• International Journal of Aeronautical and Space Sciences
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• v.8 no.1
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• pp.95-104
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• 2007

A new design approach of complex geometries such as wing/body configuration is arranged by using overset mesh techniques under large scale computing environment. For an in-depth study of the flow physics and highly accurate design, several special overlapped structured blocks such as collar grid, tip-cap grid, and etc. which are commonly used in refined drag prediction are adopted to consider the applicability of the present design tools to practical problems. Various pre- and post-processing techniques for overset flow analysis and sensitivity analysis are devised or implemented to resolve overset mesh techniques into the design optimization problem based on Gradient Based Optimization Method (GBOM). In the pre-processing, the convergence characteristics of the flow solver and sensitivity analysis are improved by overlap optimization method. Moreover, a new post-processing method, Spline-Boundary Intersecting Grid (S-BIG) scheme, is proposed by considering the ratio of cell area for more refined prediction of aerodynamic coefficients and efficient evaluation of their sensitivities under parallel computing environment. With respect to the sensitivity analysis, discrete adjoint formulations for overset boundary conditions are derived by a full hand-differentiation. A smooth geometric modification on the overlapped surface boundaries and evaluation of grid sensitivities can be performed by mapping from planform coordinate to the surface meshes with Hicks-Henne function. Careful design works for the drag minimization problems of a transonic wing and a wing/body configuration are performed by using the newly-developed and -applied overset mesh techniques. The results from design applications demonstrate the capability of the present design approach successfully.

• Proceedings of the Korean Vacuum Society Conference
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• 2015.08a
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• pp.171.1-171.1
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• 2015

Carbon nanotube emitters is very promising electron emitter for electron beam applications. We introduced the carbon nanotube electron beam (C-beam) exposure technic using triode structure. As a source, the electron beam emit from CNT emitters placed at the cathode by high electric field. Through the gate mesh, with high accelerating energy, the electron can be extracted easily and impact at the anode plate. For thin film modification, after the C-beam exposure on the amorphous silicon thin film, we found phase changes and it showed a high crystallinity from the Raman measurement. We expect that this crystallized film will be a good candidate as a new active layer of TFT.

• Structural Engineering and Mechanics
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• v.16 no.4
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• pp.479-492
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• 2003

Non-conforming membrane elements which have variable number of mid-side nodes with drilling degrees of freedom and which is designated as NMDx have been presented in this paper. The non-conforming elements with variable number of mid-side nodes can be efficiently used in the local mesh refinement for the in-plane structures. To guarantee the developed elements always pass the patch test, the direct modification method is incorporated into the element formulation. Detailed numerical tests in this study show the validity of the variable node NC elements developed in this study and a wide applicability of these elements to practical problems.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.11a
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• pp.830-833
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• 2005

SDM(Structural Dynamics Modification) is to improve dynamic characteristics of a structure, more specifically of a base structure, by adding or deleting auxiliary(modifying) structures. In this paper, I will focus on the optimal layout of the stiffeners which are attached to the plate to maximize 1st natural frequency. Recently, a new topology method was proposed by yamazaki. He uses growing and branching tree model. I modified the growing and branching tree model. The method is designated modified tree model. To expand the layout of stiffeners, I will consider non-matching problem. The problem is solved by using local lagrange multiplier without the mesh regeneration. Moreover The CMS(Component mode synthesis) method is employed to reduce the computing time of eigen reanalysis using reduced componet models.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.11a
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• pp.834-837
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• 2005

Structural Dynamics Modification (SDM) is a very effective technique to improve structure's dynamic characteristics by adding or removing auxiliary structures, changing material properties and shape of structure. Among those of SDM technique, the method to change shape of structure has been mostly relied on engineer's experience and trial-and-error process which are very time consuming. In order to develop a systematic method to change structure shape, surface grooving technique is studied and successfully applied to HDD cover model. At first, to check the effect of mesh size, surface grooving technique was tested to the fine HDD cover FEmodel. And fur the more efficient method, the algorithm is modified. Removing the low-valued modal strain energy element among the target domain, computational effort can be greatly reduced and the result of simulation is similar with the other simulation result.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 1993.10a
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• pp.120-127
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• 1993

This paper is concerned with the integrated computer program system aiming at efficiently performing the structural analysis and design. The developed computer program system is introduced and applied to a simple two-dimensional structure to show the general concept of the integrated system. Some design modifications and re-analyses are illustrated including local mesh refinement, These show the efficiency in doing design modification and analysis.

• Tunnel and Underground Space
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• v.30 no.6
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• pp.509-518
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• 2020

This study constructed a new simulation platform, including mesh generation process, numerical simulation, and post-processing for results analysis based on exploration data to perform real-scale numerical analysis considering the actual geological structure efficiently. To build the simulation platform, we applied for open-source programs. The source code is open to be available for code modification according to the researcher's needs and compatibility with various numerical simulation programs. First, a three-dimensional model(3D) is acquired based on the exploration data obtained using a drone. Then, the domain's mesh density was adjusted to an interpretable level using Blender, the free and open-source 3D creation suite. The next step is to create a 3D numerical model by creating a tetrahedral volume mesh inside the domain using Gmsh, a finite element mesh generation program. To use the mesh information obtained through Gmsh in a numerical simulation program, a converting process to conform to the program's mesh creation protocol is required. We applied a Python code for the procedure. After we completed the stability analysis, we have created various visualization of the study using ParaView, another open-source visualization and data analysis program. We successfully performed a preliminary stability analysis on the full-scale Dokdo model based on drone-acquired data to confirm the usefulness of the proposed platform. The proposed simulation platform in this study can be of various analysis processes in future research.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.41 no.11
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• pp.865-873
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• 2013

In this paper, numerical methods for wrinkle prediction of thin membrane were studied by finite element analysis. Techniques using membrane and shell elements were applied for triangular membrane. In case of membrane element method, the wrinkling was accounted for by the wrinkle algorithm of property modification, which was implemented to ABAQUS as a user subroutine. In case of shell method, geometrically nonlinear post-buckling analysis was performed to obtain the wrinkle deformation explicitly. The wrinkling deformation was induced by seeding the mesh with a random geometric imperfection. The results were investigated focusing on the mesh convergence and the solution accuracy.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.7
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• pp.1408-1415
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• 2002

In this paper, we investigate the effect and the importance of the accuracy of finite element analysis in the shape optimization based on the finite element method and improve the existing finite element which has inaccuracy in some cases. And then, the shape optimization is performed by using the improved finite element. One of the main stream to improve finite element is the prevention of locking phenomenon. In case of bending dominant problems, finite element solutions cannot be reliable because of shear locking phenomenon. In the process of shape optimization, the mesh distortion is large due to the change of the structure outline. So, we have to raise the accuracy of finite element analysis for the large mesh distortion. We cannot guarantee the accurate result unless the finite element itself is accurate or the finite elements are remeshed. So, we approach to more accurate shape optimization to diminish these inaccuracies by improving the existing finite element. The shape optimization using the modified finite element is applied to a two and three dimensional simple beam. Results show that the modified finite element has improved the optimization results.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.26 no.3
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• pp.308-314
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• 2016

This paper proposes design guidances for noise reduction of a bank teller cash recycler(TCR). The operating noise of a TCR is required to be reduced because it bothers bank tellers and customers. The operating noise from a TCR is measured and the most influential driving system is examined. To find the main sources of the noise, the frequency spectra are analyzed by comparing with excitation frequencies of the driving system. From the analysis results, we reveals that the main sources of the noise are gear mesh frequency of a certain gear train and its side band frequencies, which is attributed by vulnerable support condition. Consequently, to reduce the operating noise, the structural modification for the gear train support is suggested and its effectiveness for the noise reduction is confirmed experimentally.