2,670 research outputs found
Generation of two-dimensional water waves by moving bottom disturbances
We investigate the potential and limitations of the wave generation by
disturbances moving at the bottom. More precisely, we assume that the wavemaker
is composed of an underwater object of a given shape which can be displaced
according to a prescribed trajectory. We address the practical question of
computing the wavemaker shape and trajectory generating a wave with prescribed
characteristics. For the sake of simplicity we model the hydrodynamics by a
generalized forced Benjamin-Bona-Mahony (BBM) equation. This practical problem
is reformulated as a constrained nonlinear optimization problem. Additional
constraints are imposed in order to fulfill various practical design
requirements. Finally, we present some numerical results in order to
demonstrate the feasibility and performance of the proposed methodology.Comment: 21 pages, 7 figures, 1 table, 69 references. Other author's papers
can be downloaded at http://www.denys-dutykh.com
Dynamics of thermoelastic thin plates: A comparison of four theories
Four distinct theories describing the flexural motion of thermoelastic thin
plates are compared. The theories are due to Chadwick, Lagnese and Lions,
Simmonds, and Norris. Chadwick's theory requires a 3D spatial equation for the
temperature but is considered the most accurate as the others are derivable
from it by different approximations. Attention is given to the damping of
flexural waves. Analytical and quantitative comparisons indicate that the
Lagnese and Lions model with a 2D temperature equation captures the essential
features of the thermoelastic damping, but contains systematic inaccuracies.
These are attributable to the approximation for the first moment of the
temperature used in deriving the Lagnese and Lions equation. Simmonds' model
with an explicit formula for temperature in terms of plate deflection is the
simplest of all but is accurate only at low frequency, where the damping is
linearly proportional to the frequency. It is shown that the Norris model,
which is almost as simple as Simmond's, is as accurate as the more precise but
involved theory of Chadwick.Comment: 2 figures, 1 tabl
Emergence of geometrical optical nonlinearities in photonic crystal fiber nanowires
We demonstrate analytically and numerically that a subwavelength-core
dielectric photonic nanowire embedded in a properly designed photonic crystal
fiber cladding shows evidence of a previously unknown kind of nonlinearity (the
magnitude of which is strongly dependent on the waveguide parameters) which
acts on solitons so as to considerably reduce their Raman self-frequency shift.
An explanation of the phenomenon in terms of indirect pulse negative chirping
and broadening is given by using the moment method. Our conclusions are
supported by detailed numerical simulations.Comment: 5 pages, 3 figure
Controls insensitizing the norm of solution of a Schr\"odinger type system with mixed dispersion
The main goal of this manuscript is to prove the existence of insensitizing
controls for the fourth-order dispersive nonlinear Schr\"odinger equation with
cubic nonlinearity. To obtain the main result we prove a null controllability
property for a coupled fourth-order Schr\"odinger system of cascade type with
zero order coupling which is equivalent to the insensitizing control problem.
Precisely, by means of new Carleman estimates, we first obtain a null
controllability result for the linearized system around zero, then the null
controllability for the nonlinear case is extended using an inverse mapping
theorem.Comment: 26 pages. Comments are welcom
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