真空预载型多孔质空气静压轴承的静动态特性分析

为进一步提高轴承刚度,将真空预加载技术与多孔质空气静压轴承相结合,使轴承在没有额外预加载导轨的情况下获得双向刚度。探讨工作条件和结构参数对真空预载型多孔质空气静压轴承性能的影响,基于计算流体力学(computational fluid dynamics,CFD)方法对其静动态特性进行了数值分析。深入研究了供气压力、真空度、渗透率、真空抽气口直径、扰动幅度和扰动频率等因素对轴承性能的影响。结果表明,相比于一般多孔质空气静压轴承,真空预载型多孔质空气静压轴承的刚度提高了22.34%;工作条件和结构参数对其静态和动态特性有显著影响。该研究结果对高刚度空气静压轴承的性能研究和优化设计具有一定的指导意义。

真空预载型多孔质气体止推轴承静态特性研究

为了提高孔质静压气体轴承的刚度,将负压腔引入多孔质静压气体止推轴承的设计中,运用有限元方法对真空预载型多孔质静压气体止推轴承进行数值分析,分析负压腔真空度、负压腔面积比S_a/S(负压腔横截面积与轴承横截面积比值)、多孔材料渗透率、供气压力等因素对轴承静态特性的影响。分析结果显示:负压腔中真空度的变化对轴承的刚度几乎没有影响;真空度的增大,改变了气膜的压力分布造成轴承承载能力在一定程度上的下降;在气膜间隙5～12μm之间,真空腔的引入使气膜刚度明显增加;当S_a/S≠0,气膜间隙8～10μm时,S_a/S值的变化对轴承承载能力的影响较刚度更大;在一定承载能力下,轴承刚度随负压腔面积比增大而增大,而气膜厚度随之逐渐减小。试制真空吸附型多孔质静压气体止推轴承,并对其承载能力、刚度进行试验,实验值和理论值有较好的一致性。

真空预载小孔节流静压气浮轴承静态特性分析

气浮轴承是光刻机等高精度设备的关键部件,其静态特性直接决定设备精度。以真空预载小孔节流静压气浮轴承为研究对象,探究供气压力、真空度、真空腔面积比以及节流孔直径等因素对轴承静态特性的影响。研究发现气膜厚度与轴承的静态特性呈现4个方面相关性:1)当气膜厚度一定时,供气压力越大,轴承承载能力和刚度越大,最大刚度对应的气膜厚度为7~9μm;2)真空度越大,轴承承载能力越小,但真空度对轴承刚度影响较小;3)真空腔的加入使轴承承载能力下降,但为轴承提供了双向刚度,气膜厚度和真空腔面积比与轴承刚度呈负相关;4)节流孔直径越大,轴承承载能力越大,气膜厚度较小时,节流孔直径与轴承刚度呈负相关,最大刚度对应的气膜厚度为6~12μm。当气膜厚度超过20μm时,轴承刚度在上述分析情况下均趋于零。

Ground treatment of sea embankment by vacuum preloading with PVDs

Vacuum provides an alternative in reducing the length of preloading period for soft soil consolidation. In this method, soft clay foundation is preloaded by reducing the pore-water pressures through the application of vacuum pressure in combination with surcharge preloading. A full scale and fully instrumented test embankment was constructed. A drainage pattern system combined with 22 m prefabricated vertical drains (PVDs) length was used with triangular pattern of 1.2 m spacing. Among the foundation instrumentation, piezometers were installed in the foundation subsoil at varying depth to measure the pore-water pressures. After 6 months of vacuum pressure application at 80 kPa, the test embankments were raised to a maximum height of 5.5 m. The effect of vacuum preloading was investigated by the field conditions, maintaining higher vacuum pressures, and unloading vacuum. The results demonstrated the efficiency of combined vacuum and surcharge preloading.