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A small perturbation based optimization approach for the frequency placement of high aspect ratio wings.

机译：一种基于小扰动的优化方法，用于高纵横比机翼的频率布置。

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摘要

Design denotes the transformation of an identified need to its physical embodiment in a traditionally iterative approach of trial and error. Conceptual design plays a prominent role but an almost infinite number of possible solutions at the outset of design necessitates fast evaluations. The corresponding practice of empirical equations and low fidelity analyses becomes obsolete in the light of novel concepts. Ever increasing system complexity and resource scarcity mandate new approaches to adequately capture system characteristics.;Contemporary concerns in atmospheric science and homeland security created an operational need for unconventional configurations. Unmanned long endurance flight at high altitudes offers a unique showcase for the exploration of new design spaces and the incidental deficit of conceptual modeling and simulation capabilities. Structural and aerodynamic performance requirements necessitate light weight materials and high aspect ratio wings resulting in distinct structural and aeroelastic response characteristics that stand in close correlation with natural vibration modes.;The present research effort evolves around the development of an efficient and accurate optimization algorithm for high aspect ratio wings subject to natural frequency constraints. Foundational corner stones are beam dimensional reduction and modal perturbation redesign. Local and global analyses inherent to the former suggest corresponding levels of local and global optimization. The present approach departs from this suggestion. It introduces local level surrogate models to capacitate a methodology that consists of multi level analyses feeding into a single level optimization. The innovative heart of the new algorithm originates in small perturbation theory. A sequence of small perturbation solutions allows the optimizer to make incremental movements within the design space. It enables a directed search that is free of costly gradients. System matrices are decomposed based on a Timoshenko stiffness effect separation. The formulation of respective linear changes falls back on surrogate models that approximate cross sectional properties. Corresponding functional responses are readily available. Their direct use by the small perturbation based optimizer ensures constitutive laws and eliminates a previously necessary optimization at the local level. The scope of the present work is derived from an existing configuration such as a conceptual baseline or a prototype that experiences aeroelastic instabilities. Due to the lack of respective design studies in the traditional design process it is not uncommon for an initial wing design to have such stability problems. The developed optimization scheme allows the effective redesign of high aspect ratio wings subject to natural frequency objectives. Its successful application is demonstrated by three separate optimization studies.;The implementation results of all three studies confirm that the gradient liberation of the new methodology brings about great computational savings. A generic wing study is used to indicate the connection between the proposed methodology and the aeroelastic stability problems outlined in the motivation. It is also used to illustrate an important practical aspect of structural redesign, i.e., a minimum departure from the existing baseline configuration. The proposed optimization scheme is naturally conducive to this practical aspect by using a minimum change optimization criterion. However, only an elemental formulation truly enables a minimum change solution. It accounts for the spanwise significance of a structural modification to the mode of interest. This idea of localized reinforcement greatly benefits the practical realization of structural redesign efforts.;The implementation results also highlight the fundamental limitation of the proposed methodology. The exclusive consideration of mass and stiffness effects on modal response characteristics disregards other disciplinary problems such as allowable stresses or buckling loads. Both are of central importance to the structural integrity of an aircraft but are currently not accounted for in the proposed optimization scheme. The concluding discussion thus outlines the need for respective constraints and/or additional analyses to capture all requirements necessary for a comprehensive structural redesign study.
机译：设计表示采用传统的反复试验和反复尝试的方法，将已确定的需求转换为其物理实施方式。概念设计起着重要作用，但是在设计之初，几乎无限的可能解决方案需要快速评估。根据新颖的概念，经验公式和低保真度分析的相应实践变得过时了。日益增加的系统复杂性和资源稀缺性要求采用新方法来充分捕获系统特征。高空无人长航程飞行为探索新的设计空间以及概念建模和仿真功能的附带缺陷提供了独特的展示。结构和空气动力性能要求使轻质材料和高纵横比的机翼成为必需，从而产生与自然振动模式密切相关的独特的结构和空气弹性响应特性。;本研究工作围绕着开发高效，准确的高强度优化算法而展开。宽高比机翼受自然频率限制。基础角石是光束尺寸减小和模态扰动重新设计。前者固有的本地和全局分析建议了本地和全局优化的相应级别。本方法偏离了该建议。它引入了本地级别的代理模型，以充实一种方法，该方法包括将多级分析输入到单级优化中。新算法的创新核心源于小扰动理论。一系列小扰动解决方案使优化器可以在设计空间内进行增量运动。它可以实现无代价梯度的定向搜索。基于Timoshenko刚度效应分离将系统矩阵分解。各个线性变化的公式依赖于近似横截面特性的替代模型。相应的功能响应很容易获得。基于小型扰动的优化器直接使用它们可确保本构定律，并消除了以前在本地级别进行的必要优化。本工作的范围是从现有配置中得出的，例如概念基线或经历气动弹性不稳定性的原型。由于在传统设计过程中缺乏各自的设计研究，因此初始机翼设计经常遇到这种稳定性问题。所开发的优化方案可以有效地重新设计符合自然频率目标的高长宽比机翼。通过三项单独的优化研究证明了其成功的应用。所有三项研究的实施结果证实，新方法的梯度解放带来了可观的计算节省。通用机翼研究用于表明所提出的方法与动机中概述的气动弹性稳定性问题之间的联系。它还用于说明结构重新设计的重要实践方面，即与现有基准配置的最小偏差。通过使用最小变化优化准则，所提出的优化方案自然有益于该实践方面。但是，只有基本的配方才能真正实现最小的变化解决方案。它说明了对感兴趣模式进行结构修改的跨度意义。这种局部加固的思想极大地有益于结构重新设计工作的实际实现。实施结果也凸显了所提出方法的基本局限性。质量和刚度对模态响应特性的唯一影响忽略了其他学科问题，例如许用应力或屈曲载荷。两者对于飞机的结构完整性都至关重要，但目前并未在建议的优化方案中予以考虑。因此，结论性讨论概述了对各个约束条件和/或其他分析的需求，以捕获全面的结构重新设计研究所需的所有要求。

著录项

  • 作者

    Goltsch, Mandy.;

  • 作者单位

    Georgia Institute of Technology.;

  • 授予单位 Georgia Institute of Technology.;
  • 学科 Engineering Aerospace.
  • 学位 Ph.D.
  • 年度 2009
  • 页码 241 p.
  • 总页数 241
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 航空、航天技术的研究与探索;
  • 关键词

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