As wind turbine manufacturers seek additional ways to reduce costs and improve performance, attention has turned to improving modeling techniques as a way to reliably predict wind turbine behavior prior to expensive prototyping and testing. In particular, better designed wind-turbine blades are more effective and they create significant savings for the tower and drive train, major components in the overall system. In this regard, they reduce initial and operation costs of the entire system, thereby increasing overall competitiveness.
Originating in the aerospace industry for designing composite helicopter blades, Variational Asymptotical Beam Sectional Analysis, or VABS software, has recently gained the attention of the wind industry for its unique capabilities in realistic modeling of wind-turbine blades. The program offers users a powerful, general-purpose cross-sectional analysis tool to calculate sectional properties, including structural properties (tension center/neutral axis, centroid, elastic axis and shear center, shear correction factors, extensional, torsional, coupling, bending, shearing, and stiffness along with principal bending axes pitch angle, modulus weighted radius of gyration. Inertia properties calculated by the program include center of mass and gravity, mass per unit span, mass moments of inertia, principal inertia axes pitch angle, and mass weighted radius of gyration. Using VABS for efficient, high-fidelity design and analysis, allows saving two to three orders of magnitude in computing time relative to 3D FEA analyses, and without a loss of accuracy.
Available from AnalySwift, VABS V3.6 implements various beam theories based on the concept of simplifying the original nonlinear 3D analysis of slender structures into a 1D nonlinear beam analysis using a powerful mathematical method, the variational asymptotic method. The software models structures for which one dimension is much larger than the other two (i.e., a beam-like body), even if the structures are made of composite materials and have a complex internal structure. It takes a finite element (FE) mesh of the cross section including all the details of geometry and material as inputs to calculate the sectional properties, including structural properties and inertial properties. These properties are needed for the 1D beam analysis to predict the global behavior of the slender structure. The 3D pointwise displacement, strain, and stress distribution within the structure can also be recovered based on the global behavior of the 1D beam analysis.
Analysis can be done as efficiently and simply as conventional beam analysis, without losing accuracy compared to more complex and time-consuming 3D FEA. Users can confidently design and analyze real structures with complex microstructures due to the unique efficient, high-fidelity feature of VABS. For example, structures as complex as real composite rotor blades with hundreds of layers can be easily handled by a laptop computer.
VABS is implemented using FE techniques with a general element library that includes all typical 2D elements such as 3, 4, 5, 6-noded triangular elements and 4, 5, 6, 7, 8, 9-noded quadrilateral elements. Users are free to choose the type of elements, and different types of elements can be mixed within one mesh, when necessary. This flexibility lets VABS model beams of any shape.
The program also handles arbitrary layups. For instance, users can provide one parameter for the layup orientation and one parameter for the ply orientation to uniquely specify the material system in the global coordinate system. Nine parameters can be used for the ply orientation when a ply is highly curved and the ply angle is not uniform within an element.
There is no requirement the beam reference line be the locus of cross-sectional area centroids. The software can calculate the centroid for any arbitrary cross section, and users can choose their own reference line for the convenience of the 1D global beam analysis. Furthermore, the software can deal with isotropic, orthotropic, and general anisotropic materials.
According to Dr. Dewey Hodges, an expert in FEM and rotor blade modeling, a Senior Advisor to AnalySwift, “Because VABS is based on an asymptotic approximation of 3D nonlinear anisotropic elasticity, for a comparable set of variables it will always give results that are at least as good as the best engineering approach to beam modeling.”
A design-driven preprocessing program, PreVABS effectively generates high-resolution FE modeling data for VABS. It has the capability of modeling sophisticated cross-sectional configurations for various composite blades. It also significantly reduces intensive modeling efforts for generating a 3D FEA model, which is either time consuming or impractical, especially during the preliminary and intermediate design phases.
Commercialized by AnalySwift, VABS was originally developed at Georgia Tech and later significantly enhanced at Utah State University. Developers, users, and academic publications have extensively verified its accuracy, with continuous development spanning over 20 years. Several major wind-turbine manufacturers, national labs, the US Army, and others are using VABS. Evaluation licenses of VABS and PreVABS are available at no cost through AnalySwift.
The program can be quickly and conveniently integrated with other environments such as computer-aided design environments, multidisciplinary optimization environments, or commercial finite element packages.