• Journal of Biosystems Engineering
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• v.42 no.2
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• pp.104-111
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• 2017

Purpose: We have studied the necessary qualities of seedlings of some leafy vegetables for a riding-type two-row automatic transplanter. When seedlings are planted using a transplanter, long roots may be rounded in the bottom of the tray, and this can interfere with the separation of the seedlings. Uprightness related to leaf spread angle is an important quality for seedlings in mechanical planting. Methods: To select cultivars suitable for the transplanter, we compared varieties of Kimchi cabbage (Chukwang, Daetong, Whipalam and Namdo), head lettuce (Abi and Sensation), cabbage (YR Onnuri, YR Hogel, Harutama, and Ogane), and broccoli (Nicegreen and Earlyyou). To compare the effect of bed soil on root formation and growth, we used five types of soil: Chologi, Burger, Wonjomix, Bio, and Baroker with 2.6-3 L per tray. Growth increment and the degree of root formation were measured according to the RDA guidelines 25 days after sowing for Kimchi cabbage and head lettuce and 44 days after sowing for cabbage and broccoli. Conclusions: According to the plug tray, the optimum seedling age in both 128- and 200-hole trays was 28 days for Kimchi cabbage and 44 days for cabbage and broccoli. Head lettuce took 35 days in 128-hole trays and 31 days in 200-hole trays. Burger soil was most effective for root formation and growth of the four kinds of leafy vegetables; it appeared that smaller soil volume led to faster root formation.

• Journal of the Korean GEO-environmental Society
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• v.10 no.6
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• pp.19-25
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• 2009

The current study developed light-weighted mixed soil that can solve problems related with soft soil such as ground subsidence, sliding and lateral displacement of ground. By reducing weight of reclaimed soil through mixing phosphogypsum and recycled EPS beads with the weathered granite soil. A series of geotechnical laboratory tests including physical index test, compaction test, CBR test, and direct shear test were performed and engineering properties were reviewed in order to assess applicability of the light-weighted mixed soil for roads and abutment and various back-filling materials at the reclamation area. Based on the laboratory test results, it was found that the maximum dry unit weight of the light-weighted soil ranges $14.32{\sim}15.79kN/m^3$ and the optimum water content ranges 21.91~24.23%, which means there is 11~19.3% weight decrease effect when comparing with general weathered granite soil. Also it was found that the corrected CBR value ranges 10.4~18.4% satisfying the domestic regulations on road subgrade and back-filling material. In addition, as for shear strength parameter, cohesion ranges 10.79~18.64 kPa and internal frictional angle ranges $35.4{\sim}37.2^{\circ}$, which are similar with those of general construction soil and back-filling material used in Korea. So it can be concluded that light-weighted mixed soil with phosphogypsum can be used effectively for soft reclamation ground as actual filling material and back-filling material. From the current study, it was found that light-weighted mixed soil with phosphogypsum has not only weight reduction effect, but also has no special problems in shear strength and bearing capacity. Therefore, it is expected that phosphogypsum can be recycled in bulk as road subgrade and back-filling material at the reclamation area.

• The Journal of the Acoustical Society of Korea
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• v.39 no.5
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• pp.379-389
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• 2020

In this study, the flow and noise performances of high-speed fan motor unit for cordless vacuum cleaner is improved by optimizing the impeller which drives the suction air through flow passage of the cordless vacuum cleaner. Firstly, the unsteady incompressible Reynolds averaged Navier-Stokes (RANS) equations are solved to investigate the flow through the fan motor unit using the computational fluid dynamics techniques. Based on flow field results, the Ffowcs-Williams and Hawkings (FW-H) integral equation is used to predict flow noise radiated from the impeller. Predicted results are compared to the measured ones, which confirms the validity of the numerical method used. It is found that the strong vortex is formed around the mid-chord region of the main blades where the blade curvature change rapidly. Given that vortex acts as a loss for flow and a noise source for noise, impeller blade is redesigned to suppress the identified vortex. The response surface method using two factors is employed to determine the optimum inlet and outlet sweep angles for maximum flow rate and minimum noise. Further analysis of finally selected design confirms the improved flow and noise performance.

• Clean Technology
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• v.18 no.2
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• pp.170-176
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• 2012

A series of acrylic copolymers containing perfluoroalkyl acrylate were synthesized by 2-step emulsion polymerization of variety of acrylate monomers (ethyl acrylate, butyl acrylate or methyl methacrylate) with perfluoroalkyl ethyl acrylate (PFA) and glycidyl methacrylate (GMA) monomers. This study focused on effects of monomer compositions (the kind of acrylate monomer, contents of PFA and GMA) and composition of surfactants [(sodium dodecyl sulphate/nonylphenol 10mole ethoxylate (NP-10)] and initiator content on the contact angles and surface free energy. It was found that the copolymer having an optimum composition (BA : 87 wt%, GMA : 8.7 wt% and PFA : 4.3 wt%) was shown to be quite surface active [surface free energy : 19.89 mN/m and contact angles : $103.5^{\circ}$ (water) and $78.7^{\circ}$ (methylene iodide)] in the solid state. This result suggests that the optimal copolymer containing fluorinated monomer synthesized in this study have high potential as a low surface energy material, which may have high oil- and water-repellent surface and have been proposed as acrylic syntan for leather and also as soil-resistant/oil and water repellent coating for textiles and wood etc.

• Geotechnical Engineering
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• v.8 no.2
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• pp.5-20
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• 1992

The physical-based and lumped-parameter hydrologic groundwater flow model for predicting the rainfall-triggered rise of groundwater levels in hillside slopes is developed in this paper to assess the risk of landslides. The developed model consists of a vertical infiltration model for unsaturated zone linked to a linear storage reservoir model(LSRM) for saturated zone. The groundwater flow model has uncertain constants like soil depttL slope angle, saturated permeability, and potential evapotranspiration and four free model parameters like a, b, c, and K. The free model parameters could be estimated from known input-output records. The BARD algorithm is uses as the parameter estimation technique which is based on a linearization of the proposed model by Gauss -Newton method and Taylor series expansion. The application to examine the capacity of prediction shows that the developed model has a potential of use in forecast systems of predicting landslides and that the optimal estimate of potential 'a' in infiltration model is the most important in the global optimum analysis because small variation of it results in the large change of the objective function, the sum of squares of deviations of the observed and computed groundwater levels. 본 논문에서는 가파른 산사면에서 산사태의 발생을 예측하기 위한 수문학적 인 지하수 흐름 모델을 개발하였다. 이 모델은 물리적인 개념에 기본하였으며, Lumped-parameter를 이용하였다. 개발된 지하수 흐름 모델은 두 모델을 조합하여 구성되어 있으며, 비포화대 흐름을 위해서는 수정된 abcd 모델을, 포화대 흐름에 대해서는 시간 지체 효과를 고려할 수 있는 선형 저수지 모델을 이용하였다. 지하수 흐름 모델은 토층의 두께, 산사면의 경사각, 포화투수계수, 잠재 증발산 량과 같은 불확실한 상수들과 a, b, c, 그리고 K와 같은 자유모델변수들을 가진다. 자유모델변수들은 유입-유출 자료들로부터 평가할 수 있으며, 이를 위해서 본 논문에서는 Gauss-Newton 방법을 이용한 Bard 알고리즘을 사용하였다. 서울 구로구 시흥동 산사태 발생 지역의 산사면에 대하여 개발된 모델을 적용하여 예제 해석을 수행함으로써, 지하수 흐름 모델이 산사태 발생 예측을 위하여 이용할 수 있음을 입증하였다. 또한, 매개변수분석 연구를 통하여, 변수 a값은 작은 변화에 대하여 목적함수값에 큰 변화를 일으키므로 a의 값에 대한 최적값을 구하는 것이 가장 중요한 요소라는 결론을 얻었다.

• Polymer(Korea)
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• v.36 no.2
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• pp.155-162
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• 2012

Sulfonated poly(ether ether ketone) (SPEEK) nanofibers were prepared by electrospinning. The nanofibrous membrane for polymer electrolyte membrane fuel cell (PEMFC) was fabricated by compression molding. The maximum degree of sulfonation was 95% and the initial thermal degradation temperature was $280^{\circ}C$ and it's value was lower than that of PEEK. The contact angle of SPEEK increased with decreasing the degree of sulfonation. The optimum voltage, flow rate, tip to collector distance (TCD) and concentration of electrospinning conditions were 22 kV, 0.3 mL/hr, 15 cm, and 23 wt%, respectively. The average nanofibrous diameter was 47.6 nm. The water uptake and ion exchange capacity of SPEEK nanofibrous membrane increased with increasing the sulfonation time and the amount of sulfonating agent. The electrical resistance and proton ionic conductivity of SPEEK membrane increased with decreasing and increasing the sulfonation time, respectively. Their values were 0.58~0.06 ${\Omega}{\cdot}cm^2$and 0.099 S/cm.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.8 no.3
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• pp.181-188
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• 2010

Metal surface decontamination characteristics were investigated by using a laser ablation method. A second harmonic generation of a Q-switched Nd:YAG laser with a wave length of 532 nm, a pulse energy of 150 mJ and a pulse width of 5 ns was employed to assess the decontamination performance for metal surfaces contaminated with $CsNO_3$, $Co(NH_4)_2(SO_4)_2$, $Eu_2O_3$ and $CeO_2$. The ablation behavior was investigated for the decontamination variables such as a number of laser shots, laser fluence and an irradiation angle. Their optimum values were found to be 8, 13.3 J/$cm^2$ and $30^{\circ}$, respectively. The decontamination efficiency was different depending on the kinds of the contaminated ions, due to their different melting and boiling points and was in the order: $CsNO_3>Co(NH_4)_2(SO_4)_2>Eu_2O_3>CeO_2$. We also evaluated a correlation between the metal ablation thickness and the number of laser shots for the different laser fluences.

• Korean Journal of Applied Biomechanics
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• v.15 no.3
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• pp.143-152
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• 2005

The purpose of this study was to predict the failure or success of the Snatch-lifting trial as a consequence of the stand-up phase simulated in Kane's equation of motion that was effective for the dynamic analysis of multi-segment. This experiment was a case study in which one male athlete (age: 23yrs, height: 154.4cm, weight: 64.5kg) from K University was selected The system of a simulation included a multi-segment system that had one degree of freedom and one generalized coordinate for the shank segment angle. The reference frame was fixed by the Nonlinear Trans formation (NLT) method in order to set up a fixed Cartesian coordinate system in space. A weightlifter lifted a 90kg-barbell that was 75% of subject's maximum lifting capability (120kg). For this study, six cameras (Qualisys Proreflex MCU240s) and two force-plates (Kistler 9286AAs) were used for collecting data. The motion tracks of 11 land markers were attached on the major joints of the body and barbell. The sampling rates of cameras and force-plates were set up 100Hz and 1000Hz, respectively. Data were processed via the Qualisys Track manager (QTM) software. Landmark positions and force-plate amplitudes were simultaneously integrated by Qualisys system The coordinate data were filtered using a fourth-order Butterworth low pass filtering with an estimated optimum cut-off frequency of 9Hz calculated with Andrew & Yu's formula. The input data of the model were derived from experimental data processed in Matlab6.5 and the solution of a model made in Kane's method was solved in Matematica5.0. The conclusions were as follows; 1. The torque motor of the shank with 246Nm from this experiment could lift a maximum barbell weight (158.98kg) which was about 246 times as much as subject's body weight (64.5kg). 2. The torque motor with 166.5 Nm, simulated by angular displacement of the shank matched to the experimental result, could lift a maximum barbell weight (90kg) which was about 1.4 times as much as subject's body weight (64.5kg). 3. Comparing subject's maximum barbell weight (120kg) with a modeling maximum barbell weight (155.51kg) and with an experimental maximum barbell weight (90kg), the differences between these were about +35.7kg and -30kg. These results strongly suggest that if the maximum barbell weight is decided, coaches will be able to provide further knowledge and information to weightlifters for the performance improvement and then prevent injuries from training of weightlifters. It hopes to apply Kane's method to other sports skill as well as weightlifting to simulate its motion in the future study.

• Polymer(Korea)
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• v.29 no.5
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• pp.433-439
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• 2005

The copolymers were prepared by the emulsion copolymerization of fluoroalky lacrylate-stearylacrylate-m-isopropenyl-${\alpha},\;{\alpha}'$-dimethylbenzyl isocyanate (TMI) in order to obtain water repellent polymers. The respective copolymerization rates of the three monomers considerably depended upon the use of the nonionic emulsifier and the nonionic-cationic mixed emusifier, and the optimum conditions were obtained. The particle sizes of the copolymers were in the range of 105 to 222nm. The particle sizes of the copolymers prepared by the use of the mixed emulsifiers were smaller than those of the copolymers prepared by the use of the nonionic emulsifier. The reactions of both TMI-N-methyl acetamide and TMI-cellobiose did not take place. However, the reaction of TMI-n-butylamine occurred. The water contact angles before and after washing three times for nylon and poly(ethylene terephthalate) (PET) fabrics coated with the copolymer prepared by the use of mixed emulsifier were about $139^{\circ}\;and\;133^{\circ}$ Therefore, the copolymer showed good durable repellency for nylon and PET.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.31 no.3
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• pp.170-179
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• 2019

In this study, the wave responses in a 'Y'shape water channel resonator for amplifying wave energy of a low density has been investigated. A water channel resonator is composed of the long channel and wave guider installed at the entrance. If the period of the incident waves coincides with the natural period of the fluid in a water channel resonator, resonance occurs and the internal fluid amplifies highly to a standing wave form. In order to analyze the wave response in a water channel resonator, we used the matched asymptotic expansion method and boundary element method. The both results were in good agreement with the results of the model test carried out in the two-dimensional wave tank of Jeju National University. Wave guider has an optimum length and installation angle according to the period of the incident wave, and especially effective in enhancing the amplification factor in a period range deviated from the resonance period. It is expected that the wave energy can be effectively extracted by placing the point absorber wave energy converter at the position of anti-node where the maximum wave height is formed by the internal fluid resonance.