Tuesday 11 February 2014

Battle of the BEMs

2014 looks set to being a good year for open access code for marine renewables. Three projects are due to go online this year: WEC-Sim, OPEN-WARP, and Nemoh. The last two are Boundary Element Method (BEM) codes: if one of these turns out to the long-awaited open source equivalent to the excellent but prohibitively expensive WAMIT, this could be a real boost to marine renewables. The availability of free code for modelling WECs will considerably reduce the cost, complexity and effort associated with development at early technology readiness levels. So please spread the word:

Do you have any dusty unloved code that has slipped down the back of the couch? Time to stop sitting on it! Check out the OPEN-WARP competition.


WEC-Sim is tool for building and solving equations of motion for floating bodies. The kinematics of the problem are defined by user selectable components (bodies and joints). There are also user selectable options for components that provide impedance (springs and dampers).

The code is written in proprietary software (Matlab), so it is not open source to the core. However, Matlab is so widely used in renewable energy engineering that code written in Matlab is widely accessible (as in, understandable) to those who might need it. WEC-Sim is being co-developed by US national laboratories, NREL and Sandia. There are plans to release this to the public in June 2014.

As inputs, WEC-Sim requires hydrodynamic parameters (coefficients for the excitation and radiation forces). Presently these are being provided by proprietary code such as WAMIT, but there are plans to develop an open source alternative through the OPEN-WARP challenge.


The competition is for code that will convert outputs from a CAD model into a text file that defines the geometric mesh, and for code that will take the mesh as an input and solve the inviscid Navier-Stokes equations. The challenge is supported by the US’s DOE (Department of Energy) and is hosted by the TopCoder site, a specialist management site for open source challenges. The project is broken into several tasks, each of which might be addressed with an open competition or by invitation only.

The prize money associated with each challenge is not sufficient to cover the salary of a developer living in a wealthy country, but is enough to give the challenge an element of prestige. The prize money would be very welcome to any academic institution that had in-house or legacy code lying about. An additional pull for groups with unshared code is that a third party takes on the responsibility of hosting and maintaining the code, and ensuring that back-ends and front-ends of various bits speak the same language.


For one group who have been sitting on some BEM code for some time (and this is no sorry-it-slipped-down-the-back-of-the-couch code, but a great big beast of a work horse) the prize money was not sufficient for them to part with their pride and joy. ECN have released this version of their in-house code themselves, rather than submit it to OPEN-WARP. As a result, they have set themselves up as competition for OPEN-WARP. This can only be a good thing: it is now clear that high standards are a prerequisite. If the OPEN-WARP competition had anything to do with ECN’s decision to release Nemoh, then this DOE program should be applauded for nudging them over the tipping point.

There are plans to host Nemoh on a code sharing site such as Github or Sorceforce, but for now it can be accessed by emailing AurĂ©lien Babarit with a request for access to the DropBox location. See the OpenORE post for pretty graphics and Dr. Babarit’s details.

Final thoughts on opportunities

  • It would be great if there was some compatibility between  proprietary codes, Nemoh and OPEN-WARP, which would allow users to mix and match.
  • It would be useful if OPEN-WARP also included a task for solving the irregular frequency problem (obviously-spurious results at particular frequencies). 
  • I'm unsure of whether WEC-Sim can deal with flexible bodies, but this would certainly be a useful feature.

This is my personal wish-list for these new open access projects. Please feel free to add your own thoughts on the opportunities opened up by these projects.

Image credit:

‘Ride the duckie’ by Dee Bee: http://www.flickr.com/photos/decibell72/86704967/


  1. http://lheea.ec-nantes.fr/doku.php/emo/nemoh/start?&#nemoh

  2. WEC-Sim is now available for download: http://en.openei.org/wiki/WEC-Sim



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