• Structural Engineering and Mechanics
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• 제81권4호
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• pp.443-459
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• 2022

The paper studies the dispersion and attenuation of propagating waves in the "plate+compressible viscous fluid layer" system in the case where the fluid layer flow is restricted with a rigid wall, and in the case where the fluid layer has a free face. The motion of the plate is described by the exact equations of elastodynamics and the flow of the fluid by the linearized Navier-Stokes equations for compressible barotropic Newtonian viscous fluids. Analytical expressions are obtained for the amplitudes of the sought values, and the dispersion equation is derived using the corresponding boundary and compatibility conditions. To find the complex roots of the dispersion equation, an algorithm based on equating the modulus of the dispersion determinant to zero is developed. Numerical results on the dispersion and attenuation curves for various pairs of plate and fluid materials under different fluid layer face conditions are presented and discussed. Corresponding conclusions on the influence of the problem parameters on the dispersion and attenuation curves are made and, in particular, it is established that the change of the free face boundary condition with the impermeability condition can influence the dispersion and attenuation curves not only in the quantitative, but also in the qualitative sense.

• 한국전기전자재료학회논문지
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• 제26권2호
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• pp.126-133
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• 2013

This paper presents a study on the dispersion effect of the X-Ray diffraction, glass transition and DMA properties of organic modifier clay/epoxy nanocomposites produced in a homogenizer. Several experiments were conducted including different types of dispersion condition with varying processing conditions such as homogenizer rotor speed and applied time of homogenizer. The effects of these variables on the dispersion properties of nanocomposites were then studied. In order to fully understand the experimental results, a X-ray diffraction, DSC and DMA were used to investigate the effect of above mentioned variables on microstructure and intercalation/exfoliation of organic modifier clay/epoxy nanocomposites. The results from this work could be used to determine the best processing condition to obtain appropriate levels of d-spacing, glasss transition temperature and storage modulus in organic modifier clay/epoxy nanocomposites.

• 한국해양공학회지
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• 제12권2호통권28호
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• pp.97-110
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• 1998

The numerical damping and dispersion error characteristics associated with difference schemes and a panel shift method used for the calculation of steady free surface flows by a panel method are an analysed in this paper. First, 12 finite difference operators used for the double model flow by Letcher are applied to a two dimensional cylinder with the Kelvin free surface condition and the numerical errors with these schemes are compared with those by the panel shift method. Then, 3-D waves due to a submerged source are calculated by the difference schemes, the panel shift method and also by a higher order boundary element method(HOBEM). Finally, the waves and wave resistance for Wigley's hull are calculated with these three schemes. It is shown that the panel shift method is free of numerical damping and dispersion error and performs better than the difference schemes. However, it can be concluded that the HOBEM also free of the numerical damping and dispersion error is the most stable, accurate and efficient.

• 한국항행학회논문지
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• 제17권1호
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• pp.16-23
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• 2013

단일 모드 광섬유의 그룹 속도 분산과 비선형 효과에 의해 왜곡되는 960 Gbps 파장 분할 다중 신호의 보상을 위해 분산 제어 기술이 적용된 광전송 링크에서 분산 보상 광섬유 (DCF; dispersion compensating fiber)의 분산 계수와 중계 구간 당 잉여 분산량 (RDPS; residual dispersion per span)이 왜곡 보상에 미치는 영향을 분석하였다. 우선 왜곡 보상에 큰 영향을 미치는 최적 전체 잉여 분산량 (NRD; net residual dispersion)은 고려한 모든 DCF의 분산 계수와 RDPS에 관계없이 큰 입사 전력에서 구해야 한다는 것을 확인하였다. 중계 구간의 RDPS는 매우 작게, 반면 DCF의 분산 계수는 크게 하여야 시스템 성능이 현저하게 개선되는 것을 확인하였다.

• Journal of Mechanical Science and Technology
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• 제17권3호
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• pp.440-448
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• 2003

In the present paper, numerical simulations of buoyant plume dispersion in a neutral and stable atmospheric boundary layer have been carride out. A Lagrangian Stochastic Model (LSM) with a Non-Linear Eddy Viscosity Model (NLEVM) for turbulence is used to generate a Reynolds stress field as an input condition of dispersion simulation. A modified plume-rise equation is included in dispersion simulation in order to consider momentum effect in an initial stage of plume rise resulting in an improved prediction by comparing with the experimental data. The LSM is validated by comparing with the prediction of an Eulerian Dispersion Model (EDM) and by the measured results of vertical profiles of mean concentration in the downstream of an elevated source in an atmospheric boundary layer. The LSM predicts accurate results especially in the vicinity of the source where the EDM underestimates the peak concentration by 40% due to inherent limitations of gradient diffusion theory. As a verification study, the LSM simulation of buoyant plume dispersions under a neutral and stable atmospheric condition is compared with a wind-tunnel experiment, which shows good qualitative agreements.

• 한국항해항만학회:학술대회논문집
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• 한국항해항만학회 2014년도 춘계학술대회
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• pp.258-259
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• 2014

파랑과 해저지반의 상호작용을 규명하기 위해서는 우선 해저면의 경계조건을 고려한 새로운 분산관계식의 도입이 필요하다. 본 연구에서는 깊이가 유한한 해저지반의 투수성 및 변위를 고려한 새로운 분산관계식을 유도하였으며, 해저지반의 두께, 탄성계수, 포화도, 투수계수, 간극률 등 다양한 지반상수의 변화에 따른 파랑 감쇠율을 비교 검토하였다.

• 한국자동차공학회논문집
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• 제9권6호
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• pp.16-23
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• 2001

Spray dispersion in high pressure diesel engines have been simulated experimentally with a special emphasis on the effect of swirl by using a liquid injection technique. A constant volume chamber was designed to be rotatable in order to generate a continuous swirl and to have the flow field closely resembling a solid body rotation. Emulsified fuel was injected into the chamber and the developing process of fuel sprays was visualized. The effect of swirl on the spray dispersion was quantified by calculating non-dimensionalized dispersion area according to the spray tip penetration length. The results show that the effect of swirl on the spray dispersion is different between short and long spray penetrations. For short range of spray tip penetration, the effect of swirl on spray dispersion is quite small. However, as the spray tip is penetrated into longer distance in spray chamber, the effect of swirl on spray dispersion becomes larger. These results can be used as a basic data for designing combustion chamber and injection system of direct injection diesel engine.

• 한국자기학회지
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• 제5권5호
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• pp.383-386
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• 1995

A universal dispersion equation for magnetostatic waves(MSW) propagating in the film with arbitrary-multiple magnetic layers magnetized in an arbitrary direction was derived with a matching boundary condition method. The computing result curves of delay time were shown.

• Industrial Engineering and Management Systems
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• 제12권2호
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• pp.112-117
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• 2013

The $\overline{x}$ control chart for the process mean and either the R or s control chart for the process dispersion have been used together to monitor the manufacturing processes. However, it has been pointed out that this procedure is flawed by a fault that makes it difficult to capture the behavior of process condition visually by considering the relationship between the shift in the process mean and the change in the process dispersion because the respective characteristics are monitored by an individual control chart in parallel. Then, the ($\overline{x}$, s) control chart has been proposed to enable the process managers to monitor the changes in the process mean, process dispersion, or both. On the one hand, identifying which process parameters are responsible for out-of-control condition of process is one of the important issues in the process management. It is especially important in the ($\overline{x}$, s) control chart where some parameters are monitored at a single plane. The previous literature has proposed the multiple decision method based on the statistical hypothesis tests to identify the parameters responsible for out-of-control condition. In this paper, we propose how to identify parameters responsible for out-of-control condition using the information criterion. Then, the effectiveness of proposed method is shown through some numerical experiments.

• Journal of information and communication convergence engineering
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• 제19권4호
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• pp.199-204
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• 2021

We propose a dispersion-managed link with a non-midway optical phase conjugator (OPC), in which the residual dispersion per span (RDPS) of each fiber span is different for each transmission section before and after OPC. We numerically demonstrate the compensation for 960-Gb/s wavelength-division multiplexed (WDM) signals distorted by chromatic dispersion and Kerr nonlinearity of the fiber. We consider different cases for non-midway OPC, including six fiber spans - OPC - 14 fiber spans and 14 fiber spans - OPC - 6 fiber spans. The numerical results show that the compensation of the distorted 960 Gb/s WDM is more efficient when the OPC is placed after 6-th fiber span as compared to after the 14-th fiber span. Our simulation results also indicate that the compensation effect increases when the difference in net residual dispersion between both transmission sections is not large, but they are not the same. Under this condition, the larger the magnitude of the RDPSs of each fiber span, the greater the compensation.