Equivalent Spectral Method to Estimate the Fatigue Life of Composite Laminates Under Random Vibration Loadings

Mechanics of Composite Materials - The power spectral density (PSD) of an equivalent stress is proposed to analyze the fatigue life of composite laminates under random vibration loadings using the...     

基于外场实验的风力机叶片三维效应研究

针对一台33 kW水平轴风电机组开展了外场实验,得到其叶片7个断面翼型的压力分布曲线;基于求解时均N-S方程对风轮进行三维数值模拟,以及将叶片各断面作为二维翼型进行数值计算,分别得到各断面翼型的压力分布曲线及升阻力系数．通过将外场实验、三维和二维数值计算所得压力分布曲线及升阻力系数进行对比分析,研究了三维效应对风力机气动性能的影响．研究表明,从叶尖到叶根各断面翼型的压差先增大后逐渐减小,叶片表面压力分布曲线比较明显地反映了从叶尖到叶根流动分离的变化;叶片表面压力分布的三维数值计算结果较二维计算结果更加接近于外场实验值;风力机叶片表面的三维流动对叶片的气动性能影响较大,在叶尖和叶根部分尤为突出.     

Simulation of Buckling-Induced Failure in Composite Laminates

This contribution presents a simple model for the analysis of buckling–induced failure in thin–walled composite laminates in the framework of the finite element method. The plies are modeled with shear deformable geometrically non–linear four–node shell elements which are layered according to the classical laminate theory. Shear locking effects are reduced via the well–known assumed natural strains (ANS) approach. A ply discount model is applied for the successive failure of the plies. The cohesive zone approach which is implemented in so–called interface elements is employed for delamination. The failure processes are history dependent leading to non–recurring stiffness degradation in areas where damage is detected. A numerical example with experimental evidence highlights the performance and applicability of the proposed model. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

大型水平轴风力机叶片气动弹性计算

给出了一种考虑几何非线性的大型风力机静、 动气动弹性一体化计算方法．采用涡尾迹方法进行风力机气动载荷计算．建立风力机风轮的三维壳模型．沿周向平均风力机叶片载荷并加载到结构模型进行非线性静气动弹性分析．基于动力学小扰动假设, 在静平衡构型下进行动力学线性化, 计算风轮固有振动特性．继而结合非定常涡尾迹方法计算风力机动气动弹性响应．计算了NH 1500叶片考虑几何非线性的静气动弹性位移和动气动弹性响应．结果表明,大型风力机叶片几何非线性较为明显地减小静气动弹性位移,同时降低动气动弹性的响应幅值．大型风力机气动弹性响应计算需要考虑几何非线性     

Design of Microstrip Antennas with Composite Laminates Considering Their Structural Rigidity

Two types of conformal load-bearing antenna structures (CLAS) were designed with microwave composite laminates and Nomex honeycomb cores to secure both the structural rigidity and a good electrical performance. One was a 4 × 8 array for the synthetic-aperture radar (SAR) system and the other was a 5 × 2 array for the wireless local-area network (LAN) system. The design was based on a wide bandwidth, high polarization purity, low losses, and high structural rigidity. The design, fabrication, and structural/electrical performances of the antenna structures were studied. Their flexural behavior was examined by three-point bending, impact, and buckling tests. The electrical measurements were in a good agreement with simulation results. The complex antenna structures obtained have good flexural characteristics. The design of this antenna structure is extended to give a useful guide for sandwich panel manufacturers as well as antenna designers.     

A Probabilistic Model of the Fatigue Life of Composite Materials for Fatigue-Curve Approximations

A simple mathematical model for the fatigue life of composite materials in which the basic load is taken up by parallel rigid components (fiber strands) is offered. Based on the Markov chain theory, the model allows us to obtain an S-type curve for the growth of internal stresses and to calculate the relationship between the parameters of static strength distribution and the S-N fatigue curve (Wholer curve). The model is too simple and does not provide a numerical coincidence with experimental fatigue-test data, but, when used with additional parameters, it agrees with experiments and can be applied to the model of nonlinear regression in describing the fatigue curve and its variation as the parameters of static strength change.     

Symmetric and Asymmetric Underplatform Dampers for Turbine Blades

Friction damping devices like underplatform dampers are widely used in turbomachinery applications to reduce vibration amplitudes and to increase lifetime and reliability of the bladed disk. Nowadays, in practical applications, a variety of different underplatform damper geometries is applied. Nevertheless, a detailed study of the in.uence of the geometric and dynamic properties of the damper is still not available. Within this paper the most frequently applied damper types like cylindrical and wedge as well as asymmetrical dampers are investigated and compared to each other with respect to their effectiveness. Especially the in.uence of the damper geometry on the resonance frequency and vibration amplitude is pointed out. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Energy Absorption of Carbon-Fiber-Reinforced Composite Laminates Under Low-Velocity Impacts

Mechanics of Composite Materials - Drop-weight tests were conducted to investigate the impact responses of carbon-fiber-reinforced composite laminates under low-velocity impacts. A finite-element...     

Linear and Nonlinear Finite Element Analysis of Active Composite Laminates

The paper presents a finite element concept for analysis of thin-walled active structures featuring fiber reinforced composite laminate as a passive structural material. The structure is rendered active by embedding piezoelectric material as a multifunctional material. A 9-node degenerated shell element based on the first order shear deformation theory is developed as a modelling tool capable of predicting the general behavior of the structure for controlling purposes. The von-Kármán type nonlinearities are considered. The solution strategy of the geometrical nonlinear analysis is based on the incremental approach using the updated Lagrangian formulation. Some numerical results are given to demonstrate the behavior of the element. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

气动、结构、载荷相协调的大型风电叶片自主研发进展

从叶片设计的3个关键环节（气动设计、结构设计和载荷评估）出发,对叶片自主研发进展进行了总结分析．在气动设计方面,概述了计算流体动力学（computational fluid dynamics, CFD）方法、涡方法和叶素动量（blade element momentum, BEM）方法,并依据工程中广泛应用的BEM方法,指出了低风速区风电叶片的解决思路;在结构设计方面,简要概述了基于梁模型的传统设计分析方法,分析了其在大型复合材料叶片薄壳结构上的不足,并对有限元方法（finite element method, FEM）在叶片结构分析中的应用进展进行了介绍;在载荷评估方面,介绍了其对叶片和整机其它部件的影响,阐述了载荷预估方面的工作进展．然后,通过分析3个关键环节之间的相互关系,得到如下结论:建立气动、结构和载荷相协调的叶片优化设计体系,才能真正满足高效低成本的需要．最后,指明了需要进一步研究的主要方向,即高效低载翼型研究,结构非线性有限元分析,气动-结构耦合研究,设计标准制定．最终目标是建立适合中国风资源特点的叶片研发体系,推动我国风电产业发展.     

Failure Analysis on Shell-like Composite Laminates Using the Puck Criteria

Due to their high specific strength and stiffness, carbon fibre-reinforced polymers (CFRP) are widely used in several fields of engineering, e.g. aerospace engineering. A new design scheme aims for the exploitation of material reserves. Since design is always linked to expensive experimental investigations, reliable simulation procedures are required to lower the related costs. In terms of detecting ply failure several criteria have been proposed. In this work those of Hashin [1] and Puck [2] are applied to several numerical models and compared to experimental results [3]. (© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

对称复合材料层合板弯曲的三维数值分析

本文采用三维各向异性有限单元模拟纯弯曲载荷下的复合材料层合板，给出了应力、应变沿厚度方向的变化规律。分析结果表明，在斜交对称铺层层合板的中心区域（远离加载端和自由边的区域），板的层间粘接界面附近，有根强的应力集中现象，可称之为层间效应。层间界面处力学性质的突变导致了层间应力的产生，并使层合板处于三向应力状态。三维数值模型给出的应变分布不同于基于Ｋｉｒｃｈｈｏｆｆ－Ｌｏｖｅ直法线假设的经典层合板理论给出的应变分布。     

多椭圆孔有限大复合材料层板的热弹性分析

本文利用各向异性体平面热传导，热弹性理论中的复势方法，以保角映射，Ｆａｂｅｒ级数展开以及最小二乘边界配置技术为工具，导出了内边界条件精确满足，外边界条件近似满足的多椭圆孔复合材料层板的热传导以及热弹性问题的级数解，详细探讨了层板大小，孔径，相对孔距，孔的设置方式，椭圆度以及层板的铺层比例诸参数的影响规律，得到了一些有益结论。     

复合材料层合板低速冲击后压缩的损伤累积模型

为了分析复合材料层合板低速冲击后的压缩性能,首先用三维动态有限元素法对两种层合板进行了低速冲击损伤模拟计算,以此作为冲击后压缩（CAI）层合板的初始损伤,然后用三维静态有限元对含损伤的层合板进行压缩破坏模拟和剩余强度计算,从而实现了层合板从冲击损伤到压缩破坏损伤全过程的模拟．结果表明,损伤投影面积和CAI强度的计算值与试验结果有较好的一致性．     

农村小型风力发电机的控制与并网仿真

设计了双馈风力发电机组的定子磁链矢量控制系统,构造了容量为9MW的风力发电系统;通过MATLAB软件,分别在变风速和恒定风速两种情况时,对风力发电系统并网进行仿真.仿真结果表明,利用矢量变换技术的控制方法,风力发电系统可以实现有功功率和无功功率的快速解耦并且动态响应快,跟随性能好.     

广义疲劳等寿命曲线与二维疲劳极限概率分布

基于传统等寿命曲线,提出了广义疲劳等寿命Sa-Sm曲线概念,并找出该曲线的普遍表达式;根据相关系数优化法建立了该表达式的参数估计公式,并给出了具有可靠度p的广义疲劳等寿命P-Sa-Sm曲线公式;以广义P-Sa-Sm曲线为基础,导出了二维疲劳极限概率分布;进行了3组不同应力均值下的LY11CZ铝合金材料的二维配对升降法试验,试验结果验证了广义疲劳等寿命Sa-Sm曲线的合理性和算法的拟合精度.     

Cost Optimized Design for the Local Wind Turbine Grid of an Onshore Wind Farm

Annals of Operations Research - This document analyses the problem of designing a minimum cost local wind turbine grid (or LWTG) for an onshore wind farm. The LWTG is responsible for adding up the...     

Modeling Matrix Cracking in Composite Laminates Under Thermo‐mechanical Loading

In this paper a theoretical approach is presented for analyzing the ply cracking in general symmetric laminates subjected to any combination of in‐plane mechanical loading and uniform temperature changes. The energy release rate for a ply cracking is explicitly expressed as a function of stiffness reduction parameters of the laminate before the ply cracking and after the ply cracking. Finally, the model is used to predict the thermomechanically cracking stress for the first‐ply‐cracking.     

The Boundary Finite Element Method for Stress Concentration Problems in Composite Laminates

The Boundary Finite Element Method is presented as a very efficient method for the analyses of stress concentration problems in laminates. Results for the free-edge stress field of symmetric cross-ply laminates show to be in very good agreement with comparative finite element analyses.