Asymptotical properties for the solutions of neutral parabolic systems with Robin boundary conditions were analyzed by using the inequality analysis.The oscillations problems for the neutral parabolic systems were con...Asymptotical properties for the solutions of neutral parabolic systems with Robin boundary conditions were analyzed by using the inequality analysis.The oscillations problems for the neutral parabolic systems were considered and some oscillation criteria for the systems were established.展开更多
Almost all works in the field of boundary layer flow under the breaking wave consider the flow similar as the flow in an oscillating pressure tube. Although the two flows are similar, there are many differences. The r...Almost all works in the field of boundary layer flow under the breaking wave consider the flow similar as the flow in an oscillating pressure tube. Although the two flows are similar, there are many differences. The results achieved in such manner are therefore also only similar to the results that can be achieved during measurements in the surf zone. Present article deals with boundary layer measurements on an inclined bottom under breaking waves. The measurements over the whole wave cycle were carried out, and the shear velocity under the breaking wave was calculated based on the measurements. It was found that there is a considerable space and time variation of the term in the surf zone. The turbulence generated during the wave breaking changes the shape of the shear velocity profile in comparison to the profile measured before breaking. As the values of shear velocity are directly correlated with the description of the whole velocity field in the wave, it can be assumed that the enhanced description of the shear velocity results in better understanding of the whole velocity field under breaking waves. Therefore, the article brings a new insight into the field and aims to make a discussion about the need to rethink the way of describing the boundary layer flow in the surf zone.展开更多
In this paper the results of an experimental investigation, finalized to analyze the effect of roughness elements on the Oscillatory Boundary Layer （OBL）, were presented and discussed. These experiments can be usefu...In this paper the results of an experimental investigation, finalized to analyze the effect of roughness elements on the Oscillatory Boundary Layer （OBL）, were presented and discussed. These experiments can be useful for the characterization of the complex hydrodynamic mechanisms in coastal environment, where the bottom boundary layer is very often subject to momentum exchange processes due to the presence of macro-structures on the bottom able to strongly influence and modify its own structure. In this investigation, experiments were performed in an oscillating water tunnel, covering a range of frequencies to from 0.646 up to 2.319 rad.s^-1. The roughness elements were modelled by mean of a matrix of stiff cylinders arranged on the bottom of the tunnel and two densities of cylinders were considered, corresponding to low and high density respectively. Velocity measurements were obtained by 2C DPIV （2 Component Digital Particle Image Velocimetry） technique. A detailed visualization of the flow through adjacent cylinders, including scalar velocity maps and streamlines are presented. Furthermore phase-averaged velocity distributions are here provided. Moreover, root-mean-squared velocities are considered and an empirical relation between （1） the root-mean-squared velocities and the distance from the bottom; （2） the velocity attenuation coefficient and the Reynolds number is obtained for both the considered configurations.展开更多
文摘Asymptotical properties for the solutions of neutral parabolic systems with Robin boundary conditions were analyzed by using the inequality analysis.The oscillations problems for the neutral parabolic systems were considered and some oscillation criteria for the systems were established.
文摘Almost all works in the field of boundary layer flow under the breaking wave consider the flow similar as the flow in an oscillating pressure tube. Although the two flows are similar, there are many differences. The results achieved in such manner are therefore also only similar to the results that can be achieved during measurements in the surf zone. Present article deals with boundary layer measurements on an inclined bottom under breaking waves. The measurements over the whole wave cycle were carried out, and the shear velocity under the breaking wave was calculated based on the measurements. It was found that there is a considerable space and time variation of the term in the surf zone. The turbulence generated during the wave breaking changes the shape of the shear velocity profile in comparison to the profile measured before breaking. As the values of shear velocity are directly correlated with the description of the whole velocity field in the wave, it can be assumed that the enhanced description of the shear velocity results in better understanding of the whole velocity field under breaking waves. Therefore, the article brings a new insight into the field and aims to make a discussion about the need to rethink the way of describing the boundary layer flow in the surf zone.
文摘In this paper the results of an experimental investigation, finalized to analyze the effect of roughness elements on the Oscillatory Boundary Layer （OBL）, were presented and discussed. These experiments can be useful for the characterization of the complex hydrodynamic mechanisms in coastal environment, where the bottom boundary layer is very often subject to momentum exchange processes due to the presence of macro-structures on the bottom able to strongly influence and modify its own structure. In this investigation, experiments were performed in an oscillating water tunnel, covering a range of frequencies to from 0.646 up to 2.319 rad.s^-1. The roughness elements were modelled by mean of a matrix of stiff cylinders arranged on the bottom of the tunnel and two densities of cylinders were considered, corresponding to low and high density respectively. Velocity measurements were obtained by 2C DPIV （2 Component Digital Particle Image Velocimetry） technique. A detailed visualization of the flow through adjacent cylinders, including scalar velocity maps and streamlines are presented. Furthermore phase-averaged velocity distributions are here provided. Moreover, root-mean-squared velocities are considered and an empirical relation between （1） the root-mean-squared velocities and the distance from the bottom; （2） the velocity attenuation coefficient and the Reynolds number is obtained for both the considered configurations.
