• International Journal of Aeronautical and Space Sciences
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• 제11권2호
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• pp.110-117
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• 2010

We propose guidance laws based on a pursuit-evasion game. The game solutions are obtained from a pursuit-evasion game solver developed by the authors. We introduce a direct method to solve planar pursuit-evasion games with control variable constraints in which the game solution is sought by iteration of the update and correction steps. The initial value of the game solution is used for guidance of the evader and the pursuer, and then the pursuit-evasion game is solved again at the next time step. In this respect, the proposed guidance laws are similar to the approach of model predictive control. The proposed guidance method is compared to proportional navigation guidance for a pursuit-evasion scenario in which the evader always tries to maximize the capture time. The capture sets of the two guidance methods are demonstrated.

• 한국우주과학회:학술대회논문집(한국우주과학회보)
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• 한국우주과학회 2003년도 한국우주과학회보 제12권2호
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• pp.43-43
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• 2003

본 연구에서는 정지궤도 위성을 이용한 표준시각 동기 서비스에 실시간 궤도결정 기술을 적용하는 방안을 고려하였다. 정지궤도 위성을 이용하여 표준시각 동기신호를 전파하는 연구는 여러 나라에서 진행되고 있는데 3지역에서의 측정(Trilateration)과 미분 보정(Differential Correction) 방식이 일반적인 방법으로 채택되고 있다. 본 논고에서는 한국 항공우주연구원에서 진행 중인 표준시각 동기 서비스 연구와 이를 위해 제작중인 실시간 궤도결정 기술을 적용한 실험 소프트웨어에 대해 소개하고자 한다. 실시간 궤도결정 방법을 적용하게 되면 동기신호 전파에 있어서 가장 큰 오차의 원인이 되는 위성궤도 예측 오차를 크게 줄일 수 있을 것으로 판단된다. 본 연구에서는 기존에 궤도 결정을 위해 사용하는 톤 레인징에 의한 위상차 신호와 안테나 각도 대신에 동기신호 자체만을 사용하고 있으며 1개의 수신 데이터만으로 궤도 결정을 수행하는 방안을 강구하였다. 본 논고에서는 실시간 궤도 결정에 의한 시뮬레이션 결과와 한국항공우주연구원에서 준비 중인 실험에 대해서 간략히 소개한다. 그리고 본 연구에서 개발된 기술은 2004년 4월에 무궁화위성 2호를 이용하여 실험을 수행할 예정이다.

• Structural Engineering and Mechanics
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• 제66권6호
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• pp.693-701
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• 2018

This paper develops a nonlocal strain gradient plate model for vibration analysis of graphene sheets under thermal environments. For more accurate analysis of graphene sheets, the proposed theory contains two scale parameters related to the nonlocal and strain gradient effects. Graphene sheet is modeled via a two-variable shear deformation plate theory needless of shear correction factors. Governing equations of a nonlocal strain gradient graphene sheet on elastic substrate are derived via Hamilton's principle. Differential quadrature method (DQM) is implemented to solve the governing equations for different boundary conditions. Effects of different factors such as temperature rise, nonlocal parameter, length scale parameter, elastic foundation and aspect ratio on vibration characteristics a graphene sheets are studied. It is seen that vibration frequencies and critical buckling temperatures become larger and smaller with increase of strain gradient and nonlocal parameter, respectively.

• Structural Engineering and Mechanics
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• 제68권3호
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• pp.313-323
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• 2018

A numerical study is performed to investigate the impacts of thermal loading on the vibration and buckling of functionally graded carbon nanotube-reinforced composite (FG-CNTRC) conical shells. Thermo-mechanical properties of constituents are considered to be temperature-dependent. Considering the shear deformation theory, the energy functional is derived, and applying the variational differential quadrature (VDQ) method, the mass and stiffness matrices are obtained. The shear correction factors are accurately calculated by matching the shear strain energy obtained from an exact three-dimensional distribution of the transverse shear stresses and shear strain energy related to the first-order shear deformation theory. Numerical results reveal that considering temperature-dependent material properties plays an important role in predicting the thermally induced vibration of FG-CNTRC conical shells, and neglecting this effect leads to considerable overestimation of the stiffness of the structure.

• 한국인쇄학회지
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• 제14권1호
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• pp.115-131
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• 1996

The PVT(pressure-volume-temperature) relation of main-chain dimer liquid crystals having structures such as $\alpha$,$\omega$-bis[(4,4`-cyanobiphenyl) oxy] alkane(CBA-n with=9, 10) were studied. these dimer liquid crystals are known to form an enantiotropic nematic mesophase. In this work, we have determined the volume change as a function of temperature and pressure by using a GNOMIX PVT apparatus. In the V-Tcurves obtaind from isobaris mearements on various pressures, volume changes were observed at the nematic-isotropiz and nematic-crystal phase transitions. The volume changes at the transition exhibit slight odd-even effect with respect to the number of methylene unit n. The values of the (S)v obtained at the NI transition for CBA-9 and -10 were 6.9 and 12.6J/mol k. The valuesof (S)v for the CN transition were estimated on the basis of DSC(differential scanning calorimetry) data: 58.8(CBA-9) and 65.3J/mol k (CBA-10). For both transition, it was found that the correction about the volume change is significant, ranging from 40% to 60% of the total transition entropy observed under constant pressure.

• 대한교통학회지
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• 제17권3호
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• pp.7-20
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• 1999

차량의 정확한 위치를 자동적으로 파악하여, 차량위치정보를 필요로 하는 사용자에게 한눈에 파악할 수 있도록 지도정보와 합성하여 제공하는 차량위치파악 시스템에 관한 연구가 다양한 방법으로 발전되어져 왔다. 인터넷과 무선통신의 급속한 기술발전과 편리한 사용성, 경제성을 고려해 볼 때, 인터넷과 무선통신을 연결시킨 차량위치파악 시스템의 발전가능성 및 확장성이 클 것으로 생각된다. 이에 따라 실질적으로 기반 구축이 되어있는 현재 수준의 인터넷과 무선통신을 위성항법과 연결하여 차량위치파악 시스템을 실제로 구축해보고, 현재 제기되는 문제점들과 실시간 차량위치파악시스템을 위해 앞으로 더 개발/발전되어져야 할 기술들을 제시한다.

• 대한소아치과학회지
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• 제24권3호
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• pp.568-574
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• 1997

Inverted maxillary incisor is a state in which the maxillary incisor rotates to the upward position. The present report provides two examples of correction of inverted maxillary incisors with surgical intervention & orthodontic appliance. Through surgical exposure & direct bonding of lingual button, the central incisor were brought into proper eruption path with elastic traction. The case 1 & 2 were both treated successfully. The results showed the good position of treated teeth and satisfactory esthetics and adequate width of keratinized gingiva were achieved. Careful differential diagnosis procedure is needed in order to avoid dissatisfactory results and the treatment approaches taken in this case report provided an esthetic and functional results.

• 한국정밀공학회지
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• 제8권4호
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• pp.95-106
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• 1991

A numerical computation of turbulent wirling flow in a stationary pipe is presented in this work. Major concerns of this study are: 1) To approve similarity laws which were verified experimentally. 2) To investigate the effects of curvature modification for the K- .epsilon. model. To account for effects of swirl, Rodi's curvature correction and Kim & Chung's are applied. The governing differential equations for eliptic flow are discretized by control volume formulation method, and the discretized equations are calculated ay line by line TDMA and SIMPLE algorithm. The computational results also satisfy similarity laws which are based on swirl angle as in experiments. And the curvature modification of Rodi improves compuational accuacy than the standard K- .epsilon. model. But such lower order closure models are not adequate for the prediction of this complex flow.

• Steel and Composite Structures
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• 제20권5호
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• pp.963-981
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• 2016

A nonlocal trigonometric shear deformation beam theory based on neutral surface position is developed for bending, buckling, and vibration of functionally graded (FG) nanobeams using the nonlocal differential constitutive relations of Eringen. The present model is capable of capturing both small scale effect and transverse shear deformation effects of FG nanobeams, and does not require shear correction factors. The material properties of the FG nanobeam are assumed to vary in the thickness direction. The equations of motion are derived by employing Hamilton's principle, and the physical neutral surface concept. Analytical solutions are presented for a simply supported FG nanobeam, and the obtained results compare well with those predicted by the nonlocal Timoshenko beam theory.

• Structural Engineering and Mechanics
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• 제67권3호
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• pp.291-300
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• 2018

In this work, a new trigonometry theory of shear deformation is developed for the static analysis of thick isotropic beams. The number of variables used in this theory is identical to that required in the theory of Euler-Bernoulli, sine function is used in the displacement field in terms of the coordinates of the thickness to represent the effects of shear deformation. The advantage of this theory is that shear stresses can be obtained directly from the relationships constitute, while respecting the boundary conditions at the free surface level of the beam. Therefore, this theory avoids the use of shear correction coefficients. The differential equilibrium equations are obtained using the principle of virtual works. A thick isotropic beam is considered, whose numerical study to show the effectiveness of this theory.