Download PTU (Punjab Technical University) B.Tech (Bachelor of Technology) / BE (Bachelor of Engineering) 2021 January Automation-And-Robotics 7th Sem 71808 Mechanical Vibrations Previous Question Paper

Total No. of Pages : 03

Total No. of Questions : 18

B.Tech. (Automation & Robotics) (201 2 & Onwards) (Sem.?7)

MECHANICAL VIBRATIONS

Subject Code : BTME-803

M.Code : 71808

Time : 3 Hrs. Max. Marks : 60

INST RUCT IONS T O CANDIDAT ES :

1 .

SECT ION-A is COMPULSORY cons is ting of TEN questions carrying TWO marks

each.

2 .

SECT ION-B c ontains F IVE questions c arrying FIVE marks eac h and s tud ents

have to atte mpt any FOUR q ues tions.

3 .

SECT ION-C contains THREE questions carrying T EN marks e ach and s tudents

have to atte mpt any T WO questio ns

SECTION-A

Write briefly :

1.

Define the magnification factor.

2.

What are principal co-ordinates?

3.

What is the difference between vibration isolation and vibration absorber?

4.

Define influence coefficient.

5.

What do you mean by continuous system?

6.

What do you understand by mode orthogonality?

7.

What is structural damping?

8.

Define whirling speed of shafts.

9.

The damped natural frequency (d) of a system is 86.6Hz, while the maximum amplitude

occurs at an exciting frequency (p) of 70.7 Hz. Find the damping factor () and the

undamped natural frequency (n).

10. Define viscous damping.

SECTION-B

11. What is the difference between deterministic and random vibration? Give two practical

examples of each.

12. A simply supported beam of square cross section 5 mm ? 5 mm and length 1 m, carrying a

mass of 2.3 kg at the middle, is found to have a natural frequency of transverse vibration of

30 rad/s. Determine the Young's modulus of elasticity of the beam.

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13. What assumptions are made in finding the natural frequency of a single-degree-of freedom

system using the energy method?

14. A spring-mass system, with a spring stiffness of 5,000 N/m, is subjected to a harmonic

force of magnitude 30 N and frequency 20 Hz. The mass is found to vibrate with an

amplitude of 0.2 m. Assuming that vibration starts from rest x0 = 0 = 0, determine the mass

of the system.

15. Find the natural frequencies of a simply supported beam subjected to an axial compressive

force.

SECTION-C

16. A heavy machine, weighing 3000 N, is supported on a resilient foundation. The static

deflection of the foundation due to the weight of the machine is found to be 7.5 cm. It is

observed that the machine vibrates with an amplitude of 1 cm when the base of the

foundation is subjected to harmonic oscillation at the undamped natural frequency of the

system with an amplitude of 0.25 cm. Find :

a. The damping constant of the foundation.

b. The dynamic force amplitude on the base, and

c. The amplitude of the displacement of the machine relative to the base.

17. Find the steady-state response of the system shown in Fig.1, when the mass m1 is excited

by the force F1(t) = F10coswt. Also, plot its frequency-response curve.

FIG-1

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18. Determine the eigenvalues and eigenvectors of a vibrating system for which

1

0

0

1

2

1

m

0 2 0

and

k

2

4

2 .

0 0 1

1

2

1

NOTE : Disclosure of Identity by writing Mobile No. or Making of passing request on any

page of Answer Sheet will lead to UMC against the Student.

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This post was last modified on 26 June 2021