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.

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.

Behaviors of a Very Large Floating Structure Supported With Dolphins Under Earthquake Loading: The Second Report — In Cases of Actual Earthquake Wave and Existence of Gaps Between Fenders and Dolphins

2006 ◽  
Author(s):  
Yoshiyasu Watanabe
Keyword(s):  
Time History ◽  
Preceding Paper ◽  
Type Structure ◽  
Earthquake Loading ◽  
Rigid Plate ◽  
Floating Structure ◽  
Floating Structures ◽  
Reaction Forces ◽  
Time History Response ◽  
Very Large Floating Structures

In recent years, tremendous research efforts have been directed toward developing very large floating structures (VLFSs) for the purposes of airports, terminals etc. on the sea to utilize ocean space. There is a VLFS which has a pontoon type structure supported with many dolphins and it is important to investigate sufficiently the behaviors of such VLFS under earthquake loading, because large reaction forces will be exerted on the dolphins and fenders that connect the dolphins and the floating structure. The preceding paper reported the behaviors of the floating structure, fenders and dolphins obtained from the time history response analyses of the structure with varying the period and velocity of the sinusoidal earthquake wave, when the horizontal rigidity of the floating structure was elastic and rigid and when the gaps between the fenders and dolphins were assumed to be zero. This paper reports, succeeding to the preceding paper, the results of the time history response analyses of a VLFS supported with 49 dolphins with varying the period and velocity of the applied actual earthquake wave in both cases where gaps between the fenders and dolphins are equal to zero and non-zero. In the analyses, the floating structure supported with dolphins is modeled as both a horizontally elastic and rigid plate supported with linear springs and dashpots through gap elements.

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.

Behaviors of a Very Large Floating Structure Supported With Dolphins Under Earthquake Loading

2003 ◽  
Author(s):  
Yoshiyasu Watanabe
Keyword(s):  
Elastic Plate ◽  
Time History ◽  
Type Structure ◽  
Earthquake Loading ◽  
Rigid Plate ◽  
Floating Structure ◽  
Floating Structures ◽  
Reaction Forces ◽  
Time History Response ◽  
Very Large Floating Structures

In recent years, tremendous research efforts have been directed toward developing very large floating structures (VLFSs) for the purposes of airports, terminals etc. on the sea to utilize ocean space. There is a VLFS which has a pontoon type structure supported with many dolphins and it is important to investigate sufficiently the behaviors of such VLFSs under earthquake loading, because large reaction forces will be exerted on the dolphins and fenders that connect the dolphins and the floating structure. This paper reports the results of the time history response analyses of a VLFS supported with dolphins with varying the period and velocity of the applied sinusoidal waves as an earthquake loading when gaps between fenders and dolphins are equal to zero. In the analyses, the floating structure supported with dolphins is modeled as a horizontally elastic plate and a rigid plate both supported with springs and dashpots through gap elements.

Effects of shoulder translation on lumbar moment for two dimensional modeling strategies during lifting

1998 ◽  
Vol 1 (3) ◽  
pp. 173-187
Author(s):  
Wayne J. Albert ◽  
Joan M. Stevenson ◽  
Geneviève A. Dumas ◽  
Roger W. Wheeler
Keyword(s):  
Sagittal Plane ◽  
Tracking System ◽  
Vertical Direction ◽  
Two Dimensional ◽  
Model Type ◽  
Trunk Acceleration ◽  
Analysis System ◽  
Trunk Orientation ◽  
Shoulder Position ◽  
Dynamic Link

The objectives of this study were to: 1) develop a dynamic 2D link segment model for lifting using the constraints of four sensors from an electromagnetic motion analysis system; 2) evaluate the magnitude of shoulder movement in the sagittal plane during lifting; and 3) investigate the effect of shoulder translation on trunk acceleration and lumbar moments calculated by the developed model and comparing it with two separate 2D dynamic link segment models. Six women and six men lifted loads of 2 kg, 7 kg, 12 kg and 2 kg, 12 kg, 22 kg respectively, under stoop, squat and freestyle conditions. Trunk orientation and position, as well as shoulder position were monitored during all lifts using the Polhemus FASTRAK\trdmk. Results indicated that average range of motion was 0.05 ± 0.02 m in the horizontal direction and 0.03 ± 0.02 m in the vertical direction. Shoulder position relative to T1 was located 0.07 ± 0.02 m anteriorly, and 0.02 ± 0.04 m superiorly (0.06 and 0.00 m for males and 0.08 and 0.04 m for females, respectively). To estimate the effect of shoulder motion on trunk acceleration and L5/S1 moments, three two-dimensional dynamic link segment models were developed within the constraints of the electromagnetic tracking system and compared. Trunk segment endpoints were defined as L5/S1 and either T1 or shoulder depending on model type. For trunk accelerations, average differences between models were greater than 40 deg/s² in 70.4% trunk accelerations did not translate into significantly different moment calculations between models. Average peak dynamic L5/S1 moment differences between models were smaller than 4 Nm for all lifting conditions which failed to be statistically significant (p>0.05). The model type did not have a statistically significant effect on peak L5/S1 moments. Therefore, despite important shoulder joint translations, peak L5/S1 moments were not significantly affected.

scholarly journals GLOBAL EXISTENCE RESULTS FOR THE ANISOTROPIC BOUSSINESQ SYSTEM IN DIMENSION TWO

2011 ◽  
Vol 21 (03) ◽  
pp. 421-457 ◽  
Author(s):  
RAPHAËL DANCHIN ◽  
MARIUS PAICU
Keyword(s):  
Global Existence ◽  
Turbulent Flows ◽  
Vertical Direction ◽  
Boussinesq System ◽  
Navier Stokes ◽  
Two Dimensional ◽  
Incompressible Euler Equation ◽  
Navier Stokes Equation ◽  
Transport Diffusion ◽  
Anisotropic Viscosity

Models with a vanishing anisotropic viscosity in the vertical direction are of relevance for the study of turbulent flows in geophysics. This motivates us to study the two-dimensional Boussinesq system with horizontal viscosity in only one equation. In this paper, we focus on the global existence issue for possibly large initial data. We first examine the case where the Navier–Stokes equation with no vertical viscosity is coupled with a transport equation. Second, we consider a coupling between the classical two-dimensional incompressible Euler equation and a transport–diffusion equation with diffusion in the horizontal direction only. For both systems, we construct global weak solutions à la Leray and strong unique solutions for more regular data. Our results rest on the fact that the diffusion acts perpendicularly to the buoyancy force.

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.

Launching of Ships and Floating Structures from Horizontal Berth by Tipping Table

1998 ◽  
Vol 14 (04) ◽  
pp. 265-276
Author(s):  
Ivo Senjanovic
Keyword(s):  
Structural Dynamics ◽  
Review Paper ◽  
Offshore Structures ◽  
Model Tests ◽  
Full Scale ◽  
Strength Analysis ◽  
Test Results ◽  
Floating Structures ◽  
Measurement Results

This review paper covers extensive investigations which were undertaken in order to verify the idea of launching of ships and other floating structures from a horizontal berth by a set of turning pads. This includes structural dynamics during launching, model tests and strength analysis of the structure and the launching system. The most important results, which were used for the design of the launching system, are presented. The preparation of a barge for side launching is described, and the full-scale measurement results are compared with the test results. The advantages of building ships and offshore structures on a horizontal berth are pointed out in the conclusion.

An Improved Body-Exact Method to Predict Large Amplitude Ship Roll Responses

2018 ◽  
Author(s):  
Rahul Subramanian ◽  
Naga Venkata Rakesh ◽  
Robert F. Beck
Keyword(s):  
Incident Wave ◽  
Large Amplitude ◽  
Nonlinear Models ◽  
Body Position ◽  
Computational Cost ◽  
Offshore Structures ◽  
The Body ◽  
Surface Boundary ◽  
Strip Theory ◽  
New Formulation

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.

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