• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.34 no.12
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• pp.59-66
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• 2006

To understand the role of helical geometry on the regression rate enhancement, two competing underlying mechanisms such as turbulence enhancement and swirling motion production were studied by numerical calculations. Experimental results showed that the enhancement of heat transfer rate has the very close relation to the increase in regression rate even though the percentage of increase in heat transfer rate is different from that in regression rate. This discrepancy is presumably due to the change of turbulent flow feature caused by so-called "blowing mass flux" from the fuel surface. In this regard, the results of RANS calculation show that the blowing velocity is responsible for the reduction of the swirl generation and the increase in the turbulent kinetic energy. And the dominancy of one of the mechanisms causes the increase in the regression rate. Meanwhile, the increase in turbulent kinetic energy due to the mixing of blowing flow and free stream flow does not contribute for the enhancement of the heat transfer rate to the surface because the blowing flow pushes boundary layer away from the solid surface.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.23 no.1
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• pp.123-130
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• 1999

The objective of the current study is to understand steady 3-dimensional flow phenomena in a bifurcated duct experimentally. A bifurcation model is fabricated with transparent acrylic resin to visualize the whole flow field with the PIV system. The gray level cross-correlation method is applied to the image processing algorithm. The subpixel and the area interpolation methods are used to obtain the final velocity vectors. The finite volume predictions are used to analyze the flow patterns in the bifurcation model. The results of the computer simulation and the PIV experiment for three-dimensional flow show the recirculation zone and the formation of the paired secondary flow distal to the apex of the bifurcation model. The results obtained with the two methods also show that the branch flow strongly strikes the inner wall due to the inertial effect and accompanied helical motion as it flows toward the outer wall.

• Structural Engineering and Mechanics
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• v.53 no.6
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• pp.1105-1126
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• 2015

Many vibrating mechanical systems from the real life are modeled as combined dynamical systems consisting of beams to which spring-mass secondary systems are attached. In most of the publications on this topic, masses of the helical springs are neglected. In a paper (Cha et al. 2008) published recently, the eigencharacteristics of an arbitrary supported Bernoulli-Euler beam with multiple in-span helical spring-mass systems were determined via the solution of the established eigenvalue problem, where the springs were modeled as axially vibrating rods. In the present article, the authors used the assumed modes method in the usual sense and obtained the equations of motion from Lagrange Equations and arrived at a generalized eigenvalue problem after applying a Galerkin procedure. The aim of the present paper is simply to show that one can arrive at the corresponding generalized eigenvalue problem by following a quite different way, namely, by using the so-called "characteristic force" method. Further, parametric investigations are carried out for two representative types of supporting conditions of the bending beam.

• Korean Journal of Digital Imaging in Medicine
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• v.5 no.1
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• pp.78-84
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• 2002

To evaluate the relative time required to perform a CT(computed tomography) examination in a filmless versus a film-based system and helical versus nonhelical studies. Time and Motion studies were performed in 175 consecutive CT examinations. Images from 85 examinations were electronically transferred to a PACS, and 90 were printed to film. The time required to obtain and electronically transfer the images or print the images to film and make the current and previous studies available to the radiologists for interpretation was recorded. The time required for a radiological technologist to complete a CT examination was reduced by 43% with the PACS compared with the film-based system and nonhelical was reduced 10-20% with helical studies. This reduction was due to the elimination of a transfer and printing, such as the printing at window or level settings. The use of PACS can result in the elimination of time tasks for the radiological technologist, resulting in marked reduction in examination time. This reduction can result in decreased cost and increased productivity in PACS operation.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.39 no.6
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• pp.497-504
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• 2015

In this paper, we study the propulsive behavior related to the flagellar motion of bacteria using a spring model. A commercial program was used to conduct simulations, and we verified the numerical technique by setting an additional rotating domain and conducting a parametric study. The numerical results are in good agreement with slender-body theory, although overall, they are not in agreement with resistive-force theory. We confirm the effect of the rotational velocity, pitch, helical radius, fluid viscosity, and, in particular, the distance from the wall on the propulsion of the spring.

• Journal of Electrical Engineering and Technology
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• v.12 no.3
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• pp.1227-1234
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• 2017

The two-degree-of-freedom direct drive induction motor, which is capable of linear, rotary and helical motion, has a wide application in special industry such as industrial robot arms. It is inevitable that the linear motion and rotary motion generate coupling effect on each other on account of the high integration. The analysis of this effect has great significance in the research of two-degree-of-freedom motors, which is also crucial to realize precision control of them. The coupling factor considering the coupling effect is proposed and addressed by 3D finite element method. Then the corrected mathematical model is presented by importing the coupling factor. The results from it are verified by 3D finite element model and prototype test, which validates the corrected mathematical model.

• Progress in Medical Physics
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• v.29 no.1
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• pp.1-7
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• 2018

The $TomoTherapy^{(R)}$ beam-delivery method creates helical beam-junctioning patterns in the dose distribution within the target. In addition, the dose discrepancy results in the particular region where the resonance by pattern of dose delivery occurs owing to the change in the position and shape of internal organs with a patient's respiration during long treatment times. In this study, we evaluated the dose pattern of the longitudinal profile with the change in respiration. The superior-inferior motion signal of the programmable respiratory motion phantom was obtained using AbChes as a four-dimensional computed tomography (4DCT) original moving signal. We delineated virtual targets in the phantom and planned to deliver the prescription dose of 300 cGy using field widths of 1.0 cm, 2.5 cm, and 5.0 cm. An original moving signal was fitted to reflecting the beam delivery time of the $TomoTherapy^{(R)}$. The EBT3 film was inserted into the phantom movement cassette, and static, without the movement and with the original movement, was measured with signal changes of 2.0 s, 4.0 s, and 5.0 s periods, and 2.0 mm and 4.0 mm amplitudes. It was found that a dose fluctuation within ${\pm}4.0%$ occurred in all longitudinal profiles. Compared with the original movement, the region of the gamma index above 1 partially appeared within the target and the border of the target when the period and amplitude were changed. Gamma passing rates were 95.00% or more. However, cases for a 5.0 s period and 4.0 mm amplitude at a field width of 2.5 cm and for 2.0 s and 5.0 s periods at a field width of 5.0 cm have gamma passing rates of 92.73%, 90.31%, 90.31%, and 93.60%. $TomoTherapy^{(R)}$ shows a small difference in dose distribution according to the changes of period and amplitude of respiration. Therefore, to treat a variable respiratory motion region, a margin reflecting the degree of change of respiration signal is required.

• Laser Solutions
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• v.18 no.3
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• pp.14-19
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• 2015

A helical fabricating method using $CO_2$ laser was utilized for producing cone-shaped structure on a silica substrate. Output power and the number of scanning radiation were modified in order to control the structure. The experiment shows that the depth and width of cone-shape were increased with higher output power of the laser and the number of scanning. We demonstrate fabrication of multidirectional side-firing optical fiber with diameter of 440 um using the $CO_2$ laser fabrication technique.

• The Bulletin of The Korean Astronomical Society
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• v.37 no.2
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• pp.113.2-113.2
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• 2012

An innovative solar observing satellite, Hinode, has successfully observed the detailed evolution of a rapidly developing emerging flux region from the beginning of its appearance at the solar surface. The high spatial and temporal resolution provided by the satellite enables to capture the prominent dynamic processes such as the rotational motion of a polarity region with intense magnetic flux which is reminiscent of a cyclone on the Earth, and a running wave that spreads ahead of this rotating polarity region. This 'solar cyclone' is, on the other hand, generated differently from terrestrial cyclones, and a possible generating mechanism for it is demonstrated with a three-dimensional magnetohydrodynamic simulation of a twisted magnetic flux tube emerging from the solar interior into the solar atmosphere. The simulation shows that the rotational motion is caused by a strong downflow of plasma along the twisted field lines that form a helical pillar standing upright on the Sun.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.11b
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• pp.31-36
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• 2002

Even through the problem of misalignment is of great importance, not much work has been reported in the literature on the effect of misalignment on the vibrations of the gear-bearing systems. Therefore, the nonlinear dynamic characteristics of the gear drive system due to misalignment are investigated in this work. Transmission error for helical gear and bearing nonlinear stiffness is calculated. The equation of motion of the gear drive system is modelled using the time-varying gear meshing stiffness, bearing nonlinear stiffness, and bearing pre-load due to the housing deformation. Numerical analysis lot the gear drive system show the result of misalignment effect - sub-harmonic component, bearing pre-load effect, and another nonlinear phenomenon. And the numerical analysis are verified by the experimental result.