• Structural Engineering and Mechanics
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• 제84권4호
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• pp.517-530
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• 2022

In re-assessing the Jacket-type fixed steel structures, the current standards often allow the simplicity of corrosion sections using local buckling or equivalent section approach to applying empirical formulae of frame stress and resistance analyses. However, those approaches can lead to significant errors for non-uniform corroded frames in a specific area, including force distribution, stress, and allowable strength of the tubular section, compared to the actual cases. This paper investigates a suitable approach to determine the actual stress on non-uniform corroded tubular frames under compression through the non-linear ABAQUS model by considering the effect of large deformation on the frame axis and the frame section. There are 3 scenarios of interest. In the 1st and 2nd scenarios with simple corrosion cases, the stress ratios using the numerical model and theoretical formulae correspond to the calculation of allowable strength reduction ratios in standards. However, scenario 3, which describes non-uniform corroded sections based on survey data, provides considerable differences in results. Therefore, it proves the reliable and effective results when using this method to analyze the resistance of the actual corroded section in the Jacket platforms.

• Nuclear Engineering and Technology
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• 제55권4호
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• pp.1310-1323
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• 2023

A reactor coolant pump (RCP) is essential for transporting coolant in the primary loop of pressurized water reactors. In the advanced passive reactor, the absence of a long pipeline between the steam generator and RCP serves as a transition section, resulting in a non-uniform flow field at the pump inlet. Therefore, the characteristics of the pump should be investigated under non-uniform flow to determine its influence on the pump. In this study, the pressure pulsation characteristics were examined in the time and frequency domains, and the sources of low-frequency and high-amplitude signals were analyzed using wavelet coherence analysis and numerical simulation. From computational fluid dynamics (CFD) results, non-uniform inflow has a great effect on the flow structures in the pump's inlet. The pressure pulsation in the pump at the rated flow increased by 78-128.7% under the non-uniform inflow condition in comparison with that observed under the uniform inflow condition. Furthermore, a low-frequency signal with a high amplitude was observed, whose energy increased significantly under non-uniform flow. The wavelet coherence and CFD analysis verified that the source of this signal was the low-frequency pulsating vortex under the steam generator.

• Structural Engineering and Mechanics
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• 제22권5호
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• pp.631-645
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• 2006

Buckling capacity of compression members may change due to inadvertent changes in the member section dimensions or material properties. This may be the result of repair, modification of section properties or degradation of the material properties. In some occasions, enhancement of buckling capacity of compression members may be achieved through splicing of plates or utilization of composite materials. It is very important for a designer to predict the buckling resistance of the compression member and the important parameters that affect its buckling strength once changes in section and/or material properties took place. This paper presents an analytical approach for determining the buckling capacity of a compression member whose geometric and/or material properties has been altered resulting in a multi-step non-uniform section. This analytical solution accommodates the changes and modifications to the material and/or section properties of the compression member due to the factors mentioned. The analytical solution provides adequate information and a methodology that is useful during the design stage as well as the repair stage of compression members. Three case studies are presented to show that the proposed analytical solution is an efficient method for predicting the buckling strength of compression members that their section and/or material properties have been altered due to splicing, coping, notching, ducting and corrosion.

• 한국농공학회지
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• 제43권1호
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• pp.122-128
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• 2001

The theory of non-prismatic folded plate structures was reported by D.H. Kim in 1965 and 1966. Fiber reinforced composite materials are strong in tension. The structural element for such tension force is very thin and weak against bending because of small bending stiffnesses. Naturally, the box type section is considered as the optimum structural configuration because of its high bending stiffnesses. Such structures can be effectively analyzed by the folded plate theory with relative ease. The “hollow” bending membr with uniform cross-section can be treated as prismatic folded plates which is a special case of the non-prismatic folded plates. In this paper, the result of analysis of a folded plates with one box type uniform cross-section is presented. Each plate is made of composite laminates with fiber orientation of [ABBCAAB]r, with A=-B=45${\circ}C$, and C=90${\circ}$. The influence of the span to depth ratio is also studied. When this ratio is 5, the difference between the results of folded plate theory and beam theory is 1.66%.

• Composites Research
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• 제34권5호
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• pp.323-329
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• 2021

본 논문에서는 불균일한 접착 상태를 가지는 복합재 접착 체결 시편에 대하여 모드 I 하중에서의 파괴 특성을 분석하였다. 이를 위하여 Double Cantilever Beam(DCB) 시험을 수행하였으며 모드 I 파괴 인성을 도출하였다. 불균일한 접착 상태를 갖는 시편의 경우 안정한 균열 성장 구간과 불안정한 균열 성장 구간이 나타남을 확인하였다. DCB 시험에서 구한 하중-변위 선도와 시편의 파손 단면을 통해 각 구간의 파괴 특성을 관찰하였다. 시험에서 측정된 균열 길이를 기준으로 세분화된 구간과 각 구간의 모드 I 파괴 인성을 이용하여 유한요소해석을 수행하였다. DCB 시험 결과와 유한요소해석 결과를 통해 불균일한 접착 상태를 가지는 시편의 파괴 거동을 모사할 수 있음을 확인하였다.

• 한국소음진동공학회논문집
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• 제14권6호
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• pp.486-494
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• 2004

This paper addresses the dynamic modeling and closed-loop eigenvibration analysis of composite rotating pretwisted fan blade modeled as non-uniform thin-walled beam with bi-convex cross-section fixed at the certain presetting angle and incorporating piezoelectric induced damping capabilities. The blade model incorporates non-classical features such as transverse shear, rotary inertia and includes the centrifugal and Coriolis force field. A velocity feedback control law relating the piezoelectiriccally induced transversal bending moment at the beam tip with the appropriately selected kinematical response quantity is used and the beneficial effects upon the closed loop eigenvibration of the blade are highlighted.

• Steel and Composite Structures
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• 제48권2호
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• pp.235-250
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• 2023

The present paper examines the stability analysis of the buckling differentiae of the small-scale, non-uniform porosity-dependent functionally graded (PD-FG) tube. The high-order beam theory and nonlocal strain gradient theory are operated for the mathematical modeling of nanotubes based on the Hamilton principle. In this paper, the external radius function is non-uniform. In contrast, the internal radius is uniform, and the cross-section changes along the tube length due to these radius functions based on the four types of useful mathematical functions. The PD-FG material distributions are varied in the radial direction and made with ceramics and metals. The governing partial differential equations (PDEs) and associated boundary conditions are solved via a numerical method for different boundary conditions. The received outcomes concerning different presented parameters are valuable to the design and production of small-scale devices and intelligent structures.

• Journal of Mechanical Science and Technology
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• 제17권10호
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• pp.1520-1532
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• 2003

An experiment was performed to obtain the local heat transfer coefficient and Nusselt number in a circular duct with a 180$^{\circ}$ bend for Re=6 x 10$^4$, 8 x 10$^4$ and 1 x 10$\^$5/ under swirling flow and non-swirling flow conditions. The test tube with a circular section was made from stainless steel having a curvature ration of 9.4. Current heat flux of 5.11 kW/㎡ was applied to the test tube by electrical power and the swirling motion of air was produced by a tangential inlet to the pipe axis at 180$^{\circ}$. Measurements of local wall temperatures and the bulk mean temperatures of air were made at four circumferential positions at 16 stations. The wall temperatures showed a reduced distribution curve at the bend for the non-swirling flow, but this effect did not appear for the swirling flow. The Nusselt number distributions for the swirling flow, which was calculated from the measured wall and the bulk temperatures, were higher than that of the non-swirling flow. The average Nusselt number of the swirling flow increased by about 90-100%, compared to that of the non-swirling flow. The Nu/Nu$\_$DB/ values at the 90$^{\circ}$ station for non-swirling flow and swirling flow were approximately 2.5 and 4.8 at Re=6x10$^4$ respectively. The values agree well with Said's results for non-swirling flow.

• 대한토목학회논문집
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• 제33권3호
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• pp.865-873
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• 2013

본 연구에서는 부식이나 보강재가 고려된 비균일한 두께를 가지는 파이프라인에 대하여 일정한 외압을 받을 때의 탄성 좌굴하중을 이론적으로 산정하였다. 길이가 매우 긴 원통형 쉘 구조물인 파이프라인을 단순한 링 구조물로 가정하였고, 고유함수를 유도하여 좌굴 임계하중을 산정하였다. 또한, 두께 변화와 두께가 감소된 구간의 범위에 따른 변수해석을 수행하였다. 이론식에 의해 산정된 좌굴 임계하중 결과를 유한요소해석 결과와 비교하여 검증하였고, 두 결과는 잘 일치함을 알 수 있었다.

• 한국소음진동공학회논문집
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• 제19권6호
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• pp.620-627
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• 2009

Shaking table test was carried out to obtain dynamic characteristics of TLCDs with uniform and non-uniform sections for both horizontal and vertical tubes. The input to the table is harmonic acceleration with constant magnitude. The output is horizontal dynamic force which is measured by load cell installed below the TLCD. Transfer functions are experimentally obtained using the ratio of input and output. Natural frequency, the most important design factor, is compared to that by theoretical equation for TLCDs with five different water levels. System identification process is performed for experimentally obtained transfer functions to find the dynamic characteristics of head loss coefficient and effective mass of TLCDs. It is found that their magnitudes are larger for a TLCD with non-uniform section than with uniform section and natural frequencies are close to theoretical ones.