• 공업화학
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• 제9권2호
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• pp.294-299
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• 1998

입자당 한 개 이상의 성장라디칼이 있는 일반계에서 근사적인 psedo-homopolymerization (PHP)방법의 신뢰성을 간접적으로 증명하기 위하여, 벌크중합의 Mayo-Lewis식이 Interval II 동안 유화중합의 순간공중합조성식으로부터 확률적으로 유도됨을 보였다. Ballard등에 의하여 제안된 유화공중합의 확장된 Smith-Ewart식으로부터 0-1계(입자당 1개 이하의 성장라디칼이 있는 계)에 대하여 완전해를 얻었다. 이 해를 사용하여 입자당 평균라디칼수와 순간공중합조성이 몇 분 이내에 정상상태에 도달함을 예측할 수 있었다. 따라서 0-1계에 국한하여 PHP근사방법의 신뢰성을 직접 증명할 수 있었다. 모델계산의 목적으로 Styrene-butadiene(St-Bu)과 Styrene-methyl methacrylate(St-MMA)계를 예로 들었다.

• International Journal of Naval Architecture and Ocean Engineering
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• 제8권2호
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• pp.177-187
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• 2016

To evaluate the tractive performance of tracked trencher on seafloor surface, a new shear stress-displacement empirical model was proposed for saturated soft-plastic soil (SSP model). To validate the SSP model, a test platform, where track segment shear test can be performed in seafloor soil simulacrum (bentonite water mixture), was built. Series shear tests were carried out. Test results indicate that the SSP model can describe the mechanical behavior of track segment with good approximation in seafloor soil simulacrum. Through analyzing the main external forces applied to seafloor tracked trencher during the uniform linear trenching process, a drawbar pull prediction model was deduced with the SSP model. A tracked walking mechanism of the seafloor tracked trencher prototype was built, and verification tests were carried out. Test results indicate that this prediction model was feasible and effective; moreover, from another side, this conclusion also proved that the SSP model was effective.

• 한국CDE학회논문집
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• 제11권3호
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• pp.223-233
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• 2006

Layered manufacturing(LM) is emerging as a new technology that enables the fabrication of three dimensional heterogeneous objects such as Multi-materials and Functionally Gradient Materials (FGMs). Among various types of heterogeneous objects, more attention has recently paid on the fabrication of FGMs because of their potentials in engineering applications. The necessary steps for LM fabrication of FGMs include representation and process planning of material information inside an FGM. This paper introduces a new process planning algorithm that takes into account the processing of material information. The detailed tasks are discretization (i.e., decomposition-based approximation of volume fraction), orientation (build direction selection), and adaptive slicing of heterogeneous objects. In particular, this paper focuses on the discretization process that converts all of the material information inside an FGM into material features like geometric features. It is thus possible to choose an optimal build direction among various pre-selected ones by approximately estimating build time. This is because total build time depends on the complexity of features. This discretization process also allows adaptive slicing of heterogeneous objects to minimize surface finish and material composition error. In addition, tool path planning can be simplified into fill pattern generation. Specific examples are shown to illustrate the overall procedure.

• 한국해양공학회지
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• 제32권1호
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• pp.28-35
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• 2018

An analytical method for predicting the velocity potential around a pulsating bubble close to a free or rigid wall was established using an image method. Because the velocity potential should satisfy two boundary conditions at the bubble surface and rigid wall, we investigated the velocity in the normal direction at the two boundaries by adding the image bubbles. The potential was analyzed by decomposing the bubble motion as two independent motions, pulsation and translation, and we found that when the number of image bubbles was greater than ten, the two boundary conditions were satisfied for the translation term. By adding many image bubbles after the approximation of the pulsation term, we also confirmed that the boundary condition at the wall was satisfied.

• 한국공간구조학회논문집
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• 제6권1호
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• pp.117-127
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• 2006

경량 연성구조시스템 중 하나인 막 구조물은 대공간 구조물에 많이 사용되어진다. 막 구조물은 축강성이 강하고 휨강성이 매우 작은 재료를 주 구조재로 사용하기 때문에 다른 구조물과 달리 구조설계에서는 형상해석, 응력-변형해석 그리고 재단도 등의 일련의 과정을 필요로 한다. 재단도의 작성에는 구조물의 크기나 곡률 그리고 재료적 강성에 따라 많은 변수가 작용하며 다른 설계과정과는 매우 다르다. 따라서 일반 구조설계용 프로그램은 막 구조물의 구조설계에 부적당하다. 본 연구에서는 막 구조물의 측지선을 이용한 재단도 작성 프로그램을 개발하고, 예제를 통해 재단도 작성결과를 비교 고찰하도록 한다.

• International Journal of Aeronautical and Space Sciences
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• 제8권1호
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• pp.140-147
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• 2007

Whenever the hinge axis of aircraft wing rotates, its stiffness varies. Also, there are nonlinearities in the connection of the actuator and the hinge axis, and it is necessary to inspect the coupled effects between the actuator dynamics and the hinge nonlinearity. Nonlinear aeroelastic characteristics are investigated by using the iterative V-g method. Time domain analyses are also performed by using Karpel's minimum state approximation technique. The doublet hybrid method(DHM) is used to calculate the unsteady aerodynamic forces in subsonic regions. Structural nonlinearity located in the load links of the actuator is assumed to be friction. The friction nonlinearity of an actuator is identified by using the describing function technique. The nonlinear flutter analyses have shown that the flutter characteristics significantly depends on the structural nonlinearity as well as the dynamic stiffness of an actuator. Therefore, the dynamic stiffness of an actuator as well as the nonlinear effect of hinge axis are important factors to determine the flutter stability.

• 대한토목학회논문집
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• 제14권6호
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• pp.1445-1451
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• 1994

해안구조물에 작용하는 설계파압(設計波壓)을 수치적으로 계산하기 위해서는 먼저 쇄파한계(碎波限界)에 가까운 큰 중복파랑을 수치적으로 재현할 필요가 있다. 이를 위해서는 지배방정식(支配方程式)과 비선형항(非線形項)을 포함하는 경계조건을 효과적으로 반영해야 하며 특히, 자유표면(自由表面) 경계조건(境界條件)에서의 속도의 제곱항의 처리가 중요하다. 본 연구에서는 Newton 방법을 이용하여 제곱항을 충실히 반영하므로써 일반적인 셜계파 성향에 거의 상응하는 중복파랑을 재현하였으며 기존의 섭동법(攝動法) 또는 Fourier 전개 기법 및 수리실험 결과와 비교하여 그 정확도를 검토하였다.

• 대한기계학회논문집A
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• 제24권5호
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• pp.1175-1182
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• 2000

Diffraction systematically causes error in acoustic measurements. Most probes are designed to reduce this phenomenon. On the contrary, this paper proposes a spherical probe a] lowing acoustic inten sity measurements in three dimensions to be made, which creates a diffracted field that is well-defined, thanks to analytic solution of diffraction phenomena. Six microphones are distributed on the surface of the sphere along three rectangular axes. Its measurement technique is not based on finite difference approximation, as is the case for the ID probe but on the analytic solution of diffraction phenomena. In fact, the success of sound source identification depends on the inverse models used to estimate inverse diffraction phenomena, which has nonlinear properties. In this paper, we propose the concept of nonlinear inverse diffraction modeling using a neural network and the idea of 3 dimensional sound source identification with better performances. A number of computer simulations are carried out in order to demonstrate the diffraction phenomena under various angles. Simulations for the inverse modeling of diffraction phenomena have been successfully conducted in showing the superiority of the neural network.

• 대한기계학회논문집B
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• 제24권3호
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• pp.450-458
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• 2000

This study deals with the unsteady close-contact melting of solid blocks on a flat surface subject to convective heating. Normalizing the model equations in reference to the steady solution successfully leads them to cover constant heat flux and isothermal limits at small and large extremes of the Biot number, respectively. The resulting equations admit a compactly expressed analytical solution, which includes the previous solutions as a subset. Based on the steady solution, the characteristics of close-contact melting can be categorized into constant heat flux, transition, and isothermal regimes, the boundaries of which appear to be nearly independent of the contact force. The unsteady solutions corresponding to Biot numbers in the transition regime show intermediate behaviors between those of the two limits. With a proper approximation, the present solution procedure can cope with the case of variable fluid temperature and heat transfer coefficient. Regardless of imposed conditions, the mean normalized Nusselt number during the unsteady process asymptotically approaches to a constant value as the Biot number comes close to each limit.

• 한국해양공학회지
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• 제19권2호
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• pp.12-18
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• 2005

Typhoon Maemi landed on the southeast coast of Korea and caused a severe storm surge in Jinhae Bay and Masan Bay. The tide gage in Masan Port recorded the storm surge of a maximum of more than 2m and the area of more than 700m from the Seo Hang Wharf was flooded by the storm surge. They had not met such an extremely severe storm surge since the opening of the port. Then storm surge was hindcasted with a numerical model. The typhoon pressure was approximated by Myers' empirical model and super gradient wind around the typhoon eye wall was considered in the wind estimation. The land topography surrounding Jinhae Bay and Masan Bay is so complex that the computed wind field was modified with the 3D-MASCON model. The motion of seawater due to the atmospheric forces was simulated using a one-layer model based on non-linear long wave approximation. The Janssen's wave age dependent drag coefficient on the sea surface was calculated in the wave prediction model WAM cycle 4 and the coefficient was inputted to the storm surge model. The result shows that the storm surge hindcasted by the numerical model was in good agreement with the observed one.