• Journal of Navigation and Port Research
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• v.47 no.2
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• pp.75-84
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• 2023

Ships need to ensure safety during their navigation, which makes route determination highly important. It must be accompanied by a route following controller that can accurately follow the route. This study proposes a method for automatically generating the ship route based on deep reinforcement learning algorithm and following it using a route following controller. To generate a ship route, under keel clearance was applied to secure the ship's safety and navigation chart information was used to apply ship navigation related regulations. For the experiment, a target ship with a draft of 8.23 m was designated. The target route in this study was to depart from Busan port and arrive at the pilot boarding place of the Ulsan port. As a route following controller, a velocity type fuzzy P ID controller that could compensate for the limitation of a linear controller was applied. As a result of using the deep Q network, a route with a total distance of 62.22 km and 81 waypoints was generated. To simplify the route, the Douglas-Peucker algorithm was introduced to reduce the total distance to 55.67 m and the number of way points to 3. After that, an experiment was conducted to follow the path generated by the target ship. Experiment results revealed that the velocity type fuzzy P ID controller had less overshoot and fast settling time. In addition, it had the advantage of reducing the energy loss of the ship because the change in rudder angle was smooth. This study can be used as a basic study of route automatic generation. It suggests a method of combining ship route generation with the route following control.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.37 no.1
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• pp.1-9
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• 2000

In this paper, we design a robust output feedback controller for robot manipulators with bounded parametric uncertainties using high-gain observer. The proposed control scheme with integral action improves tracking error due to limit of the robust feedback gains. High-gain observer is used to solve the noise problem with the joint velocity measurement. This controller avoids the limitation on the variation of unknown parameters and guarantees the uniformly ultimate boundedness of the closed-loop system. The performance of the proposed method is demonstrated by simulation on a 2-link manipulator.

• Journal of computational fluids engineering
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• v.7 no.3
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• pp.9-16
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• 2002

Most of modem aerospace gas turbines must be operated at a gas temperature which is several hundreds of degrees higher than the melting temperatures of the materials used in their construction. Complicated cooling schemes need to be employed in the combustor walls and in the high pressure turbine stages. Internal passages are cast or machined into the hot sections of aero-gas turbine engines and air from the compressor is used for cooling. In many cases, the cooling system is engineered to utilize jets of high velocity air, which impinge on the internal surfaces of the components. They are categorized as 'Impinging Cooling Method' and 'Vortex Cooling Method'. Specially, research of new cooling system(Vortex Cooling Method) that overcomes inefficiency of film cooling and limitation of space. The focus of new cooling system that improves greatly cooling efficiency using less amount of cooling air on surface heat transfer elevation. Therefore, in this study, a numerical analysis has been peformed for characteristics of flow and heat transfer in the swirl chamber and compared with the flow measurements by LDV. Especially, for understanding high heat transfer efficiency in the vicinity of wall, we considered flow structure, vortex mechanism and heat transfer characteristics with variation of the Reynolds number.

• Journal of Bio-Environment Control
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• v.4 no.2
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• pp.167-174
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• 1995

This study was carried out to find a way of improving the windproof capability of greenhouse foundations. Generally, greenhouses are often collapsed due to the strong winds, because they are very light weight structures. In such a critical situations, the foundations are very often subjected to uplift and vibration at the same time. This paper describes both the wind disaster of greenhouses by the typhoon FAEY and the uplift resistance of greenhouse foundations. Followings are the results obtained from this study ; Judging from the view point of year round cultural aspects, it is recommended that some measures be taken for the preventions of greenhouse film ruptures because greenhouse structural damages are found to be directly associated with the local rupture of cover film. In the case of surveyed area, movable pipe-houses or pipe-houses of 1-2W type were found to be completely destroyed when the maximum instantaneous wind velocity was over 30m/sec or so. In the case of movable pipe-houses, the uplift resistance of greenhouse was expected to increase with the increase of pipe diameter and/or the embedment pipe length. But at present situations there is a limitation in raising the uplift resistance of movable pipe-house, because pipe diameters as well as pipe lengths customarily selected by farmers are quite a much limited.

• Journal of computational fluids engineering
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• v.21 no.4
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• pp.54-60
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• 2016

The valve used in nuclear power plant must be qualified but the limitation of the test facility leads to use the numerical analysis. The flow coefficient is calculated with the consideration of the pressure, velocity and geometry. And the flow coefficient is the important physical property which is prepared using experiment or analysis by valve manufacturer. In this study, the analysis model was made according to ISA 75.02.01 and the mass flow rate and pressure drop ratio was calculated. The model of the expansion factor was applied to the simulation result and the pressure drop ratio at the start of the choked flow in the valve was found. With the simulation result, the consideration was performed that the expansion factor is the important physical property to the system engineer in addition to the flow coefficient.

• Journal of Advanced Marine Engineering and Technology
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• v.32 no.7
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• pp.1044-1050
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• 2008

Most of developed countries, the consumption of fossil fuels has been serious problems that cause serious environment pollution like acid rain, global warming. Also, we have faced that limitation fossil fuels will be exhausted. Currently, small hydropower attracts attention because of its small, clean, renewable, and abundant energy resources to develop. By using a small hydropower generator of which main concept is based on using the different water pressure levels in pipe lines, energy which was initially wasted by use of a reducing valve at the end of the pipeline, is collected by turbine in the hydropower generator. A propeller shaped hydroturbine has been used in order to use this renewable pressure energy. In this study, in order to acquire basic design data of tubular type hydraulic turbine, output power, head, efficiency characteristics due to the flow coefficient are examined in detail. Tubular-turbine among small hydraulic power generation can be used at low-head. The purpose of this study is to research turbine's efficiency due to runner vane angle using CFD analysis.

• Journal of Information Technology Services
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• v.17 no.2
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• pp.179-190
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• 2018

This study is about the influence of authors' centrality on research outcomes in a large-scale collaborative research network. Using the social network analysis method, five types of centralities were derived. Six research outcomes of individual researchers were also derived through bibliographic information of the social science field for the last 10 years. A multivariate regression analysis was conducted to examine the causal relationship between the centrality and research outcome, and the effect of centrality on research outcomes was found to be statistically significant. The result of this study shows that the revised citation and H-index significantly influenced the authors' centrality. This result can imply that the centrality of the researcher can expect a considerable influence of the thesis as well as a certain level of productivity. The meaning of this study is to analyze the effect of centrality on the research outcomes of the large-scale collaborative research network in the past decade, and is carefully to suggest a guideline in order to support new research information services for active researchers and the advancement of collaborative research. This study has its limitation for interpreting the diverse academic fields of the social sciences in a uniform way. In future study, it is necessary to conduct studies using various weighted indices for network centrality in order to measure the influence of research.

• Journal of the Society of Naval Architects of Korea
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• v.52 no.4
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• pp.330-337
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• 2015

When a tower crane is carried by a transporter in shipyard, the height and length of the tower crane should be adjusted to meet the safety guidelines. Since the guidelines came from the field experience, the safety limitation needs to be analyzed by a computer simulation. In this paper, modeling methods are addressed to implement the appropriate transportation simulation of a tower crane. For the relation between the tower crane and the transporter, normal contact force, friction force, and kinematic constraints are compared. Assignment of relevant linear acceleration and angular velocity is considered for the transporter to start or move on an inclined ground surface. By using the examined modeling methods, the dynamic motion of tower crane transportation is analyzed by a dynamic simulation program, and comparison between the simulation result and analytic solution is made to verify the feasibility of the modeling methods.

• International Journal of Fuzzy Logic and Intelligent Systems
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• v.3 no.2
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• pp.244-250
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• 2003

In this paper, the relationship between a slave robot and the uncertain remote environment is modeled as the impedance to generate the virtual force to feed back to the operator. For the control of a tele-operated mobile robot equipped with camera, the tele-operated mobile robot take pictures of remote environment and sends the visual information back to the operator over the Internet. Because of the limitation of communication bandwidth and narrow view-angles of camera, it is not possible to watch the environment clearly, especially shadow and curved areas. To overcome this problem, the virtual force is generated according to both the distance between the obstacle and robot and the approaching velocity of the obstacle. This virtual force is transferred back to the master over the Internet and the master(two degrees of freedom joystick), which can generate force, enables a human operator to estimate the position of obstacle in the remote environment. By holding this master, in spite of limited visual information, the operator can feel the spatial sense against the remote environment. This force reflection improves the performance of a tele-operated mobile robot significantly.

• Journal of the Korean Society for Precision Engineering
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• v.26 no.10
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• pp.32-39
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• 2009

Most mobile devices provide limited input interfaces in order to maximize the mobility and the portability. In this paper, the author proposes a small cubic-shaped tangible input interface which tracks the location, the direction, and the velocity using MEMS sensor technology to overcome the physical limitations of the poor input devices in mobile computing environments. As the preliminary phase for implementing the proposed tangible input interface, the prototype design and implementation methods are described in this paper. Various experiments such as menu manipulation, 3-dimensional contents control, and sensor data visualization have been performed in order to verify the validity of the proposed interface. The proposed tangible device enables direct and intuitive manipulation. It is obvious that the mobile computing will be more widespread and various kinds of new contents will emerge in near future. The proposed interface can be successfully employed for the new contents services that cannot be easily implemented because of the limitation of current input devices. It is also obvious that this kind of interface will be a critical component for future mobile communication environments. The proposed tangible interface will be further improved to be applied to various contents manipulation including 2D/3D games.