# for a expression

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 June 13, 2014, 00:04 for a expression #1 Member   liuzexiang Join Date: Oct 2012 Location: China Posts: 69 Rep Power: 13 hi,everyone i meet a problem so i am here for help! i want to gain the information of these nodes on the surface in the model in my simulation such as current density, conductivity and so on. But i don't know how to gain the information of these nodes by expression or function. i want to use the expression to describe the motion of the surface. there is another way to reach to my aim in the simulation. i output the information of these nodes as .csv file in the cfd-post. then i compute the new coordination of x,y and z of these nodes by an equation about the current density of these nodes. But there are two questions: 1. how to save the .csv file in the cfd-post so that i can input the .csv file to the cfd-post and gain the deformation of the surface. 2. how to do when i want to use the deformation model as the new model in the next simulation. can you help me ,give me some advice or some examples. my email is lzx_527.student@sina.com thank you very much!

 June 13, 2014, 06:53 #2 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,767 Rep Power: 143 The method you describe is likely to be the least efficient multiphysics simulation ever performed. Handling this sort of data in a text file is going be very slow. Can you describe what you are trying to model and how the surface is moved by the current density and conductivity. We might be able to come up with a better way to model it.

 June 15, 2014, 02:42 #3 Member   liuzexiang Join Date: Oct 2012 Location: China Posts: 69 Rep Power: 13 hi, i am glad to see your reply. the description is showed as follow: the material of the surface is metal and the dissolution is taken place at the surface following the equation x2=x1-wit,where x2 is the new x coordination of the node and the x1 is the old x coordination of the node. so is the y and z coordination. w is the coefficient of the metal dissolution and i is the current density,t is the dissolution time. i think there are two method to solve this problem. 1. motion mesh. the dissolution along the x,y and z can be described by the expressions about the current density and then these expressions are inputted to coordinate displacement in cfx-pre. when the simulation is solved, the motion of the surface can be gained. the question is which function can gain the current density of these nodes ? 2. just output the current density of these nodes, and compute the new coordination of these nodes after t time. then input the new nodes to the model and simulation for the next simulation. the question is how to save the csv file and input it to the model, and save as the new model for the next simulation.

 June 15, 2014, 06:45 #4 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,767 Rep Power: 143 You should be able to do this with mesh motion. No need for external stuff. But I am not familiar with the electric field functions in CFX as I never use it.

 June 15, 2014, 13:28 #5 Member   liuzexiang Join Date: Oct 2012 Location: China Posts: 69 Rep Power: 13 but i think it is just a function problem, it is not a problem of electric field. just a function that can gain the information of nodes such as velocity and so on is OK

 June 15, 2014, 18:43 #6 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,767 Rep Power: 143 I do not understand what you are asking. What is your question?

 June 17, 2014, 13:04 #7 Member   liuzexiang Join Date: Oct 2012 Location: China Posts: 69 Rep Power: 13 i want to simulate the dissolution of the metal for a time. so i want to know the current density. but now i think it is not a good method because the time is too long for the simulation. maybe output the current density of these nodes and compute the value of dissolution is better. then gain the deformation of the model . but the key problem is how to use the deformation model as the next simulation. how to save this kind of model and input to the cfd-pre thank you !

 Tags cfd-post, expression