• Nuclear Engineering and Technology
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• v.54 no.4
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• pp.1167-1174
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• 2022

Cast austenitic stainless steels (CASSs) are widely used as structural materials in the nuclear industry. The main drawback of CASSs is the reduction in fracture toughness due to long-term exposure to operating environment. Even though ultrasonic non-destructive testing has been conducted in major nuclear components and pipes, the detection of cracks is difficult due to the scattering and attenuation of ultrasonic waves by the coarse grains and the inhomogeneity of CASS materials. In this study, the ultrasonic signals measured in thermally aged CASS were discriminated for the first time with the simple ultrasonic technique (UT) and machine learning (ML) models. Several different ML models, specifically the K-nearest neighbors (KNN), Support Vector Machine (SVM), and Multi-Layer Perceptron (MLP) models, were used to classify the ultrasonic signals as thermal aging condition of CASS specimens. We identified that the ML models can predict the category of ultrasonic signals effectively according to the aging condition.

• Nuclear Engineering and Technology
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• v.52 no.3
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• pp.552-559
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• 2020

This paper presents an observer-based chattering free robust optimal control scheme to regulate the total power of a nuclear reactor. The non-linear model of nuclear reactor is linearized around a steady state operating point to obtain a linear model for which an optimal second order integral sliding mode controller is designed. A second order integral sliding mode observer is also designed to estimate the unmeasurable states. In order to avoid the chattering effect, the discontinuous input of both observer and controller are designed using the super-twisting algorithm. The proposed controller is realized by combining an optimal linear tracking controller with a second order integral sliding mode controller to ensure minimum control effort and robustness of the closed-loop system in the presence of uncertainties. The condition for the selection of gains of discontinuous control based on the super-twisting algorithm is derived using a strict Lyapunov function. Performance of the proposed observer based control scheme is demonstrated through non-linear simulation studies.

• Proceedings of the KSR Conference
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• 2002.10b
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• pp.839-844
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• 2002

This research aims to test the running stability of the developed bogie with maximum operating speed of 350km/h, which of Korea TGV was 300km/h. The running stability test has been executed in status of a dummy car with one developed bogie and one dummy bogie on the roller rig to embody similar operation condition. The test has been done in the two rail conditions, i.e. excitation and non-excitation, respectively. Running speed has been increased by the roller step by step. In consequence, the developed bogie was proven to be able to run upto 400 Km/h without any unstable point in the non-excitation. Vibration characteristics of carbody also was within the value specified on the UIC 515.

• Plant Journal
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• v.18 no.3
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• pp.52-61
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• 2022

This study tested the effect of de-NOx Facility operating condition on Nox emisiion in a 125 MW wood pellet power plant in Yeongdong Eco Power Plant Unit 1, which is in operation. As SNCR urea flow rate increased, NOx emission gradually decreased, but ammonia slip after SCR increased. The boiler under test has a structure that is unfavorable to SNCR operation due to the high internal temperature, and the optimum location of the nozzle will be required. SCR dilution air temperature change did not affect the amount of NOx generated. Increasing SCR ammonia flow reduced the NOx emission at SCR outlet and also increased the NOx removal efficiency. However, the ammonia flow rate of 111 kg/h, which does not exceed the ammonia slip its own reference limit, is estimated to be the maximum operating standard. The increase in SCR mixer pressure reduced NOx emission and the removal efficiency was also measured to be the most effective variable to inhibit NOx production.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.11b
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• pp.105-108
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• 2005

The radiated noise from the automotive intake system should be predicted at the design stage. To this end, the precise measurement of in-duct acoustic source parameters of the intake system, i.e., the source strength and source impedance, is essential. Most of previous works on the measurement of acoustic source parameters were performed under a fixed engine speed condition. However, the requirement of vehicle manufacturer is the noise radiation pattern as a function of engine speed. In this study, the direct method was employed to measure the source parameters of engine intake system under a fixed engine speed and engine run-up condition. It was noted that the frequency spectra of source impedance hardly changes with varying the engine speed. Thus, it is reasonable to calculate the source strength under the engine run-up condition by assuming that source impedance is invariant with engine speed. Measured and conventional source models, i.e., constant pressure source, constant velocity source, and non-reflective source, were utilized to predict insertion loss and radiated sound pressure level. A reasonable prediction accuracy of radiated sound pressure level spectra from the intake system was given in the test vehicle when using the measured source characteristics which were acquired under the operating condition.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.8 no.5
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• pp.1026-1033
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• 2007

This paper compared simulation characteristics on the design of center strip by structure simulator with manufacture of 2.6GHz non-reciprocal element. Secures condition that affect in PIMD and confirmed change value of PIMD by change of condition. Implemented non-reciprocal element shows more than 20dB isolation characteristic at center frequency(2,650MHz) and has 0.2dB insertion loss in overall 100MHz operating bandwidth. Return losses of input and output port are measured below -20dB. IMD of non-reciprocal element exhibited superior value when there were no gaps between internal components and when materials having identical substances were used, and it showed an improving tendency when the pressure was increased higher, however, in case of applying pressure higher than a certain level, it results in damages, etc. of the magnet inside and ferrite as well, so then the characteristics of IMD was rapidly increased along with decrease of frequency characteristics.

• Journal of Korean Society of Water and Wastewater
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• v.25 no.2
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• pp.223-230
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• 2011

An electrolytic oxidation process was applied to remove odorous compounds from non-point odor sources including wastewater pipelines and manholes. In this study, a distance between the anode and the cathode of the electrolytic process was varied as a system operating parameters, and its effects on odor removal efficiencies and reaction characteristics were investigated. Odor precursors such as sediment organic matters and reduced sulfur/nitrogen compounds were effectively oxidized in the electrolytic process, and a change in oxidation-reduction potential (ORP) indicated that an stringent anaerobic condition shifted to a mild anoxic condition rapidly. At an electrode distance of 1 cm and an applied voltage of 30 V, a system current was maintained at 1 A, and the current density was 23.1 $mA/cm^{2}$. Under the condition, the removal efficiency of hydrogen sulfide in gas phase was found to be 100%, and 93% of ammonium ion was removed from the liquid phase during the 120 minute operating period. Moreover, the sulfate ion (${SO_4}^{2-}$) concentration increased about three times from its initial value due to the active oxidation. As the specific power consumption (i.e., the energy input normalized by the effective volume) increased, the oxidation progressed rapidly, however, the oxidation rate was varied depending on target compounds. Consequently, a threshold power consumption for each odorous compound needs to be experimentally determined for an effective application of the electrolytic oxidation.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.2344-2347
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• 2007

To generate negative ion, a small dielectric barrier discharge (DBD) plasma reactor was used in this study and operated by high AC voltage. With increasing of voltage, we can get more negative ions. However unfortunately, if the input voltage is too high, it will also cause formation of ozone which is very harmful to human being health. So the work of finding out the best condition of Voltage and frequency was carried out firstly. After several times of measurement, operating at 20 kHz frequency is the best condition generating high ion concentration without ozone. For the purpose of finding out the best reactor structure, two types of surface dielectric barrier discharge (DBD) reactors were examined to produce negative oxygen ions at the conditions of 20 kHz frequency. The results indicated that the surface DBD reactor with several small tips showed better characteristics for generation of negative oxygen ions at the same condition.

• The KSFM Journal of Fluid Machinery
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• v.12 no.1
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• pp.16-21
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• 2009

In the last five years, 91 accidents from portable gas ranges and non-refillable metallic gas cartridges have occurred. The gas cylinder installed with a relief valve was developed to prevent an explosive accident from the gas cartridge. In this study it was carried out to evaluate the safety of a gas cylinder mounted with a relief valve which can prevent an explosion. Under the real using condition and the extreme condition the gas cylinder is heated with an electric heater. Simultaneously, the operating pressure is checked and the suitability of releasing flux is evaluated. And the possibility of fire or explosion was tested when the gas was released from the relief valve at the real using condition. Using a numerical simulation method, the diffusion of butane gas released from a relief valve was visualized.

• Journal of ILASS-Korea
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• v.11 no.4
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• pp.228-233
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• 2006

There are two types of electric controlled fuel injection system in the gasoline engines of common vehicles. One is fuel return system and the other is fuel returnless system according to the methods of controlling injection pressures. It is important to understand the characteristics of these system in loaming and studying of engine, but it is very difficult without a special equipment in reality. The purpose of this paper is to develop the emulation system that can be compensated with the amount of injection fuel according to various driving conditions, battery voltage, cooling water temperature, and engine speed, may be appeared in real driving, and especially can analyze the difference between the electric signal controlling the amount of injection fuel and its result, and nullity injection duration. With the developed system, we can conveniently set various and completed driving condition and so can acquire the useful information such as non-uniformity rate and mass of injection fuel using waveform analysis and measurement modules. It must be a very useful and sophisticated system to instruct and learn the features and operating states of injection system, and to study f3r improving the performance of it.