Three-dimensional Numerical Simulation Of Tidal Current And Temperature Field In Luoyuan Bay

The seawater temperature directly affects the ecological environment and the survival of aquatic organisms,which is one of the most basic elements in the marine physical properties.In recent years,the large-scale thermal/nuclear power plants are often built in coastal areas,using seawater as the cooling water and discharging large amounts of waste heat into the surrounding water.Especially for the construction of power plants in the same coastal area,the hot water is discharged into the same receiving water area.Under the influence of tidal current transport and thermal diffusion,the distribution structure of the original temperature field is directly changed.The rise of seawater temperature will cause a series of problems such as deterioration of seawater quality and eutrophication,which will bring some adverse effects on the marine ecological environment.At present,the environmental problem of thermal discharge from power plant has become an important content in the study of water environmental pollution.Learning the characteristics of tidal current and scientifically predicting the distribution characteristics of temperature field under the influence of the thermal discharge can provide an important reference for environmental assessment,biological community analysis and engineering planning.In this paper,combined with the Luoyuan Bay project,the ECOMSED model is used to simulate the tidal current and temperature field and analyze the hydraulic and thermal characteristics.Based on the verification of the model with the observation data,the temperature field of Luoyuan Bay under the influence of the thermal discharge of power plants is simulated and predicted,and the temperature distribution characteristics,the heat transport rule and the influence of the construction of power plants are analyzed.The research contents and achievements in detail are as follows:(1)On the basis of consulting the relevant literature of tidal current field,temperature field and thermal discharge,the research status and methods in this field are summarized.Meanwhile,the topographic,meteorological and hydrological data of Luoyuan Bay are analyzed in detail.(2)Learn the source code of ECOMSED,focus on its hydrodynamic module and heat flux module,and establish a three-dimensional hydrothermal model suitable for Luoyuan Bay through modification and debugging.(3)According to the observation data from November to December 2012 during the operation period of Kemen Power Plant(the installed capacity of 1088 MW in spring tide and1464 MW in neap tide),the three-dimensional numerical simulation of tidal current and temperature field in Luoyuan Bay during the spring and neap tides is carried out.The calculation results of tidal level and velocity,flow direction and temperature of each layer at each station are given,and compared with the observation data.It is found that the calculated values are in good agreement with the measured values.During the spring tide and neap tide,the average relative error of tide level in a tidal day is less than 3%,and the average relative error of temperature is less than 1%.The simulated tidal current and temperature field can accurately reflect the actual tidal current and temperature distribution in Luoyuan Bay.(4)The tide in Luoyuan Bay is regular semidiurnal tide.The flood and ebb currents moved in the opposite direction and the property of reciprocating flow was obvious.When the tidal current enters the bay mouth,it is mainly divided into two streams.One stream flows along the northwest and the other flows to the southwest shallow water.The tidal power in the bay is strong,and the duration of flood tide and ebb tide is basically the same.During the spring tide of observation period,the maximum tidal range is 5.75 m,and the maximum velocity of flood tide is 0.69 m/s,and the maximum velocity of ebb tide is 1.00 m/s;during the neap tide,the maximum tidal range is 3.83 m,and the maximum velocity of flood tide is0.44 m/s,and the maximum velocity of ebb tide is 0.70 m/s.Except for the small area near the outlet of the power plant,the average temperature of the whole area is 16.5-20.0?.(5)The plane distribution characteristics of surface temperature field in Luoyuan Bay in winter under the influence of three power plants(total installed capacity is 7720MW)are analyzed.a)The water temperature in winter gradually decreases from the bay mouth to the bay,and the average temperature of the bay is 17.0-21.0?.Affected by the installed capacity,water depth and tidal current characteristics,the thermal discharge of the two power plants on the south bank has a greater impact on the water temperature,while the Luoyuan power plant on the north bank has a smaller impact.b)The movement of the heated water with tide is obvious.During the spring tide,the ability of heat transport along the tidal direction is stronger due to the stronger tidal dynamics,and the influence range of surface layer at 20.0?below is slightly larger than that of neap tide;The heat accumulation effect of neap tide is more obvious,and the influence ranges of 20.0?and above are significantly increased.The average temperature zone of 20.0?runs through the north and south banks of Kemen Channel.On the whole,the neap tide is unfavorable tide.(6)The vertical temperature distribution characteristics of Luoyuan Bay under the influence of three power plants are analyzed.The vertical temperature difference is mainly reflected near plants.The temperature field of the surface,middle and bottom layer,vertical temperature difference field and the vertical temperature distribution of typical section are given respectively.The influence area of thermal discharge is mainly in the surface and middle layer.During spring tide and neap tide,the average 1.0?temperature difference area between the middle layer and bottom layer is about 13.7%of that between the surface and bottom layer,and the average 4.0?temperature difference area between the middle layer and bottom layer is about 38.9%of that between the surface and bottom layer.The thermal discharge of Luoyuan power plant on the north bank basically does not affect the middle water temperature nearby.Compared with the spring tide,during the neap tide,the vertical mixing ability is weaker,the vertical temperature difference and the degree of vertical unevenness are more obvious.(7)With the help of temperature rise field,the influence of power plants construction on the water temperature of Luoyuan Bay can be reflected more intuitively.It is found that the construction of power plants has a great impact on the water temperature of the south bank and the southwest bayhead.During the spring tide and neap tide,the temperature rise of the southwest bayhead is above 0.5?.The area of 0.5?temperature rise in each layer is about 47.15-51.35 km~2in the spring tide,and the area in neap tide is 43.53-51.63 km~2;The high temperature rise is mainly distributed in the surface layer of the south bank.The surface4.0?temperature rise area is 0.29 km~2in spring tide and the area is 0.41 km~2in neap tide;Under the influence of strong heat accumulation in neap tide,the 2.0?temperature rise zone of Kemen power plant and Shenhua power plant is connected and the 1.0?temperature rise range of the southwest shoal increases significantly.During the neap tide,the 1.0?temperature rise areas of the surface,middle and bottom layers are 14.40 km~2,7.59 km~2and6.82 km~2respectively;The whole tide average 0.1?temperature rise zone basically surrounds the sea area of Luoyuan Bay,accounting for 78%-83%of the total the calculation area.(8)The results show that ECOMSED model can simulate the tidal current field and temperature field accurately.At the same time,the simulation results have certain reference value for power plant engineering construction and environmental assessment.