• Journal of Aerospace System Engineering
• /
• v.7 no.1
• /
• pp.1-7
• /
• 2013

Launch vehicles cause several shock events during their lift-off. The excessive shock loads in the several thousands of g's level can results in permanent damage to electronics, optics and other sensitive payload components. The shock can be attenuated by mounting a shock absorber. In this paper, we proposed a semi-active control logic to attenuate the shock so that the input acceleration to main instruments does not exceed the allowable maximum acceleration value. For the performance investigation, two elements model of variable damping and spring stiffness has been used and the analysis results indicate that the proposed semi-active control logic attenuates shock level better than an optimal passive and conventional semi-active on-off control system.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.14 no.4
• /
• pp.62-69
• /
• 2010

In this study, the serviceability performance of Waffle Shaped(WAS) and Double-Tee(DT) precast concrete slabs were evaluated and compared based on the vertical acceleration magnitude induced by walking and heel drop loads. Tests were conducted for practical building structures of which floor systems used WAS and DT slabs. Natural frequencies of the slabs were similar to those obtained by using analytical models. The measured acceleration level was evaluated by vertical floor acceleration criteria presented by ISO-2631, AIJ(1991, Japan) and a previous study regarding floor vibration limit. Test results showed that both WAS and DT slabs satisfied all the criteria and Peak acceleration level of WA slabs was lower than that of DT slabs.

• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• v.27 no.1
• /
• pp.100-106
• /
• 2017

Sound quality engineering in automobile noise applications has become more and more important under the current quiet driving condition because various noise components masked under high noise level can be audible in quieter driving situation. Many researches have been carried out for subjective and objective assessments on automobile sounds and noises. In particular, the interior sound quality has been one of research fields that can give high-quality feature to automobile products. Although many works related to the interior sound quality have been progressed or completed in foreign countries, limited research results are presented in the country. In the study, subjective assessments are first performed with 20 subjects to select perceptual adjectives suitable to the assessment of car interior noises during acceleration. The selected perceptual adjectives are employed as the assessment scales to evaluate the acceleration noises in questionnaire procedures using 35 subjects, for which several noises are created through digital filtering of the acceleration noises measured. Mean values and standard deviations for subjective assessment scores obtained by the questionnaire procedures are calculated and their reliability are also verified. Finally, various statistical analyses such as the correlation analysis and the factor analysis are carried out to reveal the interrelationship between the assessment scales and the spectrum components of the acceleration noises.

• Journal of the Korea Institute of Military Science and Technology
• /
• v.21 no.6
• /
• pp.894-903
• /
• 2018

In the case of helicopters, the development of parts technology is rapidly changing, and the complexity is rapidly increasing. Particularly, the surge of various electric and electronic systems is recognized as a problem that is directly related to the safety of the helicopter. Due to these problems, there is a growing interest in reliability evaluation in the face of the problem of confirming and certifying the reliability of parts in the development stage. In this paper, the analysis of the failure mechanism of the wiper system was carried out, and the priority and importance of each failure mode were checked by using the results, and major stress factors were derived and the corresponding acceleration model was selected. Also, the accelerated lifetime test time was calculated according to the life test time, acceleration status and acceleration level of the steady state by using the selected acceleration model and characteristic values.

• Journal of Korean Elementary Science Education
• /
• v.23 no.4
• /
• pp.357-363
• /
• 2004

The purpose of this study was to investigate the effects of Thinking Science program on the cognitive acceleration and cognitive processing skills of the elementary school students. Subjects included 305 5th grade students in three elementary schools. Subjects were divided into the experimental and the control groups. Thinking Science program was implemented to the experimental group over a period of two years. Statistically significant gains on the cognitive acceleration were shown by the experimental group compared with the control group. The intervention effects on the cognitive acceleration were shown for the girls of the elementary schools. It was also found that Thinking Science program exerted significant effect on the development of the cognitive processing skills of the students. The experimental group gained higher scores of attention and simultaneous processing skills compared with the control group. This implied that Thinking Science program was effective not only on the cognitive acceleration but also on the development of the cognitive processing skills as a far-transfer.

• Journal of the Earthquake Engineering Society of Korea
• /
• v.5 no.4
• /
• pp.51-66
• /
• 2001

There occurred a moderate size earthquake of Magnitude 5 in Whagae-Myun, Hadong-GUn, Kyongsangnam-Do on July 4, 1936. It caused severe damage to the buildings and other structures in Sang-Gye-Sa, a Buddhist Temple. The top component of a five-story stone pagoda was tipped over and fell down to the ground during the earthquake. In order to have accurate and quantitative estimate of the peak acceleration level of that earthquake, a full-scale model was constructed through rigorous verification process. The complete model was mounted on a shaking table and subjected to the dynamic tests. Two kinds of tests were performed: exploratory test and fragility test. The exploratory test was done with low acceleration level. In the fragility test, the behavior of the model was carefully monitored while increasing the acceleration level. The construction details of the model are provided and test procedures are reported. Finally important test results are presented and their implications are discussed.

• Journal of Electrical Engineering and Technology
• /
• v.9 no.1
• /
• pp.15-26
• /
• 2014

This paper proposes a Modified Particle Swarm Optimization with Time Varying Acceleration Coefficients (MPSO-TVAC) for solving economic load dispatch (ELD) problem. Due to prohibited operating zones (POZ) and ramp rate limits of the practical generators, the ELD problems become nonlinear and nonconvex optimization problem. Furthermore, the ELD problem may be more complicated if transmission losses are considered. Particle swarm optimization (PSO) is one of the famous heuristic methods for solving nonconvex problems. However, this method may suffer to trap at local minima especially for multimodal problem. To improve the solution quality and robustness of PSO algorithm, a new best neighbour particle called 'rbest' is proposed. The rbest provides extra information for each particle that is randomly selected from other best particles in order to diversify the movement of particle and avoid premature convergence. The effectiveness of MPSO-TVAC algorithm is tested on different power systems with POZ, ramp-rate limits and transmission loss constraints. To validate the performances of the proposed algorithm, comparative studies have been carried out in terms of convergence characteristic, solution quality, computation time and robustness. Simulation results found that the proposed MPSO-TVAC algorithm has good solution quality and more robust than other methods reported in previous work.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.22 no.4
• /
• pp.441-456
• /
• 2021

Enterprise is focused on R&D innovative activities in order to achieve sustainable growth & secure competitive advantage. There are many factors that influence enterprise innovation performance, but enterprise innovation activities do not always have a positive effect. Therefore, this study analyzed the effects of on innovation performance, focusing on innovation acceleration factors and innovation hindrance factors. The research model analyzed 2,081 national manufacturing enterprises that responded to the 2016 Korean Innovation Survey (STEPI). SPSS 25.0 was used to perform reliability, feasibility, and logistic regression analysis. The results are as follows. First, innovation activities have positive effects on enterprise product and process innovation performance. On the other hand, government support had the opposite results. Second, the collaboration of technology showed a positive effect on product innovation performance, independent of innovation acceleration and hindrance factors. Third, innovation activities showed a positive effect on process innovation performance, regardless of the innovation acceleration and hindrance factors. Unlike prior studies limited to technological innovation, this study analyzed the attitudes of enterprises toward innovation acceleration and hindrance factors. This study is expected to contribute to establishing a strategy for reducing the failure and risk of innovation due to its findings on how innovation performance varies by groups.

• Journal of The Korean Association For Science Education
• /
• v.22 no.4
• /
• pp.837-850
• /
• 2002

In an attempt to accelerate the development of formal reasoning ability of students, 'Thinking Science' activities developed by the Cognitive Acceleration through Science Education(CASE) project were implemented to 841 students in 7th grade aged 12+ in six middle schools over a period of two years. Homogeneity between the CASE group and control group was tested with SRT II, while the improvement of formal reasoning ability of the students was tested with SRT VII. The results were analyzed by treatment, gender, and cognitive levels of the students. Statistically significant gains were shown in the CASE group compared with those in the control group. Cognitive level of girls in the CASE group significantly increased as compared with the control group, while there was moderate effect in boys. These results implied that the thinking science activities were effective in cognitive acceleration of girls aged 12+. It was shown that much more CASE students in pre or concrete operational level shifted to formal operational level as compared with the control group while there were significant effects in all levels (ES=0.31${\sim}$1.10) without showing any tendency.

• Journal of the Korean Data and Information Science Society
• /
• v.8 no.2
• /
• pp.183-194
• /
• 1997

In accelerated life tests, the failure time of an item is observed under a high stress level and based on the time, the failure rates of items we estimated at the normal stress level. In this paper, when the mean of the prior distribution of a parameter is known in Weibull lifetime model with censored failure time data, we study various estimating methods to obtain the empirical Bayes estimator of a parameter from the empirical Bayes approach under the normal stress level by considering the fact that the Bayes estimator is the function of prior parameters and of the acceleration parameter representing the effect of acceleration. And we compare the performance of several empirical Bayes estimators of a parameter in terms of the Bayes risk.