• Solar Energy
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• v.15 no.3
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• pp.39-52
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• 1995

This study is investigated numerically on the heat transfer characteristics of surface radiation-natural convection interactions in a two dimensional enclosure assumed Ondol cavity. Mean Nusselt number of the bottom surface with surface radiation is increased by increasing wall emissivity and by decreasing dimensionless thickness of adiabatic wall. and is greater than that without radiation. Mean Nusselt number of the bottom surface for convection only with surface radiation is slightly smaller than that without surface radiation with decrease dimensionless thickness of adiabatic wall.

• The Journal of the Acoustical Society of Korea
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• v.28 no.1E
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• pp.9-15
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• 2009

In this paper, FSTL (Field Sound Transmission Loss) measured in a mock-up simulating ship cabins is studied. A mock-up is built by using 6 mm steel plate, and two identical cabins are made where 25 mm or 50 mm sandwich panel is used to construct wall and ceiling inside the steel structure. Various wall panels and ceilings are tested, where effects of wall and ceiling panel thickness, and presence of a unit toilet on FSTL are investigated. It is found that the effect of unit toilet on FSTL is at most 1 dB. From the comparison of FSTL for panels of the same thickness of 50 mm, it is observed that panel having inside air cavity of 10 mm shows higher STL than that of the panel without air cavity. Comparison of FSTL for panels of 50 mm and 25 mm thickness shows that dependency on surface density predicted by mass law is not observed. The sandwich panels act as a mass-spring system, which shows a resonant mode that cannot be explained by the mass law. It is also found that STL from laboratory test is higher than FSTL by 5- 10 dB, which can be explained by flanking structure-borne noise transmission path such as ceiling, floor and corridor-facing wall.

• Proceedings of the KACD Conference
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• 2002.11a
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• pp.669-669
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• 2002

No Abstract, See Full Text

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2005.11a
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• pp.64-71
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• 2005

To achieve efficient supersonic combustion within a manageable length, a successful fuel injection scheme must provide rapid mixing between fuel and airstream. In former days, various injection concepts have been investigated. Cavity flow is the open type, that is, length-to-depth ratio L/D=4.8, aft ramp angle is $22.5^{\circ}$. An experimental study on a transverse cross jet injection into a Mach 1.92 supersonic main stream which flows over a cavity was carried out to investigate the effect of the momentum flux ratio(J), the jet interaction characteristics, and the pressure distribution in the combustor and using the primary diagnostics : schlieren visualization and wall static pressure measurements. Fuel penetration height and jet interaction characteristics depend strongly on the momentum flux ratio.

• Journal of the Korean Society of Propulsion Engineers
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• v.5 no.3
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• pp.25-32
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• 2001

A passive control method of the interaction between a weak normal shock-wave and a turbulent boundary-layer was simulated using two-dimensional Navier-Stokes computations. The inflow Mach number just upstream of the normal shock wave was 1.33. A porous plate wall having a cavity underneath was used to control the shock-wave/turbulent boundary-layer interaction. The flows through the porous holes and inside the cavity were investigated to get a better understanding of the flow physics involved in this kind of passive control method. The present computations were validated by some recent wind tunnel tests. The results showed that downstream of the rear leg of the $\lambda$-shock wave the main stream inflows into the cavity, but upstream of the rear leg of the $\lambda$-shock wave the flow proceeds from the cavity toward to the main stream. The flow through the porous holes did not choke fur the present shock/boundary layer interaction.

• The Bulletin of The Korean Astronomical Society
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• v.44 no.2
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• pp.48.1-48.1
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• 2019

We found a diffuse Hα feature with a large size of ~2' around a Herbig star, MWC 1080. It shows a strong correlation with the elongated outflow cavity centered on the star. To investigate the diffuse Hα source and the molecular cavity in detail, we carried out the high-resolution NIR spectroscopy using IGRINS. We detected six hydrogen Brackett line series, seven H2 lines, and an [Fe II] forbidden line. With the obtained spatial, kinematic, and line ratio results, we discuss the characteristics of the central MWC 1080A, the NE outflow cavity, and the SE molecular cloud regions separately. Most of the bright Brγ sources around MWC 1080A were found to be reflection nebulae, but a point-like Brγ source close to another young star, MWC 1080E, was identified as a distinct source due to MWC 1080E itself. The narrow components of the H2 lines observed around MWC 1080A were found to trace PDRs located on the wall of the main outflow cavity. Based on the shock-excited H2 and [Fe II] lines detected just inside a bow-shock shape Hα feature, we suggest that it represents the actual shock at the head of the NE outflow from MWC 1080A. Also, we newly detected the shock-excited H2 and [Fe II] lines with highly blueshifted velocities in the SE molecular cloud region. They could be related to unrevealed outflows from other young stars existing around MWC 1080A.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.22 no.3
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• pp.472-479
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• 2013

We carried out research into an environmentally friendly injection molding process that involves filling the mold with polymer after thin films are fixed into the cavity, without the coating, plating process. Film insert injection molding is a new technique in which molten plastic resin is injected into the cavity after films are precisely attached to the side of the mold wall. In the film insert injection molding process, the insert film is moved by the flow of the molten plastic resin. Overlap defects cause a decline in the productivity and the quality of the manufactured goods. To reduce overlap defects, new injection mold parts are proposed to produce automotive exterior parts using thin films. It is suggested that the best possible method would be to fix the thin films to one side of the mold wall, and develop interior pins to fix the films in the mold. Based on this new pin fixing system, the problem of the film being moved by the flow of the molten resin was improved.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.20 no.12
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• pp.4036-4043
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• 1996

When a high-speed railway train enters a tunnel, a compression wave is generated ahead of the train and propagates along the tunnel, compressing and accelerating the rest air in front of the wave. At the exit of the tunnel, an impulsive wave is emitted outward toward the surrounding, which causes a positive impulsive noise like a kind of sonic boom produced by a supersonic aircraft. With the advent of high-speed train, such an impulsive noise can be large enough to cause the noise problem, unless some attempts are made to alleviate its pressure levels. In the purpose of the impulsive noise reduction, the present study tested the effect of porous walls on the compression wave propagating into a model tunnel. Experimental results were obtained using a shock tube with an open end. The results showed that the cavity/porous wall is very effective for the compression wave with a large nonlinear effect. The porosity of 30% is most effective for attenuation and pressure gradient reduction of the compression wave front. Also the impulsive noise reduction increases with increasing the length and height of the cavity, compared with the tunnel equivalent diameter.

• The KSFM Journal of Fluid Machinery
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• v.7 no.6 s.27
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• pp.45-54
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• 2004

Governing equations and numerical solution methods are derived for the analysis of a combination-type-staggered-labyrinth seal used in high performance steam turbines. A bulk flow is assumed for each combination-type-staggered-labyrinth cavity. Axial flow through a throttling labyrinth strip is determined by Neumann's leakage equation and circumferential flow is assumed to be completely turbulent in the labyrinth cavity. Moody's wall-friction-factor formula is used for the calculation of wall shear stresses. For the reaction force developed by the seal, linearized zeroth-order and first-order perturbation equations are developed for small motion near the centered position. Integration of the resultant first-order pressure distribution along and around the seal defines the rotordynamic coefficients of the combination-type-staggered-labyrinth seal. Theoretical results of leakage and rotordynamic characteristics for the IP4-stage seal of USC (ultra super critical) steam turbine are shown with the effect of sump pressure, the number of throttling labyrinth strip, and rotor speed.

• Restorative Dentistry and Endodontics
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• v.26 no.1
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• pp.64-76
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• 2001

Despite the improvements in bond strengths of dentin adhesives and resin-modified glass ionomers, the marginal seal of cervical restorations remains a concern. Microleakage at poorly sealed margins can result in staining, post-operative sensitivity, pulpal irritation, and recurrent caries. The objective of this study was to evaluate the effect of surface penetrating sealant(SPS) on the microleakage of cervical restorations. 45 extracted human teeth were selected, and Class V preparations were prepared on the both buccal and lingual surface of the teeth to the following dimensions : 1.5mm axially, 3mm mesiodistally, and 3mm incisogingivally. After cervical restoration with composite resin, compomer, glass ionomer each restoration was treated as three methods: No Tx., Scotchbond Multipurpose Adhesive$^{\circledR}$, Fortify$^{\circledR}$. The sections were examined with a stereomicroscope to determine the extent of microleakage at enamel and dentin margins. The results of this study were as follows. 1. All groups showed some microleakage. 2. Gingival cavity wall with cementum margin showed significantly higher leakage value than occlusal cavity wall with enamel margin. 3. The group treated with SPS showed significantly lower leakage value than no treated group(p<0.05). But there is no difference between Fortify$^{\circledR}$ and Scotchbond Multipurpose adhesive$^{\circledR}$. The results of this study suggest that SPS are effective in reducing microleakage of class V restorations. But it is certain that some microleakage still occurred despite the application of SPS.