[MUSIC] Hello, and welcome to our Fluid Structures Interaction Lab. In that session, we are going to focus on added mass and added damping. As you have seen in lectures, both can significantly effect the dynamics of a solid moving in a fluid domain. In the first experiment we will use the most simple oscillator, an aeroelastic added mass and then we will compare its dynamics in air and in water. In the second experiment we will use a hanging ribbon free to move in air or in vacuum. Let's now move to our first experiment. Here is a set up. As you can see, it is a simple spring-mass oscillator, with a small cylinder of mass close to 100 gram, diameter 5 centimeter, and height 2 centimeter, suspended to a linear spring of stiffness close to 50 newton per meter. In order to track the motion of the mass an unsteady force sensor is mounted between the hanging arm and the spring. It directly measures the restoring force which is proportional to the mass vertical displacement. For the experiment in water, we use a water tank, with size dimension close to 3.5 times the diameter of the oscillating mass. We then expect a non-negligible increase of the added mass in this confined situation. Let's now look at the behavior of the system in air and in water. In both cases, we perform a free decay test. The system is displaced from its equilibrium position and then free to oscillate. Two effects are visible. First, the frequency of oscillation is smaller in water. Second, the system is more damped in water than in air. To quantify those effects, one can analyze the temporal displacement in air, black color, and in water, the blue one. A spectral analysis gives us an oscillating frequency of 3.38 Hertz in air and 2.75 Hertz in water. Using those frequencies and the stiffness of the systems, one then finds that the added mass is 1.35 times the mass of an equivalent volume of displaced water. Concerning the damping, those results also show that the damping coefficient is ten times higher in water. Let's now to move to our second experiment. You can see in this picture a hanging ribbon of length 250 millimeter, width 12 millimeter and thickness, 0.1 millimeter. For mass, close to 1.9 gram per meter. For this experiment, we would focus on the motion of the ribbon, free to oscillate in air or in vacuum, after an initial perturbation. The motion will then be captured using a fast camera and the vacuum will be set using a vacuum bell jar, and pump system. Let's see what's going on. To the left, the ribbon is free to oscillate in here at atmospheric pressure. To the right, the ribbon oscillates in the relative vacuum of 4% of the atmospheric pressure. We clearly notice a strong damping effect in here, where the added mass impact on the frequency of oscillations, seems to be negligible. Let's take a deeper look. Here is a temporal displacement of the ribbon at 75% of it's length. In vacuum black color, and in air the blue one. One can then identify that the damping coefficient is four times lower in the vacuum configuration. But also that the oscillating frequency of the ribbon, it's 5% lower at the atmospheric pressure. This frequency effect is due to added mass in air, which in this situation is rather small, compared with the mass of the ribbon. Indeed, the theoretical added mass per unit length associated to the cross section of the ribbon is close to 6% of the mass per unit length of the ribbon. In summary we have seen that added mass and added damping effect are important for solid moving in water. In air, the added mass effect can generally be neglected unless you work with a solid of very low density. This experimental session is now over. Thank you, and see you soon. [MUSIC]