Reliability of wave energy devices WP5 - overview

Transcription

1 Reliability of wave energy devices WP5 - overview J.D. Sørensen, S. Ambühl, J.P. Kofoed Department of Civil Engineering, Aalborg University, Denmark C.B. Ferreira Det Norske Veritas BV, London, UK Department of Civil Engineering Aalborg University 1

2 Contents Introduction Characteristics of Wave Energy Devices (WED) Reliability of wind turbines vs wave energy devices Reliability modeling of WED Target reliability level for WED Summary Department of Civil Engineering Aalborg University 2

3 Introduction Objectives: Development of methodologies for Reliability assessment of a WED Electrical, mechanical and structural components + control system Risk analysis of a WED system incl. Planning of O&M Assess optimal reliability level for WED Proposals for codes / standardization / safety factors for WED Use experience / methods from: (Offshore) Wind turbines Oil & gas structures Coastal structures Department of Civil Engineering Aalborg University 3

4 Introduction Risk / reliability analysis concepts for wind turbines wave energy devices: Structural components: - use Structural Reliability Methods Electrical / mechanical components: - use System / Classical Reliability Methods Risk-based methods for life cycle management: Operation & Maintenance Department of Civil Engineering Aalborg University 4

5 Reliability wind turbines WT Failure Rates and Downtimes (examples) ISET: 2006 Department of Civil Engineering Aalborg University

6 Reliability Development / qualification phases: From Carbon Trust (DnV) 2005 Department of Civil Engineering Aalborg University

7 Reliability modelling of WED Department of Civil Engineering Aalborg University From Thies et al. 2009

8 Reliability modeling of WED WED subsystems: Reaction subsystem (foundation or moorings, the structural reference elements) Hydrodynamic subsystem (structural elements responsible for the primary power capture, typically where the wave power is turned into mechanical/hydraulic/pneumatic power) Power take-off subsystem (mechanical and electrical elements responsible for conversion of the mechanical/hydraulic/pneumatic power into electrical power) Control subsystem (electronic elements including sensors and actuators needed for optimization and control of the power take-off subsystem) Department of Civil Engineering Aalborg University 8

9 Reliability assessment WED vs WT Wave energy devices (WED): ratio between structural loadings in extreme and production conditions is in most cases very high Wind turbines (WT): ratio is significantly smaller, as wind turbine blades are pitched out of the wind in extreme conditions, making extreme loadings of the same order of magnitude as production loads. As extreme loadings and survivability drive the costs of the devices, and as income is only generated in everyday production conditions, it is of tremendous importance for WED to increase reliability and reduce cost. Department of Civil Engineering Aalborg University 9

10 Reliability elec. / mech. components Failure Rate Bath tub curve Burn-in failures Improve quality control Wear out Inspections Robustness Random failure Improve reliability Constant failure rate = 1 / Mean Time Between Failure Time Department of Civil Engineering Aalborg University 10

11 Reliability structural components Limit state equation: g( x) = 0 Probability of failure: P F ( g( X) ) Φ( β ) = P 0 Probability of failure, Reliability index, β P F ,3 3,1 3,7 4,3 4,8 5,2 Requirements: Formulation of limit state equation Stochastic modeling of uncertain parameters Physical uncertainties Statistical uncertainties Model uncertainties Measurement uncertainties Department of Civil Engineering Aalborg University

12 Reliability structural components ULS limit states: Fatigue failure of welded details Mooring failure by sliding of anchor Mooring failure by breaking of mooring line(s) Failure of structural element, leading to disintegration/change of geometry/loss of part(s) Local structural failure due to wave impact (slamming) (potentially leading to capsizing/sinking) Wear out of hinged connections... Department of Civil Engineering Aalborg University

13 Reliability level Building codes: e.g. Eurocode EN1990:2002: annual P F = 10-6 or β = 4.7 Fixed steel offshore structures: e.g. ISO 19902:2004 manned: annual P F ~ or β = 4.0 unmanned: annual P F ~ or β = 3.3 IEC : land-based wind turbines annual P F ~ 10-3 or β = 3.1 IEC : offshore wind turbines annual P F ~ or β = 3.5 Wave energy devices:??? annual P F ~ or β = 3.5 Department of Civil Engineering Aalborg University

14 Load combinations - proposal Power production control system is to some degree limiting the load effects due to wave (and wind) actions. Extreme load effects have to be determined by load extrapolation Power production and occurrence of fault(s). faults in e.g. the electrical or hydraulic system may imply extreme load effects Parked (out-of-operation): for some WED types power production is stopped for very large wave heights and loads are limited. Transportation, installation and maintenance Department of Civil Engineering Aalborg University 14

15 Summary Task 5.1: Development of methodology for reliability assessment of WEDs Based on existing techniques for reliability analysis will be applied for assessment of the reliability of electrical, mechanical and structural components in a WED Task 5.2: Collection and analysis of statistical information for structural, electrical and mechanical components Available data on failure rates and uncertain parameters - statistical analysis Estimation of reliability of selected components / WEDs Task 5.3: Risk analysis and operation & maintenance Life cycle approach - optimal planning of operation and maintenance minimize cost of energy Assessment of the minimum reliability level for different WED components Recommendations for deterministic design using e.g. the partial safety factor design methods for structural components Department of Civil Engineering Aalborg University 15

16 Thank you for your atttention This work is part of the project SDWED (Structural Design of Wave Energy Devices) Supported by Danish Council for Strategic Research Contact: Jens Peter Kofoed: John Dalsgaard Sørensen: Simon Ambühl Department of Civil Engineering Aalborg University 16