• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.6
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• pp.633-638
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• 2012

The maximum spreading is the maximum extent to which a drop can spread after impacting on a surface. It is one of the crucial factors determining the spraying performance in many applications. In this study, the existing maximum spreading models for a Newtonian liquid droplet impacting on a dry solid surface were reviewed and compared with the experimental results over the ranges of $4{\leq}Re{\leq}11700$, $23{\leq}We{\leq}786$, and $37.9^{\circ}{\leq}{\theta}_s{\leq}107.1^{\circ}$. The surface wettability was found to have only a minor influence on the maximum spreading, compared to the liquid viscosity and impact velocity. Among the models tested, the Roisman (2009) model showed the best agreement with the experimental results, matching 80% of the measured data within ${\pm}5%$.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.40 no.3
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• pp.281-288
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• 2016

The ballistic performance data of composite materials is distributed due to material inhomogeneity. In this paper, the uncertainty in residual velocity is obtained experimentally, and a method of predicting it is established numerically for the high-speed impact of a bullet into laminated composites. First, the failure strain distribution was obtained by conducting a tensile test using 10 specimens. Next, a ballistic impact test was carried out for the impact of a fragment-simulating projectile (FSP) bullet with 4ply ([0/90]s) and 8ply ([0/90/0/90]s) glass fiber reinforced plastic (GFRP) plates. Eighteen shots were made at the same impact velocity and the residual velocities were obtained. Finally, simulations were conducted to predict the residual velocities by using the failure strain distributions that were obtained from the tensile test. For this simulation, two impact velocities were chosen at 411.7m/s (4ply) and 592.5m/s (8ply). The simulation results show that the predicted residual velocities are in close agreement with test results. Additionally, the modeling of a composite plate with layered solid elements requires less calculation time than modeling with solid elements.

• Journal of the Korean Society for Railway
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• v.14 no.1
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• pp.11-18
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• 2011

This paper proposed a new 2-D multi-body dynamic modeling technique to analyze overriding behaviors taking place during train collision. This dynamic model is composed of nonlinear springs, dampers and masses by considering the deformable characteristics of carbodies as well as energy absorbing structures and components. By solving this dynamic model for rollingstock, energy absorbing capacities of collision elements, accelerations of passenger sections, impact forces applied to interconnecting devices, and overriding displacements can be well estimated. For a case study, we chose KHST (Korean High Speed Train), obtained crush characteristic data of each carbody section from 3-D finite element analysis, and established a 2-D multi-body dynamic model. This 2-D dynamic model was simulated under the train-to-train collision scenarios, and evaluated with 3-D virtual testing model. It was founded from the simulation results that this 2-D dynamic model could well predict overriding behaviors, and the modeling technique of carbody deformation was very important in overriding estimation.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.20 no.8
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• pp.1569-1580
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• 2016

For the 2.4 GHz active RFID to be successful in the market, one of the requirements is the increased battery life. However, currently we do not have any accurate power consumption estimation method. In this study we develop a simulation model, which can be used to estimate power consumption of tag accurately. Six different simulation models are proposed depending on collision algorithm and query command method. To improve estimation accuracy, we classify tag operating modes as the wake-up receive, UHF receive, sleep timer, tag response, and sleep modes. Power consumption and operating time are identified according to the tag operating mode. Query command for simplifying collection and ack command procedure and newly developed collision control algorithm are used in the simulation. Other performance measures such as throughput, recognition time for multi-tags, tag recognition rate including power consumption are compared with those from the current standard ISO/IEC 18000-7.

• Journal of the Korean Institute of Intelligent Systems
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• v.27 no.2
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• pp.113-118
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• 2017

Various studies on the method of ship collision risk assessment for alarm have been reported constantly, and the result of the studies is applied to navigation devices. However, it is known that navigators ignore or turn off frequent alarms from the devices of predicting collision risk, because they may avoid collisions in the most of situations. In oder to make the prediction of ship collision risk more useful, it is necessary to consider the customary actions of ship collision avoidance. This paper proposes a system of analyzing collision avoidance measures of ships according to the types of encounter and managing the avoidance history of each ship. The core module of the system is designed as a neuro-fuzzy based inference system, and the test of the module validates the proposed system.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2023.05a
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• pp.144-145
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• 2023

육상, 철도, 항공 등 타 교통분야에서 지속적으로 사고와 인명피해가 줄어든 반면, 해양분야는 해양사고가 증가하며 실효적 해양교통안전관리에 대한 필요성이 대두되고 있다. 최근 3년간 국내 해상에서 발생한 충돌사고 중 어선을 포함한 충돌사고가 전체의 약 84%를 차지하며, 해상교통의 주요 변수인 어선을 포함한 국가의 해상교통량 파악은 반드시 필요한 실정이다. 본 연구에서는 현 정부 국정과제인 '디지털 해상 교통망 구축'과 더불어 해양교통안전관리체계 마련의 일환으로 국내 전체 선박위치발신장치(AIS, V-PASS) 데이터를 활용하여 해상교통량을 분석하고 예측 모델을 개발한다. 이를 위해 선박 밀집도를 통한 그리드별 공간가산분석과 항적 데이터 전처리 및 선형화, 선박 길이에 따른 점용면적 산정을 통한 단위 그리드별 해상교통량을 분석한다. 또한, 과거 교통량 데이터는 딥러닝 기반의 시계열 특성을 지닌 RNN과 LSTM 모델을 활용하여 교통량 예측 모형을 개발한다. 본 연구의 결과는 해상교통량과 해양사고의 연관성 분석 및 속력제한구역 등 해상정책 수립의 정량적 근거를 제공하며, 국민에게 해상교통정보 제공을 통해 교통복지 증진에 기여할 수 있다.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.42 no.3
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• pp.270-278
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• 2014

This paper describes an improvement of space objects orbit prediction. To screen possible collisions between operational satellites and space objects, the TLE (Two-Line Element) was used as pseudo-measurement and than the orbit determination and orbit prediction were performed through the flight dynamics system. For determining the orbits, the state vectors were assumed by a series of TLEs within a certain period. The propagation error was analyzed according to the fitting period and a number of pseudo-observations. In order to find out the improvement of orbit prediction with the proposed method, KOMPSAT-2, 3 having the precise orbit in the meter-level range were first applied. Then the result applied to space objects under the same conditions was analyzed. As a result of the RMS error comparison with the orbit prediction of space object, the precision of orbit prediction was improved by approximately 90% for seven days prediction. The improved orbit prediction of space objects can be utilized in the daily analysis for initial screening of the close space objects at high risk.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.11a
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• pp.769-771
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• 2011

The satellite payloaded on the 2nd stage of KSLV-I is planned to perform CCAM(Contamination and Collision Avoidance Maneuver) not to collide with KM(Kick Motor). At the moment, the satellite should pass through low density environment not to be contaminated by KM plume due to residual thrust. Therefore, it is necessary to predict the flow field of KM plume by residual thrust. In this paper, DSMC (Direct Simulation Monte-Carlo) method, which is widely accepted to simulate in rarefied regime, is used to compute the density field of KM plume by residual thrust and the result of DSMC simulation was compared with that of FLUENT to validate it.

• Journal of Auto-vehicle Safety Association
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• v.12 no.4
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• pp.31-38
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• 2020

This study is to develop the prediction model for the HIC15 in frontal vehicle crash tests. The 28 frontal impact test results of the MY2019 and MY2020 USNCAP are utilized. The metrics for evaluating the crash pulse severity such as moving average acceleration, Restraint Quotient (RQ) and ride-down efficiency are reviewed to find out whether the metrics can predict the HIC15. It is observed that the R² values based on the linear regression of all pairs between the existing metrics and the occupant injuries such as the HIC15, 3 ms chest g's and chest deflection are very low. In this study, using the vehicle crash pulses, the linear regression model for estimating the HIC15 is developed. The vehicle crash pulse is splitted seven 10 ms intervals in 70 ms after impact for extracting the average accelerations in each intervals. The prediction model can predict effectively not only the HIC15 but also the maximum head g's, chest deflection and 3 ms chest g's of 13 vehicles out of 28 vehicles.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.39 no.11
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• pp.1033-1041
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• 2011

In this paper, a collision avoidance maneuver frequency for the KOMPSAT-2 and the KOMPSAT-5 is analyzed. For the statistical prediction of the avoidance maneuver frequency, mission orbits, responsive time, accepted collision probabilities, and positional uncertainties of primary and secondary objects are considered. In addition, the collision avoidance maneuver frequency of the KOMPSAT-2 is compared to the case that NORAD catalog during one year is used to calculate that of the KOMPSAT-2. As a result, the collision avoidance maneuver frequency is one per year on average and effective factors on the statistical prediction of the avoidance maneuver frequency are investigated. Efforts to improve its prediction accuracy are also discussed.