• 문화기술의 융합
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• 제9권6호
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• pp.941-946
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• 2023

미래 운송수단으로 거론되는 UAM을 중심으로 함께 주목받는 eVTOL 항공기의 양력과 항속속도 및 항속거리 증대를 위해 Tilt Rotor와 Tandem Wing 개념을 본 논문의 기체에 도입했다. 기체를 제작 및 비행 실험을 진행하여 비행 영상과 비행 로그를 확보했다. 비행 영상과 비행 로그를 분석한 결과 기체 모멘트가 과도하게 앞으로 쏠리는 현상이 발생했고 자세가 회복되지 않음을 파악했다. 이에 XFLR5에서 날개 붙임각과 면적을 변경하며 기체의 세로안정성을 확보하기 위한 최적의 피칭 모멘트 계수를 도출되도록 CATIA를 통해 설계된 기체를, XFLR5로 해석했다. 본 연구의 결과는 Tilt Rotor와 Tandem Wing이 적용된 기체가 안정적인 피칭 모멘트 계수를 가질 수 있도록 도움을 주며, 이를 통해 세로안정성을 더욱 향상할 수 있는 새로운 방안을 제시했다.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 1997년도 제8회 학술강연회논문집
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• pp.247-256
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• 1997

A nonlinear mathematical model of longitudinal combustion instability appropriate for ramjets and augmentors was developed based on modal analysis. The model was limited to a two-mode formulation. The associated differential equations were solved both analytically and numerically and used to perform parametric studies.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2004년도 추계학술대회 논문집
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• pp.787-792
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• 2004

LRB(Lead rubber bearing) has small resistance force against slowly acting loadings such as temporal and creep loadings vice versa large resistance force against rapid loadings such as earthquake and braking loadings. By those mechanical characteristics, it has the advantage to reduce longitudinal load acting on abutments and piers, and moreover to in1prove the running stability of train by restricting the behavior of bridge under the required level. In this study, a stability evaluation method of CWR on the bridge with LRB is presented. Several parametric studies are carried to investigate how LRB contributes to the improvement of CWR stability.

• Steel and Composite Structures
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• 제28권1호
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• pp.25-37
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• 2018

For the first time, the parametric instability characteristics of tow-steered variable stiffness composite laminated (VSCL) cylindrical panels is investigated using B-spline finite strip method (FSM). The panel is considered containing geometrical defects including cutout and delamination. The material properties are assumed to vary along the panel axial length of any lamina according to a linear fiber-orientation variation. A uniformly distributed inplane longitudinal loading varies harmoni-cally with time is considered. The instability load frequency regions corresponding to the assumed in-plane parametric load-ing is derived using the Bolotin's first order approximation through an energy approach. In order to demonstrate the capabili-ties of the developed formulation in predicting stability behavior of the thin-walled VSCL structures, some representative results are obtained and compared with those in the literature wherever available. It is shown that the B-spline FSM is a proper tool for extracting the stability boundaries of perforated delaminated VSCL panels.

• International Journal of Railway
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• 제3권4호
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• pp.126-133
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• 2010

The thermal buckling analysis of curved continuous welded rail (CWR) is studied for the lateral buckling prevention. This study includes a thermal buckling theory which accounts for both thermal and vehicle loading effects in the evaluation of track stability. The parameters include rail size, track lateral resistance, track longitudinal and torsional stiffnesses, initial misalignment amplitude and wavelength, track curvature, tie-ballast friction coefficient and truck center spacing. Parametric studies are performed to evaluate the effects of the individual parameters on the upper and lower critical buckling temperatures. The results show that the upper critical buckling temperature is highly affected by the uplift due to vehicle loads. This study provides a guideline for the improvement of stability for dynamic buckling in curved CWR track.

• 제어로봇시스템학회논문지
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• 제7권6호
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• pp.477-486
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• 2001

Many physical systems can be modeled by incorporating continuous and discrete event nature together. Such hybrid systems contain both continuous and discrete states that influence the dynamic be-havior of the systems. There has been an increasing interest in thers types of systems during the last dec-ade, mostly due to the growing usage of computers in the control of physical plants but also as a result of the hybrid nature of physical processes. The stability theory for hybrid systems is considered as extension of Lyapunov theory where the existence of an abstract energy function satisfying certain properties verifies stability, called multiple Lyapunov theory. In this paper, a hybrid stabilizing controller is proposed using the control Lyapunov function method and multiple Lyapunov theory, and the proposed method is applied to lon-gitudinal spacing control in a vehicle platoon for intelligent transportation systems(ITS).

• 한국의류학회지
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• 제22권8호
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• pp.1032-1042
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• 1998

The purpose of this study is to measure, compare, and investigate the physical properties of rayon/cotton blend fabrics treated with cellulase and cellulase & specific degeneration silicon and to present basic data which is in development a value-added fabric. The results are as follows. The condition for the treatment of cellulase was at 55$^{\circ}C$, pH 4 and the weight loss increased as the concentration of cellulase and the treated time increased. On treatment with cellulase, the crossectional view & longitudinal view of fiber noticed remarkable crack as weight loss increased and tensile strength and elongation decreased, and pilling was enhanced remarkably. KOSHI was increased, NUMERI and FUKURAMI were decreased as weight loss increased. In the basic characteristic value of clothing wearning, shape stability and drapability were decreased, but air content was improved. On treatment with cellulase & silicon, the degree of damage in the crossectional view & longitudinal view of the fiber reduced. Tensile strength, elongation, moisture regain improved. KOSHI and FUKURAMI were reduced, NUMERI was improved rather than when it was treated with cellulase. Therefore handle was improved. In the basic characteristic value of the clothing wearing, shape stability, air content, drapability were improved.

• 한국터널지하공간학회 논문집
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• 제2권2호
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• pp.32-40
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• 2000

본 논문에서는 수평보강재로 보강된 터널 막장의 거동에 대한 매개변수 연구를 다루었다. 매개변수 연구에서는 축소모형실험을 수행하였으며 실험 결과를 이용하여 보강막장의 거동을 고찰하였다. 실험결과 터널 막장은 수평보강재로 보강함에 따라 변형이 억제되어 안정성이 증대되는 경향을 보였으며, 이러한 결과는 3차원 유한요소해석 결과와 정성적인 면에서 좋은 일치를 보였다. 따라서 막장 수평보강 공법은 막장의 안정성을 향상시키는 매우 유용한 공법으로 적용될 수 있을 것으로 판단되며, 일반적인 설계법을 개발하기 위해서 3차원 유한요소해석 모델링이 활용될 수 있을 것으로 사료된다.

• 한국군사과학기술학회지
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• 제20권3호
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• pp.393-404
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• 2017

Side jet effect on the aerodynamic characteristics of a missile was investigated using experimental and computational methods. A couple of side jets were injected toward outward downstream at mid point of missile body. Cold air jet was used in the wind tunnel test, and cold and hot jet were used in the computation. Wind tunnel test was carried out with jet and without jet, and calculation was performed for three cases ; no jet, cold air jet, and hot mixture gas jet. From the comparison of measured and calculated data for all cases, two points could be deduced. Firstly, side jet made static stability to be unstable by increasing body normal force near the side jet exit and by decreasing tail normal force. Secondly, hot mixture gas had more significant effect on the static stability of a missile-type body than cold air jet.

• 한국전산구조공학회논문집
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• 제19권1호
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• pp.39-46
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• 2006

본 연구는 파 해석에 있어서 공간-시간 분할 개념을 도입하여 켈러킨 방법으로 해석하였다. 공간-시간 유한요소법은 오직 공간에 대해서만 분할하는 일반적인 유한요소법보다 간편하다. 비교적 큰 시간간격에 대해서 공간과 시간을 동시에 분할하는 방법을 제시하며 가중잔차법이 공간-시간 영역에서 유한요소 정식화에 이용되었다. 큰 시간 간격으로 인하여 문제의 해가 발산하는 경우가 동적인 문제에서 흔히 발생한다. 이러한 결점을 보완한 사각형 공간-시간 요소를 취하여 문제를 해석하고 해의 안정에 대해 기술하였다. 다수의 수치해석을 통하여 이 방법이 효과적 임을 알 수 있었다.