| 16 Oct 2025
Validation of a finite-element model of a 5 m three-row roller wind turbine blade bearing
Abstract. Large rolling bearings with complex interfaces need reliable finite-element models to determine the load distribution and deformation behavior. To ensure the accuracy of the results, it is important to validate the models against experimental data. Several works on models with different approaches are published but rarely is this validated. The present work now firstly validates a finite-element model of an original size three-row roller wind turbine blade bearing. For the validation, strain gauges are used to compare the deformation behavior of the bearing rings against experimental results. A characteristic of three-row roller bearings is the segmentation of one of the rings for manufacturing purposes. In this work, the authors investigate the influence of different coefficients of friction between the segmented outer ring and different bolt preloads on the occurring strain on the bearing rings. Two different sets of bolt preloads were considered: One to represent operational behavior with no relative movement between the segments of the split ring and one with gap opening and sliding to investigate nonlinear behavior of the bearing. The result of this work is a validated finite-element bearing and test rig model for different parameter sets and loads.
In this manuscript, the authors present a detailed FE model to simulate the static response of a large three-row roller bearing intended for wind turbine applications. The ultimate goal of the study is the validation of this model, which is achieved by comparing experimental results with those obtained from the FEM, which includes the structure of the test rig itself.
The topic addressed is undoubtedly of great relevance to the wind energy industry, since such models are widely used both in the development and in the certification process of pitch bearings. The scarcity of references on the subject—mainly due to the confidentiality with which manufacturers protect their know-how—fully justifies the interest of this work for researchers and engineers working in the field. The manuscript is also well written and well organized, making it easy to follow and understand.
However, considering that the main objective of the paper is the validation of the FE model, this reviewer thinks that it is not described in sufficient detail for the work to be reproducible and, consequently, for its contribution to be significant enough. In addition, the considerable effort invested by the authors in developing the model, along with the undoubtedly expensive experimental campaign, could be further leveraged to draw more relevant conclusions that would help structural analysts of such components to develop reliable and efficient models.
For these reasons, this reviewer raises the following comments, grouped into two sections.
* General comments regarding the scope of the work:
- It would be highly valuable to provide a modelling guideline, offering a more detailed description of the model used and giving recommendations on aspects such as mesh size selection, contact configuration (beyond simply differentiating bonded/frictional types), and other modelling details discussed below.
- Only strain results are compared, although it seems it would have been quite straightforward to also measure displacements, which would allow assessing the model’s capability to predict bearing stiffness. While strains are undoubtedly an essential parameter for model validation, the relative deformation between the inner and outer rings is not considered, even though it is strongly influenced by some of the modelling aspects discussed later. A comparison between experimental and simulated displacements would represent a meaningful contribution, without complicating the experimental setup (for instance, this could be easily done using dial gauges). Is there any specific reason why this comparison was not made? Am I missing something?
* Comments regarding the model description:
- For the simplified modelling of the ball-raceway contact, it is indeed common to use a mechanism similar to the one proposed in this paper, where springs connect the curvature centres of the raceways. However, in the case of rollers, it is more typical to use a spring bed connecting the raceways directly (Golbach 1999) or even a single spring per roller (Kania 2006), without the need for the V-shaped mechanisms shown in Figure 2. Why was this mechanism chosen instead of a spring bed or a single-spring approach? Have different modelling options been tested and compared? It would be very interesting to evaluate different alternatives in terms of accuracy and computational cost, especially in a bearing with such a large number of rollers. Furthermore, why are used 5 or 3 springs per roller, and not more or fewer? Have simulations been carried out in this regard? What conclusions were drawn? Could any guideline be derived on the number of springs to use depending on the roller length or other parameters?
- Regarding the formulation of the roller–raceway contact, there are several alternatives to the one cited in the paper (Palmgren 1964). More recent formulations, such as those by Puttock (1969), Norden (1973), Tripp (1985), Johnson (1989), Hamrock (1991), or the more recent one by Houpert (2001), could also be considered. Is the Palmgren formulation the most suitable for simulating roller–raceway contact in the case of logarithmic profiles, as studied here? Were other formulations tested?
- Concerning the implementation of the FDC formulation, and if I understood correctly, each spring is connected to the whole raceway sector that corresponds to each roller. More details on this modelling choice would be required. Why was the spring connected to the whole surface instead of only to the area where the contact is expected (which would be much smaller)? Why not use a rigid-type (MPC/RBE2) spring-raceway connection? Have comparisons been made? Such tests could lead to useful conclusions in terms of accuracy and computational cost.
- Regarding the other contacts in the model, key details are missing, such as the formulation used in each case, the penetration tolerance or the normal contact stiffness (for penalty-based contacts), and other parameters that may significantly influence the model’s behaviour and displacements/stiffness results.
- As for the mesh, was a mesh sensitivity analysis performed? Were quadratic elements used throughout the model? Could any recommendations be provided regarding mesh size and element type?
- It is essential to describe the different load steps. Given the nonlinear nature of the model, the order in which loads are applied will influence the results.
- Concerning the simulation of the test rig, figures showing the mesh and model details are missing. The description of the test rig model—beyond that of the bearing itself—is rather brief.
Most of the above aspects might not have a major impact on the strain results reported in the paper, but they could significantly affect the relative deformations between the rings, i.e. the bearing stiffness, which is a relevant parameter to consider.
Many thanks to the authors for their work. I am sorry for being so meticulous regarding the modelling aspects, but I sincerely believe that the work carried out by the authors is of great value and that the manuscript could be significantly improved by addressing these. I am also confident that the authors will be able to respond to all of them, so I have no doubt that the paper could be published (at least from this reviewer’s perspective) once these comments have been taken into consideration.