Welcome to the homepage of IITM-RANS3D. It is an in-house CFD code developed at the Department of Ocean Engineering, IIT Madras. The code has been developed with the aim of handling complex wave-structure interaction simulations in large domains over a long period of time.

IITM-RANS3D is a multiphase code based on the single-fluid formulation of the incompressible Navier-Stokes equations. The Navier-Stokes equations are solved using a semi-explicit solver over a Cartesian staggered mesh. Multiphase treatment is achieved using the VOF method. Waves are generated through a Dirichlet input from the in-house fully non-linear potential theory (FNPT) code IITM-FNPT2D. Turbulence effects are modeled using the RANS philosophy. Structures are modeled using the fictitious-domain method.

Key Features and Strengths:

  1. Strong pressure-velocity coupling realized through the staggered mesh.
  2. CICSAM scheme optimized for speed on Cartesian meshes through operator-splitting.
  3. One-way coupled with IITM-FNPT2D thus enabling very high fidelity generation of a wide range of waves.
  4. One-way coupling with IITM-FNPT2D allows for truncation of the RANS domain to the near-field of the structure. This saves computational effort by delegating the inviscid wave simulations to FNPT.
  5. Wave simulations are energy preserving even for large domains (say GWK: 350m x 5m x 7m) and for long time (say >~100 s).
  6. Turbulence effects characterizing wave-structure interaction modeled using the standard k-ε model.
  7. Fictitious-domain modeling of the structure precludes modifying the mesh topology in the vicinity of the structure thus enabling the use of Cartesian meshes even for complex structures.
  8. Parallelized using MPI. Capable of fully utilizing the computational resources offered by multi-core standalone compute nodes (SMA-shared memory architecture) as well as the VSR group server and IITM’s AQUA cluster (DMA-distributed memory architecture).
  9. Option for importing structure geometries through *.STL files.
  10. Capable of simulating forward speed problems.

Limitations (general):

  1. RANS as well as VOF formulation only applicable to Cartesian meshes.
  2. Diffuse interface treatment of the solid region ; implicit imposition of the slip boundary condition.
  3. Algebraic VOF scheme-based estimation of the interface location ; interface placement is not geometric.

Limitations (specific to release 1.0):

  1. No turbulence modeling ; laminar solver.
  2. Time discretization is first order forward Euler ; pressure and diffusion terms treatment is second-order.
  3. Two-phase Navier-Stokes formulation is non-conservative.
  4. Capable of handling complex albeit fixed structures.
  5. FNPT-RANS coupling is one-way.


Work in progress and future updates:

  1. Conservative solver to handle breaking jets.
  2. 6-DoF rigid solver, mooring lines & coupling for aero elasticity.
  3. Compressible air phase modelling for OWC, entrapped air.

Typical Application problems:

(1) Traditional Green-water loading on a obstacle modelUvel_animation

(2) Steep solitary wave interacting with a cylinder


(3) Focused waves interacting with a moonpool


(4) Steep solitary wave breaking over a sloping ridge




(5) Forward motion of the cylinder



IITM – RANS3D is an open source. We welcome researchers to either use it or change for your needs. Any clarification and suggestions you may reach us: Dr. Shaswat Saincher: shaswat.saincher@gmail.com or Myself: vsriram@iitm.ac.in

Version 1: IITM-RANS3D_1.0 (Non Conservative Solver)

Version 2: Expected Release – mid January 2022.

Developed and tested by:

Dr. Shaswat Saincher (PostDoc)

Mr. Hari Ram N. (M.S. student) – Solitary wave interaction with vegetation

Ms. Jemi Jeya (Ph.D. student) – Regular waves interacting with pile-supported caisson

Mr. Harish Selvam (Ph.D. student) – Tsunami-like bores interacting with buildings

Ms. Shrushti Shirsat (M.Tech student) – Aero-hydrodynamics of bottom-profiled OWC chambers