• International Journal of Precision Engineering and Manufacturing
• /
• v.6 no.4
• /
• pp.26-30
• /
• 2005

A rotor run-up or run-down process provide more useful information for modal analysis than normal operation conditions. A traditional difficulty associated with rotor run-up or run-down analysis is the non-stationary nature of vibration data. This paper compares Short-Time Fourier Transform (STFT) and the wavelets analysis in these non-stationary signal analyses. An Adaptive Wavelet Analysis (AWT) is proposed to analyze these signals. Although simulations and experiments in a simple rotor-bearing system show that both STFT and AWT can be used to analyze non-stationary vibration signals in rotor dynamics, proposed AWT provides better results than STFT analysis. From the amplitude-frequency curve obtained by AWT, the modal frequency and damping ratio are calculated. This paper also analyzes the characteristics of signals when the shaft touches the outer hoop in a run-up process. The AWT can give a good result in this complex dynamic analysis of the touching process.

• Smart Structures and Systems
• /
• v.24 no.3
• /
• pp.391-401
• /
• 2019

Control of vibrations against extraordinary excitations such as wind and earthquake is very important to the protection of life and financial concerns. One of the methods of structural control is to use Tuned Liquid Damper (TLD), however due to the nature of TLD only one sloshing frequency can be created when the water is sloshing. Among various ideas proposed to compensate this problem, by changing the angle of some rotatable baffles embedded inside a TLD, a frequency range is created such that these baffles are tuned manually at different frequencies. In this study, the effect of cross sectional shape of container with rotating baffles on seismic behavior of TLD is experimentally studied. For this purpose, rectangular and cylindrical containers are designed and used to suppress the vibrations of a Single Degree-Of-Freedom (SDOF) structure under harmonic and earthquake excitations considering three baffle angles. The results show that the rectangular-shaped damper reduces the structural response in all load cases more than the damper with a cylindrical shape, such that maximum differences of two dampers to reduce the structural displacement and structural acceleration are 5.5% and 3% respectively, when compared to the cases where no baffles are employed.

• Structural Engineering and Mechanics
• /
• v.69 no.1
• /
• pp.21-31
• /
• 2019

Optimizing composite structures to exploit their maximum potential is a realistic application with promising returns. In this research, simultaneous maximization of the fundamental frequency and frequency separation between the first two modes by optimizing the fiber angles is considered. A high-fidelity design optimization methodology is developed by combining the high-accuracy of finite element method with iterative improvement capability of metaheuristic algorithms. Three powerful nature-inspired optimization algorithms viz. a genetic algorithm (GA), a particle swarm optimization (PSO) variant and a cuckoo search (CS) variant are used. Advanced memetic features are incorporated in the PSO and CS to form their respective variants-RPSOLC (repulsive particle swarm optimization with local search and chaotic perturbation) and CHP (co-evolutionary host-parasite). A comprehensive set of benchmark solutions on several new problems are reported. Statistical tests and comprehensive assessment of the predicted results show CHP comprehensively outperforms RPSOLC and GA, while RPSOLC has a little superiority over GA. Extensive simulations show that the on repeated trials of the same experiment, CHP has very low variability. About 50% fewer variations are seen in RPSOLC as compared to GA on repeated trials.

• Steel and Composite Structures
• /
• v.32 no.4
• /
• pp.455-466
• /
• 2019

Despite the rapid advancement in computing resources, many real-life design and optimization problems in structural engineering involve huge computation costs. To counter such challenges, approximate models are often used as surrogates for the highly accurate but time intensive finite element models. In this paper, surrogates for first-order shear deformation based finite element models are built using a polynomial regression approach. Using statistical techniques like Box-Cox transformation and ANOVA, the effectiveness of the surrogates is enhanced. The accuracy of the surrogate models is evaluated using statistical metrics like $R^2$, $R^2{_{adj}}$, $R^2{_{pred}}$ and $Q^2{_{F3}}$. By combining these surrogates with nature-inspired multi-criteria decision-making algorithms, namely multi-objective genetic algorithm (MOGA) and multi-objective particle swarm optimization (MOPSO), the optimal combination of various design variables to simultaneously maximize fundamental frequency and frequency separation is predicted. It is seen that the proposed approach is simple, effective and good at inexpensively producing a host of optimal solutions.

• The Journal of the Convergence on Culture Technology
• /
• v.10 no.4
• /
• pp.743-750
• /
• 2024

This study analyzes the linguistic meanings of the messages displayed on the Gwanghwamun Billboard from summer 1997 to spring 2020. The Gwanghwamun Billboard, an important medium reflecting cultural and social changes in contemporary Korean society, has conveyed hope and solace to the public through various literary quotes and emotional messages. This research identifies frequently appearing themes and messages by analyzing the frequency of keywords in the postings for each season. The results reveal that spring and summer primarily feature messages emphasizing new beginnings, challenges, love, and human relationships, as well as the beauty of nature, while autumn and winter convey themes of reflection, growth, endurance, and resilience. This study demonstrates that the Gwanghwamun Billboard encourages readers to adopt a positive outlook on life through seasonally tailored messages.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.11 no.1
• /
• pp.352-360
• /
• 2010

The purpose of this study was to examine potential effects of nature- friendly hill climb sportsmen's participatory motivation and commitment experience on their sense of self-achievement and living satisfaction. To meet the goal, this study surveyed total 206 participants (male and female) in hill climb tournaments held at Daegwallyeong and Misiryeong, Gangwon province. For data processing, this study used SPSS 14.0 and amos 7.0 to conduct frequency analysis, reliability analysis, correlation analysis, descriptive statistic analysis and structural equation model analysis respectively. As a result, this study could come to the following conclusions: First, according to descriptive statistic analysis, it was found that our respondents who participated in nature-friendly hill climb sports scored relatively high points in their participatory motivation, commitment experience, sense of self-achievement and living satisfaction. Secondly, this study adopted Pearson's moment correlation analysis in order to determine potential associations among our respondents' participatory motivation, commitment experience, sense of self-achievement and living satisfaction. As a result, it was found that their participatory motivation was positively correlated with their living satisfaction, while their commitment experience was positively correlated with their sense of self-achievement. Thirdly, it was found that there were certain causalities among our respondents' participatory motivation, living satisfaction, commitment experience and sense of self-achievement.

• Ecology and Resilient Infrastructure
• /
• v.9 no.3
• /
• pp.131-140
• /
• 2022

The magnitude and frequency of extreme floods are increasing owing to the effects of climate change. Therefore, multipurpose flood management techniques incorporating nature-based solutions have been introduced to mitigate the limitations of flood management and river design methods relying on existing observation data. Nature-based solutions to prepare for such extreme flooding events include ways to retreat the embankment, expand the floodplain, and reduce flood damage. To apply these technologies, adopting appropriate location selection methods based on various evaluation factors, such as flood damage reduction effects, sustainable ecological environments, river connectivity, and physical channel structure enhancements, should be prioritized. Therefore, in this study, the optimal location for implementing the multipurpose floodplain construction project was determined by selecting the location of the floodplain expansion with objectivity in the river waterfront area upstream of Daecheong Dam to downstream of Yongdam Dam. Through the final location determination, the Dongdaeje and Jeogokje sections were included in the optimal location considering both flood damage reduction and water environment improvement.

• Journal of Korean Elementary Science Education
• /
• v.26 no.1
• /
• pp.1-11
• /
• 2007

The purpose of this study was to investigate interaction patterns and characteristics of small group discussions during elementary school science classes. Four heterogeneous groups were formed according to preferences and non-preferences, consisting of male and female students. Verbal interactions during small group discussions were audio and videotaped, transcribed and analyzed. The interaction frequency of each group was compared in terms of their cognitive and affective aspects. The results in terms of the cognitive aspect showed that there were no significant differences in the frequency of interaction between preference and non-preference groups' verbal behaviors. However, the quality of interaction was superior and the number of high level types of interaction were more frequent in the preference group. From the affective perspective, both groups of students exhibited a positive attitude in the preference group and a negative attitude in the non-preference group. The differences of interaction between the male and female student's groups were that in the case of the female group, the frequency and the quality of interaction was higher. Moreover, in contrast to male students, female students revealed satisfaction and favorable attitudes in their non-preference group because they felt more a acceptable atmosphere and attitude in that group. These results suggest that the interactions of the preference group are more interactive and elaborate in nature than those of the non-preference group.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.35 no.5
• /
• pp.397-403
• /
• 2007

Insect and birds in nature flap their wings to generate fluid dynamic forces that are required for locomotion. To develop a feasible flapping MAV, it is of crucially important to study the fundamental relations between flapping motion and thrust generation. In this paper, the onset conditions of the thrust generation of a heaving flat plate is investigated using a Lattice-Boltzmann method. For a fixed heaving amplitude of h/C=0.5, the effect of reduced frequency on the thrust generation is investigated. For several values of heaving amplitude(h/C=0.25, 0.325, 0.50), the effect of reduced frequency on the thrust generation is also investigated. It can be said that Strouhal number is more important rather than reduced frequency in case of thrust generation. It is found that the critical Strouhal number over which the flat plate starts to produce thrust is around 0.1. Thrust is an exponential function of the Strouhal number.

• Journal of the Korean Society of Marine Environment & Safety
• /
• v.18 no.5
• /
• pp.431-438
• /
• 2012

The representative risk evaluation techniques of the marine traffic environment are the FSA, PAWSA, & IWRAP. For the development of these techniques, the risk factors suitable to the marine traffic environment should be selected & the assessment criterion of the risk factors should be provided. The risk factors were selected as the factors that relate both to the frequency of casualty & to the consequence of casualty because the risk was defined as the frequency of casualty times the consequence of that casualty on the existing techniques. But, the risk factors relate to the consequence of casualty are excluded because the risk is defined as the sum of the risk factors including the frequency and the consequence by factors on this study. The 20 kinds of risk factors to compose the risk are selected and classified into 5 categories according to similar nature through the analysis of preceding study on the classification of the risk factors. Finally, as the foundation of risk assessment model's development for domestic marine traffic environment, the practical assessment criterion of the risk factors are suggested.