• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2004.03a
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• pp.734-741
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• 2004

Boundary layer ingestion in airframe-integrated scramjet engines causes engine stall (“engine un start” hereafter) and restricts engine performance. To improve the unstart characteristics in engines, boundary layer bleed and a two-staged injection of fuel were examined in Mach 4 and Mach 6 engine tests. A boundary layer bleed system consisting of a porous plate, an air coolers, a metering orifice and an ON/OFF valve, was designed for each of the engines. First, a method to determine bleed rate requirements was developed. Porous plates were designed to suck air out of the Mach 4 engine at a rate of 200 g/s and out of the Mach 6 engine at a rate of 30 g/s. Air coolers were then optimized based on the bleed airflow rates. The exhaust air temperature could be cooled below 600 K in the porous plates and the compact air coolers. The Mach 4 engine tests showed that a small bleed rate of 3% doubled the engine operating range and thrust. With the assistance of two-staged fuel injection of H2, the engine operating range was extended to Ф0.95 and the maximum thrust was tripled to 2560 N. The Mach 6 tests showed that a bleed of 30 g/s (0.6% of captured air in the engine) extended the start limit from Ф0.48 to Ф1 to deliver a maximum thrust of 2460 N.

• Structural Engineering and Mechanics
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• v.8 no.4
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• pp.383-399
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• 1999

In some space truss applications, particularly those with large spans, the choice of a triple-layer system might prove more cast effective than the more commonly used double-layer solution. However, there are currently no clear guidelines as to which system would be more competitive for intermediate span lengths. In this paper, comparisons in terms of the weight, stiffness and number of joints and members are made between the two system types and presented in order to simplify the choice process for the designer. The comparisons are carried out using an approximate analysis technique that is explained in this paper, and checked to be reasonably accurate and suitable for the preliminary design of space trusses.

• Structural Engineering and Mechanics
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• v.9 no.3
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• pp.289-304
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• 2000

This study discusses on the experimental and analytical results of the global buckling tests, carried out on aluminum alloy double layer space grids composed of tubular members, ball joints and connecting bolts at the member ends, with the purpose of demonstrating the effectiveness of a simplified analysis method using an equivalent slenderness ratio for the members. Because very few experiments have been carried out on this type of aluminum space grids, the buckling behavior is investigated experimentally over the post buckling regions using several space grid specimen with various values for the member slenderness ratio. The observed behavior duping the experiments is compared with the analytically obtained results. The comparison is made based on two different schemes; one on the plastic hinge method considering a bending moment-axial force interaction for members and the other on a method using an equivalent slenderness ratio. It is confirmed that the equivalent slenderness method can be effectively applied, even in the post buckling regions, once the effects of the rotational rigidity at the ball joints are appropriately evaluated, because the rigidity controls the buckling behavior. The effectiveness of the equivalent slenderness method will be widely utilized for estimation of the ultimate strength, even in post buckling regions for large span aluminum space grids composed of an extreme large number of nodes and members.

• Bulletin of the Korean Space Science Society
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• 2004.04a
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• pp.69-69
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• 2004

The scale of photospheric convection in red giants is generally associated, by analogy with the Sun, with the atmospheric pressure scale height and the thickness of the superadiabatic transition layer(SAL). As pointed out by Schwarzschild(1975), both of these quantities are relatively much larger in terms of the stellar radius in a red giant then in the Sun. (omitted)

• Earthquakes and Structures
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• v.9 no.4
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• pp.753-766
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• 2015

An investigation has been carried out for the propagation of torsional surface waves in an inhomogeneous prestressed layer over an inhomogeneous half space when the upper boundary plane is assumed to be rigid. The inhomogeneity in density, initial stress (tensile and compressional) and rigidity are taken as an arbitrary function of depth, where as for the elastic half space, the inhomogeneity in density and rigidity is hyperbolic function of depth. In the absence of heterogeneities of medium, the results obtained are in agreement with the same results obtained by other relevant researchers. Numerically, it is observed that the velocity of torsional wave changes remarkably with the presence of inhomogeneity parameter of the layer. Curves are compared with the corresponding curve of standard classical elastic case. The results may be useful to understand the nature of seismic wave propagation in geophysical applications.

• Structural Engineering and Mechanics
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• v.69 no.2
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• pp.121-129
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• 2019

The present study investigates the propagation of shear waves in a composite structure comprised of imperfectly bonded piezoelectric layer with a micropolar half space. Piezoelectric layer is considered to be initially stressed. Micropolar theory of elasticity has been employed which is most suitable to explain the size effects on small length scale. The general dispersion equations for the existence of waves in the coupled structure are obtained analytically in the closed form. Some particular cases have been discussed and in one particular case the dispersion relation is in well agreement to the classical-Love wave equation. The effects of various parameters viz. initial stress, interfacial imperfection and micropolarity on the phase velocity are obtained for electrically open and mechanically free system. Numerical computations are carried out and results are depicted graphically to illustrate the utility of the problem. The phase velocity of the shear waves is found to be influenced by initial stress, interface imperfection and the presence of micropolarity in the elastic half space. The theoretical results obtained are useful for the design of high performance surface acoustic devices.

• International Journal of Aeronautical and Space Sciences
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• v.16 no.3
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• pp.325-338
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• 2015

Experimental and numerical investigations were conducted to identify the wake characteristics downstream of two vane-type vortex generators over laminar flat plate boundary layer. Experimental study was carried out by using the stereoscopic particle image velocimetry. To describe the flow field around the vortex generator in detail, numerical study was performed. We considered two different planform shapes of vortex generator: triangular and rectangular shape. The height of the generator was chosen to be about the boundary layer thickness at the position of its installation. Two different lengths of the generator were chosen: two and five times the height. Wake measurements were carried out at three angles of attack for each configuration. Wake characteristics for each case such as overall vortical structure, vorticity distribution, and location of vortex center with downstream distance were obtained from the PIV data. Wake characteristics, as expected, were found to vary strongly with the geometry and angle of attack so that no general tendency could be deduced. Causes of this irregular tendency were explained by using the results of the numerical simulation.

• Journal of the Korean Society for Precision Engineering
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• v.19 no.5
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• pp.81-88
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• 2002

An interface crack of a piezoelectric medium bonded between an elastic layer and a half-space is analyzed using the theory of linear piezoelectricity. Both out-of-plane mechanical and in-plane electrical loads are applied to the piezoelectric laminate. By the use of courier transforms, the mixed boundary value problem is reduced to a singular integral equation which is solved numerically to determine the stress intensity factors. Numerical analyses for various material combinations are performed and the results are discussed.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.8
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• pp.2110-2121
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• 1993

A numerical investigation has been carried out for the flow characteristics after exchange of some filters from the original layer to the new low pressure loss layer with equal filtering efficiency. The solution domain includes upper plenum, filter layer, clean space, access panels, and lower plenum. The concept of the distributed pressure resistance was applied to describe the momentum loss in filter layer and access panels. The evolution of the flow field is simulated using the low Reynolds number k-.epsilon. over bar turbulent model and SIMPLE algorithm based on the finite volume method. As a result, after the exchange of filter layer the power requirement can be reduced by 8-9 percent. The results also demonstrate that the perpendicularity of the flow near access panels may become worse at new filter layer than origianl filter layer. But the situation can be recovered by adjusting the jopening ratio of access panels.

• Korean Institute of Interior Design Journal
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• v.17 no.3
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• pp.59-67
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• 2008

This study aims to find out the characteristics and the type classification of contemporary public libraries in terms of browsing circuit. In so doing, it is to analyze 21 recently built libraries by using the browsing circuit, the spatial depth and the spatial layout. The study makes use of codes derived from the concept of 'Classification' and 'Frame' suggested by a pedagogist, Basil Bernstein. As a result, it shows that two codes are phased in overseas cases. In other words, one type is a lower depth of space and a high rate of rings with the multi-layer circuits and the three-dimensional circuit of multi-centered. the other type is the higher depth of space and a low rate of rings with the single-layer circuit and the multi-layer circuit of single-centered. In domestic cases, 4 types are shown. The characteristics of layout are seen as a radial shape and the rate of rings is lower than the overseas cases. It can be said that these results are a transitional phenomenon. For browsing circuit, domestic public libraries would be adapted to the three-dimensional circuit of multi-centered, a lower depth of space and a high rate of rings. By instructions of this plan, the real meaning of a public library will be come true.