Accurate prediction of the roll response is of significant practical relevance not only for ships but also ship type offshore structures such as FPSOs, FLNGs and FSRUs. This paper presents a new body-exact scheme that is introduced into a nonlinear direct time-domain based strip theory formulation to study the roll response of a vessel subjected to moderately large amplitude incident waves. The free surface boundary conditions are transferred onto a representative incident wave surface at each station. The body boundary condition is satisfied on the instantaneous wetted surface of the body below this surface. This new scheme allows capturing nonlinear higher order fluid loads arising from the radiated and wave diffraction components. The Froude-Krylov and hydrostatic loads are computed on the intersection surface of the exact body position and incident wave field. The key advantage of the methodology is that it improves prediction of nonlinear hydrodynamic loads while keeping the additional computational cost small. Physical model tests have been carried out to validate the computational model. Fairly good agreement is seen. Comparisons of the force components with fully linear and body-nonlinear models help in bringing out the improvements due to the new formulation.
{"title":"An Improved Body-Exact Method to Predict Large Amplitude Ship Roll Responses","authors":"R. Subramanian, N. Rakesh, R. Beck","doi":"10.1115/OMAE2018-78720","DOIUrl":"https://doi.org/10.1115/OMAE2018-78720","url":null,"abstract":"Accurate prediction of the roll response is of significant practical relevance not only for ships but also ship type offshore structures such as FPSOs, FLNGs and FSRUs. This paper presents a new body-exact scheme that is introduced into a nonlinear direct time-domain based strip theory formulation to study the roll response of a vessel subjected to moderately large amplitude incident waves. The free surface boundary conditions are transferred onto a representative incident wave surface at each station. The body boundary condition is satisfied on the instantaneous wetted surface of the body below this surface. This new scheme allows capturing nonlinear higher order fluid loads arising from the radiated and wave diffraction components. The Froude-Krylov and hydrostatic loads are computed on the intersection surface of the exact body position and incident wave field. The key advantage of the methodology is that it improves prediction of nonlinear hydrodynamic loads while keeping the additional computational cost small. Physical model tests have been carried out to validate the computational model. Fairly good agreement is seen. Comparisons of the force components with fully linear and body-nonlinear models help in bringing out the improvements due to the new formulation.","PeriodicalId":106551,"journal":{"name":"Volume 9: Offshore Geotechnics; Honoring Symposium for Professor Bernard Molin on Marine and Offshore Hydrodynamics","volume":"24 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-06-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129438362","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}
This paper discusses the experimental and numerical investigations for the holding power of rectangular-shaped anchors. As the offshore developments are promoted, the mooring systems are often used as the station keeping systems of the marine floating structures. From a viewpoint of the energy consumption, the mechanical mooring systems with anchors are better than the dynamic mooring systems with thrusters. Up to now, however, the research and development regarding the mooring systems with the high holding anchors in the deep sea area, especially more than 500 m in depth, have hardly been carried out in Japan. In most cases, the conventional anchor shapes have experimentally and/or empirically been decided. In addition, only a few studies which relate the numerical analysis to the experimental test have been performed for the holding power. In order to obtain the optimal shape of anchors theoretically, therefore, the purpose of this study is to develop the estimation method for the holding power and to clarify the penetration mechanism of anchors in soil. In this paper, a series of experiments utilizing the small-sized anchor model is conducted. Here, the fluke shape of specimen is modeled by the rectangular flat plate for simplicity. From several experiments varying the geometric characteristics of the anchor model, the experimental results, e.g., the history of the holding power, the penetration depth, and the fluke surface angle at the maximum holding power, are obtained. Furthermore, the numerical simulation to evaluate the holding power is also carried out using the dynamic explicit non-linear finite element analysis (NLFEA) code, LS-DYNA, as well as the in-house distinct element method (DEM) code. From the comparison between the numerical results and the experimental results, the calculation accuracy is verified.
{"title":"Experimental and Numerical Study on Holding Power of Rectangular-Shaped Anchors","authors":"K. Toh, Yusuke Fukumoto, T. Yoshikawa","doi":"10.1115/OMAE2018-77814","DOIUrl":"https://doi.org/10.1115/OMAE2018-77814","url":null,"abstract":"This paper discusses the experimental and numerical investigations for the holding power of rectangular-shaped anchors. As the offshore developments are promoted, the mooring systems are often used as the station keeping systems of the marine floating structures. From a viewpoint of the energy consumption, the mechanical mooring systems with anchors are better than the dynamic mooring systems with thrusters. Up to now, however, the research and development regarding the mooring systems with the high holding anchors in the deep sea area, especially more than 500 m in depth, have hardly been carried out in Japan.\u0000 In most cases, the conventional anchor shapes have experimentally and/or empirically been decided. In addition, only a few studies which relate the numerical analysis to the experimental test have been performed for the holding power. In order to obtain the optimal shape of anchors theoretically, therefore, the purpose of this study is to develop the estimation method for the holding power and to clarify the penetration mechanism of anchors in soil.\u0000 In this paper, a series of experiments utilizing the small-sized anchor model is conducted. Here, the fluke shape of specimen is modeled by the rectangular flat plate for simplicity. From several experiments varying the geometric characteristics of the anchor model, the experimental results, e.g., the history of the holding power, the penetration depth, and the fluke surface angle at the maximum holding power, are obtained. Furthermore, the numerical simulation to evaluate the holding power is also carried out using the dynamic explicit non-linear finite element analysis (NLFEA) code, LS-DYNA, as well as the in-house distinct element method (DEM) code. From the comparison between the numerical results and the experimental results, the calculation accuracy is verified.","PeriodicalId":106551,"journal":{"name":"Volume 9: Offshore Geotechnics; Honoring Symposium for Professor Bernard Molin on Marine and Offshore Hydrodynamics","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-06-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130303891","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}
I. Chatjigeorgiou, K. Chatziioannou, V. Katsardi, Apostolos Koukouselis, E. Mistakidis
The purpose of this work is to examine a three-legged jacket tower support system subjected to wave loading. To this end, linear as well as nonlinear wave scenarios are investigated. The structure was designed for offshore wind turbines installed in intermediate water depths. The phenomenon of the wave-structure interaction is examined experimentally with a 1:18 scaled model as well as numerically with the use of Finite Element Model (FEM). The structural calculations were performed using the structural analysis software SAP2000, which was enhanced by a special programming interface that was developed to calculate the wave loading and to directly apply the wave loads on the structural members. The FEM model in combination with the key parameters that are taken into account, provides a good correlation with the experimental results. The wave theories of Airy and Stokes 5th are employed for the calculation of the wave particle kinematics. The resulting wave forces are examined both in the frequency and in the time domain.
{"title":"Numerical and Experimental Investigation of the Wave Loading on a Three-Legged Offshore Wind Turbine Jacket Platform","authors":"I. Chatjigeorgiou, K. Chatziioannou, V. Katsardi, Apostolos Koukouselis, E. Mistakidis","doi":"10.1115/OMAE2018-78416","DOIUrl":"https://doi.org/10.1115/OMAE2018-78416","url":null,"abstract":"The purpose of this work is to examine a three-legged jacket tower support system subjected to wave loading. To this end, linear as well as nonlinear wave scenarios are investigated. The structure was designed for offshore wind turbines installed in intermediate water depths. The phenomenon of the wave-structure interaction is examined experimentally with a 1:18 scaled model as well as numerically with the use of Finite Element Model (FEM). The structural calculations were performed using the structural analysis software SAP2000, which was enhanced by a special programming interface that was developed to calculate the wave loading and to directly apply the wave loads on the structural members. The FEM model in combination with the key parameters that are taken into account, provides a good correlation with the experimental results. The wave theories of Airy and Stokes 5th are employed for the calculation of the wave particle kinematics. The resulting wave forces are examined both in the frequency and in the time domain.","PeriodicalId":106551,"journal":{"name":"Volume 9: Offshore Geotechnics; Honoring Symposium for Professor Bernard Molin on Marine and Offshore Hydrodynamics","volume":"31 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-06-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"121927325","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 purpose of a gravity anchor is to moor the installation barge affected by the environmental condition during installation at the offshore site. It is important to obtain the sufficient holding capacity to prevent the anchor from dragging. There are several methods to enhance the holding capacity such as increasing its self-weight or attaching the shear key at the bottom of the gravity anchor. However, increasing the self-weight of gravity anchor is a constrained approach due to the limitation of handling equipment capacity. Therefore, it is necessary that the shear key design should be optimized to maximize the holding capacity under limited handling equipment. In this paper, reduced scale model tests simulating rock condition mixed by sand, cement, and water are performed. The actual offshore mooring condition is simulated by using towing carriage. Five types of gravity anchor models which have different shear keys are assessed to examine what type of the shear key is the optimum design. The optimum shape and the number of shear keys for maximizing the holding capacity are assessed through this study. The results of this study can be utilized to design the shear key of gravity anchor.
{"title":"Experimental Study on Gravity Anchor for Optimum Design of Shear Key","authors":"Yun-su Han, Jeong-Woo Hong, M. Oh, Jongjin Jung","doi":"10.1115/OMAE2018-78390","DOIUrl":"https://doi.org/10.1115/OMAE2018-78390","url":null,"abstract":"The purpose of a gravity anchor is to moor the installation barge affected by the environmental condition during installation at the offshore site. It is important to obtain the sufficient holding capacity to prevent the anchor from dragging. There are several methods to enhance the holding capacity such as increasing its self-weight or attaching the shear key at the bottom of the gravity anchor. However, increasing the self-weight of gravity anchor is a constrained approach due to the limitation of handling equipment capacity. Therefore, it is necessary that the shear key design should be optimized to maximize the holding capacity under limited handling equipment. In this paper, reduced scale model tests simulating rock condition mixed by sand, cement, and water are performed. The actual offshore mooring condition is simulated by using towing carriage. Five types of gravity anchor models which have different shear keys are assessed to examine what type of the shear key is the optimum design. The optimum shape and the number of shear keys for maximizing the holding capacity are assessed through this study. The results of this study can be utilized to design the shear key of gravity anchor.","PeriodicalId":106551,"journal":{"name":"Volume 9: Offshore Geotechnics; Honoring Symposium for Professor Bernard Molin on Marine and Offshore Hydrodynamics","volume":"11 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-06-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128193251","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}
Floating offshore structures used to generate wind energy are founded on submerged foundations such as anchor plates. Their extraction resistance is of major importance during and at the end of the lifetime cycle of these offshore structures. During their lifetime cycle, the foundation is suspended to complex loading conditions due to waves, tidal currents and wind loads. To guarantee a stable structure, the extraction resistance of the anchor plates has to be known. At the end of the lifetime cycle of the offshore structures, the extraction resistance is mainly influencing the removal of the anchor plates. This resistance is a lot higher than the sum of its self-weight and hydrostatic and earth pressure acting on the structure. With initiation of a motion of the anchor plate, the volume underneath this structure is increased leading to negative pore water pressure until inflowing pore water is filling the newly created volume. In order to investigate this effect, an extensive experimental study at model scale with a displacement-driven extraction is performed. Pore pressure measurements are carried out at various locations in the soil body and underneath the plate. The soil movement is tracked with a high-speed camera to investigate the shear band formation with the particle image velocimetry method (PIV). The experiments will be conducted considering different packing densities of the soil body and at different extraction velocities to investigate their effect on the extraction resistance of anchor plates.
{"title":"Experimental Study of the Influence of the Pore Water Pressure Evolution and the Shear Band Formation on the Extraction Resistance of Submerged Anchor Plates","authors":"M. Kanitz, J. Grabe","doi":"10.1115/OMAE2018-78306","DOIUrl":"https://doi.org/10.1115/OMAE2018-78306","url":null,"abstract":"Floating offshore structures used to generate wind energy are founded on submerged foundations such as anchor plates. Their extraction resistance is of major importance during and at the end of the lifetime cycle of these offshore structures. During their lifetime cycle, the foundation is suspended to complex loading conditions due to waves, tidal currents and wind loads. To guarantee a stable structure, the extraction resistance of the anchor plates has to be known. At the end of the lifetime cycle of the offshore structures, the extraction resistance is mainly influencing the removal of the anchor plates. This resistance is a lot higher than the sum of its self-weight and hydrostatic and earth pressure acting on the structure. With initiation of a motion of the anchor plate, the volume underneath this structure is increased leading to negative pore water pressure until inflowing pore water is filling the newly created volume. In order to investigate this effect, an extensive experimental study at model scale with a displacement-driven extraction is performed. Pore pressure measurements are carried out at various locations in the soil body and underneath the plate. The soil movement is tracked with a high-speed camera to investigate the shear band formation with the particle image velocimetry method (PIV). The experiments will be conducted considering different packing densities of the soil body and at different extraction velocities to investigate their effect on the extraction resistance of anchor plates.","PeriodicalId":106551,"journal":{"name":"Volume 9: Offshore Geotechnics; Honoring Symposium for Professor Bernard Molin on Marine and Offshore Hydrodynamics","volume":"3 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-06-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125501325","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}
Zhaobin Li, B. Bouscasse, L. Gentaz, G. Ducrozet, P. Ferrant
This paper presents the recent developments of the Spectral Wave Explicit Navier-Stokes Equations (SWENSE) method to extend its range of application to two-phase VOF solvers. The SWENSE method solves the wave-structure interaction problem by coupling potential theory and the Navier-Stokes (NS) equations. It evaluates the incident wave solution by wave models based on potential theory in the entire computational domain, leaving only the perturbation caused by the structure and the influence of the viscosity to be solved with CFD. The method was proven in previous studies to be accurate and efficient for wave-structure interaction problems, but it was derived for single-phase NS solvers only. The present study extends the SWENSE method by proposing a novel formulation which is convenient to implement in two-phase NS solvers. A customized SWENSE solver is developed with the open source CFD package Open-FOAM. An improvement in accuracy and stability is observed in wave simulations compared with conventional two-phase VOF solvers. The horizontal force on a vertical cylinder in regular waves is also calculated. First results show a good agreement with the experiment on the first harmonic component.
{"title":"Progress in Coupling Potential Wave Models and Two-Phase Solvers With the SWENSE Methodology","authors":"Zhaobin Li, B. Bouscasse, L. Gentaz, G. Ducrozet, P. Ferrant","doi":"10.1115/OMAE2018-77466","DOIUrl":"https://doi.org/10.1115/OMAE2018-77466","url":null,"abstract":"This paper presents the recent developments of the Spectral Wave Explicit Navier-Stokes Equations (SWENSE) method to extend its range of application to two-phase VOF solvers. The SWENSE method solves the wave-structure interaction problem by coupling potential theory and the Navier-Stokes (NS) equations. It evaluates the incident wave solution by wave models based on potential theory in the entire computational domain, leaving only the perturbation caused by the structure and the influence of the viscosity to be solved with CFD. The method was proven in previous studies to be accurate and efficient for wave-structure interaction problems, but it was derived for single-phase NS solvers only. The present study extends the SWENSE method by proposing a novel formulation which is convenient to implement in two-phase NS solvers. A customized SWENSE solver is developed with the open source CFD package Open-FOAM. An improvement in accuracy and stability is observed in wave simulations compared with conventional two-phase VOF solvers. The horizontal force on a vertical cylinder in regular waves is also calculated. First results show a good agreement with the experiment on the first harmonic component.","PeriodicalId":106551,"journal":{"name":"Volume 9: Offshore Geotechnics; Honoring Symposium for Professor Bernard Molin on Marine and Offshore Hydrodynamics","volume":"16 9 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-06-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"121021824","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}
V. R. Bernal-Colio, J. Cercos-Pita, J. Calderon-Sanchez, H. R. Díaz-Ojeda, Ricardo Abad, A. Souto-Iglesias
The aim of this work is to approach the full design of an anti-roll tank through numerical simulation, looking for the way to minimize the computational cost. The results have been validated with experiments from a rectangular tank, a tank with a C-shaped section and a rectangular tank with baffles. These tests were performed for 3 and 6 degrees of roll, and for different levels of water inside. The Open Source Computational Fluid Dynamics (CFD) tool OpenFOAM has been used to carry out the simulations and to validate the numerical model. We have worked in 3D testing different turbulence models (laminar, k-ε, k-ω, k-ω SST) and different boundary conditions (fixed values or slip). Convergence analyses of different meshes have also been performed. After filtering the outcomes, it is shown that the model k-ω SST with slip boundary estimation is the most reliable model.
{"title":"Numerical Modeling of the Forced Motion Dynamics of Antiroll Tank With OpenFOAM","authors":"V. R. Bernal-Colio, J. Cercos-Pita, J. Calderon-Sanchez, H. R. Díaz-Ojeda, Ricardo Abad, A. Souto-Iglesias","doi":"10.1115/OMAE2018-77609","DOIUrl":"https://doi.org/10.1115/OMAE2018-77609","url":null,"abstract":"The aim of this work is to approach the full design of an anti-roll tank through numerical simulation, looking for the way to minimize the computational cost. The results have been validated with experiments from a rectangular tank, a tank with a C-shaped section and a rectangular tank with baffles. These tests were performed for 3 and 6 degrees of roll, and for different levels of water inside. The Open Source Computational Fluid Dynamics (CFD) tool OpenFOAM has been used to carry out the simulations and to validate the numerical model. We have worked in 3D testing different turbulence models (laminar, k-ε, k-ω, k-ω SST) and different boundary conditions (fixed values or slip). Convergence analyses of different meshes have also been performed. After filtering the outcomes, it is shown that the model k-ω SST with slip boundary estimation is the most reliable model.","PeriodicalId":106551,"journal":{"name":"Volume 9: Offshore Geotechnics; Honoring Symposium for Professor Bernard Molin on Marine and Offshore Hydrodynamics","volume":"50 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-06-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"116874916","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 this study, we propose a new and innovative solution for harnessing offshore wind using vertical axis wind turbines (VAWT). The new type of FOWT is termed as Twin connection VAWT which uses single point mooring system consisting of two turbines capable of aligning itself against any wind direction. New-type vertical axis wind turbines are designed and developed by some of the present authors which are supported by separate floaters. The conceptual development and working mechanism of the proposed Twin connection VAWT is described in this paper based on experimental results. The yawing motion of proposed system about the moored point aligning itself to the direction of wind is confirmed in a series of dedicated experiments under only-wind condition. After aligning itself and turbines facing the direction of the wind, slow varying slewing motion phenomenon is observed during experiments. The wind forces acting on two VAWTs is examined in x-y plane and it is predicted that the forces acting perpendicular to the wind direction explains the slewing phenomenon. A physics model is conceptualized and developed to understand the yawing mechanism of the new system. A numerical simulation code is also developed to understand the yaw motion around the moored point using the steering motion equations. It is confirmed how the new system proposed can be utilized for generating clean energy.
{"title":"Slewing Effect of Twin Vertical Axis Turbines Supported by a Floating Platform Able to Rotate Around a Single Mooring System","authors":"Kazumasa Kusanagi, S. Srinivasamurthy, Y. Nihei","doi":"10.1115/OMAE2018-78410","DOIUrl":"https://doi.org/10.1115/OMAE2018-78410","url":null,"abstract":"In this study, we propose a new and innovative solution for harnessing offshore wind using vertical axis wind turbines (VAWT). The new type of FOWT is termed as Twin connection VAWT which uses single point mooring system consisting of two turbines capable of aligning itself against any wind direction. New-type vertical axis wind turbines are designed and developed by some of the present authors which are supported by separate floaters. The conceptual development and working mechanism of the proposed Twin connection VAWT is described in this paper based on experimental results. The yawing motion of proposed system about the moored point aligning itself to the direction of wind is confirmed in a series of dedicated experiments under only-wind condition. After aligning itself and turbines facing the direction of the wind, slow varying slewing motion phenomenon is observed during experiments. The wind forces acting on two VAWTs is examined in x-y plane and it is predicted that the forces acting perpendicular to the wind direction explains the slewing phenomenon. A physics model is conceptualized and developed to understand the yawing mechanism of the new system. A numerical simulation code is also developed to understand the yaw motion around the moored point using the steering motion equations. It is confirmed how the new system proposed can be utilized for generating clean energy.","PeriodicalId":106551,"journal":{"name":"Volume 9: Offshore Geotechnics; Honoring Symposium for Professor Bernard Molin on Marine and Offshore Hydrodynamics","volume":"8 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-06-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"116923374","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}
Dynamic analysis of jack-up platforms is generally carried out using approximated linear foundation springs and equivalent viscous damping. Advanced geotechnical analysis of foundations of jack-up platforms results in load-dependent stiffness and damping. Such analyses are often based on the finite element method as used for detailed site specific analyses with proper nonlinear soil models to generate nonlinear response curves, the so-called backbone curve, for the relevant loading conditions. The same FE model can be used to compute the strain energy in the soil elements and assign the corresponding energy losses in the elements based on lab tests or literature data, and integrate over the domain to compute the foundation hysteretic damping as function of loading. The state of the art method of using the backbone curve together with a kinematic hardening model to account for the hysteretic foundation response does not provide a good match between the simulated and computed damping. The hysteresis model proposed in this paper is a kinematic hardening model enhanced with a non-linear spring. It is an engineering solution to implement both a given load-dependent stiffness and load-dependent damping of a complex element subject to an irregular loading signal for purposes of time domain simulation. This model combines a kinematic hardening model which provides the required hysteresis with a non-linear elastic spring which provides the required stiffness. This model is suitable for time domain simulation of irregular loads and yields a propeller-like shape in the load-displacement plane. This paper introduces the problem of load-dependent stiffness and damping through a case study considering time domain simulation of the dynamic behavior of a jack-up platform. The paper presents a validation of the proposed model and a comparison between the common practice model and the enhanced kinematic hardening model.
{"title":"Enhanced Kinematic Hardening Model for Load-Dependent Stiffness and Damping of Jack-Up Foundations","authors":"M. Hoogeveen, H. Hofstede, A. Kaynia","doi":"10.1115/OMAE2018-77285","DOIUrl":"https://doi.org/10.1115/OMAE2018-77285","url":null,"abstract":"Dynamic analysis of jack-up platforms is generally carried out using approximated linear foundation springs and equivalent viscous damping. Advanced geotechnical analysis of foundations of jack-up platforms results in load-dependent stiffness and damping. Such analyses are often based on the finite element method as used for detailed site specific analyses with proper nonlinear soil models to generate nonlinear response curves, the so-called backbone curve, for the relevant loading conditions. The same FE model can be used to compute the strain energy in the soil elements and assign the corresponding energy losses in the elements based on lab tests or literature data, and integrate over the domain to compute the foundation hysteretic damping as function of loading. The state of the art method of using the backbone curve together with a kinematic hardening model to account for the hysteretic foundation response does not provide a good match between the simulated and computed damping. The hysteresis model proposed in this paper is a kinematic hardening model enhanced with a non-linear spring. It is an engineering solution to implement both a given load-dependent stiffness and load-dependent damping of a complex element subject to an irregular loading signal for purposes of time domain simulation. This model combines a kinematic hardening model which provides the required hysteresis with a non-linear elastic spring which provides the required stiffness. This model is suitable for time domain simulation of irregular loads and yields a propeller-like shape in the load-displacement plane. This paper introduces the problem of load-dependent stiffness and damping through a case study considering time domain simulation of the dynamic behavior of a jack-up platform. The paper presents a validation of the proposed model and a comparison between the common practice model and the enhanced kinematic hardening model.","PeriodicalId":106551,"journal":{"name":"Volume 9: Offshore Geotechnics; Honoring Symposium for Professor Bernard Molin on Marine and Offshore Hydrodynamics","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-06-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129647304","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}
This paper investigates the use of optimization for numerical-physical wave generation in wave tanks. Control signals for a wedge-shaped plunger-type wave generator are developed to produce stable non-linear, deep-water waves in both numerical and physical wave tanks. A fully non-linear potential flow solver developed at DTU is used for the numerical work. Numerical optimization proceeds by a defect correction scheme, resulting in optimized control signals for wavelengths of 0.7–2 m (corresponding to non-dimensional wave numbers kh = 2–5.5) and steepnesses of 3–11%.
{"title":"Control Signal Optimization for Non-Linear Wave Generation","authors":"J. H. Hicks, H. Bingham, R. Read","doi":"10.1115/OMAE2018-78520","DOIUrl":"https://doi.org/10.1115/OMAE2018-78520","url":null,"abstract":"This paper investigates the use of optimization for numerical-physical wave generation in wave tanks. Control signals for a wedge-shaped plunger-type wave generator are developed to produce stable non-linear, deep-water waves in both numerical and physical wave tanks. A fully non-linear potential flow solver developed at DTU is used for the numerical work. Numerical optimization proceeds by a defect correction scheme, resulting in optimized control signals for wavelengths of 0.7–2 m (corresponding to non-dimensional wave numbers kh = 2–5.5) and steepnesses of 3–11%.","PeriodicalId":106551,"journal":{"name":"Volume 9: Offshore Geotechnics; Honoring Symposium for Professor Bernard Molin on Marine and Offshore Hydrodynamics","volume":"24 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-06-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127351332","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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