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Robertson A.,National Renewable Energy Laboratory | Jonkman J.,National Renewable Energy Laboratory | Vorpahl F.,Fraunhofer Institute for Wind Energy and Energy System Technology | Popko W.,Fraunhofer Institute for Wind Energy and Energy System Technology | And 33 more authors.
Proceedings of the International Conference on Offshore Mechanics and Arctic Engineering - OMAE | Year: 2014

Offshore wind turbines are designed and analyzed using comprehensive simulation tools (or codes) that account for the coupled dynamics of the wind inflow, aerodynamics, elasticity, and controls of the turbine, along with the incident waves, sea current, hydrodynamics, mooring dynamics, and foundation dynamics of the support structure. This paper describes the latest findings of the code-to-code verification activities of the Offshore Code Comparison Collaboration Continuation project, which operates under the International Energy Agency Wind Task 30. In the latest phase of the project, participants used an assortment of simulation codes to model the coupled dynamic response of a 5-MW wind turbine installed on a floating semisubmersible in 200 m of water. Code predictions were compared from load case simulations selected to test different model features. The comparisons have resulted in a greater understanding of offshore floating wind turbine dynamics and modeling techniques, and better knowledge of the validity of various approximations. The lessons learned from this exercise have improved the participants' codes, thus improving the standard of offshore wind turbine modeling. Copyright © 2014 by ASME.

Eyckens P.,Catholic University of Leuven | Belkassem B.,Vrije Universiteit Brussel | Henrard C.,Samtech | Gu J.,Vrije Universiteit Brussel | And 6 more authors.
International Journal of Material Forming | Year: 2011

Incremental Sheet Forming (ISF) is a relatively new class of sheet forming processes that allow the manufacture of complex geometries based on computer-controlled forming tools in replacement (at least partially) of dedicated tooling. This paper studies the straining behaviour in the Single Point Incremental Forming (SPIF) variant (in which no dedicated tooling at all is required), both on experimental basis using Digital Image Correlation (DIC) and on numerical basis by the Finite Element (FE) method. The aim of the paper is to increase understanding of the deformation mechanisms inherent to SPIF, which is an important issue for the understanding of the high formability observed in this process and also for future strategies to improve the geometrical accuracy. Two distinct large-strain FE formulations, based on shell and first-order reduced integration brick elements, are used to model the sheet during the SPIF processing into the form of a truncated cone. The prediction of the surface strains on the outer surface of the cone is compared to experimentally obtained strains using the DIC technique. It is emphasised that the strain history as calculated from the DIC displacement field depends on the scale of the strain definition. On the modelling side, it is shown that the mesh density in the FE models plays a similar role on the surface strain predictions. A good qualitative agreement has been obtained for the surface strain components. One significant exception has however been found, which concerns the circumferential strain evolution directly under the forming tool. The qualitative discrepancy is explained through a mechanism of through-thickness shear in the experiment, which is not fully captured by the present FE modelling since it shows a bending-dominant accommodation mechanism. The effect of different material constitutive behaviours on strain prediction has also been investigated, the parameters of which were determined by inverse modelling using a specially designed sheet forming test. Isotropic and anisotropic yield criteria are considered, combined with either isotropic or kinematic hardening. The adopted constitutive law has only a limited influence on the surface strains. Finally, the experimental surface strain evolution is compared between two cones with different forming parameters. It is concluded that the way the plastic zone under the forming tool accommodates the moving tool (i. e. by through-thickness shear or rather by bending) depends on the process parameters. The identification of the most determining forming parameter that controls the relative importance of either mechanism is an interesting topic for future research. © 2010 Springer-Verlag France.

Massari M.,Polytechnic of Milan | Bernelli-Zazzera F.,Polytechnic of Milan | Canavesi S.,Samtech
Journal of Guidance, Control, and Dynamics | Year: 2012

The feasibility of a nonlinear state-dependent Riccati equation (SDRE) control design for relative position control of satellite formations is demonstrated. The design can include options for collision avoidance. Although there is no formal proof of the asymptotic stability of the closed-loop system, the necessary conditions for stability are verified and the test cases presented show indeed stable dynamics. Adoption of the SDRE technique requires a minimal effort to set up the state-dependent coefficient form however, once this is defined, it is rather easy to design the controller and tune its performances. The design method proposed can be extended to a higher number of satellites for the formation-keeping control, whereas a direct extension of the collision avoidance is feasible only if there is a guarantee that only one pair of satellites at a time are at risk of collision.

Remouchamps A.,SAMTECH | Bruyneel M.,SAMTECH | Fleury C.,University of Liège | Grihon S.,Airbus
Structural and Multidisciplinary Optimization | Year: 2011

In this paper, topology optimization is used to design aircraft pylons. Original results for two Airbus pylons are first presented. An innovative bi-level optimization scheme is then proposed, which combines topology and geometric optimizations. At the first level, the dimension of the design domain, that is the envelope of the structure, and the location of the fixations are variables. At the second level, topology optimization is used to determine the optimal layout for given geometric parameters. This bi-level scheme is used to solve the aero-structural optimization of a pylon. © Springer-Verlag 2011.

Pavot S.,Ecole Normale Superieure de Cachan | Florentin E.,Ecole Normale Superieure de Cachan | Pasquet P.,SAMTECH | Guinard S.,Airbus
Civil-Comp Proceedings | Year: 2012

In this work, we focus on error estimation for the assembly problem. We develop an estimator dedicated to industrial structures where the cost is of primary importance. The method is based on the constitutive relation error and associated admissible field construction. © Civil-Comp Press, 2012.

Bruyneel M.,SAMTECH | Bruyneel M.,University of Liège | Delsemme J.-P.,SAMTECH | Jetteur P.,SAMTECH | And 2 more authors.
JEC Composites Magazine | Year: 2014

In this paper, the LMS Samtech Samcef finite element code is used to assess the damage tolerance of composite structures. Delamination (ply separation), which is one of the most dangerous and predominant failure modes in laminated composites, is addressed. Two methods are used. The first one is based on a pure fracture mechanics approach, namely VCE (virtual crack extension), while the second method relies on cohesive elements and on continuum damage mechanics. These methods are implemented in the commercial version of LMS Samtech Samcef. This means that, besides the commercial FE solver, no additional (and costly) plug-ins providing such capabilities are required to solve the problem. Another advantage is that the user does not have to implement academic methods or models that may be described in the literature. Even if the openness of LMS Samtech Samcef is available via material user routines, a native implementation in a commercial software program always provides a more reliable solution.

Van Eekelen A.J.,SAMTECH | Lachaud J.,NASA
10th AIAA/ASME Joint Thermophysics and Heat Transfer Conference | Year: 2010

Direct numerical simulations of radiation heat-transfer have enabled the validation of a semi-analytical model for the effective radiative conductivity of two-dimensional carbon-fiber preforms. The effective conductivity is shown to be a function of three parameters: the local temperature, the extinction coefficient, and the sample thickness. The integration of the proposed model in state-of-the-art ablation tools is relatively simple because only the effective conductivity needs to be modified (the formulation of the energy equation is not modified). This fundamental study has been applied to ablation. In the ablation zone of low-density carbon-resin composites, the matrix is removed and the carbon fibers lie unprotected. The effective radiative conductivity is found to be about twice as large when the matrix is removed. Although the ablation zone is very thin, its presence is shown to slightly modify the internal temperature profile. © 2010 by the American Institute of Aeronautics and Astronautics, Inc.

Van Eekelen A.J.,SAMTECH | Lachaud J.,University of California at Santa Cruz
Journal of Spacecraft and Rockets | Year: 2011

The numerical validation of an effective radiation heat transfer model for fiber preforms is investigated. The fiber volume fraction of carbon-fiber preform is typically about 0.1. The model material for the direct numerical simulation (DNS) is generated using a Monte-Carlo procedure in which the non-overlapping fibers are randomly placed in a rectangular box until the required volume fraction is obtained. An electromagnetic wave or photon passing through the immediate vicinity of a fiber is either absorbed or scattered. The scattering is due to three separate phenomena that includes diffraction, reflection and refraction. The carbon-fiber surface is rough, generating a diffuse reflection. The diffraction is critical when the wavelength is not small compared with the fiber diameter. The steady-state analysis is performed for five different configurations and all five configurations are generated in such a way that they have the same fiber volume fraction, resulting in an effective density of 175.68 kg/m3.

Giraud L.,National Polytechnic Institute of Toulouse | Haidar A.,National Polytechnic Institute of Toulouse | Pralet S.,SAMTECH
Parallel Computing | Year: 2010

Large-scale scientific simulations are nowadays fully integrated in many scientific and industrial applications. Many of these simulations rely on modelisations based on PDEs that lead to the solution of huge linear or nonlinear systems of equations involving millions of unknowns. In that context, the use of large high performance computers in conjunction with advanced fully parallel and scalable numerical techniques is mandatory to efficiently tackle these problems. In this paper, we consider a parallel linear solver based on a domain decomposition approach. Its implementation naturally exploits two levels of parallelism, that offers the flexibility to combine the numerical and the parallel implementation scalabilities. The combination of the two levels of parallelism enables an optimal usage of the computing resource while preserving attractive numerical performance. Consequently, such a numerical technique appears as a promising candidate for intensive simulations on massively parallel platforms. The robustness and parallel numerical performance of the solver is investigated on large challenging linear systems arising from the finite element discretization in structural mechanics applications. © 2009 Elsevier B.V. All rights reserved.

Jetteur P.,Samtech | Pasquet P.,Samtech
European Journal of Computational Mechanics | Year: 2010

A new 3D solid shell element is developed in SAMCEF™ code. The purpose of this element is to make the meshing easier starting from a 3D definition of the structure, it is not necessary to extract the mean surface of the shell. Here, we are not concerned by the meshing; we only are concerned by the element formulation. In order to improve the quality of the results, we add internal degrees of freedom as suggested by Simo and co-authors. We use the Enhanced Assumed Strain method. A special handling of the transverse shear is performed in order to pass successfully the plate patch test (constant bending) and to avoid shear locking. The formulation is based on the work of Bathe and Dvorkin for classical shell. The element has been developed in linear and non-linear analysis; it can be a mono or multilayer element. © 2010 Lavoisier, Paris.

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