• Structural Engineering and Mechanics
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• 제75권4호
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• pp.465-475
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• 2020

The analytical approach for stability and response of iced conductor under uniform wind or turbulent wind is presented in this study. A nonlinear dynamic model is established to describe the motion of iced conductor galloping. In the case of uniform wind, the stability condition is derived by analyzing the eigenvalue associated with linearized matrix; The first order and second order approximation of galloping amplitude are obtained using multi-scale method. However, real wind has random characteristics essentially. To accurately evaluate the performance of the galloping iced conductor, turbulence wind should be described by random processes. In the case of turbulence wind, the Lyapunov exponent is conducted to judge the stability condition; The probability density of displacement is obtained by using the path integral method to predict galloping amplitude. An example is proposed to verify the effectiveness of the previous methods. It is shown that the fluctuating component of wind has little influence on the stability of iced conductor, but it can increase galloping amplitude. The analytical results on stability and response are also verified by numerical time stepping method.

• 한국통신학회논문지
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• 제37A권11호
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• pp.961-971
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• 2012

This article is concerned with effective numerical techniques for partial differential equation (PDE)-based image restoration. Numerical realizations of most PDE-based denoising models show a common drawback: loss of fine structures. In order to overcome the drawback, the article introduces a new time-stepping procedure, called the method of nonflat time evolution (MONTE), in which the timestep size is determined based on local image characteristics such as the curvature or the diffusion magnitude. The MONTE provides PDE-based restoration models with an effective mechanism for the equalization of the net diffusion over a wide range of image frequency components. It can be easily applied to diverse evolutionary PDE-based restoration models and their spatial and temporal discretizations. It has been numerically verified that the MONTE results in a significant reduction in numerical dissipation and preserves fine structures such as edges and textures satisfactorily, while it removes the noise with an improved efficiency. Various numerical results are shown to confirm the claim.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2001년도 하계학술대회 논문집 B
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• pp.840-842
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• 2001

The cogging torque and torque ripple in motor which cause noise and vibration are an inevitable phenomenon and they give a bad effect to motor performance. So we are required to reduce the cogging torque and torque ripple not by electrical controlling but by changing the inner mechanical structure and we focused on the permanent magnet. In this research, we calculated current, torque, Back-EMF(electromotive force) and cogging torque according to the change of the magnet shape using two dimensional FEM(Finite Element Method). Maxwell stress tensor and time-stepping method. From the results, we present an appropriate model that can satisfy both low cogging torque, low torque ripple and high efficiency.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2003년도 제21회 추계학술대회 논문집
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• pp.157-163
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• 2003

A systematic numerical experiment has been conducted to study droplet gasification in high pressure environments with pressure oscillations. The general frame of previous rigorous model[1] is retained but tailored for flash equilibrium calculation of vapor-liquid interfacial thermodynamics. Time-dependent conservation equations of mass, momentum, energy, and species concentrations are formulated in axisymmetric coordinate system for both the droplet interior and ambient gases. In addition, a unified property evaluation scheme based on the fundamental equation of state and empirical methods are used to find fluid thermophysical properties over the entire thermodynamic domain of interest. The governing equations with appropriate physical boundary conditions are numerically time integrated using an implicit finite-difference method with a dual time-stepping technique. A series of calculation have been carried out to investigate the gasification of an isolated n-pentane droplet in a nitrogen gas environment over a wide range of ambient pressures and frequencies. Results show that the mean pressures and frequencies of the ambient gas have strong influences on the characteristics of the droplet gasification. The amplitude of the response increases with increasing pressure, and the magnitude of the vaporization response increases with the frequency.

• Coupled systems mechanics
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• 제7권2호
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• pp.233-254
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• 2018

In order to reduce the dependency on fossil fuels, a policy to increase the production capacity of wind turbine is set up. This can be achieved with increasing the dimensions of offshore wind turbine blades. However, this increase in size implies serious problems of stability and durability. Considering the cost of large turbines and financial consequences of their premature failure, it is imperative to carry out numerical simulations over long periods. Here, an energy-conserving time-stepping scheme is proposed in order to ensure the satisfying computation of long-term response. The proposed scheme is implemented for three-dimensional solid based on Biot strain measures, which is used for modeling flexible blades. The simulations are performed at full spatial scale. For reliable design process, the wind loads should be represented as realistically as possible, including the fluid-structure interaction (FSI) dynamic effects on wind turbine blades. However, full-scale 3D FSI simulations for long-term wind loading remain of prohibitive computation cost. Thus, the model to quantify the wind loads proposed here is a simple, but not too simple to be representative for preliminary design studies.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2005년도 제36회 하계학술대회 논문집 B
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• pp.1288-1290
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• 2005

This paper analyzed the characteristics of the claw pole PM step motor by using 3D FEM. As the magnetization occurs along the z-axis of the motor, it is necessary to apply 3D FEM for analysis of the claw pole PM step motor. Considering the computation time, however, the number of the analysis model is minimized by using the "Design of Experiments(DOE)". By using the "DOE", efficient analysis was able to be done. To see the effects of the design factors, the 3D FEM is applied only to the selected models. As the design factors, the teeth shape, the number of turns and the permanent magnet overhang was selected.

• 비파괴검사학회지
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• 제30권3호
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• pp.181-193
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• 2010

The paper presents an alternative way to classical stereocorrelation. First, 2D image processing of random patterns is described. Sub-pixel displacements are determined using phase analysis. Then distortion evaluation is presented. The distortion is identified without any assumption on the lens model because of the use of a grid technique approach. Last, shape measurement and shape variation is caught by fringe projection. Analysis is based on two pin-hole assumptions for the video-projector and the camera. Then, fringe projection is coupled to in-plane displacement to give rise to 3D measurement set-up. Metrological characterization shows a resolution comparable to classical (stereo) correlation technique ($1/100^{th}$ pixel). Spatial resolution seems to be an advantage of the method, because of the use of temporal phase stepping (shape measurement, 1 pixel) and windowed Fourier transform (in plane displacements measurement, 9 pixels). Two examples are given. First one is the study of skin properties; second one is a study on leather fabric. In both cases, results are convincing, and have been exploited to give mechanical interpretation.

• 천문학회보
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• 제44권1호
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• pp.38.3-38.3
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• 2019

We investigate the stellar population properties of nine passive spiral galaxies in the CALIFA survey. They have NUV-r > 5 and no/weak nebular emission lines in their spectra. They lie in the redshift range of 0.001 < z < 0.021 and have stellar mass range of 10.2 < ${\log}(M{\star}/M{\odot})$ < 10.8. We analyze the stellar populations out to two effective radius, using the best-fitting model to the measured absorption line-strength indices in the Lick/IDS system. We compare the passive spirals with S0s selected in the same mass range. S0s cover a wide range in age, metallicity, and [${\alpha}/Fe$], and stellar populations of the passive spirals are encompassed in the spread of the S0 properties. However, the distribution of passive spirals are skewed toward higher values of metallicity, lower [${\alpha}/Fe$], and younger ages at all radii. These results show that passive spirals are possibly related to S0s in their stellar populations. We infer that the diversity in the stellar populations of S0s may result from different evolutionary pathways of S0 formation, and passive spirals may be one of the possible channels.

• The Journal of Asian Finance, Economics and Business
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• 제8권8호
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• pp.287-296
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• 2021

Stepping into the technological boom time, Vietnam has integrated into the trends of using Fintech applications as a new means of payment. This article evaluates the relationship between perceived security (including service security and platform security), knowledge, confirmation, perceived usefulness, satisfaction, attitude and lastly enterprise's images regarding the service and continuous intention to use Fintech services. The survey results of 352 Vietnamese customers using Fintech services, reliability test and extended post-acceptance model (EPAM) which is based on PAM and ECT models. From the survey, we further found out that perceived security (BSS) has no direct impact on continued intention to use, while perceived security (BSS) has positive impact on confirmation (CON), similarly, perceived usefulness (PU) and user's satisfaction (SES). Knowledge of the Mobile Fintech payment service (KNOW) has a positive impact on perceived security (BSS). Confirmation (CON) has a positive influence on perceived usefulness but in the meanwhile it has created a negative impact on user's satisfaction (SES). From the survey it can also tell that user's attitude (ATT) and enterprise image (IMG) both have a positive impact on continual intention to use Fintech services. From the research results, we also propose some recommendation to enhance the continual intention to use Fintech services in Vietnam.

• 자원ㆍ환경경제연구
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• 제25권1호
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• pp.27-60
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• 2016

기후경제통합평가모형(Integrated assessment model of climate and the economy)은 기후변화에 관한 경제 분석과 정책제안을 위한 필수적인 도구가 되어왔다. 최근에는 기후변화에 대응하기 위한 정책적 노력들이 대부분 국가 또는 지역 수준에서 일어난다는 인식 하에 국가 또는 지역에서의 기후변화 영향과 정책수단의 효과를 평가할 수 있는 기후경제통합-지역평가모형(Regional integrated assessment model of climate and the economy)의 중요성이 더욱 커지고 있다. 이 논문에서는 국내에서 기후경제통합-지역평가모형을 개발하기 위한 첫 번째 단계로서 사회후생함수를 중심으로 기후경제통합-지역평가모형을 이론적으로 유형화했으며, RICE(Regional integrated climate-economy model) 모형을 통해 기후변화 대응전략에 따른 국가별 기후변화정책의 변화를 수치적으로 살펴보았다. 변화하는 국제 상황, 새롭게 드러나는 과학적 증거, 국내 여건 등을 모두 반영한 기후변화정책을 수립하기 위해서는 이를 분석할 수 있는 효과적인 도구를 갖추고 있어야 한다. 이 논문에서 살펴본 기후경제통합-지역평가모형은 이를 위한 유용한 도구가 될 수 있다.