Frederik Vanhollebeke

Order Based Modal Analysis Versus Standard Techniques to Extract Modal Parameters of Operational Wind Turbine Gearboxes

Rotating machineries generally operate under very dynamic and complex conditions, during which structural nonlinearities, tonalities or other dynamic related phenomena may arise, affecting the assumptions made in the design phase. Techniques that allow accurately and confidently identifying the dynamic response are then of paramount importance in such complex scenarios. Wind turbine gearboxes are a typical example of such machines, as they operate under strong transient conditions caused by the turbulent and non-stationary wind speed as well as fluctuations in the electrical grid. If models can help predict these interactions, dedicated experiments need to be foreseen to characterize operational response and validate/improve the developed numerical models.

Wind Turbine Gearbox Dynamic Characterization Using Operational Modal Analysis

The aim of this paper is to characterize the dynamic behavior of a wind turbine gearbox installed on a dynamic test rig to replicate operational conditions. Wind turbines and gearboxes operate under very dynamic and complex conditions, caused by turbulent wind, fluctuations in the electricity grid etc. In those conditions, structural nonlinearities in bearings and gears cause natural frequencies to be significantly influenced by the operational conditions. To verify the dynamic response of a multi-megawatt gearbox, a comprehensive test campaign has been performed in the context of the European project ALARM at the ZF Wind Power test rig. Accelerations have been measured at more than 250 locations on the test rig and for different load levels and operating conditions. This paper focuses on the influence of the torque levels on the identified modal parameters. The acquired time histories during run-ups have been processed using different Operational Modal Analysis techniques. The aim is to provide a modal model that can be used for correlation and updating of a flexible nonlinear multibody model of the whole test rig as well as vibration levels to estimate structure-borne noise in the different operating conditions.

Dynamic Characterization of Wind Turbine Gearboxes in Operational Conditions

The gearbox is one of the key subsystems in a typical wind turbine. It has the task to transfer power from the low speed shaft connected to the rotor to the high speed shaft connected to the generator. Larger wind turbines require more power and gearboxes with higher load capacity need to be designed and a deep knowledge into gearbox dynamics becomes of fundamental importance. When dealing with a machine in operating conditions with several rotating components, components are introduced in the signal that make the application of standard techniques such as Operational Modal Analysis very difficult and in some cases almost impossible. For this reason, new techniques to tackle with these conditions were investigated in the past, such as Order Based Modal Analysis. This method represents an extension of standard OMA to extract a modal model from measurement on a machine during run-up (or run-down) conditions. The applicability limits of standard OMA are here demonstrated on the data acquired on a 13.2 MW wind turbine gearbox testing facility during controlled run-up conditions. The advantages of the proposed methodology will be demonstrated by firstly applying it on data simulated using a validated model of the testing facility. The additional challenges that need to be faced when applying the method to real data will also be presented.

Rated Life Calculation Potential of Gearbox Model Based Force Estimates

One main contributor for gearbox rated lifetime estimation is the assessment of bearing loading during predicted operating conditions. This paper investigates an approach to determine input bearing loading by means of a TPA (Transfer Path Analysis) approach. TPA is suggested to retrieve internal bearing forces from acceleration measurements acquired at the outside of the gearbox housing. However, classical TPA methods would require the gearbox to be dismantled during the transfer path determination process. This poses significant practical challenges. To overcome this issue, this paper investigates the possibility of using a flexible multibody simulation model to calculate the different frequency response functions between bearings forces and acceleration sensors. All simulations use a flexible multibody modeling approach, which has been extensively validated. Main results of this validation process have been published by the authors in the past. The paper discusses the results of such analysis on a multi-megawatt wind turbine gearbox. Here, simulated acceleration measurements on the gearbox housing are processed into bearing forces. The feasibility of using these forces for a rating life calculation is investigated.

Dynamic Response of a Multi-Megawatt Wind Turbine Drivetrain Under Voltage Dips Using a Coupled Flexible Multibody Approach

High turbine reliability is of utmost importance to keep the cost of wind energy to a minimum. A considerable problem in this regard is that of premature drivetrain failures, which have plagued the wind turbine industry since its inception. Accurate prediction of the loads encountered by the drivetrain components during their lifetime is essential for reliable wind turbine design. Of particular interest are transient load events, which are expected to have a detrimental effect on the lifetime of drivetrain components, especially when they give rise to torque reversals. At the electrical side of the wind turbine, transient events worth investigating include grid faults, emergency stops and grid loss. Unlike previous research on the impact of these events, which typically uses simplified gearbox representations, this paper investigates the dynamic behavior of wind turbine drivetrains during grid faults using a coupled simulation of a flexible multibody model of a commercial multimegawatt wind turbine drivetrain and a Simulink model of a doubly fed induction generator (DFIG) and its controller. The mathematical modeling of the DFIG as well as the flexible multibody modeling of the drivetrain are described. Both gear and bearing forces on several components of the gearbox are examined during a symmetrical and asymmetrical voltage dip, and the influence of gearbox flexibility on these loads is assessed.Copyright

The Dynamic Behavior Induced by Different Wind Turbine Gearbox Suspension Methods Assessed by Means of the Flexible Multibody Technique

The continuous demand for increase in power output for new wind parks under strict cost constraints, the greater wind resource at elevation and the desire for fewer machines per Mega-Watt to reduce operations resulted in a demand for bigger turbines. The drive train is an important component in realizing reliable and robust wind turbines. This paper investigates a geared wind turbine. In this type a gearbox is used to convert the low rotor speed to the required high generator speed. In the market several solutions are available to constrain the gearbox in the nacelle. The used configuration significantly determines the gearbox response to rotor loads and the transmission of gearbox vibrations to the turbine. This paper investigates the effectiveness of three configurations: the three point mounting, the double bearing configuration and the hydraulic damper system. The flexible multibody modeling technique can be used to accurately characterize gearbox dynamics. The goal of this work is to use an experimentally validated multibody model of a wind turbine drive train to characterize the ability of the three configurations to minimize the introduction of non-torque loads in the gearbox and the ability to isolate the gearbox vibrations from the rest of the turbine.Copyright