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September 12, 2012, 04:31 |
Is my Dynamic mesh setup correct?
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#1 |
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Location: Germany
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I am trying to simulate flapping motion of the wing using Dynamic Mesh. I have setup the case in Fluent but I have some doubts and questions regarding it. I am uploading the pictures which will show the dynamic mesh setup. Kindly tell me is it correct? The problem consist of a domain around the wing, symmetry plane, wing and fluid zones. Few questions......
1. I have declared domain(farfield) as "Stationary" zone as shown in pic1. Is it correct? how to set value of "Cell Height"(shown by a question mark in pic1)? 2. Fluid is set as "Deforming" as shown in pic2. Is it correct? values of the "Zone Parameters" will be taken from "Zone Scale Info" as shown in pic2? right? 3. S1020 is the name of wing which will be given motion using a DEFINE_GRID_MOTION udf and S1020 is set as "User Defined" as shown in pic3 is it correct? how to set value of "Cell Height"(shown by a question mark in pic3)? 4. Symmetry plane is set as "Stationary" as shown in pic4 is it correct? how to set value of "Cell Height"(shown by a question mark in pic4)? Also after the finalization of UDF I will use full structured hexa mesh for this problem. For this purpose in Dynamic mesh I will only use "Smoothing" and "Layering" for mesh update? am I right kindly comment? I cannot use "Remeshing" as it only works for unstructured meshes? right? |
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September 14, 2012, 00:25 |
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#2 |
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What i am about to you tell you works for unstructured tetrahedral mesh.
1. Cell Height is the ideal height based on which Fluent calculates whether to split or collapse cells. Ref:https://www.sharcnet.ca/Software/Flu...ug/node396.htm 2. Use DEFINE_CG_MOTION for the motion of wall. Ref:https://www.sharcnet.ca/Software/Flu.../udf/fludf.pdf 3. Symmetry plane should be set as deforming. 4. Farfield -> Stationary ? -- Not required fluid -> Deforming? -- not required |
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September 15, 2012, 00:27 |
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#3 |
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Jingchang.Shi
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1. Farfield not necessary to be stationary. I never set a certain value for the cell height. I just keep the original value. It's ok for my case.
2. Fluid not necessary to be deforming. So, do not need to worry the zone parameters. Leave them alone. 3. You should refer to the UDF manual for more infomation about DEFIEN_GRID_MOTION and DEFINE_CG_MOTION. In fact, you should use DEFINE_CG_MOTION to define the motion of your wing. And, you should set "Rigid Body" for your wing. 4. I think the symmetry plane may be better to be set as deforming. 5. I don't know whether you want to rotate the wing a big angle, say 45 degrees, or not. Smoothing is available for small degrees. I hold an opinion that layering is not suitable for your flapping case. Remeshing is designed for big degrees or big displacement movement. Actually, I do not know how to move the structural mesh for a big displacement. If you make it, please tell me how. |
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September 15, 2012, 15:27 |
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#4 | ||
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Quote:
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September 15, 2012, 15:32 |
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#5 | ||
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Quote:
Quote:
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September 19, 2012, 06:15 |
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#6 |
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Jingchang.Shi
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I agree with you on the idea that the fluid region will deform once the wing will flap. But I think that the setting of smoothing, layering and remeshing is doing this job, so we do not need to set the " deforming " option. This is my opinion.
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September 19, 2012, 06:17 |
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#7 |
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Jingchang.Shi
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I remember the macro DEFINE_GRID_MOTION is for your mesh motion, instead of your wing motion. my opinion.
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September 23, 2012, 04:50 |
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#8 | |
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Quote:
1. Farfield to set as "Stationary" 2. Symmetry also as "Stationary" 3. Fluid to define as "Deforming" 4. Wing to set as "Rigid Body" once you use DEFINE_CG_MOTION macro |
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September 23, 2012, 06:51 |
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#9 |
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Jingchang.Shi
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ok, but I also made a success without your 1, 2, 3.
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September 23, 2012, 07:07 |
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#10 |
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September 23, 2012, 08:58 |
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#11 |
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Jingchang.Shi
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Could you give me some cases for confirmation? Many thanks!
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September 24, 2012, 13:10 |
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#12 |
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September 24, 2012, 13:13 |
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#13 |
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http://www.cfd-online.com/Forums/flu...volume-3d.html
Read this thread |
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December 16, 2012, 10:37 |
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#14 |
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Vidit Sharma
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Hi All..
Sir, I am trying to rotate a 2D box or a 2D cup structure in Fluent using smoothing and remeshing. I am using tri mesh and as mentioned in Fluent Manual I am using smoothing and remeshing and also set the remeshing parameters from mesh info tab given in the remeshing menu. But the problem is that when i start simulation and it goes to first time step Fluent display "Updating mesh at time level N..." and here it stops and it happened alot of time and even waiting after a whole day it didnt worked. I also tried time step size from 0.01 to 0.000001 but it still show this problem. Can you plz help in this case? Thank u in advance |
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January 26, 2013, 15:01 |
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#15 |
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akshay
Join Date: Nov 2012
Location: IIT Bombay
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you pls check your dynamic mesh parameter properly.....if have proper idea to set or no then let me know so will help in this regard..
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November 8, 2017, 09:14 |
Deforming wall shape
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#16 |
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Join Date: May 2015
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Hi everyone,
I am new to dynamic mesh and trying to model my right wall as moving wall based on force balance. My udf looks like this(same udf as provided in user manual): #include "udf.h" static real v_prev=0.0; DEFINE_CG_MOTION(pstn, dt, vel, omega, time, dtime) { Thread *t; face_t f; real NV_VEC (A); real force, dv; /* reset velocities */ NV_S (vel, =, 0.0); NV_S (omega, =, 0.0); if (!Data_Valid_P ()) return; /* get the thread pointer for which this motion is defined */ t = DT_THREAD (dt); /* compute pressure force on body by looping through all faces */ force = 0.0; begin_f_loop (f, t) { F_AREA (A, f, t); force += F_P (f, t) * NV_MAG (A); } end_f_loop (f, t) /* compute change in velocity, i.e., dv = F * dt / mass velocity update using explicit Euler formula */ if(force>0) dv = dtime * force / 50.0; else dv=0; v_prev += dv; Message ("time = %f, x_vel = %f, force = %f\n", time, v_prev, force); Message ("yo"); /* set x-component of velocity */ vel[0] = v_prev; } However the shape of my right wall gets deformed. I want the shape to be intact. Please suggest what should be the settings in dynamic mesh. Which method should i use? |
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October 30, 2020, 07:16 |
Create a velocity UDF
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#17 | |
New Member
Rodolfo Alves Carvalho
Join Date: Jul 2020
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Hi, the forces are different, so you have a shear deformation. The solution would be to declare a global scope variable and comput it average in the face. After, you aply the same velocity in the whole thread (face, boundary, cells, etc).
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