Hello, currently i am working on Dynamic mesh of Rotary Engine(Wankel Engine). After compiling the user defined function(UDF) in Fluent 6.3 and setting all the dynamic parameters and dynamic zones paramaters when i check the dynamic mesh motion it is giving me the message of NEGATIVE VOLUME DETECTED .i.e. dynamic mesh update failed. Even after this i varied many parameters and also i refined the mesh quality still it is giving the same error message.

CAN ANY ONE PLEASE TELL ME THE SOLUTION FOR THIS PROBLEM AS EARLY AS POSSIBLE.

Thanks and Regards Vinay

it gives you this message before or after iterating (or checking motion)? I assume it's given after checking the motion. Try to reduce your time step.

Thanks for your reply, I tried this option with various steps like reducing the time step as well as increasing the time step. But still i am getting the same error. What are the reasons for negative volume error. vinay

in my cases, I got negative volume, when dynamic zones are wrong defined, or when time step are too big Are you using Layering, smoothing, remeshing methods?

I am using smoothing and remeshing. I am not using layering...In my case there are two zones .i.e. trochoid (casing) inside this casing only the rotor rotates. so for rotating body i am using rigid body and for foxed casing i am using deforming option..Then can u tell me how to define cell height. As i am not able to find the cell height for the elements what i have created in GAMBIT..

under define/dynamic mesh/parameters in the remeshing parameters you have info about your mesh height are you sure that MDM is the right choice for your model? for rotor/stator, sliding mesh yould be better are you solving 2d/3d?

i am solving 2d pbm and i am sure that i have defined correct MDM for both rotor and trochoid.

ok I can I have a look at it if you want. you can send me an email

[m.r_khani]

hello dear friend
can you send me your udf for motion pf wankel engine?

i have a simalr project that i want to see how can i write a udf for rotatin as an irrigular shape
me email: m.r_khani@yahoo.com

[sanjeetlimbu]

Hi i am using a 2D simple mesh- for simulating compression stroke. I using the profile define to get the dynamic motion.. average velocity is 9m/s to max 14m/s . cell size= 0.0001m, stroke length 254mm, clearance voume 14mm. The crevice is very important part for physics in combustion. I had the crevice and body part split between two zones. the crivece zone is moving -rigid body and body as deforming.
But when i using the preview mesh motion I am getting the negative volume error. even i tried to reduce the time step to 4.1667E-8, also getting the same error

Pl tell if I can do anything to change the negative volume error

[kennyboy]

Hi vinay. I am currently working on a wankel profile as well. Similarly, I face the problem of negative mesh volume while trying to do a 2D simulation of the eccentric motion in fluent. So I was wondering how did you solve this issue in the end?