Prediction of the vibratory properties of ship models with realistic structural configurations produced using additive manufacturing

Abstract

The use of flexible ship models to determine the dynamic behaviour of fullscale ships in waves and to compare the accuracy of numerical predictions has increased in the past few years. Segments attached to a flexible uniform backbone of suitable but simple cross section is the preferred solution. Although such models are relatively easy to manufacture with conventional processes, they do not represent accurately the structural detail, for example, of a container ship. The limitations of conventional manufacturing constraints can be potentially overcome by use of modern technologies such as additive manufacturing. Designing detailed elastic ship models requires the determination of dynamic material properties, in addition to the manufacturer mechanical properties.In this investigation, a detailed but easy-to-implement method is developed, and applied to a uniform container ship-like model, to identify the material properties that are relevant to the calculation of the natural frequencies of 3D printed thin-walled structures. It is demonstrated that modal testing of 3D printed specimens, combined with FEA modelling, can be used to accurately predict the natural frequencies of much more complex thin-walled structures. This method allows investigators to acquire all information necessary during the design stage of 3D printed structures without having to resort to full material characterisation.

The design and commissioning of a fully elastic model of a uniform container ship

“…As demonstrated previously by the authors [15], the static and dynamic moduli of 3D printed structures can be significantly different. This is likely to affect the accuracy of a bending moment calibration that is performed statically as described above.…”

“…were measured [15]. Ballasting the vessel increased its mass and reduced the natural frequencies, particularly those corresponding to symmetric responses, therefore the values in Table 7 differ noticeably from the ones included in the aforementioned publication.…”

“…Grammatikopoulos et al, demonstrated that the static and dynamic flexural moduli of 3D printed components can be significantly different, rendering standard 3-point bending tests irrelevant to the design of elastic ship models [14]. An experimental procedure, based on specimen-scale modal testing, was developed that allowed accurate prediction of several natural frequencies of the vessel [15]. Indications regarding the structural damping could also be obtained from the same procedure.…”

The effects of geometric detail on the vibratory responses of complex ship-like thin-walled structures

“…The mesh of this model is shown in Figure 2. The high accuracy of this method has also been previously demonstrated through comparison to experimental results on a different vessel [20].…”

“…Grammatikopoulos et al [20] developed a method to design and manufacture elastic models, including significant structural detail, using additive manufacturing. The produced methodology was shown to accurately predict the natural frequencies of such a model, including up to the 5 th antisymmetric mode, after which there were no experimental results to compare to the simulations.…”