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UDF: How to load data from an external file into a vector 

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June 16, 2016, 07:18 
UDF: How to load data from an external file into a vector

#1 
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Hello,
I would like to impose inlet velocity values for unsteady flow by a udf. I have 2 files, one containing a single column of time values, and the other containing a column of corresponding velocity values (let's assume that at given time, velocity is uniform across the inlet surface). I managed to make this work by creating two large arrays with time and velocity values hardcoded directly in the udf source code. Now I'm trying to have the data read from an external file, and I'm stuck. Ideally, I would like to read the values only once at startup, and then keep them in memory. Can this be done? I'm trying to use the macro DEFINE_EXECUTE_ON_LOADING(name, libname), but unfortunately I have no idea what 'libname' should be. I aslo thought about using a macro DEFINE_RW_FILE (from UDF docuemntation) but I don't manage to store the data from my external file into a vector "visible" for all the other macros of the UDF (especially the DEFINE_PROFILE) I pasted a piece of my UDF, which returns to me that the "symbol velocityExp is not defined". On a more general note, does Fluent and the UDF system support linking to external libraries? Suppose I have my own code written in C/C++ which is fairly large and does some complex computation to obtain boundary values. Is there a way of compiling this separately and then linking it to udf which would only call one highlevel function (something like (get_my_bc(time, x, y, z) ....)? Any working example code to load files on startup would be greatly appreciated. Thank you very much for your help. Emilie /**/ /* UDF code  Exctract */ /* */ /**/ extern real velocityExp[90]; void read_data_velocity(FILE *ptr_velfile) { int i; ptr_velfile = fopen("ExpData.txt", "r"); printf(":%s:\n", "Read input file for Velocity!"); for (i=0;i<90;i++) { fscanf (ptr_velfile, "%lf", &velocityExp[i]); } fclose(ptr_velfile); printf ( "%lu\n", sizeof velocityExp ); printf(":%s:\n", "Close input file for Velocity!"); } /**/ DEFINE_RW_FILE(reader_velocity, ptr_velfile) { Message0("Reading UDF data from data file...\n"); read_data_velocity(ptr_velfile); host_to_node_real(velocityExp, 90); } /**/ 

November 19, 2017, 13:57 
Same problem

#2 
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Felipe
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Hello, Emis
I am facing the same problem. I am trying to change velocity magnitude and direction of the inlet flow at some specific times. I also built a large code imputing this directly, and I am trying to do this input reading a .txt file with the velocity values. I am using the function fopen to read the file and a for loop to store the values on a vector. I used logical statements to access the values velocity[i] at the specific times, related to the CURRENT_TIME enter. The fluent interpret the UDF with no error, however, when I try to initialize to run, the fluent faces a fatal error, and closes. Does anyone know what might wrong? Emis, did you figure out what happened to your code? float velocity[4]; FILE *vel_x; vel_x = fopen("teste.txt","r"); i=1; for (i=1;i<=4;i++) { fscanf (vel_x, "%f", velocity[i]); /* read one value per line */ } fclose(vel_x); /*close file*/ 

November 19, 2017, 19:30 

#3 
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Alexander
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Nice question,
I guess, something wrong with your UDF Best regards 

November 20, 2017, 12:45 

#4 
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Felipe
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Thank you for the answers,
I also guess something is wrong with the code. Probably is on the vector part, But i still don't figuere it out what the problem is. I am posting the code, the test is a .txt file with 5 lines and one different value for each line. If anyone could help me with that, would be very helpful. thank you. regards. #include "udf.h" /************************************************** */ /*X COMPONENT*/ /************************************************** */ DEFINE_PROFILE(inlet_x_velocity, thread, nv) { real x[ND_ND]; /* Position vector*/ real y; real z; face_t f; real current_timestep; /*Atual timestep size*/ real num_timestep; real current_time; int n_timestep; int i, t=10; ////////////////////////////////////////////////////// extern float velocity[5]; FILE *vel_x; /*Read the velocty file*/ //vel_x = fopen("uvelocity.txt","r"); /*fopen("caminho para o arquivo","modo r (read)")*/ vel_x = fopen("test.txt","r"); /*LOOP TO READ THE FILE AND STORE IN A VECTOR */ i=1; /* initialize before to loop */ for (i=1;i<=5;i++) { fscanf (vel_x, "%f", velocity[i]); /* read one value per line */ } fclose(vel_x); /*close file*/ ///////////////////////////////////////////////////// n_timestep = N_TIME; current_time = CURRENT_TIME; current_timestep = CURRENT_TIMESTEP; num_timestep = N_TIME; begin_f_loop(f, thread) { F_CENTROID(x,f,thread); y = x[1]; if(num_timestep<t) { F_PROFILE(f, thread, nv)=velocity[1]; } else if(current_time<4.) { F_PROFILE(f, thread, nv)=velocity[2]; } else if(current_time<6.) { F_PROFILE(f, thread, nv)=velocity[3]; } else if(current_time<8.) { F_PROFILE(f, thread, nv)=velocity[4]; } else { F_PROFILE(f, thread, nv)=velocity[5]; } } end_f_loop(f, thread) } 

November 20, 2017, 21:14 

#5 
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Alexander
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First check, how your input file is read, successfully?
Code:
/*LOOP TO READ THE FILE AND STORE IN A VECTOR */ i=1; /* initialize before to loop */ for (i=1;i<=5;i++) { fscanf (vel_x, "%f", velocity[i]); /* read one value per line */ Message(" velocity[%d] = %f\n",i,velocity[i]); } fclose(vel_x); /*close file*/ Also, you may put read_from_file part into other function for instance DEFINE_ON_DEMAND And why do you use Code:
extern float velocity[5]; ? Code:
real velocity[5]; On the other hand, if you need dynamic array you may use this code Code:
real *velocity; int n; n = 5; // for your case, or any other value velocity = (real*)malloc((n)*sizeof(real)); 

November 21, 2017, 04:14 

#6 
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The problem: "velocity[5]" does not exist! You start counting at 1, but you should start at 0, so use velocity[0] to velocity[4].


November 21, 2017, 08:22 

#7 
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Felipe
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Thank you all for the help.
I used all of the suggestion, but I still having trouble with this code. I tested the malloc() to create a dynamic array, (velocity = (real*)malloc((n)*sizeof(real)), however I faced the same problem. The fluent reads the code and interpret without any problem, but when I initialize to run, FLUENT just crash and close. I am pretty sure that the problem is with the reading part and storage in an array. AlexanderZ suggested using the DEFINE_ON_DEMAND to read_from_file, could AlexanderZ or someone please clarify me about that.
I am trying to use this code to change the component of the velocity with time. The code below is just a test, my objective is to change the components at more time intervals. CODE: Code:
#include "udf.h" /***********COMPONENT X ****************************/ DEFINE_PROFILE(inlet_x_velocity, thread, nv) { real x[ND_ND]; /* Position vector*/ real y; real z; face_t f; real current_time; int t=2, i=0; int n=5; real *velocity; FILE *vel; vel = fopen("test.txt","r"); velocity = (real*)malloc((n)*sizeof(real)); /*store the data from file .txt to vector*/ for (i=0;i<=4;i++) { fscanf (vel, "%f", velocity[i]); /* read one value per line */ Message(" velocity[%d] = %f\n",i,velocity[i]); printf ("\n%f", velocity[i]); } fclose(vel); /*close file*/ current_time = CURRENT_TIME; ////////////////////////////////// begin_f_loop(f, thread) { F_CENTROID(x,f,thread); y = x[1]; if(current_time<t) { F_PROFILE(f, thread, nv)=velocity[1]; } else if(current_time<4.) { F_PROFILE(f, thread, nv)=velocity[2]; } else if(current_time<6.) { F_PROFILE(f, thread, nv)=velocity[3]; } else if(current_time<8.) { F_PROFILE(f, thread, nv)=velocity[4]; } else { F_PROFILE(f, thread, nv)=velocity[5]; } } end_f_loop(f, thread) } ERROR: line 76: function "CX_Message" not found (pc=97). Thanks in advance. Best regards, Felipe. 

November 21, 2017, 22:51 

#8 
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Alexander
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Do you compile this code or interpret it?
Some functions do not supported for interpretation, so you should compile this code. Best regards 

November 22, 2017, 05:00 

#9 
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The same problem remains!
You write data to


December 7, 2017, 07:20 

#10 
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Felipe
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Thank you all very much for the clarifications.
I made some corrections on the code and now I finally figured out how to read the data file and store the values into a vector. I used a DEFINE_ON_LOAD macro just for the reading process. I am new using UDF and I am still learning to deal with those different UDF macros. However, I am facing another problem working with the loops. I need to input each value at a specific time according to the timestep. For example in my test case, the interval between each velocity value is 20 sec, which means 200 timesteps (each timestep=0.1s). Furthermore, between one velocity value and the next, I will need to do a linear interpolation. I am trying to use a WHILE loop (I am not sure if it is the better way) to do so, but I am getting a fatal error on fluent. The code is compiled with no problems and I can create the library libudf with no errors. The error just shows up when I try to Initialize the case to run. I think this is more of a programming problem. Programming is not one of my strongest ability. If you guys could help me to fix my code I would really appreciate. Code:
#include "udf.h" /*Global variables*/ real *uvelocity; int *time; int n=6; /*number of lines with data on the file*/ DEFINE_EXECUTE_ON_LOADING(on_load,libudf) /*Read the .txt file and store the velocity values into a vector*/ { int i=1; float data_vel; int data_time; FILE *vel; FILE *tm; vel = fopen("test.txt","r"); tm = fopen("time.txt","r"); uvelocity = (real*)malloc((n)*sizeof(real)); time = (int*)malloc((n)*sizeof(int)); /*Places the data into the vector*/ for (i=1;i<=n;i++) { data_vel=0; data_time=0; fscanf (vel, "%f", &data_vel); fscanf (tm,"%d", &data_time); /* read one value per line */ uvelocity[i]=data_vel; time[i]=data_time; Message("* velocity_U[%d] = %f\n",i,uvelocity[i]); Message("* time[%d] = %d\n",i,time[i]); } fclose(vel); } DEFINE_ON_DEMAND(list_velocity) /*check if the values are right on the vector*/ { int i=1,j=1; for(i=1;i<=n;i++) { Message("\nVelocity_U[%d]=%f\n",i,uvelocity[i]); Message("\nTime[%d]=%d\n",i,time[j]); j++; } } DEFINE_PROFILE(inlet_x_velocity, thread, nv) /*Define profile to the x velocity component*/ { real x[ND_ND]; real y; face_t f; int n_ts; real current_time; int j=1; int tL=1, tR=199, deltat=200; /* tL= left time; tR = right Time after deltat timesteps, deltat = number of timesteps between tL and tR */ current_time = CURRENT_TIME; n_ts = N_TIME; /*Actual number of timestep*/ ////////////////////////////////// begin_f_loop(f, thread) { while(n_ts <= 1000) /*loop to set the velocity values and interpolate between a value and the next one*/ { F_CENTROID(x,f,thread); y = x[1]; if(n_ts==tL) { F_PROFILE(f, thread, nv)=uvelocity[j]; } else if(n_ts>tL && n_ts<=tR) { F_PROFILE(f, thread, nv)=((n_tstL)*(uvelocity[j+1]uvelocity[j])/(tRtL))+uvelocity[j]; } j=j+1; tL=tL+deltat; tR=tR+deltat; } end_f_loop(f, thread) } } Data set Velocity data: File test.txt Code:
5.0 3.0 6.0 4.0 6.0 0 

December 11, 2017, 03:32 

#11 
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It is the same problem as before.
Code:
uvelocity = (real*)malloc((n)*sizeof(real));
But later in your code, you write to them like this: Code:
for (i=1;i<=n;i++) { ... uvelocity[i]=data_vel; ... }
uvelocity[6] does not exist! In general: start counting at 0, not at 1! 

January 1, 2019, 01:02 
liner interpolation

#12 
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vektor
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so i read the comments, and i am pretty sure that i am bad at these UDF thing, and c programming in general
i created a simple material udf ( only viscosity for now) and, what i did is basically just create two arrays, one for temperature and the other for viscosity, followed by a simple algorithm for the linear interpolation, it goes like this Code:
DEFINE_PROPERTY(cell_viscosity, cell, thread) { real mu_lam; /* local variable */ real temp = C_T(cell, thread); /* local variable */ int i; int size_int; real T_int{ 4.57E+01, 7.21E+02, 1.94E+03, 3.19E+03, 4.05E+03, 5.35E+03, 6.21E+03, 7.15E+03, 8.90E+03, 9.76E+03, 1.05E+04, 1.18E+04, 1.31E+04, 1.45E+04, 1.66E+04, 1.83E+04, 2.06E+04, 2.39E+04, 2.68E+04, 3.00E+04}; real eta_T{8.24E+02, 3.71E+03, 6.94E+03, 9.94E+03, 1.33E+04, 1.68E+04, 1.92E+04, 2.20E+04, 2.50E+04, 2.60E+04, 2.58E+04, 2.27E+04, 1.62E+04, 9.65E+03, 4.12E+03, 2.41E+03, 1.82E+03, 1.76E+03, 1.53E+03, 1.00E+03}; /* M.capitelli et al,*/ size_int = sizeof(T_int); for i(i=1;i<= size_int;i++) { if (T_int[1]>temp  T_int[size_int]) break; else if (T_int[i]<temp && T_int[i+1]>temp) mu_lam = (eta_T[i]*(T_int[i+1]temp)+eta_T[i+1]*(tempT_int[i]))/(T_int[i+1]T_int[i]); return mu_lam; } density, electric and thermal conductivity and the specific heat capacity. thanks 

January 1, 2019, 20:44 

#13 
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Alexander
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Code:
for i(i=1;i<= size_int;i++) { if (T_int[1]>temp  T_int[size_int]) break; else if (T_int[i]<temp && T_int[i+1]>temp) mu_lam = (eta_T[i]*(T_int[i+1]temp)+eta_T[i+1]*(tempT_int[i]))/(T_int[i+1]T_int[i]);} break; is not appropriate in DEFINE_PROPERTY macro, material properties have to be defined at the whole range of simulation (temperature). else if (T_int[i]<temp && T_int[i+1]>temp), if temperature is lower than T[i] but higher than T[i+1] ?? is it possible? best regards 

January 1, 2019, 21:58 

#14  
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vektor
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Quote:
i really appreciate your help, i really just made that code without trying it, that break i put it in case (i am not sure about this) if the temperature in the model, somehow became smaller than 50[K] or higher that 30000[K] in which my material properties are not defined, so i put break so that the software will immediately exit the loop without wasting time looking for something that is none existent in the first place, i know that is not the way to do it. EDIT: it should be if (T_int[1]>temp  T_int[size_int]<temp) i forgot to add <temp in the next statement: else if (T_int[i]<temp && T_int[i+1]>temp) this will go through the loop from i=1 to the end and compare temp which i assume is the temperature solved by fluent ( also not sure about this) with the T_int which is the temperature from material properties table, it will stop at certain i in which T_int[i]<temp<T_int[i+1] and after that i used the linear interpolation formula. i got the formula from wikipedia https://en.wikipedia.org/wiki/Linear_interpolation EDIT2: Quote:
so what i am thinking/ or what i want to do in the UDF is: 1) read the model temperature from the solver at each cell. 2) compare it the tempature from the material table 3) compute the new material viscosity based on table data. 4) put in the model cell. repeat int the next time step. this is the original UDF that i modified on: /************************************************** ******************* UDF that simulates solidification by specifying a temperature dependent viscosity property ************************************************** ********************/ DEFINE_PROPERTY(cell_viscosity, c, t) { real mu_lam; real temp = C_T(c, t); if (temp > 288.) mu_lam = 5.5e3; else if (temp > 286.) mu_lam = 143.2135  0.49725 * temp; else mu_lam = 1.; return mu_lam; } 

January 1, 2019, 22:36 

#15 
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vektor
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i removed the break thing and simply put it this way, i added the possibility if temp is exactly the temperature in the table.
DEFINE_PROPERTY(cell_viscosity, cell, thread) { real mu_lam; /* local variable */ real temp = C_T(cell, thread); /* local variable */ int i; int size_int; real T_int{ 4.57E+01, 7.21E+02, 1.94E+03, 3.19E+03, 4.05E+03, 5.35E+03, 6.21E+03, 7.15E+03, 8.90E+03, 9.76E+03, 1.05E+04, 1.18E+04, 1.31E+04, 1.45E+04, 1.66E+04, 1.83E+04, 2.06E+04, 2.39E+04, 2.68E+04, 3.00E+04}; real eta_T{8.24E+02, 3.71E+03, 6.94E+03, 9.94E+03, 1.33E+04, 1.68E+04, 1.92E+04, 2.20E+04, 2.50E+04, 2.60E+04, 2.58E+04, 2.27E+04, 1.62E+04, 9.65E+03, 4.12E+03, 2.41E+03, 1.82E+03, 1.76E+03, 1.53E+03, 1.00E+03}; /* M.capitelli et all,*/ size_int = sizeof(T_int); for i(i=1;i<=size_int;i++) { if(temp == T_int[i]) mu_lam = eta_T[i]; else if (T_int[i]<temp && T_int[i+1]>temp) mu_lam = (eta_T[i]*(T_int[i+1]temp)+eta_T[i+1]*(tempT_int[i]))/(T_int[i+1]T_int[i]); return mu_lam; } 

January 2, 2019, 02:21 

#16 
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Alexander
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Code:
if(temp == T_int[i]) mu_lam = eta_T[i]; Code:
DEFINE_PROPERTY(cell_viscosity, cell, thread) { real mu_lam; /* local variable */ real temp = C_T(cell, thread); /* local variable */ int i; int size_int; real T_int{ 4.57E+01, 7.21E+02, 1.94E+03, 3.19E+03, 4.05E+03, 5.35E+03, 6.21E+03, 7.15E+03, 8.90E+03, 9.76E+03, 1.05E+04, 1.18E+04, 1.31E+04, 1.45E+04, 1.66E+04, 1.83E+04, 2.06E+04, 2.39E+04, 2.68E+04, 3.00E+04}; real eta_T{8.24E+02, 3.71E+03, 6.94E+03, 9.94E+03, 1.33E+04, 1.68E+04, 1.92E+04, 2.20E+04, 2.50E+04, 2.60E+04, 2.58E+04, 2.27E+04, 1.62E+04, 9.65E+03, 4.12E+03, 2.41E+03, 1.82E+03, 1.76E+03, 1.53E+03, 1.00E+03}; /* M.capitelli et all,*/ size_int = sizeof(T_int); for i(i=1;i<=size_int;i++) { if(temp > T_int[size_int]) mu_lam = eta_T[size_int]; else if (T_int[i]<temp && T_int[i+1]>temp) mu_lam = (eta_T[i]*(T_int[i+1]temp)+eta_T[i+1]*(tempT_int[i]))/(T_int[i+1]T_int[i]); else mu_lam = eta_T[0]; // true if temperature is equal or lower than T_int[0] return mu_lam; } best regards 

January 2, 2019, 02:53 

#17  
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vektor
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Quote:
Thanks I am still far away from running the final simulation " electric arc simulation". Since it is a bit complicated but i may come back with some more question about udfs during the process. Thank you so much. 

January 14, 2019, 01:55 

#18  
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vektor
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Quote:
it had some small problems, i fixed it and it works Code:
#include "udf.h" DEFINE_PROPERTY(cell_viscosity, cell, thread) { real mu_lam; /* local variable */ real temp = C_T(cell, thread); /* local variable */ int i; int size_T_int; real T_int[] = { 4.57E+01, 7.21E+02, 1.94E+03, 3.19E+03, 4.05E+03, 5.35E+03, 6.21E+03, 7.15E+03, 8.90E+03, 9.76E+03,1.05E+04, 1.18E+04, 1.31E+04, 1.45E+04, 1.66E+04, 1.83E+04, 2.06E+04, 2.39E+04, 2.68E+04, 3.00E+04}; real eta_T[] = {8.24E+02, 3.71E+03, 6.94E+03, 9.94E+03, 1.33E+04, 1.68E+04, 1.92E+04, 2.20E+04, 2.50E+04, 2.60E+04, 2.58E+04, 2.27E+04, 1.62E+04, 9.65E+03, 4.12E+03, 2.41E+03, 1.82E+03, 1.76E+03, 1.53E+03, 1.00E+03}; /* M.capitelli et all,*/ int size_T_int = sizeof(T_int)/sizeof(int); for (i=0;i<=size_T_int1;i++) { if(temp > T_int[size_T_int1]) mu_lam = eta_T[size_T_int1]; else if (T_int[i]<temp && T_int[i+1]>temp) mu_lam = (eta_T[i]*(T_int[i+1]temp)+eta_T[i+1]*(tempT_int[i]))/(T_int[i+1]T_int[i]); else mu_lam = eta_T[0]; // true if temperature is equal or lower than T_int[0] } return mu_lam; } 

Tags 
boundary condition u, global vector, load text file, udf 
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