• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.21 no.5
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• pp.60-67
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• 2007

In this paper, a simulation method of the internal winding fault is proposed to calculate winding current and electromagnetic force in a distribution power transformer by suing FEM program. The model of the transformer is a single phase, 60[Hz], 1[MVA], 22.9[kV]/220[V], cable-type winding. The short-circuit current and electromagnetic force are calculated by FEM(Finite Element Method) program(Flux2D) and the results we verified with theoretical formula and PSPICE program. The simulation results are fairly good agreement with the other verified methods within 5[%] error rate. The turn-to-turn short-circuit current is 500 times of the rated current and the electromagnetic force is about $20{\sim}200times$. The method presented in this study may serve as one of the useful tools in the electromagnetic force analysis of the transformer winding behavior under the short circuit condition for design of the structure.

• Journal of the Korean Institute of Gas
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• v.10 no.3 s.32
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• pp.34-40
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• 2006

This paper presents the optimized design of O-rings with a rectangular groove and dovetails, which are strongly related on the sealing performance of LPG filling unit. The computed results on the optimal design are analyzed by non-linear MARC finite element program with Taguchi method. O-rings with 4 different groove models are analyzed for 3 different elastomeric materials. The design parameters are given to polymer materials, groove depth, groove width, and diameter of O-rings. The FEM computed results showed that the affection ratios of O-ring diameter and material property are the most influential parameter among the groove width, groove depth, and compression ratio. Thus, this paper recommends model III for a rectangular groove and model IV for a dovetail groove with a given gas supply pressure of 1.764 MPa.

• Proceedings of the KSME Conference
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• 2007.05a
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• pp.372-377
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• 2007

For more than 2,500 years, surgical teaching has been based on the so called "see one, do one, teach one" paradigm, in which the surgical trainee learns by operating on patients under close supervision of peers and superiors. However, higher demands on the quality of patient care and rising malpractice costs have made it increasingly risky to train on patients. Minimally invasive surgery, in particular, has made it more difficult for an instructor to demonstrate the required manual skills. It has been recognized that, similar to flight simulators for pilots, virtual reality (VR) based surgical simulators promise a safer and more comprehensive way to train manual skills of medical personnel in general and surgeons in particular. One of the major challenges in the development of VR-based surgical trainers is the real-time and realistic simulation of interactions between surgical instruments and biological tissues. It involves multi-disciplinary research areas including soft tissue mechanical behavior, tool-tissue contact mechanics, computer haptics, computer graphics and robotics integrated into VR-based training systems. The research described in this paper addresses the problem of characterizing soft tissue properties for medical virtual environments. A system to measure in vivo mechanical properties of soft tissues was designed, and eleven sets of animal experiments were performed to measure in vivo and in vitro biomechanical properties of porcine intra-abdominal organs. Viscoelastic tissue parameters were then extracted by matching finite element model predictions with the empirical data. Finally, the tissue parameters were combined with geometric organ models segmented from the Visible Human Dataset and integrated into a minimally invasive surgical simulation system consisting of haptic interface devices and a graphic display.

• Journal of the Korean Society for Nondestructive Testing
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• v.34 no.3
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• pp.226-232
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• 2014

In the present study, the characteristics of laser ultrasound in the ablation regime are investigated using simulations and experiments. The laser ultrasonic technique has been recognized as a noncontact method in the field of nondestructive tests (NDTs). In hostile environments (such as hot temperatures), this method has various advantages over the conventional contact ultrasonic method. In particular, in the ablation regime, the laser ultrasonic technique is suitable for inspecting internal defects because of the high amplitude and directivity of the longitudinal wave. In this paper, a simulation model for laser ultrasound in the ablation regime was developed. This model was subsequently applied to a defective specimen using the B-scan method to locate defects. Finally, we performed an experimental test to verify the simulation results. Consequently, the simulation demonstrated good agreement with the experimental test.

• Tribology and Lubricants
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• v.34 no.5
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• pp.169-174
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• 2018

A multi-stage compressor (MSC) is comprised of several impellers installed in the pinion gear shaft driven by a main bull gear. In the pinion shaft, a thrust collar (TC) is installed to support the thrust load. The TC makes the lubrication system simpler in the MSC; therefore, it is widely used in similar kinds of machinery. Typically, TCs are installed on both sides of the bull gear and pressure is developed in the lubricated area by creating a taper angle on the TC and bull gear surface. In the current study, we developed a numerical analysis model to evaluate the performance of the TC considering its design parameters. We sloved the Reynolds equation using the finite element method and applied the half Sommerfeld condition to consider cavitation. Based on the pressure calculated in the lubricated area, we calculated the power loss and minimum film thickness. In addition, we calculated stiffness and damping using perturbation method. We performed parametric studies using the developed model. The results of the analysis show that the maximum pressure presents in the center area of the TC and it increases with the taper angle. The area over which pressure is developed decreases with the taper angle. The results also show that there is an optimum taper angle providing minimum power loss and maximum film thickness. Additionally, the stiffness and damping decrease with the taper angle. As the applied load increases, the power loss increases and the minimum film thickness decreases. However, the stiffness and damping increase with the applied load.

• Magazine of the Korean Society of Agricultural Engineers
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• v.38 no.1
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• pp.116-127
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• 1996

This paper dealt with FEM analysis of foundation improved with pack drain. The theory on pack drain was scrutinized and observed values in the field were compared with numerical results. Work site of Kwangyang container pier was selected as a ease study in which measurement of settlement and pore water pressure was accurately carried out. Biot's consolidation equation was selected as governing One, coupled with modified Camclay model as constitutive one. Christian and Boehmer's numerical technique was adopted. Behavior of foundation with pack drain is not simple but very complicated. Discontinuity resulted from rigidity difference between adjacent materials, smear effect and complicated boundary conditions should be considered in the behavior analysis of foundation behavior. The results of numerical analysis were influenced by smear zone. In relevant to this effect, finite element analysis was carried out using the reduced horizontal coefficient of permeability in the smear zone; The numerical results were compared with observed values in surface settlement. including pore water pressure. However only lateral di5plaoement by numerical ana1Ysis was shown since its measurement was not performed in the field. The predication of settlement to be developed later can be effectively employed for the obtimization of construction. The predication of residual settlement using the data measured in the field was made by Hoshino, Asaoka and hyperbolic method. Among them, the hyperbolic method proved best one. Settlements accorded well between numsrical and observed values while pore pressure showed a slight difference. Lateral displacement showed largest values at constant distance from ground surface. The validation of foundation analysis improved with pack drain by computer program employed in this study selecting modified Cam-clay model was satisfactorily secured.

• Transactions of the Korean Society of Automotive Engineers
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• v.22 no.1
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• pp.29-35
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• 2014

This paper aims to obtain the effect of lightweight on Radius rod. The response surface method used in the paper is the statistical method. Optimization method is performed with the Radius rod using the lightweight material. Structural analysis is executed by using the ANSYS program to find static and dynamic responses. From this study result, it is verified that the response surface method has the advantage of optimum value in comparison with other optimization methods. The analysis is also performed by response surface method to derive optimal design values. Steel model and aluminium initial model are obtained by finite element analysis to clarify design criteria and the results are compared with three models each other. The weights can be reduced by optimal design analysis results of these models similar to those of existing products. The quantitative goals in this study can also attained through results of fatigue analyses. The reliability on optimal design of Radius rod can be improved by use of structural and fatigue analysis results.

• Structural Engineering and Mechanics
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• v.76 no.2
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• pp.251-267
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• 2020

Transmission tower-line systems have come to represent one of the most important infrastructures in today's society. Recent strong earthquakes revealed that transmission tower-line systems are vulnerable to earthquake excitations, and that ground motions may arrive at such structures from any direction during an earthquake event. Considering these premises, this paper presents experimental and numerical studies on the dynamic responses of a 1000 kV ultrahigh-voltage (UHV) transmission tower-line system under different seismic incidence angles. Specifically, a 1:25 reduced-scale experimental prototype model is designed and manufactured, and a series of shaking table tests are carried out. The influence of the seismic incidence angle on the dynamic structural response is discussed based on the experimental data. Additionally, the incidence angles corresponding to the maximum peak displacement of the top of the tower relative to the ground (referred to herein as the critical seismic incidence angles) are summarized. The experimental results demonstrate that seismic incidence angle has a significant influence on the dynamic responses of transmission tower-line systems. Subsequently, an approximation method is employed to orient the critical seismic incidence angle, and a corresponding finite element (FE) analysis is carried out. The angles obtained from the approximation method are compared with those acquired from the numerical simulation and shaking table tests, and good agreement is observed. The results demonstrate that the approximation method can properly predict the critical seismic incidence angles of transmission tower-line systems. This research enriches the available experimental data and provides a simple and convenient method to assess the seismic performance of UHV transmission systems.

• Journal of The Korean Society of Agricultural Engineers
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• v.59 no.4
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• pp.43-52
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• 2017

This study analyzed pore water pressure, earth pressure and settlement through laboratory model tests in order to suggest the effective remodeling method in the case of reinforcing the upstream and downstream slope of deteriorated reservoirs that has no cores and filters or is not functional. The method of remodeling the upstream slope using dredge soil is first prevent seepage by installing the core, and the leakage water can be rapidly discharged through a filter installed on the downstream slope. Therefore, it is considered a highly efficient method of remodeling that reduces piping phenomena and increasing the storage capacity of the reservoir. The variation of earth pressure without the core and filter was greater than with it, while the change largely showed in the upstream slope, the downstream slope did not show any significant changes. The remodeling method of the downstream slope with the core appeared differently pore water pressure depending on the presence of the vertical and horizontal filters. In the upstream slope, the pore water pressure rises sharply, the base and middle gradually increased, and the downstream slope appeared small. The pore water pressure of embankment with a vertical and horizontal filter will be smaller than without it. The remodeling of deteriorated reservoir that does not have the function of the filter, the vertical filter must be installed in a position that is higher than the expected seepage line by removing portions of the downstream slopes. Since the horizontal filter is an important structure that provides stable drainage during an earthquake or concentrated leak, it is necessary to examine any change in the seepage characteristics depending on the filter intervals via three-dimensional finite element analysis, and it should be connected to the tow-drain to reduce the possibility of the collapse of the reservoir.

• Bulletin of the Korean Space Science Society
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• 2003.10a
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• pp.63-63
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• 2003

There are many actuators and sensors used for attitude control system for KOMPSAT such as Reaction Wheel Assembly, Magnetic Torque Assembly, Dual Thruster Module, Solar array Drive, Three Axis Magnetometer, Conical Earth Sensor, Fine Sun Sensor Assembly, Coarse Sun Sensor Assembly, Gyro Reference Assembly and so on. For KOMPSA T satellite it has been considered using the Magnetic Torquer (MTQ) generating the magnetic dipole moment. In general, the magnetic dipole moment for satellite attitude control system is used for dumping out the excessive reaction wheel momentum so that the reaction wheel speed is not saturated. The objective of this study is to analyze the magnetic field characteristics generated by the Magnetic Torquer using the Maxwell 2D Field Simulator software. Currently, the developing model (DM) of the MTQ is being developed and manufactured at a company under the supervision of KARL MTQ is an electromagnet consisting of a ferromagnetic cylindrical core on which an excitation coil is wound. A current is passed through the coil to produce a dipole momentum in the ferromagnetic core. The configuration of the MTQ will be introduced in the presentation. The 2 dimensional model of the MTQ is drawn as axisymmetric models in RZ plane, and each corresponding material is assigned to the each MTQ object, the core, coil, and background. After the boundary conditions, current sources, and solution parameters are set up, the magnetic field intensities, directions, and other values specified by users can be calculated by using the finite element analysis. The theoretical magnetic field quantities obtained by the Maxwell 2D Simulator can be used for the basis of the development of the MTQ.