• Nuclear Engineering and Technology
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• 제49권5호
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• pp.1100-1108
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• 2017

A thermal-hydraulic system code is an essential tool for the design and safety analysis of a nuclear power plant, and its accuracy quantification is very important for the code assessment and applications. The fast Fourier transform-based method (FFTBM) by signal mirroring (FFTBM-SM) has been used to quantify the accuracy of a system code by using a comparison of the experimental data and the calculated results. The method is an improved version of the FFTBM, and it is known that the FFTBM-SM judges the code accuracy in a more consistent and unbiased way. However, in some applications, unrealistic results have been obtained. In this study, it was found that accuracy quantification by FFTBM-SM is dependent on the frequency spectrum of the fast Fourier transform of experimental and error signals. The primary objective of this study is to reduce the frequency dependency of FFTBM-SM evaluation. For this, it was proposed to reduce the cut off frequency, which was introduced to cut off spurious contributions, in FFTBM-SM. A method to determine an appropriate cut off frequency was also proposed. The FFTBM-SM with the modified cut off frequency showed a significant improvement of the accuracy quantification.

• Nuclear Engineering and Technology
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• 제30권6호
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• pp.531-540
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• 1998

The DYLAM-3 code which overcomes the limitation of event tree/fault tree was applied to LOOP (Loss of Off-site Power) in the mid-loop operation employing HEPs (Human Error Probabilities) supplied by the ASEP (Accident Sequence Evaluation Program) and the SEPLOT (Systematic Evaluation Procedure for Low power/shutdown Operation Task) procedure in this study. Thus the time history of core uncovery frequency during the mid-loop operation was obtained. The sensitivity calculations in the operator's actions to prevent core uncovery under LOOP in the mid-loop operation were carried out. The analysis using the time dependent HEP was performed on the primary feed & bleed which has the most significant effect on core uncovery frequency. As the result, the increment of frequency is shown after 200 minutes duration of simulation conditions. This signifies the possibility of increment in risk after 200 minutes. The primary feed & bleed showed the greatest impact on core uncovery frequency and the recovery of the SCS (Shutdown Cooling System) showed the least impact. Therefore the efforts should be taken on the primary feed & bleed to reduce the core uncovery frequency in the mid-loop operation. And the capability of DYLAM-3 in applying to the time dependent concerns could be demonstrated.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2000년도 ITC-CSCC -2
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• pp.1096-1099
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• 2000

A method to analyze the high speed inter-connects that are composed of frequency dependent lossy distributed lines is presented. Network modeling of hybrid systems is implemented by using the modified nodal admittance matrix in the Laplace transformation domain. The network response is computed by different two methods. One method Is the asymptotic waveform evaluation (AWE) method and other is numerical Laplace inversion method. The merits and demerits of two methods are discussed by applying to several concrete illustrative networks.

• Steel and Composite Structures
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• 제51권4호
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• pp.363-375
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• 2024

Within the optimization field, addressing the intricate posed by fluidic pressure loads on functionally graded structures with frequency-related designs is a kind of complex design challenges. This paper thus introduces an innovative density-based topology optimization strategy for frequency-constraint functionally graded structures incorporating Darcy's law and a drainage term. It ensures consistent treatment of design-dependent fluidic pressure loads to frequency-related structures that dynamically adjust their direction and location throughout the design evolution. The porosity of each finite element, coupled with its drainage term, is intricately linked to its density variable through a Heaviside function, ensuring a seamless transition between solid and void phases. A design-specific pressure field is established by employing Darcy's law, and the associated partial differential equation is solved using finite element analysis. Subsequently, this pressure field is utilized to ascertain consistent nodal loads, enabling an efficient evaluation of load sensitivities through the adjoint-variable method. Moreover, this novel approach incorporates load-dependent structures, frequency constraints, functionally graded material models, and polygonal meshes, expanding its applicability and flexibility to a broader range of engineering scenarios. The proposed methodology's effectiveness and robustness are demonstrated through numerical examples, including fluidic pressure-loaded frequency-constraint structures undergoing small deformations, where compliance is minimized for structures optimized within specified resource constraints.

• 조명전기설비학회논문지
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• 제26권3호
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• pp.73-79
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• 2012

A counterpoise is commonly employed in grounding systems installing near the ground surface of low resistivity soils and radial-type counterpoises are used in the limited space. Recently some studies on the evaluation of ground impedance of paralleling ground electrodes have carried out, but the data for providing the frequency-dependent ground impedances considering potential interferences are not yet sufficient. In order to provide the information about the design of grounding systems for surge protection, the simulations of the frequency-dependent ground impedance of various shaped counterpoises are carried out by using the distributed parameter circuit model including the effect of potential interferences. This paper presents the theoretical simulations and actual experiments of the frequency-dependent ground impedance of paralleling and 3 or 4-arms star counterpoises. The accuracy of the simulation methodology is examined by the comparison with the measured results, and the results show a good agreement between the simulation and the experiment.

• 한국지진공학회:학술대회논문집
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• 한국지진공학회 2001년도 춘계학술대회 논문집
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• pp.453-460
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• 2001

The seismic capacity of columns usually has been tested in uniaxial loading condition. The seismic performance used to be evaluated under the same assumption. Since the real earthquake motion is multi-directional, the effects of multi-directional excitation on the seismic capacity of structures need to be carefully examined. In this paper, a frequency dependent alternate biaxial cyclic loading test is proposed as an evaluation method of seismic capacity under multi-directional excitation. Four test specimens were made and tested to study the degradation of strength, stiffness and ductility under biaxial loading condition. A multi- directional excitation. The capacity is obtained using frequency dependent alternate biaxial cyclic loading test. The orthogonal effect is taken into account by increasing the demand.

• Structural Engineering and Mechanics
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• 제21권1호
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• pp.101-119
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• 2005

An efficient methodology is presented to evaluate the seismic behavior of a Fluid-Elevated Tank-Foundation/Soil system taking the embedment effects into accounts. The frequency-dependent cone model is used for considering the elevated tank-foundation/soil interaction and the equivalent spring-mass model given in the Eurocode-8 is used for fluid-elevated tank interaction. Both models are combined to obtain the seismic response of the systems considering the sloshing effects of the fluid and frequency-dependent properties of soil. The analysis is carried out in the frequency domain with a modal analysis procedure. The presented methodology with less computational efforts takes account of; the soil and fluid interactions, the material and radiation damping effects of the elastic half-space, and the embedment effects. Some conclusions may be summarized as follows; the sloshing response is not practically affected by the change of properties in stiff soil such as S1 and S2 and embedment but affected in soft soil. On the other hand, these responses are not affected by embedment in stiff soils but affected in soft soils.

• 한국조명전기설비학회:학술대회논문집
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• 한국조명전기설비학회 2009년도 춘계학술대회 논문집
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• pp.348-351
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• 2009

In order to evaluate the performance of a grounding system against lightning or fault currents including high frequency components, the grounding impedance should be considered rather than its ground resistance. Recently, some researches on the evaluation and modeling of the grounding impedances have been carried out but the results have not been yet sufficient. This paper deals with the frequency dependence of the resistivity and relative dielectric constant of sand associated with water contents. As a result, the resistivity of sand is getting lower with increasing water content and it is nearly independent on the frequency in the range of less than 1MHz, and is decreased over the frequency range of above 1MHz. Also, the relative dielectric constant is rapidly decreased with the frequency in the range of less than 10kHz, but it is nearly not dependent on the frequency over the frequency range of 10kHz. It was found from this work that the frequency dependance of resistivity and relative dielectric constant of soil should be considered in designing the grounding systems for protection against lightning or surges.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1995년도 Proceedings of the Korea Automation Control Conference, 10th (KACC); Seoul, Korea; 23-25 Oct. 1995
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• pp.360-363
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• 1995

In this paper, we describe the composition of frequency response bands based on experimental data of plants (controlled systems) with uncertainty and nonlinearity, and the robust stability evaluation of feedback control systems. Analysis and design of control systems using the upper and lower bounds of such experimental data would be effective as a practicable method which is not heavily dependent upon mathematical models such as the transfer function. First, we present a method to composite gain characteristic bands of frequency response of cascade connected plants with uncertainty and a recurrent inequality for the composition. Next, evaluation methods of the robust stability of multi-loop control systems obtained through feedback from the output terminals and multi-loop control systems obtained through feedback into the input terminals are described. In actual control systems, experimental data of frequency responses often depends on the amplitude of input. Therefore, we present the evaluation method of the nominal value and the width of the frequency response band in such a case, and finally give numerical examples based on virtual experimental data.

• 한국지반공학회논문집
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• 제24권12호
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• pp.113-120
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• 2008

1차원 지반응답해석은 지반에 의한 지진동의 증폭현상을 모사하는 데 널리 사용되고 있다. 가장 널리 사용되고 있는 등가선형 지반응답해석기법은 유효변형률에 상응하는 전단탄성계수와 감쇠비를 전 주파수 영역에 일률적으로 적용하며, 진동주파수에 대한 지반 응답의 영향을 고려하지 않는다. 지반의 비선형 거동을 주파수영역에서 보다 정확하게 모사하기 위하여 진동주파수와 지반거동의 상관관계를 주파수-변형률 곡선으로써 모의하는 등가선형해석기법이 개발되었으며, 이 방법은 기존의 등가선형해석기법에 비하여 정확성을 향상시킨다고 알려져 있다. 이제까지 다양한 형상의 주파수변형률 곡선이 제안되었으며, 이들은 한결같이 해석의 정확성을 증가시킨다고 주장된 바 있다. 본 연구에서는 기존의 연구에서 제안되었건 두 개의 주파수-변형률 관계 완화곡선과 본 연구에서 새롭게 제안된 세 개의 곡선을 이용하여 주파수 의존성을 고려한 등가선형해석기법의 정확성을 검증하였다. 검증에는 세 개의 부지에서 기록된 6개의 지진파가 사용되었다. 해석결과, 완화곡선은 지반응답에 지배적인 영향을 미치는 것으로 나타났으며, 주파수 의존성을 고려한 해석은 정확성을 향상시킬수 있는 것으로 나타났다. 하지만, 모든 사례에서 가장 정확하게 응답을 예측하는 완화곡선은 없는 것으로 나타났으며, 해석사례별로 최적의 완화곡선이 다른 것으로 나타났다. 따라서, FDEL 해석 수행 시, 다양한 완화곡선을 사용해야 할 것으로 판단되며 등가선형해석과 병행해서 수행되어야 한다고 판단된다.