【摘要】：目前,隨著能源問題日益嚴重,減阻技術(shù)已經(jīng)成為節(jié)約能源的一項新技術(shù),模仿鯊魚的盾甲鱗結(jié)構(gòu)來實現(xiàn)減阻也成為減阻研究的一個熱點。限于鯊魚皮結(jié)構(gòu)復雜、復制困難、制造精度低、生產(chǎn)成本高的缺點,大面積復制出與真實鯊魚相似且具有較佳減阻效果的仿鯊魚皮微溝槽結(jié)構(gòu)仍是尚待解決的難題和挑戰(zhàn)。本文針對這一問題,展開如下研究： 首先,根據(jù)真實鯊魚皮微溝槽結(jié)構(gòu),簡化得到仿鯊魚皮微溝槽,并對微溝槽的結(jié)構(gòu)尺寸進行了優(yōu)化,繼而對優(yōu)化后的微溝槽進行減阻分析,結(jié)果表明：仿鯊魚皮微溝槽表面具有明顯的減阻效果,溝槽減阻的主要原因是微溝槽附近流體流動平緩以及微溝槽底部二次渦的存在。 其次,根據(jù)疏水基本理論模型,結(jié)合微溝槽的結(jié)構(gòu)特征建立了針對仿鯊魚皮微溝槽結(jié)構(gòu)的Cassie修正型方程；實驗所測得實際接觸角與根據(jù)Cassie修正型方程計算得到的理論接觸角之間的誤差小于3%,證明了本文所提出Cassie修正方程的有效性和正確性。通過理論和實驗對比,分析得出仿鯊魚皮微溝槽的疏水機理：微溝槽所具有的類似鱗片的形狀和微溝槽結(jié)構(gòu)改變了固-液接觸界面,使得固-液接觸變?yōu)楣?液、氣-液復合接觸,減弱了液體在微溝槽表面上的浸潤性,使疏水性加強。 然后,綜合考慮仿鯊魚皮微溝槽模具的尺寸大小、加工難易程度及加工成本,分別采用高速銑削和UV-LIGA兩種加工方法得到具有仿鯊魚皮微溝槽的滾壓成型金屬模具。加工結(jié)果表明：UV-LIGA加工得到的鎳模具尺寸基本接近于真實魚皮的溝槽尺寸,且結(jié)構(gòu)輪廓清晰、鑄層緊密。高速銑削加工得到的模具結(jié)構(gòu)輪廓清晰,表面粗糙度較低。兩種工藝方法得到的金屬模具尺寸結(jié)構(gòu)都已達到要求,滿足實驗的需要,驗證了兩種加工方法制作仿鯊魚皮微溝槽金屬模具的可行性。為保證仿鯊魚皮微溝槽的減阻效果,UV-LIGA工藝得到的鎳模具更適合作為滾壓成型的金屬模具。 最后,介紹了滾壓成型實驗的實驗原理、實驗設備和實驗材料,調(diào)整成型工藝參數(shù),完成PVC和PET塑料表面仿鯊魚皮微溝槽的滾壓成型實驗,研究了模具溫度、滾筒速度、壓力對成型結(jié)果的影響。結(jié)果表明：滾壓成型是一個動態(tài)漸進的成型過程,在成型工藝實驗中,模具溫度、壓力和滾筒速度是影響成型結(jié)果的重要因素,工藝過程適合在一個低模具溫度、高壓、低速的工作條件下進行,并且將模具貼附在滾筒表面不僅可以實現(xiàn)連續(xù)壓印,而且可以獲得較好的壓印結(jié)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.
【學位授予單位】：大連理工大學
【學位級別】：碩士
【學位授予年份】：2014
【分類號】：TG306;TB17

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