• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2012.05a
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• pp.219-224
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• 2012

In this work, a steady-state performance modeling and off-design performance analysis of the 2-spool separate jet turbofan engine named BR715-56 which is a power plant for the narrow body commercial aircraft is carried out for engine performance behaviors investigation and condition monitoring using a commercial code MATLAB/SIMULINK. Firstly, the engine component maps of fan, high pressure compressor, high pressure turbine and low pressure turbine are generated from similar component maps using the scaling method, and then the off-design performance simulation model is constructed by the mass flow matching and the work matching between components. The model is developed using SIMULINK, which has advantages of easy steady-stare and dynamic modelling and user friendly interface function. It is found that the off-design performance analysis results using the proposed model are well agreed with the performance analysis results by GASTURB at various operating conditions.

• Journal of the Korean Society of Propulsion Engineers
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• v.15 no.3
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• pp.47-57
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• 2011

All solid rocket propellants are divided in two basic classes according to chemical state: homogeneous(double base) and heterogeneous (composite). Today, composite propellants are extensively used as power sources covering the range from gas generators and small rocket systems to large launch vehicles in space programs. The development of composite rocket propellants in the past was mainly directed to thermoset polymers. But, the thermoset composite propellants have the complication in formulation and fabricating process to adapt to rocket system requirements. In contrast to the thermoset propellant, the PVC plastisols composite propellants have the advantages in the view of loss in manufacturing process, low cost of raw material, and stability of the handling process even though moderate ballistic and mechanical properties. It is predicted that the application field of this class will be used more widely than any other classes.

• Smart Structures and Systems
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• v.6 no.5_6
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• pp.439-459
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• 2010

Structural health monitoring (SHM) of civil infrastructure using wireless smart sensor networks (WSSNs) has received significant public attention in recent years. The benefits of WSSNs are that they are low-cost, easy to install, and provide effective data management via on-board computation. This paper reports on the deployment and evaluation of a state-of-the-art WSSN on the new Jindo Bridge, a cable-stayed bridge in South Korea with a 344-m main span and two 70-m side spans. The central components of the WSSN deployment are the Imote2 smart sensor platforms, a custom-designed multimetric sensor boards, base stations, and software provided by the Illinois Structural Health Monitoring Project (ISHMP) Services Toolsuite. In total, 70 sensor nodes and two base stations have been deployed to monitor the bridge using an autonomous SHM application with excessive wind and vibration triggering the system to initiate monitoring. Additionally, the performance of the system is evaluated in terms of hardware durability, software stability, power consumption and energy harvesting capabilities. The Jindo Bridge SHM system constitutes the largest deployment of wireless smart sensors for civil infrastructure monitoring to date. This deployment demonstrates the strong potential of WSSNs for monitoring of large scale civil infrastructure.

• Wind and Structures
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• v.17 no.3
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• pp.299-315
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• 2013

Numerical research on four typical configurations of noise mitigation structures and their characteristics of wind loads are reported in this paper. The turbulence model as well the model parameters, the modeling of the equilibrium atmospheric boundary layer, the mesh discretization etc., were carefully considered in the numerical model to improve the numerical accuracy. Also a numerical validation of one configuration with the wind tunnel test data was made. Through detailed analyses of the wind load characteristics with the inclined part and the wind incidence angle, it was found that the addition of an inclined part to a noise mitigation structure at-grade would affect the mean nett pressure coefficients on the vertical part, and that the extent of this effect depends on the length of the inclined part itself. The magnitudes of the mean nett pressure coefficients for both the vertical part and the inclined part of noise mitigation structure at-grade tended to increase with length of inclined part. Finally, a comparison with the wind load code British/European Standard BS EN 1991-1-4:2005 was made and the envelope of the mean nett pressure coefficients of the noise mitigation structures was given for design purposes. The current research should be helpful to improve current wind codes by providing more reasonable wind pressure coefficients for different configurations of noise mitigation structures.

• Journal of the Semiconductor & Display Technology
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• v.18 no.4
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• pp.30-34
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• 2019

We analyzed how the features in plasma information based virtual metrology (PI-VM) for SiO₂ etching depth with variation of 5% contribute to the prediction accuracy, which is previously developed by Jang. As a single feature, the explanatory power to the process results is in the order of plasma information about electron energy distribution function (PI_EEDF), equipment, and optical emission spectroscopy (OES) features. In the procedure of stepwise variable selection (SVS), OES features are selected after PI_EEDF. Informative vector for developed PI-VM also shows relatively high correlation between OES features and etching depth. This is because the reaction rate of each chemical species that governs the etching depth can be sensitively monitored when OES features are used with PI_EEDF. Securing PI_EEDF is important for the development of virtual metrology (VM) for prediction of process results. The role of PI_EEDF as an independent feature and the ability to monitor variation of plasma thermal state can make other features in the procedure of SVS more sensitive to the process results. It is expected that fault detection and classification (FDC) can be effectively developed by using the PI-VM.

• Journal of the Korea Society of Computer and Information
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• v.13 no.5
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• pp.195-202
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• 2008

In this paper, To improve the effectiveness of security enforcement, the first contribution in this work is that we present a clustered heterogeneous WSN(Wareless Sensor Network) architecture, composed of not only resource constrained sensor nodes, but also a number of more powerful high-end devices acting as cluster heads. Compared to sensor nodes, a high-end cluster head has higher computation capability, larger storage, longer power supply, and longer radio transmission range, and it thus does not suffer from the resource scarceness problem as much as a sensor node does. A distinct feature of our heterogeneous architecture is that cluster heads are equipped with TC(trusted computing) technology, and in particular a TCG(Trusted Computing Group) compliant TPM (Trusted Platform Module) is embedded into each cluster head. According the TCG specifications, TPM is a tamper-resistant, self-contained secure coprocessor, capable of performing cryptographic functions. A TPM attached to a host establishes a trusted computing platform that provides sealed storage, and measures and reports the integrity state of the platform.

• Journal of the Korean Magnetics Society
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• v.25 no.5
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• pp.149-155
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• 2015

The ECR (Electron Cyclotron Resonance) Ar ion milling was manufactured to fabricate the device of thin film. The ECR ion milling system applied to the device etching operated by a power of 600W, a frequency of 2.45 GHz, and a wavelength of 12.24 cm and transferred by a designed waveguide. In order to match one resonant frequency, a magnetic field of 908 G was applied to a cavity inside of ECR. The Ar gas intruded into a cavity and created the discharged ion beam. The surface of target material was etched by the ion beam having an acceleration voltage of 1000 V. The formed devices with a width of $1{\mu}m{\sim}9{\mu}m$ on the GMR-SV (Giant magnetoresistance-spin valve) multilayer after three major processes such as photo lithography, ion milling, and electrode fabrication were observed by the optical microscope.

• Progress in Superconductivity and Cryogenics
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• v.23 no.4
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• pp.19-24
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• 2021

The low normal zone propagation velocity (NZPV) of high-temperature superconducting (HTS) tape leads to a quench protection problem in HTS magnet applications. To overcome this limitation, various studies were conducted on HTS coils without turn-to-turn insulation (NI coils) that can achieve self-protection. On the other hand, NI coils have some disadvantages such as slow charging and discharging time. Previously, the HTS coils with turn-to-turn insulation (INS coils) were operated in power supply (PS) driven mode, which requires physical contact with the external PS at room-temperature, not in persistent current mode. When a quench occurs in INS coils, the low NZPV delays quench detection and protection, thereby damaging the coils. However, the rotary HTS flux pump supplies the DC voltage to the superconducting circuit with INS coils in a non-contact manner, which causes the INS coils to operate in a persistent current mode, while enabling quench protection. In this paper, a new protection characteristic of HTS coils is investigated with INS coils charging through the rotary HTS flux pump. To experimentally verify the quench protection characteristic of the INS coil, we investigated the current magnitude of the superconducting circuit through a quench, which was intentionally generated by thermal disturbances in the INS coil under charging or steady state. Our results confirmed the protection characteristic of INS coils using a rotary HTS flux pump.

• Journal of the Korea Society for Simulation
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• v.30 no.4
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• pp.1-8
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• 2021

Deep learning is one of the most widely accepted methods for the forecasting of time series data which have the complexity and non-linear behavior. In this paper, we investigate the modification of a state-of-art WaveNet deep learning architecture and walk forward validation (WFV) in order to forecast electric power consumption data 24-hour-ahead. WaveNet originally designed for raw audio uses 1D dilated causal convolution for long-term information. First of all, we propose a modified version of WaveNet which activates real numbers instead of coded integers. Second, this paper provides with the training process with tuning of major hyper-parameters (i.e., input length, batch size, number of WaveNet blocks, dilation rates, and learning rate scheduler). Finally, performance evaluation results show that the prediction methodology based on WFV performs better than on the traditional holdout validation.

• Agribusiness and Information Management
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• v.10 no.1
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• pp.1-15
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• 2018

Many paddy cultivating farmers in the country are forced to use their limited resources to produce adequate food for their family, leading to the degradation and reduction in potential of these resources. The yield levels of paddy at the farmers' level and in the Front Line Demonstrations (FLDs) conducted in the farmers' fields is not at par with potential yield of the paddy variety. The gap between potential yield of crop variety and yield realized in FLDs refers to Research gap and the yield gap between FLDs and due to farmers' practice refers to Extension gap. The earlier studies conducted in India in general and in Andhra Pradesh in particular highlighted the existence of both research and extension gaps with reference to paddy. It is essential that, the narrowing of both research and extension gaps is not static, but dynamic considering the influence of technological interventions in boosting paddy yields at FLDs level and at farmers' level and also with the improvement of the yield potential of paddy varieties. This calls for integrated and holistic approaches to address these two gaps and with this background, the researcher aimed at this in depth study. The findings revealed that, research gaps are high with reference to weed management and pest management and extension gaps are high with reference to farm mechanization followed by fertilizer management. Reliable source of seed, capital use and frequency of meetings with Scientists or Agricultural Officers significantly influence the extension gaps in paddy. Farmers also prioritized socio-economic and technical constraints and the analysis infers that, it is high time now for the farmers to adopt the planned technological interventions on scientific scale to minimize the extension gaps to the extent possible. As the enabling environment in the State of Andhra Pradesh is highly encouraging for the farmers with relevant policy instruments in the form of subsidized inputs, free power, credit at concessional rates of interest, constructing irrigation projects etc., the adoption of the proposed technological interventions significantly contribute to minimizing both research and extension gaps in paddy cultivation in Kurnool district of Andhra Pradesh.