• 한국해양공학회지
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• 제15권2호
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• pp.120-123
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• 2001

Despite the increasing necessity of accurate estimation of ring-stiffened cylinders'ultimate strength, the complex structural behavior of cylinders has made their design mainly depend on empirical formulas mostly based on limited test data rather than theoretical background. This paper has developed the imperfection method which enables the ultimate strength analysis of buckling-sensitive structures by combining two separate functions covered by common commercial finite element softwares, which are linear elastic buckling analysis and nonlinear stress analysis. Developed method was applied to two of the world most renowned softwares, MSC/NASTRAN and ABAQUS, for the analysis of ring-stiffened cylinders and unexpectedly big difference in their analysis results was found. This tells that many widely used commercial softwares have their different strong points and weak points and the choice of commercial software should be cautiously made after thorough inspection. This paper ends with some useful information about which of the two aforementioned softwares is more respectively for the linear elastic buckling analysis and the ultimate strength analysis of ring-stiffened cylinders.

• Tribology and Lubricants
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• 제7권2호
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• pp.36-40
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• 1991

The dynamic characteristics of the annular pressure seal employed in pump have been theoretically deduced with consideration of the effects of elastic deformation due to the thermal stress. The thermal deformation is developed for the two-dimensional steady thermal stress distribution in a infinite circular cylinder subject to heating of the seal and shaft surface into the surrounding fluid. To demonstrate this analysis, the effects of thermal stress on rotordynamic coefficients and logarithmic decrement for annular plain seals was shown.

• Tribology and Lubricants
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• 제16권5호
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• pp.357-364
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• 2000

In this study, the sliding wear in spur gears, using Archard's wear model, is analyzed. Formulas of tooth sliding wear depth along the line of action are derived. The tooth profile is modified Id make a smooth transmission of the normal loads and the cylinder profile for reducing the pressure spike is suggested. The sliding wear rate is calculated with these profiling results. We expect these modification methods to contribute to the reduction of sliding wear not only in the root, but the tip of tooth and tooth edge.

• 한국소음진동공학회논문집
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• 제13권6호
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• pp.452-459
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• 2003

The characteristics of fluid-elastic instability and effects of turbulent excitations for the KSNP steam generator tubes were investigated numerically. The information for the thermal-hydraulic data of the steam generator has been obtained by using the ATHOS3-MOD1 code and the flow-induced vibration(FIV) analysis has been conducted by using the PIAT(program for Integrity assessment of SG tube) code. The KSNP steam generator has the concentrated plugging zone at the vicinity of the stay cylinder inside the SG. To investigate the cause of the concentrated tube plugging zone, the FIV analysis has been performed for various column and row number of the steam generator tubes. From the results of FIV analysis the stability ratio due to the fluid-elastic instability and vibrational amplitude due to the turbulent excitation in the concentrated plugged zone have a trend of larger values than those of the outer concentrated tube Plugging zone.

• 대한조선학회지
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• 제13권4호
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• pp.1-10
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• 1976

It is a well-known phenomenon that, in the case of vibrations of an elastic body in a fluid such as water, the presence of the surrounding fluid has the effect of lowering the natural frequencies of the vibration as compared with those in air or vacuum on account of the increased inertia, i.e. added mass. In this report, defining the mass increase factor as the ratio of added mass to vibration mass of the body in air, the author investigated the mass increased factor of an elastic plate vibrating in the fluid. It is assumed that the edges of the plate are simply supported, and that the surrounding fluid is an infinite ideal one. For the problem formulation the elliptical cylindrical coordinate system is adopted, so that a rectangular plate may be represented by a sheet degenerated from an elliptical cylinder. By virtue of the coordinate system adopted, plates which are chordwisely finite and lengthwisely contineous could directly be treated, but plates which are chordwisely finite in both directions could not be treated directly. For the latter, hence, plates which are chordwisely finite and lengthwisely semi-finite are investigated as an appropriate approximation. Some examples of the mass increase factor are numerically calculated for the fundamental mode and modes of zero or one nodal line in each direction with the range of the aspect ratio from 1 to 10 or more.

• 대한치과보철학회지
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• 제34권4호
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• pp.657-664
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• 1996

The purpose of this study was to compare the dimensional stability, compression resistance, elastic recovery and surface hardness of elastomeric interocclusal recording materials. Five commonly used elastomeric interocclusal recording materials(Ramitec, Regisil, Blue-Mousse, Stat-Br, Coltoflax) were selected for this study. According to ADA specification No. 19, two types of specimen were fabricated. Cylinder type specimens were used to test compression resistance and elastic recovery and plate type specimens were used to evaluate dimensional stability and surface hardness. Paired t-test was applied to detect significance among the occlusal registration materials. The obtained results were as follows: 1. There were statistical difference in dimensional stability between the elastic interocclusal recording materials. The dimensional stability of silicone was higher than that of polyether tested(p<0.05). 2. Coltoflax was significantly less resistance to compression than the other elastic interocclusal recording materials(p<0.001). 3. The elastic recovery capacity of Blu-Mousse and Stat-Br is better than that of Coltoflax (p<0.01). 4. The surface hardness of Coltoflax was lower than that of Blu-Mousse and Stat-Br(p<0.05). 5. The percentage dimensional change of alll materials was acceptable according to the limid of 0.5% suggeted by ADA specificatin No. 19.

• 한국항공우주학회지
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• 제37권2호
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• pp.181-186
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• 2009

본 연구의 목적은 주로터 블레이드와 장애물 충돌 시 실제 파괴형상과 유사한 시뮬레이션을 통해 발생되는 하중을 구하고, 이것을 이용하여 허브 및 변속장치의 안전성을 검토함으로써 승무원의 안전성을 확보하는 것이다. 헬리콥터의 실제 운용 시에 주로터 복합재 블레이드 바깥쪽 10% 지점에 직경 203mm의 강체실린더가 충돌할 경우에도 주로터주축은 파괴가 발생하지 않아야 하고 변속장치가 탑승공간으로 침투하는 위험한 변위가 발생하지 않아야 한다. 강체와 블레이드 충돌 시 주로터의 주축과 변속장치의 영향성을 확인하기 위하여 탄소성 손상 재질을 사용하여 복합재 블레이드와 나무(강체실린더의 경우는 강체)의 해석모델을 구성하였으며, 파괴진행과정을 실제와 유사하게 구현하기 위해 여러 개의 접촉면을 생성하여 충돌해석을 수행하였고, 구형베어링 및 리드래그댐퍼에 전달되는 하중을 구하였다. 또한, 블레이드 회전속도 및 피치각도의 변화가 전달하중에 미치는 영향을 검토하였다.

• 대한기계학회논문집
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• 제16권12호
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• pp.2328-2339
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• 1992

본 연구에서는 일방향(unidirectional)으로 섬유가 강화된 복합재료를 다루게 되는데, 섬유는 직경이 모두 같고, 길이가 무한이며, 서로 평행하게 정렬되엉 불규칙 하게 분포된 원형실린더로 가정한다. 먼저, 임의의 한 기준 산란체에 의한 압축파 및 SV파의 산란을 수식화하고, 기준 산란체에 대한 나머지 산란체들이 존재할 확률을 이용하여 산란계수의 통계적 기대값을 구함으로써 그 매질내에 존재하는 파동의 전파 특성을 지배하는 분산 관계식의 해를 수치적으로 구함으로써 매질의 평균전파속도, 유 효 동탄성계수 및 감쇠계수를 주파수와 체적비의 함수로 구한다. 또 구하여진 동탄 성계수의 저주파 극한값과 정적하중상태에서 구한 Hashin-Rosen의 값들과 비교하여 봄 으로써 본 연구의 타당성을 입증한다.

• 한국재료학회지
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• 제11권5호
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• pp.372-377
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• 2001

Part I에서 도출된 기초 식을 적용하여 입자 분산 강화형, 섬유 강화형 및 적층형 복합재료의 유효탄성제수 및 열팽창계수를 산정 하였다. 일방향 섬유 강화 복합재료의 경우 섬유의 유효 축비 (aspect ratio)가 고려되었으며, 유효 탄성계수는 다른 연구 결과들과 비교하였다. 입자 분산 강화형 복합재료의 유효 체적탄성률 및 전단 탄성률은 Korner의 표식 및 Hanshin과 Shtrikman의 하한치 (lower bounds)와 일치하고 있다. 일방향 섬유 강화 복합재료에서는 6개, Hanshin과 Rosen의 모델에 나타낸 4개의 독립 탄성계수와 일치하고 있다.

• 대한치과보철학회지
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• 제41권2호
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• pp.243-257
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• 2003

The purpose of this study was to search the influences of the increase of the contents of sodium alginate in the experimental alginates on the some mechanical properties. 3 commercial alginates were selected for the purpose of comparison of the results of experiments. 7 experimental alginates were manufactured with the rise of contents of sodium alginate from 8.8% to 18.3% with the decrease of contents of diatomaceous earth and with the constant contents of calcium sulfate 12.5%. sodium phosphate 2.2%, zinc fluoride 2.0%. Splitable metal mold with 12.5mm diameter and 20.0mm height was filled with mixed alginate to prepare the cylinder shaped specimens. Strain in compression, elastic recovery, compressive strength were tested using the ISO specification number 1563, alginate impression material. Experimental groups were 7, and 10 specimens were used for each test items and each groups. Following results were obtained ; 1. Strain in compression was decreased with the increase of sodium alginate contents (p=0.0077, r2 = 0.6302). 2. Elastic recovery was decreased with the increase of sodium alginate contents but was not significant(p=0.0639, r2=0.7449). 3. Compressive strength was increased with the increase of sodium alginate contents (p<0.0001, r2 = 0.9617). These results mean that the increase of sodium alginate contents make alginate harder but may result the increased permanent deformation.