• Smart Structures and Systems
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• v.3 no.3
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• pp.245-261
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• 2007

Nonlinear time-domain system identification (SI) algorithm is proposed to assess damage in a shear building by synchronously estimating time-varying stiffness and damping parameters using measured acceleration data. Mass properties have been assumed as the a priori known information. Viscous damping was utilized for the current research. To chase possible nonlinear dynamic behavior under severe vibration, an incremental governing equation of vibrational motion has been utilized. Stiffness and damping parameters are estimated at each time step by minimizing the response error between measured and computed acceleration increments at the measured degrees-of-freedom. To solve a nonlinear constrained optimization problem for optimal structural parameters, sensitivities of acceleration increment were formulated with respect to stiffness and damping parameters, respectively. Incremental state vectors of vibrational motion were computed numerically by Newmark-${\beta}$ method. No model is pre-defined in the proposed algorithm for recovering the nonlinear response. A time-window scheme together with Monte Carlo iterations was utilized to estimate parameters with noise polluted sparse measured acceleration. A moving average scheme was applied to estimate the time-varying trend of structural parameters in all the examples. To examine the proposed SI algorithm, simulation studies were carried out intensively with sample shear buildings under earthquake excitations. In addition, the algorithm was applied to assess damage with laboratory test data obtained from free vibration on a three-story shear building model.

• Wind and Structures
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• v.30 no.3
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• pp.275-288
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• 2020

High-rise buildings are very slender and flexible. Their low stiffness values make them vulnerable to horizontal loads, such as those associated with wind or earthquakes. For high-rise buildings, the threat to serviceability caused by wind-induced vibration is an important problem. To estimate the serviceability under wind action, the response acceleration of a building at the roof height is used. The response acceleration is estimated by the same wind speed at all wind directions. In general, the effect of wind direction is not considered. Therefore, the response accelerations obtained are conservative. If buildings have typical plans and strong winds blow from relatively constant wind directions, it is necessary to account for the wind direction to estimate the response accelerations. This paper presents three methods of evaluating the response accelerations while considering the effects of wind direction. These three serviceability evaluation methods were estimated by combining the wind directional frequency data obtained from a weather station with the results of a response analysis using wind tunnel tests. Finally, the decrease in the efficiencies of the response acceleration for each serviceability evaluation method was investigated by comparing the response acceleration for the three methods accounting for wind direction with the response acceleration in which wind direction was not considered.

• Journal of Korean Society of Transportation
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• v.23 no.5 s.83
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• pp.169-176
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• 2005

This paper introduces the dynamic control of acceleration lanes at freeway-ramp junctions. The feasibility of operation with flexible length of acceleration lane was tested with most possible traffic conditions. The operational qualify was also evaluated using average speed and total thru-put at both ramp section and freeway section. A CORSIM microscopic simulation model was used to evaluate the operation quality with a variety or volume conditions and three acceleration lanes, each representing different length categories. In addition, tollgate O-D data including travel times were obtained for two sections on the Gyeong-bu Freeway where an effective merging distance has been largely reduced. Its effect was analyzed and compared to the simulation results. Finally, the effects of acceleration lane are discussed and operational improvement at junctions is presented as research findings.

• Journal of the Earthquake Engineering Society of Korea
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• v.22 no.2
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• pp.87-94
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• 2018

In this study, seismic performance of bushings and their connection parts was analyzed by performing shaking table tests for various types of bushings widely used as auxiliary equipment of main transformers in domestic substations. As a result of the seismic tests of five types of 154 kV bushings according to the manufacturers, all the bushings secured the structural integrity even at the acceleration of 1.4 g and it was found that leakage of insulating oil didn't occur. Also, the average acceleration amplification rate at the upper part of the bushings was about 2.5 to 3.0 times higher than the lower one. On the other hand, when a representative 345 kV bushing was subjected to the seismic test, the structural integrity was secured even at 1.0 g acceleration similar to the design earthquake load level, but in this test, leakage of insulating oil occurred. However, when a stiffener restricting the connection of the bushing is installed in the same 345 kV bushing, the displacement of the bushing connection is controlled and the stiffener prevent the oil from leaking even at the acceleration of the designed seismic level.

• Journal of Institute of Control, Robotics and Systems
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• v.22 no.3
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• pp.233-240
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• 2016

This paper describes a three-dimensional reference trajectory generation method for giving commands to an unmanned air vehicle (UAV). The trajectory is a set of consecutive curves with constant acceleration during each interval and passing through via-points at specified times or speeds. The functional inputs are three-dimensional positions and times (or speeds) at via-points, and velocities at both boundaries. Its output is the time series of position values satisfying the piecewise constant acceleration condition. To be specific, the shape of the trajectory, known as the path, is first represented by splines using third degree polynomials. A numeric algorithm is then suggested, which can overcome the demerits of cubic spline method and promptly generate a piecewise constant acceleration trajectory from the given path. To show the effectiveness of the present scheme, trajectory generation cases were treated, and their speed calculation errors were evaluated.

• The Bulletin of The Korean Astronomical Society
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• v.42 no.2
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• pp.61.4-62
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• 2017

In this study we have made a statistical investigation on the kinematic classification of coronal mass ejections (CMEs) using about 4,000 SOHO/LASCO CMEs from 1996 to 2015. For this we use their SOHO/LASCO C3 data and exclude all poor events. Using the constant acceleration model, we classify these CMEs into three groups: Acceleration group, Constant Velocity group, and Deceleration group. For classification we adopt four different methods: Acceleration method, Velocity Variation method, Height Contribution method, and Visual Inspection method. Our major results are as follows. First, the fractions of three groups depend on the method used. Second, the results of the Height Contribution method are most consistent with those of the Visual Inspection method, which is thought to be most promising. Third, the fractions of different kinematic groups for the Height contribution method are: Acceleration (35%), Constant speed (47%), and Deceleration (18%). Fourth, the fraction strongly depend on CME speed; the fraction of Acceleration decreases from 0.6 to 0.05 with CME speed; the fraction of Constant increases from 0.3 to 0.7; the fraction of Deceleration increases from 0.1 to 0.3. Finally we present dozens of CMEs with non-constant accelerations. It is found that about 40 % of these CMEs show quasi-periodic oscillations.

• Journal of Advanced Marine Engineering and Technology
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• v.34 no.7
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• pp.951-962
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• 2010

An experimental study was performed to investigate the improvement of response performance of a turbocharged diesel engine under the operating conditions of low speed and fast acceleration. In this study, the experiment for improving the low speed and acceleration performance is performed by means of injecting air into the intake manifold of compressor exit during the period of low speed and application of a fast acceleration from low speed. The effects of air injection into the intake manifold on the response performance were investigated at various applicant parameters such as air injection pressure, accelerating rate, accelerating time, engine speed and load. The experimental results show that air injection into the intake manifold at compressor exit is closely related to the improvement of turbocharger lag under low speed and accelerating conditions of a turbocharged diesel engine. During the rapid acceleration period, the air injection into the intake manifold of turbocharged diesel engine indicates the improvement of the combustion characteristics and gas pressure in the cylinder. At low speed range of the engine, the effect of air injection shows the improvement of the pressure distribution of turbocharger and combustion pressure during the period of gas exchange pressure.

• Journal of Fisheries and Marine Sciences Education
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• v.28 no.1
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• pp.14-21
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• 2016

Research on ship motion and seasickness is recognized as the important research area to ensure the pleasant operative environment in addition to the research of operation safety of ship. In this paper, the motion performance in waves for the training ship Kaya of Pukyong National University is obtained by using the computer program based on Strip Method. To guarantee the pleasant seafaring in ocean, the vertical acceleration of ship motion is calculated according to the habitation division location in the ship. The results of calculation by changes of location of habitation division are compared with the guideline of MSI(Motion Sickness Incidence). The degree of motion sickness is shown and discussed through the comparison between calculated vertical acceleration spectrum and MSI guideline. To improve the safety of ship in motion and the pleasant seafaring in waves, the downtrend of seasickness ratio is needed by the decrease on vertical acceleration of the ship. Through the results in this paper, the relocation of both bridge and accommodation toward the aftship reduced the vertical acceleration and MSI.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.23 no.3
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• pp.258-266
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• 2013

This paper presents the correlation between psychological and physiological acoustics for the automotive acceleration sound. The research purpose of this paper is to evaluate the sound quality of acceleration sound of a passenger car based EEG signal. The previous method for the objective evaluation of sound quality is to use sound metrics based on psychological acoustics. This method uses not only psychological acoustics but also physiological acoustics. For this work, the sounds of 7 premium passenger cars are recorded and evaluated subjectively by 33 people. The correlation between the subjective rating and sound metrics is calculated based on physiological acoustics. Finally the correlation between the subjective rating and the EEG signal measured on the brain is also calculated. Throughout these results the new evaluation system for the sound quality on the automotive acceleration sound of a passenger car has been developed based on bio-signal.

• Physical Therapy Korea
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• v.9 no.3
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• pp.39-46
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• 2002

In this study, vertical acceleration of center of mass was observed along normal gait phases in 9 healthy male volunteers (aged $25.7{\pm}2.18$). The developed wireless accelerometric device was attached on the intervertebral space between L3 and L4 using a semi-elastic waist belt. A three-dimensional motion analysis system, synchronized with the accelerometry, was used for detecting gait phases. There was no significant correlation between the body weight and the acceleration. The first peak curve covered loading response phase. The second downward peak point was matched accurately with the opposite toe-off. In mid-stance and terminal stance, the acceleration curve highly resembled the vertical ground reaction force curve. There was no significant difference in timing between the final upward peak point and the initial contact. Therefore, the developed accelerometry system would be helpful in determining determine temporal gait pattems in patients with gait disorders.