Force Measurements of the Flow Around Arrays of Three and Four Columns With Different Geometry Sections, Spacing Ratios, and Incidence Angles

2019 ◽  
Vol 142 (2) ◽  
Author(s):  
Rodolfo Trentin Gonçalves ◽  
Shinichiro Hirabayashi ◽  
Guilherme Vaz ◽  
Hideyuki Suzuki
Keyword(s):  
Degrees Of Freedom ◽  
Incidence Angle ◽  
Offshore Structures ◽  
Offshore Wind ◽  
Cfd Validation ◽  
Numerical Work ◽  
Drag Forces ◽  
Floating Offshore Wind Turbines ◽  
Spacing Ratio ◽  
Lift And Drag

Abstract An experimental campaign for the flow around a stationary array of three and four columns with low aspect ratio, H/L = 1.5, piercing the water free surface, was carried out in a towing tank. These numbers of columns correspond to typical multi-column offshore systems, such as semi-submersibles (SS), tension leg platforms (TLPs), and floating offshore wind turbines (FOWTs). Three parameters were investigated: the spacing ratio between column centers (from two up to four characteristic lengths), current incidence angles, and column section geometries (circular, square, and diamond). The Reynolds number of the experiments was 100,000. Forces were measured in each column using a three degrees-of-freedom load cell, and results of lift and drag forces were presented for each column separately and the whole system. The results of mean and standard deviation of forces were assessed using a statistical uncertainty analysis procedure for finite length measurements’ signals. This methodology not only assesses the quality of the experimental data but also facilitates validation of numerical tools. The objectives of the current work were therefore manifold: to better understand the influence of the relative position, shape, and incidence angle on multi-column offshore structures; to create a reliable database for computational fluid dynamics (CFD) validation; and to prepare the path to flow-induced motions (FIMs) experimental and numerical work of free-moving multi-column offshore systems.

A Novel Concept for Floating Offshore Wind Turbines: Recent Developments in the Concept and Investigation on Fluid Interaction With the Rotating Foundation

2010 ◽  
Author(s):  
Luca Vita ◽  
Frederik Zhale ◽  
Uwe S. Paulsen ◽  
Troels F. Pedersen ◽  
Helge A. Madsen ◽  
...  
Keyword(s):  
Wind Turbines ◽  
Vertical Axis ◽  
Operating Conditions ◽  
Offshore Wind ◽  
Navier Stokes ◽  
Drag Forces ◽  
Floating Offshore Wind Turbines ◽  
Recent Developments ◽  
Lift And Drag ◽  
Novel Concept

This paper describes the recent developments regarding a new concept for deep sea offshore vertical axis wind turbines. The concept utilizes a cylindrical foundation rotating in the water. The 2D Navier-Stokes solver EllipSys2D has been used to investigate the interaction between the rotating foundation and a water flow stream passing the turbine. Lift and drag forces, and the friction moment on the rotating foundation of the turbine have been computed. The calculations are repeated for different operating conditions of the wind turbine on a range of rotational speeds. The Reynolds number, based on the diameter of the foundation, is 5×106.

scholarly journals Preliminary Results on the Dynamics of a Pile-Moored Fish Cage with Elastic Net in Currents and Waves

2020 ◽  
Vol 9 (1) ◽  
pp. 14
Author(s):  
Gianluca Zitti ◽  
Nico Novelli ◽  
Maurizio Brocchini
Keyword(s):  
Numerical Model ◽  
Laboratory Experiments ◽  
Numerical Models ◽  
Offshore Structures ◽  
Fish Farm ◽  
Maximum Displacement ◽  
Drag Forces ◽  
Real Size ◽  
Lift And Drag ◽  
Mesh Grid

Over the last decades, the aquaculture sector increased significantly and constantly, moving fish-farm plants further from the coast, and exposing them to increasingly high forces due to currents and waves. The performances of cages in currents and waves have been widely studied in literature, by means of laboratory experiments and numerical models, but virtually all the research is focused on the global performances of the system, i.e., on the maximum displacement, the volume reduction or the mooring tension. In this work we propose a numerical model, derived from the net-truss model of Kristiansen and Faltinsen (2012), to study the dynamics of fish farm cages in current and waves. In this model the net is modeled with straight trusses connecting nodes, where the mass of the net is concentrated at the nodes. The deformation of the net is evaluated solving the equation of motion of the nodes, subjected to gravity, buoyancy, lift, and drag forces. With respect to the original model, the elasticity of the net is included. In this work the real size of the net is used for the computation mesh grid, this allowing the numerical model to reproduce the exact dynamics of the cage. The numerical model is used to simulate a cage with fixed rings, based on the concept of mooring the cage to the foundation of no longer functioning offshore structures. The deformations of the system subjected to currents and waves are studied.

scholarly journals Effect of Roughness of Mussels on Cylinder Forces from a Realistic Shape Modelling

2021 ◽  
Vol 9 (6) ◽  
pp. 598
Author(s):  
Antoine Marty ◽  
Franck Schoefs ◽  
Thomas Soulard ◽  
Christian Berhault ◽  
Jean-Valery Facq ◽  
...  
Keyword(s):  
Marine Species ◽  
Offshore Structures ◽  
Offshore Wind ◽  
Mooring Lines ◽  
Shape Modelling ◽  
Offshore Wind Turbines ◽  
Specific Effects ◽  
Hydrodynamic Loading ◽  
Floating Offshore Wind Turbines ◽  
Realistic Shape

After a few weeks, underwater components of offshore structures are colonized by marine species and after few years this marine growth can be significant. It has been shown that it affects the hydrodynamic loading of cylinder components such as legs and braces for jackets, risers and mooring lines for floating units. Over a decade, the development of Floating Offshore Wind Turbines highlighted specific effects due to the smaller size of their components. The effect of the roughness of hard marine growth on cylinders with smaller diameter increased and the shape should be representative of a real pattern. This paper first describes the two realistic shapes of a mature colonization by mussels and then presents the tests of these roughnesses in a hydrodynamic tank where three conditions are analyzed: current, wave and current with wave. Results are compared to the literature with a similar roughness and other shapes. The results highlight the fact that, for these realistic roughnesses, the behavior of the rough cylinders is mainly governed by the flow and not by their motions.

Pitch and Roll Motion Control of a Floating Wind Turbine With Hybrid Actuation

2014 ◽  
Author(s):  
Kaveh Jalili ◽  
Yaoyu Li ◽  
Mario A. Rotea
Keyword(s):  
Degrees Of Freedom ◽  
Bending Moment ◽  
Offshore Wind ◽  
Load Testing ◽  
Combined System ◽  
Actuation System ◽  
Floating Offshore Wind Turbines ◽  
Standard Design ◽  
Equivalent Load ◽  
Hybrid Actuation

Platform stabilization and load reduction are of great importance for the successful development of floating offshore wind turbines. The increased degrees-of-freedom (DOF) for the relevant dynamics presents the challenge of underactuation. Recently, a tuned-mass damper (TMD) and active vane have been proposed to control the pitch and roll motions of a floating turbine platform. Simulations have indicated that TMD in the fore-aft (FA) direction cannot reduce the damage equivalent load (DEQL) for the side-to-side (SS) bending moment at the tower-base across all the loading conditions. In this study, the TMD in the FA direction is combined with an active vertical vane to reduce both the FA and SS platform motions and DEQLs. We refer to this combined system of actuation as the “hybrid actuation system”. The effectiveness of this hybrid scheme is demonstrated via simulations which are carried out in accordance with the IEC 61400-3 standard design load case 1.2–fatigue load testing.

scholarly journals An efficient frequency-domain model for quick load analysis of floating offshore wind turbines

2018 ◽  
Vol 3 (2) ◽  
pp. 693-712 ◽  
Author(s):  
Antonio Pegalajar-Jurado ◽  
Michael Borg ◽  
Henrik Bredmose
Keyword(s):  
Wind Speed ◽  
Frequency Domain ◽  
Wind Turbines ◽  
Degrees Of Freedom ◽  
Bending Moment ◽  
Domain Model ◽  
Offshore Wind ◽  
Hydrodynamic Damping ◽  
Floating Offshore Wind Turbines ◽  
Load Analysis

Abstract. A model for Quick Load Analysis of Floating wind turbines (QuLAF) is presented and validated here. The model is a linear, frequency-domain, efficient tool with four planar degrees of freedom: floater surge, heave, pitch and first tower modal deflection. The model relies on state-of-the-art tools from which hydrodynamic, aerodynamic and mooring loads are extracted and cascaded into QuLAF. Hydrodynamic and aerodynamic loads are pre-computed in WAMIT and FAST, respectively, while the mooring system is linearized around the equilibrium position for each wind speed using MoorDyn. An approximate approach to viscous hydrodynamic damping is developed, and the aerodynamic damping is extracted from decay tests specific for each degree of freedom. Without any calibration, the model predicts the motions of the system in stochastic wind and waves with good accuracy when compared to FAST. The damage-equivalent bending moment at the tower base is estimated with errors between 0.2 % and 11.3 % for all the load cases considered. The largest errors are associated with the most severe wave climates for wave-only conditions and with turbine operation around rated wind speed for combined wind and waves. The computational speed of the model is between 1300 and 2700 times faster than real time.

Influence of Wall Proximity on the Lift and Drag of a Particle in an Oscillatory Flow

2004 ◽  
Vol 127 (3) ◽  
pp. 583-594 ◽  
Author(s):  
Paul F. Fischer ◽  
Gary K. Leaf ◽  
Juan M. Restrepo
Keyword(s):  
Lift Force ◽  
Degrees Of Freedom ◽  
Oscillatory Flow ◽  
Numerical Solutions ◽  
Stokes Equations ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Drag Forces ◽  
Lift And Drag ◽  
Two Parameters

We report on the lift and drag forces on a stationary sphere subjected to a wall-bounded oscillatory flow. We show how these forces depend on two parameters, namely, the distance between the particle and the bounding wall, and on the frequency of the oscillatory flow. The forces were obtained from numerical solutions of the unsteady incompressible Navier–Stokes equations. For the range of parameters considered, a spectral analysis found that the forces depended on a small number of degrees of freedom. The drag force manifested little change in character as the parameters varied. On the other hand, the lift force varied significantly: We found that the lift force can have a positive as well as a negative time-averaged value, with an intermediate range of external forcing periods in which enhanced positive lift is possible. Furthermore, we determined that this force exhibits a viscous-dominated and a pressure-dominated range of parameters.

scholarly journals Amphibious Aircraft Developments: Computational Studies of Hydrofoil Design for Improvements in Water-Takeoffs

Aerospace ◽  
2020 ◽  
Vol 8 (1) ◽  
pp. 10
Author(s):  
Arjit Seth ◽  
Rhea P. Liem
Keyword(s):  
Incidence Angle ◽  
Design Procedure ◽  
Computational Design ◽  
General Aviation ◽  
Dynamics Simulation ◽  
Design Framework ◽  
Drag Forces ◽  
Lift And Drag ◽  
Aircraft Conceptual Design

Amphibious aircraft designers face challenges to improve takeoffs and landings on both water and land, with water-takeoffs being relatively more complex for analyses. Reducing the water-takeoff distance via the use of hydrofoils was a subject of interest in the 1970s, but the computational power to assess their designs was limited. A preliminary computational design framework is developed to assess the performance and effectiveness of hydrofoils for amphibious aircraft applications, focusing on the water-takeoff performance. The design framework includes configuration selections and sizing methods for hydrofoils to fit within constraints from a flying-boat amphibious aircraft conceptual design for general aviation. The position, span, and incidence angle of the hydrofoil are optimized for minimum water-takeoff distance with consideration for the longitudinal stability of the aircraft. The analyses and optimizations are performed using water-takeoff simulations, which incorporate lift and drag forces with cavitation effects on the hydrofoil. Surrogate models are derived based on 2D computational fluid dynamics simulation results to approximate the force coefficients within the design space. The design procedure is evaluated in a case study involving a 10-seater amphibious aircraft, with results indicating that the addition of the hydrofoil achieves the purpose of reducing water-takeoff distance by reducing the hull resistance.

scholarly journals Study of motion of spar-type floating wind turbines in waves with effect of gyro moment at inclination

2012 ◽  
Vol 9 (1) ◽  
pp. 67-79 ◽  
Author(s):  
N. Mostafa ◽  
M. Murai ◽  
R. Nishimura ◽  
O. Fujita ◽  
Y. Nihei
Keyword(s):  
Wind Turbines ◽  
Offshore Structures ◽  
Moment Of Inertia ◽  
Offshore Wind ◽  
Irregular Waves ◽  
Scale Model ◽  
Water Tank ◽  
Offshore Wind Turbines ◽  
Floating Offshore Wind Turbines ◽  
Marine Engineering

Recently, a number of research groups have paid much attention to the study of Floating Offshore Wind Turbines (FOWTs). Similar to other offshore structures, the FOWTs are subjected to irregular waves and wind loads which cause a dynamic response in the structures. Under marine environmental conditions, they face many forces which prevent them from floating in the upright condition; they incline as a result of the winds, strong currents, typhoons, cyclones, storms etc. The motion of the FOWT might be changed by a change in gyroscopic effect which depends on the angular velocity and moment of inertia of the blade. Therefore, to investigate the effect of the gyro moment on the motion of the FOWT, two types of experiment were carried out in a water tank using a 1/360 scale model of a prototype FOWT. Firstly, the interaction between the rotary motion of the wind turbine blade and the dynamic motion of the SPAR-type FOWT was studied at small angles of inclination in regular waves. Secondly, the interaction between the change of rotational speed as well as moment of inertia of the blade and the motion of the FOWT was studied. In this paper, numerical calculations have been carried out using potential theory based on the 3D panel method. Finally, the experimental results are compared with the results of numerical simulation and findings are discussed. DOI: http://dx.doi.org/10.3329/jname.v9i1.10732 Journal of Naval Architecture and Marine Engineering 9(2012) 67-79

scholarly journals An efficient frequency-domain model for quick load analysis of floating offshore wind turbines

2018 ◽  
Author(s):  
Antonio Pegalajar-Jurado ◽  
Michael Borg ◽  
Henrik Bredmose
Keyword(s):  
Wind Speed ◽  
Frequency Domain ◽  
Wind Turbines ◽  
Degrees Of Freedom ◽  
Bending Moment ◽  
Domain Model ◽  
Offshore Wind ◽  
Hydrodynamic Damping ◽  
Floating Offshore Wind Turbines ◽  
Load Analysis

Abstract. A model for Quick Load Analysis of Floating wind turbines, QuLAF, is presented and validated here. The model is a linear, frequency-domain, efficient tool with four planar degrees of freedom: platform surge, heave, pitch and tower modal deflection. The model relies on state-of-the-art tools from which hydrodynamic, aerodynamic and mooring loads are extracted and cascaded into QuLAF. Hydrodynamic and aerodynamic loads are precomputed in WAMIT and FAST respectively, while the mooring system is linearized around the equilibrium position for each wind speed using MoorDyn. An approximate approach to viscous hydrodynamic damping is developed, and the aerodynamic damping is extracted from decay tests specific for each degree of freedom. Without any calibration, the model predicts the motions of the system in stochastic wind and waves with good accuracy when compared to FAST. The damage-equivalent bending moment at the tower bottom is estimated with errors between 0.2 % and 11.3 % for all the load cases considered. The largest errors are associated with the most severe wave climates for wave-only conditions and with turbine operation around rated wind speed for combined wind and waves. The computational speed of the model is between 1300 and 2700 times faster than real-time.

Experimental Flow-Induced Motions of a FOWT Semi-Submersible Type (OC4 Phase II Floater)

2020 ◽  
Vol 143 (1) ◽  
Author(s):  
Rodolfo T. Gonçalves ◽  
Maria E. F. Chame ◽  
Leandro S. P. Silva ◽  
Arjen Koop ◽  
Shinichiro Hirabayashi ◽  
...  
Keyword(s):  
Phase Ii ◽  
Offshore Structures ◽  
Offshore Wind ◽  
Offshore Wind Turbines ◽  
Circular Column ◽  
Deep Waters ◽  
Floating Offshore Wind Turbines ◽  
Floating System ◽  
Cable Systems ◽  
Column Design

Abstract Flow-induced motions (FIM) are an issue for floating offshore structures, such as multi-column platforms, as the phenomenon can decrease the fatigue life of the mooring, riser, and cable systems. The new concept of floating offshore wind turbines (FOWT) have a multi-column design that may be subjected to FIM. In the past, FIM was studied mainly for Oil & Gas platforms installed in deep waters. However, the FIM phenomenon of FOWT has been insufficiently explored. To rectify this, model tests were performed for the semisubmersible (SS) floating system design developed for the DeepCwind project (Offshore Code Comparison Collaboration Continuation (OC4) phase II). This paper will investigate the presence of FIM and show its importance in the design process of FOWT. Three different incidence angles of the current were tested, namely, 0, 90, and 180 deg. For each heading, 30 reduced velocities were tested, across the range 8000 < Re < 70,000. The results showed amplitudes in the transverse direction of around 70% of the diameter of the platform column, which is similar to those observed for deep-draft (DD) SS with circular columns. Note that these amplitude values are larger for a floater with a circular column, than for a platform with square columns. The results showed that as FIM occurred for this specific FOWT SS, its effect has to be considered in the mooring system and electric cable design.

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