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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 32 more authors.
Proceedings of the International Conference on Offshore Mechanics and Arctic Engineering - OMAE

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. Source

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

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. Source

Massari M.,Polytechnic of Milan | Bernelli-Zazzera F.,Polytechnic of Milan | Canavesi S.,SAMTECH
Journal of Guidance, Control, and Dynamics

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. Source

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

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. Source

Remouchamps A.,SAMTECH | Bruyneel M.,SAMTECH | Fleury C.,University of Liege | Grihon S.,Airbus
Structural and Multidisciplinary Optimization

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. Source

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