• Journal of the Korean Society for Nondestructive Testing
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• v.31 no.6
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• pp.609-615
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• 2011

Excitation and propagation of electromagnetic field of a cylindrical coil above an arbitrary number of conductive plates for pulsed eddy current testing(PECT) are very complex problems due to their complicated physical properties. In this paper, analytical modeling of PECT is established by Fourier series based on truncated region eigenfunction expansion(TREE) method for a single air-cored coil above stratified conductive structures(SCS) to investigate their integrity. From the presented expression of PECT, the coil impedance due to SCS is calculated based on analytical approach using the generalized reflection coefficient in series form. Then the multilayered structures manufactured by non-ferromagnetic (STS301L) and ferromagnetic materials (SS400) are investigated by the developed PECT model. Good prediction of analytical model of PECT not only contributes to the development of an efficient solver but also can be applied to optimize the conditions of experimental setup in PECT.

• Bulletin of the Society of Naval Architects of Korea
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• v.20 no.3
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• pp.17-20
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• 1983

There have been many investigations of predicting the added resistance of a ship in seaway since Havelock discussed this topic in 1937. Among these researches, Maruo's theoretical approach is known as the most consistent mathematical representation for added resistance of a ship in regular head sea. In his theory, the hull form of a ship is represented under the slender body approximation. But the motion responses which were used for the calculation of the added resistance have been obtained by using the strip method which is based on an approximation that the hull form may be expressed as set of two dimensional cylinder sections in longitudinal direction. Therefore two different methods for hull form representation were implicity used in Maruo's original work for the added resistance calculation. Utilizing the characteristics that hull forms are usually slender, Kan expressed the hull form as two dimensional cylinder at each station by using the Taylor series expansion for the length wise direction. Putting this idea into Maruo's original work, the added resistance can be obtained with the explicitly unique representation of the hull form. For the purpose of comparison the added resistance of a hull form(series 60, Cb=0.6) was calculated by using the motion response obtained by Shintani. The numerical result showes a good qualitative agreement with the experimental result by Sibul.

• Journal of the Society of Naval Architects of Korea
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• v.29 no.2
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• pp.66-72
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• 1992

A computational method of the Michell integral for water of finite depth is developed and the method makes use of the expansion of the hull form by the Legendre polynomial in both the longitudinal and the vertical directions. The wave resistance coefficient is given as a quadruple summation of the product of the shape factor and the hydrodynamic factor. The shape factor depends only upon the geometry of the hull form, and the hydrodynamic factor upon the depth-based Froude number and the ratios of the water depth and the draft to the ship length. Example calculations are done for the Wigley parabolic hull and the Series 60 $C_B$ 0.6, and the comparison of our results with the existing experimental data is shown.

• Journal of Korea Port Economic Association
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• v.34 no.3
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• pp.183-200
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• 2018

This study empirically tests the presence of rational bubbles in the ship prices using time series data from October 1996 to April 2017. To detect the existence of ship prices' rational bubbles, we use integration and cointegration tests, which were proposed by Campbell and Shiller(1987) and Diba and Grossman(1988), for circumventing misspecification of ship price model and applying the bubble test to nonstationary time series. The result of integration test supports existence of tanker price's rational bubble. The co-integration test also shows that drybulk ship and containership prices have been overvalued relative to the market fundamental, drybulk and container freight rates, due to non-stationary rational bubbles. These results provide Korean shipping industry and authorities implications that anticyclical ship investment and long-term and steady fleet capacity expansion policy are needed.

• Journal of Environmental Science International
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• v.30 no.10
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• pp.779-787
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• 2021

This study analyzes structural landscape changes over a time-series for a small and medium-sized city, Gangneung-Si, based on area and distribution patterns, and according to the type of land cover. Among the types of land cover, the area ratio of urbanized areas increased by 2.02% in the late 2010s as compared to the late 1980s, while there was a decrease of 2.69% in farmland and 0.69% in grassland areas. On analyzing the changes in land cover use by applying the Fragstats program, it was confirmed that landscape changes in urban and management areas were relatively severe according to the Landscape Shape Index, Largest Patch Index, and Aggregation Index. A pattern of concentrated expansion was also found around certain areas. In particular, from the analysis, it was established that the proportion of urbanized area had considerably increased and that the extent of farmland damage to management areas, including planned management areas, was large. Additionally, the Total Core Area generally indicated a reduction in the core areas of farmland and forest within urban and management areas. A medium-sized city showed significant changes besides large cities in terms of landscape structure. The developmental pressure on management areas, in particular, was quite high.

• Advances in Computational Design
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• v.4 no.3
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• pp.307-326
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• 2019

A low computational cost semi-analytical method is developed, based on eigenfunction expansion, to study the vibration of rectangular plates subjected to a series of moving sprung masses, representing a bridge deck under multiple vehicle or train moving loads. The dynamic effects of the suspension system are taken into account by using flexible connections between the moving masses and the base structure. The accuracy of the proposed method in predicting the dynamic response of a rectangular plate subjected to a series of moving sprung masses is demonstrated compared to the conventional rigid moving mass models. It is shown that the proposed method can considerably improve the computational efficiency of the conventional methods by eliminating a large number of time-varying components in the coupled Ordinary Differential Equations (ODEs) matrices. The dynamic behaviour of the system is then investigated by performing a comprehensive parametric study on the Dynamic Amplification Factor (DAF) of the moving loads using different design parameters. The results indicate that ignoring the flexibility of the suspension system in both moving force and moving mass models may lead to substantially underestimated DAF predictions and therefore unsafe design solutions. This highlights the significance of taking into account the stiffness of the suspension system for accurate estimation of the plate maximum dynamic response in practical applications.

• Journal of Korean Association for Spatial Structures
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• v.21 no.3
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• pp.35-42
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• 2021

An experimental study was carried out to evaluate the shear performance at the interface composed of structural laminates and concrete. The main variables are the number of CLT layers and the shape of the shear connector. The number of CLT layers consisted of 3 and 5 layers. A total of 6 test specimens for shear performance evaluation were prepared in the form of a shear connector, a direct screw type and a vertically embedded type. As a result of the experiment, similar behavior was shown in all specimens, regardless of the number of layers, including direct screw type (SC series) and vertically embedded type (VE series). The behavior at the joint surface was damaged due to the occurrence of initial shear cracks, expansion of shear groove cracks, and splaying at the interface after the maximum load.After the maximum load, the shear strength decreased gradually due to the effect of the shear connector. It can be seen that the shear strength of all specimens is determined by shear and compression stress failure of concrete at the interface of the notch joint.

• Journal of the Korea institute for structural maintenance and inspection
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• v.22 no.2
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• pp.124-132
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• 2018

This research presents the results of an investigation on the characteristic of multi-component blended high fluidity mortars. The binder was blended ordinary Portland cement(OPC), ground granulated blast furnace slag(GGBFS), calcium sulfoaluminate(CSA) and ultra rapid setting cement(URSC). The GGBFS was replaced by OPC from 30%(P7 series), 50%(P5 series) and 70%(P3 series), CSA and URSC was 10% or 20% mass. The superplasticizer of polycarboxylate type were used. A constant water-to-binder ratio(w/b)=0.35 was used for all mixtures. Test were conducted for mini slump, setting time, V-funnel, compressive strength and drying shrinkage. According to the experimental results, the contents of superplasticizer, V-funnel and compressive strength increases with an increase in CSA or URSC contents for all mixtures. Moreover, the setting time and drying shrinkage ratio decrease with and increase in CSA or URSC. CSA decreased dry shrinkage but URSC had less effect. However, the mixed binders of CSA and URSC had a large effect of reducing drying shrinkage by complementary effect. This is effective for improving the initial strength of URSC, and CSA is effective for the expansion and improvement of long-term strength.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.55 no.3
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• pp.141-145
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• 2006

The line current problem(2-dimensional space : point source) is not easy to analyze the magnetic field using the standard finite element method(FEM), such as overhead trolley line or transmission line. To supplement such a defect this paper is proposed the coupling scheme of analytical solution and FEM. In analysis of the magnetic field using the standard FEM. If the current region is a relatively small compared to the whole region. Therefore the current region must be finely divided using a large number of elements. And the large number of elements increase the number of unknown variables and the use of computer memories. In this paper, an analytical solution is suggested to supplement this weak points. When source is line current and the part of interest is far from line current, the analytical solution can be coupling with FEM at the boundary. Analytical solution can be described by the multiplication of two functions. One is power function of radius, the other is a trigonometric function of angle in the cylindrical coordinate system. There are integral constants of two types which can be established by fourier series expansion. Also fourier series is represented as the factor to apply the continuity of the magnetic vector potential and magnetic field intensity with tangential component at the boundary. To verify the proposed algorithm, we chose simplified model existing magnetic material in FE region. The results are compared with standard FE solution. And it is good agreed by increasing harmonic order.

• Journal of Periodontal and Implant Science
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• v.48 no.1
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• pp.3-11
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• 2018

Purpose: This study utilized a strong quasi-experimental design to test the hypothesis that the implementation of a policy to expand dental care services resulted in an increase in the usage of dental outpatient services. Methods: A total of 45,650,000 subjects with diagnoses of gingivitis or advanced periodontitis who received dental scaling were selected and examined, utilizing National Health Insurance claims data from July 2010 through November 2015. We performed a segmented regression analysis of the interrupted time-series to analyze the time-series trend in dental costs before and after the policy implementation, and assessed immediate changes in dental costs. Results: After the policy change was implemented, a statistically significant 18% increase occurred in the observed total dental cost per patient, after adjustment for age, sex, and residence area. In addition, the dental costs of outpatient gingivitis treatment increased immediately by almost 47%, compared with a 15% increase in treatment costs for advanced periodontitis outpatients. This policy effect appears to be sustainable. Conclusions: The introduction of the new policy positively impacted the immediate and long-term outpatient utilization of dental scaling treatment in South Korea. While the policy was intended to entice patients to prevent periodontal disease, thus benefiting the insurance system, our results showed that the policy also increased treatment accessibility for potential periodontal disease patients and may improve long-term periodontal health in the South Korean population.