• Proceedings of the Korean Society of Precision Engineering Conference
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• 2002.05a
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• pp.263-266
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• 2002

An optical method for surface roughness estimation based on statistical analysis of the light intensity of a scattered laser beam pattern. The method is very simple but has a disadvantage that no more information than the averaged roughness is estimated. In this study a new try was conducted to derive more advanced surface information from the details of the light intensity distribution. Some periodic ripples among the light intensity distribution being assumed to relate with scratch left on the machined surface, a corresponding surface profile is estimated from the ripples using FFT and IFFT algorithm. IFFT technique is used to extract some dominant signal components among the intensity distribution. Compared to the measured profiles by a stylus type surf-tester, the profiles obtained through the proposed method are probably acceptable in a sense of the profile shape. Calibration of the amplitude needs more works in the future.

• Transactions of the Korean Society of Automotive Engineers
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• v.11 no.1
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• pp.225-231
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• 2003

In order to improve efficiency of a system with three-dimensional flow characteristics, this paper presents a new method that overcomes three-dimensional effects by using two-dimensional CFD and response surface method. The method was applied to shape optimization of cut-off in a multi-blade fan/scroll system. As the entrance conditions of two-dimensional CFD, the experimental values at the positions out of the inactive zone were used. In order to examine the validity of the two-dimensional CFD the distributions of velocity and pressure obtained by two-dimensional CFD were compared with those of three-dimensional CFD and experimental results. It was found that the distributions of velocity and pressure show qualitatively similarity. The results of two-dimensional CFD were used for constructing the objective function with design variables using response surface method. The optimal angle and radius of cut-off were determined as $72.4^{\circ}$ and 0.092 times the outer diameter of impeller, respectively. It is quantified the previous report that the optimal angle and radius of cut-off are approximately $72^{\circ}$ and 0.08 times the outer diameter of impeller, respectively.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2004.05a
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• pp.31-34
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• 2004

A new extrusion process of the circular section product with helical fins could be developed by using rotating extrusion dies. The twisting of extruded product is caused by the twisted conical die surface connecting the die entrance section and the die exit section linearly. But, until now, because the process has used fixed extrusion dies, it needs high pressure in order to twist billet and form fin shape on the surface of billet. So, during extruding billet, in order not to twist billet, the extrusion dies is needed to rotate itself instead of twisting billet. And in order to rotate dies, the shape of inside contour of extrusion dies must have conical type with twisted Inclined die surface connecting the die entrance section and the die exit section linearly. The results of experiments show that, in spite of using twisted extrusion dies, twisting of the billet should not happen because of rotating dies in the opposite direction of twisting direction of billet during extruding billet, and, from the results, it shows that it can decrease the power of extrusion pressure and could prevent crack of teeth for fin forming.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.25 no.4
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• pp.725-733
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• 2001

Flying attitudes of the slider, which are flying height, pitch and roll, are affected by the air flow velocity, the skew angle, and the manufacturing tolerances. Traditional designs of the air bearing surface have considered only the flying performances for the variations in the air flow velocity and the skew angle, which are determined by the radial position. In this study, we present the new shape design of the air bearing surface by considering the track seek performance and the air bearing stiffness as well as the traditional design requirements. The optimization technique is used to improve the dynamic characteristics and operating performance of the newly proposed air bearing surface shape design further. The optimized configuration is obtained automatically and the optimally designed sliders show the enhanced flying and dynamic characteristics.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.06a
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• pp.1561-1569
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• 2000

Flying attitudes of the slider, which are flying height, pitch and roll, are affected by the air flow velocity, the skew angle, and the manufacturing tolerances. Traditional designs of the air bearing surface have considered only the flying performances for the variations in the air flow velocity and the skew angle, which are determined by the radial position. In this study, we present the new shape design of the air bearing surface by considering the track seek performance and the air bearing stiffness as well as the traditional design requirements. The optimization technique is used to improve the dynamic characteristics and operating performance of the newly proposed air bearing surface shape design further. The optimized configuration is obtained automatically and the optimally designed sliders show the enhanced flying and dynamic characteristics.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2002.10a
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• pp.754-758
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• 2002

According to the enlargement of production facilities and structures, the requirements of high-capacity load cells are increased for monitoring the process conditions in many fields. Generally, however, the accuracy of the column-type high-capacity load cells is not enough due to the geometric nonlinearity. It is supposed to result from the fact that the whole spring element is under high-level stress for the uniform strain field. In this paper, a new shape of spring element is developed which utilizes the stress concentration. As a design criterion, an object function which quantifies the degree of nonlinearity is defined and optimized by use of response surface modeling. As a result, the weight of the spring element is reduced shout 50% in comparison to the conventional shape. The bonding positions of stain gages are found. which show theoretically zero geometrical nonlinearity, while the ratio of overload protection is reduced from 130% to 125% Also it is shown that the response surface method is very efficient in the optimization approach by use of FEM.

• Advances in aircraft and spacecraft science
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• v.9 no.2
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• pp.131-148
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• 2022

The paper presents the surface-modified NACA 2412 airfoil performance with variable cavity characteristics such as size, shape and orientation, by numerically investigated with the pre-validation study. The study attempts to improve the airfoil aerodynamic performance at 30 m/s with a variable angle of attack (AOA) ranging from 0° to 20° under Reynolds number (R_e) 4.4×10⁵. Through passive surface control techniques, a boundary layer control strategy has been enhanced to improve flow performance. An intense background survey has been carried out over the modifier orientation, shape, and numbers to differentiate the sub-critical and post-critical flow regimes. The wall-bounded flows along with its governing equations are investigated using Reynolds Average Navier Strokes (RANS) solver coupled with one-equational transport Spalart Allmaras model. It was observed that the aerodynamic efficiency of cavity airfoil had been improved by enhancing maximum lift to drag ratio ((l/d) max) with delayed flow separation by keeping the flow attached beyond 0.25C even at a higher angle of attack. Detailed investigation on the cavity distribution pattern reveals that cavity depth and width are essential in degrading the early flow separation characteristics. In this study, overall general performance comparison, all the cavity airfoil models have delayed stalling compared to the original airfoil.

• Geomechanics and Engineering
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• v.34 no.2
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• pp.187-195
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• 2023

Intensive rainfall during the summer season in Korea has triggered numerous devastating landslides outside of downtown in mountainous areas. The 2D slope stability analysis that is generally used for cut slopes and embankments is inadequate to model slope failure in mountainous areas. This paper presents a new 3D slope stability formulation using the global sliding vector in the limit equilibrium method, and it uses an ellipsoidal slip surface for static and quasi-static analyses. The slip surface's flexibility of the ellipsoid shape gives a lower FS than the spherical failure shape in the Fellenius, Bishop, and Janbu's simplified methods. The increasing sub-columns of each column tend to increase the FS and converge to a steady value. The symmetrical geometric conditions of the convex turning corners do not indicate symmetrical failure of the surface in 3D analysis. Pseudo-static analysis shows that the horizontal seismic force decreases the FS and increases the mass volume at the critical failure state. The stability index takes the FS and corresponding sliding mass into consideration to assess the potential risk of slope failure in complex mountainous terrain. It is a valuable parameter for selecting a vulnerable area and evaluating the overall risk of slope failure.

• Proceedings of the KSME Conference
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• 2001.06e
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• pp.158-161
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• 2001

A new type baghouse with tangential inlet and inner tube was developed and it's performances were evaluated. Experiments with variable shapes of inner tube were performed to suggest an optimum shape of inner tube which might decrease the dust loading onto bag filter surface and the amount of reentrained particles by internal gas flow. The dust loading was lower when inner tubes parallel to outer casing exist. When an inner tube covering around the lower portion of bag filters was used, the dust particles detached from the filter surface by cleaning process were reentraind by internal recirculating gas flow.

• 제어로봇시스템학회:학술대회논문집
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• 1991.10b
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• pp.1758-1763
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• 1991

This paper describes a new method to determine the 3D-shape of objects consisting of specular planar surfaces. This method exploits a light source which is made of a diffuse plane with a grid pattern encoded in an M-sequence and uses a single image of the light source reflected by the objects to acquiring orientations and positions of the surfaces of the objects. When grid lines of the light source are reflected by a specular planar surface and perspectively projected on an image plane, a set of lines vanishing at a point are obtained on the image plane. The orientation of the specular planar surface is determined by using the vanishing point, and the position is determined by using the correspondence between lines on the image and lines on the light source, which is obtained by employing a characteristic regularity of the M-sequence. Before the vanishing points are calculated, the lines on the image are classified and correlated with the surfaces of objects by using slopes and positions of the lines and the regularity of the M-sequence. This method requires only a single image.