• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.42 no.6
• /
• pp.468-477
• /
• 2014

In this research, how a solar powered HALE (high altitude long endurance) UAV (Unmanned Aerial Vehicle) can climb and reach mission altitude, 18km, starting from the ground using only solar energy. A glider type aircraft was assumed as a baseline configuration which has wing area of $35.98m^2$ and aspect ratio of 25. Configuration parameters, lift and drag coefficients were calculated using OpenVSP and XFLR5 that are NASA open source programs, and climb flights were predicted through energy balance between available energy from solar power and energy necessary for a climb flight. Minimum time climb flight was obtained by minimizing flight velocities at each altitude and total time and total energy consumption to reach the mission altitude were predicted for different take off time. Also, aircraft moving distances due to westerly wind and flight speed were calculated.

• Journal of Advanced Navigation Technology
• /
• v.25 no.1
• /
• pp.17-28
• /
• 2021

Recently, eVTOL, the next-generation of eco-friendly transportation, has been in the spotlight due to global warming along with traffic jams in large cities of many countries. This study benchmark the external features of Hyundai Motors S-A1, a compound eVTOL combined fixed and tilt rotors among many types of eVTOLs, to create the basic configuration using reverse design techniques. Basic configurations were created using CATIA and aerodynamic analyses were performed using the aircraft design and aerodynamic analysis programs, OpenVSP, XFLR5, and the aircraft wetted area, drag, and lift were calculated after selecting the airfoil, incidence angle, and dihedral and anhedral angles through trade study. Also, required powers were estimated for completing the given mission profile and components weight and the total weight were predicted using the estimation formula and data survey.

• Korean Chemical Engineering Research
• /
• v.55 no.2
• /
• pp.201-213
• /
• 2017

Water is removed from crude oil containing water by using oil separator. This study aims to develop a three-dimensional (3D) Eulerian computational fluid dynamics (CFD) model to predict the separation efficiency of air-water-oil separator. In the incompressible, isothermal and unsteady-state CFD model, air is defined as continuous phase, and water and oil are given as dispersed phase. The momentum equation includes the drag force, lift force and resistance force of porous media. The standard k-${\varepsilon}$ model is used for turbulence flow. The exit pressures of water and oil play an important role in determining the liquid level of the oil separator. The exit pressures were identified to be 6.3 kPa and 5.1 kPa for water and oil, respectively, to keep a liquid level of 25 cm at a normal operating condition. The time evolution of volume fractions of air, water and oil was investigated. The settling velocities of water and oil along the longitudinal separator distance were analyzed, when the oil separator reached a steady-state. The oil separation efficiency obtained from the CFD model was 99.85%, which agreed well with experimental data. The relatively simple CFD model can be used for the modification of oil separator structure and finding optimal operating conditions.

• Journal of the Korean Society of Fisheries and Ocean Technology
• /
• v.9 no.1
• /
• pp.1-18
• /
• 1973

For regulating the depth of midwater trawl nets towed at the optimum constant speed, the changes in the shape of warps caused by adding a weight on an arbitrary point of the warp of catenary shape is studied. The shape of a warp may be approximated by a catenary. The resultant inferences under this assumption were experimented. Accordingly feasibilities for the application of the result of this study to the midwater trawl nets were also discussed. A series of experiments for basic midwater trawl gear models in water tank and a couple of experiments of a commercial scale gears at sea which involve the properly designed depth control devices having a variable attitude horizontal wing were carried out. The results are summarized as follows: 1. According to the dimension analysis the depth y of a midwater trawl net is introduced by $$y=kLf(\frac{W_r}{R_r},\;\frac{W_o}{R_o},\;\frac{W_n}{R_n})$$) where k is a constant, L the warp length, f the function, and $W_r,\;W_o$ and $W_n$ the apparent weights of warp, otter board and the net, respectively, 2. When a boat is towing a body of apparent weight $W_n$ and its drag $D_n$ by means of a warp whose length L and apparent weight $W_r$ per unit length, the depth y of the body is given by the following equation, provided that the shape of a warp is a catenary and drag of the warp is neglected in comparison with the drag of the body: $$y=\frac{1}{W_r}\{\sqrt{{D_n^2}+{(W_n+W_rL)^2}}-\sqrt{{D_n^2+W_n}^2\}$$ 3. The changes ${\Delta}y$ of the depth of the midwater trawl net caused by changing the warp length or adding a weight ${\Delta}W_n$_n to the net, are given by the following equations: $${\Delta}y{\approx}\frac{W_n+W_{r}L}{\sqrt{D_n^2+(W_n+W_{r}L)^2}}{\Delta}L$$ $${\Delta}y{\approx}\frac{1}{W_r}\{\frac{W_n+W_rL}{\sqrt{D_n^2+(W_n+W_{r}L)^2}}-{\frac{W_n}{\sqrt{D_n^2+W_n^2}}\}{\Delta}W_n$$ 4. A change ${\Delta}y$ of the depth of the midwater trawl net by adding a weight $W_s$ to an arbitrary point of the warp takes an equation of the form $${\Delta}y=\frac{1}{W_r}\{(T_{ur}'-T_{ur})-T_u'-T_u)\}$$ Where $$T_{ur}^l=\sqrt{T_u^2+(W_s+W_{r}L)^2+2T_u(W_s+W_{r}L)sin{\theta}_u$$ $$T_{ur}=\sqrt{T_u^2+(W_{r}L)^2+2T_uW_{r}L\;sin{\theta}_u$$ $$T_{u}^l=\sqrt{T_u^2+W_s^2+2T_uW_{s}\;sin{\theta}_u$$ and $T_u$ represents the tension at the point on the warp, ${\theta}_u$ the angle between the direction of $T_u$ and horizontal axis, $T_u^2$ the tension at that point when a weights $W_s$ adds to the point where $T_u$ is acted on. 5. If otter boards were constructed lighter and adequate weights were added at their bottom to stabilize them, even they were the same shapes as those of bottom trawls, they were definitely applicable to the midwater trawl gears as the result of the experiments. 6. As the results of water tank tests the relationship between net height of H cm velocity of v m/sec, and that between hydrodynamic resistance of R kg and the velocity of a model net as shown in figure 6 are respectively given by $$H=8+\frac{10}{0.4+v}$$ $$R=3+9v^2$$ 7. It was found that the cross-wing type depth control devices were more stable in operation than that of the H-wing type as the results of the experiments at sea. 8. The hydrodynamic resistance of the net gear in midwater trawling is so large, and regarded as nearly the drag, that sweeping depth of the gear was very stable in spite of types of the depth control devices. 9. An area of the horizontal wing of the H-wing type depth control device was $1.2{\times}2.4m^2$. A midwater trawl net of 2 ton hydrodynamic resistance was connected to the devices and towed with the velocity of 2.3 kts. Under these conditions the depth change of about 20m of the trawl net was obtained by controlling an angle or attack of $30^{\circ}$.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.33 no.6
• /
• pp.2359-2368
• /
• 2013

Cone penetration tests (CPTs) have been increasingly used for site characterizations. However, the site investigations using CPTs are often limited due to soil conditions depending on the cone size and capacity of the CPT system. The small sectional area of a miniature cone improves the applicability of the CPT system due to the increased capacity of the CPT system. A continuous intrusion system using a coiled rod allows fast and cost effective site investigation. In this study, the performance of the continuous intrusion miniature cone penetration test (CIMCPT) system has been evaluated by comparison tests with the standard CPT system at several construction sites in Korea. The results show that the CIMCPT system has a same performance with the CPT system and has advantages on the mobility and applicability. According to field verification tests for scale effect evaluation, the cone tip resistance evaluated by CIMCPT overestimates by 10% comparing to standard CPTs. A crawler mounted with the CIMCPT system has been implemented to improve accessibility to soft ground, and has shown improvement over the truck type CIMCPT system. Therefore, the improved CIMCPT system can be utilized as a cost effective and highly reliable soil investigation methodology to detect the depth of soft ground and to evaluate soil classification.

• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.29 no.6
• /
• pp.369-381
• /
• 2017

It has been presumed that highly nonlinear skewed waves frequently observed in a surf zone could significantly influence the transmission behaviour via a porous wave breaker due to its larger inertia force than its nonlinear counterparts of zero skewness [Cnoidal waves]. In this study, in order to confirm this perception, a numerical simulation has been implemented for 6 waves the skewness of that range from 1.02 to 1.032. A numerical simulation are based on the Tool Box called as the ihFoam that has its roots on the OpenFoam. Skewed waves are guided by the shoal of 1:30 slope, and the flow in the porous media are analyzed by adding the additional damping term into the RANS (Reynolds Averaged Navier-Stokes equation). Numerical results show that the highly nonlinear skewed waves are of higher transmitted ratio than its counterparts due to its stronger inertia force. In this study, in order to see whether or not the damping at the porous structure has an effect on the wave celerity, we also derived the dispersive relationships of Nonlinear Shallow Water Eq. [NSW] with damping at the porous structure being accounted. The newly derived dispersive relationships shows that the phase lag between the damping friction and the free surface elevation due to waves significantly influence the wave celerity.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.21 no.2
• /
• pp.521-527
• /
• 2020

In offshore structures, the mean viscous drift force due to drag is considered to be a design part that has not been considered until recently. In particular, it is most important to calculate the drift force acting on a vertical cylinder considering both waves and currents in the low frequency region. This paper presents a process for deriving analytical solutions for the drift forces acting on a fixed vertical cylinder considering waves and currents. The area of the cylinder was considered by dividing it into a splash zone above the free surface and a submerged zone below the free surface. The presence of waves is considered only in the Splash Zone, and in the case of waves and currents, the equations were obtained for both the splash and submerged zones. The results show that drift forces occur due to the significant viscous effects in both the splash zone and the submerged zone. Therefore, the analytical solutions derived in this study can be used to calculate the drift force using the given design variables and form a theoretical basis for judging whether the magnitude of the drift force in each case has a dominant influence within a specific physical range.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.43 no.9
• /
• pp.765-772
• /
• 2015

Aerodynamic force measurements and phase-locked PIV study were carried out to check the bio-mimetic MAV applicability of a swift flight. Two-rotational DOF robotic wing model and blowing-type wind tunnel were employed. The amplitude of twist angle were ${\pm}0$, ${\pm}5$, ${\pm}10$, and ${\pm}20$ deg. and stroke angles were manipulated by simple harmonic function with out-of-phase in regards to the stroke motion. It is acknowledged that the time-varying lift coefficients in accordance with the change of the twist angle did not result in any noticeable differences, just the small decrease and delay. However, the drag exhibited that the small change of the twist angle can produce large thrust. These findings imply why a swift uses small twist angle during flight. The PIV results displayed that the delay of aerodynamic forces is highly associated with the vortical structures around the wing. It is therefore indicated that a process of designing a swift-based Micro Air Vehicle should take the twist angle into consideration, as the essential parameter.

• Composites Research
• /
• v.32 no.5
• /
• pp.284-289
• /
• 2019

In the present paper, the dynamic force-moment equilibrium equations, driving power and energy equations are analyzed to formulate the equation for fuel economy(km/liter) equivalent to the driving distance (km) divided by the fuel volume (liter) of the vehicle, a selected model of gasoline powered KIA K3 (1.6v). In addition, the effects of the dynamic parameters such as speed of vehicle (V), vehicle total weight(M), rolling resistance ($C_r$) between tires and road surface, inclined angle of road (${\theta}$), as well as the aerodynamic parameters such as drag coefficient ($C_d$) of vehicle, air density(${\rho}$), cross-sectional area (A) of vehicle, wind speed ($V_w$) have been analyzed. And the possibility of alternative materials such as lightweight metal alloys, fiber reinforced plastic composite materials to replace the conventional steel and casting iron materials and to reduce the weight of the vehicle has been investigated by Ashby's material index method. Through studies, the following results were obtained. The most influencing parameters on the fuel economy at high speed zone (100 km/h) were V, the aerodynamic parameters such as $C_d$, A, ${\rho}$, and $C_r$ and M. While at low speed zone (60 km/h), they are, in magnitude order, dynamic parameters such as V, M, $C_r$ and aerodynamic ones such as $C_d$, A, and ${\rho}$, respectively.

• Journal of the Korean Geotechnical Society
• /
• v.26 no.8
• /
• pp.27-37
• /
• 2010

Downdrag force develops when a pile is driven through a soil layer which will settle more than a pile. There is no obvious criterion for application of the current pile design method considering the negative skin friction. Therefore, in this study, numerical analyses were performed to investigate the behavior of a single pile subjected to negative skin friction and their results were used to determine the applicability of the current design method. Including three different sites in Song-do area and two different cases with friction pile and end bearing pile conditions, total six cases were considered. The load-settlement relationships and the neutral points were estimated for different end bearing conditions and the allowable bearing capacity of piles with negative skin friction was investigated through parametric studies. Based on the results showed that the negative skin friction made a major influence on the settlement of a pile and its stress. However the allowable bearing capacity may not be influenced by the negative skin friction. Compared with the allowable bearing capacity obtained from the ultimate bearing capacity with the safety factor of 3, the current design method with the safety factor of 3 underestimated the allowable bearing capacities regardless of the end bearing conditions. On the other hand, the current design method with the safety factor of 2 yielded reasonable results depending on the end bearing conditions.