• Smart Structures and Systems
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• v.20 no.3
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• pp.351-368
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• 2017

To peruse the free vibration of curved functionally graded piezoelectric (FGP) nanosize beam in thermal environment, nonlocal elasticity theory is applied for modeling the nano scale effect. The governing equations are obtained via the energy method. Analytically Navier solution is employed to solve the governing equations for simply supported boundary conditions. Solving these equations enables us to estimate the natural frequency for curved FGP nanobeam under the effect of a uniform temperature change and external electric voltage. The results determined are verified by comparing the results by available ones in literature. The effects of various parameters such as nonlocality, uniform temperature changes, external electric voltage, gradient index, opening angle and aspect ratio of curved FGP nanobeam on the natural frequency are successfully discussed. The results revealed that the natural frequency of curved FGP nanobeam is significantly influenced by these effects.

• Structural Engineering and Mechanics
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• v.60 no.4
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• pp.707-727
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• 2016

In this paper, thermal vibration of a nonlocal functionally graded (FG) plates with arbitrary boundary conditions under linear and non-linear temperature fields is explored by developing a refined shear deformation plate theory with an inverse cotangential function in which shear deformation effect was involved without the need for shear correction factors. The material properties of FG nanoplate are considered to be temperature-dependent and graded in the thickness direction according to the Mori-Tanaka model. On the basis of non-classical higher order plate model and Eringen's nonlocal elasticity theory, the small size influence was captured. Numerical examples show the importance of non-uniform thermal loadings, boundary conditions, gradient index, nonlocal parameter and aspect and side-to-thickness ratio on vibrational responses of size-dependent FG nanoplates.

• Structural Engineering and Mechanics
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• v.66 no.3
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• pp.369-377
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• 2018

In this article, buckling and free vibration of functionally graded (FG) nanobeams resting on elastic foundation are investigated by developing various higher order beam theories which capture shear deformation influences through the thickness of the beam without the need for shear correction factors. The elastic foundation is modeled as linear Winkler springs as well as Pasternak shear layer. The material properties of FG nanobeam are supposed to change gradually along the thickness through the Mori-Tanaka model. The small scale effect is taken into consideration based on nonlocal elasticity theory of Eringen. From Hamilton's principle, the nonlocal governing equations of motion are derived and then solved applying analytical solution. To verify the validity of the developed theories, the results of the present work are compared with those available in literature. The effects of shear deformation, elastic foundation, gradient index, nonlocal parameter and slenderness ratio on the buckling and free vibration behavior of FG nanobeams are studied.

• Steel and Composite Structures
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• v.11 no.4
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• pp.341-358
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• 2011

This paper presents the effects of thermal environment and temperature-dependence of the material properties on axisymmetric bending of functionally graded (FG) circular and annular plates. The material properties are assumed to be temperature-dependent and graded in the thickness direction. In order to accurately evaluate the effect of thermal environment, the initial thermal stresses are obtained by solving the thermoelastic equilibrium equations. Governing equations and the related boundary conditions, which include the effects of initial thermal stresses, are derived using the virtual work principle based on the elasticity theory. The differential quadrature method (DQM) as an efficient and robust numerical tool is used to obtain the initial thermal stresses and response of the plate. Comparison studies with some available results for FG plates are performed. The influences of temperature rise, temperature-dependence of material properties, material graded index and different geometrical parameters are carried out.

• Advances in nano research
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• v.5 no.4
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• pp.313-336
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• 2017

This article investigates vibration behavior of magneto-electro-elastic functionally graded (MEE-FG) nanobeams embedded in two-parameter elastic foundation using a third-order parabolic shear deformation beam theory. Material properties of MEE-FG nanobeam are supposed to be variable throughout the thickness based on power-law model. Based on Eringen's nonlocal elasticity theory which captures the small size effects and using the Hamilton's principle, the nonlocal governing equations of motions are derived and then solved analytically. Then the influences of elastic foundation, magnetic potential, external electric voltage, nonlocal parameter, power-law index and slenderness ratio on the frequencies of the embedded MEE-FG nanobeams are studied.

• Steel and Composite Structures
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• v.43 no.2
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• pp.185-200
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• 2022

A Closed-form solution for dynamic response of a functionally graded (FG) nonlocal nanobeam due to action of moving harmonic load is presented in this paper. Due to analyzing in small scale, a nonlocal elasticity theory is utilized. The governing equation and boundary conditions are derived based on the Euler-Bernoulli beam theory and Hamilton's principle. The material properties vary through the thickness direction. The harmonic moving load is modeled by Delta function and the FG nanobeam is simply supported. Using the Laplace transform the dynamic response is obtained. The effect of important parameters such as excitation frequency, the velocity of the moving load, the power index law of FG material and the nonlocal parameter is analyzed. To validate, the results were compared with previous literature, which showed an excellent agreement.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.11
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• pp.5930-5938
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• 2013

The sigmoid functionally graded mateiral(S-FGM) theory is reformulated using the nonlocal elatictiry of Erigen. The equation of equilibrium of the nonlocal elasticity are derived. This theory has ability to capture the both small scale effects and sigmoid function in terms of the volume fraction of the constituents for material properties through the plate thickness. Navier's method has been used to solve the governing equations for all edges simply supported boundary conditions. Numerical solutions of biaxial buckling of nano-scale plates are presented using this theory to illustrate the effects of nonlocal theory and power law index of sigmoid function on buckling load. The relations between nonlocal and local theories are discussed by numerical results. Further, effects of (i) power law index, (ii) length, (iii) nonlocal parameter, (iv) aspect ratio and (v) mode number on nondimensional biaxial buckling load are studied. To validate the present solutions, the reference solutions are discussed.

• Journal of Korea Trade
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• v.27 no.1
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• pp.79-100
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• 2023

Purpose - The purpose of this study is to analyze the market power of the Korea Container Shipping Market (Intra Asia, Korea-Europe, and Korea-U.S.) to verify the existence of collusion empirically, and to answer whether the joint actions of liner market participants in Korea have formed market dominance for each route. Precisely, it will be verified through the Lerner index as to whether the regional market of Asia is a monopoly, oligopoly, or perfect competition. Design/methodology - This study used a Lerner index adjusted with elasticity presented in the New Imperial Organization (NEIO) studies. NEIO refers to a series of empirical studies that estimate parameters to judge market power from industrial data. This study uses B-L empirical models by Bresnahan (1982) and Lau (1982). In addition, NEIO research data statistically contain self-regression and stability problems as price and time series data. A dynamic model following Steen and Salvanes' Error Correction Model was used to solve this problem. Findings - The empirical results are as follows. First, λ, representing market power, is nearly zero in all three markets. Second, the Korean shipping market shows low demand elasticity on average. Nevertheless, the markup is low, a characteristic that is difficult to see in other industries. Third, the Korean shipping market generally remains close to perfect competition from 2014 to 2022, but extreme market power appears in a specific period, such as COVID-19. Fourth, there was no market power in the Intra Asia market from 2008 to 2014. Originality/value - Doubts about perfect competition in the liner market continued, but there were few empirical cases. This paper confirmed that the Korea liner market is a perfect competition market. This paper is the first to implement dynamics using ECM and recursive regression to demonstrate market power in the Korean liner market by dividing the shipping market into Deep Sea and Intra Asia separately. It is also the first to prove the most controversial problems in the current shipping industry numerically and academically.

• Journal of Energy Engineering
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• v.21 no.3
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• pp.301-308
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• 2012

This paper attempts to estimate the demand function for the transport LPG and to analyze long-run and short-run price and income elasticities. In addition, the paper measures consumer surplus and economic value ensuing from the transport LPG consumption by utilizing the estimated long-run price elasticity. The price and the income data are the monthly real transport LPG price and the monthly composite index adjusted by real transport LPG price from 2003 to 2012. Unit root test, co-integration test and error correction model are to take the procedure of estimation of demand curve. The demand for transport LPG is considered to be inelastic and the long-run demand is more elasticity than that of short-run. Price elasticity of demand estimate here is -0.422, and the estimated consumer surplus and economic value in 2010/03 are 966 and 1,781 billion won, respectively.

• Journal of Preventive Medicine and Public Health
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• v.38 no.1
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• pp.107-116
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• 2005

Objectives : We analyzed the changes from 1996 to 2002 in distributive equity of the contribution burden in the Korean National Health Insurance. Methods : The study subjects were a total of 8,923 employee households and a total of 7,296 self-employed households over the period from 1996 to 2002. Those were the households meeting the two criteria as completing each annual survey and having no change in the job of head of the household during that period from the raw data of the Household Income and Expenditure Survey annually conducted by the Korean National Statistical Office. The unit of analysis was a household, and this was the standard for assessing the contribution that is now applied on a monthly basis. Deciles Distribution Ratio, Contribution Concentration Curve and Contribution Concentration Index were estimated as the index of inequality. Multiple regression analysis was conducted to compare the annual ability-to-pay elasticity of the contribution to the reference year of 1996 for three groups (all households, the employee households, and the self-employed households). Results : For the index of inequality, the distributive equity of contribution was improved in all three groups. In particular, the employee group experienced a substantial improvement. Using multiple regression analysis, the ability-to-pay elasticity of the contribution in the employee group significantly increased ($\beta$=0.232, p<0.0001) in the year 2002 as compared to the reference year of 1996. The elasticity in the self-employed group also significantly increased ($\beta$=0.186, p<0.05), although its change was smaller than that in the employee group. Conclusions : The employee group had a greater improvement for the distributive equity of the contribution burden than the self-employed group. Within the observation period, there were two important integration reforms: one was the integration of 227 self-employed societies in 1998 and the other was the integration of 139 employee societies in 2000. We expected that the equity of the contribution burden would be improved for the self-employed group since the integration reform of 1998. However, it was not improved for the self-employed group until the year 2000. This result suggests that capturing exactly the beneficiaries' ability-to-pay such as income is the precedent for distributive equity of the contribution burden, although a more sophisticated imposition standard of contribution is needed.