NEMOH-Presentation

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NEMOH is a Boundary Element Methods (BEM) code dedicated to the computation of first order wave loads on offshore structures (added mass, radiation damping, diffraction forces). It has been developed by researchers at Ecole Centrale de Nantes for 30 years. It is still used in many of our research projects. Typical use is estimation of dynamic response of floating structures or performance assessment of wave energy converters.

NEMOH is the world first open source BEM code. Since January 2014, it has been released under the terms of the Apache 2 licence. Copy of the license may be obtained at http://www.apache.org/licenses/LICENSE-2.0

Unlike other BEM softwares, NEMOH’s approach decouples the resolution of the linear free surface Boundary Value Problem (BVP) and the definition of the boundary condition on the body (body condition). This feature makes it easy to deal with flexible structure, hydroelasticity, generalised modes and unconventional degrees of freedom with NEMOH.

News

•November 2016: The Matlab routine for the calculation of the mean drift forces has been updated. It includes a verification test for a submerged hemisphere.

•August 2016: IMPORTANT NOTICE: if you are planning to model an OWC with NEMOH, be aware that it may not work. Recent comparisons of WAMIT and NEMOH for an OWC with the water column modelled as a rigid piston show discrepancies. Mesh convergence seems challenging with NEMOH in the case of OWC. For more details, see the user forum.

•August 2015: A “developer group” is being created in order to improve NEMOH. The first meeting of this developer group will take place on Monday, September 7 during the EWTEC2015 conference in Nantes, France. More information on NEMOH’s forum http://lheea.ec-nantes.fr/redmine/projects/nemoh

•March 2015: NEMOH v2.02 has been released. It is now possible to specify water density and gravity in the meshing tools.

•July 2014: NEMOH v2.0 has been released. Major modifications are (i) Code acceleration by a factor typically 7 when using the Matlab routine. Gain depends on the number of BVP per frequency and (ii) More logical conventions for wave elevation and excitation force.

Overview

NEMOH is composed of three programs which are supposed to be run one after the other.


A Matlab wrapper NEMOH.m is provided in the Matlab routine folder. It makes it easy to use NEMOH from the Matlab environment. Meshing tools are also provided. See the matlab routines axiMesh.m, Mesh.m in the Matlab routine folder and the Mesh code.
Examples are shown in the example section below.

Reference

Publication or report using NEMOH should refer to:
• A. Babarit, G. Delhommeau: Theoretical and numerical aspects of the open source BEM solver NEMOH. In Proc. of the 11th European Wave and Tidal Energy Conference (EWTEC2015), Nantes, France