• Journal of the Korean Society of Fisheries and Ocean Technology
• /
• v.37 no.4
• /
• pp.313-320
• /
• 2001

In the presence of incident waves with different frequencies, there are second order sum and difference frequency wane exciting forces due to the nonlinearty of the incident waves. Although the magnitudes of these nonlinear forces are small, they act at sum and difference frequencies away from those of the incident waves. So, the second order sum and difference frequency wane loads occurring close to the natural frequencies of TLPs often give greater contributions to high and low frequency resonant responses. The components of the second order forces which depend on first order quantities have been evaluated using the three dimensional source distribution method. The numerical results of time domain motion analysis for the nonlinear wave exciting forces in regular waves are compared with the numerical ones of frequency domain analysis. The results of comparison confirmed the validity of the proposed approach.

• Journal of Electrical Engineering and Technology
• /
• v.13 no.4
• /
• pp.1644-1654
• /
• 2018

Eigenvalue distributions for a periodic metal-insulator-metal waveguide, classified into the point spectrum and the discretized continuous spectrum (DCS), are investigated as functions of frequencies, gap widths, and periods. Muller's method is suggested for solving exact eigenvalues, and we propose the scheme for finding proper initial values in the Muller's method by considering only ${\Re}e({\varepsilon}_r)$ in the dispersion equation. We then find that anti-crossing behavior, repulsive effect between the point spectrum and the DCS, becomes stronger when the real parts of the roots in the point spectrum have smaller values. Finally, we examine the transmittances of a single subwavelength slit for real metals using the mode matching technique. The transmittances in real metals similarly follow those of the perfect electric conductor (PEC) at low frequencies, while the patterns at higher frequencies begin to differ from the PEC.

• The Transactions of the Korean Institute of Electrical Engineers P
• /
• v.59 no.4
• /
• pp.440-443
• /
• 2010

This paper deals with the method of vibration measurement of a gun barrel structure using mechanical filter. When a bullet with high speed is moving within a gun barrel type structure with low bending vibration frequencies, it is difficult to measure the bending vibration signals of the structure. For example, noncontact type sensors such as displacement or velocity sensor are not appropriate for the measurement of vibrational signals because of the movement effect of the equipment frame through the moving structures or effect of the ground vibration. One of contact type sensors such as accelerometer is profitable for measurement of vibrational signals because of its wide measurement ranges. In the case of a gun barrel structure including high vibrational signals like shock waves, however, it is necessary to propose vibration measurement method filtering high frequencies. The purpose of the paper is to propose the proper vibrational measurement technique filtering high frequencies of a gun barrel type structure.

• Journal of ILASS-Korea
• /
• v.29 no.1
• /
• pp.23-31
• /
• 2024

This study conducted a 3D thermo-acoustic analysis based on the helmholtz solver to analyze the major resonance modes causing combustion instability in a single-can combustor. The experimental investigations were carried out on a test rig designed by the Korea Institute of Machinery & Materials (KIMM) under various conditions of hydrogen co-firing and fuel staging. Through these experiments, two primary unstable frequencies were identified. To determine the resonance modes of these frequencies, a 3D thermo-acoustic analysis was conducted using temperature information from the test rig. The results confirmed that the unstable frequencies observed in the experiments were all longitudinal modes. Additionally, the mode shapes identified in the analysis facilitated a simplification of the exit geometry for the low-order network model, confirming that this did not significantly affect the fundamental resonance modes.

• Journal of The Korean Association For Science Education
• /
• v.34 no.3
• /
• pp.221-233
• /
• 2014

In this study, we analyzed verbal interactions among 32 students in 7th graders' science cooperative learning at the levels of turns, interaction units, and conflict behavior units, and compared their verbal interaction patterns between the heterogeneous and homogeneous groups by students' collectivism. The relationships of verbal interactions with the achievement test scores and the increase of the achievement test scores were also investigated. In the analyses of turns, the distributions of the subcategories of the statements related to the task were found to be similar in both groups, and the frequency of 'explain' was highest. The frequencies of interaction units were higher in the homogeneous groups than the heterogeneous groups, and the frequency of 'symmetric interaction' was highest. In the heterogeneous groups, the frequencies of turns and interaction units for the students of high collectivism were higher than those of low collectivism. The frequencies of conflict behavior units were generally low, but the rates were similar in both groups. In the case of the homogeneous groups, the frequencies of 'avoiding' and 'competing' for the students of low collectivism were high, and the frequency of 'cooperating' for the students of high collectivism was high. In addition, the qualitative differences between the two groups were found in the interaction units and conflict behavior units. The achievement test scores and the increase of the achievement test scores were positively related with the sum of the frequencies of the statements related to the task.

• Animal cells and systems
• /
• v.3 no.3
• /
• pp.269-273
• /
• 1999

The distribution and relative frequency of somatostatin-immunoreactive cells in the pancreas were studied during developmental stages (fetus, neonate, 1-month-old, 6-month-old and adult) of the Korean native goat by immunohistochemical methods. Somatostatin-immunoreactive cells were detected in the exocrine of all ages, in the endocrine portions (pancreatic islets) from the neonate, and in the pancreatic duct of the 1-month-old. The relative frequencies of these cells in the pancreatic islets increased with age. However, there were no age-related changes in the relative frequencies of somatostatin-immunoreactive cells in the exocrine and pancreatic duct. Generally, they were distributed in the interacinar spaces, the epithelium of the pancreatic duct, or dispersed in the peripheral zone of the pancreatic islets in all ages. However, clusters consisting of 3-4 cells were also found in the subepithelial connective tissues from the 1-month-old. In addition, the distributions in the endocrine portions of the adult were divided into two patterns: 1) they are dispersed in the marginal regions with moderate or low frequencies, or 2) in the inner zone with high frequencies.

• The Journal of Korean Physical Therapy
• /
• v.25 no.5
• /
• pp.316-321
• /
• 2013

Purpose: The aimed of this study was to investigate muscle activation related to postural stability according to different frequency of whole body vibration during quiet standing, to identify the most effective training conditions that cause the highest neuromuscular responses, and to evaluate the difference of EMG activation according to the anatomical position of the muscle - proximal or distal from the vibration platform. Methods: Eighteen healthy subjects voluntarily participated in this single-group, repeated-measures study in which EMG data from upper trapezius, rectus abdominalis, external oblique abdominalis, elector spinae, gluteus maximus, rectus femoris, semitendinosus, and gastrocnemius were collected over different frequencies (0-5-10-15-20-25Hz) for each subject during quiet standing. Results: We observed a statistically significant difference in the mean values of %RVC of muscular activation according to different frequencies of whole body vibration during quiet standing in all muscles (p<0.05). Conclusion: Our results indicate that lower frequencies of vibration result in low muscular activation, and higher frequencies elicit high muscular activation. However, the most effective training condition that caused the highest activation was 20 Hz. In addition, the proximally located lower extremity muscles (GCM, RF, ST, GM) showed higher activation than the distally located trunk and neck muscles (ES, EO, RA, UT) together with increasing frequency.

• Proceedings of the KSRS Conference
• /
• v.2
• /
• pp.938-941
• /
• 2006

Satellite synthetic aperture radar (SAR) images from 1995 to 2001 and field measurements of sea surface wind, sea state, and vertical stratification are used for statistical analyses of internal wave (IW) occurrence and SAR imaging conditions in the northern South China Sea (NSCS). Latitudinal distribution of IW packets shows that 22% of IW packets distributed in the east of $118^{\circ}E$ and 78% of IW packets in the west of $118^{\circ}E$. The yearly distribution of IW occurrence frequencies reveals an interannual variability. The monthly SAR-observed IW occurrence frequencies show that the high frequencies are distributed from April to July and reach a peak in June. The low occurrence frequencies are distributed in winter from December to February of next year. These statistical features are explained by solitary wave dynamics.

• Wind and Structures
• /
• v.21 no.4
• /
• pp.443-460
• /
• 2015

In this paper, an integrator based method to estimate the effective wind speed in wind turbine systems is proposed. First, the aerodynamic torque was accurately estimated through a proportional gain based observer where the generator speed is the measured output of the system. The torque signal contains not only useful frequencies of the wind, but also high frequencies and the ones due to structural vibration. The useful information of the wind signal is low frequency. A spectral analysis permitted the determination of the useful frequencies. The high frequencies were then filtered before introducing the torque signal in the wind speed observer. The desired effective wind speed was extracted through an integrator based observer using the previously estimated aerodynamic torque. The strength of the method is to avoid numerical solutions used in literature of the wind speed estimation. The effectiveness of the proposed wind speed estimator and its use to control the generator speed has been tested under turbulent situations using the FAST software (Fatigue, Aerodynamics, Structures, and Turbulence), for large scale Megawatt turbine.

• Journal of Soil and Groundwater Environment
• /
• v.20 no.5
• /
• pp.16-25
• /
• 2015

The City of Boulder is located at an average elevation of 1,655 m (5,430 feet), the foothills of the Rocky Mountains in Colorado. Its daily air temperature is much varying and snow is very frequent and heavy even in spring. This paper examines characteristics of shallow (surface and depth = 10 cm) soil temperatures measured from January to May 2015 in the high elevation city Boulder, Colorado. The surface soil temperature quickly responded to the air temperature with the strongest periodicity of 1 day while the subsurface soil temperatures showed a less correlation and delayed response with that. The short-time Fourier of the soil temperatures uncovered their very low frequencies characteristics in heavy snow days while it revealed high frequencies of their variations in warm spring season. The daily minimum air temperature exhibited high cross-correlations with the soil temperatures without lags unlike the maximum air temperature, which is derived from its higher and longer auto-correlation and stronger spectrums of low frequencies than the maximum air temperature. The snow depth showed an inverse relationship with the soil temperature variations due to snow's low thermal conductivity and high albedo. Multiple regression for the soil temperatures using the air temperature and snow depth presented its predicting possibility of them even though the multiple r² of the regression is not that much satisfactory (r² = 0.35-0.64).