• Structural Engineering and Mechanics
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• 제20권3호
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• pp.347-362
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• 2005

The input energy to a base-isolated (BI) building during an earthquake is considered and formulated in the frequency domain. The frequency-domain approach for input energy computation has some notable advantages over the conventional time-domain approach. Sensitivities of the input energy to the BI building are derived with respect to uncertain parameters in the base-isolation system. It is demonstrated that the input energy can be of a compact form via the frequency integration of the product between the input component (Fourier amplitude spectrum of acceleration) and the structural model component (so-called energy transfer function). With the help of this compact form, it is shown that the formulation of earthquake input energy in the frequency domain is essential for deriving the sensitivities of the input energy to the BI building with respect to uncertain parameters. The sensitivity expressions provide us with information on the most unfavorable combination of the uncertain parameters which leads to the maximum energy input.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1999년도 하계학술대회 논문집 B
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• pp.761-763
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• 1999

When the controller designed by the $H{\infty}$ control technique is applied to the object system, sometimes the controller does not satisfy the robust stability and robust performance but only satisfy the nominal performance. In this paper, we derive the region on the frequency response curve of the open-loop transfer function which satisfy the robustness and robust performance of the designed controller. We also derive the region for the suitableness of the weighting function on the frequency response curve of the weighting function. We showed that the robust stability and the robust performance of the $H{\infty}$ optimal control)or by applying the designed controller on an electromechanical actuator system could be improved by determining parameter ${\gamma}$ and weighting function gain ${\alpha}$ using the derived region.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2002년도 추계학술대회논문집
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• pp.122-127
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• 2002

A frequency-domain PES estimation and its prediction method are proposed for the tightly-coupled servo/mechanical design of high-TPI HDD system above 100 kTPI. The major two disturbance energies which are related with mechanical vibrations inside of HDD are used to predict the drive-level PES, while considering closed-loop servo dynamics. One is the torque disturbance which mainly comes from aerodynamic excitation of HSA system and the other is the displacement disturbance from disk-spindle dynamics. In order to obtain the accurate error transfer function of closed-loop servo control, the plant model is measured by accurate experiment. The measured PES is compared with predicted one in terms of frequency-domain PES spectrum and its standard variation value. It is proved that the proposed frequency-domain PES estimation/prediction method is capable of predicting drive-level PES of high-TPI hard disk drive.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 추계학술대회논문집A
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• pp.646-653
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• 2001

LQG/LTR Control Methology is recently used for the analysis of multi-variable control in frequency domain. Target filter loop is designed by the demanding requirements such as cross-over frequency, disturbance rejection in low frequency domain, zero steady-state error, identification of maximum and minimum singular values and sensor noise rejection in high frequency domain. Loop transfer recovery is accomplished by solving the cheap control and then simulation close to the target filter loop. In this study, LQG/LTR Control Methodology is applied to the seat suspension system. It is found that this technique is very effective to control the system and improve the ride quality of human body.

• 한국해양공학회지
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• 제15권1호
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• pp.12-18
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• 2001

This study concentrates on the second-order diffraction problem around circular cylinders in multi-frequency waves. The method of solution is a time-domain Rankine panel method which adopts a higher-order approximation for the velocity potential and wave elevation. In the present study, the multiple second-order quadratic transfer functions are extracted from the second-order time signal generated in random waves, and the comparison with other bench-mark test results shows a good agreement. This approach is directly applicable to prediction of nonlinear forces on offshore structures in random ocean.

• 한국산업융합학회 논문집
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• 제23권5호
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• pp.747-756
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• 2020

In recent years, measurement in a smart-phone environment is attracting attention in various fields due to its easy set-up process, various functions, convenience and expandability. Even in the field of safety evaluation and maintenance of large-scale infra-structures, the appropriate application of these effective and convenient measurement techniques can be of great help. In this paper, an experimental study was conducted to investigate the effectiveness, problems and complementary methods of applying smart-phone accelerometers to the measurement in infra-structure such as bridges. In model bridge subjected to impact and moving loads, the measured accelerations using a smart-phone and a professional accelerometer were directly compared in time domain. And the statistical and frequency characteristics of the measured signal and transfer function were also examined in frequency domain. The results show that the accuracy of measurement using smart-phone sensor is primarily affected by its incomplete sampling performance. In conclusion, smart-phone sensors cannot be considered suitable for precise assessment, where measurements must be accurate over a wide frequency range, but we can say that the technique is still useful and fairly accurate for some purpose over a limited frequency range, such as the low pass frequency range, which is a major concern for civil structures.

• Smart Structures and Systems
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• 제23권1호
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• pp.71-79
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• 2019

In general, it may be advantageous to measure the pressure pulsation near a valve to detect a valve defect in a linear compressor. However, the acceleration signals are more advantageous for rapid classification in a mass-production line. This paper deals with the performance improvement of fault classification using only the compressor-shell acceleration signal based on the relation between the refrigerant pressure pulsation and the shell acceleration of the compressor. A transfer function was estimated experimentally to take into account the signal noise ratio between the pressure pulsation of the refrigerant in the suction pipe and the shell acceleration. The shell acceleration signal of the compressor was modified using this transfer function to improve the defect classification performance. The defect classification of the modified signal was evaluated in the acceleration signal in the frequency domain using Fisher's discriminant ratio (FDR). The defect classification method was validated by experimental data. By using the method presented, the classification of valve defects can be performed rapidly and efficiently during mass production.

• Geomechanics and Engineering
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• 제6권6호
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• pp.517-530
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• 2014

Seismic ground response analysis is one of the most important issues in geotechnical earthquake engineering. Conventional seismic site response and free field analysis of layered soils does not consider the effect of surcharge mass which may be present on the top layer. Surcharge mass may develop extra inertial force to the soil and, hence, significantly affect on the results of seismic ground response analysis. Methods of analysis of ground response may also be categorized into time domain and frequency domain concepts. Simplicity in developing analytical relations and accuracy in considering soil dynamic properties dependency to loading frequency are benefits of frequency domain analysis. In this part of the paper, seismic ground response is analyzed using transfer function method for soil layers considering surcharge mass on the top layer. Equation of motion, wave equation, is solved using amended boundary conditions which effectively take the impact of surcharge mass into account. A computer program is developed by MATLAB software based on the solution method developed for wave equation. Layered soils subjected to earthquake loading were numerically studied and solved especially by the computer program developed in this research. Results obtained were compared with those given by DEEP SOIL computer program. Such comparison showed the accuracy of the program developed in this study. Also in this part, the effects of geometrical and mechanical properties of soil layers and especially the impact of surcharge mass on transfer function are investigated using the current approach and the program developed. The efficiency and accuracy of the method developed here is shown through some worked examples and through comparison of the results obtained here with those given by other approaches. Discussions on the results obtained are presented throughout in this part.

• 조명전기설비학회논문지
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• 제22권1호
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• pp.118-123
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• 2008

본 논문은 주파수영역에서 첨두공진점을 갖는 고차모델을 저차모델로 근사화하기 위한 주파수 전달함수 합성법을 제안한다. 제안된 근사화 방법은 근사화된 모델의 분모 다항식에 가중된 오차함수의 최소화에 근거하며, 근사화된 모델의 주파수 전달함수에 대한 계수벡터를 추정하기 위해 RLS 기법을 이용한다. 제안된 방법은 저주파수와 첨두공진점에서 우수한 정합특성을 나타내며, 예제에 의해 제안된 방식의 유용성을 검증한다.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제53권5호
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• pp.248-252
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• 2004

Since DC ground resistance, which is a good index of the performance of a grounding system in low frequency. does not show the performance in transient state. We measured ground impedances in frequency domain ranging from 0.1 Hz to 900 KHz maximum to quantify the transient grounding performance of 4 types of grounding system. Transfer function was derived from the measured frequency-dependant ground impedance of a grounding grid. A simulation has been performed to verify the transfer function using EMTP (Electro-Magnetic Transient Program).