• Journal of the Korean Solar Energy Society
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• v.25 no.2
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• pp.53-62
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• 2005

In this study, the thermal performance of multi-story double-skin facade(DSF) with variation of cavity height is evaluated to offer useful data in determining cavity height of multi-story DSF. For this, thermal criteria for multi-story DSF is adopted and a DSF model for evaluation of the thermal performance is established. Through the evaluation of CFD simulation, the recommended height of multi-story DSF is 5 stories or less to improve the thermal performance during the intermediate season.

• Tribology and Lubricants
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• v.16 no.4
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• pp.247-252
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• 2000

As the demand for higher areal recording densities requires a lower flying height of the slider, the variation of the flying height of the slider during drive operation becomes of great concern. The variation of the flying height is closely related with the slider design parameters such as air bearing shape, cavity depth, shallow step depth, crown, camber, pitch offset, roll offset, gram load, and so on. The objective of this work is to optimize the cavity depth and the shallow step depth, which are the control factors in air bearing design, using Robust Design method. It was found that the shallow step depth was statistically significant in affecting the variation of flying height, therefore the level of the shallow step depth should be chosen to minimize the variation of flying height.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2006.11a
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• pp.319-322
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• 2006

Rapid mixing of air-fuel (<1 ms) is needed to accomplish supersonic combustion. In this experiment, helium was injected laterally in to the Mach 1.92 air flow. 2 kinds of model, flat plate/cavity, were used in this experiment and images were taken by schlieren visualization. Pressure was affected by shock structure in the supersonic duct, and penetration height was increased by increasing J. Penetration height was higher in the cavity model than flat plate model.

• Journal of the Korean Geosynthetics Society
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• v.17 no.1
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• pp.55-64
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• 2018

The purpose of this study is to evaluate the suitability of emergency underground cavity restoration method filling cavity with expansive material based on numerical analysis. For the numerical analysis, experiments were conducted to evaluate properties of expansive material. Based on the measured expansion pressure of the expansive material from the experiment, behavior of underground cavity restoration with various cavity dimensions (variation of height and width of rectangular-shape cavity) was numerically assessed. As a result of analysis, the vertical displacements of the top and bottom of cavity were significantly influenced by the cavity width and lateral displacements of cavity sides were highly dependent on cavity height. These vertical and lateral displacements were increased with increasing expansion pressure of expansive material. Also, when the expansion pressure was applied, the vertical displacement of the upper surface layer of the road was less dependent on cavity height, and was greatly influenced by cavity width.

• The KSFM Journal of Fluid Machinery
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• v.16 no.6
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• pp.19-25
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• 2013

The effect of tip gap height on heat/mass transfer characteristics on the floor of cavity squealer tip has been investigated in a turbine cascade for power generation by employing the naphthalene sublimation technique. The squealer rim height is chosen to be an optimal one of $h_{st}/c$ = 5.51% for the tip gap height-to-chord ratios of h/c = 1.0, 2.0, 3.0 and 4.0%. The results show that heat transfer on the cavity floor is strongly dependent upon the behavior of the cavity flow falling down onto the floor. For lower h/c, the floor heat transfer is influenced by the tip leakage flow falling down along the inner face of the suction-side squealer, whereas the floor heat transfer for higher h/c is augmented mainly due to the impingement of leakage flow on the floor near the leading edge. Compared to the plane tip surface heat transfer, the cavity floor heat transfer is less influenced by h/c. For h/c = 1.0%, the average thermal load is as low as a half of the plane tip surface one, and the difference in the thermal load between the two cases tends to decrease with increasing h/c.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.9 no.6
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• pp.630-636
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• 2016

In this paper, a novel triple-mode cavity structure, designed for compactness and operating at 850 MHz, is analyzed. A cylindrical dielectric resonator is loaded into a metallic cylindrical cavity. Previous study has been focused on the analysis of the cylindrical dielectric resonator, but in this paper, the effect of the cylindrical metallic cavity has been analyzed. Enclosing the dielectric resonator inside the metallic cavity increases the resonant frequency of the dielectric resonator; however, this increases the quality factor and introduces the possibility of installing coupling screws. The principle of generation of triple-mode was investigated by parametric analysis. The generated triple-mode is TE011 mode and two orthogonally generated HEM121 modes. By adjusting the radius of the dielectric resonator, the height of the dielectric resonator, or the radius of the cylindrical metallic cavity, three modes could be coincided. However, the height of the metallic cavity keeps three modes separated. The mode characteristics of the proposed cavity are analyzed using a full-wave electromagnetic (EM) simulation. The proposed triple-mode cavity could be developed to triple-mode filter using a coupling screw, and the commercial application for the miniaturized filter below 1 GHz could be expected.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.25 no.3
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• pp.182-188
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• 2016

This study investigates cavity flows through a guide grill above a resonator. Vortex distributions and intake flows are simulated for various shapes of the guide grill. The flows are assumed to be compressible, unsteady, and turbulent. Numerical simulations are conducted using a large eddy simulation (LES) model. To analyze the effect of the guide grill shape, three cavity lengths (0.2H, 0.6H, and 1.0H) and cavity angles ($30^{\circ}$, $45^{\circ}$ and $60^{\circ}$) are considered based on resonator height (H). The results show that the vortex generated in the resonator by cavity flow increases with cavity length. Thus, the intake flow is minimum at the smallest cavity length and angle. However, when cavity length is equal to resonator height, the intake flow decreases. The maximum intake flow occurs at a cavity angle $45^{\circ}$ at higher cavity lengths owing to the interaction between the vortex in the resonator and intake flow.

• Geomechanics and Engineering
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• v.37 no.2
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• pp.97-107
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• 2024

The accurate prediction of grouting upward diffusion height is crucial for estimating the bearing capacity of tip-grouted piles. Borehole construction during the installation of bored piles induces soil unloading, resulting in both radial stress loss in the surrounding soil and an impact on grouting fluid diffusion. In this study, a modified model is developed for predicting grout diffusion height. This model incorporates the classical rheological equation of power-law cement grout and the cavity reverse expansion model to account for different degrees of unloading. A series of single-pile tip grouting and static load tests are conducted with varying initial grouting pressures. The test results demonstrate a significant effect of vertical grout diffusion on improving pile lateral friction resistance and bearing capacity. Increasing the grouting pressure leads to an increase in the vertical height of the grout. A comparison between the predicted values using the proposed model and the actual measured results reveals a model error ranging from -12.3% to 8.0%. Parametric analysis shows that grout diffusion height increases with an increase in the degree of unloading, with a more pronounced effect observed at higher grouting pressures. Two case studies are presented to verify the applicability of the proposed model. Field measurements of grout diffusion height correspond to unloading ratios of 0.68 and 0.71, respectively, as predicted by the model. Neglecting the unloading effect would result in a conservative estimate.

• International Journal of Naval Architecture and Ocean Engineering
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• v.12 no.1
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• pp.799-809
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• 2020

In this study, the supercavitating flow of a high-velocity moving body near air-water surface is calculated and analyzed based on a commercial CFD software ANSYS Fluent. The effect of regular wave parameters including both wave height and wavelength on the cavitating flow and force characteristics of a body at different velocities is investigated. It is found that the cavity shape, lift coefficient and drag coefficient of the body vary periodically with wave fluctuation, and the variation period is basically consistent with wave period. When the wavelength is much greater than the cavity length, the effect of wave on supercavitation is the alternating effect of axial compression and radial compression. However, when the wavelength varies around the cavity length, the cavity often crosses two adjacent troughs and is compressed periodically by the two wave troughs. With the variation of wavelength, the average area of cavity shows a different trend with the change of wave height.

• Journal of the Korean Geosynthetics Society
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• v.17 no.1
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• pp.45-54
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• 2018

In this study, numerical analysis is performed to determine highly influential factors that increase the possibility of asphalt road collapse due to cavity underneath the road. The considered influence factors on road collapse due to underground cavity were the asphalt layer thickness, the cover depth, the cavity width, and the cavity height. The concentrated load and uniform distributed pressure were applied on the top surface of asphalt pavement layers with different shape of cavity and asphalt thickness. For each analysis case of given cavity and asphalt thickness, failure load was analyzed under displacement controlled condition. Based on the analyzed failure loads, the applicability of the cavity management system developed by Seoul city was evaluated. As a result of the analysis, the effect of cavity height on road collapse was not significant while the other factors considerably influenced road collapse. Consequently, degree of road collapse susceptibility should be classified by failure load rather than by the condition of existing cavity.