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    Challenges in calculation of critical buckling load of tubular members of jacket platforms in finite element modeling

    , Article Journal of Marine Science and Technology (Japan) ; 2019 ; 09484280 (ISSN) Tabeshpour, M. R ; Erfani, M. H ; Sayyaadi, H ; Sharif University of Technology
    Springer Tokyo  2019
    Abstract
    Accurate estimation of the capacity curve of offshore jacket structures to achieve performance levels and ductility is of great importance. Proper modeling of compressive members to correctly investigate global and local buckling is crucial in estimation of the capacity curve. Buckling modes and deformations due to local buckling can be considered, if the compressive braces are modeled by shell or solid elements. The purpose of this paper is to achieve the correct compressive behavior of braces with solid type elements and investigate the effects of five different parameters such as D/t, L/D, mesh size, mesh size ratio, and imperfections. ABAQUS FE software is used for this purpose. The... 

    Challenges in calculation of critical buckling load of tubular members of jacket platforms in finite element modeling

    , Article Journal of Marine Science and Technology (Japan) ; 2019 ; 09484280 (ISSN) Tabeshpour, M. R ; Erfani, M. H ; Sayyaadi, H ; Sharif University of Technology
    Springer Tokyo  2019
    Abstract
    Accurate estimation of the capacity curve of offshore jacket structures to achieve performance levels and ductility is of great importance. Proper modeling of compressive members to correctly investigate global and local buckling is crucial in estimation of the capacity curve. Buckling modes and deformations due to local buckling can be considered, if the compressive braces are modeled by shell or solid elements. The purpose of this paper is to achieve the correct compressive behavior of braces with solid type elements and investigate the effects of five different parameters such as D/t, L/D, mesh size, mesh size ratio, and imperfections. ABAQUS FE software is used for this purpose. The... 

    Optimum arrangement of braces in jacket platform based on strength and ductility

    , Article Marine Structures ; Volume 71 , 2020 Tabeshpour, M. R ; Fatemi, M ; Sharif University of Technology
    Elsevier Ltd  2020
    Abstract
    Nonlinear behavior of jacket platforms is important in both design and rehabilitation issues that depends on the bracing arrangement. Both ductility and strength of the structures derived from pushover analysis are highly related to configuration of the braces. Considering a suitable criterion such as constant weight or constant stiffness and period of the structure in all arrangement cases, one can compare the capacity curves and find the best configuration. In this paper a simple logical method for investigating the strength and ductility of the jacket structure is presented, it is shown that global geometry and configuration of the braces are very important and effective in both strength... 

    Investigation of the effect of the added mass fluctuation and lateral vibration absorbers on the vertical nonlinear vibrations of the offshore wind turbine

    , Article Nonlinear Dynamics ; Volume 103, Issue 2 , 2021 , Pages 1499-1515 ; 0924090X (ISSN) Ghabraei, S ; Moradi, H ; Vossoughi, G ; Sharif University of Technology
    Springer Science and Business Media B.V  2021
    Abstract
    In this article, the effects of the changes in the mass of the floating wind turbine (as a multi-body system) on its nonlinear vertical vibrations are investigated. The fluctuations of the hydrodynamic added mass of the floating platform and the mass of the vibration absorbers, which added to the structure to mitigate the lateral vibrations, change the mass and consequently the dynamics of the vertical vibrations. In this regard, first, the governing equations of the vertical vibrations of the floating wind turbine are derived. The FAST code is used to validate the proposed model of the dynamics of the vertical vibrations through numerical simulations. Then, derived equations are solved... 

    Aerodynamic enhancement and improving the performance of a six-megawatt dowec wind turbine by micro-plasma actuator

    , Article International Journal of Mechanical Sciences ; Volume 195 , 2021 ; 00207403 (ISSN) Omidi, J ; Mazaheri, K ; Sharif University of Technology
    Elsevier Ltd  2021
    Abstract
    We have investigated the usage of a Dielectric Barrier Discharge (DBD) plasma actuator to improve the aerodynamic performance of an offshore 6 MW wind turbine. By controlling the aerodynamic load combined with pitch angles of 2, 5, and 10 degrees, we studied the plasma actuator effect on the overall harvested power. Actuators were installed in single and tandem configurations in different chord-wise locations to find the optimum design. The improved phenomenological model developed by authors was used in an analysis to simulate the interaction of the electrostatic field, the ionized particles and the fluid flow. A design software was used to estimate the harvested power of the real 3D blade.... 

    Conceptual study on dynamic response of semi-submersible

    , Article Proceedings of the Institution of Civil Engineers: Maritime Engineering ; 2021 ; 17417597 (ISSN) Tabeshpour, M. R ; Hajnoruzi, F ; Sharif University of Technology
    ICE Publishing  2021
    Abstract
    Hydrodynamic analysis of semi-submersible offshore structures has been the topic of many researches performed numerically and experimentally in the past. In this paper, the effect of structure alignment and mooring lines on dynamic behaviour of semi-submersible platforms has been taken into account. The contribution of pitch and roll in heave motion of side points is also investigated. Mooring lines are connected to semi-submersible at sides and therefore total displacement of side points is related to total displacement of mooring lines and total tension as well. A three dimensional boundary element model of Amirkabir platform in Caspian Sea is implemented using boundary element method... 

    Vortex shedding modes around oscillating non-uniform double heave plates

    , Article Proceedings of the Institution of Mechanical Engineers Part M: Journal of Engineering for the Maritime Environment ; Volume 235, Issue 2 , 2021 , Pages 558-569 ; 14750902 (ISSN) Abazari, A ; Alvandi, M ; Behzad, M ; Thiagarajan, K. P ; Sharif University of Technology
    SAGE Publications Ltd  2021
    Abstract
    Multiple co-axial heave plates of uniform geometry are attached to offshore platforms for inducing damping and added mass. These effects generally decrease the magnitude of the dynamic response of the platform under applied environmental excitation forces. When spacing between heave plates is decreased the damping and added mass performance are altered due to their strong vortex interaction. A new non-uniform plate configuration is proposed that may create different hydrodynamic characteristics. The modes of vortex shedding around plate edges in a non-uniform arrangement under forced harmonic oscillation are investigated via the CFD method. Furthermore, a new simplified formula for the total... 

    Hydrodynamic damping enhancement by implementing a novel combined rigid-elastic heave plate

    , Article Journal of Marine Science and Technology (Japan) ; Volume 26, Issue 1 , 2021 , Pages 216-232 ; 09484280 (ISSN) Abazari, A ; Behzad, M ; Thiagarajan, K ; Sharif University of Technology
    Springer Japan  2021
    Abstract
    Heave plates are structural components used for reducing the vibrations caused by environmental forces on marine and offshore structures by changing the hydrodynamic properties. The fact that the added mass increase via heave plates does not always lead to the structural response reduction underscores the role of damping in maintaining the vibration amplitude within allowable limits. In the present experimental study, a novel combined rigid-elastic design is used to improve the damping through the velocity increase in the elastic part and added mass creation in the central rigid part. The desired percentage of total added mass and damping can be adjusted by changing the rigid-to-elastic... 

    Vortex shedding modes around oscillating non-uniform double heave plates

    , Article Proceedings of the Institution of Mechanical Engineers Part M: Journal of Engineering for the Maritime Environment ; Volume 235, Issue 2 , 2021 , Pages 558-569 ; 14750902 (ISSN) Abazari, A ; Alvandi, M ; Behzad, M ; Thiagarajan, K. P ; Sharif University of Technology
    SAGE Publications Ltd  2021
    Abstract
    Multiple co-axial heave plates of uniform geometry are attached to offshore platforms for inducing damping and added mass. These effects generally decrease the magnitude of the dynamic response of the platform under applied environmental excitation forces. When spacing between heave plates is decreased the damping and added mass performance are altered due to their strong vortex interaction. A new non-uniform plate configuration is proposed that may create different hydrodynamic characteristics. The modes of vortex shedding around plate edges in a non-uniform arrangement under forced harmonic oscillation are investigated via the CFD method. Furthermore, a new simplified formula for the total... 

    Hydrodynamic damping enhancement by implementing a novel combined rigid-elastic heave plate

    , Article Journal of Marine Science and Technology (Japan) ; Volume 26, Issue 1 , 2021 , Pages 216-232 ; 09484280 (ISSN) Abazari, A ; Behzad, M ; Thiagarajan, K ; Sharif University of Technology
    Springer Japan  2021
    Abstract
    Heave plates are structural components used for reducing the vibrations caused by environmental forces on marine and offshore structures by changing the hydrodynamic properties. The fact that the added mass increase via heave plates does not always lead to the structural response reduction underscores the role of damping in maintaining the vibration amplitude within allowable limits. In the present experimental study, a novel combined rigid-elastic design is used to improve the damping through the velocity increase in the elastic part and added mass creation in the central rigid part. The desired percentage of total added mass and damping can be adjusted by changing the rigid-to-elastic... 

    A mixed integer-programming model for periodic routing of special vessels in offshore oil industry

    , Article International Journal of Industrial Engineering : Theory Applications and Practice ; Volume 22, Issue 5 , 2015 , Pages 524-548 ; 10724761 (ISSN) Jahromi Eshraghniaye, A ; Yazdeli Roohollah, I ; Sharif University of Technology
    University of Cincinnati  2015
    Abstract
    In order to maintain the production of offshore oil wells, the National Iranian Oil Company periodically services facilities and equipment located in oil wellheads with mobile wellhead servants. It also gives technical supports to oil wellheads and mobile wellhead servants with supporter vessels. Due to supply limitations, there are not enough special vessels (namely supporter vessels and mobile wellhead servants) compared to the number of oil wellheads. The failure of special vessels to service oil wellheads and supporter vessels to technically support mobile wellhead servants based on a predetermined plan, will lead to considerable loss in production performance of oil wells and hence... 

    Experimental study on gyroscopic effect of rotating rotor and wind heading angle on floating wind turbine responses

    , Article International Journal of Environmental Science and Technology ; Volume 15, Issue 12 , 2018 , Pages 2531-2544 ; 17351472 (ISSN) Bahramiasl, S ; Abbaspour, M ; Karimirad, M ; Sharif University of Technology
    Abstract
    Limited fossil resources, daily increasing rate of demand for energy and the environmental pollution fact have made people revert to renewable sources of energy as a solution. One type of renewable energy is offshore wind energy which has high potential without any sound and visual noises. Recently, a lot of researchers have carried out on the issue of offshore wind turbine. Because of incapability of most of software programs to simulate gyroscopic effect of rotating rotors, in this articles a significant effort has been made to fabricate and test an offshore wind turbine under different rotor rotation velocities and different heading angle of wind so as to obtain the effects of these... 

    Dynamic risk assessment of decommissioning offshore jacket structures

    , Article Proceedings of the International Conference on Offshore Mechanics and Arctic Engineering - OMAE, 17 June 2018 through 22 June 2018 ; Volume 3 , 2018 ; 9780791851227 (ISBN) Babaleye, A ; Khorasanchi, M ; Kurt, R. E ; Ocean, Offshore and Arctic Engineering Division ; Sharif University of Technology
    American Society of Mechanical Engineers (ASME)  2018
    Abstract
    The need to develop an integrated dynamic safety and risk analysis model for decommissioning offshore jacket structures is driven by the risky, expensive and complex nature of the operation. Many of the existing risk analysis techniques applicable to offshore assets failed to recognise and capture evolving risks during different stages of the decommissioning operation. This paper describes risk-based safety model to conduct quantitative risk analysis for offshore jacket decommissioning failure. First, a bow-tie technique is developed to model the accident cause-consequence relationship. Subsequently, a Bayesian belief network is used to update the failure probabilities of the contributing... 

    Vibration suppression of offshore wind turbine foundations using tuned liquid column dampers and tuned mass dampers

    , Article Ocean Engineering ; Volume 172 , 2019 , Pages 286-295 ; 00298018 (ISSN) Hemmati, A ; Oterkus, E ; Khorasanchi, M ; Sharif University of Technology
    Elsevier Ltd  2019
    Abstract
    Highly dynamic nature of the applied loads on flexible and lightly damped offshore wind turbine (OWT) foundations affects the lifetime and serviceability of the system. In this study, the excessive vibration responses of OWTs are minimized using tuned mass dampers (TMD) and tuned liquid column dampers (TLCD). Due to high efficiency of TLCDs and TMDs for certain loading conditions, a combined TLCD-TMD is also utilized to improve the overall performance in a wide range of loading conditions. First, a parametric study was performed that highlights the sensitivity of these structural control devices. The effect of two devices on fixed offshore wind turbine foundations for the benchmark 5 MW NREL... 

    Seismic performance assessment of fixed offshore structures by endurance time method

    , Article Ships and Offshore Structures ; Volume 14, Issue 7 , 2019 , Pages 709-722 ; 17445302 (ISSN) Dastan Diznab, M. A ; Mehdigholi, H ; Seif, M. S ; Sharif University of Technology
    Taylor and Francis Ltd  2019
    Abstract
    The aim of this paper is to consider the ability of endurance time (ET) method to estimate the seismic response of fixed offshore platforms at various excitation levels. In this way, various sources of nonlinear behaviour and challenging issues in the ET approach are included in the three-dimensional model of a real jacket platform utilising the finite element method. In addition to common-designed, over-designed and under-designed cases of this platform have been investigated to examine the effects of the structural characteristics on the ET response. To consider the accuracy and reliability of this approach, results of the ET method are compared with results of nonlinear time history... 

    Seismic performance assessment of fixed offshore structures by endurance time method

    , Article Ships and Offshore Structures ; Volume 14, Issue 7 , 2019 , Pages 709-722 ; 17445302 (ISSN) Dastan Diznab, M. A ; Mehdigholi, H ; Seif, M. S ; Sharif University of Technology
    Taylor and Francis Ltd  2019
    Abstract
    The aim of this paper is to consider the ability of endurance time (ET) method to estimate the seismic response of fixed offshore platforms at various excitation levels. In this way, various sources of nonlinear behaviour and challenging issues in the ET approach are included in the three-dimensional model of a real jacket platform utilising the finite element method. In addition to common-designed, over-designed and under-designed cases of this platform have been investigated to examine the effects of the structural characteristics on the ET response. To consider the accuracy and reliability of this approach, results of the ET method are compared with results of nonlinear time history... 

    Vortex shedding modes around oscillating non-uniform double heave plates

    , Article Proceedings of the Institution of Mechanical Engineers Part M: Journal of Engineering for the Maritime Environment ; 2020 Abazari, A ; Alvandi, M ; Behzad, M ; Thiagarajan, K. P ; Sharif University of Technology
    SAGE Publications Ltd  2020
    Abstract
    Multiple co-axial heave plates of uniform geometry are attached to offshore platforms for inducing damping and added mass. These effects generally decrease the magnitude of the dynamic response of the platform under applied environmental excitation forces. When spacing between heave plates is decreased the damping and added mass performance are altered due to their strong vortex interaction. A new non-uniform plate configuration is proposed that may create different hydrodynamic characteristics. The modes of vortex shedding around plate edges in a non-uniform arrangement under forced harmonic oscillation are investigated via the CFD method. Furthermore, a new simplified formula for the total... 

    Hydrodynamic damping enhancement by implementing a novel combined rigid-elastic heave plate

    , Article Journal of Marine Science and Technology (Japan) ; 2020 Abazari, A ; Behzad, M ; Thiagarajan, K ; Sharif University of Technology
    Springer  2020
    Abstract
    Heave plates are structural components used for reducing the vibrations caused by environmental forces on marine and offshore structures by changing the hydrodynamic properties. The fact that the added mass increase via heave plates does not always lead to the structural response reduction underscores the role of damping in maintaining the vibration amplitude within allowable limits. In the present experimental study, a novel combined rigid-elastic design is used to improve the damping through the velocity increase in the elastic part and added mass creation in the central rigid part. The desired percentage of total added mass and damping can be adjusted by changing the rigid-to-elastic... 

    Fatigue performance of polymer and ordinary cement concrete under corrosive conditions: A comparative study

    , Article Engineering Failure Analysis ; Volume 111 , 2020 Ghassemi, P ; Rajabi, H ; Toufigh, V ; Sharif University of Technology
    Elsevier Ltd  2020
    Abstract
    Many concrete structures such as bridges, offshore structures, and pavements are under cyclic loads when they are exposed to different environmental conditions during their lifespan. The durability and fatigue performance of these structures are significant issues that should be considered. Therefore, this study investigated the long-term environmental effects on Polymer Concrete (PC) and Ordinary Cement Concrete (OCC) subjected to cyclic fatigue loading under four different environmental conditions (freshwater, seawater, acidic and alkaline) for six months. Concrete specimens are tested under high cyclic loading with the frequency of 6 Hz and low cyclic loading with a frequency of 1 Hz.... 

    Effects of motion and structural vibration–induced loadings on the coupled dynamic response of a mono-column tension-leg-platform floating wind turbine

    , Article Proceedings of the Institution of Mechanical Engineers Part M: Journal of Engineering for the Maritime Environment ; Volume 234, Issue 2 , 2020 , Pages 426-445 Imani, H ; Abbaspour, M ; Tabeshpour, M. R ; Karimirad, M ; Sharif University of Technology
    SAGE Publications Ltd  2020
    Abstract
    Floating wind turbines are subjected to highly dynamic and complicated environmental conditions leading to significant platform motions and structural vibrations during operation and survival conditions. These motions and vibrations alter the induced loading characteristics; and consequently, affect the dynamic behavior of the system. In order to better understand the influence of such motions and structural vibrations, herein elastic structural disturbance of tower, on the system behavior, the spectral and statistical characteristics of a floating wind turbine dynamic responses under operational and survival conditions are fully explored using a fully coupled...