• Structural Engineering and Mechanics
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• v.75 no.3
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• pp.377-387
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• 2020

Modern long-span floor system typically possesses low damping and low natural frequency, presenting a potential vibration sensitivity problem induced by human activities. Field test and numerical analysis methods are available to study this kind of problems, but would be inconvenient for design engineers. This paper proposes a simplified method to determine the acceleration amplitudes of long-span floor system subjected to walking or running load, which can be carried out manually. To theoretically analyze the acceleration response, the floor system is simplified as an anisotropic rectangular plate and the mode decomposition method is used. To facilitate the calculation of acceleration amplitude a_P, a coefficient α_wmn or α_Rmn is introduced, with the former depending on the geometry and support condition of floor system and the latter on the contact duration t_R and natural frequency. The proposed simplified method is easy for practical use and gives safe structural designs.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.11
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• pp.2245-2252
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• 2002

Design sensitivity analysis scheme is proposed in an elasto -plastic finite element method with explicit time integration using a direct differentiation method. The direct differentiation is concerned with large deformation, the elasto-plastic constitutive relation, shell elements with reduced integration and the contact scheme. The design sensitivities with respect to the process parameter are calculated with the direct analytical differentiation of the governing equation. The sensitivity results obtained from the present theory are compared with that obtained by the finite difference method in a class of sheet metal forming problems such as hemi-spherical stretching and cylindrical cup deep-drawing. The result shows good agreement with the finite difference method and demonstrates that the preposed sensitivity calculation scheme is a pplicable in the complicated sheet metal forming analysis and design.

• Transactions of the Korean Society of Automotive Engineers
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• v.6 no.5
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• pp.10-19
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• 1998

The erosion of electrode in spot welding of aluminium alloy by direct current is dependent on the electric polarity. The positive electrode is much more eroded than the negative one. To explain this phenomenon, Peltier effect has been generally accepted as a unique theory. In this study Peltier effect was evaluated by calculations on the basis of some references and experiments. The difference of heat generated by Peltier effect on both electrode surfaces was, however, only 4% of total heat generated during wel- ding. Because of insufficient explanation, Kohler theory, which is mainly affected by thin oxide film, was introduced. A theoretical calculation showed 17% of the temperature difference between the positive and negative electrode, in case "surface voltage" resulted from oxide film was 30% of total contact voltage. This revealed that the erosion of electrode could be more affected by Kohler theory than effect.an effect.

• Korean Journal of Materials Research
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• v.13 no.1
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• pp.11-17
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• 2003

DC characteristics of recessed gate 4H-SiC MESFET were investigated using the device/circuit simulation tool, PISCES. Results of theoretical calculation were compared with the experimental data for the extraction of modeling parameters which were implemented for the prediction of DC and gate leakage characteristics at high temperatures. The current-voltage analysis using a fixed mobility model revealed that the short channel effect is influenced by the defects in SiC. The incomplete ionization models are found out significant physical models for an accurate prediction of SiC device performance. Gate leakage is shown to increase with the device operation temperatures and to decrease with the Schottky barrier height of gate metal.

• Journal of the Korean Society for Precision Engineering
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• v.21 no.12
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• pp.119-126
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• 2004

Permanent magnetic gears are magneto-mechanical devices that are widely used to replace the ordinary mechanical gear and to transmit torque without the mechanical contact. This study investigates the characteristics of touch free permanent magnetic gear according to the employing systems. The effect of the magnetic torque is analyzed by using 3 dimensional Finite Element Method (FEM). To estimate the transmission torque of FEM model, the numerical results are compared with the experimental results. The influences of geometry size, magnet number on transmission torque are obtained. As results of this paper, it is confirmed that the transmission torque behavior is associated with the configuration of the magnet numbers and the air gap between the two permanent magnetic gears.

• Journal of the Korean Society of Marine Environment & Safety
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• v.6 no.1
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• pp.35-45
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• 2000

The slipway, which is one of stern construction, is necessary for stern trawler to let fishing implements, such as fishing net, otter board and warp, go out effectively. It may be doubtable whether there is any possibility for deckwetness to occur because the slipway is obliquely in contact with sea surface. The author discusses any possibility for deckwetness through slipway of stern trawler in wind and waves. A 350 G/T class, ocean-going stern trawler is adopted for the present study. The stem trawler is particularly assumed to drift with fishing implements hung down the slipway due to internal or external accident during fishing operation in real sea. The author considers two factors as possibility for deckwetness to occur through slipway. One is mooring effect of fishing implements hung down the slipway under wind pressure, and the other is relative ship motion in vertical direction in waves. Through the numerical calculation, the author clarifies that there is thin possibility for deckwetness to occur from above two points of view.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1995.10a
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• pp.179-184
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• 1995

A new cutting parameter is defined in the spherical part of ball end-mill cutter. A series of slot cutting experiments were carried out to obtain the cutting parameter. The cutter contact area is expressed as the grid posiotion in the cutting plane using Z map. The cutting forces in each grid are calculated and saved as force map, prior to the average cutting forces calculation. The cutting force, in the arbitrary cutting area, can be easily calculated by summing up the cutting forces of the engaged grid in the force map. This model was verified in the inclined surface cutting by cutting test of a cylindrical part.

• KSTLE International Journal
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• v.6 no.1
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• pp.17-20
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• 2005

The object of the present work is the natural lre%uency analysis of femto slider, HeaHdisk interaction during starustop and constant speed were detected by using the acoustic emission (AE) test system. The frequency spectrum analysis wasperformed using the AE signal obtained during the head/disk interaction. The FFT (Fast Fourier Transform) analysis of the AEsignals is used to understand the interaction between the AE signal and the state of contact. Natural frequency analysis wasperformed using the ANSYS program. The results indicate acceptable accordance of finite element calculation results with theexperimental results.

• Tribology and Lubricants
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• v.12 no.3
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• pp.100-106
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• 1996

Gerotor pumps and motors are widely used in lubrication and hydraulic actuator systems. Compared with internal gear pumps and motors, they have many advantages. However, the gerotor profiles have not been suff'lciently analyzed theoretically. Therefore, it is very difficult for designer to decide the specifications of the gemtor profiles, and calculation of flow rate and minimum distance of clearance in the contact point of inner and outer rotor is not yet confirmed. In this paper, when we design inner and outer rotor concurently, we have analyzed the gerotor profiles and displayed the calculated results such as flow rate, minimum distance between inner and outer rotor and gerotor profiles.

• 유체기계공업학회:학술대회논문집
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• 2001.11a
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• pp.482-487
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• 2001

Leaf type foil bearings have been used successfully in many aerospace applications such as air cycle machines, turbocompressors and turboexpander. These applications are characterized by light loads, constant speeds and low to moderate temperatures. But, as system on start-up or shutdown, sliding contact between the shaft and foil surfaces cause wear. So, in present study, to understand pressure-flow characteristics and deformation of foil bearing, flow/structure interaction analysis was used. and using this method, 2D and 3D calculation was peformed for shape of foil bearing to know circumferential direction flow and leakage flow characteristics of axial direction.