• Korean Chemical Engineering Research
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• v.54 no.4
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• pp.479-486
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• 2016

The efficient steam drum should be required to reduce carbon oxide emissions and heat recovery in oxygen converter hood system. However, steam generation is limited to the time of the oxygen blowing period, which is intermittent or cyclical in operation of steel-making process. Thus, steam drum should be optimized for an effective steam generation during the oxygen blowing portion of the converter cycle. In this study, a three-dimensional computational fluid dynamics (CFD) model has been developed to describe the impacts of changing various operating conditions and geometric shape on thermo-fluid characteristics and performance of the steam drum. This model encompasses not only fluid flow and heat transfer but also evaporation and condensation at the interfacial surface in the steam drum by using VOF (Volume of Fluid) method. To validate the prediction performance of this model, comparison of the steam flow rate between numerical and experimental result has been performed, resulting in the accuracy of the relative error by less than 3.2%.

• Proceedings of the Korea Water Resources Association Conference
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• 2022.05a
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• pp.100-100
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• 2022

일반적으로 유체와 구조물간 상호작용의 수리동역학적 모의에서는 벽경계조건을 통하여 유동에 대한 구조물의 영향이 반영된다. 하지만 도심지에서 발생한 홍수를 예측하려는 경우 이러한 방법으로는 밀집한 구조물들 사이에 형성된 좁은 길들로 인하여 세밀한 격자망을 요하여 큰 계산량을 유발하고 빠른 예측 속도를 기대할 수 없게 한다. 최근 이러한 문제를 극복하기 위해 성긴 격자망에서도 구조물의 유체에 대한 영향을 반영할 수 있도록 하는 방법들이 큰 관심을 받고 있다. 그 중에서도 다공성 천수방정식은 벽경계조건 대신 다공도(posority)의 개념을 이용한 모형으로 도시범람모의에 있어 계산량과 정확도를 가장 적절하게 타협한 모형으로 보고되고 있다. 이러한 흐름에 맞추어 본 연구는 다공도 천수방정식을 해석하는 수치 기법을 개발하였고, 여기에 최근 쌍곡선계 방정식의 수치적 연구들에서 소개된 주요 특징들이 반영되도록 설계하였다. 우선, WENO 기법과 Runge-Kutaa 기법을 통하여 공간과 시간에 대한 고차 정확도를 만족시켰다. 이 때, 재구성 변수와 알고리즘를 새롭게 제시하여 정상흐름조건에 대한 플럭스항과 생성·소멸항간 절단오차에 의한 비물리적인 흐름생성을 억제하였다. 또한, 수치모의 중 음수심의 발생으로 인하여 수치모형이 불안정해지는 현상을 막기 위해, 양-보존성 제한자를 구축하였다. 마지막으로 도심지에서 즐비한 인위적인 구조물에 의해 나타나는 지형적인 불연속의 효과를 적절하게 반영할수 있도록 정상파 재구축의 단계를 구축하여 수치 기법에 반영하였다. 이렇게 구성된 수치기법은 리만문제의 해석해에 기반하여 기존의 주요 연구들의 결과와 비교되었고, 그 결과 본 연구의 방법이 정확성, 수렴성, 안전성의 측면에서 가장 우수함을 수치적으로 증명하였다.

• Journal of the Society of Naval Architects of Korea
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• v.34 no.1
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• pp.11-23
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• 1997

This paper contains a new approach to blade section design method for marine propellers. The hydrodynamic characteristics of 2-D section are highly influenced by its geometrical parameters i.e., thickness and camber distributions and leading edge radius etc. To consider fully turbulent flow field near 2-D section. the finite volume method with k-${\varepsilon}$ turbulent model which solve Reynolds time averaged Navier-Stokes(RANS) equation is applied. In this study, O-type grid system that can provide many calculation points on blade surface is used. The results were compared with those of the experiment of NACA0012 to confirm the accuracy of the developed codes. The goal of this study is the development of a blade section with high efficiency and low drag. To achieve this, we carried out the tests of lift, drag and cavitation characteristics in cavitation tunnel. The results of experiment were compared with numerical results in order to validate the proposed blades design method. By comparing the numerical results with the experiments, we found that the new blade section, KH28 allows superior performance in efficiency and cavitation avoidance characteristics. We further investigated the blade section design method and an application study of this section, KH28 to apply to the marine propeller. In order to improve the accuracy of numerical results on prediction of lift and drag, we conclude here that the 2-layer boundary model must be used.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.38 no.2
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• pp.183-190
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• 2014

A multiphase pump was developed in this study. The optimum multiphase pump design was arrived at, and the interactions among the different geometric configurations were explained by applying numerical analysis and the DOE (design of experiments) method. First, we designed the base model to meet the specifications. Then, we defined the design parameters related to the meridional plane and the blade angle. Each design parameter was used for generating experiment sets, and numerical analyses were performed on these sets. Finally, the optimized design was selected based on the results of the DOE analysis. The numerical optimization resulted in the optimum model having higher efficiency than the base model. In addition, performance degradation due to changes in the GVF (gas volume fraction) is discussed.

• Journal of the Society of Naval Architects of Korea
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• v.49 no.6
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• pp.461-468
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• 2012

In this study, a Cartesian-grid method based on finite volume approach is applied to simulate the ship motions in large amplitude waves. Fractional step method is applied for pressure-velocity coupling and TVD limiter is used to interpolate the cell face value for the discretization of convective term. Water, air, and solid phases are identified by using the concept of volume-fraction function for each phase. In order to capture the interface between air and water, the tangent of hyperbola for interface capturing (THINC) scheme is used with weighed line interface calculation (WLIC) method which considers multidimensional information. The volume fraction of solid body embedded in the Cartesian grid system is calculated using a level-set based algorithm, and the body boundary condition is imposed by a volume weighted formula. Numerical simulations for the two-dimensional barge type model and Wigley hull in linear waves have been carried out to validate the newly developed code. To demonstrate the applicability for highly nonlinear wave-body interactions such as green water on the deck, numerical analysis on the large-amplitude motion of S175 containership is conducted and all computational results are compared with experimental data.

• Proceedings of the Korean Nuclear Society Conference
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• 1998.05a
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• pp.603-608
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• 1998

유체내의 물체 주위에서 유동박리로 인해 생성되는 와류쉐딩은 열전달이나 물질전달을 촉진시키는 이점이 있으나, 항력을 증가시키거나 유동 및 온도의 요동에 의해 구조물을 손상시키는 단점이 있다. 특히 물체와 주위 유동 사이에 공진이 일어나면 항력값이 증가하면서 항력과 양력의 진폭이 급격히 증가하여 물체에 심각한 손상을 초래할 수 있다. 본 연구에서는 레이놀즈수 200 이하의 층류유동에서 공진시 물체 주위의 유동현상과 이로 인한 양력과 항력의 변화들을 수치해석방법을 통하여 분석하였다 수치해석은 일반좌표계에서 유한체적법을 적용하여 Navier-Stokes 방정식을 차분화하였다. 이때 방정식의 종속변수로는 공변속도를 채택하였으며, 이산화된 방정식은 분리단계법을 이용하여 수치해를 구하였다. 입구유속의 강제진동에 의한 사각실린더 주위의 와류쉐딩시 공진이 발생하는 강제진동수의 범위는 원통실린더의 경우와 유사하였으나 상대적으로 폭이 더 좁았다 그리고 공진이 발생하는 강제진동수의 범위는 진폭이 증가할수록 증가하였다. 쉐딩 진동수가 일정하면서 입구유속의 진폭이 증가하면 이에 비례하여 실린더 주위의 유속이 상대적으로 증가하게 되어 와도가 강해지면서 입추유속 진폭에 비례하여 항력의 평균값 뿐 아니라 항력과 양력의 진폭도 증가하였다. 그리고 실린더 뒷면의 와류 생성영역은 진폭에 비례하여 감소하였다. 진폭의 변화에 따라 상변화가 서로 상이한 것은 실린더 뒤쪽의 와류들이 상하면의 합력차이를 변화시켰고 이것이 진폭변화에 따라 상변화를 상이하게 나타나게 한 원인으로 진폭이 클수록 실린더 뒤쪽에서 압력변화가 심하게 변하면서 실린더 앞쪽까지 더 많은 영향을 미쳤기 때문이다.선원의 사용자에게 제공되는 최종방사능을 평가하는데 유용하게 사용될 수 있다.r의 분포를 보였다.cting the effect of earthquake on structures. This paper is based on the presented paper at the Bertero Symposium held in January 31an4 February 1 at Berkeley, California, USA which was entitled "Needs to Evaluate Real Seismic Performance of Buildings-Lessons from 1995 Hyogoken-Nambu Earthquake-". The lessons for buildings from the damage due to the Hyogoken-Nambu Earthquake are necessity to develop more rational seismic design codes based upon a performance-based design concept, and to evaluate seismic performance of existing buildings. In my keynote lecture at the Korean Association for Computational Structural Engineering, the history of seismic design and use of structural analysis in Japan, the lessons for buildings from the Hyogoken-Nambu Earthquake, the

• Journal of the Society of Naval Architects of Korea
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• v.51 no.5
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• pp.409-418
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• 2014

Simulation of flow past a complex marine structure requires a fine resolution in the vicinity of the structure, whereas a coarse resolution is enough far away from it. Therefore, a lot of grid cells may be wasted, when a simple Cartesian grid system is used for an Immersed Boundary Method (IBM). To alleviate this problems while maintaining the Cartesian frame work, we adopted an Adaptive Mesh Refinement (AMR) scheme where the grid system dynamically and locally refines as needed. In this study, We implemented a moving IBM and an AMR technique in our basic 3D incompressible Navier-Stokes solver. A Volume Of Fluid (VOF) method was used to effectively treat the free surface, and a recently developed Lagrangian Dynamic Subgrid-scale Model (LDSM) was incorporated in the code for accurate turbulence modeling. To capture vortex induced vibration accurately, the equation for the structure movement and the governing equations for fluid flow were solved at the same time implicitly. Also, We have developed an interface by using AutoLISP, which can properly distribute marker particles for IBM, compute the geometrical information of the object, and transfer it to the solver for the main simulation. To verify our numerical methodology, our results were compared with other authors' numerical and experimental results for the benchmark problems, revealing excellent agreement. Using the verified code, we investigated the following cases. (1) simulating flow around a floating sphere. (2) simulating flow past a marine structure.

• Journal of the Korean Society for Marine Environment & Energy
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• v.8 no.1
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• pp.39-45
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• 2005

In the situation which Russia's ratification of the Kyoto protocol at February,2004, ANNEX I nations must reduce GHG(Green House Gas) discharge rate from 2008 by 2012 to the reduction level at 1990. We introduce the CO₂ ocean sequestration that is one of promising method for getting the stable CO₂ concentration in the atmosphere. There are four categories : ocean transportation technique, ocean initial dissolution technique, ocean deep current evaluation technique, and ocean biological evaluation technique. In this paper, we carried out the fundamental numerical study on the ocean initial dissolution technique, when the Liquidized CO₂ is emitted at the deep ocean, It is very important to the dissolution rate of movable CO₂ interface because it Is directly impact to the ocean organism. In order to investigate the relation of the interface movement and rate of the dissolution, we develope CR(Computational Fluid Dynamics) code that was constructed by the finite volume method based on the unstructured mesh, and a droplet's boundary surface can move and one direction dissolution from disperse phase into continuous phase adopted as its physics be. This study clarifies hydrodynamic relation between solubility and movement of the droplet through the verification of the Cm code.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.40 no.7
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• pp.441-448
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• 2016

The thrust force created by a propeller depends on the incoming flow velocity and the rotational velocity of the propeller. The performance of the propeller can be described by dimensionless variables, advanced ratio, thrust coefficient, and power coefficient. This study included the application of the immersed boundary lattice Boltzmann method (IBLBM) with the stereo lithography (STL) file of the rotating object for performance analysis. The immersed boundary method included the addition of the external force term to the LB equation defined by the velocity difference between the lattice points of the propeller and the grid points in the domain. The flow by rotating a 4-blade propeller was simulated with various Reynolds numbers (Re) (including 100, 500 and 1000), with advanced ratios in the range of 0.2~1.4 to verify the suggested method. The typical tendency of the thrust efficiency of the propeller was obtained from the simulation results of different advanced ratios. It was also necessary to keep the maximum mesh size ratio of the propeller surface to a grid size below 3. Additionally, a sufficient length of the downstream region in the domain was maintained to ensure the numerical stability of the higher Re and advanced ratio flow.

• Journal of Advanced Marine Engineering and Technology
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• v.36 no.8
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• pp.1091-1096
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• 2012

The aerodynamic characteristics of circular cylinder in a channel are studied to make clear the flow feature by solving the Navier-Stokes equation based on the finite volume method with unstructured grids. Reviews are made on with the vorticity, velocity, dynamic pressure, residual and drag, where the Reynolds numbers are 50 and 100. The flows for $Re{\succeq}50$ shows the vortex shedding in the wake, and the result is the same as the case of moving cylinder. The ground effect of flat bottom results in the growth of vortex, being generated in the upper side of the cylinder and elongated in the rear. As the cylinder approaches to wall, for example 0.6, the cylinder plays as a role of blockage to obstruct the flow between the cylinder and wall. The drag coefficients are compared with others' results to confirm the validity of the present numerical simulation.