Water basin and force sensors
The tests were carried out in the Fluid Mechanics Laboratory at TU Delft. The laboratory has an area of approximately 5,000 m², 1,700 m² of which are used for carrying out experiments. There are eight water channels available for experiments which can provide a water flow of 2 cubic meters per second. De Almeida’s experiments were carried out in one of the largest water channels in the laboratory which is 42 m long, 80 cm wide and 1 m deep. At the end of the channel, there is a solid concrete block of 80 x 80 x 100 cm, on which an aluminum plate 1 cm thick is mounted using aluminum sections. Nine HBM U3 force sensors are installed in a row between the aluminum frame and the metal plate, with a range of 1.0 kN. HBM recommended that the researchers use these particular load cells because they are made from stainless steel, are not susceptible to temperature effects and are, therefore, ideally suited to the wet test setup. Moreover, they have high intrinsic stiffness, compensate for bending moments and are insensitive to lateral forces, making the measurement results highly reliable.
The sensors are linked to measuring amplifiers developed by TU Delft itself. They record the impact of waves at a sample rate of 5000/s. De Almeida can view the measurement data in real time on a monitor screen which shows the height of the waves and the impact on the structure. The setup is flexible, thereby allowing him to adjust the height of the metal plate, the dimensions of the overhang and the positions of the force sensors.
A series of regular and irregular waves are created in the water channel using a wave generator, which is equipped with active reflection compensation that neutralizes returning waves in order to not influence the measurement data. Eight sensors, which measure the characteristics of the waves, hang about forty centimeters apart in the water, a few meters in front of the metal plate. Three cameras record the images of the tests, thereby making it possible to study the associated images for special measurement results.