Study on Influence of Vortex Induced Loads on the Motion of Spar-Type Wind Turbine Based on Aero-Hydro-Vortex-Mooring Coupled Model

2017 ◽  
Author(s):  
Yougang Tang ◽  
Yan Li ◽  
Liqin Liu ◽  
Weichen Jin ◽  
Xiaoqi Qu
Keyword(s):  
Coupled Model ◽  
Numerical Code ◽  
Wave Loads ◽  
Frequency Wave ◽  
Nonlinear Motion ◽  
Restoring Forces ◽  
Mooring Forces ◽  
Vortex Shedding Frequency ◽  
Set Up ◽  
Heave Motion

The coupled nonlinear motion and the influence of vortex induced loads on the motion of Spar type FOWT is studied based on the aero-hydro-vortex-mooring coupled model. The first order and second order difference-frequency wave loads are calculated based on 3D potential theory; the aerodynamic loads on the rotor are calculated based on blade element momentum theory; the vortex induced loads are simulated with CFD approach; the mooring forces are solved by the catenary theory and the nonlinearity of restoring forces are also considered. The nonlinear coupled model is set up and a numerical code is developed for solving the motion of OC3-Hywind Spar-type FOWT in time domain. The responses of FOWT are calculated under different load cases. It is shown that the amplitudes of sway and roll are excited by vortex excited force, and the roll amplitudes can reach to pitch value order in some circumstances. Due to the coupling effects, the heave motion is also influenced by vortex-induced forces. When vortex-shedding frequency is close to roll natural frequency, not only the roll but also the motions in other DOFs are increased and the super-harmonic resonance response occurs in heave motion.

The Effect of Wave Directionality on Low Frequency Motions and Mooring Forces

2009 ◽  
Author(s):  
Olaf J. Waals
Keyword(s):  
Water Depth ◽  
Transfer Functions ◽  
Low Frequency ◽  
Sensitivity Study ◽  
Wave Loads ◽  
Offshore Structure ◽  
Frequency Wave ◽  
Drift Theory ◽  
Mooring Forces ◽  
Drift Forces

Operability of offshore moored ships can be affected by low frequency wave loads. The low frequency motions of a moored ship may limit the uptime of an offshore structure such as an LNG offloading terminal. The wave loads that cause the main excitation of these low frequency motions are usually computed using second order wave drift theory for long crested waves, which assumes that the low frequency components are only related to waves coming from the same direction. In this method short crested seas are dealt with as a summation of long crested seas, but no interaction between the wave components traveling in different directions is usually taken into account. This paper describes the results of a study to the effect of 2nd order low frequency wave loads in directional seas. For this study the drift forces related to the interaction between waves coming from different directions is also included. This is done by computing the quadratic transfer functions (QTF) for all possible combinations of wave components (frequencies and directions). Time traces of drift forces are generated and compared to the results without wave directional interaction after which the motions of an LNG carrier are simulated. A sensitivity study is carried out towards the number of direction steps and the water depth. Finally the motions of an LNG carrier in shallow water (15m water depth) are simulated and mooring forces are compared for various amounts of wave spreading.

scholarly journals Influence of Vortex-Induced Loads on the Motion of SPAR-Type Wind Turbine: A Coupled Aero-Hydro-Vortex-Mooring Investigation

2018 ◽  
Vol 140 (5) ◽  
Author(s):  
Yan Li ◽  
Liqin Liu ◽  
Qiang Zhu ◽  
Ying Guo ◽  
Zhiqiang Hu ◽  
...  
Keyword(s):  
Wind Turbine ◽  
Vortex Shedding ◽  
Coupling Effect ◽  
Coupled Model ◽  
Offshore Wind ◽  
Numerical Code ◽  
Offshore Wind Turbine ◽  
Nonlinear Stiffness ◽  
Wave Loads ◽  
The Mean

The nonlinear coupling effect between degree-of-freedom (DOFs) and the influence of vortex-induced loads on the motion of SPAR-type floating offshore wind turbine (FOWT) are studied based on an aero-hydro-vortex-mooring coupled model. Both the first- and second-order wave loads are calculated based on the three-dimensional (3D) potential theory. The aerodynamic loads on the rotor are acquired with the blade element momentum (BEM) theory. The vortex-induced loads are simulated with computational fluid dynamics (CFD) approach. The mooring forces are solved by the catenary theory and the nonlinear stiffness provided by the SPAR buoy is also considered. The coupled model is set up and a numerical code is developed for calculating the dynamic response of a Hywind SPAR-type FOWT under the combined sea states of wind, wave, and current. It shows that the amplitudes of sway and roll are dominated by lift loads induced by vortex shedding, and the oscillations in roll reach the same level of pitch in some scenarios. The mean value of surge is changed under the drag loads, but the mean position in pitch, as well as the oscillations in surge and pitch, is little affected by the current. Due to the coupling effects, the heave motion is also influenced by vortex-induced forces. When vortex-shedding frequency is close to the natural frequency in roll, the motions are increased. Due to nonlinear stiffness, super-harmonic response occurs in heave, which may lead to internal resonance.

Effect of Air Fraction on Force Coefficients in Oscillatory Flow

2021 ◽  
Author(s):  
Malene Hovgaard Vested ◽  
Erik Damgaard Christensen
Keyword(s):  
High Speed ◽  
Offshore Structures ◽  
Air Injection ◽  
Wave Loads ◽  
Morison Equation ◽  
Force Coefficients ◽  
Air Content ◽  
Set Up ◽  
High Level ◽  
Spilling Breakers

Abstract The forces on marine and offshore structures are often affected by spilling breakers. The spilling breaker is characterized by a roller of mixed air and water with a forward speed approximately equal to the wave celerity. This high speed in the top of the wave has the potential to induce high wave loads on upper parts of the structures. This study analyzed the effect of the air content on the forces. The analyses used the Morison equation to examine the effect of the percentage of air on the forces. An experimental set-up was developed to include the injection of air into an otherwise calm water body. The air-injection did introduce a high level a turbulence. It was possible to assess the amount of air content in the water for different amounts of air-injection. In the mixture of air and water the force on an oscillating square cylinder was measured for different levels of air-content, — also in the case without air. The measurements indicated that force coefficients for clear water could be use in the Morison equation as long as the density for water was replaced by the density for the mixture of air and water.

A Numerical Simulation of Non-Linear Air-Gap for Deepwater Semi-Submersible Platform

2021 ◽  
Author(s):  
Zhuang Kang ◽  
Yansong Zhang ◽  
Haibo Sui ◽  
Rui Chang
Keyword(s):  
Air Gap ◽  
Second Order ◽  
Difference Frequency ◽  
Hydrodynamic Performance ◽  
Wave Loads ◽  
Order Difference ◽  
Motion Response ◽  
Nonlinear Motion ◽  
Non Linear ◽  
Simulation Results

Abstract Air gap is pivotal to the hydrodynamic performance for the semi-submersible platform as a key characteristic for the strength assessment and safety evaluation. Considering the metocean conditions of the Norse Sea, the hydrodynamic performance of a semi-submersible platform has been analyzed. Based on the three-dimensional potential flow theory, and combined with the full QTF matrix and the second-order difference frequency loads, the nonlinear motion characteristics and the prediction for air gap have been simulated. The wave frequency motion response, the second-order nonlinear air gap response and nonlinear motion response of the platform have been analyzed. By comparing the simulation results, the air gap response of the platform considering the nonlinear motion is more intense than the results simulated by the first-order motion without considering the second-order difference frequency loads. Under the heavy metocean conditions, for the heave and pitch motion of the platform, the non-linear simulation values for some air gap points and areas are negative which means the wave slam has been occurred, but the calculation results of linear motion response indicate that the air gap above has not appeared the wave slamming areas. The simulation results present that the influence of the second-order wave loads is a critical part in the air gap prediction for the semi-submersible platform.

Calibration of a Time-Domain Hydrodynamic Model for A 12 MW Semi-Submersible Floating Wind Turbine

2021 ◽  
Author(s):  
Carlos Eduardo Silva de Souza ◽  
Nuno Fonseca ◽  
Petter Andreas Berthelsen ◽  
Maxime Thys
Keyword(s):  
Numerical Model ◽  
Wind Turbine ◽  
Time Domain ◽  
Quadratic Model ◽  
Wave Loads ◽  
Frequency Wave ◽  
Load Models ◽  
Wave Drift ◽  
Floating Wind Turbine ◽  
Decay Tests

Abstract Design optimization of mooring systems is an important step towards the reduction of costs for the floating wind turbine (FWT) industry. Accurate prediction of slowly-varying horizontal motions is needed, but there are still questions regarding the most adequate models for low-frequency wave excitation, and damping, for typical FWT concepts. To fill this gap, it is fundamental to compare existing load models against model tests results. This paper describes a calibration procedure for a three-columns semi-submersible FWT, based on adjustment of a time-domain numerical model to experimental results in decay tests, and tests in waves. First, the numerical model and underlying assumptions are introduced. The model is then validated against experimental data, such that the adequate load models are chosen and adjusted. In this step, Newman’s approximation is adopted for the second-order wave loads, using wave drift coefficients obtained from the experiments. Calm-water viscous damping is represented as a linear and quadratic model, and adjusted based on decay tests. Additional damping from waves is then adjusted for each sea state, consisting of a combination of a wave drift damping component, and one component with viscous nature. Finally, a parameterization procedure is proposed for generalizing the results to sea states not considered in the tests.

scholarly journals A Coupled Model for Solution Flow and Bioleaching Reaction Based on the Evolution of Heap Pore Structure

2014 ◽  
Vol 2014 ◽  
pp. 1-6
Author(s):  
Shenghua Yin ◽  
Xun Chen ◽  
Chi Ma ◽  
Leiming Wang ◽  
Aixiang Wu
Keyword(s):  
Coupled Model ◽  
Small Particles ◽  
Copper Ore ◽  
Solution Flow ◽  
Pore Evolution ◽  
Main Factors ◽  
Set Up ◽  
Seepage Law ◽  
Leaching Reaction ◽  
The Relationship

Based on the basic seepage law, equations have been derived to descript the solution flow within the copper ore heap which is treated as anisotropy porous media. The relationship between heap permeability and pore ratio has been revealed. Given the consideration of cover pressure and particle dissolution, pore evolution model has been set up. The pore evolution mechanism, due to the process of dissolution, precipitation, blockage, collapse, and caking, has been investigated. The comprehensive model for pore evolution and solution flow under the effect of solute transport and leaching reaction has been established. A trapezoidal heap was calculated, and the estimated results show that permeability decreases with the decreasing of pore ratio. Therefore, the permeability of the heap with small particles is relatively low because of its low pore ratio. Furthermore, permeability and height are found to be the two main factors influencing the solution flow.

Numerical Simulation of Coaxial Evaporating Spray in Nozzle Region of Circulating Fluidized Reactor

2002 ◽  
Author(s):  
Chao Zhu ◽  
Xiaohua Wang ◽  
Guangliang Liu
Keyword(s):  
Circulating Fluidized Bed ◽  
Experimental System ◽  
Droplet Size Distribution ◽  
Numerical Code ◽  
Solid Flow ◽  
Full Field ◽  
Lagrangian Simulation ◽  
Solids Loading ◽  
Set Up ◽  
Evaporating Spray

Full field hydrodynamic mixing of a coaxial evaporating spray in the nozzle region of a circulating fluidized reactor was numerically investigated. An Eulerian-Lagrangian numerical code was developed for the field description of evaporating spray characteristics with strong phase interactions among evaporating droplets, solids and gas. The gas-solid flow is simulated using multi-fluid method coupled with kinetic theory modeling for inter-particle collisions while the spray is treated as the discrete droplets in a pseudo-continuum gas-solid flow. The Lagrangian simulation of the spray provides the needed coupling terms for the Eulerian simulation of gas-solid flows, such as droplet evaporation rate and interactions among phase of droplets, gas and solids. Phase distributions of temperature, velocity and concentration were achieved to explain the mixing process of evaporating spray in gas-solid flows. Effects of inlet solids loading and droplet size distribution on both spray structure and spray penetration depth were illustrated. An experimental system of liquid nitrogen spray into a circulating fluidized bed of fluid catalytic cracking particles is set up to provide experimental validation of our model. Good comparisons of the simulation and measurements are illustrated.

scholarly journals Integrated Optimization of Floating Wind Turbine Systems

2014 ◽  
Author(s):  
Frank Sandner ◽  
David Schlipf ◽  
Denis Matha ◽  
Po Wen Cheng
Keyword(s):  
Wind Turbine ◽  
Degrees Of Freedom ◽  
Dynamic Models ◽  
Controller Design ◽  
Coupled Model ◽  
Optimal Solution ◽  
Wave Loads ◽  
Nonlinear Simulation ◽  
Floating Wind Turbine ◽  
Wind Turbine System

The purpose of this paper is to show an exemplary methodology for the integrated conceptioning of a floating wind turbine system with focus on the spar-type hull and the wind turbine blade-pitch-to-feather controller. It is a special interest to use a standard controller, which is easily implementable, even at early design stages. The optimization of the system is done with adapted static and dynamic models through a stepwise narrowing of the design space according to the requirements of floating wind turbines. After selecting three spar-type hull geometries with variable draft a simplified nonlinear simulation model with four degrees of freedom is set up and then linearized including the aerodynamics with the blade pitch controller in the closed-loop. The linear system allows conventional procedures for SISO controller design giving a theoretically suitable range of controller gains. Subsequently, the nonlinear model is used to find the optimal controller gains for each platform. Finally, a nonlinear coupled model with nine degrees of freedom gives the optimal solution under realistic wind and wave loads.

Glacier-plume or glacier-fjord circulation models? A model intercomparison for Hansbreen-Hansbukta system, Svalbard

2020 ◽  
Author(s):  
Eva De Andrés ◽  
Jaime Otero ◽  
Francisco Navarro
Keyword(s):  
Information Exchange ◽  
Computational Cost ◽  
Coupled Model ◽  
High Sensitivity ◽  
Coupled Models ◽  
Plume Model ◽  
Fjord Circulation ◽  
Iceberg Calving ◽  
Front Shape ◽  
Set Up

<p> <span>Up to 30% of the global tidewater mass loss corresponds to frontal ablation through submarine melting and calving. However, the glacier-fjord interactions remain poorly understood and challenging to constrain in the models. We have developed a 2D glacier flowline-plume coupled model that includes subglacial discharge, submarine melting and iceberg calving to simulate Hansbreen-Hansbukta system (SW Svalbard). We run the model for 20 weeks, from April to September of 2010, with weekly information exchange between glacier and plume models. The same set up and constraints of a previous glacier-fjord </span><span>circulation </span><span>model are used here, making the results of both simulations comparable. We consider a 200 m-width subglacial discharging channel, which was found to be a good approximation in the previous glacier-fjord model. Submarine melt rates show high sensitivity to the subglacial-discharge and ambient fjord-temperature intraseasonal evolution. Calving rates are highly dependent on both submarine melting and crevasse water depth. Glacier-plume and glacier-fjord coupled models differ in vertically-accumulated submarine melt rates (up to 30 % higher for the glacier-plume model) and show different melt-undercutting front shapes, which have an influence on the net stress fields near the glacier front. The quasi-linear melt-undercutting morphology exhibited by the glacier-plume model promotes higher calving rates than the quasi-parabolic front shape resulting from the glacier-fjord model, although both models predict similar front positions. Given that the glacier-plume model diminishes the computational cost by a factor of >50, we think that it is a good option for projection studies, as long as we apply appropriate constraints to subglacial discharge fluxes and ambient fjord temperatures.</span></p>

The Study on Vibration of Marine Riser under Deep Water

2010 ◽  
Vol 97-101 ◽  
pp. 2816-2819
Author(s):  
Chun Jie Han ◽  
Tie Yan
Keyword(s):  
Water Depth ◽  
Deep Water ◽  
Wave Loads ◽  
Lateral Vibration ◽  
Actual Situation ◽  
Marine Riser ◽  
Drilling Engineering ◽  
Set Up

With the development of deep water drilling engineering, marine riser has become the important equipment. With the increase in water depth, the failure of marine riser is very serious, the vibration is the main reason. According to the actual situation, the model of marine is set up, the rule of lateral vibration is obtained. The result is helpful to avoid the phenomena of resonance of marine riser under wave loads.

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