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Experiments by Invited Researchers

 

Slamming wave forces on truss structures

Project acronym: HyIV-FZK-05
Name of Group Leader: Prof. Ove T. Gudmestad
User-Project Title: Slamming wave forces on truss structures
Facility: Large Wave Channel (GWK)
Proceedings TA Project: WAVE SLAMMING FORCES ON TRUSS STRUCTURES IN SHALLOW WATER
Data Management Report: Report

User-Project Objectives

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 AIS, 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 models for monopods, show that the forces from the plunging breaking waves are governing the responses of the structures and the foundations. However, there are considerable uncertainties in the calculated plunging breaking wave forces when applying the models for monopods to truss structures. The objective of the research is to improve the method to calculate forces from plunging breaking waves on truss structures through model tests on a large scale.

Short description of the work carried out

(1) Data recorded were according to the data collection plan. (2) By adjusting the wave parameters wave breaking was obtained near, at the structure and slightly beyond the structure. (3) An extensive range of regular wave tests were performed using wave heights ranging from 0.5m to 1.9m and wave periods of 3s to 5.55s. (4) The primary water depth of 4.3m was used during testing but an additional set of tests were performed at a slightly lower water level (4.1 m) to obtain conditions that broke in front of the structure. (5) Simultaneous wave profiles and wave induced forces (local and total) on the structure were measured. (6) The wave force data was recorded at 10KHz and the wave profiles at 100Hz. (7) ADV current measurements were obtained at three water depths at the location of the structure. (8) Video recorded by three cameras (one high-speed and two normal speed) with variable quality. (9) Wave run up on the structure was also recorded using the high speed video. (10)Accelerometers were placed at 4 strategic positions to measure the response of the structure during testing. (11) An additional set of structural response tests were performed using a special impulse hammer to determine the transfer function of the structure. (12) A limited range of irregular wave tests were tested due to time constraints however one specific irregular wave condition was tested for 5 different spectra to obtain some statistical information. (13) The data acquisition program was very ambiguous, and the FZK staff did an excellent job in assisting to complete within time available at the facility. (14) The instrumentation worked very well, except for one total force transducer that caused a day delay. A couple of wave gauges malfunctioned and at the end of the test program we had to run without one wave gauge. (15) Frequently the data acquisition system ran into "Block Count Error'" and stopped, with the consequence that the test had to be restarted.

Highlights of important research results

(1) The dynamics of the test structure must be taken into account when analyzing the data. (2) The recorded impact response forces depend on the location and the shape of the breaking front. (3) Methodology to extract transducer dynamics is being developed using the detailed response data collected during the impulse tests.

Publications
Christy Ushanth Navaratnam, Alf T?rum, ?ivind A. Arntsen PRELIMINARY ANALYSIS OF WAVE SLAMMING FORCE RESPONSE DATA FROM TESTS ON A TRUSS STRUCTURE IN LARGE WAVE FLUME, HANNOVER, GERMANY , 2013 Report no. BAT/MB-R1/2013. ISBN 978-82-8289-000-7 (Paper Version) ISBN 978-82-8289-001-4 (Electronic Version) Number of pages 59 Availability: Open
Ignacio Eugenio Rausa Heredia Characterization of wave slamming forces for a truss structure within the framework of the WaveSlam project , 2014 Department of Civil and Transport Engineering, Norwegian University of Science and Technology.
Alf T?rum Preliminary ANALYSIS OF FORCE RESPONSE DATA FROM TESTS ON A MODEL OF A TRUSS STRUCTURE SUBJECTED TO PLUNGING BREAKING WAVES , 2013 Norwegian University of Science and Technology, Department of Civil and Transport Engineering, Report no.: NTNU-IBAT/MB TN January 2013
Rausa, I.E.; Muskulus, M.; Arntsen, ?.A.; W?sj?, K.Characterization of wave slamming forces for a truss structure within the framework of the WaveSlam project , 2015
Jithin Jose, Olga Podrazka, Charlotte Obhrai, Ove Tobias Gudmestad Experimental Analysis of Slamming Load for Truss Structures within the framework of WaveSlam Project , 2015 University of Stavanger, UiS, Norway; University og Gdansk, Poland
Ying Tu, Thorvald C. Grindstad, Michael Muskulus Inverse Estimation of Local Slamming Loads on a Jacket Structure , 2017 Norwegian University of Science and Technology, Norway; Norwegian University of Science and Technology, Norway
Ying Tua, Zhengshun Chengb, Michael Muskulusa Global slamming forces on jacket structures for offshore wind applications , 2018 Department of Civil and Environmental Engineering, Norwegian University of Science and Technology, Høgskoleringen 7A, 7491 Trondheim, Norway; Department of Marine Technology, Centre for Autonomous Marine Operations and Systems, Norwegian University of Science and Technology, Otto Nielsens veg 10, 7491 Trondheim, Norway
Jithin Jose Offshore Structures Exposed to Large Slamming Wave Loads , 2017 Department of Mechanical and Structural Engineering and Materials Science

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