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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 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]

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]

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 extended Korteweg de Vries (eKdV) theory and Morison's equation, a theoretical model of internal solitary wave (ISW) loads on a submerged slender body is investigated, and experimental measurements are further carried out in a large stratified fluid flume. The results show that the theoretical results are in good agreement with the experimental results. The horizontal force of the ISW on the slender body is consists of the horizontal dynamic pressure force and the friction force, in which the horizontal dynamic pressure force plays a dominant role. The vertical force includes the vertical wave force and the reduced gravity during the interaction between a slender body and an ISW. The magnitude of the force increases with increasing ISW amplitude, while its direction remains unchanged, and the force is closely related to the submerged depth of the slender body in the density pycnocline, which affects both the magnitude and the direction of the force. • The ISW force on a submerged slender body is measured experimentally in a stratified fluid flume. • A theoretical study of ISW loads is conducted on a submerged slender body based on the Morison equation. • The experimental and theoretical results are compared for different ISW amplitudes and submerged depths. [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]