• 한국항공우주학회지
• /
• 제31권4호
• /
• pp.26-34
• /
• 2003

본 논문에서는 이동최소자승 근사법 등의 무요소 근사법을 이용하여 유한요소모델 절점의 연결성과 무관하게 유한요소 절점을 자유로이 활성화시킬 수 있는 절점활성화 기법을 제안하고, 제안된 방법의 타당성을 고찰하기 위해 일관성 조건, 수치해의 유계성 등에 대한 이론적 고찰을 수행한다. 제안된 절점활성화 기법을 이용하면 많은 수의 유한요소 절점 중 관심이 있는 일부 절점만을 선택, 활성화시켜 이들만을 미지수로 이용하여 문제를 해석할 수 있기 때문에 설계 및 재해석을 효율적으로 수행할 수 있다.

• International Journal of Aeronautical and Space Sciences
• /
• 제13권2호
• /
• pp.127-153
• /
• 2012

This paper presents an advanced computational method for the prediction of the responses in the frequency domain of general linear dissipative structural-acoustic and fluid-structure systems, in the low-and medium-frequency domains and this includes uncertainty quantification. The system under consideration is constituted of a deformable dissipative structure that is coupled with an internal dissipative acoustic fluid. This includes wall acoustic impedances and it is surrounded by an infinite acoustic fluid. The system is submitted to given internal and external acoustic sources and to the prescribed mechanical forces. An efficient reduced-order computational model is constructed by using a finite element discretization for the structure and an internal acoustic fluid. The external acoustic fluid is treated by using an appropriate boundary element method in the frequency domain. All the required modeling aspects for the analysis of the medium-frequency domain have been introduced namely, a viscoelastic behavior for the structure, an appropriate dissipative model for the internal acoustic fluid that includes wall acoustic impedance and a model of uncertainty in particular for the modeling errors. This advanced computational formulation, corresponding to new extensions and complements with respect to the state-of-the-art are well adapted for the development of a new generation of software, in particular for parallel computers.

• 한국항공우주학회지
• /
• 제41권11호
• /
• pp.865-873
• /
• 2013

본 논문에서는 유한요소해석에 의한 막재료의 주름 해석 기법에 관하여 연구하였다. 삼각형 세일 형상에 대해 멤브레인 요소와 쉘 요소를 사용하여 주름해석을 수행하였다. 멤브레인 요소를 이용한 기법에서는 주름을 벌칙매개변수에 의한 물성치를 수정하는 알고리즘을 상용프로그램 내 사용자 서브루틴을 통하여 구현하였다. 쉘 요소에 의한 기하학적 비선형 후좌굴 기법에서는 면외방향의 좌굴을 발생시키기 위하여 모델의 메쉬에 작은 크기의 기하학적 결함을 심는 방법을 사용하였다. 쉘 방법에서는 내연 및 외연해석 기법을 고려하였다. 요소수의 증가에 따른 수렴성과 결과의 정확도의 관점에서 멤브레인 요소법과 쉘 요소법의 효율성을 비교하였다.

• 한국강구조학회 논문집
• /
• 제19권6호
• /
• pp.599-610
• /
• 2007

이 연구에서는 박벽 뼈대 구조물의 3차원 기하 비선형 해석을 위한 Corotational 정식화를 유도하였으며, 특히 변형 후 부재좌표계 결정에서 모호했던 기존의 이론을 단면의 물리적 적합 조건을 이용하여 해결하였다. 부재 양단의 순수 비틀림 회전값이 서로 크기는 같고 방향은 반대가 되는 상태를 적합조건으로 적용하고, 이를 특별히 ZTSC(Zero Twisted Section Condition)이라고 명명하였다. 개발된 방법의 타당성을 검증하기 위하여 기존의 다른 연구자가 사용한 방법과 비교하여 대회전변위가 발생한 경우에 대한 순수회전변위 결과를 검토하였으며, 개발된 Corotational 정식화를 이용하여 3차원 대변위가 발생하는 세장한 구조물의 후좌굴 해석을 성공적으로 수행하였다.

• International Journal of Aeronautical and Space Sciences
• /
• 제12권1호
• /
• pp.84-91
• /
• 2011

A finite element analysis for the wing and landing gear of a composite target-drone air vehicle was performed. For the wing analysis, two load cases were considered: a 5g symmetric pull-up and a -1.5g symmetric push-over. For the landing gear analysis, a sinking velocity of 1.4 m/s at a 2g level landing condition was taken into account. MSC/NASTRAN and LS-DYNA were utilized for the static and dynamic analyses, respectively. Finite element results were verified by the static test of a prototype wing under a 6g symmetric pull-up condition. The test showed a 17% larger wing tip deflection than the finite element analysis. This difference is believed to come from the material and geometrical imperfections incurred during the manufacturing process.

• International Journal of Aeronautical and Space Sciences
• /
• 제18권4호
• /
• pp.601-613
• /
• 2017

An adjoint-based error estimation and mesh adaptation study is conducted for two-dimensional viscous flows on unstructured hybrid meshes. The error in an integral output functional of interest is estimated by a dot product of the residual vector and adjoint variable vector. Regions for the mesh to be adapted are selected based on the amount of local error at each nodal point. Triangular cells in the adaptive regions are refined by regular refinement, and quadrangular cells near viscous walls are bisected accordingly. The present procedure is applied to single-element airfoils such as the RAE2822 at a transonic regime and a diamond-shaped airfoil at a supersonic regime. Then the 30P30N multi-element airfoil at a low subsonic regime with a high incidence angle (${\alpha}=21deg.$) is analyzed. The same level of prediction accuracy for lift and drag is achieved with much less mesh points than the uniform mesh refinement approach. The detailed procedure of the adjoint-based mesh refinement for the multi-element airfoil case show that the basic flow features around the airfoil should be resolved so that the adjoint method can accurately estimate an output error.

• 한국의류학회지
• /
• 제26권2호
• /
• pp.292-302
• /
• 2002

The purpose of this study was to research on Characteristic of Consumer and Clothing Purchase Orientations according to Internet Shopping Mall Type. The results were as follows; First, the clothing purchase orientations consisted of 5 dimension; product recondition, consumer service, shopping experience, risk of functional recognition, and of economical recognition. Second, the analysis of items of 5 dimension on clothing purchase orientations according to Internet shopping mall type produced as follows; 1. Product recognition - Variety of products appeared to be important elements and the average of specialized shopping mall was higher than that of general shopping mall. 2. Consumer service - Reliability of product information appeared to be more critical than others and the average of specialized shopping mall was bigger than that of others 3. Shopping experience - The item of convenience over time and space, the hard sell and over-service were found critical elements. Especially convenience over time of Mall of Malls, the convenience a far from hard sell element of department style shopping mall, and convenience over space of specialized mall were higher than that of others. 4. Risk element of functional recognition - No specific distinction appeared according to shopping mall type. 5. Risk element of economical recognition - Mending and additional cost arising from bad choice were found being critical element.

• KCI Concrete Journal
• /
• 제13권1호
• /
• pp.19-25
• /
• 2001

Based on the orthotropic hypoelasticity formulation, a constitutive material model of concrete taking account of triaxial stress state is presented. In this model, the ultimate strength surface of concrete in triaxial stress space is described by the Hsieh's four-parameter surface. On the other hand, the different ultimate strength surface of concrete in strain space is proposed in order to account for increasing ductility in high confinement pressure. Compressive ascending and descending behavior of concrete is considered. Concrete cracking behavior is considered as a smeared crack model, and after cracking, the tensile strain-softening behavior and the shear mechanism of cracked concrete are considered. The proposed constitutive model of concrete is compared with some results obtained from tests under the states of uniaxial, biaxial, and triaxial stresses. In triaxial compressive tests, the peak compressive stress from the predicted results agrees well with the experimental results, and ductility response under high confining pressure matches well the experimental result. The reinforcing bars embedded in concrete are considered as an isoparametric line element which could be easily incorporated into the isoparametric solid element of concrete, and the average stress - average strain relationship of the bar embedded in concrete is considered. From numerical examples for a reinforced concrete simple beam and a structural beam type member, the stress state of concrete in the vicinity of talc critical region is investigated.

• International Journal of Aeronautical and Space Sciences
• /
• 제17권2호
• /
• pp.157-166
• /
• 2016

Aerodynamic loads for a horizontal axis wind turbine of the National Renewable Energy Laboratory (NREL) Phase VI rotor in yawed condition were predicted by using the blade element momentum theorem. The classical blade element momentum theorem was complemented by several aerodynamic corrections and models including the Pitt and Peters' yaw correction, Buhl's wake correction, Prandtl's tip loss model, Du and Selig's three-dimensional (3-D) stall delay model, etc. Changes of the aerodynamic loads according to the azimuth angle acting on the span-wise location of the NREL Phase VI blade were compared with the experimental data with various yaw angles and inflow speeds. The computational flow chart for the classical blade element momentum theorem was adequately modified to accurately calculate the combined functions of additional corrections and models stated above. A successive under-relaxation technique was developed and applied to prevent possible failure during the iteration process. Changes of the angle of attack according to the azimuth angle at the specified radial location of the blade were also obtained. The proposed numerical procedure was verified, and the predicted data of aerodynamic loads for the NREL Phase VI rotor bears an extremely close resemblance to those of the experimental data.

• 한국항공우주학회지
• /
• 제39권8호
• /
• pp.711-718
• /
• 2011

본 논문에서는 열화학적 분해 및 열기계학적 변형이 고려된 구성 방정식을 사용하여 다공성 탄소/페놀릭 복합재료의 열탄성 거동을 예측하였다. 다공성 복합재료의 온도 의존성 및 열화학적 분해 과정에서의 기공도, 분해 가스에 의한 기공 압력, 재료의 수축을 고려하였다. 기공도와 기공 압력이 고려된 대표 체적 요소 모델의 유한요소 해석을 통해 산출된 거시적 기공 탄성 계수를 구성 방정식에 적용하였다. 간단한 수치 실험을 통해 기공탄성 계수가 다공성 재료의 열탄성 거동에 미치는 영향을 분석하였으며, 재료 내부에 형성된 기공과 기공 압력에 의한 응력 구배 및 변형을 확인하였다.