• Nuclear Engineering and Technology
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• v.53 no.8
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• pp.2728-2745
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• 2021

The purpose of this study is to reduce seismic responses of an actual nuclear piping system using a tuned mass damper (TMD) device. A numerical piping model was developed and validated based on shaking table test results with actual nuclear piping. A TMD for nuclear piping was newly devised in this work. A TMD shape design suitable for nuclear piping systems was conducted, and its operating performance was verified after manufacturing. The response reduction performance of the developed TMD under earthquake loading on actual piping was investigated. Results confirmed that, on average, seismic response reduction rates of 34% in the maximum acceleration response, 41% in the root mean square acceleration response, and 57% in the spectral acceleration response were shown through the TMD application. This developed TMD operated successfully within the seismic response reduction rate of existing TMD optimum design values. Therefore, the developed TMD and dynamic interpretation help improve the nuclear piping's seismic performance.

• Journal of the Korea Institute of Military Science and Technology
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• v.25 no.6
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• pp.596-605
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• 2022

In this study, analysis of dynamic characteristics and flight vibration was performed to unmanned aerial vehicles. The analysis model was supplemented by performing a dynamic characteristic test and a random vibration test using manufactured dummy aerial vehicle. For the dynamic characteristic test, a bungee cable was used to implement the free end boundary condition. Prior to the flight vibration test using a multiple electric shaker, a random vibration test was performed to predict the excitation force during the actual flight vibration test. It was judged that the actual test could be predicted more accurately by supplementing the analysis model from the test results. In addition, it was possible to determine the feasibility of the test by predicting the excitation force of the flight vibration test.

• Journal of the Korea Institute of Military Science and Technology
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• v.26 no.3
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• pp.252-261
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• 2023

Analysis of dynamic characteristics and flight vibration test for unmanned aerial vehicles was studied by using dummy test body. The FEM model for dummy test body was supplemented by results of modal and random vibration test. The free end boundary condition to simulate flight environments was made by test setup using bungee cable. Prior to the flight vibration test using a dual electric vibration exciters, the test procedure to calculate quantitative vibration level was studied by using military specification. The actual test was successfully done by using the analysis and pretest results. From the analysis results, it was possible to determine the feasibility of the test by predicting the excitation force of the flight vibration test and to get the response of any point which could not be measured by the test. The results of this study will much contribute to the Test and Evaluation of unmanned aerial vehicles.

• Journal of The Korean Astronomical Society
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• v.56 no.2
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• pp.149-157
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• 2023

The propagation speed of a circumstellar pattern revealed in the plane of the sky is often assumed to represent the expansion speed of the wind matter ejected from a post-main-sequence star at the center. We point out that the often-adopted isotropic wind assumption and the binary hypothesis as the underlying origin for the circumstellar pattern in the shape of multilayered shells are, however, mutually incompatible. We revisit the hydrodynamic models for spiral-shell patterns induced by the orbital motion of a hypothesized binary, of which one star is losing mass at a high rate. The distributions of transverse wind velocities as a function of position angle in the plane of the sky are explored along viewing directions. The variation of the transverse wind velocity is as large as half the average wind velocity over the entire three dimensional domain in the simulated models investigated in this work. The directional dependence of the wind velocity is indicative of the overall morphology of the circumstellar material, implying that kinematic information is an important ingredient in modeling the snapshot monitoring (often in the optical and near-infrared) or the spectral imaging observations for molecular line emissions.

• Journal of the Korean Association of Geographic Information Studies
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• v.18 no.4
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• pp.100-118
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• 2015

This study established a land-cover classification method on objects using satellite images, and figured out distributional patterns of land cover according to categories through spatial statistics techniques. Object-based classification generated each land cover classification map by spectral information, texture information, and the combination of the two. Through assessment of accuracy, we selected optimum land cover classification map. Also, to figure out spatial distribution pattern of land cover according to categories, we analyzed hot spots and quantified them. Optimal weight for an object-based classification has been selected as the Scale 52, Shape 0.4, Color 0.6, Compactness 0.5, Smoothness 0.5. In case of using the combination of spectral information and texture information, the land cover classification map showed the best overall classification accuracy. Particularly in case of dry fields, protected cultivation, and bare lands, the accuracy has increased about 12 percent more than when we used only spectral information. Forest, paddy fields, transportation facilities, grasslands, dry fields, bare lands, buildings, water and protected cultivation in order of the higher area ratio of DMZ according to categories. Particularly, dry field sand transportation facilities in Yanggu occurred mainly in north areas of the civilian control line. dry fields in Cheorwon, forest and transportation facilities in Inje fulfilled actively in south areas of the civilian control line. In case of distributional patterns according to categories, hot spot of paddy fields, dry fields and protected cultivation, which is related to agriculture, was distributed intensively in plains of Yanggu and in basin areas of Cheorwon. Hot spot areas of bare lands, waters, buildings and roads have similar distribution patterns with hot spot areas related to agriculture, while hot spot areas of bare lands, water, buildings and roads have different distributional patterns with hot spot areas of forest and grasslands.

• Journal of Yeungnam Medical Science
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• v.22 no.1
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• pp.43-51
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• 2005

Background: To examine the ultrasonographic and magnetic resonance (MRI) imaging findings of a cervical mass type cervical pregnancy. Materials and Methods: The ultrasonographic and MRI findings of 5 patients pathologically confirmed as having a cervical pregnancy were analyzed retrospectively. On ultrasonography, the size and echo pattern of the uterine cervix, the shape and echo pattern of the lesion, the degree and the pattern of blood flow on the color Doppler study and the spectral Doppler pattern were analyzed. The shape, signal intensity, and degree and pattern of enhancement of the lesion were evaluated on MRI. Results: The uterine cervix was enlarged and the size of the lesion was 6.1 to 7.1 (average, 6.5) cm. The endocervical canal was irregularly dilated and showed heterogeneous echogenicity in all 5 cases. Four of the 5 lesions were heterogeneously hyper- or mixed echoic and remaining one was relatively homogeneous echogenic. Doppler ultrasonography revealed an increased vascularity of the peritrophoblastic flow pattern. In all 4 cases where MRI performed, the lesion was irregular in shape and the margin was not sharply demarcated. The T2-weighed image showed that the lesions were mixed signal intensity. Three of the 4 lesions contained high signal intensity nodular portions and a low signal intensity rim was observed along the margin of the nodular portions. The T1-weighted image revealed multiple signal voids along the periphery of the lesions and high signal intensity portions as a result of hemorrhage were noted. The dynamic enhanced study showed that the high signal intensity portions on the T2-weighted image were strongly enhanced similar to the vessels on the early phase and the contrast enhancement gradually decreased with time. Conclusion: A cervical mass type cervical pregnancy can be correctly diagnosed using the patient's clinical symptom, the elevation in the serum ${\beta}$-HCG level, and characteristic ultrasonographic and MRI findings.

• The Journal of the Acoustical Society of Korea
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• v.33 no.1
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• pp.10-20
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• 2014

To study the water-entry impact noise, on-board experiment using a small launcher firing various objects was performed in the Yellow Sea. As the launcher fires a cylindrical object from the ship vertically, generated noise is measured with a hydrophone on the starboard of Chung-hae, Marine surveyor. Three types of cylindrical objects, which have noses of flat-faced, conical, and hemisphere, were used during the experiment. The measured noise exhibits a time-dependency which can be divided into three phases: (1) initial impact phase, (2) open cavity flow phase, (3) cavity collapse and bubble oscillation phase. In most cases, the waveform of bubble oscillation phase is dominant rather than that of initial impact phase. Pinch-off time, where a cavity begins to collapse, occurs at 0.18 ~ 0.2 second and the average lasting time of bubble was 0.9 ~ 1.3 second. The energy of water-entry impact noise is focused in the frequency region lower than 100 Hz, and the generated noise is influenced by the nose shapes, object mass, and launching velocity. As a result, energy spectral density on the bubble frequency is higher in the order of flat-faced, conical, hemisphere nose, and the increase of initial energy raises the energy spectral density on the bubble frequency in the cylinder body of same shape. Finally, we compare the measurements with the simulated signals and spectrum based on the bubble explosion physics, and obtain satisfactory agreements between them.

• Journal of the Korean earth science society
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• v.37 no.3
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• pp.162-172
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• 2016

Since the Northridge earthquake in 1994 and the Kobe earthquake in 1995 occurred, the concept of performance based design has been introduced for designing various kinds of important structures and buildings. Uniform hazard spectra (UHS), with annual exceedance probabilities, corresponding to the performance level of each structure, are required for performance-based design. The probabilistic seismic hazard analysis was performed using spectral ground motion prediction equations, which were developed from both Korean Peninsula and Central and Eastern US region, and several seismotectonic models suggested by 10 expert panel members in seismology and tectonics. The uniform hazard spectra for 5 highly populated cities in Korea, with recurrence period of 500, 1,000, and 2,500 years using the seismic hazard at the frequencies of 0.5, 1.0, 2.0, 5.0, 10.0 Hz and Peak ground acceleration (PGA) were analyzed using the probabilistic seismic hazard analysis. The sensitivity analysis suggests that spectral ground motion prediction equations impact much more on seismic hazard than what seismotectonic models do. The uniform hazard spectra commonly showed a maximum hazard at the frequency of 10 Hz and also showed the similar shape characteristics to the previous study and related technical guides to nuclear facilities.

• Korean Journal of Remote Sensing
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• v.27 no.2
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• pp.75-87
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• 2011

This paper presents a method for region-based building extraction from high resolution satellite images(HRSI) using integrated information of spectral and color invariant features without user intervention such as selecting training data sets. The purpose of this study is also to evaluate the effectiveness of the proposed method by applying to IKONOS and QuickBird images. Firstly, the image is segmented by the MSRG method. The vegetation and shadow regions are automatically detected and masked to facilitate the building extraction. Secondly, the region merging is performed for the masked image, which the integrated information of the spectral and color invariant features is used. Finally, the building regions are extracted using the shape feature for the merged regions. The boundaries of the extracted buildings are simplified using the generalization techniques to improve the completeness of the building extraction. The experimental results showed more than 80% accuracy for two study areas and the visually satisfactory results obtained. In conclusion, the proposed method has shown great potential for the building extraction from HRSI.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.11 no.4
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• pp.201-215
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• 1999

Field measurements were made for long- and short-period waves and current velocities at the harbor mouth using pressure-type wave gauges and a current meter, respectively, at the Gamcheon Harbor which has a rectangular shape with a narrow entrance. The measured pressure data were subjected to spectral analyses after removing tidal effects by applying trend removal and high-pass filtering. For the band averaging of the raw spectra, in order to obtain good resolution over the entire frequency, instead of a constant band width, variable band widths were used, which gradually increase as marching from the lowest frequency towards higher frequencies. The Helmholtz resonance mode at the Gamcheon Harbor shows the relative amplification ratio of 9.2 at the wave period of 31.7 minutes, which is quite large compared with those at the harbors located on the east coast of Korea. The second and the third resonance period was 10.3 and 5.4 minute, respectively. On the other hand, the analysis of every 24 hours data shows that during storms the spectral densities are very large compared to those during calm seas and also the second and third resonances are predominant.