• Journal of the Korean Society of Marine Environment & Safety
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• v.27 no.6
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• pp.856-866
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• 2021

The increasing international awareness regarding air pollutant reduction has resulted in increasing demand for eco-friendly ships; hence, electric ships are being actively developed by various countries. Presently, studies on electric ships are mainly focused on electric propulsion systems and electric motors. However, from the ship perspective, there are no studies on conceptual designs for coastal car ferries powered by removable power supply systems. In the present study, the main research consideration is regarding the conceptual design of a fully electrified car ferry using a battery-based removable system as the main power source. By analyzing the dimensions of more than 100 domestic coastal car ferries, the main criteria satisfying the requirements for developing a suitable vessel were derived, and a study on intact/damage stability was conducted considering the application of a removable battery truck. Further analyses of the problems concerning the conceptual design were also performed to derive solutions.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.20 no.10
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• pp.19-26
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• 2021

In fine-particle injection processing, hard fine particles, such as silicon carbide or aluminum oxide, are injected - using high-pressure air, and a small amount of material is removed by applying an impact to the workpiece by spraying at high speeds. In this study, a two-axis stage device capable of sequence control was developed to spray various shapes, such as circles and squares, on the surface during the micro-particle jetting process to understand the surface-shape micro-particle-processing characteristics. In the experimental device, two stepper motors were used for the linear movement of the two degree-of-freedom mechanism. The signal output from the microcontroller is - converted into a signal with a current sufficient to drive the stepper motor. The stepper motor rotates precisely in synchronization with the pulse-signal input from the outside, eliminating the need for a separate rotation-angle sensor. The major factors of the processing conditions are fine particles (silicon carbide, aluminum oxide), injection pressure, nozzle diameter, feed rate, and number of injection cycles. They were identified using the ANOVA technique on the design of the experimental method. Based on this, the surface roughness of the spraying surface, surface depth of the spraying surface, and radius of the corner of the spraying surface were measured, and depending on the characteristics, the required spraying conditions were studied.

• Journal of IKEEE
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• v.25 no.3
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• pp.556-564
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• 2021

This paper presents trends of safety improvement technologies for an electric propulsion system of eco-friendly ships. As an effort to reduce a green house effect, demands for eco-friendly ships have been increased. An energy storage system (ESS) is one of key systems in an eco-friendly ship and a lithium-ion battery generally used in an ESS system due to its high power density and efficiency. However, a lithium-ion battery is considered as one of reasons for ESS fire hazard. Since a fire extinguishing facility is especially limited in the ocean, safety issue in an eco-friendly ship is important. In this paper, recent safety improvement technologies for traction motors, ESS batteries and structures for eco-friendly ships are presented.

• Journal of Technology Innovation
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• v.29 no.2
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• pp.1-30
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• 2021

Recent years have witnessed various attempts of firms to acquire new knowledge. Purchasing intellectual property or merger and acquisition (M&A) can be such attempts, but joint venture can also be an effective way internalizing new complementary assets from external partners. However, due to difficulties in the formation and implementation of learning strategies, many joint ventures have failed to acquire necessary knowledge. In this respect, based on contingency theory and dynamic capability, the current research aims to investigate the failure case of knowledge transfer in an international joint venture - KEFICO established by Hyundai motors and BOSCH. Case firm optimized for hardware technology but did not establish a differentiated learning strategy and organizational structure to acquire software skills, which are intellectuals of different natures. Due to this inconsistency, it was not able for KEFICO to absorb new type of knowledge (skills related to engine control system). This study suggests the theoretical framework illustrating the case and provides some important implications for organizational learning.

• Journal of Powder Materials
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• v.26 no.2
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• pp.146-155
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• 2019

Rare earth magnets are the strongest type of permanent magnets and are integral to the high tech industry, particularly in clean energies, such as electric vehicle motors and wind turbine generators. However, the cost of rare earth materials and the imbalance in supply and demand still remain big problems to solve for permanent magnet related industries. Thus, a magnet with abundant elements and moderate magnetic performance is required to replace rare-earth magnets. Recently, $a^{{\prime}{\prime}}-Fe_{16}N_2$ has attracted considerable attention as a promising candidate for next-generation non-rare-earth permanent magnets due to its gigantic magnetization (3.23 T). Also, metastable $a^{{\prime}{\prime}}-Fe_{16}N_2$ exhibits high tetragonality (c/a = 1.1) by interstitial introduction of N atoms, leading to a high magnetocrystalline anisotropy constant ($K_1=1.0MJ/m^3$). In addition, Fe has a large amount of reserves on the Earth compared to other magnetic materials, leading to low cost of raw materials and manufacturing for industrial production. In this paper, we review the synthetic methods of metastable $a^{{\prime}{\prime}}-Fe_{16}N_2$ with film, powder and bulk form and discuss the approaches to enhance magnetocrystalline anisotropy of $a^{{\prime}{\prime}}-Fe_{16}N_2$. Future research prospects are also offered with patent trends observed thus far.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.3
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• pp.465-469
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• 2019

In this paper, the design of BLDC (brushless direct current) motors based on torque and back-EMF equations was carried out to assess the application of the motor in concrete vibrators. The air gap flux density of the motor is an important parameter because the length of the motor and the size of the diameter are given. The air gap magnetic flux density was calculated through a simplified magnetic circuit, and basic design of the shape and dimensions of the motor were then determined by carrying out experiments based on torque, back-EMF, and air magnetic flux density equations. After setting the outer and inner diameters, stack lengths, and rated speed of the motor, a detailed design was performed by simulations using the finite element method by designating the diameter and thickness of the motor as the key parameters. The final design to satisfy the target torque and the lowest THD (Total Harmonic Distortion) was carried out along with a simulation.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.11
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• pp.521-528
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• 2018

Military vehicles use run-flat wheels for emergency situations. Run-flat wheels can run required distance in a defined duration with the pressure loss tire. For the application of a run-flat system, wheels are designed in 2 pieces, including an inner rim and outer rim. These rims are assembled using clamping bolts. Clamping bolts determine the durability of military vehicle wheels because fracture of clamping bolts account for most wheel failures. For improving wheel durability, clamping bolt durability must be improved. In this study, wheel test conditions and bolt design were investigated. Existing test standards are not sufficient to conduct endurance tests. Supplementary conditions were investigated. Using these modified test conditions, the durability of wheels including clamping bolts was tested and verified. Results found the durability of wheels improved more than 168%. This study also proposes improvements in the design process of clamping bolts.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.6
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• pp.592-597
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• 2019

A conventional method to improve transient stability in power system is the use of reactive power compensation devices such as STATCOM and SVC. However, this traditional method cannot prevent a rapid voltage collapse brought on by motors stalling due to system fault. On the other hand, ESS(Energy Storage System) provides fast-acting, flexible reactive and active power control. The fast active power compensation with energy storage system plays a significant role in transient stability enhancement after a major fault of power system. In this paper, transient stability enhancement method by using energy storage system is proposed for the power system including a dynamic load such as large motor. The effectiveness of energy storage system compared to conventional devices in enhancing transient stability of power system is presented. The results of simulations show that the simultaneous injection of active and reactive power can enhance more effectively transient stability.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.6
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• pp.306-313
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• 2019

Owing to the present problems of air pollution and fossil fuel exhaustion, ongoing research has been actively focused on developing an electric actuator system that can utilize diverse energy sources without producing any exhaust gas. Since the motors of such electric vehicles generally rotate at a high speed, the initial acceleration capability required for an automobile is insufficient. In this study, the motor output was decelerated by the transmission; the initial acceleration of the vehicle was increased, and the motor size and weight were reduced. The driving motor and transmission, which each form isolated structures, were integrated to simplify the connector for input and output. By reducing the cooling system's capacity, a vehicle was designed and manufactured that represents a structural change in effective technology.

• Journal of The Korean Astronomical Society
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• v.51 no.6
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• pp.207-214
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• 2018

A coelostat is often used for solar observations, because it corrects the image rotation automatically by guiding sunlight into a fixed telescope with two plane mirrors. For the purposes of education and spectroscopic observation, the solar group at Seoul National University (SNU) plans to develop the SNU coelostat (SNUC) and install it in the SNU Astronomical Observatory (SAO). Requirements of the SNUC are < 1" positioning accuracy with 30 cm beam size on the entrance pupil in the compact dome. To allow for installation in the small dome, we design a compact slope type coelostat with a 45 cm primary plane mirror and a 39 cm secondary plane mirror. The motion of the SNUC is minimized by fixing the position of the slope frame. Numerical simulations of the available observational time of the designed coelostat shows that the sun can be observed ay all times from June to early August and at least three hours in other months. Since the high accuracy driving motors installed in the SNUC can be affected by external environment factors such as humidity and temperature variations, we design a prototype to test the significance of these effects. The prototype consists of a 20 cm primary plane mirror, a 1 m slope rail, a direct drive motor, a ballscrew, a linear motion guide, an AC servo motor, a reduction gear and a linear encoder. We plan to control and test the accuracy of the prototype with varying atmospheric conditions in early 2019. After testing the prototype, the SNUC will be manufactured and installed in SAO by 2020.