The QBlade Software
QBlade is a beyond the state of the art aero-servo-hydro-elastic code, covering the complete range of aspects required for wind turbine design, simulation, and certification. QBlade has been developed, tested, and validated during more than 10 years from the ground up, favoring a modular implementation of highly efficient novel aerodynamic, structural dynamic and hydrodynamic solvers in a modern, object-oriented C++ framework.
Designed from ground up for modern PC architecture
QBlade leverages the current computer architecture by thoroughly utilizing CPU (via OpenMP) and GPU (via OpenCL) parallelization techniques for an unprecedented numerical performance. This enables us to run simulations with advanced physical models of thousands degrees of freedom with an incomparable accuracy and faster than real time performance. QBlade is a platform independent software, and can be deployed on workstations or clusters running Windows, Unix or MacOS based operating systems.
Advanced wind turbine simulations for everyone
A driving force during our whole development process is to make wind turbine design and simulation effortless, fun and accessible to everyone. To realize this, we equipped QBlade with an intuitive graphical user interface that aids the user during the whole wind turbine design process. All turbine and simulation details are readily available to be accessed and modified in a logical well-structured and tested interface.
Simulation results are presented in dynamic graphs that give insight into every simulation detail. Simulations and turbine designs are fully rendered in real time to reinforce user interaction, and to aid with the comprehension and evaluation of our complex multi-physics models. QBlade makes it simple to serialize the complete model data, setup and results into project files to enable simple sharing and collaboration of complex simulation and turbine design projects.
The Community Edition (CE) of QBlade is freely available to everyone under the public-source Academic Public License.
What Drives Us
Wind turbine designs have changed dramatically over the past 30 years, with ever increasing rotor sizes, higher complexity in blade and tower and on- and offshore foundation designs. However, during the same time, the aerodynamic methods that are used to design these wind turbines have not significantly changed or improved, and still rely on a largely simplified model that was developed almost 100 years ago, the Blade Element Momentum (BEM) method.
Owing to the ever increasing importance of aeroelastic phenomena that occur in larger, softer rotors and the recent introduction of floating turbine structures, undergoing large movements, many of the assumptions that are fundamentally inherent in the BEM theory are violated or completely broken – and cause a growing uncertainty during the whole turbine design process.
A new standard for wind turbine simulations
Our motivation is to set the new standard for wind turbine aerodynamic simulation tools, by substituting the BEM method with its modern counterpart, the LLFVW (Lifting Line Free Vortex Wake) method.
The LLFVW eliminates almost all of the assumptions that are inherent in the BEM, increasing the accuracy and reducing the uncertainty of numerical simulations and enabling more efficient on-point turbine designs.
Due to its general, assumption free formulation the LLFVW enables the simulation of unusual turbine geometries, such as vertical axis wind turbines, highly swept blades or multi-rotor turbines and their wake interaction. Especially in dynamic conditions, when blades undergo large deflections, during emergency stops or when floaters are operated in severe sea states the LLFVW leads to considerable improvements in load prediction accuracy of up to 15%.
Aerodynamic Model
QBlade employs a highly optimized and thoroughly validated Lifting Line Free Vortex Wake Method for its aerodynamic calculations. Instead of approximating the wake aerodynamics with a steady-state momentum balance (BEM), the rotor wake is explicitly modeled through Lagrangian vortex elements. This results in a more accurate and detailed spatial and temporal representation of the rotor induction, when compared to BEM, and fully resolves velocity distribution around the rotor. This allows to assess wind turbine wake interactions, accurately accounts for the aerodynamics of oscillating floating wind turbine structures and explicitly resolves unsteady vertical axis wind turbine wake dynamics.
The LLFVW method requires the same input data as the conventional BEM method, so existing BEM models of a rotor design can simply be reevaluated in LLFVW simulations for increased accuracy and more detailed insights.
Integrated dynamic stall models
QBlade integrates several ways to include dynamic stall in its aerodynamic model. Dynamic stall can be modeled via the advanced ATEFlap model, the commonly used Oye dynamic stall model or the Gormont-Berg model that is specifically adapted for vertical axis wind turbine operation.
Active flaps and other aerodynamic add-ons
Through the use of dynamic polar sets QBlade can model rotor blades with distributed active control surfaces. The actuation of these control surfaces can be controlled by turbine controller libraries or simple harmonic functions.
Ready for design load calculations
Running a highly optimized code with OpenCL GPU parallelization, OpenMP CPU parallelization and wake coarsening techniques reduces the computational cost by 5-6 orders of magnitude, compared to a naïve sequential implementation. This allows the integration of aerodynamic simulations with unprecedented accuracy and detailed rotor wake insights into the turbine design and certification process for the first time with faster than real time numerical performance on a workstation.
Structural Dynamics Model
The structural dynamics in QBlade are modeled in a true multi-body formulation. The sub components of the multi-body model are made up of rigid- or flexible nonlinear Euler beam elements in a co-rotational formulation.
For floating offshore simulations QBlade integrates cable elements in the absolute nodal coordinate formulation (ANCF) which meet the requirements to effectively model the nonlinear dynamics of complex mooring systems.
The different structural sub components are assembled using a range of constraints, fixing their relative positions along the required degrees of freedom. In addition springs or dampers can be specified to allow a compliant movement of structural parts.
The structural models can be linearized around any turbine operating point to assess the Eigen modes and frequencies of the structure.
Highly flexible, efficient and stable
Our multi-body formulation, based on the open source multi-physics library Project Chrono, exhibits an unrivaled numerical stability and performance. Even extreme situations, such as wind turbines operating during an earthquake or floating turbines in the most severe sea states can be modeled in real time. The flexibility of this formulation allows for a large freedom when designing custom wind turbine substructures, such as new offshore floater concepts, truss towers or multi rotor turbine assemblies.
Simple model setup and data import
Setting up detailed structural models in QBlade is simple and fun, all structural assemblies can be investigated in detail in the graphical user interface. QBlade makes it easy to import existing structural definitions in HAWC2, BLADED or FAST format and can interpret a range of different file formats
Hydrodynamic Model
Both bottom-fixed and floating offshore wind turbine systems can be modeled in QBlade. The hydrodynamic loads on the wind turbine’s substructure are calculated either via the potential flow theory, the Morison equation-based strip theory or a user defined combination of the two. The integrated potential flow approach also includes the higher order slow drift forces obtained from quadratic transfer functions. QBlade integrates with potential flow data from common software such as the WAMIT, NEMOH or BEMUSE toolboxes.
A true local formulation for flexible floaters
Multiple potential flow bodies can be combined into a single substructure definition. In general, the floaters are composed of several flexible structural elements that are connected rigidly, via compliant constraints or even through mooring lines.
During the simulation all hydrodynamic loads are evaluated locally at the current displaced position of each hydrodynamic element to include the effects of the current floater position, its orientation and structural deformation. To obtain realistic wave velocities near the sea level several methods for wave stretching are implemented.
Buoyancy can be introduced through a linear hydrodynamic stiffness matrix or can be evaluated explicitly for each structural element in detail, based on the current local sea elevation, the element orientation and its submerged volume.
A simple solution to the added mass instability
The added mass instability phenomena, often encountered in fluid-structure interaction problems is solved by including the added mass forces through the instantaneous adjustment of an additional non-uniformly distributed inertia matrix at each hydrodynamic element, allowing the use of highly efficient loosely coupled numerical solvers for the fluid structure interaction problem.
Controller Integration
Full supervisory wind turbine controllers can easily be integrated with all wind turbine designs. QBlade supports both Bladed- and DTU style DLL controllers, so existing controllers can be reused without any modifications. In addition we have published our own open-source controller architecture, the TUB controller [8], with advanced functionality such as individual blade pitch control (IPC), which is parametrized in a convenient XML format.
Wind Generation
NREL’s TurbSim software is seamlessly integrated with QBlade, to generate IEC compliant, turbulent windfields on the fly that can represent any inflow condition. Furthermore, QBlade handles the generation of all deterministic IEC inflow conditions automatically through its Design Load Case (DLC) preprocessor and is compatible with NREL’s hub height (.hht) wind data format. In steady operating conditions uniform wind, power law or logarithmic wind profiles and linear directional wind gradients can be defined for a simulation.
Wave Generation
QBlade incorporates its own sophisticated generatror for linear wave fields. Several spectra (Jonswap, ISSC, Torsethaugen, Ochi Hubble, custom) are available to generate uni- or multidirectional irregular wavefields. The user can choose between the equal energy or the equal frequency step discretization methods for the wave spectrum. In addition, custom, user-defined spectra, wave components or wave timeseries can easily be imported into QBlade.
