• International Journal of CAD/CAM
• /
• 제6권1호
• /
• pp.199-211
• /
• 2006

Practical automated flat pattern generation with inbuilt production features for doubly curved sheet metal components (SMCs) is addressed here utilizing a new and unique Point Transformation Algorithm (PTA). This is the third in the series of papers on practical Flat Pattern Development (FPD) [8] and Production Loft Generation Systems (PLGS) [9] complementing the pioneering work [6,7]. In the first two publications, automated loft generation programs have addressed sheet metal components having a Principal Flat Surface (PFS) only. The flat pattern development of 3-D components that do not have the flat surface(termed as Non-PFS components) having complex features of double curvature in addition to cutouts and nibbled holes typical of aircraft components were so far not addressed due to lack of relevant published algorithms. This paper traces the evolution of developments and provides the record of fully illustrated, automated loft generation scheme for aircraft SMCs including the Non-PFS components which underwent validation through production tests by sponsors. Details of some of the unique features of the system like simplified surface model generation, termed as topological model and powerful algorithms deployed with potential for CAD/CAM applications are included.

• 대한수학회논문집
• /
• 제15권4호
• /
• pp.649-668
• /
• 2000

In this paper we prove the following : Let M be a real (2n-1)-dimensional compact minimal semi-invariant submanifold in a complex projective space P(sub)n+1C. If the scalar curvature $\geq$2(n-1)(2n+1), then m is a homogeneous type $A_1$ or $A_2$. Next suppose that the third fundamental form n satisfies dn = 2$\theta\omega$ for a certain scalar $\theta$$\neq$c/2 and $\theta$$\neq$c/4 (4n-1)/(2n-1), where $\omega$(X,Y) = g(X,øY) for any vectors X and Y on a semi-invariant submanifold of codimension 3 in a complex space form M(sub)n+1 (c). Then we prove that M has constant principal curvatures corresponding the shape operator in the direction of the distingusihed normal and the structure vector ξ is an eigenvector of A if and only if M is locally congruent to a homogeneous minimal real hypersurface of M(sub)n (c).

• 한국구조물진단유지관리공학회 논문집
• /
• 제18권1호
• /
• pp.150-159
• /
• 2014

본 논문은 초기하중을 받는 직사각형판 및 역대칭 Angle-Ply 적층판의 좌굴 및 진동특성을 무재하시의 고유진동수를 이용하여 산정하는 간편법을 제시하였다. 마주보는 두변이 단순지지된 직사각형판의 운동방정식은 곡률항을 고려한 Mindlin 판이론과 에너지원리를 이용한 Rayleigh-Ritz법을 이용하여 유도하였다. 초기응력을 받는 직사각형판의 무차원화 고유진동수, 임계좌굴계수 및 동적불안정영역 문제들을 무재하시의 무차원화 고유진동수로서 각각의 특성을 정립하였다. 본 연구에서 제안한 진동특성에 관한 간편산정식의 타당성과 사용성을 입증하기 위해 수치예를 들어 검토하였다.

• 한국재난정보학회 논문집
• /
• 제11권4호
• /
• pp.527-533
• /
• 2015

본 논문은 초기하중을 받는 역대칭 Cross-Ply 원통쉘의 동적특성을 고유진동수를 이용하여 해석하였다. 마주보는 두변이 단순지지된 적층 원통쉘의 운동방정식은 곡률항을 고려한 Mindlin 쉘이론과 에너지원리를 이용한 Rayleigh-Ritz법을 이용하여 유도하였다. 초기응력을 받는 적층쉘의 고유진동수, 임계좌굴계수 및 동적불안정영역 문제들을 무재하시의 무차원화 고유진동수로서 각각의 특성을 정립하였다. 본 연구에서 제안한 진동특성에 관한 간편산정식의 타당성과 사용성을 입증하기 위해 수치예를 들어 검토하였다.

• 콘크리트학회논문집
• /
• 제11권3호
• /
• pp.89-100
• /
• 1999

The purpose of this study is to develop an analytic model of the concrete column strengthened with laminated CFS, and to provide a basic guideline for the strengthening design by CFS considering orthotropic properties of laminate. In this study, an analytical stress-strain model of laminated CFS is presented based on Tsai-Hill failure criterion. This model has been implemented in an algorithm which can evaluate the confinement effect of CFS. Through this algorithm, the stress-strain relationship of confined concrete is obtained and compared with experimental results of other studies. Using the constitutive relationships, section analyses of concrete column strengthened with CFS are done, and load-moment and load-curvature interaction curves are obtained. In addition, the strengthening effects of CFS according to various laminated angles are analyzed. Analytical results show that the strengthening effects of the strengthened concrete columns are significantly different in compression, flexure, and ductility according to the laminated ways. In compressive direction of principal stress shows the superiority, where an in flexural strengthening effects, [0/90]s does. In the aspect of ductility, [90]s shows the best effect.

• 대한토목학회논문집
• /
• 제29권2C호
• /
• pp.71-79
• /
• 2009

본 연구에서는 국내 철도 토공노반 재료로 가장 흔히 사용되는 입도조정쇄석, 화강풍화토, 암버럭-토사 혼합 재료에 대해 평균유효주응력과 축변형률의 함수로 표현되는 회복탄성계수 예측모델을 결정하였다. 회복탄성계수 예측모델은 대표적인 동적물성치인 변형률에 따른 전단탄성계수 감소곡선의 표현과 같이 최대영탄성계수와 정규화 영탄성계수 감소곡선으로 구성된다. 평균유효주응력의 함수로 표현되는 최대영탄성계수의 모델인자는 $A_E$와 $n_E$이고, 비선형 영역의 정규화 영탄성계수 감소곡선은 기준변형률(${\varepsilon}_r$)과 곡률계수(a)를 모델인자로 하는 수정 쌍곡선 모델로 표현된다. 제안된 회복탄성계수 예측모델을 검증하기 위해 3차원 다층탄성해석 프로그램(GEOTRACK)을 이용하여 평택 시험 철도노반의 탄성거동을 평가하였고, 화물열차 및 여객열차가 시험구간을 통과할 때 계측한 노반의 수직 탄성변위와 비교하였다. 현장계측은 자갈도상 아래의 재료가 각각 입도조정쇄석과 양질의 화강풍화토인 두 개소에서 수행되었다. 자갈도상 아래에서 계산된 수직 탄성변위는 대략 0.6mm 이내였고 계측 결과와 잘 일치하였다. 본 연구를 통해 제안된 회복탄성계수 예측모델이 열차하중에 의한 노반의 탄성거동을 적절히 표현하고 있음을 확인하였다.

• 대한기계학회논문집A
• /
• 제26권12호
• /
• pp.2636-2646
• /
• 2002

This research presents an analytical model to investigate vibration due to ball bearing waviness in a rotating system supported by two or more ball bearings, taking account of the centrifugal force and gyroscopic moment of the ball. The waviness of rolling elements is modeled by the sinusoidal function, and it is incorporated into the position vectors of the race curvature center. The Hertzian con tact theory is applied to calculate the elastic deflection and nonlinear contact force while the rotor has translational and angular motions. Both the centrifugal force and gyroscopic moment of the ball and the waviness of the rolling elements are included in the kinematic constraints and force equilibrium equations of a ball to derive the nonlinear governing equations of the rotor, which are solved by using the Runge-Kutta-Fehlberg algorithm to determine the new position of the rotor. The proposed model is validated by the comparison of the results of the prior researchers. This research shows that the centrifugal force and gyroscopic moment of the ball plays the important role in determining the bearing frequencies, i.e. the principal frequencies, their harmonics and the sideband frequencies resulting from the waviness of the rolling elements of ball bearing. It also shows that the bearing vibration frequencies are generated by the waviness interaction not only between the rolling elements of one ball bearing but also between those of two or more ball bearings constrained by the rotor.

• Steel and Composite Structures
• /
• 제26권6호
• /
• pp.771-791
• /
• 2018

This paper deals with the low velocity impact response and dynamic stresses of composite sandwich truncated conical shells (STCS) with compressible or incompressible core. Impacts are assumed to occur normally over the top face-sheet and the interaction between the impactor and the structure is simulated using a new equivalent three-degree-of-freedom (TDOF) spring-mass-damper (SMD) model. The displacement fields of core and face sheets are considered by higher order and first order shear deformation theory (FSDT), respectively. Considering continuity boundary conditions between the layers, the motion equations are derived based on Hamilton's principal incorporating the curvature, in-plane stress of the core and the structural damping effects based on Kelvin-Voigt model. In order to obtain the contact force, the displacement histories and the dynamic stresses, the differential quadrature method (DQM) is used. The effects of different parameters such as number of the layers of the face sheets, boundary conditions, semi vertex angle of the cone, impact velocity of impactor, trapezoidal shape and in-plane stresses of the core are examined on the low velocity impact response of STCS. Comparison of the present results with those reported by other researchers, confirms the accuracy of the present method. Numerical results show that increasing the impact velocity of the impactor yields to increases in the maximum contact force and deflection, while the contact duration is decreased. In addition, the normal stresses induced in top layer are higher than bottom layer since the top layer is subjected to impact load. Furthermore, with considering structural damping, the contact force and dynamic deflection decrees.

• Structural Engineering and Mechanics
• /
• 제25권4호
• /
• pp.481-500
• /
• 2007

The dynamic instability of doubly curved panels, subjected to non-uniform tensile in-plane harmonic edge loading $P(t)=P_s+P_d\;{\cos}{\Omega}t$ is investigated. The present work deals with the problem of the occurrence of combination resonances in contrast to simple resonances in parametrically excited doubly curved panels. Analytical expressions for the instability regions are obtained at ${\Omega}={\omega}_m+{\omega}_n$, (${\Omega}$ is the excitation frequency and ${\omega}_m$ and ${\omega}_n$ are the natural frequencies of the system) by using the method of multiple scales. It is shown that, besides the principal instability region at ${\Omega}=2{\omega}_1$, where ${\omega}_1$ is the fundamental frequency, other cases of ${\Omega}={\omega}_m+{\omega}_n$, related to other modes, can be of major importance and yield a significantly enlarged instability region. The effects of edge loading, curvature, damping and the static load factor on dynamic instability behavior of simply supported doubly curved panels are studied. The results show that under localized edge loading, combination resonance zones are as important as simple resonance zones. The effects of damping show that there is a finite critical value of the dynamic load factor for each instability region below which the curved panels cannot become dynamically unstable. This example of simultaneous excitation of two modes, each oscillating steadily at its own natural frequency, may be of considerable interest in vibration testing of actual structures.