Running Nemoh ============= Workflow -------- Nemoh provides 4 main programs that need to be run in sequence: - ``preProc``: to read the input data, setup the computations, and compute the Froude-Krylov forces - **[optional]** ``hydrosCal``: to compute the hydrostatic stiffness and estimated inertia matrices - ``solver``: to solve the linear system of equations for each frequency and direction - ``postProc``: to compute the radiation and diffraction forces from the results of the solver Additionally, Nemoh provides a 5th program called ``mesh`` that does the same as ``hydrosCal`` but also refines the mesh with a target number of panels. .. warning:: In a standard workflows, avoid using the ``mesh`` program. A dedicated meshing tool like GMSH will always provide better meshes. Details oubout the input and output files of each program can be found in the `Nemoh documentation `__. Main input files ---------------- Nemoh.cal ^^^^^^^^^ The main input file for Nemoh is the ``Nemoh.cal`` file. A template is provided at the root of the project. .. literalinclude:: ../../Nemoh.cal .. important:: The number of vertices and panels must be specified in the ``Nemoh.cal`` file. They can easily be obtained with Meshmagick: .. code:: console $ meshmagick Buoy.mar --info Mesh.cal ^^^^^^^^ The ``Mesh.cal`` file is dedicated to the ``mesh`` and ``hydrosCal`` programs. It is used to specify parameters for mesh refinement and hydrostatics calculations. .. note:: This tutorial does not use the ``mesh`` program, so most of the parameters in the ``Mesh.cal`` file are not used. .. literalinclude:: ../../Mesh.cal input_solver.txt ^^^^^^^^^^^^^^^^ The ``input_solver.txt`` file is used to specify numerical parameters for the solver. .. hint:: The default values are usually sufficient for most cases. .. literalinclude:: ../../input_solver.txt Running the programs -------------------- To run the programs, open a terminal and navigate to the project folder: .. code:: console $ cd Then, run the following commands. .. note:: Instead of moving to the project folder, you can also specify the full path to the project directory in the commands, e.g.: .. code:: console $ preProc For brevity, the following will assume that your terminal is in the project directory. Pre-processor ^^^^^^^^^^^^^ .. code:: console $ preProc This outputs a summary of the computations: .. code:: none Summary of calculation -> Infinite water depth -> 50 wave frequencies from 0.1000 to 2.0000 -> 1 wave directions from 0.0000 to 0.0000 -> 6 radiation problems -> 6 forces -> Half-body mesh (symmetric) with Npanels= 872 Hydrostatics calculator ^^^^^^^^^^^^^^^^^^^^^^^ .. code:: console $ hydrosCal This program displays the buoyancy center and other hydrostatic properties. .. code:: none -> Calculate hull mass and inertia - Coordinates of buoyancy centre XB = -0.000m YB = 0.000m ZB = -0.953m - Displacement = 0.5314125E+02 m^3 - Waterplane area = 0.2822894E+02 m^2 - Mass = 0.5314125E+05 Kg .. warning:: The inertia matrix computed by ``hydrosCal`` is only an estimation, under the assumption that the weight of the body perfectly conpensates the buoyancy force, and that the resulting mass is distributed evenly on a infinitely thin skin on the mesh (shell model). For accurate results, the inertia matrix should be computed using the actual weight distribution of the rigid body, including the emerged part. Solver ^^^^^^ .. code:: console $ solver The progress of the solver is displayed in the terminal: .. code:: none -> Initialisation NP Gauss Quadrature Integ.: 4 EPS min z : 1.00000005E-03 . Done ! -> Solve BVPs and calculate forces Linear Solver: LU DECOMPOSITION STARTING TIME: Date: 23 - 1 - 2025 Time: 15 : 26 : 18 Problem 1 / 350 [...] Computation time 79.9782486 [s] . Done ! Post-processor ^^^^^^^^^^^^^^ .. code:: console $ postProc The post-processor outputs a brief message in the terminal: .. code:: none -> Initialisation . . Done ! -> Save results Results ------- The Nemoh programs output files in several directories: - ``mesh``: contains copies of the mesh files and other intermediate files used by the solver and post-processor - ``Mechanics``: contains the results of the hydrostatics calculations as well as input files for the RAO computation - ``results``: contains the main results of the computations: added mass, radiation damping and excitation (diffraction + Froude-Krylov) forces There are also several output files in the root of the project: - ``logfile.txt``: a log file with information about the solver - ``Normalvelocities.dat``: the normal velocities on the body surface (for each panel) Details about the output files can be found in the `Nemoh documentation `__.