仿鲨鱼皮减阻微沟槽滚压复制技术研究

发布时间：2018-08-16 13:24

【摘要】：目前,随着能源问题日益严重,减阻技术已经成为节约能源的一项新技术,模仿鲨鱼的盾甲鳞结构来实现减阻也成为减阻研究的一个热点。限于鲨鱼皮结构复杂、复制困难、制造精度低、生产成本高的缺点,大面积复制出与真实鲨鱼相似且具有较佳减阻效果的仿鲨鱼皮微沟槽结构仍是尚待解决的难题和挑战。本文针对这一问题,展开如下研究：首先,根据真实鲨鱼皮微沟槽结构,简化得到仿鲨鱼皮微沟槽,并对微沟槽的结构尺寸进行了优化,继而对优化后的微沟槽进行减阻分析,结果表明：仿鲨鱼皮微沟槽表面具有明显的减阻效果,沟槽减阻的主要原因是微沟槽附近流体流动平缓以及微沟槽底部二次涡的存在。其次,根据疏水基本理论模型,结合微沟槽的结构特征建立了针对仿鲨鱼皮微沟槽结构的Cassie修正型方程；实验所测得实际接触角与根据Cassie修正型方程计算得到的理论接触角之间的误差小于3%,证明了本文所提出Cassie修正方程的有效性和正确性。通过理论和实验对比,分析得出仿鲨鱼皮微沟槽的疏水机理：微沟槽所具有的类似鳞片的形状和微沟槽结构改变了固-液接触界面,使得固-液接触变为固-液、气-液复合接触,减弱了液体在微沟槽表面上的浸润性,使疏水性加强。然后,综合考虑仿鲨鱼皮微沟槽模具的尺寸大小、加工难易程度及加工成本,分别采用高速铣削和UV-LIGA两种加工方法得到具有仿鲨鱼皮微沟槽的滚压成型金属模具。加工结果表明：UV-LIGA加工得到的镍模具尺寸基本接近于真实鱼皮的沟槽尺寸,且结构轮廓清晰、铸层紧密。高速铣削加工得到的模具结构轮廓清晰,表面粗糙度较低。两种工艺方法得到的金属模具尺寸结构都已达到要求,满足实验的需要,验证了两种加工方法制作仿鲨鱼皮微沟槽金属模具的可行性。为保证仿鲨鱼皮微沟槽的减阻效果,UV-LIGA工艺得到的镍模具更适合作为滚压成型的金属模具。最后,介绍了滚压成型实验的实验原理、实验设备和实验材料,调整成型工艺参数,完成PVC和PET塑料表面仿鲨鱼皮微沟槽的滚压成型实验,研究了模具温度、滚筒速度、压力对成型结果的影响。结果表明：滚压成型是一个动态渐进的成型过程,在成型工艺实验中,模具温度、压力和滚筒速度是影响成型结果的重要因素,工艺过程适合在一个低模具温度、高压、低速的工作条件下进行,并且将模具贴附在滚筒表面不仅可以实现连续压印,而且可以获得较好的压印结果。
[Abstract]:At present, with the increasingly serious energy problem, drag reduction technology has become a new energy saving technology, imitation of shark shield scale structure to achieve drag reduction has become a hot spot in the research of drag reduction. Because shark skin has complex structure, difficult replication, low manufacturing precision and high production cost, it is still a difficult problem and challenge to replicate the micro-groove structure of shark skin similar to real shark and with better drag reduction effect. In this paper, the following researches are carried out: firstly, according to the structure of real shark skin microgrooves, the imitation shark skin micro-grooves are simplified, and the structural dimensions of the micro-grooves are optimized. Then the drag reduction analysis of the optimized microgrooves is carried out. The results show that the surface of the microgrooves in the shark skin has obvious drag reduction effect. The main reasons for the drag reduction are the smooth fluid flow near the microgrooves and the existence of secondary vortices at the bottom of the microgrooves. Secondly, according to the hydrophobic basic theory model and the structural characteristics of micro-grooves, a modified Cassie equation for shark skin microgrooves is established. The error between the actual contact angle measured by the experiment and the theoretical contact angle calculated according to the modified Cassie equation is less than 3, which proves the validity and correctness of the modified Cassie equation proposed in this paper. Through theoretical and experimental comparison, the hydrophobic mechanism of microgrooves in shark skin is analyzed. The shape of microgrooves and the structure of microgrooves change the solid-liquid contact interface, which makes the solid-liquid contact become solid-liquid. Gas-liquid composite contact weakens the wettability of liquid on the surface of microgrooves and strengthens hydrophobicity. Then, considering the size, processing difficulty and processing cost of the micro-grooves, the rolling forming metal dies with the micro-grooves of shark skin were obtained by high-speed milling and UV-LIGA, respectively. The results show that the size of nickel mold produced by UV-LIGA is close to that of the real fish skin, and the structure is clear and the cast layer is close. The molds obtained by high speed milling have clear profile and low surface roughness. The size and structure of the metal die obtained by the two methods have met the requirements of the experiment, and the feasibility of the two processing methods to make the metal mould with micro-grooves imitating shark skin has been verified. In order to ensure the drag reduction effect of the micro-grooves of shark skin, the nickel mould obtained by UV-LIGA process is more suitable for the metal mould of rolling molding. Finally, the experimental principle, experimental equipment and experimental materials of rolling molding experiment were introduced, and the processing parameters were adjusted to complete the rolling forming experiment of PVC and PET plastic surface imitation shark skin microgroove. The mold temperature and roller speed were studied. The influence of pressure on the forming result. The results show that the rolling process is a dynamic and progressive process. In the process experiment, the mold temperature, pressure and roller speed are the important factors that affect the forming result. The process is suitable for a low mold temperature and high pressure. The die attached to the cylinder surface can not only achieve continuous embossing, but also obtain better imprint results.
【学位授予单位】：大连理工大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TG306;TB17

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