This section covers our basic research in fluid mechanics. We mainly deal with vortex induced vibration on simple shaped bodies. Vortex-induced vibrations are caused by periodic vortex shedding from a body that has some free to move or deform. The mutual interaction between fluid and body modifies the properties of the vortex shedding (with respect to the case of the fixed body in the flow), giving rise to oscillations that are substantially different from classical resonance. Real examples of vortex-induced vibrations occur on overhead and marine cables, risers, stacks, tall buildings and in many other engineering applications.

These oscillations can be very dangerous and their prevention or suppression is of practical interest. We are investigating the elastically mounted cylinder and the tethered sphere in air and water. The motion of the body, the flow-induced forces, the flow field around the body are measured in order to have a complete description of the phenomenon.

Moreover, we have dealt with flow around bluff bodies; in particular, we have studied the flow around a rectangular cylinder, focusing on the effects that flow confinement, such as wall and free surface, have on the flow structure and flow-induced forces. This work took his motivation from the problem of bridge loading during flood condition.

Particle streak velocimetry (PSV) is used to measure flow velocity: this technique allows to obtain instantaneous velocity fields, by capturing long exposed images of the flow with a CCD. The portion of interest of the flow is enlighten with a light sheet and seeded with particles, which track their streaks of the images. The technique was entirely developed here at Politecnico di Milano. Fluid forces on bodies are measured through a balance, specially built for fluid dynamic models.

Parallel to the experimental tests, numerical simulations are performed. Fluid-structure interaction is addressed through CFD simulation and co-simulation of CFD (computational fluid dynamic) and FEM (finite element method). In particular co-simulation allows the step-by-step calculation of flow field and body deformation according to the force exerted by the fluid. Simulations give a better understanding of the whole mechanism involved in the process and they let to extend the experimental test condition..

*Selected publications*

*Selected publications*

- Negri M, Mirauda D, Malavasi S, 2018. VIV trajectories of an elastically mounted sphere. Applied Ocean Research, 70, 62–75.
- Mirauda D, Negri M, Martinelli L, Malavasi S, 2018. Influence of boundary conditions on the hydrodynamic forces of an oscillating sphere. EPJ Web of Conferences, 180, 02067.
- Mirauda D, Volpe Plantamura A, Malavasi S, 2014. Dynamic response of a sphere immersed in a shallow water flow. Journal of Offshore Mechanics and Arctic Engineering, 136, 021101-1-021101-6.
- Ardito R, Perotti F, Mandelli S, Novarina D, Malavasi S, 2014, Fluid-Structure Interaction and Co-Simulation: Analysis of a Beam-supported Sphere for VIV application, PVP 2014.
- Mandelli S, Malavasi S, Muggiasca S, 2013, Numerical Simulation of an Oscillating Cylinder at High Reynolds Number, OMAE 2013.
- Arslan T, Malavasi S, Pettersen B, Andersson H.I, 2013, Turbulent Flow Around a Semi-Submerged Rectangular Cylinder, Journal Of Offshore Mechanics And Arctic Engineering-Transactions Of The Asme, Vol. 135, pp. 1-11.
- Zappa E, Malavasi S, Negri M, 2013, Uncertainty budget in PSV technique measurements, Flow and Measurements Instrumentation. 30, pp. 144 – 153.
- Malavasi S, Blois G, 2012, Wall effects on the flow structure around a rectangular cylinder. MECCANICA Vol. 47, pp. 805 – 815.
- Malavasi S, Corretto R, Fossati F, 2011, PSV and marker detection techniques for the wake investigation of an oscillating cylinder in a wind tunnel, Flow and Measurement Instrumentations, 22, pp. 428 – 437.
- Mirauda D, Volpe Plantamura A, Malavasi S, 2011, Boundaries effects on the movements of a sphere immersed in a free surface flow, Journal Of Offshore Mechanics And Arctic Engineering-Transactions Of The Asme, Vol. 133, pp. 1-5.
- Negri M, Cozzi F, Malavasi S, 2011, Self-synchronized phase averaging of PIV measurements in the base region of a rectangular cylinder. Meccanica, Vol. 46, pp. 423 – 435.
- Malavasi S, Guadagnini A, 2007, Interactions between a rectangular cylinder and a free-surface flow, Journal of Fluid and Structures, Vol. 23, pp. 1137–1148.

**Vortex Induced Vibration Energy (VIVE)**

**Vortex Induced Vibration Energy (VIVE)**

Vortex-induced vibrations (VIV) have recently being studied under the point of view of the energy harnessing: the movement of a body induced by vortex shedding can be exploited to generate clean electricity. In this perspective, VIV should be enhanced rather than suppressed (VIV are normally very dangerous for structures). We are experimentally testing an elastically mounted sphere undergoing VIV in a water flow, with a particular kind of power take-off inside it, which produces electric energy.

*Research Projects*

*Research Projects*

- 2005/07 “Flow induced vibration on flexible structures” - PRIN2005 project.