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Torgeir Moan - One of the best experts on this subject based on the ideXlab platform.

  • ringing loads on Tension Leg Platform wind turbines
    Ocean Engineering, 2014
    Co-Authors: Erin E Bachynski, Torgeir Moan
    Abstract:

    The present work identifies realistic wave (and associated wind) conditions which could induce ringing responses in Tension Leg Platform wind turbines (TLPWTs). The simulation results show the importance of ringing forces, the effects of turbine operation, and the sensitivity of the ringing response to Platform stiffness and viscous damping. To model the ringing loads, the second order quadratic transfer function and a bandwidth-limited summation formulation for the third order wave forces were implemented. The chosen formulation avoids the spectrum cut-off dependency and the low-frequency components of a direct implementation of the irregular wave Faltinsen, Newman, Vinje (FNV) formula. Depending on the natural period and damping, the difference between a direct implementation and this formulation was 5–25%. Ringing-type responses were simulated for 50-year wind and wave conditions. Various hydrodynamic models were used to isolate physics in different approaches. For Platforms with 14–18 m diameters, ringing loads resulted in larger extreme loads and increased short-term fatigue damage in the tendons and tower. Ringing effects were particularly severe for Platforms with a pitch/bending natural period of 3–4 s. The viscous damping coefficient had a negligible influence on the ringing response, while aerodynamic damping could be important in damping the oscillations following the initial maximum.

  • second order wave force effects on Tension Leg Platform wind turbines in misaligned wind and waves
    ASME 2014 33rd International Conference on Ocean Offshore and Arctic Engineering, 2014
    Co-Authors: Erin E Bachynski, Torgeir Moan
    Abstract:

    Although the majority of studies of Tension Leg Platform wind turbines (TLPWTs) have focused on aligned wind and wave conditions, it is not uncommon for the wind and waves to be significantly misaligned. Wind-wave misalignment is expected to influence both ultimate and fatigue loads. The present work compares the dynamic response of a representative TLPWT in both aligned and misaligned wind and wave conditions, with and without second order sum-frequency potential forces. The contribution of the second order loads to the maximum stress and to the short-term fatigue damage at the tower base, tower top, and tendon fairleads is examined for several operational conditions. The same TLPWT with softened tendons is also studied in order to examine the sensitivity of the results to the system natural frequencies. The fatigue damage decreased in misaligned wind and wave conditions, but the effect of second order forces increased. For the soft TLPWT design, second order forces had an important effect on fatigue in both aligned and misaligned conditions. Despite the increase in side-side loading in misaligned conditions, aligned conditions were associated with larger maximum stresses (in operational conditions).Copyright © 2014 by ASME

  • hydrodynamic modeling of Tension Leg Platform wind turbines
    ASME 2013 32nd International Conference on Ocean Offshore and Arctic Engineering, 2013
    Co-Authors: Erin E Bachynski, Torgeir Moan
    Abstract:

    In order to compute the system response of Tension Leg Platform wind turbines (TLPWTs), it is important to accurately capture the hydrodynamic loading not only at the wave frequency, but also in the low (difference) and high (sum) frequency ranges. The current work compares the dynamic response of several single column TLPWT designs in different wind and wave conditions using three hydrodynamic models: first order potential flow with viscous drag, first and second order potential flow with viscous drag, and a Morison’s equation model. Second order wave forces were found to have a relatively small effect on the structural load predictions: increased tendon Tension variation of approximately 2–10% was observed in storm conditions, while negligible effects were observed in operational conditions. The Morison model, however, gave significantly larger pitch forcing near the natural period, leading to larger structural load predictions in all sea states.Copyright © 2013 by ASME

  • point absorber design for a combined wind and wave energy converter on a Tension Leg support structure
    ASME 2013 32nd International Conference on Ocean Offshore and Arctic Engineering, 2013
    Co-Authors: Erin E Bachynski, Torgeir Moan
    Abstract:

    A combined wind and wave energy extraction device is studied, consisting of a single column Tension Leg Platform (TLP) which supports a 5MW wind turbine (WT) and 3 point absorber wave energy converters (WECs). Two variations of the WECs are considered: one that is constrained to purely heave motion relative to the TLP hull, and a hinged device which moves in coupled surge and pitch as well as heave. The effects of both types of WECs on the WT power takeoff; on structural loads in the turbine tower and blades, WEC supporting structure, and tendons; and on the Platform motions are examined for operational and 50-year extreme environmental conditions.Copyright © 2013 by ASME

  • design considerations for Tension Leg Platform wind turbines
    Marine Structures, 2012
    Co-Authors: Erin E Bachynski, Torgeir Moan
    Abstract:

    Abstract Tension Leg Platform wind turbines (TLPWTs) represent one potential method for accessing offshore wind resources in moderately deep water. Although numerous TLPWT designs have been studied and presented in the literature, there is little consensus regarding optimal design, and little information about the effect of various design variables on structural response. In this study, a wide range of parametric single-column TLPWT designs are analyzed in four different wind-wave conditions using the Simo, Riflex, and AeroDyn tools in a coupled analysis to evaluate Platform motions and structural loads on the turbine components and tendons. The results indicate that there is a trade-off between performance in storm conditions, which improves with larger displacement, and cost, which increases approximately linearly with displacement. Motions perpendicular to the incoming wind and waves, especially in the parked configuration, may be critical for TLPWT designs with small displacement. Careful choice of natural period, diameter at the water line, ballast, preTension, and pontoon radius can be used to improve the TLPWT performance in different environmental conditions and water depths.

Erin E Bachynski - One of the best experts on this subject based on the ideXlab platform.

  • ringing loads on Tension Leg Platform wind turbines
    Ocean Engineering, 2014
    Co-Authors: Erin E Bachynski, Torgeir Moan
    Abstract:

    The present work identifies realistic wave (and associated wind) conditions which could induce ringing responses in Tension Leg Platform wind turbines (TLPWTs). The simulation results show the importance of ringing forces, the effects of turbine operation, and the sensitivity of the ringing response to Platform stiffness and viscous damping. To model the ringing loads, the second order quadratic transfer function and a bandwidth-limited summation formulation for the third order wave forces were implemented. The chosen formulation avoids the spectrum cut-off dependency and the low-frequency components of a direct implementation of the irregular wave Faltinsen, Newman, Vinje (FNV) formula. Depending on the natural period and damping, the difference between a direct implementation and this formulation was 5–25%. Ringing-type responses were simulated for 50-year wind and wave conditions. Various hydrodynamic models were used to isolate physics in different approaches. For Platforms with 14–18 m diameters, ringing loads resulted in larger extreme loads and increased short-term fatigue damage in the tendons and tower. Ringing effects were particularly severe for Platforms with a pitch/bending natural period of 3–4 s. The viscous damping coefficient had a negligible influence on the ringing response, while aerodynamic damping could be important in damping the oscillations following the initial maximum.

  • second order wave force effects on Tension Leg Platform wind turbines in misaligned wind and waves
    ASME 2014 33rd International Conference on Ocean Offshore and Arctic Engineering, 2014
    Co-Authors: Erin E Bachynski, Torgeir Moan
    Abstract:

    Although the majority of studies of Tension Leg Platform wind turbines (TLPWTs) have focused on aligned wind and wave conditions, it is not uncommon for the wind and waves to be significantly misaligned. Wind-wave misalignment is expected to influence both ultimate and fatigue loads. The present work compares the dynamic response of a representative TLPWT in both aligned and misaligned wind and wave conditions, with and without second order sum-frequency potential forces. The contribution of the second order loads to the maximum stress and to the short-term fatigue damage at the tower base, tower top, and tendon fairleads is examined for several operational conditions. The same TLPWT with softened tendons is also studied in order to examine the sensitivity of the results to the system natural frequencies. The fatigue damage decreased in misaligned wind and wave conditions, but the effect of second order forces increased. For the soft TLPWT design, second order forces had an important effect on fatigue in both aligned and misaligned conditions. Despite the increase in side-side loading in misaligned conditions, aligned conditions were associated with larger maximum stresses (in operational conditions).Copyright © 2014 by ASME

  • hydrodynamic modeling of Tension Leg Platform wind turbines
    ASME 2013 32nd International Conference on Ocean Offshore and Arctic Engineering, 2013
    Co-Authors: Erin E Bachynski, Torgeir Moan
    Abstract:

    In order to compute the system response of Tension Leg Platform wind turbines (TLPWTs), it is important to accurately capture the hydrodynamic loading not only at the wave frequency, but also in the low (difference) and high (sum) frequency ranges. The current work compares the dynamic response of several single column TLPWT designs in different wind and wave conditions using three hydrodynamic models: first order potential flow with viscous drag, first and second order potential flow with viscous drag, and a Morison’s equation model. Second order wave forces were found to have a relatively small effect on the structural load predictions: increased tendon Tension variation of approximately 2–10% was observed in storm conditions, while negligible effects were observed in operational conditions. The Morison model, however, gave significantly larger pitch forcing near the natural period, leading to larger structural load predictions in all sea states.Copyright © 2013 by ASME

  • point absorber design for a combined wind and wave energy converter on a Tension Leg support structure
    ASME 2013 32nd International Conference on Ocean Offshore and Arctic Engineering, 2013
    Co-Authors: Erin E Bachynski, Torgeir Moan
    Abstract:

    A combined wind and wave energy extraction device is studied, consisting of a single column Tension Leg Platform (TLP) which supports a 5MW wind turbine (WT) and 3 point absorber wave energy converters (WECs). Two variations of the WECs are considered: one that is constrained to purely heave motion relative to the TLP hull, and a hinged device which moves in coupled surge and pitch as well as heave. The effects of both types of WECs on the WT power takeoff; on structural loads in the turbine tower and blades, WEC supporting structure, and tendons; and on the Platform motions are examined for operational and 50-year extreme environmental conditions.Copyright © 2013 by ASME

  • design considerations for Tension Leg Platform wind turbines
    Marine Structures, 2012
    Co-Authors: Erin E Bachynski, Torgeir Moan
    Abstract:

    Abstract Tension Leg Platform wind turbines (TLPWTs) represent one potential method for accessing offshore wind resources in moderately deep water. Although numerous TLPWT designs have been studied and presented in the literature, there is little consensus regarding optimal design, and little information about the effect of various design variables on structural response. In this study, a wide range of parametric single-column TLPWT designs are analyzed in four different wind-wave conditions using the Simo, Riflex, and AeroDyn tools in a coupled analysis to evaluate Platform motions and structural loads on the turbine components and tendons. The results indicate that there is a trade-off between performance in storm conditions, which improves with larger displacement, and cost, which increases approximately linearly with displacement. Motions perpendicular to the incoming wind and waves, especially in the parked configuration, may be critical for TLPWT designs with small displacement. Careful choice of natural period, diameter at the water line, ballast, preTension, and pontoon radius can be used to improve the TLPWT performance in different environmental conditions and water depths.

Nagan Srinivasan - One of the best experts on this subject based on the ideXlab platform.

  • Hydrodynamic Analysis of Tension Based Tension Leg Platform
    Volume 1: Offshore Technology, 2012
    Co-Authors: R. Panneer Selvam, Nagan Srinivasan
    Abstract:

    Tension Leg Platforms (TLPs) are one of the best options for offshore industry in deep waters due to proven motion response characteristics. These are water depth sensitive structures and the motion responses in vertical plane motions (heave, roll and pitch) are critical for a TLP. Tension Based TLP (TBTLP) is a new concept and finds application in much deeper waters. A provision of a Tension base at mid-depth results in an economical design of TLP. In fact, the TLP installed at a certain depth without any modifications can be made to be deployed in much deeper water depths by means of a Tension base. In this paper, the concept of TBTLP is highlighted and hydrodynamic analysis of the chosen Platform has been carried out using ANSYS AQWA package. The motion responses in terms of Response Amplitude Operators (RAOs) of TBTLP with one Tension Base in surge, heave and pitch have been obtained and compared with a TLP without a Tension base.© 2012 ASME

  • Tension based Tension Leg Platform technologies for ultra deepwater applications
    ASME 2010 29th International Conference on Ocean Offshore and Arctic Engineering, 2010
    Co-Authors: Nagan Srinivasan
    Abstract:

    This paper is about technology of the Tension Leg Platform (TLP) for use in ultra deepwater to support dry-tree in oil and gas production. New TLP concept for ultra deepwater development is introduced in this paper. A technically feasible and cost-effective artificial sea-bed is used to ease the tendon design practical at such deep water in harsh environment. The truss-pontoon is utilized to reduce the vertical and horizontal wave loadings. A simple and slim hull easy to design, fabricate, transport and install is obtained. Installation method is illustrated. Optional riser-support tower is proposed to make production risers feasible in 8000 ft of water depth with no riser pre-Tension to the hull and with no vortex induced vibration problems. The paper enhances the TLP capability in deepwater.Copyright © 2010 by ASME

Srinivasan Chandrasekaran - One of the best experts on this subject based on the ideXlab platform.

  • Health monitoring of Tension Leg Platform using wireless sensor networking: experimental investigations
    Journal of Marine Science and Technology, 2019
    Co-Authors: Srinivasan Chandrasekaran, Thailammai Chithambaram
    Abstract:

    Process of deploying wireless sensor network in offshore structures for structural health monitoring is presented in this paper. Offshore structures are subjected to environmental loads with high uncertainties that are capable of causing damage during their service life. Preventive measures to safeguard the offshore Platforms from such damages are not only innovative but also inevitable. Structural damages can be readily identified by monitoring their response behavior deploying dense array of sensors. Deploying wireless structural health monitoring (SHM) system ensures reduced installation time, compact design and cost reduction in comparison to that of the traditional wired systems. Wireless sensor network architecture for monitoring offshore Platforms, proposed in the present study will acquire data using network of sensor nodes and transmits to the base station for post-processing. Present study compares the structural responses of offshore Tension Leg Platform under different postulated failure cases through experimental investigations on scaled model. Acquired data are also hosted in the webpage after analyzing and post-processing. The alert monitoring system, which is an integral part of SHM triggers alert messages is an indigenous design.

  • response control of Tension Leg Platform with passive damper experimental investigations
    Ships and Offshore Structures, 2017
    Co-Authors: Srinivasan Chandrasekaran, Deepak Kumar, Ranjani Ramanthan
    Abstract:

    Response control of offshore Tension Leg Platforms (TLP) using a passive damper is studied. The study is attempted to control the large surge motion of a TLP. Tuned mass damper (TMD) is used for the control purpose as it effectively controls the motion of the primary structure under the lateral loads. Experimental investigations are carried out on a scaled model of TLP with TMD under regular waves to examine the effectiveness of TMD in controlling the surge response of TLP. TMDs with two different mass ratios, which are tuned to that of the structural characteristics of TLP model, are used in the study. Based on the studies conducted, it is seen that there is an effective control of surge response in certain bandwidths of wave periods under the chosen mass ratio. It is also seen that the presence of TMD controls heave and pitch response as well in addition to exhibiting reduction in tether Tension variation. Attempted study is novel in terms of its application to offshore compliant structures although TMD...

  • dynamic response of Tension Leg Platform with tuned mass dampers
    Journal of Naval Architecture and Marine Engineering, 2013
    Co-Authors: Srinivasan Chandrasekaran, Deepak Kumar, Ranjani Ramanathan
    Abstract:

    Tension Leg Platform (TLP) is a taut-moored compliant offshore Platform that deploys tethers under high initial preTension to counteract the excess buoyancy. TLPs show large amplitude responses under the encountered lateral forces, which challenges the serviceability of the Platform in critical sea states. One of the passive control device i.e. Tuned Mass Damper (TMD) is attempted in the present study to control large amplitude motion of TLPs. In the present study, response control of TLP using single and multiple TMDs is compared. Optimized parameters of multiple tuned mass dampers (MTMD) are obtained using H 2 optimization algorithm for the maximum control of the motion of the Platform. Based on the studies conducted, it is seen that MTMD systems show better response control in comparison to the single TMD. Higher robustness of the MTMD system is also examined to highlight the use of MTMD over a wide range of excitation frequencies in extreme sea states. DOI: http://dx.doi.org/10.3329/jname.v10i2.16184

  • Dynamic analysis of a Tension Leg Platform under extreme waves
    Journal of Naval Architecture and Marine Engineering, 2013
    Co-Authors: Srinivasan Chandrasekaran, Koshti Yuvraj
    Abstract:

    Recent observations of the sea state that result in the undesirable events confirm the presence of extreme waves like freak waves, which is capable of causing irreparable damages to offshore installations and (or) create inoperable conditions to the crew on board. Knowledge on the extreme wave environment and the related wave-structure interaction are required for safer design of deep-water offshore structures. In the current study, typical long crested extreme waves namely:  i) New Year wave at offshore Norway; and ii) Freak wave at North Sea are simulated using the combined wave model. Dynamic response of the Tension Leg Platforms (TLP) under these extreme waves is carried out for different wave approach angles. Based on the analytical studies cared out, it is seen that the TLPs are sensitive to the wave directionality when encountered by such extreme waves; ringing type response is developed in TLPs which could result in tether pull out. DOI: http://dx.doi.org/10.3329/jname.v10i1.14518

  • offshore triangular Tension Leg Platform earthquake motion analysis under distinctly high sea waves
    Ships and Offshore Structures, 2008
    Co-Authors: Srinivasan Chandrasekaran
    Abstract:

    TLPs are compliant structures designed to withstand moderate loads without damage and severe loads without seriously endangering the occupants. Dynamic behavior of TLPs under distinctly high sea waves in the presence of both horizontal and vertical seismic excitations is examined and method of analysis is discussed. Seismic forces imposed at tether bottom make tether Tension unbalanced when the hull is under offset condition. Tether Tension varies nonlinearly under vertical seismic excitations generated using Kanai-Tajimi ground acceleration spectrum. Analytical studies conducted on triangular TLPs show that this Tension variation is much higher than the regulation values indicating the necessity for examining them for seismic safety. Clearly, the peaks seen in the response of all active degrees-of-freedom occurring near to the average sum frequencies of waves and input ground motion is a significant influence of seismic excitations on TLP tethers under high sea waves. The numerical results obtained also ...

Antonio Carlos Fernandes - One of the best experts on this subject based on the ideXlab platform.

  • Coupled wave motions on a Tension Leg Platform and tender-assisted drilling
    Marine Systems & Ocean Technology, 2017
    Co-Authors: Miguel A M Ramirez, Antonio Carlos Fernandes
    Abstract:

    Tender-assisted drilling (TAD) has been revealed as an efficient and effective solution in deep water installations to support drilling operations of tendon Leg Platforms (TLP). Although this concept is new in offshore Brazil, this has been used for more than 30 years not only in the Southeast Asia but also in the Gulf of Mexico, West Africa, and the North Sea. Due to the complex scenario of two floaters moored in close proximity, an extensive and careful hydrodynamic analysis is required to guarantee a successful execution. This work presents a numerical study of coupled wave motions on the TLP–TAD multibody system with the aim of investigating first-order loads, mean drift loads, and wave frequency responses using frequency and time domain approaches. Hydrodynamic coefficients were calculated by the 3D diffraction–radiation panel method; the mooring systems and the mechanical connection between the floaters were modeled through stiffness matrixes. In frequency domain analysis, several relative positions between the floaters were considered. On the other hand, in time domain studies, the finite element method (FEM) was used to represent moored systems and mechanical connections between the floaters. FEM allows the inclusion of drag forces, added mass, and interactions between mooring lines and floaters into the nonlinear dynamic simulations.

  • novel experimental investigation on vortex induced motions of a Tension Leg Platform
    ASME 2016 35th International Conference on Ocean Offshore and Arctic Engineering, 2016
    Co-Authors: Miguel A M Ramirez, Antonio Carlos Fernandes
    Abstract:

    Recently, a growing interest has been seen in vortex induced motions of offshore units. These induced motions are significantly relevant for the design of mooring systems and risers of offshore Platforms.This work analyzes the vortex induced motions (VIM) of a Tension Leg Platform (TLP) when submitted to currents. The model tests were carried out in the fKN@LOC/COPPE-UFRJ laboratory facilities. Furthermore, a novel arrangement to represent the TLP tendons in shallow current channels is presented and discussed. This experimental set-up is innovative since, to avoid the set down, a tower has been implemented. TLP vertical motions are restrained and necessary stiffness for horizontal modes is provided by springs.The ultra-reduced model with four square columns and four pontoons in closed configuration was built using a scale of 1:200. The range of current velocities was from 0.33 to 2.59 m/s. and five angles of attack were considered: 0, 11.25, 22.50, 33.75, 45 degrees. The reduced velocity reached a very high value of 32 for 45 degrees of heading.Results have shown that the induced motions are dependent on the angle of attack and the current speed. For zero degrees of heading a typical bell curve of VIM was observed. On the other hand, for 45 degrees, motions increase steadily with current speed.Copyright © 2016 by ASME