• Proceedings of the KIEE Conference
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• 2003.07c
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• pp.1448-1450
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• 2003

The suspension insulators are subjected to harsh environment in service for a long time. Long term reliability of the insulators is required for both mechanical and electrical performances. We studied an analysing method to find out a deformation of brittle porcelain with a thermal expansion of simulation analysis and experimental results show that cement volume growths affect severely to be mechanical failure ageing.

• Advances in nano research
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• v.7 no.4
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• pp.249-263
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• 2019

In the current paper, an exact solution method is carried out for analyzing the thermo-mechanical vibration of curved FG nano-beams subjected to uniform thermal environmental conditions, by considering porosity distribution via nonlocal strain gradient beam theory for the first time. Nonlocal strain gradient elasticity theory is adopted to consider the size effects in which the stress for not only the nonlocal stress field but also the strain gradients stress field is considered. It is perceived that during manufacturing of functionally graded materials (FGMs) porosities and micro-voids can be occurred inside the material. Material properties of curved porous FG nanobeam are assumed to be temperature-dependent and are supposed to vary through the thickness direction of beam which modeled via modified power-law rule. Since variation of pores along the thickness direction influences the mechanical and physical properties, porosity play a key role in the mechanical response of curved FG nano-structures. The governing equations and related boundary condition of curved porous FG nanobeam under temperature field are derived via the energy method based on Timoshenko beam theory. An analytical Navier solution procedure is utilized to achieve the natural frequencies of porous FG curved nanobeam supposed to thermal loading. The results for simpler states are confirmed with known data in the literature. The effects of various parameters such as nonlocality parameter, porosity volume fractions, thermal effect, gradient index, opening angle and aspect ratio on the natural frequency of curved FG porous nanobeam are successfully discussed. It is concluded that these parameters play key roles on the dynamic behavior of porous FG curved nanobeam. Presented numerical results can serve as benchmarks for future analyses of curve FG nanobeam with porosity phases.

• Nuclear Engineering and Technology
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• v.47 no.6
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• pp.766-775
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• 2015

The integrity assessment of reactor vessel internals should be conducted in the design process to secure the safety of nuclear power plants. Various loads such as self-weight, seismic load, flow-induced load, and preload are applied to the internals. Therefore, the American Society of Mechanical Engineers (ASME) Code, Section III, defines the stress limit for reactor vessel internals. The present study focused on structural response analyses of the upper guide structure upper flange. The distributions of the stress intensity in the flange body were analyzed under various design load cases during normal operation. The allowable stress intensities along the expected sections of stress concentration were derived from the results of the finite element analysis for evaluating the structural integrity of the flange design. Furthermore, seismic analyses of the upper flange were performed to identify dynamic behavior with respect to the seismic and impact input. The mode superposition and full transient methods were used to perform time-history analyses, and the displacement at the lower end of the flange was obtained. The effect of the damping ratio on the response of the flange was also evaluated, and the acceleration was obtained. The results of elastic and seismic analyses in this study will be used as basic information to judge whether a flange design meets the acceptance criteria.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.11
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• pp.1361-1370
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• 2012

A shape optimization is proposed to obtain the desired final shape of forming and forging products in the manufacturing process. The final shape of a forming product depends on the shape parameters of the initial blank shape. The final shape of a forging product depends on the shape parameters of the billet shape. Shape optimization can be used to determine the shape of the blank and billet to obtain the appropriate final forming and forging products. The equivalent static loads method for non linear static response structural optimization (ESLSO) is used to perform metal forming and forging optimization since nonlinear dynamic analysis is required. Stress equivalent static loads (stress ESLs) are newly defined using a virtual model by redefining the value of the material properties. The examples in this paper show that optimization using the stress ESLs is quite useful and the final shapes of a forming and forging products are identical to the desired shapes.

• Structural Engineering and Mechanics
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• v.33 no.1
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• pp.79-93
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• 2009

This paper investigates the possibility of controlling the response of typical portal frame structures to blast loading using a combination of semi-active and passive control devices. A one storey reinforced concrete portal frame is modelled using non-linear finite elements with each column discretised into multiple elements to capture the higher frequency modes of column vibration response that are typical features of blast responses. The model structure is subjected to blast loads of varying duration, magnitude and shape, and the critical aspects of the response are investigated over a range of structural periods in the form of blast load response spectra. It is found that the shape or length of the blast load is not a factor in the response, as long as the period is less than 25% of the fundamental structural period. Thus, blast load response can be expressed strictly as a function of the momentum applied to the structure by a blast load. The optimal device arrangements are found to be those that reduce the first peak of the structural displacement and also reduce the subsequent free vibration of the structure. Semi-active devices that do not increase base shear demands on the foundations in combination with a passive yielding tendon are found to provide the most effective control, particularly if base shear demand is an important consideration, as with older structures. The overall results are summarised as response spectra for eventual potential use within standard structural design paradigms.

• Journal of the Korean Society for Precision Engineering
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• v.28 no.6
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• pp.732-737
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• 2011

The planetary gear reducer becomes more and more widely used in machine industries. The planetary gear reducer has a significant role to transmit power to wheel & tire module in the In-wheel system. Thus, the planetary gear reducer should have strong stiffness and durability. In this paper, the contact and bending stresses at the tooth of the planetary gear reducer are analyzed using MASTA, a commercial gear design and analysis software. Stress distribution at the tooth face of the sun, planetary and annulus gears are obtained using the finite element method. The design modification is performed using the response surface method. The usefulness of the design modification and optimization method presented in this paper is verified by comparing the maximum stresses of the original and optimized planetary gear tooth.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.24 no.6
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• pp.632-638
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• 2015

Many failures have been reported in gas turbine facilities owing to repeated startups and prolonged use of the turbines. In this study, the causes and mechanism of fatigue failure in the first blade of a gas turbine were analyzed using a finite element method to calculate the centrifugal force, bending force, and a modal analysis based on the stress-stiffening effect and harmonic response under the operating conditions. The results show that, fatigue damage was caused by the resonance conditions encountered, in which the first natural frequency declined along with an increase in the metal temperature of the blade. The position of the expected fatigue damage was shown to match the actual position of the cracking at the root area of the blade, which was on the concave side. In addition, the equivalence fatigue stress was observed to approach the fatigue limit.

• JSTS:Journal of Semiconductor Technology and Science
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• v.7 no.3
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• pp.151-160
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• 2007

We report the label-free biomolecules detection based on nanomechanical micro cantilevers operated in dynamic mode for detection of two marker proteins (myoglobin and creatin kinase-MB (CK-MB)) of acute myocardical infarctions. When the specific binding between the antigen and its antibody occurred on the fuctionalized microcantilever surface, mechanical response (i.e. resonant frequency) of microcantilevers was changed in lower frequency range. We performed the label-free biomolecules detection of myoglobin and CK-MB antigen in the low concentration (clinical threshold concentration range) as much as 1 ng/ml from measuring the dynamic response change of micro cantilevers caused by the intermolecular force. Moreover, we estimate the surface stress on the dynamic microcantilevers generated by specific antibody-antigen binding. It is suggested that our dynamic microcantilevers may enable one to use the sensitive label-free biomolecules detection for application to the disease diagnosis system based on mechanical immuno-sensor.

• Journal of Ocean Engineering and Technology
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• v.27 no.2
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• pp.27-32
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• 2013

A valve is a marine structure that is subjected to multiple seawater loads. Therefore, it is necessary to define the kind of loads applied to it to confirm whether the structure has sufficient strength. In this research, we aimed to find the optimal solution for the stress and deformation of valves under various loads. We first selected design variables and implement a finite element analysis according to changes in the thickness of each component of a valve based on a central composite design. Next we developed a regression model of the response surface. Using this model, we calculated the optimal objective value based on NSGA-II. Finally, to confirm the correspondence between the optimal objective value and the real FEM value, we compared the optimal result and structural analysis result to verify the performance of NSGA-II.

• International Journal of Railway
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• v.3 no.4
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• pp.117-122
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• 2010

In transportation geotechnical engineering, stress-strain behavior of earth structures has been analyzed by numerical simulations with the implemented plasticity constitutive model. It is a fact that many advanced plasticity constitutive models on predicting the mechanical behavior of soils have been developed as well as experimental research works for geotechnical applications in the past decades. In this study, recently developed, a unified constitutive model for both clay and sand, which is referred to as CASM (clay and sand model), was compared with a classical constitutive model, Cam-Clay model. Moreover, integration methods of stress-strain rate equations using CASM were presented for simulation of undrained and drained triaxial compression tests. As a conclusion, it was observed that semi-implicit integration method has more improved accuracy of capturing strain rate response to applied stress than explicit integration by the multiple correction and iteration.