The Experts below are selected from a list of 297 Experts worldwide ranked by ideXlab platform

Mohamed Abdelrohma - One of the best experts on this subject based on the ideXlab platform.

  • multi loop feedback control of offshore steel jacket platforms
    Computers & Structures, 1999
    Co-Authors: Mohamed Terro, Magdi S Mahmoud, Mohamed Abdelrohma
    Abstract:

    Abstract In this paper, a new multi-loop feedback-control design is developed and applied to an offshore steel jacket platform. The platform is subjected to wave-induced self-excited hydrodynamic forces. The nonlinear Morison Equation is employed to estimate these wave forces. The feedback control design proceeds in two consecutive loops: an inner loop for regulating a linear part of the platform dynamics and an outer loop to accommodate the nonlinearities while maintaining the overall stability. A SIMULINK model is designed to simulate the response of a three-floor steel jacket platform example. Results of the simulation of this structure with and without feedback-control are discussed to demonstrate the effectiveness of this control method.

Hiroki Kikuchi - One of the best experts on this subject based on the ideXlab platform.

  • development of an analysis code of rotor floater coupled response of a floating offshore wind turbine
    ASME 2013 32nd International Conference on Ocean Offshore and Arctic Engineering, 2013
    Co-Authors: Hideyuki Suzuki, Hajime Shibata, H Fujioka, Shinichiro Hirabayashi, Kimiko Ishii, Hiroki Kikuchi
    Abstract:

    Coupled rotor-floater response analysis is essentially important for the design of Rotor Nacelle Assembly (RNA) and floating support structure of Floating Offshore Wind Turbine (FOWT). The authors have developed an analysis code UTWind for analysis of the coupled structural response. Blades and floater are modeled as frame structure with beam elements. Lumped mass model is use for mooring. Aerodynamic load on blade is calculated by Blade Element Momentum Theory (BEM), and hydrodynamic load is calculated by Hooft’s method, and Morison Equation was modified to be applicable to cylindrical element with cross section with two axes of lines symmetry. The Equations of motion of rotor, floater and mooring are solved in time domain by weak coupling algorithm. The numerical results by the code were compared with responses measured by experiment in wave and wind-and-wave coexistence field with/without blade pitch control and showed good agreement. Response by negative damping was reproduced by the code and showed good agreement with experiments.Copyright © 2013 by ASME

Guillaume De Hauteclocque - One of the best experts on this subject based on the ideXlab platform.

  • stochastic linearization of the Morison Equation applied to an offshore wind turbine
    ASME 2015 34th International Conference on Ocean Offshore and Arctic Engineering, 2015
    Co-Authors: Charaf Ouled Housseine, Charles Monroy, Guillaume De Hauteclocque
    Abstract:

    This paper aims at comparing different implementations of the Morison Equation for seakeeping analysis in frequency domain. For more consistency, different wave models are considered and the total wave field (incoming wave, the diffracted and the radiated wave field) is included in the Morison Equation.A state-of-the-art of theMorison Equation and the drag force linearized forms are presented. The implementation procedure, based on an iterative frequency domain scheme, is developed for the regular and the irregular wave cases.Seakeeping analysis of an offshore wind turbine is considered as an application case. A comparison between numerical simulations and measured responses is presented.For the floater’s numerical model, skirts damping effect and hydrodynamic loads applied on cylindrical bracings are modeled using the Morison Equation. The drag and inertia coefficients are considered constant for all sea states and calibrated using the experimental results.Response amplitude operators (RAOs) and short-termstatistics of motions show a good agreement between experimental and numerical results. The influence of different calculation parameters including the wave model (regular/irregular) and the wave fields (incident/total) are investigated.Copyright © 2015 by ASME

Erik Lund - One of the best experts on this subject based on the ideXlab platform.

  • Structural optimization with fatigue and ultimate limit constraints of jacket structures for large offshore wind turbines
    Structural and Multidisciplinary Optimization, 2017
    Co-Authors: Jacob Oest, René Sørensen, Lars Chr. T. Overgaard, Erik Lund
    Abstract:

    The purpose of the research presented in this paper is to develop and implement an efficient method for analytical gradient-based sizing optimization of a support structure for offshore wind turbines. In the jacket structure optimization of frame member diameter and thickness, both fatigue limit state, ultimate limit state, and frequency constraints are included. The established framework is demonstrated on the OC4 reference jacket with the NREL 5 MW reference wind turbine installed at a deep water site. The jacket is modeled using 3D Timoshenko beam elements. The aero-servo-elastic loads are determined using the multibody software HAWC2, and the wave loads are determined using the Morison Equation. Analytical sensitivities are found using both the direct differentiation method and the adjoint method. An effective formulation of the fatigue gradients makes the amount of adjoint problems that needs to be solved independent of the amount of load cycles included in the analysis. Thus, a large amount of time-history loads can be applied in the fatigue analysis, resulting in a good representation of the accumulated fatigue damage. A reduction of 40 % mass is achieved in 23 iterations using the CPLEX optimizer by IBM ILOG, where both fatigue and ultimate limit state constraints are active at the optimum.

Norimi Mizutani - One of the best experts on this subject based on the ideXlab platform.

  • numerical estimation of the wave forces acting on a three dimensional body on submerged breakwater
    Coastal Engineering, 2003
    Co-Authors: Norimi Mizutani
    Abstract:

    Numerical models have been developed to estimate the wave forces acting on a three-dimensional body on a submerged breakwater. These models combine the VOF model and porous body model to simulate the nonlinear wave deformation including wave breaking and its interaction with a porous structure. One model is two-dimensional and is associated with empirical wave force formulae, like the Morison Equation. The other one is three-dimensional and does not require any empirical formula or coefficients. Comparison of estimated and measured wave forces shows good agreement, both in two- and three-dimensional model cases, and the present estimation methods are revealed to be powerful tools for estimation of wave force acting on a three-dimensional body, even for breaking wave condition.

  • wave forces on a structure installed on a submerged breakwater and applicability of Morison Equation
    PROCEEDINGS OF CIVIL ENGINEERING IN THE OCEAN, 1999
    Co-Authors: Norimi Mizutani, Donsu Hur, Yoshitomo Yonese, Katsuhiko Kurata, Masao Endoh, Koichiro Iwata
    Abstract:

    Wave forces on a structure installed on a submerged breakwater have been measured to investigate their characteristics. It has been observed that the impulsive wave force due to wave breaking acts on the structure located the vicinity of the leading crown of the breakwater. Them agnitude of the impulsive wave force has been revealed to be much larger than those of then on-breaking waves. Thet imev ariation of the impulsive wave force is well evaluated with the Morison Equation by adopting the velocity and acceleration at the front face of the structure. Moreover, it has been revealed that the drag coefficients decrease for higher values of KC approaching the constanv talue. On the other hand, the inertia coefficients are almost constant for all the tested values of KC.

  • estimation method of stable weight of spherical armor unit of a submerged wide crown breakwater
    Coastal Engineering, 1996
    Co-Authors: Teofilo Monge Rufin, Norimi Mizutani, Koichiro Iwata
    Abstract:

    Abstract The armor stone is idealized as a sphere and the stable weight of a spherical armor unit of a submerged wide-crown breakwater is analyzed in relation to the wave force acting. The pertinent wave characteristics of wave force and the behavior of its generating mechanisms are clarified. General stability models are then derived based on the acting wave forces, method of placement, type and direction of movement, and other physical quantities affecting the stability of a spherical armor unit in a submerged wide-crown breakwater. The proposed models are in good agreement with the experimental values. The vicinity around the leading crown-edge is revealed to be the most critical location of the structure. Moreover, the applicability of Morison Equation in the estimation of wave force for both breaking and non-breaking conditions is also discussed; and, the relationship of the drag and inertia force coefficients with the KC number is confirmed.