Numerical and Experimental Investigation Regarding the Landing Manoeuvre of a Catamaran Vessel at an Offshore Wind Turbine in Waves

2015 ◽  
Author(s):  
Daniel Ferreira González ◽  
Matthias Lemmerhirt ◽  
Moustafa Abdel-Maksoud ◽  
Marcel König ◽  
Alexander Düster
Keyword(s):  
Experimental Investigation ◽  
Time Domain ◽  
Offshore Structures ◽  
Offshore Wind ◽  
Irregular Waves ◽  
Offshore Wind Turbine ◽  
Reaction Forces ◽  
Simulation Results ◽  
The Time Domain ◽  
Hydrodynamic Effects

In this work, the landing manoeuvre of a catamaran vessel at a monopile foundation is investigated by experiments compared with numerical simulations. Therefore, a method is presented which allows simulating the described landing manoeuvre at offshore structures. The simulation in the time domain is based on potential theory using a boundary element method (BEM) and it computes the motions of the rigid body due to the hydrodynamic loads which consist of the incoming waves and the diffraction caused by the monopile. Further, a fender model is implemented, considering the reaction forces due to the friction and the deformation of the fender. The model is further able to distinguish between slip and non-slip condition of the fender. Apart from this, model tests of the landing manoeuvre were carried out with a catamaran model. During the tests the model pushed its fender against an equally scaled monopile. The motions of the vessel and the forces at the attachment of the fender were measured in regular and irregular waves. The obtained data which leads to a better understanding of the hydrodynamic effects during a landing manoeuvre is compared with the simulation results in order to improve the numerical method. The validation with experimental results shows that the method is applicable to quantify the risk of the fender suddenly slipping.

Aero-Elastic-Control-Floater-Mooring Coupled Dynamic Analysis of Floating Offshore Wind Turbine in Maximum Operation and Survival Conditions

2014 ◽  
Vol 136 (2) ◽  
Author(s):  
Y. H. Bae ◽  
M. H. Kim
Keyword(s):  
Dynamic Analysis ◽  
Clean Energy ◽  
Offshore Wind ◽  
Irregular Waves ◽  
Offshore Wind Turbine ◽  
Coupled Dynamic Analysis ◽  
Floating Offshore Wind Turbines ◽  
Mooring Dynamics ◽  
Dynamics And Control ◽  
The Time Domain

Increasing numbers of floating offshore wind turbines (FOWTs) are planned in the coming years due to their high potential in the massive generation of clean energy from ocean wind. In the present study, a numerical prediction tool has been developed for the fully coupled dynamic analysis of an FOWT system in the time domain including aero-loading, tower/blade elasticity, blade-rotor dynamics and control, mooring dynamics, and platform motions so that the influence of aero-elastic-control dynamics on the hull-mooring performance and vice versa can be assessed. The Hywind spar design with a 5 MW National Renewable Energy Laboratory (NREL) turbine is selected as an example and two different collinear wind-wave-current environmental conditions, maximum operational and survival conditions, are applied for this study. The maximum operational condition means the maximum environmental condition with normal blade-turbine operation and the survival condition represents the extreme situation without any blade-turbine operation. Through this study, it is seen that the ultimate-loading environments for different structural components of the FOWT can be different. The developed technology and numerical tool are readily applicable to the design of any type of future FOWTs in any combinations of irregular waves, dynamic winds, and steady currents.

Assessment of Allowable Sea States During Installation of Offshore Wind Turbine Monopiles With Shallow Penetration in the Seabed

2016 ◽  
Vol 138 (4) ◽  
Author(s):  
Lin Li ◽  
Wilson Guachamin Acero ◽  
Zhen Gao ◽  
Torgeir Moan
Keyword(s):  
Time Domain ◽  
Dynamic Responses ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Offshore Wind Turbines ◽  
Heavy Lift ◽  
Characteristic Values ◽  
Limiting Parameters ◽  
The Time Domain ◽  
Penetration Depths

Installation of offshore wind turbines (OWTs) requires careful planning to reduce costs and minimize associated risks. The purpose of this paper is to present a method for assessing the allowable sea states for the initial hammering process (shallow penetrations in the seabed) of a monopile (MP) using a heavy lift floating vessel (HLV) for use in the planning of the operation. This method combines the commonly used installation procedure and the time-domain simulations of the sequential installation activities. The purpose of the time-domain simulation is to quantitatively study the system dynamic responses to identify critical events that may jeopardize the installation and the corresponding limiting response parameters. Based on the allowable limits and the characteristic values of the limiting response parameters, a methodology to find the allowable sea states is proposed. Case studies are presented to show the application of the methodology. The numerical model of the dynamic HLV–MP system includes the coupling between HLV and MP via a gripper device, and soil–MP interaction at different MP penetration depths. It is found that the limiting parameters are the gripper force and the inclination of the MP. The systematic approach proposed herein is general and applies to other marine operations.

Comparing Frequency and Time Domain Simulations for Geometry Optimization of a Floating Offshore Wind Turbine Mooring System

2018 ◽  
Author(s):  
Ajit C. Pillai ◽  
Philipp R. Thies ◽  
Lars Johanning
Keyword(s):  
Frequency Domain ◽  
Time Domain ◽  
Pareto Front ◽  
Geometry Optimization ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Mooring System ◽  
Efficient Design ◽  
Frequency Domain Methods ◽  
The Time Domain

This paper explores geometry optimization of an offshore wind turbine’s mooring system considering the minimization of the material cost and the cumulative fatigue damage. A comparison of time domain simulations against frequency domain simulations is made to explore the suitability of these methods to the design process. The efficient design options, the Pareto front, from the frequency domain study are also re-evaluated using time domain simulations and compared against the time domain Pareto front. Both the time and frequency domain results show optimal results utilizing similar design philosophies, however, the frequency domain methods severely under predict the fatigue loads in the mooring system and incorrectly class infeasible solutions as feasible. The frequency domain is therefore not suitable for optimization use without some external means of applying engineering constraints. Furthermore, re-evaluation of the frequency domain solutions provides guidance to the uncertainty and the necessary design fatigue factors required if implementing frequency domain methods in design.

Response Analysis of a Nonstationary Lowering Operation for an Offshore Wind Turbine Monopile Substructure

2015 ◽  
Vol 137 (5) ◽  
Author(s):  
Lin Li ◽  
Zhen Gao ◽  
Torgeir Moan
Keyword(s):  
Wind Turbine ◽  
Time Domain ◽  
Dynamic Responses ◽  
Offshore Wind ◽  
Irregular Waves ◽  
Offshore Wind Turbine ◽  
Response Analysis ◽  
Steady State Condition ◽  
Strip Theory ◽  
Lifting System

This study addresses numerical modeling and time-domain simulations of the lowering operation for installation of an offshore wind turbine monopile (MP) with a diameter of 5.7 m and examines the nonstationary dynamic responses of the lifting system in irregular waves. Due to the time-varying properties of the system and the resulting nonstationary dynamic responses, numerical simulation of the entire lowering process is challenging to model. For slender structures, strip theory is usually applied to calculate the excitation forces based on Morison's formula with changing draft. However, this method neglects the potential damping of the structure and may overestimate the responses even in relatively long waves. Correct damping is particularly important for the resonance motions of the lifting system. On the other hand, although the traditional panel method takes care of the diffraction and radiation, it is based on steady-state condition and is not valid in the nonstationary situation, as in this case in which the monopile is lowered continuously. Therefore, this paper has two objectives. The first objective is to examine the importance of the diffraction and radiation of the monopile in the current lifting model. The second objective is to develop a new approach to address this behavior more accurately. Based on the strip theory and Morison's formula, the proposed method accounts for the radiation damping of the structure during the lowering process in the time-domain. Comparative studies between different methods are presented, and the differences in response using two types of installation vessel in the numerical model are also investigated.

Foundation Structure Design and Analysis for Offshore Wind Turbine

2009 ◽  
Vol 419-420 ◽  
pp. 105-108
Author(s):  
Liang Zhang ◽  
Jing Zhao ◽  
Jian Hua Zhang ◽  
Jun Hao
Keyword(s):  
Wind Turbine ◽  
Time Domain ◽  
Electrical Power ◽  
Structure Design ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Concept Design ◽  
The Time Domain ◽  
Foundation Structure ◽  
Mechanical Characters

Offshore Wind Turbine (OWT) is a device to extract and convert offshore wind energy into useful electrical power. The typical concept design of monopile foundation structure for 1.5MW OWT is raised in this paper. The arrangement of the monopile and related accessorial facilities are especially considered during design. Mechanical characters of the foundation structure are emphatically analyzed, including static analysis, dynamic analysis, fatigue analysis and bucking analysis. The time domain approach is preferable for the dynamic response of foundation under the condition of earthquake and wave. Based on the analysis results, the reliability of the structure is proved to be satisfied with the requirements .The paper provides the reference for the design of OWT.

scholarly journals Maintenance Planning of Offshore Wind Turbine Using Condition Monitoring Information

2009 ◽  
Author(s):  
Jose´ G. Rangel-Rami´rez ◽  
John D. So̸rensen
Keyword(s):  
Condition Monitoring ◽  
Wind Turbines ◽  
Wind Farm ◽  
Offshore Structures ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Maintenance Planning ◽  
Offshore Wind Turbines ◽  
Inspection And Maintenance ◽  
Monitoring Information

Deterioration processes such as fatigue and corrosion are typically affecting offshore structures. To “control” this deterioration, inspection and maintenance activities are developed. Probabilistic methodologies represent an important tool to identify the suitable strategy to inspect and control the deterioration in structures such as offshore wind turbines (OWT). Besides these methods, the integration of condition monitoring information (CMI) can optimize the mitigation activities as an updating tool. In this paper, a framework for risk-based inspection and maintenance planning (RBI) is applied for OWT incorporating CMI, addressing this analysis to fatigue prone details in welded steel joints at jacket or tripod steel support structures for offshore wind turbines. The increase of turbulence in wind farms is taken into account by using a code-based turbulence model. Further, additional modes t integrate CMI in the RBI approach for optimal planning of inspection and maintenance. As part of the results, the life cycle reliabilities and inspection times are calculated, showing that earlier inspections are needed at in-wind farm sites. This is expected due to the wake turbulence increasing the wind load. With the integration of CMI by means Bayesian inference, a slightly change of first inspection times are coming up, influenced by the reduction of the uncertainty and harsher or milder external agents.

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.

Experimental Investigation on the Dynamic Response of a Three Legged Articulated Type Offshore Wind Tower

2016 ◽  
Author(s):  
Chinsu Mereena Joy ◽  
Anitha Joseph ◽  
Lalu Mangal
Keyword(s):  
Dynamic Response ◽  
Wind Turbine ◽  
Renewable Energy Sources ◽  
Offshore Structures ◽  
Dynamic Responses ◽  
Offshore Wind ◽  
Experimental Investigations ◽  
Offshore Wind Turbine ◽  
Ocean Engineering ◽  
Study Results

Demand for renewable energy sources is rapidly increasing since they are able to replace depleting fossil fuels and their capacity to act as a carbon neutral energy source. A substantial amount of such clean, renewable and reliable energy potential exists in offshore winds. The major engineering challenge in establishing an offshore wind energy facility is the design of a reliable and financially viable offshore support for the wind turbine tower. An economically feasible support for an offshore wind turbine is a compliant platform since it moves with wave forces and offer less resistance to them. Amongst the several compliant type offshore structures, articulated type is an innovative one. It is flexibly linked to the seafloor and can move along with the waves and restoring is achieved by large buoyancy force. This study focuses on the experimental investigations on the dynamic response of a three-legged articulated structure supporting a 5MW wind turbine. The experimental investigations are done on a 1: 60 scaled model in a 4m wide wave flume at the Department of Ocean Engineering, Indian Institute of Technology, Madras. The tests were conducted for regular waves of various wave periods and wave heights and for various orientations of the platform. The dynamic responses are presented in the form of Response Amplitude Operators (RAO). The study results revealed that the proposed articulated structure is technically feasible in supporting an offshore wind turbine because the natural frequencies are away from ocean wave frequencies and the RAOs obtained are relatively small.

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