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 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.Esta tesis se centra en el estudio de efectos de laboratorio que tienen lugar durante la medida de impactos violentos generados por olas rompientes sobre estructuras rígidas. Para su fin, se ha llevado a cabo una extensa campaña experimental en el canal de pequeña escala CIEMito del LIM-UPC BarcelonaTech y se ha realizado más de 4000 ensayos con oleajes regulares. Se ha analizado el efecto de la frecuencia de muestreo, la tipología del sistema de medida y el layout experimental en los resultados registrados. Tras confirmar experimentalmente el comportamiento prácticamente aleatorio del fenómeno y, para poder realizar comparativas estadísticamente validas, se ha realizado un alto número de repeticiones del mismo oleaje. Se ha analizado en particular los siguientes efectos: - Frecuencias de muestreo entre 50 y 19200 kHz - Células de carga, sensores de presión y un innovador sistema táctil de medidas de presión - Seis diferentes layouts experimentales. Los máximos resultados de fuerza y presión se han medido siempre a la máxima frecuencia de muestreo y se han obtenido diferencias del orden del 150% con los ensayos muestreados a 50 Hz. La resultante medida de la fuerza en todo el ancho del canal tiende a subestimar el valor de la fuerza cuando se compara con medidas en la porción central. Aunque en valor promedio los resultados son comparables, en el caso de los sensores de presión los resultados son más dispersos en comparación con los resultados de las células de carga. El sensor táctil de presión destaca por su elevada densidad espacial (196 sensores en un área de 49cm2) pero en su contra, requiere de una calibración dinámica y un set-up particular para su utilización en agua y para que los resultados sean comparables con los de los sistemas clásicos de medida. Para este trabajo se comparó una calibración con la caída de un martillo y con la caída de un volumen controlado de agua, siendo ésta última la seleccionada para estos ensayos. Entre los resultados obtenidos se destacaque a partir de una comparativa directa entre la integral de las presiones medidas del sensor táctil calibrado y la fuerza medida en la misma área por una célula de carga, se ha evidenciado errores del orden del ±20%. El sensor táctil tiende a subestimar las presiones de pico, aunque si se consideran los valores extremos medidos, los errores son del ±10%. Se ha evidenciado también un efecto de reducción del pico de presión cuando las medidas de presión están acopladas con medidas de células de carga. Aunque no hay una alternativa perfecta para esta tipología de medidas la combinación de los tres sensores parece la mejor solución posible. Las células de carga dan un resultado directo y muy fiable de la fuerza total, pero su instalación, sobretodo en ensayos de gran escala puede ser complicada. El sensor táctil tampoco se presenta como la alternativa absoluta a los sensores de presión y se aconseja un uso combinado para ensayos que requieran más altos niveles de precisión espacial que en magnitud. Una frecuencia de muestreo entorno a 4000 Hz en ensayos a pequeña escala presenta la justa combinación entre velocidad de muestreo y cantidad de datos registrados para detectar el fenómeno impulsivo generado por el impacto violento del oleaje en estructuras rígidas. Si se considera que se ha trabajado con una escala de trabajo alrededor entre 1/50 y 1/100, se propone una frecuencia de muestreo a escala prototipo entorno a 500 Hz. El seguimiento de estas recomendaciones metodológicas permite no sólo generar unas medidas más fiables sino también permitirá una mejor comprensión/evaluación de las posibles incertidumbres en fase de ensayo y análisis de datos. Una correcta medida del fenómeno impulsivo del impacto del oleaje en estructuras rígidas aporta más fiabilidad al proyecto de estructuras rompeolasPostprint (published version

Experimental set-up and calibration errors for mapping wave-breaking pressures on marine structures

Capturing the detailed spatial variation of pressures induced by breaking waves on physical model structures has become possible using a high resolution mapping system. It can provide data with 4 measuring points/cm2, whereas the denser pressure measurements reported so far, for wave-structure interaction experiments, were limited to 0.4 pressure transducers/cm2. The paper explores the main parameters affecting the accuracy and errors of pressure data induced by laboratory set-up and system calibration. The quality of pressure maps deteriorates due to cushioning effects associated to air trapped in the sensor during manufacturing. The sensor's response is also shown to depend on the loading conditions. Non-calibrated outputs returned for impact pressures induced by impinging water-jets are more than three times smaller than the outputs recorded for static pressures, and/or for pressures developed when a material less compliant than water comes forcibly in contact with the sensor. Therefore, the calibration settings must be similar to the conditions anticipated in the experiments. To this end, a set-up and calibration methodology, designed specifically for hydraulic model tests with waves breaking on structures, are proposed and discussed in the paper.Peer ReviewedPostprint (author's final draft

LCA Sensitivity Analysis of an Energy-Biochar Chain from an Italian Gasification Plant: Environmental Trade-offs Assessment

Due to its potential applications in bioenergy production, coproducts (bio-oil and syngas), mitigation of global warming, sustainable agriculture, pollutant removal, and other uses, biochar has drawn interest from all over the world. Producing and using soil-based biochar as a method of carbon sequestration could help reduce emissions while benefiting the soil and opening up possibilities for bioenergy production. However, to characterize the production cycle’s environmental and energy loads and confirm all of the advantages of biochar, Life Cycle Assessment (LCA) represents a reliable tool for evaluation. This work is based on continuing the study of Marzeddu and Cappelli (Marzeddu, Cappelli, et al., 2021) to understand the environmental impact of an energy-biochar chain involving a gasification plant in Italy. In the LCA carried out in the previous paper for the characterization of biochar, which is used as a soil conditioner, soil carbon sequestration, nitrous oxide emissions, fertilizer use, and water use for irrigation were considered. The results showed that the use of gasification for energy and biochar is an attractive strategy for mitigating the environmental impact analysis, especially climate change, with a net decrease of about ‒8.3·103 kg CO2, eq. The previous study was lacking a sensitivity analysis. For this reason, a sensitivity analysis is proposed in this study to consistently assess the environmental trade-offs of the biochar and the amended soil. In specific for the upstream processes the sensitivity is addressed to the selection of a different type of woodchips, for the core process in terms of selection of different packing material, and to the entire cradle-to-grave perspective by improving the logistics of the transportation, the distances within the supply chain and the choice of BAT technology for the transportation vehicles. This study highlights strategic research developments that combine to find potential environmental trade-offs and thresholds towards using biochar and its final use as a soil conditioner

Impulsive wave loads on rigid structure, an experimental approach

Within the European project ‘Hydralab IV’, HyRes we aim to improve the characterization of wave loads on rigid structures and the associated response by carrying out some laboratory experiments. Wave loads on rigid structures are divided into quasi static loads and impact loads. If the physics of quasi-static loads due to waves is well known, this cannot be said the same for wave impact loads. A comprehensive method to design maritime rigid structures under impact loads does not exist yet and the actual design method suggests avoiding scenarios where impact loads can take place. In the last decade, some laboratory experiments have been carried out; however some questions remain still unanswered. The use of different sensors can lead to significant changes in the results and an “exhaustive comparison” between dissimilar types of sensors has not been done yet. Even the magnitude of these forces can be underestimated during a laboratory test just for the choice of sample frequencies which are too low. This paper describes the experiments performed on a small scale flume at UPC on a scaled vertical breakwater in order to compare the results of pressure transducers and force load cells. Moreover, a high frequency sampler (up to 20 KHz) was used in order to understand the importance of sample frequency on the magnitude of the results. A simplified scenario has been set up in order to make the data analysis easier.Postprint (published version

Measuring wave impact induced pressures with a pressure mapping system

The use of a pressuremapping system formeasuring wave impact induced pressures is evaluated in this paper. A set-up and a calibrationmethodology are suggested and employed for thiswork. The system is validated against pressure transducer and load cell measurements and for a range of waves breaking on a vertical seawall. For a large number (120 measurements for each case considered) of breaking and broken waves interacting with the wall, the peak pressure (Ppeak) profiles and the pressure distribution maps reported by the system agree wellwith results acquired using pressure transducers. Although the pressuremapping system tends to underestimate Ppeak, differences on themean of the 3, 5 and 10 highest Ppeak rangewithin±10%, while for themajority of the measurements the error on the integral of the acting pressures (the acting force compared with the force measured by the load cell) ranges within ±20%. It is concluded, that through careful calibration and set-up the pressure mapping system has the capacity to provide pressure distribution maps with a good accuracy. It is not, however, considered to constitute the absolute alternative to pressure transducers and thus a combined use is suggested for applications where a very high level of accuracy is required.Postprint (author's final draft

LOS PÉREZ. LUGAREJO, LAS HOYAS, SIBERIO, PARRALILLO [Material gráfico]

Copia digital. Madrid : Ministerio de Educación, Cultura y Deporte, 201

Indagine sperimentale sui processi di trasmissione di energia e massa a tergo di barriere frangiflutti a porosità controllata

Postprint (published version

Impulsive wave loads on rigid structure, an experimental approach

Within the European project ‘Hydralab IV’, HyRes we aim to improve the characterization of wave loads on rigid structures and the associated response by carrying out some laboratory experiments. Wave loads on rigid structures are divided into quasi static loads and impact loads. If the physics of quasi-static loads due to waves is well known, this cannot be said the same for wave impact loads. A comprehensive method to design maritime rigid structures under impact loads does not exist yet and the actual design method suggests avoiding scenarios where impact loads can take place. In the last decade, some laboratory experiments have been carried out; however some questions remain still unanswered. The use of different sensors can lead to significant changes in the results and an “exhaustive comparison” between dissimilar types of sensors has not been done yet. Even the magnitude of these forces can be underestimated during a laboratory test just for the choice of sample frequencies which are too low. This paper describes the experiments performed on a small scale flume at UPC on a scaled vertical breakwater in order to compare the results of pressure transducers and force load cells. Moreover, a high frequency sampler (up to 20 KHz) was used in order to understand the importance of sample frequency on the magnitude of the results. A simplified scenario has been set up in order to make the data analysis easier

Impulsive wave loads on rigid structure, an experimental approach

Within the European project ‘Hydralab IV’, HyRes we aim to improve the characterization of wave loads on rigid structures and the associated response by carrying out some laboratory experiments. Wave loads on rigid structures are divided into quasi static loads and impact loads. If the physics of quasi-static loads due to waves is well known, this cannot be said the same for wave impact loads. A comprehensive method to design maritime rigid structures under impact loads does not exist yet and the actual design method suggests avoiding scenarios where impact loads can take place. In the last decade, some laboratory experiments have been carried out; however some questions remain still unanswered. The use of different sensors can lead to significant changes in the results and an “exhaustive comparison” between dissimilar types of sensors has not been done yet. Even the magnitude of these forces can be underestimated during a laboratory test just for the choice of sample frequencies which are too low. This paper describes the experiments performed on a small scale flume at UPC on a scaled vertical breakwater in order to compare the results of pressure transducers and force load cells. Moreover, a high frequency sampler (up to 20 KHz) was used in order to understand the importance of sample frequency on the magnitude of the results. A simplified scenario has been set up in order to make the data analysis easier