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Mohammad Rahmati - One of the best experts on this subject based on the ideXlab platform.

  • high fidelity cfd simulations of two wind turbines in arrays using nonlinear Frequency Domain Solution method
    Renewable Energy, 2021
    Co-Authors: Shine Win Naung, M E Nakhchi, Mohammad Rahmati
    Abstract:

    Abstract Aerodynamics of a wind turbine within windfarms is strongly influenced by the wake of neighbouring turbines. In particular, the performance of a wind turbine can be dramatically reduced depending on its location in the wake region of an upstream turbine. A detailed investigation of the effect of the upstream turbine on the downstream turbine with respect to their distances is essential for the design and optimisation of wind farm layouts. Conventional time Domain Solution methods, such as Unsteady Reynolds Averaged Navier Stokes (URANS) based Computational Fluid Dynamics (CFD) model of wind turbines in arrays, can provide a detailed analysis of this interaction effect. These methods are, however, impractical due to a high computational cost required for modelling turbines in array configurations. In this paper, a novel modelling and computational method is proposed to simulate two wind turbines in arrays by considering them as a multi-stage turbine. A nonlinear Frequency Domain Solution method is then employed to model flow nonlinearities due to their interactions. The distances between the turbines are varied, and the effects of the upstream wind turbine on the downstream one are thoroughly investigated. Extensive validations of the nonlinear Frequency Domain Solution method against the conventional time Domain Solution method reveal that the proposed Frequency Domain Solution method provides accurate results while reducing the computational cost by one to two orders of magnitude.

  • nonlinear Frequency Domain Solution method for aerodynamic and aeromechanical analysis of wind turbines
    Renewable Energy, 2021
    Co-Authors: Shine Win Naung, Mohammad Rahmati, Hamed Farokhi
    Abstract:

    Abstract The aerodynamic simulations of wind turbines are typically carried out using a steady inflow condition. However, the aerodynamics and aeroelasticity of wind turbine blades can be significantly affected by inflow wakes due to the environmental conditions or the presence of neighbouring wind turbines. In this paper, the effects of flow unsteadiness on the aerodynamics and aeroelasticity of the wind turbine rotor are investigated. It is found that the unsteadiness of the wake can have an impact on the aerodynamic flow field around the wind turbine rotor and it could also influence the aeroelasticity of the wind turbine. One of the distinctive features of this paper is the application of the highly efficient nonlinear Frequency Domain Solution method for modelling harmonic disturbances for the aerodynamic and aeromechanical analysis of wind turbines. A test case wind turbine is selected for the aerodynamic and aeromechanical analysis as well as for the validation of the method used. The effects of different material properties along with a large vibration amplitude on the aeroelasticity parameter known as aerodynamic damping of the wind turbine blade are also investigated in the present work. Compared to the conventional time Domain Solution methods, which require prohibitively large computational cost for modelling and solving aerodynamics and aeroelasticity of wind turbines, the proposed Frequency Domain Solution method can reduce the computational cost by one to two orders of magnitude.

Shine Win Naung - One of the best experts on this subject based on the ideXlab platform.

  • high fidelity cfd simulations of two wind turbines in arrays using nonlinear Frequency Domain Solution method
    Renewable Energy, 2021
    Co-Authors: Shine Win Naung, M E Nakhchi, Mohammad Rahmati
    Abstract:

    Abstract Aerodynamics of a wind turbine within windfarms is strongly influenced by the wake of neighbouring turbines. In particular, the performance of a wind turbine can be dramatically reduced depending on its location in the wake region of an upstream turbine. A detailed investigation of the effect of the upstream turbine on the downstream turbine with respect to their distances is essential for the design and optimisation of wind farm layouts. Conventional time Domain Solution methods, such as Unsteady Reynolds Averaged Navier Stokes (URANS) based Computational Fluid Dynamics (CFD) model of wind turbines in arrays, can provide a detailed analysis of this interaction effect. These methods are, however, impractical due to a high computational cost required for modelling turbines in array configurations. In this paper, a novel modelling and computational method is proposed to simulate two wind turbines in arrays by considering them as a multi-stage turbine. A nonlinear Frequency Domain Solution method is then employed to model flow nonlinearities due to their interactions. The distances between the turbines are varied, and the effects of the upstream wind turbine on the downstream one are thoroughly investigated. Extensive validations of the nonlinear Frequency Domain Solution method against the conventional time Domain Solution method reveal that the proposed Frequency Domain Solution method provides accurate results while reducing the computational cost by one to two orders of magnitude.

  • nonlinear Frequency Domain Solution method for aerodynamic and aeromechanical analysis of wind turbines
    Renewable Energy, 2021
    Co-Authors: Shine Win Naung, Mohammad Rahmati, Hamed Farokhi
    Abstract:

    Abstract The aerodynamic simulations of wind turbines are typically carried out using a steady inflow condition. However, the aerodynamics and aeroelasticity of wind turbine blades can be significantly affected by inflow wakes due to the environmental conditions or the presence of neighbouring wind turbines. In this paper, the effects of flow unsteadiness on the aerodynamics and aeroelasticity of the wind turbine rotor are investigated. It is found that the unsteadiness of the wake can have an impact on the aerodynamic flow field around the wind turbine rotor and it could also influence the aeroelasticity of the wind turbine. One of the distinctive features of this paper is the application of the highly efficient nonlinear Frequency Domain Solution method for modelling harmonic disturbances for the aerodynamic and aeromechanical analysis of wind turbines. A test case wind turbine is selected for the aerodynamic and aeromechanical analysis as well as for the validation of the method used. The effects of different material properties along with a large vibration amplitude on the aeroelasticity parameter known as aerodynamic damping of the wind turbine blade are also investigated in the present work. Compared to the conventional time Domain Solution methods, which require prohibitively large computational cost for modelling and solving aerodynamics and aeroelasticity of wind turbines, the proposed Frequency Domain Solution method can reduce the computational cost by one to two orders of magnitude.

Hamed Farokhi - One of the best experts on this subject based on the ideXlab platform.

  • nonlinear Frequency Domain Solution method for aerodynamic and aeromechanical analysis of wind turbines
    Renewable Energy, 2021
    Co-Authors: Shine Win Naung, Mohammad Rahmati, Hamed Farokhi
    Abstract:

    Abstract The aerodynamic simulations of wind turbines are typically carried out using a steady inflow condition. However, the aerodynamics and aeroelasticity of wind turbine blades can be significantly affected by inflow wakes due to the environmental conditions or the presence of neighbouring wind turbines. In this paper, the effects of flow unsteadiness on the aerodynamics and aeroelasticity of the wind turbine rotor are investigated. It is found that the unsteadiness of the wake can have an impact on the aerodynamic flow field around the wind turbine rotor and it could also influence the aeroelasticity of the wind turbine. One of the distinctive features of this paper is the application of the highly efficient nonlinear Frequency Domain Solution method for modelling harmonic disturbances for the aerodynamic and aeromechanical analysis of wind turbines. A test case wind turbine is selected for the aerodynamic and aeromechanical analysis as well as for the validation of the method used. The effects of different material properties along with a large vibration amplitude on the aeroelasticity parameter known as aerodynamic damping of the wind turbine blade are also investigated in the present work. Compared to the conventional time Domain Solution methods, which require prohibitively large computational cost for modelling and solving aerodynamics and aeroelasticity of wind turbines, the proposed Frequency Domain Solution method can reduce the computational cost by one to two orders of magnitude.

Anthony T Patera - One of the best experts on this subject based on the ideXlab platform.

  • a two level parameterized model order reduction approach for time Domain elastodynamics
    Computer Methods in Applied Mechanics and Engineering, 2021
    Co-Authors: Mohamed Aziz Bhouri, Anthony T Patera
    Abstract:

    Abstract We present a two-level parameterized Model Order Reduction (pMOR) technique for the linear hyperbolic Partial Differential Equation (PDE) of time-Domain elastodynamics. In order to approximate the Frequency-Domain PDE, we take advantage of the Port-Reduced Reduced-Basis Component (PR-RBC) method to develop (in the offline stage) reduced bases for subDomains; the latter are then assembled (in the online stage) to form the global Domains of interest. The PR-RBC approach reduces the effective dimensionality of the parameter space and also provides flexibility in topology and geometry. In the online stage, for each query, we consider a given parameter value and associated global Domain. In the first level of reduction, the PR-RBC reduced bases are used to approximate the Frequency-Domain Solution at selected frequencies. In the second level of reduction, these instantiated PR-RBC approximations are used as surrogate truth Solutions in a Strong Greedy approach to identify a reduced basis space; the PDE of time-Domain elastodynamics is then projected on this reduced space. We provide a numerical example to demonstrate the computational capability and assess the performance of the proposed two-level approach.

Qingchang Zhong - One of the best experts on this subject based on the ideXlab platform.

  • Frequency Domain Solution to delay type nehari problem
    Automatica, 2003
    Co-Authors: Qingchang Zhong
    Abstract:

    This paper generalizes the Frequency-Domain results on the delay-type Nehari problem in the stable case to the unstable case. The solvability condition of the delay-type Nehari problem is formulated in terms of the nonsingularity of three matrices. The optimal value @c"o"p"t is the maximal @c@?(0,~) such that one of the three matrices becomes singular. All sub-optimal compensators are parameterized in a transparent structure incorporating a modified Smith predictor.

  • Frequency Domain Solution to the delay type nehari problem
    IFAC Proceedings Volumes, 2002
    Co-Authors: Qingchang Zhong
    Abstract:

    Abstract Abstract This paper presents a Frequency Domain Solution to the delay-type Nehari problem. The solvability condition is formulated in terms of nonsingularities of three matrices. The optimal value γopt is the maximal value such that one of the three matrices becomes singular when γ decreases from + ∞ to 0. The all sub-optimal compensators are parameterized in a transparent structure with a modified Smith predictor. The J-spectral factorization of a general para-Hermitian matrix is also given in this paper as a requisite for proof.