Pinpoint accurate adaptive structures for heliostats made from high performance concrete for central tower power plants

在spp1542的第二个资助期，申请人最近研究了“用于抛物线槽式发电厂的微增强UHPC轻变形优化外壳结构”。研究表明，高性能混凝土有望实现最精确和稳定的结构成员。到目前为止，导出了由风洞试验确定的具体作用效应和太阳能集热器的整体精度准则。此外，还建立了模块化有限元模型，该模型考虑了复杂结构的有效刚度，例如根据实验结果放置局部孔隙成形器。这些都是补充多层次优化与先验方差为基础的敏感性分析。最后，一个特定的混凝土已经组成，满足持久形状和抗拉强度的所有要求，以实现原型（3,2 x 2,2 m）。现在，太阳能行业的这些见解和强烈兴趣鼓励转移到类似的应用领域，即定日镜，设想以批量生产和工业精度制造。目标是进一步提高精度，从而建立自适应收集器形状，并扩大整个生产链。应通过预应力减少甚至避免常规加固。通过这种方式，可以实现广泛应用的低成本生产。其中，定日镜是太阳能收集器，能够双轴跟踪太阳，并将太阳辐射集中在太阳塔的中央接收器上。关于反射特性，与抛物线槽相比，必须达到高达十倍的精度。然而，自适应制造是必不可少的，因为定日镜的几何形状，更准确地说，它的抛物面，随着到焦点的距离而变宽。设想的是圆形外壳，外部支撑由相似形状的重复部分组成。为了与工业合作伙伴合作实现设备齐全且经过几何验证的全尺寸原型，必须先满足理论和基于生产的先决条件。关键是基于多尺度优化的结构设计，这种结构设计是可持续的，高度精确的，并且能够抵御几何和材料带来的不确定性。通过少量控制参数确定控制几何变化，并能够设计一个自适应和经济有效的精密模板，允许随后完成内表面。原型将采用周向预应力，并具有反射器以及与配备测量装置的子结构的成熟链接。预计壳体表面的有效厚度为2-3厘米（壳体和支架的平均厚度），高精度可达亚毫米范围。

In the second funding period of SPP 1542, the applicants recently work on "Light deformation-optimised shell structures made from micro-reinforced UHPC for parabolic trough power plants". The investigations revealed high-performance concrete being promising for utmost precise and stable structural members. So far, specific action effects, determined by wind tunnel testing and a holistic accuracy criterion for solar collectors were derived. Additionally modular FE-models were set-up, that respect an effective stiffness of complex structures e.g. by means of local void formers placed according to experimental results. These are complemented by multi-level optimisation with a priori variance-based sensitivity analysis. Finally a specific concrete has been composed matching all demands of persistent shape and tensile strength to realize a prototype (3,2 x 2,2 m). Now, these insights and strong interest from the solar industry encourage a transfer to similar fields of application namely heliostats, envisaged to be manufactured in serial production and industrial precision. The objectives are to further increase the accuracy, to establish adaptive collector shapes consequently and to augment the entire production chain. Conventional reinforcement shall be reduced or even avoided by pre-stressing. That way cost-efficient production for a wide range of applications can be achieved. Among these, heliostats are solar collectors able to biaxially track the sun and to focus solar irradiation on a central receiver at the solar tower. Regarding reflection properties up to tenfold precision has to be achieved compared to parabolic troughs. However, adaptive manufacturing is indispensable, since the heliostats geometry, more precisely its paraboloidal surface, widens with the distance to the focal point. Envisaged are circular shells with outer bracings composed from repeated segments of similar shape. In order to realise a fully equipped and geometrically verified full-scale prototype in cooperation with industrial partners, theoretical and production-based prerequisites must be met before. Key is a multi-scale optimisation-based structural design that is sustainable, highly accurate and robust against uncertainties arising from geometry and material. Governing geometric variations are identified by means of few control parameters and enable to design an adaptive and cost-effective precision formwork allowing for finishing inner surfaces subsequently. The prototype will be circumferentially pre-stressed and possesses reflectors as well as mature links to the substructure equipped with measuring devices. Expected is a shell surface with an effective thickness of 2-3 cm (average of shell and bracings) that is highly accurate up to the submillimetre range.