Hydrodynamic Characteristics of Floating Pipes in Random Waves

2013 ◽  
Author(s):  
Tiaojian Xu ◽  
Guohai Dong ◽  
Yunpeng Zhao ◽  
Xiaozhou Ma ◽  
Yuxiang Ma
Keyword(s):  
Rayleigh Distribution ◽  
Hydrodynamic Performance ◽  
Experimental Program ◽  
Hydrodynamic Characteristics ◽  
Random Waves ◽  
Mooring Lines ◽  
Pipe Model ◽  
Motion Responses ◽  
Analysis Of Results ◽  
Set Up

The hydrodynamic performance characteristics of a round floating pipe model moored to the flume floor with pre-tensioned moorings has been investigated in random waves through an experimental program. The details of the models, set-up, experimental procedure and analysis of results are presented and discussed. The drag coefficient of floating pipes in random waves are analyzed. The motion responses, as well as the variations in the forces on the seaside mooring lines, are presented. In addition, statistical analysis has been carried out to prove that the heave and surge motions, as well as the peak mooring forces, follow the Rayleigh distribution.

Hydrodynamic characteristics of moored floating pipe breakwaters in random waves

2003 ◽  
Vol 217 (2) ◽  
pp. 95-110 ◽  
Author(s):  
V Sundar ◽  
R Sundaravadivelu ◽  
S Purushotham
Keyword(s):  
Hydrodynamic Performance ◽  
Hydrodynamic Characteristics ◽  
Random Waves ◽  
Mooring Lines ◽  
Reflection And Transmission ◽  
Transmission Coefficients ◽  
Motion Responses ◽  
Analysis Of Results ◽  
Mooring Forces ◽  
Set Up

The hydrodynamic performance characteristics of a floating pipe breakwater (FPBW) model (row of pipes separated by a distance equivalent to the pipe diameter) moored to the flume floor with slack moorings has been investigated in random waves through an experimental programme. The tests have been conducted on three models each with pipes of different diameter. The average reflection and transmission coefficients are evaluated from measurements and reported as a function of relative breakwater width. The motion responses, as well as the variations in the forces on the seaside and lee side mooring lines, are also presented. In addition, statistical analysis has been carried out to prove that the heave and surge motions, as well as the peak mooring forces, follow the Raleigh distribution. The details of the models, set-up, experimental procedure and analysis of results are presented and discussed.

Numerical and Experimental Investigation on Hydrodynamic Characteristics of FLNG With an Account of the Inner-Tank Sloshing

2011 ◽  
Author(s):  
Wenhua Zhao ◽  
Jianmin Yang ◽  
Zhiqiang Hu ◽  
Tao Peng
Keyword(s):  
Numerical Simulations ◽  
Model Tests ◽  
Hydrodynamic Performance ◽  
Hydrodynamic Characteristics ◽  
Fast Fourier Transformation ◽  
Motion Responses ◽  
Comparison Results ◽  
New Type ◽  
Lng Liquefaction ◽  
Tank Sloshing

FLNG is a new type of floating LNG platform which is ship-shaped FPSO hull equipped with LNG storage tanks and liquefaction plants and has been developed as an alternative to long pipelines to LNG liquefaction plant on land for stranded offshore fields. Different to the conventional FPSO, the hydrodynamic performance of the being-proposed FLNG can be significantly affected by the inner-tank liquid sloshing, due to the fact that LNG performs better liquidity than crude oil. In order to investigate the hydrodynamic characteristics of FLNG with large hull and high center of gravity, a series of numerical simulations on an FLNG designed by CNOOC and MARIC were conducted with the help of the well-known code WADAM. In addition, corresponding model tests on the same vessel with solid ballast were completed, serving as a verification of the numerical simulations. In order to inspect the sloshing effects of inner tanks on the global motion responses of the FLNG vessel, model tests with liquid ballast were also conducted. Comparisons were made between numerical and experimental results with methods of Fast Fourier Transformation technology and spectral analysis. The numerical simulation results were in good accordance with those of the model tests, which proves the feasibility of the numerical simulations. Furthermore, the effects of the inner tank sloshing on the FLNG hydrodynamic characteristics were summed up. Conclusions obtained from the comparison results would be of significant importance for the design of the FLNG system.

Hydrodynamic characteristics of a submerged trapezoidal artificial reef unit

2019 ◽  
Vol 233 (4) ◽  
pp. 1226-1239
Author(s):  
Lokesha ◽  
SA Sannasiraj ◽  
Vallam Sundar
Keyword(s):  
Artificial Reef ◽  
Hydrodynamic Performance ◽  
Artificial Reefs ◽  
Hydrodynamic Characteristics ◽  
Leeward Side ◽  
Random Waves ◽  
Relative Water ◽  
Marine Flora ◽  
Water Depths ◽  
Crest Height

Submerged structures serve as wave attenuators and are widely adopted for protecting the coast against erosion or to reduce forces on structures situated on its leeward side. Conventional submerged breakwaters are composed of rubble stones, and the sources for quarrying such stones have depleted drastically over a period of time. The artificial reefs are a replacement for submerged breakwaters formed by natural rocks due to its minimum impact on the marine environment, flexibility in molding to any desired shape and size. It is also believed to serve as a habitable environment to marine flora and fauna. In this study, a comprehensive experimental investigation is carried out in order to examine the effect of perforations on a submerged artificial reef exposed to regular and random waves. The tests with models of crest width ( B) of 0.2 m and crest height ( h) of 0.4 m are conducted for three different degrees of submergence ( d/ h) of 1.5, 1.38 and 1.25 in three different water depths, d. The article emphasizes the influence of relative water depth, relative crest width and the nature of the surface of the structure (impermeable or permeable) on its hydrodynamic performance characteristics.

Hydrodynamic characteristics of vertical and quadrant face pile supported breakwater under oblique waves

2021 ◽  
pp. 147509022110313
Author(s):  
T J Jemi Jeya ◽  
V Sriram ◽  
V Sundar
Keyword(s):  
Experimental Study ◽  
Hydrodynamic Performance ◽  
Hydrodynamic Characteristics ◽  
Scattering Parameter ◽  
Oblique Waves ◽  
Test Conditions ◽  
Relative Water ◽  
Identical Test ◽  
Run Up ◽  
Water Depths

This paper presents the results from a comprehensive experimental study on the Quadrant Face Pile Supported Breakwater (QPSB) in two different water depths exposed to three different oblique wave attacks. The results are compared with that for a Vertical face Pile Supported Breakwater (VPSB) for identical test conditions. The paper compares the reflection coefficient, transmission coefficient, energy loss coefficient, non-dimensional pressure, and non-dimensional run-up as a function of the relative water depth and scattering parameter. The results obtained for QPSB are validated with existing results. The salient observations show that QPSB experiences better hydrodynamic performance characteristics than the VPSB under oblique waves.

Coupled Dynamic Analysis for Multi-Unit Floating Offshore Wind Turbine in Maximum Operational and Survival Conditions

2015 ◽  
Author(s):  
H. K. Jang ◽  
H. C. Kim ◽  
M. H. Kim ◽  
K. H. Kim
Keyword(s):  
Wind Turbine ◽  
Wind Turbines ◽  
Time Domain ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Random Waves ◽  
Mooring Lines ◽  
Floating Offshore Wind Turbine ◽  
Coupled Dynamic Analysis ◽  
Floating Offshore Wind Turbines

Numerical tools for a single floating offshore wind turbine (FOWT) have been developed by a number of researchers, while the investigation of multi-unit floating offshore wind turbines (MUFOWT) has rarely been performed. Recently, a numerical simulator was developed by TAMU to analyze the coupled dynamics of MUFOWT including multi-rotor-floater-mooring coupled effects. In the present study, the behavior of MUFOWT in time domain is described through the comparison of two load cases in maximum operational and survival conditions. A semi-submersible floater with four 2MW wind turbines, moored by eight mooring lines is selected as an example. The combination of irregular random waves, steady currents and dynamic turbulent winds are applied as environmental loads. As a result, the global motion and kinetic responses of the system are assessed in time domain. Kane’s dynamic theory is employed to formulate the global coupled dynamic equation of the whole system. The coupling terms are carefully considered to address the interactions among multiple turbines. This newly developed tool will be helpful in the future to evaluate the performance of MUFOWT under diverse environmental scenarios. In the present study, the aerodynamic interactions among multiple turbines including wake/array effect are not considered due to the complexity and uncertainty.

On the Model Scaling of Polyester Mooring Lines for Offshore Applications

2002 ◽  
Author(s):  
Antonio Carlos Fernandes ◽  
Ronaldo Rosa Rossi
Keyword(s):  
Steel Wire ◽  
Random Excitation ◽  
Model Tests ◽  
Early Model ◽  
Random Waves ◽  
Mooring Lines ◽  
New Approach ◽  
Linear Behavior ◽  
Non Linear ◽  
Similarity Laws

With the introduction of the polyester ropes as mooring lines of large systems such as semi-submersibles, the need to simulate these lines in model tests became a necessity. Although the non-linear behavior is clear, depending on the type of cycling, the polyester rope responds in ways that may be considered linear as a steel wire rope. Because of that, the early model tests have been performed using a linear restoring capability, with different restoring coefficients. The use of equivalent springs seemed the proper way. However, with the help of fundamental investigation on the similarity laws, the present work shows that the use of very thin polyester lines in model scaling is feasible and will indeed allow a closer physical representation. By avoid using springs, but using the same material as in full scale, the same non-linear behavior is present during the tests and even the response to random excitation due to random waves is better represented. The paper closely describes the application of these ideas in a model test of a FPSO (Floating Production Storage and Offloading) comparing both the linear springs and new approach with the model scale equivalent polyester line.

Experimental Study on the Influence of Hull Spacing on Hard-Chine Catamaran Motions

2001 ◽  
Vol 45 (03) ◽  
pp. 216-227
Author(s):  
R. Centeno ◽  
K. S. Varyani ◽  
C. Guedes Soares
Keyword(s):  
Experimental Study ◽  
Cross Flow ◽  
Experimental Program ◽  
Two Dimensional ◽  
Regular Waves ◽  
Viscous Forces ◽  
Motion Responses ◽  
Resonance Frequencies ◽  
Flow Drag ◽  
Wave Induced

An experimental program was performed with hard-chine catamaran models in regular waves. The distance between the demi-hulls of the models was changed to assess its effects on the wave-induced motions. The results allowed the study of some aspects related to catamaran motions, like the interference between the hulls and resonance frequencies. The experimental results are compared with calculations performed with a recently developed code based on a two-dimensional potential flow theory in which viscous forces are included through a cross-flow drag approach. The effect of the hull distance in the heave and pitch motion responses and the importance of the viscous forces in such hull configurations are shown.

Optimization of the Dynamic Response of Semi-Submersibles: Influence of the Mooring System

2019 ◽  
Author(s):  
Shengtao Zhou ◽  
Frank Lemmer ◽  
Wei Yu ◽  
Po Wen Cheng ◽  
Chao Li ◽  
...  
Keyword(s):  
Life Cycle Cost ◽  
Design Space ◽  
Optimization Techniques ◽  
Optimization Process ◽  
Manufacturing Cost ◽  
Mooring System ◽  
Mooring Lines ◽  
Nsga Ii ◽  
Simulation Code ◽  
Set Up

Abstract The design and manufacturing cost of substructures is a major component of the total expenditure for a floating wind project. Applying optimization techniques to hull shape designs has become an effective way to reduce the life-cycle cost of a floating wind system. The mooring system is regarded as the component with the highest risk, mainly due to the poor accessibility. This paper extends the previous work by investigating the influences of the mooring design on the optimization process of a semisubmersible substructure. Two optimization loops are set up. In the first loop, only the main dimensions of a semi-submersible platform are parameterized without considering mooring lines (keep a constant mooring design). Nevertheless, the second loop introduces additional variables of the mooring lines. The objective is to minimize the tower-top displacement, fairlead fatigue damage, which are calculated by the in-house nonlinear dynamic simulation code SLOW, and the manufacturing cost of platform and mooring lines. The multi-objective optimization algorithm NSGA-II is employed to search for the optimal designs within the defined design space. The design space and the Pareto fronts are compared between the two optimizations. It is found that, although the mooring design does not have a significant impact on the platform design space, one obtains a different optimal set (Pareto front) if the mooring design and mooring loads are introduced into the platform optimization process. The results of this study are expected to give a better understanding in the relationship between platform and mooring design and serve as a basis for the optimization process of semi-submersible floating wind turbines.

Effects of Variations on the Experimental Set-Up on the Motion Response of a Floating Wind Semisubmersible (OC4 Type)

2019 ◽  
Author(s):  
Sebastien Gueydon
Keyword(s):  
Low Frequency ◽  
Test Results ◽  
Complex Behaviour ◽  
Code Comparison ◽  
Motion Responses ◽  
Wave Basin ◽  
Complex Test ◽  
Inertia Properties ◽  
Set Up ◽  
Work Done

Abstract With their light weights, small components like braces and heave plates and steady trim angle caused by the wind loads acting on the rotor, semisubmersible foundations used as support platform for wind turbines exhibit a complex behaviour where viscous loading play an important role. The work done by the Offshore Code Comparison Collaboration Continued with Correlation (OC5) project has shown that standard engineering tools were not always able to predict accurately the motions of the DeepCwind semisubmersible that were measured in a basin. The correct amplitude of the motions at the natural periods of this system appeared to be difficult to obtain with simulations (especially the low frequency surge, and the pitch resonant motion). In view of the complexity of the system, it was not possible to clearly identify the causes of the differences between the simulations and the model-test results. A follow-on validation campaign was therefore performed at the Maritime Research Institute Netherlands (MARIN) under the MARINET2 project with the same floating substructure, with a focus on better understanding the hydrodynamic loads and reducing uncertainty in the tests by minimizing the system complexity. The wind turbine was replaced by a stiff tower with resembling inertia properties. The mooring system was simplified by using taut-spring lines with equivalent linear stiffness in surge. This paper reviews the new tests done with the simplified set-up and examines the differences with previous tests done with more complex test set-ups. The main motivation of this work is to study how variations of an experimental set-up can affect the outcome of tests in a wave basin. To start with, the main parameters of the systems (inertia, hydrostatics, and mooring stiffness) for all set-ups are characterized to check how similar they are. Then the level of damping in all systems is compared. Finally, the paper looks at how well the motion responses of this semisubmersible in waves correlate between all these campaigns.

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