arXiv subjects

L. G. Martins

Publications and source records attributed to L. G. Martins.

4 recordsLinked to original sources

arXiv2025

Flow Structures Beneath Stationary Waves with Constant Vorticity Over Variable Topography

The flow structures beneath waves have received significant attention from both theoretical and numerical perspectives. Most studies on this topic assume a flat bottom, leading to questions about the effects of variable bottom topography. To address this gap, we investigate the flow structures beneath stationary waves with constant vorticity, considering the influence of variable topography. Specifically, we numerically analyze the role of vorticity in the emergence of stagnation points and the pressure distribution within the fluid in two bottom topography scenarios: a bump and a hole. Our numerical approach is based on a variation of the classical Dyachenko, Zakharov, and Kuznetsov conformal mapping technique for free-boundary water wave problems. Our results reveal the existence of saddle points beneath wave crests and center beneath depression solitary waves. Additionally, we observe that the pressure can exhibit distinctive features, such as a global minimum on the bottom boundary -- behavior that is markedly different from the usual flat-bottom case.

physics.flu-dyn↗

arXiv2023

A forced Boussinesq model with a sponge layer

The movement of water waves is a topic of interest to researchers from different areas. While their propagation is described by Euler equations, there are instances where simplified models can also provide accurate approximations. A well-known reduced model employed to study the wave dynamics is the Boussinesq model. Despite being extensively studied, to our knowledge, there is no research available on a Boussinesq model featuring a sponge layer. Therefore, in this work, we present a Boussinesq model with a sponge layer. Furthermore, we carry out a numerical investigation to explore the advantages and limitations of the proposed model. For this purpose, we compare the numerical solutions of the model with and without the sponge in three different scenarios. The numerical solutions are computed by a pseudospectral method. Our results show that the Boussinesq model with a sponge layer is numerically stable and advantageous because it is able to absorb low-amplitude waves, allowing it to run the numerical simulations for long periods of time without requiring a large spatial domain, but it is not able to absorb high-amplitude waves.

math.NA↗

arXiv2019

Quantum cosmology of a Hořava-Lifshitz model coupled to radiation

In the present paper, we canonically quantize an homogeneous and isotropic Hořava-Lifshitz cosmological model, with constant positive spatial sections and coupled to radiation. We consider the projectable version of that gravitational theory without the detailed balance condition. We use the ADM formalism to write the gravitational Hamiltonian of the model and the Schutz variational formalism to write the perfect fluid Hamiltonian. We find the Wheeler-DeWitt equation for the model, which depends on several parameters. We study the case in which parameter values are chosen so that the solutions to the Wheeler-DeWitt equation are bounded. Initially, we solve it using the {\it Many Worlds} interpretation. Using wavepackets computed with the solutions to the Wheeler-DeWitt equation, we obtain the scalar factor expected value $\left $. We show that this quantity oscillates between finite maximum and minimum values and never vanishes. Such result indicates that the model is free from singularities, at the quantum level. We reinforce this indication by showing that by subtracting one standard deviation unit from the expected value $\left $, the latter remains positive. Then, we use the {\it DeBroglie-Bohm} interpretation. Initially, we compute the Bohm's trajectories for the scale factor and show that they never vanish. Then, we show that each trajectory agrees with the corresponding $\left $. Finally, we compute the quantum potential, which helps understanding why the scale factor never vanishes.

gr-qc↗

arXiv2017

DeBroglie-Bohm interpretation of a Hořava-Lifshitz quantum cosmology model

In the present letter, we consider the DeBroglie-Bohm interpretation of a Hořava-Lifshitz quantum cosmology model in the presence of a radiation perfect fluid. We compute the Bohm's trajectories for the scale factor and show that it never goes to zero. That result gives a strong indication that this model is free from singularities, at the quantum level. We also compute the quantum potential. That quantity helps understanding why the scale factor never vanishes.

gr-qc↗