• Proceedings of the Optical Society of Korea Conference
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• 2000.02a
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• pp.12-13
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• 2000

진행파형 광 검출기는 전기적으로 분포된(distributed) 구조이므로, 그 대역폭은 RC 시정수에 의해 제한되기보다는 광 흡수계수와 광과 마이크로파 사이의 진행속도 차에 의해 제한된다$^{(1)(2)}$ . 진행파형 광검출기에서 광과 마이크로파 사이의 속도 부정합이 대역폭에 미치는 영향은 속도 부정합 임펄스 반응(velocity-mismatch impulse response)의 제시를 통해 이미 분석되었다$^{(1)(2)}$ . 그러나, 대역폭에 제한에 큰 영향을 미칠 것이 예상되는 진성 흡수 영역에서의 전송자 표류 시간은 아직 구체적으로 고려되지 않았다. 본 논문에서는 진성 흡수영역에서의 전송자 표류 시간을 고려하였다. 그 전이 시간(transit time)을 고려하기 위해 속도 부정합 임펄스 반응을 수정하여 제시하였다. 새로히 제시된 임펄스 반응은 광 도파로 해석과 진성 영역 분할에 의해 모델화 되었으며, 이 임펄스 반응을 통해 전이 시간과 속도 부정합이 대역폭에 미치는 영향을 살펴보았다. (중략)

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.06a
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• pp.239-245
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• 2000

Adaptive bang-bang control algorithm has been proposed by the authors to improve peak response reduction of building structures under unexpected large earthquake. At the previous research, control performance of the proposed algorithm was experimentally confirmed by using a I-DOF test structure. As an extended research, performance tests on a multi-DOF model structure have been conducted to prove the usefulness of the adaptive bang-bang control algorithm using a hydraulic AMD. It is confirmed that the proposed adaptive bang-bang algorithm is applicable to suppress the vibration of multi-DOF structures subject to severe external excitations.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.06a
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• pp.257-262
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• 2000

This research is concerned with the active vibration control of slewing smart structures subjected to rotating disturbance. When cantilever beam rotates about axes perpendicular to the undeformed beam's longitudinal axis, it experiences inertial loading. Hence, the beam vibrates after the slewing ends. In this paper, the analytical model for a single slewing flexible beam with surface bonded piezoelectric sensor and actuator is developed using the Hamilton's principle with discretization by the assumed mode method. The theoretial model is verified by the experimental open loop frequency response data. The controller is designed for residual vibration suppression after slewing. The designed cotroller is a positive position feedback (PPF) controller for controlling the first mode vibration.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.06a
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• pp.519-524
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• 2000

The types of responses which are generally measured in the modal testing are displacement, velocity or acceleration. In strain modal testing, however, strain responses subject to excitation forces are measured. In this paper, the characteristics of strain modal testing are investigated experimentally. Investigated are the effects of frequency range, excitation force level, and excitation signal on the quality of measured strain frequency response functions. It has been shown that a strain FRF at a point can be predicted from displacement FRFs and strain FRFs at other points.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.06a
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• pp.633-638
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• 2000

This paper reports an example of flow-induced vibration in a very large plant and the whole procedure of reducing the vibration. During the operation of flue gas desurfurization unit of the thermal power plant, serious vibration occurred at all around the unit. The worst vibration was recorded on the heat exchanger surface, which weighed 180 tones, as 17.8 m/$s^2$ in vibration amplitude at 34Hz. To identify the vibration, frequency analysis on the response vibration, the expected excitation force and the system resonance was executed. This investigation revealed that the cause of the vibration was vortex shedding from the circular pipes in the heat exchanger. Vortices from the pipes excited acoustic resonance in the heat exchanger room, which, in turn, made the structure vibrate. Through inserting the baffles between the pipes, which had an effect of cutting the acoustic wave at resonance frequency, the vibration was eliminated dramatically.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.06a
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• pp.531-535
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• 2000

If the displacement of the structure is obtained by integrating the signal from accelorometer and laser, the vibration mode can be examined. This conventional method, however, has the disadvantage of the necessity of multiple accelerometers and many data processing steps such as frequency response function(FRF). In order to get smooth mode shape, we should also use algorithms of cubic spline or others. In this paper, we propose a method which gets the mode shape by using the velocity signal directly obtained from the plane scanning. In this method, we just use coefficients and phases for specific frequency.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.06a
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• pp.571-575
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• 2000

The physical properties of the spatial model, mass, stiffness and damping matrix, can be defined by a specific natural frequency, damping ratio and mode shape. These modal parameters can be determined from a set of frequency response function(FRF) measured by exciting the structure and measuring the responses at various points around the structure. In this paper, The Transfer Matrix is obtained by experimental modal analysis for the 3-story scaled building model which TMD is installed on top and the physical properties of the spatial model is determined using the residue matrix and the location of poles from FRF measurement using polynomial curve fitting methods.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.06a
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• pp.1577-1582
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• 2000

In this study, the experimental modal analysis is performed to investigate the dynamic characteristics of slider-air bearings in hard disk drives. Bump response of the slider is acquired by measuring the relative velocity for two points using the laser interferometer, in which the disk is scratched lightly by a sharp knife to make a bump. From the measurements, the modal parameters of the head slider, modal frequencies and damping ratios of roll and pitch, are estimated by data processing and parameter estimation.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.06a
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• pp.1661-1666
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• 2000

Nowadays, the two microphone method is accepted as the standard as specified in ASTM E1050-90 for measuring in-duct acoustic properties. However, research results on using the least square method with multiple measurement points and broadband excitation have been reported for enhancing the frequency response of the two microphone method. In this paper, the effects of varying the relative measurement positions on errors in the estimation of the acoustic quantities is studied for the multiple microphone method. Both of the theoretical and experimental results show that, among every possible sensor positioning configurations, the equidistant positioning of sensors yields the smallest error within the effective measurement frequency range. In addition, it is noted that the measurement accuracy can be increased and the effective frequency range can be widened by increasing the number of equidistant sensors. Measurement examples are shown and the results support the findings.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.06a
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• pp.972-977
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• 2000

One of the major differences of Korean residential building compared with other countries is a rigid diaphragm of a floor due to the panel heating system. An increment of a gravity floor load might cause vibration problem when the composite floor system is introduced to the panel heating system. Since the noise criteria of a residential building is lower than that of an office building, the development of a noise absorbing system should be preceded. The response evaluation was performed for the finished floor, that is with panel heating and noise absorbing system. The natural frequency was obtained both from an experimental study and an analytical study. An appropriate vibration condition of a floor with panel heating and noise absorbing systems was evaluated from this study.