{"title":"Numerical Study of Phase Change Influence on Wave Impact Loads in LNG Tanks on Floating Structures","authors":"M. Ancellin, L. Brosset, J. Ghidaglia","doi":"10.1115/OMAE2018-78643","DOIUrl":"https://doi.org/10.1115/OMAE2018-78643","url":null,"abstract":"Understanding the physics of sloshing wave impacts is necessary for the improvement of sloshing assessment methodology based on sloshing model tests, for LNG membrane tanks on floating structures. The phase change between natural gas and liquefied natural gas is one of the physical phenomena involved during a LNG wave impact but is not taken into account during sloshing model tests.\u0000 In this paper, some recent numerical and analytical works on the influence of phase change are summarized and discussed. For the impact of an ideally shaped wave, phase change influences two different steps of the impact in different ways: during the gas escape phase, phase change leads to a higher impact velocity; for entrapped gas pockets, phase change causes a reduction of the pressure in the gas pocket. However, this influence is quantitatively small.\u0000 The generalization to more realistic wave shapes (including e.g. liquid aeration) should be the focus of future works.","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":"124833791","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}
{"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}
{"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}
{"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}
R. Beemer, A. N. Bandini-Maeder, J. Shaw, Ulysse Lebrec, M. Cassidy
{"title":"The Granular Structure of Two Marine Carbonate Sediments","authors":"R. Beemer, A. N. Bandini-Maeder, J. Shaw, Ulysse Lebrec, M. Cassidy","doi":"10.1115/OMAE2018-77087","DOIUrl":"https://doi.org/10.1115/OMAE2018-77087","url":null,"abstract":"Calcareous sediments are prominent throughout the low-latitudinal offshore environment and have been known to be problematic for offshore foundation systems. These fascinating soils consist largely of the skeletal remains of single-celled marine organisms (plankton and zooplankton) and can be as geologically complex as their onshore siliceous counter parts. To enable an adequate understanding of their characteristics, in particular, their intra-granular micro-structure, it is important that geotechnical engineers do not forget about the multifaceted biological origins of these calcareous sediments and the different geological processes that created them. In this paper, the 3D models of soils grains generated from micro-computed tomography scans, scanning electeron microscope images, and optical microscope images of two calcareous sediments from two different depositional environments are presented and their geotechnical implications discussed. One is a coastal bioclastic sediment from Perth, Western Australia that is geologically similar to carbonate sediments typically used in micro-mechanics and particle crushing studies in the literature. The other is a hemipelagic sediment from a region of the North West Shelf of Australia that has historically been geotechnically problematic for engineers. The results show there is a marked difference between coastal bioclastic and hemipelagic sediments in terms of geological context and the associated particle micro-structures. This brings into question whether a coastal bioclastic calcareous sediment is a good micro-mechanical substitute for a hemipelagic one.","PeriodicalId":106551,"journal":{"name":"Volume 9: Offshore Geotechnics; Honoring Symposium for Professor Bernard Molin on Marine and Offshore Hydrodynamics","volume":"13 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":"124431894","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}
{"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}
{"title":"Performance of Embedded Mooring Lines During Keying and Diving of Gravity Installed Anchors","authors":"Yanbing Zhao, Haixiao Liu","doi":"10.1115/OMAE2018-78034","DOIUrl":"https://doi.org/10.1115/OMAE2018-78034","url":null,"abstract":"Gravity installed anchors (GIAs) are the most recent generation of anchoring solution to moor floating facilities for deepwater oil and gas developments. After the installation of GIAs, the anchors are connected with the floating facility via the mooring lines, which interact with the anchors at the shackle and influence the keying and diving performance of GIAs. In the present work, a three-dimensional large deformation finite element (LDFE) model is established using the coupled Eulerian–Lagrangian method to investigate the performance of embedded mooring lines during keying and diving of GIAs. To verify the efficiency of the LDFE model, comparisons with the plasticity models are performed. Then, a parametric study is undertaken to quantify the relationship between the drag force Ta and drag angle θah at the shackle and the drag force T0 and drag angle θ0 at the mudline, in terms of the frictional coefficient, drag angle at the mudline and soil strain rate and strain softening. It is demonstrated that the drag angle at the mudline has the most significant effect on the performance of embedded mooring lines and hence the keying and diving of GIAs.","PeriodicalId":106551,"journal":{"name":"Volume 9: Offshore Geotechnics; Honoring Symposium for Professor Bernard Molin on Marine and Offshore Hydrodynamics","volume":"22 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":"130664922","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
{"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}
{"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}
{"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}