• Proceedings of the Korean Society For Composite Materials Conference
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• 2003.10a
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• pp.71-74
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• 2003

The cell modeling homogenization method to derive the constitutive equation considering the microstructures of the fiber reinforced composites has been previously developed for composites with simple microstructures such as 2D plane composites and 3D rectangular shaped composites. Here, the method has been further extended for 3D circular braided composites, utilizing B-spline curves to properly describe the more complex geometry of 3D braided composites. For verification purposes, the method has been applied for orthotropic elastic properties of the 3D circular braided glass fiber reinforced composite, in particular for the tensile property. Prepregs of the specimen have been fabricated using the 3D braiding machine through RTM (resin transfer molding) with epoxy as a matrix. Experimentally measured uniaxial tensile properties agreed well with predicted values obtained fer two volume fractions.

• Journal of the Korean Society for Precision Engineering
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• v.18 no.11
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• pp.67-73
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• 2001

This paper aims at developing a torque model for the high-speed tapping with small-diameter taps. As recent industries such as automobile and information technology grows, taps smaller than 5mm in diameter are needed much more. In that occasion, the friction force between a tap surface and a workpiece plays much more important role in the tapping torque than in he larger tapping. Tapping mechanism was analysed based on the tap geometry. It has two steps : one is a forward cutting composed of the chamfered threading and full threading and the other is the backward cutting. The torque by the cutting force in the chamfered threading is calculated using the cutting area and the specific cutting force while the torque by the friction force, which is rather dominant than the cutting force both in the full threading and in the backward cutting, is calculated using the normal force on the threads and the friction coefficient. The experiment has shown that the results by the proposed torque model fit quite well with the acutal measurements within the error of 10%.

• Journal of Electrical Engineering and Technology
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• v.8 no.5
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• pp.1163-1168
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• 2013

In this paper, Adaptive Neuro-Fuzzy Inference System (ANFIS) is applied for modeling and simulation of DC characteristic of cylindrical Silicon Nanowire Transistor (SNWT). Device Geometry parameters, terminal voltages, temperature and output current were selected as the main factors of modeling. The results obtained are compared with numerical method and a good match has been observed between them, which represent accuracy of model. Finally, we imported the ANFIS model as a voltage controlled current source in a circuit simulator like HSPICE and simulated a SNWT inverter and common-source amplifier by this model.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1996.04a
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• pp.587-591
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• 1996

Usually triangular patches are used to transfer geometric shape in Rpaid Prototyping CAM system. STL, a list of triangles, is de facto in RP industry. Because STL has no topology data, it can cause errornous results. So, STL should be verified before using. After adding support structures to anchor the part to the platform and to prevent sagging or distortion, slicing and layer by layer manufacturing process are done. But triangular patch is surface model and cannot provide dufficient information on geometry in the above processes. So, geometric modeling is necessary in verifying STL, adding support structures, and slicing. It is natural that triangle based modeling is the best when traingular patches are used as input. Considering support structures, solid and faces coexist in RP process. Therefore non-manifold modeler is required. In this study, triangle based non-manifold geometric modeling is proposed for RP system consitent with STL input.

• Korean Journal of Computational Design and Engineering
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• v.3 no.4
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• pp.293-303
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• 1998

The objective of this study is to develop a PC level freeform surface modeling system which explicitly represents information of part geometry. Surface modeler uses nonuniform rational B-spline (NURBS) function with nonuniform knot vector for the flexible modeling work. The results of this study are as follows. 1) By implementation surface modeler through applying representation scheme proposed to represent free-form surface explicity, the technical foundation to develop free-from surface modeling system using parametric method. 2) Besides the role to model geometric shape of a surface, geometric modeler is developed to model arbitrary geometric shape. By doing this, the availability of the modeling system is improved. Geometric modeler can be utilized application fields such as collision test of tool and fixture, and tool path generation for NC machine tool.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.03a
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• pp.243-246
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• 2008

This paper is to consider analytical thermodynamic modeling of bipropellant propulsion system. The objective of thermodynamic modeling is to predict thermodynamic conditions such as pressures, temperatures and densities in the pressurant tank and the propellant tank in which heat and mass transfer occur. In this paper also it shows analytic equations that calculate the evolution of ullage volume and interface areas. Since the ullage interface areas are time-varying,(the liquid propellant volume decreases as the rocket engine is firing; the change of ullage volume correspond to the change of liquid propellant volume) for a numerical convenience non-dimensionalized correlations are commonly used in most literatures with limitations; a few percentages of inherent error. The analytic equations are derived from analytic geometry, subsequently without inherent error. Those equations are important to calculate the heat transfer areas in the heat transfer equations. It presents the comparison result of both analytic equations and correlation method.

• International Journal of Precision Engineering and Manufacturing
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• v.6 no.1
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• pp.65-72
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• 2005

Drilling process is one of the most common, yet complex operations among manufacturing processes. The performance of a drill is largely dependent upon drilling forces, Many researches focused on the effects of drill parameters on drilling forces. In this paper, an effective theoretical model to predict thrust and torque in drilling is presented. Also, with the predicted forces, the stress analysis of the drill tool is performed by the finite element method. The model uses the oblique cutting model for the cutting lips and the orthogonal cutting model for the chisel edge. Thrust and torque are calculated analytically without resorting to any drilling experiment, only by tool geometry, cutting conditions and material properties. The stress analysis is performed by the commercial FEM program ANSYS. The geometric modeling and the mesh generation of a twist drill are performed automatically. From the study, the effects of the variation of the geometric features of the drill and of the cutting conditions of the drilling on the drilling forces and the stress distributions in the tool are calculated analytically, which can be applicable for designing optimal drill geometry and for improving the drilling process.

• Proceedings of the KSME Conference
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• 2007.05a
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• pp.672-677
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• 2007

Recently, the new finite element method which uses NURBS as shape functions was proposed. It is very promising because it can directly use CAD data to describe geometry and discretize problem domain. In this case, CAE models are not approximated but represent exact geometry. So, it can contribute to more accurate results. In addition, it can greatly reduce CAE costs in that simulation models don't have to be made up independently. But in spite of these advantages, the method using NURBS have also some disadvantages. NURBS surface cannot be refined locally. T-splines are recently developed surface modeling technique. A T-spline surface is a NURBS surface with T-junctions and is defined by a control grid called T-mesh. The T-junctions enable T-spline surfaces to be refined locally. That is, it is possible to add a single control point to a T-spline control grid without propagating an entire row or column of control points and without altering the surface. In this research, the finite element analysis using T-splines is studied. In this analysis, CAD data are used directly for engineering analysis. Some problems with complex geometry are solved. And the results will be compared with ones of conventional FEM.

• Transactions of the Korean Society of Automotive Engineers
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• v.15 no.2
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• pp.65-73
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• 2007

The use of an Exhaust Gas Recirculation(EGR) for a diesel engine with variable geometry turbocharger(VGT) has confronted how to obtain the amount of EGR for NOx reduction requirement at wide operating range and less side effect. Through a combined effort of modeling(wave action simulation) and experiment, an investigation into the effect of EGR area ratio and pipe length on EGR characteristics of common rail diesel engine with VGT has been performed. For accurate computation, calibration of constants involved in empirical and semi-empirical correlations has been performed at a specific operating point, before of its use for engine simulation. From the results of this study, it was found that EGR rate is sharply increased with increasing EGR area ratio until area ratio of 0.3. However, the effect of EGR area ratio on EGR rate is negligible beyond this criteria. This study also investigates the effect of EGR pipe length on a EGR amount and pulsating flow characteristics at EGR junction. The results showed that the longer EGR pipe length, the lower EGR amount was achieved due to the flow loss resulting in lower amplitude of pressure wave.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2003.06a
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• pp.1634-1637
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• 2003

Any given object on the motor-driven turntable is pictured from 8 to 72 different views with a digital camera. 3D shape reconstruction is performed with the integrated software called by Scanware from these multiple digital photographs. There are several steps such as configuration, calibration, capturing, segmentation, shape creation, texturing and merging process during the shape reconstruction process. 3D geometry data can be exported to cad data such as Autocad input file. Also 3D image model is generated from 3D geometry and texture data, and is used to advertise the model in the internet environment. Consumers can see the object realistically from wanted views by rotating or zooming in the internet browsers with Scanbull spx plug-in. The spx format allows a compact saving of 3D objects to handle or download. There are many types of scan equipments such as laser scanners and photogrammetric scanners. Line or point scan methods by laser can generate precise 3D geometry but cannot obtain color textures in general. Reversely, 3D image modeling with photogrammetry can generate not only geometries but also textures from associated polygons. We got various 3D image models and introduced the process of getting 3D image model of an internet-connected watchdog robot.