• Proceedings of the Korean Geotechical Society Conference
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• 2009.09a
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• pp.905-912
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• 2009

1-g shaking table test is conducted to evaluate the dynamic behavior of a soil-structure system under seismic loading condition. A consistent similitude law between the model and prototype is needed to predict the behavior of the prototype structure, quantitatively. The natural frequency of geomaterial decreases with the increase of shaking intensity because of the non-linear property of the geomaterial. This phenomenon affects the applicability of similitude laws in 1-g shaking table tests. In this study, a simple method is suggested to determine the frequency of the input motions in 1-g tests in order to enhance the applicability of similitude laws. Modified input frequency is calculated using the frequency ratio with consideration of the variation of the natural frequency according to the intensity of input ground acceleration. To verify the applicability of the suggested method, a series of 1-g shaking table tests were performed for three different sizes of model piles having an overburden mass on their heads by varying the acceleration and the frequency of input motion. The acceleration amplification ratio on the overburden mass, the lateral displacement at the pile head and the maximum bending moment along the pile depth were measured. The projected behaviors of the virtual prototype based on the measured values of the model tests, where the input frequencies were calculated by the new method, showed good consistency, verifying the applicability of the suggested method.

• Journal of the Society of Naval Architects of Korea
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• v.29 no.4
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• pp.87-97
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• 1992

Of various design factors affecting icebreaking capability of an icebreaker, the stem angle(i.e., angle between bow stem and ice sheet) is the most important one under continuous icebreaking operation. This study focuses on the relationship between the bow stem angle of an icebreaker and its icebreaking capability. Considering relatively high loading-rate conditions with typical advancing speed of 3 to 4 knots, the material properties and deformation characteristics of sea ice are regarded as entirely elastic and brittle. In this paper the interaction process of icebreaker with level ice is simplified as a beam of finite length supported by Winkler-type elastic foundation simulating water buoyancy. The wedge type ice beam is loaded by the vertical impact forces due to the inclined bow stem of icebreaking vessels. The numerical model provides locations of maximum bending moment where extreme tensile stress arises and also possible fracture occurs. The model can predict a characteristic length of broken ice sheet upon the given environmental and design parameters.

• Journal of the Earthquake Engineering Society of Korea
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• v.10 no.3 s.49
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• pp.1-11
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• 2006

This paper presents a seismic fragility analysis method for a cable-stayed bridge with energy dissipation devices. Model uncertainties represented by random variables include input ground motions, characteristics of energy dissipation devices and the stiffness of cable-stayed bridge. Using linear regression, we established demand models for the fragility analysis from the relationship between maximum responses and the intensity of input ground motions. For capacity models, we considered the moment and shear force of the main tower, longitudinal displacement of the girder, deviation of the stay cables tension and the local buckling of the main steel tower as the limit states for cable-stayed bridge. As a numerical example, fragility analysis results for the 2nd Jindo bridge are presented. The effect of energy dissipation devices is also briefly discussed.

• Aerospace Engineering and Technology
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• v.1 no.1
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• pp.8-27
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• 2002

In this study, the load analysis of a composite canard aircraft is performed numerically. Excel visual basic program for PC is used to calculate aerodynamic coefficients, loads and moments etc.. The basic data required for the load analysis such as aircraft configuration and dimension, parts and its weight and coordinate etc. are obtained from Catia modeling, measurement or material density. Aircraft weight, center of gravity, inertia moment, structural design speeds, wing load distribution, forces and moments are evaluated by using these data. V-n diagram is also represented for selecting critical loads applied to the wing and fuselage. The V-n diagram is investigated to decide the flight envelope of canard aircraft for design speed VA, VC, VD and load factor +3.8G, -1.52G at maximum weight of 2,573 lbs and sea level. In the future, the results of the wing and fuselage load analysis is to represented by using selected critical loads.

• Journal of the Korean Vacuum Society
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• v.19 no.4
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• pp.256-264
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• 2010

In this paper, a digital controller of magnetic bearing system for a high vacuum turbomolecular pump (TMP) is designed and examined. For stabilizing and providing damping in magnetic bearing, the digital PID controller is applied for each 5 control axes, and the inter-axis cross feedback controller is also applied to suppress low frequency vibration caused by gyroscopic moment of the rotor at high speed of rotation. The fabricated rotor-shaft has its first flexible natural frequency lower than maximum speed, about 614Hz, so the two lead filters are applied to increase damping of flexible mode. Notch filters with rotating frequency were selected to reduce vibration of the pump housing caused by unbalance load. The implemented controllers are verified by examination of frequency response and rotating test up to 40,000 rpm, which is higher than critical speed of backward flexible mode.

• International Journal of Automotive Technology
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• v.7 no.1
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• pp.1-7
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• 2006

The ignition delay of a dual fuel system has been numerically investigated by adopting a constant volume chamber as a model problem simulating diesel engine relevant conditions. A detailed chemical kinetic mechanism, consisting of 28 species and 135 elementary reactions, of dimethyl ether (DME) with methane ($CH_{4}$) sub-mechanism has been used in conjunction with the multi-dimensional reactive flow KIVA-3V code to simulate the autoignition process. The start of ignition was defined as the moment when the maximum temperature in the combustion vessel reached to 1900 K with which a best agreement with existing experiment was achieved. Ignition delays of liquid DME injected into air at various high pressures and temperatures compared well with the existing experimental results in a combustion bomb. When a small quantity of liquid DME was injected into premixtures of $CH_{4}$/air, the ignition delay times of the dual fuel system are longer than that observed with DME only, especially at higher initial temperatures. The variation in the ignition delay between DME only and dual fuel case tend to be constant for lower initial temperatures. It was also found that the predicted values of the ignition delay in dual fuel operation are dependent on the concentration of the gaseous $CH_{4}$ in the chamber charge and less dependent on the injected mass of DME. Temperature and equivalence ratio contours of the combustion process showed that the ignition commonly starts in the boundary at which near stoichiometric mixtures could exists. Parametric studies are also conducted to show the effect of additive such as hydrogen peroxide in the ignition delay. Apart from accurate predictions of ignition delay, the coupling between multi-dimensional flow and multi-step chemistry is essential to reveal detailed features of the ignition process.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.25 no.9B
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• pp.1551-1562
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• 2000

In the using of FBG developed in home land, we designed and manufactured three types of FBG sound transducers the first in Korea. On FBG transducers manufactured we made an demonstrated on respective frequency response peculiarties in the water and analyzed the special characters. As the experimental result on frequency response peculiarities, we made t possible underwater acoustic detection on C type to maximum 18kHz, And for the purpose of realization on multi-point signal detection on wide scope in the water, in the using of WDM(Wavelength Division Multiplexing) method and passive band-pass filter system, established arrays system and succeeded in multi-point underwater acoustic signal detection to the frequency 1.3KHz out of the two B type FBG transducers. Additionally, it would be possible directivity detection for the objects of its source as the intensity of detection signal varies with the sound source's direction and angle. From now on we prepared a new moment on the practical used study on FBG hydrophone.

• Journal of Intelligence and Information Systems
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• v.8 no.2
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• pp.1-13
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• 2002

In this paper, we propose an object tracking system which can be convinced of moving area shaped on objects through color sequential images, decided moving directions of foot messengers or vehicles of image sequences. In static camera, we suggests a new evaluating method extracting co-occurrence matrix with feature vectors of RGB after analyzing and blocking difference images, which is accessed to field of camera view for motion. They are energy, entropy, contrast, maximum probability, inverse difference moment, and correlation of RGB color vectors. we describe how to analyze and compute corresponding relations of objects between adjacent frames. In the clustering, we apply an algorithm of FCM(fuzzy c means) to analyze matching and clustering problems of adjacent frames of the featured vectors, energy and entropy, gotten from previous phase. In the matching phase, we also propose a method to know correspondence relation that can track motion each objects by clustering with similar area, compute object centers and cluster around them in case of same objects based on membership function of motion area of adjacent frames.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.11
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• pp.7285-7292
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• 2015

The purpose of this study was to investigate possibility of a forward gait with backward mechanism(dance gait) as rehabilitation and/or walking exercise by means of biomechanical variables. Thirteen professional women dancers(age, $21.1{\pm}1.3yrs$; height, $159.3{\pm}7.2cm$; body mass, $45.1{\pm}8.4kg$)participated in this study. We found that speed, stride length and double limb support time of a dance gait were more greater than backward gait, but stride width of dance gait less than a backward gait. Maximum RoMs, moments and powers of the lower limb joints on a dance gait were more frequent than a backward dance. These results were judged to be sufficient by the possibility of dance gait as rehabilitation and walking exercise.

• Bulletin of the Korean Space Science Society
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• 2010.04a
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• pp.40.4-41
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• 2010

Using magnetic field and plasma moment data obtained by THEMIS satellites(A, D, and E), we selected 203 fast flow events accompanied by dipolarization in the near-Earth region( X(GSM) = -7 ~ -12 RE) and statistically examined their properties. It was found that most of the fast flows show the maximum velocity between 1 minute before dipolarization onset and 2 minutes after onset and proceed earthward and duskward. We also found that only the flows with low velocity of less than 400 km/s are observed at X > -8 RE, while the high velocity flows(as well as low velocity flows) are observed at the further tailward region(X < -8 RE). And most of the tailward flows are slow regardless of distance at X(GSM) = -7 ~ -12 RE. On the other hand, if we consider the fast flow as a bubble (Pontius and Wolf, 1990), the entropy parameter, PV5/3 is an important factor to describe the plasma sheet dynamics. Thus we investigated the relationship between the flow velocity and the amount of change in PV5/3 before and after dipolarization onset and found out that the dipolarizations with more depleted entropy parameter tend to show higher flow velocity. Also we examined how the magnetic field at geosynchronous orbit responds to the fast flow accompanied by dipolarization in the near-earth plasma sheet, using the measurements from GOES 11 and 12 statellites. We found that most of the fast flows do not reach geosynchronous orbit as suggested by Ohtani et al. (2006).