• KSCE Journal of Civil and Environmental Engineering Research
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• v.31 no.5A
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• pp.351-360
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• 2011

Jacket-type offshore structures are always exposed to severe environmental conditions such as salt, high speed of current, wave, and wind compared with other onshore structures. In spite of the importance of maintaining the structural integrity for offshore structure, there are few cases to apply structural health monitoring (SHM) system in practice. The impedance-based SHM is a kind of local SHM techniques and to date, numerous techniques and algorithms have been proposed for local SHM of real-scale structures. However, it still requires a significant challenge for practical applications to compensate unknown environmental effects and to extract only damage features from impedance signals. In this study, the impedance-based SHM was carried out on a 1/20-scaled model of an Uldolmok current power plant structure under changes in temperature and transverse loadings. Principal component analysis (PCA) was applied using conventional damage index to eliminate principal components sensitive to environmental change. It was found that the proposed PCA-base approach is an effective tool for long-term SHM under significant environmental changes.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.23 no.6
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• pp.265-271
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• 2013

Czochralski (CZ) growth process is one of the most important techniques for growing high quality sapphire single crystal for LED application. In this study, the inductively-heated CZ growth processes for the sapphire crystal of 300 mm length have been analyzed numerically using finite element method. The hot zone structures were modified with the crucible geometry change and the additional insulation layer installed above the crucible. The results show that the solid-liquid interface height decreased from about 80 mm at initial stage to 40 mm after mid-stage due to achieve the growth speed balance. Also the optimal input power of the modified system was similar with the original one due to the compensation effects of the crucible geometry and additional insulation. The crystal temperature grown by the modified CZ grower was increased about 10 K than the original one. Therefore the sapphire crystal of 300 mm height was grown successfully.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.28 no.2
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• pp.139-144
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• 2015

Recently, to realize sound-absorbing structures, we have to insert sound-absorbing materials into wall. These shapes are taken limitations because sound-absorbing materials should be fixed. Therefore, the sound absorption is changed by environment that used the sound-absorbing materials. On the other hand, we will take same effect without sound-absorbing material, if we change the shape of wall to sound absorbing structure. If we use this sound absorbing structure, we can get benefits by removing limitation of materials. Therefore we suggest perforated plate for effective sound-absorbing structure. We confirmed the function of sound-absorption of this structure using equivalent property. Then, we found the similarity between perforated plate and resonator. Also, we verify these theories through computer simulation by FEM(Finite Element Method). Finally, we validated that perforated plate has function of sound absorption without sound-absorbing material. This perforated plate is used for sound-absorbing material of buildings and transportations such as vehicle, train etc. Also, these results could be further used basic tool for design of sound-absorption structure.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.42 no.7 s.337
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• pp.35-40
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• 2005

This paper proposes a fractional-N phase-locked loop (PLL) frequency synthesizer using the 3rd order ${\Delta}{\sum}$ modulator for 900MHz medium speed wireless link. The LC voltage-controlled oscillator (VCO) is used for the good phase noise property. To reduce the lock-in time, a charge pump has been developed to control the pumping current according to the frequency steps and the reference frequency is increased up to 3MHz. A 36/37 fractional-N divider is used to increase the reference frequency of the phase frequency detector (PFD) and to reduce the minimum frequency step simultaneously. A 3rd order ${\Delta}{\sum}$ modulator has been developed to reduce the fractional spur VCO, Divider by 8 Prescaler, PFD and Charge pump have been developed with 0.25um CMOS, and the fractional-N divider and the third order ${\Delta}{\sum}$ modulator have been designed with the VHDL code, and they are implemented through the FPGA board of the Xilinx Spartan2E. The measured results show that the output power of the PLL is about -lldBm and the phase noise is -77.75dBc/Hz at 100kHz offset frequency. The minimum frequency step and the maximum lock-in time are 10kHz and around 800us for the maximum frequency change of 10MHz, respectively.

• The Journal of the Acoustical Society of Korea
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• v.39 no.6
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• pp.606-614
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• 2020

In this paper, we analyze the influences of ship traffic and marine weather information on underwater ambient noise. Ambient noise is an important environmental factor that greatly affects the detection performance of underwater sonar systems. In order to implement an automated system such as prediction of detection performance using artificial intelligence technology, which has been recently studied, it is necessary to obtain and analyze major data related to these. The main sources of ambient noise have various causes. In the case of sonar systems operating in offshore seas, the detection performance is greatly affected by the noise caused by ship traffic and marine weather. Therefore, in this paper, the impact of each data was analyzed using the measurement results of ambient noise obtained in coastal area of the East Sea of Korea, and public data of nearby ship traffic and ocean weather information. As a result, it was observed that the underwater ambient noise was highly correlated with the change of the ship's traffic volume, and that marine environment factors such as wind speed, wave height, and rainfall had an effect on a specific frequency band.

• The Korean Journal of Malacology
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• v.32 no.3
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• pp.185-188
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• 2016

PANM-DB (version 1.0) was constructed as a web-based interface for the analysis and annotation of Next-Generation Sequencing (NGS) data of Mollusca, Arthropoda, and Nematoda. The database collected the sequences of Protostomes (Mollusca, Arthropoda, and Nematoda) from the NCBI Taxonomy Browser, and the same were compiled in a multi-FASTA format and stored using the formatdb program. This improved the processing of the RNA-seq sequences in terms of speed and hit percentage. PANM-DB has been successfully used for the transcriptome annotation of butterfly, land snail, and other commercial mollusca. We have improved the database by updating the same with new sequences and version 2.0 contains a total of 7,571,246 protein sequences (two times more as compared to version 1.0). Furthermore, the updated version contains the Cephalopoda database. The constructed web interface is available that independently analyses following these updates that is an improvement of the mollusks BLAST server. The updated version of PANM-DB will be helpful for the analysis of the NGS based sequencing data of non-model species, especially Mollusca, Arthropoda, Nematoda.

• Journal of the Korean Geosynthetics Society
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• v.18 no.4
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• pp.115-127
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• 2019

The low-flow grouting injection technique, the target construction method for this study, is a method of pouring mortar into the ground by non-emission replacement principle, which can be expected to increase the density of the ground, and, in some cases, be used as a base file using the strength of the high injection solids, along with low noise, low pollution, and high durability. To verify that the dynamic characteristics of the ground are improved by the low-flow injection technique, the test work was conducted on the site and physical tests were performed, and the quality of the improvement formed in the ground was verified through the indoor test on the core and core recovery rate was analyzed. The density logs test layer calculated the volume density of the ground layer by using the Compton scattering of gamma-rays, and the sonic logs was tested on the ground around the drill hole using a detector consisting of sonar and receiver devices inside the drill hole. As a result of the measurement of the change in physical properties (density and sonic logs) before and after grouting, both properties were basically increased after infusion of grout agent. However, the variation in density increase was greater than the increase in speed after grouting, and the ground density measurement method was thought to be effective in measuring the fill effect of the filler. Strength and core recovery rates were measured from specimens taken after the age of 28 days, and the results of the test results of the diffusion and strength test of the improved products were verified to satisfy the design criteria, thereby satisfying the seismic performance reinforcement.

• KIPS Transactions on Computer and Communication Systems
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• v.6 no.11
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• pp.445-452
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• 2017

Electric pole is a supporting beam used for power transmission/distribution which accelerometer are used for measuring a external force. The meteorological condition has various effects on the external forces of electric pole. One of them is the elasticity change of the aerial wire. It is very important to perform modelling. The acceleration sensor is converted into a pitch and a roll angle. The meteorological condition has a high correlation between variables, and selecting significant explanatory variables for modeling may result in the problem of over-fitting. We constructed high deviance explained model considering multicollinearity using the Generalized Additive Model which is one of the machine learning methods. As a result of the Variation Inflation Factor Test, we selected and fitted the significant variable as temperature, precipitation, wind speed, wind direction, air pressure, dewpoint, hours of daylight and cloud cover. It was noted that the Hours of daylight, cloud cover and air pressure has high explained value in explonatory variable. The average coefficient of determination (R-Squared) of the Generalized Additive Model was 0.69. The constructed model can help to predict the influence on the external forces of electric pole, and contribute to the purpose of securing safety on utility pole.

• Journal of the Korean Society of Marine Environment & Safety
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• v.21 no.1
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• pp.40-46
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• 2015

Arctic Ocean has rapidly melted due to global warming, by this, commercial ship has been operating through the area. Reason to develop the Northern Sea Route(NSR) even in extreme conditions, the distance than the existing route is shortened, which bring economic benefits. For these reason, the International Maritime Organization(IMO) established safety standards of the Arctic navigation(Polar Code) in order to ensure safe operation in the Northern Sea Route. In this study, it has been described ice types and safety standards of Artic vessel what officer needs to know for safe navigation on the Arctic Ocean. And It was verified by simulation the theoretical knowledge for the safe operation of the Arctic vessel. As a result, it was found that ship needs to reduce speed and analyze ice for safe operation before enter into the ice, it is necessary to enter at right angle to break ice safety and efficiently. Also according to the result of the simulation of navigation entering in ice channel(Lead), it was difficult to change course, it is believed that require emergency training for passing Vessel. In the future, It shall be analyzed precisely under various conditions of scenario.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.40 no.9
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• pp.1754-1766
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• 2015

Packet classification carried out in Internet routers is one of the challenging tasks, because it has to be performed at wire-speed using five header fields at the same time. In this paper, we propose a leaf-pushed AQT bitmap trie. The proposed architecture applies the leaf-pushing to an area-based quad-trie (AQT) to reduce unnecessary off-chip memory accesses. The proposed architecture also applies a bitmap trie, which is a kind of multi-bit tries, to improve search performance and scalability. For performance evaluation, simulations are conducted by using rule sets ACL, FW, and IPC, with the sizes of 1k, 5k, and 10k. Simulation results show that the number of off-chip memory accesses is less than one regardless of set types or set sizes. Additionally, since the proposed architecture applies a bitmap trie, the required number of on-chip memory accesses is the 50% of the leaf-pushed AQT trie. In addition, our proposed architecture shows good scalability in the required on-chip memory size, where the scalability is identified by the stable change in the required memory sizes, as the size of rule sets increases.