Open Access
Mode-displacement method for structural dynamic analysis of bio-inspired structures: a palm-tree stem subject to wind effects
(Taylor & Francis, 2022) Plaza Puértolas, Aitor; Vargas Silva, Gustavo Adolfo; Iriarte Goñi, Xabier; Ros Ganuza, Javier; Ingeniería; Ingeniaritza
Biological materials (orthotropic materials), like wood, can offer good mechanical properties with a minimum amount of material, making their internal structure the suitable one to be applied on bio-inspired structures. The knowledge of the exceptional structural performance of palm trees, and specially its response to different loading conditions, provides useful information when lightweight structures with high slenderness ratio are desired. Recent researches focused on the analysis of palm trees subject to static loading conditions, ignoring the fluctuating nature of the wind speed. The purpose of this study is to simulate in a computational efficient way the effect of dynamic loading conditions applied on palm trees. Using the mode displacement method, the number of degrees of freedom of a dynamic finite element analysis can be drastically reduced with a minimal loss of accuracy. It was applied to simulate the behavior of structures comprised of an orthotropic material subject to a stochastic dynamic load. The influence of the number of selected degrees of freedom has also been studied. In addition, an exponential integration method is proposed to perform the time integration procedure. The results obtained show that a properly reduced model suitably represents the full finite element model without any appreciable loss of accuracy; it is also shown that computational cost can be drastically reduced. This method could give an appropriate computational representation of the behavior of orthotropic structures, and it could be used for studying more complex bio-inspired structures.
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
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.

Iriarte Goñi, Xabier

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