• Journal of the Korean Society of Fisheries and Ocean Technology
• /
• v.31 no.2
• /
• pp.190-198
• /
• 1995

Many industrial servo amplifiers employ power transister as output device. Thyristor converters are not adopted to drive servo motor, although thyristor is superior to power TR in power rating, noise immunity, price, and size. The reason is, thyristor has no ability of self turn - off. Here in this paper line commutation, in which thyristor is turned off naturally since cathode voltage is higher than anode as time goes by, is employed to turn on thyristor with a delicate sequence. We developed thyristor servo amplifier which does not cause any damage on thyristor because it is designed to prevent triggering the two SCRs in the same arm simultaneously. And it was made clearly how to trigger SCR without any power line shorting and also harmonic analysis is carried out with the aid of FFT analyzer and proved that it can be used even severe reactive load. The designed circuit operated as a good DC amplifier in conventinal servomotor and the results can be use as a position control system application.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.15 no.5
• /
• pp.2553-2558
• /
• 2014

Military rotorcraft should be designed taking into account the condition of the fuel cell bullet impact. The internal fluid pressure, stress of metal fitting and fuel cell, bullet kinetic energy can be included as the design factor for the fuel cell. The best way to obtain the important design data is to conduct the verification test with actual product. But, the verification test requires huge cost and long-term effort. Moreover, there is high risk to fail because of the sever test condition. Thus, the numerical simulation is required to reduce the risk of trial-and-error together with prediction of the design data. In the present study, the bullet impact simulation based on SPH(smoothed particle hydrodynamics) is conducted with the commercial package, LS-DYNA. As the result of the numerical simulation, the internal pressure of fuel cell is calculated as 350~360MPa and the equivalent stress caused by hydro-ram effect is predicted as 260~350MPa on metal fittings.

• Journal of the Korea Society for Simulation
• /
• v.26 no.3
• /
• pp.35-46
• /
• 2017

Spare engine plays an important role for securing readiness of military strength during unexpected fault occurrences and field/depot planned maintenances. The purpose of this research is to present an approach towards the optimal number of spare engines/modules for diversity of aircraft types. We first reviewed two representative approaches, METRIC and meta model. We then investigated military aircrafts and categorized them into 5 types with regard to the engine type and number of engines/modules per aircraft. Through rigorous investigation of planned/non-planned maintenance of each type, we drew parameters and variables involved. As known, due to the complexity of the problem, it is impossible to develop a simple mathematical model with a closed form solution. Based on the airbase operation and maintenance logic with parameters/variable drawn, we developed a simulation model using ARENA well representing real field exercises. For the optimal solution, we applied OptQuest. It has shown that the program developed generates reliable results through a set of case examples.

• Journal of the Korean Society for Railway
• /
• v.10 no.5
• /
• pp.499-505
• /
• 2007

The major effective of this study is to investigate the fatigue effects of rail pad on High Speed Railway with concrete slab track system. It analyzed the mechanical behaviors of HSR concrete slab track with applying rail pad stiffness based on fatigue effect (hardening and increasing stiffness) on the 3-dimensional FE analysis and laboratory test for static & dynamic characteristics. As a result, the hardening of rail pad due to fatigue loading condition are negative effect for the static & dynamic response of concrete stab track which is before act on fatigue effect. The analytical and experimental study are carried out to investigate rail pad on fatigue effected increase vertical acceleration and stress and decrease suitable deflection on slab track. And rail pad based on fatigue effect induced dynamic maximum stresses, the increase of damage of slab track is predicted by adopting fatigue effected rail pad. after due consideration. The servicing HSR concrete slab track with resilient track system has need of the reasonable determination after due consideration fatigue effect of rail pad stiffness which could be reducing the effect of static and dynamic behavior that degradation phenomenon of structure by an unusual response characteristic and a drop durability.

• Journal of Korean Society of Forest Science
• /
• v.107 no.4
• /
• pp.446-455
• /
• 2018

With respect to the quantity, quality and social value of forest jobs, we have developed three major criteria and 11 indicators for evaluating decent forest jobs. The importance and weighted value of the criteria and indicators were investigated through a survey which was conducted on 50 experts involved in Governmental Forest Job Committee, academic and different groups of communities. The 35 experts responded to the survey chose the 'job creation potential' as the most important criterion, and they recognized the 'job quality' has a relatively higher importance than the 'social contribution'. The survey results showed that 'political will' and 'job security' have the highest weighted values among indicators while 'wage level' has the lowest value. The developed criteria and indicators are able to be used as a means of evaluating degree of decent forest jobs for both new and existing jobs.

• Journal of Advanced Navigation Technology
• /
• v.22 no.6
• /
• pp.623-629
• /
• 2018

In this paper, we propose a real-time obstacle detection and avoidance path generation algorithm for UAV. 2-D Lidar is used to detect obstacles, and the detected obstacle data is used to generate real-time histogram for local avoidance path and a 2-D SLAM map used for global avoidance path generation to the target point. The VFH algorithm for local avoidance path generation generates a real-time histogram of how much the obstacles are distributed in the vector direction and distance, and this histogram is used to generate the local avoidance path when detecting near fixed or dynamic obstacles. We propose an algorithm, called modified $RRT^*-Smart$, to overcome existing limitations. That generates global avoidance path to the target point by creating lower costs because nodes are checked whether or not straight path to a target point, and given arbitrary lengths and directionality to the target points when nodes are created. In this paper, we prove the efficient avoidance maneuvering through various simulation experiment environment by creating efficient avoidance paths.

• Journal of Korean Society of Forest Science
• /
• v.107 no.4
• /
• pp.428-435
• /
• 2018

The purpose of this study is to analyze the satisfaction level of regular safety education to reduce and prevent accidents of forest workers. To achieve this goal, a questionnaire survey targeting 362 members of forest working group in National Forestry Cooperative Federation on the status of safety education, requirements for improving safety education, and satisfaction level of safety education. As a result of the analysis, the majority of the respondents said that the safety education should be improved by adding more training related to forestry work and practical education rather than the current lecture. In the effective safety education cycle, 43.8% of respondents said that the most effective once a week, and the most important factors that affect the satisfaction of safety education were the safety method and teaching ability, which were statistically significant.

• The Journal of the Acoustical Society of Korea
• /
• v.40 no.2
• /
• pp.109-120
• /
• 2021

This paper proposes the H∞ norm based data association gate method to apply robustly the data association gate of passive sonar automatic target tracking which is on non-linear targets in dense cluttered environment. For target tracking, data association method selects the measurements within validated gate, which means validated measuring extent, as candidates for the data association. If the extent of the validated gate in the data association is not proper or the data association executes under dense cluttered environment, it is difficult to maintain the robustness of target tracking due to interference of clutter measurements. To resolve this problem, this paper proposes a novel gating method which applies H∞ norm based bisection algorithm combined with 3-σ gate method under Gaussian distribution assumption and tracking error covariance. The proposed method leads to alleviate the interference of clutters and to track the non-linear maneuvering target robustly. Through analytic method and simulation to utilize simulated data of horizontal and vertical bearing measurements, improvement of data association robustness is confirmed contrary to the conventional method.

• Korean Journal of Occupational Health Nursing
• /
• v.28 no.4
• /
• pp.187-196
• /
• 2019

Purpose: The purpose of this study was to investigate the association of job stress and health promotion behaviors with the quality of life in female riot police officers. Methods: A cross-sectional design was adopted, and a convenience sample of 182 female riot police officers from 5 Metropolitan Police Agencies in South Korea. All participants completed a self-administered survey questionnaire that assessed job stress, health promotion behavior, and quality of life in May 2018. The collected data were analyzed using t-test, analysis of variance, and correlation and multiple linear regression analyses, all of which were executed using SPSS/WIN 23.0 and STATA 13.0. Results: The level of job stress among participants was moderate, and the mean was 45.25 out of a maximum possible score of 100. The mean scores that emerged for health promotion behaviors and the quality of life were 2.62 (maximum=4) and 56.59 (maximum=100), respectively. Job stress (r=-.380, p<.001) and health promotion behaviors (r=.559, p<.001) were correlated with the quality of life. The statistically significant predictors of the quality of life were job stress (${\beta}=-.212$, p=.001) and health promotion behaviors (${\beta}=.417$, p<.001). Conclusion: The variables that were associated with the quality of life of female riot police officers were job stress and health promotion behaviors. Therefore, interventions that can enhance job stress management and health promotion behaviors are needed to improve the quality of life of female riot police officers.

• Korean Journal of Legislative Studies
• /
• v.24 no.2
• /
• pp.101-134
• /
• 2018

This study examines the effects of members' legislative performance on their renominations in the $19^{th}$ Korean National Assembly. We measure how many bills each member has proposed and passed in the Assembly. In addition, we also include rate of passing bills as an indicator of legislative performance. Particularly, we analyze 320 members in total, and 270 members who got in on the competition for nomination separately. The empirical findings of our study show that, firstly, among the total members in the Assembly, as they propose bills more and pass bills fewer, they are more likely to be renominated in the very next election. However, this is a result of different types of members rather than legislative performance. Secondly, among the members who actually competed for renomination, the legislative performance of members can not affect their renomination. Therefore, we argue that it is necessary to stipulate nominations criteria and transform top-down nomination method to bottom-up one in order to raise responsiveness and enhance representative democracy.