• 비파괴검사학회지
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• 제28권2호
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• pp.199-204
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• 2008

The generation of axisymmetric Lamb waves and interaction with wall thinning (corrosion) defects in hollow cylinders are simulated using the finite element method. Guided wave interaction with defects in cylinders is challenged by the multi-mode dispersion and the mode conversion. In this paper, two longitudinal, axisymmetric modes are generated using the concept of a time-delay periodic ring arrays (TDPRA), which makes use of the constructive/destructive interference concept to achieve the unidirectional emission and reception of guided waves. The axisymmetric scattering by the wall thinning extending in full circumference of a cylinder is studied with a two-dimensional FE simulation. The effect of wall thinning depth, axial extension, and the edge shape on the reflections of guided waves is discussed.

• 반도체디스플레이기술학회지
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• 제10권3호
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• pp.61-65
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• 2011

The capabilities of finite elements codes allow now accurate simulations of blanking processes when appropriate materials modelling are used. Over the last decade, numerous numerical studies have focused on the influence of process parameters such as punch-die clearance, tools geometry and friction on blanking force and blank profile. In this study, three dimensional finite element analysis is carried out to design a lead frame blanking die using LS-Dyna3D package. After design of the blanking die, an experiment is also carried out to investigate the characteristics of blanking for nickel alloy Alloy42, a kind of IC lead frame material. In this paper, it has been researched the investigation to examine the influence of process parameters such as clearance and air cylinder pressure on the accuracy of sheared plane. Through the experiment results, it is shown that the quality of sheared plane is less affected by clearance and air cylinder pressure.

• Wind and Structures
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• 제1권2호
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• pp.127-144
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• 1998

In this paper, the wake structures behind a square cylinder at the Reynolds number of 22,000 are simulated using the large eddy simulation, and the main features of the wake structure associated with unsteady vortex-shedding are investigated. The Smagorinsky model is used for parametrization of the subgrid scales. The finite element method with isoparametric linear elements is employed in the computations. Unsteady computations are performed using the explicit method with streamline upwind scheme for the advection term. The time integration incorporates a subcycling strategy. No-slip condition is enforced on the wall surface. A comparative study between two-and three-dimensional computations puts a stress on the three-dimensional effects in turbulent flow simulations. Simulated three-dimensional wake structures are compared with numerical and experimental results reported by other researchers. The results include time-averaged, phase-averaged flow fields and numerically visualized vortex-shedding pattern using streaklines. The results show that dynamics of the vortex-shedding phenomenon are numerically well reproduced using the present method of finite element implementation of large eddy simulation.

• Steel and Composite Structures
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• 제22권6호
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• pp.1391-1415
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• 2016

Limit load of pressure bearing structures was reviewed in this article. By means of the finite element analysis, limit load of pressurized cylinder with nozzle was taken as an example. Stress classification method and Elastic-plastic finite element analysis combining with limit load determination methods were used to determine limit load of cylinder with nozzle. Comparison of limit load determined by different methods, the results indicated that limit load determined by linearization method was the smallest. Limit load determined by twice elastic slope criterion was the nearest than experimental results. Elastic-plastic finite element analysis had comparably computational precision, but required time consuming. And then the requirements of computer processing and storage capacity by power system became higher and higher. Most of criteria for limit load estimation included any human factors based on a certain substantive characteristics of experimental results. The reasonable criterion should be objective and operational.

• 한국안전학회지
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• 제3권2호
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• pp.25-34
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• 1988

The stress concentration phenomena due to the structural incontinuty are studied by finite element method. In this study, a circular cylinder is treated. Under the axial load, the membrance action is dominate and the 24 D.O.F. cylindrical membrane finite element is used. The assembly of this element can successfully represent the original structure geometrically. The internal displacement function is such organized that the inter element compatibility condition is fully satisfied. In this study, the stress concentration factors due to the presence of a hole on the cylinder wall are obtained, and the factors versus the location of the hole is computed and plotted. It is found that the hole effect on the stress concentration disappears beyond the neighboring region of the hole size form the edge of the hole. Those results are useful for practical design in determining the region where the re-inforcing is necessary.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2000년도 제32회 추계학술대회 정기총회
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• pp.199-204
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• 2000

A cylindrical brake device with plastic deformation is designed to stop the object moving at high velocity. Baseline model is determined based on the design specification and analytic solutions. Using finite element method, effects of various design parameters, such as thickness of the cylinder, clearance between cylinder and rod, and cone angle, to the performance of the brake device are investigated. Cone-type brake device shows better performance than cylindrical brake device with constant thickness in that plastic hinges are generated sequentially from impact end to fixed boundary, thus increasing the reliability of braking operation.

• 한국전자파학회논문지
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• 제11권3호
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• pp.388-402
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• 2000

주기적인 구형격자를 갖는 유전체 코팅된 도체 실린더에 대해 무한 주기 구조와 유한 주기 구조에 대한 누설 파 안테나의 복사 특성을 이론적으로 해석하였다. 무한 주기 구조에 대하여는 모드 정합 법을 적용하여 해석하 였고, 유한 주기 구조에 대하여는 퓨리에 변환과 모드 전개를 사용하여 적분 방정식을 유도하고 선형 연립 방정 식을 얻는다. 구형격자의 폭, 깊이, 유전체 코팅두께, 도체 실린더의 반경, 유한 구형격자 개수의 영향이 위상 상 수, 누설 상수 및 복사패턴 등과 복사 특성에 미치는 영향을 조사하였고, 유한 주기 구조와 무한 주기 구조의 결 과를 비교하고 잘 일치함을 확인할 수 있었다. 균일 유한 주기 구형격자에 의한 높은 측엽을 줄이기 위해 안테나 의 전후단 부에 테이퍼링과 비균일 준주기 슬롯배열을 고려하였다. 또한 구형격자 표면파 안테나에 사용되는 구 형격자 주기. 폭, 깊이에 대해 테이퍼링을 통해 낮은 측엽을 갖는 endfire 복사패턴을 얻을 수 있었다.

• Wind and Structures
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• 제29권1호
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• pp.65-75
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• 2019

A heated square cylinder (with height $A^*$) is kept parallel to the cold wall at a fixed gap height $0.5A^*$ from the wall. Another adiabatic rectangular cylinder (of same height $A^*$ and width $0.5A^*$) is placed upstream in an inline tandem arrangement. The spacing between the two cylinders is fixed at $3.0A^*$. The inlet flow is taken as Couette-Poiseuille flow based non-linear velocity profile. The conventional fluid (also known as base fluid) is chosen as water (W) whereas the nanoparticle material is selected as $Al_2O_3$. Numerical simulations are performed by using SIMPLE algorithm based Finite Volume approach with staggered grid arrangement. The dependencies of hydrodynamic and heat transfer characteristics of the cylinder on non-dimensional parameters governing the nanofluids and the fluid flow are explored here. A critical discussion is made on the mechanism of improvement/reduction (due to the presence of the upstream cylinder) of heat transfer and drag coefficient, in comparison to those of an isolated cylinder. It is observed that the heat transfer increases with the increase in the non-linearity in the incident velocity profile at the inlet. For the present range studied, particle concentration has a negligible effect on heat transfer.

• Composites Research
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• 제24권4호
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• pp.17-22
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• 2011

본 연구에서는, 복합재 샌드위치를 수중운동체용 구조물에 적용하기 위한 기초연구로서, 샌드위치 복합재 원통의 제작, 좌굴 해석 및 시험 방법, 중량저감 효과를 분석하였다. 우선 변재에 주름이 생기지 않도록 하는 2단계 샌드위치 제작 방법을 소개하고, 이를 사용하여 원통을 제작하여 수압시험을 수행하였다. 동시에 MSC Nastran의 셀요소와 고체요소를 사용한 유한 요소해석을 수행하여 시험결과와 비교하였다. 시험과 해석의 결과 비교로부터 선형 유한요소해석으로도 샌드위치 원통의 좌굴압력을 3% 내외의 오차로 정확히 예측할 수 있음을 확인하였다. 또한 필라멘트 와인딩 원통에 대한 인자연구를 통해 샌드위치를 사용할 경우 동일한 지지압력에서 필라멘트 와인딩 원통보다 최소 30% 이상 무게가 줄어드는 것을 확인하였다.

• 한국전산유체공학회지
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• 제13권4호
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• pp.33-38
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• 2008

For study on the unsteady blockage effect, flows around a rotationally oscillating circular cylinder with relatively low forcing frequency in closed test-section wind tunnels have been numerically investigated by solving compressible Navier-Stokes equations. The numerical scheme is based on a node-based finite-volume method with the Roe's flux-difference splitting and an implicit time-integration method coupled with dual time-step sub-iteration. The computed results of the oscillating cylinder in the test section showed that the fluctuations of lift and drag are augmented by the blockage effects. The drag further increases because of low base pressure. The pressure on the test section wall shows the harmonics having the oscillating and the shedding frequencies contained in the blockage effect.