By horizontal tangent into the air filter layer, rotate and foreign get down to the oil, oil level of shock wave and flow surfaces by a foam, the air in the oil to get oil bath.

The contact Angle is the Angle between the tangent line at the contact point and the horizontal line of the solid surface.

The critical aspect ratio of the fiber is defined as the crosspoint of the tangent value of the inflexion and the asymptote of the maximum elastic modulus.