Introduction to interfacial waves

By Prof. Ratul Dasgupta   |   IIT Bombay
Learners enrolled: 82
The course is an introduction to the rich field of interfacial waves. The first half of the course prepares the student for studying wave phenomena by introducing discrete mechanical analogues of wave phenomena in fluid systems. The basic principles of normal mode analysis are introduced through point-mass systems connected through springs. The exact solution to the (nonlinear) pendulum equation is used to introduce the notion of amplitude dependence on frequency of the oscillator. The Kapitza pendulum is introduced as a discrete analogue for Faraday waves. Basic perturbation techniques are then introduced for subsequent use. The second half of the course introduces basics of interfacial waves viz. shallow and deep-water approximations, phase and group velocity, frequency and amplitude dispersion etc.. Capillary as well as capillary-gravity waves in various base state geometries (rectilinear, spherical (drops and bubbles), cylindrical (filaments) are taught and the corresponding dispersion relation derived. The Stokes travelling wave is derived using the Lindstedt-Poincare technique and the amplitude dependence in the dispersion relation is highlighted. Side-band instability of the Stokes wave is discussed. Introductory ideas in resonant interactions among surface gravity waves are discussed. The fundamental aspects studied in the course will be related to various engineering applications continuously.

INTENDED AUDIENCE Chemical & Mechanical Engineering students

PRE-REQUISITES Introductory Transport Phenomena / Fluid Mechanics

INDUSTRY SUPPORT Industrial personnel working on two phase flows
Course Status : Completed
Course Type : Elective
Duration : 12 weeks
Category :
  • Chemical Engineering
  • Minor 3 in Chemical
Credit Points : 3
Level : Postgraduate
Start Date : 25 Jul 2022
End Date : 14 Oct 2022
Enrollment Ends : 08 Aug 2022
Exam Date : 29 Oct 2022 IST

Note: This exam date is subjected to change based on seat availability. You can check final exam date on your hall ticket.

Page Visits

Course layout

Week-1: Introduction to waves and oscillations, Normal modes of linear vibrating systems with finite degrees of freedom, Eigenmodes (shapes of oscillation) and frequencies, continuum limit
Week-2: Normal modes of a string with fixed ends, a clamped rectangular and circular membrane, Introduction to elliptic functions
Week-3: Nonlinear pendulum: exact solution using elliptic integrals, amplitude dependence of frequency, intro. to perturbation methods, non-dimensionalisation
Week-4Perturbative solution to projectile equation, regular perturbative solution to the non-linear pendulum, Lindstedt Poincare technique, Damped harmonic oscillator, regular perturbation, method of multiple scales
Week-5Multiple scales solution (contd..), Duffing equation, Parametric instability and the Kapitza Pendulum, Introduction to Floquet theory
Week-6: Mathieu equation stability tongues, Introduction to inviscid, irrotational surface gravity waves in deep water, boundary conditions, non-dimensionalisation and linearisation, dispersion relation
Week-7: General solution for surface gravity waves, linearised standing and travelling waves, phase and group velocity, Cauchy-Poisson problem for surface waves in deep water: rectilinear geometry, waves in cylindrical geometry
Week-8: Cauchy Poisson problem in cylindrical geometry, Cauchy-Poisson problem for delta function at origin and group velocity, similarity solution, stationary phase approximation, capillary-gravity waves
Week-9: Waves on finite depth pool, shallow and deep water approx., group velocity and energy propagation, axisymmetric Cauchy-Poisson problem with a Gaussian, engineering applications, Rayleigh-Plateau instability
Week-10: Waves and instability on a coated cylinder, waves and instability on a cylindrical air column, physical
interpretation, shape oscillations of drops and bubbles, physical interpretation of zero frequency
Week-11: Applications of shape oscillations, Faraday instability on a fluid interface, subharmonic response, Floquet
analysis, atomization from Faraday waves, engineering applications, waves on shear flows & Kelvin-Helmholtz
Week-12: Stokes wave in deep water, stability of Stokes wave (sideband instability), comparison of deep and shallow-water theory, non-linear Schrodinger equation and KdV equation, Resonant interactions among water waves

Books and references

  1. Vibrations and Waves, A. P. French, M.I.T. Introductory Physics Series
  2. A modern introduction to the mathematical theory of water waves, R. S. Johnson, Cambridge Texts in Applied Mathematics
  3. Waves in Fluids, J. Lighthill, Cambridge Mathematical Library
  4. Linear and nonlinear waves, G. B. Whitham, Wiley Interscience
  5. Fluid Mechanics – P. K. Kundu, Ira. M. Cohen, D. Dowling, Academic Press
  6. Nonlinear water waves – L. Debnath, Academic Press
  7. Perturbation Methods – Ali H. Nayfeh, Wiley-VCH
  8. The acoustic bubble - T. G. Leighton, Academic Press

Instructor bio

Prof. Ratul Dasgupta

IIT Bombay
Dr. Ratul Dasgupta is an Associate Professor at the Chemical Engg. Department at IIT Bombay. He completed his Ph.D. at the Jawaharlal Nehru Centre for Advanced Scientific Research in Bangalore and was a postdoctoral fellow subsequently at the Weizmann Institute of Science in Israel. He has been on the faculty at IIT Bombay since 2014. He works on interfacial waves, hydrodynamic stability and the mechanics of amorphous materials employing a combination of theoretical and computational tools and occasionally simple experiments.

Course certificate

The course is free to enroll and learn from. But if you want a certificate, you have to register and write the proctored exam conducted by us in person at any of the designated exam centres.
The exam is optional for a fee of Rs 1000/- (Rupees one thousand only).
Date and Time of Exams: 29 October 2022 Morning session 9am to 12 noon; Afternoon Session 2pm to 5pm.
Registration url: Announcements will be made when the registration form is open for registrations.
The online registration form has to be filled and the certification exam fee needs to be paid. More details will be made available when the exam registration form is published. If there are any changes, it will be mentioned then.
Please check the form for more details on the cities where the exams will be held, the conditions you agree to when you fill the form etc.


Average assignment score = 25% of average of best 8 assignments out of the total 12 assignments given in the course.
Exam score = 75% of the proctored certification exam score out of 100

Final score = Average assignment score + Exam score

YOU WILL BE ELIGIBLE FOR A CERTIFICATE ONLY IF AVERAGE ASSIGNMENT SCORE >=10/25 AND EXAM SCORE >= 30/75. If one of the 2 criteria is not met, you will not get the certificate even if the Final score >= 40/100.

Certificate will have your name, photograph and the score in the final exam with the breakup.It will have the logos of NPTEL and IIT Bombay.It will be e-verifiable at nptel.ac.in/noc.

Only the e-certificate will be made available. Hard copies will not be dispatched.

Once again, thanks for your interest in our online courses and certification. Happy learning.

- NPTEL team

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