Open Access
Impact of strain gauge misalignment and model parameters on load estimation in wind turbines
(Elsevier, 2026-01-15) Bacaicoa Díaz, Julen; Iriarte Goñi, Xabier; Aginaga García, Jokin; Plaza Puértolas, Aitor; Ingeniería; Ingeniaritza; Institute of Smart Cities - ISC; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
Accurate load estimation in wind turbines is important for understanding the structural behaviour and optimising performance. Loads are commonly measured using strain gauges, but the process is strongly based on accurate placement and alignment. This work explores the influence of geometric, material, misplacement, and misalignment parameters on the performance of different strain gauge configurations for obtaining load estimates. An analytical model for a single gauge is presented which establishes the relationship between exerted loads and measured strain. Using second-order approximations, the sensitivities of the estimated loads are calculated in terms of the uncertainty of the model parameters. The model allows to calculate how the secondary loads affect the estimation of those of interest, which is particularly useful in wind turbines where all three forces and three moments occur simultaneously. When estimating a single load, analytic results show that sensitivities to geometric and material parameters remain consistent regardless of secondary loads, while sensitivities to gauge bonding parameters reveal a cross-talk effect. As these sensitivity results depend on the model parameters and the instantaneous values of the secondary loads (which vary with time) the sensitivities will strongly depend on the application cases. In this paper a horizontal-axis wind turbine is simulated, calculating the loads at the Low Speed Shaft and the Tower Base. The sensitivity results for these subsystems using Montecarlo simulations show that while some loads can be precisely estimated, other loads will be very poorly estimated even when the gauges are bonded with tiny misalignment errors.
Open Access
A unified analytical disk cam profile generation methodology using the Instantaneous Center of Rotation for educational purpose
(Elsevier, 2024) Iriarte Goñi, Xabier; Bacaicoa Díaz, Julen; Plaza Puértolas, Aitor; Aginaga García, Jokin; Ingeniería; Ingeniaritza; Institute of Smart Cities - ISC; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
Cam design is a fundamental part of the Mechanism and Machine Theory (MMT) and is included in the vast majority of MMT books. Cam profile design is usually determined with graphical and analytical methods. Graphical methods are didactically very successful to introduce the theory of cam profile generation in a simple way. In turn, analytical methods allow computer implementations of cam profile generation in order to reproduce it accurately. Most modern MMT books describe analytical methods using geometric equations and envelope theory. However, the analytical profile definition depends on the specific type of follower and there is a lack of a general formulation. This work presents a unified and general analytical formulation for the disk cam profile determination. Based on the Instantaneous Center of Rotation and the kinematic inversion, the formulation provides analytical expressions of the cam profile and is applicable to any type of follower. Thus, the unified formulation can be used in forthcoming books on this discipline.
Open Access
Optimal strain-gauge placement for mechanical load estimation in circular cross-section shafts
(Elsevier, 2021) Iriarte Goñi, Xabier; Aginaga García, Jokin; Gainza González, Gorka; Ros Ganuza, Javier; Bacaicoa Díaz, Julen; Institute of Smart Cities - ISC
The customary electrical circuit configuration for estimating mechanical loads with strain gauges uses Wheatstone full- or half-bridges. For each mechanical load to be estimated, a dedicated bridge with two or four gauges has to be mounted, placing the strain gauges in specific configurations along the measured part. In this paper the strain of individual gauges is measured by means of quarter-bridges and all the mechanical loads exerted on a shaft are estimated jointly as different linear combinations of the strains of the gauges. The location of the gauges on the shaft are determined optimally and the influence of apparent strain related to temperature variations is avoided. Results show several configurations of reduced sets of gauges capable of optimally estimating the six components of the mechanical loads exerted on a circular cross-section shaft. The validation of the approach in a dedicated rig has shown the complexity of its experimental implementation.
Open Access
Design, manufacturing, validation of a multi-orientation tilt test bench for testing vehicles rollover and tests of ATV-Quad for agricultural applications
(MDPI, 2021) Bacaicoa Díaz, Julen; Ballesteros Egüés, Tomás; Arana Navarro, Ignacio; Aginaga García, Jokin; Latorre Biel, Juan Ignacio; Ingeniería; Ingeniaritza; Institute of Smart Cities - ISC
A rollover test bench has been designed, manufactured, and validated for analyzing the all-terrain vehicle (ATV)-Quad overturn of diverse vehicles in different configurations, such as installing a rollover protection system (ROPS), considering drivers of different physical constitutions, the appropriate use of safety belts, or having a full or empty fuel tank. The main purpose of this research is to determine the tilt angle of the vehicle that triggers the ATV-Quad overturn. The scope of the design and development of the newly conceived bench include the mechanical structure, the electronics and the control. It can simulate static and dynamic rollover in different directions. As a main conclusion, it can be stated that the performance of the test bench was successful, since it allowed for the development of several ATV models, equipped with different dummies, in a variety of configurations. In particular, it was possible to assess the effectivity of the AD-ROPS system (automatically deployed ROPS), regarding the protection of the driver of the vehicle. Moreover, multiple tests, performed with diverse ATV-Quads in the developed bench and in different configurations, have been reported and their results discussed.
Embargo
D-optimal strain sensor placement for mechanical load estimation in the presence of nuisance loads and thermal strain
(Elsevier, 2025-02-01) Iriarte Goñi, Xabier; Bacaicoa Díaz, Julen; Aginaga García, Jokin; Plaza Puértolas, Aitor; Szczepanska-Álvarez, Anna; Ingeniería; Ingeniaritza; Estadística, Informática y Matemáticas; Estatistika, Informatika eta Matematika; Institute of Smart Cities - ISC; Gobierno de Navarra / Nafarroako Gobernua
The measurement of loads in circular cross-section geometries using strain gauges or other types of strain sensors is well-known in the field of mechanical engineering. Typical stress measurement configurations use 4 strain sensors strategically placed on the surface of the shaft and connected in the form of a complete Wheatstone bridge. Thus, 4 strain sensors are used to estimate each of the six load components to which a shaft may be subjected. Some typical configurations are designed to compensate for temperature effects, making them robust to temperature changes. Despite being used for decades, there is no record of any algorithm that serves to calculate these configurations, demonstrate that they are optimal or determine new configurations with other requirements. In this article, an algorithm is developed that allows calculating the optimal configurations of strain sensors to estimate one or several load components, compensating for the effect of other loads and temperature variations. This algorithm is based on the measurement of the strain of each gauge using Wheatstone quarter bridges and uses the same set of sensors for the estimation of various load components. The results are two-fold: on the one hand the traditional configurations are shown to be optimal and on the other hand a series of additional optimal configurations are obtained to estimate various sets of load components compensating for the influence of the rest. Additionally, a means of calculating the estimation variance of the loads of interest is provided.
Open Access
Optimal strain gauge configurations for the estimation of mechanical loads in the main shaft of HAWT
(IOP Publishing, 2020) Iriarte Goñi, Xabier; Aginaga García, Jokin; Lerga Valencia, Francisco Javier; Gainza González, Gorka; Ros Ganuza, Javier; Bacaicoa Díaz, Julen; Ingeniaritza; Institute of Smart Cities - ISC; Ingeniería
In Structural Health Monitoring of wind turbines, measuring the mechanical loads is a key issue. The customary techniques for this task use a full-bridge strain gauge configuration to measure each of the six load components exerted on the shaft. However, using only six strain gauges should be sufficient to estimate the six load components if a one-to-one correspondence was achieved. In this paper a different approach to mechanical loads estimation is presented where, measuring the strain of individual gauges in quarter-bridge configurations, it is possible to estimate all the load components from a single set of gauges. The configurations are optimally determined making use of the D-optimality criterion, which maximises the observability of the estimated components. The approach also provides configurations where the apparent strain related to temperature variations is automatically compensated. Results show several optimal configurations for different measuring conditions and shows that six strain gauges are enough to estimate all the load components. The new approach also opens the possibility to obtain configurations with more strain gauges as well as configurations that have to meet other requirements.
Open Access
Mechanical sensitivity analysis of strain gauge configurations in the main shaft of wind turbines
(IOP Publishing, 2022) Bacaicoa Díaz, Julen; Iriarte Goñi, Xabier; Aginaga García, Jokin; Plaza Puértolas, Aitor; Ingeniaritza; Institute of Smart Cities - ISC; Ingeniería
Wind turbines are reaching their remaining useful life, thus it is important to guarantee the well status of its components. A common way to check the status is to measure the loads on the Low Speed Shaft with strain gauges, but not always are bonded perfectly. In this work a sensitivity analysis of strain gauge con gurations is carried out, where the infuence of geometric and material parameters, and misplacement and misalignment parameters is analyzed. An analytical model for a single gauge was developed, obtaining a relation between the exerted loads and the strain measured by the strain gauge. By means of Taylor approximations the estimated loads were approached in order to have into account the in uence of the uncertainty of parameters. Results shown that the sensitivities with respect to the geometric and material parameters did not depend on the secondary loads while in the sensitivities with respect to the gauge bonding parameters the cross-talk e ect was present. In order to obtain realistic numerical results, a horizontal-axis NREL 5-MW wind turbine was simulated in OpenFAST with two wind-speed scenarios. The uncertainty of the estimated loads by the strain gauge con gurations was calculated.