Initial Conditions

This allows control over the following initial conditions for simulations.

Initial azimuth angle: This is normally zero, but a different value may be specified here. Note that for parked simulations, the initial azimuth angle defined in parked conditions is used instead.

Initial nacelle angle (from North): This is normally zero such that an upwind turbine points towards North (negative global x-axis direction), but a different value may be specified here. The initial nacelle angle matches the definition of the yaw bearing angular position. Note that if yaw dynamics is set to None or passive yaw motion option is deactivated the initial yaw direction cannot be set.

Define initial mooring position (only enabled for floating turbines): For floating turbines, the initial position of the platform can be defined. The position entered in this screen is the initial displacement of the Modal reference node defined in the tower screen in global coordinates relative to its defined position. If the Define initial mooring position box is unchecked the position of the floating wind turbine will be iterated so that steady state aerodynamic, hydrostatic, gravitational and current loads are in equilibrium.

Relaxation of the Initial Conditions

It can be necessary to add a relaxation factor to help the convergence of the numerical scheme used to calculate the initial condition of the turbine. This is especially important for complex multi-part blades and for floating offshore turbines.

Relaxation of the Modal States During Initial Conditions

A relaxation factor can be added to stabilise the calculation of the initial modal deflection. This is particularly important for multi-part blade models as no relaxation can result in poor initial deflections. The default value is 0.4 and can be adjusted in the Additional Items window. Figure 1 illustrates the initial condition algorithm and how the relaxation factor, \(R\), is introduced.

Figure 1: The initial condition algorithm with relaxation for modal deflections.

Relaxation of the Initial Platform Condition for FOWT

A relaxation factor can be added during the calculation of the initial platform position of a floating turbine to improve the convergence of the algorithm. This is useful in situations where the initial condition algorithm attempts an excessively large step that results in the turbine hitting the water or the mooring stiffnesses exceeding the range of the lookup table if used. The default value is 0.4 and can be adjusted in the Additional Items window. Figure 2 illustrates the implementation of the relaxation factor, \(R\).

Figure 2: Platform initial position algorithm with relaxation factor added.

Last updated 23-08-2024