Category Archives: Computational model

openWEC: an easy-to-use, all-in-one WEC simulation tool

openWEC

Previously, software allowing users to simulate WECs, from meshing through power absorption, has only been commercially available. However, now, in order to give wave energy researchers and students an easy-to-use, all-in-one WEC simulation tool, the software openWEC has been created.
openWEC is written in python, and uses the Qt design language for the GUI development. Both the source code and a compiled executable are available open-source via Github:

When executing the program, the user can choose between several WEC simulators:

  • Wavestar Simulator
  • Oyster Simulator
  • Pelamis Simulator
  • Custom Simulator

The first three options are simplified versions of actual wave energy converter prototypes. Here, the user has only limited control over the parameters. When a user wants to develop a completely new WEC device, the Custom Simulator should be selected.

After selecting a simulator, the user enters the main GUI. There are 4 tab windows, each with a different purpose (see Figure):

  • Mesh tool: creation of the mesh. The device can be constructed by combining different basic shapes into a single WEC device
  • Nemoh: frequency-domain modelling of the WEC. Here, the hydrodynamic parameters are calculated using the open-source BEM solver Nemoh.
  • Simulation: time-domain modelling of the WEC in a specific sea state. Regular and irregular waves are possible. Two PTO strategie can be chosen: a linear damper or a coulomb damper. The position and velocity of the WEC are calculated, together with the absorbed power.
  • Post-processing: a simple post-processor allowing the user to plot the frequency-domain and time-domain parameters.

The user has the ability to save all the selected parameters and reload them when the model needs to be rerun. The current version only allows for single body WECs, but multibody simulations will be supported in the future.

WEC3: codes that work

wec3

At EWTEC 2015, a great project wave presented: WEC3 (pronounced WEC cubed), which stands for Wave Energy Converter Code Comparison. From their EWTEC paper (which can be found here):

The objectives of WEC3 are to verify and validate numerical modelling tools that have been developed specifically to simulate wave energy conversion devices and to inform the upcoming IEA OES Annex VI Ocean Energy Modelling Verification and Validation project. WEC3 is divided into two phases. Phase 1 consists of a code-to-code verification and Phase II entails code-to-experiment validation.

The codes under consideration are:

Comparison of codes to one another and to experiments benefits the code developers, giving them confidence in their results (something which is very important in numerical modelling), and benefits the community as a whole, providing validated tools for WEC design.

WEC-Sim Version 1.2

Version 1.2 of WEC-Sim is now available on GitHub, and there are lots of great updates!

The NREL/SNL team is also implementing a multi-branch approach, allowing users to use the stable ‘master’ branch or the more advanced/under development ‘dev’ branch.

Updates in ‘master’

  • Nonlinear Froude-Krylov hydrodynamics and hydrostatics
  • State space radiation
  • Wave directionality
  • User-defined wave elevation time-series
  • Imports non-dimensionalized BEMIO hydrodynamic data (instead of fully dimensional coefficients)
  • ‘Variant Subsystems’ implemented to improve code stability (instead of if statements)
  • Bug fixes

Updates in ‘dev’:

  • Morison Elements
  • Body2Body Interactions

WEC-Sim (Wave Energy Converter SIMulator) is an open source wave energy converter simulation tool being developed as a joint effort between the National Renewable Energy Laboratory (NREL) and Sandia National Laboratories (SNL) with funding from the U.S. Department of Energy’s Wind and Water Power Technologies Office.  The code is developed in MATLAB/SIMULINK using the multi-body dynamics solver SimMechanics. WEC-Sim has the ability to model devices that are comprised of rigid bodies, power-take-off systems, and mooring systems. Simulations are performed in the time-domain by solving the governing WEC equations of motion in 6 degrees-of-freedom as described in the WEC-Sim Theory Manual.

The NREL/SNL team would like to receive feedback on how WEC-Sim can be improved in the future and to facilitate this process a questionnaire has been created.  It is highly encouraged of all users to fill out the questionnaire as soon as possible.  Thank you for your time and please direct any questions about the current release to Nathan Tom, Nathan.tom@nrel.gov.

SDWED

The Structural Design of Wave Energy Devices (SDWED) project, led by Aalborg University, has had an amazing output of free software including advanced hydrodynamic models, wave to wire models, and a spectral fatigue model:

www.sdwed.civil.aau.dk/software/

Also, at the bottom of that page is a list many other free software products.

“The Structural Design of Wave Energy Devices project (SDWED) 2010-2014 is an international research alliance supported by the Danish Council for Strategic Research. The project is a five-year endeavour to harness the energy potential in wave energy at competitive costs.” (www.sdwed.civil.aau.dk/)

MoorDyn, an open-source mooring model

segments

 

MoorDyn is a lumped-mass mooring line model designed for easy coupling with other software (i.e. floating platform models). It supports arbitrary line interconnections, clump weights and floats, and different line properties. The model accounts for internal axial stiffness and damping forces, weight and buoyancy forces, hydrodynamic forces from Morison’s equation, and vertical spring-damper forces from contact with the seabed.

The original version is written in C++ and has been successfully coupled with FAST v7 and other tools/models in Matlab and Simulink. A separate Fortran-based version has recently been incorporated into FAST v8 (nwtc.nrel.gov/FAST8). More information and downloads can be found at www.matt-hall.ca/software/moordyn.