大变形复合材料柔性梁静,动特性的试验研究

本文对两种铺层的复合材料柔性梁进行了静、动特性的试验研究，重点研究了挠度、结构耦合、梁的根部安装角等对变形、固有频率的影响。得出的结论有助于直升机旋翼桨叶的设计和发展，并且验证了大挠度复合材料柔性梁的分析模型     

复合材料水翼水动力与结构强度特性数值研究

针对复合材料水翼存在的流固耦合求解问题,结合其自身特有属性,对复合材料水翼结构变形特性进行了数值仿真计算研究.研究建立了复合材料水翼流固耦合数值计算模型,并将数值计算结果与Zarruk等的实验结果进行对比,验证模型的正确性,得出复合材料水翼尖端扭转角随雷诺数的增加而增加的研究结论.基于数值计算模型,系统地研究了不同铺层角对复合材料水翼水动力特性及强度特性的影响,结果表明:不同铺层角复合材料水翼的尖端扭转角,随铺层角的增大而减小,而其尖端位移量随铺层角的增大先减小后增大.为了削弱工程常数的影响对复合材料水翼变形的影响,研究提出了无量纲扭转角和无量纲位移量,进一步探究复合材料水翼结构的弯扭耦合作用对其变形特性的影响.最后利用蔡-吴失效准则进行复合材料水翼强度特性的判断和分析,结果表明:不同铺层角复合材料水翼的蔡-吴系数,随铺层角的增大呈现先减小后增大的趋势,其中0°铺层时的复合材料水翼蔡-吴系数最小,50°铺层时的复合材料水翼的蔡-吴系数最大.     

复合材料水翼水动力与结构强度特性数值研究

针对复合材料水翼存在的流固耦合求解问题,结合其自身特有属性,对复合材料水翼结构变形特性进行了数值仿真计算研究.研究建立了复合材料水翼流固耦合数值计算模型,并将数值计算结果与Zarruk等的实验结果进行对比,验证模型的正确性,得出复合材料水翼尖端扭转角随雷诺数的增加而增加的研究结论.基于数值计算模型,系统地研究了不同铺层角对复合材料水翼水动力特性及强度特性的影响,结果表明:不同铺层角复合材料水翼的尖端扭转角,随铺层角的增大而减小,而其尖端位移量随铺层角的增大先减小后增大.为了削弱工程常数的影响对复合材料水翼变形的影响,研究提出了无量纲扭转角和无量纲位移量,进一步探究复合材料水翼结构的弯扭耦合作用对其变形特性的影响.最后利用蔡$\!$-$\!$-$\!$吴失效准则进行复合材料水翼强度特性的判断和分析,结果表明:不同铺层角复合材料水翼的蔡$\!$-$\!$-$\!$吴系数,随铺层角的增大呈现先减小后增大的趋势,其中0$^\circ$铺层时的复合材料水翼蔡$\!$-$\!$-$\!$吴系数最小,50$^\circ$铺层时的复合材料水翼的蔡$\!$-$\!$-$\!$吴系数最大.      

考虑强度与固化变形的复合材料加筋壁板铺层优化方法

加筋壁板是复合材料飞行器主承力构件的主要结构形式,通过复合材料铺层参数设计可以有效优化壁板的强度,但铺层参数的变化也会影响壁板的固化变形.因此,复合材料加筋壁板铺层设计过程中需要综合考虑整体强度和固化变形.本文针对复合材料加筋壁板结构,建立了失效分析模型和固化变形分析模型;基于实验设计方法、NSGA-Ⅱ遗传算法以及上述分析模型,建立了综合考虑强度与固化变形的加筋壁板铺层优化方法.优化结果显示复合材料加筋壁板在强度提高的同时,固化变形显著降低.     

渐近均匀化理论预报缝纫复合材料弹性性能

基于缝纫复合材料的结构特征,假定其具有周期性细观结构.利用渐近均匀化方法并结合摄动技术建立一系列控制方程,考虑由于缝纫扰动造成的材料的非均匀分布,由此确定缝纫复合材料的宏观等效性能.已有的试验结果相比较,本文预报结果与试验吻合较好.研究发现,缝纫造成了层合板刚度的下降,在面内方向缝纫密度越大,刚度降低越明显.缝纫产生的纤维变形区的宽度增加对刚度有利,纤维变形区的长度对拉伸刚度影响不大.并对缝纫参数对缝合板性能的影响进行了预报,为实际工程问题提供了预测材料性能的方法.     

含椭圆孔的变角度复合材料层合板的屈曲性能研究

本文利用变角度复合材料的纤维方向角可沿平面位置任意连续变化的特点,提出在孔附近采用与孔同心的椭圆曲线作为纤维铺设路径的层合板铺层方案,以改善含椭圆孔的层合板的孔边应力集中,进而提高层合板的抗屈曲性能.主要研究内容有:利用ABAQUS软件分析本文提出的孔边特殊铺层方式下变角度复合材料层合板的面内应力分布及屈曲性能,通过与传统直线铺层方式以及线性变角度铺层方式进行比较,说明了本文提出的新铺层方式的优越性,并详细分析了椭圆孔的离心率、开孔尺寸及开孔方位对层合板的屈曲临界荷载的影响.研究结果可为含椭圆孔的变角度复合材料层合板的结构设计和优化提供一定的参考.     

形状记忆合金混杂复合材料薄壁梁主动变形模型

提出具有变形主动驱动作用的SMA纤维混杂复合材料单闭室薄壁截面梁的力-位移本构关系模型.基于变分渐近法导出具有SMA主动纤维的复合材料薄壁空心梁的二维截面刚度系数以及截面内力(矩)与位移(转角)关系方程,含SMA纤维层合板材料性能由混合率进行预测.基于Tanaka的SMA应力应变关系以及Lin的线性相变动力模型,导出了SMA诱发的轴力、扭矩与弯矩的数学表达式.由该文建立的具有拉伸-扭转-弯曲静变形耦合的一般公式出发,讨论周向均匀刚度配置以及周向反对称刚度配置特殊情形,并给出了简化的本构方程.在不考虑SMA纤维含量和温度变化的情况下,本文的模型可以退化为普通纤维复合材料单闭室薄壁截面梁的已有结果.通过数值计算揭示了SMA对弯曲-扭转静变形特性的作用规律,分析了SMA纤维含量、驱动温度和复合材料铺层角的影响.     

卫星用复合材料压力容器力学特性研究

为了研究航天复合材料压力容器内衬与复合材料双层壳体的力学特性,通过优化复合材料网格理论算法,针对钛合金内衬(TC4)/碳纤维(T1000GB)缠绕柱形复合材料压力容器进行了应力应变特性分析.以纤维预紧应力为自变量,研究其对内衬/纤维双层壳体在预紧压力、工作压力、验证压力和爆破压力下应力的影响,提出了优化设计的解析解法,指出内衬与复合层力学特性对容器性能的影响机理,为结构设计和同类产品设计提供了计算方法和理论指导.     

基于响应面法的纤维金属层合板抗弹性能优化设计

纤维金属层合板因其复合材料的各向异性和层合结构特征而具有较好的可设计性，开展金属纤维层合板的优化设计研究对其力学性能的增强和轻量化具有重要意义。为提高纤维金属层合板的抗弹性能，基于响应面分析法对纤维金属层合板的铺层方向和铺层厚度进行了优化设计。采用Box-Behnken方法进行方案设计，以纤维金属层合板各铺层相对厚度比为设计变量，以结构的比吸能为设计目标，根据设计的方案进行参数化建模获取样本点，在对设计样本进行方差分析和参数估计的基础上，建立了结构比吸能的响应面模型并验证了其精确度。采用遗传算法对响应面方程进行寻优分析，通过显式动力学计算程序ABAQUS/Explicit验证优化效果。最终，在最优的铺层方案下，层合板的质量减小了11.70%，能量吸收增加了19.40%，抗弹性能显著提升。     

基于铺层参数的铺层方式与纤维分布协同优化的层合板最大刚度设计

纤维增强复合材料层合板的弹性性质依赖于单层板的纤维含量(体分比)以及铺层方式(总层数、各单层的厚度与铺设方向)。本文研究在给定材料用量条件下层合板的最大刚度设计问题,采用铺层参数作为铺层方式的描述参数、以铺层参数和单层板纤维含量体分比在层合板面内的分布的描述参数为设计变量,以层合板的柔顺性最小为目标,建立了铺层方式和纤维分布协同优化的层合板最大刚度设计问题的提法和求解方法,给出了具有最大刚度的层合板最优铺层方式和纤维含量的分布规律的设计实例。     

Fluid–structure interaction analysis of flexible composite marine propellers

There is an increasing interest in the marine industry to use composites to improve the hydrodynamic and structural performance of naval structures. Composite materials have high strength-to-weight and stiffness-to-weight ratios, and the fiber orientations can be exploited to tailor the structural deformation to reduce the load and stress variations by automatically adjusting the shape of the structure. For marine propellers, the bending–twisting coupling characteristics of anisotropic composites can be exploited to passively tailor the blade rake, skew, and pitch distributions to improve propeller performance. To fully explore the advantages of composite marine propellers, a coupled boundary element (BEM) and finite element (FEM) approach is presented to study the fluid–structure interaction of flexible composite propellers in subcavitating and cavitating flows. An overview of the formulation for both the fluid and structural models is presented. Experimental validation studies are shown for two composite propellers tested at the Naval Surface Warfare Center (NSWCCD). The feasibility of passive hydroelastic tailoring of composite marine propellers is discussed.     

Performance-based design and analysis of flexible composite propulsors

Advanced composite propellers, turbines, and jet engines have become increasingly popular in part because of their ability to provide improved performance over traditional metallic rotors through exploitation of the intrinsic bend–twist coupling characteristics of anisotropic composite materials. While these performance improvements can be significant from a conceptual perspective, the load-dependent deformation responses of adaptive blades make the design of these structures highly non-trivial. Hence, it is necessary to understand and predict the dependence of the deformations on the geometry, material constitution, and fluid–structure interaction responses across the entire range of expected loading conditions.The objective of this work is to develop a probabilistic performance-based design and analysis methodology for flexible composite propulsors. To demonstrate the method, it is applied for the design and analysis of two (rigid) metallic and (flexible) composite propellers for a twin-shafted naval combatant craft. The probabilistic operational space is developed by considering the variation of vessel thrust requirements as a function of the vessel speed and wave conditions along with the probabilistic speed profiles. The performance of the metallic and composite propellers are compared and discussed. The implications of load-dependent deformations of the flexible composite propeller on the operating conditions and the resulting performance with respect to propeller efficiency, power demand, and fluid cavitation are presented for both spatially uniform and varying flows. While the proposed framework is demonstrated for marine propellers, the methodology can be generally applied for any marine, aerospace, or wind energy structure that must operate in a wide range of loading conditions over its expected life.     

On the use of bend–twist coupling in full-scale composite marine propellers for improving hydrodynamic performance

Marine propellers are designed to work for a particular operating condition. However, a propeller often requires to operate at different off-design conditions, when its hydrodynamic efficiency drops. In this paper, a comprehensive numerical study is presented on the use of bend–twist coupling of composite propeller blades for improving their hydrodynamic efficiency at off-design conditions. The analysis is carried out on a full-scale propeller of diameter 4.2 m, considering the complete viscous turbulent flow, as the loading and deformation of model propellers that have been typically studied in literature for this purpose cannot be extrapolated to a full-scale prototype propeller. The open water performance is estimated using the finite volume method employing the pressure based RANS equation for the steady, incompressible, turbulent flow. The deformation analysis is done using the finite element method based on the first order shear deformation theory for composite laminates. The fluid–structure interaction is incorporated in an iterative manner. The effect of laminate configurations on the maximum twist achieved in the blade is studied for four different composite materials. The numerical study reveals that, within the limits of material safety, the twist generated in the deformed propeller using commonly used composite materials is inadequate to create any noticeable change in the hydrodynamic efficiency. When the material failure is ignored, however, it is possible to generate sufficient deformation and twist that can cause appreciable improvement in the hydrodynamic performance.     

Utilization of bend–twist coupling for performance enhancement of composite marine propellers

Self-twisting composite marine propellers, when subject to hydrodynamic loading, will not only automatically bend but also twist due to passive bend–twist (BT) coupling characteristics of anisotropic composites. To exploit the BT coupling effects of self-twisting propellers, a two-level (material and geometry) design methodology is proposed, formulated, and implemented. The material design is formulated as a constrained, discrete, binary optimization problem, which is tackled using an enhanced genetic algorithm equipped with numerical and analytical tools as function evaluators. The geometry design is formulated as an inverse problem to determine the unloaded geometry, which is solved using an over-relaxed, nonlinear, iterative procedure. A sample design is provided to illustrate the design methodology, and the predicted performance is compared to that of a rigid propeller. The results show that the self-twisting propeller produced the same performance as the rigid propeller at the design flow condition, and it produced better performance than the rigid propeller at off-design flow conditions, including behind a spatially varying wake.     

Computation of hydrodynamic mass and damping coefficients for a cavitating marine propeller flow using a panel method

The present paper deals with the numerical calculation of hydrodynamic mass and damping coefficients under consideration of unsteady sheet cavitation on marine propeller flows. In the first part of the paper, the mathematical and numerical background behind the numerical method is introduced. The numerical calculations carried out in this work are based on a low-order panel method. Panel methods belong to the class of collocation techniques and are applied to obtain a numerical solution of a potential flow based system of boundary integral equations. They are suitable for the present application because of their short computation time which makes them applicable in the design process of marine propellers.Additionally, two different approaches for the determination of hydrodynamic masses and damping are introduced in this work. The hydrodynamic masses and damping are important in studies of the ship motion in seaway and in the analysis of vibrations of a vessel and its appendages. The developed approaches are applied on a propeller flow in heave motion. Hereby, the calculations are performed for a non-rotating and rotating propeller under non-cavitating and cavitating conditions. The results obtained from the simulations are discussed in detail and an outlook is given.     

螺旋桨梢涡不稳定性机理与演化模型研究

螺旋桨尾流场的涡流特性是一个基础但又十分复杂的流体力学问题, 它的复杂性源于其蕴含复杂的漩涡系统, 且该漩涡系统会在高速的剪切层流动中不断演化, 其流体动力学行为, 如由稳定态演变为不稳定态的机理以及复杂工况环境中的流动现象, 一直是流体力学领域的难点和备受关注的热点问题. 从工程应用的角度看, 桨后梢涡的演化特性与船舶结构物的宏观特性直接相关, 更好地理解多工况下螺旋桨尾流的动力学特性, 将有助于改善与振动、噪声以及结构问题等相关的推进器性能, 对综合性能优良的下一代螺旋桨的设计和优化有着重要的现实意义. 本文基于延迟分离涡模拟、大涡模拟和无湍流模型模拟方法以及粒子图像测速流场测试分别开展了螺旋桨尾流动力学特性的数值与试验研究, 对螺旋桨尾流不稳定性的触发机理进行了揭示. 基于均匀来流中螺旋桨梢涡的演化机理, 提出了螺旋桨梢涡演化模型. 该模型能够较为准确地模拟螺旋桨梢涡的演化过程, 预测螺旋桨梢涡融合的时间和位置, 对螺旋桨流噪声预报和控制以及性能优良的螺旋桨设计具有重要意义.      

Cavitation Research and Ship Propeller Design

The role of cavitation research in the design of ship propellers and the influence of research on propeller design is reviewed. The historical development of research on bubble cavitation is an example of a lack of communication between research and design. Research on sheet cavitation is starting now and simplifications such as two dimensional cavitation are being made. It is argued from observations on propellers that the use of two-dimensional cavitaties is not a proper simplification to investigate sheet cavitation. An illustration is also given of the gap between the assessment of the risk of erosion on propeller models and research on erosion. Finally, the simplifications of tip vortex inception and the problems of the inception speed of propellers are discussed.     

Mean velocity and moments of turbulent velocity fluctuations in the wake of a model ship propulsor

Pod drives are modern outboard ship propulsion systems with a motor encapsulated in a watertight pod, whose shaft is connected directly to one or two propellers. The whole unit hangs from the stern of the ship and rotates azimuthally, thus providing thrust and steering without the need of a rudder. Force/momentum and phase-resolved laser Doppler anemometry (LDA) measurements were performed for in line co-rotating and contra-rotating propellers pod drive models. The measurements permitted to characterize these ship propulsion systems in terms of their hydrodynamic characteristics. The torque delivered to the propellers and the thrust of the system were measured for different operation conditions of the propellers. These measurements lead to the hydrodynamic optimization of the ship propulsion system. The parameters under focus revealed the influence of distance between propeller planes, propeller frequency of rotation ratio and type of propellers (co- or contra-rotating) on the overall efficiency of the system. Two of the ship propulsion systems under consideration were chosen, based on their hydrodynamic characteristics, for a detailed study of the swirling wake flow by means of laser Doppler anemometry. A two-component laser Doppler system was employed for the velocity measurements. A light barrier mounted on the axle of the rear propeller motor supplied a TTL signal to mark the beginning of each period, thus providing angle information for the LDA measurements. Measurements were conducted for four axial positions in the slipstream of the pod drive models. The results show that the wake of contra-rotating propeller is more homogeneous than when they co-rotate. In agreement with the results of the force/momentum measurements and with hypotheses put forward in the literature (see e.g. Poehls in Entwurfsgrundlagen für Schraubenpropeller, 1984; Schneekluth in Hydromechanik zum Schiffsentwurf, 1988; Breslin and Andersen in Hydrodynamics of ship propellers, 1996; Schneekluth and Bertram in Ship design for efficiency and economy, 1998), the co-rotating propellers model showed a much stronger swirl in the wake of the propulsor. The anisotropy of turbulence was analyzed using the anisotropy tensor introduced by Lumley and Newman (J Fluid Mech 82(1):161–178, 1977). The invariants of the anisotropy tensor of the wake flow were computed and were plotted in the Lumley–Newman-diagram. These measurements revealed that the anisotropy tensor in the wake of ship propellers is located near to the borders of the invariant map, showing a large degree of anisotropy. They will be presented and will be discussed with respect to applications of turbulence models to predict swirling flows.     

仿鱼尾推进器在动力航向控制上的应用

传统的螺旋桨推进器工作噪声大,效率低,而仿鱼尾推进器技术有望改进这些不足,从而提出利用仿鱼尾推进动力定位的思想。通过对鱼尾推进模式和动力学的研究,设计出了最佳参数的仿鱼尾推进器。首先根据力的分解和拉格朗日动力学方程,计算出了前向推进力和各关节转矩,为课题研究奠定了力学基础;在动力定位控制研究中,通过惯性测量装置获取运动信息,采用卡尔曼滤波的数据融合算法实现姿态信息的解算,建立x方向上的空间运动模型并使用模糊自适应PID算法和传统PID算法仿真模拟。系统稳定性分析显示,PID控制存在14%的超调,而模糊自适应PID控制算法没有出现超调,两者的稳定时间均在240 s左右。最后由仿真分析验证模糊自适应PID算法更适合动力定位控制。     

基于ANSYS ACP的复合材料螺旋桨流固耦合计算方法

针对复合材料螺旋桨的流固耦合水弹性行为,为形成双向耦合的集成平台,对复合材料螺旋桨进行了流固耦合计算方法的研究。在ANSYS Workbench平台中,采用ACP模块对复合材料螺旋桨的建模进行了分析,介绍了复合材料螺旋桨的建模流程、流体计算模型和固体计算模型。通过静态加载试验对复合材料螺旋桨建模方法的可靠性进行了验证,计算值与试验值的偏差在5.1%以内,且反映出材料的各向异性。通过空泡水洞模型试验对复合材料螺旋桨流固耦合敞水性能计算方法的精确度进行了验证,在转速为12.7r/s和25r/s两个工况下计算的推力和扭矩与试验值吻合较好。验证了基于ANSYS ACP的复合材料螺旋桨稳态流固耦合计算方法合理可行,为复合材料螺旋桨的流固耦合振动特性分析提供了参考。