Realistic ship models for experimental investigation

Abstract

After several decades of hydroelastic experiments, scaled ship models are still predominantly constructed with a simplified structure. A rigid vessel is divided into segments and the flexibility is provided by a backbone or a series of flexible joints, usually with a uniform stiffness distribution. Although continuous models have been used, there are no documented cases of a model with an internal structure resembling a ship, a so-called elastic model.

In the present investigation, 3D printing is proposed as a manufacturing method to produce elastic models and the associated advantages and constraints are investigated. Design of a 3D printed elastic ship model is found to be challenging, partly because of the lack of material properties available and the inadequacy of traditional methods, such as 3-point bending tests, to determine the properties relevant to structural vibration. A method based on cellular specimens subjected to modal testing combined with FEA simulations is developed to accurately predict the natural frequencies of the model during the design stage, as well as estimate structural damping.

A 3D printed elastic model of a ship is designed and manufactured and its vibratory performance in air and water is investigated. It is demonstrated that the natural frequencies of the vessel can be accurately predicted using the newly-developed specimen method mentioned above. A step-by-step procedure for the design and production of 3D printed elastic models of ships is developed.

Bending moment measurements on the model in head waves and the corresponding strain distribution within the cross section indicate beam-like behaviour and agree with existing theory and literature, thus verifying the concept of a 3D printed elastic ship model. Additionally, locally increased stiffness due to the tow post attachment demonstrates the capability of the model to capture local responses, which are absent in segmented models. The methodology developed here will allow investigators to introduce a more accurate representation, in model scale, of a ship's cross-sectional properties, such as torsional stiffness distribution and shear centre location.

Results from such investigations are crucial for the improvement of state-of-the-art hydroelastic codes and, consequently, assessment of ship safety.

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Identifiers

ORCID for Apostolos Grammatikopoulos: orcid.org/0000-0003-1800-7406

ORCID for Joseph Banks: orcid.org/0000-0002-3777-8962

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