{"id":159411,"date":"2021-06-11T19:02:15","date_gmt":"2021-06-11T19:02:15","guid":{"rendered":"\/forum\/forums\/topic\/how-to-export-particle-history-data-every-particle-time-step\/"},"modified":"2021-06-21T06:37:11","modified_gmt":"2021-06-21T06:37:11","slug":"how-to-export-particle-history-data-every-particle-time-step","status":"closed","type":"topic","link":"https:\/\/innovationspace.ansys.com\/forum\/forums\/topic\/how-to-export-particle-history-data-every-particle-time-step\/","title":{"rendered":"How to Export Particle History Data every Particle Time Step"},"content":{"rendered":"
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Hello everyone,<\/p>\n

I am simulating discrete particles and I am interested in the particle-particle collisions. Therefore, I am using the DEM collision model available in Fluent. This forces me to work with instationary particles (although I am looking for a steady solution, where the particle collisions dictate the spread).<\/p>\n

My idea is to inject particles, until the fluid and the particles have achieved a steady state.<\/p>\n

Due to the use of the DEM model, and the collisions between different sized particles, I am forced to use a very small particle time step size (10^-8) in order to get “physical” collisions\/the right overlap.<\/p>\n

Since I am continuously injecting particles, the simulation would be too slow if I had 1 particle time step for each fluid time step, so I increased the number of particle iterations per time step to speed the process up. <\/p>\n

Desirable would be e.g. a number of Time Steps=1e6 for particle time step size 1e-8 so that I get 0,01sec simulation time with only one fluid iteration.<\/p>\n

So far, I have worked out a solution that fits my needs:<\/p>\n

Setup->General->Time: Steady<\/p>\n

Setup->Models->Discrete Phase (On)<\/p>\n

Discrete Phase Model:<\/p>\n

               Interaction with Continuous Phase (On)<\/p>\n

               DPM Iteration Interval: 1<\/p>\n

Unsteady Particle Tracking (On)<\/p>\n

Particle Time Step Size: 1e-8<\/p>\n

Number of Time Steps: 1e6<\/p>\n

Physical Models->DEM Collision (On)<\/p>\n

Injections:<\/p>\n

               File Injection using a unsteady file.inj as described in the Manual<\/p>\n

               Start Time: 0<\/p>\n

               Stop Time: 5<\/p>\n

               Start Flow-time in File: 0<\/p>\n

               Repeat Interval in File: 1e-6 (so that a new particle is injected every particle time step)<\/p>\n

Run Calculation -> Number of Iterations: 1<\/p>\n

 <\/p>\n

The simulation runs as desired and is obviously much faster than the setup (Particle Time Step Size:1e-8\/No of Steps:1\/DPM Iteration Interval:1\/Number of (Fluid) Iterations:1e6).<\/p>\n

 <\/p>\n

However, I encounter problems when it comes to view the results:<\/p>\n

I want to investigate the collisions etc. in CFD-Post and therefore I want to export the particle history data.<\/p>\n

The way Solution->Calculation Activities->Automatic Export -> Create Particle History Data Export does not work for me, since it only is executed every fluid time step.<\/p>\n

I do not need an export every fluid time step but every (nth) Particle Time Step, because I want to visualize the collisions and particle trajectories properly.<\/p>\n

I could increase the number of fluid time steps and decrease number of particle time steps but this would slow down my simulation.<\/p>\n

Furthermore, it seems possible with a transient simulation, but this is also not what I want.<\/p>\n

 <\/p>\n

I made two more ideas to approach a solution but was not successful with them:<\/p>\n

1.)<\/p>\n

I had the idea to use an UDF, more accurate the “DEFINE_DPM_SCALAR_UPDATE” and in this UDF execute the following scheme text command:<\/p>\n

(ti-menu-load-string<\/p>\n

(format #f "file\/export\/particle-history-data cfdpost tracktest injection-0 , acc-total-mag force-coll-mag force-total-mag , ,"))<\/p>\n

But I get a compiling error when trying it. <\/p>\n

I read that it is eventually not possible to execute TI-commands by UDF. <\/p>\n

It might be an option to export the data to a .txt file, e.g. like this:<\/p>\n

https:\/\/www.cfd-online.com\/Forums\/fluent-udf\/215456-udf-current-particle-position.html<\/a><\/p>\n

\n
\n

#include "udf.h"<\/p>\n

#include "dpm.h"<\/p>\n

<\/p>\n<\/p>\n

DEFINE_DPM_SCALAR_UPDATE(gpif,c,t,initialize,p)<\/p>\n

{<\/p>\n

int n;<\/p>\n

n = N_TIME;<\/p>\n

char filename[50];<\/p>\n

real current_time = CURRENT_TIME;<\/p>\n

snprintf(filename,50,"particleposition_%d.txt",n);<\/p>\n

FILE *fid1;<\/p>\n

fid1 = fopen(filename,"a");<\/p>\n

if (P_TIME(p) == CURRENT_TIME)<\/p>\n

{<\/p>\n

fprintf(fid1, "%f %f %f %f %f %f %f %"int64_fmt"
\n",P_POS(p)[0],P_POS(p)[1],P_POS(p)[2],P_VEL(p)[0],P_VEL(p)[1],P_VEL(p)[2],P_TIME(p),p->part_id);<\/p>\n

}<\/p>\n

else<\/p>\n

{<\/p>\n

printf("time is not reached");<\/p>\n

}<\/p>\n

fclose(fid1);<\/p>\n

}<\/p>\n","protected":false},"template":"","class_list":["post-159411","topic","type-topic","status-closed","hentry","topic-tag-cfd-post","topic-tag-collision","topic-tag-dpm-dem-fluent","topic-tag-particle-tracking","topic-tag-udf-fluent"],"aioseo_notices":[],"acf":[],"custom_fields":[{"0":{"_bbp_author_ip":[""],"_bbp_old_reply_author_name_id":["Anonymous"],"_bbp_old_is_reply_anonymous_id":["false"],"_btv_view_count":["3121"],"_bbp_likes_count":["0"],"_bbp_topic_status":["unanswered"],"_bbp_status":["publish"],"_bbp_topic_id":["159411"],"_bbp_forum_id":["27792"],"_bbp_engagement":["22555","197999"],"_bbp_voice_count":["2"],"_bbp_reply_count":["9"],"_bbp_last_reply_id":["181909"],"_bbp_last_active_id":["181909"],"_bbp_last_active_time":["2021-06-21 06:37:11"]},"test":"hansdampforgmail-com"}],"_links":{"self":[{"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/topics\/159411","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/topics"}],"about":[{"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/types\/topic"}],"version-history":[{"count":0,"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/topics\/159411\/revisions"}],"wp:attachment":[{"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/media?parent=159411"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}