• Journal of Korean Society of Transportation
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• v.24 no.3 s.89
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• pp.17-27
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• 2006

Car following model is a theory that examines changes of condition and interrelationship of acceleration deceleration. headway, velocity and so on closely based on the hypothesis that the Posterior vehicle always follows the preceding vehicle. Car following mode) which is one of the research fields of microscopic traffic flow was first introduced in 1950s and was in active progress in 1960s. However, due to the limitation of data gathering the research depression was prominent for quite a while and then soon was able to tune back on track with development in global positioning system using satellite and generalization of computer use. Recently, there has been many research studies using reception materials of global Positioning system(GPS). Introducing GPS technology to traffic has made real time tracking of a vehicle position possible. Position information is sequential in terms of time and simultaneous measurement of several vehicles in continuous driving is also practicable. Above research was focused on judging whether it is feasible to overcome the following model research by adopting the GPS reception device that was restrictively proceeded due to the limitation of data gathering. For practical judgment, we measured the accuracy and confidence level of the GPS reception devices material by carrying out a practical experiment. Car following model is also being applied in simulations of traffic flow analysis, but due to the difficulty of estimating parameters the basis of the above result. it is our goal to produce an accurate calibration of car following model's parameters that is suitable in this domestic actuality.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.27 no.5
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• pp.429-436
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• 2014

This paper presents the seismic performance of a geometrically unsymmetrical reinforced concrete building considering torsional effect and material nonlinearity of concrete and steel. The reinforced concrete building is a structure for seismic performance evaluation in the SMART-2013 international benchmark program. Nonlinear constitutive models for concrete and steel were constructed, and their numerical performance was demonstrated by various local tests. Modal analysis showed that the first three natural frequencies and mode shapes were close to the experimental results from the SMART-2013 program. In the time history analysis for low-intensity seismic loadings, displacement and acceleration responses at sampling points were similar to the experimental results. In the end, nonlinear time history analysis was conducted for Northridge earthquake to predict the behavior of the reinforced concrete structure under high-intensity seismic loadings.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.26 no.4
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• pp.263-269
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• 2013

In this study, the strain based monitoring method to evaluate the lateral structural response of buildings is presented and an applicability of the proposed method is confirmed through the numerical study. It is assumed that the fiber Bragg grating(FBG) strain sensor is employed to measure the strain response of members due to the excellent properties such as multiplexing, and higher sampling frequency. These properties of FBG sensors is proper for buildings the a lot of sensors are required to monitor the reponses of those. FBG sensors measure the strain response of vertical members and are employed to calculate the curvatures of members using the measured strain responses. Then the lateral displacement, and lateral acceleration is evaluated based on the curvatures of vertical members. Additionally, these dynamic responses of buildings are used to evaluate the dynamic properties of buildings such as the natural frequencies and mode shapes using the frequency domain decomposition(FDD) method. Through the application of nine-story steel moment frame example structure, it is confirmed that the proposed method is appropriate to evaluate the lateral structural responses and dynamic properties of buildings.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.14 no.6
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• pp.1299-1308
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• 1994

This paper is considered on the dynamic behavior and the dynamic impact coefficient on the cable-stayed bridge under the vehicle load. The method of static analysis, that is, the transfer matrix method is used to get influence values about displacements, section forces of girder and cable forces. Gotten influence values were used as basic data to analyse dynamic behavior. This paper used the transfer matrix method because it is relatively simpler than the finite element method, and calculating speed of computer is very fast and the precision of computation is high. In the process of dynamic analysis, the uncoupled equation of motion is derived from simultaneous equation of the motion of cable-stayed bridge and vehicle travelling by using mode shape, which was borne from system of undamped free vibration. The solution of the uncoupled equation of motion, that is, time history of response of deflections, velocity and acceleration on reference coordinate system, is found by Newmark-${\beta}$ method, a kind of direct integral method. After the time history of dynamic response was gotten, and it was transfered to the time history of dynamic response of cable-stayed bridge by linear transformation of coordinates. As a result of this numerical analysis, effect of dynamic behavior for cable-stayed bridge under the vehicle load has varied depending on parameter of design, that is, the ratio of span, the ratio of main span length, tower height, the flexural rigidity of longitudinal girder, the flexural rigidity of tower, and the cable stiffness, investigated. Very good agreements with the existing solution in the literature are shown for the uncracked plate as well as the cracked plate.

• Journal of the Korea institute for structural maintenance and inspection
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• v.18 no.1
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• pp.174-182
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• 2014

To monitor the wind-induced responses of buildings, conventional real-time kinematic (RTK) methods based on two global positioning system (GPS) receivers (e.g., a reference and a rover) are widely applied. However, these methods can encounter problems such as difficulty in securing and maintaining a space for a reference station. With the recently developed virtual reference station (VRS)-RTK approach, the position of a structure can be measured using only a rover receiver. In this study, to evaluate the applicability of VRS-RTK methods in monitoring the lateral structural responses of frame structures, we performed free vibration tests on a one-story frame model (the first natural frequency of 1 Hz) and a three-story frame model (the first natural frequency of 0.85 Hz). To assess the reliability of the displacement and acceleration responses measured by the GPS, we performed a concurrent measurement using laser displacement sensors and an accelerometer. The accelerometer results were consistent with the GPS measurements in terms of the time history and frequency content. Furthermore, to derive an appropriate sampling rate for the continuous monitoring of buildings, the errors in the displacement responses were evaluated at different GPS sampling rates (5, 10, 20 Hz). The results indicate that as the sampling rate increased, the errors in the displacement responses decreased. In addition, in the three-story model, all modal components (first, second, and third modes) could be recorded at a sampling rate of 20 Hz.

• Journal of the Korea institute for structural maintenance and inspection
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• v.19 no.4
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• pp.125-135
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• 2015

The tendency of more longer span length being required economical in railway bridges is studying about PSC I shaped girder. In this case, it is important to analyze and choose the effective girder section for stiffness of bridge. This study investigates the dynamic properties and safety of PSC I shaped girder being used wide upper flange whose selection based on radii and efficiency factor of flexure for railway bridge in different span type. In addition, 40m PSC Box girder bridge adopted in Honam high speed railway is further analyzed to compare dynamic performance of PSC I shaped girder railway bridge with same span length. Time history response is acquired based on the mode superposition method. Static analysis is also analyzed using standard train load combined with the impact factor. Consequently, the result met limit values in every case including vertical displacement, acceleration and distort.

• Korean Journal of Materials Research
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• v.27 no.12
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• pp.705-709
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• 2017

The electronic and optical characteristics of molybdenum disulphide ($MoS_2$) film significantly vary with its thickness, and thus a rapid and accurate estimation of the number of $MoS_2$ layers is critical in practical applications as well as in basic researches. Various existing methods are currently available for the thickness measurement, but each has drawbacks. Transmission electron microscopy allows actual counting of the $MoS_2$ layers, but is very complicated and requires destructive processing of the sample to the point where it will no longer be useable after characterization. Atomic force microscopy, particularly when operated in the tapping mode, is likewise time-consuming and suffers from certain anomalies caused by an improperly chosen set point, that is, free amplitude in air for the cantilever. Raman spectroscopy is a quick characterization method for identifying one to a few layers, but the laser irradiation causes structural degradation of the $MoS_2$. Optical microscopy works only when $MoS_2$ is on a silicon substrate covered with $SiO_2$ of 100~300 nm thickness. The last two optical methods are commonly limited in resolution to the micrometer range due to the diffraction limits of light. We report here a method of measuring the distribution of the number of $MoS_2$ layers using a low voltage field emission electron microscope with acceleration voltages no greater than 1 kV. We found a linear relationship between the FESEM contrast and the number of $MoS_2$ layers. This method can be used to characterize $MoS_2$ samples at nanometer-level spatial resolution, which is below the limits of other methods.

• Journal of ILASS-Korea
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• v.23 no.4
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• pp.212-220
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• 2018

As increase the number of vehicles, the issue of greenhouse gas that was emitted by them became important. As a result, greenhouse gas (GHG) regulations are being strengthened and efforts are being actively made to reduce greenhouse gas emissions in the automotive industry. In the other hand, regulations for harmful emission of vehicles have been reinforced by step. Especially, the lastly applied step, so called Euro 6, not only decreased NOx limit down to half of Euro 5 but also introduced real driving emission limit for NOx and PN. It is a challenge for manufacturers to meet the recent GHG regulation as well as the latest emission regulation. To overcome these regulations a De-NOx after-treatment system is being applied to diesel vehicles that are known emitting the lowest GHG among conventional internal combustion engines. At the time of the introduction of Euro 6 emission standard in Korea, in the domestic fuel economy certification test, some diesel vehicles emitted more $CH_4$ than Euro 5 vehicles. As a result, it was confirmed that LNT-equipped vehicles emitted a high level $CH_4$ and the level exceeded the US emission standard. In order to determine the reason, various prior literature was investigated. However, it was difficult to find a detailed study on the methane increase with LNT. In this paper, to determine whether the characteristics of vehicles equipped with LNT the affects the above issue and other greenhouse gases, 6 passenger cars were tested on several emission test modes and ambient temperatures with a environment chamber chassis dynamometer. 2 cars of these were equipped with LNT only, other 2 cars had SCR only, and LNT + SCR were applied to remaining 2 cars. The test result shown that the vehicles equipped with LNT emitted more $CH_4$ than the vehicles with SCR only. Also, $CH_4$ tended to increase as the higher acceleration of the test mode. However, as the test temperature decreases, $CH_4$ tended to decreased. $CO_2$ was not affected by kinds of De-NOx device but characteristic of the test modes.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.22 no.3
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• pp.777-783
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• 2021

Aircraft are affected by various vibrations during maneuvering. These vibrations may have a fatal effect on the survival of aircraft in some cases, so the safety of components applied to the aircraft should be proven against various vibrations through random vibration analysis. In this study, the structural robustness of an external fuel tank and pylon for military aircraft was evaluated under random vibration conditions using commercial software, MSC Random. In the random vibration analysis, a frequency response analysis was performed by imposing a unit load on the boundary condition point, and then excitation was performed with a PSD profile. In this process, the required mode data was extracted through a modal analysis method. In addition, the random vibration profile specified in the US Defense Environment Standard was applied as random vibration conditions, and the PSD profile given in units of G's was converted into units of gravitational acceleration. As a result of the numerical analysis, we evaluated the structural robustness of the external fuel tank and pylon by identifying the safety margins of beam elements, shell elements, and solid elements in a numerical model for random vibration in the x, y, and z directions.

• Journal of the Korea institute for structural maintenance and inspection
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• v.24 no.6
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• pp.17-24
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• 2020

In this study, series of nonlinear seismic analysis were performed on a reinforced concrete intake tower surrounded by water. To consider the fluid effect around the structure, analysis models were composed using an added mass and CEL approach. At this time, the implicit method was used for the added mass model, and the explicit method was used for the fluid structure interaction model. The input motions were scaled to correspond to 500, 1000, and 2400 years return period of the same artificial earthquake. To estimate the counteractivity of the fluid coupled model, models without fluid effect were constructed and used as a reference. The material models of concrete and reinforcement were selected to consider the nonlinear behavior after yielding, and analysis were performed by ABAQUS. As results, in the acceleration response spectrum of the structure, it was found that the influence of the surrounding fluid reducing the peak frequency and magnitude corresponding to the fundamental frequency of the structure. However, the added mass model did not affect the peak value corresponding to the higher mode. The sectional moments were increased significantly in the case of the added mass model than those of the reference model. Especially, this amplification occurred largely for a small-sized earthquake response in which linear behavior is dominant. In the fluid structure interaction model, the sectional moment with a low frequency component amplifies compared to that of the reference model, but the sectional moment with a high requency component was not amplified. Based in these results, it was evaluated that the counteractivity of the additive mass model was greater than that of the fluid structure interaction model.