Optical measurement techniques are becoming more and more important for MARIN and its customers.


Optical measurement techniques lead to highly acc deformation measurements


between the measuring sensor and the measured object, which is therefore not being “disturbed”. This opens the door to new measurement possibilities where complexity and high precision are key.


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The use of cameras or lasers to obtain quantitative data is not a new concept (see PIV article in this issue); however, both the interest in these technologies and their possibilities are growing rapidly. A good example are autonomous vehicles, where optical measurements are used to scan the surroundings in real time and are the core of the object detection and collision avoid- ance systems.


We are actively involved in the development of optical measurements and their application for the maritime and offshore industries: these techniques have been applied to measure flow speeds (e.g. ship wake fields) using PIV, ship motions during operations, wave surfaces and deformations of objects using image correlation techniques, amongst others.


Gert-Jan Zondervan & Nicola Grasso


g.j.d.zondervan@marin.nl 16 report


An example application is the deformation of the flexible blades of composite ship propellers or those of energy harvesting tidal turbines. The dynamics of these blade


he main advantage of such measurement techniques is the absence of a physical contact


deformations under hydrodynamic loading is complex, involving simultaneous bending and twisting of the blades. This dynamic behaviour is important information and can be used to improve designs. For instance through (local) relieve of hydrodynamic load on propellers due to twisting and bending of its blades. For ship propellers this could lead to the reduction of cavitation nuisance (i.e. noise and vibrations) without efficiency being affected, as commonly seen for conventional metal propellers. For tidal turbines the load relief behaviour can be exploited to increase the total energy yield of these devices. Experimental investigation of the hydro- elastic behaviours of such blades is needed in a carefully controlled experimental environ- ment to validate the results of numerical simulations and to explore the potential benefits and desired behaviour of these flexible blades. Being able to determine the dynamic deformations is a great challenge.


In recent years we have developed and applied a method for measuring deformations based on Digital Image Correlation. DIC is a full-field image analysis method that uses the image data collected by a stereo-camera system to measure displacements and deformations of objects in the three dimen- sional space. This optical technique can be used in multiple applications, including the deformation measurement of flexible propellers.


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