Welcome to Nemoh-Workshop!

The aim of this lab work is to become familiar with a linear potential flow solver for the diffraction-radiation loads acting on a floating structure. To this end, the Boundary Element Method (BEM) code NEMOH is used on the simple test case of a free floating buoy in infinite water depth. NEMOH is open-source, developed at Centrale Nantes and available on GitLab. As many other BEM solvers (WAMIT, DIODORE …), NEMOH can be used to compute a hydrodynamic database using linear potential flow theory. This database gives hydrodynamic coefficients, such as added-mass, damping and excitation force in frequency domain. It is then possible to compute the motion of such a system in time-domain in various environmental conditions.

During these lab work sessions, the goals are to:

• Set-up a calculation for NEMOH

• Generate a converged mesh for the linear potential flow solver Nemoh

• Understand the characteristics of the radiation and diffraction loads for different wave frequencies.

• Solve the equation of motion of the cylinder in waves to compute its motion transfer functions (RAO for Response Amplitude Operator)

Warning

Please follow this tutorial in order.

Contents:

• Theory reminder
  • Hypotheses
  • Body motions
  • Loads acting on the body
  • Response Amplitude Operator
  • Impulse Response Functions
• Pre-requisites
  • GMSH
  • Meshmagick
  • Nemoh
• Meshing
  • Studied case
  • Creating the mesh with GMSH
  • Converting the mesh with Meshmagick
• Running Nemoh
  • Workflow
  • Main input files
  • Running the programs
  • Results
• Post-processing
  • Post-processing 2D data
  • Post-processing 3D data
• Mesh convergence
• Response analysis
  • Plotting the RAO
  • Design choices