mass flow rate measurement

Submitted by NSalloum on Mon, 11/12/2018 - 15:28

hello,

I am trying to measure the mass flow rate of a material flowing out of a hopper, but I please need some help.

I drew using a CAD software a 3D plate with a hole having the same diameter of the hopper opening and call it into LIGGGHTS using the fix "mesh/surface", because I want to measure the mass flow rate of the material exiting the whole area of the opening and not only at a single point, and then used the following fix:

fix mflow all massflow/mesh mesh CAD vec_side 0. 0. -1. (for example)

But I am getting the following error:

ERROR: Fix massflow/mesh (id mflow): requires a planar face mass flow measurement or using 'point_at_outlet' (../fix_massflow_mesh.cpp:339)

so I thought about using the "mesh/surface/planar" fix, but I am getting the following error:

ERROR: Face defined as planar face is in fact not planar . You might want to check the 'curvature' setting (../tri_mesh_planar .cpp:71)

So how am I supposed to draw a meshed planar surface and import it as stl file to liggghts?

best wishes,
Nizar

paul | Mon, 11/12/2018 - 21:04

You are using only a surface, right? Not a body? please upload the stl file if you're unsure.

CAD programs are usually crappy at creating good stl surfaces. using the curvature settings may help you. otherwise, use a better mesher maybe?

In any case, why don't you just define a region and output the number of particles?

NSalloum | Tue, 11/13/2018 - 08:30

Actually I drew a body in the CAD software as I didn't find an option for meshing a surface in it.
Moreover, as I understood from the documentation, in order to measure the mass flow rate in LIGGGHTS, I am supposed to use the "massflow/mesh" fix which introduces the usage of meshed surface and not a region unless I want to measure the mass flow rate at a specific point, the thing that actually I am not interested in, as I want rather to measure the mass flow rate exiting the area of the hopper's opening.

So what do you suggest me to do in this regards?

best wishes,
Nizar

paul | Tue, 11/13/2018 - 10:32

Surface =/= volume body. I'd recommend learning how to remove individual faces from your body before creating the stl mesh. This is also recommended for all geometries - only include those with particle contact in your mesh for better performance.

Solidworks: Insert -> Face -> Delete, Select Delete only, select the faces to delete.
Then save as stl, ideally increase resolution in the dialogue and do not move to positive half-space.

bariksan | Mon, 02/22/2021 - 07:53

Hi
I am a beginner in Liggghts. I want to know the meanings of 5 output columns in a mass vs time txt output file. Please check the attached file.

# Fix print output for fix data
8.02 23.3459604069891 145 1168.46648683632 7257.25725725743
8.04 50.2340665309006 312 1344.40530619561 8350.0000000002
8.06 77.1221726548121 479 1344.40530619561 8350.0000000002
8.08 106.103364884178 659 1449.05961146832 9000.00000000021
8.1 136.855629972005 850 1537.61325439142 9550.00000000023

mschramm | Tue, 03/09/2021 - 17:23

Hello,
Where is your attached file?
From the docs

This fix also computes a global vector of length 6. This vector can be accessed via “f_ID”, where ID is the fix id. The first vector component is equal to the total mass which has crossed the mesh surface, the second vector component indicates the particle count. The third vector component is equal to the total mass which has crossed the mesh surface since the last output divived by the time since the last output (i.e., the mass flow rate), the fourth vector component indicates the particle count since the last output divived by the time since the last output (i.e., the number rate of particles). The fifth and sixth vector components are the deleted mass and the number of deleted particles.