• Fisheries and Aquatic Sciences
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• v.11 no.1
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• pp.41-49
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• 2008

Internal waves and internal tides occur frequently along the eastern coast of Korea. During the spring-tide period in April 2003, the East Korean Warm Current (EKWC) flowed near the Korean East Coast Farming Forecast System (KECFFS; a moored oceanographic measurement system), creating a strong thermocline at the intermediate layer. Weakened stratification and well-mixed water appeared frequently around the KECFFS, with duration of approximately 1 day. The results suggest the following scenario. Baroclinic motion related to the internal tide generated high frequency internal waves around the thermocline. The breaking of those waves then created turbulence around the thermocline. After well-mixed water appeared, a current component with perpendicular direction to the EKWC appeared within the inertial period. The change in stratification around the KECFFS locally broke the geostrophic balance as a transient state. This local vertical mixing formed an ageostrophic current within the inertial period.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.28 no.5
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• pp.607-623
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• 1995

A numerical model of hydraulic resistance by hanging aquaculture facilities is developed and applied to a model basin and a field. A drag stress term formulated by the quadratic law of drag force is introduced Tn the equations of motion for a two-dimensional depth-averaged flow. In the model basin, numerical experiments ave tarried out for the various shape of obstructions, string density and layout of facilities etc.. The flow pattern around the facilities is affected sensitively by the density of string and the layout of facilities. On the other hand, the velocity decay due to the hanging oyster aquaculture facilities is observed in Kamak bay, where the maximum velcocity decay rate is $25\%$ in spring tide. The model is also applied to the field, Kamak bay. The velocity decay rate in the model is comparable with the field measurement data. The velocity decreases around the down-stream area of the facilities, .hut it increases in the other region. The water elevation decreases during the flood and it increases during the ebb.

• Journal of the Korean Institute of Intelligent Systems
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• v.26 no.3
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• pp.196-201
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• 2016

This paper analyses the characteristics of a stiffness-based rehabilitation mechanism for improving the function of the elbow joint of a human. We consider an elastic string as a tool for the elbow joint rehabilitation, where the string has been modeled as a linear spring with a stiffness. For effective rehabilitation training by using such a mechanism, we need to analyse the available torque characteristics of the elbow joint according to the stiffness of the string. Through various simulations, the torque pattern and its range of the elbow joint by assigning the stiffness of the string have been identified for a pre-defined trajectory of motion of the elbow joint. Finally, we show that the specified stiffness-based rehabilitation scheme can be used for effective rehabilitation of the elbow joint.

• Journal of The Korean Astronomical Society
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• v.29 no.spc1
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• pp.119-122
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• 1996

The case for a massive black hole in the center of the Galaxy is reassessed using improved modeling techniques and observational data. A dark mass of ${\~}{\times} 10^6$ Mo is present within 0.2 pc of the Galactic center. However, the available data can be modeled, without appealing to a massive black hole, using an extended distribution of dark stellar remnants (neutron stars and stellar mass black holes) provided that the stellar initial mass function in the central parsec is deficient in stars less massive than $\~$1 Mo. Such a situation may be a natural consequence of repeated gas build-up followed by starbursts in the central region. A clear distinction between this and the massive central black hole model cannot be made using red giant tracers outside 0.2 pc due to uncertainties in the radial velocity dispersion distribution. The cluster of massive early-type emission-line stars in the central parcsec more effectively probe the mass distribution close to Sgr A $\ast$, but their small number and partial rotational support complicate mass determinations. Proper motion determinations for stars within 0.5' of Sgr A$\ast$ may be the most effective means of unambiguously determining the mass distribution in the immediate vicinity of the Galactic center.

• Ocean Systems Engineering
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• v.4 no.1
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• pp.63-82
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• 2014

Declutching control is applied to a hemispherical wave energy converter with direct linear electric Power-Take-Off systems oscillating in heave direction in both regular and irregular waves. The direct linear Power-Take-Off system can be simplified as a mechanical spring and damper system. Time domain model is applied to dynamics of the hemispherical wave energy converter in both regular and irregular waves. And state space model is used to replace the convolution term in time domain equation of the heave oscillation of the converter due to its inconvenience in analyzing the controlled motion of the converters. The declutching control strategy is conducted by optimal command theory based on Pontryagin's maximum principle to gain the controlled optimum sequence of Power-Take-Off forces. The results show that the wave energy converter with declutching control captures more energy than that without control and the former's amplitude and velocity is relatively larger. However, the amplification ratio of the absorbed power by declutching control is only slightly larger than 1. This may indicate that declutching control method may be inapplicable for oscillating wave energy converters with direct linear Power-Take-Off systems in real random sea state, considering the error of prediction of the wave excitation force.

• Advances in nano research
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• v.9 no.4
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• pp.237-250
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• 2020

An accurate plate theory for assessing sandwich structures is of interest in order to provide precise results. Hence, this paper develops Layer-Wise (LW) theory for reaching precise results in terms of buckling and vibration behavior of Functionally Graded Carbon Nanotube-Reinforced Composite (FG-CNTRC) annular nanoplates. Furthermore, for simulating the structure much more realistic, its edges are elastically restrained against in-plane and transverse displacement. The nano structure is integrated with piezoelectric layers. Four distributions of Single-Walled Carbon Nanotubes (SWCNTs) along the thickness direction of the core layer are investigated. The Differential Quadrature Method (DQM) is utilized to solve the motion equations of nano structure subjected to the electric field. The influence of various parameters is depicted on both critical buckling load and frequency of the structure. The accuracy of solution procedure is demonstrated by comparing results with classical edge conditions. The results ascertain that the effects of different distributions of CNTs and their volume fraction are significant on the behavior of the system. Furthermore, the amount of in-plane and transverse spring coefficients plays an important role in the buckling and vibration behavior of the nano-structure and optimization of nano-structure design.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.13 no.7
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• pp.562-569
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• 2003

An iterative modal analysis approach is developed to determine the effect of transverse open cracks on the dynamic behavior of simply supported pipe conveying fluid subject to the moving mass. The equation of motion Is derived by using Lagrange’s equation. The influences of the velocity of moving mass and the velocity of fluid flow and a crack have been studied on the dynamic behavior of a simply supported pipe system by numerical method. The presence of crack results In higher deflections of pipe. The crack section is represented by a local flexibility matrix connecting two undamaged beam segments i.e. the crack is modelled as a rotational spring. Totally. as the velocity of fluid flow and the crack severity are increased, the mid-span deflection of simply supported pipe conveying fluid Is Increased. The time which produce the maximum dynamic deflection of the simply supported pipe Is delayed according to the increment of the crack severity.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.26 no.1
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• pp.82-88
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• 2016

This paper proposes a new type of semi-active direct-drive valve(DDV) car suspension system using piezoelectric actuator associated with displacement amplifier. As a first step, controllable piezoelectric DDV damper is designed and governing equation of a quarter-vehicle suspension system consisting of sprung mass, spring, tire and the piezostack DDV damper is constructed. After deriving the equations of the motion, in order to control spool displacement and damping force the skyhook controller is designed and applied. The performance evaluation of the proposed semi-active suspension system is conducted with different displacement of spool. Then, the ride comfort analysis is undertaken in time domain with bump road profile.

• Journal of Electrical Engineering and Technology
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• v.11 no.3
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• pp.733-740
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• 2016

To achieve bipedal walking in real human environments, a bipedal robot should be capable of modifiable walking both on uneven terrain with different heights and on flat terrain. In this paper, a novel walking pattern generator based on a 3-D linear inverted pendulum model (LIPM) is proposed to achieve this objective. By adopting a zero moment point (ZMP) variation scheme in real time, it is possible to change the center-of-mass (COM) position and the velocity of the 3-D LIPM throughout the single support phase. Consequently, the proposed method offers the ability to generate a modifiable pattern for walking on uneven terrain without the necessity for any extra footsteps to adjust the COM motion. In addition, a control strategy for bipedal walking on uneven terrain with unknown height is developed. The torques and ground reaction force are measured through force-sensing resisters (FSRs) on each foot and the foot of the robot is modeled as three virtual spring-damper models for the disturbance compensation. The methods for generating the foot and vertical COM of 3-D LIPM trajectories are proposed to achieve modifiable bipedal walking on uneven terrain without any information regarding the height of the terrain. The effectiveness of the proposed method is confirmed through dynamic simulations.

• Earthquakes and Structures
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• v.11 no.5
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• pp.905-924
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• 2016

Several two-dimensional analytical beam column joint models with varying complexities have been proposed in quantifying joint flexibility during seismic vulnerability assessment of non-ductile reinforced concrete (RC) frames. Notable models are the single component rotational spring element and the super element joint model that can effectively capture the governing inelastic mechanisms under severe ground motions. Even though both models have been extensively calibrated and verified using quasi-static test of joint sub-assemblages, a comparative study of the inelastic seismic responses under nonlinear time history analysis (NTHA) of RC frames has not been thoroughly evaluated. This study employs three hypothetical case study RC frames subjected to increasing ground motion intensities to study their inherent variations. Results indicate that the super element joint model overestimates the transient drift ratio at the first story and becomes highly un-conservative by under-predicting the drift ratios at the roof level when compared to the single-component model and the conventional rigid joint assumption. In addition, between these story levels, a decline in the drift ratios is observed as the story level increased. However, from this limited study, there is no consistent evidence to suggest that care should be taken in selecting either a single or multi component joint model for seismic risk assessment of buildings when a global demand measure such as maximum inter-storey drift is employed in the seismic assessment framework.