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#1 |
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Enrique Pérez Heredia
Join Date: May 2018
Location: Madrid, Spain.
Posts: 16
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Hello, I'm trying to simulate a fixed velocity fall of a body into a fluid, I am setting up the domain and introducing this UDF.
DEFINE_CG_MOTION(OW_fall, dt, vel, omega, time, dtime) { vel[1] = -5; } It is as simple as that but it does not work, when I start the simulation the body does not move at all and remains like that for any time. Thank you in advance. Enrique P. __
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#2 |
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Join Date: Sep 2017
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Hi Enrique,
Please could you sketch out how you have set up the Dynamic Mesh Zones? (I think you need a deforming cell zone plus a Rigid Body for the moving face zones. The Rigid Body is where you hook in the UDF.) Also describe the type of Dynamic Mesh that you have set up -- layering, smoothing, or whatever -- and summarise the settings there. Thanks, Ed |
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#3 |
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Enrique Pérez Heredia
Join Date: May 2018
Location: Madrid, Spain.
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Hi Obscureed, thanks for the answer.
I have my rigid body which is a cylinder, surrounded by another zone made by an inflation which moves with the cylinder. I have layering and remeshing that work nice because I have already used them to study the free fall under gravity of the same cylinder. I attach some images with the setting of the dynamic mesh. Cylinder_6DOF.PNG Cylinder_inflation.PNG Remeshing.PNG Smoothing.PNG
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#4 |
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Hi Enrique,
Thanks for those images. A couple of thoughts come to mind: -- Is 6DOF what you want in this model? I think if you want to impose a fixed motion, 6DOF should be off. I am actually confused about how the motion is currently defined: the UDF, the specified velocity in the Dynamic Mesh Zones window, or 6DOF. I think you need a setup where the UDF is more clearly in control. You also want a setup where a UDF of type DEFINE_CG_MOTION is called for -- currently, your UDF of this type is hooked in where DEFINE_SDOF_PROPERTIES would be appropriate. -- You seem to have given the same motion settings to the cylinder and to the fluid. (Although, as in my previous point, I am not entirely sure what those motion settings are.) So perhaps you would not expect to see relative motion. I think a correct setup would have the cylinder (boundary face zone) being given rigid-body motion, and the moving_fluid (surrounding cell zone) deforming without motion. By the way, I would recommend following the example in the help files to set the other velocities to zero: Code:
/* reset velocities */ NV_S(vel, =, 0.0); NV_S(omega, =, 0.0); if (!Data_Valid_P()) return; Good luck! Ed |
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#5 |
New Member
Enrique Pérez Heredia
Join Date: May 2018
Location: Madrid, Spain.
Posts: 16
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Thank you again Obscureed
You are right, I don't reallt want 6DOF but I didn't know where to introduce the UDF function. I tried in the same way as the free fall simulation (I did the free fall case with DEFINE_SDOF_PROPERTIES and it works properly). The "moving_fluid" zone that is in the simulation is only the portion of fluid with fixed mesh wich moves along with the body not the whole domain. Sorry about that, I should have uploaded an image of the mesh setup. To be clear, the only motion that I want is the one of the cylinder falling at constant velocity (and the surrounding zone aswell). Where shall I hook up the DEFINE_CG_MOTION UDF?
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#6 |
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Enrique Pérez Heredia
Join Date: May 2018
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Thansk for the help.
My error was to enable the 6DOF solver as obscureed pointed out ![]() Now I get to the point of obtaining results of pressures and forces. I'll update you or ask for more help. Enrique P. __
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#7 |
New Member
Enrique Pérez Heredia
Join Date: May 2018
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Im having some trouble again trying to impose the movement in two directions.
My UDF is the following: DEFINE_CG_MOTION(OW_fall, dt, vel, omega, time, dtime) { /* reset velocities */ NV_S(vel[0], =, 40.0); NV_S(vel[1], =, -1.5); NV_S(omega, =, 0.0); if (!Data_Valid_P()) return; } I get an error of the type "error: subscripted value is neither array nor pointer". Apparently it is related with the definition of the array vel which I think is defined by default as a 3-d array. Any suggestions? Thnaks.
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#8 |
New Member
Enrique Pérez Heredia
Join Date: May 2018
Location: Madrid, Spain.
Posts: 16
Rep Power: 4 ![]() |
Im having some trouble again trying to impose the movement in two directions.
My UDF is the following: DEFINE_CG_MOTION(OW_fall, dt, vel, omega, time, dtime) { /* reset velocities */ NV_S(vel[0], =, 40.0); NV_S(vel[1], =, -1.5); NV_S(omega, =, 0.0); if (!Data_Valid_P()) return; } I get an error of the type "error: subscripted value is neither array nor pointer". Apparently it is related with the definition of the array vel which I think is defined by default as a 3-d array. Any suggestions? Thnaks.
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body, fixed velocity, udf |
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