• Structural Engineering and Mechanics
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• 제4권5호
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• pp.553-568
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• 1996

Finite element stiffness matrix methods are presented for finding natural frequencies (or buckling loads) and modes of repetitive structures. The usual approximate finite element formulations are included, but more relevantly they also permit the use of 'exact finite elements', which account for distributed mass exactly by solving appropriate differential equations. A transcendental eigenvalue problem results, for which all the natural frequencies are found with certainty. The calculations are performed for a single repeating portion of a rotationally or linearly (in one, two or three directions) repetitive structure. The emphasis is on rotational periodicity, for which principal advantages include: any repeating portions can be connected together, not just adjacent ones; nodes can lie on, and members along, the axis of rotational periodicity; complex arithmetic is used for brevity of presentation and speed of computation; two types of rotationally periodic substructures can be used in a multi-level manner; multi-level non-periodic substructuring is permitted within the repeating portions of parent rotationally periodic structures or substructures and; all the substructuring is exact, i.e., the same answers are obtained whether or not substructuring is used. Numerical results are given for a rotationally periodic structure by using exact finite elements and two levels of rotationally periodic substructures. The solution time is about 500 times faster than if none of the rotational periodicity had been used. The solution time would have been about ten times faster still if the software used had included all the substructuring features presented.

• Steel and Composite Structures
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• 제19권5호
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• pp.1115-1144
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• 2015

Current climate conditions along with advances in technology make further design and verification methods for structural strength and reliability of wind turbine towers imperative. Along with the growing interest for "green" energy, the wind energy sector has been developed tremendously the past decades. To this end, the improvement of wind turbine towers in terms of structural detailing and performance result in more efficient, durable and robust structures that facilitate their wider application, thus leading to energy harvesting increase. The wind tower industry is set to expand to greater heights than before and tapered steel towers with a circular cross-section are widely used as more capable of carrying heavier loads. The present study focuses on the improvement of the structural response of steel wind turbine towers, by means of internal stiffening. A thorough investigation of the contribution of stiffening rings to the overall structural behavior of the tower is being carried out. These stiffening rings are placed along the tower height to reduce local buckling phenomena, thus increasing the buckling strength of steel wind energy towers and leading the structure to a behavior closer to the one provided by the beam theory. Additionally to ring stiffeners, vertical stiffening schemes are studied to eliminate the presence of short wavelength buckles due to bending. For the purposes of this research, finite element analysis is applied in order to describe and predict in an accurate way the structural response of a model tower stiffened by internal stiffeners. Moreover, a parametric study is being performed in order to investigate the effect of the stiffeners' number to the functionality of the aforementioned stiffening systems and the improved structural behavior of the overall wind converter.

• 대한조선학회논문집
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• 제36권2호
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• pp.50-60
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• 1999

안전하고 경제적인 쌍동선형을 설계하기 위해서는 횡갑판(cross deck)에 작용하는 파랑 동하중의 정확한 추정이 필요하다. 본 논문에서는 Lee 등[3]이 제시한 2차원 스트립 방법을 6자유도 운동을 갖는 3차원의 경우로 확장하여 임의 입사파에서 파랑하중(수직 및 수평 전단력, 굽힘모멘트 및 비틀림모멘트)을 추정하였고, 발표된 계산 결과(스트립 방법 및 3차원 패널법) 및 Wahab 등[2]의 실험 결과와 비교하였다. 일반적으로 2차원 결과보다 3차원 방법이 실험 결과와 잘 일치하였으나, 같은 이론을 사용한 3차원 방법에 있어서도 몇몇 경우에 계산값의 차이가 있었다. 파랑하중 추정의 정도를 향상시키기 위해서 점성항의 고려 및 엄밀한 속도항의 고려가 필요하다고 생각된다.

• 한국태양에너지학회 논문집
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• 제33권2호
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• pp.101-107
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• 2013

It is evident that in the wind energy business as an economic activity there is a close relationship between the wind speed and the revenues. The wind turbine test facility for wind turbine accreditation is intended to be used by the industry for testing of both main components and systems. This paper suggest the wind test site for certification of prototype wind turbine with international regulations. The test site has an environmental permit for wind turbines with a maximum hub height of 120m and a rotor diameter up to 120m, and can accommodate prototypes with installed electrical powers up to 5MW each. A wind turbine manufacturer can lease the location for a period of type certification. And also researchers are the development of new methods for measuring the influence, performance and durability of the components, a mathematical and numerical modelling of component responses by using the site.

• 사상체질의학회지
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• 제27권4호
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• pp.436-443
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• 2015

Objectives The aim of this study was to report an improvement on the symptoms of Eosinophilic Colitis (EC) by Yeoldahanso-tang.Methods The patient was diagnosed with Taeumin Ganyeol-paeJo Symptomatology and treated with Yeoldahanso-tang. The gastroendoscopy and eosinophilic infitration of mucosa of colitis are investigated. Also patient's subjective symptom of abdominal pain was scored using the Numerical Rating Scale(NRS) during the treatment period. And the number of defecation in a day is also used to decide the degree of colitis.Results and Conclusions The patient had been treated from December 13, 2014 to August 8, 2015. Eosinophilic infiltration of colon was disappeared after the treatment although chronic inflammation still existed. Subjective pain of abdominal pain was measured as NRS 6~8 at the beginning of the remedy, but diminished through the treatment sessions and became NRS 0 in the end. The number of defecation was in average 3, and at the endpoint it became 1. In conclusion, this study suggests that Sasang constitutional Medicine used for treating EC of Taeumin may be effective.

• 사상체질의학회지
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• 제27권4호
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• pp.419-428
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• 2015

Objectives The aim of this study was to report an improvement on the symptoms of Restless Legs Syndrome (RLS) after using Hyeongbangsabaeksan.Methods The patient was diagnosed with Soyangin Soyang-sangpung Symptomatology and treated with Hyeongbangsabaeksan. The patient's subjective symptoms of pain on the lower limb and discomfort in sleeping were observed using the Numerical Rating Scale(NRS) and Visual Analogue Scale(VAS) respectively during the treatment period. And other specific symptoms of RLS were assessed once per week for a total of three times with Korean Versions of the International Restless Legs Scale.Results and Conclusions The pain on the patient's lower limb decreased from NRS 4 to NRS 0 after one week of treatment. And discomfort in sleeping decreased from VAS 5.5 to VAS 0 after one week of treatment. Furthermore, the score of Korean Versions of the International Restless Legs Scale decreased from 40 to 5 after two weeks of treatment. In conclusion, this study shows that Sasang Constitutional Medicine can be an effective treatment for Soyangin patient with Restless Legs Syndrome as Soyangin Soyang-sangpung Symptomatology.

• 한국철도학회논문집
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• 제19권1호
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• pp.67-76
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• 2016

아스팔트콘크리트 궤도는 궤도구조에서 유지관리와 경제적 측면에서 많은 장점들을 가지고 있어 최근 많은 관심을 받고 있다. 이와 더불어 개발에 따른 실용성을 효과적으로 검증할 수 있는 방법 또한 제시되어야 한다. 본 연구에서는 기 개발된 아스팔트콘크리트 궤도에서 사용된 아스팔트콘크리트 재료의 탄성 및 점탄성 특성과 주어진 설계 두께를 고려한 수치해석을 통하여 아스팔트콘크리트 궤도에서 발생 가능한 동적특성을 분석하였다. 해석의 불확실성을 줄이기 위하여 3차원 동적해석을 수행하여 실제적인 거동분석이 가능하도록 하였으며, 궤도노반의 영향거리 분석을 통한 최적 모델링 도출과 무한요소 경계조건을 이용하여 반무한지반을 고려하였다. 아스팔트콘크리트 도상을 등방 탄성체로 간주한 기본설계 조건에서의 거동을 점탄성재료 조건과 비교하였으며 동적증폭계수 산정을 통하여 아스팔트 콘크리트 궤도의 향후 설계방향을 제시하고자 하였다.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2008년도 춘계학술대회 논문집
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• pp.2101-2108
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• 2008

Most of train fires which occur in usual cases do not grow up significantly on a large scale enough to bring about casualties and harmful damages. However, the consequence of some train fire accidents can be devastating disaster so that it would be even recorded in history in unusual cases. Accordingly, such a probability of fire disaster cannot be ignored in aspect of the railway safety assesment. A scale of injury and damage is very difficult to predict and analyze. Because it is depend on various factors, i.e. fire load, burning period, facilities, environment condition, and so on. Thus, a prediction of fire load could be understood as a one methodology to estimate railway safety assesment. The summation method which is one of them is used to evaluate the overall fire load by assuming that sum of heat release rate per unit area or mass of each composite material equals the total. However, since the train fire is classified into a compartment fire in under-ventilation condition. The summation method do not estimate a fire load completely. In this journal, Various methods to predict fire load are introduced and evaluated. Especially the fire simulation tool FDS(Fire Dynamics Simulator)which is based on the CFD(Computational Fluid Dynamics) is introduced, too. Through the FDS simulation, numerical analyses for the fire load and flame spread are performed. Then, these results of the simulation are validated through the comparison study with the experimental data. Then, limitations and approximations including in simulation process are discussed. The future direction of research is proposed.

• Nuclear Engineering and Technology
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• 제50권1호
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• pp.54-67
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• 2018

There have been recent efforts to establish methods for high-fidelity and multi-physics simulation with coupled thermal-hydraulic (T/H) and neutronics codes for the entire core of a light water reactor under accident conditions. Considering the computing power necessary for a pin-by-pin analysis of the entire core, subchannel-scale T/H analysis is considered appropriate to achieve acceptable accuracy in an optimal computational time. In the present study, the applicability of in-house code CUPID of the Korea Atomic Energy Research Institute was extended to the subchannel-scale T/H analysis. CUPID is a component-scale T/H analysis code, which uses three-dimensional two-fluid models with various closure models and incorporates a highly parallelized numerical solver. In this study, key models required for a subchannel-scale T/H analysis were implemented in CUPID. Afterward, the code was validated against four subchannel experiments under unheated and heated single-phase incompressible flow conditions. Thereafter, a subchannel-scale T/H analysis of the entire core for an Advanced Power Reactor 1400 reactor core was carried out. For the high-fidelity simulation, detailed geometrical features and individual rod power distributions were considered in this demonstration. In this study, CUPID shows its capability of reproducing key phenomena in a subchannel and dealing with the subchannel-scale whole core T/H analysis.

• 한국전산구조공학회논문집
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• 제15권4호
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• pp.619-628
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• 2002

본 논문은 배플을 설치한 수평으로 놓인 원통형 탱크내 슬로싱 고유진동에 대한 유한요소 해석을 다룬다. 지배방정식으로 포텐셜 이론을 기반으로 한 라플라스 방정식을 적용한다. 이 문제를 선형의 등매개 요소를 적용한 유한요소법을 이용해 해석한다. 탱크와 배플은 강체로 가정하였으며, 배플의 효과 구현은 배플의 설치 위치에 절점을 두 개로 분리함으로써 얻을 수 있다. 고유주파수와 고유모드의 추출을 위하여 Lanczos 변환법 및 Jacobi 반복법을 도입하였다. 종진동과 횡진동 모드에 대한 수치 해석결과가 참고 문헌과 비교해 볼 때 잘 일치함을 알 수 있었다. 또한 유체 높이, 배플 개수, 내공 크기, 배플 위치 등의 파라메트릭 해석을 통하여 슬로싱 특성 및 링형 배플의 영향을 고찰하였다.