Technical specifications

Ashes utilizes the finite element method (FEM) in conjunction with a co-rotational formulation of beam elements to determine the dynamic response of the structure. The co-rotational formulation leads to accurate results in arbitrarily large displacements and rotations in space. For instance, centrifugal forces appear naturally in e.g. the blades. A linear solution of the equations of motion can be used in cases where nonlinear effects are unimportant, while a full Newton-Raphson iterative scheme can be utilized when nonlinear effects are of interest. Ashes automatically selects the appropriate solver based on the model, analysis type and characteristics of the load cases. Linearized buckling can further be studied.

Aerodynamic loads are determined by using the blade element momentum (BEM) theory, which are fully coupled to the structural response. Ashes includes models of losses due to the presence of the tower and the hub, as well as tip losses. Steady wind, yawed inflow, wind shear and different turbulence models are supported. Wave loads are computed using the Morison equation coupled with the structural response. Buoyancy loads, both linear and nonlinear can be included.

A customizable proportional-integral (PI) controller controls the applied generator torque and pitching of the blades. Custom control systems can further be included through an external DLL file compatible with Bladed.

The user interface is built on the Qt framework while OpenGL is used for 3-D visualization. Except for Qt, Ashes uses no external libraries. All code is written in C++ on object-oriented principles. We mainly develop for releasing on Windows desktops, but also consider specializing Ashes for use on mobile devices.