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The experimental study on the interaction between a mode-2 internal solitary wave (ISW) and a horizontal transverse cylinder has been carried out in a large gravity-stratified fluid flume. One kind of making-wave method of "rotating-blade-gate" is proposed to achieve the experimental simulation of the standard mode-2 ISW in the laboratory flume. The conductivity probe array and particle image velocimetry are used to measure the mode-2 ISW and its wave-flow structure of the interaction with the horizontal transverse cylinder, and the micro-amplitude force sensor is used to measure the forces of the mode-2 ISW on the cylinder model. It is shown that the mode-2 ISW geometric structure is characterized by a convex and concave oval wave envelope shape and the counterclockwise and clockwise circulations are formed in its convex and concave domains, respectively. The resulting pair of upper and lower antisymmetric circulations moves forward together, which causes a horizontal strong flow at the symmetric center of the wave envelope consistent with the wave propagation direction. The horizontal transverse cylinder is subjected to the combined action of horizontal flow, vertical flow, and density change induced by the mode-2 ISW, in which the horizontal strong flow, induced flow separation, and vortex structure located at the symmetric center of the wave envelope are the signature features that are different from other positions. The theoretical analysis model of the forces exerted by the mode-2 ISW on a horizontal transverse cylinder is established. The spatial distribution characteristic of the force exerted by the mode-2 ISW on a horizontal cylinder is obtained, and the essential reason for the maximum horizontal and vertical loads on the cylinder is revealed. The horizontal maximum load corresponds to the inhomogeneous change of the horizontal velocity along the depth, and the vertical maximum load depends on the maximum density change along the depth, of which variation trend corresponds to the linear change of wave amplitudes. [ABSTRACT FROM AUTHOR]

Two internal solitary waves (ISWs) with very long fronts observed by synthetic aperture radar (SAR) images in the northern South China Sea (NSCS) are comparatively analyzed based on oceanic reanalysis data and the Korteweg–de Vries (KdV) theory. The differences in the environmental parameters, wave half-width, and amplitude of the two ISW fronts in the two distinct oceanic environments are studied. In the presence of a weak westward surface current of approximately 0.05 m/s, the values of the linear wave speed increase by up to 0.056 m/s, and the retrieved ISW amplitudes decrease by up to 14 m. On the contrary, for another background oceanic environment considering a relatively strong eastward surface current of approximately 0.2 m/s, there are decreases of up to 0.17 m/s in the linear wave speed and increases of up to 32 m in the retrieved amplitudes. However, the results retrieved from both the SAR observations commonly show that the ISW amplitudes along the fronts reach their maximums at roughly 21°N and decrease toward the southern and northern sides, in spite of their distinct background environments. [ABSTRACT FROM AUTHOR]

The vertical inhomogeneous structure of an internal solitary wave (ISW) in a continuous density pycnocline and its force exerted on a horizontal transverse cylinder are investigated theoretically and experimentally. The Dubreil–Jacotin–Long equation is used to describe the inhomogeneous vertical structure of the ISW, and a formula for calculating the vertical force on the cylinder in the inhomogeneous vertical structure is proposed. The inhomogeneous vertical structure of the ISW and its vertical force on a horizontal transverse cylinder are experimentally measured in a large stratified fluid flume. It is shown that the inhomogeneous vertical structure of the ISW is characterized by both inhomogeneous vertical distributions of ISW envelopes and amplitudes. The inhomogeneous vertical structure of the flow field is characterized by the shear distribution of the horizontal velocity above and below the continuous density pycnocline, as well as the reversed distribution of the vertical velocity on the windward and leeward sides of the ISW. The vertical force characteristics on the cylinder in the continuous density pycnocline, as well as the physical mechanism of the influence of the ISW inhomogeneous vertical structure on the vertical force, are obtained. The peak value of the vertical force on the cylinder situated at the pycnocline increases with the increase in ISW amplitude, and also, it increases and then decreases with the increase in submerged depth. Considering the inhomogeneous vertical structure characteristics of the ISW in an actual ocean environment, the average relative error in the vertical force calculation can be more effectively reduced by using the continuous density pycnocline force model than the strict two-layer fluid force model. The actual characteristics of ISWs in a stratified ocean environment can be objectively described, and the estimation accuracy of the vertical force on underwater objects can be greatly improved. [ABSTRACT FROM AUTHOR]

The evolution, breaking, and energy dissipation of internal solitary waves (ISWs) beneath different sea ice models were investigated using dye-tracing labeling and a wave-flow measurement technique. The ISW waveform exhibited various phenomena including a narrower wave width, smaller wave height, fission, or flipping after passing through ices. The wave amplitude decreased at the front slope and increased at the back slope. The wave speed decreased at the front slope, while it initially slightly increased and then decreased (Gaussian, triangular ice) or remained unchanged before then decreasing (rectangular ice) at the back slope. The wave surface was uplifted and the windward side of the wave evolved into a vortex. The time and location of these phenomena were closely related to the shape and height of the ice. The thickness of the upper fluid was influenced by different ices, causing a change in the intensity of the flow field. The energy dissipation was mainly caused by the frictional effect at the front slope and wave breaking at the back slope. The energy dissipation rate beneath the different ices increased in the order of Gaussian, triangular, and rectangular ice, and the higher the Gaussian ice, the greater the energy dissipation rate. • The propagation of internal solitary wave beneath the different sea ice models is studied in the laboratory. • The dynamic evolution of internal solitary waves are influenced by the shape and height of sea ices. • The energy dissipation of the ISW is thoroughly studied based on the evolution of the wave-flow field of ISW. [ABSTRACT FROM AUTHOR]

An experimental investigation of the vertical structure characteristics of internal solitary waves (ISWs) was systematically carried out in a large gravitationally stratified fluid flume. Four different stratifications were established, and basic elements of ISWs were measured by a conductivity probe array. The vertical distributions of the amplitude, characteristic frequency and waveform of two types of ISWs under different stratifications were obtained, and the experimental results were compared with the theoretical model. The study shows that most vertical structures of the amplitude under different stratifications agree with those of the theoretical model, while there are some deviations for ISWs with large amplitudes. Neither the two-layer model nor the continuously stratified model can effectively describe the variation in the characteristic frequency at different depths with amplitude. For a single small-amplitude ISW, the characteristic frequency first increases and then decreases with increasing depth. The characteristic frequency is largest at the depth of the maximum buoyancy frequency. For an ISW with a relatively large amplitude, there is likely to be a local minimum of the characteristic frequency near the depth where the maximum buoyancy frequency lies. In different stratifications, the sech 2 function of KdV theory can describe the waveforms of ISWs at different depths well. [ABSTRACT FROM AUTHOR]

Laboratory experiments were conducted to investigate the evolution characteristics of a type-a ISW packet propagating over a gentle slope. The elevation type-a ISW packet was generated by the gravity collapse of stratified density fluid, and its transformation process over the gentle slope was measured by use of the multichannel conductivity-probe arrays. The energy transmission and loss of the ISW packets during its evolution over the gentle slope were further analyzed. The experimental results showed that the evolution and energy transmission of the type-a ISW packet over the gentle slope is closely related to the amplitude of the leading wave in the wave packet. The conversion of the wave packet type is caused by the variations in amplitudes of the leading and tailing waves in the type-a ISW packet due to the topography effect. The distance between the adjacent waves in a type-a ISW packet gradually increases with the increasing propagation distance on the slope, as well as its increase rate is also enlarged. The wave speeds of both the leading and tailing waves always decrease with the propagation distance. The energy loss of the whole ISW packet increases with both the incident wave amplitude and the propagation distance. • The evolution process of a type-a ISW packet over a gentle slope was experimentally measured. • The wave amplitude, wave speed, and spatial distance variation of the leading and tailing waves of the type-a ISW packet with increasing propagation distance were analyzed. • The energy transmission and loss during the evolution process of a type-a ISW packet over a gentle slope and their influence factors were also analyzed. [ABSTRACT FROM AUTHOR]

Based on the experimental measurements of the ISW force on a horizontal transverse cylinder in a gravitationally stratified fluid flume, the modification formulas of the empirical coefficients in the ISW force calculations are proposed by use of parameter optimization methods such as the least square method and wavelet transform. The time series and spatial characteristics of various forces exerted on a horizontal transverse cylinder by an ISW, including the wave force, the reduced gravity and the vortex shedding force, were obtained, and their description precision was improved. It is shown that those forces exerted on a horizontal transverse cylinder involve the empirical coefficients, including the inertial force coefficient C m and the drag force coefficient C d in the Morison formula, and the vortex shedding lift coefficient C l in virtue of the vortex shedding frequency ω s , in which the fitting modification formulae of the empirical coefficients and vortex shedding frequency with the Reynolds number R e (1000–3000) by use of experimental data are approximated to the exponential function and the polynomial function, respectively. The calculation accuracy of the ISW force with modified coefficients is significantly improved compared with those forces having constant coefficients, in which the average relative errors of the horizontal force and the vertical vortex shedding lift with modifications are reduced by approximately 71% and 46%, respectively. In addition, some characteristic descriptions closer to the actual processes are obtained, including the time series variation of various forces, its contribution to the horizontal pushing or pulling force, and to the vertical downward drag or the 'double peak' force, and to its spatial variation with varying cylinder submerged depth, which further improves the understanding of the temporal and spatial features of the ISW acting on structural objects. • The ISW force on a horizontal transverse cylinder is measured experimentally. • The modification formulas of the empirical coefficients in the ISW force calculations are proposed. • The time series and spatial characteristics of various forces exerted on a horizontal transverse cylinder by an ISW are given. [ABSTRACT FROM AUTHOR]

It is essential to give the applicable range of nonlinear theories of the internal solitary wave in different classification conditions and water depth. The nonlinear theories used to describe the ISW, including KdV, eKdV and MCC theories were compared with experimental results. The characteristic parameters of ISW (waveform, phase speed, and wave frequency) and its load on slender body were chosen to provide a quantitatively applicable range of three nonlinear theories at different water depths. In general, the optimal theories are KdV, eKdV and MCC in turns for most conditions. However, for the description of phase speed, both the eKdV and MCC theories can describe it well, where the KdV theory has a large error in describing phase speed at large ISW amplitude. For the vertical force, the KdV and eKdV theories can describe it well in turns, while the MCC theory has a large error in calculating the vertical force. A diagram of the applicable range under different classification conditions and at different water depths is proposed for choosing a better theory in different fields. [ABSTRACT FROM AUTHOR]

The propagation of oceanic internal solitary waves (ISWs) with spatial irregularity and temporal instability is referred to as nonstationary evolution. To simplify the contraction and expansion of strait channels in the ocean into a sinusoidal geometric structure of a convex side boundary, numerical simulations with turbulent models were conducted in this study, supplemented by laboratory experiments in a stratified fluid flume, to verify the nonstationary evolution characteristics of ISWs propagating along a convex side boundary. This study reveals that when ISWs approach the convex side boundary, the wave amplitude begins to increase, and the horizontal shear increases. Upon entering the contraction segment of the side boundary, due to obstruction from the boundary, the wave shape undergoes vertical stretching and horizontal contraction, leading to a further increase in wave amplitude but a reduction in horizontal shear. The shear is the strongest when passing through the center of the convex side boundary with the smallest transect. However, the wave shape undergoes vertical contraction and horizontal stretching, resulting in decreases in both amplitude and shear compared to those at the center of the convex side boundary. • Characteristics of internal solitary waves propagating along a convex side boundary are studied. • The waveform undergoes vertical stretching and horizontal contraction upon entering the contraction segment and vice versa. • The wave amplitude and shear reach their maximums when passing through the center of the convex side boundary. [ABSTRACT FROM AUTHOR]