Characteristics Analysis Of Shallow Water Tidal Constituents In The Huanghai And Bohai Sea Based On FVCOM

Under the influence of terrain and other factors,the tidal wave movement in the coastal sea is very significant.This area is also the sea where human activities are extremely frequent.When the tidal wave enters the shallow water area,under the influence of sea bottom friction and the nonlinear effect between the astronomical tides,they will form shallow water tides.Both the Huanghai sea and the Bohai sea are shallow continental shelf seas,where the shallow water tide is relatively large.Therefore,the study of shallow water tide is of great significance to grasp the characteristics of tides and tidal currents in the Huanghai and Bohai sea.In this paper,based on the unstructured grid finite volume method FVCOM model,in the Huanghai sea and the Bohai sea,numerical simulation of tide and tidal current was carried out.The latitude and longitude range of the selected research area is 117.5°?127°E,and 34.5°?41°N.The whole region consists of 25,281 nodes and 48,759 cells.The spatial resolution of the near-shore region is set to 0.02°,and that of the near-open boundary region is set to 0.05°.The vertical range is divided into five intervals of sigma level.This paper simulated the 40 days of tide and tidal current.In order to avoid the initial oscillation caused by cold start,harmonic analysis was carried out on the calculated results of tide level in the last 30 days.The measured data of tidal station are used to compare the simulation results.It can be found that the errors of the calculation results are either positive or negative,which fully shows that the simulation results do not have errors on the system.Then the absolute mean deviation of M₂ and K₁,the two main tidal amplitudes and the late Angle,is calculated.It is found that the simulation results are in good agreement with the measured data.The numerical simulation results of tide and tidal current in the Huanghai and Bohai sea are compared between the unstructured grid FVCOM model and the structured grid POM model.The simulation results of the two models M2 partial tidal amplitude and the measured data of the late Angle heel tidal station were fitted and analyzed.The determination coefficients of M2 tidal amplitude and late Angle of FVCOM model were 97.86%and 98.91%respectively,while the determination coefficients of M2 tidal amplitude and late Angle of POM model were 93.56%and95.92%respectively.It is found that both models can well simulate the tidal system of the Huanghai and Bohai sea.However,the unstructured grid FVCOM model is better than the structured grid POM model in the application of tidal wave simulation in the Huanghai and Bohai sea.In this paper,three shallow water tides M₄,MS₄ and M₆ were studied.Through the cotidal chart,it is not difficult to find that the tide wave system of MS₄ in the Huanghai and Bohai sea is similar to that of M₄.There are four amphidromic points rotating anticlockwise in the Bohai sea and four amphidromic points in the Huanghai sea,two of which rotate counterclockwise.M₆ tidal constituent has a total of 11 amphidromic points in the Huanghai and Bohai seas,5 in the Bohai sea and 6 in the Huanghai sea,of which 6 rotate counterclockwise.According to their tidal current study,the three shallow water tides M₄,MS₄ and M₆ are the strongest flow areas in Jianghua bay and west Korea bay,and the weak flow areas are mainly distributed in the open sea and the central sea area.The tidal current velocity increases gradually from the central sea area to the top of each bay.M₄and MS₄ tidal current flow to most of the sea clockwise rotation.However,the M₆ tidal current situation is complex,clockwise and counterclockwise rotation crisscross.Article further explores the three shallow water wave generation mechanism.Through the comparison of five experiments,M₄ and M₆ are mainly generated by the deformation of M₂ tidal component introduced by the open seas.Nevertheless,the addition of S2 can inhibit the formation of M₄ and M₆ tidal fractions in the study area.It was also found that the addition of other major tidal components had more complex effects on M₄ and M₆.For MS₄ tidal constituent,the interaction between M₂ and S₂ is the main factor of its generation.Adding M₂ and S₂ tide alone cannot produce MS₄ tide.In addition,the interaction between M₂ and S₂ tide and other major tides can promote the formation of MS₄ to some extent.Finally article discusses the three tidal energy flux of shallow water wave.It is found that the tidal energy flux of M₄,MS₄ and M₆ is very small under the influence of the reciprocating current in the Bohai sea.In the Huanghai sea,the M₄ and MS₄constituent tidal energy flux distribution are similar.There are maxima in West Korea bay,Jianghua bay,east of south yellow sea and Haizhou bay.In general,it spreads from the shallow water near the shoreline to the deep water area.The energy flux of M₆ tidal constituent is large in West Korea bay and Jianghua bay and tidal energy generated in Jianghua bay can spread westward to the west bank of the south Huanghai sea.In general,the tidal energy flux of MS₄ tidal constituent is less than that of M₄ tidal constituent but still on the same order,while M6 tidal constituent is one order less than the previous two.The comparison of tidal energy dissipation at the bottom boundary of three shallow water tides is similar to the tidal energy flux.M₄ is similar to MS₄,and M₆is one order less than the previous two.The tidal energy dissipation of the bottom boundary gradually increases from the central sea area to the top of each bay.