• 한국추진공학회지
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• 제5권4호
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• pp.1-11
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• 2001

다공성 카본 페놀릭 복합재의 재료상수를 실험데이터로부터 결정하기 위하여 시간의존 이론과 유한요소법을 적용하였다. 이 이론은 Biot 의 상수와 투과율 사이의 관계를 다공성의 함수로 사용하여 기존의 Lee, Salamon, Sullivan[1］의 논문을 수정하였다. 수정된 유한요소 프로그램과 재료의 모델링은 (1) 다공성 재료 이론에 더 충실하고 (2) 새롭게 발견된 해석적 단순함을 포함하고 (3) 재료의 성질을 더욱 정확하게 기술하였다. 실험 데이터에 대한 적용과 비교는 어떻게 재료의 파라미터들이 재료의 응답 즉 온도에 따르는 압력의 크기와 최대치의 위치 지배되는지 명백하게 나타낸다. 특별히 응답이 투과율에 매우 민감하게 나타났다.

• Journal of Electrical Engineering and Technology
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• 제13권4호
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• pp.1655-1662
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• 2018

This paper studies the magnetic fields between the power lines which are finite length and other ones which are infinitely long around the first tower in the proximity of the power transformers. They will be used as a source of disturbance applied to the power line. The method applied in this study was gradual; develop the theoretical formulation of the magnetic fields of these lines which are finite length and other ones which are infinitely long, examine the effects of different couplings between the different neighboring lines and the distribution transformers on behavior of magnetic fields. The method also focused on the experimental results analyzing the magnetic fields which will be used as a source applied to the auditory implants EMC. The theoretical and experimental results were compared and discussed for three power lines (90kV, 150kV and 225kV) near the power station, and it proved the effect of these substations on the simulated and measured results of the magnetic field. The maximum intensities of magnetic fields measured at the height of 1m from the ground for the circuit of three lines close to each substation were significantly lower than the ICNIRP reference levels for occupational and non occupational exposures.

• Nuclear Engineering and Technology
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• 제30권6호
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• pp.581-591
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• 1998

Numerical analysis was peformed for the two-dimensional turbulent natural convection for a long horizontal line with different end temperatures. The turbulent model has been applied a standard k-$\varepsilon$ two equation model of turbulence similar to that the proposed by the Launder and Spalding. The dimensionless governing equations are solved by using SIMPLE (Semi-Implicit Method for Pressure Linked Equations) algorithm which is developed using control volumes and staggered grids. The numerical results are verified by comparison with the operating PWR test data. The analysis focuses on the effects of variation of the heat transfer rates at the pipe surface, the thermal conductivities of the pipe material and the thickness of the pipe wall on the thermal stratification. The results show that the heat transfer rate at the pipe surface is the controlling parameter for mitigating of thermal stratification in the long horizontal pipe. A significant reduction and disappearance of the thermal stratification phenomenon is observed at the Biot number of 4.82$\times$10$^{-1}$ . The results also show that the increment of the thermal conductivity and thickness of the wall weakens a little the thermal stratification and somewhat reduces temperature gradient of y-direction in the pipe wall. These effects are however minor, when compared with those due to the variation of the heat transfer rates at the surface of the pipe wall.

• 한국소음진동공학회논문집
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• 제18권12호
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• pp.1262-1269
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• 2008

Though multilayered foam-panel structures have been widely used to reduce sound transmission in various fields, most of the previous works to design them were conducted by repeated analyses or experiments based on initially given configurations or sequences. Therefore, it was difficult to obtain an optimal sequence of multilayered foam-panel structure yielding superior sound isolation capability. In this work, we propose a new design method to sequence a multi-panel structure lined with a poroelastic material having maximized sound transmission loss. Being formulated as a one-dimensional topology optimization problem fur a given target frequency, the optimal sequencing of panel-poroelastic layers is systematically carried out in an iterative manner. In this method, a panel layer is expressed as a limiting case of a poroelastic layer to facilitate the optimization process. This means that main material properties of a poroelastic material are treated as interpolated functions of design variable. The designed sequences of panel-poroelastic multilayer were shown to be significantly affected by the target frequencies; more panels were obtained at higher target frequency. The sound transmission loss of the system was calculated by the transfer matrix derived from Biot's theory.

• Geomechanics and Engineering
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• 제21권3호
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• pp.279-288
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• 2020

The permeation grouting is a commonly used technique to improve the engineering geology condition of the soft ground. It is of great significance to predict the permeation range of the grout so as to ensure the effects of grouting. This paper conducts a theoretical analysis of jet-grouting effects in ground improvement and rotary grouting pile installation by utilizing deformation-permeation coupled poroelastic solutions based on Biot's theory and Laplace-Fourier integral transform technique. The exponential function and the intermittent trigonometric function are chosen to represent time-dependent grouting pressure usually encountered in ground improvement and rotary grouting pile installation process, respectively. The results, including the radial displacement, the hoop stress, the excess pore fluid pressure, the radial discharge, and the permeation radius of grout, are presented for different grouting time, radial positions and grouting lengths. Parametric study is conducted to explore the effects of variation of the exponent in the exponential grouting pressure-time relationship on grouting-induced responses. It is expected that the proposed solutions can be used to estimate the permeation range of grouting in ground improvement and rotary grouting pile installation.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2008년도 추계학술대회 논문집
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• pp.208-213
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• 2008

In recent society, the quality of human life has improved due to the use of electric appliances and the high powered electrical equipments. However, lots of electric appliances and equipments generate the electromagnetic field hazard. Many studies have been made about the wrong behavior of machines due to electromagnetic fields, the interferences in communication equipments, the possibility of the electromagnetic field hazard in human body, etc. There exist international standards about the RF equipments (ex. mobile phone, antenna, etc.). But, many researchers involved in power frequency electric and magnetic field only propose the prudential avoidance. In this paper, induced currents in a human body model due to magnetic fields in high speed railway are calculated by two dimensional impedance method. Power frequency(60Hz) magnetic fields are calculated and induced currents are simulated by Faraday's law. Induced currents are simulated with induced voltage, human body model impedances due to Ohm's law, magnetic fields derived from Biot-Savart's law and Transmission Line Method in high speed railway.

• 한국초전도ㆍ저온공학회논문지
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• 제12권4호
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• pp.13-16
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• 2010

The Lorentz force distribution of a high $T_c$ superconducting tape with increasing transport currents in magnetic field ($H_a$) was visualized. The external magnetic field was applied normally to the coated conductor tape surface after zero-field cooling, and the transport current ($I_a$) was increased stepwise from 0 to 90 % of the values of the critical current ($I_c$ ($H_a$)) at applied filed, Ha. The field distribution (H(x)) near the sample surface across the tape width (2w) was measured using the scanning Hall probe method. Applying an inversion to the measured field distribution, we obtained the underlying current distribution (J(x)), from which the magnetic induction, B(x) was calculated with Biot-Savart law. Then Lorentz force per unit length was calculated using F(x)=J(x)${\times}$B(x), which appears to be very inhomogeneous along the tape width due to the complicated distributions of J(x) and B(x).

• 한국지반공학회지:지반
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• 제1권2호
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• pp.17-26
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• 1985

본문의 필자들은 연약지반의 다차원감밀을 포함하여 각종 개양공법을 시행할 경추 재하에 의한 웅전의 관력과 변형 그리고 문극수감거동 등의 해석과 나아가 시공관리 등을 포괄하는 연약지반해 석연의 다목적 프로그램의 개발을 목표로 연구를 진행중에 있다. 1)-4) 그동안 몇차례에 걸헉 본프로 그램의 이론적 배경과 구성내용 그리고 개양공법별 유용성데 관하여 학술지나 학술발표회를 통해 발 표한 바 있는데 본문은 이어서 Sand Drain공법의 적용에 대하여 연구한 결과를 발표한 것이다. Sand Drain공법은 점토우에 사완을 두어 성토하중에 의해 여밀을 촉진한다. 이 설계이론은 주지하다시피 Barron의 이론을 이용한 것인데 그러나 이 이론은 Terzaghi계 이론의 결함과 변형경건이 불분명하다는 것은 잘알혀진 사실이다. 그리고 사항데 대한 응력집중은 전혀 고려되어 있지 않다. 본 프로그램은 기본적으조 다차원려밀은 Biot계리론을 채택하였다. 이 다차원견밀을 해석하는테 사항의 응력집중을 해명하기 위하여 사항i61 강성을 고쳐하지 않은 경우와 고려하는 경우를 자연지반 상태의 탄밀(이차원)상태와 비교하여 응력집중이 어떻게 일어나는7'1를 고찰하였다. 이 때 모래(사항)와 성토재료는 비선형탄성모델로 생각하고 점토는 비등방성에 Creep효과를 함께 고려할 수 있는 구성방정식으로서 탄점소성모델을 채택하였다. 그 결과는 강성을 고려하는 Sand drain이 헌실적이며 동시에 그와같은 해석이나 설계도 가능하다는 것을 밟힌 것이다.

• International Journal of Naval Architecture and Ocean Engineering
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• 제9권4호
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• pp.418-428
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• 2017

In offshore area, newly deposited Quaternary loose seabed soils are widely distributed. There are a great number of offshore structures has been built on them in the past, or will be built on them in the future due to the fact that there would be no very dense seabed soil foundation could be chosen at planed sites sometimes. However, loosely deposited seabed foundation would bring great risk to the service ability of offshore structures after construction. Currently, the understanding on wave-induced liquefaction mechanism in loose seabed foundation has been greatly improved; however, the recognition on the consolidation characteristics and settlement estimation of loose seabed foundation under offshore structures is still limited. In this study, taking a semi-coupled numerical model FSSI-CAS 2D as the tool, the consolidation and settlement of loosely deposited sandy seabed foundation under an offshore breakwater is investigated. The advanced soil constitutive model Pastor-Zienkiewics Mark III (PZIII) is used to describe the quasi-static behavior of loose sandy seabed soil. The computational results show that PZIII model is capable of being used for settlement estimation problem of loosely deposited sandy seabed foundation. For loose sandy seabed foundation, elastic deformation is the dominant component in consolidation process. It is suggested that general elastic model is acceptable for subsidence estimation of offshore structures on loose seabed foundation; however, Young's modulus E must be dependent on the confining effective stress, rather than a constant in computation.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2009년도 춘계학술대회 논문집
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• pp.676-679
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• 2009

The bottom-simulating reflector (BSR) is the most commonly observed seismic indicator of gas hydrate in the Ulleung Basin, East Sea. We processed ten representative seismic reflection profiles, selected from a large data set, for amplitude variation with offset (AVO) analysis of the BSR to estimate gas-hydrate concentrations. First, BSRs were divided into five groups based on their seismic amplitudes and associated sediment types: (1) very high-amplitude BSRs in turbidite/hemipelagic sediments, (2) high-amplitude BSRs in debris-flow deposits, (3) moderate-amplitude BSRs in turbidite/hemipelagic sediments, (4) very low-amplitude BSRs in debris-flow deposits, and (5) very low-amplitude BSRs in seismic chimneys. The AVO responses of the group 1 and 3 BSRs are characterized by a rapid decrease and a relatively slow decrease in magnitude with offset, respectively. The AVO response of the group 2 BSR is characterized by a relatively slow increase in magnitude with offset. The AVO responses of the groups 4 and 5 BSRs are characterized by a flat AVO with very small zero-offset amplitude. Theoretical AVO curves, based on the three-phase Biot theory, suggest that the group 1 and 3 BSRs may be related to high (> 40%) concentrations of gas hydrate whereas the group 2 BSRs may indicate low (< 20%) concentrations of gas hydrate. The AVO responses of the group 4 and 5 BSRs cannot be compared with the theoretical models because of their very small zero-offset amplitudes. The comparison of the AVO response of the BSR at the UBGH-04 well with theoretical models suggests about 10% gas-hydrate concentration above the gas-hydrate stability zone.