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

在SPP 1542的第二个资助期内，申请人最近致力于“由微增强UHPC制成的用于抛物槽式发电厂的轻型变形优化壳体结构”。调查显示，高性能混凝土有望成为最精确和稳定的结构构件。到目前为止，具体的行动效果，确定风洞测试和太阳能集热器的整体精度标准。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，例如通过根据实验结果放置的局部空隙形成器。这些都是由多层次优化与先验方差为基础的敏感性分析的补充。最后，一个特定的混凝土已经组成匹配的持久形状和抗拉强度的所有要求，实现原型（3.2 × 2.2米）。现在，这些见解和太阳能行业的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，从而建立适应性的收集器形状，并扩大整个生产链。应通过预应力减少甚至避免常规钢筋。通过这种方式，可以实现广泛应用的成本效益生产。其中，定日镜是能够双轴跟踪太阳并将太阳辐射聚焦在太阳能塔的中央接收器上的太阳能收集器。关于反射特性，与抛物线槽相比，必须实现高达十倍的精度。然而，自适应制造是必不可少的，因为定日镜的几何形状，更准确地说是其抛物面，随着到焦点的距离而变宽。设想的是圆形壳体，其外支撑由形状相似的重复段组成。为了与工业合作伙伴合作实现一个设备齐全并经过几何验证的全尺寸原型，必须满足理论和生产方面的先决条件。关键是基于多尺度优化的结构设计，可持续，高度准确，并能抵御几何形状和材料带来的不确定性。通过几个控制参数来识别控制几何变化，并能够设计出自适应且具有成本效益的精密模板，从而允许随后对内表面进行精加工。原型将在圆周上施加预应力，并具有反射器以及与配有测量装置的下部结构的成熟连接。预计炮弹表面的有效厚度为2-3厘米（炮弹和支撑的平均厚度），高度精确到亚毫米范围。

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.