• Steel and Composite Structures
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• v.21 no.6
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• pp.1183-1210
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• 2016

Viscoelastic sandwich structures (VSSs) are widely used in mechanical equipment, but in the service process, they always suffer from aging which affect the whole performance of equipment. Therefore, aging state recognition of VSSs is significant to monitor structural state and ensure the reliability of equipment. However, non-stationary vibration response signals and weak state change characteristics make this task challenging. This paper proposes a novel method for this task based on adaptive second generation wavelet packet transform (ASGWPT) and multiwavelet support vector machine (MWSVM). For obtaining sensitive feature parameters to different structural aging states, the ASGWPT, its wavelet function can adaptively match the frequency spectrum characteristics of inspected vibration response signal, is developed to process the vibration response signals for energy feature extraction. With the aim to improve the classification performance of SVM, based on the kernel method of SVM and multiwavelet theory, multiwavelet kernel functions are constructed, and then MWSVM is developed to classify the different aging states. In order to demonstrate the effectiveness of the proposed method, different aging states of a VSS are created through the hot oxygen accelerated aging of viscoelastic material. The application results show that the proposed method can accurately and automatically recognize the different structural aging states and act as a promising approach to aging state recognition of VSSs. Furthermore, the capability of ASGWPT in processing the vibration response signals for feature extraction is validated by the comparisons with conventional second generation wavelet packet transform, and the performance of MWSVM in classifying the structural aging states is validated by the comparisons with traditional wavelet support vector machine.

• Nuclear Engineering and Technology
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• v.42 no.4
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• pp.450-459
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• 2010

The present paper investigates the collapse pressure of cylinders with intermediate thickness subjected to external pressure based on detailed elastic-plastic finite element (FE) analyses. The effect of the initial ovality of the tube on the collapse pressure was explicitly considered in the FE analyses. Based on the present FE results, the analytical yield locus, considering the interaction between the plastic collapse and local instability due to initial ovality, was also proposed. The collapse pressure values based on the proposed yield locus agree well with the present FE results; thus, the validity of the proposed yield locus for the thickness range of interest was verified. Moreover, the partial safety factor concept based on the structural reliability theory was also applied to the proposed collapse pressure estimation model, and, thus, the priority of importance of respective parameter constituting for the collapse of cylinders under external pressure was estimated in this study. From the application of the partial safety factor concept, the yield strength was concluded to be the most sensitive, and the initial ovality of tube was not so effective in the proposed collapse pressure estimation model. The present deterministic and probabilistic results are expected to be utilized in the design and maintenance of cylinders subjected to external pressure with initial ovality, such as the once-through type steam generator.

• Transactions of Materials Processing
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• v.30 no.5
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• pp.219-225
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• 2021

When extruding Al6061 alloys, deformation energy is deposited inside the extruded alloy depending on the deformation and the temperature of extrusion. This creates a Peripheral Coarse Grain (PCG) on the surface, where relatively more deformation energy. of the extruded alloy has been accumulated. Furthermore, since the deformation of materials continues while the materials recrystallize, it is important to examine the effect of deformation energy on dynamic recrystallization in the process of extruding Al alloys along with their microstructure. Prior studies explain the theory behind PCG growth though quantitative analysis on PCG growth of Al alloys during extrusion processes has not yet been addressed. This study aims to measure the generated PCG thickness which determines the correlation between extrusion outlet temperature and its effect on mechanical properties. Surface structure observations were performed using Optical Microscope (OM) and mechanical properties were evaluated through tensile strength and hardness measurement. Throughout this study, we endevoured to find the optimum condition of extrusion exit temperature of Al6061 and confirmed improved d reliability. This study describes the effect of the complex process variables such as exit temperature on the thickness of PCG layer for the Al6061 alloy using the 200 tons extrusion press. We therefore, discovered that the PCG layer thickness was 117 ㎛ at temperatures between 460 ℃ to 520 ℃.

• The Journal of the Korea Contents Association
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• v.21 no.9
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• pp.184-197
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• 2021

Prior to the establishment of 'Employment-Related Big Data Center (tentative name)' to support the development of customized employment services. This Paper examines the current status and limitation of employment-related data in korea. Then, the implications were derived through foreign employment-related big data construction cases. Through the above analysis, I proposed measures to build and utilize employment-related big data at the individual level, focusing on the Transitional Labour Markets theory that emphasizes the implementation of individual labor force states. Finally, we presented future challenges such as massive maintenance of employment-related DB, increased representation of big data to be built around employment insurance DB, and increased reliability of DB presented.

• Journal of the Society of Naval Architects of Korea
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• v.58 no.3
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• pp.137-143
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• 2021

In this study, the fracture strength of Flexible Secondary Barrier (FSB) composites was standardized by conducting a distribution analysis of the fracture probability, considering that the fracture strength of FSB composites such as glass fiber reinforced composites is relatively large. As the mechanical performance of FSB composites varies with the fiber direction, 20 replicate uniaxial tensile tests were performed for different temperatures ranging from the ambient to cryogenic conditions, considering the actual operating environment of liquefied natural gas. For the probability statistical analysis, the Weibull distribution analysis derived from the weakest link theory was used, considering the large variance in the fracture strength and brittle fracture behavior. The results of the Weibull distribution analysis were used to calculate the standard fracture strength of the FSB composites for different fiber directions. The findings can help ensure the reliability of the FSB mechanical properties in different fiber directions in the design of the secondary barrier and structural analyses.

• Korean Journal of Child Education & Care
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• v.19 no.2
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• pp.165-176
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• 2019

Objective: The purpose of this study is to develop a measure of the Early Childhood Teacher's Guidance Efficacy Scale based on guidance and teacher-efficacy theory. Methods: This subjects were 243 teachers in Seoul and Gyeonggi-do. Results: An exploratory factor analysis was conducted on the data collected of 4 factors, namely, guidance efficacy for problem behavior, children understanding, home-connected, basic life habits. In addition, there are significant positive correlations between the sub-area score and the overall in the early childhood teacher's guidance efficacy scale(r = .26 ~ .72, p < .001). Internal consistency and split-half reliability of each sub scale were reasonably accept. Conclusion/Implications: 'The guidance efficacy scale for early childhood teachers' developed in this study is an appropriate tool. Therefore, the developed scale can become a useful tool to measure the overall guidance efficacy level of early childhood teachers.

• The Journal of the Korea Contents Association
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• v.19 no.2
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• pp.296-304
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• 2019

The Amazon Go was the catalyst of O4O era. O4O is an advanced business model from O2O, which is the integration of offline service to online, especially through smart phone network. We also find the O2O strategy of digital contents companies such as Kakao and Line. This study examined the relation between online character experience and offline purchasing intention on related character products. The SEM was designed on the former study that based on the theory of user experience and brand attitude. The result of this study shows that the users' online experience have influence on the purchasing intention of offline related products and there exist the mediating routes of satisfaction of user experience, brand preference and brand reliability. There are no statistical support to the relation between satisfaction of user experience and purchasing intention. These points illustrate what marketers better to focus on transmedia strategies.

• Journal of the Korean Society of Marine Environment & Safety
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• v.23 no.7
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• pp.948-955
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• 2017

Currently, porous materials (e.g., mineral wool) are the core materials used in offshore plant panels, but in spite of their superb acoustic performance, these items must be replaced for environmental reasons. A honeycomb structure is widely used throughout the industry because of its high strength-to-weight ratio. However, research in terms of noise and vibration is minimal. An acoustic study should be conducted by taking advantage of honeycomb structures to replace porous materials. In this study, a simulation was performed assuming that a honeycomb panel is a superposition of symmetric mode and antisymmetric mode. Reliability was verified by comparing a simulation results based on a theory with a experimental results, and the possibility of the panel as a core material was evaluated by studying the sound insulation characteristics of a honeycomb. As the panel thickness increased, the coincidence frequency shifted to low frequency. As the angle between horizontal line and oblique wall and cell-size decreases, the sound insulation performance is improved. And as the cell-wall thickness increased, the sound insulation performance improved.

• Structural Engineering and Mechanics
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• v.71 no.6
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• pp.627-641
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• 2019

The paper focuses on bending analysis of the functionally graded (FG) plates with arbitrary shapes and boundary conditions. The material property of FG plates is modelled by using the power law distribution. Based on the first order shear deformation plate theory (FSDT), the governing equations as well as boundary conditions are formulated and obtained by using the principle of virtual work. The coupled Boundary Element-Radial Basis Function (BE-RBF) method is established to solve the complex FG plates. The proposed methodology is developed by applying the concept of the analog equation method (AEM). According to the AEM, the original governing differential equations are replaced by three Poisson equations with fictitious sources under the same boundary conditions. Then, the fictitious sources are established by the application of a technique based on the boundary element method and approximated by using the radial basis functions. The solution of the actual problem is attained from the known integral representations of the potential problem. Therefore, the kernels of the boundary integral equations are conveniently evaluated and readily determined, so that the complex FG plates can be easily computed. The reliability of the proposed method is evaluated by comparing the present results with those from analytical solutions. The effects of the power index, the length to thickness ratio and the modulus ratio on the bending responses are investigated. Finally, many interesting features and results obtained from the analysis of the FG plates with arbitrary shapes and boundary conditions are demonstrated.

• The Journal of the Korea Contents Association
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• v.19 no.5
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• pp.194-204
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• 2019

The mobile payment app market has been expanding recently. However, the usage rate of mobile payment apps is not meeting service providers' expectations due to concerns about security and privacy. This study investigated how personal predisposition and how the security signals of the payment app affect users' perceived privacy and security risks, and how these factors ultimately affect the trust of mobile payment apps. The results showed that privacy concerns increase the risk of perceived personal information leaks and reduce perceived mobile system security, while familiarity, perceived reputation, and assurance seal reduce the risk of perceived personal information leaks and increase perceived mobile system security. Finally, it revealed that the reduced risk of perceived personal information leaks and the increased security of mobile systems had a positive impact on the reliability of mobile payment apps.