The Experts below are selected from a list of 1098 Experts worldwide ranked by ideXlab platform

Kristian Maalø - One of the best experts on this subject based on the ideXlab platform.

  • detailed analysis of Clump Weight interference with subsea pipelines
    ASME 2012 31st International Conference on Ocean Offshore and Arctic Engineering, 2012
    Co-Authors: Kristian Maalø, Hagbart S Alsos, Svein Saevik
    Abstract:

    This paper focuses on the interference between pipelines and fishing gear such as Clump Weights. The objective is to examine the Clump Weight behavior as it is pulled across pipelines. Numerical analyses which simulate the integrated response between Clump Weight and pipelines are performed [1] and compared with actual tests performed by Statoil during 2004 for the Kristin field development. The experiments involved scaled down pull-over tests over idealized free spanning pipelines.A detailed model of the experimental model setup is established using the nonlinear finite element software SIMLA. Simulations are carried out for trawl gear interference with pipelines in various idealized free-span conditions. In each case the models force-displacement responses are compared with normalized test results.Finally, trawl interference with a full scale 1000 m pipeline section resting on uneven seabed is studied. The interaction forces from fully integrated pipeline-trawl analyses are compared directly with design interference loads from DNV-RP-F111, [2]. The objective of this is to quantify the potential safety margin provided by DNV-RP-F111.Copyright © 2012 by ASME

  • Clump-Weight Trawl Gear Interaction with Submarine Pipelines
    2011
    Co-Authors: Kristian Maalø
    Abstract:

    A recent development in bottom trawling is the use of twin trawl equipment, where two trawl nets are towed side by side from a single vessel. This increases the catch rate and efficiently of the trawler. Governed by cost and catch optimization, the use of twin trawl systems are expected to become more popular in the future. Using two trawl nets will, in addition to trawl doors on each side, require a heavy Clump Weight in the middle to prevent the trawl nets lifting from the seabed. The largest Clump Weights can have a mass up to 9000 kg and can cause substantial load towed across subsea pipelines, and may in many cases be the governing design load with respect to external loads in pipeline design. The main objective in this thesis work was to simulate and investigate pull-over forces from Clump Weights on free spanning pipelines. All simulations were carried out in the computer software SIMLA. Six different small scale tests were simulated in order to verify the finite element model, a very good agreement was obtained. Design loads from trawl gear are generally implemented according to DNV-RP-F111. The calculation methods provided in this recommended practice are based on the same small scale tests which was made available to this thesis work for verification purposes. The validity range of DNV-RP-F111 reflects the range of the small scale tests i.e. only valid for rigid pipelines. The effect of increasing pipeline flexibility was investigated. Simulations were carried out for span heights 0.25m, 0.50m and 0.75m for a 12” pipeline. Two different pipeline models was applied, a 25 m rigid pipeline model with spring representing the lateral pipeline stiffness, and a 1000m pipeline model including realistic soil resistance. The major finding was that pull-over forces decrease for increasing pipeline flexibility. Compared to DNV-RP-F111 the obtained pull-over loads was found considerably lower, both in magnitude and duration. To avoid over-conservatism it is thus recommended that a design method accounting for pipeline flexibility should be developed and used in future pipeline designs. The effect of warp angle was simulated varying the warp line length from 2.5 to 3.5 times the water depth. The horizontal pull-over force was found to increase for increasing warp line length. Regarding Clump Weight design and towing configuration, simulations have shown that a forward Clump Weight center of gravity will reduce the pull-over loads. Applying a lower warp line attachment point resulted in a more uniform sliding motion of the Clump Weight during interference and pull-over loads was almost complete reduced to a case of initial impact. It is thus suggested that future Clump Weight design should reflect this to reduce interference loads on both trawl gear and subsea pipelines.

Svein Saevik - One of the best experts on this subject based on the ideXlab platform.

  • detailed analysis of Clump Weight interference with subsea pipelines
    ASME 2012 31st International Conference on Ocean Offshore and Arctic Engineering, 2012
    Co-Authors: Kristian Maalø, Hagbart S Alsos, Svein Saevik
    Abstract:

    This paper focuses on the interference between pipelines and fishing gear such as Clump Weights. The objective is to examine the Clump Weight behavior as it is pulled across pipelines. Numerical analyses which simulate the integrated response between Clump Weight and pipelines are performed [1] and compared with actual tests performed by Statoil during 2004 for the Kristin field development. The experiments involved scaled down pull-over tests over idealized free spanning pipelines.A detailed model of the experimental model setup is established using the nonlinear finite element software SIMLA. Simulations are carried out for trawl gear interference with pipelines in various idealized free-span conditions. In each case the models force-displacement responses are compared with normalized test results.Finally, trawl interference with a full scale 1000 m pipeline section resting on uneven seabed is studied. The interaction forces from fully integrated pipeline-trawl analyses are compared directly with design interference loads from DNV-RP-F111, [2]. The objective of this is to quantify the potential safety margin provided by DNV-RP-F111.Copyright © 2012 by ASME

Hagbart S Alsos - One of the best experts on this subject based on the ideXlab platform.

  • detailed analysis of Clump Weight interference with subsea pipelines
    ASME 2012 31st International Conference on Ocean Offshore and Arctic Engineering, 2012
    Co-Authors: Kristian Maalø, Hagbart S Alsos, Svein Saevik
    Abstract:

    This paper focuses on the interference between pipelines and fishing gear such as Clump Weights. The objective is to examine the Clump Weight behavior as it is pulled across pipelines. Numerical analyses which simulate the integrated response between Clump Weight and pipelines are performed [1] and compared with actual tests performed by Statoil during 2004 for the Kristin field development. The experiments involved scaled down pull-over tests over idealized free spanning pipelines.A detailed model of the experimental model setup is established using the nonlinear finite element software SIMLA. Simulations are carried out for trawl gear interference with pipelines in various idealized free-span conditions. In each case the models force-displacement responses are compared with normalized test results.Finally, trawl interference with a full scale 1000 m pipeline section resting on uneven seabed is studied. The interaction forces from fully integrated pipeline-trawl analyses are compared directly with design interference loads from DNV-RP-F111, [2]. The objective of this is to quantify the potential safety margin provided by DNV-RP-F111.Copyright © 2012 by ASME

Mattiazzo Giuliana - One of the best experts on this subject based on the ideXlab platform.

  • Experimental Validation and Comparison of Numerical Models for the Mooring System of a Floating Wave Energy Converter
    'MDPI AG', 2020
    Co-Authors: Paduano Bruno, Giorgi Giuseppe, Gomes, Rui P. F., Pasta Edoardo, Henriques, Joao C. C., Gato, Luis M. C., Mattiazzo Giuliana
    Abstract:

    The mooring system of floating wave energy converters (WECs) has a crucial impact on power generation efficiency, cost of delivered energy, proper operation, reliability and survivability. An effective design, addressing such competing objectives, requires appropriate mathematical models to predict mooring loads and dynamic response. However, conversely to traditional offshore engineering applications, experience in modelling mooring systems for WECs is limited, due to their unique requirement of maximising the motion while minimising loads and costs. Even though modelling approaches and software are available for this application, guidelines and critical comparison are still scarce. This paper proposes a discussion and validation of three mooring-line models: one quasi-static approach (developed in-house) and two dynamic lumped-mass approaches (the open source MoorDyn and the commercial OrcaFlex). The case study is a 1:32-scale prototype of a floating oscillating water column WEC tested in a wave tank, with three mooring lines, each one comprising of a riser and a Clump Weight. Validation, performed by imposing fairlead displacements and comparing resulting tensions, shows good agreement. The small scale may induce numerical instabilities and uncertainties in the parameter estimation. Finally, likely due to internal resonance of this particular mooring system, high-frequency content in the mooring tension is found, albeit absent in the kinematics of the floater

  • The Effect of Mooring Line Parameters in Inducing Parametric Resonance on the Spar-Buoy Oscillating Water Column Wave Energy Converter
    'MDPI AG', 2020
    Co-Authors: Giorgi Giuseppe, Gomes, Rui P. F., Bracco Giovanni, Mattiazzo Giuliana
    Abstract:

    Although it is widely accepted that accurate modeling of wave energy converters is essential for effective and reliable design, it is often challenging to define an accurate model which is also fast enough to investigate the design space or to perform extensive sensitivity analysis. In fact, the required accuracy is usually brought by the inclusion of nonlinearities, which are often time-consuming to compute. This paper provides a computationally efficient meshless nonlinear Froude–Krylov model, including nonlinear kinematics and an integral formulation of drag forces in six degrees of freedom, which computes almost in real-time. Moreover, a mooring system model with three lines is included, with each line comprising of an anchor, a jumper, and a Clump Weight. The mathematical model is used to investigate the highly-nonlinear phenomenon of parametric resonance, which has particularly detrimental effects on the energy conversion performance of the spar-buoy oscillating water column (OWC) device. Furthermore, the sensitivity on changes to jumper and Clump-Weight masses are discussed. It is found that mean drift and peak loads increase with decreasing line pre-tension, eventually leading to a reduction of the operational region. On the other hand, the line pre-tension does not affect power production efficiency, nor is it able to avoid or significantly limit the severity of parametric instability

M Ramana V Murthy - One of the best experts on this subject based on the ideXlab platform.

  • hydrodynamic analysis of an inverted catenary coldwater pipeline of a lttd plant
    ASME 2015 34th International Conference on Ocean Offshore and Arctic Engineering, 2015
    Co-Authors: M V Ajeesh, Panneer R Selvam, R Sundarvadivelu, G Dhinesh, R Saravanan, S Phani V S Kumar, M Ramana V Murthy
    Abstract:

    Drinking water is a precious commodity with growing demand, motivating the researchers to explore innovative and cost effective measures to augment the available resources. Low Temperature Thermal Desalination (LTTD) is one among the ideas that utilizes the ocean thermal gradient for the production of freshwater. The cold water from deep sea is drawn and transported to the coast or to a floating platform to aid the conversion of surface seawater to fresh water. The behavior of this cold water pipeline in open waters is to be studied through analytical, numerical and experimental studies before actual field implementation.This paper presents the preliminary analysis of a flexible cold water pipe made up of High Density Polyethylene (HDPE) catering for an island based desalination plant. The water is drawn at a depth of 400 m and transferred to the shore. The site with coral reef demands an inverted catenary profiled pipeline to minimize damages and is connected to sump at the shallow end and a Clump Weight at the deep end. Preliminary hydrodynamic analysis of the cold water pipeline is carried out using OrcaFlex software under regular waves. Obtaining the effect of flexible pipeline under regular waves besides carrying out vortex induce vibration analysis and modal analysis forms the scope of this study. Variation of VonMises stresses, and effective tension at salient points (top end, middle and bottom end) are included.Copyright © 2015 by ASME