• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.50 no.7
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• pp.471-478
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• 2022

This paper is about research and development of Korea Aerospace University's Solar-Powered UAV System that named of KAU-SPUAV, and describes the design process of the 4.2 m solar UAV that succeeded in a long flight of 32 hours and 19 minutes at June 2020. In order to improve the long-term flight performance of the KAU-SPUAV, For reduce drag, a circular cross-section of the fuselage was designed, and manufactured light and sturdy fuselage by applying a monocoque structure using a glass fiber composite material. In addition, a solar module optimized for the wing shape of a 4.2 m solar drone was constructed and arranged, and a propulsion system applied with the 23[in] × 23[in] propeller was constructed to improve charging and flight efficiency. The developed KAU-SPUAV consumes an average of 55W when cruising and can receive up to 165W of energy during the day, and its Long-term Endurance was verified through flight tests.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.36 no.4
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• pp.213-220
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• 2023

This paper presents a model simulating the folding process and collision dynamics of "ddakji", a traditional Korean game played using paper tiles (which are also referred to as ddakji). The model uses two A4 sheets as the base materials for ddakji. The folding process involves a series of boundary conditions that transform the wing part of the paper structure into a twisted configuration. A rigid plate boundary condition is also adopted for squeezing, establishing the shape and stress state of the game-ready ddakji through dynamic relaxation analysis. The gaming process analysis involves a forced displacement of the striking ddakji to a predetermined collision position. Collision analysis then follows at a given speed, with the objective of overturning the struck ddakji--a winning condition. A genetic algorithm-based optimization analysis identifies the optimal collision conditions that result in the overturning of the struck ddakji. For efficiency, the collision analysis is divided into two stages, with the second stage carried out only if the first stage predicts a possible overturn. The fitness function for the genetic algorithm during the first stage is the direction cosine of the struck ddakji, whereas in the second stage, it is the inverse of the speed, thus targeting the lowest overall collision speed. Consequently, this analysis provides optimal collision conditions for various compression thicknesses.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.9 no.1
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• pp.1-18
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• 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 $30^{\circ}$.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.33 no.2
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• pp.118-131
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• 1997

An opening efficiency experiment of anchovy boat seine has been carried out using a half size of the ordinary seine to reduce the size of the seine net and to improve the fishing efficiency from field operation. The intervals of towing boats were set at 100, 200 and 300m, and the towing speed, at 0.6, 0.9, and 1.2k't by possible combinations of them. The vertical openings of wing net, inside wing net, bagnet and flapper as well as the spreads of the seine net and the towing tension of the warp were measured, to find out efficient fishing gear and method of the anchovy boat seine. The results obtained are as follows : 1. The vertical opening of the inside wing net ranged from 8.7m to 12.0m at the normal current and from 7.0m to 10.0m at the counter current, and that of the wing net, from 8.4m to 19.8m at the normal current and from 4.9m to 16.3m at the counter current. The vertical opening of the wing net and inside wing net decreased as the towing speed and intervals of the boats increase, from 66% to 16% and from 32% to 18% of the normal opening, respectively. 2. The vertical opening of the fore of bag net ranged from 7.9m to 12.8m at the normal current and from 7.4m to 9.7m at the counter current, and that of the flapper, from 3.4m to 5.1m at the normal current and from 4.4m to 5.1m at the counter current, and that of the flapper, from 3.4m to 5.1m at the normal current and from 4.4m to 5.1m at the counter current. The vertical opening of the bag net was from 98% to 57% of the normal opening and the flapper showed a circular shape and it rose up to the upper layer with a slower towing speed. 3. The vertical opening of the end of the bag net ranged from 7.1m to 9.3m at the normal current and from 7.4m to 8.8m at the counter current. The end of the bag net rose up to the upper layer, This phenomenon was more apparent as the towing speed and the interval of the boats increase. 4. The towing tension of the experimental nets increased from 648kg to 2,716kg at the normal current and from 1,050kg to 6,010kg at the counter current with increasing towing speed. 5. The net depth of the anchovy seine was stable with the higher towing speed and the wider interval of the boats, but it was unstable by rising up to the upper layer with the lower towing speed and the narrower interval of towing boats.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.23 no.8
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• pp.759-769
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• 2013

Electronic equipment has been applied to virtually every area associated with commercial, industrial, and military applications. Specifically, electronics have been incorporated into avionics components installed in aircraft. This equipment is exposed to dynamic loads such as vibration, shock, and acceleration. Especially, avionics components installed in a helicopter are subjected to simultaneous sine and random base excitations. These are denoted as sine on random vibrations according to MIL-STD-810F, Method 514.5. In the past, isolators have been applied to avionics components to reduce vibration and shock. However, an isolator applied to an avionics component installed in a helicopter can amplify the vibration magnitude, and damage the chassis, circuit card assembly, and the isolator itself via resonance at low-frequency sinusoidal vibrations. The objective of this study is to investigate the dynamic characteristics of an avionics component installed in a helicopter and the structural dynamic modification of its tray plate without an isolator using both a finite element analysis and experiments. The structure is optimized by dynamic loads that are selected by comparing the vibration, shock, and acceleration loads using vibration and shock response spectra. A finite element model(FEM) was constructed using a simplified geometry and valid element types that reflect the dynamic characteristics. The FEM was verified by an experimental modal analysis. Design parameters were extracted and selected to modify the structural dynamics using topology optimization, and design of experiments(DOE). A prototype of a modified model was constructed and its feasibility was evaluated using an FEM and a performance test.

• Journal of the Korean Institute of Traditional Landscape Architecture
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• v.28 no.1
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• pp.27-37
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• 2010

This study tries to illuminate the features and values of the Buddhist temple Palkyung by closely examining the forms, structures, and meanings of Tongdo-palkyung(通度八景) handed down at Tongdosa Temple, the best among Korea's Buddhist temples with its three treasures of Buddha, law of Buddha and Buddhist monks. The findings of this study can be summarized as the following. First of all, it reveals the meaning of the geographical name Yeongchuksan(靈鷲山), located to the west of Tongdosa, and a spectacular sight spread like an eagle's spread wings, as well as its location and spatial features. In particular, the arrangement features of a number of attached hermitages clearly show Yeongchuksan's world as being a temple with buddhist treasures. The multi-layered unfolding and centripetal intention of the scenery can be perceived through the shape of the Sshangryongnongju(雙龍弄珠形), around Tongdosa and the feature of the enclosed landscape encircling the steps of Hyeolcheo(穴處) Geumganggyedan. The substances and components of Tongdopalkyung include sound-based spectacles derived from Beoneumgu(梵音具) creating sounds related to religious rituals to enlighten and redeem mankind, such as Yeongji(影池: a holy pond with shadow reflections), drum sounds, and bell sounds along with physical features like pine trees, Dae(臺), waterfalls, Dongcheon (洞天), and a glow in the sky. On the other hand, Palkyung's geographical arrangements exhibit a circular spatial formation based on the main motif as Buddhist symbolism, beginning with the 'Gukjangsangseokpyo(國長生石標)' awakening the territoriality of Tongdosa and locating the first scene 'Mupunghansong(舞風寒松)' in its introductory area, with the features of water, bridge, pine grove, and Iljumun(gate) to stand for the influx. Six other scenes including 'Anyangdongdae(安養東臺)' are placed in the sacred precincts around Daeungjeon and Geumganggyedan while the glow of sunset at 'Danjoseong' just outside the domain closes the symbolic circular formation of the Tongdopalkyung, which coincides with the development of the Mandala figure symbolizing 'Gusanpalhae(九山八海)' centered in Sumisan(須彌山). What is more, Tongdopalkyung, while excluding primary scenic elements inside the temple, maximizes the domain of the mountain's entrance and the effects of the multi-layered mountain, mountain upon mountain, by intensifying the influx and centripetal qualities. The Tongdopalkyung analysis reveals the antithesis of four-coupled scenes conveying buddhist principles and thoughts on the basis of seasons, directions, space and time to display a narrative structural landscape when viewed from the temple's territoriality. Likewise, the characteristics and porch structures of Tongdopalkyung are tools and language of symbols to both externally strengthen the temple's territoriality and to internally, maximize the desires to the Land of Happiness as well as intensify religious wishes and the Mandala's multi-layered qualities through the meanings of time and space.

• Journal of the Korean Magnetics Society
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• v.27 no.4
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• pp.123-128
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• 2017

The magnetic isotropy property from the magnetoresistance (MR) curve and magnetization (MH) loop for the PtMn based spin valve (SV) multilayer films fabricated with different the bottom structure after post-annealing treatment was investigated. The exchange biased coupling field ($H_{ex}$), coercivity ($H_c$), and MR ratio of Glass/Ta(10 nm)/CoFe(6 nm)/Cu(2.5 nm)/CoFe(3 nm)/Ta(4 nm) SV multilayer film without antiferromagnetic PtMn layer are 0 Oe, 25 Oe, and 3.3 %, respectively. MR curve for the Glass/Ta(10 nm)/CoFe(6 nm)/Cu(2.5 nm)/CoFe(3 nm)/PtMn(6 nm)/Ta(4 nm) SV multilayer film showed $H_{ex}=2Oe$, $H_c=316Oe$, and MR (%) = 4.4 % with one butterfly MR curve having by the effect of antiferromagnetic PtMn layer. MR curve for the dualtype Glass/Ta(10 nm)/CoFe(6 nm)/Cu(2.5 nm)/CoFe(3 nm)/PtMn(6 nm)/CoFe(3 nm)/Cu(2.5 nm)/CoFe(6 nm)/Ta(4 nm) SV multilayer film showed $H_c=37.5Oe$ and 386 Oe, MR = 3.5 % and 6.5 % with two butterfly MR curves and square-like hysteresis MH loops. The anisotropy property in CoFe spin valve-PtMn multilayer is neglected by the effects of a very small value of $H_{ex}$ and a very slightly shape magnetic anisotropy. This result is possible to explain the effect of magnetization configuration spin array of the bottom SV film and the top SV film of PtMn layer.