• Journal of the Korean Society for Precision Engineering
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• v.31 no.6
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• pp.543-550
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• 2014

A magnet gear composed of two layers of permanent magnets repeated circumferentially can transmit the power without mechanical contact. In the topology called by the magnet shutter gear known as the most competitive concept among the existing concepts, the number of pole-pairs on the high speed rotor corresponds to that of low speed rotor through electric steel set functioning as a magnetic modulator. The methodology is classified into radial type and axial type according to its magnetic path as in the motor. However, the magnetic modulator has multiple poles located separately. So, it is very complicated to assemble each module of the magnet gear mechanically and to sustain a mechanical stiffness of the modulator. The practical trouble can be solved partially through reconfiguring the modules. This paper deals with the novel magnetic shutter gear topology varying the magnetic path and its effectiveness is verified through real hardware implementation.

• Computers and Concrete
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• v.4 no.5
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• pp.331-346
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• 2007

A computer program was developed to analyze the non-linear, cyclic flexural performance of reinforced concrete structural members under various types of loading paths including non-sequential variations in axial load. This performance is significantly affected by the loading history. Different monotonic material models as well as hysteresis rules for confined and unconfined concrete and steel, some developed and calibrated against test results on material samples, were implemented in a fiber-based moment-curvature and in turn force-deflection analysis. One of the assumptions on curvature distribution along the member was based on a method developed to address the variation of the plastic hinge length as a result of loading pattern. Functionality of the program was verified by reproduction of analytical results obtained by others for several cases, and accuracy of the analytical process and the implemented models were evaluated against the experimental results from large-scale reinforced concrete columns tested under the analyzed loading cases. While the program can be used to predict the response of a member under a certain loading pattern, it can also be used to examine various analytical models and methods or refine a custom material model against test data.

• International Journal of Fluid Machinery and Systems
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• v.9 no.1
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• pp.1-16
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• 2016

Behaviors of surges appearing near the stall stagnation boundaries in various fashions in systems of a single-stage compressor and flow-path systems were studied analytically and were tried to put to order. Deep surges, which enclose the stall point in the pressure-mass flow plane, tend to have either near-resonant surge frequencies or subharmonic ones. The subharmonic surge is a multiple-loop one containing, for example, in a (1/2) subharmonic one, a deep surge loop and a mild surge loop, the latter of which does not enclose the stall point, staying only within the stalled zone. Both loops have nearly equal time periods, respectively, resulting in a (1/2) subharmonic surge frequency as a whole. The subharmonic surges are found to appear in a narrow zone neighboring the stall stagnation boundary. In other words, they tend to appear in the final stage of the stall stagnation process. It should be emphasized further that the stall stagnation initiates fundamentally at the situation where a volume-modified reduced resonant-surge frequency becomes coincident with that for the stagnation boundary conditions, where the reduced frequency is defined by the acoustical resonance frequency in the flow-path system, the delivery flow-path length and the compressor tip speed, modified by the sectional area ratio and the effect of the stalling pressure ratio. The real surge frequency turns from the resonant frequency to either near-resonant one or subharmonic one, and finally to stagnation condition, for the large-amplitude conditions, caused by the non-linear self-excitation mechanism of the surge.

• Structural Engineering and Mechanics
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• v.22 no.2
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• pp.169-184
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• 2006

A close form solution of the maximum deflection for cracked columns with rectangular cross-sections was developed and thus the elastic buckling behavior and ultimate bearing capacity were studied analytically. First, taking into account the effect of the crack in the potential energy of elastic systems, a trigonometric series solution for the elastic deflection equation of an arbitrary crack position was derived by use of the Rayleigh-Ritz energy method and an analytical expression of the maximum deflection was obtained. By comparison with the rotational spring model (Okamura et al. 1969) and the equivalent stiffness method (Sinha et al. 2002), the advantages of the present solution are that there are few assumed conditions and the effect of axial compression on crack closure was considered. Second, based on the above solutions, the equilibrium paths of the elastic buckling were analytically described for cracked columns subjected to both axial and eccentric compressive load. Finally, as examples, the influence of crack depth, load eccentricity and column slenderness on the elastic buckling behavior was investigated in the case of a rectangular column with a single-edge crack. The relationship of the load capacity of the column with respect to crack depth and eccentricity or slenderness was also illustrated. The analytical and numerical results from the examples show that there are three kinds of collapse mechanisms for the various states of cracking, eccentricity and slenderness. These are the bifurcation for axial compression, the limit point instability for the condition of the deeper crack and lighter eccentricity and the fracture for higher eccentricity. As a result, the conception of critical transition eccentricity $(e/h)_c$, from limit-point buckling to fracture failure, was proposed and the critical values of $(e/h)_c$ were numerically determined for various eccentricities, crack depths and slenderness.

• International Journal of Fluid Machinery and Systems
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• v.9 no.4
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• pp.338-353
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• 2016

Information on the surge behaviors and stall stagnation boundaries for a nine-stage axial flow compressor are summarized on the basis of analytical data in comparison with those for a single-stage one, with attention to the pressure ratio effect. The general trends of the surge loop behaviors of the pressure-mass flow are similar for both compressors including the fact that the subharmonic surges tend to appear very near the stall stagnation boundaries. With respect to the nine-stage compressor, however, the mild loops in the subharmonic surges tend to be very small in size relative to the deep loops, and at the same time, insufficient surge recovery phenomenon, which is a kind of subharmonic surge, appears also far from the stagnation boundary for relatively short delivery flow-paths. The latter is found to be a rear-stage surge caused by unstalling and re-stalling of the rear stages with the front-stages kept in stall in the stalled condition of the whole compressor, which situation is caused by stage-wise mismatching in the bottom pressure levels of the in-stall multi-stage compressor. The fundamental information on the stall stagnation boundaries is given by a group of normalized geometrical parameters including relative delivery flow-path length, relative suction flow-path length, and sectional area-pressure ratio, and by another group of normalized frequency parameters including relative surge frequencies, modified reduced resonance frequencies, and modified reduced surge frequencies. Respective groups of the normalized parameters show very similar tendency of behaviors for the nine-stage compressor and the single-stage compressor. The modified reduced resonance frequency could be the more reasonable parameter suggesting the flow-induced oscillation nature of the surge phenomena. It could give the stall stagnation boundary in a more unified manner than the Greitzer's B parameter.

• Proceedings of the KSME Conference
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• 2007.05a
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• pp.642-647
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• 2007

Determination of loading conditions for tube hydroforming(THF) process that implies an amount of the increment in axial feeding and internal pressure for each step is one of the most important constituents at the process design level. On account of the fact that those design factors mentioned above are imposed simultaneously during the process, suitable loading conditions are required to obtain robust products without any failure such as buckling, necking, bursting and so on. In which, especially, bursting is well known as the most frequently occurred failure in general THF process. In this study, therefore, determination of the loading condition based on the adaptive method was carried out to obtain safe loading paths. In addition, forming limit curves are applied to evaluate the derived loading conditions by using the simulation results. Consequently, it is found that described method in this study for THF process design is useful and has a feasibility.

• Structural Engineering and Mechanics
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• v.4 no.2
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• pp.149-162
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• 1996

A postbuckling analysis is presented for a simply supported, moderately thick rectangular plate subjected to combined axial compression and uniform temperature loading and resting on a two-parameter elastic foundation. The two cases of thermal postbuckling of initially compressed plates and of compressive postbuckling of initially heated plates are considered. The initial geometrical imperfection of the plate is taken into account. The formulations are based on the Reissner-Mindlin plate theory considering the first order shear deformation effect, and including the plate-foundation interaction and thermal effect. The analysis uses a deflection-type perturbation technique to determine the buckling loads and postbuckling equilibrium paths. Numerical examples cover the performances of perfect and imperfect, moderately thick plates resting on Winkler or Pasternak-type elastic foundations. Typical results are presented in dimensionless graphical form.

• Journal of the Korean Geotechnical Society
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• v.15 no.5
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• pp.43-55
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• 1999

This study evaluated Yasufuku's constitutive model in terms of its capability to accurately consider the observed behavior of Iksan compacted weathered granite soil for various stress-paths. The strains calculated from the model are in reasonable agreement with those measured, but some discrepancies occur. The largest differences between measured and calculated strains occur for axial strain of proportional loading with increasing stress. Yasufuku's constitutive model can consider the observed behavior of Iksan compacted weathered granite soil with accuracy for conventional triaxial compression and for p'-constant loading with increasing stress ratio.

• Proceedings of the IEEK Conference
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• 2002.06b
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• pp.201-204
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• 2002

A large area inductively coupled plasma which is applicable to LCD processing is built with a modified single loop RF antenna. Combination of parallel and series paths of RF current through the antenna induces local enhancement of plasma density, which in turn provides uniform plasma density near the substrate. The plasma density distribution is measured and compared with that of the conventional single loop antenna. Aisotropic etching of photoresist is performed, and it is found that etch uniformity is improved by 3％ from 15% of the conventional etcher over 350$\times$300mm glass substrates. Photoresist etching rate and uniformity can be further improved by applying a periodic weak axial magnetic fieid.

• Current Optics and Photonics
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• v.2 no.2
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• pp.172-178
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• 2018

We propose a precise 3D endoscopic technique for medical and industrial applications. As the 3D measuring principle, the continuously scanning structured illumination microscopy (CSSIM), which enables to obtain 3D sectional images by the synchronous axial scanning of the target with the lateral scanning of the sinusoidal pattern, is adopted. In order to reduce the size of the probe end, the illumination and detection paths of light are designed as coaxial and a coherent imaging fiber bundle is used for transferring the illumination pattern to the target and vice versa. We constructed and experimentally verified the proposed system with a gauge block specimen. As the result, it was confirmed that the 3D surface profile was successfully measured with $16.1{\mu}m$ repeatability for a gauge block specimen. In order to improve the contrast of the sinusoidal illumination pattern reflected off on the target, we used polarizing optical components and confirmed that the visibility of the pattern was suitable in CSSIM.