• Journal of KIISE:Software and Applications
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• v.26 no.10
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• pp.1167-1167
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• 1999

Although spatial databases support an efficient spatial management on objects in the real world, they have a characteristic that process only spatial information valid at current time, So in case of change in the spatial domain, it is very hard to support an efficient historical management for time-varying spatial information because they delete an old value and then replace with new value that is valid at current time. To solve these problems, there are rapidly increasing of interest for spatiotemporal databases, which serve historical functions for spatial information as well as spatial management functions for an object. However most of them presented in an abstract time-varying spatial phenomenon, but have not presented a concrete policy in spatiotemporal databases. In this paper, we propose a spatiotemporal data model that supports bitemporal time concepts in three dimensional architecture. In the proposed model, not only data types and their operation for object of spatiotemporal databases have been classified, but also mathematical expressions using formal semantics for them have been given. Then, the data structures and their operations based on relational database model as well as object-oriented database model are presented.

• The KSFM Journal of Fluid Machinery
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• v.19 no.2
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• pp.21-26
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• 2016

The objective of present study is to assess the performance of the first stage compressor in a total 3-stage 5000 HP-level turbo compressor. CFD commercial code, CFX has been used to predict three-dimensional flow characteristics inside of the impeller. Shear Stress Transport (SST) model has been used to simulate turbulent flows through Reynolds-averaged Navier-Stokes (RANS) equations. Grid dependency has been also checked to get optimal grid distribution. Numerical results have been compared with the experimental test results to elucidate performance characteristics of the present compressor. In addition, flow characteristics of the impeller only have been studied for various blade configurations. Angular offset in leading edge of the blade has been selected for the optimal blade design. Performance characteristics in region of low mass flow rate and high pressure ratio between the impeller entrance and exit have been investigated for the selection of optimal blade design. Also, flow instability such as stall phenomena has been studied and anti-stall characteristics have been checked for various blade configurations in the operational window.

• Korea-Australia Rheology Journal
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• v.21 no.3
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• pp.193-200
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• 2009

We present a direct simulation technique for two-dimensional mold-filling simulations of fluids filled with a large number of circular disk-like rigid particles. It is a direct simulation in that the hydrodynamic interaction between particles and fluid is fully considered. We employ a pseudo-concentration method for the evolution of the flow front and the DLM (distributed Lagrangian multipliers)-like fictitious domain method for the implicit treatment of the hydrodynamic interaction. Both methods allow the use of a fixed regular discretization during the entire computation. The discontinuous Galerkin method has been used to solve the concentration evolution equation and the rigid-ring description has been introduced for freely suspended particles. A buffer zone, the gate region of a finite area subject to the uniform velocity profile, has been introduced to put discrete particles into the computational domain avoiding any artificial discontinuity. From example problems of 450 particles, we investigated the particle motion and effects of particles on the flow for both Newtonian and shear-thinning fluid media. We report the prolonged particle movement toward the wall in case of a shear-thinning fluid, which has been interpreted with the shear rate distribution.

• Tunnel and Underground Space
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• v.21 no.6
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• pp.439-449
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• 2011

The characteristics of rock fractures for engineering rock classification are investigated by analyzing three dimensional point cloud generated from adjusted digital images of a tunnel face during construction and the tunnel is reinforced based on the supporting pattern suggested by the RMR and the Q system using parameters extracted from those images. As results, it is possible saving time required from face mapping to tunnel reinforcing work, enhancing safety during face mapping work in tunnels and reliability of both the mapping information and selecting supporting pattern by storing the files of digital images and related information which can be checked again, if necessary sometime in the future.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2006.05a
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• pp.343-344
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• 2006

Powder injection molding(PIM) is widely used for many parts in the field of automotives, electronics and medical industries, due to the capability of net shaping for complex 3-D geometry. Powder injection mold design fur the dental scaler tip, a component of medical appliance, was presented. In comparison with conventional machining process, powder injection molding has many advantages, specially in price and dimensional stability, for molding dental scaler tip which has complex geometry. Both product design and mold design for dental scaler tip were presented. The 'rapid mold' concept was applied to manufacture the various forms of dental scaler tip.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.11 no.1
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• pp.302-320
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• 2017

In this paper, an innovative robust feature detection and matching strategy for visual odometry based on stereo image sequence is proposed. First, a sparse multiscale 2D local invariant feature detection and description algorithm AKAZE is adopted to extract the interest points. A robust feature matching strategy is introduced to match AKAZE descriptors. In order to remove the outliers which are mismatched features or on dynamic objects, an improved random sample consensus outlier rejection scheme is presented. Thus the proposed method can be applied to dynamic environment. Then, geometric constraints are incorporated into the motion estimation without time-consuming 3-dimensional scene reconstruction. Last, an iterated sigma point Kalman Filter is adopted to refine the motion results. The presented ego-motion scheme is applied to benchmark datasets and compared with state-of-the-art approaches with data captured on campus in a considerably cluttered environment, where the superiorities are proved.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2002.10a
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• pp.176-180
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• 2002

All types of VLM-s process include the linear heat cutting of EPS foam to generate a layer with 3D shape. The dimensional accuracy and part quality of the cut part are dependent on the thermal characteristics in the EPS foam. The thermal characteristics are determined by operating parameters such as an effective heat input and cutting angle. The objective of this study is to investigate into the influence of cutting angle on the kerfwidth and the melted length of the cut part using the numerical analysis and the experiments in generally sloped cutting with two cutting angles. In order to estimate an accurate temperature field, the transient thermal analysis using moving coordinate system, the fully conformed mesh and the heat flux model with two cutting angles is carried out. From the results of the analysis and the experiments, it has been found that the influence of the rotational angle about x-axis in which the rotational axis is normal with hotwire cutting direction is appreciably negligible in comparison with that of the rotational angle about y-axis.

• Journal of the Korean Society for Heat Treatment
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• v.14 no.4
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• pp.228-234
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• 2001

The present study was an attempt for systematic data conversion between FDM and FEM in order to evaluate the thermal stress distribution during quenching process. It has been generally recognized that FDM is efficient in flow and temperature analysis and FEM in that of stress. But it induced difficulty and tedious work in analysis that one uses both FDM and FEM to take their advantages because of the discrepancy of nodes between analysis tools. So we proposed field data conversion procedure from FDM to FEM in 3-dimensional space, then applied this procedure to analysis of quenching process. The simulation procedure calculates the distributions of temperature and microstructure using FDM and microstructure evolution equations of diffusion and diffusionless transformation. FEM was used for predicting the distributions of thermal stress. The present numerical code includes coupled temperaturephase transformation kinetics and temperature-microstructure dependent material properties. Calculated results were compared with previous experimental data to verify the method, which showed good agreements.

• Transactions of the Korean Society of Automotive Engineers
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• v.3 no.6
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• pp.8-22
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• 1995

Three dimensional numerical study of non-evaporating and evaporating spray characteristics was performed in a quiescent and motoring condition of direct injection diesel engine. The calculation parameter was breakup model. The breakup models used were Reitz & Diwakar model and TAB model. The modified k-${\varepsilon}$ turbulence model considering the compressibility effect due to the compression and expansion of piston was used. The calculation results of the spray tip penetration and tip velocity using the TAB model showed similar trends comparing with the experimental data. Although the evaporation rate was not nearly affected with the breakup model at the higher injection pressure, in the low injection case, the evaporation rate result using the TAB model became higher than that of R&D model. The evaporation rate was increased with the injection pressure due to the vigorous interaction with the gas field.

• Transactions of the Korean Society of Automotive Engineers
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• v.3 no.2
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• pp.16-29
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• 1995

In this study a tracked vehicle is idealized as a 2-dimensional 9-degrees-of-freedom model which takes into account the effects of HSU units, torsion bars, and track. For the model equations of motion are derived using Kane's method. By using the equations of motion, a numerical example is solved and results are compared to those obtained by using a general purpose multi body dynamic analysis program. The comparison study shows the reasonable coherence between the two results. which confirms the effectiveness of the model. With the model, dynamic response optimization is carried out. The objective function is the peak value of the vertical acceleration of the vehicle at the driver's seat, and the constraints are the wheel travel limits, the ground clearance. and the limits of other design variables. Three different sets of design variables are chosen and used for the optimization. The results show the attenuation of the acceleration peak value. Thus the procedure presented in this study can be utilized for the design improvement of the real system.