• 대한수학회지
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• 제58권3호
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• pp.553-569
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• 2021

In this paper, we present and analyze a fully discrete numerical method for solving the time-fractional diffusion wave equation: ∂^β_tu - div(a∇u) = f, 1 < β < 2. We first construct a difference formula to approximate ∂^β_tu by using an interpolation of derivative type. The truncation error of this formula is of O(△t^2+δ-β)-order if function u(t) ∈ C^2,δ[0, T] where 0 ≤ δ ≤ 1 is the Hölder continuity index. This error order can come up to O(△t^3-β) if u(t) ∈ C³ [0, T]. Then, in combinination with the linear finite volume discretization on spatial domain, we give a fully discrete scheme for the fractional wave equation. We prove that the fully discrete scheme is unconditionally stable and the discrete solution admits the optimal error estimates in the H¹-norm and L₂-norm, respectively. Numerical examples are provided to verify the effectiveness of the proposed numerical method.

• 대한수학회보
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• 제55권3호
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• pp.957-965
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• 2018

We study the class $C{\mathcal{V}} ({\Omega})$ of analytic functions f in the unit disk ${\mathbb{D}}=\{z{\in}{\mathbb{C}}$ : ${\mid}z{\mid}$ < 1} of the form $f(z)=z+{\sum}_{n=2}^{\infty}a_nz^n$ satisfying $$1+\frac{zf^{{\prime}{\prime}}(z)}{f^{\prime}(z)}{\in}{\Omega},\;z{\in}{\mathbb{D}}$$, where ${\Omega}$ is a convex and proper subdomain of $\mathbb{C}$ with $1{\in}{\Omega}$. Let ${\phi}_{\Omega}$ be the unique conformal mapping of $\mathbb{D}$ onto ${\Omega}$ with ${\phi}_{\Omega}(0)=1$ and ${\phi}^{\prime}_{\Omega}(0)$ > 0 and $$k_{\Omega}(z)={\displaystyle\smashmargin{2}{\int\nolimits_{0}}^z}{\exp}\({\displaystyle\smashmargin{2}{\int\nolimits_{0}}^t}{\zeta}^{-1}({\phi}_{\Omega}({\zeta})-1)d{\zeta}\)dt$$. Let $z_0,z_1{\in}{\mathbb{D}}$ with $z_0{\neq}z_1$. As the first result in this paper we show that the region of variability $\{{\log}\;f^{\prime}(z_1)-{\log}\;f^{\prime}(z_0)\;:\;f{\in}C{\mathcal{V}}({\Omega})\}$ coincides wth the set $\{{\log}\;k^{\prime}_{\Omega}(z_1z)-{\log}\;k^{\prime}_{\Omega}(z_0z)\;:\;{\mid}z{\mid}{\leq}1\}$. The second result deals with the case when ${\Omega}$ is the right half plane ${\mathbb{H}}=\{{\omega}{\in}{\mathbb{C}}$ : Re ${\omega}$ > 0}. In this case $CV({\Omega})$ is identical with the usual normalized class of convex univalent functions on $\mathbb{D}$. And we derive the sharp upper bound for ${\mid}{\log}\;f^{\prime}(z_1)-{\log}\;f^{\prime}(z_0){\mid}$, $f{\in}C{\mathcal{V}}(\mathbb{H})$. The third result concerns how far two functions in $C{\mathcal{V}}({\Omega})$ are from each other. Furthermore we determine all extremal functions explicitly.

• 태양에너지
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• 제4권2호
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• pp.13-28
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• 1984

Direct Absorption Receiver and Thermal Storage System is a complex problem. This paper describes only characteristic of fluid flow on the receiver. The fluid thicknesses of Molten Salts (Melting Point : $397^{\circ}C$) flowing on the receiver of modified protopype ($10m{\times}10m$) were calculated theorectically, changing the receiver slope from 60 degree to 85 degree (5 steps). The receiver temperatures were $430^{\circ}C$ at the top part and $950^{\circ}C$ at the low part. The flow thickness of the Molten Salts at the top part of the receiver are around 1.9mm in the case of maximum insolution ($50{\times}10^6$juoule/sec; 58.898kg/sec of flow rate) and 2.0mm at the low part. In the case of 3/10 of maximum insolation (flow rate = 17.669kg/sec) the flow thickness at the top part are around 0.9mm and 0.4mm at the low part, and in the case of 1/10 of maximum insolation (flow rate = 5.889 kg/see) the flow thickness at the top part are around 0.6mm and 0.3mm at the low part. From experimental measurements of a normal fresh water thickness flowing on the model plate ($12.7cm{\times}111.76cm$), around 0.8mm at the top part of the plate and around 0.7mm at the low part were obtained in the case of maximum insolation (flow rate = 0.12496 kg/see). In the case of 3/10 (flow rate = 0.03748 kg/see) and 1/10 (flow rate = 0.012496 kg/see) of maximum insolation, around 0.5mm and 0.4mm at the top part, and around 0.3mm and 0.2mm at the low part were obtained respectively. The reason why the thickness of the Molten Salts increase at the low part of the receiver only in case of maximum insolation is that decreasing rate of the viscosity of the Molten Salts is larger than decreasing rate of the density of the Molten Salts during temperature increase from the top to the low receiver plate and decrease of the fluid velocity in accordance with continuity principle. In all cases without the above maximum insolation, the thickness of the Molten Salts and the fresh water decreased at the low part of the plate because of gravity force effects rather than friction effects and of continuity principle. All simillar flow patterns were obtained through all cases of the insolation making an exception of only maximum insolation.

• International Journal of CAD/CAM
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• 제6권1호
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• pp.59-64
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• 2006

A new method to obtain explicit re-parameterization that preserves the curve degree and parametric domain is presented in this paper. The re-parameterization brings a curve very close to the arc length parameterization under $L_2$ norm but with less segmentation. The re-parameterization functions we used are $C^1$ continuous piecewise rational linear functions, which provide more flexibility and can be easily identified by solving a quadratic equation. Based on the outstanding performance of Mobius transformation on modifying pieces with monotonic parametric speed, we first create a partition of the original curve, in which the parametric speed of each segment is of monotonic variation. The values of new parameters corresponding to the subdivision points are specified a priori as the ratio of its cumulative arc length and its total arc length. $C^1$ continuity conditions are imposed to each segment, thus, with respect to the new parameters, the objective function is linear and admits a closed-form optimization. Illustrative examples are also given to assess the performance of our new method.

• Nuclear Engineering and Technology
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• 제51권6호
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• pp.1589-1595
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• 2019

In this paper, the CLAM steel strengthened by micro-scale Y-Zr-O was prepared by vacuum induction melting followed by electroslag remelting (VIM-ESR). Yttrium (Y) and zirconium (Zr) were easy to aggregates into massive yttrium-zirconium-rich inclusions in the steel melted by vacuum induction melting (VIM), which would interrupt the continuity of the matrix and reduce the mechanical properties of steel. Micron-sized Y-Zr-O inclusions would be produced with the removal of original blocky Y-Zr-rich inclusions and the submicron-sized inclusions smaller than $0.2{\mu}m$ could be retained in the steel. The small grain size and the better refinement and distribution uniformity of Y-Zr-O inclusions after remelting would be responsible for the better yield strength and toughness. For VIM-ESR alloy, the ultimate tensile strength is 749 MPa and the yield strength is 642 MPa at room temperature, meanwhile they are 391 MPa and 367 MPa at $600^{\circ}C$, respectively. Meanwhile, the ductile-brittle transition temperature (DBTT) reduced from $-43^{\circ}C$ (VIM) to $-76^{\circ}C$ (VIM-ESR).

• 해양환경안전학회지
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• 제29권3호
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• pp.288-295
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• 2023

The purpose of this study is to evaluate the feasibility of the new marine leisure ships. In order to achieve the research purpose, the cost and income were calculated based on the operating of other marine leisure ships, and the feasibility of the project was empirically analyzed. This study established a research model that applies the values derived by empirically analyzing ships with similar specifications, to the new marine leisure ships. We then calculated the cost-benefit analysis, net present value, and internal return, and evaluated the feasibility of the project based on this. As a result of the business feasibility analysis of investing in marine leisure ship, it was found that economic feasibility exists with a B/C of 1.042 and 1.049 for new and secondhand ships, respectively; however, considering the stability of the ship and the publicity and continuity of the business operation, it is recommended to invest in new ships compared to secondhand ships. The total benefit over the 10-year operating period using a social discount rate of 4.5% was evaluated to be about KRW 292.0 billion, which is higher than the total cost of KRW 256.6 billion. In conclusion, the profitability analysis showed that the B/C was 1.042, the NPV was KRW 193 billion, and the IRR was 2.1%, which indicates that profitability is weakly secured.

• 한국태양에너지학회 논문집
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• 제27권3호
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• pp.117-125
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• 2007

This study proposes a CFD(Computational Fluid Dynamics) analysis as a method of verification of the designed-data and a supplement of the insufficient experiences in geothermal system, which shows a rapid growth among the renewable energies. The followings are the results. FLUENT 6.2.12 is used as a CFD tool on this study, with the equations of continuity, motion, energy for unsteady flow through pipes and k-epsilon turbulent model. S-type model which has one borehole with diameter 12m by depth 206m and T-type model which has 3 boreholes with $12m{\times}20m{\times}206m$ are proposed, and also the boundary conditions are described. The temperature differences between temperatures by CFD analysis and by on-site measurement are less than 1.5%, this shows a high reliability of CFD analysis process which this study proposes. After 11 days simulation operated 12 hours interval On/Off mode, it is clearly predicted that the outlet temperatures of geothermal pipes are increased by $1.2^{\circ}C$, and $2.2^{\circ}C$ after 4 months. And the outlet temperatures of geothermal pipes increased with increase of the mass flow rates through the pipes. T-type model shows that the 4m distance between boreholes are reasonable because the temperatures at 2m and 6m from boreholes are nearly same.

• 전자공학회논문지C
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• 제34C권9호
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• pp.22-32
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• 1997

This paper proposes an imprecise compuitation model for DCT considering QOS of images and a two dimensional DCT architecture for imprecise computations. In case that many processes are scheduling in a hard real time system, the system resources are shared among them. Thus all processes can not be allocated enough system resources (such as processing power and communication bandwidth). The imprecise computtion model can be used to provide scheduling flexibility and various QOS(quality of service)levels, to enhance fault tolerance, and to ensure service continuity in rela time systems. The DCT(discrete cosine transform) is known as one of popular image data compression techniques and adopted in JPEG and MPEG algorithms since the DCT can remove the spatial redundancy of 2-D image data efficiently. Even though many commercial data compression VLSI chips include the DCST hardware, the DCT computation is still a very time-consuming process and a lot of hardware resources are required for the DCT implementation. In this paper the DCT procedure is re-analyzed to fit to imprecise computation model. The test image is simulated on teh base of this model, and the computation time and the quality of restored image are studied. The row-column algorithm is used ot fit the proposed imprecise computation DCT which supports pipeline operatiions by pixel unit, various QOS levels and low speed stroage devices. The architecture has reduced I/O bandwidth which could make its implementation feasible in VLSI. The architecture is proved using a VHDL simulator in architecture level.

• 대한토목학회논문집
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• 제8권2호
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• pp.155-166
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• 1988

본 연구는 복합체의 단부영향을 고려한 등각균등질, 이방성의 모델개발과 이에따른 유한요소해석 프로그램 개발에 중점을 두었다. 복합체는 2차원의 수평층을 가지며 선형, 탄성, 작은변형에 제한을 두었다. 본 연구에서 개발된 등가 균등질의 이론은 복합체의 전반적인 거동을 포함시킴은 물론 층과 수직인 경계면과 그 부근에 형성되는 단부의 영향과 층의 경계면에 생기는 응력집중 현상을 나타낼 수 있게 하였다. 이론개발에 있어 1차변수는 $C_0$연속의 유한요소 근사치를 가지도록 하였으며 이를위해 최고 1차의 미분치가 변형에너지에 나타나도록 변수를 택하였다. 결과적으로 유한요소해석은 매우 간단하고 경제적이었으며 이들의 정당성과 정확도를 입증하기위하여 여러하중 조건하의 복합체를 풀이하였다.

• 한국토양비료학회지
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• 제25권3호
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• pp.213-219
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• 1992

충북(忠北) 괴산군(槐山郡)에 위치한 옥천계(沃川系) 천매암토양(千枚岩土壤)의 특성을 사면경사(斜面傾斜)에 따라 토양(土壤) catena를 구명하고, 옥천계토양(沃川系土壤)의 분포를 조사하고자 수행하였다. 1. 옥천계모암(沃川系母岩)은 216천ha 분포하였으며, 옥천계토양(沃川系土壤)은 목(目) 2 아목(亞目) 3 대군(大群) 4 아군(亞群) 5 토양통(土壤統) 9개로 밝혀졌다. 2. 사면경사(斜面傾斜)는 토색연속계(土色連續系)를 이루었으며, 토색지수와 $Fe_2O_3$ 함량은 배수가 양호할 수록 증가하였다. 3. 미사/점토비(比)와 Ca/Mg比는 상대표고(相對標高)가 높을 수록 그리고 토심이 깊을 수록 좁아졌다. 4. 토양의 생성년령은 산견(山肩)>산복(山腹)>산록(山麓)>산지경사(山肢傾斜), 토양모재의 생선년령은 C>B>A층의 순이었다. 5. 토양단면내 토색지수와 $Fe_2O_3$ 함량은 고도의 유의성을 나타내었다. 6. 생성학적 유형은 C/D형이었으며, 토심>12cm에서의 토양성질 변화는 연속함수(連續函數)를 갖는다.