Papers by Constantine Memos
1st International Scientific Conference on Design and Management of Port Coastal and Offshore Works (DMPCO), 2019
In this paper we present the evolvement of an integrated numerical model (WAVE-L) for the simulat... more In this paper we present the evolvement of an integrated numerical model (WAVE-L) for the simulation of wave propagation and transformation in areas around and inside ports and harbors. WAVE-L is a high-resolution phase-resolving wave model based on the hyperbolic mild-slope equations, capable of simulating the transformation of complex wave fields over varying bathymetries in harbors and coastal areas in the vicinity of ports. The modeled wave processes include shoaling, refraction, diffraction, total and partial reflection from structures, energy dissipation due to wave breaking and bottom friction in a combined way. The new version of WAVE-L incorporates wave generation simulated on any boundary (longitudinal, lateral or oblique) with corresponding expansion of peripheral sponge layers, providing potential to spatially restrict the computational field in areas adjacent to ports, thus reducing demand of computational time and resources. Moreover, the modified WAVE-L version is able to simulate quasi-irregular, multi-directional waves, whose generation and propagation may furthermore account for various angles and directions simultaneously. WAVE-L is one-way coupled to coarser implementations of an open-sea spectral wave model and a 2-DH hydrodynamic circulation model for storm surges that provide input and boundary conditions. WAVE-L model is thoroughly validated against experimental data on diffraction and multidirectional spectral wave propagation; pilot implementations of it are carried out at the Greek port basin of Thessaloniki. The ultimate goal is to create a tool for high-resolution operational forecasts of wave conditions around and inside significant ports with high traffic load and commercial value (project Accu-Waves).
Computational modeling aspects of weak plunging wave breaking, over a relatively mild sloping lab... more Computational modeling aspects of weak plunging wave breaking, over a relatively mild sloping laboratory beach, are investigated in the present paper. Smoothed Particle Hydrodynamics (SPH) method is implemented as a numerical tool and specifically the recently enhanced version of the academic ‘open source’ code SPHysics v.2 is used. Thorough calibration of the model is attempted through fine spatial resolution, based on recent elaborate experimental data. Basic goal is to enhance the effectiveness of the Sub-Particle Scale Smagorinsky-type turbulence closure model that treats energy dissipation of eddy formations for the unresolved flow scales. Fine visual reproduction of the violent free-surface deformations is supplemented with plausible results concerning classic wave dynamics characteristics and sophisticated turbulent surf-zone features as well as wave-induced cross-shore currents.
New forms of coastal structures are being investigated nowadays, catering also for the aesthetic ... more New forms of coastal structures are being investigated nowadays, catering also for the aesthetic value of the nearshore landscape. Among those structures, the submerged breakwater is becoming attractive for obvious reasons. The wave transmission coefficient associated with the latter has been studied extensively in the past. However, an aspect not thoroughly investigated so far is the effect of the structure porosity on the above coefficient. In this paper a review of the transmission coefficient over submerged breakwaters is given, based on application of empirical formulas and numerical models to a case study. Apart from the porosity, a second parameter was investigated, namely the friction along the breakwater perimeter. It was found that porosity can have a significant effect on the transmission coefficient, and that it can be adequately described by one of the wave models tested and by an empirical formula. The bed friction was found to have a smaller effect on the wave transmission coefficient than permeability has.
Ocean Modelling, Feb 2016
The wave breaking of weak plungers over a relatively mild slope is investigated in this paper. Nu... more The wave breaking of weak plungers over a relatively mild slope is investigated in this paper. Numerical modeling aspects are studied, concerning the propagation and breaking of shore-normal, nonlinear and regular waves. The two-dimensional (2-D) kinematics and dynamics (fluctuating flow features and large 2-D eddies) of the wave-induced flow on a vertical cross-section over the entire surf zone are simulated with the use of Smoothed Particle Hydrodynamics (SPH). The academic ‘open source’ code SPHysics v.2 is employed and the viscosity treatment is based on a Sub-Particle Scale (SPS) approach, similarly to the Large Eddy Simulations (LES) concept. Thorough analysis of the turbulent flow scales determines the necessary refinement of the spatial resolution. The initial particle discretization reaches down to the demarcation point between integral turbulence length scales and Taylor micro-scales. A convolution-type integration method is implemented for the transformation of scattered Lagrangian particle data to Eulerian values at fixed gauges. A heuristic technique of ensemble-averaging is used for the discrimination of the fluctuating flow components from coherent structures and ordered wave motion. Comparisons between numerical and experimental data give encouraging results for several wave features. The wave-induced mean flows are simulated plausibly, and even the ‘streaming’ effect near the bed is reproduced. The recurring vorticity patterns are derived, and coherent 2-D structures inside the surf zone are identified. Fourier spectral analysis of velocities reveals isotropy of 2-D fluctuating dynamics up to rather high frequencies in shear intensified regions. The simulated Reynolds stresses follow patterns that define the characteristic mechanism of wave breaking for weak plungers. Persisting discrepancies at the incipient breaking region confirm the need for fine, massively ‘parallel’ 3-D SPS-SPH simulations.
The wave transmission over submerged breakwaters is investigated using existing formulae and wave... more The wave transmission over submerged breakwaters is investigated using existing formulae and wave models. The objective is to assess their performance and pinpoint research paths for their improvement. Application was made on a case study with two submerged detached breakwaters. It was found that some of the recent relations give satisfactory results of the transmission coefficient, while the predictability of the models tested depends on the wave breaking formulation assumed. In general, wave breaking and porosity of the structure are the most crucial factors that need further study for the improvement of the prediction of wave transmission over submerged breakwaters.
Continuing our previously published work, plunging wave breaking over relatively mild sloping
bea... more Continuing our previously published work, plunging wave breaking over relatively mild sloping
beach-type formations is investigated in this paper. Numerical modeling aspects on the matter
are discussed, by pursuing comparisons against experimental data. The modern robust method
Smoothed Particle Hydrodynamics is used and the recently enhanced version of the academic
‘open source’ code SPHysics v.2 is being validated. Spatial resolution is discerned as the most
crucial factor in forming plausible results. Exquisite visual representation of the violent freesurface
deformations is further upheld by coincidence of numerical and experimental results of
classic and sophisticated flow characteristics, in terms of wave heights, ensemble-averaged
values of hydrodynamic features, Fourier spectral analysis of turbulent velocities, vorticity
patterns and wave-induced mean flows. Further need to verify the model’s ability to capture the
near-shore wave breaking dynamics and surf/swash zone turbulence sets the path of future
research, based on extremely refined simulations with a new ‘parallel’ version of SPHysics.
The use of the academic ‘open source’ code SPHysics, in the framework of wave breaking simulation... more The use of the academic ‘open source’ code SPHysics, in the framework of wave breaking simulation over a relatively mild–sloping beach, is discussed in this paper. Thorough calibration of the relevant code’s wide range of parameters and assumptions is attempted through the comparison between numerical and experimental data. A general validation of the Smoothed Particle Hydrodynamics (SPH) method’s ability to capture the dynamics of near–shore wave breaking features and the characteristics of surf and swash zone turbulence, is implemented. Plausible qualitative agreement is achieved and inherent drawbacks and calibration weaknesses of the model are detected, based upon quantitative discrepancies. Moreover, particular amendments of the classic Smagorinsky–type turbulence model, incorporated in SPHysics, are suggested and the use of a more efficient one is introduced, setting the grounds for prospective research.
Numerical simulation of wave breaking over relatively mild sloping beaches is pursued in this stu... more Numerical simulation of wave breaking over relatively mild sloping beaches is pursued in this study with the implementation of a modern promissory method called Smoothed Particle Hydrodynamics. Validation of the method is attempted through the use and calibration of a recent free academic ‘open source’ code called SPHysics. Its various assumptions and parameters are adjusted to simulate experimental results. An effort is undertaken to confirm its ability to capture the near-shore wave breaking and consequent bore formation dynamics in the surf/swash zone. Inherent and calibration defects of the model are highlighted and particular upgrading measures are suggested for oncoming re-search.
Wave breaking over relatively mild sloping beaches is discussed in this paper. Experimental and n... more Wave breaking over relatively mild sloping beaches is discussed in this paper. Experimental and numerical aspects are investigated and comparisons between results are pursued. In this framework, a modern promisingly efficient method called Smoothed Particle Hydrodynamics is used and the academic ‘open source’ code SPHysics is being validated against experimental data. Moreover, an attempt is made to verify its ability to capture the dynamics of near-shore wave breaking features and the characteristics of surf and swash zone turbulence. Drawbacks of the model are pin-pointed and specific improvements are proposed for future research.
Στις μέρες μας, νέες μορφές παρακτίων έργων ερευνώνται, λαμβάνοντας υπόψη την
αισθητική αξία του ... more Στις μέρες μας, νέες μορφές παρακτίων έργων ερευνώνται, λαμβάνοντας υπόψη την
αισθητική αξία του παράκτιου τοπίου. Ανάμεσα σε αυτές, οι Ύφαλοι Κυματοθραύστες
(Υ/Κ) προσελκύουν όλο και περισσότερο την προσοχή των μελετητών για προφανείς
λόγους. Η μετάδοση του κυματικού πεδίου κατάντη τέτοιων κατασκευών έχει μελετηθεί
στο πρόσφατο παρελθόν, κυρίως σε εργαστηριακές διατάξεις και λιγότερο με
υπολογιστικές μεθόδους. Μία πλευρά του ζητήματος που δεν έχει μελετηθεί εκτενώς είναι
η επίδραση του πορώδους της κατασκευής στον παραπάνω συντελεστή κυματικής
μετάδοσης. Στην παρούσα εργασία επιχειρείται μία επισκόπηση των μεθόδων υπολογισμού
του πιο πάνω συντελεστή σε Υ/Κ, βασισμένη στη χρήση διαφόρων ημι-εμπειρικών
εκφράσεων και αριθμητικών προσομοιωμάτων, στο πλαίσιο μιας πρωτότυπης εφαρμογής
δύο συγγραμικών αποσπασμένων Υ/Κ για την προστασία ελαφρών παράκτιων κατοικιών
πάνω σε πασσάλους. Στόχος είναι η αξιολόγηση της απόδοσης των μοντέλων και των
σχέσεων, η επισήμανση της μελλοντικής ερευνητικής πορείας πάνω στο αντικείμενο και η
ανάδειξη χρήσιμων τεχνικών συστάσεων προς τον μελετητή μηχανικό. Παράλληλα,
εξετάζεται η επιρροή της διαπερατότητας του Υ/Κ και της τριβής του νερού στην
εξωτερική στρώση θωράκισης, στον υπολογισμό του συντελεστή κυματικής μετάδοσης.
Βρέθηκε πρώτον ότι η ικανότητα πρόβλεψης των προσομοιώσεων εξαρτάται κατά κύριο
λόγο από τη θεώρηση του κατάλληλου μοντέλου θραύσης των κυματισμών και δεύτερον
ότι το πορώδες της κατασκευής παίζει σημαντικό ρόλο στη διαμόρφωση του συντελεστή.
Ο τελευταίος φαίνεται ότι μπορεί να συναχθεί ικανοποιητικά από ένα κυματικό μοντέλο
και μία εμπειρική σχέση. Η τριβή στην επιφάνεια του Υ/Κ, αποδεικνύεται ότι έχει
μικρότερη επίδραση από την διαπερατότητά του, στον υπολογισμό του συντελεστή
μετάδοσης.
Coastal Engineering 2000, 2001
Coastal Engineering 2006 - Proceedings of the 30th International Conference, 2007
Wave forecasting is accomplished today via numerical models. In this work we apply stochastic tec... more Wave forecasting is accomplished today via numerical models. In this work we apply stochastic techniques using actual measurements to improve wave height forecast in real time. Application of these techniques in four locations of the Aegean Sea results in significant improvement of the forecast in the time domain retaining the same pattern of modifications, suggesting, thus, this method for operational use in deep and intermediate waters. The improvement is obtained by four regression models, which take into account the variable of the significant wave height as measured and forecasted by the model. Space-wise extension of the method was also investigated and applied to the Aegean Sea and the Indian Ocean, where its performance was remarkable.
The prime goal of the present study is the detailed numerical simulation of surf zone hydrodynami... more The prime goal of the present study is the detailed numerical simulation of surf zone hydrodynamics, due to weakly
plunging breakers on a relatively mild impermeable slope. Smoothed Particle Hydrodynamics method is used in
combination with a Smagorinsky-type model for the sub-particle scales of the flow, similarly to a Large Eddy Simulations’
approach; hence the academic ‘open-source’ code SPHysics is implemented. We undertake thorough pre-processing
analysis of experimental eddy sizes in regular wave breaking and thus choose a spatial resolution approaching the
demarcation point between integral turbulence length scales and Taylor micro-scales. Moreover, a combination of
heuristic techniques for the discrimination of turbulent fluctuations from the ordered wave motion is proposed as a postprocessing
manipulation of SPH Lagrange-type data. The model is validated against experimental data, concerning
several wave features. Spectral analysis of the fluctuating components for the velocity field is used to investigate its
isotropic substance. Results in the surf zone concern wave-induced mean flows, dynamic characteristics of weak plungers
and consequent bores, coherent structures on vertical cross-sections, and intermittent events at fixed gauges. The
recurring patterns of vorticity are studied both in Eulerian and Lagrangian perspective, and reveal plausible reproduction of
classic coherent vortical structures, which define the topology and properties of the wave breaking mechanism. The latter
is supported by the derivation of coherent structures of turbulent kinetic energy (TKE) and Reynolds stresses, too.
Additionally, the cross-shore variation of intermittent fluctuations due to wave breaking is investigated by empirical
identification of coherent and intense events. The statistics of intermittency agree with experimental data; e.g. coherent
intermittent events occur only for a small portion (<20%) of the TKE time-series, but contribute significantly to its
magnitude by containing a significant amount (>50%) of all motions. Correlations between shear stresses and TKE are
detected, allowing us to define possible cross-shore sediment transport patterns related to them.
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Papers by Constantine Memos
beach-type formations is investigated in this paper. Numerical modeling aspects on the matter
are discussed, by pursuing comparisons against experimental data. The modern robust method
Smoothed Particle Hydrodynamics is used and the recently enhanced version of the academic
‘open source’ code SPHysics v.2 is being validated. Spatial resolution is discerned as the most
crucial factor in forming plausible results. Exquisite visual representation of the violent freesurface
deformations is further upheld by coincidence of numerical and experimental results of
classic and sophisticated flow characteristics, in terms of wave heights, ensemble-averaged
values of hydrodynamic features, Fourier spectral analysis of turbulent velocities, vorticity
patterns and wave-induced mean flows. Further need to verify the model’s ability to capture the
near-shore wave breaking dynamics and surf/swash zone turbulence sets the path of future
research, based on extremely refined simulations with a new ‘parallel’ version of SPHysics.
αισθητική αξία του παράκτιου τοπίου. Ανάμεσα σε αυτές, οι Ύφαλοι Κυματοθραύστες
(Υ/Κ) προσελκύουν όλο και περισσότερο την προσοχή των μελετητών για προφανείς
λόγους. Η μετάδοση του κυματικού πεδίου κατάντη τέτοιων κατασκευών έχει μελετηθεί
στο πρόσφατο παρελθόν, κυρίως σε εργαστηριακές διατάξεις και λιγότερο με
υπολογιστικές μεθόδους. Μία πλευρά του ζητήματος που δεν έχει μελετηθεί εκτενώς είναι
η επίδραση του πορώδους της κατασκευής στον παραπάνω συντελεστή κυματικής
μετάδοσης. Στην παρούσα εργασία επιχειρείται μία επισκόπηση των μεθόδων υπολογισμού
του πιο πάνω συντελεστή σε Υ/Κ, βασισμένη στη χρήση διαφόρων ημι-εμπειρικών
εκφράσεων και αριθμητικών προσομοιωμάτων, στο πλαίσιο μιας πρωτότυπης εφαρμογής
δύο συγγραμικών αποσπασμένων Υ/Κ για την προστασία ελαφρών παράκτιων κατοικιών
πάνω σε πασσάλους. Στόχος είναι η αξιολόγηση της απόδοσης των μοντέλων και των
σχέσεων, η επισήμανση της μελλοντικής ερευνητικής πορείας πάνω στο αντικείμενο και η
ανάδειξη χρήσιμων τεχνικών συστάσεων προς τον μελετητή μηχανικό. Παράλληλα,
εξετάζεται η επιρροή της διαπερατότητας του Υ/Κ και της τριβής του νερού στην
εξωτερική στρώση θωράκισης, στον υπολογισμό του συντελεστή κυματικής μετάδοσης.
Βρέθηκε πρώτον ότι η ικανότητα πρόβλεψης των προσομοιώσεων εξαρτάται κατά κύριο
λόγο από τη θεώρηση του κατάλληλου μοντέλου θραύσης των κυματισμών και δεύτερον
ότι το πορώδες της κατασκευής παίζει σημαντικό ρόλο στη διαμόρφωση του συντελεστή.
Ο τελευταίος φαίνεται ότι μπορεί να συναχθεί ικανοποιητικά από ένα κυματικό μοντέλο
και μία εμπειρική σχέση. Η τριβή στην επιφάνεια του Υ/Κ, αποδεικνύεται ότι έχει
μικρότερη επίδραση από την διαπερατότητά του, στον υπολογισμό του συντελεστή
μετάδοσης.
plunging breakers on a relatively mild impermeable slope. Smoothed Particle Hydrodynamics method is used in
combination with a Smagorinsky-type model for the sub-particle scales of the flow, similarly to a Large Eddy Simulations’
approach; hence the academic ‘open-source’ code SPHysics is implemented. We undertake thorough pre-processing
analysis of experimental eddy sizes in regular wave breaking and thus choose a spatial resolution approaching the
demarcation point between integral turbulence length scales and Taylor micro-scales. Moreover, a combination of
heuristic techniques for the discrimination of turbulent fluctuations from the ordered wave motion is proposed as a postprocessing
manipulation of SPH Lagrange-type data. The model is validated against experimental data, concerning
several wave features. Spectral analysis of the fluctuating components for the velocity field is used to investigate its
isotropic substance. Results in the surf zone concern wave-induced mean flows, dynamic characteristics of weak plungers
and consequent bores, coherent structures on vertical cross-sections, and intermittent events at fixed gauges. The
recurring patterns of vorticity are studied both in Eulerian and Lagrangian perspective, and reveal plausible reproduction of
classic coherent vortical structures, which define the topology and properties of the wave breaking mechanism. The latter
is supported by the derivation of coherent structures of turbulent kinetic energy (TKE) and Reynolds stresses, too.
Additionally, the cross-shore variation of intermittent fluctuations due to wave breaking is investigated by empirical
identification of coherent and intense events. The statistics of intermittency agree with experimental data; e.g. coherent
intermittent events occur only for a small portion (<20%) of the TKE time-series, but contribute significantly to its
magnitude by containing a significant amount (>50%) of all motions. Correlations between shear stresses and TKE are
detected, allowing us to define possible cross-shore sediment transport patterns related to them.
beach-type formations is investigated in this paper. Numerical modeling aspects on the matter
are discussed, by pursuing comparisons against experimental data. The modern robust method
Smoothed Particle Hydrodynamics is used and the recently enhanced version of the academic
‘open source’ code SPHysics v.2 is being validated. Spatial resolution is discerned as the most
crucial factor in forming plausible results. Exquisite visual representation of the violent freesurface
deformations is further upheld by coincidence of numerical and experimental results of
classic and sophisticated flow characteristics, in terms of wave heights, ensemble-averaged
values of hydrodynamic features, Fourier spectral analysis of turbulent velocities, vorticity
patterns and wave-induced mean flows. Further need to verify the model’s ability to capture the
near-shore wave breaking dynamics and surf/swash zone turbulence sets the path of future
research, based on extremely refined simulations with a new ‘parallel’ version of SPHysics.
αισθητική αξία του παράκτιου τοπίου. Ανάμεσα σε αυτές, οι Ύφαλοι Κυματοθραύστες
(Υ/Κ) προσελκύουν όλο και περισσότερο την προσοχή των μελετητών για προφανείς
λόγους. Η μετάδοση του κυματικού πεδίου κατάντη τέτοιων κατασκευών έχει μελετηθεί
στο πρόσφατο παρελθόν, κυρίως σε εργαστηριακές διατάξεις και λιγότερο με
υπολογιστικές μεθόδους. Μία πλευρά του ζητήματος που δεν έχει μελετηθεί εκτενώς είναι
η επίδραση του πορώδους της κατασκευής στον παραπάνω συντελεστή κυματικής
μετάδοσης. Στην παρούσα εργασία επιχειρείται μία επισκόπηση των μεθόδων υπολογισμού
του πιο πάνω συντελεστή σε Υ/Κ, βασισμένη στη χρήση διαφόρων ημι-εμπειρικών
εκφράσεων και αριθμητικών προσομοιωμάτων, στο πλαίσιο μιας πρωτότυπης εφαρμογής
δύο συγγραμικών αποσπασμένων Υ/Κ για την προστασία ελαφρών παράκτιων κατοικιών
πάνω σε πασσάλους. Στόχος είναι η αξιολόγηση της απόδοσης των μοντέλων και των
σχέσεων, η επισήμανση της μελλοντικής ερευνητικής πορείας πάνω στο αντικείμενο και η
ανάδειξη χρήσιμων τεχνικών συστάσεων προς τον μελετητή μηχανικό. Παράλληλα,
εξετάζεται η επιρροή της διαπερατότητας του Υ/Κ και της τριβής του νερού στην
εξωτερική στρώση θωράκισης, στον υπολογισμό του συντελεστή κυματικής μετάδοσης.
Βρέθηκε πρώτον ότι η ικανότητα πρόβλεψης των προσομοιώσεων εξαρτάται κατά κύριο
λόγο από τη θεώρηση του κατάλληλου μοντέλου θραύσης των κυματισμών και δεύτερον
ότι το πορώδες της κατασκευής παίζει σημαντικό ρόλο στη διαμόρφωση του συντελεστή.
Ο τελευταίος φαίνεται ότι μπορεί να συναχθεί ικανοποιητικά από ένα κυματικό μοντέλο
και μία εμπειρική σχέση. Η τριβή στην επιφάνεια του Υ/Κ, αποδεικνύεται ότι έχει
μικρότερη επίδραση από την διαπερατότητά του, στον υπολογισμό του συντελεστή
μετάδοσης.
plunging breakers on a relatively mild impermeable slope. Smoothed Particle Hydrodynamics method is used in
combination with a Smagorinsky-type model for the sub-particle scales of the flow, similarly to a Large Eddy Simulations’
approach; hence the academic ‘open-source’ code SPHysics is implemented. We undertake thorough pre-processing
analysis of experimental eddy sizes in regular wave breaking and thus choose a spatial resolution approaching the
demarcation point between integral turbulence length scales and Taylor micro-scales. Moreover, a combination of
heuristic techniques for the discrimination of turbulent fluctuations from the ordered wave motion is proposed as a postprocessing
manipulation of SPH Lagrange-type data. The model is validated against experimental data, concerning
several wave features. Spectral analysis of the fluctuating components for the velocity field is used to investigate its
isotropic substance. Results in the surf zone concern wave-induced mean flows, dynamic characteristics of weak plungers
and consequent bores, coherent structures on vertical cross-sections, and intermittent events at fixed gauges. The
recurring patterns of vorticity are studied both in Eulerian and Lagrangian perspective, and reveal plausible reproduction of
classic coherent vortical structures, which define the topology and properties of the wave breaking mechanism. The latter
is supported by the derivation of coherent structures of turbulent kinetic energy (TKE) and Reynolds stresses, too.
Additionally, the cross-shore variation of intermittent fluctuations due to wave breaking is investigated by empirical
identification of coherent and intense events. The statistics of intermittency agree with experimental data; e.g. coherent
intermittent events occur only for a small portion (<20%) of the TKE time-series, but contribute significantly to its
magnitude by containing a significant amount (>50%) of all motions. Correlations between shear stresses and TKE are
detected, allowing us to define possible cross-shore sediment transport patterns related to them.