Norimi Mizutani

Numerical estimation of the wave forces acting on a three-dimensional body on submerged breakwater

Numerical models have been developed to estimate the wave forces acting on a three-dimensional body on a submerged breakwater. These models combine the VOF model and porous body model to simulate the nonlinear wave deformation including wave breaking and its interaction with a porous structure. One model is two-dimensional and is associated with empirical wave force formulae, like the Morison equation. The other one is three-dimensional and does not require any empirical formula or coefficients. Comparison of estimated and measured wave forces shows good agreement, both in two- and three-dimensional model cases, and the present estimation methods are revealed to be powerful tools for estimation of wave force acting on a three-dimensional body, even for breaking wave condition.

Nonlinear regular wave, submerged breakwater and seabed dynamic interaction

Abstract Numerical and physical models have been developed to study the nonlinear dynamic interaction between water waves and permeable submerged breakwater over a finite thickness sand seabed. Modified Navier–Stokes equations have been used to solve the flow inside the porous media, and Biots equations have been applied to solve the poro-elastic media. A combined BEM–FEM model has been modified to simulate the flow inside the porous media and the wave deformation outside it. A poro-elastic finite element model has also been adapted and utilized under the effect of the nonlinear wave pressure, computed by the BEM–FEM model, along the surface boundary. A physical model has been made to record the water surface levels around the breakwater and the dynamic pore–water pressure inside the breakwater and foundation. The BEM–FEM model reproduces the experimental results in the wave field fairly well. The pore–water pressures computed by the poro-elastic and BEM–FEM models are compared with the experiment. The influence of the breakwater size on the wave deformation and the effect of the seabed thickness and stiffness on the breakwater stability are examined.

TSUNAMI SCOUR AROUND A SQUARE STRUCTURE

Tsunami-induced local scour around a land-based square structure on a sand foundation was investigated with laboratory experiments and numerical simulations. The laboratory experiments revealed that a scour hole at the seaward corner of the structure could be reproduced and the maximum scour depth was affected by the relative tsunami wave height and embedded depth of the structure. It was also found with the numerical simulations that a scour hole around the seaward corner of the structure could be evaluated with not only flow velocities but also effective stresses because restricting force between sand particles decreased with the effective stresses.

A NUMERICAL WAVE TANK USING DIRECT-FORCING IMMERSED BOUNDARY METHOD AND ITS APPLICATION TO WAVE FORCE ON A HORIZONTAL CYLINDER

In this paper, we propose a new numerical wave tank model capable of handling interface problems with complex geometry on a standard regular Cartesian grid, using direct-forcing immersed boundary method. Additional force terms are incorporated in the momentum equations to represent the interface on a fixed Cartesian grid and they are calculated on a finite number of Lagrangian points distributed over the structure-fluid interface. The wave field around a horizontal circular cylinder has been chosen in order to validate the applicability of the proposed numerical wave tank model. The calculated wave forces acting on the cylinder are compared with previous experimental and numerical results. The results obtained using the proposed model are in good agreement with experimental results.

BEM-FEM COMBINED ANALYSIS OF NONLINEAR INTERACTION BETWEEN WAVE AND SUBMERGED BREAKWATER

A study of alternatives including a shoreline evolution numerical modelization has been carried out in order to both diagnose the erosion problem at the beaches located between Cambrils Harbour and Pixerota delta (Tarragona, Spain) and select nourishment alternatives.

Application of Direct-Forcing IB-VOF Method to the Simulation of Wave Deformation by Submerged Structures

Abstract PENG, W.; LEE, KWANG-HO, and MIZUTANI, N., 2012. Application of direct-forcing IB-VOF method to the simulation of wave deformation by submerged structures. In this work, direct numerical simulation is employed to estimate the deformations of free-surface waves by submerged fixed structures using the immersed boundary method and volume of fluid method. The direct-forcing immersed boundary method is applied to handle solid object boundaries that are replaced with a proper force in the Navier–Stokes equations imposed on the body surface. The volume of fluid method is employed to track the free surface. Submerged obstacles of different shapes, including rectangles, trapezoids, and semicircles, are investigated to validate the ability of the numerical model to simulate fluid structure problems involving geometrically complex solid boundaries. The comparisons between the results of the developed numerical model, available experimental data, and previous numerical estimations reveal a favorable agreement between the water particle velocity fields as well as the free-surface profiles. The fully nonlinear phenomenon such as the flow separation and vortex generation can be reproduced and captured accurately using the proposed model.

NONLINEAR WAVE-INDUCED SEABED INSTABILITY AROUND COASTAL STRUCTURES

Seabed liquefaction at the toe of coastal structures is one of the most serious problems threatening their stability. Various simplified techniques have been commonly used to quantify this phenomenon, but often with shortcomings. An integrated technique, using numerical models developed by the authors, is presented to analyze the conditions and extents of seabed liquefaction and slip failure. This includes: a BEM-FEM model for the dynamic interaction among wave, structure and the seabed; a poro-elastic FEM model for the dynamic interaction between structure and the seabed; and a model for the wave-induced seabed response based on Yamamotos analytical solution (1977). The proposed technique is applied to the seabed subject to progressive waves, around vertical seawall with/without a rubble toe as well as in the vicinity of submerged and composite breakwaters. In this work, the permeability and porewater compressibility have been found to play a key role in controlling the seabed instability. The nonlinear...

Estimation method of stable weight of spherical armor unit of a submerged wide-crown breakwater

Abstract The armor stone is idealized as a sphere and the stable weight of a spherical armor unit of a submerged wide-crown breakwater is analyzed in relation to the wave force acting. The pertinent wave characteristics of wave force and the behavior of its generating mechanisms are clarified. General stability models are then derived based on the acting wave forces, method of placement, type and direction of movement, and other physical quantities affecting the stability of a spherical armor unit in a submerged wide-crown breakwater. The proposed models are in good agreement with the experimental values. The vicinity around the leading crown-edge is revealed to be the most critical location of the structure. Moreover, the applicability of Morison equation in the estimation of wave force for both breaking and non-breaking conditions is also discussed; and, the relationship of the drag and inertia force coefficients with the KC number is confirmed.

THREE-DIMENSIONAL ANALYSIS OF NONLINEAR INTERACTION BETWEEN WATER WAVES AND VERTICAL PERMEABLE BREAKWATER

This paper investigates the wave-induced flow field and water particle movement inside and around a vertical permeable structure, which is affected by the interaction between water waves and porous media. A three-dimensional fully nonlinear numerical model is developed to study the interaction between water waves and permeable structures. Modified resistance terms inside the equations of motion are proposed, which are able to consider the size of porous material directly inside the governing equations. It is understood that the wave-induced flow field and water particle movement inside and around the permeable structure are strongly influenced by the wave period or relative width of the permeable structure (structure width to wavelength ratio). Other parameters such as porous material size, porosity, and resistance coefficients affect the flow field. However, their degree of influence differs depending on the wave period.

STABILITY OF ARMOR STONES OF A SUBMERGED WIDE-CROWN BREAKWATER

A special reflecting wall 12 m long and 2.1 m high was built off the beach at Reggio Calabria, and 30 wave gauges were assembled before the wall and were connected to an electronic station on land. It was possible to observe the reflection of wind waves generated by a very stable wind over a fetch of 10 Km. The experiment aimed to verify the general closed solution for the wave group mechanics (Boccotti, 1988, 1989), for the special case of the wave reflection.Significant features on Wadden Sea wave climate are evaluated in respect of the state of the art. Main emphasis was laid on an analysis of the governing boundary conditions of local wave climate in island sheltered Wadden Sea areas with extensions being sufficient for local wind wave growth. Explanatory for significant wave heights a reliable parametrization of local wave climate has been evaluated by using generally available data of water level and wind measurements.