• 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.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2000년도 추계학술발표대회 논문집
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• pp.187-190
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• 2000

Cyclocopter is air vehicle to vertically take-off and land like a helicopter. This is an efficient and quiet means of being able to direct thrust compared to a helicopter. The rotor consists of several blades rotating about a horizontal axis perpendicular to the direction of normal flight. The direction of blade span is parallel to rotating axis and both end roots are connected to the hub to resist centrifugal force and to transmit the power. The pitch of the individual blades to the tangent of the circle of the blade's path is varied cyclically to gain thrust. In the paper, the design and manufactures of cyclocopter rotor blades are presented. Stress at the roots of cyclocopter blades is great due to centrifugal and aerodynamic forces and aeroelastic instabilities appear. The blades consist of main spar, front spar, polyurethan foam, weight, and skin and spars and skin are made of glass/epoxy composite.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2004년도 춘계학술발표대회 논문집
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• pp.91-94
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• 2004

A cyclocopter with the cycloidal blades system can be the type of UAV which can combine the high-speed characteristics of the conventional airplane with the low-speed characteristics of the helicopter. The cycloidal blades system, which can be described as a horizontal rotary wing, offers powerful thrust levels, and a unique ability to change the direction of the thrust almost instantly. Rotor blades are designed to withstand tremendous transverse centrifugal loadings, and responding to a number of aerodynamic harmonic vibratory forcing frequencies. To reduce the weight and increase the strength, the blades are made of composite materials. The blades consist of the skin, spar, and trailing stiffener. In this study, static and dynamic behaviors of cyclocopter rotor blades are analyzed by using MSC/NASTRAN.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2004년도 추계학술대회논문집
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• pp.902-905
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• 2004

Recently, the composite materials are widely used for manufacturing the helicopter rotor blades. furthermore, composites show great potential on the design of rotor blades due to the advantages of strength, durability and weight of the materials. To keep with this advantages, it is necessary to calculate natural frequencies of a rotating blades for avoiding resonance. In this paper, the structural design process of airfoil cross section is introduced, and natural frequencies of composite rotor blades with variable rpm we investigated.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2005년도 춘계학술발표대회 논문집
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• pp.187-190
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• 2005

A simple beam model based on a mixed method is proposed for the analysis of thin-walled composite blades with a two-cell airfoil section. A semi-complementary energy functional is used to obtain the beam force-displacement relations. The theory accounts for the effects of elastic couplings, shell wall thickness, warping, and warping restraint. All the kinematic relations as well as the cross-section stiffnesses are evaluated in a closed-form through the current beam formulation. The theory has been applied to two-cell composite blades with extension-torsion couplings and fairly good correlation has been observed in comparison with a detailed analysis and other literature.

• 대한기계학회논문집A
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• 제21권11호
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• pp.1765-1772
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• 1997

The layered composites have a character to change of structure stiffness with respect to the layup angles. The deformations in the fan-blades to be initially designed by considering efficiency and noise, etc., which arise due to the pressure during the fan operation, can make the fan inefficient. Thus, so as to minimize the deformations of the blades, it is needed to increase the stiffness of the blades. An investigation has been performed to develop the three dimensional layered composite shell element with the drilling degree of freedom and the optimization module for finding optimal layup angles with sensitivity analysis. And then they have been verified. In this study, the analysis model is engine cooling fan of automobile. In order to analyzes the stiffness of the composite fan blades, finite element analysis is performed. In addition, it is linked with optimal design process, and then the optimal angles that can maximize the stiffness of the blades are found. In the optimal design process, the deformations of the blades are considered as multiobjective functions, and this results minimum bending and twisting simultaneously.

• 한국전산구조공학회논문집
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• 제25권3호
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• pp.203-209
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• 2012

본 논문에서는 상온 및 방사선 경화 복합재 풍력 블레이드의 구조성능을 비교하기 위하여 단면 강성, 정적응력 및 동적 고유 진동수를 해석하였다. 먼저 상온 및 방사선 경화공정에 의한 복합재료 시편의 탄성계수 등 물성 값을 적용하였다. 블레이드의 단면 강성 값은 고형 복합재료 보 이론을 적용하여 유한요소 적분법으로 계산하였다. 허브 체결부위를 포함한 소형 풍력 블레이드를 상용 유한요소 프로그램으로 모델링하여 최대 변위와 응력분포 등을 확인하였다. 또한, 풍력 블레이드의 회전속도에 따른 원심력 효과를 고려하여 고유 진동수 해석을 병행하였다. 이와 같은 일련의 해석결과를 상호 비교함으로써, 상온 및 방사선 경화 복합재료의 물성 값 차이에서 기인하는 풍력 블레이드의 구조성능 변화를 정량적으로 분석하였다.

• Journal of Mechanical Science and Technology
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• 제19권11호
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• pp.2016-2024
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• 2005

In this work, a mixed beam approach that combines both the stiffness and the flexibility methods has been performed to analyze the coupled composite blades with closed, two-cell cross-sections. The Reissner's semi-complementary energy functional is used to derive the beam force-displacement relations. Only the membrane part of the shell wall is taken into account to make the analysis simple and also to deliver a clear picture of the mixed method. All the cross section stiffness coefficients as well as the distribution of shear across the section are evaluated in a closed-form through the beam formulation. The theory is validated against experimental test data, detailed finite element analysis results, and other analytical results for coupled composite blades with a two-cell airfoil section. Despite the simple kinematic model adopted in the theory, an accuracy comparable to that of two-dimensional finite element analysis has been obtained for cases considered in this study.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2006년도 춘계학술대회논문집
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• pp.300-303
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• 2006

The rotor blade of a helicopter is the key structural units and provides three components such as vertical lifting force, horizontal propulsive force and control force. With advancements in aerospace technology, composite materials have been widely used in lightweight structures. In addition, composites show great potential on the design of rotor blades due to the advantages of strength, durability and weight of the materials. In the operational condition of a helicopter, it is required the vibration characteristics of the rotating blades for avoiding resonance and analysis of efficient performance prediction et al. In this study, the CAMRAD-II is used for analyzing the vibration characteristics of rotating composite blades. The effects of rotating speed and collective angles are investigated. Also, the numerical results are compared with experimental data.

• International Journal of Aeronautical and Space Sciences
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• 제4권1호
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• pp.9-18
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• 2003

In this work, a closed-form analysis is performed for the structural response of coupled composite blades with multi-cell sections. The analytical model includes the effects of shell wall thickness, transverse shear, torsion warping and constrained warping. The mixed beam approach based on Reissner's semi-complementary energy functional is used to derive the beam force-displacement relations. The theory is validated against experimental test data and other analytical results for coupled composite beams and blades with single-cell box-sections and two-cell airfoils. Correlation of the present method with experimental results and detailed finite element results is found to be very good.