• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2012.10a
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• pp.725-730
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• 2012

In this paper, flow noise characteristics of Savonius-type vertical-axis wind turbines are numerically investigated using hybrid CAA techniques. High frequency harmonics as well as BPF components are identified in the predicted noise spectra from a Savonius wind turbine. As the BPF components belong to infrasound, the higher harmonic components affects human response dominantly. Further analysis is performed to investigate the reason causing the higher frequency harmonic noise by changing operational conditions of a Savonius wind turbine. Based on this result, it is revealed that the frequency of higher harmonic components is determined by the radius of blades and angular velocity of Savonius wind turbine.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.6 no.3
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• pp.9-16
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• 1997

A numerical method based on the spectral collocation method is developed for the steady rotating flows in eccentric annulus. Steady flows between rotating cylinders are of interest on lubrication in large rotating machinery. Steady rotating flow is generated by the rotating inner cylinder with constant angular velocity. The governing equations for laminar flow are simplified from Navier-Stokes equations by neglecting the non-linear convection terms. Integrating the pressure round the rotating cylinder based on the half Sommerfeld method, the load on the cylinder is evaluated with eccentricity. The attitude angle and Sommerfeld variable are calculated from the load. It is found that those values are influenced by the eccentricity. The attitude and Sommerfeld reciprocal are decreased with eccentricity. As expected, the effect of the annular gap ratio on them is negligible.

• 한국신재생에너지학회:학술대회논문집
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• 2010.11a
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• pp.180.1-180.1
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• 2010

This paper introduces a 3MW embedded Permanent Magnet Synchronous Generator(PMSG) for wind turbine. The generator features 313mm stator inner radius and 974mm stator length. The blade rotor angular velocity is 15.7 rpm and the gear ratio is set to be 92.93. The nominal generator rpm at rated load is about 1459. The number of poles is six and embedded in the generator rotor. Embedded permanent magnet excitation shows higher reliability, and better efficiency. Using the finite element method, electromagnetic and thermal results are simulated by ANSYS and the results are summarized in this report.

• Fisheries and Aquatic Sciences
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• v.11 no.1
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• pp.61-69
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• 2008

Using empirical data of fish performance and physiological limits as well as physical stimuli and environmental data, a cod-end selectivity model based on a chaotic behavior model using the psycho-hydraulic wheel and neural-network approach was established to predict fish escape or herding responses in trawl and cod-end designs. Fish responses in the cod-end were categorized as escape or herding reactions based on their relative positions and reactions to the net wall. Fish movements were regulated by three factors: escape time, a visual looming effect, and an index of body girth-mesh size. The model was applied to haddock in a North Sea bottom trawl including frequencies of movement components, swimming speed, angular velocity, distance to net wall, and the caught-fish ratio; simulation results were similar to field observations. The ratio of retained fish in the cod-end was limited to 37-95% by optomotor coefficient values of 0.3-1.0 and to 13-67% by looming coefficient values of 0.1-1.0. The selectivity curves generated by this model were sensitive to changes in mesh size, towing speed, mesh type, and mesh shape.

• Nuclear Engineering and Technology
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• v.34 no.1
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• pp.30-41
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• 2002

The neutron beam is fully characterized for the prompt gamma activation analysis facility at Hanaro in the Korea Atomic Energy Research Institute(KAERI). The facility uses thermal neutrons which are diffracted vertically from a horizontal beam port by a set of pyrolytic graphite(PG) crystals positioned at the Bragg angle of 45" Neutron spectra, neutron flux and Cd-ratio are determined for the three extraction modes of diffracted beam by means of the theoretical and experimental efforts. To obtain theoretical result, the reflectivity of pyrolytic graphite is calculated in the diffraction model for mosaic crystal and the angular divergence after diffraction by mosaic crystal is estimated from Monte Carlo simulation. The time-of-flight spectrometer and gold activation wire are used for measuring the neutron spectra. Both the calculated and measured spectra have proven that the unique feature of polychromatic beam obtained by PG crystals are useful for PGAA. The thermal neutron flux of 7.9$\times$107 n/cm$^2$s and the Cd-ratio of 266 for gold have been achieved at the sample position while the reactor operates at 24 MW The uniformity of beam flux is 12% in the central 1$\times$1 cm$^2$ area. Finally, the beam is briefly characterized by the effective velocity and temperature which are determined by measuring the prompt Y-ray spectra for thin and thick boron samples.ples.

• Korean Journal of Applied Biomechanics
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• v.32 no.3
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• pp.103-110
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• 2022

Objective: The aim of this study was to investigate effect of core stabilization exercises on the erector spinae contractile properties and trunk isokinetic muscle function of middle age with low physical activity and sedentary lifestyle. Method: Twenty (female: n=10, male: n=10) middle-age subjects (age: 37.25 ± 6.08 years, height: 168.01 ± 6.84 cm, weight: 71.37 ± 11.75 kg) participated in this study. Tensiomyography was measured on the erector spinae, and the isokinetic trunk muscle function test was measured at an angular velocity of 60 °/s and 90 °/s. All subjects performed the core stabilization exercises for 60 min per day, 3 times a week, for 7 weeks. A paired t-test was performed with a significance level of 0.05. Results: Tensiomyography of the erector spinae revealed a significant post-exercise increase in the maximum radial displacement (p < .05) and velocity of contraction (p < .05), however, there wasn't a significant post-exercise change in the contraction time. Additionally, the isokinetic muscle function test of the trunk revealed a significant post-exercise increase in trunk extensor relative strength (p < .05) and strength ratio (p < .05). Conclusion: Our results indicated that core stabilization exercises reduced erector spinae muscle stiffness, increased the velocity of erector spinae contraction. Additionally, data showed the improvement in the trunk extensor strength help induce a more balanced development in trunk muscle.

• Journal of the Korean Institute of Navigation
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• v.10 no.2
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• pp.97-114
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• 1986

Ship's maneuverability is very important factor in safe ship handling and economical ship operation. Steering characteristics are consisted of course stability and maneuverability. Today in many advanced ship-building countries, they study ship's course stability, using model ship tests, such as straight line tests, rotating arm tests and Planar Motion Mechanism (PMM) etc., in tow in tanks. It is the purpose of this paper to provide ship's handlers with better understanding of steering characteristics and to help them in safe controlling and manevering . In this paper, the author simulated response of various vessels, running straight course with constant speed, and they are disturbed by small external disturbance of one degree yaw angle with no angular velocity . The author used the hydrodynamic derivtives resulted at tests of Davidson's laboratory in Stevens Institute of Technology, New Jersey, U.S.A. Course stability was evaluated and analyzed in various respects, such as block coefficient, ratio of ship's length to beam, draft and rudder area ratio etc. The obtained results are as follows : (1) The ship's course stability is affected by magnitude of block coefficient greatly. In case that the block coefficient is more than 0.7, the deviation varies at nearly same rate but the requistite time to reach the steady course is different. (2) The ship's course stability is affected by magnitude of L/B. When the dimensionless time reaches about 3, the deviation and requisite time to reach the steady course are influenced nearly same. After the dimensionless time is about 3, they change on invariable ratio. (3) The effect to course stability by L/T and RA' can be neglected. (4) The reason why thy VLCC and container feeder vessel are unstable on their course is that their block coefficient is generally more than 0.8 and the ratio of ship's length to beam is about 6.0.

• Coupled systems mechanics
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• v.3 no.3
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• pp.247-265
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• 2014

This article discusses the dynamic response of Bernoulli-Euler straight beam with angular elastic supports subjected to moving load with variable velocity. A new engineering approach for determination of the dynamic effect from the moving load on the stressed and strained state of the beam has been developed. A dynamic coefficient, a ratio of the dynamic to the static deflection of the beam, has been defined on the base of an infinite geometrical absolutely summable series. Generalization of the R. Willis' equation has been carried out: generalized boundary conditions have been introduced; the generalized elastic curve's equation on the base of infinite trigonometric series method has been obtained; the forces of inertia from normal and Coriolis accelerations and reduced beam mass have been taken into account. The influence of the boundary conditions and kinematic characteristics of the moving load on the dynamic coefficient has been investigated. As a result, the dynamic stressed and strained state has been obtained as a multiplication of the static one with the dynamic coefficient. The developed approach has been compared with a finite element one for a concrete engineering case and thus its authenticity has been proved.

• Publications of The Korean Astronomical Society
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• v.30 no.2
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• pp.115-118
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• 2015

We made phase-referencing Very Long Baseline Interferometry (VLBI) observations of Galactic 22 GHz $H_2O$ maser sources with VLBI Exploration of Radio Astrometry (VERA). We measured the parallax distances of G48.61+0.02, G48.99-0.30, G49.19-0.34, ON1, IRAS 20056+3350, IRAS 20143+3634, ON2N, and IRAS 20126+4104, which are located near the tangent point and the Solar circle. The angular velocity of the Galactic rotation at the LSR (i.e. the ratio of the Galactic constants) is derived using the measured parallax distances and proper motions of these sources. The derived value of ${\Omega}_0=28.8{\pm}1.7km\;s^{-1}kpc^{-1}$ is consistent with recent values obtained using VLBI astrometry but 10% larger than the International Astronomical Union (IAU) recommended value of $25.9km\;s^{-1}kpc^{-1}=(220km\;s^{-1})$ / (8.5 kpc).

• KIEE International Transaction on Electrical Machinery and Energy Conversion Systems
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• v.2B no.3
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• pp.125-132
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• 2002

PMSMS (permanent magnet synchronous motors) are widely used in industrial applications and home appliances because of their high torque to inertia ratio, superior power density, and high efficiency. For high performance control, accurate informations about the rotor position is essential. Sensorless algorithms have lately been studied extensively due to the high cost of position sensors and their low reliability in harsh environments. A novel position sensorless speed control for PMSMs uses indirect flux estimation and is presented in this paper. Rotor position and angular velocity are estimated by the proposed indirect flux estimation. Linkage flux and magnetic field flux are calculated by the voltage equations and the measured phase current without any integration. Instead of linkage flux calculation with integral operation, indirect flux and differential magnetic field are used for the estimation of rotor position. A proper rejection technique fur current noise effect in the calculation of differential linkage flux is introduced. The proposed indirect flux detecting method is free from the integral rounding error and linkage flux drift problem, because differential linkage flux can be calculated without any integral operation. Furthermore, electrical parameters of the PMSM can be measured by the proposed TCM (time compression method) for soft starting and precise estimation of rotor position. The position estimator uses accurate electrical parameters that are obtained from the proposed TCM at starting strategy. In the operating region, a proper compensation method fur temperature effect can compensate fir the estimation error from the variation of electrical parameters. The proposed novel position sensorless speed control scheme is verified by the experimental results.