• Journal of the Korean Society of Marine Environment & Safety
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• v.27 no.5
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• pp.656-665
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• 2021

In this study, trim tabs were attached to end of stern hull of a small high-speed vessel of length approximately 10 m and Froude number 1.0 to improve resistance performance and passenger comfort. Before computational fluid dynamics (CFD) simulations to assess the performance according to various geometries of the trim tab, the scale effect had been found through a previous study, so full-scale simulations were performed. The trim tab chord length was set to 0.5 %, 1.0 % and 1.5 % of L_PP, and its angle to base line was varied in intervals of 5°. It decreased trim by stern and flotation: the greater the angle and length, the greater was the effect. Then it had pressure resistance decreased and shear resistance increased, and reduction ratio of total resistance varied accordingly. The results of this study indicated that the resistance performance was improved about 27 % at optimal running attitude that was the trim by stern about 1.5°.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.13 no.1
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• pp.69-85
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• 2019

BeiDou navigation satellite system (BDS) is one of the four main types of global navigation satellite systems. The current system has been widely used by the military and by the aerospace, transportation, and marine fields, among others. However, challenges still remain in the BeiDou system, which requires rapid responses for delay-sensitive devices. A differential positioning algorithm called the data center-based differential positioning (DCDP) method is widely used to avoid the influence of errors. In this method, the positioning information of multiple base stations is uploaded to the data center, and the positioning errors are calculated uniformly by the data center based on the minimum variance or a weighted average algorithm. However, the DCDP method has high delay and overload risk. To solve these problems, this paper introduces edge computing to relieve pressure on the data center. Instead of transmitting the positioning information to the data center, a novel method called edge computing-based differential positioning (ECDP) chooses the nearest reference station to perform edge computing and transmits the difference value to the mobile receiver directly. Simulation results and experiments demonstrate that the performance of the ECDP outperforms that of the DCDP method. The delay of the ECDP method is about 500ms less than that of the DCDP method. Moreover, in the range of allowable burst error, the median of the positioning accuracy of the ECDP method is 0.7923m while that of the DCDP method is 0.8028m.

• Journal of Hydrogen and New Energy
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• v.30 no.4
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• pp.303-311
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• 2019

Reversible solid oxide fuel cell (RSOFC) has become a prospective device for energy storage and hydrogen production. Many studies have been conducted around the world focusing on system efficiency improvement and realization. The system should have not only high efficiency but also a certain level of simplicity for stable operation. External waste steam utilization was proved to remarkably increase the efficiency at solid oxide electrolysis system. In this study, RSOFC system coupled with waste steam was proposed and optimized in term of simplicity and efficiency. Ejector for fuel recirculation is selected due to its simple design and high stability. Three system configurations using ejector for fuel recirculation were investigated for performance of design condition. In parametric study, the system efficiencies at different current density were analyzed. The system configurations were simulated using validated lumped model in EBSILON(R) program. The system components, balance of plants, were designed to work in both electrolysis and fuel cell modes, and their off-design characteristics were taken into account. The base case calculation shows that, the system with suction pump results in slightly lower efficiency but stack can be operated more stable with same inlet pressure of fuel and air electrode.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.49 no.7
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• pp.573-580
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• 2021

Paraffin wax is attracting many attentions for promising solid fuel of hybrid rocket because of its higher regression than other fuels. However, even with paraffin fuel combustion, unsteady low-frequency oscillation of combustion pressure is still observed. And, this is related to the formation of liquid layer and the entrainment of fuel droplets entering the axial combustion gas flow. This study investigates the effect of additional combustion of fuel droplets on the occurrence of low-frequency combustion instability. On the other hand, the formation of fuel droplets depends on Weber Number (the ratio of the inertial force to the surface tension of the liquid) and Reynolds Number of the oxidizer flow. Therefore, a laboratory-scale hybrid rocket was used to monitor the occurrence of combustion instability while changing We number. A series of combustion tests were conducted to control We number by changing the oxidizer flow rate or adding LDPE (low density polyethylene) to base fuel. In the results, it was confirmed that there is a critical We number above which the low-frequency combustion instability occurs.

• Journal of the Korean Society of Propulsion Engineers
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• v.25 no.5
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• pp.65-72
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• 2021

700 W class laboratory model Hall thruster, which can be used for the orbit control or station keeping of small satellites, was developed. The size of the discharge channel was determined using a scaling law, and the magnetic field was designed to be symmetric with respect to the midline of the discharge channel and to be maximized outside the discharge channel. Base pressure of a vacuum chamber was maintained below 2.0×10^-5 Torr during experiments, and the thrust was measured by a thrust stand. The anode flow rate and coil current were varied with the fixed anode voltage at 300 V. Under the operation condition at 2.36 mg/s anode flow rate and 2.4 A coil current, performance was optimized as 38 mN thrust, 1,540 s total specific impulse, and 50 % anode efficiency at 620 W anode power.

• Journal of the Korean GEO-environmental Society
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• v.22 no.12
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• pp.71-77
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• 2021

As the number of using road in Korea increases, maintenance costs and traffic congestion costs also increase. In order to reduce maintenance cost and time of road, existing long - lived modular road system has been proposed. In this study, the design and performance evaluation of the adaptable support module, which is the substructure of the proposed system, was performed. Two adaptable (Cross-Beam type)support modules were designed and fabricated to determine the load and shape. A adaptable support module was constructed and a static load test was carried out to select the type with better performance. As a result of the load test, the maximum value of the measured earth pressure difference is about 158 kPa and the settlement amount is about 0.032 mm in the two types of adaptable support modules. Based on these results, it is concluded that the performance of the adaptable support module of the bottom curved cross-beam type is better.

• Nuclear Engineering and Technology
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• v.21 no.4
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• pp.259-266
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• 1989

An improved version of RELAP5/MOD2 Cycle 36.04 code is assessed for LOFI LBLOCA Test L2-5. Minor modifications to the original version have been done to avoic reflood related errors. Based on the modified version, one base case and two cases for sensitivity study on downcomer and core channel modelling are calculated. The calculation results are compared with the experimental data for primary system pressure, break mass How rate and cladding temperature at hot spot According to the comparison, it is found that the hydraulic system behaviors are well predicted, excessive core cooling exist in blowdown phase for a single core channel and a combined downcomer case, and a better result can be obtained for a two core channel case.

• Imaging Science in Dentistry
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• v.53 no.1
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• pp.53-60
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• 2023

Purpose: This study evaluated maxillary sinus volume changes in military jet aircraft pilot candidates before and after the training program, in comparison with a control group, considering the effects of pressurization, altitude, and total flight hours, through multislice computed tomography. Materials and Methods: Fifteen fighter pilots were evaluated before initiating the training program and after the final approval. The control group consisted of 41 young adults who had not flown during their military career. The volumes of each maxillary sinus were measured individually before and at the end of the training program. Results: When comparing the initial and final volumes in the pilots, a statistically significant increase was observed both in the left and right maxillary sinuses. When evaluating the average total volume of the maxillary sinuses(i.e., the average volume of the right and left maxillary sinuses together), a significant increase in the volume of the maxillary sinuses was observed in the pilot group when compared to the control group. Conclusion: The maxillary sinus volumes in aircraft pilot candidates increased after the 8-month training program. This may be explained by changes in the gravitational force, the expansion of gas, and positive pressure from oxygen masks. This unprecedented investigation among pilots might lead to other investigations considering paranasal sinus alterations in this singular population.

• Physical Therapy Rehabilitation Science
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• v.13 no.1
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• pp.86-94
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• 2024

Objective: To evaluate the changes in bladder capacity and storage through non-invasive neuromodulation by application of repetitive Trans magnetic stimulation (rTMS) and genital nerve stimulation (GNS) in traumatic spinal cord survivors. Design: A Single Case Study. Method: The Patient was registered in trail with the clinical trial registry of India (CTRI/2022/05/042431). The Patient was interposed with rTMS on lumbar area, from T11-L4 vertebrae with 1 Hz and the intensity was 20% below that elicited local paraspinal muscular contraction for 13 minutes. GNS was placed over dorsum of the penis with the cathode at the base and anode 2 cm distally at 20 Hz, 200 microseconds, Continuous and biphasic current was delivered and amplitude of stimulation necessary to elicit the genito-anal reflex. For assessment, Neurological examination was done for peri-anal sensation (PAS), voluntary anal contraction (VAC) and bulbocavernous reflex (BCR), deep anal pressure (DAP), and American Spinal Injury Association Impairment Scale (ASIA scale). Outcome assessment was done using Urodynamics, Spinal Cord Independence Measure Scale Version-III (SCIM-III), American Spinal Injury Association Impairment Score (ASIA Score), Beck's Depression Inventory Scale (BDI). The baseline evaluation was taken on Day 0 and on Day 30. Results: The pre-and post-data were collected through ASIA score, SCIM-III, BDI and Urodynamics test which showed significant improvement in bladder capacity and storage outcomes in the urodynamics study across the span of 4 weeks. Conclusion: rTMS along with GNS showed improvement in bladder capacity & storage, on sensory-motor score, in functional independence of individual after SCI.

• Resources Recycling
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• v.15 no.3 s.71
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• pp.38-45
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• 2006

The thermal filter press dewatering(TFPD) technology to improve the dewaterability through increasing the inner vapor pressure, lowering the filtration viscosity and forming the porosity easily within cake as applying the heat at the sludge layer was developed in this study. The hot water with temperature of $95^{\circ}C$ and pressure of $1.2kg_f/cm^2$ was supplied to the heating plate equipped between filter plates with plate size of $470{\times}470mm$ and material of polypropylene. Sludge was dewaterd by supplying pressure of $5kg_f/cm^2$ and then by squeezing pressure of $15kg_f/cm^2$. As a results of estimating the characteristics of thermal dewatering to consider the initial water content and organic content to be influenced by a period of water shortage and rainwater, the dewatered cake water content was about 35 wt% and dewatering velocity was $4DSkg/m^2{\cdot}hr$ under the rainwater period, and the dewatered cake water content was about 50 wt% and dewatering velocity was $1.5DSkg/m^2{\cdot}hr$ in the case of sludge of water shortage season. These results was superior to the mechanical dewatering performance with water content of 70wt% and dewatering velocity of $0.9DSkg/m^2{\cdot}hr$. On the base of the results of TFPD, energy consumpted to deal with DS(Dry Solid) of 1kg was estimated by 300 kJ. It was analyzed that the energy consumption of TFPD was decreased about one third with comparison to the dryer system. Dewatering velocity of this technology was faster than the one of mechanical dewatering equipment and it was easier to product low water content cake. Therefore, this technology was recognized that dewaterability was predominant because of the fast of dewatering velocity and production of low water content cake, and also this known as economical efficiency was excellent because of low energy consumption in comparison with dryer.