Fatigue Analysis of a Point Absorber Wave Energy Converter Subjected to Passive and Reactive Control

2015 ◽  
Vol 137 (5) ◽  
Author(s):  
A. S. Zurkinden ◽  
S. H. Lambertsen ◽  
L. Damkilde ◽  
Z. Gao ◽  
T. Moan
Keyword(s):  
Fatigue Damage ◽  
Wave Energy ◽  
Stress Responses ◽  
Fatigue Analysis ◽  
Wave Energy Converter ◽  
Wave Loads ◽  
Reactive Control ◽  
Energy Converter ◽  
Set Up ◽  
Frequency Domain Approach

This paper investigates the effect of a passive and reactive control mechanism on the accumulated fatigue damage of a wave energy converter (WEC). Interest is focused on four structural details of the Wavestar arm, which is used as a case study here. The fatigue model is set up as an independent and generic toolbox, which can be applied to any other global response model of a WEC device combined with a control system. The stress responses due to the stochastic wave loads are computed by a finite element method (FEM) model using the frequency-domain approach. The fatigue damage is calculated based on the spectral-based fatigue analysis in which the fatigue is described by the given spectral moments of the stress response. The question will be discussed, which control case is more favorable regarding the tradeoff between fatigue damage reduction and increased power production.

Loads and Dynamic Response of a Floating Wave Energy Converter due to Regular Waves From CFD Simulations

2016 ◽  
Author(s):  
Anna Büchner ◽  
Thomas Knapp ◽  
Martin Bednarz ◽  
Philipp Sinn ◽  
Arndt Hildebrandt
Keyword(s):  
Dynamic Response ◽  
Boundary Conditions ◽  
Wave Energy ◽  
Single Point ◽  
Breaking Waves ◽  
Wave Energy Converter ◽  
Wave Loads ◽  
Regular Waves ◽  
Energy Converter ◽  
Set Up

The commercial CFD code ANSYS Fluent is used for the three-dimensional estimation of wave loads and the dynamic response of a floating single point wave energy converter of the SINN Power wave power plant due to non-breaking and unidirectional waves in coastal waters. The VoF method is used to model the free surface and wave theories to set up the boundary conditions at the inlet for regular waves. The wave induced vertical motions of the floating module are computed by a sixDoF solver. Preliminary 2D and 3D studies to set up boundary conditions, mesh densities and solver settings were performed. The numerical results were compared to analytical solutions in form of water surface elevations and wave kinematics which showed good agreement. The paper presents the dynamic response of the floating module for different load cases in terms of non-breaking waves. The resulting horizontal and vertical forces at the floating module will be presented and explained by the flow dynamics. Time and space depending velocities and pressure distributions including details on vortex separation will be given, which reveal valuable insights on the contribution of inertia and drag forces leading to the dynamic structural response of the floating devices.

Umbilical Fatigue Analysis for a Wave Energy Converter

2021 ◽  
Author(s):  
Yi-Hsiang Yu ◽  
Billy Ballard ◽  
Jennifer van Rij
Keyword(s):  
Wave Energy ◽  
Fatigue Analysis ◽  
Wave Energy Converter ◽  
Energy Converter

Performance Characteristics of a Tightly Moored Piston-Like Wave Energy Converter Under First- and Second-Order Wave Loads

2008 ◽  
Author(s):  
Spyros A. Mavrakos ◽  
George M. Katsaounis ◽  
Ioannis K. Chatjigeorgiou
Keyword(s):  
Wave Energy ◽  
Second Order ◽  
Wave Energy Converter ◽  
Performance Characteristics ◽  
Hydrodynamic Characteristics ◽  
Diffraction Radiation ◽  
Wave Loads ◽  
Energy Converter ◽  
Eigenfunction Expansions ◽  
First Order

The paper deals with the presentation of a model to predict performance characteristics of a tightly moored piston-like wave energy converter which is allowed to move in heave, pitch and sway modes of motion. The WEC’s piston-like arrangement consists of two floating concentric cylinders, the geometry of which allow the existence of a cylindrical moonpool between the external cylinder, the ‘torus’ and the inner cylinder, the ‘piston’. The first-order hydrodynamic characteristics of the floating device, i.e. exciting wave forces and hydrodynamic parameters, are evaluated using a linearized diffraction-radiation semi-analytical method of analysis that is suited for the type of bodies under consideration. According to the analysis method used, matched axisymmetric eigenfunction expansions of the velocity potentials in properly defined fluid regions around the body are introduced to solve the respective diffraction and radiation problems and to calculate the floats’ hydrodynamic characteristics in the frequency domain (Mavrakos et al. 2004, 2005). Based on these characteristics, the retardation forcing terms are calculated, which account for the memory effects of the motion. In this procedure, the coupling terms between the different modes of motion are properly formulated and taken into account (Cummins, 1962; Faltinsen, 1990). The floating WEC is connected to an underwater hydraulic cylinder that feeds a hydraulic system with pressurized oil. The performance of the system under the combined excitation of both first- and second order wave loads is here analyzed. To this end, the diffraction forces originated from the second order wave potentials are computed using a semi-analytical formulation which, by extension of the associated first-order solution, is based on matched axisymmetric eigenfunction expansions.

Performance Assessment of a Floating Coaxial Ducted OWC Wave Energy Converter for Oceanographic Purposes

2015 ◽  
Author(s):  
Juan C. C. Portillo ◽  
Joao C. C. Henriques ◽  
Luis M. C. Gato ◽  
Rui P. F. Gomes ◽  
Antonio F. O. Falcão
Keyword(s):  
Wave Energy ◽  
Numerical Study ◽  
Time Domain Analysis ◽  
Turbine Rotor ◽  
Wave Energy Converter ◽  
Energy Converter ◽  
Mean Power ◽  
Air Turbine ◽  
Mean Power Output ◽  
Frequency Domain Approach

This paper presents a numerical study on a floating coaxial ducted OWC wave energy converter equipped with a biradial air turbine to meet the requirements of an oceanographic sensor-buoy. The study used representative sea states of the Monterey Bay, California, USA. The geometry of the coaxial ducted OWC was hydrodynamically optimized using a frequency domain approach considering a linear air turbine. Afterwards, a time domain analysis was carried out for the system equipped with a biradial turbine. The turbine rotor diameter and the optimum generator’s control curves were determined, based on results for representative sea states. Results show that mean power output fulfills the requirement for oceanographic applications (300–500W) using a turbine rotor diameter of 0.25 m. Furthermore, the system’s performance is strongly influenced by the inertia of the turbine and the generator rated power. These results confirmed the suitability of using the coaxial ducted OWC as a self-sustainable oceanographic sensor-buoy.

Finite Element Analysis for Water Turbine of Horizontal Axis Rotor Wave Energy Converter

2014 ◽  
Vol 530-531 ◽  
pp. 906-910
Author(s):  
Dong Dong Hu ◽  
Yan Jun Liu ◽  
Li Kang Hong ◽  
Xiao Chen Guo
Keyword(s):  
Finite Element ◽  
Stress Response ◽  
Wave Energy ◽  
Stress Responses ◽  
Wave Energy Converter ◽  
Horizontal Axis ◽  
Linear Wave ◽  
Energy Converter ◽  
Element Analysis ◽  
Water Turbine

Horizontal axis rotor wave energy converter is a new form for utilization of ocean wave energy, and the axis of its water turbine is parallel with the sea level and perpendicular to the direction of wave. This paper employed the linear wave theory and Froude-Krylov presumptive method to calculate the wave force, which was exerted on the wave energy converter in extremely arduous wave conditions. The finite element research on the deformation and the stress response of the water turbine was carried out to assess its security. The results show that the deformation and the stress responses both reach their maximum values at the 3rd mode shape about 90Hz, and the deformation response is 0.4208mm and the stress response is 0.8052MPa at this frequency, which are both within the required security range.

scholarly journals A Set-Up of 7 Laser Triangulation Sensors and a Draw-Wire Sensor for Measuring Relative Displacement of a Piston Rod Mechanical Lead-Through Transmission in an Offshore Wave Energy Converter on the Ocean Floor

2012 ◽  
Vol 2012 ◽  
pp. 1-32 ◽  
Author(s):  
E. Strömstedt ◽  
O. Svensson ◽  
M. Leijon
Keyword(s):  
Energy Conversion ◽  
Measurement System ◽  
Wave Energy ◽  
Relative Displacement ◽  
Operating Conditions ◽  
Wave Energy Converter ◽  
Laser Triangulation ◽  
Energy Converter ◽  
Set Up ◽  
Offshore Wave

A concept for offshore wave energy conversion is being developed at the Swedish Centre for Renewable Electric Energy Conversion at Uppsala University in Sweden. The wave energy converter (WEC) in focus contains a piston rod mechanical lead-through transmission for transmitting the absorbed mechanical wave energy through the generator capsule wall while preventing seawater from entering the capsule. A set-up of 7 laser triangulation sensors has been installed inside the WEC to measure relative displacement of the piston rod and its corresponding seal housing. A draw-wire sensor has also been set up to measure translator position and the axial displacement of the piston rod. The paper gives a brief introduction to the Lysekil research site, the WEC concept, and the direct drive of WEC prototype L2. A model of operation for the piston rod mechanical lead-through transmission is given. The paper presents sensor choice, configuration, adaptation, mounting, and measurement system calibration along with a description of the data acquisition system. Results from 60 s measurements of nominal operation two months apart with centered moving averages are presented. Uncertainty and error estimations with statistical analyses and signal-to-noise ratios are presented. Conclusions are drawn on the relative motions of the piston rod and the seal housing under normal operating conditions, and an assessment of the applicability of the measurement system is made.

Structural Modeling and Analysis of a Wave Energy Converter Applying Dynamical Substructuring Method

2013 ◽  
Author(s):  
Andrew S. Zurkinden ◽  
Lars Damkilde ◽  
Zhen Gao ◽  
Torgeir Moan
Keyword(s):  
Wave Energy ◽  
Structural Modeling ◽  
Wave Energy Converter ◽  
Computational Time ◽  
Response Analysis ◽  
Fe Model ◽  
Wave Loads ◽  
Energy Converter ◽  
Modeling And Analysis ◽  
Survival Mode

This paper deals with structural modeling and analysis of a wave energy converter. The device, called Wavestar, is a bottom fixed structure, located in a shallow water environment at the Danish Northwest coast. The analysis is concentrated on a single float and its structural arm which connects the WEC to a jackup structure. The wave energy converter is characterized by having an operational and survival mode. The survival mode drastically reduces the exposure to waves and therfore to the wave loads. Structural response analysis of the Wavestar arm is carried out in this study. Due to the relative stiff behavior of the arm the calculation can be reduced to a quasi-static analysis. The hydrodynamic and the structural analyses are thus performed separately. In order to reduce the computational time of the finite element calculation the main structure is modeled as a superelement. The structural detail, where the stress analysis is carried out, is connected with the superstructure by interface nodes. The analysis is conducted for two different control situations. Numerical results will be presented which can be further used to carry out fatigue analysis in which a more refined FE model is required to obtain the stress concentration factors.

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