Nonlinear vibrations and stability of shells and panels in presence of fluid and flow

随着材料科学和工程的不断进步以及对改进设计、安全和能效要求的不断提高，需要建立和验证新的非线性理论来描述薄壁结构与周围流体之间的相互作用。该研究考虑了考虑流固耦合作用的薄壁结构的非线性振动和动力稳定性研究。传统的层合复合材料和功能梯度材料的薄壳、板和曲板(具有单曲率或双曲率)在许多工程应用中都可以找到，例如在飞机、航天器、火箭、汽车、计算机磁盘(CD)、DVD、硬盘、潜艇、船只、储罐和建筑物的屋顶。贝壳结构也是许多生物系统的一部分，例如人体中发现的肺通道和静脉。这项研究的目的有两个：(I)用实验、理论和数值研究方面的开创性创新来研究开放问题，以及(Ii)使用统一的方法来合并过去分开进行但存在许多共同问题的研究分支。这项研究还旨在改进现有的壳体非线性力学理论模型，例如通过建立一个新的考虑三阶剪切变形和转动惯量的一致的非线性壳体理论，这对先进材料尤为重要。非线性分析将(I)通过开发基于降阶模型的创新数值代码进行数值计算，以及(Ii)通过实验开发复杂的测量系统和程序，包括对放置在水和风洞中的试件进行激光多普勒测振仪，以便验证数值代码、研究复杂的动力学和评估几何缺陷的影响。具体地说，实验过程还将涉及(A)突发随机激励或冲击激励的实验模态分析；以及(B)使用反馈控制的阶跃激励来识别非线性响应，改变激励频率以诱导滞后和跳跃。

The continuous advancement of material science and engineering along with the increasing demand for improved design, safety and energy efficiency requirements necessitates the establishment and verification of new nonlinear theories to describe the interaction between thin-walled structures and the surrounding fluid. The proposed research considers the study of nonlinear vibrations and dynamic stability of thin-walled structures with fluid-structure interaction. Thin shells, plates and curved panels (with single or double curvature) of traditional, laminated composite and functionally graded materials can be found in many engineering applications e.g. in aircraft, spacecraft, rockets, cars, computer disks (CD), DVD, hard-disks, submarines, boats, storage tanks and roof of buildings. Shell structures are also part of many biological systems such as the pulmonary passage and veins found in the human body. The objective of the research is twofold: (i) to develop a study approaching open problems with ground-breaking innovations in experimental, theoretical and numerical investigation, and (ii) to use an unifying approach to merge branches of research that have proceeded separately in the past but that present many common problems. This research also aims to improve existing theoretical models for the nonlinear mechanics of shells, e.g. by constructing a new consistent nonlinear shell theory including third-order shear deformation and rotary inertia, which is particularly important for advanced materials. The nonlinear analysis will be (i) performed numerically, by developing innovative numerical codes based on reduced-order models and, (ii) experimentally, by developing a sophisticated measuring system and procedure, including a laser Doppler vibrometer used on specimens placed in water and wind tunnels, in order to validate the numerical codes, study the complex dynamics and evaluate the effect of geometric imperfections. Specifically, the experimental procedure will also involve (a) experimental modal analysis with burst random or impact excitation; and (b) identification of the nonlinear response using feedback controlled step-sine excitation, altering the excitation frequency to induce hysteresis and jumps.