Towards a finite element model of a batch of experimental violins: validation on sub-structural components

During the Bilbao project, six violins were built with systematic geometry control in order to investigate the influence of the plate thickness on the dynamics, sound and playing characteristics of the complete instruments. To this end, three violins with medium backs, each paired with a thin, normal, or thick top and three with medium tops, each paired with a thin, medium, or thick back were made. Despite careful control and reduction of the influence of handwork by a numerically controlled machining cutting means on the outside of the plates, there remains various sources of variability, in particular in the wood properties. In order to separate the effect on the vibratory behavior of the intentional thickness variations from irreducible variability in wood properties and geometric tolerance, a complete finite element model is being developed using COMSOL software. This model takes into account the geometry of the Bilbao project violins while the wood properties are obtained by optimising the numerical vibratory behavior to match the experimental modal data of the free plates, just after they were CNC routed. This paper explains in detail this optimisation process and show the results for the six top and six back plates. The proposed approach enables the identification of material properties in multiple directions and ensures a step-by-step control of the accuracy of the modeled parts compared to the real ones.