Forschungszentrum Küste (FZK) Forschung Projekte im GWK
WAVESLAM - Wave Slamming Forces on Truss Structures in Shallow Water

WAVESLAM - Wave Slamming Forces on Truss Structures in Shallow Water

© Forschungszentrum Küste
Leitung:  Professor Ove T. Gudmestad, UiS und Associate Professor Øivind A. Arntsen
Jahr:  2013
Förderung:  HYDRALAB IV - Transnational Access
Bemerkungen:  6 Wochen


 A consortium headed by the University of Stavanger, Norway (UiS) and the Norwegian University of Science and Technology, Trondheim, Norway, (NTNU)  is carrying out experiments to investigate the slamming forces from plunging breaking waves on truss structures in shallow water. The consortium partners are:

 1. Norwegian University of Science and Technology, Norway.

2. University of Stavanger, Norway

3. University of Gdansk, Poland.

4. University of Rostock, Germany

5. Reinertsen AS, engineering consulting company, Trondheim, Norway.

 Additionally, five companies/institutions have decided to join the research project WAVESLAM:  Areva Wind, DNV, NORCOVE, NOWITECH and Statoil.


 Wind turbine foundation structures in shallow water may be prone to slamming forces from breaking waves in shallow water, typically plunging breaking waves.

Currently there are models available to estimate the highest impact forces from plunging breaking waves on monopods.   Reinertsen A/S, Trondheim, has been involved in the design of a truss support structure for wind turbines on the Thornton Bank, Belgian Coast. Plunging breaking waves has been specified for this area. Calculations, based on model for monopods, show that the forces from the plunging breaking waves are governing the responses of the structure and the foundations.  

 However, there are considerable uncertainties when applying the models for monopods for truss structures on the calculated plunging breaking wave forces.

 The objective of the proposed research is to investigate the slamming forces from plunging breaking waves on truss structures in shallow water, e.g. bottom mounted support structures for wind turbines and to improve the method to calculate those forces through model tests in large scale.

Model test set-up

 Following small scale (1:50) model tests at NTNU a 1:8 scale model of the truss structure is constructed and will be tested at the Large Wave Flume.

Although the tests will not be for a specific truss structure, we have in mind a structure similar to the one that Reinertsen Engineering has designed for the Thornton bank.  We know that the slamming forces from plunging breaking waves governs the design of this structure.

 There will be wave measurements at 15 locations and water particle measurements with Acoustic Doppler Velocity meter (ADV). It is always tricky to measure water particle velocities in breaking waves because of the entrained air. We will therefore also calculate the water particle velocities numerically with a computer program specifically developed for this purpose. This program will be validated by data taken by LDV for plunging breaking waves on a uniformly sloping bottom. We have obtained these data from Prof. Jim Kirby from the University of Delaware, USA.  The measured water particle velocities in the Large Wave Channel will then serve to validate the program for a different bottom configuration, at least in areas where water particle measurements cannot be carried out, due to air entrainment.

 The structure is equipped with a total of 12 two-axis force transducers distributed along six bracings of the structure. 10 force transducers mounted in 40 mm high sections on the front legs will give information of the vertical distribution of the forces.

 The majority of the tests will be carried out with regular waves of a range of frequencies and wave heights. The reason for that is that the slamming forces vary significantly from wave to wave. The reason for this variation is not precisely known, but it is believed it is due to small variations from wave to wave in the front slope of the plunging breaking waves. Some tests with irregular waves will also be considered.


The analysis of the force data is challenging because the set-up is not “perfect” as there will be dynamic effects for such short duration slamming forces, e.g. we measure a response and have to reveal what forces caused that response. Different methods will be considered: 1. Duhamel integral method (used by Wienke and Oumeraci (2005), Arntsen et al. (2011))  2. A method used by Määttänen (1979), Tørum (2012). 3. Methods used by Kai Irschik for his PhD on the subject of wave slamming forces (personal communication from prof. Oumeraci, University of Braunschweig,  to Alf Tørum).

Once the forces have been revealed they will be analyzed in view of the wave kinematics.

Resulting publications

Rausa, I.E.; Muskulus, M.; Arntsenc, Ø.A.; Wåsjø, K. (2015): Characterization of wave slamming forces for a truss structure within the framework of the WaveSlam project. 12th Deep Sea Offshore Wind R&D Conference, EERA DeepWind'2015.

cited References

Arntsen, Ø., Ros, X. and Tørum, A. (2011): Impact forces on a vertical pile from plunging breaking waves. Proceedings of the international  conference Coastal Structures 2011.     

Määttänen, M. (1979): Laboratory tests for dynamic ice-structure interaction. Proceedings “Port and Ocean Engineering under Arctic Conditions” (POAC), Norwegian Institute of technology, 1979.

Tørum, A. (2012): Analysis of force response data from tests on a model of a truss structure subjected to plunging breaking waves. Preliminary note.

Wienke, J. and Oumeraci, H. (2005): Breaking wave impact forces on vertical and inclined slender pile – theoretical and large scale model investigations. Coastal Engineering, Elsevier, 52 (2005), pp 435 – 462.