A fully nonlinear,three-dimensional nonhydrostatic model driven by four principal tidal constituents(M2,S2,K1,and O1) is used to investigate the spatial-temporal characteristics and energetics of internal tides in Luzon Strait(LS).The model results show that,during spring(neap) tides,about 64(47) GW(1 GW=109 W) of barotropic tidal energy is consumed in LS,of which 59.0%(50.5%) is converted to baroclinic tides.About 22(11) GW of the derived baroclinic energy flux subsequently passes from LS,among which 50.9%(54.3%) flows westward into the South China Sea(SCS) and 45.0%(39.7%) eastward into the Pacific Ocean,and the remaining 16(13) GW is lost locally owing to dissipation and convection.It is revealed that generation areas of internal tides vary with the spring and neap tide,indicating different source areas for internal solitary waves in the northern SCS.The region around the Batan Islands is the most important generation region of internal tides during both spring and neap tides.In addition,the baroclinic tidal energy has pronounced seasonal variability.Both the total energy transferred from barotropic tides to baroclinic tides and the baroclinic energy flux flowing out of LS are the highest in summer and lowest in winter.
Energetic near-inertial internal waves （NlWs） were observed on the continental slope of the northern South China Sea in September 2008. Characteristics of the observed near-inertial waves were examined based on current data recorded by a moored acoustic Doppler current profiler. Results of a simple slab model indicated that the NIWs were generated by the surface winds of Typhoon Hagupit. Following Hagupit＇s passage, the wave field was dominated by baroclinic NIWs. The near-inertial currents were surface-intensified with a maximum of 0.52 m/s but still reached 0.1 m/s at the depth of 210 m. Moreover, the near-inertial currents were clockwise-polarized and slightly elliptical. A depth-leading phase of the near- inertial currents was evident, which indicated downward energy propagation. However, the rotary vertical wavenumber spectra suggested that upward energy propagation also existed, which was consistent previous theoretical study. The frequency of the NIWs, modified by the positive background vorticity, was 0.714 2 cycles per day, which was 0.02f0 higher than the local inertial frequency （f0）. The near-inertial kinetic energy evolved exponentially and had an e-folding timescale of about 3 days. The vertical phase and group velocity were estimated to be 10 and 2.1 m/h, respectively, corresponding to a vertical wavelength of 340 m. The NlWs were dominated by the second mode with a variance contribution of 〉50%, followed by the third mode, while the first mode was insignificant.
During the observational period of our study, Typhoon Hagupit passed over the mooring site and induced strong near-inertial waves （NIWs）, which provided an opportunity to investigate the interactions between internal tides （ITs） and NIWs. Based on the mooring data, we compared the current spectra during the typhoon period and non-typhoon period in the northern South China Sea, and found that the high- frequency waves （fD1 and fD2） were evident during the former. Moreover, the observations of the current revealed that fD1 and fD2 occurred near the depth of strong vertical shear in the NlWs. In order to confirm the generation mechanism of fD1 and fD2, we compared the positions of strong vertical shear in the NIWs and strong vertical velocity in the ITs. It was established that the vertical shear of the horizontal current of the NIWs and the vertical current of the ITs contributed to the generation of fDt and fD2.
Remotely operated vehicles(ROVs) are unique tools for underwater industrial exploration and scientific research of offshore areas and the deep ocean. With broadening application of ROVs, the study of factors that affect their safe operation is important. Besides the technical skills to control ROV movement, the dynamical ocean environment may also play a vital role in the safe operation of ROVs. In this paper, we investigate the influence of large-amplitude internal solitary waves(ISWs), focusing on the forces exerted on ROVs by ISWs. We present a methodology for modeling ISW-induced currents based on Kd V model and calculate the ISW forces using the Morrison equation. Our results show that an extremely considerable load is exerted by the ISW on the ROV, resulting in a strong disturbance of the vehicle's stability, affecting the ROV control. The numerical results of this work emphasize the importance of considering dynamical conditions when operating underwater vessels, such as ROV. Further laboratory and field investigation are suggested to gain more understanding of this subject.
A variable coefficient, rotation-modified extended Kortweg-deVries （vReKdV） model is applied to the study of the South China Sea （SCS）, with focus on the effects of the high-order （cubic） nonlinearity and the rotation on the disintegration process of large-amplitude （170 m） Internal Solitary Waves （ISWs） and the semi-diurnal internal tide propagating from the deep basin station to the slope and shelf regions in a continuously stratified system. The numerical solutions show that the high-order nonlinearity significantly affects the wave profile by increasing the wave amplitude and the phase speed in the simulated area. It is shown that the initial KdV-type ISW will decay faster when the rotation dispersion is considered, however the wave profile does not change significantly and the rotation effect is not important. The simulations of the semi-diurnal internal tide indicate that the phase of the wave profile is shifted earlier when the rotation effect is included. A solitary wave packet emerges on the shelf, and the wave speed is also greater when considering the rotation dispersion. In addition, the effects of the background currents are discussed further in this paper It is found that the background currents generally change the magnitude and occasionally change the sign of the nonlinear coefficients in the northern SCS.
By means of the Lie algebra B 2,a new extended Lie algebra F is constructed.Based on the Lie algebras B 2 and F,the nonlinear Schro¨dinger-modified Korteweg de Vries（NLS-mKdV） hierarchy with self-consistent sources as well as its nonlinear integrable couplings are derived.With the help of the variational identity,their Hamiltonian structures are generated.
Both large amplitude depression and elevation internal solitary waves （ISWs） were observed on the continental shelf of the northwest South China Sea （SCS） during the Wenchang Intemal Wave Experiment. In this study, we investigate the characteristics of depression and elevation ISWs based on comparisons between observational results and internal wave theories. It is suggested that the large amplitude depression wave is better represented by the extended Korteweg-de Vries （EKdV） theory than by the KdV model, whereas the large amplitude elevation wave is in better agreement with the KdV equation than with the EKdV theory. Wave-induced forces on a supposed small-diameter cylindrical pile by depression and elevation waves are also estimated using the internal wave theory and Morison formula. The wave-induced force by elevation ISWs is rarely reported in the literature. It is found that the force induced by the elevation wave differs significantly fi＇om that by the depression wave, and the elevation wave generally produces greater force on the pile in the lower water column than the depression wave. These results show that ISWs in the study area can present a serious threat to ocean engineering structures, and should not be ignored in the design of oil platforms and ocean operations.
