Miguel A. Losada

Bio: Miguel A. Losada is an academic researcher from University of Granada. The author has contributed to research in topics: Breaking wave & Breakwater. The author has an hindex of 38, co-authored 244 publications receiving 4399 citations. Previous affiliations of Miguel A. Losada include Spanish National Research Council & University of Cantabria.

Reflection and transmission from porous structures under oblique wave attack

Abstract: The linear theory for water waves impinging obliquely on a vertically sided porous structure is examined. For normal wave incidence, the reflection and transmission from a porous breakwater has been studied many times using eigenfunction expansions in the water region in front of the structure, within the porous medium, and behind the structure in the down-wave water region. For oblique wave incidence, the reflection and transmission coefficients are significantly altered and they are calculated here. Using a plane-wave assumption, which involves neglecting the evanescent eigenmodes that exist near the structure boundaries (to satisfy matching conditions), the problem can be reduced from a matrix problem to one which is analytic. The plane-wave approximation provides an adequate solution for the case where the damping within the structure is not too great. An important parameter in this problem is Γ 2 = ω 2 h ( s - i f )/ g , where ω is the wave angular frequency, h the constant water depth, g the acceleration due to gravity, and s and f are parameters describing the porous medium. As the friction in the porous medium, f , becomes non-zero, the eigenfunctions differ from those in the fluid regions, largely owing to the change in the modal wavenumbers, which depend on Γ 2 . For an infinite number of values of ΓF 2 , there are no eigenfunction expansions in the porous medium, owing to the coalescence of two of the wavenumbers. These cases are shown to result in a non-separable mathematical problem and the appropriate wave modes are determined. As the two wavenumbers approach the critical value of Γ 2 , it is shown that the wave modes can swap their identity.

Hydrodynamics induced by wind waves in a vegetation field

Abstract: The wave-induced kinematics and dynamics of a submerged or emerged vegetation field is analyzed. Using potential flow and an eigenfunction expansion, the problem is solved considering regular as well as irregular incident waves. The model takes into account the vegetation motion and solves for the complete wave system on the vegetation field and in its vicinity. The model is validated against experimental laboratory data obtained by other authors, showing a much better agreement than previous theoretical models. In this paper the model is used to evaluate wave height evolution (damping), vegetation and fluid motion, and forces and moments on the vegetation. Furthermore, the inclusion of irregular waves provides force and moment distributions on the vegetation field depending on the wave climate statistics.

3-D non-breaking regular wave interaction with submerged breakwaters

Abstract: Modelling of the transformation and interaction of regular wave trains with submerged permeable structures is carried out. The existing literature, is summarized relevant theories presented, and theoretical results are compared with existing laboratory data. Special attention is paid to wave reflection. The influence of wave characteristics including oblique incidence, structure geometry and porous material properties on the kinematics and dynamics over and inside the breakwater is considered. Two different models are presented: an eigenfunction expansion 3-D model and a 2-D model based on a mild-slope equation for porous media to account for breakwater slope.

Propagation of oblique incident waves past rigid vertical thin barriers

Abstract: The linear theory for waves impinging obliquely on a vertical thin barrier is examined. Three types of structures are analysed: a barrier descending from the water surface to a distance, d, an underwater barrier, and a barrier with a submerged horizontal slit. Theoretical solutions are obtained by an eigenfunction expansion method for the transmission and reflection coefficients. The plane wave approximation is further examined and compared to the full solution. The distribution of the pressure along the barrier is also calculated and the maximum horizontal force is compared to the case of a vertical wall.

Characteristics of Solitary Wave Breaking Induced by Breakwaters

Abstract: Laboratory experiments are presented for the breaking of solitary waves over breakwaters. A variety of behaviors is observed, depending on both breakwater and incident wave height: for emerged breakwaters, waves may collapse over the crown, or break backward during rundown; and for submerged breakwaters, waves may break forward or backward, downstream of the breakwater. The limit of overtopping and wave transmission and reflection coefficients are experimentally determined. It is seen that transmission is large over submerged breakwaters (55–90%), and may also reach 20–40% over emerged breakwaters. Computations using a fully nonlinear potential model agree well with experimental results for the submerged breakwaters, particularly for the smaller waves (\IH/d\N<0.4). For emerged breakwaters, computations correctly predict the limit of overtopping, and the backward collapsing during rundown.

Linear and nonlinear waves, by G. B. Whitham. Pp.636. £50. 1999. ISBN 0 471 35942 4 (Wiley).

Abstract: to be done in this area. Face recognition is a problem that scarcely clamoured for attention before the computer age but, having surfaced, has involved a wide range of techniques and has attracted the attention of some fine minds (David Mumford was a Fields Medallist in 1974). This singular application of mathematical modelling to a messy applied problem of obvious utility and importance but with no unique solution is a pretty one to share with students: perhaps, returning to the source of our opening quotation, we may invert Duncan's earlier observation, 'There is an art to find the mind's construction in the face!'.

반도체 공정 overview

Abstract: With digital equipment becoming increasingly networked, either on wired or wireless networks, for personal and professional use alike, distributed software systems have become a crucial element in information and communications technologies. The study of these systems forms the core of the ARLES' work, which is specifically concerned with defining new system software architectures, based on the use of emerging networking technologies. In this context, we concentrate on the study of distributed systems which bring to life the vision of ubiquitous computing systems, also known as ambient intelligence.