• Proceedings of the Korean Society of Precision Engineering Conference
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• 2001.04a
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• pp.964-967
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• 2001

Aspherical lens with the higher numerical aperture has been needed in the optical storage device to increase the recording density on the disk. However, high numerical aperture means the large slope angle at the clear aperture of the lens. Therefore, the measurement and manufacturing technique including the lens molding process for the slope angle should be developed. In this paper, the evaluation technique was described for the optical performance of the aspherical lens. Aspherical form error brings about the wavefront error and the side lobe of the beam intensity profile. A schematic diagram of the aspherical lens manufacturing was drawn to explain the aspherical form error compensation. Finally, form error of the aspherical lens was defined and plotted using the raw data of the Formtalysurf.

• 한국전산유체공학회:학술대회논문집
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• 2005.04a
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• pp.123-127
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• 2005

The numerical analyses of the complicated flows are widely attempted in these days. Because of the enormous demanding memory and calculation time, parallel processing is used for these problems. In order to obtain calculation efficiency, it is important to choose proper domain decomposition technique and numerical algorithm. In this research we enhanced the efficiency of the CFDS code developed by ADD, using parallel computation and newly developed numerical algorithms. For the huge amount of data transfer between blocks non-blocking method is used, and newly developed data transfer algorithm is used for non-aligned block interface. Recently developed RoeM scheme is adpoted as a spatial difference method, and AF-ADI and LU-SGS methods are used as a time integration method to enhance the convergence of the code. Analyses of the flows around the ONERA M6 wing and the high angle of attack missile configuration are performed to show the efficiency improvement.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.939-944
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• 2003

The analysis involves an adaptive grid that is created under a criterion of element categorization of filling states and locations in the total region at each time step. By using an adaptive grid wherein the elements, finer than those in internal and external regions, are distributed at the surface region through refinement and coarsening procedures, a more efficient analysis of transient fluid flow with free surface is achieved. Using the proposed numerical technique, the collapse of a dam is analyzed. The numerical results agree well with the theoretical solutions as well as with the experimental results. Through comparisons with the numerical results of several cases using different types of grids, the efficiency of the proposed technique is verified.

• International Journal of Naval Architecture and Ocean Engineering
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• v.7 no.1
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• pp.115-127
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• 2015

The aim of this study is to develop a simplified formula for added mass coefficients of a two-dimensional floating body moving vertically in a finite water depth. Floating bodies with various sectional areas may represent simplified structure sections transformed by Lewis form, and can be used for floating body motion analysis using strip theory or another relevant method. Since the added mass of a floating body varies with wave frequency and water depth, a correction factor is developed to take these effects into account. Using a developed two-dimensional numerical wave tank technique, the reference added masses are calculated for various water depths at high frequency, and used them as basis values to formulate the correction factors. To verify the effectiveness of the developed formulas, the predicted heave added mass coefficients for various wetted body sections and wave frequencies are compared with numerical results from the Numerical Wave Tank (NWT) technique.

• International Journal of Automotive Technology
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• v.7 no.1
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• pp.61-68
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• 2006

In design of the friction clutches of automobiles, knowledge on the thermo-elasticity a priori is very informative in the initial design stage. Especially, the precise prediction technique of maximum temperature and stress should be requested in design of mechanical clutches for their durability and compactness. In this study, an efficient and reliable analysis technique for the design of the mechanical clutches by using computer modeling and numerical method was developed. A commercial software STAR-$CD^{TM}$ was used to find the convective heat-transfer coefficients. MSC/$NASTRAN^{TM}$ software was followed to predict the temperature of clutch with utilization of estimated coefficients. Some experiments were also performed with a dynamometer to verify the procedure and calibrate the thermal load. As a conclusion, a design procedure, including numerical steps and experimental techniques for calibration, was proposed.

• Korean Journal of Computational Design and Engineering
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• v.1 no.1
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• pp.56-64
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• 1996

A quadrilateral-triangular mixed grid method for the solution of incompressible viscous flow is presented. The solution domain near the body surface is meshed using elliptic grid geneator to acculately simulate the viscous flow. On the other hand, we used unstructured triangular grid system generated by advancing front technique of a simple automatic grid generation algorithm in the rest of the computational domain. The present method thus is capable of not only handling complex geometries but providing accurate solutions near body surface. The numerical technique adopted here is PISO type finite element method which was developed by the present author. Investigations have been made of two-dimensional unsteady flow of Re=550 past a circular cylinder. In the case of use of the unstructured grid only, there exists a considerable amount of difference with the existing results in drag coefficient and vorticity at the cylinder surface; this may be because of the lack of the grid clustering to the surface that is a inevitable requirement to resolve the viscous flow. However, numerical results on the mixed grid show good agreements with the earlier computations and experimental data.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.4
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• pp.35-43
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• 2003

In this paper, an efficient computational algorithm for the implementation of the newly proposed node activation technique is presented, and its computational aspects are thoroughly investigated. To verify the validity, convergence, and efficiency of the node activation technique, various numerical examples are worked out including the problems of Poisson equation, 2D elasticity problems, and 3D elasticity problems. From the numerical tests, it is verified that one can arbitrarily activate and handle the nodal points of interest in finite element model with very little loss of the numerical accuracy.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.30 no.11 s.254
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• pp.1093-1100
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• 2006

Combustion stability rating of jet injector is conducted numerically using air-injection technique in a model chamber, where air is supplied to oxidizer and fuel manifolds of the model five-element injector head. A sample F(fuel)-O(oxidizer)-O-F impinging-jet injector is adopted. In this technique, we can simulate mixing process of streams flowing through oxidizer and fuel orifices under cold-flow condition without chemical reaction. The model chamber was designed based on the methodologies proposed in the previous work regarding geometrical dimensions and operating conditions. From numerical data, unstable regions can be identified and they are compared with those from air-injection acoustic and hot-fire tests. The present stability boundaries are in a good agreement with experimental results. The proposed numerical method can be applied cost-effectively to stability rating of jet injectors when mixing of fuel and oxidizer jets is the dominant process in instability triggering.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2004.05a
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• pp.635-644
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• 2004

A method of identifying structural parameters such as stiffness and damping coefficients at interfacial points of vibro-acoustic systems is suggested using an optimization technique. To identify the parameters using a numerical optimization algorithm, cost functions are defined. The cost function should be zero at the correct parameter values. To minimize the cost functions using an optimization technique, a design sensitivity analysis procedure is developed in the framework of the multi-domain FRF-based substructuring method. As a numerical example, a ladder-like structure problem is introduced. With known parameter values and different initial guesses of the parameters, convergence characteristics to the exact value are compared f3r the three cost functions. Investigating the contours of the cost functions, we find the first cost function has the largest convergent region to the correct value. As another practical problem, stiffnesses of engine mounts and bushings in a passenger car are identified. The numerical examples show that the proposed method is efficient and accurate far realistic problems.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.14 no.6
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• pp.536-545
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• 2004

A method of identifying structural parameters such as stiffness and damping coefficients at interfacial points of vibro-acoustic systems is suggested using an optimization technique. To identify the parameters using a numerical optimization algorithm, cost functions are defined. The cost function should be zero at the correct parameter values. To minimize the cost functions using an optimization technique, a design sensitivity analysis procedure is developed in the framework of the multi-domain FRF-based substructuring method. As a numerical example, a ladder-like structure problem is introduced. With known parameter values and different initial guesses of the parameters, convergence characteristics to the exact value are compared for the three cost functions. Investigating the contours of the cost functions, we find the first cost function has the largest convergent region to the correct value. As another practical problem, the stiffnesses of engine mounts and bushings in a passenger car are identified. The numerical examples show that the proposed method is efficient and accurate for realistic problems.