Transient modelling of the rotor-tower interaction of wind turbines using fluid-structure interaction simulations

In this work, we focus on the effect of supporting structures on the loads acting on a large horizontal axis wind turbine. The transient fluid-structure interaction (FSI) is simulated by an in-house code which couples two solvers, one for the computational fluid dynamics (CFD) and one for the computational structure mechanics (CSM). Strong coupling is applied as the force and displacement equilibriums are always enforced on the fluid- structure interface. The flexibility of the three blades of the considered machine is taken into account. The accurate CSM model reproduces in details the composite layups, foam, adhesive and internal stiffeners of the blades. On the other hand, the supporting structures (tower and nacelle) are considered to be rigid. On the fluid side, a fully hexahedral mesh is generated by a multi-block strategy. The same mesh is continuously deformed and adapted according to the displacement of the fluid- structure interface. The atmospheric boundary layer (ABL) under neutral conditions is included and consistently preserved along the computational domain. Using the outlined model, the blade deflections with and without supporting structure are compared. The effects of this transient interaction are highlighted throughout the rotation of the rotor, in terms of both wind energy conversion performance of the machine and structural response of each component. The maximal stress in the blade material as a function of time is compared with and without the presence of the tower in the wake of the rotor. Only a few similar works are reported to appear in literature [1, 2], whereas none of them currently includes the ABL or show detailed information about the internal stresses in the composite blades

Micro-scale finite element simulation of the viscoelastic damping in unidirectional fiber reinforced composites

A micro-scale finite element method is proposed to study the damping behavior of composite materials. The study focuses on the unidirectional fiber reinforced composites including viscoelastic constituents. The proposed method is demonstrated with the simulations performed on periodic Representative Volume Elements (RVEs) composed of idealistic square packed glass fibers in an epoxy polymer. The boundary problem is solved for a cyclic loading and thereby the different loss factors are computed through the homogenized stress and strain values. The results are compared to the strain energy method which is often used in the damping study of micro-scale composites. Finally, influence of fibers distribution and fiber volume fraction on the damping behavior of a unidirectional fiber reinforced composite is investigated

On the nonlinear evolution of the Poisson’s ratio under quasi-static loading for a carbon fabricreinforced thermoplastic, Part I:

a b s t r a c t When observing or describing the damage state in a composite material, often only Young's modulus or residual deformation are considered. Generally, however, the Poisson's ratio is more sensitive to damage than those properties. Rather than observing the Poisson's ratio as function of crack density, the evolution of the Poisson's ratio as function of the longitudinal strain was studied in part I of this research, where a peculiar shape of the evolution was observed and proven to be entirely due to the material itself, rather than the sensors used for the strain measurement. In this article, a theoretical explanation for the peculiar evolution of the Poisson's ratio as function of the longitudinal strain is presented. Based on this explanation, extra experiments were conducted for validation purposes. The material used for this study is a carbon fabric-reinforced PPS

Implementation of fatigue model for unidirectional laminate based on finite element analysis : theory and practice

The aim of this study is to deal with the simulation of intra-laminar fatigue damage in unidirectional composite under multi-axial and variable amplitude loadings. The variable amplitude and multi-axial loading is accounted for by using the damage hysteresis operator based on Brokate method [6]. The proposed damage model for fatigue is based on stiffness degradation laws from Van Paepegem combined with the 'damage' cycle jump approach extended to deal with unidirectional carbon fibres. The parameter identification method is here presented and parameter sensitivities are discussed. The initial static damage of the material is accounted for by using the LadevSze damage model and the permanent shear strain accumulation based on Van Paepegem's formulation. This approach is implemented into commercial software (Siemens PLM). The validation case is run on a bending test coupon (with arbitrary stacking sequence and load level) in order to minimise the risk of inter-laminar damages. This intra-laminar fatigue damage model combined efficient methods with a low number of tests to identify the parameters of the stiffness degradation law, this overall procedure for fatigue life prediction is demonstrated to be cost efficient at industrial level. This work concludes on the next challenges to be addressed (validation tests, multiple-loadings validation, failure criteria, inter-laminar damages...)

Experimental Study and Numerical Simulation of the Large-Scale Testing of Polymeric Composite Journal Bearings: Two-Dimensional Modeling and Validation

Abstract The self-lubricating properties of some polymeric materials make them very valuable in bearing applications, where the lubrication is difficult or impossible. Composite bearings combine the self-lubricating properties of polymeric materials with better mechanical and thermal properties of the fibers. At present, there are few studies about these bearings and their design is mainly based on manufacturers' experiences. This study includes an experimental and numerical study of the large-scale testing of fiber-reinforced polymeric composite bearings. In the first part of this article, a new tribological test setup for large composite bearings is demonstrated. Besides, a two-dimensional finite-element model is developed in order to study the stress distribution in the composite bearing and kinematics of the test setup. A mixed Lagrangian-Eulerian formulation is used to simulate the rotation of the shaft and the contact between the composite bearing and the shaft. Simulation results correspond closely to the experimental data, and provide careful investigation of the stress distribution in the bearing. In the second part of this article, three-dimensional quasi-static and twodimensional dynamic models are studied

A progessive damage fatigue model for unidirectional laminated composites based on finite element analysis: theory and practice

The simulation of the fatigue damage of laminated composites under multi-axial and variable amplitude loadings has to deal with several new challenges and several methods of damage modelling. In this paper we present how to account for the complex loading by using the damage hysteresis operator approach for fatigue. It is applied to a fatigue model for intra-laminar damage based on stiffness degradation laws from Van Paepegem and has been extended to deal with unidirectional carbon fibres. The parameter identification method is presented here and parameter sensitivities are discussed. The initial static damage of the material is accounted for by using the Ladevèze damage model and the permanent shear strain accumulation based on Van Paepegem’s formulation. This approach has been implemented into commercial software. The intra-laminar fatigue damage model combines efficient methods with a low number of tests to identify the parameters of the stiffness degradation law, this overall procedure for fatigue life prediction is demonstrated to be cost efficient at industrial level

A progessive damage fatigue model for unidirectional laminated composites based on finite element analysis: theory and practice

The simulation of the fatigue damage of laminated composites under multi-axial and variable amplitude loadings has to deal with several new challenges and several methods of damage modelling. In this paper we present how to account for the complex loading by using the damage hysteresis operator approach for fatigue. It is applied to a fatigue model for intra-laminar damage based on stiffness degradation laws from Van Paepegem and has been extended to deal with unidirectional carbon fibres. The parameter identification method is presented here and parameter sensitivities are discussed. The initial static damage of the material is accounted for by using the Ladevèze damage model and the permanent shear strain accumulation based on Van Paepegem’s formulation. This approach has been implemented into commercial software. The intra-laminar fatigue damage model combines efficient methods with a low number of tests to identify the parameters of the stiffness degradation law, this overall procedure for fatigue life prediction is demonstrated to be cost efficient at industrial level