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Waves generated by a horizontally moving disturbance on the seabed have been studied by developing two numerical models, namely, the Navier–Stokes and the Green–Naghdi equations. Various geometries of the bottom disturbances are considered, and waves generated due to a single motion and multiple oscillatory motions of the bottom disturbances are investigated by the two models. Discussion is provided on how the motion of the disturbance on the seafloor results in the generation of surface waves. The wave-field parameters investigated include the surface elevation, velocity, pressure fields and wave celerity. A parametric study is conducted to assess the effect of the geometry of the disturbance and the kinematic characteristics on the wave generation. It is shown that both linear and nonlinear waves can be generated by a horizontally moving disturbance on the seabed. Long waves, followed by a series of dispersive waves, are produced by the single motion of the bottom disturbance. It is also found that, under appropriate conditions, there would be a balance between nonlinearity and dispersion, such that the generated waves propagate over a flat seafloor with little to no change in their form and shape. [ABSTRACT FROM AUTHOR]

The underlying pathophysiological mechanisms of exercise-induced laryngeal obstruction (EILO) remain to be fully established. It is hypothesized that high inspiratory flow rates can exert a force on laryngeal airway walls that contribute to its inward collapse causing obstruction. Computational fluid dynamics (CFD) presents an opportunity to explore the distribution of forces in a patient-specific upper airway geometry. The current study combined exercise physiological data and CFD simulation to explore differences in airflow and force distribution between a patient with EILO and a healthy matched control. Participants underwent incremental exercise testing with continuous recording of respiratory airflow and laryngoscopic video, followed by an MRI scan. The respiratory and MRI data were used to generate a subject-specific CFD model of upper respiratory airflow. In patient with EILO, the posterior supraglottis experiences an inwardly directed net force, whose magnitude increases nonlinearly with larger flow rates, with slight changes in the direction toward the center of the airway. The control demonstrated an outwardly directed force at all regions of the wall, with a magnitude that increases linearly with larger flow rates. A comparison is made between the CFD results and endoscopic visualization of supraglottic collapse, and a very good agreement is found. The current study presents the first hybrid physiological and computational approach to investigate the pathophysiological mechanisms of EILO, with preliminary findings showing great potential, but should be used in larger sample sizes to confirm findings. NEW & NOTEWORTHY: The current study is the first to use a hybrid combined computational fluid dynamics (CFD) and exercise physiology approach to investigate pathophysiology in exercise-induced laryngeal obstruction (EILO). The hybrid methodology is a promising approach to explore the pathophysiological mechanisms underlying the condition. Notable differences occur in the distribution of airflow and wall forces between the EILO and control participants, which align with symptoms and visual observations. [ABSTRACT FROM AUTHOR]

Interaction of nonlinear shallow water waves with a deformable seafloor represented by an infinitely long elastic sheet lying on a viscoelastic foundation is investigated. The study is motivated by damping features of muddy coastal areas on ocean waves. The mathematical model utilizes the Level I Green–Naghdi equations for the fluid flow and the thin plate theory for the elastic bottom deformations. The methodology is validated through comparisons with the linear water wave theory and available numerical data. Theoretical predictions of the coupled seafloor vertical displacement and free-surface elevation are provided for a range of the incoming wave parameters and the seafloor characteristics. The results demonstrate that the wave experiences significant decrease in amplitude and propagation speed, as a result of the interaction with the deformable seabed. An exponential decay of periodic waves with propagating distance is observed. It is found that the foundation stiffness is of dominating importance, as compared to other parameters of the deformable seafloor. It is shown that waves with shorter wavelength are dissipated strongly by the action of the deformable seafloor while the bottom conditions have less impact on long wave dissipation. Just the opposite, long waves experience significant wave diffraction when compared to the waves with shorter wavelength. Patterns of the velocity field are shown to be modulated in magnitude and wavelength contributed by the seafloor. [ABSTRACT FROM AUTHOR]

We consider a horizontal, submerged plate in shallow water that is allowed to oscillate in the vertical direction due to the wave loads. The plate is attached to a linear spring and damper to control the oscillations. The focus of the study is on the transformation of the wave field by the submerged oscillating plate. To estimate energy scattering, wave reflection and transmission coefficients are determined from four wave gauges: two placed upwave and two placed downwave of the oscillating plate. The flow is governed by the nonlinear level I Green-Naghdi (GN) equations, coupled with the equations of the vertical oscillations of the plate. Time series of water surface elevation recorded at gauges upwave and downwave of the plate obtained by the GN model are compared with the available laboratory experiments and other data, and very good agreement is observed. Wave reflection and transmission coefficients are then determined for a range of involved parameters, including wave conditions (wavelength and wave height), initial submergence depth of the plate, plate length, and the spring-damper system attached to the plate. It is found that a submerged oscillating plate can have a remarkable effect on the wave field and that nonlinearity plays an important role in this wave-structure interaction problem. Discussion is provided on how the wave reflection and transmission coefficients vary with the wave conditions, plate characteristics, initial submergence depth, and spring-damper system properties. [ABSTRACT FROM AUTHOR]

Head-on collision of two solitary waves in the presence of linear shear currents is studied by the use of the High-Level Green–Naghdi (HLGN) theory. The finite difference method is used to solve the HLGN model in the time-domain simulation. The initial values are obtained by the steady solution of solitary waves in the presence of linear shear currents. Shear currents with different velocities are considered to assess their effect on the solitary-wave collision. Three aspects of the head-on collision process in the presence of shear current are studied, namely, the wave elevation, velocity field, and particle trajectory. Results show that the background linear shear current significantly affects the wave elevation, velocity field, and particle trajectory during the head-on collision. It is observed that in the presence of the current, the wave elevation is narrower near the maximum surface displacement and is wider near the still-water level. It is also shown that near the seafloor, the horizontal velocity is opposite of the current direction, while it is following the current direction near the free surface. The opposite shear current results in the formation of a vortex in the fluid field. At the point of the collision, the vortex appears at a lower vertical position and shifts upstream of the current direction. Following the particle trajectories in the presence of the shear current, it is observed that the particles do not return to their initial positions after the head-on collisions, and the loop motions of the particles become smaller with larger current velocities. [ABSTRACT FROM AUTHOR]

Diffraction and refraction of nonlinear shallow water waves due to uneven bathymetry are studied by use of the Green-Naghdi (GN) equations in three dimensions. A numerical wave tank consisting of deep, transitional, and shallow regions is created. Various forms of three-dimensional bathymetry, consisting of ramps with nonuniform profiles and large slopes, are used to connect the deep-water side of the tank to the shallow water shelf. A wavemaker is placed at the upwave side of the domain, capable of generating solitary and cnoidal waves of the GN equations. A numerical wave absorber is located downwave of the domain to minimize the wave reflection back into the domain. The system of equations is solved numerically in time domain by use of a second-order finite-difference approach for spatial discretization, and in a boundary-fitted coordinate system, and by use of the modified Euler method for time marching. Results include solitary and cnoidal wave surface elevation and particle velocities and are compared with the existing solutions where possible. Overall, very good agreement is observed. Discussion is provided on the nonlinearity and dispersion effects on the wave diffraction and refraction by the various forms of the ramps, as well as on the performance of the GN equations in solving these problems. [ABSTRACT FROM AUTHOR]