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Richard Large - One of the best experts on this subject based on the ideXlab platform.

  • prediction of Fatigue life of shallow water offshore platforms using Spectral Fatigue Analysis method
    ASME 2010 29th International Conference on Ocean Offshore and Arctic Engineering, 2010
    Co-Authors: Qin Feng, Richard Large
    Abstract:

    Spectral Fatigue Analysis approach is highly recommended for fixed offshore platform design and reassessment by API. This method is a computationally efficient method, being able to handle the random nature of environmental ocean wave conditions during calculating wave loads on the offshore platforms and subsequent structural responses. However, its fundamental theory is based on the assumption of linearity of both structural system and wave loading mechanism. Although this method is critically appropriate to be applied in offshore platform design and Fatigue assessment for deep water scenarios where wave and force nonlinearities are not very severe, it has still been widely utilized for the design and assessment of shallow water platforms in offshore industry without carefully considering possible errors caused by strong nonlinear factors between ocean waves and forces. The source giving rise to the errors is because of the difficulties in choosing suitably correct wave heights for a series of wave periods required for producing transfer functions between sea state spectra and structural response spectra. Therefore, the studies to justify the possible errors of the Spectral Fatigue Analysis method for shallow water platforms have been provoked. This paper presents the results of the studies of investigating the errors from currently existing Spectral Fatigue Analysis method. A new technical approach that can reduce the errors in the Spectral Fatigue Analysis of shallow water platforms is introduced. The proposed technical approach is mainly focused on producing realistic transfer functions between sea state spectra and structural response spectra, which can reasonably reflect the individually local sea state data by using wave height-period joint probability density function. Hence the Fatigue damage and life at the tubular joints of offshore platforms can be more precisely predicted. The Spectral Fatigue Analysis of a practical shallow water jacket platform in the recent platform design project has been performed using the proposed approach and the results are discussed.Copyright © 2010 by ASME

Qin Feng - One of the best experts on this subject based on the ideXlab platform.

  • prediction of Fatigue life of shallow water offshore platforms using Spectral Fatigue Analysis method
    ASME 2010 29th International Conference on Ocean Offshore and Arctic Engineering, 2010
    Co-Authors: Qin Feng, Richard Large
    Abstract:

    Spectral Fatigue Analysis approach is highly recommended for fixed offshore platform design and reassessment by API. This method is a computationally efficient method, being able to handle the random nature of environmental ocean wave conditions during calculating wave loads on the offshore platforms and subsequent structural responses. However, its fundamental theory is based on the assumption of linearity of both structural system and wave loading mechanism. Although this method is critically appropriate to be applied in offshore platform design and Fatigue assessment for deep water scenarios where wave and force nonlinearities are not very severe, it has still been widely utilized for the design and assessment of shallow water platforms in offshore industry without carefully considering possible errors caused by strong nonlinear factors between ocean waves and forces. The source giving rise to the errors is because of the difficulties in choosing suitably correct wave heights for a series of wave periods required for producing transfer functions between sea state spectra and structural response spectra. Therefore, the studies to justify the possible errors of the Spectral Fatigue Analysis method for shallow water platforms have been provoked. This paper presents the results of the studies of investigating the errors from currently existing Spectral Fatigue Analysis method. A new technical approach that can reduce the errors in the Spectral Fatigue Analysis of shallow water platforms is introduced. The proposed technical approach is mainly focused on producing realistic transfer functions between sea state spectra and structural response spectra, which can reasonably reflect the individually local sea state data by using wave height-period joint probability density function. Hence the Fatigue damage and life at the tubular joints of offshore platforms can be more precisely predicted. The Spectral Fatigue Analysis of a practical shallow water jacket platform in the recent platform design project has been performed using the proposed approach and the results are discussed.Copyright © 2010 by ASME

  • Spectral Fatigue Analysis of shallow water jacket platforms
    Journal of Offshore Mechanics and Arctic Engineering-transactions of The Asme, 1996
    Co-Authors: N W M Bishop, Qin Feng, P Schofield, M G Kirkwood, T Turner
    Abstract:

    The Spectral Analysis approach is a very elegant and computationally efficient method of analysing the Fatigue life of offshore jacket platforms. The primary limitation of the approach is that is assumes linearity of both the structural system and the wave loading mechanism. Various methods have been proposed to enable the Spectral method to be used for some non-linear situations, including a new approach which uses Longuet-Higgins wave height-period joint probability density function in order to obtain a better linearization technique. This linearization process is associated with the particular wave heights chosen for producing the transfer functions. The new approach provides a better method for choosing the appropriate height of each so called base wave case. In order to verify the new approach a time series Analysis, including wave loading nonlinearities, has been adopted to obtain a reference Fatigue life. The sea surface elevation spectrum has been decomposed into a set of equivalent harmonic components. The water particle velocities and accelerations were then individually evaluated and the appropriate (Morison's) wave loading was computed for each time step in the sea surface time history. The structural stress response time history was then calculated, from which a Fatigue life estimate was obtained. This paper presents the results obtained using this new approach, as well as comparative results obtained using the deterministic, Spectral and time domain approaches applied with a representative sea state. The results show that the deterministic-Spectral potential, especially for new design work where weight savings and/or increased confidence levels may be achieved.

Yingguang Wang - One of the best experts on this subject based on the ideXlab platform.

  • Spectral Fatigue Analysis of a ship structural detail a practical case study
    International Journal of Fatigue, 2010
    Co-Authors: Yingguang Wang
    Abstract:

    The Fatigue life of a ship structural detail is calculated by using a Spectral approach. The wave-induced vertical and horizontal bending moments, two base vessel loading conditions and the non-operating time have all been taken into account in the Spectral Fatigue damage calculation. The predicted Fatigue life value by using the Spectral approach is compared with the one calculated by using the IACS R 56, and various factors inducing uncertainties in the Spectral method are further identified and investigated. Finally, recommendations on how to choose the specific parameters and how to model the random wave environment in the Spectral approach are outlined.

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

  • Spectral Fatigue Analysis of jacket platform under wave load equipped with viscous damper
    Journal of Marine Science and Technology, 2019
    Co-Authors: Hossein Janbazi Rokni, Mohammad Reza Tabeshpour
    Abstract:

    Offshore jacket platforms are exposed to environmental loads such as wind, wave, current, and earthquake throughout the lifetime of operation. Due to dynamic and periodic nature and Fatigue phenomenon in the structure, wave forces are the most important loads among others. There are diverse methods to explore the Fatigue life of jackets, including deterministic, Spectral, and time domain Analysis. Among these methods, Spectral method is a reliable method, which considers the random nature of sea waves in Fatigue Analysis. In the current study, a Spectral method is introduced for assessment and rehabilitation of jacket platform structure. To this end, a computer program has been developed, meanwhile, probability Spectral density functions of displacement and stress are calculated in each joint of jacket elements. Furthermore, using S – N curve approach, cumulative Fatigue damage in critical members of an example jacket is obtained. Finally, several configurations of viscous dampers are applied to jacket, and damage and Fatigue lifetime are discussed with and without dampers. Consequently, the best arrangement of dampers is achieved. Results indicate the best cumulative Fatigue damage with dampers which was about 0.01 times of cumulative Fatigue damage without a damper.

Myongjin Park - One of the best experts on this subject based on the ideXlab platform.

  • Fatigue Analysis on the mooring chain of a spread moored fpso considering the opb and ipb
    International Journal of Naval Architecture and Ocean Engineering, 2019
    Co-Authors: Myongjin Park
    Abstract:

    Abstract The appropriate design of a mooring system to maintain the position of an offshore structure in deep sea under various environmental loads is important. Fatigue design of the mooring line considering OPB/IPB(out-of-plane bending/in-plane bending) became an essential factor after the incident of premature Fatigue failure of the mooring chain due to OPB/IPB in the Girassol region in West Africa. In this study, mooring line Fatigue Analysis was performed considering the OPB/IPB of a spread moored FPSO in deep sea. The tension of the mooring line was derived by hydrodynamic Analysis using the de-coupled Analysis method. The floater motion time histories were calculated under the assumption that the mooring line behaves in quasi-static manner. Additional time domain Analysis was carried out by prescribing the obtained motions on top of the selected critical mooring line, which was determined based on Spectral Fatigue Analysis. In addition, nonlinear finite element Analysis was performed considering the material nonlinearities, and both the interlink stiffness and stress concentration factors were derived. The Fatigue damage to the chain surface was estimated by combining both the hydrodynamic and stress Analysis results.

  • Fatigue Analysis on the mooring chain of a spread moored FPSO considering the OPB and IPB
    Elsevier, 2019
    Co-Authors: Yooil Kim, Min-suk Kim, Myongjin Park
    Abstract:

    The appropriate design of a mooring system to maintain the position of an offshore structure in deep sea under various environmental loads is important. Fatigue design of the mooring line considering OPB/IPB(out-of-plane bending/in-plane bending) became an essential factor after the incident of premature Fatigue failure of the mooring chain due to OPB/IPB in the Girassol region in West Africa. In this study, mooring line Fatigue Analysis was performed considering the OPB/IPB of a spread moored FPSO in deep sea. The tension of the mooring line was derived by hydrodynamic Analysis using the de-coupled Analysis method. The floater motion time histories were calculated under the assumption that the mooring line behaves in quasi-static manner. Additional time domain Analysis was carried out by prescribing the obtained motions on top of the selected critical mooring line, which was determined based on Spectral Fatigue Analysis. In addition, nonlinear finite element Analysis was performed considering the material nonlinearities, and both the interlink stiffness and stress concentration factors were derived. The Fatigue damage to the chain surface was estimated by combining both the hydrodynamic and stress Analysis results. Keywords: Mooring chain, Out-of-plane bending, In-plane bending, De-coupled Analysis, Fatigue, Interlink stiffnes