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## alaska/Wind Features

The direct integration of alaska/Wind into the multi-body dynamics simulation environment alaska/MultibodyDynamics ensures that the interactions of aerodynamics, flexible structures, detailed pitch, yaw and powertrain models, control systems and the plant environment (electrical network, earthquake, etc.) are automatically taken into account.

Key characteristics of alaska/Wind are:

#### Model development in the alaska/ModellerStudio

The development and use of alaska/Wind simulation models is done directly in the alaska/ModellerStudio. The usage of alaska/Wind-specific model components works in the exact same manner as for other alaska model components. The modeling process is interactive. New model components are defined using drag and drop. Alternatively, simulation models can be 'programmed', i. e. defined with any ASCII editor using the alaska model description language.

#### Extensibility of the basic simulation model

The basic simulation model of alaska/Wind is an example of a wind turbine with three rotor blades and horizontal drive train. Based on this simulation model, the user can develop his own simulation models. These can significantly exceed the functionality of the basic model. Both the model structure and the depth of modeling can be freely adapted to current requirements. Detailed drive trains with high-resolution transmission models (assisted by alaska/Gear), detailed pitch and azimuth drives and absorber models are possible, as well as hubs with different number of blades or other drive train concepts.

#### Nonlinear system analysis in alaska/ModellerStudio

The nonlinear analysis of simulation models in alaska/ModellerStudio offers the user direct visual and numerical feedback. The current system behavior is displayed simultaneously with the calculation. Especially in the development of simulation models, the user thus has immediate access to all MBD simulation results such as the current movement state of bodies and joints, reaction forces and moments in coupling points, current acting forces such as wind forces at blade stations, input and output data of controllers, etc.

#### Linear system analysis in alaska/ModellerStudio

alaska/Wind simulation models can be subjected to a linear analysis. The behavior of the simulation model in the frequency domain is determined. This analysis can be performed both for the idle state of the modelled wind turbines and for any operating state. The calculated eigenfrequencies and the associated eigenmodes of vibration are displayed in the alaska/ModellerStudio in arbitrary 3D-views and can be exported in a user selectable form.

#### Automatic system analysis with alaska/Batch

For routine calculations with a validated simulation model, alaska/Batch can be used. alaska/Batch is the command line oriented variant of the alaska/ModellerStudio. With alaska/Batch all available analyses, e. g. non-linear and linear system analysis, can be carried out completely automated. The process of calculating wind turbines can thus become an integrated sub-process in a superordinate process consisting of data provision, calculation and evaluation.

#### Use of nonlinear non-reduced FE beam models

An essential component of wind turbine simulation models are rotor blade models. The flexibility of the rotor blades is taken into account by using modal reductions of FE beam models. With increasing slenderness of the rotor blades, this simplification is often no longer sufficient. Therefore, alaska/Wind offers the possibility to use FE beam models for rotor blades and towers in an unreduced form. For rotor blade simulation models, relevant properties such as bending torsion coupling and geometric stiffening are considered a priori.

#### Efficient solver for numerically stiff systems

alaska/MultibodyDynamics offers different integrators for the analysis in the time domain. Depending on the type of model description and thus the type of equations to be solved, explicitly and implicitly working integrators are available. For numerically stiff systems, resulting e. g. from the use of non-reduced FE beam structures, a generalized alpha method is used. This method solves these systems very efficient and extremely robust.

#### Definition of arbitrary results

The simulation environment allows access to all results of the system analysis. In addition, the user is free to define his own model observation variables, which can be calculated from the primary results. Standard interfaces are available for output. Via an additional freely programmable interface, the user is given the possibility to export calculation results in any format according to his post-processing.

#### Use of the alaska sub-model technique

alaska/Wind simulation models can consist of sub-models. Complete models are combined from several sub-models. The connection of the sub-models is completely automatic. The exchange of information between sub-models is carried out via data channels. The sub-models are connected by defining coupling points. The alaska/Wind basic simulation model consists of sub-models. Based on this, the user can develop his own sub-models. alaska sub-models offer very good possibilities to separate the parameterized model definitionfrom the model configuration, i. e. the parameter values to be used at the moment.

Sub-models can be run independently and can therefore be developed, tested and used separately. This means that, for example, a blade or drive train or parts of it can be loaded individually, subjected to loads and analysed. This offers, for example, the possibility to carry out virtual test rig investigations. Likewise, any sub-model combinations, e. g. rotors consisting of hub and blades or nacelles with drive train can be simulated individually.

#### Using ParameterSets

alaska ParameterSets are the basis for defining different design load cases in alaska/Wind. ParameterSets are separate files in XML format that contain model parameter values sorted in tabular order. These files can be generated either with a special editor from the alaska/ModellerStudio or, based on the documented format, with a user-specific external program, e. g. from a simulation data management program. Via ParameterSets any model data can be varied.

#### Load case calculation with alaska/DC

For the large number of load case calculations that usually occur during the development of wind turbines, alaska/DC can be used. DC stands for distributed computation. alaska/DC automatically and very efficiently distributes many individual calculation tasks, which are grouped together in ParameterSets, to several computers connected to each other in the network or to computing clusters.

#### Definition of seismic influences

By describing the alaska/Wind simulation model directly in the general MBD modeling and simulation environment alaska/MultibodyDynamics, any disturbances occurring at the wind turbine can be modelled. The effect of earthquakes can be described, for example, by specifying the movement of the foundation using externally defined time series.

#### Definition of extreme load scenarios

In addition to the load scenarios generally to be taken into account in the development and design of wind power plants, which take into account certain wind influences (gusts, turbulence etc.) and the effects of control/operation management (start up processes, emergency shutdown etc.), it is possible to depict extreme load scenarios using the MBD modelling capabilities of alaska/MultibodyDynamics, e. g. to simulate extreme load scenarios. These include dropping entire rotor blades or parts of them and extreme gusts during construction and much more.

#### System matrices and transfer function

For the development of controllers, for example, the system matrices A, B, C and D of the linearized system of the simulation model and, for defined inputs and outputs, the transfer function can be exported.