Laboratory technologies I

Understanding marine dynamics, particularly in coastal areas with high wave activity, cannot be achieved without physical modeling. However, when it comes to downscaled physical wave modeling, accurately recording wave data becomes a challenge, especially near coastlines where disturbances are common. To overcome the both inaccurate and impractical limitations, this study presents a new data acquisition system (DAQ) utilizing resistive sensors and wireless transmission protocols to enhance the accuracy of wave measurements in laboratory-scale experiments. 
The data acquisition technology effectively measures water surface electric potential by utilizing specialized resistive probes. The recorded data is efficiently handled by Arduino® board controllers, allowing for convenient wireless transmission for laboratory usage. This exceptional system surpasses traditional methods, offering a combination of versatility, cost-efficiency, and enhanced accuracy in capturing wave characteristics. This study highlights their seamless integration into a unified solution for superior wave data collection.

The effect of vegetation on sediment dynamics gains increasing attention for coastal protection. To assess these effects, laboratory experiments with live or artificial vegetation are widely applied. A major challenge in such experiments lies in the measurement of bed level and bedforms since standard optical and acoustic measurement techniques cannot obtain data below vegetation canopies. 
Here, we tested underwater photogrammetry and an adapted sediment-erosion-bar (SEB) for the assessment of sediment dynamics in and around an artificial seagrass meadow. First results show that SEBs are capable of obtaining data even within dense vegetation, however, they indicate limitations in SEB accuracy due to pin dimensions and sinking into soft sediment. Underwater photogrammetry showed first promising results regarding bed level detection outside the meadow, but failed to obtain data within the dense meadow. Both methods are potential alternatives to existing bed level measurement techniques, provided that their individual limitations are considered.

The influence of directional spreading of waves is significant for wave-induced loads, wave breaking and nonlinearity of the waves. For physical model testing performed at test facilities such as the Ocean and Coastal Engineering Laboratory at Aalborg University, it is crucial to validate if the test conditions match the target sea states by measurement and analysis of the generated directional wave field. Examples of phenomena that often occur in the laboratory, but seldom are included in the mathematical model for directional spectrum estimation are reflections and cross modes. These will contribute with additional directions in the sea state, that existing methods struggle to handle. The current study will present a new extension of an existing method applicable for waves generated from the single summation method. The new method allows for separation of oblique reflections, which is not yet covered by the existing methods.