• Journal of the Korean Society for Aviation and Aeronautics
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• v.20 no.3
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• pp.35-43
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• 2012

Medium size rotorcraft consist of approximately 5,000 key components. The components must satisfy the target weight and performance requirement through optimization. Therefore a rotorcraft component has approximately 100 times higher unit cost for mass production than the equivalent of an automobile's, along with huge development cost. Configuration management consists of four main parts : configuration identification, configuration control, configuration audit, and data management. In development programme, configuration management is one of the methods to save development cost, and setting a well-structured configuration management system according to the Military Standard is an important factor in success of the programme. The paper proposes a configuration management system suitable for development of various multi-use components development and presents that the configuration management was performed successfully during dual-use component development programme using the established system.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 1999.10a
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• pp.464-469
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• 1999

Recently, the need for designing multi-stage gear drive has been increased as the hear drives are used more in the applications with high-speed and small volume. The design of multi-stage gear drives includes not only dimensional design but also configuration design of various machine elements. Until now, however, the researches on the design of gear drives are mainly focused on the single-stage gear drives and the design practices for multi-stage gear drives, especially in configuration design activity, mainly depend on the experiences and 'sense' of the designer by trial and error. We propose a design algorithm to automate the dimension design and the configuration design of multi-stage gear drives. The design process consists of four steps. The number of stage should be determined in the first step. In second step, the gear ratios of each reduction stage are determined using random search, and the ratios are basic input for the dimension design of gears, which is performed by the exhaustive search in third step. The designs of gears are guaranteed by the pitting resistance and bending strength rating practices by AGMA rating formulas. In configuration design, the positions of gears are determined to minimize the volume of gearbox using simulated annealing algorithm. The effectiveness of the algorithm is assured by the design example of a 4-stage gear drive.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2000.10a
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• pp.398-403
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• 2000

The design of multi-stage gear drives is a time-consuming process that includes additional design problems, which are not considered in the design of single-stage gear drives. In the previous research works, the authors have proposed a new algorithm to design multi-stage gear drives at the preliminary design phase. The proposed design algorithm automates the design process by integrating the dimensional design and the configuration design process. In the configuration design process, the positions of gears and shafts are determined by minimizing the geometrical volume (size) of a gearbox. However, various types of spatial constraints should be satisfied in practical design situation. To locate input and output shaft in specified positions is the typical example of such problems. In this paper, the authors show the formulations of spatial constraints applied to the design of four-stage gear drives. The design solution shows considerably good results, and the design system is confirmed to be readily applicable to practical design situation.

• The Transactions of the Korean Institute of Power Electronics
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• v.19 no.1
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• pp.31-40
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• 2014

This paper describes an optimal configuration for multi-central inverters in a medium-voltage (MV) grid, which is suitable for large-scale photovoltaic (PV) power plants. We theoretically analyze a proposed common-mode equivalent model for problems associated with multi-central transformerless-type three-phase full bridge(3-FB) PV inverters employing two-winding MV transformers. We propose a synchronized PWM control strategy to effectively reduce the common-mode voltages that may simultaneously occur. In addition, we propose that the existing 3-FB topology may also have the configuration of a multi-central inverter with a two-winding MV transformer by making a simple circuit modification. Simulation and experimental results of three 350kW PV inverters in a multi-central configuration verify the effectiveness of the proposed synchronization control strategy. The modified transformerless-type 3-FB topology for a multi-central PV inverter configuration is verified using an experimental prototype of a 100kW PV inverter.

• Korean Journal of Computational Design and Engineering
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• v.20 no.4
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• pp.337-347
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• 2015

This paper presents a dynamic association and natural interaction method for multi-displays composed of smart devices. Users can intuitively associate relations among smart devices by shake gestures, flexibly modify the layout of the display by tilt gestures, and naturally interact with the multi-display by multi-touch interactions. First of all, users shake their smart devices to create and bind a group for a multi-display with a matrix configuration in an ad-hoc and collaborative situation. After the creation of the group, if needed, their display layout can be flexibly changed by tilt gestures that move the tilted device to the nearest vacant cell in the matrix configuration. During the tilt gestures, the system automatically modifies the relation, view, and configuration of the multi-display. Finally, users can interact with the multi-display through multi-touch interactions just as they interact with a single large display. Furthermore, depending on the context or role, synchronous or asynchronous mode is available to them for providing a split view or another UI. We will show the effectiveness and advantages of the proposed approach by demonstrating implementation results and evaluating the method by the usability study.

• International Journal of Precision Engineering and Manufacturing
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• v.2 no.2
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• pp.65-72
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• 2001

The design of multi-stage gear drives is a time-consuming process, since on includes more complicated problems, which are not considered in the design of single-stage gear drives. The designer has th determine the number of reduction stages and the gear ratios of each reduction state. In addition, the design problems include not only the dimensional design but also the configuration design of gear drive elements. There is no definite rule and principle for these types of design problems. Thus the design practices largely depend on the sense and the experiences of the designer , and consequently result in undesirable design solution. We propose a new generalized design algorithm to support the designer at the preliminary design phase of multi-stage gear drives. The proposed design algorithm automates the design process by integrating the dimensional design and the configuration design process. The algorithm consists of four steps. In the first step, a designer determines the number of reduction stage. In the second step. gear ratios se chosen by using the random search method. In the third step, the values of basic design parameter are chosen by using the generate and test method. Then, the values of other dimension, such ad pitch diameter, outer diameter, and face width, are calculated for the configuration design in the final step. The strength and durability of a gear is guaranteed by the bending strength and the pitting resistance rating practices by using the AGMA rating formulas. In the final step, the configuration design is carried out b using the simulated annealing algorithm. The positions of gears and shafts are determined to minimize the geometrical volume(size) of a gearbox, while satisfying spatial constraints between them. These steps are carried out iteratively until a desirable solution is acquired. The propose design algorithm has been applied to the preliminary design of four-stage gear drives in order to validate the availability. The design solution have shown considerably good results in both aspects of the dimensional and the configuration design.

• International Journal of Aeronautical and Space Sciences
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• v.18 no.1
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• pp.70-81
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• 2017

Various components of an engine nozzle are modeled as flexible multi-body components that are operated under high temperature and pressure. In this paper, in order to predict complex behavior of an engine nozzle, thermo-fluid-flexible multi-body dynamics coupled analysis framework was developed. Temperature and pressure on the nozzle wall were obtained by the steady-state flow analysis for a two-dimensional nozzle. The pressure and temperature-dependent material properties were delivered to the flexible multi-body dynamics analysis. Then the deflection and strain distribution for a nozzle configuration was obtained. Heat conduction and thermal analyses were done using MSC.NASTRAN. The present framework was validated for a simple nozzle configuration by using a one-way coupled analysis. A two-way coupled analysis was also performed for the simple nozzle with an arbitrary joint clearance, and an asymmetric flow was observed. Finally, the total strain result for a realistic nozzle configuration was obtained using the one-way and two-way coupled analyses.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.11 no.1
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• pp.146-170
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• 2017

Joint channel assignment and routing is a well-known problem in multi-radio wireless mesh networks for which optimal configurations is required to optimize the overall throughput and fairness. However, other objectives need to be considered in order to provide a high quality service to network users when it deployed with high traffic dynamic. In this paper, we propose a re-configuration optimization model that optimizes the network throughput in addition to reducing the disruption to the mesh clients' traffic due to the re-configuration process. In this multi-objective optimization model, four objective functions are proposed to be minimized namely maximum link-channel utilization, network average contention, channel re-assignment cost, and re-routing cost. The latter two objectives focus on reducing the re-configuration overhead. This is to reduce the amount of disrupted traffic due to the channel switching and path re-routing resulted from applying the new configuration. In order to adapt to traffic dynamics in the network which might be caused by many factors i.e. users' mobility, a centralized heuristic re-configuration algorithm called State-Aware Joint Routing and Channel Assignment (SA-JRCA) is proposed in this research based on our re-configuration model. The proposed algorithm re-assigns channels to radios and re-configures flows' routes with aim of achieving a tradeoff between maximizing the network throughput and minimizing the re-configuration overhead. The ns-2 simulator is used as simulation tool and various metrics are evaluated. These metrics include channel-link utilization, channel re-assignment cost, re-routing cost, throughput, and delay. Simulation results show the good performance of SA-JRCA in term of packet delivery ratio, aggregated throughput and re-configuration overhead. It also shows higher stability to the traffic variation in comparison with other compared algorithms which suffer from performance degradation when high traffic dynamics is applied.

• International Journal of Aeronautical and Space Sciences
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• v.14 no.1
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• pp.99-104
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• 2013

Configuration design, analysis, and wind tunnel test of a vane-type multi-function air data probe (MFP) was described. First, numerical analysis was conducted for the initial configuration of the MFP in order to investigate aerodynamic characteristics. Then, the design was modified to improve static and dynamic stability for better response characteristics. The modified configuration design was verified through wind tunnel tests. The test results are also used to verify the accuracy of the analytical method. The analytically estimated aerodynamic damping provided by the Navier-Stokes equation solver correlated well with the wind tunnel test results. According to the calculation, the damping coefficient estimated from ramp motion analysis yielded a better correlation with the wind tunnel test than pitch oscillation analysis.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 1999.10a
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• pp.470-475
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• 1999

Recently as the application of gear drive increases in high-speed and high-loading, the concern of designing multi-stage gear drive is being risen. Until now however, the research of gear drive is focused on single-stage gear drive and the design depends on experiences and know-how of designer and is carried out by trial and error. This research automated the basic design and the configuration design for two and three-stage gear drives which consist of cylindrical gears. In basic design, design is executed with two design processes, which minimize the overall volume of gear, and whose results are compared each other. In configuration design, the positions of gears are determined to minimize the volume of gearbox using the result of basic design and simulated annealing algorithm.