• Wind and Structures
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• 제5권2_3_4호
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• pp.101-114
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• 2002

Both a Finite Volume and a Discrete Vortex technique to solve the unsteady Navier-Stokes equations have been employed to study the air flow around long-span bridge decks. The implementation and calibration of both methods is described alongside a quasi-3D extension added to the DVM solver. Applications to the wind engineering of bridge decks include flow simulations at different angles of attack, calculation of aerodynamic derivatives and fluid-structure interaction analyses. These are being presented and their specific features described. If a numerical method shall be employed in a practical design environment, it is judged not only by its accuracy but also by factors like versatility, computational cost and ease of use. Conclusions are drawn from the analyses to address the question of whether computer simulations can be practical design tools for the wind engineering of bridge decks.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2008년도 학술대회
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• pp.197-203
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• 2008

In the present study, we carry out numerical simulations of energy harvesting eel by using the immersed boundary method. Eel is modeled by a flexible filament and is placed behind a circular cylinder. We perform systematic simulations in order to explore the effects of Reynolds number. The instantaneous eel motion is analyzed under different conditions and surrounding vortical structures are identified. The flapping frequency of eel has been compared with that in case of plate alone as well as filament alone. As increasing Reynolds number, we can see that the flexible filament flaps passively by obtaining the Strouhal number of cylinder alone and filament with cylinder.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2008년도 학술대회
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• pp.57-70
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• 2008

A high-order accurate Euler flow solver based on a discontinuous Galerkin finite-element method has been developed for the numerical simulations of blade-vortex interaction phenomena on unstructured meshes. A free vortex in freestream was investigated to assess the vortex-preserving property and the accuracy of the present flow solver. Blade-vortex interaction problems in subsonic and transonic freestreams were simulated by adopting a multi-level solution-adaptive dynamic mesh refinement/coarsening technique. The results were compared with those of other numerical and experimental methods. It was shown that the present discontinuous Galerkin flow solver can preserve the vortex structure for significantly longer vortex convection time and can accurately capture the complex unsteady blade-vortex interaction flows, including generation and propagation of acoustic waves.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2008년 추계학술대회논문집
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• pp.57-70
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• 2008

A high-order accurate Euler flow solver based on a discontinuous Galerkin finite-element method has been developed for the numerical simulations of blade-vortex interaction phenomena on unstructured meshes. A free vortex in freestream was investigated to assess the vortex-preserving property and the accuracy of the present flow solver. Blade-vortex interaction problems in subsonic and transonic freestreams were simulated by adopting a multi-level solution-adaptive dynamic mesh refinement/coarsening technique. The results were compared with those of other numerical and experimental methods. It was shown that the present discontinuous Galerkin flow solver can preserve the vortex structure for significantly longer vortex convection time and can accurately capture the complex unsteady blade-vortex interaction flows, including generation and propagation of acoustic waves.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2008년 추계학술대회논문집
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• pp.197-203
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• 2008

In the present study, we carry out numerical simulations of energy harvesting eel by using the immersed boundary method. Eel is modeled by a flexible filament and is placed behind a circular cylinder. We perform systematic simulations in order to explore the effects of Reynolds number. The instantaneous eel motion is analyzed under different conditions and surrounding vortical structures are identified. The flapping frequency of eel has been compared with that in case of plate alone as well as filament alone. As increasing Reynolds number, we can see that the flexible filament flaps passively by obtaining the Strouhal number of cylinder alone and filament with cylinder.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 추계학술대회논문집B
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• pp.102-105
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• 2001

Numerical simulations of coal combustion were carried out to identify what kind of burner design parameters are affecting the NOx emission. Where used burner design parameters are primary air velocity, secondary air velocity, $2^{nd}/3^{rd}$ air ratio, tertiary air velocity, and tertiary air injection location. Taguchi method was used to find the effective burner design parameters related to NOx formation. The results of numerical simulations showed that secondary air velocity and $2^{nd}/3^{rd}$ air ratio was the key parameters reducing the NOx emission. The total number of simulation cases was reduced by Taguchi method.

• Structural Engineering and Mechanics
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• 제74권6호
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• pp.771-787
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• 2020

The paper provides an inside look into experimental measurements, followed by numerical simulations and their related uncertainties. The goal of the paper is to present findings related to blast loading and the handling of defects that are inherent in experiments. Very often it might seem that experiments are simplified reflections of real-life conditions. In most cases this is true, but there is a good reason for that. The more complex an experiment is, the larger the amount of uncertainties that can be expected. This especially applies when the blast loading of concrete is the subject of research. When simulations fail to reproduce the results of experimental measurements, it does not necessarily mean there is something wrong with the numerical model. The problem could be missing information. Put differently, the numerical simulation may lack information that seemed irrelevant with regard to the experiment. In the presented case, a reference simulation with a proven material model unexpectedly failed to replicate the results of an experiment where concrete slabs were exposed to blast loading. This resulted in a search for possible unknowns. When all of the uncertainties were examined, the missing information turned out to be the orientation of the charge to the concrete slab. Since the experiment was burdened with error, a sensitivity study had to take place so the influence of this factor could be better understood. The findings point to the fact that even the smallest defect during experiments must somehow be taken into account when designing numerical simulations. Otherwise, the simulations are not correlated to the experiments, but merely to some expectations.

• 대한조선학회논문집
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• 제60권4호
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• pp.266-277
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• 2023

In this study, fundamental research is conducted for the generation technique and analysis of multi-directional irregular waves in the Deep Ocean Engineering Basin (DOEB). A three-dimensional boundary element method-based numerical tank is implemented to perform wave generation simulations, and directional spectrum estimation is carried out using the results of simulations. The wave generation technique of the Snake type wave maker, generating multi-directional irregular waves, is implemented using the Fast Fourier Transform (FFT) and Inverse Fast Fourier Transform (IFFT) algorithms. The wave generation technique is validated by comparing the wave spectrum from simulations and experiments. A Maximum Likelihood Method (MLM) based estimation code is developed for estimating the directional wave spectra. The multi-directional irregular waves are tested in the DOEB and the numerical tank, and directional wave spectra obtained from two methodologies are estimated and compared. A correction procedure for the directional distribution of multi-directional waves is established, and the possibility of correcting the directional spreading function using the numerical tank is validated.

• 한국수자원학회논문집
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• 제48권11호
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• pp.957-967
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• 2015

측면 위어의 수위-유량 관계가 알려지지 않더라도, 저류지에 의한 홍수 조절 효과를 평가할 수 있는 2차원 수치모의에 대해 검토하였다. 수치해법으로서 천수방정식에 대해 유한체적법을 적용하고, 흐름률의 정확한 계산을 위해 근사 Riemann 해법을 도입하여 수심적분 2차원 수치모형을 구성하였다. 모의 결과를 수로와 저류지에서 자유월류와 잠긴 흐름이 발생되는 실험실 실험의 결과와 비교하였다. 자유 월류 상태에서 예측된 측면 위어의 유량 계수와 실험에 의한 그것 사이의 차이는 매우 작았다. 또한, 잠긴 흐름에 대한 모의 결과도 측정 결과와 잘 일치하였으며, 그 기구가 잘 재현되었다. 이 연구를 통해 2차원 수치모형으로 측면 위어에 대한 유량 계수를 정확하게 결정할 수 있으며, 저류지에 대한 홍수 방어능력의 검토 또한 상당한 수준의 정확도로 이루어질 수 있음이 확인되었다. 따라서 저류지의 계획, 설계안의 검토, 관리를 위한 기존 저류지의 평가 등에 이 모형의 실용적인 적용이 기대된다.

• International Journal of Naval Architecture and Ocean Engineering
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• 제7권6호
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• pp.1034-1043
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• 2015

This is the continuation of a numerical study on vortex shedding from a blunt trailing-edge of a hydrofoil. In our previous work (Lee et al., 2015), numerical schemes for efficient computations were successfully implemented; i.e. multiple domains, the approximation of domain boundary conditions using cubic spline functions, and particle-based domain decomposition for better load balancing. In this study, numerical results through a hybrid particle-mesh method which adopts the Vortex-In-Cell (VIC) method and the Brinkman penalization model are further rigorously validated through comparison to experimental data at the Reynolds number of $2{\times}10^6$. The effects of changes in numerical parameters are also explored herein. We find that the present numerical method enables us to reasonably simulate vortex shedding phenomenon, as well as turbulent wakes of a hydrofoil.