• Journal of the Korean Society of Marine Environment & Safety
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• v.27 no.1
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• pp.38-46
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• 2021

In the era of the 4th Industrial Revolution, the interest in autonomous ship technology is increasing as high-tech technologies are being increasingly utilized throughout the industry. Therefore, we conducted a basic study on autonomous ships. In particular, a passenger ship model was produced and an autonomous navigation system was established by applying the ardupilot used for drones. The possibility of automatic control of the autonomous ship operations was confirmed by executing various voyage plans using the built model ship. In the performance test for maintaining the course the model ship could not follow the designated course straight and sailed up to 5.4 m away from the course while navigating in a zigzag (S-shape); however, after the parameters were modified, the deviation distance was reduced to a maximum of 1.8 m. In the turning performance test, the maximum diameter of the turning sphere was found to be approximately 9.3 m, but no significant change could be confirmed even after the parameters were modified. However, the results of our tests on slowing down the ship before arriving at the WP confirmed that the diameter of the turning sphere was reduced to a maximum of approximately 3.2 m. In order to evaluate the stopping performance, the last scheduled stopping position of all experiments was compared with the actual stopping position of the model ship and it was confirmed that the model ship stopped at a point at least 0.4 m and a maximum of 6.2 m away from the stopping position. In the future, improvement of course stability, turning performance, and stopping performance is required through modification and supplementation of various parameters. Moreover, a study on automatic berthing of the model ship through automatic control is planned.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1997.10a
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• pp.385-388
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• 1997

As the environmental regulations become stricter, new machining technologies are being developed which takes envi ronmenta 1 aspects into account . Since cut t ing oi I has some impact on environment. many researches are being carried out to minimize the use of cutting oi I. The methods for minimizing cutting oil usage includes the following techniques: I ) Cooling of tools and work piece. 2) Useage of compressed cooling air for the removal of chip. 3) Minimal useage of environment-friendly vegetable cutt:ngoiI for lubrication between chip and tools. Since the turning machine is continuous, tools are under constant thermal load and tool wear increases as the lubricative performance degrades. Also surface roughnesses have a direct influence on turning. In order to examine the characteristics of turningmachining, this work investigates experimentally the degree of tool wear and characteristics of surface roughness in relation to machining conditions, supply methods, and cooling methods.

• Journal of the Korean Society for Precision Engineering
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• v.27 no.5
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• pp.14-21
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• 2010

In this study, presintered low purity alumina ceramics were machined with various tools to clarify the effects of the tool material, cutting condition and tool geometry on machinability. The main conclusions obtained were as follows. (a)The wear of tungsten carbide tool becomes smaller with the increase of the feed and clearance angle, and with the decrease of rake angle, especially exhibiting considerably smaller wear with both the decrease of rake angle and the increase of clearance angle. (b) So far as turning the ceramic presintered at low temperature, the diamond tool shows the best performance with higher feed. (c) The effect on the tool wear of the feed, clearance angle and rake angle becomes smaller in turning the ceramic presintered at higher temperature. (d) The tool wear is not severely affected by the depth of cut.

• Journal of Sensor Science and Technology
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• v.8 no.6
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• pp.469-475
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• 1999

The chips may be produced in the form of either broken chips or unbroken chips in turning process. The unbroken chips are dangerous to the operator and difficult to handle at high speed machining. The signal of Acoustic Emission is related to cutting conditions, tool materials, test conditions and tool geometry in turning. The relationship between AE signal and chip formation was experimentally investigated. The experimental results show that two types of chip formations are possible to classify from the statistical analysis of the amplitude of AE signal. The AE-sensor could be used to monitor the chip condition in turning.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.1
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• pp.113-120
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• 1994

The dynamic characteristics of turning processes are complex, non-linear and time-varying. Consequently, the conventional techniques based on crisp mathematical model may not guarantee cutting force regulation. This paper presents a fuzzy controller which can regulate cutting force in turning process under varying cutting conditions. The fuzzy control rules are extablished from operator experience and expert knowledge about the process dynamics. Regulation which increases productivity and tool life is achieved by adjusting feedrate according to the variation of cutting conditions. The performance of the proposed controller is evaluated by cutting experiments in the converted conventional lathe. The results of experiments show that the proposed fuzzy controller has a good cutting force regulation capability in spite of the variation of cutting conditions.

• The Journal of Korean Physical Therapy
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• v.25 no.2
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• pp.88-95
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• 2013

Purpose: The purpose of this study was to conduct an analysis of kinematics of lower extremities and trunk in stance phase of walking according to turning direction. Methods: Ten university students (five male, five female) who were in their 20s (mean age was 20.6 years old) participated in this study. Participants did not have participants did not have any problem with skeletal muscular system. We used the "Qualisys motion capture system" for analysis of trunk and lower extremity movement in stance phase of walking according to turning direction. We collected data while subjects walked a distance of 10 m, and at the 6 m line, subjects were required to turn to the left side and the right leg was positioned in stance phase and the left leg was positioned in swing. For data analysis, the SPSS for Windows ver. 20.0 statistics program was used in performance of one way analysis of variance according to turning direction. Results: Significant difference of trunk and lower extremities was observed for turning direction according to walking cycle (p<0.05). Upper trunk movement showed a greater increase at three dimensions than lower trunk, and in heel off phase, pelvic movement showed a greater increase than lower trunk (p<0.05). In 45 degree and 90 degrees of turning direction, all movements of trunk and lower extremities were significantly different among three events of stance phase (p<0.05). Conclusion: We suggest that three-dimensional movement analysis of trunk and lower extremities during turning movement was very important in order to indicate increasing balance or walking ability for people with impaired movement or walking.

• Transactions of the Korean Society of Automotive Engineers
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• v.9 no.1
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• pp.20-27
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• 2001

A variable configuration tracked vehicle(VCTV) is developed to reduce turning energy and improve climbing ability for stairs. This mechanism has four track T-type frames. By changing the driving direction, each track T-type frame rotates to minimize the contact area with ground. It also has better performance than other VCTV in energy consumption of turning. Futhermore this mechanism is more stable than other VCTV on the rough terrain. When climbing stairs, each track T-type frame rotates to obtain a front attack angle and keep stability on steep stairs. The design parameters of components of track T-type frames are optimized to enhance the performance of climbing stairs. Performance indices include a stable angle, a climbing ability, a height of the vertical obstacle. In case that the overall length of the mechanism is 0.2m, it is required that the radius of the wheels should be 5mm and the length track contacted with he ground should be 0.09m to climb higher and steeper stairs.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2001.10a
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• pp.3-7
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• 2001

In this study, the effect of WC and group IV elements on the cutting performance in turning is investigated. The composition of WC was changed from 5 to 20% to determine the effect of WC on the cutting performance of cermet tool. The more WC was added, the longer the tool life of the cermet tool was. The cermet with 20% WC showed the best fracture toughness. The cermet tool with 20% WC showed the best cutting performance among the various WC composition. The effect of group IV elements ; ZrC, ZrN and HfC was also investigated by adding each of them to manufacture the cermet tool with fixed 14% WC composition. The cermet with 1% group IV HfC and 14% WC showed the best cutting performance among the investigated cermet tools.

• Transactions of the Korean Society of Automotive Engineers
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• v.4 no.6
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• pp.39-51
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• 1996

In the turning maneuver of the vehicle, its motion is mainly dependent on the genuine steering characteristics in view of the directional stability for stable turning ability. The under steer vehicle has an ability to maintain its own directonal performance for unknown external disturbances to some extent. From a few years ago, in order to acquire the more enhanced handling performance, some types of four wheel steering vehicle were considered and constructed. And, various rear wheel control logics for external disturbances has not been suggested. For this reason, in this posed rear wheel control logic is based on the yaw rate feed back type and is slightly modified by an yaw rate tuning factor for more stable turning performance. And an external disturbance is defined as a motivation of the additional yaw rate in the center of gravity by an uncertain input. In this study, an external disturbance is applied to the vehicle as a form of the additional yawing moment. Finally, the proposed rear wheel control logic is tested on the multi-body analysis software(ADAMS). J-turn and double lane change test are performed for the validation of the control logic.

• Journal of the Society of Naval Architects of Korea
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• v.53 no.3
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• pp.217-227
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• 2016

Recent accidents of crude oil tankers have resulted in sinking, grounding of vessels and significant levels of marine pollution. Therefore, International Maritime Organization (IMO) has been strengthening the regulations of ship maneuvering performance in MSC 137. The evaluation of maneuvering performance can be made at the early design stage; it can be investigated numerically or experimentally. The main objective of this paper was to investigate the maneuvering performance of a VLCC due to the increase of rudder force at an early design stage for low speed in shallow water conditions. It was simulated in various operating condition such as deep sea, shallow water, design speed and low speed by using the numerical maneuvering simulation model, developed using MMG maneuvering motion equation and KVLCC 2 (SIMMAN 2008 workshop). The effect of increasing the rudder force can be evaluated by using numerical simulation of turning test and ZIG-ZAG test. The research showed that, increasing the rudder force of a VLCC was more effective on improving the turning ability than improving the course changing ability especially. The improvement of turning ability by the rudder force increasing is most effective when the ship is sailing in shallow water at low forward speed.