MAE 454 Quiz 7 Soln(1)
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West Virginia University *
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Course
454
Subject
Aerospace Engineering
Date
Dec 6, 2023
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4
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Name: Mailbox MAE 454 –Quiz 7
October 30, 2023 The quiz is closed book and notes. You are not permitted to work or share your responses with anyone. Assume gravity acts vertically down. Place your responses in the space provided. (100 points) 1. In a hydrodynamically lubricated journal bearing, how does the temperature rise of the lubricant through the bearing affect the analysis? (10 points) Shigley
’
s hydrodynamic bearing analysis presents a graphical approach. The independent parameter (Sommerfeld number) on the graphs depends on the viscosity of the lubricant. The viscosity is temperature dependent. Hence, the lubricant temperature affects the analysis. 2. In hydrodynamic lubricated journal bearings, Trumpler provided four different parameters with recommended values. Maximum temperature was one of these parameters. Name one of the other three parameters. (10 points) Minimum Film Thickness, Maximum Startup Load, Minimum Factor of Safety 3. A hydrodynamic lubricated bearing with a 4.0” diameter, 4.0” long, and a 0.002” radial clearance has a Sommerfeld number of 0.5. What is the coefficient of friction? See separate figures. Since calculators are not permitted, provide the answer in an equation with all values substituted so that a value can be solved for. Include appropriate units. (20 points) From the chart, fr/c=10. Therefore, f = 10(0.002/2). 4. For the bearing in question 3, what is the minimum film thickness? See separate figures. Since calculators are not permitted, provide the answer in an equation with all values substituted so that a value can be solved for. Include appropriate units. (20 points) From the chart, h
o
/c=0.75. Therefore, h
o
= 0.75(0.002) inches.
5. What is the governing failure mode for a boundary lubricated bearing? (10 points) Wear 6. Other than the failure mode for Problem 5, what is another operating requirement for a boundary lubricated bearing? (10 points) P<Pmax, V<Vmax, PV<PVmax, T<Tmax 7. Explain when a journal bearing would be analyzed using hydrodynamic lubricated analysis approach and when it would be analyzed using a boundary lubricated analysis approach. (20 points) Hydrodynamic –
there is sufficient lubrication that provides a film layer thick enough so that no surface-to-surface contact occurs. The relative motion between the journal and the bearing builds a sufficient pressure in the fluid film to support the radial load acting on the shaft. Hydrodynamic lubrication depends on the lubricant (viscosity), speed, load, and bearing geometry. Boundary –
there is insufficient lubrication to provide a fluid film and surface-to-surface contact occurs. Relative high loads, low speeds, high temperatures (low viscosity) and or journal to bearing alignment can lead to boundary lubrication conditions.
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