本文選題：稀薄效應 + 分層理論　； 參考：《昆明理工大學》2017年碩士論文

【摘要】：隨著我國制造水平的不斷提升,我國對精密及超精密的加工設備需求不斷增加,空氣靜壓導軌是超精密加工機床中常用的引導移動裝置。常規(guī)供氣條件下,當空氣靜壓導軌工作氣膜厚度達到幾微米時,氣膜內氣體流態(tài)發(fā)生變化,氣浮導軌的承載性、剛度、穩(wěn)定性隨之發(fā)生變化,此時,需要充分考慮尺度效應對氣膜內潤滑規(guī)律的影響。本文根據分子動力學和薄膜潤滑理論對氣浮導軌支撐區(qū)潤滑氣膜開展了深入研究,主要研究內容如下。首先,根據空氣靜壓導軌氣膜內氣體流態(tài)及氣體密度和滑移速度分布規(guī)律,沿氣膜高度方向初步提出氣體分層理論。根據氣膜內氣體分子運動規(guī)律,將氣膜內氣體沿高度方向分為近壁層、稀薄層、連續(xù)流層,建立相關物理模型并給出相應的數學控制方程。通過LAMMPS數值模擬計算出氣膜內沿高度方向速度、壓力分布,并且模擬出氣膜內氣體分子運動,驗證膜內氣體分層理論的合理性。其次,根據氣膜內部壓力梯度的變化特征,沿氣體流動方向初步提出氣膜分區(qū)理論。空氣靜壓導軌氣膜內沿氣體流動方向壓力梯度變化呈現先驟降再緩慢遞減的趨勢,本文根據膜內徑向壓力變化規(guī)律,提出了氣體分區(qū)理論,沿氣膜徑向方向分為壓力驅動區(qū)和牛頓摩擦區(qū),并建立相應的數學描述和控制方程。通過Fluent、LAMMPS數值模擬計算膜內氣體壓力、速度等,驗證分區(qū)模型的合理性。此外,通過結合速度滑移現象,分析了近壁層、稀薄層、連續(xù)流層在壓力驅動區(qū)、牛頓摩擦區(qū)的速度滑移規(guī)律。再次,建立基于分層模型的全域速度滑移模型。根據氣體分子在近壁層、稀薄層、連續(xù)流層的滑移規(guī)律,結合氣膜內氣體分層模型,建立氣膜內氣體分子速度滑移模型,并給出相應的數學表達式。此外,對氣膜內氣體黏度進行修正。通過LAMMPS、COMSOL、2DMD分析計算了氣膜內的黏度、速度、壓力等,對速度滑移全域模型進行了驗證。最后,分別搭建基于密度變化的分層模型實驗裝置和分區(qū)理論實驗裝置。由于現階段國內外就微米級氣膜測量還無法實現直接測試,本文設計搭建一種基于密度變化和氣膜特性的測試裝置,通過間接方法驗證氣膜分層理論的有效性。對于氣膜分區(qū)結論的驗證,本文專門設計加工制造了一套準確測量膜內壓力分布的裝置,實驗結果與數值計算進行了比較,進一步驗證分區(qū)模型的準確性。此外,通過測量不同氣膜厚度下,流量的變化規(guī)律,也論證了前期得到的邊界速度滑移結論。
[Abstract]:With the continuous improvement of manufacturing level in China, the demand for precision and ultra-precision machining equipment is increasing in our country. Air static pressure guideway is a commonly used guiding and moving device in ultra-precision machining machine tools. Under the condition of conventional air supply, when the working film thickness of the air static pressure guideway reaches several microns, the gas flow state in the film changes, and the bearing capacity, stiffness and stability of the air floating guide rail change accordingly. The influence of the scale effect on the lubrication law in the film should be fully considered. Based on the theory of molecular dynamics and film lubrication, the lubrication film in the support region of air bearing guideway has been studied in this paper. The main contents are as follows. Firstly, according to the gas flow state, gas density and slip velocity distribution in the gas film of the air static guide rail, the theory of gas stratification is put forward along the direction of the film height. According to the motion law of gas molecules in the film, the gas in the film is divided into the near wall layer, the rarefied layer and the continuous flow layer along the direction of the height. The relevant physical model is established and the corresponding mathematical control equation is given. The velocity and pressure distribution along the height of the film are calculated by LAMMPS numerical simulation, and the molecular movement of gas in the film is simulated, which verifies the rationality of the theory of gas stratification in the film. Secondly, according to the variation characteristics of internal pressure gradient of the film, the theory of gas film zoning is put forward along the gas flow direction. The variation of pressure gradient along the gas flow direction in the air static guideway shows a tendency of first plummeting and then decreasing slowly. According to the variation law of radial pressure in the film, the theory of gas partition is put forward in this paper. Along the radial direction of the film, it is divided into pressure driving region and Newtonian friction region, and the corresponding mathematical description and governing equation are established. The rationality of the zonal model is verified by calculating the pressure and velocity of gas in the film by numerical simulation of fluentum lamps. In addition, the velocity-slip law of near wall layer, rarefied layer and continuous flow layer in the pressure driven region and Newton friction region is analyzed by combining the velocity slip phenomenon. Thirdly, a global velocity-slip model based on layered model is established. According to the slip law of gas molecules in the near wall layer, thin layer and continuous flow layer, combined with the gas stratification model in the film, the velocity slip model of the gas molecule in the film is established, and the corresponding mathematical expression is given. In addition, the gas viscosity in the film is modified. The viscosity, velocity and pressure in the gas film are calculated by Lamps ComSol 2DMD, and the global model of velocity slip is verified. Finally, the layered model experimental device and the partition theoretical experimental device are built based on the density variation. Since the direct measurement of micrometer film can not be realized at present at home and abroad, a testing device based on density variation and film characteristics is designed and built, and the effectiveness of the theory of film stratification is verified by indirect method. For the verification of gas film partition conclusion, this paper specially designed and manufactured a set of equipment to measure accurately the pressure distribution in the film. The experimental results were compared with the numerical calculation, and the accuracy of the partition model was further verified. In addition, the boundary velocity-slip conclusions obtained in the previous period are also demonstrated by measuring the flow rate variation law under different film thickness.
【學位授予單位】：昆明理工大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：TG502.39

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