Dear All,
I am using EFDC to simulate a highly stratified river. The surface of the river and the bottom of the river have the difference of around 10 degrees in average. What are the parameters to adjust in EFDC to properly calibrate the temperature ? I believe there are several things that we can change. I believe the horizontal and vertical momentum diffusion coefficient have to do a lot with the mixing and stratification. I couldn’t find the range of the variables for the Hydrodynamic processes in EFDC.
Several other parameters such as Evaporation transfer coefficient, clear water light extinction, minimum fraction of solar rad absorbed in the top layer, initial bed temperature, heat transfer coefficient between Bed/WC. WOuld somebody give me clear idea of how each variables affect the temperature and suggest/recommend read any articles or books in which all the parameters used in EFDC have proper description ?
I have already run the model but seems like I need to adjust a lot of parameters. It seems I need more heat loss on the surface and more stratification on the bottom layer i.e lower temperature.
Thank you . Looking for quick reply asap.
John
What are the parameters to adjust in EFDC to properly calibrate the temperature? As you mentioned above, the momentum diffusion coefficients, especially vertical diffusion, has strong influence on the stratification of flow. These parameters are able to be adjusted through EFDC_Explorer as follows: >Hydrodynamics>Modify>Turbulent diffusion: Activate HMD with Smagorinsky, Wall Drag and WC Diffusion [ul] [li]Decrease Background/Constant Horizontal Eddy Viscosity for more stratification[/li] [li]Decrease Dimensionless Hor. Momentum Diff[/li] [li]Change value of Wall roughness[/li] [li]Decrease Vertical Eddy Viscosity[/li] [li]Decrease Maximum Kinematic Viscosity if Use Maximum is checked[/li] [li]Decrease Maximum Eddy Diffusivity if Use Maximum is checked [/li][/ul] In regards to the ranges of these parameters: You can change them so that the computed results fit well the measured data. However, they must be less than 1 and the range of kinematic viscosity should be based on the formula proposed by Chung, 2007; Soulsby,1997: υ = ( 4.43∙〖10〗^(-5))/(23.1+T_e ) Several other parameters involving the process of stratification The process of heat transfer certainly depends on the parameters as mentioned above. The heat exchanges with outside environment through the boundary conditions at bottom and water surface. This problem you should refer Zhen-Gang Ji, 2008, in which the methods and parameterization for EFDC were described in more detail. The boundary condition at water surface: -(ρC_p A_b)/H ∂T/∂z=H_L+H_E+H_c Where ρ is water density, C_p water specific heat, A_p vertical turbulent mass mixing coefficient, H water depth, H_Lthe heat flux of long wave radiation, H_E latent heat flux and H_c sensible heat flux. These heat fluxes are related to emissivity of water body, Stefan-Boltzmann constant, actual vapor pressure, cloud fraction, water surface temperature, air temperature, turbulent exchange coefficient, specific heat of air, wind speed, etc. The boundary condition at bed: A_b/H ∂T/∂z=-C_hb (ρC_p)/(ρ_b C_pb ) √(u_1^2+v_1^2 ) (T_b-T_1 ) Where ρ_b is sediment density, C_pb specific heat of water-sediment mixture and T_b bed temperature. So, in order to calculate the heat exchange at bed we have to include sediment transport term in the simulation. I need more heat loss on the surface and more stratification on the bottom layer i.e lower temperature My suggestion is that the following items should be taken into account: [ul] [li]Strongly decrease horizontal and vertical diffusion coefficients[/li] [li]Use wind field and atmospheric data[/li] [li]Include sediment transport[/li] [li]Use the vertical distribution of temperature for initial condition [/li][/ul] References Zhen-Gang Ji, 2008. Hydrodynamics and Water Quality modeling Rivers, Lakes and Estuaries. John Wiley & Sons, Inc. Soulsby R. 1997. Dynamics of Marine Sands, London: Thomas Telford Publications. Dang Huu Chung, 2007. Effects of temperature and salinity on the suspended sand transport. Int Journal of Numerical Methods for Heat & Fluid Flow, Vol.17, N.5, pp.512-521
Thank you EE development team for your detailed information about the stratification and the casuses.
I was trying to use your guidance to run my model. However, when I check the constant vertical eddy viscosity or diffusivity or maximum kinematic viscosity / Maximum Eddy Viscosity I always get negative error or maximum iterations exceed the external soluation. I tried changing the values for the eddy viscosity, kinematic viscosity and reducing the time step, I still get the error. Would you please tell me how to get rid of such kind of error ? I am already using the time step in range of 2 sec.
Thank you so much.
John
Sorry for the delay in replying to your question John.
Setting the vertical diffusivity to a constant is only for testing and very simple cases. It is not applicable for real world applications and therefore not surprising that the model crashes.
The maximum eddy viscosity option works fine, when vertical eddy diffusivity are being computed (the standard approach). You just need to make sure the maximum specified makes sense for your application.