• 한국해양공학회지
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• 제21권5호
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• pp.55-60
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• 2007

Bellows are mechanical components which prevent the damage of system by absorption of the vibration and the displacement of axle and radial direction. Thermal piping system is expanded by the fluid of the high temperature from the heat engine inside. At this time, bellows prevent the damage of the piping due to the thermal expansion. Recently, design of bellows is required to fit some other operational environments which are not suggested in the E.J.M.A code book. And it is difficult to produce and to maintain bellows of high temperature and high pressure bemuse of its complicated shape and this causes the manufacturing cost to rise. The objective of this study is to determine optimum shape of bellows which can endure in the high temperature and high pressure. The maximum stress has an effect on the fatigue life of bellows, therefore it needs to be minimized. This study attempts to find a shape which minimizes the stress occurring in the bellows by the design of experiment. The model used in this study is not presented in the E.J.M.A code book, therefore, from the result of design of experiment we find the factors which give effects on the characteristic value and we presents the recession model using the RSM, which can predict the characteristic values depending on the change of factor values.

• 한국음향학회:학술대회논문집
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• 한국음향학회 1999년도 학술발표대회 논문집 제18권 1호
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• pp.263-268
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• 1999

Psychoacoustic characteristics of automobile hems influence subject's subjective evaluation and psychophysiological reactions on the sounds of car horns. However, differentiation of physiological responses to commercially availablenfluence subject's subjective evaluation and psychophysiological reactions on the s horns is a complicated task due to the small contrast in technical features of horns and the influence of habituation. Using 10 college students, comparative analysis of physiological reactivity was carried out in order to identify the effect of habituation on decrement of psychophysiological responsivity, assess the ability to differentiate subjectively most and least preferred/appropriate horns according to physiological manifestations. EEG and autonomic responses to 7 automobile horns were analyzed during 3 blocks of trials (each block was varied in order for presenting stimuli and acoustic parameters of horns). It was shown that electrodermal and cardiovascular responses had different reactivity patterns to repeated stimulation. Skin conductance variables (SCL, SCR) were habituated as a function of trial. Cardiac reactivity (HR, RSA) showed no signs of habituation. In contrast, sensitization was shown in the vascular component of response (pulse volume). The temporal EEG exhibited marked habituation of fast beta band power, while alpha-blocking effect did not habituate during the course of experiment. Differentiation of physiological responses of most and least preferred/appropriate horns was possible in this study. That is, some cardiovascular reactivity variables (HR, RSA, pulse volume, etc.) were differentiated between the least and the most preferred/appropriate horns during the experiment. However, EEG and electrodermal parameters showed significant differences only during first block of trials and were later affected by habituation.

• Smart Structures and Systems
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• 제19권4호
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• pp.341-350
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• 2017

Based on the super elastic properties of the shape memory alloy (SMA) and the inverse piezoelectric effect of piezoelectric (PZT) ceramics, a kind of hybrid semi-active control device was designed and made, its mechanical properties test was done under different frequency and different voltage. The local search ability of genetic algorithm is poor, which would fall into the defect of prematurity easily. A kind of adaptive immune memory cloning algorithm(AIMCA) was proposed based on the simulation of clone selection and immune memory process. It can adjust the mutation probability and clone scale adaptively through the way of introducing memory cell and antibody incentive degrees. And performance indicator based on the modal controllable degree was taken as antigen-antibody affinity function, the optimization analysis of damper layout in a space truss structure was done. The structural seismic response was analyzed by applying the neural network prediction model and T-S fuzzy logic. Results show that SMA and PZT friction composite damper has a good energy dissipation capacity and stable performance, the bigger voltage, the better energy dissipation ability. Compared with genetic algorithm, the adaptive immune memory clone algorithm overcomes the problem of prematurity effectively. Besides, it has stronger global searching ability, better population diversity and faster convergence speed, makes the damper has a better arrangement position in structural dampers optimization leading to the better damping effect.

• 한국강구조학회 논문집
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• 제20권6호
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• pp.761-771
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• 2008

열차운행주파수가 철도교의 고유진동수와 일치하면, 철도교의 공진은 피할 수 없다. 또한, 열차가 교량을 매우 빠르게 통과하면, 계측 가능한 시간응답의 샘플 수는 매우 적다. 본 논문은 그러한 경우에 대하여 철도 교량의 동특성을 매우 효과적으로 추출할 수 있는 TDD기법과 SI기법을 소개한다. 열차통과 직후에 교량의 자유진동 시간응답구간의 상호상관을 이용하여 모드형상은 TDD기법으로 추출하고, 고유진동수 및 감쇠비 등의 시간변수들은 SI기법으로 추출한다. 경부고속철도 시스템에 위치한 2경간 강합성교량의 동특성 추출실험을 통하여 TDD기법과 SI기법의 현장 적용성이 검토되었다. 동특성 추정결과는 기존의 ERADC기법의 결과와 비교 검토되었다. 추정결과는 기존의 방법을 이용하여 획득된 결과와 매우 잘 일치한다.

• 한국진공학회지
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• 제12권2호
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• pp.93-104
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• 2003

저진공펌프의 내구성평가와 관련하여 펌프의 성능이나 상태의 저하에 관한 기술적 근거를 확보함으로써 펌프의 운전상태를 진단할 수 있는 기초기술을 확보할 수 있으며, 이는 진공펌프의 기계적 결함 및 성능평가 장치의 동적 응답과 신뢰도 구축에 중점을 두고 신호 분석을 통하여 실험적으로 기계적인 동적 특성을 확인하는 과정을 통하여 수행할 수 있다. 저진공펌프의 압축일에 소요되는 전력을 이론적으로 규명하고 펌프의 압축일을 계산하였으며, 소비전력에 대한 진공펌프의 에너지 효율을 예측하여 펌프 노화에 따르는 소비전력의 증가 원인을 규명하는 자료로 활용할 수 있다. 또한 저진공펌프의 가동 중에 측정한 진동, 압력신호, 배기속도 및 소비전력을 측정하고 분석하여 펌프 운전상태를 감시하는데 매우 유용한 인자가 무엇인지 확인하였으며 추후 연구의 방향과 내구성평가의 기초기술을 확보하였다.

• Tribology and Lubricants
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• 제36권5호
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• pp.279-289
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• 2020

In this paper, a method is proposed for establishing an approximate prediction model of rotor-dynamics through modal testing. In particular, the proposed method is applicable to systems that cannot be established according to conventional methods owing to the absence of information regarding the dimensions and material of the rotor-bearing system. The proposed method is demonstrated by employing a motor dynamometer driven by a 1 MW class induction motor without dimension and material information. The proposed method comprises a total of seven steps, wherein an initial model is established by incorporating approximate dimensions and material information, and the model is improved on the basis of the natural frequency characteristics of the system. During model improvement, the modification factor is introduced for adjusting the elastic modulus and shear modulus of the system. Analysis of critical speed and imbalance response indicates that the separation margin is 67% and the maximum vibration amplitude is less than the amplitude limit of 0.032 mm under the API 611 standard, which means that the motor dynamometer can stably operate at a rated speed of 1800 rpm. Hence, the obtained results validate the feasibility of the proposed method. Furthermore, for broad usage, it is necessary to accordingly apply and validate the proposed method for various rotor-bearing systems.

• 한국자동차공학회논문집
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• 제19권3호
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• pp.29-37
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• 2011

The modal characteristics of a compressor wheel of an automotive turbocharger have been investigated using an experimental method based on an acoustic frequency response function, p/f(${\omega}$), where p is sound pressure radiated from a structure, and f is impact force. First, a well-defined annular disc with narrow radial slots was examined to check whether the vibro-acoustic test could precisely determine natural quencies and vibration modes of structures showing that the vibro-acoustic test proposed in this paper was comparable to the conventional modal test with an accelerometer and the numerical analysis. The conventional method has been found to be inappropriate for compressor wheel because of additional mass due to the accelerometer and additional damping from the accelerometer cable alter the dynamic responses of the wheel blades. odal characteristics of the wheel have been defined using vibro-acoustic test and verified with the results from another conventional method using a laser vibrometer. Natural quencies and mode shapes of a turbocharger wheel, which can't be precisely obtained with onventional method, could be defined accurately without the additional effects from sensor and cable. Proposed method can be applied to small structures where conventional sensors and cables could generate troubles.

• 한국전산구조공학회논문집
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• 제30권4호
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• pp.319-327
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• 2017

본 연구에서는 콘크리트 석션식 지지구조물을 사용한 해상풍력발전시스템의 지진응답 해석을 수행하여 그 거동 특성을 파악한다. 전체 시스템을 RNA, 타워, 지지구조물로 구성된 구조계와 이에 접하고 있는 유체 및 지반의 부분구조로 분리하여 운동방정식을 유도한다. 구조계에 작용하는 유체의 동수압과 지반의 상호작용력을 산정하고, 이를 구조계의 운동방정식과 결합하여 전체 시스템의 지배방정식을 도출한 후, 이 방정식의 해를 구하여 해상풍력발전시스템의 지진응답을 계산한다. 해석 결과로부터 지반-구조물 상호작용은 콘크리트 석션식 지지구조물에 의해 지지된 해상풍력발전시스템의 지진응답을 크게 증가시킬 수 있음을 확인할 수 있다. 특히, 지반의 유연성으로 인해 시스템의 고차 고유모드 응답이 증가할 수 있으므로, 해상풍력발전시스템의 동적거동 산정 시에는 반드시 지반-구조물 상호작용의 효과를 고려하여야 할 것이다.

• Smart Structures and Systems
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• 제15권3호
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• pp.717-733
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• 2015

Modal parameters of a structure are commonly used quantities for system identification and damage detection. With a limited number of studies on the statistics assessment of modal parameters, this paper presents procedures to properly account for the uncertainties present in the process of extracting modal parameters. Particularly, this paper focuses on how to deal with the measurement error in an ambient vibration test and the modeling error resulting from a modal parameter extraction process. A bootstrap approach is adopted, when an ensemble of a limited number of noised time-history response recordings is available. To estimate the modeling error associated with the extraction process, a model prediction expansion approach is adopted where the modeling error is considered as an "adjustment" to the prediction obtained from the extraction process. The proposed procedures can be further incorporated into the probabilistic analysis of applications where the modal parameters are used. This study considers the effects of the measurement and modeling errors and can provide guidance in allocating resources to improve the estimation accuracy of the modal data. As an illustration, the proposed procedures are applied to extract the modal data of a damaged beam, and the extracted modal data are used to detect potential damage locations using a damage detection method. It is shown that the variability in the modal parameters can be considered to be quite low due to the measurement and modeling errors; however, this low variability has a significant impact on the damage detection results for the studied beam.

• Wind and Structures
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• 제10권3호
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• pp.233-247
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• 2007

The insertion of steel braces has become a common technique to limit the deformability of steel framed buildings subjected to wind loads. However, when this technique is inadequate to keep floor accelerations within acceptable levels of human comfort, dampers placed in series with the steel braces can be adopted. To check the effectiveness of braces equipped with viscoelastic (VEDs) or friction dampers (FRDs), a numerical investigation is carried out focusing attention on a three-bay fifteen-storey steel framed building with K-braces. More precisely, three alternative structural solutions are examined for the purpose of controlling wind-induced vibrations: the insertion of additional diagonal braces; the insertion of additional diagonal braces equipped with dampers; the insertion of both additional diagonal braces and dampers supported by the existing K-braces. Additional braces and dampers are designed according to a simplified procedure based on a proportional stiffness criterion. A dynamic analysis is carried out in the time domain using a step-by-step initial-stress-like iterative procedure. Along-wind loads are considered at each storey assuming the time histories of the wind velocity, for a return period $T_r=5$ years, according to an equivalent wind spectrum technique. The behaviour of the structural members, except dampers, is assumed linear elastic. A VED and an FRD are idealized by a six-element generalized model and a bilinear (rigid-plastic) model, respectively. The results show that the structure with damped additional braces can be considered, among those examined, the most effective to control vibrations due to wind, particularly the floor accelerations. Moreover, once the stiffness of the additional braces is selected, the VEDs are slightly more efficient than the FRDs, because they, unlike the FRDs, dissipate energy also for small amplitude vibrations.