A scale model for hydrostructural investigation
Conference/JournalMARIN Report 146
Date20 Jan 2026
If ships become larger, they become more flexible, and this can have an important influence on the design loads of ships. Typically, this means cutting the model into a number of segments and connecting them using a steel or aluminium beam.
Whipping is the transient elastic vibration of the ship’s hull girder which can be caused by slamming for example. For the double-ended ferry, whipping is an important phenomenon to consider when determining design loads. It was therefore necessary to test the ferry using a flexible model.
In order to scale the hull girder flexibility, it is important to represent the shapes and frequencies of the first few global flexural vibration modes. This means that the mass and stiffness distribution of the ship should be adequately represented. For the double-ended ferry modelling, the first vertical global flexural mode illustrated in Figure 1 was deemed sufficient.
Whipping is the transient elastic vibration of the ship’s hull girder which can be caused by slamming for example. For the double-ended ferry, whipping is an important phenomenon to consider when determining design loads. It was therefore necessary to test the ferry using a flexible model.
In order to scale the hull girder flexibility, it is important to represent the shapes and frequencies of the first few global flexural vibration modes. This means that the mass and stiffness distribution of the ship should be adequately represented. For the double-ended ferry modelling, the first vertical global flexural mode illustrated in Figure 1 was deemed sufficient.
Contact
Ingo Drummen
senior project manager | team leader
Tests in water and air
After designing the flexible beam properties and completing the assembly, the shapes and frequencies of the vibration modes were measured and compared with what was specified. These tests were done both in water and air. Tests in water are carried out by placing the instrumented model in water and exciting it by applying an impulsive load. The disadvantage is that the vibrations of the model also result in the movement of the water. This results in additional mass that is added to the mass of the model. This added mass can be calculated, but it does result in a level of uncertainty.
Model on balloons to determine dry natural frequencies.