offshore structures thesis

Performance of skirted foundations for offshore structures

Research output : Thesis › Doctoral Thesis

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• Offshore Structure Engineering 100%
• Centrifuge Engineering 66%
• Mooring Engineering 66%
• Cyclic Loading Engineering 66%
• Experimental Result Engineering 33%
• Stress History Engineering 33%
• Monotonic Loading Engineering 33%
• Cyclic Loading Condition Engineering 33%

T1 - Performance of skirted foundations for offshore structures

AU - Watson, Phillip

N2 - Skirted foundations are being used increasingly as foundation systems for offshore structures. Uses include skirted gravity base structures, suction anchors (as alternatives to drag anchors) for catenary moorings, and caisson foundations for either taut leg moorings (such as tension leg platforms) or jacket structures. The behaviour of caisson foundations in calcareous sediments, subjected to combined monotonic and cyclic loading conditions, is the primary focus of this thesis. The main thrust of the research is experimental, with a wide range of model tests conducted in a geotechnical centrifuge. In order to allow interpretation of foundation results, the research has been extended to include a review of soil characterisation procedures, including an examination of existing strength measurement techniques, and the study of new test devices. Results from tests conducted in a range of material types and stress histories are examined, and conclusions drawn regarding the derivation of in situ soil strength. From tests conducted in either kaolin clay, calcareous silt or calcareous sand, the response of skirted foundations to applied monotonic vertical and horizontal loads has been examined. In addition, general numerical solutions for installation resistance, bearing capacity, tension capacity and lateral capacity are compared to the experimental results obtained. Included in the discussion is the potential for significant increases in bearing and lateral capacity arising from the application of preload. Finally, combined loading tests (in V-H load space) have been used to investigate empirically the form of a yield envelope for caisson foundations, and the potential use of an associated flow rule to define plastic deformation at yield. Cyclic caisson response has also been investigated in the centrifuge, with a detailed programme of model caisson testing undertaken. This has involved 2-way and 1-way lateral cyclic loading, and either compressive or tensile vertical loads. General foundation behaviour is summarised in the form of a series of contour diagrams describing foundation deformation (vertical settlement and lateral displacement) with respect to the amplitude of cyclic loading and the number of cycles performed. These diagrams are then used in the derivation of empirical prediction methods to estimate foundation response to complex loading situations, such as arising during storm loading. Finally, two case examples exploring the use of skirted foundations for offshore structures are examined. In each example, both the monotonic and cyclic response is investigated, and conclusions are drawn with respect to the observed foundation behaviour.

AB - Skirted foundations are being used increasingly as foundation systems for offshore structures. Uses include skirted gravity base structures, suction anchors (as alternatives to drag anchors) for catenary moorings, and caisson foundations for either taut leg moorings (such as tension leg platforms) or jacket structures. The behaviour of caisson foundations in calcareous sediments, subjected to combined monotonic and cyclic loading conditions, is the primary focus of this thesis. The main thrust of the research is experimental, with a wide range of model tests conducted in a geotechnical centrifuge. In order to allow interpretation of foundation results, the research has been extended to include a review of soil characterisation procedures, including an examination of existing strength measurement techniques, and the study of new test devices. Results from tests conducted in a range of material types and stress histories are examined, and conclusions drawn regarding the derivation of in situ soil strength. From tests conducted in either kaolin clay, calcareous silt or calcareous sand, the response of skirted foundations to applied monotonic vertical and horizontal loads has been examined. In addition, general numerical solutions for installation resistance, bearing capacity, tension capacity and lateral capacity are compared to the experimental results obtained. Included in the discussion is the potential for significant increases in bearing and lateral capacity arising from the application of preload. Finally, combined loading tests (in V-H load space) have been used to investigate empirically the form of a yield envelope for caisson foundations, and the potential use of an associated flow rule to define plastic deformation at yield. Cyclic caisson response has also been investigated in the centrifuge, with a detailed programme of model caisson testing undertaken. This has involved 2-way and 1-way lateral cyclic loading, and either compressive or tensile vertical loads. General foundation behaviour is summarised in the form of a series of contour diagrams describing foundation deformation (vertical settlement and lateral displacement) with respect to the amplitude of cyclic loading and the number of cycles performed. These diagrams are then used in the derivation of empirical prediction methods to estimate foundation response to complex loading situations, such as arising during storm loading. Finally, two case examples exploring the use of skirted foundations for offshore structures are examined. In each example, both the monotonic and cyclic response is investigated, and conclusions are drawn with respect to the observed foundation behaviour.

U2 - 10.4225/23/5a124f8c50df4

DO - 10.4225/23/5a124f8c50df4

M3 - Doctoral Thesis

Marine growth and the hydrodynamic loading of offshore structures

Downloadable content.

• Theophanatos, Andreas.
• https://stax.strath.ac.uk/thesis_copyright_statement/
• University of Strathclyde
• Doctoral (Postgraduate)
• Doctor of Philosophy (PhD)
• Department of Mechanical and Process Engineering.
• This thesis presents the results of a study on the effects of marine growth on the hydrodynamic loading of offshore structures and proposes an approach that can be adopted by designers and operators to quantify these effects. The approach is based upon the realistic characterisation of marine growth and its temporal variations during the life span of template structures. Past research work and current design, inspection and maintenance practices are critically reviewed and their limitations with respect to marine growth are highlighted. The ecology of marine growth for a sample of North Sea platforms was examined to establish the variety and physical attributes of the fouling colonies. The traditional single-parameter characterisation of marine roughness was found to be inadequate. Appropriate parameters, verified by fluid loading experiments, are established. Details of the laboratory experiments undertaken with both real marine growth and artificial macro-roughness on circular cylinders are given. These tests were carried out at large scale (cylinders up to 521mm diameter) in a novel "buoyant cylinder" test rig (steady flow) and in a large wave flume (regular waves). A wide range of parametric variations were undertaken for the various types of marine growth in an attempt to establish a comprehensive database from which the loading effect of any likely, practically occuring, marine growth pattern can be estimated. The extent to which this is achieved and the requirements for further research are discussed in detail. It is concluded that the effects of marine growth are both substantial and diverse. Drag forces vary with type of fouling, overall thickness, surface cover, and distribution. Finally, detailed procedures are recommended for the design of new structures and the improved loading assessment of existing ones.
• Doctoral thesis
• 10.48730/qx63-8r70
• uk.bl.ethos.382439

• Research repository
• Education Repository
• Cultural Heritage

Lattice Tower Design of Offshore Wind Turbine Support Structures

Moe, G. (mentor)

Civil Engineering and Geosciences

section Hydraulic Engineering

CoMEM - Coastal and Marine Engineering and Management

Optimal design of support structure including foundation and turbine tower is among the most critical challenges for offshore wind turbine. With development of offshore wind industry heading for deeper ocean areas, new support structural concept such as a full lattice tower could be proven to be more advantageous than others when consideration of cost, safety and even environment aspects, etc are taken into. This thesis first gave introduction of present industrial applications of hybrid support structural concept combing a lattice foundation and monotower in relatively deep water areas before the presenting and introduction of challenges with the transition piece component. Conceptual model of transition piece design for a full lattice tower support structure proposal was discussed extensively which included consideration of structural form, functional requirement, mechanical condition, etc. A mechanical model of transition piece with regards to boundary condition and load conditions was also provided. Design and analysis of two different types of transition piece models under various load conditions were performed during preliminary design and with conclusion drawn, a refined final design of transition piece model for the full lattice tower support structural concept which has also included more practical aspects was assessed through investigation of its performance under varying load conditions and different load cases. This refined final design was found to be the most optimal design fulfilling all relevant requirements at a comparable structural cost. Conclusion and recommendation was therefore given in the last part. This thesis work is serving for a novel proposal of support structural concept for future offshore wind industry and relevant present experience is in fact nonexistent. The work applied present industrial information of hybrid support structure as basis along with consideration of offshore wind turbine structural and operational mechanism and their respective requirement. Structural analysis of transition piece design was conducted by means of finite element analysis technique and structural load conditions were simulated through up-to-date numerical modeling code for offshore wind turbine structure. Due to absence of relevant verification sources, advice and correction of the thesis content is much appreciated.

offshore wind turbine wind turbine support structure transition piece lattice tower

http://resolver.tudelft.nl/uuid:60cbccec-d00f-4814-933f-d20c3bb3c4fc

Student theses

master thesis

(c) 2011 Gong, W.

• About DTU Orbit

Efficient computations of wave loads on offshore structures

Research output : Book/Report › Ph.D. thesis

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• Ph Final published version, 20.3 MB

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• Calculation Physics 100%
• Impact Physics 100%
• Domains Physics 83%
• Directional Engineering 50%
• Circular Cylinder Engineering 50%
• Load Cycle Engineering 50%
• Steepness Engineering 50%
• Cycles Physics 50%

Projects per year

Efficient CFD computation of extreme wave loads on wind turbine foundations

Paulsen, B. T., Bingham, H. B. , Bredmose, H. , Christensen, E. D. , Grue, J. & Yeung, R. W.

Institut, samfinansiering

01/09/2010 → 22/11/2013

Project : PhD

• Impact 100%
• Calculation 100%
• Domains 83%
• Load Cycle 50%
• Steepness 50%

T1 - Efficient computations of wave loads on offshore structures

AU - Paulsen, Bo Terp

N2 - The present thesis considers numerical computations of fully nonlinear wave impacts on bottom mounted surface piercing circular cylinders at intermediate water depths. The aim of the thesis is to provide new knowledge regarding wave loads on foundations for offshore wind turbines. Hence, the dimensions of the cylinders and the chosen wave parameters were inspired by typical monopile foundations for offshore wind turbines.The numerical computations are carried out using three numerical solvers. That is, the fully nonlinear Navier-Stokes/VOF solver provided as a part of the open-source CFD-toolbox OpenFoam R, the fully nonlinear potential flow solver OceanWave3D and finally a fully nonlinear domain decomposed solver, which was developed as part of this project. In the domain decomposed solver, the outer wave field is described by the potential flow solver, whereas the inner wave field, in the vicinity of a given structure, is described by the Navier-Stokes/VOF solver.All numerical models are carefully validated either in terms of convergence by grid refinement or by comparisons to experimental measurements. Special attention is paid to the newly developed domain decomposed solver, which is carefully validated against experimental measurements of regular-, irregular- and multi-directional irregular waves. The ability of the numerical model to accurately reproduce experiments is also investigated.Wave impacts on a bottom mounted circular cylinder from steep regular waves are presented. Here, the inline forces and the motion of the free surface is described as a function of the non-dimensional wave steepness, the relative water depth, the relative cylinder diameter and a co-existing current. From the computations, higher harmonic forces are determined and compared against the Morison equation and established analytical force formulations accurate to the third order in wave steepness.The physics related to the strongly nonlinear load phenomena “secondary load cycles” is described and an explanation of the wave load phenomena is provided. To further support the explanation a simple inviscid kinematic model flow is derived.The discussion of wave impacts on circular cylinders is further extended to uni- and bi-directional phase-focused waves. Here, the influence of the nondimensional wave steepness and wave directionality is discussed. For the steepest wave impacts “secondary load cycles” are observed and the physics of the impact and the mechanisms related to the “secondary load cycle“ are discussed and compared to the observations made for regular waves.Additionally, attention is paid to experimental determination of hydrodynamic forces. Significant differences between experimentally measured and computed higher harmonic forces are observed and the differences are explained in terms of the eigenmotion of the test setup. Finally, the application of the domain decomposed solver is discussed in an engineering context. Here, a simple and robust way of identifying forces, which may be inaccuvii rately estimated by the Morison equation, is presented. It is suggested that these impacts are recomputed by the domain decomposed solver.

AB - The present thesis considers numerical computations of fully nonlinear wave impacts on bottom mounted surface piercing circular cylinders at intermediate water depths. The aim of the thesis is to provide new knowledge regarding wave loads on foundations for offshore wind turbines. Hence, the dimensions of the cylinders and the chosen wave parameters were inspired by typical monopile foundations for offshore wind turbines.The numerical computations are carried out using three numerical solvers. That is, the fully nonlinear Navier-Stokes/VOF solver provided as a part of the open-source CFD-toolbox OpenFoam R, the fully nonlinear potential flow solver OceanWave3D and finally a fully nonlinear domain decomposed solver, which was developed as part of this project. In the domain decomposed solver, the outer wave field is described by the potential flow solver, whereas the inner wave field, in the vicinity of a given structure, is described by the Navier-Stokes/VOF solver.All numerical models are carefully validated either in terms of convergence by grid refinement or by comparisons to experimental measurements. Special attention is paid to the newly developed domain decomposed solver, which is carefully validated against experimental measurements of regular-, irregular- and multi-directional irregular waves. The ability of the numerical model to accurately reproduce experiments is also investigated.Wave impacts on a bottom mounted circular cylinder from steep regular waves are presented. Here, the inline forces and the motion of the free surface is described as a function of the non-dimensional wave steepness, the relative water depth, the relative cylinder diameter and a co-existing current. From the computations, higher harmonic forces are determined and compared against the Morison equation and established analytical force formulations accurate to the third order in wave steepness.The physics related to the strongly nonlinear load phenomena “secondary load cycles” is described and an explanation of the wave load phenomena is provided. To further support the explanation a simple inviscid kinematic model flow is derived.The discussion of wave impacts on circular cylinders is further extended to uni- and bi-directional phase-focused waves. Here, the influence of the nondimensional wave steepness and wave directionality is discussed. For the steepest wave impacts “secondary load cycles” are observed and the physics of the impact and the mechanisms related to the “secondary load cycle“ are discussed and compared to the observations made for regular waves.Additionally, attention is paid to experimental determination of hydrodynamic forces. Significant differences between experimentally measured and computed higher harmonic forces are observed and the differences are explained in terms of the eigenmotion of the test setup. Finally, the application of the domain decomposed solver is discussed in an engineering context. Here, a simple and robust way of identifying forces, which may be inaccuvii rately estimated by the Morison equation, is presented. It is suggested that these impacts are recomputed by the domain decomposed solver.

M3 - Ph.D. thesis

BT - Efficient computations of wave loads on offshore structures

PB - Technical University of Denmark

CY - Kgs. Lyngby

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• Published: 24 April 2024

Ocean management

Ecological role of offshore structures

• Andrew R. Gates   ORCID: orcid.org/0000-0002-2798-5044 1 &
• Daniel O. B. Jones   ORCID: orcid.org/0000-0001-5218-1649 1  

Nature Sustainability volume  7 ,  pages 383–384 ( 2024 ) Cite this article

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Oil and gas installations, offshore windfarms and other artificial constructions may enhance marine ecosystems and have been proposed to help meet conservation targets. A study synthesizes existing literature to reveal global patterns in their ecological effectiveness.

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Fowler, A. M. et al. Front. Ecol. Environ. 16 , 571–578 (2018).

Article   Google Scholar  

Claisse, J. T. et al. Proc. Natl Acad. Sci. USA 111 , 15462–15467 (2014).

Article   CAS   Google Scholar  

Lemasson, A. J. et al. Nat. Sustain. https://doi.org/10.1038/s41893-024-01311-z (2024).

Paolo, F. S. et al. Nature 625 , 85–91 (2024).

Cordes, E. E. et al. Front. Environ. Sci. 4 , 58 (2016).

Scarborough Bull, A. & Love, M. S. Ocean Coast. Manag. 168 , 274–306 (2019).

Knights, A. M. et al. J. Environ. Manage. 352 , 119897 (2024).

Lemasson, A. J. et al. Environ. Evid. 11 , 35 (2022).

Jones, D. O. B., Gates, A. R., Huvenne, V. A. I., Phillips, A. B. & Bett, B. J. Sci. Total Environ. 668 , 835–853 (2019).

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