• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.03a
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• pp.690-699
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• 2008

In this paper a conventional approach for design and analysis of subsonic air vehicle is used. First of all subsonic aerodynamic coefficients are calculated using Computational Fluid Dynamics(CFD) tools and then wind-tunnel model was developed that integrates vehicle components including control surfaces and initial data is validated as well as refined to enhance aerodynamic efficiency of control surfaces. Experimental data and limited computational fluid dynamics solutions were obtained over a Mach number range of 0.5 to 0.8. The experimental data show the component build-up effects and the aerodynamic characteristics of the fully integrated configurations, including control surface effectiveness. The aerodynamic performance of the fully integrated configurations is comparable to previously tested subsonic vehicle models. Mathematical model of the dynamic equations in 6-Degree of Freedom(DOF) is then simulated using MATLAB/SIMULINK to simulate trajectory of vehicle. Effect of altitude on range, Mach no and stability is also shown. The approach presented here is suitable enough for preliminary conceptual design. The trajectory evaluation method devised accurately predicted the performance for the air vehicle studied. Formulas for the aerodynamic coefficients for this model are constructed to include the effects of several different aspects contributing to the aerodynamic performance of the vehicle. Characteristic parameter values of the model are compared with those found in a different set of similar air vehicle simulations. We execute a set of example problems which solve the dynamic equations to find the aircraft trajectory given specified control inputs.

• 한국노년학
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• v.37 no.3
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• pp.617-635
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• 2017

The aim of this study was to investigate both poverty and depression among older adults, focusing on the relationship of these two trajectories. For expanding the understanding about elderly poverty and depression, the study measured the longitudinal patterns of various transition in these two variables. The data for the study is 1st to 9th waves (2006-2014) of Korea Welfare Panel Study (KoWePS), and 4,431 older adults were used for the final analysis. For data analysis, Semi-parametric group-based modeling and Dual trajectory model were selected. The main results of this study were followings; First, The trajectory groups were identified: non-poverty, decrease poverty, increase poverty, remain high-poverty, chronic poverty groups and 4 trajectories of depression: stable, remain low-depression, risk of depression, chronic depression groups. Second, the study was tried to anticipate the longitudinal transition of poverty and depression status, and investigate the concurrent relationship in these two variables. It turned out that the stable poverty status led the stable depression, and vice versa. Based on these result, this study for elderly welfare were discussed to reduce risk for poverty and depression.

• Journal of Advanced Navigation Technology
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• v.25 no.3
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• pp.217-222
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• 2021

EOTS(Electro-Optical Tracking System) is utilized in acquiring visual information to assess a guided missile's performance. As the missile travels so fast, it is almost impossible for operator to re-capture the lost target. The RADAR or telemetry data are used to re-capture the lost target however facilities to receive real time data is required, which constrains selection of tracking site. Unlike aforementioned data, pre-calculated nominal trajectory can be used without communication facility. This paper proposes a method to predict lost target's state by employing nominal trajectory. Firstly, observed trajectory and nominal trajectory are compared using DTW and current target's state is predicted. The predicted state is used as observation in Kalman filter's correction phase to predict target's next state. The plausibility of the proposed method is verified by applying on actual missile trajectory.

• Journal of the Korean Society of Marine Environment & Safety
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• v.26 no.7
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• pp.759-766
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• 2020

In recent years, the maritime traffic environment has been changing in various ways, and the traffic volume has been increasing constantly. Accordingly, the requirements for maritime traffic analysis have become diversified. To this end, traffic characteristics must first be analyzed using vessel trajectory data. However, as the conventional method is mostly manual, it requires a considerable amount of time and effort, and errors may occur during data processing. In addition, ensuring the reliability of the analysis results is difficult, because this method considers the subjective opinion of analysts. Therefore, in this paper, we propose an automated method of traffic network generation for maritime traffic analysis. In the experiment, spatiotemporal features are analyzed using data collected at Mokpo Harbor over six months. The proposed method can automatically generate a traffic network reflecting the traffic characteristics of the experimental area. In addition, it can be applied to a large amount of trajectory data. Finally, as the spatiotemporal characteristics can be analyzed using the traffic network, the proposed method is expected to be used in various maritime traffic analyses.

• Journal of Space Technology and Applications
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• v.1 no.3
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• pp.302-318
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• 2021

A basic study was conducted on how to determine the launch timing of a space probe targeting an Earth-approaching asteroid. In the future, when a probe mission targeting an asteroid approaching Earth's orbit is conducted in Korea, in order to determine the launch time, an appropriate solution should be obtained by applying the Global Optimization technique. For this, accurate current orbit information of each asteroid must be obtained first, and prior scenarios such as Earth's orbit information, main engine performance information of the probe and launch vehicle, the number of gravity-assisted maneuvers, and maximum flight time limit should be discussed. Also, the criteria for optimization should be determined first. In this paper, based on these prerequisites and information, a method for finding the launch time of an asteroid probe was studied using the open source software such as PyKEP and Evolutionary Mission Trajectory Generator (EMTG) which are the programs for interplanetary trajectory generation purpose.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.57 no.4
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• pp.334-341
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• 2021

The fishery compensation by marine spatial planning such as routeing of ships and offshore wind farms is required objective data on whether fishing vessels are engaged in a target area. There has still been no research that calculated the number of fishing operation days scientifically. This study proposes a novel method for calculating the number of fishing operation days using the fishing trajectory data when investigating fishery compensation in marine spatial planning areas. It was calculated by multiplying the average reporting interval of trajectory data, the number of collected data, the status weighting factor, and the weighting factor for fishery compensation according to the location of each fishing vessel. In particular, the number of fishing operation days for the compensation of driftnet fishery was considered the daily average number of large vessels from the port and the fishery loss hours for avoiding collisions with them. The target area for applying the proposed method is the routeing area of ships of Jeju outer port. The yearly average fishing operation days were calculated from three years of data from 2017 to 2019. As a result of the study, the yearly average fishing operation days for the compensation of each fishing village fraternity varied from 0.0 to 39.0 days. The proposed method can be used for fishery compensation as an objective indicator in various marine spatial planning areas.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.35 no.1
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• pp.1-8
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• 2022

This study proposes a penetration model in soil considering the wake separation and reattachment based on the integrated force law (IFL). Rigid body dynamics, the IFL, and semi-empirical resistance function about soil are utilized to formulate the motion of the hard projectile. The model can predict the trajectory in soil considering the spherical cavity expansion phenomenon under various oblique angles and angles of attack (AOA). The Mohr-Coulomb yield model is utilized as the resistance function of the soil. To confirm the feasibility of the proposed model, a comparative study is conducted with experimental results described in the open literature. From the comparative study, the penetration depth estimated from the proposed model had about 13.4% error compared to that of the experimental results. In general, the finite element method is widely used to predict the trajectory in soil for a projectile. However, it takes considerable time to construct the computational model for the projectile and perform the numerical simulation. The proposed model only needs to the dimension of the projectile and can predict the trajectory of the projectile in a few seconds.

• Journal of the Korean Society of Marine Environment & Safety
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• v.23 no.4
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• pp.385-392
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• 2017

This research presents the results of a study on the trajectory characteristics of barges with different configurations. A towing experiment was carried out in a water tank with three types of barges in two cases: with and without skegs. The effects of towline length on trajectory were also observed. This study analyzed and compared the length and amplitude of trajectory shapes for each barge in various combinations. It revealed that the trajectory of a barge is influenced not only by skegs but also by the length of the towline. As a result of this work, it can be clearly seen that skegs significantly improve the course stability of a towed barge regardless of differences in bow shape or towline length. Water tank test results also indicated that the length of a towline plays a key role in affecting the trajectory characteristics of a barge-towing system. The length and amplitude of the slewing motion of a barge increased with an increase in the length of the towline connected to the barge. Validation of the present research results should be carried out by further experiments and computational comparisons in the near future.

• Survey Research
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• v.12 no.2
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• pp.113-144
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• 2011

The purposes of the present study were (1) to identify the latent classes depending on youth employees' trajectories in job satisfaction and turnover intention and (2) to test the effects of person-job fit(major fit, education level fit, skill level fit) on job satisfaction and turnover intention using Youth Panel 2001. In order to estimate latent classes of job satisfaction and turnover intention changes simultaneously and study probabilities linking latent class membership in trajectory across the two variables, we applied dual trajectory model, an extension of semi-parametric group-based approach, Results showed that four latent classes were identified for job satisfaction, which were defined, based on the trajectory patterns, as increasing group, decreasing group, medium-level group, and high-level group. And, three latent classes estimated for turnover intention were defined as low-level group, maintaining group, and rapidly decreasing group. To test the effects of person-job fit variables, we added the variables as time-dependant variables to the unconditional latent class model. The effect of education level fit and skill level fit were found significant in the groups which are low in job satisfaction and have high in turnover intention. Findings from this study suggest the need to consider trajectory heterogeneity in the study of youth employees' job satisfaction and turnover intention to capture the dynamic dimension of overlap between the two constructs.

• International Journal of Precision Engineering and Manufacturing
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• v.7 no.2
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• pp.56-59
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• 2006

A vibrational model of powder transfer equipment based on the lumped parameter method was developed, in which the operating motion consists of surging, bouncing, and pitching. After decoupling the equation of motion, the vibrational excitation source of the pitching motion was removed. So the designers are able to plan the optimum design to adjust the motion trajectory of the powder transfer equipment. That is, a procedure to adjust the motion trajectory of powder transfer equipment by changing design specifications such as the installation position, the direction of the motor, the driving speed, the mass unbalance, the stiffness coefficient, and the installation position of the support spring, is presented in this paper. The powder transfer equipment manufactured according to the results of this study did not suffer fatigue destruction, since the maximum stress on the basket structure was sufficiently small.