• Journal of the Earthquake Engineering Society of Korea
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• v.26 no.6
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• pp.227-235
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• 2022

For a member model in nonlinear structural analysis, a lumped plastic model that idealizes its flexural bending, shear, and axial behaviors by springs with the nonlinear hysteretic model is widely adopted because of its simplicity and transparency compared to the other rigorous finite element methods. On the other hand, a challenging task in its numerical solution is to satisfy the equilibrium condition between nonlinear flexural bending and shear springs connected in series. Since the local forces between flexural and shear springs are not balanced when one or both springs experience stiffness changes (e.g., cracking, yielding, and unloading), the additional unbalanced force due to overshooting or undershooting each spring force is also generated. This paper introduces an iterative scheme for numerical solutions satisfying the equilibrium conditions between flexural bending and shear springs. The effect of equilibrium iteration on analysis results is shown by comparing the results obtained from the proposed method to those from the conventional scheme, where the equilibrium condition is not perfectly satisfied.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.06a
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• pp.480-480
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• 2008

Vacuum circuit breaker(VCB) is now emerging as an alternative of gas circuit breaker(GCB) which uses SF6 gas as insulating material whose dielectric strength is outstanding. But we have to reduce SF6 gas because SF6 gas is one of greenhouse gas and efforts to reduce greenhouse gas are now trend of the world. Therefore, we can say VCB is the optimal alternative of GCB because vacuum is environmentally friendly. The vacuum interrupter is the core part of VCB to interrupt arcing current. There are mainly two methods to extinguish arc. One is radial magnetic field (RMF) method and the other is axial magnetic field (AMF) method. We deals with RMF method in this paper. Compared with AMP, RMF arc quenching method has different principle to extinguish arc. In case of RMF method, pinch effect is much larger than AMF method. Because of pinch effect RMF type contact electrodes have the single large spot which is severly damaged and melted while AMF type contact electrodes have small and multiple spots which are slightly damaged and melted. To prevent contact electrode being damaged and melted from high temperature-arc, RMF method uses Lorentz force to move arc. In this paper we calculated and compared the arc driving force of two cases and we analyzed the force acting on each part of arc by means of commercial finite element method software Maxwell 3D. They have 3petals and we considered two cases. One is the case when fixed(upper) and movable(lower) contacts are in mirror arrangement (Case 1). The other is the case when one of two contacts (movable contact) is revolved at maximum angle as possible as it can be (Case 2). And at each case above, we analyzed arc driving force at two positions, position 1 is the closest to the center of contact and position 2 is near the edge of petal on fixed contact. As a result we could find that Case 2 generated stronger arc driving force than Case 1 at position 1. But at position 2 Case 1 generated stronger arc driving force than Case 2. This simulation method can contribute to optimizing spiral-type electrode designs in a view of arc driving force.

• Journal of KSNVE
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• v.7 no.1
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• pp.99-106
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• 1997

Centrigugal fans are widely used due to their ability to achieve relatively high pressure ratios in a short axial distance compared to axial fans. Because of their widespread use, the noise generated by these machines causes one of serious problems. In general, centrigugal fan noise is often dominated by tones at BPF(blade passage frequency) and its higher harmonics. This is a consequence of the strong interaction between the periodic flow discharged radially from the impeller and the stator blades or the cutoff. But in vacuum cleaner fan the noise is dominated by not only the discrete tones of BPF but also broadband frequencies. In this study we investigate the mechanism of broadband noise and predict for the unsteady flow field and the acoustic pressure field associated with the centrifugal fan. DVM(discrete vortex method) is used to calculates the flow field and the Lowson's method is used to predict the acoustic pressures. From the results we find that the broadband noise of a circular casing centrifugal fan is due to the unsteady force fluctuation around the impeller blades related to the vortex shedding. The unsteady forces associated with the shed vortices at impeller and related to the interactions to the diffuser and the exit.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.22 no.3
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• pp.336-345
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• 1998

The substantial loss behind axial flow rotor was generated by wake, various vortices in the hub region and the leakage vortex in the tip region. Particularly, the leakage vortex formed near blade tip was one of the main causes of the reduction of performance, the generation of noise and the aerodynamic vibration in rotor downstream. In this study, the three-dimensional flowfields in an axial flow rotor for various tip clearances were calculated, and the numerical results were compared with the experimental ones. The numerical technique was based on SIMPLE algorithm using standard k-.epsilon. model (WFM). Through calculations, the effects of the tip clearance on the overall performance of rotor and the loss distributions, and the increase in the displacement, momentum, and blade-force-deficit thickness of the casing wall boundary layer were investigated. The mass-averaged flow variables behind rotor agreed well with the experimental results. The presence of the tip leakage vortex behind rotor was described well. Although the loci of leakage vortex by calculation showed some differences compared with the experimental results, its behavior for various tip clearances was clarified by examining the loci of vortex center.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.10
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• pp.6453-6457
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• 2015

In this paper, the theoretical analysis for a solenoid with a finite length was verified by the finite element simulation. The solenoids are widely being used in the field of mechanical, industrial, medical industry due to their simple structure and fast responses. Solenoid actuators use an electromagnetic force. A magnetic field is formed around the solenoid coil when a current is applied. The magnetic force generated by the magnetic field enables an inside plunger to move linearly. The axial and radial magnetic fields (magnetic flux density, B) at a certain point were calculated from the Biot-Savart's law and compared with the simulation analysis from the ANSYS-Magnetostatic S/W. Comparison result, an error exists in the error range, and could therefore verify the accuracy.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.10
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• pp.1269-1278
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• 2013

The cutting area changes periodically in the end-milling process because of its form generation mechanism. In this study, the effects of the cutting area on end-milled side walls are studied by developing a cutting area model that simulates the area formed by engagement between a workpiece and a cutting edge of the end mill. To do this, the straightness profile of the side wall in the axial direction is investigated. Models for estimating the cutting area and the transition point, where the slope of the straightness profile changes suddenly, are verified from real end-milling experiments under various radial and axial depth of cut conditions. Through this study, it is confirmed that the final end-milled side wall is generated in the regions where cutting areas are constant and decreasing in the down-cut. Similarly, in stable up-cut, it is also generated in the regions where cutting areas are increasing and constant. It is found that the transition point appears when the region changes.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.22 no.4
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• pp.708-716
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• 2013

This study aims to understand the applied forces and related vibrational characteristics of a tripod joint (TJ), which is mostly used in front-drive-type middle-sized sedans in South Korea. The plunging force (PF) and generated axial force (GAF) are the most influential quantities related to the vibrational characteristics of a driveshaft. To obtain meaningful data, specially designed tests were performed using MTS test sets. The results of direct measurements reveal that higher PF and GAF values appear to worsen the vibrational characteristics of the vehicle. On the other hand, the measured apparent mass is useful for calculating the applied forces for a short driveshaft that has no dynamic vibration absorber. Among diversely controlled samples, it shows that the viscosity and tight fit are very sensitive to shudder vibrations of the vehicle. Therefore, these are good design factors for quality controls in the production line of constant-velocity joints.

• Journal of Ocean Engineering and Technology
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• v.23 no.5
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• pp.39-44
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• 2009

The hydrostatic slipper bearing is generally used in high pressure axial piston pumps to support the load generated from two surfaces which are sliding relatively at low speed. The object of the bearing is to remove the possibility of direct contact by maintenance of an adequate oil film thickness between two metal surfaces. Because the bearing performance is influenced by the bearing deformation, it is highly dependent on the injection pressure, the bearing surface profile and so on. In this study, the deformation characteristics of a hydrostatic slipper bearing is investigated according to the injection pressure by the finite element analysis. In the analysis, the special boundary condition to take the fluid-structure interaction (FSI) into account is used on the interactive surface. The results, such as bearing deformation, stress and lifting force, obtained from the fully coupled analysis are compared with those from the single step sequential method.

• Steel and Composite Structures
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• v.9 no.3
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• pp.191-208
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• 2009

Observations from experiments and real fire indicate that restrained steel beams have better fire-resistant capability than isolated beams. Due to the effects of restraints, a steel beam in fire condition can undergo very large deflections and the run away damage may be avoided. However disgusting damages may occur in the beam-to-column connections, which is considered to be mainly caused by the enormous axial tensile forces in steel beams resulted from temperature decreasing after fire dies out. Over the past ten years, the behaviour of restrained steel beams subjected to fire during heating has been experimentally and theoretically investigated in detail, and some simplified analytical approaches have been proposed. While the performance of restrained steel beams during cooling has not been so deeply studied. For the safety evaluation and repair of steel structures against fire, more detailed investigation on the behaviour of restrained steel beams subjected to fire during cooling is necessary. When the temperature decreases, the elastic modulus and yield strength of steel recover, and the contraction force in restrained steel beams will be produced. In this paper, an incremental method is proposed for analyzing the behaviour of restrained steel beams subjected to cooling. In each temperature decrement, the development of deformation and internal forces of a restrained beam is divided into four steps, in order to consider the effect of the recovery of the elastic modulus and strength of steel and the contraction force generated by temperature decrease in the beam respectively. At last, the proposed approach is validated by FE method.

• Journal of Magnetics
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• v.19 no.2
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• pp.130-139
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• 2014

This paper focuses on the modeling and analysis a novel two-axis rotary normal-stress electromagnetic actuator with compact structure for fast steering mirror (FSM). The actuator has high force density similar to a solenoid, but its torque output is nearly a linear function of both its driving current and rotation angle, showing that the actuator is ideal for FSM. In addition, the actuator is designed with a new cross topology armature and no additional axial force is generated when the actuator works. With flux leakage being involved in the actuator modeling properly, an accurate analytical model of the actuator, which shows the actuator's linear characteristics, is obtained via the commonly used equivalent magnetic circuit method. Finally, numerical simulation is presented to validate the analytical actuator model. It is shown that the analytical results are in a good agreement with the simulation results.