The Experts below are selected from a list of 318 Experts worldwide ranked by ideXlab platform

Khac Duc Do - One of the best experts on this subject based on the ideXlab platform.

  • inverse optimal gain assignment control of evolution systems and its application to boundary control of Marine Risers
    Automatica, 2019
    Co-Authors: Khac Duc Do
    Abstract:

    This paper formulates and solves an inverse optimal gain assignment control problem for the evolution systems perturbed by unknown (bounded) disturbances in Hilbert spaces. The control design ensures global well-posedness and global (practical) K∞-exponential (respectively, strong or weak asymptotic) stability of the closed-loop system, minimizes a cost functional that appropriately penalizes state, control, and disturbances in the sense that a cost functional, which is positive definite in state and control, and is negative definite in disturbances, is minimized. Thus, the proposed control law minimizes both state and control while attenuates the disturbances. Moreover, it is not required to solve a Hamilton–Jaccobi–Isaacs equation (HJIE) but the Lyapunov functional used in the control design is exactly the solution of a family of HJIEs. The developed results are illustrated via an application to design new inverse optimal gain assignment boundary control laws for mitigating vibration of extensible Marine Risers under either a positive or zero or even negative pretension subject to sea loads. This optimal control problem for Marine Risers has not been addressed in the literature.

  • boundary control of transverse motion of flexible Marine Risers under stochastic loads
    Ocean Engineering, 2018
    Co-Authors: Khac Duc Do
    Abstract:

    Abstract A constructive design of boundary controllers is proposed to stabilize transverse motion of flexible Marine Risers under stochastic loads induced by restoring membrane and fluid/air velocity. For stability analysis and boundary control design, global well-posedness (existence and uniqueness) and global stability criteria are developed for nonlinear stochastic evolution systems in Hilbert space subject to both state-dependent and additive stochastic disturbances. These criteria are obtained by developing Lyapunov sufficient conditions from local well-posedness and stability results. The well-posedness and stability developments are not only applied to ensure well-posedness and almost sure (practical) stability of the variational (strong) solution of the stochastic riser system but also to other hyperbolic systems.

  • boundary stabilization of extensible and unshearable Marine Risers with large in plane deflection
    Automatica, 2017
    Co-Authors: Khac Duc Do, Anthony D Lucey
    Abstract:

    This paper proposes a constructive design of boundary controllers for globally (practically) K-exponential stabilization of extensible and unshearable Marine Risers with large in-plane deflection under sea loads. Linearization or Maclaurin expansion of the strain and cross section rotation are not required. The control design is based on the Lyapunov direct method. Well-posedness and stability of the closed-loop system are analyzed by two Lyapunov-type theorems developed for study of existence and uniqueness, and stability of nonlinear evolution systems in Hilbert space.

  • stochastic boundary control design for extensible Marine Risers in three dimensional space
    Automatica, 2017
    Co-Authors: Khac Duc Do
    Abstract:

    This paper presents a new design of boundary controllers for global practical K-exponential p-stabilization of vibration motions of extensible Marine Risers in three-dimensional (3D) space under both stochastic and deterministic sea loads. The control design and analysis of well-posedness and stability of the closed-loop system are carried out based on a new Lyapunov-type theorem, which is developed for studying well-posedness and p-stability of a class of stochastic evolution systems (SESs) in Hilbert space. Since this theorem eases difficulties in verification of the coercivity condition but requires conditions of a form similar to Lyapunov-type theorems for stochastic lumped-parameter systems, it has a potential application to other stochastic distributed-parameter systems.

  • boundary control design for extensible Marine Risers in three dimensional space
    Journal of Sound and Vibration, 2017
    Co-Authors: Khac Duc Do
    Abstract:

    Abstract A design of boundary controllers is proposed for (practical) exponential stabilization of extensible Marine Risers in three-dimensional (3D) space under sea loads. The design removes flaws in existing works. Two Lyapunov-type theorems are developed for study of existence and uniqueness, and stability of nonlinear evolution systems in Hilbert space. These theorems have their potential use in control design and stability analysis for flexible systems including Marine Risers.

S B Leen - One of the best experts on this subject based on the ideXlab platform.

  • a global local fretting analysis methodology and design study for the pressure armour layer of dynamic flexible Marine Risers
    Tribology International, 2020
    Co-Authors: Sinead M Ohalloran, Adrian Connaire, Annette M Harte, S B Leen
    Abstract:

    Abstract In this paper, a global-local fretting design methodology for the pressure armour layer of flexible Marine Risers is outlined. This includes global dynamic riser analysis, geometrical and analytical sub-models and local nub-groove contact finite element analysis. Furthermore, a fretting test rig is developed and utilised to quantify coefficient of friction and wear coefficient under representative nub-groove loading conditions. The combination of the global-local computational methodology and experimental characterisation of pressure armour wire material allows for the development of running condition fretting maps. This identifies design criteria for critical riser global curvatures that are associated with minimum number of cycles to failure. The design methodology presented in this paper is applied to a realistic riser design study, using extreme sea-state loading conditions. In this case study, the predicted pressure armour fretting fatigue lives are found to be in the same range as the plain fatigue lives of the tensile armour layer.

  • a strain gradient crystal plasticity model for microstructure sensitive fretting crack initiation in ferritic pearlitic steel for flexible Marine Risers
    International Journal of Fatigue, 2018
    Co-Authors: P J Ashton, Annette M Harte, S B Leen
    Abstract:

    Abstract A three-dimensional, strain-gradient, crystal plasticity methodology is presented for prediction of microstructure-sensitive length-scale effects in crack initiation, under fatigue and fretting fatigue conditions, for a ferritic-pearlitic steel used in flexible Marine Risers. The methodology, comprising length-scale dependent constitutive model and scale-consistent fatigue indicator parameters, is calibrated and validated for representative (measured) dual-phase microstructures under strain-controlled low cycle fatigue conditions. Prediction of the effects of length-scale on fretting crack initiation is based on a three-dimensional, crystal plasticity, frictional contact model to predict fretting crack location and initial growth path, accounting for the effects of crystallographic orientation. The length-scale dependent fatigue and fretting simulations predict (i) significant beneficial effect of reducing length-scale for low cycle fatigue life, (ii) complex cyclically- and spatially-varying effects and differences due to changing contact and grain length-scales, and (ii) that fretting damage generally decreases with decreasing (contact-grain) length-scale.

  • a combined wear fatigue design methodology for fretting in the pressure armour layer of flexible Marine Risers
    Tribology International, 2017
    Co-Authors: Sinead M Ohalloran, P H Shipway, Adrian Connaire, S B Leen, Annette M Harte
    Abstract:

    This paper presents a combined experimental and computational methodology for fretting wear-fatigue prediction of pressure armour wire in flexible Marine Risers. Fretting wear, friction and fatigue parameters of pressure armour material have been characterised experimentally. A combined fretting wear-fatigue finite element model has been developed using an adaptive meshing technique and the effect of bending-induced tangential slip has been characterised. It has been shown that a surface damage parameter combined with a multiaxial fatigue parameter can accurately predict the beneficial effect of fretting wear on fatigue predictions. This provides a computationally efficient design tool for fretting in the pressure armour layer of flexible Marine Risers.

Annette M Harte - One of the best experts on this subject based on the ideXlab platform.

  • a global local fretting analysis methodology and design study for the pressure armour layer of dynamic flexible Marine Risers
    Tribology International, 2020
    Co-Authors: Sinead M Ohalloran, Adrian Connaire, Annette M Harte, S B Leen
    Abstract:

    Abstract In this paper, a global-local fretting design methodology for the pressure armour layer of flexible Marine Risers is outlined. This includes global dynamic riser analysis, geometrical and analytical sub-models and local nub-groove contact finite element analysis. Furthermore, a fretting test rig is developed and utilised to quantify coefficient of friction and wear coefficient under representative nub-groove loading conditions. The combination of the global-local computational methodology and experimental characterisation of pressure armour wire material allows for the development of running condition fretting maps. This identifies design criteria for critical riser global curvatures that are associated with minimum number of cycles to failure. The design methodology presented in this paper is applied to a realistic riser design study, using extreme sea-state loading conditions. In this case study, the predicted pressure armour fretting fatigue lives are found to be in the same range as the plain fatigue lives of the tensile armour layer.

  • a strain gradient crystal plasticity model for microstructure sensitive fretting crack initiation in ferritic pearlitic steel for flexible Marine Risers
    International Journal of Fatigue, 2018
    Co-Authors: P J Ashton, Annette M Harte, S B Leen
    Abstract:

    Abstract A three-dimensional, strain-gradient, crystal plasticity methodology is presented for prediction of microstructure-sensitive length-scale effects in crack initiation, under fatigue and fretting fatigue conditions, for a ferritic-pearlitic steel used in flexible Marine Risers. The methodology, comprising length-scale dependent constitutive model and scale-consistent fatigue indicator parameters, is calibrated and validated for representative (measured) dual-phase microstructures under strain-controlled low cycle fatigue conditions. Prediction of the effects of length-scale on fretting crack initiation is based on a three-dimensional, crystal plasticity, frictional contact model to predict fretting crack location and initial growth path, accounting for the effects of crystallographic orientation. The length-scale dependent fatigue and fretting simulations predict (i) significant beneficial effect of reducing length-scale for low cycle fatigue life, (ii) complex cyclically- and spatially-varying effects and differences due to changing contact and grain length-scales, and (ii) that fretting damage generally decreases with decreasing (contact-grain) length-scale.

  • a combined wear fatigue design methodology for fretting in the pressure armour layer of flexible Marine Risers
    Tribology International, 2017
    Co-Authors: Sinead M Ohalloran, P H Shipway, Adrian Connaire, S B Leen, Annette M Harte
    Abstract:

    This paper presents a combined experimental and computational methodology for fretting wear-fatigue prediction of pressure armour wire in flexible Marine Risers. Fretting wear, friction and fatigue parameters of pressure armour material have been characterised experimentally. A combined fretting wear-fatigue finite element model has been developed using an adaptive meshing technique and the effect of bending-induced tangential slip has been characterised. It has been shown that a surface damage parameter combined with a multiaxial fatigue parameter can accurately predict the beneficial effect of fretting wear on fatigue predictions. This provides a computationally efficient design tool for fretting in the pressure armour layer of flexible Marine Risers.

Narakorn Srinil - One of the best experts on this subject based on the ideXlab platform.

  • viv fatigue reliability analysis of Marine Risers with uncertainties in the wake oscillator model
    Engineering Structures, 2016
    Co-Authors: Narakorn Srinil
    Abstract:

    Abstract Uncertainties are rife in the fatigue life prediction of Marine Risers subjected to vortex-induced vibration (VIV). Industry deals with this issue by imposing large factors of safety that may not be properly justified, resulting in over-conservative riser designs in general. One important source of uncertainty arises from the VIV prediction models. This paper focusses on identifying the uncertainties of a wake oscillator model which approximates the fluctuating hydrodynamic force coupled with the riser equation of motion for nonlinear fluid–structure interaction analysis. This van der Pol-type oscillator relies on two wake coefficients which are described deterministically by empirical equations obtained via curve-fitting. However, the underlying data exhibit wide scatter; thus, it is proposed to model the two key coefficients as random variables. Based on experimental data, the joint probability density function of the variables is approximated. A new fast reliability approach is proposed for the VIV fatigue reliability analysis, while Monte Carlo simulations are performed for comparisons. Case studies of a vertical riser in a uniform flow show that the proposed method compares favorably with Monte Carlo in terms of predicting the failure probability as well as safety factors conforming to prescribed reliability levels. Moreover, this study reveals that the randomness of wake coefficients leads to large variability in the riser fatigue damage. The correlation between the coefficients should be properly incorporated as it affects the fatigue reliability of Risers experiencing VIV.

  • coupled axial lateral viv of Marine Risers in sheared currents
    ASME 2015 34th International Conference on Ocean Offshore and Arctic Engineering OMAE 2015, 2015
    Co-Authors: Hossein Zanganeh, Narakorn Srinil
    Abstract:

    Modelling and prediction of vortex-induced vibrations (VIV) of Marine Risers is a challenging task due to the associated multi degrees of freedom in both cross-flow/in-line directions and the multi-mode fluid-structure interactions. In addition, the axial motion and its geometrically nonlinear coupling with lateral responses can be significant, especially at higher-order modes. Nevertheless, several papers in the literature dealing with VIV predictions have often overlooked such aspects. Therefore, this study aims to investigate and understand the effect of axial or longitudinal motion through a theoretical model and numerical approach in time domain. Attention is paid to VIV of vertical Risers subjected to linearly sheared currents. To capture a three-dimensional aspect of the flexible cylinder experiencing VIV, a semiempirical model is developed consisting of nonlinear equations of cross-flow, in-line and axial structural oscillations which are coupled with the distributed van der Pol-type wakeoscillators modelling the fluctuating fluid lift/drag forces. The mean drag force is also taken into account. These model equations are numerically solved via a space-time finite difference scheme, and the obtained numerical results highlight several aspects of VIV of elastic cylinders along with the axial motion effects. Apart from the validation of the numerical model with published experimental results, this study reveals how the effect of axial motion and its nonlinear coupling with the two lateral cross-flow/in-line motions can be very important. These depend on the flow velocity, the fluid-structure parameters, the single or multi-mode lock-in condition, and the standing-wave or travelling-wave feature. We recommend that the axial response should be accounted for in VIV analysis and prediction model.

  • numerical and experimental comparisons of vortex induced vibrations of Marine Risers in uniform sheared currents
    ASME 2010 29th International Conference on Ocean Offshore and Arctic Engineering OMAE2010, 2010
    Co-Authors: Narakorn Srinil, Patrick Obrien, Marian Wiercigroch
    Abstract:

    This paper presents a general theoretical reduced-order model capable of evaluating the multi-mode nonlinear dynamics of Marine Risers subject to uniform and sheared currents. The main objectives are to predict the vortex-induced vibration responses and parametrically compare between numerical and experimental results. The emphasis is placed on the analysis of cross-flow vibrations due to unsteady lift forces. The nonlinear equations governing riser axial/transversal motions are derived based on a top-tensioned beam model with typical pinned-pinned boundary conditions. The riser geometric nonlinearities owing to possible large dynamic displacements and multi-mode interactions are accounted for. To approximate the space-time varying lift force, the empirical hydrodynamic model, based on a nonlinear van der Pol wake oscillator with a distributed diffusive term, is used. A low-dimensional dynamic model and computationally-robust time-domain tool are then developed to evaluate the multi-mode fluid-riser interactions. These are very useful in dealing with large parametric studies involving varying system parameters.

Suhail Ahmad - One of the best experts on this subject based on the ideXlab platform.

  • 3D Finite Element Analysis of Marine Risers under Random Loads
    2014
    Co-Authors: Rizwan Ahmed Khan, Suhail Ahmad
    Abstract:

    The dynamic response of Marine Risers under long crested random sea is obtained in time domain using finite element solver ABAQUS/AQUA. The response analysis is based on a simulation technique which duly considers various nonlinear effects such as relative velocity squared drag force, variable added mass due to variable submergence and nonlinearity due to large excursions. It also accounts for variable tension in the riser due to variable submergence, variable buoyancy and wave forces. Results are presented which illustrates the effects of nonlinearities, long-term drift oscillations and instantaneous motion of the vessel and current velocity on the bending stress in the Marine Risers. The response time histories are obtained and presented in terms of bending stress envelopes and spectra showing contribution of various harmonics which is significant because of a nonlinear system. Keywords : Marine Risers, random waves, vessel motion, drift oscillation, dynamic response

  • fatigue reliability evaluation of Marine Risers under vortex induced vibration
    ASME 2013 32nd International Conference on Ocean Offshore and Arctic Engineering, 2013
    Co-Authors: Rizwan Ahmed Khan, Suhail Ahmad
    Abstract:

    Depleting oil reserves in shallow waters, off-shore oil fields are opening the avenues of new ventures in deep sea conditions. A Marine riser is a major component of an offshore drilling and production system that are either fixed or floating in nature. Deepwater Risers are quite long and significant currents usually excite natural bending mode that is much higher than the fundamental bending mode. In ultra deep environment currents usually change in magnitude and direction with depth, thereby inducing possibility of exciting multiple modes of the riser vibration due to VIV. Vortex induced vibration analysis has been carried out of a long Marine riser in a probable deep sea location. To improve the understanding under deepwater harsh environments, the behavior of the riser under these forces is thoroughly investigated. 3D Nonlinear dynamic analysis of riser is obtained in the time domain using finite element software package ABAQUS/Aqua. The response histories so obtained are employed for the study of fatigue reliability analyses of riser. Uncertainty modeling, especially of fatigue crack growth parameters, is undertaken using bi-linear crack growth relationship. Results pertaining to fatigue reliability and fatigue crack size evolution are presented using Monte Carlo Simulation. The bi-linear crack growth models are found to lead to higher fatigue life estimation. Sensitivity behavior pertinent to limit state adopted has been thoroughly investigated. These findings implicate inspection schemes for components of the Marine structures to ensure minimization of the surprises due to wide scatter of the fatigue phenomenon in Marine environment.Copyright © 2013 by ASME

  • nonlinear dynamic analysis of Marine Risers under random loads for deepwater fields in indian offshore
    Procedia Engineering, 2011
    Co-Authors: Rizwan Ahmed Khan, Arshdeep Kaur, S P Singh, Suhail Ahmad
    Abstract:

    Abstract The paper presents a numerical Analysis of deep water Steel Catenary Riser (SCR) under random sea loads. A finite element method is implemented in the time domain using Newmark's-Beta method. The response analysis is based on a simulation technique which duly considers the various non-linear effects such as relative velocity squared drag force, variable added mass due to variable submergence and nonlinearity due to large excursions. It also accounts for variable tension in riser due to variable submergence, variable buoyancy and wave forces. Results are presented which illustrates the effects of nonlinearities, long term drift oscillations and current velocity on the bending stress in the Marine Risers. The bending stress response time histories are obtained and presented in terms of bending stress envelopes and spectra showing contribution of various harmonics which is significant because of a non-linear system.

  • nonlinear response analysis of Marine Risers
    Computers & Structures, 1992
    Co-Authors: Suhail Ahmad, T. K. Datta
    Abstract:

    Abstract A frequency domain iterative procedure method is presented for the determination of nonlinear dynamic response of Marine Risers to both regular and random waves. In the dynamic response analysis, the effect of the relative velocity squared drag term, the long-term drift oscillation and the instantaneous motion of the top vessel and the current velocity are duly considered. The frequency domain iterative method is shown to be much more efficient than the time integration method and can adequately consider all the nonlinearities mentioned above.