• 한국자동차공학회논문집
• /
• 제15권1호
• /
• pp.56-63
• /
• 2007

In case of bus rollover, the body structure of the bus should be designed to ensure the survival space for passengers. So, this study focuses on evaluating rollover strength through a computer simulation using the commercial code, LS-DYNA3D at the initial stage of vehicle development. For this study, section structure was modeled using a simple beam element, and impact boundary conditions required by ECE(Economic Commission for Europe) regulation No.66 were applied. In order to confirm the validity of the beam element bus model, the results compared with the test results and shell element bus model. The analysis errors from beam element bus model are due to the difference in strain energy of joint area between beam and shell model. In this study, a method for the joint modeling was suggested by using nonlinear springs to which the collapse mechanisms were applied.

• 한국소성가공학회:학술대회논문집
• /
• 한국소성가공학회 2008년도 춘계학술대회 논문집
• /
• pp.201-204
• /
• 2008

In this paper, several process parameter studies of the manufacturing process of the steel cords are carried out to verify the relation between the process parameters and the residual stresses on the steel cords. At first, the finite element analysis of the drawing process is performed and the residual stress distributions with respect to the wire material and the area reduction ratio are obtained. The residual stress of the drawn wire is imported the finite element analysis of the twisting process as an initial stress. After that a parameter study of the twisting process is carried out. The process parameters are the applied tension, the over-twisting angle and the tensile strength of the drawn wire. Based on these studies, the optimum values of the process parameters which can remove or reduce the undesired residual stresses are determined. The optimum value of the process parameters are confirmed by the finite element analysis of the elastic recovery process of the steel cords. Finally, the finite element analysis of the roller straightening process is done to study the variation of the distribution of the residual stress before and after the process.

• Steel and Composite Structures
• /
• 제29권5호
• /
• pp.623-633
• /
• 2018

A robust element is essential for successful design of steel frames with Direct analysis (DA) method. To this end, an innovative and efficient curved-quartic-function (CQF) beam-column element using the fourth-order polynomial shape function with end-springs in series is proposed for practical applications of DA. The member initial imperfection is explicitly integrated into the element formulation, and, therefore, the P-${\delta}$ effect can be directly captured in the analysis. The series of zero-length springs are placed at the element ends to model the effects of semi-rigid joints and material yielding. One-element-per-member model is adopted for design bringing considerable savings in computer expense. The incremental secant stiffness method allowing for large deflections is used to describe the kinematic motion. Finally, several problems are studied in this paper for examining and validating the accuracy of the present formulations. The proposed element is believed to make DA simpler to use than existing elements, which is essential for its successful and widespread adoption by engineers.

• 한국전산구조공학회:학술대회논문집
• /
• 한국전산구조공학회 2008년도 정기 학술대회
• /
• pp.216-221
• /
• 2008

Shape design optimization for linear elasticity problem is performed using isogeometric analysis method. In many design optimization problems for real engineering models, initial raw data usually comes from CAD modeler. Then designer should convert this CAD data into finite element mesh data because conventional design optimization tools are generally based on finite element analysis. During this conversion there is some numerical error due to a geometry approximation, which causes accuracy problems in not only response analysis but also design sensitivity analysis. As a remedy of this phenomenon, the isogeometric analysis method is one of the promising approaches of shape design optimization. The main idea of isogeometric analysis is that the basis functions used in analysis is exactly same as ones which represent the geometry, and this geometrically exact model can be used shape sensitivity analysis and design optimization as well. In shape design sensitivity point of view, precise shape sensitivity is very essential for gradient-based optimization. In conventional finite element based optimization, higher order information such as normal vector and curvature term is inaccurate or even missing due to the use of linear interpolation functions. On the other hands, B-spline basis functions have sufficient continuity and their derivatives are smooth enough. Therefore normal vector and curvature terms can be exactly evaluated, which eventually yields precise optimal shapes. In this article, isogeometric analysis method is utilized for the shape design optimization. By virtue of B-spline basis function, an exact geometry can be handled without finite element meshes. Moreover, initial CAD data are used throughout the optimization process, including response analysis, shape sensitivity analysis, design parameterization and shape optimization, without subsequent communication with CAD description.

• 한국해양공학회지
• /
• 제28권5호
• /
• pp.411-422
• /
• 2014

A helideck is a very valuable offshore structure for the take-off and landing of a helicopter. In order to design a helideck, the design parameters and various loads defined by the regulations related to the design of a helideck should be applied. In this study, a risk analysis was performed based on the helicopter accidents for seven years, and the frequency and possible reasons for accidents involving helidecks were investigated. In addition, a finite element analysis of a steel helideck mounted on the upper deck of a ship (shuttle tanker) was performed with the load that should be considered when designing a helideck. Based on the results, a parametric study of helideck was carried out by applying a variety of design parameters, and an improved helideck design was presented. This improved helideck reduced the steel used by up to 24% compared to the initial helideck design, and the results of a finite element analysis were analyzed and compared with those of the initial analysis.

• 한국철도학회논문집
• /
• 제13권2호
• /
• pp.147-151
• /
• 2010

충돌에너지는 다이에 의해 확관되는 팽창튜브의 소성변형에너지로 흡수된다. 충돌에너지를 성공적으로 흡수하기 위하여 튜브가 팽창되는 동안 좌굴이 발생해서는 안 된다. 팽창튜브의 좌굴불안전성은 초기경계조건과 튜브 두께 그리고 길이에 영향을 받는다. 본 연구는 동적 축 하중을 받는 팽창튜브의 좌굴을 예측하기 위한 경계조건의 결정, 기하학적 결함의 적용 그리고 재료의 비선형성과 동적효과를 적용하는 일련의 해석방법 및 절차를 제안하였다. 또한, 기하학적 결함의 적용이 튜브의 좌굴하중과 좌굴형상에 미치는 영향을 유한요소해석 결과를 통하여 분석하였고 튜브두께와 기하학적 결함의 상관관계를 연구하였다. 해석결과 기하학적 결함과 튜브의 좌굴형상은 밀접한 관계가 있었고 튜브의 두께가 작으면 기하학적 결함에 상관없이 좌굴하중은 변하지 않았다. 하지만, 두께가 증가할 경우 결함율이 증가하면 좌굴하중이 감소하는 경향을 보였다.

• Steel and Composite Structures
• /
• 제28권5호
• /
• pp.559-571
• /
• 2018

In current engineering practice, circular concrete-filled steel tubular (CFST) columns have been used as effective structural components due to their significant structural and economic benefits. To apply these structural components into steel-concrete composite moment resisting frames, increasing number of research into the column-base connections of circular CFST columns have been found. However, most of the previous research focused on the strength, rigidity and seismic resisting performance of the circular CFST column-base connections. The present paper attempts to investigate the demountability of bolted circular CFST column-base connections using the finite element method. The developed finite element models take into account the effects of material and geometric nonlinearities; the accuracy of proposed models is validated through comparison against independent experimental results. The mechanical performance of CFST column-base connections with both permanent and demountable design details are compared with the developed finite element models. Parametric studies are further carried out to examine the effects of design parameters on the behaviour of demountable circular CFST column-base connections. Moreover, the initial stiffness and moment capacity of such demountable connections are compared with the existing codes of practice. The comparison results indicate that an improved prediction method of the initial stiffness for these connections should be developed.

• 대한토목학회논문집
• /
• 제33권4호
• /
• pp.1489-1498
• /
• 2013

본 연구에서는 불포화 사면에서 선행강우의 영향을 고려하고자 지반의 초기 포화도를 3가지(36, 51, 77%)로 설정하여 수리학적-역학적 동시 유한요소해석(monolithically coupled finite element analysis)을 수행하였다. 선행강우에 의한 불포화 사면의 불안정성은 사면 내 모관흡수력 분포와 사면표층의 변위를 통하여 확인할 수 있다. 또한 Drucker-Prager model의 항복경계기준(trial failure criterion)을 적용하여 강우 침투에 의한 불포화 사면의 탄성 및 소성거동을 파악하였다. 그 결과, 선행강우에 의한 지반의 초기 포화도가 클수록 강우에 의한 변위가 크게 발생하며 모관흡수력 또한 감소한다. 특히, 모관흡수력은 지반이 건조할수록 빠르게 감소하며, 초기에 동일한 모관흡수력을 갖는 사면표층에서 포화도가 작은 지반일수록 더 빠른 모관흡수력 감소를 보였다. 풍화토의 탄성과 소성거동을 구분하기 위해 사용된 Drucker-Prager model을 통해 사면 파괴가 시작되는 항복경계지점을 확인 할 수 있었다.

• 한국정밀공학회지
• /
• 제21권10호
• /
• pp.57-64
• /
• 2004

The objective of this study is to suggest the form rolling technology to produce high precision worm on the base of three dimensional finite element simulation and experiment. It is important to determine the initial workpiece diameter in form rolling because it affects the quality of tooth profile. The calculation method of the initial workpiece diameter in form rolling is suggested and it is verified by finite element simulation. The form rolling processes of worm shaft used as automotive part using both the rack dies of counter flow type and the roll dies are considered and simulated with the same numerical model as actual process by the commercial finite element code, BEFORM-3D. Deformation modes of workpiece between the form rolling by the rack dies of counter flow type and the roll dies are investigated from the result of simulation. The experiments using rack dies and roll dies are performed under the same conditions as those of simulation. The surface roughness, the straightness and the profile of worm are measured precisely using the worm shafts obtained from experiment. The results of simulation and experiment in this study show that the form rolling process of worn shaft using the rack dies is decidedly superior to that using roll dies from the aspect of the precision of worm such as the surface roughness, the straightness and the profile of worm.

• Structural Engineering and Mechanics
• /
• 제34권6호
• /
• pp.719-738
• /
• 2010

The aim of this paper concerns with the nonlinear analysis of cable-stayed bridges including the vibration effect of cable stays. Two models for the cable stay system are built up in the study. One is the OECS (one element cable system) model in which one single element per cable stay is used and the other is MECS (multi-elements cable system) model, where multi-elements per cable stay are used. A finite element computation procedure has been set up for the nonlinear analysis of such kind of structures. For shape finding of the cable-stayed bridge with MECS model, an efficient computation procedure is presented by using the two-loop iteration method (equilibrium iteration and shape iteration) with help of the catenary function method to discretize each single cable stay. After the convergent initial shape of the bridge is found, further analysis can then be performed. The structural behaviors of cable-stayed bridges influenced by the cable lateral motion will be examined here detailedly, such as the static deflection, the natural frequencies and modes, and the dynamic responses induced by seismic loading. The results show that the MECS model offers the real shape of cable stays in the initial shape, and all the natural frequencies and modes of the bridge including global modes and local modes. The global mode of the bridge consists of coupled girder, tower and cable stays motion and is a coupled mode, while the local mode exhibits only the motion of cable stays and is uncoupled with girder and tower. The OECS model can only offers global mode of tower and girder without any motion of cable stays, because each cable stay is represented by a single straight cable (or truss) element. In the nonlinear seismic analysis, only the MECS model can offer the lateral displacement response of cable stays and the axial force variation in cable stays. The responses of towers and girders of the bridge determined by both OECS- and MECS-models have no great difference.