• 한국전산유체공학회:학술대회논문집
• /
• 2007.04a
• /
• pp.87-90
• /
• 2007

A general purpose program NUFLEX for the analysis 3-D thermo/fluid flow and pre/post processor in complex geometry has been developed, which consists of a flow solver based on FVM and GUI based pre/post processor. The solver employs a general non-orthogonal grid system with structured grid and solves laminar and turbulent flows with standard/RNG ${\kappa}-{\varepsilon}\;SST$ turbulence model. In addition, NUFLEX is incorporated with various physical models, such as interfacial tracking, cavitation, MHD, melting/solidification and spray model. For the purpose of verification of the program and testing the applicability, many actual problems are solved and compared with the available data. Comparison of the results with that by STAR-CD or FLUENT program has been also made for the same flow configuration and grid structure to test the validity of NUFLEX.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.1 no.3
• /
• pp.83-94
• /
• 1993

Design and production of wiring for automobile systems provide the background for the development of concurrent engineering framwork. Key issues include with different parts of the wiring design process and the development of hierarchical representations that capture the different characteristics(e.g., connectivity, geometry) of the harnesses. The abstraction of design information results in features, while the abstraction of operations leads to the development of agents. These abstracts are essential for efficient transactions among people and computer tools in a domain that involves numerous interacting constraints. We have decomposed the wiring design process into four basic categories of tasks that are each addressed by an "agent" : the Environment Editor(EE), the Free Space Manager(FSM), the Wiring Editor(WE), and the Part Selector(PS). In this paper the strategy for the problem decomposition, the definition of features, and the ways in which features are used by various agents, are discussed. We conclude with a discussion of some of the issues raised by the project and the steps underway to address them.

• Journal of Astronomy and Space Sciences
• /
• v.20 no.1
• /
• pp.1-10
• /
• 2003

A precise kinematic orbit determination (P-KOD) procedure for Low Earth Orbiter(LEO) using the GPS ion-free triple differenced carrier phases is presented. Because the triple differenced observables provide only relative information, the first epoch's positions of the orbit should be held fixed. Then, both forward and backward filtering was executed to mitigate the effect of biases of the first epoch's position. p-KOD utilizes the precise GPS orbits and ground stations data from International GPS Service (IGS) so that the only unknown parameters to be solved are positions of the satellite at each epoch. Currently, the 3-D accuracy off-KOD applied to CHAMP (CHAllenging Min-isatellite Payload) shows better than 35 cm compared to the published rapid scientific orbit (RSO) solution from GFZ (GeoForschungsZentrum Potsdam). The data screening for cycle slips is a particularly challenging procedure for LEO, which moves very fast in the middle of the ionospheric layer. It was found that data screening using SNR (signal to noise ratio) generates best results based on the residual analysis using RSO. It is expected that much better accuracy are achievable with refined prescreening procedure and optimized geometry of the satellites and ground stations.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2011.04a
• /
• pp.443-444
• /
• 2011

This paper discusses a model order reduction for large order rotor dynamics systems results from the finite element discretization. Typical rotor systems consist of a rotor, built-on parts, and a support system, and require prudent consideration in their dynamic analysis models because they include unsymmetric stiffness, localized nonproportional damping and frequency dependent gyroscopic effects. When the finite element model has a very large number of degrees of freedom because of complex geometry, repeated dynamic analyses to investigate the critical speeds, stability, and unbalanced response are computationally very expensive to finish within a practical design cycle. In this paper, the Krylov-based model order reduction via moment matching significantly speeds up the dynamic analyses necessary to check eigenvalues and critical speeds of a Nelson-Vaugh rotor system. With this approach the dynamic simulation is efficiently repeated via a reduced system by changing a running rotational speed because it can be preserved as a parameter in the process of model reduction. The Campbell diagram by the reduced system shows very good agreement with that of the original system. A 3-D finite element model of the Nelson-Vaugh rotor system is taken as a numerical example to demonstrate the advantages of this model reduction for rotor dynamic simulation.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.19 no.5
• /
• pp.125-133
• /
• 2011

The wear of rubber track being in contact with the road surface is an important subject because it decreases the traction performance and the operating efficiency of tracked vehicle. For the above reasons, many attempts have been made to quantitatively calculate the rubber track. However, it depends on the experimental methods which are highly time- and cost-consuming. Therefore, the numerical simulation approach is highly desirable, but it needs to model the complex geometry and the material behavior in details as well as the interaction with the road surface. In this study, the rubber track and its material behavior are elaborately modeled since these factors are very important in the prediction of the wear rate of the rubber track. Accordingly to the studies on the rubber wear by previous investigations, it has been found that the wear is greatly influenced by the frictional energy. The frictional energy of rubber track is computed by utilizing the 3D finite element analysis of the rubber track, and the wear rate is evaluated making use of the frictional energy and a wear model.

• Fisheries and Aquatic Sciences
• /
• v.11 no.2
• /
• pp.113-123
• /
• 2008

We modeled fish school movements as a capture process in relation to the purse seine method using the three steps of the stimulus-response process (i.e., input stimuli, central decision-making and output reaction). Input stimuli of the model were categorized as either physical stimuli such as visual stimulus, sound stimulus, water flow, and weather or as biological stimuli such as species and size, swimming performance, sensual sensitivity, and presence of prey or predators. The output process determining the spatial orientation of the fish school for 3-D movements was based on swimming speed and angular change in the fish response, and these movements were animated as the relative geometry between the fish school and the purse seine. Simulations were carried out for skipjack tuna (Katsuwonus pelamis) schools reacting to a pelagic purse seine in the southwest Pacific Ocean. Simulation results showed that escape ratios varied from 20 to 70% by the relevant ranges in the stimulus-response thresholds, swimming speeds, and angular changes of fish schools were similar to those observed in the field. Therefore, with knowledge of relevant parameters, this model can be used to predict capture and escape probabilities of purse seine operations for different fish species or conditions.

• Nuclear Engineering and Technology
• /
• v.35 no.3
• /
• pp.234-242
• /
• 2003

The full energy peak efficiency of a hyper pure germanium (HPGe) detector was calibrated in a wide energy range from 0.06 to 11 MeV. Both the experimental technique and the Monte Carlo method were used for the efficiency calibration. The measurement was performed using the standard radioisotopes in the low energy region of $60{\sim}1408$ keV, which was further extended up to 11 MeV by using the $^{14}N(n,r)\;and\;^{35}Cl(n,r)$ reactions. The GEANT Monte Carlo code was used for efficiency calculation. The calculated efficiency had the same dependency on the r-ray energy with the measurement, and the discrepancy between the calculation and the measurement was minimized by fine-tuning of the detector geometry. From the calculated result, the efficiency curve of the HPGe detector was reliably determined particularly in the high energy region above several MeV, where the number of measured efficiency points is relatively small despite the wide energy region. The calculated efficiency agreed with the measurement within about $7\%$. In addition to the efficiency calculation, the origin of the local minimum near 600 keV on the efficiency curve was analyzed as a general characteristics of a HPGe detector.

• The Transactions of The Korean Institute of Electrical Engineers
• /
• v.61 no.12
• /
• pp.1820-1827
• /
• 2012

This paper is to present a new method of cogging torque reduction for axial flux PM machines of multiple rotor surface mounted magnets. In order to start softly and to run a power generator even the case of weak wind power, reduction of cogging torque is one of the most important issues for a small wind turbine, Cogging torque is an inherent characteristic of PM machines and is caused by the geometry shape of the machine. Several methods have been already applied for reducing the cogging torque of conventional radial flux PM machines. Even though some of these techniques can be also applied to axial flux machines, manufacturing cost is especially higher due to the unique construction of the axial flux machine stator. Consequently, a simpler and low cost method is proposed to apply on axial flux PM machines. This new method is actually applied to a generator of 1.0kW, 16-poles axial flux surface magnet disc type machine with double-rotor-single-stator for small wind turbine. Design optimization of the adjacent magnet pole-arc which results in minimum cogging torque as well as assessment of the effect on the maximum available torque using 3D Finite Element Analysis (FEA) is investigated in this design. Although the design improvement is intended for small wind turbines, it is also applicable to larger wind turbines.

• ETRI Journal
• /
• v.33 no.4
• /
• pp.517-527
• /
• 2011

Currently, there is a considerable interest in 3D object reconstruction using terrestrial laser scanner (TLS) systems due to their ability to automatically generate a considerable amount of points in a very short time. To fully map an object, multiple scans are captured. The different scans need to be registered with the help of the point cloud in the overlap regions. To guarantee reliable registration, the scans should have large overlap ratio with good geometry for the estimation of the transformation parameters among these scans. The objective of this paper is to propose a registration method that relaxes/eliminates the overlap requirement through the utilization of photogrammetrically reconstructed features. More specifically, a point-based procedure, which utilizes non-conjugate points along corresponding linear features from photogrammetric and TLS data, will be used for the registration. The non-correspondence of the selected points along the linear features is compensated for by artificially modifying their weight matrices. The paper presents experimental results from simulated and real datasets to illustrate the feasibility of the proposed procedure.

• Proceedings of the Korean Society For Composite Materials Conference
• /
• 2004.04a
• /
• pp.18-21
• /
• 2004

A GFRP based composite blade was developed for a 750kW wind energy conversion system of type class I. The blade sectional geometry was designed to have a general shell-spar structure. The load cases specified in the IEC61400-1 international specification were considered. For withstanding all relevant extreme loads, the structural analysis for the complete blade was performed using a commercial FEM code. The static load carrying capacity, buckling stability, blade tip deflection and natural frequencies at various rotational speeds were evaluated to satisfy the strength requirements in accordance with the IEC61400-1 and GL Regulations. For designing a lightweight blade, the thickness and the lay-up pattern of the skin-foam sandwich structures were optimized iteratively using the DOT program T-bolts were used for joining the blade root and the hub, which were modeled using a 3D FE volume model. In order to confirm the safety of the root connection, the static stresses of the thick root laminate and the steel. bolts were predicted by taking account of the bolt pretension and the root bending moments. The calculated stresses were compared with the material strengths.