10:30
Advanced experimental techniques
Chair: Simen Ådnøy Ellingsen
10:30
30 mins
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THE APPLICATION OF PARTICLE IMAGE VELOCIMETRY FOR THE ANALYSIS OF HIGH-SPEED CRAFT HYDRODYNAMICS
Gunnar Jacobi, Cornel Thill, Rene Huijsmans
Abstract: The particle image velocimetry (PIV) technique has become a reliable method for capturing the velocity field and its derivatives, even in complex flows and is now also widely used for validation of numerical codes. As the imaging system is sensitive to vibrations, the application in environments such as towing tanks makes it a challenging task. Especially when operating the towing tank carriage at higher speeds structural vibrations increase significantly. However, to apply this technique for the analysis of planing and semi-planing vessels, this is absolutely necessary. To assess the ability of a PIV system to capture the flow features close to a ship model while being towed at high speeds, a stereo PIV system was installed in the TU Delft towing tank. Measurements are conducted in the transom region of a generic high-speed vessel hull with a flat bottomed aft section, which is equipped with an interceptor at the transom. It is shown that with increasing carriage speed, vibrations of the imaging system increase, which ultimately can affect the quality of PIV recordings. The effect of vibrations is quantified by analysis of successive recordings and based on this, a shift correction is applied. A comparison with numerical results shows that the flow around the interceptor is well captured by the PIV system.
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11:00
30 mins
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EXPERIMENTAL VERIFICATION OF WALL SHEAR STRESS MEASUREMENT WITH MEMS SENSORS ARRAY FOR UNDERWATER APPLICATIONS WITH FLAT PLATE BENCHMARK TESTS
Tian Yu Kui, Shen Xue, Sun Hai Lang, Zhang Xuan, Xie Hua, Zhang Nan
Abstract: Underwater wall shear stress measurement based on a newly developed MEMS sensors array is experimentally verified by means of a set of flat plate benchmark tests conducted in a precision water flume. The array consisting of 8 MEMS sensors is firstly calibrated in a well defined 2D flow and then flush embeded on the plate surface at the location centred 80% chord to measure WSS directly. The local freestream velocities ranging 0.1m/s to 0.7m/s are adopted for the test cases of naturally developing flow and deliberately stimulated turbulence. The boundary layer profiles of the investigated area upon the plate surface are correspondingly detected with LDV and mean WSS values are extrapolated from suitable fits to known profile shapes for flat plate with a zero pressure gradient. The results from the MEMS sensors match well with those from the LDV velocity profile fits and are in good agreement with empirical estimations with an overall bias less than 5% when compared in combination, as well, the direct simutaneous measurements from multiple sensors on the MEMS array favorably exibit the streamwise variation of the wall-bounded flow. Generally the MEMS sensors array based underwater wall shear stress measurement is characterized of desirable accuracy and spatial resolution for further practical applications.
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11:30
30 mins
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WAVE-INDUCED TEMPERATURE PROFILE EVOLUTION OF A FROZEN SAND BOTTOM AND ITS EFFECT ON EROSION
Maciej Paprota, Wojciech Sulisz, Dawid Majewski
Abstract: ABSTRACT
Novel and original experiments are conducted to study the problem of evolution of temperature profile of a frozen sand bottom layer under wave action. The study is a part of a comprehensive laboratory investigation of wave-induced erosion of permafrost in context of climate changes undertaken within the framework of the ARCOASTS project [1, 2]. A model of a frozen sand layer is prepared and installed in a separated and insulated section of a wave flume, where temperature of water is decreased to simulate polar conditions. The model is exposed to waves of selected parameters and different thermal conditions. Exact and precise measurements of a wave field and temperature profiles of water and frozen soil are used to recognise physical processes leading to enhanced warming of the frozen sand bottom under the action of waves. The set of temperature sensors is installed in the wave flume to measure the thermal response of the frozen sand under different wave conditions generated by the wavemaker motion. The temperature distribution in the sand layer and in the water column is a key parameter affecting wave-induced erosion of the frozen sediments. The results from laboratory experiments indicate that water waves not only induce sediment transport of the sandy layer but most importantly affect the thawing of the frozen sand. A faster increase of sand temperature under the wave action makes the sand more vulnerable to erosion.
ACKNOWLEDGEMENTS
The research leading to these results has received funding from the Polish-Norwegian Research Programme operated by the National Centre for Research and Development under the Norwegian Financial Mechanism 2009-2014 in the frame of Project Contract No. POL-NOR/200336/95/2014.
REFERENCES
[1] A. Reda, W. Sulisz, D. Majewski, M. Paprota, and M. Szmytkiewicz, "Application of a new approach for modeling coastal erosion in Arctic areas", Proc. of the 2nd International Workshop on Hydraulic Structures: Data Validation. Red. Rita F. Carvalho, Stefano Pagliara, Coimbra, Portugal, University of Coimbra, pp. 217-221, (2015)
[2] W. Sulisz, M. Szmytkiewicz, D. Majewski, M. Paprota, A. Reda, "A new approach for the prediction of coastal erosion in Arctic areas", Proc. of the 9th Symposium on River, Coastal and Estuarine Morphodynamics, At Iquitos, Peru, (2015)
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