Very Large Floating Structures

2007 ◽  
Author(s):  
H. Suzuki ◽  
H. R. Riggs ◽  
M. Fujikubo ◽  
T. A. Shugar ◽  
H. Seto ◽  
...  
Keyword(s):  
Design Procedure ◽  
Offshore Structures ◽  
Floating Structure ◽  
Floating Structures ◽  
Design Procedures ◽  
Novel Technology ◽  
Hydroelastic Analysis ◽  
Behavior Design ◽  
Hydroelastic Response ◽  
Near Future

Very Large Floating Structure (VLFS) is a unique concept of ocean structures primary because of their unprecedented length, displacement cost and associated hydroelastic response. International Ship and Offshore Structures Congress (ISSC) had paid attention to the emerging novel technology and launched Special Task Committee to investigate the state of the art in the technology. This paper summarizes the activities of the committee. A brief overview of VLFS is given first for readers new to the subject. History, application and uniqueness with regard to engineering implication are presented. The Mobile Offshore Base (MOB) and Mega-Float, which are typical VLFS projects that have been investigated in detail and are aimed to be realized in the near future, are introduced. Uniqueness of VLFS, such as differences in behavior of VLFS from conventional ships and offshore structures, are described. The engineering challenges associated with behavior, design procedure, environment, and the structural analysis of VLFS are introduced. A comparative study of hydroelastic analysis tools that were independently developed for MOB and Mega-Float is made in terms of accuracy of global behavior. The effect of structural modeling on the accuracy of stress analysis is also discussed. VLFS entails innovative design methods and procedure. Development of design criteria and design procedures are described and application of reliability-based approaches are documented and discussed.

Hydrodynamic Behavior of Truss Pontoon Mobile Offshore Base Platform

2016 ◽  
Author(s):  
Somansundar Sakthivel ◽  
Panneer Selvam Rajamanickam ◽  
Nagan Srinivasan
Keyword(s):  
Bending Moment ◽  
Offshore Structures ◽  
Elastic Behavior ◽  
Response Analysis ◽  
Vertical Acceleration ◽  
Floating Structures ◽  
Operational Conditions ◽  
Box Structure ◽  
Mobile Offshore Base ◽  
Hydroelastic Response

Very Large Floating Structures (VLFS) are highly specialized floating structures with variety of applications ranging from airport strips to floating motels offshore ports etc. Their economic design is based on their hydro-elastic behavior due to wave environmental forces. VLFS are extra large in size and mostly extra long in span and for that reason they are mostly modularized into several smaller structures and integrated. VLFSs may be classified into two broad categories, namely the semi-submersible type and the pontoon-type. The former type of VLFSs having their platform raised above the sea level and supported by columns resting on submerged pontoons and can minimize the effects of wave actions. In open sea, where the wave heights are relatively large, the semi-submersible VLFSs are preferred. On the other hand, the pontoon-type VLFS is a simple flat box structure floating on the sea surface. It is very flexible compared to other kinds of offshore structures, and so its elastic deformations are more important than their rigid body motions. The critical problem is the longitudinal bending moment of the long floating vessel in waves/current environment. Most of the present available VLFS designs are not economical for applications in hostile ocean. This paper presents hydrodynamic analysis carried out on an innovative VLFS called truss pontoon Mobile Offshore Base (MOB) platform concept proposed by Srinivasan [1]. The concept uses a strong deck with strong longitudinal beams to take care of the needed bending moment of the vessel for the survival, standby and operational conditions of the wave. At the submerged bottom just above the keel-tank top, a simple open-frame truss-structure is used instead of a heavy shell type pontoon. Thus the truss-pontoon provides the necessary flow transparency for the reduction of the wave exciting forces and consequently the heave motions and the vertical acceleration. Numerical analysis of truss pontoon MOB platform is carried out using HYDroelastic Response ANalysis (HYDRAN). Responses of the isolated scaled module in waves are obtained from these numerical tools and compared with published literature. Unconnected two modules and three modules are analysed using HYDRAN and the responses are compared with the isolated module. The proposed concept yielded lesser responses as compared to semisubmersible conventional MOB platform.

Physical Modeling of Wind Load on a Floating Offshore Structure

2001 ◽  
Vol 123 (4) ◽  
pp. 170-176 ◽  
Author(s):  
Bertrand Bobillier ◽  
Subrata Chakrabarti ◽  
Poul Christiansen
Keyword(s):  
Dynamic Effect ◽  
Feedback System ◽  
Offshore Structures ◽  
Wind Load ◽  
Design Criterion ◽  
Wind Effect ◽  
Offshore Structure ◽  
Floating Structure ◽  
Floating Structures ◽  
Wave Basin

Wind is an important environmental parameter that influences the design of floating offshore structures, particularly in harsh environment. Because wind spectrum is broad-banded, computation of wind load on the floating structure is complicated. Moreover, the wind-induced slow-drift oscillation is an important design criterion. Simulated environment in a model test often includes wind effect. Accurate modeling of wind in a laboratory environment is, however, a difficult task. The wind tunnel provides a steady load on the superstructure quite accurately, but fails to show the effect of the changing free surface as well as dynamic effect. Therefore, simultaneous simulation of wind in the wave basin is desirable. A weight representing the steady wind load with a string and pulley arrangement at the center of the application of the superstructure is inadequate since it fails to simulate the variation of the wind spectrum. The generation and control of the design wind spectrum by an overhead bank of fans facing the model superstructure is an extremely difficult task due to large windage area. This paper presents an accurate and highly controllable method of the generation of variable wind simultaneously with waves and current in the wave basin that can be used with a variety of floating structure model. The concept was originally proposed by Kvaerner Oil & Gas International and implemented by the offshore model basin (OMB). In this method, a fan equipped with a constant-speed motor and blades with an adjustable pitch angle is directly mounted on the model deck above water. A digital signal generated from the specified wind spectrum is used to run the fan much like the wavemaker. A feedback system ensures the proper generation of the wind with the model motion. The method was successfully applied in several model tests of deepwater floating structures in which broad-banded wind spectra were generated. An example from an earlier such test is given here. The importance of the effect of the simulated wind spectrum on floating structures should be clear to a design engineer from this example.

Reducing Hydroelastic Response of Interconnected Floating Beams Using Semi-Rigid Connections

2009 ◽  
Author(s):  
Chien Ming Wang ◽  
Muhammad Riyansyah ◽  
Yoo Sang Choo
Keyword(s):  
Fluid Motion ◽  
Beam Theory ◽  
Beam Equation ◽  
Floating Structure ◽  
Mechanical Joint ◽  
Hydroelastic Analysis ◽  
Hydroelastic Response ◽  
Frequency Domain Approach ◽  
Euler Bernoulli Beam ◽  
Element Method

This paper is concerned with the hydroelastic response of interconnected beams by a mechanical joint. A frequency domain approach is developed for the hydroelastic analysis. The fluid is modelled as an ideal fluid, whereas the beam is modelled by the Euler-Bernoulli beam theory. The boundary element method (BEM) and finite element method (FEM) are applied to solve the governing equations of fluid motion and beam equation of motion, respectively. This study investigates the design of the mechanical joint in reducing the hydroelastic response. The design involves varying the rotational stiffness and the location of such a mechanical joint to obtain a significant reduction of the hydroelastic response of the interconnected beams that model a longish very large floating structure (VLFS).

scholarly journals Hydroelastic analysis of floating structures under wave loads

2021 ◽  
Vol 2141 (1) ◽  
pp. 012002
Author(s):  
Xuhui Deng ◽  
Liang Ding ◽  
Liuyang Meng
Keyword(s):  
Expansion Method ◽  
Ocean Waves ◽  
Hydrodynamic Characteristics ◽  
Wave Loads ◽  
Floating Structure ◽  
Modal Expansion ◽  
Reliability Design ◽  
Floating Structures ◽  
Modal Expansion Method ◽  
Hydroelastic Response

Abstract Accurate prediction of hydroelastic response in ocean waves is of great significance to the structural design and reliability design of floating structures. In this paper, based on the potential flow theory, a large floating structure is simplified as a thin-plate material, and the hydrodynamic characteristics of the structure are calculated by using the modal expansion method and the boundary element method. The correctness of the theory and calculation is verified by comparing the experimental and numerical results. Further, the wave properties and structural materials characterization were changed, this paper calculates the stress and deflection of the structure under wave action, and analyzes the effects of hydroelastic response on the safety of the structure.

scholarly journals Hydroelasticity of the barge near island affected by bathymetry based on THAFTS software

2019 ◽  
Vol 234 (1) ◽  
pp. 48-58
Author(s):  
Ye Lu ◽  
Pandeli Temarel ◽  
Ye Zhou ◽  
Chao Tian
Keyword(s):  
Shallow Water ◽  
Three Dimensional ◽  
Water Area ◽  
Dynamic Responses ◽  
Response Analysis ◽  
Three Dimension ◽  
Floating Structure ◽  
Floating Structures ◽  
Hydroelastic Analysis ◽  
Water Depths

Floating structures are sometimes deployed in shallow water areas close to reefs and islands as facilities serving tourists. In contrast to the open sea, the marine environment, such as wave and current, in the nearshore shallow water area will be affected by the non-uniform complex seabed bottom, and the hydrodynamic interaction between the floating structure and the seabed bathymetry should be investigated, instead of being ignored as the case when a uniform seabed is assumed. A hydroelastic analysis method for slowly varying water depths is proposed to calculate the hydroelastic responses of the floating structures, considering the seabed as a fixed boundary condition. This method was integrated into the software THAFTS (Three Dimension Hydroelastic Analysis of Floating and Translating, developed by China Ship Scientific Research Center). Based on the THAFTS software, the three-dimensional hydroelastic motion response analysis of a barge is carried out, in which the effects of different water depths and the complex bathymetry are investigated by comparing the results of the motion and structural responses of the barge. The stress distribution of the barge with the effect of the bathymetry taken into account is presented in this article as well as the modal stresses. The strength evaluation of the barge indicates that the effect of the inhomogeneous seabed plays a large role in the dynamic responses of the barge when it is deployed near reefs.

Two-Dimensional Hydroelastic Analysis of Very Large Floating Structures

1992 ◽  
Vol 29 (01) ◽  
pp. 13-24
Author(s):  
Xiling Che ◽  
Dayun Wang ◽  
Minglun Wang ◽  
Yingfan Xu
Keyword(s):  
Deformable Body ◽  
Vertical Direction ◽  
Offshore Structures ◽  
Integrated System ◽  
Flexible Beam ◽  
Two Dimensional ◽  
Floating Structure ◽  
Floating Structures ◽  
Strip Theory ◽  
Very Large Floating Structures

We have reached a stage at which we are capable of building very large floating structures to meet the steadily increasing needs of ocean resource utilization or to fulfill some special industrial or civil purpose. When such a structure is large enough, its behavior in waves may be substantially different from that of ordinary offshore structures due to low resonant frequencies of the deformable body, and its analysis may require different techniques. In this paper, a two-dimensional hydroelastic theory is applied to a very large floating structure that may be multimodule and extend in the longitudinal direction. A revised strip theory is employed to analyze the hydrodynamic coefficients, but some modifications are introduced to allow for multibody cross sections. The structure is considered to be a flexible beam responding to waves in the vertical direction. Numerical examples are presented with reference to an integrated system of semisubmersibles. A simple model for engineering estimation is also presented.

Novel Hybrid System for Reducing Hydroelastic Response of Very Large Floating Structures

2012 ◽  
Author(s):  
Chien Ming Wang ◽  
Rui Ping Gao ◽  
Chan Ghee Koh ◽  
Sritawat Kitipornchai
Keyword(s):  
Hybrid System ◽  
Velocity Potential ◽  
Plate Theory ◽  
Expansion Method ◽  
Mindlin Plate ◽  
Floating Structure ◽  
Gill Cells ◽  
Hydroelastic Analysis ◽  
Hydroelastic Response ◽  
Element Method

This paper presents a novel hybrid system for reducing the hydroelastic response of pontoon-type, very large floating structure (VLFS) under wave action. The hybrid system comprises flexible connectors and “gill cells” which are compartments in VLFS with holes or slits at their bottom surfaces for allowing water to enter or leave freely. The gill cells are modeled by eliminating the buoyancy forces at their locations. In the hydroelastic analysis, the water is assumed to be an ideal fluid and its motion is irrotational so that a velocity potential exists. The VLFS is modeled as an isotropic plate according to the Mindlin plate theory. In order to decouple the fluid-structure interaction problem, the modal expansion method is adopted for the hydroelastic analysis which is carried out in the frequency domain. The boundary element method is used to solve the Laplace equation for the velocity potential, whereas the finite element method is employed for solving the equations of motion of the floating plate. It is found that by appropriately positioning the flexible line connector and a suitable distribution of gill cells in the VLFS, the hydroelastic response and stress resultants of the VLFS can be significantly reduced.

Hydroelastic Analysis of Floating Performance Stage at Marina Bay, Singapore

2008 ◽  
Author(s):  
C. M. Wang ◽  
J. H. Song ◽  
T. Utsunomiya ◽  
H. S. Koh ◽  
Y. B. Lim
Keyword(s):  
Element Model ◽  
Mode Shapes ◽  
Plate Model ◽  
Flexural Behaviour ◽  
Floating Structure ◽  
Young’S Moduli ◽  
Model Match ◽  
Hydroelastic Analysis ◽  
Hydroelastic Response ◽  
Bending Response

This paper presents the hydroelastic analysis of the floating performance stage that was constructed at the Marina Bay. The challenge posed in the hydroelastic analysis was the modeling of an equivalent plate that captures the dynamic flexural behaviour of the floating stage. By using a plate model with plate strips along the connecting lines of the floating stage, their Young’s moduli and Poisson’s ratios are adjusted so that the free vibration frequencies and mode shapes of the equivalent plate model match the results of the rigorous finite element model of the floating stage. The analysis shows that the hydroelastic response of the floating structure is relatively mild due to the calm waters in the Marina Bay when compared to the static bending response from imposed loads.

scholarly journals Research on Hydroelastic Response of an FMRC Hexagon Enclosed Platform

Symmetry ◽  
2021 ◽  
Vol 13 (7) ◽  
pp. 1110
Author(s):  
Wei-Qin Liu ◽  
Luo-Nan Xiong ◽  
Guo-Wei Zhang ◽  
Meng Yang ◽  
Wei-Guo Wu ◽  
...  
Keyword(s):  
Time Domain ◽  
Numerical Models ◽  
Structural Response ◽  
Deep Ocean ◽  
Surface Model ◽  
Large Area ◽  
Floating Structure ◽  
Small Depth ◽  
Response Amplitude Operators ◽  
Hydroelastic Response

The numerical hydroelastic method is used to study the structural response of a hexagon enclosed platform (HEP) of flexible module rigid connector (FMRC) structure that can provide life accommodation, ship berthing and marine supply for ships sailing in the deep ocean. Six trapezoidal floating structures constitute the HEP structure so that it is a symmetrical very large floating structure (VLFS). The HEP has the characteristics of large area and small depth, so its hydroelastic response is significant. Therefore, this paper studies the structural responses of a hexagon enclosed platform of FMRC structure in waves by means of a 3D potential-flow hydroelastic method based on modal superposition. Numerical models, including the hydrodynamic model, wet surface model and finite element method (FEM) model, are established, a rigid connection is simulated by many-point-contraction (MPC) and the number of wave cases is determined. The load and structural response of HEP are obtained and analyzed in all wave cases, and frequency-domain hydroelastic calculation and time-domain hydroelastic calculation are carried out. After obtaining a number of response amplitude operators (RAOs) for stress and time-domain stress histories, the mechanism of the HEP structure is compared and analyzed. This study is used to guide engineering design for enclosed-type ocean platforms.

A Numerically Efficient Method for Analysis of Very Large Articulated Floating Structures

1998 ◽  
Vol 42 (03) ◽  
pp. 174-186
Author(s):  
C. J. Garrison
Keyword(s):  
Hydrodynamic Interaction ◽  
Near Field ◽  
Three Dimensional ◽  
Computational Effort ◽  
Floating Structure ◽  
Complete Structure ◽  
Field Interaction ◽  
Floating Structures ◽  
Computing Effort ◽  
The Individual

A method is presented for evaluation of the motion of long structures composed of interconnected barges, or modules, of arbitrary shape. Such structures are being proposed in the construction of offshore airports or other large offshore floating structures. It is known that the evaluation of the motion of jointed or otherwise interconnected modules which make up a long floating structure may be evaluated by three dimensional radiation/diffraction analysis. However, the computing effort increases rapidly as the complexity of the geometric shape of the individual modules and the total number of modules increases. This paper describes an approximate method which drastically reduces the computational effort without major effects on accuracy. The method relies on accounting for hydrodynamic interaction effects between only adjacent modules within the structure rather than between all of the modules since the near-field interaction is by far the more important. This approximation reduces the computational effort to that of solving the two-module problem regardless of the total number of modules in the complete structure.

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