• 한국해안해양공학회지
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• 제7권3호
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• pp.209-218
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• 1995

비선형 간섭항들을 고려하여 다방향 심해 불규칙파를 해석하였다. 선형 위상함수를 사용하여 섭동해를 파기을기의 3차항까지 구하였으며, 비선형 간섭에 기인하는 파특성들의 변조를 살펴보았다. 해의 수렴성은 파기울기뿐 아니라 파성분들 사이의 파장비에도 크게 영향을 받는다. 섭동해중 장파의 특성을 나타내는 성분은 빠른 수렴속도를 가지나, 장파의 의해 간섭되어지는 단파의 섭동해는 수렴속도가 매우 느리거나 발산하는 경향을 보인다. 단파해에서 발생하는 수렴의 어려움은 단파 주파수의 연조특성을 선형파형법이 정확히 표현하지 못하기 때문이다. 따라서 광대역 파스텍트럼의 특성을 갖는 해양파에서 고주파 성분의 특성을 해석하기 위한 목적으로는 선형파형법의 사용이 부적합하다.

• 한국정밀공학회지
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• 제34권2호
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• pp.125-131
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• 2017

2-Axis Pan and Tilt Motion Platform, a complex multivariate non-linear system, may incur any disturbance, thus requiring system controller with robustness against various disturbances. In this study, we designed an adaptive backstepping compensated controller by estimating the disturbance and error using the Radial Basis Function Neural Network (RBF NN). In this process, Uniformly Ultimately Bounded (UUB) was demonstrated via Lyapunov and stability was confirmed. By generating progressive disturbance to the irregular frequency and amplitude changes, it was verified for various environmental disturbances. In addition, by setting the RBF NN input vector to the minimum, the estimated disturbance compensation process was analyzed. Only two input vectors facilitated compensatory function of RBF NN via estimating the modeling and control error values as well as irregular disturbance; the application of the process resulted in improved backstepping controller performance that was confirmed through simulation.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2008년도 춘계학술대회 논문집
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• pp.1308-1314
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• 2008

In this paper, Seoulmetro that is the first operation organization which operates a city railroad rolling-stock maintenance RIMS(rolling stock information maintenance system) collected and analyzed a light maintenance data and introduced time a series analysis technique to find the way how to contribute to a use efficiency improvement of a city railroad. The purpose of time a series analysis is to remove a seasonal change including data and to check an irregular fluctuation. First of all, a collection range of the data comes under a light maintenance, however it needs a data of more than 3 years to check the seasonal change. We put a study for an accumulated scope that the data satisfy a period like this and are able to extend a range of the study when time flys forward. The data used for study is filtered using a movement average method after passing proper selection working and is solved with a method which looks for season index. Using the season index that was getten in here, we predict a light working frequency, if it has an irregular change, we will contribute it to a city railroad a use efficiency improvement and establish the cause by carrying out prevent maintenance in advance.

• 천문학논총
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• 제32권3호
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• pp.421-438
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• 2017

Through the short-period variability survey program, we obtained time-series BV CCD images for $1.5^{\circ}{\times}1.0^{\circ}$ region around the young open cluster NGC 457. As a result, we have detected 61 variable stars including 31 new ones after checking light curves of all stars by eyes. The 61 variable stars were included 14 ${\delta}$ Scuti variable stars, a ${\beta}$ Cephei variable star, 10 variable Be and slowly pulsating B stars, 13 eclipsing binary stars, 21 semi-long periodic or slow irregular variables and an RR Lyrae variable star, respectively. Many variable B-type stars were known through a well-defined zero-age main sequence to the ${\beta}$ Cepheid region of NGC 457. Most of the variable B-type stars found this paper were known variable stars. But, 11 out of 14 ${\delta}$ Scuti variable stars were newly discovered. The new variable stars except for ${\delta}$ Scuti stars were 4 variable B-type stars, 5 eclipsing binaries and 11 semi-long periodic or slow irregular variables. We have performed frequency analysis for all ${\delta}$ Scuti stars, a ${\beta}$ Cepheid star and an RR Lyrae star.

• International Journal of Naval Architecture and Ocean Engineering
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• 제9권1호
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• pp.25-34
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• 2017

The concentric dual-buoy Wave Energy Converter (WEC), which consists of external buoy (hallow-cylinder) with toroidal appendage and cylindrical internal buoy within the moon-pool is suggested in this research and its performance in various wave conditions is studied. The Linear Electric Generator (LEG), consisting of a permanent magnet and coils, is used as a direct Power Take-Off (PTO) system. To maximize the electrical energy extracted from the PTO system, the relative heave motions between the dual buoys must be highly amplified by the multiple resonance phenomena of dual-buoy and internal-fluid motions. The high-performance range can be widened by distributing those natural frequencies with respect to the peak frequency of the wave spectrum. The performance of the newly developed dual-buoy WEC was measured throughout the systematic 1:5.95-model test in regular and irregular waves conducted in a wave tank at Seoul National University. The model-test results are also validated by an independently developed numerical method.

• Imaging Science in Dentistry
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• 제52권3호
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• pp.309-317
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• 2022

Purpose: The aim of this study was to introduce a category of jaw lesions comprising cysts and tumors associated with scalloped borders. Materials and Methods: General search engines and specialized databases including Google Scholar, PubMed, PubMed Central, and Scopus, as well as an authoritative textbook, were used to find relevant studies by using keywords such as "jaw lesion," "jaw disease," "scalloping," "scalloped border," "scalloped margin," "irregular border," and "irregular margin." Out of 289 articles, 252 records were removed because they were duplicates, did not have a relevant title, or did not mention the frequency of findings described using the term "scalloped border." Finally, 37 closely related articles were chosen. Results: According to the relevant literature, scalloped borders are found most frequently in ameloblastoma, followed by simple bone cyst, central giant cell granuloma, odontogenic keratocyst, and glandular odontogenic cyst. Conclusion: The lesions most frequently reported to have scalloped borders are ameloblastoma, central giant cell granuloma, odontogenic keratocyst, simple bone cyst, and glandular odontogenic cyst.

• 한국해양공학회:학술대회논문집
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• 한국해양공학회 2004년도 학술대회지
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• pp.167-171
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• 2004

The Spar platform with deep draft is characterized as effective structure in extreme wave condition, which has larger natural period than that of waves in sea. In this paper, the time simulation of motion responses of Spar with catenary mooring line is presented in irregular waves. The memory effect is modeled by added mass at infinite frequency and convolution integrals in terms of wave damping coefficients. The added mass, wave damping coefficients and wave exciting forces are obtained from three-dimensional panel method in the frequency domain. The motion equations are consisted of forces for inetia, memory effect, hydrostatic restoring, wave exciting and mooring line. The forces of mooring line are modeled as quasi-static catenary cable.

• Journal of Biosystems Engineering
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• 제22권3호
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• pp.269-278
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• 1997

An automatic level measurement system was developed to level the land fer direct seeding of rice. A laser transmitter/receiver set was used to measure land-level. The inclination error occurred in level measurement on irregular land surface could be compensated by attaching rotating mass. The level measuring experiments were performed on three kinds of different shapes(step, random, sine). This system could accurately measure step level of which amplitude was 40mm in 0.5s, random level change within $\pm$ 5mm maximum measurement error, and sine level change of which spatial frequency was 0.5m-1. To verify performance of the inclination error compensation system, frequency transfer function(acceleration input vs. inclination error) was computed by spectral analysis. The inclination error was decreased about 20㏈ by error compensation system.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 1998년도 춘계학술대회논문집; 용평리조트 타워콘도, 21-22 May 1998
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• pp.88-93
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• 1998

Since rattling noise, which occur in mechanical linkage with free play or glove boxes in passenger cars, play an important role in the generation of industrial noise and vibration, it is interest to study these dynamics. A difference equations are derived which described the motions of a mass constrained by pre-compressed spring and forced by a high frequency base excitation. Two types of saddle are founded from these difference equations and the stable and unstable manifolds are constructed in these saddle point. For a certain region in a parameter space of exciting displacement and coefficient of restitution, transversal intersections of stable and unstable manifolds exist. Therefore it is founded that there are large families of periodic and irregular non-periodic motions in rattling system i.e. chaos motion is observed.

• 한국음향학회지
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• 제18권4호
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• pp.65-70
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• 1999

고유모드분포가 다른 정형(직방체), 부정형 잔향실을 해석대상으로 선정, 각각의 모델에 대한 음압의 공간편차에 대하여 유한요소법을 이용한 수치계산으로 검토하였다. 그 결과, 잔향실 내표면의 임피던스가 무한대인 경우는 주파수대역에 따른 편차가 부정형 잔향실이 작게 나타났다. 반면, 임피던스가 유한한 경우는 직방체 잔향실도 2변 혹은 3변의 치수가 같거나 정수배인 것을 제외하면 편차가 부정형 잔향실과 같은 정도라는 것이 확인되었다.