ASSIGNMENT 3 (50 marks)
Note:
• There shall be four sets for this assignment. Students shall be allotted ONLY ONE of
these sets based on their choice as per instructions from the course instructor.
• Questions 3 must be solved by all students.
• Submit in the forum specified by the course instructor.
• Deadline: 19 February 2025.
Question 1: For your respective set, plot the solution trajectories in the phase plane and
indicate the singular (fixed) points, their types and separatrices. [15 marks]
Set A: 𝑢̈ + 𝑢 − 𝑢3 = 0
Set B: 𝑢̈ − 𝑢 + 𝑢3 = 0
Set C: 𝑢̈ − 𝑢 − 𝑢3 = 0
Set D: 𝑢̈ + 𝑢 + 𝑢3 = 0
Question 2: Determine a two-term expansion for the frequency amplitude relationship
for systems governed by the following equations. [15 marks]
Set A: 𝑢̈ − 𝑢 + 𝑢3 = 0
Set B: 𝑢̈ + 𝜔02 𝑢 + 𝑢|𝑢| = 0
Set C: 𝑢̈ + 𝜔02 𝑢(1 + 𝑢2 )−1 = 0
Set D: 𝑢̈ + 𝜔02 𝑢 + 𝛼𝑢5 = 0
NONLINEAR VIBRATIONS (ME613)@IITG, JAN–MAY 2025,
ASSIGNMENT 3
Question 3: As shown in Fig. 1, a rigid rod is attached to an axle. The wheels roll without
slip as the pendulum swings back and forth. Only the ball at the end of the pendulum has
appreciable mass and it may be considered as a particle.
(a) Derive the governing equation for 𝜃 (5 marks)
(b) For small but finite motions, determine a two-term approximate frequency-
amplitude relationship. (15 marks)
Fig. 1