• 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.

• Smart Structures and Systems
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• 제14권3호
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• pp.419-444
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• 2014

Within this paper a new approach for early damage detection in rotor blades of wind energy converters is presented, which is shown to have a more sensitive reaction to damage than eigenfrequency-based methods. The new approach is based on the extension of Gasch's proportionality method, according to which maximum oscillation velocity and maximum stress are proportional by a factor, which describes the dynamic behavior of the structure. A change in the proportionality factor can be used as damage indicator. In addition, a novel deflection sensor was developed, which was specifically designed for use in wind turbine rotor blades. This deflection sensor was used during the experimental tests conducted for the measurement of the blade deflection. The method was applied on numerical models for different damage cases and damage extents. Additionally, the method and the sensing concept were applied on a real 50.8 m blade during a fatigue test in the edgewise direction. During the test, a damage of 1.5 m length was induced on the upper trailing edge bondline. Both the initial damage and the increase of its length were successfully detected by the decrease of the proportionality factor. This decrease coincided significantly with the decrease of the factor calculated from the numerical analyses.

• 한국정밀공학회지
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• 제18권6호
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• pp.59-66
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• 2001

Fatigue strength of the welding structure is governed by the residual stress at the weldment toe and static tensile overloads were known as relieving the residual stresses. In this study, static tensile overloads were applied to the welding structures which caused the relief of residual stresses. The amount of residual stress relief was found as proportional to the change of fatigue limit at the given conditions. Based on the fact of the proportionality between the change of fatigue limit and that of residual stress, simple measurement technique is proposed. Modified stress-life curves base on proposed technique gave good agreement with test results.

• 한국공간구조학회논문집
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• 제18권1호
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• pp.127-134
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• 2018

This study suggests the tangent modulus $E_t$ associated with partially yielded section of steel member under axially compressed. The provisions for column strength does not provide a information about failure mode of structural system. So, designers can not evaluate that a failure comes from member buckling or material yielding. The material of the axially compressed column under inelastic behavior reaches yielding point before the axial force renders the column bent. If axial members yields not by buckling effect but gradually yielding effect of material, the design code should accept related tangent modulus Et which is based on gradual yielding effect of material. This study provides the new effective tangent modulus $E_t$ derived in the case that residual stress is 30 percent and 50 percent of yielding stress respectively. The study considers idealized I section of steel which ignores web and general I section of steel with web respectively and makes conclude that tangent modulus $E_t$ with idealized I section of steel is rational.

• 한국구조물진단유지관리공학회 논문집
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• 제22권2호
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• pp.161-168
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• 2018

이 연구는 CRC기둥강도곡선의 비탄성영역에 대한 해석적 고찰이다. CRC기둥강도곡선의 비탄성영역은 최대 잔류응력 크기 $0.5{\sigma}_y$와 Bleich이론을 기초로 하고 있다. 이는 실제로 알려진 최대 압축 잔류응력의 크기가 $0.3{\sigma}_y$인 경우 보다 다소 보수적이다. 본 연구는 열압연강재의 최대 압축 잔류응력의 크기를 $0.3{\sigma}_y$으로 고려하여 그에 따른 기둥강도곡선과 접선탄성계수 Et를 제안하고 이를 CRC에서 제안하고 있는 값들과 각각 비교 고찰한다. 축 압축력을 받는 비탄성 기둥의 응력은 기둥에 작용하는 하중이 좌굴을 일으키기 전에 재료의 비례한도를 넘어 항복점에 도달할 것이다. 따라서 점차적인 단면의 항복 상태에 따른 기둥강도곡선을 검토할 필요가 있다. 본 연구는 최대 압축 잔류응력 ${\sigma}_r=0.5{\sigma}_y$을 사용하여 재료의 항복에 따른 임계하중 곡선식을 유도하고 이를 CRC기둥강도곡선과 비교 고찰한다.

• 한국식품조리과학회지
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• 제4권1호
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• pp.17-26
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• 1988

The polysaccharide produced by pseudomonas elodea, Gellan gum, was rheologically characterized, compared with agar. Rheological properties were determined from the change in the value of intrinsic viscosity with the pH and salt concentration. At the range of pH 2∼ll and salt 0∼0.16M KC1, the intrinsic viscosity of Gellan gum ranged from 8.8 to 21.2dl/g and agar ranged from 1.97 to 11.46d1/g. In the absence of salt, the intrinsic viscosity of Gellan gum increased as the pH of solution increased up to neutral pH then decreased slightly at alkaline pH, whearas the intrinsic viscosity of agar increased as the pH of solution increased up to pH 9 then decreased slightly. Intrinsic viscosity of Gellan gum and agar decreased with an increase in salt concentration. The chain stiffness parameter for the Gellan gum was 0.033. The overlap parameter of Gellan gum and agar were 0.047g/dl and 0.087g/dl, respectively. Gellan gum and agar were shear rate dependent or pseudoplastic. The yield stress and proportionality constant of Gellan gum increased slightly as the concentration increase, on the other hand, the shear index of Gellan gum showed a maximum at 0.75g/dl and gradually decreased as the concentration increase. The apparent viscosity of Gellan gum and agar decreased as the temperature increase. A lower concentration of the divalent cations calcium and magnesium is required to obtain maximum gel strength than for the monovalent cations sodium and potassium.

• 한국수산과학회지
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• 제12권4호
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• pp.293-296
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• 1979

굴(Crassostrea gigas)의 질소배설과 산소소비에 미치는 수온 및 염분의 상호영향을 조사한 결과는 다음과 같다. 1. 굴은 수온과 염분변화에 따라 질소배설율과 배설암모니아 및 아미노산간의 배설비에 현저한 변동을 보였으며 산소소비량에도 역시 많은 변동을 보였다. 2. 질소배설율과 산소소비율은 염분이 증가함에 따라 특히 고염분일 때 고수온$(29^{\circ}C)$의 경우에 현저히 감소하였으나 저온분에서는 상당히 증가하였다. 이것은 생리적 내성의 고온단계와 저염분에 대한 포상작용에 기인한 결과라고 생가된다. 3. 암모니아를 주로 배설하였으나 상당한 량의 아미노-질소도 배설하였으며, 특히 상염분-온난온도대$(32.5\%_{\circ}-22^{\circ}C$에서는 아미노산의 배설량이 우세하였다. 그리고 어느 실험온도에서나 고염분에서 아미노-질소의 배설량은 감소하였고 저염분에서는 증가하였다. 4. 배설암모니아-질소에 대한 소비산소의 원자비 (O: N비)는 저온$(15^{\circ}C)$에서는 현저히 낮고 상온 및 고온($22^{\circ}$ 및 $29^{\circ}C$)에서는 높았다. 그러나 저온분의 경우 고온에서는 현저히 감소되었다.