• Proceedings of the Korean Geotechical Society Conference
• /
• 2002.03a
• /
• pp.221-228
• /
• 2002

Thickness of concrete lining, voids at the back of lining or shotcrete are very important elements for inspecting the safety of tunnels. Therefore, the inspection of tunnel lining structure means to investigate the inner layer boundaries of the structure. For this purpose, seismic reflection survey is the most desirable method if it works in good conditions. However, the conventional seismic reflection method can not be properly used for investigating thin layers in the lining structure. In other words, to detect the inner boundaries, it is desirable for the wavelength of source to be less than the thickness of each layer and for the receiver to be capable of detecting high frequency(ultrasonic) signals. To this end, new appropriate source and receiver devices should be developed above all for the ultrasonic reflection survey. This paper deals primarily with the development of source and receiver devices which are essential parts of field measuring system. Interests are above all centered in both the radiation pattern, energy, frequency content of the source and the directional sensitivity of the receiver. With these newly devised ones, ultrasonic physical modeling has been performed on 3-D physical model composed of bakelite, water-proof and concrete, The measured seismograms showed a clear separation of wave arrivals reflected from each layer boundary. Furthermore, it is noteworthy that reflection events from the bottom of concrete below water-proof could be also observed. This result demonstrates the usefulness of the both devices that can be applied to benefit the ultrasonic reflection survey. Future research is being focus on dealing with at first an optimal configuration of source and receiver devices well coupled to tunnel wall, and further an efficient data control system of practical use.

• Journal of the Korean Society of Propulsion Engineers
• /
• v.8 no.1
• /
• pp.44-53
• /
• 2004

This paper is to investigate the combustion characteristics with a three dimensional chemical reacting flow on the aspect ratio of an exit configuration of the slit type nozzle for the fuel injection and to device the methods of combustion／mixing enhancement. The results show that both inside inflow and slit side vertices should be considered from a viewpoint of the mixing. The combustion efficiency becomes the smallest at aspect ratio, where the aspect ratio is less and more than unity, respectively. The total pressure loss becomes the largest at aspect ratio of unity due to the high penetration. All results imply that a streamwise very long slit is desirable with respect to the combustion and the pressure loss.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 2002.05a
• /
• pp.108-113
• /
• 2002

This paper presents a multi-step structural design optimization method fur machine tool structures using a genetic algorithm with dynamic penalty. The first step is a sectional topology optimization, which is to determine the best sectional construction that minimize the structural weight and the compliance responses subjected to some constraints. The second step is a static design optimization, in which the weight and the static compliance response are minimized under some dimensional and safety constraints. The third step is a dynamic design optimization, where the weight static compliance, and dynamic compliance of the structure are minimized under the same constraints. The proposed design method was examined on the 10-bar truss problem of topology and sizing optimization. And the results showed that our solution is better than or just about the same as the best one of the previous researches. Furthermore, we applied this method to the topology and sizing optimization of a crossbeam slider for a high-speed machining center. The topology optimization result gives the best desirable cross-section shape whose weight was reduced by 38.8% than the original configuration. The subsequent static and dynamic design optimization reduced the weight, static and dynamic compliances by 5.7 %, 2.1% and 19.1% respectively from the topology-optimized model. The examples demonstrated the feasibility of the suggested design optimization method.

• Journal of Sensor Science and Technology
• /
• v.23 no.5
• /
• pp.305-309
• /
• 2014

Well-ordered $TiO_2$ nanotubes with Au nanoparticles are a desirable configuration to enhance the gas sensing properties such as response and selectivity due to their high surface area to volume ratio and catalytic effect of Au nanoparticles. We have synthesized the well-ordered $TiO_2$ nanotubes directly on a Pt IDEs patterned $SiO_2/Si$ substrate and then decorated Au nanoparticles on inner and outer surface of $TiO_2$ nanotubes using electrodeposition method. The Au-decorated $TiO_2$ nanotubes shows ultrahigh response to $C2_H_5OH$ and the highest increasing ratio to $H_2$ compared with other gases.

• Journal of the Korean Society of Industry Convergence
• /
• v.19 no.1
• /
• pp.10-17
• /
• 2016

In general, articulated robot control technology is limited to the design of robot arm control systems considering each joint of the robot joint as a simple servomechanism. This method describes the varying dynamics of a manipulator inadequately because it neglects the motion and configuration of the whole arm mechanism. The changes of the parameters in the controlled system are significant enough to render conventional feedback control strategies ineffective. This basic control system enables a manipulator to perform simple positioning tasks such as in the pock and place operation. However, joint controllers are severely limited in precise tracking of fast trajectories and sustaining desirable dynamic performance for variations of payload and parameter uncertainties. In many servo control applications the linear control scheme proposes unsatisfactory, therefore, a need for nonlinear techniques that increasing. for Forging process automation.

• Proceedings of the KSME Conference
• /
• 2003.11a
• /
• pp.1240-1245
• /
• 2003

Reduced activation ferritic steel (JLF-1) is considered as a promising candidate material for blanket or first-wall structure of D-T fusion reactors. The fracture tests of fracture resistance curve (J-R curve) and $J_{IC}$ are desirable to investigate the exact fracture toughness of JLF-1 steel, since it has a high ductility. The fracture toughness of JLF-1 steel is affected by the configuration of test specimen such side groove, specimen thickness or specimen size. In this study, the fracture toughness tests were performed with various size(plane size and thickness) and various side groove of specimens. The test results showed the standard specimen with the side groove of 40 % represented a valid fracture toughness. The fracture resistance curve increased with increasing plane size and decreased with increasing thickness. However, the fracture resistance curve of half size specimen was similar to that of the standard specimen.

• Proceedings of the Materials Research Society of Korea Conference
• /
• 2010.05a
• /
• pp.20.1-20.1
• /
• 2010

'Electronic paper (EP)' provides desirable viewing characteristics of paper with being thin, lightweight, flexible, and recordable with minimal power consumption. Currently, a number of different technologies to realize the EP are actively competing. Here we demonstrate a newly developed monolayer rotating ball (MRB) electronic paper display where optically anisotropic rotating balls were disposed in a monolayer, and controllably closely packed with respect to one another. The close packed monolayer configuration provides high brightness and improved contrast with better electrical and optical features in comparison with the typical (Gyrion) rotating ball display. In this talk, we present characteristics of the MRB display in terms of performance, with particular emphasis on the response time as a function of the electric field.

• International Journal of Contents
• /
• v.5 no.1
• /
• pp.21-26
• /
• 2009

Peer to Peer (P2P) utilizes the resources of an offered service without the need for a central server or preexistent server-client, making it a desirable network environment for data exchange based on direct connection between peers. Proposed by Sun Microsystems. JXTA(Juxtapose) is a typical P2P system and distributed computing model that does not require central service resources and is flexible to deal with various network configuration changes. Meanwhile. Mobile Ad-hoc NETwork(MANET) is a typical wireless network configured with mobile nodes and without an infrastructure. where a network is established by direct connection or through other peers in the propagation area. Thus, MANET maintains the latest path information by establishing paths and changing path information for communication between peers in a highly mobile wireless network. Accordingly. this article proposes the JXTAMANET method for wireless networks to enable JXTA to be applied to MANET. NS2 is used to evaluate the performance and the proposed architecture is shown to produce better results than a conventional flooding method.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
• /
• v.28 no.6
• /
• pp.60-67
• /
• 2014

Power system fault analysis is commonly based on well-known symmetrical component method, which describes power system elements by positive, negative and zero sequence impedance. The majority of fault in transmission lines is unbalanced fault, such as line-to-ground faults, so that both positive and zero sequence impedance is required for fault analysis. When unbalanced fault occurs, zero sequence current flows through earth and ground wires in overhead transmission systems and through cable sheaths and earth in underground transmission systems. Since zero sequence current distribution between cable sheath and earth is dependent on both sheath bondings and grounding configurations, care must be taken to calculate zero sequence impedance of underground cable transmission lines. In this paper, EMTP-based sequence impedance calculation method was described and applied to 345kV cable transmission systems. Calculation results showed that detailed circuit analysis is desirable to avoid possible errors of sequence impedance calculation resulted from various configuration of cable sheath bonding and grounding in underground cable transmission systems.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.11 no.4
• /
• pp.58-67
• /
• 2003

An automotive engine cooling system is closely related with overall engine performances, such as reduction of fuel consumption, decrease of air pollution, and increase of engine life. Because of complex reaction between each component, the direct experiment, using a vehicle, takes high cost, long time, and slow response to the system change. Therefore, a computer simulation would provide the designer with an inexpensive and effective tool for design, development, and optimization of the engine cooling system over a wide range of operating conditions. In this work, it has been predicted the thermal performance of the engine cooling system in cases of stationary mode, constant speed mode, and city-drive mode by mathematical modelling of each component and numerical analysis. The components are engine, radiator, heater, thermostat, water pump, and cooling fans. Since the engine model is the most important, that is divided into eight sub-sections. The volume mean temperature of eight sub-sections are simultaneously calculated at a time. For detail calculation, the radiator and heater are also divided into many sub-sections like control volumes in finite difference method. Each sub-section is assumed to consist of three parts, coolant, tube with fin, and air. Hence it has been developed the simulation program that can be used in case of design and system configuration changes. The overall performance results obtained by the program were desirable and the time-traced tendencies of the results agreed fairly well with those of actual situations.