• Ocean Systems Engineering
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• 제7권1호
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• pp.53-74
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• 2017

Ship shaped FPSO (Floating Production, Storage and Offloading) units are the most commonly used floating production units to extract hydrocarbons from reservoirs under the seabed. These structures are usually much larger than general cargo ships and have their natural frequency outside the wave frequency range. This results in the response to first order wave forces acting on the hull to be negligible. However, second order difference frequency forces start to significantly impact the motions of the structure. When the difference frequency between wave components matches the roll natural frequency, the structure experiences a significant roll motion which is also termed as second order roll. This paper describes the theory and numerical implementation behind the calculation of second order forces and motions of any general floating structure subjected to waves. The numerical implementation is validated in zero speed case against the commercial code OrcaFlex. The paper also describes in detail the popular approximations used to simplify the computation of second order forces and provides a discussion on the limitations of each approximation.

• Bulletin of the Korean Chemical Society
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• 제16권10호
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• pp.957-968
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• 1995

Generalized Multichannel Quantum Defect theory (MQDT) was implemented to the vibrational predissociation of triatomic van der Waals molecules in the previous paper [Bull. Korean Chem. Soc, 12, 228 (1991)]. Implementation was limited to the calculation of the scattering matrix. It is now extended to the calculation of the predissociation spectra and the final rotational distribution of the photofragment. The comparison of the results with those obtained by other methods, such as Golden-rule type calculation, infinite order sudden approximation (IOS), and close-coupling method, shows that the implementation is successful despite the fact that transition dipole moments show more energy dependence than other quantum defect parameters. Examination of the short-range channel basis functions shows that they resemble angle-like functions and provide the validity of the IOS approximation. Besides the validity of the latter, only a few angles are found to play the major role in photodissociation. In addition to the implementation of MQDT, more progress in MQDT itself is made and reported here.

• 한국정보과학회논문지:시스템및이론
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• 제31권10호
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• pp.562-574
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• 2004

본 논문에서는 고정 우선순위 경성 실시간 시스템에 대한 에너지 측면에서의 최적의 전압 스케줄링 문제를 고려한다. 먼저, 이 문제가 NP-hard임을 증명한다. 다음으로 이 문제에 대한 fully polynomial time approximation scheme(FPTAS)을 제시한다 제안한 FPTAS는 주어진 임의의 $\varepsilon$>0에 대해 에너지 소모량이 최적의 전압 스케줄에 비해 (1＋$\varepsilon$)배 이내에 있는 전압 스케줄을 문제의 입력의 크기와 1/$\varepsilon$의 다항함수 이내의 시간에 계산해준다. 실험 결과, 제안된 FPTAS는 기존의 휴리스틱에 비해 더 효율적인 전압 스케줄을 더 빠른 시간에 찾아주었다.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2010년도 춘계학술대회 논문집
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• pp.78-79
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• 2010

• 한국정보과학회논문지:시스템및이론
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• 제30권7_8호
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• pp.387-396
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• 2003

본 논문은 STP-MSP을 위한 근사 알고리즘을 제안한다. 이 문제에 대해 근접한 최적 해법을 제공하는 PTAS를 가지는 것이 불가능하기 때문에, 본 논문의 연구는 $n^{O(1)}$의 실행 시간과 근사 비율 2를 가지는 하나의 대안을 제시한다. 본 연구의 중요성은 관련된 다른 미해결문제에 대하여 해결 가능성을 제시하는 것이다. 본 논문의 주요 제안내용은 문제 인스턴스에게 허용오차를 배분하는 것이다. 이로 인해 우리는 무한적 경우에서 다항적 범위로 실행시간을 줄일 수 있다. 관련연구[1,2]가 근사 비율이 2보다 크지만 보다 현실적인 실행시간을 갖는 근사 알고리즘들을 제시한 것이라면, 본 연구는 근사 비율이 2인 근사 알고리즘의 존재를 밝힌 것이다.

• Communications for Statistical Applications and Methods
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• 제15권3호
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• pp.465-481
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• 2008

문항반응이론(Item response theory: IRT)에서는 문항이 가지고 있는 특성을 기초로 피험자의 능력을 추정하고 동시에 각 문항별 문항특성곡선(Item characteristics curve: ICC)을 이용하여 문항모수를 추정하게 된다. 그러나 모수추정에 있어서 최대 우도추정의 경우는 초기값과 다른 여러 문제들이 발생할 수 있다. 본 연구에서는 추정 문제 해결방법의 대안으로 점근적 근사화 방법(Asymptotic approximation method: AAM)을 제안한다. 이는 자료의 수가 적거나 국소 변동이 있는 경우에 효과적인 추정방법이라고 할 수 있다. 이에 개발된 'Any Assess' 시스템을 모의실험을 통하여 신뢰성을 검정하였다.

• Bulletin of the Korean Chemical Society
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• 제16권9호
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• pp.873-885
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• 1995

The local structural and thermodynamical properties of blends A-B/H of a diblock copolymer A-B and a homopolymer H are studied using the polymer reference interaction site model (RISM) integral equation theory with the mean-spherical approximation closure. The random phase approximation (RPA)-like static scattering function is derived and the interaction parameter is obtained to investigate the phase transition behaviors in A-B/H blends effectively. The dependences of the microscopic interaction parameter and the macrophase-microphase separation on temperature, molecular weight, block composition and segment size ratio of the diblock copolymer, density, and concentration of the added homopolymer, are investigated numerically within the framework of Gaussian chain statistics. The numerical calculations of site-site interchain pair correlation functions are performed to see the local structures for the model blends. The calculated phase diagrams for A-B/H blends from the polymer RISM theory are compared with results by the RPA model and transmission electron microscopy (TEM). Our extended formal version shows the different feature from RPA in the microscopic phase separation behavior, but shows the consistency with TEM qualitatively. Scaling relationships of scattering peak, interaction parameter, and temperature at the microphase separation are obtained for the molecular weight of diblock copolymer. They are compared with the recent data by small-angle neutron scattering measurements.

• 한국근적외분광분석학회:학술대회논문집
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• 한국근적외분광분석학회 2001년도 NIR-2001
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• pp.1132-1132
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• 2001

This work is a further development of the method created by G. Krivoshiev in 1996 for elimination of peel interference and prediction of fruit flesh optical density. In this investigation, as it was earlier, the objects are observed as being structured by three successive layer “AlongrightarrowOlongrightarrowB” denoting “peel-flesh-peel”. In the first version of the method the transmittances of the surface layers A and B were measured according to Kubelka-Munk theory by means of their diffuse reflectance. At that the overall transmittance T was approximated in the form of a multiplication approximation being valid for plane-parallel layers of a non-scattering material. In this work this approximation was done away with applying the theory of discontinuum, respectively Benfor's equations. As a result two mathematical models were created for non-destructive prediction of fruit flesh optical density. These models are different from the ones based solely on Kubelka-Munk theory, the destruction being marked by the terms 1n (1 - $R_{A}R_{0}$) and 1n (1 - $R_{A}R_{B}$), where: $R_{A}$ and $R_{B}$ are reflectance values for the surface layers A and B; $R_{0}$ is the average reflectance of the internal layer that could be obtained empirically by means of a preliminary measurement of sufficiently large number of physically peeled fruits of a given species and variety.

• Structural Engineering and Mechanics
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• 제65권5호
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• pp.513-521
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• 2018

In this paper, the resonance response of spar-type floating platform in coupled heave and pitch motion is investigated using a CPU time-effective numerical method. A coupled nonlinear 2-DOF equation of motion is derived based on the potential wave theory and the rigid-body hydrodynamics. The transient responses are solved by the fourth-order Runge-Kutta (RK4) method and transformed to the frequency responses by the digital Fourier transform (DFT), and the first-order approximation of heave response is analytically derived. Through the numerical experiments, the theoretical derivation and the numerical formulation are verified from the comparison with the commercial software AQWA. And, the frequencies of resonance arising from the nonlinear coupling between heave and pitch motions are investigated and justified from the comparison with the analytically derived first-order approximation of heave response.

• 한국경영과학회:학술대회논문집
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• 한국경영과학회 2008년도 추계학술대회 및 정기총회
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• pp.65-75
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• 2008

Over the last three decades, there are many researches focusing on the practice and theory of RM in airlines. Most of them have dealt with a seat assignment problem for maximizing the total revenue. In this study, we focus on a seat assignment problem in airlines. The seat assignment problem can be modeled as a stochastic programming model which is difficulty to solve optimally. However, with some assumptions on the demand distribution functions and a linear approximation technique, we can transform the complex stochastic programming model to a Linear Programming model. Some computational experiments are performed to evaluate out model with randomly generated data. They show that our model has a good performance comparing to existing models, and can be considered as a basis for further studies on improving existing seat assignment models.