• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.48 no.5
• /
• pp.391-399
• /
• 2020

KASI (Korea Astronomy and Space Science Institute) has been developing the multipurpose laser tracking system with three functions of satellite laser tracking, adaptive optics and space debris laser tracking for scientific research and national space missions. The space debris laser tracking system provides the distance to space debris without a laser retro-reflector array by using a high power pulse laser, which employs a spinning disk to change the optical path between the transmit and receive beams. The spinning disk causes the collision band which is unable to reflect the returned signal to a detector and then has an effect on the tracking coverage of space debris. This study proposed the mathematical model for tracking coverage by taking into account the various specifications of spinning disk such as disk size, spinning velocity and collision rate between the disk and hole. In addition, the spinning disk specifications were analyzed in terms of tracking coverage and collision band based on the mathematical model to investigate tracking requirements of the Geochang laser tracking system.

• Journal of the Korean Vacuum Society
• /
• v.7 no.1
• /
• pp.59-65
• /
• 1998

Multi-layer diamond-like carbon (DLC) films were deposited by 13.56 MHz r.f. PACVD method. Multi-layer DLC film was composed of 2.5 $mu extrm{m}$ thick pure DLC filml and 0.2$\mu\textrm{m}$ thick Si incorporated DLC (Si-DLC) film as a surface layer. Tribological behaviors of the multi-layer DLC film were investigated with a ball-on-disk type tribometer in ambient atmosphere using AISI 52100 steel ball. Low friction coefficient (<0.1) period increased with increasing the Si content in the surface Si-DLC film. The wear rate after 44,000 cycles and 158,400 cycles were the $2.5\times10^{-8}\sim1.8\times10^{-7}\textrm{mm}^3$/rev. and $7.1\times10^{-9}\sim1.8\times10^{-8}\textrm{mm}^3$/rev.,respectively. The wear rate of the multi-layer DLC film after 158,400 cycles was about 2 times smaller than that of pure DLC films of 2.7 $\mu\textrm{m}$ thickness. This high wear resistance and low friction coefficient was caused by the formation of Si oxide layer on the wear scar surface, as confirmed by the debris composition analysis. It was further shown that this si oxide debris layer on the wear scar surface is formed again even after removing the debris of the steel ball, which maintain the low friction coefficient between multi-layer DLC films and steel ball.

• Journal of Korean Society of Disaster and Security
• /
• v.12 no.2
• /
• pp.1-13
• /
• 2019

In this study, we propose rainfall frequency criteria for the development of early-warning system based on the evaluation of the highway debris flow that includes the contents of the rainfall recurrence cycle. The rainfall criterion was recommended based on the results of previous researches and the recommended rainfall criterion was 1 hour, 6 hours, and 3 days. At this time, the study subjects were located in Gangwon area and the probability rainfall of 8 stations in Gangwon area was collected. Also, the probabilistic distribution of the 1 hour, 6 hour, and 3 day rainfall criteria to be used for the early warning for the highway debris flow in Kangwon area was estimated through the probability analysis. In addition, we analyzed the correlation between 3 types of rainfall criteria selected from the rainfall data and the actual destructive damages of debris flow at 12 points in 7 lines of Gangwon highways. At this time, the rainfall criterion on the probability distribution was divided into an average value and a lower limit value. As a result of the review, it was found that the case of using the lower limit value of the rainfall according to the recurrence intervalwell simulates the situation of actual debris flow hazards.

• Journal of the Korean Society of Marine Environment & Safety
• /
• v.28 no.6
• /
• pp.906-917
• /
• 2022

This study aimed to compare differences according to categories of fishery and marine environmental policies for the (estimated) amount of fishery waste generated by fishing, and to analyze the correlation between associated independent and dependent variables. The independent variables were divided into three dif erent sectors. The first sector included precautionary policies that observed eco-friendly fishing support program, institutional prevention activities, and physical barriers installation. The second sector with the current management policies included the relevant vessel operations, establishment of fishery order, fishery restructuring, and fishery ground clean-up. Thirdly, post-response policies comprised the litter purification from river to shoreline, the collection and removal of marine, sedimentary, and floating debris, purchasing salvaged debris generated while fishing, fishery waste disposal, and repairing damage caused by marine litter. The indicator used was the settlement amount by each program. The dependent variable was the estimated amount of fishery waste and the indicator was the sum of the loss of traps and gill nets and the loss of their appendages. According to the results of Kruskal-Wallis Test, the estimated amount of fishery waste was highest in the East Sea in terms of sea area and the highest in the Si(city) according to basic local municipality. The settlement amount related to the marine environment services was largest in the Gun(county). Further, there were significant differences between Gun(county) and the other regions(Si(city) and Gu(autonomous district)) with respect to most variables. The variables related to the estimated amount of fishery debris were the project purchasing salvaged debris generated while fishing and fishery waste disposal program in the post-response policies.

• Aerospace Engineering and Technology
• /
• v.13 no.1
• /
• pp.184-192
• /
• 2014

In this paper, the lifetime of the artificial space objects in the LEO is analysed by using TLE data, which is provided by JSpOC. We observed the change of the number of space objects from 1957 and determined the reason of space debris generation. And then, we performed the analysis about present condition of space debris environment. The lifetime analysis includes a total of 11,792 artificial space objects and performed until the year 2050 by orbit propagation. We analyze the annual reentry frequency for the high RCS objects such as nonoperational satellites and rocket bodies, which have the possibility of earth ground impact through STK/Lifetime Tool for accurate and effective calculation. The results show that 9 payloads or rocket bodies will be decayed annually and 2 or 3 objects of total value have the possibility of ground impact. In addition, it is also shown that the 40% of a total analysed objects have the lifetime over 200 years.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.40 no.4
• /
• pp.354-363
• /
• 2012

Now there are a lot of expired satellites or space debris around the earth orbit and they threaten the operating satellites and manned space missions. KOMPSAT-2 that scheduled to operate the mission by July, 2013 also has to consider the space debris. This paper introduces the '25 years rules' that must be re-entered within 25 years after the space mission for LEO satellites and describes the removal trajectory design that satisfies the '25 years rules' and minimizes fuel consumption. And this paper suggests monte-carlo simulation for risk analysis that causes the approaching object to the removal trajectory. The result shows that the collision probability of worst case presents 6.0741E-07 and it need to more analysis about precise satellite safety during removal maneuver because there is no information about the object size that approaching to the satellites.

• Nuclear Engineering and Technology
• /
• v.45 no.6
• /
• pp.767-790
• /
• 2013

MAAP4 is a computer code that can simulate the response of a light water reactor power plant during severe accident sequences, including actions taken as part of accident management. The code quantitatively predicts the evolution of a severe accident starting from full power conditions given a set of system faults and initiating events through events such as core melt, reactor vessel failure, and containment failure. Furthermore, models are included in the code to represent the actions that could mitigate the accident by in-vessel cooling, external cooling of the reactor pressure vessel, or cooling the debris in containment. A key element tied to using a code like MAAP4 is an uncertainty analysis. The purpose of this paper is to present a MAAP4 based analysis to examine the sensitivity of a key parameter, in this case hydrogen production, to a set of model parameters that are related to a Level 2 PRA analysis. The Level 2 analysis examines those sequences that result in core melting and subsequent reactor pressure vessel failure and its impact on the containment. This paper identifies individual contributors and MAAP4 model parameters that statistically influence hydrogen production. Hydrogen generation was chosen because of its direct relationship to oxidation. With greater oxidation, more heat is added to the core region and relocation (core slump) should occur faster. This, in theory, would lead to shorter failure times and subsequent "hotter" debris pool on the containment floor.

• Fire Science and Engineering
• /
• v.28 no.4
• /
• pp.64-72
• /
• 2014

Flammable liquids residues in fire debris and pyrolysis products of flammable materials were analyzed by using Gas detecting tube, Gas Chromatograph/Mass Spectrometers (GC/MS), and Pyrolyzer. Comparison studies between chemical components detected in debris fired with and without Flammable liquids were performed. Though Flammable liquids were not present in debris, Gas detecting tube colors were also changed. Chemical components produced from conventional combustions were different from those produced from pyrolysis. Due to the difference of the reaction conditions between combustions and pyrolysis, different chemical products were produced. Petrochemical products of PVC wood-linoleum block could produce ignitable chemicals, such as toluene, ethylbenzene, undecane, and dodecane. So, for better fire investigation more consideration of those chemicals will be porformed.

• Journal of Korean Society of Environmental Engineers
• /
• v.37 no.7
• /
• pp.426-431
• /
• 2015

Korea severely suffers from plastic-induced ocean pollution, but only few studies predicted the trajectory of marine plastic debris and provided their collection method. This study used Ocean Surface CURrent Simulator (OSCURS) of National Oceanic and Atmospheric Administration (NOAA) in order to predict the trajectories of marine plastic debris flowing into the East Sea and Yellow Sea for each season during 2004 to 2013. Results suggest that efficient collection hubs through the high betweenness centrality index. Most hubs were located in the seashores regardless of season, suggesting the seashore of Uljin for the East Sea and the seashore between Saemangeum and Shinan for the Yellow Sea as the most efficient hubs.

• Nuclear Engineering and Technology
• /
• v.16 no.3
• /
• pp.141-154
• /
• 1984

An analysis is presented of key phenomena and scenario which imply some general trends for beyond design-basis-accident in Kori-1 PWR dry containment. The study covers a wide range of severe accident sequences initiated by small break LOCA. The MARCH computer code, with KAERI modifications was used in this analysis. The major emphasis of the paper are two folds, 1) the phenomenologic understanding of severe accident and 2) a study of H2 combustion and debris/ water interactions in a specific small break LOCA for Kori-1 plant. The sensitivity studies for the specific plant data and thermal interaction modelings used in the SASA were performed. The results show that if hydrogen burning does occur at low concentration, the resulting peak pressure does not exceed the design value, while the lower concentration assumption results in repeated burning due to the continuing H$_2$ generation. For debris/water interaction, the particle size has no effect on the magnitude of peak pressure for the amount of water assumed to be in the reactor cavity. But, the occurrence of peak pressure is considerably delayed in case of using the dryout correlation. The peak containment pressure predicted from the hydrogen combustion and steam pressure spite during full core meltdown scenario does not present a severe threat to the containment integrity.