• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.5
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• pp.9-17
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• 2005

In the early stage of helicopter design, an optimal configuration is usually determined after a numerous parametric study about the aerodynamic performance due to geometric variation. In order to improve the aerodynamic performance of a shrouded tail rotor, optimization of the tip clearance gap between blade and shroud, the blade planform shape, and the arrangement of blade spacing is required. In the present study, the aerodynamic performance characteristics of a shrouded tail rotor due to geometric variation was investigated by using an inviscid compressible unstructured mesh flow solver for rotary wings.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.5
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• pp.1-9
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• 2003

Detailed flow of a shrouded tail rotor in hover is studied by using a compressible inviscid flow solver on unstructured meshes. The numerical method is based on a cell-centered finite-volume discretization and an implicit Gauss-Seidel time integration. Numerical simulation is made for a single blade attached to the center body and guide by the duct by imposing a periodic boundary condition between adjacent rotor blades. The results show that the performance of an isolated rotor without shroud compares well with experiment. In case of a shrouded rotor, correction of the collective pitch angle is made such that the overall performance matches with experiment to account for the uncertainties of the experimental model configuration. Details of the flow field compare well with the experiment confirming the validity of the present method.

• Journal of Aerospace System Engineering
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• v.16 no.4
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• pp.1-9
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• 2022

A design factor analysis was conducted to reduce the thrust reduction in the off-design, due to the driving of the aerospike pintle nozzle. The close (NPR 100) as well as the open (NPR 11) stroke were fixed, as under-expansion conditions. The pintle contour, pintle head radius (R), cowl angle (θ), and cowl exit length (L) were selected as design factors. The change in thrust was analyzed, using a verified numerical analysis technique. First, the pintle head radius and the length of the cowl exit had little influence on the thrust. The cowl angle changed the mass flow rate by affecting the effective nozzle throat area, and created a reverse pressure gradient at the cowl exit. As a result of applying the dual aerospike contour, it was confirmed that the thrust in the design-off increased by approximately 1.2%, compared to the reference case and by approximately 3.4% compared to the worst case.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 1996.11a
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• pp.147-153
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• 1996

발사관의 밀폐 및 분리성능을 위해 앞, 뒤 덮개의 재질을 내열성이 높고, 수분흡수성이 낮은 Noryl Plastic 재질로 선정하여 기계적 물성을 확인하였으며 덮개의 형상설계를 하였다. 유한요소 구조해석을 수행하여 분포하중 및 집중하중에 의한 응력상태를 고찰하고 분리성능을 검증하기 위해 공압 및 유도탄 충돌시험을 수행하였다. 이상의 과정를 통하여 개발된 덮개는 여러 가지 체계요구조건을 만족시켜 주는 것을 알 수 있다.

• Journal of Korean Society of Steel Construction
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• v.12 no.2 s.45
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• pp.111-122
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• 2000

In this study, A series of fatigue tests have been performed on the fillet welded joints of cover plates in steel plate girders in order to quantitatively assess the fatigue characteristics according to the shapes of cover plates. From the results of fatigue tests, it has been shown that the fatigue strengths were slightly different according to their shapes, but satisfied the fatigue design curves in Korea and other countries. Also, from the results of beachmark tests, it has been confirmed that the points of fatigue crack initiation were closely related to the shapes of weld bead toes, and fatigue cracks simultaneously initiated from several points in weld bead toes have been grown as semi-elliptical surface cracks, and these cracks have been coalesced each other, and grown as through thickness cracks, and finally reached to fracture. Besides, from the results of fracture mechanics approaches, stress gradient factors were the most dominant factors among crack correction factors obtained from the existing equations and finite element analysis, and the fatigue life on fillet welded joints of cover plates could be estimated using the relations between fatigue crack growth rate and stress intensity factor range obtained from finite element analysis.

• Proceedings of the Korean Institute of Industrial Safety Conference
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• 2000.06a
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• pp.215-222
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• 2000

반복하중을 받는 대부분의 토목구조물은 정적하중보다 훨씬 낮은 하중에서 파괴가 발생하는 경우가 있는데 이러한 현상을 피로라고 하며, 특히 강교량을 구성하는 부재중에서 2차 부재에 해당되는 덮개판, 수평보강재, 수직보강재, 거셋트 등의 용접부에서는 여러 원인으로 인해서 피로손상이 발생하게 되어 결국에는 구조물의 성능에 크게 영향을 미치게 된다. (중략)

• Journal of the Korean Institute of Telematics and Electronics D
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• v.36D no.1
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• pp.90-99
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• 1999

In this work, we consider the effect of the presheath on the ion angular distribution. The recent shows the ion-neutral collision in the presheath and the calculated energy flux with the ion angular distribution at the presheath edge in plasma reactor. We also propose a new approximation analytical model for the ion angular distribution and the energy flux distribution with ion temperature. The ion passing the presheath region, Shows a ion scattering effect without ion-neutral collisions. This because the kinetic energy by the ambipolar diffusion field is changed by the gas collision,. Using the proposed approximation analytical model, we show the simulated results of a deposit profile on variable trench shape.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2017.05a
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• pp.664-671
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• 2017

This paper presents a numerical analysis of behaviors of rear closer of vertical launch system under rocket plume based on fluid structure interaction analysis. The rocket plume loading is modeled by fully Eulerian method and elasto-plastic behavior of rear cover is calculated by total Lagrangian method based on a 9-node planar element. The interface motion and boundary conditions are described by a hybrid particle level-set method within the ghost fluid framework. We compare the fluid flow pattern between different rear closer models which are elast-plastic and rigid deformation.

• Proceedings of the Korean Vacuum Society Conference
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• 2003.08a
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• pp.107-107
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• 2003

• Journal of Korean Society of Steel Construction
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• v.29 no.5
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• pp.389-400
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• 2017

Based on U-shaped composite beam, the new form of AU-composite beam were developed to create economical and efficient components reducing the cost and shortening the length of construction work. Because the U-shaped sections are open and needs to be fixed by topping concrete securely. Therefore, it is required to maintain the U-shaped sections in a structure and to work in the safe condition through construction. It also requires accessories that resist the horizontal shear force for synthesis between the top and bottom of the U-shaped section. To reinforce these shortcomings, a shear connector has been developed with various purposes of steel plate anchors. In this study, the steel plate anchors were directly tested and the shear force was evaluated by the horizontal shear force. The experiment was divided into two types, depending on the applicable deck plates. As a result of the experiment, the continuous type specimens showed greater resistance in both strength and displacement than the ones of stud anchor specimen. In discontinuous type case, due to shear simulations and simple element analysis, the less increase the ratio of width to height and the more shear strength decreased. Thus, the shear strength equation of the stud anchor was modified to suggest the new shear strength based on the testing results.