• Structural Engineering and Mechanics
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• 제63권6호
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• pp.703-712
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• 2017

The composite blades of offshore wind turbines accumulate structural damage such as fatigue cracking due to harsh operation environments during their service time, leading to premature structural failures. This paper investigates various fatigue crack models for reproducing crack development in composite blades and proposes a stochastic approach to predict fatigue crack evolution and to analyse failure probability for the composite blades. Three typical fatigue models for the propagation of fatigue cracks, i.e., Miner model, Paris model and Reifsnider model, are discussed to reproduce the fatigue crack evolution in composite blades subjected to cyclical loadings. The lifetime probability of fatigue failure of the composite blades is estimated by stochastic deterioration modelling such as gamma process. Based on time-dependent reliability analysis and lifecycle cost analysis, an optimised maintenance policy is determined to make the optimal decision for the composite blades during the service time. A numerical example is employed to investigate the effectiveness of predicting fatigue crack growth, estimating the probability of fatigue failure and evaluating an optimal maintenance policy. The results from the numerical study show that the stochastic gamma process together with the proper fatigue models can provide a useful tool for remaining useful life predictions and optimum maintenance strategies of the composite blades of offshore wind turbines.

• Journal of Computing Science and Engineering
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• 제8권3호
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• pp.129-136
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• 2014

This paper presents the equivalent circuit modelling and eigenfrequency analysis of a wideband robust capacitive radio frequency (RF) microelectromechanical system (MEMS) switch that was designed using Poly-Si and Au layer membrane for highly reliable switching operation. The circuit characterization includes the extraction of resistance, inductance, on and off state capacitance, and Q-factor. The first six eigenfrequencies are analyzed using a finite element modeler, and the equivalent modes are demonstrated. The switch is optimized for millimeter wave frequencies, which indicate excellent RF performance with isolation of more than 55 dB and a low insertion loss of 0.1 dB in the V-band. The designed switch actuates at 13.2 V. The R, L, C and Q-factor are simulated using Y-matrix data over a frequency sweep of 20-100 GHz. The proposed switch has various applications in satellite communication networks and can also be used for devices that will incorporate the upcoming IEEE Wi-Fi 802.11ad protocol.

• 한국암반공학회:학술대회논문집
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• 한국암반공학회 2000년도 암반공학문제의 수치해석(Numerical Analysis in Rock Engineering Problems)
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• pp.163-170
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• 2000

절리가 발달한 암반의 거동 특성을 효율적으로 모델링 할 수 있는 수치해석 방법으로서 널리 알려진 개별요소법은 서로 다른 알고리즘에 기초하여 개발된 두 가지 형태의 수치해석 방법으로 발전해 왔다. 본 논문에서는 Plesha 등에 의해 개발된 implicit알고리즘에 기초한 NURBM과 저자에 의해 개발된 explicit 알고리즘에 기초한 CBLOCK을 이용하여 불연속체 암반의 기초적인 거동 특성을 수치해석적으로 고찰하고 모델링상의 문제점들을 비교 분석하였다. CBLOCK 계산 결과에 의하면 절리의 수직 및 접선 강성비는 절리 분포에 따라 불연속체 암반의 안정성을 좌우하는 중요한 지수로서 사용될 수 있는 것으로 나타나고 있으나 NURBM 제산은 상이한 결과를 보였다. 또한 구조물의 안정성과 국부적인 파괴 거동의 해석에서 두 방법이 상이한 결과를 가져올 수 있는 것으로 나타났고 이는 수치해석적 모델링의 제약적 요소로 작용할 수 있음을 보여 주었다.

• 터널과지하공간
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• 제10권3호
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• pp.410-417
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• 2000

절리가 발달한 암반의 거동 특성을 효율적으로 모델링 할 수 있는 수치해석 방법으로서 널리 알려진 개별요소법은 서로 다튼 알고리즘에 기초하여 개발된 두 가지 형태의 수치해석 방법으로 발전해 왔다. 본 논문에서는 Plesha 등에 의해 개발된 implicit 알고리즘에 기초한 NURBM과 저자에 의해 개발된 explicit 알고리즘에 기초한 CBLOCK을 이용하여 불연속체 암반의 기초적인 거동 특성을 수치해석적으로 고찰하고 모델링상의 문제점들을 비교 분석하였다. CBLOCK 계산 결과에 의하면 절리의 수직 및 접선 강성비는 절리 분포에 따라 불연속체 암반의 안정성을 좌우하는 중요한 지수로서 사용될 수 있는 것으로 나타나고 있으나 NURBM 계산은 상이한 결과를 보였다. 또한 구조물의 안정성과 국부적인 파괴 거동의 해석에서 두 방법이 상이한 결과를 가져올 수 있는 것으로 나타났고 이는 수치해석적 모델링의 제약적 요소로 작용할 수 있음을 보여주었다.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2008년도 추계 학술발표회
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• pp.466-474
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• 2008

The purpose of this study was to comparatively analyze the measured values and modelling values when a sample mountain was cut and thereby, assess the fitness of the prediction model. For this purpose, the researcher analyzed the relationship between the groundwater levels measured at 7 monitoring holes set within the area of the underground flow prediction model and the levels of the groundwater monitoring holes before and after mountain cutting. As a result of this analysis, it was found that the MODFLOW program itself was limited and uncertain in terms of calibration of the modelling values. Since the model was based on the assumption that the same amount of rainfalls would permeate into the ground when the sample mountain area was cut up to 50m high, it was deemed inevitable that the result of modelling was different from the actual measurement.

• Advances in concrete construction
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• 제3권2호
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• pp.127-143
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• 2015

Steel fibre reinforced concrete (SFRC) is an anisotropic material due to the random orientation of the fibres within the cement matrix. Fibres under different inclination angles provide different strength contribution of a given crack width. For that the pull-out response of inclined fibres is of great importance to understand SFRC behaviour, particularly in the case of fibres with hooked ends, which are the most widely used. The paper focuses on the numerical modelling of the pull-out response of this kind of fibres from high-strength cementitious matrix in order to study the effects of different inclination angles of the fibres to the load-displacement pull-out curves. The pull-out of the fibres is studied by means of accurate three-dimensional finite element models, which take into account the nonlinearities that are present in the physical model, such as the nonlinear bonding between the fibre and the matrix in the early stages of the loading, the unilateral contact between the fibre and the matrix, the friction at the contact areas, the plastification of the steel fibre and the plastification and cracking of the cementitious matrix. The bonding properties of the fibre-matrix interface considered in the numerical model are based on experimental results of pull-out tests on straight fibres.

• Computers and Concrete
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• 제10권3호
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• pp.307-330
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• 2012

This work intends to contribute for the improvement of the procedure suggested by Brazilian Technical Code that takes into account the cracked concrete stiffness in the estimative of the displacement of reinforced concrete beams submitted to service loads. A damage constitutive model accounting for induced anisotropy, plastic deformations and bimodular elastic response is used in order to simulate the concrete behaviour, while an elastoplastic behaviour is admitted for the reinforcement. The constitutive models were implemented in a program for bars structures analysis with layered finite elements. Initially, the damage model is briefly presented as well as the parametric identification of the materials that have been used in the reinforced concrete beams. After that, beams with different geometries and reinforcement area are analyzed and a statistical method (ANOVA) is employed in order to identify the main variables in the problem. Soon after, the same procedure is used with another resistance of concrete, where the compression strength is changed. The numerical responses are compared with the ones obtained by Brazilian Technical Code and experimental tests in order to validate the use of the damage model. Finally, some remarks are discussed based on responses presented in this work.

• Nuclear Engineering and Technology
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• 제54권12호
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• pp.4560-4570
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• 2022

Dynamic fault tree (DFT) and its related research methods have received extensive attention in safety analysis and reliability engineering. DFT can perform reliability modelling for systems with sequential correlation, resource sharing, and cold and hot spare parts. A technical modelling method of DFT is proposed for modelling ship collision accidents and loss-of-coolant accidents (LOCAs). Qualitative and quantitative analyses of DFT were carried out using the cutting sequence (CS)/extended cutting sequence (ECS) method. The results show nine types of dynamic fault failure modes in ship collision accidents, describing the fault propagation process of a dynamic system and reflect the dynamic changes of the entire accident system. The probability of a ship collision accident is 2.378 × 10^-9 by using CS. This failure mode cannot be expressed by a combination of basic events within the same event frame after an LOCA occurs in a marine nuclear reactor because the system contains warm spare parts. Therefore, the probability of losing reactor control was calculated as 8.125 × 10^-6 using the ECS. Compared with CS, ECS is more efficient considering expression and processing capabilities, and has a significant advantage considering cost.

• Structural Engineering and Mechanics
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• 제6권4호
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• pp.439-455
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• 1998

A three-dimensional static nonlinear finite element analysis was performed on the NUPEC large-scale flanged shear wall, which was the subject of an international study program. Details of the constitutive models and analysis procedures used are provided, and the results of the analysis are presented and discussed. The analytical results are compared to the experimentally observed behaviour, and reasonable correlation is observed. Deficiencies in the modelling are identified. In addition, a parametric study is undertaken to investigate factors and mechanisms influencing both the observed behaviour and the calculated response. Finally, a cyclic load analysis of the wall is described and discussed. The paper serves to point out aspects in modelling that are critical to both producing realistic results, and correctly interpreting those results.

• 한국산학기술학회논문지
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• 제18권3호
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• pp.718-723
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• 2017

구조설계 실무 현장에서의 구조해석 모델링 방법을 조사해 보면, 대부분의 경우, 삼차원 구조해석을 위해 슬래브를 판요소를 이용한 메쉬의 형태로 모형화 하고, 전단벽을 쉘요소 또는 벽요소를 사용하여 모형화 하고 있다. 여기서 주목할 점은 해석모형 작성의 편의성을 위하여 전단벽을 층과 층 및 기둥선과 기둥선 사이에 존재하는 한 개의 요소로 모형화 한다는 것이다. 이와 같은 모형화 방법은 사용되는 컴퓨터 프로그램에 따라 해석 오류를 발생시킬 수 있으며, 이러한 오류는 해석 결과의 신뢰성을 저하시키게 된다. 따라서 구조해석의 신뢰성을 확보하기 위해서는 이러한 오류가 발생하는 원인을 조사하고 합리적인 모형화 방법을 찾기 위한 연구가 필요하다. 원인 분석을 위한 비교 대상 해석 프로그램은 MIDAS와 SAP2000 및 neoMAX등과 같은 상용프로그램과 요소의 강성을 추측하기 위해 연구용인 sNs를 사용하였다. 본 연구에서는, 구조해석 실무현장에서 사용하고 있는 전단벽 모형화 방법에 따른 해석오류의 원인들을 분석해 보고자 한다. 또한 이러한 분석 결과를 바탕으로 전단벽 모형화를 위한 몇 가지 고려사항들을 제시하고자 한다.