• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
• /
• 2013.05a
• /
• pp.59-60
• /
• 2013

In order to analyze optical waveguide, the FDTD method can be applied. But structure of optical waveguide is relatively larger than wavelength of center frequency. But optical waveguide system must be periodic structure and the solution of the waveguide can be obtained from a simulation in one period of the structure by applying PBC(Periodic boundary condition). In this paper, an efficient FDTD algorithm incorporating PBC in inhomogeneous medium is introduced and estimated.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2005.11a
• /
• pp.696-701
• /
• 2005

조화가진력이 작용하는 고정경계를 가진 완전원판의 비선형 진동에 대한 응답특성을 연구하였다. 원판의 비대칭모드의 고유진동수 근처에 가진주파수가 작용하는 주공진에서의 응답은 정상파(standing wave)뿐만 아니라 진행파(traveling wave)가 존재 한다고 알려져 있다. 주공진 근처의 정상상태 응답곡선에서 최대한 5개의 안정한 응답이 존재하는 것으로 밝혀졌으며, 이들은 1개의 정상파와 4개의 진행파로 나타난다. 이 진행파 중 2개는 가진진동수가 변화함에 따라 Hope분기에 의해 안정성을 잃은 후 주기배가운동을 거쳐 흔돈운동에 이르게 된다. 초기조건에 의해 각각의 끌개(attractor)에 흡인되는 흡인영역의 경계를 주평면의 개념을 통하여 구하였으며, 가진진동수가 변화함에 따라 안정한 해가 혼돈운동에 이르는 과정에 대해 흡인영역의 경계가 변화되는 특성을 관찰하였으며, 흡인영역 경계에 대한 프랙털 차원(fractal dimension)을 계산하였다.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
• /
• v.16 no.2
• /
• pp.203-209
• /
• 2018

To correctly predict the neutron behavior based on diffusion calculations, it is necessary to adopt well-specified boundary conditions using suitable diffusion approximations to transport boundary conditions. Boundary conditions such as the zero net-current, the Marshak, the Mark, the zero scalar flux, and the Albedo condition have been used extensively in diffusion theory to approximate the reflective and vacuum conditions in transport theory. In this paper, we derive and analyze these conditions to prove their mathematical validity and to understand their physical implications, as well as their relationships with one another. To show the validity of these diffusion boundary conditions, we solve a sample problem. The results show that solutions of the diffusion equation with these well-formulated boundary conditions are very close to the solution of the transport equation with transport boundary conditions.

• Proceedings of the KSME Conference
• /
• 2008.11b
• /
• pp.2477-2482
• /
• 2008

Effect of computational domain size in simulating of periodic obstacle flow has been investigated for the flow past tube banks. Reynolds number, defined by freestream velocity (U) and cylinder diameter (d), was fixed as 200, and center-to-center distance (P) as 1.5d. In-line square array was considered. Drag coefficient, lift coefficient and Strouhal number were calculated depending on domain size. Circular cylinders were implemented on a Cartesian grid system by using an immersed boundary method. Boundary condition is periodic in both streamwise and lateral directions. Previous studies in literature often use a square domain with a side length of P, which contains only one cylinder. However, this study reveals that size is improper. Especially, RMS values of flow-induced forces are most sensitive to the domain size.

• Journal of the Korea Institute of Building Construction
• /
• v.13 no.4
• /
• pp.321-332
• /
• 2013

Costs and expenses are intertwined and incurred throughout an entire construction project, even from the pre-construction phase, and each phase has a different impact on the life cycle cost (LCC). However, the cost breakdown structure (CBS) is different in each phase of a building construction project, which makes it hard to reasonably calculate construction cost. For this reason, the boundary conditions were analyzed in this study based on the life cycle cost break structure (LCCBS). In addition, breakdown factors were analyzed based on the boundary conditions to derive a linkage method. The validity of the linkage method was verified through application to actual construction projects. Through the analysis, it was found that the problem of items being left out was reduced by more than 97.2 percent, and the work was done an average of 6 hours faster compared to the conventional method. It is expected that by applying the new LCC system, LCC will be both reduced and calculated in a more efficient manner.

• Journal of the Korean Society of Hazard Mitigation
• /
• v.2 no.3 s.6
• /
• pp.119-125
• /
• 2002

The objective of this study is to evaluate elastic modulus of bridge-axis direction for optimum structure system in the cable-stayed bridge design. In numerical example of this study, a slight change in axis direction elastic modulus causes major modifications of the bridge characteristics when it is $1\times10^4$ tonf/m/bearing or less. Therefore, the elastic modulus was set at this lower limit of $1\times10^4$ tonf/m/bearing where the strength of the entire bridge system is still determined by girder strength and the entire system is insensitive to variations in elastic modulus. Besides, cable-stayed bridge with freely supported girders have slightly longer vibration periods in the horizontal direction for earthquake forces.

• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.35 no.2
• /
• pp.41-48
• /
• 2023

In this study, simplified linear numerical method that can simulate wave generation and transformation by a moving bottom is introduced. Numerical analysis is conducted in wave number domain after continuity equation, linear dynamic and kinematic free surface boundary conditions and linear kinematic bottom boundary condition are Fourier transformed, and the results are expressed in space domain by an inverse Fourier transform. In the wavenumber domain, the dynamic free water surface boundary condition and the kinematic free water surface boundary condition are numerically calculated, and the velocity potential in the mean water level (z = 0) satisfies the continuity equation and the kinematic bottom boundary condition. Wave generation and transformation are investigated when the triangular and rectangular shape of bottoms move periodically. The results of the simplified numerical method are compared with the results of previous analytical solutions and agree well with them. Stability of numerical results according to the calculation time interval (Δt) and the calculation wave number interval (Δk) was also investigated. It was found that the numerical results were appropriate when Δt ≤ T(period)/1000 and Δk ≤ π/100.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
• /
• v.3 no.2
• /
• pp.31-38
• /
• 2010

It is difficult to design accurately the bandgap of metamaterial depending on metamaterial pattern and array configuration. In this paper, we propose a design method for the wanted bandgap frequency using any metamaterial pattern in 2 dimensional array. Metamaterial structure is consisted of periodic array. Therefore the calculation area in FDTD(finite difference time domain) method can be reduced by applying the periodic boundary condition to 2-D metamaterial array. The method for design and calculation the L and C values by using 2-D is also considered. So it can be designed more accurately and rapidly. For example, we designed metamaterial square pattern array in 5 GHz, and compared with the 1-D metamaterial pattern using analysis method in microstrip line. As a result, we found that the accuracy of this proposed method can be incresed to 14.7%.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.28 no.12
• /
• pp.1950-1957
• /
• 2004

Analysis for structures composed of materials containing regularly spaced in-homogeneities is usually executed by using averaged material properties. In order to evaluate the effective properties, a unit cell is defined and loaded somehow, and its response is investigated. The imposed loading, however, should accord to the status of unit cells immersed in the macroscopic structure to secure the accuracy of the properties. In this study, mathematical description for the periodicity of the displacement field is derived and its direct implementation into FE models of unit cell is attempted. Conventional finite element code needs no modification, and only the boundary of unit cell should be constrained in a way that the periodicity is preserved. The proposed method is applicable to skew arrayed in-homogeneity problems. Homogenized in-plane elastic properties are evaluated for a few representative cases and the accuracy is examined.

• Proceedings of the Computational Structural Engineering Institute Conference
• /
• 2011.04a
• /
• pp.693-696
• /
• 2011

본 논문에서는 레벨셋 방법을 이용하여, 소음을 차단하기 위한 음향 구조물의 형상 최적 설계를 수행하였다. 음향 결정 구조에서는 음향이 흩어져 있는 결정 구조에 의해서 굴절되기 때문에 결정 모양을 조정함으로써, 음향 거동을 제어 할 수 있다. 형상 최적 설계의 목적은 특정한 각도와 각속도로 입사되는 입사파에 대해서 음향 투과율(acoustic transmittance)이 최소가 되도록 음향 결정의 형상(inclusion shape)을 결정하는 것이다. 음향 압력(acoustic pressure)은 주기성을 갖는 음향 결정에 대해서 헬몰츠(Helmoltz)형태의 지배 방정식을 풀어서 얻을 수 있다. 본 연구에서는 음향 구조물로 결정이 수평 방향으로는 주기적으로 무한히 분포하고 수직방향으로는 유한한 층간 구조를 가지고 있는 소음 방어벽 (Noise barrier)을 고려한다. 결정의 위치는 고정되어 있고, 결정의 형상을 설계 변수로서 음파의 거동을 제어할 수 있도록 하였다. 주기적 구조물을 고려하기 때문에 결정의 좌와 우에 Bloch 이론을 적용해 주기적 경계조건을 부과하였고, 소음 방어벽 위와 아래에는 임피던스 행렬(impedance matrix)를 이용하여, 무한 균질 영역과 소음 방어벽사이의 음파 투과를 모사하였다. 복잡한 형상 변화를 표현하기 위해 임시적 경계를 이용한 레벨셋 방법을 사용하였다. 설계 민감도 해석을 통해 목적함수가 감소하는 방향으로 경계에서의 수직 벡터를 계산하고, 이를 헤밀턴-자코비(Hamilton-Jacob) 방정식에 대입하여, 최적의 형상을 나타내는 레벨셋 함수를 구하였다.