Helicopters that can respond rapidly to medical accidents are used frequently on sites that require firefighting and medical services. Therefore, Korea recommends that high-rise buildings install heliports for easy evacuation through an alteration to the Building Act. However, because heliport installation laws are inconsistent with the specifications of each heliport on high-rise buildings being different, helicopter landing in emergencies may be hindered. This may result in failure to respond to an accident. To minimize complications, the International Civil Aviation Organization (ICAO) and the Federal Aviation Administration (FAA) determine helicopter take-off and landing regulations as well as heliport operations. This method minimizes human error in pilots and allows for the maintenance of facilities, minimizing technical errors. Therefore, this study investigates the current status of domestic rooftop heliports and attempts to derive measures that improve domestic legislation through comparison with overseas standards to identify higher standards.
Purpose Complicated motion of vortex is frequently observed in the wake of islands. These kinds of swirling fluid cause the trap of sediments or pollutants, subsequently inducing the dead zone, odor or poor water quality. Therefore, the understanding of flow past a circular cylinder is significant in predicting water quality and positioning the immersed structures. This study aims to investigate the flow properties around a structure using Navier-slip boundary conditions. Design/methodology/approach Boundary conditions are a major factor affecting the flow pattern because the magnitude of flow detachment on a surface can redistribute the tangential stress on the wall. Therefore, the authors performed an analysis of laminar flow passing through a circular structure to investigate the effect of boundary conditions on the flow pattern. Findings The authors examined the relationship between the partial-slip boundary conditions and the flow behavior at low Reynolds number past a circular cylinder considering velocity and vorticity distributions behind the cylinder, lift coefficient and Strouhal number. The amplitude of lift coefficient by the partial slip condition had relatively small value compared with that of no-slip condition, as the wall shear stress acting on the cylinder became smaller by the velocity along the cylinder surface. The frequency of the asymmetrical vortex formation with partial slip velocity was increased compared with no-slip case due to the intrinsic inertial effect of Navier-slip condition. Originality/value The ability to engineer slip could have dramatic influences on flow, as the viscous dominated motion can lead to large pressure drops and large axial dispersion. By the slip length control, no-slip, partial-slip and free-slip boundary conditions are tunable, and the velocity distributions at the wall, vortex formation and wake pattern including the amplitude of lift coefficient and frequency were significantly affected by slip length parameter.
The optimal size of a diversion structure should be carefully studied to ensure economic viability and safety during construction. In practice, to determine the size of a diversion structure, design flood frequency is selected as the suggested return period presented by the design standard, which is presented differently. This study proposes a methodology for the design of a diversion structure with a concrete cofferdam adopting risk analysis to reflect the more practical hazard and risk of diversion structure during dam construction. The proposed methodology is based on a risk-based least-cost design process and risk analysis. The optimization result is presented as the lowest expected monetary value, which accounts for construction cost, reconstruction cost, and delay liquidated damage with the failure probability and recovery cost with the overflow probability. This methodology was applied to the case study of the Gulpur hydropower project in Pakistan. The results showed that the optimal design flood frequency is 1 year for a recovery cost of USD 0.5 mil. and 1~2 years for a recovery cost of USD 1.0~2.0 mil. with 3, 4, and 5 years of the usage period of the diversion structure. Furthermore, 2~10 years is the optimal value for a recovery cost of USD 3.0~4.0 mil. These results indicated that the optimal design flood frequency increases as the recovery cost and usage period of the diversion structure increase. The results of the study reveal that the recovery cost and the period of use of the diversion structure affect the design flood frequency of the diversion structure. From a design perspective, the period of use is determined by the construction period of the project or the construction method, whereas the recovery cost depends on the countermeasure method. Therefore, after preparing a proactive plan and estimating the recovery cost, the design flood frequency for the diversion structure should be determined.
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