Wave action on shallow water and applications to coastal hazard

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Abstract
The mechanics of wave breaking in shallow water has been a major
research field for many years, and a very large number of published
results are available. No attempt is made here to review the whole
literature. Some interesting – if somewhat outdated  descriptions of
waves breaking on beaches are presented by Peregrine (1983), Battjes
(1988) or LiberatorePetti (1992).
In fact, the most important process in the near coast zone of the
shoreline motion is wave breaking. Some waves break in shallow water,
some of them break at the water’s edge and in other circumstances
waves do not break at all (with steep beach slopes, incident waves with
low steepness  or long waves). In general, breaking in deep water is rarer
than breaking in shallow water. The latter is triggered by the bottom and
is more predictable, although the simple question ‘where breaking starts’
is far from having a unique answer, even in controlled physical
experiments. The breaker types are, generally, classified as spilling (where
the water spills down the front face), plunging (with a jet emanating from
the front crest), surging (characterized by a rise in water surface before
the breaking) and collapsing (between plunging and surging).
The fluid dynamics of nonbreaking waves can be described using
potential theory in most of the flow field except near the bottom and
near the free surface, where vorticity develops and is confined to a
boundary layer. As long as the details near the free surface (e.g. necessary
for wind–wave interaction) and/or near the bottom (e.g. necessary for
sediment transport analysis) are not of interest, the potential theory
approach is sufficient. After breaking, ‘waves’ and ‘eddies’, essentially a
potential component and a rotational component of the flow field, are
intimately mixed.
The surf and swash zones are characterized by the complete
transformation of the organized motion of the incident, seaswell, waves
into motions of different types and scales, including smallscale (less than
a wave period) turbulence, and largescale (much greater than the wave
period) mean flows [Battjes, 1988].
It is obvious that [Stive and Wind, 1982; Lin and Liu, 1998a; Svendsen et
al., 2000; Svendsen, 2005] contributions from terms which have
traditionally been neglected in the traditional assumptions of hydrostatic
pressure, depth uniform velocity profile, and negligible turbulence, are
important and must be taken into full account in surf zone
hydrodynamics.
Non Linear Shallow Water equations (‘800) and Boussinesq models
[Peregrine, 1967] have intrinsic limitations and can only simulate wave
breaking and its evolution by assuming on semiempirical ad hoc
assumptions and threshold values to represent wave dissipation.
Moreover, these models lack the capability to determine spatial
distribution of the turbulent kinetic energy, which is of great importance
for sediment transport studies [Lin and Liu, 1998b].
Given all this, it was only natural that the NavierStokes solvers now
widely tested and developed in other fields of fluid mechanics, with less
restricted assumptions involved, no wave theory assumed beforehand,
and the capability to simulate complex turbulent processes, should soon
become one of the main approaches to describe nearshore processes.
Numerical modeling of threedimensional breaking waves is extremely
difficult. Several challenging tasks must be overcome. First of all, one
must be able to track accurately the free surface location during the wave
breaking process so that the near surface dynamics is captured. Secondly,
one must properly model the physics of turbulence production, transport
and dissipation throughout the entire wave breaking process. Thirdly,
one needs to overcome the huge demand in computational resources.
There have been some successful twodimensional results. For instance,
more recent is the treatment of the free surface within such an Eulerian
framework with the marker and cell (MAC) method [e.g., Johnson et
al.1994] and the volume of fluid method (VOF) [e.g., Ng and Kot 1992,
Lin and Liu, 1998a].
The most common approach for simulating breaking waves is presently
the application of 2DReynolds Averaged NavierStokes (RANS)
equations with a Volume of Fluid (VOF) surface computation and a
turbulence closure model. Such an approach, while being often tested for
many years by many various Authors (see for instance Bovolin et al,
2004) only reached full maturity with a fundamental paper by Lin and
Liu (1998a). This line of research has been going on successfully for
many years to the point that reliable procedures now exist to simulate
wave breaking, run up and interaction with structures.
The next obvious step. i.e. the application of Large Eddy Simulation
(LES) models has so far not been equally successful [Watanabe and
Saeki, 1999; Christensen and Deigaard, 2001; Lubin et al, 2006;
Christensen, 2006].
LES models necessarily require a fully threedimensional solution and
threedimensional turbulence effects might be indeed important in the
prediction of velocity within the surf zone, especially in the case of
plunging breaker [Watanabe and Saeki, 1999]. Such models certainly are
a promising tool in the study of surf zone hydrodynamics; however, the
LES approach requires much finer grid resolution and a lager
computational domain than the RANS approach, resulting in the very
high demand on computational resource, at least for the time being.
They are however a definite perspective for the future.
Smoothed Particle Hydrodynamics (SPH) method, adapted from
astrophysics into a number of fields, is a relatively new method for
examining the propagation of highly nonlinear and breaking waves
[Monaghan et al, 1977; Dalrymple et al, 2005; Viccione et al, 20072008].
SPH offers a variety of advantages for fluid modeling, particularly those
with a free surface.
The Lagrangian method is meshfree; the equivalents of mesh points are
the fluid particles moving with the flow. The free surface requires no
special approaches, such as the volumeoffluid method or a Lagrangian
surface tracking. Furthermore, the method can treat rotational flows with
vorticity and turbulence.
SPH is a technique based on computing the trajectories of particles of
fluid, which interact according to the Navier–Stokes equations. Each of
such particles carries scalar information, density, pressure, velocity
components, etc.
The work presented here is therefore mainly based on the application of
the Eulerian 2dimensional RANS/VOF equations to the study of surf
zone processes on a beach. In particular the work is aimed at
demonstrating the capability of RANS/VOF to improve the current
modeling of surf zone hydrodynamics on sloping natural beach and in
front of shallow water coastal structures , comparing its performance
with laboratory observations and other theoretical and numerical results. [edited by author]
Descrizione
20082009
Collections
Data
20100518Autore
Monaco, Marina
Metadata
Mostra tutti i dati dell'itemAutori  Monaco, Marina  
Data Realizzazione  20101112T08:47:33Z  
Date Disponibilità  20101112T08:47:33Z  
Data di Pubblicazione  20100518  
Identificatore (URI)  http://hdl.handle.net/10556/127  
Descrizione  20082009  en_US 
Abstract  The mechanics of wave breaking in shallow water has been a major research field for many years, and a very large number of published results are available. No attempt is made here to review the whole literature. Some interesting – if somewhat outdated  descriptions of waves breaking on beaches are presented by Peregrine (1983), Battjes (1988) or LiberatorePetti (1992). In fact, the most important process in the near coast zone of the shoreline motion is wave breaking. Some waves break in shallow water, some of them break at the water’s edge and in other circumstances waves do not break at all (with steep beach slopes, incident waves with low steepness  or long waves). In general, breaking in deep water is rarer than breaking in shallow water. The latter is triggered by the bottom and is more predictable, although the simple question ‘where breaking starts’ is far from having a unique answer, even in controlled physical experiments. The breaker types are, generally, classified as spilling (where the water spills down the front face), plunging (with a jet emanating from the front crest), surging (characterized by a rise in water surface before the breaking) and collapsing (between plunging and surging). The fluid dynamics of nonbreaking waves can be described using potential theory in most of the flow field except near the bottom and near the free surface, where vorticity develops and is confined to a boundary layer. As long as the details near the free surface (e.g. necessary for wind–wave interaction) and/or near the bottom (e.g. necessary for sediment transport analysis) are not of interest, the potential theory approach is sufficient. After breaking, ‘waves’ and ‘eddies’, essentially a potential component and a rotational component of the flow field, are intimately mixed. The surf and swash zones are characterized by the complete transformation of the organized motion of the incident, seaswell, waves into motions of different types and scales, including smallscale (less than a wave period) turbulence, and largescale (much greater than the wave period) mean flows [Battjes, 1988]. It is obvious that [Stive and Wind, 1982; Lin and Liu, 1998a; Svendsen et al., 2000; Svendsen, 2005] contributions from terms which have traditionally been neglected in the traditional assumptions of hydrostatic pressure, depth uniform velocity profile, and negligible turbulence, are important and must be taken into full account in surf zone hydrodynamics. Non Linear Shallow Water equations (‘800) and Boussinesq models [Peregrine, 1967] have intrinsic limitations and can only simulate wave breaking and its evolution by assuming on semiempirical ad hoc assumptions and threshold values to represent wave dissipation. Moreover, these models lack the capability to determine spatial distribution of the turbulent kinetic energy, which is of great importance for sediment transport studies [Lin and Liu, 1998b]. Given all this, it was only natural that the NavierStokes solvers now widely tested and developed in other fields of fluid mechanics, with less restricted assumptions involved, no wave theory assumed beforehand, and the capability to simulate complex turbulent processes, should soon become one of the main approaches to describe nearshore processes. Numerical modeling of threedimensional breaking waves is extremely difficult. Several challenging tasks must be overcome. First of all, one must be able to track accurately the free surface location during the wave breaking process so that the near surface dynamics is captured. Secondly, one must properly model the physics of turbulence production, transport and dissipation throughout the entire wave breaking process. Thirdly, one needs to overcome the huge demand in computational resources. There have been some successful twodimensional results. For instance, more recent is the treatment of the free surface within such an Eulerian framework with the marker and cell (MAC) method [e.g., Johnson et al.1994] and the volume of fluid method (VOF) [e.g., Ng and Kot 1992, Lin and Liu, 1998a]. The most common approach for simulating breaking waves is presently the application of 2DReynolds Averaged NavierStokes (RANS) equations with a Volume of Fluid (VOF) surface computation and a turbulence closure model. Such an approach, while being often tested for many years by many various Authors (see for instance Bovolin et al, 2004) only reached full maturity with a fundamental paper by Lin and Liu (1998a). This line of research has been going on successfully for many years to the point that reliable procedures now exist to simulate wave breaking, run up and interaction with structures. The next obvious step. i.e. the application of Large Eddy Simulation (LES) models has so far not been equally successful [Watanabe and Saeki, 1999; Christensen and Deigaard, 2001; Lubin et al, 2006; Christensen, 2006]. LES models necessarily require a fully threedimensional solution and threedimensional turbulence effects might be indeed important in the prediction of velocity within the surf zone, especially in the case of plunging breaker [Watanabe and Saeki, 1999]. Such models certainly are a promising tool in the study of surf zone hydrodynamics; however, the LES approach requires much finer grid resolution and a lager computational domain than the RANS approach, resulting in the very high demand on computational resource, at least for the time being. They are however a definite perspective for the future. Smoothed Particle Hydrodynamics (SPH) method, adapted from astrophysics into a number of fields, is a relatively new method for examining the propagation of highly nonlinear and breaking waves [Monaghan et al, 1977; Dalrymple et al, 2005; Viccione et al, 20072008]. SPH offers a variety of advantages for fluid modeling, particularly those with a free surface. The Lagrangian method is meshfree; the equivalents of mesh points are the fluid particles moving with the flow. The free surface requires no special approaches, such as the volumeoffluid method or a Lagrangian surface tracking. Furthermore, the method can treat rotational flows with vorticity and turbulence. SPH is a technique based on computing the trajectories of particles of fluid, which interact according to the Navier–Stokes equations. Each of such particles carries scalar information, density, pressure, velocity components, etc. The work presented here is therefore mainly based on the application of the Eulerian 2dimensional RANS/VOF equations to the study of surf zone processes on a beach. In particular the work is aimed at demonstrating the capability of RANS/VOF to improve the current modeling of surf zone hydrodynamics on sloping natural beach and in front of shallow water coastal structures , comparing its performance with laboratory observations and other theoretical and numerical results. [edited by author]  en_US 
Lingua  en  en_US 
Editore  Universita degli studi di Salerno  en_US 
Soggetto  Regular Waves  en_US 
Soggetto  Numerical Modelling  en_US 
Soggetto  Eulerian RANS/VOF  en_US 
Soggetto  Turbulence Models  en_US 
Titolo  Wave action on shallow water and applications to coastal hazard  en_US 
Tipo  Doctoral Thesis  en_US 
MIUR  ICAR/01 IDRAULICA  en_US 
Coordinatore  Napoli, Rodolfo Maria Alessandro  en_US 
Ciclo  VIII n.s.  en_US 
Tutor  Pugliese Carratelli, Eugenio  en_US 
CoTutor  Foti, Enrico  en_US 
CoTutor  Dentale, Fabio  en_US 
Dipartimento  Ingegneria civile  en_US 