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.
Open Access
4P operational harmonic and blade vibration in wind turbines: a real case study of an active yaw system and a concrete tower
(Elsevier, 2024) Torres Elizondo, Antonio; Gil Soto, Javier; Plaza Puértolas, Aitor; Aginaga García, Jokin; Ingeniería; Ingeniaritza; Institute of Smart Cities - ISC; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
This study aims to comprehensively investigate the impact of mechanical loads on the performance and lifetime of wind turbines, with particular emphasis on blade vibration at the 4P operational harmonic. Experiments and advanced aeroelastic simulations are combined to assess how active yaw systems and concrete towers affect this specific vibration. Contrary to previous assumptions, field tests have shown that there is a resonance phenomenon in the blade. Specifically, the first edgewise mode of the blade resonates at the 4P frequency, which did not happen in the aeroelastic simulations. Remarkably, thorough aeroelastic simulations show that this resonance is triggered by the excitation of the Edgewise Backward Whirling mode of the rotor, which occurs at the 3P operating harmonic. This study highlights the need for accurate and precise modelling using aeroelastic simulations to reproduce the resonance phenomenon and analyse the contributing factors. A major breakthrough is the discovery that stiffening the active yaw system significantly reduces the 3P hub fixed motions, resulting in reduced blade vibration at the 4P frequency. Furthermore, the simulations show the sensitivity of the 4P vibration to different wind characteristics, providing valuable insights for the design of wind turbines in different environmental conditions.
Embargo
D-optimal strain sensor placement for mechanical load estimation in the presence of nuisance loads and thermal strain
(Elsevier, 2024-12-08) 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
Trayectorias de máxima rigidez de un robot redundante actuando como soporte en el mecanizado de paredes delgadas
(Universitat Politècnica de València, 2023) Aginaga García, Jokin; García Cuesta, Iván; Iriarte Goñi, Xabier; Plaza Puértolas, Aitor; Ingeniería; Ingeniaritza; Institute of Smart Cities - ISC
La precisión de un robot está ligada a su rigidez. En comparación con la máquina herramienta tradicional, los robots industriales tienen un gran espacio de trabajo como ventaja, pero una rigidez reducida como desventaja. Además, la rigidez tiene una gran dependencia y variabilidad con la postura o configuración del robot. De ahí que resulte necesario un análisis de rigidez de los robots, que se evalúa mediante la matriz de rigidez. En este trabajo se presenta un análisis de rigidez de un robot serie. Ante la diversidad de índices representativos extraídos a partir de la matriz de rigidez, se ha propuesto el uso de un índice que tenga en cuenta la dirección de las cargas que soporta el robot y la dirección en que se desea que el robot aporte rigidez en la aplicación específica. Asimismo, se ha utilizado el índice de rigidez para llevar el robot a configuraciones que mejoren la rigidez, hecho que resulta posible en aplicaciones en las que el robot tiene al menos un grado de libertad (GDL) redundante. La metodología se ha aplicado a un robot de 7 GDL utilizado como robot de soporte en el mecanizado de paredes delgadas. Dado que para definir la trayectoria únicamente son necesarios 5 GDL, se utilizan 2 GDL reduntantes para mejorar la rigidez.
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
Inertia transfer concept based general method for the determination of the base inertial parameters
(Springer, 2015) Ros Ganuza, Javier; Plaza Puértolas, Aitor; Iriarte Goñi, Xabier; Aginaga García, Jokin; Ingeniería; Ingeniaritza; Institute of Smart Cities - ISC
This paper presents a new algorithm to obtain the symbolic expressions of any of the possible base inertial parameter sets of a multibody system. Based on the ¿inertia transfer concept¿, a procedure is proposed to write a system of equations from which the base parameters are obtained. This leads to an automatizable and general method to obtain these parameters symbolically. The method can also be used to determine base inertial parameters numerically, and it can be even more straightforward to implement and use than the standard numerical methods. An example is presented to illustrate in detail the application of the algorithm, and to compare its results with those of a standard numerical procedure. The symbolic base inertial parameters can be of interest in symbolic simplification of the dynamic equations for real-time applications, design optimization, dynamic parameter identification, model reduction, and in other fields.
Open Access
Comprehensive analysis of rotor edgewise whirling mode interaction with rotor speed harmonics
(IOP Publishing, 2024) Torres Elizondo, Antonio; Gil Soto, Javier; Plaza Puértolas, Aitor; Aginaga García, Jokin; Ingeniería; Ingeniaritza; Institute of Smart Cities - ISC
This paper presents a model that investigates the interaction between rotor edgewise whirling modes and rotor speed harmonics in wind turbines. The model is based on kinematic and dynamic principles, with a focus on the multi-blade coordinate transformation, which is critical for simulating the behaviour of the rotor whirling modes in wind turbines. The research has two objectives: to investigate the interaction between the rotor edgewise whirling modes and the rotor speed harmonics, and to provide clearer graphs that explain the complex nature of this non-intuitive rotor dynamics. The paper concludes by highlighting the practical implications of the research findings, in particular the effectiveness of visualisation techniques in identifying and explaining unexpected interactions.
Open Access
Kinematic design of a new four degree-of-freedom parallel robot for knee rehabilitation
(ASME, 2018) Aginaga García, Jokin; Iriarte Goñi, Xabier; Plaza Puértolas, Aitor; Mata, Vicente; Ingeniería Mecánica, Energética y de Materiales; Mekanika, Energetika eta Materialen Ingeniaritza; Institute of Smart Cities - ISC
Rehabilitation robots are increasingly being developed in order to be used by injured people to perform exercise and training. As these exercises do not need wide range movements, some parallel robots with lower mobility architecture can be an ideal solution for this purpose. This paper presents the design of a new four degree-of-freedom (DOF) parallel robot for knee rehabilitation. The required four DOFs are two translations in a vertical plane and two rotations, one of them around an axis perpendicular to the vertical plane and the other one with respect to a vector normal to the instantaneous orientation of the mobile platform. These four DOFs are reached by means of two RPRR limbs and two UPS limbs linked to an articulated mobile platform with an internal DOF. Kinematics of the new mechanism are solved and the direct Jacobian is calculated. A singularity analysis is carried out and the gained DOFs of the direct singularities are calculated. Some of the singularities can be avoided by selecting suitable values of the geometric parameters of the robot. Moreover, among the found singularities, one of them can be used in order to fold up the mechanism for its transportation. It is concluded that the proposed mechanism reaches the desired output movements in order to carry out rehabilitation maneuvers in a singularity-free portion of its workspace.