Measuring impact loads on rigid coastal structures
The aim of this work is the study of laboratory effects on the measurement of wave impact induced loads on rigid maritime structures. A high number of experiments (more then 4000 using regular wave attacks) have been carried out in the small scale wave flume "CIEMito" in the laboratory of...
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| Tipo de recurso: | tesis doctoral |
| Estado: | Versión publicada |
| Fecha de publicación: | 2016 |
| País: | España |
| Institución: | CBUC, CESCA |
| Repositorio: | TDR. Tesis Doctorales en Red |
| OAI Identifier: | oai:www.tdx.cat:10803/393926 |
| Acceso en línea: | http://hdl.handle.net/10803/393926 https://dx.doi.org/10.5821/dissertation-2117-96334 |
| Access Level: | acceso abierto |
| Palabra clave: | Àrees temàtiques de la UPC::Enginyeria civil 004 620 624 69 |
| Sumario: | The aim of this work is the study of laboratory effects on the measurement of wave impact induced loads on rigid maritime structures. A high number of experiments (more then 4000 using regular wave attacks) have been carried out in the small scale wave flume "CIEMito" in the laboratory of the LIM-UPC BarcelonaTech. The effects on the results of sample frequency, measurement systems and experimental layout has been deeply studied. A high number of repetitions of the same wave attack has been performed in order to have statistically robust results since the almost-random behavior of the studied phenomenon. -Sample frequencies from 50 to 19200 Hz - Load cells, pressure transducers and an innovative tactile pressure map - Six different experimental layouts effects have been tested The maximum results of force and pressures have been always measured at the maximum sample frequency. Differences of the 150% has been found between the measurements at 50 and 19200 Hz. The total load measured considering all the width of the flume tends to sub estimate the total force measured only in a slice in the middle of the flume. Even if the average value is comparable, the pressure transducers tends to return much spread results than the load cells. The tactile pressure mapping system stands out for his very high spatial density (196 sensels in a 49cm2 area) but an experimental specific calibration and an ad-hoc set-up are necessary for the utilization with water and in order to can collect reliable results comparable with the classic measurement systems. For this work 3 types of calibration methodology have been compared: static, instrumented pendulum and water jets. The last has to be considered the best choice and the selected for the definitive tests. Among all the results the ones to be highlighted are: the integral of pressures (the force applied over the whole sensor) acting on the tactile sensor differ from simultaneous load cell measurements by less than ±20%. The pressure mapping system tends to underestimate the pressure peak. However, if the average values of the 3, 5 and 10 highest peaks are considered they differ by up to ±10%. Has been shown a reduction effect of the pressure peak when pressure measurement systems are coupled with load cells. A perfect set-up for these kind of measurement hasn't found yet but the combination of the three measurement systems seems to be the best possible solution. Load cells return a direct and reliable result of the total load, but the set-up could be complicated especially at large scales. The pressure mapping system neither seems to be the perfect alternative to the pressure transducers and a combined use is suggested for these experiments that require a high level of precision both in space and magnitude. A sample frequency around 4000 Hz, for small scale experiments, present the right combination between sample density, memory storage and added signal noise for the correct characterization of the impulsive phenomenon of the wave generated violent impact loads on rigid structures. Considering a working scale in between 1/50 and 1/100, a frequency of 500Hz is proposed for measurement at full scale. Following these methodologic recommendations not only will permit better and more reliable measurement but also will permit a better comprehension/evaluation of the test and analysis uncertainties. In this manner it will be possible to extrapolate, in a reliable way, scale test results to the design process of breakwaters. |
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