• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.37 no.2
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• pp.156-165
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• 2009

Threat due to malfunction of space launch vehicles is significant since it is bigger and flights longer range than military missiles or scientific rockets. It is necessary to implement a flight safety system to minimize the possible hazard. Design objective of the tracking filter for the flight safety system is different from conventional tracking filters since estimation reliability is more emphasized than estimation accuracy. In this paper, a fusion tracking filter was implemented for processing multi-sensor data from a space launch vehicle. The filter performance is evaluated by analyzing the error of the estimated position and instantaneous impact point. Also a fault detection algorithm is implemented to guarantee fusion filter's reliability under any sensor failure and verified to maintain stability successfully.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.8
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• pp.18-24
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• 2017

The process of transmitting messages through a medium with a limited bandwidth or channel dispersion inevitably involves signal distortion and noise influxes, resulting in the degradation of transmission quality due to the inter-symbol interference and additional noise, which increases the error rate of the received symbols. The main role of the equalizer is to remove the channel distortion and noise from the received signal to recover the transmitted messages. A number of studies on the equalizer composed of a combination of linear filter and error control coding have shown that they played a key role in enhancing the transmission efficiency, which is essential for digital communication. This paper proposes a new algorithm to correct the residual symbol errors in the message signal. In general, equalizer performance improvement algorithms were developed to improve the initial convergence speed or steady-state error. In this paper, however, the equalizer input signal was reconstructed using the equalizer decision symbols and the channel estimates to directly correct the decision errors by analyzing the statistical characteristics of the difference signal between the actual received signal and the reconstructed signal.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.4 no.4
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• pp.793-801
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• 2000

This paper presents the effect of lightning impulse current on ZnO varistors(390[V], 6.5[kA]) used in low-voltage AC mains as a protective device against transient overvoltages. The electrical characteristics of ZnO varistors are deteriorated by overtime impulse current, and a deteriorated ZnO varistor is brought to a thermal runaway and finally destroyed even in normal operating voltage. Therefore, it is important to estimate the changes of the electrical characteristics of ZnO varistors. A lightning impulse current standardized in IEC 61000-4-5 is applied to the varistors to accelerate deterioration, and the energy applied to the varistor at each time is about 12 [J]. In the experiment, various parameters such as leakage current, reference voltage are measured with the number of applied impulse current. Also, micro-structure changes of the varistors after applying the lightning impulse current of 200 times are compared. The electrical characteristics of the varistors are degraded by overtime impulse current, showing increase in leakage current and decrease in reference voltage.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.2
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• pp.207-212
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• 2011

A hydraulic breaker is an attachment installed at the end of excavator arm and is used for breaking. As per the authors' knowledge, there have been no research results on reducing the weight of the hydraulic breaker even though this weight reduction is very important for improving the performance of the excavator. In this study, we minimize the weight of the housing of the hydraulic breaker under normal operating conditions, while the maximum stress of the housing is lower than the allowable stress. A meta-model, which is generated by using the CAE results for the sampling design points determined by an orthogonal array, is used to solve the minimization problem. The weight of the housing according to the optimal design is found to be lower than the original weight by 4.8% while satisfying the constraint on the maximum stress.

• Journal of the Korean Institute of Intelligent Systems
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• v.18 no.3
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• pp.297-305
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• 2008

Recently, kernel methods have attracted great interests in the areas of pattern classification, function approximation, and anomaly detection. The role of the kernel is particularly important in the methods such as SVM(support vector machine) and KPCA(kernel principal component analysis), for it can generalize the conventional linear machines to be capable of efficiently handling nonlinearities. This paper considers the problem of combining radar and rain gauge observations utilizing the regression approach based on the kernel-based gaussian process and support vector learning. The data-assimilation results of the considered methods are reported for the radar and rain gauge observations collected over the region covering parts of Gangwon, Kyungbuk, and Chungbuk provinces of Korea, along with performance comparison.

• Journal of the Korea Society of Computer and Information
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• v.24 no.11
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• pp.29-39
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• 2019

As mobile robot applications increase in real life, the need of low cost autonomous driving are gradually increasing. We propose a novel vision-based real-time lane detection and tracking system that supports autonomous driving of mobile robots in constrained tracks which are designed considering indoor driving conditions of mobile robots. Considering the processing of lanes with various shapes and the pre-adjustment of operation parameters, the system structure with multi-operation modes are designed. In parameter tuning mode, thresholds of the color filter is dynamically adjusted based on the geometric property of the lane thickness. And in the unstable input mode of curved tracks and the stable input mode of straight tracks, lane feature pixels are adaptively extracted based on the geometric and temporal characteristics of the lanes and the lane model is fitted using the least-squared method. The track centerline is calculated using lane models and the motion model is simplified and tracked by a linear Kalman filter. In the driving experiments, it was confirmed that even in low-performance robot configurations, real-time processing produces the accurate autonomous driving in the constrained track.

• Journal of the Korean Society of Propulsion Engineers
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• v.13 no.2
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• pp.42-53
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• 2009

Gas turbine engine simulation program has been developed. In compressor and turbine, 2-D NS implicit code is used with k-$\omega$ SST turbulent model. In combustor, 0-D lumped method chemical equilibrium code is adopted under the limitations, the products are only 10 species of molecular and air-fuel is perfectly mixed state with 100% combustion efficiency at constant pressure. Fluid properties are shared on interfaces between engine components. The outlet conditions of compressor have been used as the inlet condition of combustor. The inlet condition of turbine comes from the compressor The back pressure in compressor outlet is transferred by the inlet pressure of turbine. Unsteady phenomena at rotor-stator in compressor and turbine is covered by mixing-plane method. The state of engine can be determined only by given inlet condition of compressor, outlet condition of turbine, equivalence ratio and rotating speed.

• Journal of the Institute of Convergence Signal Processing
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• v.21 no.4
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• pp.202-208
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• 2020

Recently, the importance of non-face-to-face has been emphasized due to COVID-19, and the use of sharing spaces is also expanding. The use of uncontact check-in technology for access control of sharing spaces reduces waiting time and optimizes workers' efficiency, resulting in operational cost savings. In this paper, we propose a sharing space access management system based on a mobile key and RCU (Room Control Unit), access to the facility using a mobile key, and monitor the facility using an RCU. Proposal system is for shared accommodation, rental field (residence, sale-selling hotel), shared office, etc. when there is a one-time visitor on a specific day and time, the corresponding password is delivered to the mobile platform to expose and key the existing password. It is supported by a field-adaptive system that can reduce discomfort such as delivery. In order to test the operation of the proposed integrated system, tests were conducted according to scenarios to understand the overall status of the user's reservation, check-in, and check-out, and a 100% success rate was derived for each item by setting performance indicators to prove test reliability.

• Journal of IKEEE
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• v.26 no.3
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• pp.488-493
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• 2022

In manufacturing sites, bearing fault in eletrically driven motors cause the entire system to shut down. Stopping the operation of this environment causes huge losses in time and money. The reason of this bearing defects can be various factors such as wear due to continuous contact of rotating elements, excessive load addition, and operating environment. In this paper, a motor driving environment is created which is similar to the domestic manufacturing sites. In addition, based on the established environment, we propose a dataset for bearing fault detection by collecting changes in vibration characteristics that vary depending on normal and defective conditions. The sensor used to collect the vibration characteristics is Microphone G.R.A.S. 40PH-10. We used various machine learning models to build a prototype bearing fault detection system trained on the proposed dataset. As the result, based on the deep neural network model, it shows high accuracy performance of 92.3% in the time domain and 98.3% in the frequency domain.

• Journal of the Korea Society for Simulation
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• v.19 no.3
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• pp.71-79
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• 2010

The simulator models for 500MW fossil power plant have been developed, and interconnected with the turbine control system to test and validate the digital instrumentation & control (I&C) systems before they are implemented in operating power plants. When the performance of a selected digital I&C system is tested, the corresponding simulator model is replaced by the plant digital I&C systems which is considered as a non-tunable system. The input/out variables of simulator models and control systems were mapped using the LabView in interface systems. This paper describes the interconnection method between the simulator model and the digital I&C system, and summarizes the validation test results performed at the condition of steady-state operation, normal evolution, and malfunction. The integrated validation method of digital I&C systems using the simulator models showed that the simulator can be used as a test bed for the implementation of digital I&C systems in power plants.