Question

MECHANICS OF MACHINES AND VIBRLTIONS 3I PART B (Answer ALL Question)w JAWA OKL QUESTION3 Figure Q3 shows a shaft carrying an electric motor C of mass 40 kg and two rotors A and B with 10 kg mass each. The motor, shaft and rotor are supported by two bearings L and R; and the motor is rotating constantly at 600 rpm. It is found that the shaft, motor and rotor are initially totally balance. What do you understand by the term of "initially totally balance". (A) 2 marks (B) After sometime in operation, rotor A and B are found to have a radius of eccentrity of 2 cm at 180° and 1 cm at 90° respectively. Determine the dynamics force acting on bearing L and R. (C) What is the mass should be added at plane L and R, at position of 90° and 180P respectively with 20 cm radius of eccentricity to balance the shaft. 18 marks] (Note: use the given reference of direction to solve the problem). Reference 90° 180-0 270 10 cm 15 cm i 15 am 10 cm 20 m 20 cm Figure Q3/ Rajah S3

Answer 1

Ans:

(A): Initially, the motor is in steady state there where no force acting on the motor or rotor If the motor started due to rotation centrifugal force exists in the system. It leads to shaft rotates offset from its axis of rotation, normally bent occurs in the shaft after certain speed shaft leads to failure. Force exerts only during the running of the motor. Initially, it is in a balanced condition.

(B) & (C)

Step 1: find the centrifugal force (F), kg cmand couple kg. cm²

Step 2: construct the couple polygon since the single unknown is required.

Step 3: Construct a force polygon.

ve Ref ve 2.0 0 ㄑㄧ一一5.0 Pbne mas Rad. 「ouple in e, c m 나.oo ma nm Doo 1 o 1 0

Scal e 40o K9. 800 12. 16 レ'9.1m

Slep 3 -p 2 2 9 ANS C0)

ANS c) ce . CW beo tw will Wo.