time-domain fatigue response and reliability analysis of … dong.pdf · 2013-06-10 · time-domain...

Time-domain Fatigue Response and Reliability Analysis of Offshore Wind Turbines with

Emphasis on Gear Components

Dr. Wenbin Dong

Det Norske Veritas (DNV)

CeSOS Highlights and AMOS Visions Conference27-29th May 2013

Education and work experience 2000-2004: Naval Architecture and Ocean Engineering (Tianjin University

of China , Bachelor )

2002-2004: Finance Management (Tianjin University of China , Minor Bachelor )

2004-2007: Naval Architecture and Ocean Engineering (Tianjin University of China , Master)

2008-2012: Centre for Ships and Ocean Structures-CeSOS (Norwegian University of Science and Technology-NTNU, Ph.D) Supervisor: Prof. Torgeir Moan, Adj. Assoc. Prof. Zhen GaoResearch Topic: Reliability of offshore wind turbinesDefense: 09.12.2012

2012 - : Structural Engineer in Det Norske Veritas (DNV)

2007-2008: Project Officer (Maritime Research Centre-MRC, NanyangTechnology University of Singapore-NTU)

Outline

Background

Objectives and scope

Gear contact fatigue response and reliability analysis

Conclusions

Background Climate change and atmospheric pollution are greatly influenced by theenergy sector.

Wind is one of the most rapidly growing renewable energy sources, as it isclean and environmentally friendly.

Compared to land-based wind energy, there is more available space, morestable and higher wind speed, and less visual disturbance and noise foroffshore wind energy.

Offshore wind turbines (OWTs) are subjected to environmental loads due towaves, current and wind, as well as the effect of corrosion from salt water,and in some cases floating ice; Moreover, they are less accessible than landbased turbines. The operation of OWTs is more expensive than work on land.

The reliability of OWTs is crucial. Fatigue is one of the design drivingcriteria

Background Up to now, offshore fixed wind turbines with monopile, gravity-based and tripod foundations are mainly used for shallow water depths of 20-30 m.

Research work is ongoing for larger water depths (>40 m, Jacket, Semi-submersible, Spar, TLP, etc. ) In the midlevel water depth (40-100 m), jacket structures are competitive and usually used.

Outline

Background



Conclusions

The main objective of this study is to investigate simplified reliability-basedfatigue design methods for key mechanical components of OWTs by evaluatingload effects by time-domain simulations.


The emphasis is on reliability-based gear contact fatigue analysis of thedrive train of an on-land wind turbine under dynamic wind loads.

The main tasks of this study are to:

• Perform gear contact fatigue analysis of the drive train for anon-land wind turbine under dynamic conditions, with emphasison subsurface pitting.

• Present a framework for reliability-based fatigue designmethod of gears in the drive train with emphasis onsurface/subsurface pitting.

Outline

Background



Conclusions

Time-domain based simulation model of 750 kW land-based wind turbine

Gear contact fatigue analysis of a wind turbine drive train under dynamic conditions

Reliability-based gear contact fatigue analysis - a framework


Time domain based simulation model of 750 kW land-based wind turbine

General Description of the Wind Turbine

General Design Operation

Blades

NREL 750kw land-based wind turbine model(SIMPACK 8904)

Model information-wind turbine:


Main shaft

Main bearing

Gearbox

Generator

GRC Drive train configuration

750kw gearbox model in SIMPACK

Model information-drive train:


(Haines and Ollerton,1963; Kalker,1990)

• Gear pair Component Force Element FE:225 in SIMPACK;

• The slicing method is used for helical gears;

Helical gear wheel consisting of several thin independent spur gear teeth. (Flodin and Andersson, 2001)

Gearbox model in SIMPACK

Planet gear

Sun gear(output) Ring gear

Model information-Gearbox:


Global response analysisin FAST

Time series of Torque

tooth -1

tooth +1

tooth 0

De-coupled analysis method:


Global model withoutgearbox

Global model with gearbox

Main purpose:

(1) Check the effects of gearboxon the Torque calculation;

(2) Check the effects of global model on the contact forcecalculation.

Comparison between coupled and decoupled analysis method:


Comparison of the mean value and the standard deviation

(More details: Dong, et al., energies 2012; Int. J. Fatigue2013).

Post-processing of SIMPACK results


Post processing of gear contact forces

Gear contact fatigue response and reliability analysis Time-domain based simulation model of 750 kW land-based wind

turbine




• Crack initiation:

Predictive models to estimate service lives

The first stage of the pitting process

Surface roughness, surface damage, lubrication Single crystal materials

Polycrystalline materials

• Present study: Crack initiation is neglected

The initial crack size


• Deterministic model for crack propagation:

Linear elastic fracture mechanics (LEFM) model is used:

_

m

II effda C KdN

, :C m material parameters, which can be determined by experiments;

:a half crack length;

:N cycle numbers;

_ :II effK effective Mode II (shear) stress intensity factor range ;

For subsurface initiated pitting, the driving force for crack propagation in rollingcontact has been postulated to depend on hardness and the maximum shear stress,which was shown in experiments (Jiang et al., 1993; Chen et al., 1988).


A new equation for predicting the gear contact fatigue life :

maxp Maximum contact pressure range (MPa)

cHV Core hardness (HV)

sHV Surface hardness (HV)

effz Effective case depth (mm)

a Crack length(mm)

tK

U

maxp Equivalent Maximum contact pressure range (MPa)

Surface hardness (HV)

Account for the matrix microstructureThe coefficient of friction of the contact surfacesThe porosity fraction

A factor related to crack closure

(a) Contact model of two gear flanks and(b) Equivalent model of two cylinders

(Glodez, et al.,1997)

Schematic of crack propagation

0 2 max max

1, , , , , , , ,

ca

p m m ma a t c s eff

N daC G a K HV HV z p U a p

max

1

max max max max0

m

mpp p f p d p

(More details: Dong, et al., Int. J. Fatigue 2013)


• Mean wind speed :wU 4-24m/s with an increment of 2m/s;

• The simulation time for each wind speed is taken as 700s, and the first 100’s results arethrown away.

Four different GG models

Long-term fitting results of the maximum contactpressure range generated in the representativetooth of the sun gear for case 1.

Point 0

Environmental conditions and long-term fitting results


Gear contact fatigue analysis results

Practical cycle numbers based on time domain simulation

Estimated pitting service lives of the sun gear and the planet gears

Gear contact fatigue response and reliability analysis Time-domain based simulation model of 750 kW land-based wind

turbine



Reliability-based gear contact fatigue analysis-a frame work

Based on the deterministic model for crack propagation, the following limitstate function can be obtained, If the two-parameter Weibull function is used tofit the long-term probability distribution of :

0

0 02 max

1 1, , , , , , , ,

cam

c m ma a t c s eff

mg a a da C T ABG a K HV HV z p U a

0

02 max

1 1, , , , , , , ,

cam m m mload dyn gearm m

a a t c s eff

mg da C T ABG a K HV HV z p U a

Limit state function

Uncertainty treatment

(More details: Dong, et al., ICOSSAR2013)

Reliability-based gear contact fatigue analysis-a frame work

Gear contact fatigue reliability analysis

planet gearplanet gear

sun gear sun gear

Outline

Background



Conclusions

ConclusionsThe main conclusions of this study are summarized as follows:

A new simplified predictive subsurface pitting model for estimating service lives of gearsunder dynamic conditions is presented, and verified by comparison with publishedexperimental evidence.

A two-parameter Weibull function, the generalized gamma function and the three-parameter Weibull function could be used to fit the long-term probability distribution of thegear contact pressures under dynamic conditions.

A framework for reliability-based probabilistic fatigue design of gears for onshore andoffshore wind turbines is suggested. Its application is presented through examples

The environmental conditions have a big effect on gear contact fatigue life, whichshould be considered in the real gear design for wind turbines, especially for offshoreapplications.

Reference

Flodin A, Andersson S. A simplified model for wear prediction in helical gears. Wear 2001;241:285–92.Jiang B, Zheng X, Wang M. Calculation for rolling contact fatigue life and strength of case-hardened gear materials by computer. J Test Eval 1993;21(1):9–13.Chen Q, Leng X, Shao E. Influence of microstructure and residual stress on the stages of case crushing. Wear 1988;122:45–55.Glodez S, Winter H, Stuwe HP. A fracture mechanics model for the wear of gear flanks by pitting. Wear 1997;208:177–83.

Dong WB, Xing YH, Moan T. Time domain modeling and analysis of dynamic gear contact force in wind turbine gearbox with respect to fatigue assessment. Energies 2012;5(11):4350–71.

Haines, D.J.; Ollerton, E. Contact stress distributions on elliptical contact surfaces subjected to radial and tangential forces. Proc. Inst. Mech. Eng. 1963, 177, 95–114.

Kaller, J.J. Three-Dimensional Elastic Bodies in Rolling Contact; Kluwer Academic Publishing: Dordrecht, The Netherlands, 1990.

Dong, W.B.; Xing, Y.H.; Moan, T.; Gao, Z. Time domain based gear contact fatigue analysis of awind turbine drivetrain under dynamic conditions. Int. J. Fatigue 2013; 48: 133–146.

Dong, W.B.; Moan, T.; Gao, Z. Reliability-based gear contact fatigue analysis for wind turbines under stochastic dynamic conditions. 11th International Conference on Structural Safety & Reliability (ICOSSAR 2013). New York, USA. June 2013.

time-domain fatigue response and reliability analysis of … dong.pdf · 2013-06-10 · time-domain...

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