• Journal of the Korean Society for Nondestructive Testing
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• v.31 no.1
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• pp.68-76
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• 2011

Acoustic emission(AE) has emerged as a powerful nondestructive tool to detect any further growth or expansion of preexisting defects or to characterize failure mechanisms. Recently, this kind of technique, that is an in-situ monitoring of inside damages of materials or structures, becomes increasingly popular for monitoring the integrity of large structures like a huge wind turbine blade. Therefore, it is required to find a symptom of damage propagation before catastrophic failure through a continuous monitoring. In this study, a new damage location method has been proposed by using signal mapping algorithm, and an experimental verification is conducted by using small wind turbine blade specimen; a part of 750 kW real blade. The results show that this new signal mapping method has high advantages such as a flexibility for sensor location, improved accuracy, high detectability. The newly proposed method was compared with traditional AE source location method based on arrival time difference.

• Journal of Advanced Navigation Technology
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• v.26 no.5
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• pp.319-324
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• 2022

If radio interference occurs or there is no navigation device, radio navigation of high-speed moving object becomes impossible. Nevertheless, if there are multiple ground stations and precise range measurement between the high-speed moving object and the ground station can be secured, it is possible to estimate the position of moving object. This paper proposes a position estimation method using high-precision TDOA measurement generated using TLM signal. In the proposed method, a common error of moving object is removed using the TDOA measurements. The measurements is generated based on TLM signal including SOQPSK PN symbol capable of precise timing synchronization. Therefore, since precise timing synchronization of the system has been performed, the timing error between ground stations has a very small value. This improved the position estimation performance by increasing the accuracy of the measured values. The proposed method is verified through software-based simulation, and the performance of estimated position satisfies the target performance.

• The Journal of the Acoustical Society of Korea
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• v.39 no.6
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• pp.600-605
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• 2020

In this paper, we propose a sound event detection method using a multi-channel multi-scale neural networks for sound sensing home monitoring for the hearing impaired. In the proposed system, two channels with high signal quality are selected from several wireless microphone sensors in home. The three features (time difference of arrival, pitch range, and outputs obtained by applying multi-scale convolutional neural network to log mel spectrogram) extracted from the sensor signals are applied to a classifier based on a bidirectional gated recurrent neural network to further improve the performance of sound event detection. The detected sound event result is converted into text along with the sensor position of the selected channel and provided to the hearing impaired. The experimental results show that the sound event detection method of the proposed system is superior to the existing method and can effectively deliver sound information to the hearing impaired.

• Journal of Korean Society on Water Environment
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• v.32 no.3
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• pp.243-252
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• 2016

In cases of water pollution accidents, accurate prediction for arrival time and concentration of contaminants in a river is essential to take proper measures and minimize their impact on downstream water intake facilities. It is critical to fully understand the behavior characteristics of contaminants on river surface, especially in case of oil spill accidents. Therefore, in this study, the effects of main parameters of advection and diffusion of contaminants were analyzed and validated by comparing the results of Lagrangian particle tracking (LPT) simulation of Environmental Fluid Dynamic Code (EFDC) model with those of Global Position System (GPS)-equipped drifter experiment. Prevention scenario modeling was accomplished by taking cases of movable weir operation into account. The simulated water level and flow velocity fluctuations agreed well with observations. There was no significant difference in the speed of surface particle movement between 5 and 10 layer modeling. Therefore, 5 layer modeling could be chosen to reduce computational time. It was found that full three dimensional modeling simulated wind effects on surface particle movements more sensitively than depth-averaged two dimensional modeling. The diffusion range of particles was linearly proportional to horizontal diffusivity by sensitivity analysis. Horizontal diffusivity estimated from the results of GPS-equipped drifter experiment was 0.096 m²/sec, which was considered to be valid for applying the LPT module in this area. Finally, the scenario analysis results showed that particle movements could be stagnant when discharge from the upstream weir was reduced, implying the possibility of securing time for mitigation actions such as oil boom installation and wiping oil contaminants. The outcomes of this study can help improve the prediction accuracy of particle tracking simulation to establish the most suitable mitigation plan considering the combination of movable weir operation.

• Geomechanics and Engineering
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• v.25 no.3
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• pp.207-219
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• 2021

Several additives are used to enhance the geotechnical properties (e.g., shear wave velocity, shear modulus) of soils to provide sustainable, economical and eco-friendly solutions in geotechnical and geo-environmental engineering. In this study, piezoelectric ring actuators are used to measure the shear wave velocity of unreinforced, fiber, cemented, and fiber reinforced cemented Toyoura sand. One dimensional oedometer tests are performed on medium dense specimens of Toyoura sand-cement-fiber-silica flour mixtures with different percentages of silica flour (0-42%), fiber and cement (e.g., 0-3%) additives. The experimental results indicate that behavior of the mixtures is significantly affected by the concentration of silica flour, fiber and cement additives. Results show that with the addition of 1-3% of PVA fibers, the shear wave velocity increases by only 1-3%. However, the addition of 1-4% of cement increases the shear wave velocity by 8-35%. 10.5-21% increase of silica flour reduces the shear wave velocity by 2-5% but adding 28-42% silica flour significantly reduces the shear wave velocity by 12-31%. In addition, the combined effect of cement and fibers was also found and with only 2% cement and 1% fiber, the shear wave velocity increase was found to be approximately 24% and with only 3% cement and 3% fibers this increased to 35%. The results from this study for the normalized shear modulus and normalized mean effective stress agree well with previous findings on pure Toyoura sand, Toyoura silty sand, fiber reinforced, fiber reinforced cemented Toyoura sand. Any variations are likely due to the difference in stress history (i.e., isotropic versus anisotropic consolidation) and the measurement method. In addition, these small discrepancies could be attributed to several other factors. The potential factors include the difference in specimen sizes, test devices, methods of analysis for the measurement of arrival time, the use of an appropriate Ko to convert the vertical stresses into mean effective stress, and sample preparation techniques. Lastly, it was investigated that there is a robust inverse relationship between α factor and 𝞫₀ exponent. It was found that less compressible soils exhibit higher 𝜶 factors and lower 𝞫₀ exponents.

• The Journal of the Acoustical Society of Korea
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• v.43 no.4
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• pp.414-421
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• 2024

In this paper, we design and verify a system that can detect piping leakage noise in an environment with significant reverberation and reflection using a multi-channel acoustic sensor module as a technology to prevent major plant accidents caused by leakage. Four-channel microphones arranged in a tetrahedron are designed as a single sensor module to measure three-dimensional sound intensity vectors. In an environment with large effects of reverberation and reflection, the measurement error of each sensor module increases on average, so after placing multiple sensor modules in the field, measurement results showing locations with large errors due to effects such as reflection are excluded. Using the intersection between three-dimensional vectors obtained from several pairs of sensor modules, the coordinates where the sound source is located are estimated, and outliers (e.g., positions estimated to be outside the site, positions estimated to be far from the average position) are detected and excluded among the points. For achieving aforementioned goal, an excluding algorithm by deciding the outliers among the estimated positions was proposed. By visualizing the estimated location coordinates of the leakage sound on the site drawing within 1 second, we construct and verify a system that can detect the location of the leakage sound in real time and enable immediate response. This study is expected to contribute to improving accident response capabilities and ensuring safety in large plants.

• Journal of the Korean Society of Marine Environment & Safety
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• v.19 no.5
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• pp.531-537
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• 2013

In this study, we conducted real-time measurement at the ship arrivals and departures at the port and at a constant speed of 150 rpm for exhaust emissions from a main engine installed on the training ship, HANBADA, of Korea Maritime University. The result showed that the concentration of nitrogen oxide was measured in the range of 800 ppm to 1,000 ppm at constant speed mode. On the other hand, the concentration of nitrogen oxide during ship arrivals and departures was significantly fluctuated between 210 ppm and 1,230 ppm. And, the concentration of carbon oxide at the arrivals and departures was also larger than that of at constant speed mode. These results show that the ship maneuvering skills to prevent a sudden load change of main engine at the arrivals and departures of ship is needed. Additionally, it means that the difference of exhaust emissions generated between the constant speed mode and the arrival/departure has to be considered when invented many technologies are adopted into the reduction technologies of air pollutants from ships.

• Journal of IKEEE
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• v.25 no.2
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• pp.243-251
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• 2021

In this paper, we propose a measurement technique of indoor location based on markerless applicable to AR. The proposed technique has the following originality. The first is to extract feature points and use them to generate local patches to enable faster computation by learning and using only local patches that are more useful than the surroundings without learning the entire image. Second, learning is performed through deep learning using the convolution neural network structure to improve accuracy by reducing the error rate. Third, unlike the existing feature point matching technique, it enables indoor location measurement including left and right movement. Fourth, since the indoor location is newly measured every frame, errors occurring in the front side during movement are prevented from accumulating. Therefore, it has the advantage that the error between the final arrival point and the predicted indoor location does not increase even if the moving distance increases. As a result of the experiment conducted to evaluate the time required and accuracy of the measurement technique of indoor location based on markerless applicable to AR proposed in this paper, the difference between the actual indoor location and the measured indoor location is an average of 12.8cm and a maximum of 21.2cm. As measured, the indoor location measurement accuracy was better than that of the existing IEEE paper. In addition, it was determined that it was possible to measure the user's indoor location in real time by displaying the measured result at 20 frames per second.

• KIPS Transactions on Computer and Communication Systems
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• v.1 no.2
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• pp.79-86
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• 2012

An economic ship routing means to sail a ship with a goal of minimizing the fuel consumption by utilizing weather forecast information, and various such systems have been recently studied. For a successful economic ship routing system, an efficient algorithm is needed to search an optimal geographical path, and most of the previous systems were approaching to that problem through a minimal static-cost path search algorithm based on the Dijkstra algorithm. To apply that kind of search algorithm, the cost of every edge assigned with the estimated fuel consumption should be constant. However, that assumption is not practical at all considering that the actual fuel consumption is determined by the weather condition when the ship will pass the edge. To overcome such a limitation, we propose a new optimal ship routing system based on a minimal dynamic-cost path search algorithm by properly modifying the Dijkstra algorithm. In addition, we propose a method which efficiently reduces the search space by using the $A^*$ algorithm to decrease the running time. We compared our system with the shortest path-based sailing method over ten testing routes and observed that the former reduced the estimated fuel consumption than the latter by 2.36% on average and the maximum 4.82% with little difference of estimated time of arrival.

• Journal of Trauma and Injury
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• v.25 no.4
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• pp.166-171
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• 2012

Purpose: In patients with traumatic hemoperitoneum or pelvic bone fracture who underwent angiography and embolization, we want to find the prognostic factors related with mortality. Methods: Patients(333 patients) who visited our hospital with traumatic injury from March 2008 to April 2012 were included in this study. Only 37 patients with traumatic hemoperitoneum or pelvic bone fracture underwent angiography and embolization. A retrospective review was conducted, and Glasgow coma scale (GCS), Revised trauma score (RTS), Injury severity score (ISS), initial laboratory finding and time interval, the amount of transfusion from the arrival at the ER to the start of embolization, and the vital signs before and after procedure were checked. Stastical analysis was conducted using the Chi square and Mann-Whitney U test. Results: In univariate analysis, the amount of transfusion, the base deficit before procedure, the systolic blood pressure before and after the procedure, the GCS, the RTS and the ISS were significantly associated with prognosis. In the multivariate analysis, the ISS and the base deficit had significant association with prognosis. Of the 37 patients who underwent angiography and embolization, 31 patients needed not additional procedure (Group A) while the other 6 patients needed an additional procedure (Group B). After procedure, a statistically significant higher blood pressure was observed in Group A than in Group B. As to the difference in blood pressure before and after the procedure, a statistically significant decrease in systolic blood pressure was observed in Group B, but an increase was observed in Group A. Conclusion: In traumatic hemoperitoneum or pelvic bone fracture patients who underwent angiography and embolization, GCS, ISS, RTS, transfusion amount before the procedure, initial base deficit and systolic blood pressure were factors related to mortality. When patients who underwent angiography and embolization only were compared with patients who underwent re-embolization or additional procedure after the first embolization, an increase in systolic blood pressure after embolization was a prognostic factor for successful control of bleeding.