• 대한전기학회논문지
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• 제31권8호
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• pp.33-38
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• 1982

This paper deals with the simplification of the transfer function in a frequency domain, viz. the integral of the squared errors between the original and the simplified model is minimized and the latter is estimated by the Walsh function. It tries to minimize the errors between the frequency responses of the two functions. This method is compared with the existing method by means of a numercal example. The frequency response of this simplified model approximates closely to that of the original model. The proposed method is simpler in analysis and easier in implementation than the existing methods. Though the Walsh function can be easily generated with the discrete values, it has errors because its zero crossings are not continuous. This method aims at the reduction of the errors in the real parts and the imaginary parts of the two functions by dividing into the more sub-intervals, and selecting the reduced-order model according to the response of the model. As a result, it can be applied for the simplification of higher order functions into lower order functions and for the design of control systems.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2013년도 전력전자학술대회 논문집
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• pp.47-48
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• 2013

In order to evaluate the response of the grid-connected systems, Phase lock technology is widely used in power electronic devices to obtain the phase angle, amplitude, and frequency of the grid voltage because phase locked loop (PLL) algorithms are very important for grid synchronization and monitoring in the grid connected power electronic devices. This paper presents a performance evaluation in tracking grid angular frequency through single phase synchronization techniques which are an enhanced PLL (EPLL), second-order generalized integrator-PLL (SOGI-PLL), and second-order generalized integrator-frequency locked loop (SOGI-FLL). These techniques are properly analyzed through several steps to get the best technique which can track the frequency accurately and smoothly.

• Structural Engineering and Mechanics
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• 제77권3호
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• pp.315-327
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• 2021

Here, in this research we have studied a two dimensional problem in a homogeneous orthotropic magneto-thermoelastic medium with higher order dual-phase-lag heat transfer with combined effects of rotation and hall current in generalized thermoelasticity due to time harmonic sources. As an application the bounding surface is subjected to uniformly distributed and concentrated loads (mechanical and thermal source). Fourier transform technique is used to solve the problem. The expressions for displacement components, stress components and temperature change are derived in frequency domain. Numerical inversion technique has been used to obtain the results in physical domain. The effect of frequency has been depicted with the help of graphs.

• Coupled systems mechanics
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• 제11권4호
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• pp.297-313
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• 2022

The objective of this paper is to study the effect of frequency in a two-dimensional orthotropic thermoelastic rotating solid with fractional order heat transfer in generalized thermoelasticity with two-temperature due to inclined load. As an application the bounding surface is subjected to uniformly and linearly distributed loads (mechanical and thermal source). The problem is solved with the help of Fourier transform. Assuming the disturbances to be harmonically time dependent, the expressions for displacement components, stress components, conductive temperature and temperature change are derived in frequency domain. Numerical inversion technique has been used to determine the results in physical domain. The results are depicted graphically to show the effect of frequency on various components. Some particular cases are also discussed in the present research.

• ETRI Journal
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• 제35권2호
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• pp.218-225
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• 2013

The pull-out frequency of a second-order phase lock loop (PLL) is an important parameter that quantifies the loop's ability to stay frequency locked under abrupt changes in the reference input frequency. In most cases, this must be determined numerically or approximated using asymptotic techniques, both of which require special knowledge, skills, and tools. An approximating formula is derived analytically for computing the pull-out frequency for a second-order Type II PLL that employs a sinusoidal characteristic phase detector. The pull-out frequency of such PLLs can be easily approximated to satisfactory accuracy with this formula using a modern scientific calculator.

• 한국통신학회논문지
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• 제28권12A호
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• pp.1019-1024
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• 2003

본 논문에서는 주파수 체배기를 이용하여 2차, 3차 고조파 신호를 발생시켜 3차, 5차 혼변조 왜곡성분을 개별적으로 선형화 하는 새로운 구조의 전치왜곡 선형화기를 제안하였다. 이 구조는 2체배기를 이용하는 3차 혼변조왜곡신호 제어부와 3체배기를 이용하여 5차 혼변조 왜곡신호 제어부를 포함하여 출력신호들의 합성 및 격리를 위한 Wilkinson 전력합성기로 구성되었다. 제안된 개별차수 조정 전치왜곡 선형화기는 870∼880 MHz대역에서 3차 혼변조 왜곡특성은 약 -l6dB와 5차 혼변조 왜곡특성은 약 -l8dB의 개선효과를 얻었으며 출력전력은 34 dBm/tone이었다.

• Nuclear Engineering and Technology
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• 제53권5호
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• pp.1391-1402
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• 2021

The aim of this work is to prepare a neutron noise calculator based on the second order of average current nodal expansion method (ACNEM). Generally, nodal methods have the ability to fulfill the neutronic analysis with adequate precision using coarse meshes as large as a fuel assembly size. But, for the zeroth order of ACNEM, the accuracy of neutronic simulations may not be sufficient when coarse meshes are employed in the reactor core modeling. In this work, the capability of second order ACNEM is extended for solving the neutron diffusion equation in the frequency domain using coarse meshes. For this purpose, two problems are modeled and checked including a slab reactor and 2D BIBLIS PWR. For validating of results, a semi-analytical solution is utilized for 1D test case, and for 2D problem, the results of both forward and adjoint neutron noise calculations are exploited. Numerical results indicate that by increasing the order of method, the errors of frequency dependent coarse mesh solutions are considerably decreased in comparison to the reference. Accordingly, the accuracy of second order ACNEM can be acceptable for the neutron noise calculations by using coarse meshes in the nuclear reactor core.

• Journal of Advanced Marine Engineering and Technology
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• 제39권2호
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• pp.130-135
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• 2015

Recently, as a result of the application of large and multi-blade propellers with high efficiency for large vessels, the vertical bending stiffness of propulsion shafting system tends to be declined. For some specific vessels, the shaft arrangement leads to the forward stern tube bearing to be omitted, decreasing vertical bending stiffness. In this respect, decreased vertical bending stiffness causes the problem which is the blade order resonance frequency to be placed within the operational rpm range of propulsion shafting system. To verify whirling vibration, the measurement should be carried out covering from operating rpm up to target rpm, however, the range is un-measurable generally. In order to resolve the measurement issue, this study shows the measuring method and the assessment method of relevant natural frequency of whiling vibration by using measured harmonic order component of whirling vibration.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2003년도 춘계학술대회논문집
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• pp.827-832
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• 2003

There has been a number methods for the presentation of time-frequency analysis of non-stationary signal. In this paper, STFT(short time Fourier transform), wavelet transform, Wigner distribution, and higher order Wigner distribution are discussed in details with simulation signals. They are also applied to the analysis of the wave propagation of a semi finite beam. Wigner distribution and higher order Wigner distribution have good time-frewuency resolutions. Wavelet transform is required for impact analysis but should be applied carefully. STFT suffers from time-frequency resolutions. Each method is has its advantage and disadvantage depending on each application signals.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2007년도 하계종합학술대회 논문집
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• pp.125-126
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• 2007

In this paper, we analyze the channel estimation performances associated with the interpolation order for OFDM systems. We first analyze the time varying channel and frequency selective channel, and then we derive the channel Index which indicates the ratio of time axis variation and frequency axis variation. The analyzed results show that time interpolation followed by a frequency interpolation is adequate for the channel with a channel index larger than a certain threshold value and vice versa. Computer simulation explains that the method which decides Interpolation order outperforms fixed order estimation.