• The KSFM Journal of Fluid Machinery
• /
• v.10 no.5
• /
• pp.54-63
• /
• 2007

A barrel is a high length-to-diameter ratio cylinder that is influenced by environmental factors such as sunlight, precipitation, wind and clouds. Cross-barrel temperature differences caused by uneven heating or cooling lead to thermal deformation that degrades accuracy. Therefore, a barrel is covered by thermal shrouds to minimize the type of thermal deformation, "fall-of-shot". In this paper, an analytical and experimental study is presented to design the thermal shrouds for a gun barrel and to evaluate the thermal shroud effect. First, an analytical study on the thermal shroud effect to minimize thermal deformation of a gun barrel by sunlight and wind is performed. The coupled analysis of thermal fluid dynamics of the air flow between a barrel and thermal shrouds and thermal stresses of a barrel Is performed to clarify both the thermal shroud effect and the drift in gun muzzle orientation by thermal deformation. Second, experiments are carried out to test and evaluate the thermal shroud effect on the performance of a gun barrel. The drift in gun muzzle orientation against the solar radiation is confirmed by the experiments, and the results well agree with the analytical estimation. Third, three principal design factors that are presumed to have an effect on the performance of the thermal shrouds are also analyzed; sorts of shroud materials, wall-thickness of thermal shrouds, and distance of the gap between a barrel and thermal shrouds.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
• /
• 2003.05a
• /
• pp.157-164
• /
• 2003

Introduction of wave model, considered the effect of tide, wind and wave induced currents at the coastal waters of complex bathymetry, is a very important factor for most coastal engineering design and disaster protection problems. As the steady state spectral wave model could simulate depth induced wave shoaling and refraction, current induced refraction effect, steepness induced wave breaking, diffraction, wind wave growth, and wave-wave interaction that redistribute energy, this would support and compensate the gap in the real field of design where other wave models could not deal and cause wrong estimation. In this study, for that sense, we applied the spectral wave model t the large coastal waters near Gaduck Island where the Busan new port construction project is going on, for better understanding and analysis of wave transformation process. We also compared the simulation results with the calculated from the existing model. From such a trial of this study, we hope that broader and sager use of the spectral model in the area of port design and disaster prevention system come through in near future.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
• /
• v.27 no.8
• /
• pp.83-89
• /
• 2013

In this paper, discharge characteristics of air in the vertical arrangement of three rods(dome-shaped, cylinder-shaped, and needle-shaped rod) and plane gap having propane flame on the plane electrode are examined under the application of a.c. and d.c. high-voltages. As the result of the experiment, flashover voltages in the presence of the flame are substantially lowered than those in the absence of flame, and relative a.c. flashover voltages in the dome-shaped, cylinder-shaped, and needle-shaped rod gaps are found 32.5%, 32.1%, and 26.4% respectively. The polarity effects with the d.c. voltages are shown, and flashover voltages in negative polarity are much lowered than those in positive one. The negative flashover voltages in the dome-shaped and cylinder-shaped gaps are found 18.3% and 18.7% respectively, but the positive ones are found 53.5% and 43.2% respectively. In the needle-shaped rod gaps, meanwhile, the flame is extinguished by corona wind, and the quenching voltages are found 28.4% under the application of a.c. voltages. The ion winds of corona and the reduction of air density are the main factors of flashover reduction owing to the flame in the case of a.c. voltages, but the electrifications of the positive ion by thermal ionization besides the above factors are remarkably found in the case of d.c. voltages.

• Wind and Structures
• /
• v.23 no.2
• /
• pp.109-125
• /
• 2016

Flow interference is investigated between two tripped cylinders of identical diameter D at stagger angle ${\alpha}=0^{\circ}{\sim}180^{\circ}$ and gap spacing ratio $P^*$ (= P/D) = 0.1 ~ 5, where ${\alpha}$ is the angle between the freestream velocity and the line connecting the cylinder centers, and P is the gap width between the cylinders. Two tripwires, each of diameter 0.1D, were attached on each cylinder at azimuthal angle ${\beta}={\pm}30^{\circ}$, respectively. Time-mean drag coefficient ($C_D$) and fluctuating drag ($C_{Df}$) and lift ($C_{Lf}$) coefficients on the two tripped cylinders were measured and compared with those on plain cylinders. We also conducted surface pressure measurements to assimilate the fluid dynamics around the cylinders. $C_D$, $C_{Df}$ and $C_{Lf}$ all for the plain cylinders are strong function of ${\alpha}$ and $P^*$ due to strong mutual interference between the cylinders, connected to six interactions (Alam and Meyer 2011), namely boundary layer and cylinder, shear-layer/wake and cylinder, shear layer and shear layer, vortex and cylinder, vortex and shear layer, and vortex and vortex interactions. $C_D$, $C_{Df}$ and $C_{Lf}$ are very large for vortex and cylinder, vortex and shear layer, and vortex and vortex interactions, i.e., the interactions where vortex is involved. On the other hand, the interference as well as the strong interactions involving vortices is suppressed for the tripped cylinders, resulting in insignificant variations in $C_D$, $C_{Df}$ and $C_{Lf}$ with ${\alpha}$ and $P^*$. In most of the (${\alpha}$, $P^*$ ) region, the suppressions in $C_D$, $C_{Df}$ and $C_{Lf}$ are about 58%, 65% and 85%, respectively, with maximum suppressions 60%, 80% and 90%.

• Wind and Structures
• /
• v.28 no.5
• /
• pp.285-298
• /
• 2019

For super long-span bridges, the aerodynamic forces induced by the flow passing the box girder should be considered carefully. And the Reynolds number sensitively of aerodynamic characteristics is one of considerable issue. In the study, a numerical study on the Reynolds number sensitivity of aerodynamic characteristic (flow pattern, pressure distribution and aerodynamic forces) of a twin-box girder were carried out using large eddy simulation (LES) with the dynamic Smagorinsky-Lilly subgrid model. The results show that the aerodynamic characteristics have strong correlation with the Reynolds number. At the leading edge, the flow experiences attachment, departure, and reattachment stages accompanying by the laminar transition into turbulence, causing pressure plateaus to form on the surface, and the pressure plateaus gradually shrinks. Around the gap, attributing that the flow experiences stages of laminar cavity flow, the wake with alternate shedding vortices, and turbulent cavity flow in sequence with an increase in the Reynolds number, the pressures around the gap vary greatly with the Reynold number. At the trailing edge, the pressure gradually recovers as the flow transits to turbulence (the flow undergoes wake instability, shear layer transition-reattachment station), In addition, at relative high Reynolds numbers, the drag force almost does not change, however, the lift force coefficient gradually decreases with an increase in Reynolds number.

• Journal of Navigation and Port Research
• /
• v.29 no.7
• /
• pp.627-634
• /
• 2005

Gunsan-Janghang Harbor is located at the mouth of Gum River, on the central west coast of Korea The harbor and coastal boundaries are protected from the effects of the open ocean by natural coastal islands and shoals due to depositions from the river, and two breakwaters. The navigation channel commences at the gap formed by the outer breakwater and extends through a bay via a long channel formed by an isolated jetty. For better understanding and analysis of wave transformation process where a wide coastline changes appear due to on-going reclamation works, we applied the spectral wave model including wind effect to the related site, together with the energy balance models. This paper summarizes comparisons of coastal responses predicted by several numerical wave predictions obtained at the coastal waters near Gunsan-Janghang Harbor. Field and numerical model investigations were initially conducted for the original navigation channel management project. We hope to contribute from this study that coastal engineers are able to use safety the numerical models in the area of port and navigational channel design.

• Proceedings of the KSR Conference
• /
• 2011.05a
• /
• pp.613-618
• /
• 2011

More than 7 million persons use Seoul Metropolitan Subways (SMS) everyday and the number has been in increasing trend. With the increasing trend of concerns on indoor air quality(IAQ), the management of IAQ has become an important issue, especially in case of subway operators, because most of subway lines are placed underground with poor ventilation condition. The ultimate object of study develop independent cleaning device that reduce efficient fine particle and $CO_2$. Urban subway has characteristics about proper clean air flow, must be installed in narrow space and maintenance cycle has enough time. Two layered electrically pre-charged filters were used for removing particulate matters and gas absorbers are packed between two layer filters for removing gases pollutants such $CO_2$, VOCs and HCHO. Urban subway has characteristics about proper clean air flow, must be installed in narrow space and maintenance cycle has enough time. SCAP prototype is producted as all in one method which decrease fine dust, $CO_2$ and noxious gas. and basic test carry out with quantity of wind, a gap of pressure, sampling efficiency.

• Fire Science and Engineering
• /
• v.17 no.2
• /
• pp.25-34
• /
• 2003

In this paper, characteristics of the DC flashover voltage in the horizontal air gap of sphere-sphere/needle-needle electrode system were investigated when the combustion flame of paraffin oil was present between the two electrodes. The reduction characteristic of DC flashover voltage was discussed with the thermal ionization process, the relative air density and the deflection phenomena in the shape of flames that caused by the corona wind and Coulomb's force. As the results of an experimental investigation, It was found that the reduction characteristics of DC flashover voltages with flames were affected strongly by the flame deflection and the change of relative air density. It was also found that the thermal ionization phenomena were not important in the range of combustion flame temperature.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.12 no.4
• /
• pp.11-22
• /
• 1992

It this study, the aerodynamic responses of circular cylinder behind a pair of circular cylinders arranged side by side in a uniform flow were investigated. We confirmed that four types of oscillation are occured on downstream cylinder in such an arrangement. Influenced by upstream cylinders, the amplitude of vortex induced oscillation is increased and wake buffeting occured when S/D(S: distance between the centers of upstream cylinders, D: diameter of cylinder) is smaller than 1.2. When S/D is larger than 1.2, gap flow introduces to oscillation which maintains a uniform amplitude in spite of increasing wind speed. This oscillation is reduced to "wake galloping" if its amplitude exceeds the limit point.

• Proceedings of the KIEE Conference
• /
• 2009.07a
• /
• pp.700_701
• /
• 2009

In comparison with conventional motors, Superconducting Homopolar Synchronous Motors (SHSMs) have advantages that it generates high magnetic field by superconducting winding. Therefore, superconducting coil used in SHSM can reduce the motor size and enhance the motor efficiency for high torque applications under the space constraints for propulsion system. During the design process of SHSM, it is required to evaluate the performance of initial design model, that is accurately analyzed using 3D magnetic field modeling large air-gap and flux distribution of axial direction is properly taken into account. In this paper, we analyze magnetic field of a homopolar motor with a 4-pole homopolar rotor and a stator of 3 phase windings. The field analysis is done using 3D finite element analysis which can reflect the end effect and overhang winding. And we extract mutual inductances between a rotor wind and the 3 stator windings. The extracted inductances are used for evaluation of overall motor performances that are calculated with generalized circuit theory of electrical machines.