• Journal of the Korean Society of Propulsion Engineers
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• v.21 no.1
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• pp.44-50
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• 2017

Vehicle Holding Device(VHD) has a role that holding the launch vehicle on its launch pad until the engine therust reaches a steady condition. The analytical study of shape parameters and dynamic characteristics of hydraulic cylinders is carried out. The contraction of cylinder is considered as the major factor of releasing mechanism. Through the analysis, the decreasing of cylinder slit size and increasing initial charging pressure increase the contraction force. Through the transient analysis, cylinder load, displacement and inner pressure distribution are confirmed. The cylinder contraction force is converged to the cylinder external force when the cylinder starts to move. Also, the pressure distribution in the hydraulic cylinder is constant.

• Composites Research
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• v.20 no.5
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• pp.34-42
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• 2007

Strength and failure of adhesively bonded carbon composite-to-aluminum single-lap joints were studied by experiment. The main objective of this study is to investigate the effect of various parameters such as curing pressure for bonding, overlap lengths, and adherend thickness on the failure loads and modes of the bonded Joints with dissimilar materials. Experimental results show that the bonding pressure for composite-to-aluminum dissimilar materials should be 4 atm at the lowest. Failure load of the joints increases as the overlap length increases, but the strength (failure load divided by bonded area) decreases rapidly after the overlap width-to-length ratio is greater than 1. When the adherend thickness increase to double, bonding strength increase $12{\sim}55%$. Major failure mode of the joints is the delamination in the composite laminate and the location of delamination goes deeper into the laminates as the bonding pressure and overlap length increase.

• Journal of the Korean Orthopaedic Association
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• v.55 no.2
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• pp.127-134
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• 2020

Purpose: The aims of this study were (1) to investigate the relationship between the characteristics of allogenic bone block and the compressive strength of an allogenic bone block measured by biomechanical experiments, and (2) to compare the maximum pressure load of allogenic bone block with the gap pressure measured at the high tibial opening osteotomy. Materials and Methods: Ten patients who provided informed consent for gap pressure measurements during opening wedge high tibial osteotomy (OWHTO) were included. The gap pressures were measured at 1 mm intervals while opening the osteotomy site from 8 mm to 14 mm. Seventeen U-shaped allogenous wedge bone blocks were made from the femur, tibia, and humerus. The height, width, cross-sectional area, and cortex thickness of the bone blocks were measured, along with the maximum compressive load just before breakage. The relationship between these characteristics and the maximum pressure load of the bone blocks was evaluated. The gap pressures measured in OWHTO were compared with the maximum pressure loads of the allogenous wedge bone blocks to evaluate the possibility of inserting allogenous wedge bone blocks into the osteotomy site without a distractor in OWHTO. Results: The OWHTO gap pressure increased with increasing osteotomy site opening. The mean gap pressure, which occurred at a 14-mm opening, was 282±93 N; the maximum pressure was 427 N. The maximum pressure load of the allografts was 13,379±6,469 N (minimum, 5,868; maximum, 29,130 N) and was correlated significantly with the cortical bone thickness (correlation coefficient=0.693, p=0.002) and cross-sectional area (correlation coefficient=0.826, p<0.001). Depending on the sterilization method, the maximum pressure loads for the bone blocks were 13,406±5,928 N for freeze-dried and 13,348±7,449 N for fresh frozen. The maximum compressive load of the allogenous wedge bone blocks was 13.7-times greater than that in OWHTO opened to 14 mm (5,868 N vs. 427 N). Conclusion: The compressive strength of allogenous wedge bone blocks was sufficiently greater than the gap pressure in OWHTO. Therefore, allogenous wedge bone blocks can be inserted safely into the osteotomy site without a distractor.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.50 no.10
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• pp.701-708
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• 2022

Since the propellant tank structure of the projectile is mainly subjected to a compressive force, there is a high risk of damage due to buckling. Large and lightweight structures such as propellant tank have a complex manufacturing process. So it requires a non-destructive test method to predict buckling load to use the structure after testing. Many studies have been conducted on Vibration Correlation Technique(VCT), which predicts buckling load using the relationship between compressive load and natural frequency, but it requires a large compressive load to predict the buckling load accurately, and it tends to decrease prediction accuracy with increasing internal pressure in structure. In this paper, we analyzed the causes of the decrease in prediction accuracy when internal pressure increases and proposed a method increasing prediction accuracy under the low compressive load for being usable after testing, through VCT combined testing and FEA result. The prediction value by the proposed method was very consistent with the measured actual buckling load.

• Tunnel and Underground Space
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• v.19 no.6
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• pp.473-478
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• 2009

The accuracy of point load apparatus is depend on point to point coaxial fitting. Also, the estimation of applied point load using the pressure gauge frequently lead to erroneous results. An improved point load apparatus has been developed in this study by mounting linear bearing on polished support rod, and eccentric error of point to point axis has been sustained less than 0.1 mm even under series of extreme work load conditions. Two digital displacement gauges are attached to measure the distance from point to point with sample specimen. A load cell mounted at the end of upper conical platen measure the applied net load on sample instead of preassure gauge. Total of 107 point load tests has been achieved to assure the quality and performance of developed apparatus. This exercise turned out to be successful.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.6
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• pp.31-38
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• 2005

Aerodynamic influence coefficient linearly relates pressure with downwash in panel method for load analysis in which the viscosity of a flow is ignored and the compressibility cannot be taken into account in transonic region. Since the planform of an aerodynamic surface determines the coefficient, the panel method has a limit to the analysis of low Reynolds number flow. The accuracy of the pressure distribution can be improved by a direct correction to the pressure or a correction to the downwash, which is considered the change of camber or thickness, using the aerodynamic coefficients from wind tunnel test as constraints. A premultiplying correction method as well as a postmultiplying correction method is applied to a micro air vehicle to provide more accurate aerodynamic pressure for trim and load analyses. Theoretical aerodynamic pressure is obtained from the panel method. Correction factor matrix and correct pressure coefficient are computed for the conditions with two constraints in addition to single constraint. The postmultiplying correction method gives a better improvement in pressure distribution on micro air vehicle due to the flow characteristics on it.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2009.04a
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• pp.500-503
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• 2009

본 논문에서는 이중곡률을 갖은 막구조물의 동적 불안정 현상을 연구하였다. 풍하중을 받는 막구조물의 지배방정식을 정식화할 경우 가장 중요한 것은 막 표면의 공기 압력을 합리적으로 산정하는 것이다. 베르누이 윈리에 의하여 유체 압력은 속도 퍼텐셜과 관계를 가지며 얇은 날개 원리에 의해 막 표면 공기의 움직임을 일련의 와류로 간주하고 속도 퍼텐셜을 구할 수 있다. 이 논문에서는 가장 많이 쓰이는 3 절점 삼각형 막요소를 이용하여 가중 잔여치 갤러킨법을 적용한 안정 평가의 판별식을 유도하였다. 임계 풍속에 대한 초기인장력, 풍방향과 곡률의 영향도 분석하였다.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1992.06a
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• pp.66-70
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• 1992

고전적 동수압유체윤활이론은 유막 내의 점성을 일정하다고 가정한다. 유막의 전개방향이나 유막두께방향으로의 온도변화를 결정하는 데 이론적으로나 실험적으로 어려움이 있으므로 이 간소화는 베어링설계에 널리 사용되었다. 그러나 많은 실험적 관찰은 등점성 동수압유체윤활이론은 유막내의 온도상승이나 하중지지용량의 감소를 설명하지 못함을 입증하였다. Fogg는 평행한 추력베어링이 하중을 지지할 수 있음을 발견하였으며 이 fogg의 효과는 동수압 유체윤활이론의 예측과 반대되는 것이고 Thermal wedge라는 개념으로 설명되었다. Hunter와 Zienkiewicz는 유막내에서의 에너지 균형에 관한 이론적 연구를 소개하였고, 온도효과와 이로 인한 유막두께 방향의 점도 변화는 무시될 수 없다는 결론을 내렸다. 본 해석에서는 압력분포를 근사해법으로 구하여, 선지지되는 2차원 틸팅패드 트러스트베어링에서 패드의 탄성 변형을 고려한 열유체윤활해석과 고려하지 않은 얼유체윤활 해석의 결과를 서로 비교함으로서 패드의 변형이 유막의 압력장과 온도장에 미치는 영향과 패드두께의 변화가 유막의 온도장과 압력장에 미치는 영향을 고찰하고자 한다.

• Proceedings of the Korean Nuclear Society Conference
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• 1998.05a
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• pp.541-546
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• 1998

증기 제트 응축에서 발생하는 응축하중을 실험적으로 고찰하였다. 네 가지 서로 다른 직경의 노즐 (5, 10, 15, 20mm) 과 증기분사기를 응축실험에 사용하였으며, 증기 질량유속과 물온도를 변화하면서 동압을 측정하였다. 실험결과에 의하면 압력파의 진폭은 노즐 직경이 작을수록 작았다. 한편 압력파의 진폭은 일반적으로 물온도가 증가할수록 증가하나 물온도가 어느 한도 이상으로 증가하면 오히려 감소하는 경향을 보였다. 그러나 물온도가 아주 높고 증기 질량유속이 큰 경우에는 불안정한 압력파가 발생할 가능성이 관찰되었다.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.12 no.3
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• pp.475-484
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• 1999

압력절점은 요소의 균등한 압력증분을 1개의 자유도로 갖는 절점이며, 유한요소의 하중-변위 평형방정식에 체적과 압력의 관계를 추가하여 한계압력 이후에서도 체적변화에 따른 압력증분을 직접적으로 제저할 수 있는 절점이다. 본 연구에서는 철근콘크리트의 평면 구성 방정식과 적층정식화에 적용한 쉘 요소에 압력절점을 추가하고 해석시 체적을 제어함으로써 철근콘크리트 원통형 구조에 대해 파괴까지의 극한내압 능력을 해석할 수 있는 체적제어 비선형 해석기법을 개발하였다. 본 논문에서 제안한 해석기법을 이용하여 철근콘크리트 원통형 구조물에 대하여 비선형 해석을 수행하여 한계압력과 한계압력 이후의 구조물의 거동을 예측하였으며 실험결과와 비교 검증하였다.