Abstract Stage I: Two-mass Oscillator Stage II: Torsional Multi-body

Progressive Dynamical Drive Train Modeling As Part of NREL

Gearbox Reliability Collaborative 

Progressive Dynamical Drive Train Modeling As Part of NREL

Francisco Oyague cisco Oyague

Stage III: Gear Elements 

The information contained in this poster is subject to a government license | WINDPOWER 2008 | Houston, Tx | June 1–4, 2008 | PO-500-43068

Stage V: High Fidelity Semistatic

Validation

The Gearbox reliability Collaborative (GRC) seeks to develop 

a model representative of the current standards in the

industry that can be extrapolated to a large number of

turbines with different sizes and dimensions, but with the 

same configuration. Thus, the GRC’s analysis and

experimentation is performed on a carefully selected,

preexisting machine with a significant operating history. This 

approach assures that the information revealed by the testing 

and analysis will be more valuable and relevant to the current 

industry.

The GRC analysis also seeks to integrate several numerical 

models that capture the dynamical nature of the drive train 

into the drive train design process. These dynamical models 

which are progressively complex aim to reveal new insight 

into the internal forces inherent to the dynamical behavior of 

the drive train. Additionally, the progressive nature of these 

models allows them to be validateed by comparing models of 

less complexity to models of higher complexity, thus 

eliminating error in the model development. These models 

will allow for the filtration of sensitive information between the 

different parties of the design process; therefore, ultimately 

increasing transparency.

 This model accounts for the torsional 

compliances of each individual stage of the 

gearbox, as well as, each individual shaft.

 It also accounts for the changes in torque 

and angular velocities generated by the 

gearbox. 

 The overall response of the drive train

should be similar to the response observed 

in the first model.

 This model implements gear elements capable 

of accounting for backlash, gear tooth contact 

and changes in center distances.

 The joints in this model have a single degree of 

freedom that only allows rotation.

 The compliances and clearance contribution of 

the bearings are neglected.

 Relevant load cases were generated in the

aeroelastic software FAST_AD 

 The load cases included: 

3⁄4Braking maneuvers

3⁄4Fault loads cases

3⁄4Turbulent conditions 

 The load cases are imported into the models of 

higher fidelity

 The integration of FAST_AD and the multibody

system models results in a comprehensive

analytical tool.

 The two-mass oscillator, is the simplest

simulated form of the drive train. 

 It is a simple, two-mass torsional vibration 

system in which one mass represents the 

rotor and one mass represents the generator. 

 The entire drive train is represented by a 

torsional spring damper connection.

 This rudimentary approach is used by

many aeroelastic simulation codes. 

Stage IV: Bearing Compliance 

 This model adds degrees of freedom to the 

joints in the stage III model.

 The joints are constrained by the use of force 

elements that represent the stiffness of the 

bearings.

 This model better represents the bearing load 

distribution, and gear misalignment. 

 The different models and parameters calculated were validated with data collected from the field

 Validation included: 

3⁄4 Airfoils and power curve characteristics

3⁄4 Modal behavior of the blades and tower

Load Generation 

4 Pole Generator

Generator shift

6 Pole Generator 

-200

-100

0

100

200

300

400

500

600

0 100 200 300 400 500 600

Time [sec]

Torque [kNm]

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

shaft bending [V]

LSS Torque

LSS Bending

 The stage of highest complexity includes a full 

finite element model of the gearbox.

 Housing deformation will be modeled to

account for the overall misalignment of the 

internal components of the gearbox. 

 High fidelity gear finite element analysis will be 

performed to reveal gear tooth load distribution.

3⁄4 Natural frequency and drive train stiffness 

3⁄4 Inertial characteristics of the generator