【作者】 张营川；

【导师】 赵德有； 马骏；

【作者基本信息】 大连理工大学 ， 船舶与海洋结构物设计制造， 2011， 博士

【摘要】 结构旋涡发放问题通常指的是静止结构的涡激共振现象,即对于来流中的静止结构,流体会在结构后方产生交替的旋涡发放,形成垂直来流方向的涡激升力和顺来流方向的阻力,当旋涡发放频率接近结构固有频率时,引起涡激共振,涡激力的长期作用会造成结构的疲劳损伤。在船舶工程领域,相关研究热点主要是筒型的深海立管及平台桩腿在流载荷作用下的涡激共振响应研究,以及筒型的船舶桅杆在风载荷作用下的涡激共振响应研究；实际上,结构旋涡发放问题还应该包含运动结构的涡激力推进现象,即对于来流中原本静止的结构,在被施加以垂直来流方向的往复运动时,由于结构运动的影响,旋涡发放产生的涡激升力和阻力的方向与来流方向形成一定的夹角,特定的条件下它们在来流方向上的合力会推动结构逆流前进。在船舶工程领域,采用翼型结构以获得更大的涡激力作为推力,相关的研究热点主要是仿生鱼推进器、单翼推进器以及双翼地效推进器的原理和应用。综上所述,本文选取有代表性的筒型结构和翼型结构作为具体的研究对象,通过对它们的旋涡发放过程进行数值仿真研究,尝试把结构的旋涡发放问题表述完整,将之划分为两个部分：即静止结构在来流中的旋涡发放问题和运动结构在来流中的旋涡发放问题,它们都隶属于结构旋涡发放这一大的概念之中。本文研究工作的具体内容和主要结论为：在筒型结构旋涡发放问题的研究方面,引入精细积分方法代替传统的Newmark-β方法,对船舶筒型桅杆在空气中的涡激共振响应进行了数值求解,这部分内容反应了静止结构旋涡发放现象的危害性。1.改进了风载荷作用下筒型结构涡激共振方程的数值求解方法,并拓展了精细积分算法的工程应用领域。遵循精细积分方法的基本思想,独自推导了外激励四次多项式拟合时的精细积分递推公式；在精细积分算法中,对比和分析了不同参考文献提供的外激励多项式拟合系数的求解方法,以及它们各自的特点和应用范围；以11万吨成品油船试航时的实测数据为基础,编写了Newmark-β法、精细积分线性算法、精细积分二次多项式算法、精细积分四次多项式算法和精细积分简谐算法的matlab程序,将上述数值方法的计算结果和实测结果对比后,绘制了精度对比曲线。基于数值方法的计算稳定性和计算精度,在船舶筒型桅杆的涡激共振响应求解中,确定精细积分简谐算法是最佳的求解方法。2.计算得到了船舶筒型桅杆在覆盖一定厚度冰层情况下的风致涡激共振响应,并分析了涡激共振响应与裹冰因素的具体关系。在桅杆裹冰状态下,涡激共振响应随裹冰厚度增加而增大；当裹冰的厚度相同时,裹冰的密度越小,船舶桅杆结构涡激共振响应越大；裹冰后桅杆阻尼、质量和迎风面积等因素会发生改变,具体的计算结果说明,迎风面积的增加是涡激共振响应增加的主要原因。在翼型结构旋涡发放问题的研究方面,引入相容拉格朗日—欧拉方法代替传统的拉格朗日动网格方法,对翼型结构在水中的旋涡发放现象进行了数值计算。由于问题的复杂性,选取了两个典型的算例,其中,双翼地效推进器的翼型结构在水中利用涡激力推动自身前进,这反应了运动结构的旋涡发放现象可以被合理利用；而螺旋桨推进器的桨叶结构也存在旋涡发放现象,当桨叶随边发放的旋涡频率与桨叶的固有频率接近时,桨叶会产生剧烈振动并发出噪音,这称为螺旋桨“唱音”问题。在本文中,由于计算能力的限制,只研究了一个桨叶的旋涡发放现象,并将桨叶根部进行了刚固处理,前方施加来流模拟桨叶转动时与水的相对运动,所以这部分研究内容实际上也体现了静止结构旋涡发放现象的危害性。1.系统地总结和对比了流固耦合计算中常用的数值方法,阐述了相容拉格朗日—欧拉方法在模型建立和流体运动描述方面的优势。2.研究双翼地效推进器的翼型结构的弹性模量、材料类型和结构变形对仿真结果的影响。针对两组弹性双翼地效推进器,其中一组选用不同的有机材料,而另一组弹性模量层次性递减,分别对其进行推进性能和结构响应数值计算。最终结果表明,随着翼型结构的弹性模量降低,双翼的推力系数和推进效率呈抛物线分布,在一定的弹性模量区间有最佳推进性能。选择合适的有机材料代替钢铁材料,能够有效地提高双翼推进器的性能；双翼局部的应力集中大小随着翼型结构的弹性模量降低而减小,变形较大的翼型结构,其最大应力值较小。3.对螺旋桨桨叶的翼型结构和周围流体建立了有限元模型,通过适当的简化,观察到了桨叶后方旋涡的破裂与相互作用现象；计算得到了桨叶的结构响应,比较分析了桨叶叶面不同位置的响应差别及形成原因。更多还原

【Abstract】 Vortex shedding phenomenon is usually harmful. For example, like a cylinder in fluid, the vortices will shed alternating behind the cylinder when fluid flows. It can make the cylinder vibrate and generate the lift force in transverse direction and the drag fore in flow direction. The VIV (Vortex-induced vibration) causes fatigue damage to the structures and affects the duability, leading great difficulties to the maintenance. In ship engineering, related researches include the VIV of barrel-shaped mast under wind load and the VIV of riser under stream load. However, there is also a bright side in vortex shedding phenomenon. For instance, like a foil in horizontal flow, directions of lift and drag forces are changed along with directions of structure motion. Lift and drag forces can create propulsive force in horizontal direction under proper condition. In ship engineering, related researches are the applications of single foil oscillating propulsor and the WIG (Wing-In-Ground) thrusters. Therefore, based on numerical simulation, this paper studied vortex shedding phenomenon of barrel-shaped and foil-shaped structures, which revealed different features of static structure in flow and moving structure in flow.The main contents and conclusions are as follows:On one hand, this paper studied the VIV of a barrel-shaped mast, which displayed the drawback from vortex shedding phenomenon of static structure. And, HPD (High Precision Direct) integration scheme was selected into sloving the structural responses.1. This paper established the fluid-structure coupling model of VIV by wind when Reynolds number was in subcritical area. The structural responses of VIV were calculated under several numerical methods, such as Newmark-β, HPD-L (High Precision Direct integration scheme-Linear form) and HPD-S (High Precision Direct integration scheme-Sinusoidal form), etc.. According to the measured value, the accuracy curves were given to show the best method, which was more stable and accurate than others.2. Furthermore, assuming barrel-shaped mast covered with ice, this paper revealed ice influnces to structural responses of VIV. The increase of ice thickness or the decrease of ice density can enlarge structural responses. The results also supported that the change of structural responses was mainly decided by the front face area. On the other hand, this paper not only studied the vortex-induced force propulsion of the WIG thrusters’foil-shaped wing, but also investigated the VIV of a fixed propeller’s foil-shaped blade. The former expressed the advantage from vortex shedding phenomenon of moving structure, and the latter represented the disadvantage from vortex shedding phenomenon of static structure. An advanced fluid-structure interaction approach CLE (Compatible Lagrangian-Eulerian) was adopted into above numerical simulations.1. Based on the comparison of CLE and single Lagrangian, it was confirmed that CLE was more efficient in building model and more proper in describing fluid flow.2. Assuming that different WIG thrusters have different elastic ratios or material types, both hydrodynamic data and structural dynamic responses were showed after the numerical simulations. The thrust force coefficient CT and the propulsive efficientηwere in parabolic distribution under elastic ratio decrease. And, the maximum structural stress reduced along with elastic ratio cutting down. Moreover, the results also agreed that proper organic foil can provide better performance and lower structural stress than steel foil.3. The fluid-blade interaction model was built for studing vortex shedding phenomenon and structural responses of propeller’s blade. It displayed the vortex broken positions due to irregular shape of blade. And, the interaction among vortexes decreased the vortex pressure and disordered the whole flow field. Finally, it calculated and showed structural responses of blade different parts.更多还原