• 대한기계학회논문집
• /
• 제17권2호
• /
• pp.371-379
• /
• 1993

The wrinkling in the electromagnetic tube compression with a mandrel is remarkably smaller than that of the process without it. To analyze this phenomenon, the critical forming parameters such as the ratio of the clearance to the shell radius, the ratio of the thickness to the shell radius, and the ratio of the applied pressure to the standard pressure are introduced tp consider the effect of the mandrel, in addition to those of the thickness of shell and applied loads. The amplification ratio is also used to observe the magnitude of amplification. The results obtained by 2-D finite element method show that the initial imperfection embedded in the radius of cylindrical shell is the dominant factor to determine the final shape of the tube compression, and that the amplification ratio tends to have smaller values with the smaller clearance ratio and also with the larger thickness and pressure ratios.

• 한국소성가공학회:학술대회논문집
• /
• 한국소성가공학회 1999년도 춘계학술대회논문집
• /
• pp.98-101
• /
• 1999

The plastic instable flow phenomenon happens in practical forming process I. e. upsetting backward extrusion piercing indentation. And also it is difficult to control precisely the shape and dimensions of forming process. It is found that instabilities of the process are mainly connected with imperfection in the lubrication billet eccentricity inclined punch alignment. In view of the direct relationship between instable material flow and quality defects of the products and it is for better control of forming operation we should necessarily find out their phenomena. In this study we used the friction disturbance due to inclined punch angle and introduced the method considering kinematic hardening effect Analysis of upset forging is carried out using the rigid plastic FEM and slab method with eccentricity.

• 한국해양공학회지
• /
• 제10권4호
• /
• pp.28-37
• /
• 1996

A finite element analysis code considering elasto-plastic large deformation is developed to predict the ultimate strength of circular cylinders subject to external pressure loading by introducing a new type of axisymmetric shell element which can take into account the plasticity effect due to the circumferential bending while drastically saving the computing efforts compared with the tree dimensional finite element analysis. It is observed that analsis results of present approach show good agreement with the test results of previous works. Parametric study gives the effects of initial imperfections on ultimate strength ahd this information is recommended to be used to modify the actual test data to the ones which can be used more reasonably in making empirical design formulas.

• 한국공간구조학회:학술대회논문집
• /
• 한국공간구조학회 2005년도 춘계학술발표회 및 정기총회 2권1호(통권2호)
• /
• pp.161-166
• /
• 2005

In spatial structures with large spaces, one important issue in structures with large spaces is how to carry the weight of the roof. A tensegrity cable dome structure is a kind of soft structural system using the tension cable and compression column as a main element. The tensegrity cable dome is built into a variety of shape around the world but then a collapse accident is increasing. Owing to a collapse accident we must grip of the collapse mechanism to prevent an accident and construct the structure with safety and economy. In this study, I investigated the unstable characteristics of the Geiger-type and Flower-type tcnsegrity cable dome structures, which is the lightweight hybrid structures using compression and tension elements continuously, according to the difference of loading conditions.

• 한국농공학회지
• /
• 제43권4호
• /
• pp.89-96
• /
• 2001

In this study non-linear finite element analysis of dynamic response of steel arch under partially distributed dynamic load was discussed. Material and geometric non-linearities were included in finite element formulation and steel behavior was modeled with Von Mises yield criteria. Either radial or vertical dynamic load was dealt in numerical examples. Normal arch and arch with maximum shape imperfection of L/11,000 were studied. The analysis results showed that maximum displacement at the center of arch was occurred when 70% of arch span was loaded. The maximum displacement at a quarter of arch span was occurred when 50% of arch span was loaded and the displacement was larger than that of center of arch. Ratio of arch rise to arch span within 0.2∼-.3 seems to be appropriate for arch under radial or vertical load.

• Structural Engineering and Mechanics
• /
• 제15권6호
• /
• pp.653-668
• /
• 2003

Many papers which deal with the dynamic instability of shell-like structures under the STEP load have been published. But, there have been few papers related to the dynamic instability of hybrid cable domes. In this study, the dynamic instability of hybrid cable domes considering geometric nonlinearity is investigated by a numerical method. The characteristic structural behaviour of a cable dome shows a strong nonlinearity, so we determine the shape of a cable dome by applying initial stress and examine the indirect buckling mechanism under dynamic external forces. The dynamic critical loads are determined by the numerical integration of the nonlinear equation of motion, and the indirect buckling is examined by using the phase plane to investigate the occurrence of chaos.

• 한국전산구조공학회:학술대회논문집
• /
• 한국전산구조공학회 2001년도 가을 학술발표회 논문집
• /
• pp.167-174
• /
• 2001

A shape resistant shell structure is an extremely efficient mechanical creation because it transmits forces mainly by in-plane forces, but at a certain load level it changes from a stable condition to an unstable condition or vise versa. The instability phenomenon of Geiger-type cable dome structure is generated due to the in-plane twisting near critical load level. Therefore the effect of bracing reinforcement is investigated for the Geiger-type model reinforced by bracing. The effect of initial imperfection is also studied since the structural instability behavior characteristic of shell-like structure is significantly sensitive according to the initial condition.

• 한국공간구조학회논문집
• /
• 제23권1호
• /
• pp.69-76
• /
• 2023

A timber lattice roof, which has around 30m span, was constructed. In order to figure out the realistic buckling load level, the structural analysis of this roof structure was performed especially by stiffness of connection with various asymmetric snow load. Due to the characteristics of application of snow load, the load combinations of snow should be considered not only global area but also local part so that the critical buckling load could be observed as easy as possible. Geometrical imperfection was simulated to consider inaccurate shape of structure. And then nonlinear analysis were performed. Finally, this paper could investigate that the asymmetric snow load with the lower level stiffness of connection decreased the level of buckling load significantly.

• Investigative Magnetic Resonance Imaging
• /
• 제10권2호
• /
• pp.70-80
• /
• 2006

목적: 본 연구의 목적은 스핀에코(spin-echo) 자기공명영상 시퀀스 (sequence)에서 혈류 (blood flow)의 영상 저하를 줄이기 위한 새로운 경사자장 널링 (Gradient moment nulling) 방법 연구에 있다. 대상 및 방법: 스핀에코 시퀀스에서 사용하는 180도 펄스 주위에 혈류 보상과 동시에 180도 펄스의 불완전에서 생기게 되는 영상 저하를 줄일 수 있는 역할을 하는 경사자장을 이용한다. 이 경사자장은 혈류의 1차 (linear flow), 2차 (acceleration flow) 및 3차 (jurk flow) 운동에 대해 항상 같은 형태를 같기 때문에 통일된 경사자장의 형태를 갖는다. 이 기술을 이용하여 1차, 2차 및 3차 혈류 움직임에 의한 보상을 할 수 있는 스핀에코 시퀀스를 만들고 그 것을 펜텀과 사람의 뇌 영상에 사용하였다. 결과: 시뮬레이션을 이용한 혈류의 움직임에 대한 보상을 확인하였고 본 연구에서 제시된 새로운 기술이 기존에 제시된 기술에 비하여 향상된 결과를 펜텀 실험과 사람의 뇌 영상에서 보여 주었다. 결론: 본 연구에서 제시된 방법을 임상에 이용하면 혈류의 움직임에 대한 보상을 최적화 할 수 있으리라고 본다.

• 한국강구조학회 논문집
• /
• 제30권1호
• /
• pp.25-35
• /
• 2018

균일 외압을 받는 링 보강 원형단면 강재 쉘에 대하여 재료 및 기하학적 비선형 유한요소법(GMNIA)을 적용하여 외압강도를 평가하였다. 링 보강 쉘의 기하학적 초기결함의 진폭, 반경 대 두께 비, 링 보강재 간격 대 반경비 등이 외압강도에 미치는 영향을 분석하였으며, Eurocode 3과 DNV 설계기준에 의한 설계 외압 강도와 유한 요소해석으로 구한 외압강도를 비교 평가하였다. 기하학적 초기결함의 형상은 선형탄성 좌굴해석에 의한 좌굴모드를 적용하였으며 보강 쉘의 반경 대 두께 비는 250~500범위를 고려하였다.