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Collaborating Authors
Results
Influence of Joint Flexibility on Local Dynamics of a Jacket Support Structure
Popko, Wojciech (Fraunhofer Institute for Wind Energy and Energy System Technology IWES Northwest) | Georgiadou, Sofia (Norwegian University of Science and Technology) | Loukogeorgaki, Eva (Fraunhofer Institute for Wind Energy and Energy System Technology IWES Northwest) | Vorpahl, Fabian (Aristotle University of Thessaloniki)
Abstract The effect of different modeling techniques of the local joint flexibility on the local dynamics of a jacket support structure for an offshore wind turbine is investigated. Two numerical models of a jacket supporting a generic turbine are analyzed in the aero-hydro-servo-elastic tool ADCoSOffshore. The first model is setup with Euler-Bernoulli beam elements, while the second one utilizes superelements for the joints' representation and Euler-Bernoulli beams for the remaining parts of the structure. Time domain simulations are run for deterministic and stochastic load cases and local jacket dynamics are investigated. The local response of the braces is compared with the global response at the jacket legs in terms of power spectral densities. Damage equivalent loads are calculated at several positions along the jacket to capture the impact of local and global dynamics on those loads. It is observed that the superelement model leads in general to higher fatigue loads than the beam model. A methodology to remove the global motion component from the displacement time history of the brace central joint is discussed. Larger displacements of the brace central joints are observed for the superelement model than for the beam model. It is recommended to use superelement modeling technique for more a accurate representation of joints in the jacket support structures.
- Europe (1.00)
- North America > United States (0.68)
Abstract In the present study, a CFD-based ship hydrodynamic optimization tool has been further developed by integrating a surrogate based method to the optimization module to optimize hull forms for reduced drag and improved seakeeping performance. Specifically, a radial basis function (RBF) based surrogate model is developed to approximate the objective functions (the drag and seakeeping performance) in the CFD-based hydrodynamic optimization of ship hull forms. In order to construct the RBF-based surrogate model, a practical steady ship flow solver (SSF) based on the Neumann-Michell theory and a ship motion program (SMP) based on the strip theory are employed to evaluate the drag and the seakeeping performance of the sampling hull forms, respectively. For the purpose of illustration, the developed tool is applied to the optimization of the Series 60 hull, where the original Series 60 hull with an added bulbous bow is taken as an initial hull to be optimized by minimizing the drag, the heave motion and the pitch motion when the ship advances at a constant forward speed in head seas. Numerical results show that the present computational tool can be used to optimize ship hull forms for reduced drag and improved seakeeping performance, and the developed RBF-based surrogate model can reduce computational costs associated with the CFD runs.
- Transportation > Marine (0.72)
- Shipbuilding (0.58)
In the construction of ship structures, welding deformation causes various problems. To reduce welding deformation, analyses by the finite element method (FEM) are ve ry useful. However, in a ship structure, the computing scale becomes enormous and so the prediction of welding deformation is difficult. To predict the welding deformation of ship construction, this research employed Idealized Explicit FEM, which was developed for analyses of large-scale welding problems. To attain more efficient computation, a multigrid method was introduced into Idealized Explicit FEM, and its capability is evaluated in the analysis of welding deformation of a ship structure consisting of almost 10,000,000 degrees of freedom. The analysis finished in practical computing time and confirms that mu ltigrid-method Idealized Explicit FEM is effective for the analysis of large-scale thin-plate structures such as ship structures.
Abstract Dynamic compaction is known as one of the most cost-effective soil improvement techniques. In this method the soil at the ground surface or at a relatively deep depth is compacted by repeatedly dropping heavy weights on the ground. Since its introduction, dynamic compaction has exhibited its versatility and simplicity of use in different types of civil engineering projects, including building structures, container terminals, highways, airports, dockyards, and harbours. However, despite the abundance of experimental data and field observation reports, few numerical approaches have been established in the literature to effectively deal with soil behaviour under dynamic compaction. This is mainly due to the dependence of soil dynamic response on variations in the moisture content. Therefore, to achieve a comprehensive understanding of dynamic compaction the soil should be modelled as a three-phase porous medium. The presence of a non-wetting and a wetting phase, together with the existence of inertia forces in each phase, makes the solution of the coupled dynamic system computationally demanding. Moreover, large deformations often take place during dynamic compaction; hence the infinitesimal strain theory cannot be employed for higher impact loads. In this paper a finite element approach is introduced to numerically simulate the problem of dynamic compaction under the framework of unsaturated soil mechanics. The governing equations are derived based upon the overall momentum balance of the mixture, the mass balance of the liquid phase, and the mass balance of the gas phase. Phase changes and chemical reactions are not considered. Among other important parameters, the effect of the degree of saturation on the soil response will be addressed.
Dynamic Responses of Top Tensioned Risers under Earthquake Excitations
Xing, Shutao (Independent Riser Engineering Consultants) | Dai, Wentao (Independent Riser Engineering Consultants) | Moorthy, Dakshina (Independent Riser Engineering Consultants) | Xiang, Xuxia (Independent Riser Engineering Consultants)
Abstract The purpose of this study was to investigate the seismic behavior of near vertical risers, specifically top-tensioned risers (TTR) for deep water field development. This paper developed a simplified dynamic model of TTR and conducted seismic analysis of the riser under extreme level of historical recorded earthquake excitations. The dynamic responses of the riser under the earthquake excitations were analyzed in terms of displacement and stress. The modal analysis of the riser was conducted and its modal frequencies were studied against the frequency range of earthquake waves to find correlations.
Development of Performance Evaluation Methodology and Criteria of Rockfall Barriers
An, Jai-Wook (Korea Infrastructure Safety & Technology Corporation) | Kim, Yong-Soo (Korea Infrastructure Safety & Technology Corporation) | Kim, Hong-Kyoon (Korea Infrastructure Safety & Technology Corporation) | Lee, Jong-Gun (Korea Infrastructure Safety & Technology Corporation) | Suk, Jae-Wook (Korea Infrastructure Safety & Technology Corporation)
Abstract This research was conducted to understand how the real behaviors of the rockfall barrier system are reacted when it is hit from falling rock by obtaining experimental data from the full scale tests. South Korea is a country where about 64% of its land consists of mountainous. Due to these geographical characteristics, a number of cut slopes are constantly increasing and it is inevitable for national land development. Recently, on the very steep and weathered rock slopes, the damage is variously occurred by falling rocks. The installations of rockfall barriers are one of the most common ways to protect roads and infrastructures against the falling rock. However, designing and constructing the rockfall prevention facilities without considering the conditions of site caused that the rockfall barrier can't effectively protect against rockfall energy exceeding its absorbable energy. Thus, it is necessary to develop a performance evaluation method of rockfall barriers. To study on performance evaluation method, a case study on damage by rockfall was conducted and an analysis of global trends in this field was carried out. But the types of rockfall barrier were proposed by the American (NCHRP, 2003) or European (EOTA, 2008) guidelines were different to our standard. Full scale test has been developed by considering the field circumstance in Korea. A series of tests have been successfully conducted with free falling rocks which are made in the lab. The full scale tests have been performed to obtain data from the actual impact on rockfall barrier system. During the test, Scene of experiments were recorded by high speed camera to analyze the real behavior of materials such as wire netting, wire rope and steel posts. As a result of the test, the stress of wire ropes increases with rising rockfall energy. The braking times and displacement were dependent on the types of wire and whether it has a shock absorber or not. Also, the instantaneous maximum displacements were very important check point. The statistical analysis of results obtained from full scale testing of rockfall barriers was discussed.
- North America > United States (0.29)
- Asia > South Korea (0.24)
Abstract The given article is dedicated to problems, bound with the solving of hydrodynamic problems by a boundary element method. The problem of hydroelastic interaction of a vessel shell with a contacting liquid (vibration of elastic design in a liquid) is esteemed. Thus the version is esteemed if there is a free surface of liquid. The problem is stated in ideas of a module-element method. The vessel shell is modelled by spatial module-elements. The liquid is modelled by spatial boundary elements. In the article the special boundary element is offered. This boundary element has the form by an arbitrary spatial thin shell (copy the form of a wetted surface of a vessel). This boundary element has a title "module-boundary element" (MBE). In the article the mathematical model of a problem in general is given and the basic mathematical equations for a module-boundary element of liquid are given.
- Europe (0.48)
- Asia > Russia (0.30)
- North America > United States (0.29)
Transient Effects of an FPSO with a Broken Mooring Line
Girón, Aldo Roberto Cruces (Mexican Petroleum Institute (IMP)) | Kim, Byoung Wan (Korea Research Institute of Ships & Ocean Engineering (KRISO)) | Farfán, José Alberto Martínez (Mexican Petroleum Institute (IMP)) | Hernández, Alberto Omar Vázquez (Mexican Petroleum Institute (IMP))
Abstract Breaking of mooring lines is a topic that must be analyzed during the design process of a floating production system. In current design codes this subject is treated as an accidental case. Nevertheless, transient effects after breaking of a line are not considered as relevant. In this paper an analysis of the relevance of the transient effects, in tautleg mooring line systems made of chain-polyester-chain in an FPSO with ultra-deep depth under severe storm conditions, is considered. Several coupled analysis in time domain in two ways were performed:When a mooring line is absent since the beginning of simulation (with no transient effects); Breaking a line during simulation (with transient effects).
Abstract In some papers, the hydrodynamic effects of sidehulls of surface effect ship (SES) are simply ignored with the prejudice that the displacement of sidehulls only takes a few proportions, e.g. 20% of the total displacement. To verify the conclusion, the seakeeping motions of a TCraft together with hydrodynamic effect of sidehulls are investigated in this work. The transformable craft ‘T-Craft’ is a newly developed vessel by the Office of Naval Research (ONR) that could transform itself from ACV to SES or inversely. When operated in SES mode, T-Craft is mainly supported by the air cushion while partially supported by sidehulls. In this paper, based on linear potential theory, a numerical TCraft (SES) seakeeping analysis method with consideration of sidehull hydrodynamics is firstly set up and validated by the model test results. Then by using the numerical method, the seakeeping performance of the T-Craft with various sidehull displacement ratios at low speed is investigated and compared with that of absence of sidehull effect. The investigation results suggest that the sidehulls could make significant influence on the T-Craft pitch motion, even when the sidehull displacement ratio is only 20% of the total one.
- Asia > China (0.70)
- North America > United States > Hawaii (0.16)
- Transportation > Marine (0.47)
- Government > Military > Navy (0.34)
Interface Friction Parameters for the Mathematical Modeling of Shell Structures with Infill
Bekker, Alexander T. (Far Eastern Federal University) | Tsimbelman, Nikita Ya. (Far Eastern Federal University) | Chernova, Tatiana I. (Far Eastern Federal University) | Bruss, Vadim D. (Far Eastern Federal University) | Bilgin, Ömer (University of Dayton, School of Engineering)
Abstract Thin metal or reinforced concrete shells with granular infill structures are considered in this article. These structures are massive and they are used as support for the construction of berthing quays, piers, artificial islands, shore protection, and other structures of coastal infrastructure. It is more convenient to use the thin shell structures during the development of the Arctic shelf, because it is possible to install them from the ice side. In addition, it is possible to enhance the technology and install thin shells with infill on deeper solid foundation layers. A mathematical model for the stresses on a compressible foundation soil in front of a thin cylindrical shell with infill due to the eccentric loading is developed. A modeling and experimental determination of the interface strength of the contact surface between the infill and the inner surface of the shell is proposed. The details of the construction stages and testing of the physical model used for the experiments are discussed. The effects of the interface friction on the shell behavior and on the foundation stresses in front of the wall are investigated. The influence of parameters affecting the interaction between the soil infill and the inner surface of the shell material is determined. It is based on a comparison of experimental results with calculations performed using the proposed mathematical model. The obtained parameters and proposed methods can be used in numerical simulations using the finite element method to analyze and design the thin shell structures with soil infill. The findings of the study and proposed methods can also be applied to the thin shell structures used in other facilities such as hydraulic, industrial, civil, and transportation.