• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2005년도 제24회 춘계학술대회논문집
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• pp.386-393
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• 2005

The objective of the present study is to develop a new type of the Ballistic range, called 'two-stage light gas gun'. A computational work has been performed to investigate the aerodynamics of a projectile which is launched from the two-stage light gas gun. A moving coordinate method for a multi-domain technique is employed to simulate unsteady projectile flows with a moving boundary. The effect of a virtual mass is added to the axisymmetric unsteady Euler equation systems. The computed results reasonably capture the major flow characteristics which are generated in launching the projectile supersonically, such as the interaction between the shock wave and the blast wave, the interaction between the vortical flow and the barrel shock, and the steady under-expanded jet. The present computational results properly predict the velocity, acceleration, and drag histories of the projectile.

• 대한기계학회논문집A
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• 제24권2호
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• pp.421-430
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• 2000

We apply the Rayleigh Ritz method to analyze multi-layered plates with residual stresses. The method is very simple, straight forward, and easily programmable, but it should be applied to structure s only in simple shapes. We derive coupled variational equations based on the principle of virtual displacement, and investigate what kind of basis functions is desirable for the analysis of rectangular plates with various boundary conditions. We demonstrate the effectiveness and usefulness of the method through several examples. The analysis results obtained with the method are in good agreement with those available in literature. A multi-layered MEMS plate example shows that the coupling effect should not be ignored and that residual stresses do influence the stiffness of the structure very much.

• 한국멀티미디어학회논문지
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• 제10권12호
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• pp.1591-1600
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• 2007

Camera position information from 2D face image is very important for that make the virtual 3D face model synchronize to the real face at view point, and it is also very important for any other uses such as: human computer interface (face mouth), automatic camera control etc. We present an algorithm to detect human face region and mouth, based on special color features of face and mouth in $YC_bC_r$ color space. The algorithm constructs a mouth feature image based on $C_b\;and\;C_r$ values, and use pattern method to detect the mouth position. And then we use the geometrical relationship between mouth position information and face side boundary information to determine the camera position. Experimental results demonstrate the validity of the proposed algorithm and the Correct Determination Rate is accredited for applying it into practice.

• Advances in aircraft and spacecraft science
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• 제2권1호
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• pp.77-94
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• 2015

The paper focuses on the integration of a non-linear one-dimensional model of Synthetic Jet (SJ) actuator in a well-assessed numerical simulation method for turbulent compressible flows. The computational approach is intended to the implementation of a numerical tool suited for flow control simulations with affordable CPU resources. A strong compromise is sought between the use of boundary conditions or zero-dimensional models and the full simulation of the actuator cavity, in view of long-term simulation with multiple synthetic jet actuators. The model is integrated in a multi-domain numerical procedure where the controlled flow field is simulated by a standard CFD method for compressible RANS equations, while flow inside the actuator is reduced to a one-dimensional duct flow with a moving piston. The non-linear matching between the two systems, which ensures conservation of the mass, momentum and energy is explained. The numerical method is successfully tested against three typical test cases: the jet in quiescent air, the SJ in cross flow and the flow control on the NACA0015 airfoil.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2006년도 제26회 춘계학술대회논문집
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• pp.371-375
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• 2006

Ballistic Range로부터 발사되는 발사체의 공기역학적 특성을 조사하기 위하여 축대칭 비정상 압축성 오일러 방정식에 이동경계법을 적용하여, 수치계산을 수행하였다. 그 결과, 발사체의 형상과 질량을 변화시켜 발사체의 순간속도, 가속도, 공기저항력을 조사한 결과, 발사 직후 발사체의 거동과 주위 유동장의 특성을 예측할 수 있었다.

• Steel and Composite Structures
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• 제19권4호
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• pp.829-841
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• 2015

In this paper, a refined exponential shear deformation beam theory is developed for bending analysis of functionally graded beams. The theory account for parabolic variation of transverse shear strain through the depth of the beam and satisfies the zero traction boundary conditions on the surfaces of the beam without using shear correction factors. Contrary to the others refined theories elaborated, where the stretching effect is neglected, in the current investigation this so-called "stretching effect" is taken into consideration. The material properties of the functionally graded beam are assumed to vary according to power law distribution of the volume fraction of the constituents. Based on the present shear deformation beam theory, the equilibrium equations are derived from the principle of virtual displacements. Analytical solutions for static are obtained. Numerical examples are presented to verify the accuracy of the present theory.

• Advances in aircraft and spacecraft science
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• 제7권1호
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• pp.19-40
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• 2020

In the present study, a fifth-order shear and normal deformation theory using a polynomial function in the displacement field is developed and employed for the static analysis of laminated composite and sandwich simply supported spherical shells subjected to sinusoidal load. The significant feature of the present theory is that it considers the effect of transverse normal strain in the displacement field which is eliminated in classical, first-order and many higher-order shell theories, while predicting the bending behavior of the shell. The present theory satisfies the zero transverse shear stress conditions at the top and bottom surfaces of the shell. The governing equations and boundary conditions are derived using the principle of virtual work. To solve the governing equations, the Navier solution procedure is employed. The obtained results are compared with Reddy's and Mindlin's theory for the validation of the present theory.

• 대한조선학회 특별논문집
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• 대한조선학회 2013년도 특별논문집
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• pp.85-89
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• 2013

In the engine room and the aft body, there are so many fluid tanks such as fresh water tank and oil tank. The vibration analysis for the fluid tank structures has to consider the added mass effect due to the fluid. However, it is known that the result of the fluid tank has the difference according to the boundary condition of the fluid field such as infinite fluid and finite fluid. In this paper, a numerical case study is carried out for the research about the vibration characteristics of the fluid tank with various fluid field. In addition, an experimental study is carried out to verify the validity of the vibration analysis for the fluid tank structure.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 1997년도 춘계학술대회논문집
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• pp.50-54
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• 1997

An expert drawbead model is developed to model a cranky drawbead in the finite element analysis of stamping processes. The expert model calculates the drawbead restraining forces (DBRF's) and bead-exit thinning, which are boundary conditions. DBRF's are calculated by considering bending force, unbending force, and friction force in order. Bead-exit thinning are due to the bending and tension during the deformation. The DBFR's and thinning computed form the mathematical model for the basic beads are compared with measurements and correction factors compensating for the differences are found using the multiple linear regression method. The composition beads are assumed to be a combination of basic beads so that the DBRF's and bead-exit thinning are computed to the sum of those of basic beads.

• 천문학회지
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• 제46권2호
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• pp.93-96
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• 2013

Modified Newtonian Dynamics (MOND) is a possible solution for the missing mass problem in galactic dynamics; its predictions are in good agreement with observations in the limit of weak accelerations. However, MOND does not derive from a physical mechanism and does not make predictions on the transitional regime from Newtonian to modified dynamics; rather, empirical transition functions have to be constructed from the boundary conditions and comparisons with observations. I compare the formalism of classical MOND to the scaling law derived from a toy model of gravity based on virtual massive gravitons (the "graviton picture") which I proposed recently. I conclude that MOND naturally derives from the "graviton picture" at least for the case of non-relativistic, highly symmetric dynamical systems. This suggests that-to first order-the "graviton picture" indeed provides a valid candidate for the physical mechanism behind MOND and gravity on galactic scales in general.