Hydrodynamic forces in marine-fouled floating aquaculture cages: Physical modelling under irregular waves

2021 ◽  
Vol 105 ◽  
pp. 103331
Author(s):  
F. Nobakht-Kolur ◽  
M. Zeinoddini ◽  
A. Ghalebi
Keyword(s):  
Physical Modelling ◽  
Hydrodynamic Forces ◽  
Irregular Waves

Hybrid Scaled Testing of a 5MW Floating Wind Turbine Using the SiL Method Compared With Numerical Models

2018 ◽  
Author(s):  
Felipe Vittori ◽  
Faisal Bouchotrouch ◽  
Frank Lemmer ◽  
José Azcona
Keyword(s):  
Wind Turbine ◽  
Numerical Models ◽  
Hydrodynamic Forces ◽  
Irregular Waves ◽  
Mooring Line ◽  
Global Dynamics ◽  
Aerodynamic Forces ◽  
Wave Tank ◽  
Aerodynamic Damping ◽  
Floating Wind Turbine

The design of floating wind turbines requires both, simulation tools and scaled testing methods, accurately integrating the different phenomena involved in the system dynamics, such as the aerodynamic and hydrodynamic forces, the mooring lines dynamics and the control strategies. In particular, one of the technical challenges when testing a scaled floating wind turbine in a wave tank is the proper integration of the rotor aerodynamic thrust. The scaling of the model based on the Froude number produces equivalent hydrodynamic forces, but out of scale aerodynamic forces at the rotor, because the Reynolds number, that governs the aerodynamic forces, is not kept constant. Several approaches have been taken to solve this conflict, like using a tuned drag disk or redesigning the scaled rotor to provide the correct scaled thrust at low Reynolds numbers. This work proposes a hybrid method for the integration of the aerodynamic thrust during the scaled tests. The work also explores the agreement between the experimental measurements and the simulation results through the calibration and improvement of the numerical models. CENER has developed a hybrid testing method that replaces the rotor by a ducted fan at the model tower top. The fan can introduce a variable force which represents the total wind thrust by the rotor. This load is obtained from an aerodynamic simulation that is performed in synchrony with the test and it is fed in real time with the displacements of the platform provided by the acquisition system. Thus, the simulation considers the displacements of the turbine within the wind field and the relative wind speed on the rotor, including the effect of the aerodynamic damping on the tests. The method has been called “Software-in-the-Loop” (SiL). The method has been applied on a test campaign at the Ecole Centrale de Nantes wave tank of the OC4 semisubmersible 5MW wind turbine, with a scale factor of 1/45. The experimental results have been compared with equivalent numerical simulations of the floating wind turbine using the integrated code FAST. Simple cases as only steady wind and free decays with constant wind showed a good agreement with computations, demonstrating that the SiL method is able to successfully introduce the rotor scaled thrust and the effect of the aerodynamic damping on the global dynamics. Cases with turbulent wind and irregular waves showed better agreement with the simulations when mooring line dynamics and second order effects were included in the numerical models.

Yaw Drift Moment of a Floating Structure in Waves

2005 ◽  
Author(s):  
Dimitris Spanos ◽  
Apostolos Papanikolaou
Keyword(s):  
Hydrodynamic Forces ◽  
Computational Method ◽  
Irregular Waves ◽  
Linear Potential ◽  
Floating Bodies ◽  
Floating Structure ◽  
Natural Wave ◽  
Positioning Systems ◽  
Floating Structures ◽  
Wave Induced

The wave induced yaw drift moment on floating structures is of particular interest when the lateral yaw motion of the structure should be controlled by moorings and/or active dynamic positioning systems. In the present paper, the estimation of the yaw drift moment in the modeled natural wave environment is conducted by application of a nonlinear time domain numerical method accounting for the motion of arbitrarily shaped floating bodies in waves. The computational method is based on linear potential theory and includes the non-linear hydrostatic terms in an exact way, whereas the higher-order wave-induced effects are partly approximated. Despite the approximate modeling of the second order hydrodynamic forces, the method proved to satisfactorily approach the dominant part of the exerted hydrodynamic forces enabling the calculation of drift forces and of other drift effects in irregular waves. Hence, the subject yaw drift moment in the modeled natural wave environment is derived, resulting to a basic reference for the design of similar type floating structures.

Computation of Slowly Varying Second-Order Hydrodynamic Forces on Floating Structures in Irregular Waves

1989 ◽  
Vol 111 (3) ◽  
pp. 223-232 ◽  
Author(s):  
T. Matsui
Keyword(s):  
Velocity Potential ◽  
Near Field ◽  
Fluid Pressure ◽  
Hydrodynamic Forces ◽  
Second Order ◽  
Irregular Waves ◽  
Floating Structures ◽  
Slow Drift ◽  
Submerged Body ◽  
Element Technique

An exact second-order formulation is presented for computing the slowly varying second-order hydrodynamic forces on floating structures in irregular waves. The near-field approach based on direct integration of the fluid pressure on the submerged body surface is employed in conjunction with numerical first-order solutions by means of the hybrid finite element technique. Green’s second identity is exploited to evaluate the second-order forces due to the second-order velocity potential. Numerical results are presented for the slow drift excitation forces on an articulated column and a semi-submersible platform. It is shown that the contribution from the second-order velocity potential is more significant to the roll moment than to the sway and heave forces on the semi-submersible.

Physical Modelling of Motions and Forces on a Moored Ship at the Leixões Port

2019 ◽  
Vol 396 ◽  
pp. 60-69
Author(s):  
João Alfredo Santos ◽  
Liliana V. Pinheiro ◽  
Hossam S. Abdelwahab ◽  
Conceição Juana E.M. Fortes ◽  
Francisco G.L. Pedro ◽  
...  
Keyword(s):  
Physical Modelling ◽  
Irregular Waves ◽  
Scale Model ◽  
Wave Direction ◽  
Mooring Lines ◽  
Detailed Model ◽  
Significant Wave ◽  
Measurement Analysis ◽  
Wave Heights ◽  
Spring System

This paper describes the physical model, experimental setup and tests performed at the Portuguese Civil Engineering Laboratory (LNEC), to study the motions and forces of a moored ship at the Leixões port, for different sea states in irregular waves. The tests were carried out at one of the wave tanks of LNEC, where the Leixões port layout was implemented at scale 1:80 with the detailed model similar to the prototype bathymetry and surrounding structures. The moored ship is a 3.43 m long scale model of the well-known “Esso Osaka” tanker and is moored to the pier A of the oil terminal at 0.135 m draft. Several types of measurements were recorded in this study. The free-surface elevation and wave direction were measured with a set of resistive wave gauges. The wave velocities at the entrance of the harbour were measured with an acoustic Doppler velocimeter. Motions of the moored ship were measured with the OptiTrackTM motion capture system whereas forces on fenders and mooring lines were measured with load cells attached to a complex spring system developed at LNEC. Several tests were carried out for a number of incident sea states characterized by a JONSWAP spectrum, with different significant wave heights and peak periods. The measurement, analysis and results obtained for the incident wave conditions characterized by a significant wave height of 6 m and a peak wave period of 14 s are presented and discussed in this paper.

scholarly journals PERFORMANCE ANALYSIS OF COMPOSITE SEMICIRCULAR BREAKWATERS OF DIFFERENT CONFIGURATIONS AND POROSITIES

2012 ◽  
Vol 1 (33) ◽  
pp. 38 ◽  
Author(s):  
Hee Min Teh ◽  
Vengatesan Venugopal ◽  
Tom Bruce
Keyword(s):  
Free Surface ◽  
Energy Dissipation ◽  
Performance Analysis ◽  
Physical Modelling ◽  
High Energy ◽  
Immersion Depth ◽  
Irregular Waves ◽  
Hydrodynamic Characteristics ◽  
Semicircular Breakwater ◽  
High Energy Dissipation

The perforated free surface semicircular breakwater developed by Teh et al. (2010) was experimentally proven to be an effective anti-reflection structure with high energy dissipation ability. However, the performance characteristics of the breakwater deteriorated with a decrease in the immersion depth and an increase in wavelength. To enhance the performance of the breakwater with limited immersion depth, wave screens of different configurations and porosities were introduced below the free surface semicircular caisson. The hydrodynamic characteristics of these composite breakwaters were investigated in irregular waves using physical modelling. Comparisons of the experimental results showed that the semicircular caisson with a double screen of 25% porosity was a better breakwater configuration compared to that with a single screen. The extension of wave screen was also found to be particularly helpful in attenuating longer waves.

Hydrodynamic Forces on Pipelines: Model Tests

1992 ◽  
Vol 114 (4) ◽  
pp. 231-241 ◽  
Author(s):  
M. B. Bryndum ◽  
V. Jacobsen ◽  
D. T. Tsahalis
Keyword(s):  
Cross Flow ◽  
Hydrodynamic Forces ◽  
Irregular Waves ◽  
Regular Waves ◽  
Force Coefficients ◽  
Steady Current ◽  
Sea Bottom ◽  
Least Squares Fit ◽  
Wide Range ◽  
Flow Directions

An extensive model test program on the hydrodynamic forces on a submarine pipeline resting on the sea bottom and exposed to steady current, regular waves, combined steady current and regular waves, irregular waves, and combined steady current and irregular waves has been performed. The hydrodynamic forces in both the in-line and the cross-flow directions have been analyzed using three different methods, i.e., least-squares-fit analysis based on Morison-type equations, Fourier analysis, and maximum force analysis. The force coefficients associated with each method have been determined for a wide range of environmental conditions. The results of the tests are presented in terms of the calculated force coefficients and their dependence on various nondimensional parameters is discussed. Furthermore, comparisons with other test data are presented.

scholarly journals Physical modelling in biomechanics

2003 ◽  
Vol 358 (1437) ◽  
pp. 1589-1596 ◽  
Author(s):  
M. A. R. Koehl
Keyword(s):  
Mathematical Models ◽  
Parameter Space ◽  
Physical Modelling ◽  
Hydrodynamic Forces ◽  
Physical Models ◽  
Comparative Approach ◽  
Physical Measurements ◽  
Performance Consequences ◽  
Living Organisms ◽  
Sessile Organisms

Physical models, like mathematical models, are useful tools in biomechanical research. Physical models enable investigators to explore parameter space in a way that is not possible using a comparative approach with living organisms: parameters can be varied one at a time to measure the performance consequences of each, while values and combinations not found in nature can be tested. Experiments using physical models in the laboratory or field can circumvent problems posed by uncooperative or endangered organisms. Physical models also permit some aspects of the biomechanical performance of extinct organisms to be measured. Use of properly scaled physical models allows detailed physical measurements to be made for organisms that are too small or fast to be easily studied directly. The process of physical modelling and the advantages and limitations of this approach are illustrated using examples from our research on hydrodynamic forces on sessile organisms, mechanics of hydraulic skeletons, food capture by zooplankton and odour interception by olfactory antennules.

scholarly journals Numerical analysis of varies geometries on dynamic analysis on the gravity platform

2019 ◽  
Vol 7 (2) ◽  
Author(s):  
Tina Rezaei ◽  
Atefeh Mosahebi Mohammadi ◽  
Elham Mina ◽  
Mohammad Reza Kavianpour
Keyword(s):  
Analytical Methods ◽  
Soil Mechanics ◽  
Wave Length ◽  
Hydrodynamic Forces ◽  
Irregular Waves ◽  
Sea Bed ◽  
Rocking Motion ◽  
Effective Depth ◽  
Gravity Platform ◽  
The Impact

On Gravity platform Dynamic Response is a support structure held in place by gravity. Given that the gravity platforms are supportedby the sea bed but not attached to the ground, the motion of them is known as a rocking fluctuation. During the fluctuations, theplatform maybe overturned if the angle is large. In this study, using Ansys Aqwa hydrodynamic software and analytical methods withregard to the performance, the dynamic interaction of platform’s geometry on hydrodynamic forces have been simulated. Theobjective of this study was to analyze the hydrodynamic parameters of the sea and rocking fluctuations of gravity platforms under theimpact of regular wave’s moment considering the soil mechanics and hydrodynamic features of the structure. In order to achievethe objective the hydrodynamic forces using numerical simulations and analytical methods for one column and three hollow columnsplatforms were analyzed. Finally, responses of the platform to irregular waves were studied using numerical simulation. The resultsshowed that with the increasing of the depth, the impact of wave’s force and moment on the base of platform are reduced throughexponential relationship. The reductions are due to the effective depth that is equal to half the wave length. The results suggestthat the response of the rocking motion of gravity platform shows significant changes in relation to height and wavelength. Based onthe curves fitted to the data of the fluctuation angle, sustainability of the platform in the rocking motion can be thoroughly andcompletely investigated.

Bulk drag coefficient of a subaquatic vegetation subjected to irregular waves: Influence of Reynolds and Keulegan-Carpenter numbers

2020 ◽  
pp. 34-42
Author(s):  
Thibault Chastel ◽  
Kevin Botten ◽  
Nathalie Durand ◽  
Nicole Goutal
Keyword(s):  
Drag Coefficient ◽  
Wave Height ◽  
Wave Attenuation ◽  
Empirical Relationship ◽  
Breaking Waves ◽  
Irregular Waves ◽  
Geometrical Parameters ◽  
Flume Experiments ◽  
Seagrass Meadows ◽  
Artificial Vegetation

Seagrass meadows are essential for protection of coastal erosion by damping wave and stabilizing the seabed. Seagrass are considered as a source of water resistance which modifies strongly the wave dynamics. As a part of EDF R & D seagrass restoration project in the Berre lagoon, we quantify the wave attenuation due to artificial vegetation distributed in a flume. Experiments have been conducted at Saint-Venant Hydraulics Laboratory wave flume (Chatou, France). We measure the wave damping with 13 resistive waves gauges along a distance L = 22.5 m for the “low” density and L = 12.15 m for the “high” density of vegetation mimics. A JONSWAP spectrum is used for the generation of irregular waves with significant wave height Hs ranging from 0.10 to 0.23 m and peak period Tp ranging from 1 to 3 s. Artificial vegetation is a model of Posidonia oceanica seagrass species represented by slightly flexible polypropylene shoots with 8 artificial leaves of 0.28 and 0.16 m height. Different hydrodynamics conditions (Hs, Tp, water depth hw) and geometrical parameters (submergence ratio α, shoot density N) have been tested to see their influence on wave attenuation. For a high submergence ratio (typically 0.7), the wave attenuation can reach 67% of the incident wave height whereas for a low submergence ratio (< 0.2) the wave attenuation is negligible. From each experiment, a bulk drag coefficient has been extracted following the energy dissipation model for irregular non-breaking waves developed by Mendez and Losada (2004). This model, based on the assumption that the energy loss over the species meadow is essentially due to the drag force, takes into account both wave and vegetation parameter. Finally, we found an empirical relationship for Cd depending on 2 dimensionless parameters: the Reynolds and Keulegan-Carpenter numbers. These relationships are compared with other similar studies.

Investigations on Orbital Velocities and Pressures in Irregular Waves

1982 ◽  
Author(s):  
K. -F. Daemrick ◽  
W. -D. Eggert ◽  
H. Cordes
Keyword(s):  
Irregular Waves
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