Example application of reliability assessment of coastal structures

During the last few decades the believe that absolute security could be provided has been recognized to be mistaken in many branches of engineering. This happens as a consequence of the imperfect predictability of load intensity, structural characteristics and structural behavior, as well as a consequence of human gross errors during the design and construction phases or during the using (exploiting) period. In the field of coastal engineering this became particularly evident when breakwaters were constructed in deep-water condition, i.e. where water-depth ceases the beneficial effect in limiting the design wave height. Beyond this special case, it is rat her common in coastal engineering practice to dwell with uncertain environmental conditions and sometimes even with uncertain structural behavior. A method which can account for the multiform information available and which can produce a rational risk evaluation is therefore highly advisable. A rationalization of the risk assessment produce some advantages: 1 - The various uncertainties are rationally incorporated and balanced in the assessment of the reliability of the structure. 2 - A more balanced design of components of the overall system can he made, avoiding the coexistence of overdesigned components blowing up the costs and of underdesigned components causing the risk. 3 - Cost of the structural solution to risk (building a stronger structure) can be assessed and compared to the non structural solution (reducing the uncertainty). 4 - A better insight into how the failure probability is built up from the various uncertainties is obtained: priorities can he established for further research aiming to improve the description of the system and reduce the uncertainty margins. In the example presented failure and risk are looked at from the client point of view. CONCLUSIONS A complete and objective risk assessment is not always possible due to the lack of reliable models for some of the relevant failure modes. A model is suitable for this kind of use, if its reliability has been tested and quantified (the statistics of the model related variabie Z should be known). The statistics of all the relevant parameters should be known at least in a simplified form (a central value and one or two fractiles characterizing the distribution on the cautious side). A good pile of scientific and technical work must still he done in order to translate the actual knowledge of the basic phenomena into a rationally based level 1 risk assessment procedure, suitable for the everyday design praxis. Nevertheless even a not completely objective risk assessment can be useful to answer in a conclusive manner such questions as: - How deep the preliminary environment characterization should be brought? Does risk come only from the climate vagary or also from our imperfect knowledge of the past and of the present? Does it come from our poor knowledge of some relevant phenomenon? - What are the relevant failure modes? Could we substantially reduce the risk by controlling carefully the construct ion? - Is a physical model or any other more reliable and expensive evaluation tool useful or necessary? Should an overdesign he preferred to a strictly controlled construction or a more deep analysis?ICCE 199

Wave action on rubble mound breakwaters: The problem of scale effects

The present report, produced within the framework of the EU funded project DELOS, attempts to recognise and analyse main scale effects in the physical modeHing of rubble mound breakwaters used in offshore and coastal engineering. Scale effects appear in physical modeHing because the ratios between the farces of interest, as present in prototype, cannot be maintained in a scaled model. The report is by no means intended to resolve the problems associated with scale effects, given the complexity of this issue. However this discussion provides a preliminary understanding of these effects. Respect to the aforementioned objectives, the present report is structured as foHows. The properties of sea water are summarised in Section 2. Section 3 provides a brief overview of sealing rules used in hydraulic physical modeHing. Section 4 is dedicated to surface tension effects on breakers. Section 5 deals with the complex problem of sealing air content from prototype sea water to model fresh water. A general overview of main scale effects in relation to the different processes associated to the interaction between waves and rubble mound breakwaters is presented in Section 6. Sealing of movable-bed models are addressed in Section 7. The effects of marine organisms on water and mound units are described in Section 8. In Section 9 conclusions are drawn, which summarise the main points worth consiclering when addressing the problem of scale effects in wave-related models with rubble mound breakwaters. Selected issues are further discussed in the attached appendices. Example of the Hydrodynamics at Pellestrina. Example of the sediment budget at Lido de Pellestrina.Delo

Reshaping breakwater: Profile parametrisation

Berm or reshaping breakwaters represent a relatively new -type of wave barrier; more precisely the conscious acceptation of stone movement during reshaping and of the eventual dynamic equilibrium of the units in the exposed mound is new. Stones of the armour layer are accepted to move under the wave attack until a new equilibrium of the seaward profile is formed. The shape of the new profile was already studied, and a model was developed providing a typical shape and parametrisation (Vellinga, 1986) and equations describing the evolution of the profile characteristic points under some assigned wave attack (Van der Meer, 1988). The purpose of this paper is to check the goodness of the existing model, to recalibrate it, if it is felt necessary, using the wider data-set that was reconstructed from several experiments carried out in the last years, and, eventually, to suggest a description of the profile using a smaller number of equations and parameters.Berm Breakwater

Delos final report

Summary of all results of the Delos (Environmental design of low crested structures) project. Objectives of Delos were (1) to provide an inventory of Low Crested Structures (LCS), (2) analyse LCS hydrodynamic an stability and their effects on morphology (3) investigate impacts of LCS (4) develop methodology for Integrated Coastal Zone Management (5) provide guidelines for the design of LCS. This report is the administative final report. For technical details is referred to the book "Environmental design guidelines for low crested coastal structures" by Burcharth et.al.Delo

Reshaping breakwater: Description of the profile evolution / Irregular wave induced forces on armor unit on berm breakwater

In order to develop a model able to describe how berm breakwaters reshape under the attack of waves, a large quantity of data from 2D and 3D tests was collected and arranged in a database. The data were first standardised, and since data come from models with very different size, all the lengths were scaled with the nominal diameter (Dn50) of berm stones. Since the information regarding the wave conditions in shallow water or in front of the breakwater was not always available the wave conditions were estimated in front of the breakwater by using formulae proposed by Goda (1985) and Stive, (1986). The profiles were schematised as suggested by Vellinga (1986) and van der Meer (1988) using six parameters; with the aid of PCA the original variables were transformed into uncorrelated components describing decreasing quotes of the total variance. Three of them account for 95% of the variance of our data-base. In this manner the dimensionality of the phenomenon was reduced from six to three. Each component describes part of the behaviour of the reshaping breakwater and for each of them a model was developed relating components to the environmental and structural parameters. The model respects approximately (relatively to the 1st PC) the composition principle and gives results for any condition. At the end the model was compared with the experimental profiles and with the output of BREAKWAT.Berm Breakwater

The MoonWEC, a new technology for wave energy conversion in the Mediterranean Sea

This work presents the MoonWEC, a new device for wave energy conversion. This new concept encompasses several working principles as the heaving point absorber, the oscillating water column and the overtopping. The development of the new WEC has been carried out through numerical modelling. Three main parts of the device have been simulated: a hollow floating structure, a central moonpool and a CALM mooring system. All the parts of the model have been coupled to obtained the general behaviour of the device under the effect of irregular sea states. The device has been designed according to the Mediterranean Sea wave climate. Its dimensioning aims to maximize the power absorption by tuning both,device and moonpool, natural periods with the identified prevailing sea states. Six mooring system configurations have been tested in order to obtain a stable, safe and yet effective behaviour. Finally, performance indicators have been drawn to assess power production in two selected locations in the Mediterranean Sea.Coastal Engineerin

Economic and social valuation about European Coastal Sites

Economic evalulation of the recreational beaches at Lido di Dante, Trieste, Ostia and Pellestrina Island. Assessment of option value and non-use values at Venice and Normerven (Netherlands). Prefence of different structures and beach materials, case of Lido di Dante, Ostia and Pellestrina Island.Delo

Syngas production by electrocatalytic reduction of CO ₂ using Ag-decorated TiO ₂ nanotubes

Huge efforts have been done in the last years on electrochemical and photoelectrochemical reduction of CO 2 to offer a sustainable route to recycle CO 2 . A promising route is to electrochemically reduce CO 2 into CO which, by combination with hydrogen, can be used as a feedstock to different added-value products or fuels. Herein, perpendicular oriented TiO 2 nanotubes (NTs) on the electrode plate were grown by anodic oxidation of titanium substrate and then decorated by a low loading of silver nanoparticles deposited by sputtering (i.e. Ag/TiO 2 NTs). Due to their quasi one-dimensional arrangement, TiO 2 NTs are able to provide higher surface area for Ag adhesion and superior electron transport properties than other Ti substrates (e.g. Ti foil and TiO 2 nanoparticles), as confirmed by electrochemical (CV, EIS, electrochemical active surface area) and chemical/morphological analysis (FESEM, TEM, EDS). These characteristics together with the role of the TiO 2 NTs to enhance the stability of CO 2 ·- intermediate formed due to titania redox couple (Ti IV /Ti III ) lead to an improvement of the CO production in the Ag/TiO 2 NTs electrodes. Particular attention has been devoted to reduce the loading of noble metal in the electrode(14.5 %w/%w) and to increase the catalysts active surface area in order to decrease the required overpotential. Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.ChemE/Catalysis Engineerin

Measurement of the diffractive cross-section in deep inelastic scattering

Diffractive scattering of $\gamma^* p \to X + N$, where $N$ is either a proton or a nucleonic system with $M_N~<~4$~GeV has been measured in deep inelastic scattering (DIS) at HERA. The cross section was determined by a novel method as a function of the $\gamma^* p$ c.m. energy $W$ between 60 and 245~GeV and of the mass $M_X$ of the system $X$ up to 15~GeV at average $Q^2$ values of 14 and 31~GeV$^2$. The diffractive cross section $d\sigma^{diff} /dM_X$ is, within errors, found to rise linearly with $W$. Parameterizing the $W$ dependence by the form d\sigma^{diff}/dM_X \propto (W^2)^{(2\overline{\mbox{\alpha_{_{I\hspace{-0.2em}P}}}} -2)} the DIS data yield for the pomeron trajectory \overline{\mbox{\alpha_{_{I\hspace{-0.2em}P}}}} = 1.23 \pm 0.02(stat) \pm 0.04 (syst) averaged over $t$ in the measured kinematic range assuming the longitudinal photon contribution to be zero. This value for the pomeron trajectory is substantially larger than \overline{\mbox{\alpha_{_{I\hspace{-0.2em}P}}}} extracted from soft interactions. The value of \overline{\mbox{\alpha_{_{I\hspace{-0.2em}P}}}} measured in this analysis suggests that a substantial part of the diffractive DIS cross section originates from processes which can be described by perturbative QCD. From the measured diffractive cross sections the diffractive structure function of the proton F^{D(3)}_2(\beta,Q^2, \mbox{x_{_{I\hspace{-0.2em}P}}}) has been determined, where $\beta$ is the momentum fraction of the struck quark in the pomeron. The form F^{D(3)}_2 = constant \cdot (1/ \mbox{x_{_{I\hspace{-0.2em}P}}})^a gives a good fit to the data in all $\beta$ and $Q^2$ intervals with $a = 1.46 \pm 0.04 (stat) \pmComment: 45 pages, including 16 figure