• Proceedings of the Korea Technical Association of the Pulp and Paper Industry Conference
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• 2001.04a
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• pp.184-184
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• 2001

캘린더령은 지펼의 표면을 평활하게 하고, 두께를 감소시켜 균일하게 하는 역할을 한다. 그러나 이는 필연적으로 불투명도와 같은 광학적 성질과 인장강도 등의 강도적 성질 의 저하를 유발한다. 따라서 캘린더링 공정변수인 온도, 압력, 속도 등이 종이의 물성에 미 치는 영향을 정확하게 파악하는 것은 캘린더령에 따라 발생할 수 있는 물성 저하를 최소화 하기 위해 필수적으로 요청된다. 본 연구에서는 최근들어 저평량화에 대한 관심이 증가하면 서 그 중요성이 더해지고 있는 불투명도가 캘린더링에 따라 변화되는 양상을 분석하기 위해 서 화상분석 기법을 이용하여 종이의 두께방향 밀도 변이를 평가하고 밀도변이와 불투명도 와의 상관관계를 해석코자 하였다. 또 캘린더링에 따른 불투명도를 저하를 최소화시키기 위 한 캘린더링 조건을 모색하였다. 캘린더링에 의해 발생하는 종이의 두께 변형은 두께방향의 위치에 따라 다르게 나 타난다. 이러한 종이의 두께 방향으로 발생하는 밀도 변이와 이에 따른 불투명도 변화를 평 가하기 위하여 동일한 평량의 종이를 캘린더령 조건을 달리하여 두께방향 밀도변이가 다른 시편을 준비하고 두께 방향 단면을 SEM으로 촬영하였다. 이후 화상분석기를 통해 단면을 이치화하고, 각 픽셀의 흑백 값을 구해 CD방향으로 평균을 내어 두께 방향에 대한 밀도 변 이를 평가하였다. 그 결과 압력보다는 온도를 높여 캘린더링한 경우 종이의 두께 방향 밀도 경사가 커진다는 사실을 확인할 수 있었다. 이는 고온에 의해 표층이 고밀화되고 상대적으 로 내부가 별크해졌기 때문이다. 이러한 밀도 변이가 종이의 광학적 성질인 불투명도에 미 치는 영향을 구명하기 위해서 캘린더링 전후에 두께 및 불투명도를 측정하여 5% 유의수준 에서 회귀분석을 실시하였다. 밀도경사를 지닌 종이의 불투명도를 이론적으로 해석하기 위해 다층 모델을 가정하 고 각 층의 비광산란계수(5)와 비광흡수계수(k)를 달리 부여하고 Kubelka-Munk 이론을 근 거로 하여 이론적 불투명도를 계산하였다. 불투명도에 대한 분석를 통해 동일한 두께 변형 을 가지는 샘플에 대해서 압력보다는 온도를 증가시켜 두께를 감소시키는 캘린더링 처리가 불투명도의 저하를 최소화한다는 것을 확인하였다.

• Journal of Naturopathy
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• v.10 no.1
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• pp.26-32
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• 2021

Purpose: At acupoint pressure, the pressing direction of all acupoints is usually vertical. However, it is not clear whether the vertical direction is toward the belly button or the body's center in the BL52. In this study, the effective direction of acupressure was studied by measuring the pressure pain threshold according to the direction of acupressure in 30 subjects. Methods: The distance from the subject's GV4 to the left and right BL52 and the distance from GV4 to the navel were measured, and then using the ellipse where the left and right BL52 of GV4 pass through the navel, the angles of the navel direction and the body's center were calculated in the left and right BL52. The pressure at the time when the subjects felt pain while pressing the BL52 in two directions was used as the acupressure pain threshold. The pain threshold was measured 3 times at 3 minute intervals on the left and right BL52s of the subject. Results: The acupressure pain threshold measured in the left and right BL52 of the subjects was significantly decreased when pressed toward the trunk center (p < .05). In BL52, it was more sensitive to pressure when the direction of pressure is toward the body's center. Conclusions: Acupressure therapy of acupoint is more sensitive to external stimuli than the surrounding. In this study, acupressure directed toward the trunk center is more efficient than toward the belly button in BL52.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.48 no.9
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• pp.653-661
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• 2020

This study derives numerically the shell Knockdown factors for the isogrid-stiffened cylinders of space launch vehicles when the axially compressive force and internal pressure are applied simultaneously. A commercial nonlinear finite element analysis software, ABAQUS, is used for the present work. Nonlinear postbuckling analyses are conducted to calculate the global buckling loads of a cylinder without and with the internal pressure. The shell Knockdown factor is numerically derived using the predicted global buckling loads without and with the geometrically initial imperfection of a cylinder. When the internal pressure of 500 kPa and compressive force are applied to the cylinder, the global buckling load and Knockdown factor increases by 304% and 53%, respectively, as compared to the results without the internal pressure.

• The Journal of the Acoustical Society of Korea
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• v.41 no.6
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• pp.705-712
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• 2022

A sudden pressure drop caused by the pressure relief valve acts as a strong noise source and propagates the compressible pressure fluctuation along the pipe wall, which becomes a excitation source of Acoustic Induced Vibration (AIV). Therefore, in this study, the numerical methodology is developed to evaluate the reduction effect of compressible pressure fluctuation due to curved pipe in the pressure relief valve system. To describe the acoustic wave caused by density fluctuation, unsteady compressible Large Eddy Simulation (LES) technique, which is high accuracy numerical method, Smagorinsky-Lilly subgrid scale model is applied. Wavenumber-frequency analysis is performed to extract the compressible pressure fluctuation component, which is propagated along the pipe, from the flow field, and it is based on the wall pressure on the upstream and downstream pipe from the curved pipe. It is shown that the plane wave and the 1st mode component in radial direction are dominant along the downstream direction, and the overall acoustic power was reduced by 3 dB through the curved pipe. From these results, the noise reduction effect caused by curved pipe is confirmed.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1993.04a
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• pp.97-107
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• 1993

프시톤 형상에 관한 연구는 엔진의 열효율을 상승시키는데 중점을 두었으나 캘리포니아주의 환경 관련 법안을 계기로 공해 물질의 배출을 중이는 방향으로 연구가 이루어지고 있다. 즉, 실린더내의 최고 온도와 압력을 적정한 수준에서 조절하여 공해물질의 방출을 극소화시키면서 열효율을 높힐 수 있는 방안에 대한 연구를 많이 진행하고 있다. 본 논문은 유한요소법을 이용하여 저마찰 패드식 피스톤에 대한 트라이볼로지적 해석으로 피스톤의 편심에 따른 압력 분포도 해석, 마찰력과 피스톤의 동특성에 대하여 알아보고자 한다. 이들을 해석하기 위한 가장 중요한 역학적 상태량은 피스톤 표면의 압력 분포와 피스톤의 편심량이며 특히, 압력 분포 해석은 피스톤의 유막 설계시 기본이 된다.

• Proceedings of the KAIS Fall Conference
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• 2003.06a
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• pp.125-128
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• 2003

본 연구는 현재 시판되고 있는 Papst사의 4100 mod디을 대상으로 축방향 송풍기의 사출성형에 대해 MoldFlow 프로그램을 사용하여 제품에 대한 최적의 게이트 위치를 조사하였고 이를 바탕으로 2매 구성금형과 3매 구성금형에 따른 게이트를 설정하여 사출압력, 온도의 변화, 충전 시간 둥을 비교하여 경제성을 고려한 최적의 게이트 위치를 결정하였다. 다수 뽑기 금형에서의 제품 성형에 있어 중요한 변수가 되는 유동주입시스템에서 러너의 크기 변화에 따른 유동선단의 흐름 및 압력과 온도의 변화를 살펴보았고 이러한 시뮬레이션을 통해 시행오차를 최소화 하여 생산비 절감과 품질 향상을 위한 설계를 구현하고자 시도하였다.

• Composites Research
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• v.34 no.4
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• pp.257-263
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• 2021

Composite materials have been widely applied for fabricating pressure vessels used for storing gaseous and liquid fuel because of their high specific stiffness and specific strength. Accordingly, the accurate measurement of their mechanical property, particularly the burst pressure or fracture strain, is essential prior to the commercial release. However, verification of the safety of composite pressure vessels using conventional test methods poses some limitations because it may lead to the deformation of the load transferring media or provoke an additional energy loss that cannot be ignored. Therefore, in this study, the segment-type ring burst test device was designed considering the theoretical load transferring ratio and applicable displacement of the vertical column. Moreover, to verifying the uniform distribution of pressure of the segment type ring burst test device, the hoop stress and strain distribution of ring specimens were compared with that of the hydraulic pressure test method via FEM. To conduct a simulation of the fracture behavior of the composite pressure vessel, a Hashin failure criterion was applied to the ring specimen. Furthermore, the fracture strain was also measured from the experiment and compared with that of the result from the FEM.

• The Journal of the Petrological Society of Korea
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• v.21 no.2
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• pp.249-261
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• 2012

Olivine is a dominant mineral in the upper mantle and is elastically very anisotropic. When olivine is deformed under stress at high pressure and high temperature, lattice preferred orientation (LPO) is formed. It is known that the LPO of olivine is affected by water, stress, and pressure. In this paper, I reviewed the papers dealing with the effects of water, stress, and pressure on the LPO of olivine, summarized the papers on the LPOs of olivine in natural mantle rocks, and discussed its implications for seismic anisotropy in the upper mantle. In addition, I also described four types of LPOs of orthopyroxene recently found in natural spinel lherzolite.

• Journal of Radiation Protection and Research
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• v.32 no.4
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• pp.168-177
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• 2007

A neural network model to evaluate the neutron exposure on the reactor pressure vessel inner diameter was developed. By using the three dimensional synthesis method described in Regulatory Guide 1.190, a simple linear equation to calculate the neutron spectrum on the reactor pressure vessel was constructed. This model can be used in a quick estimation of fast neutron flux which is the most important parameter in the assessment of embrittlement of reactor pressure vessel. This model also used in the selection of an optimum core loading pattern without the neutron transport calculation. The maximum relative error of this model was less than 3.4% compared to the transport calculation for the calculations from cycle 1 to cycle 23 of Kori unit 1.

• Composites Research
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• v.16 no.6
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• pp.1-9
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• 2003

In this paper, probabilistic failure analysis based on Weibull distribution function is proposed to predict the fiber strength of composite pressure vessel. And, experimental tests were performed using fiber strand specimens, unidirectional laminate specimens and composite pressure vessels to confirm the volumetric size effect on the fiber strength. As an analytical method, the Weibull weakest link model and the sequential multi-step failure model are considered and mutually compared. The volumetric size effect shows the clearly observed tendency towards fiber strength degradation with increasing stressed volume. Good agreement of fiber strength distribution was shown between test data and predicted results for unidirectional laminate and hoop ply in pressure vessel. The site effect on fiber strength depends on material and processing factors, the reduction of fiber strength due to the stressed volume shows different values according to the variation of material and processing conditions.