• International journal of advanced smart convergence
• /
• v.11 no.3
• /
• pp.222-228
• /
• 2022

As a means to cope with the climate change crisis caused by global warming, automobile manufacturers continue to make efforts to use the driving energy of vehicles as electricity. As a result, parts industry such as battery, motor, and controller are attracting attention. China is often seen in large cities, with electric vehicles such as electric bicycles, electric motorcycles, and small electric vehicles popularized and commercialized, mainly in large cities. However, small electric vehicles are not popular in Korea, which is why the country's topography is high in hills. In order to drive the hilly domestic roads, power performance including vehicle climbing ability should be improved. In order to improve the power performance and the climbing capacity of small electric vehicles, the capacity of the motor should be increased. However, when the performance of the motor is improved, the weight of the motor becomes heavy and the price competitiveness is likely to decrease. In addition, in order to operate a high-performance motor, the power consumption of the battery is rapidly increased, so various problems must be solved. In order to commercialize a small electric vehicle for one or two people who do not emit harmful exhaust gas to the human body in a hilly domestic terrain, it is effective to have a separate transmission system. In this study, we were conducted dynamometer test to produce a continuously variable transmission(CVT) system prototype using a spring that can be applied to a small electric vehicle and to install a CVT system prototype manufactured in a small electric vehicle. The dynamometer test results showed that the maximum speed performance, acceleration performance, and climbing performance were improved.

• KEPCO Journal on Electric Power and Energy
• /
• v.8 no.1
• /
• pp.15-19
• /
• 2022

The radial distribution systems (RDS) commonly used around the world has the following disadvantages. First, when the DL is operated on a radial system, the line utilization rate is usually kept low. Second, if a fault occurs in the radial DL, a power outage of 3 to 5 minutes is occurring depending on the operator's proficiency and fault situation until the fault section is separated and the normal section is replaced. To solve this problem, Various methods have been proposed at domestic and foreign to solve this problem, and in Korea, research is underway on the advanced system of operating multiple linked DL always. A system that is electrically linked always, and that is built to enable high-speed communication during the protection coordination is named networked distribution system (NDS). Because the load shares the DL, the line utilization rate can be improved, and even if the line faults, the normal section does not need to be cut off, so the normal section does not experience a power outage. However, since it is impossible to predict in which direction the fault current will flow when a failure occurs in the NDS, a communication-based protection coordination is used, but there is no backup protection coordination method in case of communication failure. Therefore, in this paper, we propose a protective cooperation method to apply as a backup method when communication fails in NDS. The new method is to change TCC by location of CB using voltage drop in case of fault.

• Journal of Ocean Engineering and Technology
• /
• v.36 no.3
• /
• pp.143-152
• /
• 2022

To reach a port, a ship must pass through a shallow water zone where seabed effects alter the hydrodynamics acting on the ship. This study examined the maneuvering characteristics of an autonomous surface ship at 3-DOF (Degree of freedom) motion in deep water and shallow water based on the in-port speed of 1.54 m/s. The CFD (Computational fluid dynamics) method was used as a specialized tool in naval hydrodynamics based on the RANS (Reynolds-averaged Navier-Stoke) solver for maneuvering prediction. A virtual captive model test in CFD with various constrained motions, such as static drift, circular motion, and combined circular motion with drift, was performed to determine the hydrodynamic forces and moments of the ship. In addition, a model test was performed in a square tank for a static drift test in deep water to verify the accuracy of the CFD method by comparing the hydrodynamic forces and moments. The results showed changes in hydrodynamic forces and moments in deep and shallow water, with the latter increasing dramatically in very shallow water. The velocity fields demonstrated an increasing change in velocity as water became shallower. The least-squares method was applied to obtain the hydrodynamic coefficients by distinguishing a linear and non-linear model of the hydrodynamic force models. The course stability, maneuverability, and collision avoidance ability were evaluated from the estimated hydrodynamic coefficients. The hydrodynamic characteristics showed that the course stability improved in extremely shallow water. The maneuverability was satisfied with IMO (2002) except for extremely shallow water, and collision avoidance ability was a good performance in deep and shallow water.

• Journal of Korea Society of Industrial Information Systems
• /
• v.14 no.3
• /
• pp.50-57
• /
• 2009

We propose a network node search scheme to address the network fragmentation due to high node mobility in the VANET. VANET is very similar to MANET in that a multi-hop ad-hoc network is configured by wireless communication between vehicles without any network infrastructure. However, high speed mobility, high node density, and frequent topology change induce frequent network fragmentation so that overall network traffic can be increased. In this paper, new broadcasting protocol called an adaptive relay node search protocol is proposed to decrease the network fragmentation. It reduces the network fragmentation and network traffic by researching nodes outside the dangerous area only in case of network fragmentation. Simulation results show that the proposed protocol decreases network fragmentation by up to 39.9% and increase informed rate by up to 41.9% compared to the existing broadcasting protocol.

• Korean Journal of Remote Sensing
• /
• v.39 no.4
• /
• pp.441-458
• /
• 2023

Tropical cyclones frequently occur in the Southwest Pacific Ocean and are considered one of the driving forces for coastal alterations. Therefore, this study investigates the frequency and intensity of tropical cyclonesfrom 2000 to 2021 and their influence on the surface winds and wave conditions around the atoll nation Tuvalu. Cyclone best-track and ERA5 single-level reanalysis data are utilized to analyze the condition of the surface winds, significant wave heights, mean wave direction, and mean wave period. Additionally, the scatterometer-derived wind information was employed to compare wind conditions with the ERA5 data. On average, nine cyclones per year originated here, and the frequency increased to 11 cyclones during the last three years while the intensity decreased by 25 m/s (maximum sustained wind speed). Besides, a total of 14 cyclones were observed around Tuvalu during the period from 2015 to 2021, which showed an increase of 3 cyclones compared to the preceding period of 2001 to 2007. During cyclones, the significant wave height reached the highest 4.8 m near Tuvalu, and the waves propagated in the east-southeast direction during most of the cyclone events (52%). In addition, prolonged swells with a mean wave period of 7 to 11 seconds were generated in the vicinity of Tuvalu, for which coastal alteration can occur. After this preliminary analysis, it was found that the waves generated by cyclones have a crucial impact in altering the coastal area of Tuvalu. In the future, remotely sensed high-resolution satellite data with this wave information will be used to find out the degree of alterations that happened in the coastal area of Tuvalu before and after the cyclone events.

• KNOM Review
• /
• v.22 no.2
• /
• pp.1-11
• /
• 2019

The paradigm of science and technology and R&D system changes from the existing form of independent research to community research which transmits and stores large-capacity data generated from observation and experiment to the research site through a high-speed network. Network-dependent advanced research is improves form of collaboration, sharing, globalization. For this purpose, not only the integration of science and IT technology, but also the optimized network infrastructure and technology for real-time sharing of the enormous data is necessary. This paper explains the direction of change through the case of KREONET's network-dependent advanced research and analyzes the technology and network resources supported in each research field. Through this, we propose a network optimization model for each advanced research field with the main data flow and satisfy the network required performance by advanced applications on KREONET.

• Journal of Hydrogen and New Energy
• /
• v.34 no.1
• /
• pp.59-68
• /
• 2023

In this study, the performance of high-pressure fuel pumps was compared to find a high-pressure pump suitable for dimethyl ether (DME) fuel, and to establish a database of basic data on flow rates. The use of DME in compression ignition engines can reduce pollutant emissions. The cetane value of DME is higher than that of diesel fuel. The physical properties of DME are similar to liquefied gasoline gas (LPG), and when pressurized at a pressure of 6 bar or more, it changes from gas to liquid. Two types of high pressure pumps used in this study were independent injection type pump and a wobble plate type pump. Two high-pressure pumps with different injection types were compared. By measuring and comparing the performance changes of the two high-pressure pumps, a pump suitable for DME was selected and performance improvement measures were proposed. The changed experimental conditions to measure the performance change of the high pressure pump were increased in the units of 100 to 1,000 rpm and 100 rpm, and the experiment was performed at common rail pressures 300 and 400 bar. it was confirmed that the DME inside the fuel supply system remained in a liquid state through temperature sensors, pressure sensors, and pressure gauges. As a result of the experiment, it was confirmed that the flow rate discharged from the high-pressure fuel pump increased as the motor rotational speed increased, and the flow rate of the high-pressure fuel pump

• Journal of the Korean Geotechnical Society
• /
• v.25 no.8
• /
• pp.95-106
• /
• 2009

This study was intended to identify the effect of the wetting on a long-term compression settlement of the rock/soil mixture used as fill material, depending on compaction and grading conditions. The relatively large settlement happened under the fully-submerged condition, and a repeated settlement was monitored when moisture content increased over and over again like the rainfall infiltration. In case of the materials without fine fractions or compacted in wet condition, the settlement caused by wetting was relatively low. In conclusion, the long-term compression settlement of granular (rock/soil mixture) fill material is more affected by the increase of water content and temperature change (freezing and thawing) than creep.

• The Journal of the Acoustical Society of Korea
• /
• v.41 no.2
• /
• pp.122-129
• /
• 2022

In this paper, we propose a method to improve the performance of Transformer-based speech recognizers using data augmentation that locally adjusts the frame rate. First, the start time and length of the part to be augmented in the original voice data are randomly selected. Then, the frame rate of the selected part is changed to a new frame rate by using linear interpolation. Experimental results using the Wall Street Journal and LibriSpeech speech databases showed that the convergence time took longer than the baseline, but the recognition accuracy was improved in most cases. In order to further improve the performance, various parameters such as the length and the speed of the selected parts were optimized. The proposed method was shown to achieve relative performance improvement of 11.8 % and 14.9 % compared with the baseline in the Wall Street Journal and LibriSpeech speech databases, respectively.

• Journal of KIBIM
• /
• v.13 no.2
• /
• pp.1-15
• /
• 2023

Since the 1960s, the Korean Peninsula, which consists of 77.4 of the country's land and mountains, has seen a surge in demand for buildings due to population concentration due to urbanization and industrialization. Since then, the development of slopes has been inevitable due to the concentration and expansion of the city's population. When building a building on a slope, it is important to set the height of the surface. In this case, the means of regulating buildings in construction-related laws, such as the building closure ratio, floor area ratio, number of floors and total floor area of buildings, have an overall effect on buildings through the height of the surface. In the Korean Building Act, the setting of the height of the ground affects the calculation of the building height limit standard and the calculation of the underground floor, and it takes a long time to calculate. Therefore, the time required for attempts to change various design plans of buildings increases. The purpose of this study is to speed up the time required to calculate the weighted average of the surface when constructing buildings on slopes. In addition, the existing calculation process allows various design attempts compared to the same time given.