• Geotechnical Engineering
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• v.7 no.3
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• pp.5-20
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• 1991

동하중을 받는 진동기계기초의 동적해석을 수행하기 위해서는 지반의 임피던스함수의 적절한 산 출이 필수적이며, 회전기계 -기초 -지반의 상호작용이 고려된 동적해석이 요구된다. 이제까지 지 반의 임퍼던스함수는 주로 원형기초에 한하여 제시되어 왔으나, 기초의 형상은 실제로 지반의 임퍼 던스함수에 중요한 역할을 한다. 그러므로 본 연구에서는 여러가지 형상 및 매립된 기초에 적용할 수 있는 임퍼던스함수를 제시하였다. 그리고, 제시된 임퍼던스함수를 바탕으로, 회전기계 -기초- 지반의 상호작용이 고려된 동적해석을 수행할 수 있는 프로그램을 개발하였으며, 개발된 프로그램 을 이용하여 예제해석을 통하여 각종 임피던스함수의 적용에 따른 기계기초의 응답을 비교 검토하였다. 본 연구의 주된 결론은 다음과 같이 요약할 수 있다. 1) 주파수독립 임퍼던스함수와 주파수종속 임피던스함수를 이용한 결과를 비교해 볼 때,수평방 향과 회전방향에 대해서는 동적응답이 커다란 차이를 보이지 않으나, 연직방향 운동에 대해서는 상 당한 차이를 보인다. 2) 표면기초와 매립기초를 비교해 본 결과, 매립기초에 있어서 수평방향과 회전방향에 있어서는 동적응답이 거의 일정한 간에 도달하므로 기초가 어느 정도 매립된다면 안전측에 들어간다고 볼 수 있다. 그러나, 연직방향에 있어서는 매립여부에 따라 상당한 차이를 보인다.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.20 no.3
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• pp.960-967
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• 1996

Directional frequency response functions(dFRFs) are introduced for isotropic rotating disks, treating pairs of excitations and measurements as the complex input and output, respectively. It is shown that the dFRFs can be effectively used for separation of the forward and backward travelling wave modes and identification of the diametrical node numbers associated with modes of interst. Numerical simuations and experimental works are performed to demonstrate the analytical development and its validity.

• Journal of the Korea Convergence Society
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• v.12 no.1
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• pp.205-210
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• 2021

In this study, I studied how to generate input values to achieve the same value as the target value. The general procedures are explained to regenerate the excitation input, which is made by using the frequency response function between input-output. In this study, a mount model connected by a bushing was used as a numerical model. The response value for the excitation input was compared with the target value. The excitation input was corrected to obtain the same response as the target value. Through the iterative process, the reconstructed input value was obtained to have the same response as the test.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.35 no.8
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• pp.726-734
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• 2007

구조물에 손상이 발생하면 구조물의 강성변화로 구조물의 고유진동수에 변화가 발생하게 된다. 실험을 통해 얻을 수 있는 손상 전 구조물의 고유진동수와 해석적 방법을 사용하여 구하는 고유진동수가 같다고 가정하고 해석적인 방법으로 손상전후 고유진동수비를 구하여 3차원 그래프로 표시하였다. 손상이 한 부위에 존재할 경우 진동실험으로 구한 고유진동수비를 고유진동수비 그래프와 비교하여 손상의 위치, 크기 및 방향을 알 수 있었으나 여러 지점에 손상이 발생할 경우에는 손상을 파악하기 위해 고유진동수비 그래프 외에 주파수 응답함수를 병행하여 사용하였다.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2004.05a
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• pp.681-686
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• 2004

Identification of asymmetry and anisotropy of rotor system is important for diagnosis of rotating machinery. Directional frequency response functions (dFRFs) are known to be powerful tool in effectively detecting the presence of asymmetry or anisotropy. In this paper, an estimation method of dFRFs for rotors is newly developed, when both asymmetry and anisotropy are present. The method transforms the finite degrees-of-freedom time-varying linear differential equation of motion to an infinite degree-of-freedom time-invariant linear one, employing the modulated coordinates. The validity of the method is demonstrated by numerical simulation with a simple rotor model.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2008.04a
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• pp.735-741
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• 2008

Identification of asymmetry and anisotropy of rotor system is important for diagnosis of rotating machinery. Directional frequency response functions (dFRFs) are known to be a powerful tool in effectively detecting the presence of asymmetry or anisotropy. In this paper, an input noise effect of dFRFs for rotors is estimated, when both asymmetry and anisotropy are present. The normalized random errors of the dFRFs are calculated to verify the validity of the method, which is demonstrated by numerical simulation with a simple rotor model.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.05a
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• pp.941-944
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• 2005

Asymmetry of rotor systems is an important factor for identification of dynamic characteristics including the stability and response of rotors and for condition monitoring. In this work, asymmetry of rotors is identified by applying curve-fitting method to the directional frequency response functions (dFRFs), which are known as a powerful tool for detecting the presence and degree of asymmetry. This method minimizes least square error between analytical and measured dFRFs by iteratively updating physical parameters associated with rotor asymmetry. The effectiveness of the identification method is demonstrated by experiments with a laboratory test rotor.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.16 no.5
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• pp.434-444
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• 1991

An improved 2-D quadrature polar separable (QPS) filter and its applications to texture processing are discussed in thie paper. The frequency response of the filter consists of two independent parts. The first is a radial weighting function based on the prolate spheridal sequence(PSS). The second is the same orientational function of the angle as in the Knutsson filter. The new filter is suboptimal in the energy loss because we let the polar angle function approximate the radial weighting function as in the 2-D Cartesian filter composed of two PSS's. It is easy to control as it depends only upon the design specification of the bandwidth, the drectional agnle, and the central freqneucy. Also the filter is circularly more symmetric in the frequency domain than the Knutsson filter. In order to estimate the orientation and the frequency component of loca textures in the frequency domain, some applications of the new filter, such as the generation of synthetic textures, the estimation of texture orientations, and texture segementations, are discussed.

• The Journal of the Acoustical Society of Korea
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• v.24 no.7
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• pp.371-378
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• 2005

The objective or this paper is to measure the in-plane vibration intensity of a beam with a damped end that means the magnitude and direction of vibration power. Three experimental methods have been implemented to measure the in-plane vibration intensity over the beam. The first method is the accelerometer array method using two accelerometers. The second method is the frequency response function method using the only one accelerometer. The third method is the reference accelerometer method using a fixed reference accelerometer and another moving accelerometer. Those methods have been used to measure the spatial distribution of in-plane vibration intensity over the beam. The results obtained with those methods have been compared with each other. The results have been compared with an input power. It showed that the frequency response function method and the reference accelerometer method as well as the accelerometer array method can be effectively used to measure the in-plane vibration intensity in beams.

• The Journal of the Korea institute of electronic communication sciences
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• v.5 no.6
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• pp.581-587
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• 2010

In this study, we investigated the effect of the simplification for low frequency region in Head-Related Transfer Function(HRTF) on the sound localization. For this purpose, HRTF was measured and analyzed. The result in the standard deviation of HRTF showed that the directional dependence of low frequency was smaller than that of high frequency region, which means the possibility of simplification in the low frequency region. Simplification was performed by flattening of the low frequency amplitude characteristics with the insertion of the high-pass filter, whose cutoff frequency is given by boundary frequency. Auditory experiments were performed to evaluate the simplified HRTF. The result showed that direction perception was not influenced by the simplification of the frequency characteristics of HRTF for the error of sound localization. The rate of confusion for the front and back was not affected by the simplification of the frequency characteristics within 1kHz of HRTF. Finally, we made it clear that the sound localization was not affected by the simplification of frequency characteristics of HRTF within 1kHz. The result is expected to be utilized to reduce the size of speech information with no deterioration of the directional characteristics of the speech signal.