超疏水表面微结构的减阻模型研究及其3D打印制备技术

While sea transportation is the major tool for the international trading, the resulting massive energy-consuming and air pollution need to be controlled. Therefore, ship drag reduction is of great importance. Among all the drag reduction techniques, the superhydrophobic drag reduction technique has been considered as a promising one, which is due to its attractive characteristics, such as large drag-reducing effects, high designability, and no need for extra energy input. To ensure the drag reduction produced by the superhydrophobic surfaces, the surface must be maintained in a nonwetted state and the effective slip length on the surface need to be large enough to influence the fluid surrounding the ship. The objectives of this proposal are to investigate the drag reduction model on the superhydrophobic microstructures and to fabricate superhydrophobic surfaces using three-dimensional (3D) printing. The proposal will include three parts. The aim of the first part is to test the overall feasibility of 3D printing on the fabrication of superhydrophobic surfaces. Laser-based 3D printing will be implemented to fabricate the superhydrophobic surfaces, and the shape fidelity of the printed surface microstructures will be investigated to prove the ability of 3D printing on the modification of the surface structural details. The aim of the second part is to develop a drag reduction model on the superhydrophobic surfaces based on the genetic algorithm. This model is expected to describe the relationship between the surface nonwetting stability and the geometric properties of the microstructures, and to predict the effective slip length on the surface with given structural design. The correctness of the model will be validated by experimental studies of the nonwetting stabilities and the effective slip lengths of printed surfaces. The aim of the last part is to validate the drag reduction model and the drag-reducing effects of the printed superhydrophobic surfaces on ship through ship model towing experiments. The superhydrophobic surfaces on the ship model will be classified and divided in to different parts according to a tailored design method based on the boundary conditions on the ship surface. Then, each part of superhydrophobic surfaces will be designed and optimized based on the drag reduction model. Ship model with properly attached superhydrophobic surfaces will be tested in a ship model towing tank to investigate the drag-reducing effects produced by the superhydrophobic surfaces. A standard measurement methodology for the drag-reducing effects produced by the superhydrophobic surfaces will be proposed based on this experimental study.

船舶运输在全球货物贸易中占据着主导地位，但是也带来了越来越严重的能源消耗和空气污染问题。因此，船舶的减阻降排意义重大，其中仿生超疏水表面减阻由于其减阻效果好、可设计性强以及不需要额外能量输入等优点而备受关注。实现船舶超疏水减阻的关键是在维持表面非浸润态稳定性的前提下，使表面有效滑移长度与船舶周围流体边界层厚度相当。本申请书针对船舶减阻的需求，研究超疏水表面微结构的减阻模型，并通过3D打印技术制备超疏水表面。首先，基于激光3D打印建立快速制备超疏水表面的方法，并验证方法对结构微观细节的调控能力。然后，根据遗传算法构建描述超疏水表面减阻能力的数学模型，基于该模型研究表面的非浸润稳定性、预测有效滑移长度，并进行小尺度的试验验证。最后，选择典型船型制作船模，根据船体表面压力分布的不同，基于裁剪法分片设计并布置超疏水表面，通过船模拖曳水池试验研究超疏水表面的减阻效果，并提出减阻测量的统一衡准。

针对船舶减阻的需求，本项目展开了超疏水表面微结构的减阻模型及其3D打印制备技术的研究，主要包含以下研究内容：1）超疏水表面微结构的3D打印制备技术研究；2）基于超疏水表面微结构形貌参数的疏水模型研究；和3）超疏水表面微结构的减阻效果测量技术与减阻模型研究。为了实现对生物界中柔性疏水表面的仿生，本研究的主要研究对象是含柔性表面微结构的超疏水表面。首先，通过综合论证分析，选择了基于层成型的数字光投影3D打印技术来进行高效、高精度的含微结构阵列表面的打印，并搭建了相应的3D打印系统。通过试验证明了该3D打印系统在制备含柔性微结构阵列表面和复杂几何构型结构时的可行性，并重点研究建立了通过该系统进行结构打印时的材料可打印性研究流程。接着，通过数值模拟和试验研究相结合的方式，探讨了表面微结构形貌与疏水程度之间的关系，建立表面微结构形貌参数的疏水模型。该模型表明，当微结构单元为刚性时，其单元的宽高比越小时，对应含微结构阵列表面的疏水性能越好。当微结构单元为柔性时，其疏水特性会随着微柱本身变形量的变化而变化，当微柱刚度越小和微柱高度越小时，表面越容易被浸润而导致疏水性下降。通过相应的表面处理，还可以实现表面疏水/亲水性的调节。最后，通过综合论证分析，选择了基于表面流体切应力测量的表面减阻效果衡量方法，并搭建了基于旋转流变仪的减阻效果测量平台。通过试验研究探讨了超疏水表面微结构的减阻效果与表面形貌之间的关系。研究表明，含刚性微结构单元的表面比含柔性微结构单元的表面的减阻效果好。对于含柔性微结构单元的表面而言，其微结构单元的直径越大、高度越低、间距越大，表面的减阻效果越好。在高剪切速率下，由于柔性微结构单元的变形，会导致减阻效果的降低甚至失效。本文的研究在实验室尺度证明了超疏水表面减阻的可行性，为无能耗船舶表面减阻提供了一种可供参考的新思路。