• Journal of Positioning, Navigation, and Timing
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• v.2 no.2
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• pp.101-108
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• 2013

GPS is the most widely-used Positioning, Navigation, and Timing (PNT) system. Since GPS is an important PNT infrastructure, the vulnerability of GPS to signal jamming has received significant attention. Especially, South Korea has experienced intentional high-power jamming from North Korea for the past three years, and thus realized the necessity of a complementary PNT system. South Korea recently decided to deploy a high-power terrestrial navigation system, eLoran, as a complementary PNT system. According to the plan, the initial operational capability of the Korean eLoran system is expected by 2016, and the full operational capability is expected by 2018. As a necessary research tool to support the Korean eLoran program, an eLoran performance simulation tool for Korea is under development. In this paper, the received signal strength, which is necessary to simulate eLoran performance, from the suggested Korean eLoran transmitters is simulated with the consideration of effective ground conductivities over Korea. Then, eLoran signal-to-noise ratios are also simulated based on atmospheric noise data over Korea. This basic simulation tool will be expanded to estimate the navigation performance (e.g., accuracy, integrity, continuity, and availability) of the Korean eLoran system.

• Wind and Structures
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• v.35 no.5
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• pp.309-322
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• 2022

Due to the complex terrain around high-speed railways, the windbreaks were established along different landforms, resulting in irregular windbreak transition regions between different subgrade infrastructures (flat ground, cutting, embankment, etc). In this paper, the effect of a windbreak transition on the wind flow around railways subjected to crosswinds was studied. Wind tunnel testing was conducted to study the wind speed change around a windbreak transition on flat ground with a uniform wind speed inflow, and the collected data were used to validate a numerical simulation based on a detached eddy simulation method. The validated numerical method was then used to investigate the effect of the windbreak transition from the flat ground to cutting (the "cutting" is a railway subgrade type formed by digging down from the original ground) for three different wind incidence angles of 90°, 75°, and 105°. The deterioration mechanism of the flow fields and the reasons behind the occurrence of the peak wind velocities were explained in detail. The results showed that for the windbreak transition on flat ground, the impact was small. For the transition from the flat ground to the cutting, the influence was relatively large. The significant increase in the wind speeds was due to the right-angle structure of the windbreak transition, which resulted in sudden changes of the wind velocity as well as the direction. In addition, the height mismatch in the transition region worsened the protective effect of a typical windbreak.

• Structural Engineering and Mechanics
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• v.67 no.5
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• pp.427-437
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• 2018

Structural pounding is commonly observed phenomenon during major ground motion, which can cause both structural and architectural damages. To reduce the amount of damage from pounding, the best and effective way is to increase the separation distance. Generally, existing design procedures for determining the separation distance between adjacent buildings subjected to structural pounding are based on approximations of the buildings' peak relative displacement. These procedures are based on unknown safety levels. The aim of this research is to estimate probabilistic separation distance between adjacent structures by considering the variability in the system and uncertainties in the earthquakes characteristics through comprehensive numerical simulations. A large number of models were generated using a robust Monte-Carlo simulation. In total, 6.54 million time-history analyses were performed over the adopted models using an ensemble of 25 ground motions as seismic input within OpenSees software. The results show that a gap size of 50%, 70% and 100% of the considered design code for the structural periods in the range of 0.1-0.5 s, leads to have the probability of pounding about 41.5%, 18% and 5.8%, respectively. Finally, based on the results, two equations are developed for probabilistic determination of needed structural separation distance.

• Journal of the Korea Society for Simulation
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• v.27 no.3
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• pp.89-97
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• 2018

In future warfare, most part of resources and their platforms would be replaced by unmanned system like UGV(Unmanned Ground Vehicle). They are also connected each other with communication network and it is called NCW(Network Centric Warfare) environment. Hence how to measure the effectiveness of UGV operated in NCW circumstance become an important issue. However, there are few research paper to deal with this kind of UGV effectiveness issue coupled with communication failure. In this paper, we proposed a new ABM process to measure the UGV effectiveness combined with communication success ratio based on terrain condition of the ground engagement. Additionally, we also provide the effectiveness analysis result when communication repeater is applied in case of communication failure.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.21 no.3
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• pp.368-375
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• 2012

Durability performance evaluation of automotive components is very important and time consuming task. In this paper, to reduce vehicle component development time and cost virtual testing simulation technology is used to evaluate durability performance of a passenger car front aluminum sub-frame. Multibody dynamics based vehicle model and virtual test simulation model of a half car road simulator are validated by comparisons between rig test results and simulation results. Durability life prediction of the sub-frame is carried out using the model with road load data of proving ground which can evaluate accelerated durability life. We found that the durability performance of the sub-frame is sufficient and it can be predicted within short time compared to rig test time.

• International Journal of Aeronautical and Space Sciences
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• v.13 no.3
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• pp.377-385
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• 2012

The Automatic Dependent Surveillance Broadcast (ADS-B) system is a key component of CNS/ATM recommended by the International Civil Aviation Organization (ICAO) as the next generation air traffic control system. ADS-B broadcasts identification, positional data, and operation information of an aircraft to other aircraft, ground vehicles and ground stations in the nearby region. This paper explores the ADS-B based trajectory prediction and the conflict detection algorithm. The multiple-model based trajectory prediction algorithm leads accurate predicted conflict probability at a future forecast time. We propose an efficient and accurate algorithm to calculate conflict probability based on approximation of the conflict zone by a set of blocks. The performance of proposed algorithms is demonstrated by a numerical simulation of two aircraft encounter scenarios.

• Journal of the Korean Society for Precision Engineering
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• v.16 no.6
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• pp.160-165
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• 1999

In surface grinding, the conditions of the grinding wheel give a significant effect on the ground workpieces comparing with other metal removal provesses. In this paper, to assist the development, a non-contacting optical method by the laser beam is introduced. The in-process measurement of scattering intensities has been made during surface grinding processes and the surface textures of wheel working surfaces are captured. Also, in order to determine the dressing time monitoring method of a grinding wheel, a three-dimensional computer simulation of the grinding operation has been attempted based on the contact mechanism and the surface-shaping system between the grinding wheel and the workpiece. The optimal dressing time is determined by the amount of the grain wear and work surface roughness.

• Proceedings of the KSR Conference
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• 2006.11b
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• pp.1454-1460
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• 2006

This paper assesses communication performance using a roaming simulator when roaming occurs between onboard and ground wireless communication devices for communication based train control system (CBTC). Generally, CBTC is defined as the system regularly collecting location and speed data from each train, transmitting distance information to a train, and optimizing train speed according to train performance. When a train is moving, roaming is also performed to continuously transmit and receive train control information between the ground controller and the train. To operate CBTC, packet loss rate should be less than 1%, roaming time less than 100ms during roaming. We developed a roaming simulator to check communication performance before installing ground and onboard equipments on actual wireless sections. The roaming simulator to be introduced in this paper is for roaming simulation before conducting CBTC field test, which is the project to develop Urban Rail Signaling System Standards, being conducted in KRRI. The simulation consists of one onboard wireless communication device and three ground wireless communication devices, and the roaming simulator estimate packet loss rate occurring during roaming process of the two devices. Therefore, if you use the roaming simulator before the field test, you can predict various problems to occur in actual environment and reduce time, cost and people necessary to resolve these problems.

• Earthquakes and Structures
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• v.17 no.6
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• pp.557-566
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• 2019

The evaluation of the seismic hazard for a given site is to estimate the seismic ground motion at the surface. This is the result of the combination of the action of the seismic source, which generates seismic waves, the propagation of these waves between the source and the site, and site local conditions. The aim of this work is to evaluate the sensitivity of dynamic response of extended structures to spatial variable ground motions (SVGM). All factors of spatial variability of ground motion are considered, especially local site effect. In this paper, a method is presented to simulate spatially varying earthquake ground motions. The scheme for generating spatially varying ground motions is established for spatial locations on the ground surface with varying site conditions. In this proposed method, two steps are necessary. Firstly, the base rock motions are assumed to have the same intensity and are modelled with a filtered Tajimi-Kanai power spectral density function. An empirical coherency loss model is used to define spatial variable seismic ground motions at the base rock. In the second step, power spectral density function of ground motion on surface is derived by considering site amplification effect based on the one dimensional seismic wave propagation theory. Several dynamics analysis of a curved viaduct to various cases of spatially varying seismic ground motions are performed. For comparison, responses to uniform ground motion, to spatial ground motions without considering local site effect, to spatial ground motions with considering coherency loss, phase delay and local site effects are also calculated. The results showed that the generated seismic signals are strongly conditioned by the local site effect. In the same sense, the dynamic response of the viaduct is very sensitive of the variation of local geological conditions of the site. The effect of neglecting local site effect in dynamic analysis gives rise to a significant underestimation of the seismic demand of the structure.

• Journal of the Korea Society for Simulation
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• v.21 no.4
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• pp.75-80
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• 2012

This paper describes the development and applications of maintainability simulation system based on virtual reality technology. The immersive type maintainability simulator using virtual reality is developed and assembly simulation using DELMIA software is conducted for an air-to-ground munition as an example. The simulation processes and result validate the feasibility and effectiveness of maintainability simulation system for logistic element development.