Hydraulic structures are essential for flood protection, water management and navigation in coastal, delta and lake regions. Their importance will continue to grow in the coming years and decades, because of two main factors. Firstly, because of the consequences of climate change and sea level rise. Secondly, because of the continuous development and urbanization of coastal, delta and lake regions, with an increase in the value of the assets and activities in those locations combined with more strict safety requirements. Those factors will lead to the construction of a series of new hydraulic structures and the renovation of several existing structures around the world.

Wave loads acting on such hydraulic structures are crucial for their design and safety assessment. This study addresses two different types of wave loads acting on hydraulic structures: confined wave impact loads and bimodal wave loads. To this end, a series of laboratory experimental test campaigns were carried out in a wave flume. ... Read more

Hydraulic structures are crucial for navigation, water management and flood protection in low-lying coastal and delta regions. Their importance is expected to continue growing in the coming years, because of the consequences of climate change and the continuous development and urbanization of these regions combined with more strict safety requirements. These factors will lead to the construction of a series of new hydraulic structures around the world. In addition, existing hydraulic structures will be renovated after reaching the end of the envisaged design lifetime, and/or due to the previously described modification of load conditions and/or safety standards. Wave loads play a significant role in the stability of these hydraulic structures and a knowledge gap was identified regarding the characterization of confined wave impacts acting on vertical hydraulic structures with overhangs. For this type of wave impact, no validated load prediction method or design approach was previously available. This research addresses this knowledge gap, providing an experimentally calibrated load prediction model and a design approach for characterizing confined wave impact loads acting on vertical hydraulic structures with overhangs. ... Read more

For the design of vertical hydraulic structures pulsating wave forces need to be calculated. The total wave force is a result of every wave component (long waves and short waves) within a wave field. The common formulae are derived for regular or unimodal narrow sea states and use one characteristic wave height and period. Broad-banded spectra like bimodal sea states are present at many locations. Moreover, new hydraulic structures like Panamax or post-Panamax locks do have a large vertical surface exposed to pulsating wave loads. Swell components within the wave spectrum are disproportionally contributing to the total wave force compared to short waves. This depth effect for broad-banded or bimodal wave spectra is not considered by the traditional wave formulae which could result in significant underestimations of wave forces on hydraulic structures. This paper aims to determine the wave loads of irregular non-breaking wave fields under any wave spectrum: narrow banded, broad-banded, or bimodal. Spectral linear wave theory (LWT) is used to transform any wave spectrum to a wave force spectrum. The wave force or wave pressure at any level can directly be evaluated from the wave force spectrum or wave pressure spectrum for any shape of the wave spectrum considered within this research. Spectral LWT is compared to the outcome of wave flume experiments with bimodal seas and other wave force formulae, like the Goda formula and quasi-regular LWT and the NewWave theory. This paper gives a description and evaluation of the spectral LWT applied for bimodal wave spectra and a comparison of the accuracy and validity of other wave force formulae. The peak forces and peak pressures distribution obtained by spectral wave theory compare well to the measurements. It appears that the use of a spectral LWT to obtain characteristic extreme forces improves the accuracy of the extreme load more than the use of a second order wave model with a quasi-regular assumption (i.e. where the spectral shape is not considered). For the typical conditions that occur at hydraulic structures (horizontal bed, intermediate to deep water, non-breaking, and uni- and bimodal seas) the often-used Goda formula can both under of overestimate the peak loads. Goda is well applicable for conditions with (breaking) waves narrow wave spectra and values of kph <0.5. ... Read more

This study focuses on standing wave impacts on vertical hydraulic structures with relatively short overhangs. It addresses the demand for extended knowledge and loading prediction expressions for these structures. Based on laboratory experimental data from 146 tests, this paper works on two complementary objectives. Firstly, this study extends the knowledge on this type of wave impacts addressing the following aspects: changes in hydraulic loading conditions (regular/irregular waves and varying freeboards) and changes in the structure geometry (lateral constriction and loading reducing ventilation gaps). All laboratory tests consider relatively short overhangs, with ratios of wave length to overhang length between 10 and 40, and ratios of overhang height to overhang length of 3 and 6. The regular wave tests showed that the tests with the longer overhang were related to longer impact durations and larger loading variability compared to the tests with the shorter overhang. Also, tests with reduced freeboards produced larger impact loads. In addition, repeated tests presented equal impulse values (I, Beta, td, Lambda). Furthermore, the pressure peaks measured at one location were found to not represent the pressure peaks averaged over the structure width, while the pressure-impulses measured at one location were found to properly represent the pressure-impulses averaged over the width. The constriction tests showed that a lateral constriction amplifies pressure peaks and pressure-impulses at the constriction edge. The ventilation gap tests showed that ventilation gaps are effective in reducing force peaks and force-impulses. The irregular wave tests highlighted that the dynamic interactions of the incident waves with the structural configurations are even more dynamic and variable in tests with irregular wave conditions. Secondly, this study presents loading prediction expressions for preliminary loading estimations built up by the previously developed pressure-impulse theory that is empirically calibrated using the presently acquired experimental data. To that end, the relation between the effective bounce-back factor (1<Beta<2) with the Gamma Parameter is described. These loading prediction expressions may be used for preliminary load estimations and in combination with structural response models. ... Read more

In this paper the development of a high-power pulsed LED line light and its use to apply particle image velocimetry (PIV) during wave impact measurements are described. An electrical circuit that generates high-current pulses is designed and built, which is used to overdrive a number of commercially available LEDs. The limit for this overdrive-capacity is determined as function of pulse duration for various commercial available LEDs. Two systems of cylindrical convex lenses are designed to act as a collimator and reduce divergence of the LED bundle and the resulting light sheet properties (maximum light intensity and sheet thickness) are investigated. An array of LEDs of 60 cm length (referred to as the LED line light) is designed and manufactured. For the two lens systems, the LED line light provides proper light sheet conditions to illuminate measurement regions in the order of either 0.3 × 0.3 m ², or 1 × 1 m ², at a sufficiently constant light sheet thickness of 5 mm. The application of the LED line light is demonstrated by quantifying the instantaneous flow field of a wave impacting on a blunt object in a wave flume. PIV measurements are conducted at an acquisition rate of 25 frame pairs per second, quantifying maximum flow velocities in the order of 1.0 m s ^-1 at a LED pulse width of 200 µs. The system, consisting of the LED line light, a CMOS camera and open source PIV processing software provides the possibility to perform 2D planar PIV measurements for a fraction of the costs of a commercially available laser based PIV system. ... Read more

This paper establishes a computationally efficient model to predict flood gate vibrations due to wave impacts including fluid–structure interaction. In contrast to earlier models, composite fluid domains are included to represent the situation of a flood gate in a dewatering sluice with the presence of an overhang that causes the confined-wave impacts. The dynamic response of the gate-fluid system is derived in the frequency domain using a substructuring mode matching technique, in which the gate vibrations are first expressed in terms of in-vacuo modes while the liquid motion is described as a superposition of linear potentials. Pressure impulse theory is employed to predict the impulsive wave impact loads, which are superposed on the quasi-steady wave loads. The computational efficiency of the developed model allows for a large number of simulations. This makes it possible for the first time to perform probabilistic evaluations for this type of problems without doing concessions on the accuracy of the physical modelling of the involved fluid–structure interaction processes. This is demonstrated by application of the developed models within a probabilistic framework resulting in the explicit quantification of the failure probability of flood gates subjected to wave impacts. ... Read more

This study focusses on increasing the understanding on vertical hydraulic structures with relatively short overhangs subjected to standing wave impacts. To this end, the impact velocity and the entrapped air are studied in detail, given their influence on the impulsive loading characteristics and consequently on the structural dynamic response. This study is based on regular wave laboratory experimental data obtained for relatively short overhangs with respect to the wave length and with respect to the overhang height. The laboratory tests illustrate the complex wave hydrodynamics before the wave impacts, influenced by the incident wave conditions and structural characteristics. Regarding the impact velocity, the experimental measurements with a wall wave gauge in the tests without overhangs show that the maximum upward velocities deviate from linear wave theory between +5.5% and +13.0%, while the zero-crossing upward velocities deviate from linear wave theory between +1.9% and +7.0%. The zero-crossing upward velocities estimated from third order wave theory deviate from the linear wave theory between +1.8% and +4.7%. In the tests with overhangs, the maximum upward velocity below the overhang estimated by camera recording measurements deviates from linear wave theory between −11.8% and +13.4%. It was also found that when considering the experimental impact velocity from camera recordings in the tests with overhangs, the mean effective bounce-back factor β deviates relatively little from when linear wave theory is used (≈1%), while the uncertainty described by the standard deviation increases significantly (≈35%). Regarding the entrapped air, it is shown that the interaction between incident wave parameters and structural configurations leads to a large variation in the entrapped air area, up to a factor of 5.7 for shorter overhangs and a factor of 9.5 for longer overhangs. This variability in entrapped air characteristics leads to significant effects on the loading on the structure, as observed by the variability on pressure measurements. The experimental results showed increasing impact durations and increasing effective bounce-back factor β in the tests with increasing entrapped air dimensions. This study highlights the importance of the details of the impact velocity and entrapped air for load estimations during the design of vertical hydraulic structures exposed to standing wave impacts. This is particularly important for thin structures such as steel gates which are susceptible to a dynamic behaviour under such impulsive loads. ... Read more

The applicability of pressure-impulse theory is evaluated for predicting wave impact loading magnitudes for non-breaking standing wave impacts on vertical hydraulic structures with relatively short overhangs. To this end, tests were carried out on a schematized but realistic configuration with low steepness regular wave impacts on a straight overhang perpendicular to a vertical wall. This paper aims to fill the existing knowledge gap on this type of wave impact with reliable and simple expressions. Pressure-impulses and force-impulses are the wave impact loading magnitudes considered in this study, which are defined as the integral of the impulsive pressures/forces over time during a wave impact. These impulses can be used to determine the resulting stresses in a structure for sudden, impulsive loads. The proposed theoretical model is based on the pressure-impulse theory and validated with laboratory experiments. The laboratory tests are done with regular waves for relatively short overhangs, with ratios of wave length to overhang length between 12.1 and 43.6, and ratios of overhang height to overhang length of 3 and 6. Thus, the theory is verified for conditions where the wave impact takes place along the full length of the overhang. From the experimental results, a mean effective bounce-back factor β=1.17 is obtained, accounting for the bounce-back effect of entrapped air and other secondary sources of discrepancies between theoretical and experimental results. The standard deviation of β for all the different tests is σβ=0.11. This method seems suitable for carrying out preliminary loading estimations, including the pressure-impulse profile at the wall and the total force-impulse at the wall. This study also shows that the force-impulse is a more stable magnitude compared with the force peaks, with about half the relative standard deviation. The impulses predicted by this model are recommended to be coupled with fluid-structure interaction models for analysing the response of the loaded structure. ... Read more

Physical model tests were performed in a wave flume at Deltares with rock armoured slopes. A shallow foreshore was present. At deep water, the same wave conditions were used, but by applying different water levels, the wave loading on the rock armoured slopes increased considerably with increasing water levels. This allowed an assessment of the effects of sea level rise. Damage was measured by using digital stereo photography (DSP), which provides information on each individual stone that is displaced. Two test series were performed five times. This allowed for a statistical analysis of the damage to rock armoured slopes, which is uncommon due to the absence of statistical information based on a systematic repetition of test series. The statistical analysis demonstrates the need for taking the mean damage into account in the design of rock armoured slopes. This is important in addition to characterising the damage itself by erosion areas and erosion depths. The relation between damage parameters, such as the erosion area and erosion depth, was obtained from the tests. Besides tests with a straight slope, tests with a berm in the seaward slopes were also performed. A new method to take the so-called length effect into account is proposed to extrapolate results from physical model tests to real structures. This length effect is important, but is normally overlooked in the design of rubble mound structures. Standard deviations based on the presented model tests were used. ... Read more

In order to design reliable coastal structures, for present and future scenarios, universal and precise damage assessment methods are required. This study addresses this need, and presents improved damage characterization methods for coastal structures with rock armored slopes. The data used in this study were obtained from a test campaign carried out at Deltares within the European Union (EU) Hydralab+ framework. During these tests, advanced measuring techniques (digital stereo photography) were used, which are able to survey the full extension of the structure and identify local variations of damage. The damage characterization method proposed here is based on three fundamental aspects: clear damage concepts, precise damage parameters, and high resolution measuring techniques. Regarding damage concepts, first, the importance of the characterization width is studied. For damage parameters obtained from the maximum erosion depth observed in a given width (E3D,m), the measured damage increases continuously with increased characterization width. However, for damage parameters obtained from width-averaged profiles (S and E2D), the measured damage reduces with increased characterization width. Second, a new definition of damage limits (damage initiation, intermediate damage, and failure) is presented and calibrated. Regarding the damage parameters, the parameter E3D,5, which describes the maximum erosion depth within the characterization width, is recommended as a robust damage parameter for conventional and non-conventional configurations based on four main characteristics: its low bias, its low random error, the ability to distinguish damage levels, and its validity and suitability for all types of structures (conventional and non-conventional). In addition, the results from this study show that the damage measured with the damage parameter E3D,5 presents an extreme value distribution. ... Read more

The study of wave impact physics and magnitudes are key for the design of vertical coastal hydraulic structures. This research addresses the study of standing wave impacts on vertical coastal hydraulic structures with a relatively short horizontal overhang, which is especially relevant for structures such as lock gates, sluice gates, dewatering sluices, flood gates and storm surge barriers. This paper applies the pressure-impulse theory to predict the pressure-impulse caused by standing wave impacts. These theoretical estimates are compared with results from four extensive regular wave tests from laboratory experiments conducted at the Hydraulic Engineering Laboratory of the Delft University of Technology. The agreement for two test cases is good, while differences are observed in the other two cases. This study concludes that a prediction method based on the pressure-impulse theory will allow to carry out preliminary load estimations from standing wave impacts on vertical structures with overhangs. Nevertheless, further research is required considering a larger range of structure dimensions, incident wave characteristics and influencing processes such as air entrapment. ... Read more

Flood gates in storm surge barriers or outlet sluices can be prone to violent wave impacts. When an obstruction is present at the sea side above the gate, confinement of the incoming waves can lead to impulsive wave loads, even when the waves are non-breaking. The large loads can increase the stresses in the gate and structure considerably. One of the measures that is often discussed to relieve the pressures of these impacts is to apply small openings in the gates. In this paper the potential effect of these venting holes on the wave impact loads is determined. The decrease in impact pressure impulse is determined for a range of venting hole geometries is determined by numerical 2D and 3D solutions of a schematized wave impact. In this model the pressure impulse P (integral of the local pressure over the small impact duration) is determined directly by the so-called pressure impulse theory. The potential decrease in pressure impulse due to wave impacts is presented. Moreover, some initial CFD modelling is applied, and the applicability of the pressure impulse theory is discussed. ... Read more

In order to design reliable coastal structures, for present and future scenarios, universal and precise damage assessment methods are required. This study addresses this need, and presents improved damage characterization methods for coastal structures with rock armoured slopes. The data used in this study was obtained from a test campaign carried out at Deltares within the EU Hydralab+ framework. During these tests, advanced measuring techniques (Digital Stereo Photography) were used, which are able to survey the full extension of the structure and identify local variations of damage. The here proposed damage characterisation method is based on three fundamental aspects: clear damage concepts, precise damage parameters and high resolution measuring techniques. Regarding damage concepts, first the importance of the characterization width is studied. For damage parameters obtained from the maximum erosion depth observed in a given width (E3D,m), the measured damage increases continuously with increased characterization width. But for damage parameters obtained from width-averaged profiles (S and E2D), the measured damage reduces with increased characterization width. Second, a new definition of damage limits (damage initiation, intermediate damage and failure) is presented and calibrated. Regarding the damage parameters, the parameter E3D,5, which describes the maximum erosion depth within the characterization width, is recommended as a robust damage parameter for conventional and non-conventional configurations based on three main characteristics: its low bias, its low random error, the ability to distinguish damage levels and is its validity and suitability for all types of structures (conventional and non-conventional). In addition, the results from this study show that the damage measured with the damage parameter E3D,5 presents an extreme value distribution. ... Read more

Physical model tests were performed in a wave flume at Deltares with rock armoured slopes. A shallow foreshore was present. At deep water the same wave conditions were used but, by applying different water levels, the wave loading on the rock armoured slopes increased considerably with increasing water levels. This allows the assessment of effects of sea level rise. Damage has been measured by using Digital Stereo Photography (DSP) which provides information on each individual stone that has been displaced. Two test series have been performed five times. This allows for a statistical analysis of the damage to rock armoured slopes. The statistical analysis demonstrates the need to take the spreading around a mean damage into account in the design of rock armoured slopes. This is important in addition to characterising the damage itself by erosion areas and erosion depths. The relation between damage parameters such as erosion area and erosion depth has been obtained from the tests. Besides tests with a straight slope also tests with a berm in the seaward slopes have been performed. A method to take the so-called length effect into account has been proposed to extrapolate results from physical model tests to real structures. Use is made of standard deviations based on the presented model tests. ... Read more

No âmbito do projeto HYDRALAB+ (H2020-INFRAIA-2014-2015), foi realizado no LNEC um conjunto de ensaios em modelo físico bidimensional (2D) de um perfil de um quebra-mar de talude em enrocamento, construído à escala geométrica 1:30, para diferentes condições de agitação marítima e níveis de maré correspondentes a cenários de alterações climáticas. Estas experiências tinham como objetivo analisar o dano, o espraiamento e o galgamento, nesses cenários.
Em paralelo, na FEUP, e em colaboração com Deltares, foram realizados testes com a mesma configuração de quebra-mar, mas utilizando um modelo físico tridimensional (3D), construído à escala geométrica 1:35. Os resultados obtidos permitiram analisar a evolução do dano no manto resistente do quebra-mar (talude de barlamar, talude de sotamar e cabeça), assim como o galgamento, para condições com e sem sobrelevação do nível médio do mar, considerando ou não a reconstrução do talude do quebra-mar entre testes consecutivos da mesma série de testes. Foram também realizados testes com ondas multidirecionais.
O presente trabalho incide sobre a análise da evolução do dano para as diferentes sequências de tempestade em cenários de alterações climáticas. O dano é avaliado com base no tradicional método de contagem de blocos removidos e ainda com base no parâmetro adimensional do dano, S recorrendo a técnicas estereofotogramétricas. É também feita uma avaliação do parâmetro E2D.
Em termos gerais, concluiu-se que não havia diferenças significativas entre os testes com danos cumulativos e com a reconstrução do quebra-mar após cada teste. Observou-se, também, que o dano era mais elevado na proximidade da superfície livre e que aumentava com a altura de onda significativa. Os danos foram, em geral, menores nos testes com ondas multidirecionais. ... Read more