• 대한기계학회논문집A
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• 제36권3호
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• pp.313-318
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• 2012

캐나다형 중수로에서 피더관은 중수로 압력관에 중수를 공급하고 가열된 중수를 증기발생기로 보내는 배관으로 가동 중에 유동 가속 부식현상에 의해 감육이 발생한다. 배관에 감육이 발생하게 되면 배관의 건정성이 떨어진다는 결과는 앞선 연구에서 확인하였다. 본 논문에서는 45 도와 60 도의 굽힘각도를 갖는 피더관의 한계하중을 제시하고 제시된 연구결과를 바탕으로 임의의 굽힘각도를 갖는 피더관에서 감육이 발생했을 경우의 한계하중을 예측 할 수 있는 식을 제시하였다. 본 연구에서는 유한요소 해석을 통하여 굽힘 하중과 내압을 받는 경우에 대하여 연구를 진행하였고 특히 굽힘 하중의 경우 면내 열림 방향과 면내 닫힘 방향으로 나누어 진행하였다. 재료는 대변형 효과를 고려하고 탄성-완전소성 재료로 가정하였다.

• 대한기계학회논문집A
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• 제27권1호
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• pp.42-47
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• 2003

Nonlinear models for a thin ring rotating at a constant speed are developed. The geometric nonlinearity of displacements is considered by adopting the Lagrange strain theory for the circumferential strain. By using Hamilton’s principle, the coupled nonlinear partial differential equations are derived, which describe the out-of-plane and in-plane bending, extensional and torsional motions. The natural frequencies are calculated from the linearized equations at various rotational speeds. Finally, the computation results from the nonlinear models are compared with those from a linear model. Based on the comparison, this study recommends which model is appropriate to describe the behavior of the rotating ring.

• 대한기계학회논문집A
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• 제21권10호
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• pp.1580-1588
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• 1997

A modeling method for the flapwise bending vibration of a rotating cantilever beam which has small slenderness ratio is presented in this paper. It is shown that as the slenderness ratio decreases the shear and rotary inertia effects increase. Such effects become critical for the accurate estimation of the natural frequencies and modeshapes, especially higher frequencies and modes, as the angular speed increases. It is also shown that the flapwise bending natural frequencies are higher than the chordwise bending natural frequencies. The discrepancy between first natural frequencies are especially significant when the hub radius ratio is small.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2012년도 춘계학술대회 논문집
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• pp.144-149
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• 2012

The transfer matrix method is used to determine the dynamic characteristics(natural frequencies and mode shapes) by rotational speed of wind turbine blade. The problems treated on this study is coupled flapwise bending and chordwise bending of pre-twisted nonuniform wind turbine blade. The orthogonality relations that exist between the vibrational modes is derived and the algorithm for determination of the natural vibrational characteristics is suggested.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회A
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• pp.299-304
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• 2008

This paper presents plastic limit loads of piping branch junctions with local wall thinning under combined pressure and in-plane bending, based on systematic three-dimensional finite element limit analyses using elastic-perfectly plastic materials. An ideal branch junction without weld or reinforcement around the intersection is considered with two locations of wall thinning; one in the run pipe, and the other in the branch pipe. Based on FE results, effects of thinning geometries on plastic limit moments are quantified and simple approximations of plastic limit loads are proposed.

• 대한조선학회논문집
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• 제47권4호
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• pp.580-588
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• 2010

OPB(out-of-plane bending)-induced failure of mooring chain was firstly addressed by CALM (catenary anchor leg mooring)-type offloading buoy, located approximately one mile away from the bow of the Girassol FPSO which was installed offshore area of Angola in September 2001. This study deals with verifying the load transfer mechanism between the first free chain link and connected two chain links inside the chain hawse. OPB moment to angle variation relationships are proposed by extensive parametric study where the used design variables are static friction coefficients, proof test loads, nominal tension forces, chain link diameters, chain link grades and chain link types. The stress ranges due to OPB moments are obtained using nonlinear FEAs (finite element analyses). Final stress ranges are derived considering ones from IPT (in-plane tension) forces. Also a formula for OPB fatigue assessment is briefly introduced.

• 한국해양공학회지
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• 제31권4호
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• pp.299-307
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• 2017

The design of the mooring line to maintain the position of an offshore structure in rough marine environments is recognized as a very important consideration. Conventional fatigue evaluation of a mooring line was performed by considering the tensile force acting on the mooring line, but the mooring line broke after 238 days in the girassol area even though the expected fatigue life was expected to be longer. The causes of this event are known to be due to OPB/IPB (out-of-plane bending/in-plane bending) caused by chain link friction due to the excessive tensile strength of the mooring line. In this study, three models with different boundary conditions were proposed for fatigue analysis of a mooring line considering OPB/IPB. Interlink stiffness was calculated by nonlinear structure analysis and a stress concentration factor was derived. In addition, the sensitivity of interlink stiffness according to the magnitude of tensile force, large deformation effect, and coefficient of friction was analyzed, and the effect of critical elastic slip and bending moment calculation position on interlink stiffness was confirmed.

• Composites Research
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• 제23권3호
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• pp.58-63
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• 2010

MWCNT의 형상비 차이에 따른 MWCNT/에폭시 복합재료의 인장 및 굽힘 특성과 전기전도도를 비교하였다. 호모믹서(homomixer)와 3단롤밀(three-roll mill)을 사용하여 분산된 MWCNT와 에폭시 혼합물을 금형에 부어 압축 성형법으로 시편을 제조하였다. 에폭시 내 MWCNT의 분산 정도를 평가하기 위해 SEM을 사용하여 시편의 파단면을 관찰하였다. MWCNT의 첨가로 인해 인장강도는 최대 7%증가 하였으나 굽힘강도는 증가가 미미하였으며 형상비가 가장 큰 MWCNT의 경우에는 감소하였다. MWCNT 포함량을 변화시켰을 때 CM-95의 경우 인장강도는 1wt%에서, 굽힘강도는 0.5wt%에서 최대값을 보였으나 더 많은 포함량에서는 감소하였다. MWCNT/에폭시 복합재료의 두께 방향 및 면내방향 전기전도도는 2단자법에 의한 저항값으로부터 계산되었으며 MWCNT의 형상비가 클수록, 또 포함량이 증가할수록 전기전도도 값은 증가하였다.

• 대한조선학회논문집
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• 제53권3호
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• pp.237-248
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• 2016

As OPB and IPB moment-induced fatigue damage on mooring chain links were reported for a offloading buoy, verification of OPB and IPB fatigue has been a key engineering item in offshore structure mooring design. Mathematical and physical features of the conventional approach which was mainly explained in BV guideline are reviewed and disadvantages of the conventional approach are addressed in terms of stress proportionality and nonlinearity of OPB and IPB moments. In order to eradicate these disadvantages, a novel approach is newly proposed which is able to dispel apprehension on stress proportionality and is not dependent of nonlinearities of OPB and IPB moments. Significant differences between two approaches are suggested by comparing relations of OPB moment versus OPB interlink angle and IPB moment versus IPB interlink angle. For periodic OPB tension angle processes having three different OPB angle ranges with a simple irregular tension process, fatigue damage calculation reveals that OPB moment-induced fatigue damage has dominant portion to total fatigue damage. Comparative studies between two approaches also show that the conventional approach based on BV guideline predicts fatigue damage far conservatively since it assume unrealistic high stress concentration factor for tension load. Meanwhile IPB moment-induced fatigue damage is negligible compared to tension-induced fatigue damage.

• 대한기계학회논문집A
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• 제34권11호
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• pp.1675-1680
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• 2010

캐나다형 중수로에서 피더관은 가동 중에 유동 가속 부식에 의해 감육이 발생한다. 피더관에 감육이 발생하면 배관 건전성이 떨어진다. 본 논문은 원형 감육이 발생한 피더관에서의 기기신뢰성 평가를 위한 한계 하중을 연구하였다. 유한요소 해석을 통하여 면내 굽힘 하중과 내압을 받는 경우에 대하여 연구하였다. 재료는 대변형 효과를 고려하고 탄성-완전소성 재료로 가정하였다. 원형 감육이 발생한 피더관에 대하여 내압과 닫힘 방향, 열림 방향 굽힘 하중에 대하여 한계하중해를 제시하였다.