• Computational Structural Engineering
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• v.10 no.2
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• pp.139-148
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• 1997

A finite element method is programmed to analyse the nonlinear behavior of axisymmetric structures. The lst order Mindlin shell theory which takes into account the transversal shear deformation is used to formulate a conical two node element with six degrees of freedom. To evade the shear locking phenomenon which arises in Mindlin type element when the effect of shear deformation tends to zero, the reduced integration of one point Gauss Quadrature at the center of element is employed. This method is the Updated Lagrangian formulation which refers the variables to the state of the most recent iteration. The solution is searched by Newton-Raphson iteration method. The tangent matrix of this method is obtained by a finite difference method by perturbating the degrees of freedom with small values. For the moment this program is limited to the analyses of non-linear elastic problems. For structures which could have elastic stability problem, the calculation is controled by displacement.

• Journal of Korean Society of Steel Construction
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• v.16 no.3 s.70
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• pp.345-353
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• 2004

One of the key issues in spatial structures with large spaces is how to carry the weight of the roof. This can be solved by the effective use of tension members. A cable dome structural system facilitates the construction of a large space structure. As external load increases, however, the cable dome structural system is put at risk due to global buckling. This study measures the shape of the Geiger and Flower-type cable dome by applying an initial stress. This unstable phenomenon is also examined using a perfectly shaped model and an imperfect model, which are both subjected to an axisymmetric load.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.2862-2867
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• 2007

The steady non-reacted compressible flow field in a symmetric micro-thruster, which is used for the accurate attitude control of a satellite, is analyzed varying the nozzle pressure ratio (NPR) to investigate the plume characteristics. The nozzle throat diameter is 0.06 inch and the area ratio is 56. The recirculation region is found just behind the normal shock at the several NPRs due to the locally adverse pressure gradient along the nozzle centerline when the environmental pressure is atmospheric. This phenomenon, the cause of flow loss, is similar to the flow behind a blunt body. As NPR increases the location of Mach disk, characteristics of the normal shock, moves downstream and its strength increases. The Mach number distribution appears in a wave-type patter after the normal shock because oblique shocks are reflected on the shock boundaries especially when NPRs are very high.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.11a
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• pp.867-868
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• 2011

Transient Analysis on heat transfer of rocket engine combustion chamber and wall temperature variation was carried out, especially, calculations of LOx/kerosene rocket engine with/without fuel film-cooling were conducted. Convective and radiative heat flux inside combustion chamber wall were calculated by the empirical equations for rocket engine combustion, and conduction of wall interior was calculated by numerical method with 2D axisymmetric grid. In this calculations the transient variations of wall temperature, the location changes of peak temperature and so on affected by film-cooling were analyzed.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.23 no.2
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• pp.235-243
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• 2010

Three-dimensional structural analysis system for nuclear containment building is presented in this paper. This system includes high-performance plate/shell elements as finite element library. It also adopts numerical modeling technique for unbonded tendon as well as bonded tendon in prestressed concrete structures. This system is constructed by connecting several in-house program to a commercial program DIANA, and then is capable of performing nonlinear analysis for ultimate pressure capacity of nuclear containment building. Finally, three-dimensional structural analysis of CANDU-type containment building is carried out in order to test the reliability of this system. These numerical results are compared with reference values, which obtained from axisymmetric structural analysis.

• Journal of the Korean Society of Propulsion Engineers
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• v.14 no.5
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• pp.1-7
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• 2010

Dual throat nozzle(DTN) is recently attracting much attention as a new concept of the thrust vectoring technique. This DTN is designed with two throats, an upstream minimum and a downstream minimum at the nozzle exit, with a cavity in between the upstream throat and exit. In the present study, a computational work has been carried out to analyze a fundamental performance of a dual throat nozzle(DTN) at various nozzle pressure ratios(NPR) and throat area ratios. Two-dimensional, axisymmetric, steady, compressible Navier-Stokes equations were solved using a fully implicit finite volume scheme. NPR was varied in the range of NPR from 2.0 to 10.0, at different throat area ratios. The present computational results were validated with some experimental data available. Based upon the present results, the performance of DTN is discussed in terms of the discharge coefficient and thrust efficiency.

• Journal of Energy Engineering
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• v.5 no.1
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• pp.19-27
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• 1996

Self-pressurization of cylindrical container of cryogen is numerically analyzed. The container is axi-symmetric and heated from side wall with constant heat flux. Natural convection by external heat flux is studied numerically using finite difference method. Oxygen, nytrogen and hydrogen are working fluids in this paper. Liquid is considered incompressible fluid and vapor is assumed to behave as gas meeting with virial equation of gas. The Second virial coefficients of gas are obtained from Lennard-jones model. The important variables which have effects on self-pressurization are external heat flux, heat capacity of wall and initial ullage in container. The most important variable of them is external heat flux. The pressure rise calculated from the virial gas model is slightly different from that calculated using Ideal gas model for oxygen.

• Proceedings of the KSME Conference
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• 2001.06a
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• pp.932-938
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• 2001

This study is concerned with the shape optimization of stem for the artificial hip prosthesis with unbonded cement mantle. The artificial hip prosthesis with unbonded cement mantle allows a stem to slip on cement mantle because of polished stem surface. Unbonded cement mantle type has several advantages compared with bonded cement mantle type, for example, small micro motion, preventing stress shielding and so on. In this study, 2-dimensional axisymmetric model was developed with considering characteristics of unbonded cement mantle. Moreover, optimal shape of stem was obtained by using feasible direction method. The objective of this optimization is maximizing supported vertical loading. The slip motion and stresses of stem, cement mantle and bone is used for constraints. The optimal shape which obtained by this study has slope of 0.15 in proximal part and maintains the width about 5mm in distal part In addition, simplified 3-dimensional analysis which applying optimal shape is carried out. The result of 3-dimensional analysis showed that optimal shape has some advantages for cement mantle stress. However, more realistic 3-dimensional analysis which including bending effect, complex geometries etc. is needed in further research.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2010.11a
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• pp.363-366
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• 2010

Among the many different types of wind tunnels, Ludwieg Tube(LT) is the most suitable facility for high Reynolds number testing. Depending on the location of diaphragm, there are two types of LTs. In the present study, a computational work has been carried out to compare the operation characteristics of upstream- and downstream-diaphragm LTs. Two-dimensional, axisymmetric, unsteady, compressible Navier-Stokes equations were solved using a fully implicit finite volume scheme. Based on the present results, the flow mechanism of the starting process was discussed in detail using wave diagrams and characteristics of starting time and working time were investigated.

• Journal of the Korean Society of Propulsion Engineers
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• v.5 no.3
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• pp.33-40
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• 2001

In order to investigate the operating characteristics of a supersonic steam ejector, the axisymmetric, compressible, Reynolds-averaged, Wavier-Stokes computations are performed using a finite volume method. The secondary and back pressures of the ejector system with a second throat are changed to investigate their effects on the suction mass flow. Three operation modes of the steam ejector system, the critical mode, subcritical mode and back flow mode, are discussed to predict the critical suction mass flow. The present computations are validated with some experimental results. The secondary and back pressures of the supersonic steam ejector significantly affect the critical suction mass flow. The present computations predict the experimented critical mass flow with fairly good accuracy A good correlation is obtained for the critical suction mass flow. The present results show that provided the primary nozzle configuration and secondary pressure are blown, we can predict the critical mass flow with good accuracy.