• Wind and Structures
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• 제31권4호
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• pp.373-380
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• 2020

For large-scale 5MW offshore wind turbines, the discrete equation of fluid domain and the motion equation of structural domain with geometric nonlinearity were built, the three-dimensional modeling of the blade considering fluid-structure interaction (FSI) was achieved by using Unigraphics (UG) and Geometry modules, and the numerical simulation and the analysis of the vibration characteristics for wind turbine structure under rotating effect were carried out based on ANSYS software. The results indicate that the rotating effect has an apparent effect on displacement and Von Mises stress, and the response and the distribution of displacement and Von Mises stress for the blade in direction of wingspan increase nonlinearly with the equal increase of rotational speeds. Compared with the single blade model, the blade vibration period of the whole machine model is much longer. The structural coupling effect reduces the response peak value of the blade displacement and Von Mises stress, and the increase of rotational speed enhances this coupling effect. The maximum displacement difference between two models decreases first and then increases along wingspan direction, the trend is more visible with the equal increase of rotational speed, and the boundary point with zero displacement difference moves towards the blade root. Furthermore, the Von Mises stress difference increases gradually with the increase of rotational speed and decreases nonlinearly from the blade middle to both sides. The results can provide technical reference for the safe operation and optimal design of offshore wind turbines.

• 대한기계학회논문집A
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• 제20권1호
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• pp.88-99
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• 1996

The explicit scheme for finite element analysis of sheet metal forming problems has been widely used for providing practical solutions since it improves the convergency problem, memory size and computational time especially for the case of complicated geometry and large element number. The explicit schemes in general use are based on the elastic-plastic modeling of material requiring large computataion time. In the present work, a basic formulation for rigid-plastic explicit finite element analysis of plain strain sheet metal forming problems has been proposed. The effect of some basic parameters involved in the dynamic analysis has been studied in detail. Thus, the effective ranges of parameters have been proposed for numerical simultion by the rigid-plastic explicit finite element method. A direct trial-and-error method is introduced to treat contact and friction. In computation, sheet material is assumed to possess normal anisotropy and rigid-plastic workhardening characteristics. In order to show the validity and effectiveness of the proposed explicit scheme, computations are carried out for cylindrical punch stretching and the computational results are compared with those by the implicit scheme as well as with a commercial code. The proposed rigid-plastic exlicit finite element method can be used as a robust and efficient computational method for analysis of sheet metal forming.

• 한국항공우주학회지
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• 제30권5호
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• pp.32-40
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• 2002

희박상태나 극소장치에 관련된 기체운동을 해석하는 문제가 최근 중요한 연구주제로 부각되고 있다. 잘 알려진 DSMC와 더불어 모우멘트 기법, Chapman-Enskog 기법으로 분류되는 고차 비평형 유동 해석모델들이 이 문제에 적용되어 왔다. 본 연구에서는 Eu의 일반유체역학을 근간으로 이원자 기체에 관한 고차 해석모델을 개발하고자 한다. 회전 비평형 효과는 기체의 용적 점성계수에 관한 초과 수직응력을 고려하여 감안하였다. 개발된 계산모델을 일차원 충격파 내부구조와 단순 형상 외부의 희박 극초음속 유동장 해석에 적용하였다. 충격파 내부구조 및 전단유동 해석을 통해 회전 비평형에 의한 용적 점성계수 효과가 중요함을 확인하였다. 충격파 내부구조에 관한 이론적 예측이 실험과 잘 일치함도 확인하였다.

• 한국수자원학회논문집
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• 제33권3호
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• pp.331-340
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• 2000

본 연구의 목적은 하천에서의 실시간 범람위험도 해석을 위해서 DAMBRK 모형과 Kalman filter를 연계한 수치모형을 개발하는데 있다. 본 모형은 1차원 동역학 방정식의 비선형 유한차분 근사해인 음해법을 기본으로 하고 있다. 추계학적 추정법으로서 최적의 갱신 예측치를 얻기 위해 확장된 Kalman filter 기법을 사용하였다. 이 과정은 확정론적 모형에 의한 예측치를 Kalman filter gain factor에 의해 보정된 실시간 관측치와 조합함으로써 수행되었다. 홍수범람위험도는 하도단면의 기하형상과 Manning 조도계수의 변동성을 고려하여 Monte Carlo 모의를 적용하여 예측되었다. 본 모형은 1990년 9월과 1995년 8월의 남한강 홍수에 적용하여 검증하였다. Kalman filter에 의한 해석은 이 기간 동안에 확정론적 해석결과와 비교하여 실측자료와 잘 일치되는 양상이 나타났으며, 이에 따라 제방의 월류위험도를 모의된 홍수위와 제방고를 비교함으로써 얻을 수 있었다.

• 한국수학교육학회지시리즈A:수학교육
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• 제45권2호
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• pp.191-204
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• 2006

Computer technology has a potential to change the contents of school mathematics and the way of teaching mathematics. But in our country, the problem whether computer technology should be introduced into mathematics classroom or not was not resolved yet. As a tool, computer technology can be used by teachers who are confident of the effectiveness and who can use it skillfully and can help students to understand mathematics. The purpose of this study was to investigate the effective way to introduce and utilize computer technology based on the status quo of mathematics classroom setting. One possible way to utilize computer technology in mathematics classroom in spite of the lack of computer and the inaccessibility of useful software is using domain specific simulation software like 'Polyhedron'. 'Polyhedron', as we can guess from the name, can be used to explore regular and semi regular polyhedra and the relationship between them. Its functions are limited but it can visualize regular polyhedra, transform regular polyhedra into other polyhedra. So it is easier to operate than other dynamic geometry software like GSP. To investigate the effect of using this software in mathematics class, three classes(one in 6th grade from science education institute for the gifted, two in 7th grade) were chosen. Activities focused on the relationship between regular and semi regular polyhedra. After the class, several conclusions were drawn from the observation. First, 'Polyhedron' can be used effectively to explore the relationship between regular and semi regular polyhedra. Second, 'Polyhedron' can motivate students. Third, Students can understand the duality of polyhedra. Fourth, Students can visualize various polyhedra by reasoning. To help teachers in using technology, web sites like NCTM's illuminations and NLVM of Utah university need to be developed.

• Structural Engineering and Mechanics
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• 제37권2호
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• pp.233-251
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• 2011

The seismic provisions of the current edition (2005) of the National Building Code of Canada (NBCC) differ significantly from the earlier edition. The current seismic provisions are based on the uniform hazard spectra corresponding to 2% probability of exceedance in 50 years, as opposed to the seismic hazard level with 10% probablity of exeedance in 50 years used in the earlier edition. Moreover, the current code is presented in an objective-based format where the design is performed based on an acceptable solution. In the light of these changes, an assessment of the expected performance of the buildings designed according to the requirements of the current edition of NBCC would be very useful. In this paper, the seismic performance of a set of six, twelve, and eighteen story buildings of regular geometry and with concrete moment resisting frames, designed for Vancouver western Canada, has been evaluated. Although the effects of non-structural elements are not considered in the design, the non-structural elements connected to the lateral load resisting systems affect the seismic performance of a building. To simulate the non-structural elements, infill panels are included in some frame models. Spectrum compatible artificial ground motion records and scaled actual accelerograms have been used for evaluating the dynamic response. The performance has been evaluated for each building under various levels of seismic hazard with different probabilities of exceedance. From the study it has been observed that, although all the buildings achieved the life-safety performance as assumed in the design provisions of the building code, their performance characteristics are found to be non-uniform.

• 대한조선학회지
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• 제20권2호
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• pp.1-20
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• 1983

In this paper design criteria for semi-submersibles, effective at the stage of basic design, are reviewed first generally. Thereafter an extensive study is focussed on essential problematic areas such as design load, heaving motion, overall structural analysis and welding technique. The necessity for this kind of research is apparent in the light of the fact that ocean exploration and exploitation becomes extended to deeper ocean and that semi-submersibles are the most favorite unit for operation under this environment. In some sense principles in naval architecture are indeed applicable to the design of semi-submersible. However, because of the difference in geometry between ships and semi-submersibles, there are significant deviations in design method. A thorough discussion is made on particular behaviours of a semi-submersible in stability, wave load, motion characteristics and structural responses. Then some calculation-procedures and design guidelines are tentatively proposed. A numerical calculation for a semi-submersible Sedco 708 is exemplified for better understanding of the concept. The structure has 4 main and another 4 secondary stabilizing columns with catamaran-type lower hull. In this example design condition is supposed to be 28m wave height, 90 knots wind speed for survival condition and seastate 6 for operational condition in water of 100m depth. The numerical result implies that the actual design of this model can be assessed close to optimum. Further intensive research is strongly required in the subject fields of dynamic stability, rational evaluation of wave load statistical basis for fatigue life judgement.

• 한국지진공학회논문집
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• 제13권3호
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• pp.21-28
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• 2009

지반-말뚝-구조의 상호작용을 정밀하게 해석하기 위해서는 토층, 말뚝 그리고 구조물의 적절한 묘사가 필요하다. 일반적으로 사용하는 유한요소해석의 경우에는 지반이나 구조물의 물성이 바뀌는 경계를 따라서 요소의 경계가 정해지게 된다. 그러나 실제로는 토층 단면과 말뚝의 형상이 매우 복잡하여 요소의 배열이 매우 어려운 작업이 될 수 있다. 이 어려움을 해결하기 위하여, 이 논문에서는 불연속선의 위치에 관계없이 규칙적인 요소를 사용하여 쉽게 적분을 가능하게 하는 다른 적분 방법을 채택하였다. 이 방법을 적용함으로 써 요소는 매우 빠르고 규칙적인 강성 매트릭스를 만든다. 구조물 응답에 대한 토층과 말뚝의 영향을 조사하였고, 예를 통하여 본 방법의 유효성을 보였다. 탄성 말뚝의 사용으로 20% 대의 가속도 감소 효과를 얻었고 지반 층의 모양에 따라 그 영향이 변하는 것을 확인하였다.

• Transactions on Electrical and Electronic Materials
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• 제7권6호
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• pp.313-318
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• 2006

This paper introduces a partial discharge (PD) severity metric, S, based on the evaluation of time-sequence PD data capture and resulting Time-Sequence-Analysis Discharge (TSAD) level distributions. Basically based on an IEC60270 measurement technique, each PD event is time stamped and the discharge level noted. By evaluating the time differences between a previous and subsequent discharge, a 3D plot of time-sequence activity and discharge levels can be produced. From these parameters a measurement of severity, which takes into account dynamic or instantaneous variations in both the time of occurrence and the level of discharge, rather than using standard repetition rate techniques, can be formulated. The idea is to provide a measure of the severity of PD activity for potentially measuring the state of insulation within an item of plant. This severity measure is evaluated for a simple point-plane geometry in $SF_{6}$ as a function of gap distance and applied high voltage. The results show that as the partial discharge activity increases, the severity measure also increases. The importance of future investigations, quantifications and evaluations of the robustness, sensitivity and importance of such a severity measurement, as well as comparing it with typical repetition rate assessment techniques, and other monitoring techniques, are also very briefly discussed.

• 한국전산구조공학회논문집
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• 제30권4호
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• pp.289-296
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• 2017

본 논문에서는 곤충 모방 날갯짓 초소형 비행체에 적용될 끈을 이용한 날갯짓 구동 장치의 구동 원리와 그 최적화 과정이 소개된다. 이 날갯짓 구동 장치는 끈을 이용하여 구조의 경량화와 관성력 감소로 인한 에너지 효율 상승을 목적으로 설계되었다. 먼저 장력만 전달할 수 있는 끈의 특성을 고려하여 운동학적인 수식이 정립되었으며, 이를 통해 구동 장치의 거동 특성을 파악할 수 있었다. 이 수식들은 수정된 패턴 검색 최적화 과정에 포함되어 메커니즘의 운동학적 최적화를 가능하게 만들었다. 최적화된 형상으로 제작된 시제품은 설계의 구동 원리에 맞게 운동하였으며, 그 날갯짓 폭은 목표한 날갯짓 폭을 만족시켰다. 수치적 시뮬레이션과 실험 결과는 잘 일치하여 제시된 구동 장치가 실제로 활용될 수 있음을 보였다.