Saarblitz, Wind farm in HDR,, creative commons by-nc-sa 2.0


FOCUS6 is an integrated software package for the development and design of wind turbines. FOCUS6 is developed on a database which facilitates the interaction of various computer programs that are involved in the wind turbine design process. Among these programs is PHATAS 'Program for Horizontal Axis wind Turbine Analysis and Simulation', part of the Aeroelasticy II module of FOCUS6. FOCUS6 is developed and supported by the Knowledge Centre WMC, see

PHATAS was developed in late eighties and was benchmarked since in all major European benchmark projects. This development has resulted in a program that is suitable for the design and certification of bottom-fixed land- or offshore- wind turbines.  The implementation under FOCUS6 facilitates the calculation of a complete design load set following the IEC or GL design standards. For the application to wind turbines on a floating support, a re-structured version is available that couples with programs for the hydrodynamic motion of a floating body such as aNySIM (by MARIN) or Ansys-AWQA. The public turbine (OWEC) that is modelled in PHATAS is the NREL 5MW within the OC3 and OC4 projects.

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Submitted by Martijn van Roermund on September 10, 2015 - 11:32am
Main hypothesis
The computer program Phatas, ”Program for Horizontal Axis wind Turbine Analysis and Simulation”, is developed for the time-domain calculation of the dynamic behaviour and the corresponding loads on a Horizontal Axis wind Turbine. Phatas calculates the dynamic response of a wind turbine that covers the structural dynamic deformation of the turbine structure, the unsteady aerodynamic loads on the blades and tower, and the interactions from an operational controller and a Supervisory controller. The mutual equilibrium between all these sub-models is obtained by performing each time step an iterative solution of the full non-linear set of coupled equations. The program Phatas is developed as a tool under the design package FOCUS6, maintained by WMC. Within FOCUS6, the aerodynamic capabilities can be extended by linking Phatas to external calculation modules, such as the ECN Aeromodule.
Structural dynamics
Turbulence model
A turbulent wind field is generated by the tool SWIFT. The underlying algorithm of SWIFT is based on a Fourier synthesis method for the simulation of multivariate, multidimensional random processes.In particular SWIFT simulates numerically an uni-variate (only the u-component of the wind speed vector) , three-dimensional (time and two polar coordinates) random field. The wind simulation method has been outlined by P.S. Veers.
Wave kinematics
Wave theory
Forces on the support structure from waves and current are calculated following the Morison equation. These forces include the drag from the relative velocity of the water w.r.t. the tower elements, and the inertia forces from water acceleration and also from acceleration of the tower elements. The basic approach treats the support structure as monopole. A recent development on basis of a FEM model allows to describe the wave forces on each of the structural elements. The latter approach takes the 3D-orientation of the tower elements (with respect to the water velocity vector) into account, and also includes the variation of the Archimedes forces with wave height.
Free surface correction
The variation of wave height is included by stretching the wave kinematics (velocities and accelerations) linear from the seabed to the wave surface, which is named Wheeler stretching. This Wheeler stretching is implemented in the program Phatas while reading the wave kinematics files.
Wave spectrum
The wave kinematics can be generated with the program ROWS or with the program Streamfunction. ROWS generates a file with random wave spectrum based on linear Airy wave theory. The wave file applies to e.g. the Pierson Moskowiz spectrum or the JONSWAP spectrum, depending on the input for the 'peakedness parameter'. Streamfunction generates a file with a non-linear (extreme) wave, of which the order can be set by the user.

[1]    Lindenburg C., “PHATAS Release ‘Jan-2014a’ User’s manual.” ECN-I--05-005, ECN Petten, 2005

[2]    Lindenburg C. and J.G. Schepers, “PHATAS-IV AEROELASTIC MODELLING” ECN-CX-00-027, 2001

[3]   Winkelaar D., “SWIFT - Program for Three-Dimensional Wind Simulation,” ECN-R–92-013,  2013.

[4]    Peeringa J.M., “Current ROWS manual” ECN-X–12-059, ECN Petten, 2013.

[5]    Peeringa J.M., “STREAM FUNCTION WAVE PROGRAM User's manual” ECN-C-05-028,  2005.

[6]    Gueydon, S., K. Lindeburg, and J. Peeringa, “Coupling of PHATAS to aNySIM,” MARIN & ECN, Proposal no. 2.1, Sep. 2011.

[7]    Marin, “ANYwiki.” Oct-2014.

A coupling with Marin aNySIM has been made for floating wind turbines. Please refer to aNySIM documentation or the aNySIM Wiki to learn more about the capabilities of aNySIM on hydrodynamic interaction and mooring lines.

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