A current investigation subject of geotechnical modelling is the realistic representation of the installation process of offshore piles and its influences on the surrounding soil. Depending on the soil conditions piles can be installed with different installation technologies like impact driving, vibratory driving or jacking. The soil disturbances produced as a consequence of the pile installation affect the pile capacity. The dimension of the affected region depends on the installation process itself and its parameters as well as the soil initial state and the pile geometry. Currently, there are no general approaches which can predict the effects of pile installation on the soil conditions. In this contribution a brief summary of published data describing installation effects for impact driven, vibratory driven and jacked piles is given. Secondly, the influences of different pile installation methods on the surrounding soil are presented based on experimental results for non-cohesive soils from various projects. These will be analyzed by means of a comparison of dynamic probe light (DPL) and cone penetration tests (CPT) executed before and after the pile installations. Additionally the area of influence will be quantified with respect to their relative distance to the pile axis. Finally, based on these results recommendations for future works will be given.
{"title":"Influence of Different Pile Installation Methods on Dense Sand","authors":"Severin Spill, T. Quiroz, A. Foglia","doi":"10.1115/omae2019-96109","DOIUrl":"https://doi.org/10.1115/omae2019-96109","url":null,"abstract":"\u0000 A current investigation subject of geotechnical modelling is the realistic representation of the installation process of offshore piles and its influences on the surrounding soil. Depending on the soil conditions piles can be installed with different installation technologies like impact driving, vibratory driving or jacking. The soil disturbances produced as a consequence of the pile installation affect the pile capacity. The dimension of the affected region depends on the installation process itself and its parameters as well as the soil initial state and the pile geometry. Currently, there are no general approaches which can predict the effects of pile installation on the soil conditions. In this contribution a brief summary of published data describing installation effects for impact driven, vibratory driven and jacked piles is given. Secondly, the influences of different pile installation methods on the surrounding soil are presented based on experimental results for non-cohesive soils from various projects. These will be analyzed by means of a comparison of dynamic probe light (DPL) and cone penetration tests (CPT) executed before and after the pile installations. Additionally the area of influence will be quantified with respect to their relative distance to the pile axis. Finally, based on these results recommendations for future works will be given.","PeriodicalId":23567,"journal":{"name":"Volume 1: Offshore Technology; Offshore Geotechnics","volume":"28 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2019-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"72787973","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The axial resistance of pipelines is an important design input, influencing a variety of analyses such as buckling and axial walking. As such, accurate assessment of the frictional behaviour of the soil-pipeline interface is necessary to properly model axial behaviour. Smooth polymer coated pipelines are commonly used subsea, yet despite their common application, limited guidance exists in the main governing standards concerning the expected level of axial friction to be used in design. Related guidance that does exist (e.g. BSI, 2016) suggests a minimum friction coefficient of 0.55 for sand-pipeline interfaces. This paper reviews various aspects of sand-polymer direct shear interface testing that must be considered and presents the results of some experimental research TechnipFMC have undertaken in collaboration with the University of Bristol. These results indicate that a sand-pipeline friction coefficient of 0.55 is often unrealistic for smooth polymer coated pipelines and in many design scenarios a lower frictional coefficient is more appropriate. The experimental test program considered the main factors believed to influence axial friction of smooth polymers on sand including D50 grain size, sand density and a range of stress levels (including the low stresses expected for subsea pipelines). All tests were conducted fully saturated to mimic subsea conditions and the roughness of the pipe coating samples was thoroughly characterised. TechnipFMC project experience has found that use of lower axial friction is sometimes beneficial (e.g. axial feed-in to trigger buckle initiation). In other cases, a higher axial friction may be better for design (e.g. limiting axial walking). Being able to better characterise the friction range is therefore important to ensure a robust design and to assist in avoiding more costly mitigation measures where they may not actually be needed.
{"title":"Axial Resistance of Smooth Polymer Pipelines on Sand","authors":"Henry Milewski, M. Dietz, A. Diambra, L. D. Leeuw","doi":"10.1115/omae2019-95938","DOIUrl":"https://doi.org/10.1115/omae2019-95938","url":null,"abstract":"\u0000 The axial resistance of pipelines is an important design input, influencing a variety of analyses such as buckling and axial walking. As such, accurate assessment of the frictional behaviour of the soil-pipeline interface is necessary to properly model axial behaviour. Smooth polymer coated pipelines are commonly used subsea, yet despite their common application, limited guidance exists in the main governing standards concerning the expected level of axial friction to be used in design. Related guidance that does exist (e.g. BSI, 2016) suggests a minimum friction coefficient of 0.55 for sand-pipeline interfaces. This paper reviews various aspects of sand-polymer direct shear interface testing that must be considered and presents the results of some experimental research TechnipFMC have undertaken in collaboration with the University of Bristol. These results indicate that a sand-pipeline friction coefficient of 0.55 is often unrealistic for smooth polymer coated pipelines and in many design scenarios a lower frictional coefficient is more appropriate.\u0000 The experimental test program considered the main factors believed to influence axial friction of smooth polymers on sand including D50 grain size, sand density and a range of stress levels (including the low stresses expected for subsea pipelines). All tests were conducted fully saturated to mimic subsea conditions and the roughness of the pipe coating samples was thoroughly characterised. TechnipFMC project experience has found that use of lower axial friction is sometimes beneficial (e.g. axial feed-in to trigger buckle initiation). In other cases, a higher axial friction may be better for design (e.g. limiting axial walking). Being able to better characterise the friction range is therefore important to ensure a robust design and to assist in avoiding more costly mitigation measures where they may not actually be needed.","PeriodicalId":23567,"journal":{"name":"Volume 1: Offshore Technology; Offshore Geotechnics","volume":"25 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2019-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"79095756","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Evaluation of dynamic responses under extreme environmental conditions is important for the structural design of offshore wind turbines. Previously, a modified environmental contour method has been proposed to estimate extreme responses. In the method, the joint distribution of environmental variables near the cut-out wind speed is used to derive the critical environmental conditions for a specified return period, and the turbulence intensity (TI) of wind is assumed to be a deterministic value. To address more realistic wind conditions, this paper considers the turbulence intensity as a stochastic variable and investigates the impact on the modified environmental contour. Aerodynamic simulations are run over a range of mean wind speeds at the hub height from 9–25 m/s and turbulence levels between 9%–15%. Dynamic responses of a monopile offshore wind turbine under extreme conditions were studied, and the importance of considering the uncertainties associated with wind turbulence is highlighted. A case of evaluating the extreme response for 50-year environmental contour is given as an example of including TI as an extra variant in environmental contour method. The result is compared with traditional method in which TI is set as a constant of 15%. It shows that taking TI into consideration based on probabilistic method produces a lower extreme response prediction.
{"title":"Effect of Wind Turbulence on Extreme Load Analysis of an Offshore Wind Turbine","authors":"Xiaolu Chen, Zhiyu Jiang, Qinyuan Li, Ye Li","doi":"10.1115/omae2019-95634","DOIUrl":"https://doi.org/10.1115/omae2019-95634","url":null,"abstract":"\u0000 Evaluation of dynamic responses under extreme environmental conditions is important for the structural design of offshore wind turbines. Previously, a modified environmental contour method has been proposed to estimate extreme responses. In the method, the joint distribution of environmental variables near the cut-out wind speed is used to derive the critical environmental conditions for a specified return period, and the turbulence intensity (TI) of wind is assumed to be a deterministic value. To address more realistic wind conditions, this paper considers the turbulence intensity as a stochastic variable and investigates the impact on the modified environmental contour. Aerodynamic simulations are run over a range of mean wind speeds at the hub height from 9–25 m/s and turbulence levels between 9%–15%. Dynamic responses of a monopile offshore wind turbine under extreme conditions were studied, and the importance of considering the uncertainties associated with wind turbulence is highlighted. A case of evaluating the extreme response for 50-year environmental contour is given as an example of including TI as an extra variant in environmental contour method. The result is compared with traditional method in which TI is set as a constant of 15%. It shows that taking TI into consideration based on probabilistic method produces a lower extreme response prediction.","PeriodicalId":23567,"journal":{"name":"Volume 1: Offshore Technology; Offshore Geotechnics","volume":"114 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2019-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"79237404","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
As a consequence of the planned exit from fossil-based energy in the European Union the exploitation of renewable energies has become a major aspect of the Offshore Industry. Especially the construction and operation of offshore wind energy turbines pose a challenge which is met by the use of jack-up vessels with extendible legs. In order to dimension the vessel’s manoeuvring devices in the early design stage and to ensure a safe jack-up process for given environmental loads the dynamic positioning capability during the jacking including the influence of the legs has to be calculated. As part of the development of a holistic dynamic analysis this paper presents the implementation of the legs’ influence in an existing manoeuvring method. The manoeuvring method solves the equations of motion in three degrees of freedom (surge, sway, yaw). It is based on a force model which comprises various modular components. Therefore another component for the leg-forces is added. A Morison approach is chosen to calculate the hydrodynamic forces on the cylindrical legs. The legs’ hydrodynamic added masses are accounted for and added to the hull’s inertial terms. The benefit of the presented method is the possibility to calculate the dynamic positioning capability with extended legs without being dependent on the results of either time-consuming or non-specific model tests. Therefore the method represents a fast computing tool to design the vessel for the specific environmental conditions of the site of operation.
{"title":"Calculation of the Dynamic Positioning Capability of an Offshore Wind Farm Vessel During the Jack-Up Process in the Early Design Stage","authors":"M. Liebert","doi":"10.1115/omae2019-95248","DOIUrl":"https://doi.org/10.1115/omae2019-95248","url":null,"abstract":"\u0000 As a consequence of the planned exit from fossil-based energy in the European Union the exploitation of renewable energies has become a major aspect of the Offshore Industry. Especially the construction and operation of offshore wind energy turbines pose a challenge which is met by the use of jack-up vessels with extendible legs. In order to dimension the vessel’s manoeuvring devices in the early design stage and to ensure a safe jack-up process for given environmental loads the dynamic positioning capability during the jacking including the influence of the legs has to be calculated. As part of the development of a holistic dynamic analysis this paper presents the implementation of the legs’ influence in an existing manoeuvring method. The manoeuvring method solves the equations of motion in three degrees of freedom (surge, sway, yaw). It is based on a force model which comprises various modular components. Therefore another component for the leg-forces is added. A Morison approach is chosen to calculate the hydrodynamic forces on the cylindrical legs. The legs’ hydrodynamic added masses are accounted for and added to the hull’s inertial terms. The benefit of the presented method is the possibility to calculate the dynamic positioning capability with extended legs without being dependent on the results of either time-consuming or non-specific model tests. Therefore the method represents a fast computing tool to design the vessel for the specific environmental conditions of the site of operation.","PeriodicalId":23567,"journal":{"name":"Volume 1: Offshore Technology; Offshore Geotechnics","volume":"1 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2019-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"89824583","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
J. Kyoung, H. Lim, D. Sidarta, N. Tcherniguin, T. Lefebvre
This paper presents Part 2 in the development of an Artificial Neural Network (ANN) model for detection of mooring line failure of a spread-moored FPSO, global performance analysis used to generate the training and test data for the study. The development of an ANN model for detection of mooring line failure requires a comprehensive training data that is most practically available from the results of numerical simulations. Time domain analysis is necessary to capture the nonlinear behavior of a moored FPSO system and to represent the behavior of the physical system as accurate as possible. Given the wide range of sea-state conditions, of direction of the sea-states and of draft conditions of the FPSO, the number of time domain simulations is easily larger than 100,000. Therefore, an accurate and numerically efficient tool is necessary for carrying this task. The FPSO hull motion analysis is performed using MLTSIM, a TechnipFMC in-house, nonlinear time domain floating body motion analysis program. MLTSIM captures various non-linear load and response effects such as mooring stiffness, riser loads, drag and drift forces, as well as various user defined loads. MLTSIM is a numerically efficient and fast time domain solver which can run on both high-performance computing (HPC) system and a single laptop. Numerical model of a FPSO system has been validated using the results of model tests. In addition, the results of numerical simulations, in terms of hull motions and mooring line tensions, are compared with the results of model tests and a commercial software OrcaFlex. This well-calibrated model is then used for generating the numerical data required for the development of the ANN model.
{"title":"Detection of Mooring Line Failure of a Spread-Moored FPSO: Part 2 — Global Performance Analysis Using MLTSIM","authors":"J. Kyoung, H. Lim, D. Sidarta, N. Tcherniguin, T. Lefebvre","doi":"10.1115/omae2019-96339","DOIUrl":"https://doi.org/10.1115/omae2019-96339","url":null,"abstract":"\u0000 This paper presents Part 2 in the development of an Artificial Neural Network (ANN) model for detection of mooring line failure of a spread-moored FPSO, global performance analysis used to generate the training and test data for the study.\u0000 The development of an ANN model for detection of mooring line failure requires a comprehensive training data that is most practically available from the results of numerical simulations. Time domain analysis is necessary to capture the nonlinear behavior of a moored FPSO system and to represent the behavior of the physical system as accurate as possible. Given the wide range of sea-state conditions, of direction of the sea-states and of draft conditions of the FPSO, the number of time domain simulations is easily larger than 100,000. Therefore, an accurate and numerically efficient tool is necessary for carrying this task.\u0000 The FPSO hull motion analysis is performed using MLTSIM, a TechnipFMC in-house, nonlinear time domain floating body motion analysis program. MLTSIM captures various non-linear load and response effects such as mooring stiffness, riser loads, drag and drift forces, as well as various user defined loads. MLTSIM is a numerically efficient and fast time domain solver which can run on both high-performance computing (HPC) system and a single laptop.\u0000 Numerical model of a FPSO system has been validated using the results of model tests. In addition, the results of numerical simulations, in terms of hull motions and mooring line tensions, are compared with the results of model tests and a commercial software OrcaFlex. This well-calibrated model is then used for generating the numerical data required for the development of the ANN model.","PeriodicalId":23567,"journal":{"name":"Volume 1: Offshore Technology; Offshore Geotechnics","volume":"17 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2019-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"88405435","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The installation of shallow foundation systems for offshore wind turbines like gravity foundations requires the excavation of the weak top soil of the seabed to place the structure on more stable ground. This excavation can be done through suction dredging resulting in a pit. Different slope angles of this pit can be realized using this technique. As the failure mechanisms of artificial submarine slopes using suction dredging are barely investigated, relatively small final slope angles of max. 10 degree are reached to guarantee stability. Nevertheless, small-scale experiments show that submarine slopes with overcritical slope inclinations can be stable for a while when prepared with suction dredging. Steeper inclinations would significantly reduce the disturbance of the marine fauna and the amount of sand to be removed and therefore meet both economic and ecological interests. The investigations of the failure mechanism in the submarine slope during suction dredging are carried out with a coupled Euler-Lagrange approach, namely the combination of the Computational Fluid Dynamics (CFD) and the Discrete Element Method (DEM). This method enables the computation of particle-particle as well as the fluid-particle interaction forces and hence their influence on the investigated submarine slope behavior. The calculations are carried out with the open source software package CFDEM® coupling, which combines the discrete element code LIGGGHTS® with CFD solvers based on OpenFOAM®. Additionally, small scale model tests of suction dredging of sandy submarine slopes are carried out. The displacement of the soil grains is monitored with a high-speed camera. To take into account effects of contractancy and dilatancy, a loosely and a densely packed sand are investigated and the influence of the packing density on the failure mechanism is evaluated. The experimentally gained results will be compared to the numerical ones to evaluate the capability of the coupled CFD-DEM method to depict the failure behavior of submarine slopes during suction dredging.
{"title":"Influence of Suction Dredging on the Failure Mechanism of Sandy Submarine Slopes: Revisited With a Coupled Numerical Approach","authors":"M. Kanitz, J. Grabe","doi":"10.1115/omae2019-95151","DOIUrl":"https://doi.org/10.1115/omae2019-95151","url":null,"abstract":"\u0000 The installation of shallow foundation systems for offshore wind turbines like gravity foundations requires the excavation of the weak top soil of the seabed to place the structure on more stable ground. This excavation can be done through suction dredging resulting in a pit. Different slope angles of this pit can be realized using this technique. As the failure mechanisms of artificial submarine slopes using suction dredging are barely investigated, relatively small final slope angles of max. 10 degree are reached to guarantee stability. Nevertheless, small-scale experiments show that submarine slopes with overcritical slope inclinations can be stable for a while when prepared with suction dredging. Steeper inclinations would significantly reduce the disturbance of the marine fauna and the amount of sand to be removed and therefore meet both economic and ecological interests. The investigations of the failure mechanism in the submarine slope during suction dredging are carried out with a coupled Euler-Lagrange approach, namely the combination of the Computational Fluid Dynamics (CFD) and the Discrete Element Method (DEM). This method enables the computation of particle-particle as well as the fluid-particle interaction forces and hence their influence on the investigated submarine slope behavior. The calculations are carried out with the open source software package CFDEM® coupling, which combines the discrete element code LIGGGHTS® with CFD solvers based on OpenFOAM®. Additionally, small scale model tests of suction dredging of sandy submarine slopes are carried out. The displacement of the soil grains is monitored with a high-speed camera. To take into account effects of contractancy and dilatancy, a loosely and a densely packed sand are investigated and the influence of the packing density on the failure mechanism is evaluated. The experimentally gained results will be compared to the numerical ones to evaluate the capability of the coupled CFD-DEM method to depict the failure behavior of submarine slopes during suction dredging.","PeriodicalId":23567,"journal":{"name":"Volume 1: Offshore Technology; Offshore Geotechnics","volume":"37 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2019-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"90267856","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Vortex-Induced Vibration (VIV) is one of the main sources of fatigue damage for long slender risers. Typical VIV assessment of risers is conducted using semi-empirical software tools with the sectional hydrodynamic coefficients derived from forced-oscillation model tests on short rigid riser sections. The Steel Lazy Wave Riser (SLWR) with buoyancy sections is an attractive concept for improving fatigue performance in deep water developments, but there is limited model test data available for the hydrodynamic coefficients on SLWR’s. CFD simulation is an alternative VIV assessment tool, once it is validated for an existing model test. It can provide accurate estimates of VIV response and help to design configurations of SLWR’s without additional model tests. The present CFD simulations are performed to validate hydrodynamic coefficients of a SLWR section. The predicted drag and excitation (lift) coefficients on both bare riser and buoyancy sections are compared to the test data with respect to oscillation frequency and amplitude.
{"title":"Numerical Investigation for Vortex-Induced Vibrations of Steel-Lazy-Wave-Risers: Part I — CFD Validation Against Forced Oscillation Model Test","authors":"Hyunchul Jang, Jang-Whan Kim","doi":"10.1115/omae2019-96401","DOIUrl":"https://doi.org/10.1115/omae2019-96401","url":null,"abstract":"\u0000 Vortex-Induced Vibration (VIV) is one of the main sources of fatigue damage for long slender risers. Typical VIV assessment of risers is conducted using semi-empirical software tools with the sectional hydrodynamic coefficients derived from forced-oscillation model tests on short rigid riser sections. The Steel Lazy Wave Riser (SLWR) with buoyancy sections is an attractive concept for improving fatigue performance in deep water developments, but there is limited model test data available for the hydrodynamic coefficients on SLWR’s. CFD simulation is an alternative VIV assessment tool, once it is validated for an existing model test. It can provide accurate estimates of VIV response and help to design configurations of SLWR’s without additional model tests. The present CFD simulations are performed to validate hydrodynamic coefficients of a SLWR section. The predicted drag and excitation (lift) coefficients on both bare riser and buoyancy sections are compared to the test data with respect to oscillation frequency and amplitude.","PeriodicalId":23567,"journal":{"name":"Volume 1: Offshore Technology; Offshore Geotechnics","volume":"10 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2019-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"82315721","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The lateral resistance between a subsea pipeline and the surrounding seabed is important for assessing stability and susceptibility to lateral buckling. The breakout, or peak, lateral resistance can exhibit undrained or drained behaviour depending on the rate of pipeline displacement relative to the permeability of the seabed. A drained response is common in coarse-grained soil but also can occur in transitional soil such as silty sands. While undrained breakout resistance is well understood, robust solutions for drained lateral breakout resistance of exposed subsea pipelines are lacking. The models currently used in practice exclude links to relevant soil properties such as the soil or interface friction angles despite their influence on the drained lateral breakout resistance. The lack of an industry-wide accepted approach for assessing drained lateral breakout resistance leads to an increase in the level of uncertainty being applied in routine design. To address this gap in pipe–soil interaction assessment, a parametric study using limit and finite element analyses is presented to illustrate the sensitivity of various input parameters on the lateral breakout resistance. The numerical results are compared to established drained lateral resistance models and model test data.
{"title":"Drained Lateral Breakout Resistance of Subsea Pipelines","authors":"J. Ballard, Z. Westgate","doi":"10.1115/omae2019-96174","DOIUrl":"https://doi.org/10.1115/omae2019-96174","url":null,"abstract":"\u0000 The lateral resistance between a subsea pipeline and the surrounding seabed is important for assessing stability and susceptibility to lateral buckling. The breakout, or peak, lateral resistance can exhibit undrained or drained behaviour depending on the rate of pipeline displacement relative to the permeability of the seabed. A drained response is common in coarse-grained soil but also can occur in transitional soil such as silty sands. While undrained breakout resistance is well understood, robust solutions for drained lateral breakout resistance of exposed subsea pipelines are lacking. The models currently used in practice exclude links to relevant soil properties such as the soil or interface friction angles despite their influence on the drained lateral breakout resistance. The lack of an industry-wide accepted approach for assessing drained lateral breakout resistance leads to an increase in the level of uncertainty being applied in routine design. To address this gap in pipe–soil interaction assessment, a parametric study using limit and finite element analyses is presented to illustrate the sensitivity of various input parameters on the lateral breakout resistance. The numerical results are compared to established drained lateral resistance models and model test data.","PeriodicalId":23567,"journal":{"name":"Volume 1: Offshore Technology; Offshore Geotechnics","volume":"107 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2019-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"82548967","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
In the dense sand-over-clay strata, there is a potential for an installing spudcan to experience a sudden uncontrolled punch-through failure. Such a punch-through failure would seriously threaten safety of the rig structure, even cause casualties. To estimate the potential spudcan punch-through failure, this paper presents a simplified numerical method to calculate the full load-penetration resistance profile. The present approach allows the progressive failure of the overlying dense sand to be properly simulated by using an extended Mohr-Coulomb model. A series of large deformation finite-element (LDFE) analyses are carried out, varying the strength parameters. A fairly good performance of the present approach is verified by validating against groups of centrifuge tests data. Additionally, comparisons with the typical existing LDFE analyses in which both the simple and sophisticated constitutive models are conducted, show that the present approach performs fairly well to calculate the penetration resistance of a spudcan on dense sand overlying clay.
{"title":"Simplified Numerical Simulation of the Dense Sand Progressive Failure Involved in Spudcan Punch-Through Failure","authors":"J. Zhao, F. Sun, Wenbo Jin","doi":"10.1115/omae2019-95911","DOIUrl":"https://doi.org/10.1115/omae2019-95911","url":null,"abstract":"\u0000 In the dense sand-over-clay strata, there is a potential for an installing spudcan to experience a sudden uncontrolled punch-through failure. Such a punch-through failure would seriously threaten safety of the rig structure, even cause casualties. To estimate the potential spudcan punch-through failure, this paper presents a simplified numerical method to calculate the full load-penetration resistance profile. The present approach allows the progressive failure of the overlying dense sand to be properly simulated by using an extended Mohr-Coulomb model. A series of large deformation finite-element (LDFE) analyses are carried out, varying the strength parameters. A fairly good performance of the present approach is verified by validating against groups of centrifuge tests data. Additionally, comparisons with the typical existing LDFE analyses in which both the simple and sophisticated constitutive models are conducted, show that the present approach performs fairly well to calculate the penetration resistance of a spudcan on dense sand overlying clay.","PeriodicalId":23567,"journal":{"name":"Volume 1: Offshore Technology; Offshore Geotechnics","volume":"33 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2019-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80786564","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
J. Serret, T. Tezdogan, T. Stratford, P. Thies, V. Venugopal
This paper presents the preliminary design of the Deep Turbine Installation-Floating (DTI-F) concept. The DTI-F concept is a hybrid spar buoy-based floating offshore substructure capable of supporting a 7MW wind turbine with the uniqueness of being able to raise and lower the tower and nacelle, which simplifies construction, installation, maintenance, and decommissioning. A relevant subset of design load cases (DLCs) derived from the International Electrotechnical Commission (ICE) standards is simulated with NREL-FAST software, and the aero-elastic loads are used for the structural assessment. The paper presents the principal dimensions and crucial hydrostatic and hydrodynamic properties. The floating platform with three different mooring configurations is designed using ANSYS AQWA software, and the design is validated with experiments in laboratory conditions. The paper evaluates the design regarding the natural frequencies and the stability of the platform for a chosen site off the Scottish coast. Further, a novel construction method, the materials chosen for the construction, and the installation and assembly processes are also outlined.
{"title":"Baseline Design of the Deep Turbine Installation-Floating, a New Floating Wind Concept","authors":"J. Serret, T. Tezdogan, T. Stratford, P. Thies, V. Venugopal","doi":"10.1115/OMAE2019-95477","DOIUrl":"https://doi.org/10.1115/OMAE2019-95477","url":null,"abstract":"\u0000 This paper presents the preliminary design of the Deep Turbine Installation-Floating (DTI-F) concept. The DTI-F concept is a hybrid spar buoy-based floating offshore substructure capable of supporting a 7MW wind turbine with the uniqueness of being able to raise and lower the tower and nacelle, which simplifies construction, installation, maintenance, and decommissioning.\u0000 A relevant subset of design load cases (DLCs) derived from the International Electrotechnical Commission (ICE) standards is simulated with NREL-FAST software, and the aero-elastic loads are used for the structural assessment.\u0000 The paper presents the principal dimensions and crucial hydrostatic and hydrodynamic properties. The floating platform with three different mooring configurations is designed using ANSYS AQWA software, and the design is validated with experiments in laboratory conditions. The paper evaluates the design regarding the natural frequencies and the stability of the platform for a chosen site off the Scottish coast.\u0000 Further, a novel construction method, the materials chosen for the construction, and the installation and assembly processes are also outlined.","PeriodicalId":23567,"journal":{"name":"Volume 1: Offshore Technology; Offshore Geotechnics","volume":"1 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2019-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"78315580","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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