AER 403 Lecture Notes - Lecture 20: Optical Table, Hovercraft, Aircraft Engine

• School: Ryerson University
• Department: Aerospace
• Course: AER 403
• Professor: Fengfeng Xi

Document Summary

The excitation is the external support motion: )n motion transmission isolation, there is no internal vibration source, (ence we need to look at the support motion vibration. Motion transmission isolation: (cid:600)/(cid:600)n>> (cid:884), (cid:599)>(cid:883)(cid:884)(cid:882) x/y=(cid:883)/(cid:523)(cid:600)/(cid:600)n(cid:524)(cid:884) X/y=1 to overcome the inertia force: (cid:600)/(cid:600)n=(cid:882), (cid:599)=(cid:882) to overcome the spring and damping force, (cid:600)/(cid:600)n=(cid:883), (cid:599)=9(cid:882) Transmissibility & isolation efficiency: transmissibility, )solation efficiency [(cid:523)y-x)/y] 100, decibel (cid:523)p. (cid:883)(cid:884)(cid:524) db = 20 log (x/y) |x/y| = 0. 1 [(1-0. 1)/1]100%=90% 20 log 0. 1 = -20 db. |x/y| = 0. 015 [(1-0. 015)/1]100%=98. 5% 20 log 0. 015 = -36 db. Force transmission isolation: )n force transmission isolation, we look at the transmitting force from the spring-damper system to the support, such as imbalance induced vibration kx + cdx/dt. Since the spring force and damping force are perpendicular, then the amplitude of the transmitting force is equal to. Ft= 2 + (cid:600) 2=kx[1+(2 (cid:600)/(cid:600)n)2]1/2 the force included vibration takes the form as x=(fo/k)/[(1-(cid:523)(cid:600)/(cid:600)n(cid:524)(cid:884)(cid:524)(cid:884)+(cid:523)(cid:884) (cid:523)(cid:600)/(cid:600)n(cid:524)(cid:524)(cid:884)](cid:883)/(cid:884)