• Proceedings of the Korean Institute of Communication Sciences Conference
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• 1984.10a
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• pp.82-87
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• 1984

A 2-D digital filter with rational frequency response can be expanded into an infinite sequence of filterins operations. Each filtering operation can be implemented by convolution with a Low-order 20D finite-extent impulse response. If a convergence constraint is satisfied, the sequence of estimates will approach the desired output signal. In practice, as the number of iterations is finite, the frequency response implemented by iterative computations is an approximation to the desired rational frequency response.

• Journal of the Korean Society for Precision Engineering
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• v.22 no.8 s.173
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• pp.128-135
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• 2005

This paper presents a scheme for experimentally analyzing bounce, roll and pitch frequencies of major systems of a large truck using a multi-axial road simulator. The excitation input (amplitude and frequency range) fur a frequency response test with the multi-axial road simulator is selected in order that bounce, roll and pitch modes are not coupled each other, the excitation amplitude can be reproduced in a specified excitation frequency range, and tires do not lose contact with posters. Three accelerometers, one gyroscope and four displacement meters are used in the frequency response test using the multi-axial road simulator. The reliability of the presented bounce mode frequency response test scheme is validated by comparing the result from a test using the multi-axial road simulator with the result from a road driving test. The road driving test is performed with velocities of 20km/h and 30km/h, and in an unladen state. The vertical accelerations at the cab and the front axle are measured in the road driving test. The roll and pitch mode frequency response tests are also performed with the presented frequency response test scheme. Roll and pitch frequencies of major systems of a large truck that are hard to acquire from a road driving test are analyzed as well as bounce frequency.

• Journal of Industrial Technology
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• v.16
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• pp.239-245
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• 1996

Modal parameters determine the frequency response characteristics of vibration system or acoustic system. When the two systems are fully coupled, however, coupling changes the vibrational and acoustic model parameters into those of the coupled system. In this case, it is very difficult to obtain the modified model parameters and response characteristics. In this paper, coupling effect is analytically investigated on the natural frequency, mode and frequency response characteristics. The result can be applied to understand and to design the frequency response characteristics of the vehicle passenger compartment.

• Journal of Electrical Engineering and Technology
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• v.1 no.4
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• pp.534-542
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• 2006

This paper presents results of frequency domain spectroscopy (FDS) measurements on oil-impregnated pressboard insulation, their analyses and use of the data for modeling high frequency response (FRA) of transformers. The dielectric responses were measured in a broad frequency range, i.e. from 0.1 mHz to 1 MHz, on model samples containing different amount of moisture. The responses were parameterized with terms representing dc conductivity, low frequency dispersion and Cole-Cole polarization mechanisms and they were thereafter used to model the FRA response of a three-phase transformer.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2002.09a
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• pp.35-42
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• 2002

Frequency responses for most of the local seismic sensors in Korea have been roughly checked by mutual comparison of Fourier spectra of seismic records from accelerometer and seismometer, both of which are installed at the same location. Especially, because the frequency content of the seismic energy is usually above 1 Hz for local earthquakes, the reliability of low frequency response could have not been evaluated. Fortunately a recent large earthquake, Ms=7.2 on 02/06/29 containing dominant low frequency energy makes it possible to check the low frequency response of the seismic sensors, especially EpiSensor and JC-V100. Considering two types of sensor pairs, (STS-2 and EpiSensor, JC-V100 and EpiSensor), the low frequency response of EpiSensor is confirmed first by comparison with STS-2 which has proved low frequency response. Second, reliable low frequency limit of instrumentally corrected seismic data from JC-V100 data is estimated to be about 0.03 Hz by comparison with EpiSensor data.

• Journal of Korean Association for Spatial Structures
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• v.15 no.2
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• pp.113-120
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• 2015

This study investigate the dynamic response changes of rib dome structure according to property changes of Substructure. Eigenvalue analysis is conducted in first natural frequency of rib dome versus substructure and searched in the dominant mode of horizontal and vertical direction. Resonance frequency by each first natural frequency of the rib dome structure, substructure and total structure is applied for a seismic wave. That is analyzed about maximum displacement response ratio and maximum acceleration response ratio.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.22 no.2
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• pp.458-466
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• 1998

In this work, a frequency domain method is tested numerically and experimentally to improve nonlinear model parameters using the frequency response function at the nonlinear element connected point of structure. This method extends the force-state mapping technique, which fits the nonlinear element forces with time domain response data, into frequency domain manipulations. The force-state mapping method in the time domain has limitations when applying to complex real structures because it needd a time domain lumped parameter model. On the other hand, the frequency domain method is relatively easily applicable to a complex real structure having nonlinear elements since it uses the frequency response function of each substurcture. Since this mehtod is performed in frequency domain, the number of equations required to identify the unknown parameters can be easily increased as many as it needed, just by not only varying excitation amplitude bot also selecting excitation frequency domain method has some advantages over the classical force-state mapping technique in the number of data points needed in curve fit and the sensitivity to response noise.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.41 no.10
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• pp.905-913
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• 2017

In this work, a method of size optimization is proposed to maximize the natural frequency of a rod that consists of a hidden shape in one part and an exposed shape in the other. The frequency response function of a rod composed of two parts is predicted by using the frequency response functions of each of the parts instead of the shapes of the parts. The mass and stiffness matrices of the rod are obtained by using the mass and stiffness matrices of the equivalent vibration systems, which are obtained by applying the experimental modal analysis method to the frequency response functions of the parts. Through several numerical examples, the frequency response function obtained by using the proposed method is compared with that of a rod to validate the prediction method based on equivalent vibration systems. A size optimization problem is formulated for maximizing the first natural frequency of a combined rod, which is replaced with an equivalent vibration system, and a rod structure is optimized by using an optimization algorithm.

• Journal of Electrical Engineering and Technology
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• v.3 no.4
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• pp.499-508
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• 2008

Frequency regulation in off-normal conditions has been an important problem in electric power system design/operation and is becoming much more significant today due to the increasing size, changing structure and complexity of interconnected power systems. Increasing economic pressures for power system efficiency and reliability have led to a requirement for maintaining power system frequency closer to nominal value. This paper presents a decentralized frequency control framework using a modified low-order frequency response model containing a proportional-integral(PI) controller. The proposed framework is suitable for near-normal and emergency operating conditions. An $H_{\infty}$ control technique is applied to achieve optimal PI parameters, and an analytic approach is used to analyse the system frequency response for wide area operating conditions. Time-domain simulations with a multi-area power system example show that the simulated results agree with those predicted analytically.

• The Korean Journal of Ecology
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• v.25 no.1
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• pp.25-28
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• 2002

The advertisement call of anurans functions to attract potential mates. The dominant frequency of an advertisement call is generally getting lower with increased snout-vent length (SVL) of the caller Rana rugosa has an advertisement call tilth a particularly high frequency modulation. We conducted a playback experiment to verify the function of frequency modulation, and investigated the territorial behavior of the frog. The frog has five types of territory defense strategy. Strategy choice depended on the caller's SVL. Small males became satellites or lowered the dominant frequency of their advertisement call, whereas large males actively defended their territory with encounter calls. In response to high frequency (1107 Hz) playback, the frogs lowered their advertisement call frequency, and towered them further in response to the low frequency (1028 Hz) playback. In addition, the number of pulses in a call was increased in response to the playback. These results indicate that the frog avoids physical conflict with competitors by selecting a territory defense strategy suitable for the caller's size, and by lowering its call frequency to disguise its SVL.