제28권6호
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• pp.547-554
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• 2018

크라우드소싱을 활용한 센서 자료 수집은 기존의 방식으로 얻기 어려운 고밀도 지반 진동 정보의 수집이 가능하다. 본 연구에서는 스마트폰과 같은 소형 전자기기에 탑재된 MEMS 센서를 활용한 크라우드소싱 방식 지반 진동 수집 시스템을 개발하였으며, 이를 위한 기반 체계 설계 및 클라이언트와 서버에 대한 구현을 수행하였다. 해당 시스템은 Android 기반의 스마트폰이나 Android Things 기반의 고정식 장비를 통해 진동 데이터를 신속히 수집하면서 하드웨어의 전력 및 데이터 사용량을 최소화할 수 있도록 설계되었다.

• Smart Structures and Systems
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• 제32권1호
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• pp.61-81
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• 2023

This study presents an ensemble learning based Bayesian model updating approach for structural damage diagnosis. In the developed framework, the structure is initially decomposed into a set of substructures. The autoregressive moving average (ARMAX) model is established first for structural damage localization based structural motion equation. The wavelet packet decomposition is utilized to extract the damage-sensitive node energy in different frequency bands for constructing structural surrogate models. Four methods, including Kriging predictor (KRG), radial basis function neural network (RBFNN), support vector regression (SVR), and multivariate adaptive regression splines (MARS), are selected as candidate structural surrogate models. These models are then resampled by bootstrapping and combined to obtain an ensemble model by probabilistic ensemble. Meanwhile, the maximum entropy principal is adopted to search for new design points for sample space updating, yielding a more robust ensemble model. Through the iterations, a framework of surrogate ensemble learning based model updating with high model construction efficiency and accuracy is proposed. The specificities of the method are discussed and investigated in a case study.

• 대한인간공학회지
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• 제32권4호
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• pp.309-319
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• 2013

Objective: The aim of this study is to review and summarize human vibration measurement process, and necessity and methods of frequency weightings for human vibration. Background: Prolonged human exposure to hand-arm vibration and whole-body vibration can result in a range of adverse conditions and the development of occupational diseases such as vibration white finger. For preventing these adverse effects, it is important to correctly apply human vibration measurement process. Method: This manuscript was based on the review and summary of mechanical and human vibration relevant texts, academic papers, materials obtained through web surfing. Results: This manuscript summarizes human vibration measurement process described in ISO standards and relevant texts. The sensitivity of the human body to mechanical vibration is known to be dependent on both the frequency and direction of vibration. To take this into account, varying frequency weighting functions have been developed, and RMS frequency-weighted accelerations are used as the most important quantity to evaluate the effects of vibration on health. ISO provided nine frequency weighting functions in the form of curves and tables. Researches on frequency weightings are focused on development and validation of new frequency weightings to truly reflect the relationship between vibration exposure and its adverse effects. Application: This would be useful information for systematically applying human vibration measurement and analysis process, and for selecting appropriate frequency weighting functions.

• Smart Structures and Systems
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• 제7권5호
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• pp.393-416
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• 2011

Hybrid acceleration-impedance sensor nodes on Imote2-platform are designed for damage monitoring in steel girder connections. Thus, the feasibility of the sensor nodes is examined about its performance for vibration-based global monitoring and impedance-based local monitoring in the structural systems. To achieve the objective, the following approaches are implemented. First, a damage monitoring scheme is described in parallel with global vibration-based methods and local impedance-based methods. Second, multi-scale sensor nodes that enable combined acceleration-impedance monitoring are described on the design of hardware components and embedded software to operate. Third, the performances of the multi-scale sensor nodes are experimentally evaluated from damage monitoring in a lab-scaled steel girder with bolted connection joints.

• Structural Engineering and Mechanics
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• 제21권6호
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• pp.635-658
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• 2005

The possibility of detecting a crack in L-shaped pipes filled with fluid based on measurement of transverse natural frequencies is examined. The problem is solved by representing the crack by a massless rotational spring, simulating the out-of-plane transverse vibration only without solving the coupled torsional vibration and using the transfer matrix method for solution of the governing equation. The theoretical solutions are verified by experiments. The cracks considered are external, circumferentially oriented and have straight front. Pipes made of aluminium and mild steel are tested with water as internal fluid. Crack size to pipe thickness ratio ranging from 0.20 to 0.57 and fluid (gauge) pressure in the range of 0 to 10 atmospheres are examined. The rotational spring stiffness is obtained by an inverse vibration analysis and deflection method. The details of the two methods are given. The results by the two methods are presented graphically and show good agreement. Crack locations are also determined by the inverse analysis. The maximum absolute error in the location is 13.80%. Experimentally determined variation of rotational spring stiffness with ratio of crack size to thickness is utilized to predict the crack sizes. The maximum absolute errors in prediction of crack size are 17.24% and 16.90% for aluminium and mild steel pipes respectively.