An optical instrument based on defocusing for dynamic response model testing in water or wind tunnels

• The optical technique allows non-intrusive accurate measurements of the dynamics of solids.
• The tool has many advantages if compared to traditional measurement methods.
• Test model preparation and design can be very simple if this tool is used.
• Validation is done by measuring the rigid body motions of a spar floater in a water tank.

The design and performance of an optical measurement system that can be used for studying the three-dimensional dynamic response of flexibly mounted rigid or elastic bodies in laboratory facilities is presented. The photogrammetric technique implemented on the instrument is based on the defocusing principle, which was first introduced for three-dimensional (3D) robotic vision applications. The technique was later on applied for the measurement of seeded 3D flow velocity fields. The emphasis of this work is given to the design of the tool itself as well as to its validation by using an application that involves the dynamics of a spar floater in a water tank. The final purpose of this work is to produce a non-intrusive and accurate instrument for measuring the fluid-induced responses or deformations of bodies in laboratory facilities. The result is an optical tool that provides an accurate and better alternative to other traditional dynamic response measurement techniques used to study vortex-induced vibrations (VIV), wave-induced motions (WIM), etc. in water or wind tunnels.