• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2008년 영문 학술대회
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• pp.531-535
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• 2008

Present study examines the detonation wave propagation characteristics in annular channel. A normalized value of channel width to the annular radius was considered as a geometric parameter. Numerical approaches used in the previous studies of detonation wave propagation were extended to the present study with OpenMP parallelization for multicore SMP machines. The major effect of the curved geometry on the detonation wave propagation seems to be a flow compression effect, regardless of the detonation regimes. The flow compression behind the detonation wave by the curved geometry of the circular channel pushes the detonation wave front and results in the overdriven detonation waves with increased detonation speed beyond the Chapmann-Jouguet speed. This effect gets stronger as the normalized radius smaller, as expected. The effect seems to be negligible beyond the normalized radius of 10.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2007년도 제29회 추계학술대회논문집
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• pp.367-370
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• 2007

Present study examines detonation wave propagation characteristics in annular channel. A normalized value of channel width to the annular radius was considered as a geometric parameter. A parametric study was carried out for a various regimes of detonation waves from weakly unstable to highly unstable detonation waves. Numerical approaches that used in the previous study of numerical requirements of the simulation of detonation wave propagations in 2D and 3D channel were used also for the present study with OpenMP parallization for multi-core SMP machines. The major effect of the curved geometry on the detonation wave propagation seems to be a flow compression effect, regardless of the detonation regimes. The flow compression behind the detonation wave by the curved geometry of the circular channel pushes the detonation wave front and results in the overdriven detonation waves with increased detonation speed beyond the Chapmann-Jouguet speed. This effect gets stronger as the normalized radius smaller, as expected. The effect seems to be negligible beyond the normalized radius of 10.

• Structural Engineering and Mechanics
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• 제39권2호
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• pp.169-186
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• 2011

This paper is devoted to the development of the equations which describe the elastic response of a curved laminate subjected to in-plane loads and bending moments. Similar to the classic $6{\times}6$ ABD matrix constitutive relation of a flat laminate, a new $6{\times}6$ matrix constitutive relation between force resultants, moment resultants, mid-plane strains and deformed curvatures for a curved laminate is formulated. This curved lamination theory will provide the fundamental basis for the analyses of curved laminated structures. The stress predictions by the present curved lamination theory are compared to those by the curved laminate analysis that neglected the nonlinear terms in the derivation of the constitutive relation. The results show that the curved laminate analysis that neglected the nonlinear terms cannot reflect the effect of curvature and can no longer predict the stresses accurately as the curvature becomes noticeable. In this paper, a curved lamination theory that retains the nonlinear terms and, therefore, accounts for the effect of the non-flat geometry of the structure will be developed.

• Structural Engineering and Mechanics
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• 제22권6호
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• pp.741-759
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• 2006

A general theory which describes the elastic response of a curved anisotropic plate subjected to stretching and bending will be developed by considering the nonlinear effect that reflecting the non-flat geometry of the structure. By applying a newly derived $6{\times}6$ matrix constitutive relation between force resultants, moment resultants, mid-plane strains and deformed curvatures, the governing differential equations for a curved anisotropic plate is developed in the usual manner, namely, by consideration of the constitutive relation and equilibrium equations. Solutions are obtained for simply-supported boundary conditions and compared to corresponding solutions that neglecting the nonlinear effect in the analysis. The comparisons indicate that the nonlinear terms in the equations that caused by the curvature of the structure is crucial for the curved plate analysis. Under certain curved plate geometries the unreasonable results will be induced by neglecting the nonlinear effect in the analysis.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2009년 추계학술발표대회
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• pp.22-22
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• 2009

Laser forming is a promising technology in manufacturing, such as in the shipbuilding, automobile, microelectronics, aerospace and other manufacturing industries. This process forms the sheet metal by utilization of laser-induced thermal stresses. Laser forming process has been studied extensively for rectangular shape geometry. This basic study presents the change in deformation behavior of sheet metal during transition from linear to curved geometries and irradiations as well. A series of experiments have been conducted on a wide range of specimen geometries such as quarter-circular and half circular plate. The reasons for this behavior have been analyzed. Results are compared and analyzed by simulations using ABAQUS. Influence of developed stresses on the bending has been investigated. This study provides the more understanding of forming mechanism influenced by geometry effect.

• 대한기계학회논문집A
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• 제21권2호
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• pp.288-296
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• 1997

Curved beam elements with two nodes based on shallow beam geometry and strain interpolations are employed in eigenvalue analysis. In these elements, the displacement interpolation functions and mass matrices are consistent with strain fields. To assess the quality of the element mass matrix in free vibration problems, several numerical experiments are performed. In these analysis, both the inconsistent mass matrices using linear displacement interpolation function and the consistent mass matrices are used to show the difference. The numerical results demonstrate that the accuracy is closely related to the property of the mass matrix as well as that of the stiffness matrix and that the mass matrix consistent with strain fields is very beneficial to eigenvalue analysis. Also, it is proved that the strain based elements are very efficient in a wide range of element aspect ratios and curvature properties.

• Advances in aircraft and spacecraft science
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• 제5권1호
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• pp.21-49
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• 2018

In this paper, geometric nonlinear bending characteristics of single wall carbon nanotube reinforced composite (SWCNTRC) doubly curved shell panels subjected to uniform transversely loadings are investigated. The nonlinear mathematical model is developed for doubly curved SWCNTRC shell panel on the basis of higher-order shear deformation theory and Green- Lagrange nonlinearity. All nonlinear higher order terms are included in the mathematical model. The effective material properties of SWCNTRC are estimated by using Eshelby-Mori-Tanaka micromechanical approach. The governing equation of the shell panel is obtained using the total potential energy principle and a Newton-Raphson iterative method is employed to compute the nonlinear displacement and stresses. The present results are compared with published literature. The effect of SWCNT volume fraction, width-to-thickness ratio, radius-to-width ratio (R/a), boundary condition, linear and nonlinear deflection, stresses and different types of shell geometry on nonlinear bending response is investigated.

• Advances in aircraft and spacecraft science
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• 제10권1호
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• pp.51-65
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• 2023

In this paper, the effect of deepness on in-plane free vibration behavior of a curved functionally graded (FG) nanobeam based on nonlocal elasticity theory has been investigated. Differential equations and boundary conditions have been developed based on Hamilton's principle. In order to figure out the size effect, nonlocal theory has been adopted. Properties of material vary in radial direction. By using Navier solution technique, the amount of natural frequencies has been obtained. Also, to take into account the deepness effect on vibrations, thickness to radius ratio has been considered. Differences percentage between results of cases in which deepness effect is included and excluded are obtained and influences of power-law exponent, nonlocal parameter and arc angle on these differences percentage are studied. Results show that arc angle and power law exponent parameters have the most influences on the amount of the differences percentage due to deepness effect. It has been observed that the inclusion of geometrical deep term and material distribution results in an increase in sensitivity of dimensionless natural frequency about variation of aforementioned parameters and a change in variation range of natural frequency. Finally, several numerical results of deep and shallow curved functionally graded nanobeams with different geometry dimensions are presented, which may serve as benchmark solutions for the future research in this field.

• 대한기계학회논문집A
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• 제27권11호
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• pp.1986-1996
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• 2003

Methodology based on the elastic-plastic fracture mechanics has been widely accepted in predicting the critical crack length(CCL) of pressure tubes of CANDU nuclear plants. A conservative estimate of CCL is obtained by employing the J-resistance curves measured with the specimens satisfying plane strain condition as suggested in the ASTM standard. Due to limited thickness of the pressure tubes the curved compact tension(CT) specimens taken out from tile pressure tube have been used in obtaining J-resistance curves. The curved CT specimen inevitably introduce slant fatigue crack during precracking. Hence, effect of specimen geometry and slant crack on J-resistance curve should be explored. In this study, the difference of J integral values between the standard CT specimens satisfying plane strain condition and the nonstandard curved CT with limited thickness (4.2mm) is estimated using finite element analysis. The fracture resistance curves of Zr-2.5Nb obtained previously by other authors are critically discussed. Various finite element analysis were conducted such as 2D analysis under plane stress and plane strain conditions and 3D analysis for flat CT, curved CT with straight crack and curved CT with slant crack front. J-integral values were determined by local contour integration near the crack tip, which was considered as accurate J-values. J value was also determined from the load versus load line displacement curve and the J estimation equation in the ASTM standard. Discrepancies between the two values were shown and suggestion was made for obtaining accurate J values from the load line displacement curves obtained by the curved CT specimens.

• 한국산학기술학회논문지
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• 제20권5호
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• pp.577-584
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• 2019

최근 국내 사장교는 경관적인 요소를 위하여 비정형적인 형태가 시도되고 있다. 새로운 기하구조가 적용된 사장교는 그 특성을 명확히 분석하여 구조안전성을 확보할 필요가 있다. 본 연구 대상 교량은 S자형 곡선 보도사장교로 S자형 평면곡선과 역삼각형트러스 횡단면을 가진 보강거더, 곡선반경 내측에 1면으로 배치된 경사 주탑과 modified Fan 타입 주케이블, 수직 백스테이케이블이 적용되었다. 곡선사장교는 직선사장교와 같이 종방향의 거동에만 초점을 두고 장력을 조정할 경우 횡방향으로 과다한 변위와 모멘트가 발생 할 수 있다. 본 연구는 주케이블이 교량의 횡방향 거동에 미치는 영향을 분석하기 위해서, 장력에 의한 주탑의 횡방향 변위 방향에 따라 케이블을 2개 그룹으로 나누었다. 지간중앙부 케이블 그룹을 GR1, 주탑지점부 케이블 그룹을 GR2라 할 때 GR1과 GR2의 조합비율이 보강거더, 받침, 주탑 그리고 수직앵커케이블에 미치는 영향을 분석하였다. 연구대상 교량에 적용된 장력비율을 1.0GR1+1.0GR2라 하였을 때, 1.2GR1+0.8GR2의 조합에서 주탑지점부 보강거더의 좌측과 우측 상현재 응력이 최소가 되었고, 좌우 부재의 편차도 최소가 되었다. 또한, 받침의 수평력, 주탑의 횡방향 변위와 모멘트, 수직백스테이케이블의 장력도 감소하였다. 본 연구는 유사한 기하구조를 가진 사장교의 장력 결정시 기초 자료로 활용될 것으로 기대된다.