• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.05a
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• pp.82-87
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• 2003

Nuclear fuel with a big slenderness ratio is susceptible to flow-induced vibration under very severe conditions of high temperature, high flow and exposure to irradiation in nuclear reactor. The fuel assembly should, therefore, be designed to escape any resonance due to the vibration during the reactor operation, in particular, in case of the design changes. In addition, the amplitudes due to the grid vibration, the fuel rod vibration and the fuel assembly vibration should be minimized to reduce the grid-to-rod fretting wear. Fuel assembly vibration tests in air at room temperature and in water at high temperature have been performed to investigate fuel vibration behaviors. The frequency and damping during the test in air have been compared to those in water. Through the hydraulic test, the advanced assembly has been evaluated not to be susceptible to any resonance. In addition, the test data from the tests can be used to make fuel model and to evaluate grid-to-rod fretting wear.

• The Journal of the Acoustical Society of Korea
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• v.13 no.2
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• pp.23-29
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• 1994

In this paper, the measured in-water radiation impedance of cylindrical piezoelectric radiator with finite baffle is compared to the existing theoretical result of that with infinite baffle and the effect of baffle on the radiation impedance is examined. Comparision between measurement and theoretical result of radiation impedance shows that the measured radiation impedance tends to be that of the infinite baffle as the baffle length increases. Another finding of the comparision in that the effect of baffle is more dominant in radiation reactance than in radiation resistance. Therefore, for the use of theoretical radiation impedance of infinite baffle on the design of acoustic transducer, the impedance compensation to the baffle length should conducted.

• International Journal of Automotive Technology
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• v.6 no.2
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• pp.133-139
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• 2005

In this study, a three-dimensional transient simulation with a knock model was performed to predict knock occurrence and autoignition site in a heavy-duty LPG engine. A FAE (Flame Area Evolutoin) premixed combustion model was applied to simulate flame propagation. The coefficient of the reduced kinetic model was adjusted to LPG fuel and used to simulate autoignition in the unburned gas region. Engine experiments using a single-cylinder research engine were performed to calibrate the reduced kinetic model and to verify the results of the modeling. A pressure transducer and a head-gasket type ion-probe circuit board were installed in order to detect knock occurrences, flame arrival angles, and autoignition sites. Knock occurrence and position were compared for different piston bowl shapes. The simulation concurred with engine experimental data regarding the cylinder pressure, flame arrival angle, knock occurrence, and autoignition site. Furthermore, it provided much information about in-cylinder phenomena and solutions that might help reducing the knocking tendency. The knock simulation model presented in this paper can be used for a development tool of engine design.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2004.05b
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• pp.635-641
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• 2004

This paper presents a new low-cost RF Built-In Self-Test (BIST) circuit for measuring transducer voltage gain, noise figure and input impedance of 5.25GHa low noise amplifier (LNA). The BIST circuit is designed using 0.18${\mu}{\textrm}{m}$ SiGe technology. The test technique utilizes input impedance matching and output transient voltage measurements. The technique is simple and inexpensive. Total chip size has additional area of about 18% for BIST circuit.

• Advances in Computational Design
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• v.4 no.4
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• pp.367-379
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• 2019

Multiple Inputs and Multiple Outputs (MIMO) Fuzzy logic model is developed to predict the engine performance and emission characteristics of pongamia pinnata biodiesel with hydrogen injection. Engine performance and emission characteristics such as brake thermal efficiency (BTE), brake specific energy consumption (BSEC), hydrocarbon (HC), carbon monoxide (CO), carbon dioxide ($CO_2$) and nitrous oxides ($NO_X$) were considered. Experimental investigations were carried out by using four stroke single cylinder constant speed compression ignition engine with the rated power of 5.2 kW at variable load conditions. The performance and emission characteristics are measured using an Exhaust gas analyzer, smoke meter, piezoelectric pressure transducer and crank angle encoder for different fuel blends (Diesel, B10, B20 and B30) and engine load conditions. Fuzzy logic model uses triangular and trapezoidal membership function because of its higher predictive accuracy to predict the engine performance and emission characteristics. Computational results clearly demonstrate that, the proposed fuzzy model has produced fewer deviations and has exhibited higher predictive accuracy with acceptable determination correlation coefficients of 0.99136 to 1 with experimental values. The developed fuzzy logic model has produced good correlation between the fuzzy predicted and experimental values. So it is found to be useful for predicting the engine performance and emission characteristics with limited number of available data.

• Journal of Soil and Groundwater Environment
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• v.18 no.5
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• pp.39-45
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• 2013

Many researchers have studied the effectiveness of ultrasound in chemical and environmental engineering fields including material synthesis, pollutant removal, cleaning, extraction, and disinfection. Acoustic cavitation induced by ultrasound irradiation in aqueous phase can cause various sonophysical and sonochemical reactions without any chemicals. However most of the previous studies focused only on the relationships between ultrasonic conditions and the results of sonochemical reactions in lab-scale sonoreactors. As a results of this, only a few studies have been devoted to design and optimization of industrial scale sonoreactors. In this study, the effect of the distance between two opposite transducer modules on sonochemical reactions was investigated in single and dual irradiation systems (334 kHz) for four distances including 50, 100, 150, and 200 mm using KI dosimetry. It was found that the dual irradiation systems provided higher performance in terms of the zeroth reaction coefficient and the cavitation yield compared to the single irradiation systems. The sonochemiluminescence (SCL) images for the visualization of the cavitation field showed that cavitation active zone was larger and sonochemical reaction intensity was much higher in the dual irradiation system than in the single irradiation system.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.18 no.6
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• pp.69-75
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• 2019

In recent years, the driving performance and exhaust sound quality in automobiles have been recognized as important factors, as they maximize the driving fun to fulfil the demands of customers. Therefore, many automobile manufacturers are studying various exhaust pipe shapes to improve sound quality and optimize exhaust pressure. The objective of the exhaust pipe design is to maximize the engine efficiency using optimal exhaust pressure settings. In this study, an exhaust system was fabricated with different junction shapes, and the results were analyzed through various experiments. The exhaust gas pressure acting inside the exhaust pipe was measured using a pressure transducer. Meanwhile, the vibration generated in the vehicle was measured in three axial directions and analyzed. The ground noise generated in the indoor and outdoor of the vehicle was measured, and the noise generated at the maximum output was measured and analyzed.

• Journal of Sensor Science and Technology
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• v.31 no.5
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• pp.324-329
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• 2022

This paper proposes a shift-register-based multichannel ultrasonic focusing delay control method using a complex programmable logic device (CPLD) for a high resolution of ultrasonic focusing system. The proposed method can achieve the ultrasonic focusing through the delay control of driving signals of each ultrasonic transducer of an ultrasonic array. The delay of the driving signals of all ultrasonic channels can be controlled by setting the shift register in the CPLD. The experiment verified that the frequency of the clock used for the delay control increased, the error of the focusing point decreased, and the diameter of the focusing point decreased as the length of the shift register in the proposed method. The proposed method used only one CPLD for ultrasonic focusing and did not require to use complex hardware circuits. Therefore, the resources required for the design of an ultrasonic focusing system could be reduced. The proposed method can be applied to the fields of human computer interaction (HCI), virtual reality (VR) and augmented reality (AR).

• The Journal of the Acoustical Society of Korea
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• v.28 no.3
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• pp.213-221
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• 2009

The time reversal mirror (TRM) method for underwater communications has been developed to improve transmission performance with low complexity. However, digital communication parameters for TRM have not been researched deeply. This paper demonstrates that the TRM scheme obtains spatial diversity gain similar to multiple antennas, and proposes design methodologies of symbol interval, frame duration and transmission protocol for time reversal mirror transmission. Simulation results show that spatial diversity gain is achieved and the effect of ISI decreases as the number of transducer increases.

• The Journal of the Acoustical Society of Korea
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• v.33 no.5
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• pp.300-308
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• 2014

Photoacoustic imaging is a useful tool for the diagnosis of atherosclerosis because it is capable of providing anatomical and pathological information at the same time. A photoacoustic signal detector is a pivotal element to achieve high spatial resolution, so that it should have broadband spectrum with a high center frequency. Since a photoacoustic imaging probe is directly inserted into blood vessel to diagnose atherosclerosis, the total size of the photoacoustic signal detector should be less than 1 mm. The main purpose of this paper is to demonstrate that PVDF can be used as an active material for the photoacoustic signal detector with a high frequency and broadband characteristic. The photoacoustic signal detector developed in this study was a single element ultrasound transducer with an aperture of $0.5{\times}0.5mm$ and the total size of 1 mm. In the design stage, the natural focal depth was adjusted for an effective focal area to cover the region of interest, i.e., 1~5 mm in depth. This was because geometrical focusing could not be used due to the small aperture. Through a pulse-echo test, it was ascertained that the developed photoacoustic signal detector has the -6 dB bandwidth ranging between 40.1 and 112.8 MHz and the center frequency of 76.83 MHz.