Griddata generates duplicate points while plotting CFD imported 3D data on an xy Plane

Hi All,

I have multiple 3D snapshots of a tractor trailer exported from CFD. I am doing some other data analysis on them and then I want to visualise contour of this processed data. For start, I am just trying to plot CFD data directly using x,y,z cordinate and velocity values.

The problem I am mainly having is:

a. Contour does not capture the geometry boundaries properly and shape looks distorted. My x,y,z,u,v, and w are column vector. when I make mesh grid of x.y at z=0, I use griddata command to reshape my velocity vector into same n by n vector as mesh grid is.

b. When I am trying to reshape my velocity vector on the meshgrid using GRIDDATA() command, it gives warning of duplicate data points have been detected and averaged. I think this is the problem area. However I tried to use unique() command and it has removed some duplicate points, I dont know how these duplicate points exist in the data. But I am still getting same duplicate data point warning when I use Griddata command.

I have attached some matlab pictures of my results and a picture of CFD result which I am expecting to see.Please find the link below of one snapshot of data if someone wants to give a try.

DATA

below is the code I am using. I use for loop as later I will be using multiple files.

clear all; clc; close all;
%Read data Files%
dataName='saved_data';           % save a file in the directory to keep all data
save(dataName);                  %Save empty file
dinfo = dir('*.txt');            %Read directory for all text files
files={dinfo.name};              %save names of all text files in files to use in the loop
delimiterIn=' ';                 %How data is seperated 
headerlinesIn=1;                 %is there any header
 
n=numel(files);                  % number of snapshots
for j=1:n
currentFile=files{1,j};          %load jth snapshot
raw_data=importdata(currentFile,delimiterIn,headerlinesIn);  %read data in the snapshot 
                                                                                               %and save it in raw data
end
%% Raw data%%
 X=raw_data.data(:,2);
 Y=raw_data.data(:,3);
 Z=raw_data.data(:,4);
 U=raw_data.data(:,11);
 V=raw_data.data(:,12);
 W=raw_data.data(:,13);
  %% Scatter interpolant%%
[~, I, ~] = unique([X Y Z],'first','rows'); %here I noticed that there were some duplicate data points which I removed
X1 = X(I);
Y1 = Y(I);
Z1 = Z(I);
U1=U(I);
V1=V(I);
W1=W(I);
U2 = scatteredInterpolant(X1, Y1, Z1, U1); %this does not have any duplicate warning now
V2 = scatteredInterpolant(X1, Y1, Z1, V1); 
W2 = scatteredInterpolant(X1, Y1, Z1, W1); 
spacing=200;
x1=(linspace(min(X)/5,max(X)/4,spacing))';
y1=(linspace(min(Y),max(Y)/8,spacing))';
z1=(linspace(min(Z)/4,max(Z)/4,spacing))';
[xmesh, ymesh] = meshgrid(x1,y1,0:0);
%% Make velocity grid with U, V and W%%
u1=griddata(X1,Y1,U2.Values,xmesh,ymesh); % Again giving duplicate data point warning and removed however the size is still 20 by 200.
v1=griddata(X1,Y1,V2.Values,xmesh,ymesh);
w1=griddata(X1,Y1,W2.Values,xmesh,ymesh);
res_vel=sqrt(u1.^2+v1.^2+w1.^2);
%% Contourf Plot U,V data%%
h_fig1 = figure(1);
contourf(xmesh,ymesh,res_vel,0.0001:20)
colorbar()
caxis([-1, 27]);

To summarise, Any suggestion how to avoid duplicate data point warning while solving griddata command. Or any alternate to grid data?

secondly, if the problem is not with the grid data then any way of improving the quality of boundary captured and results. I noticed the velocity in the surrounding area is high but contour is showing small value.

I really appriciate any help as I am stuck here for long time.

Thanks

Answer 1

[Walter Roberson]

[~, I, ~] = unique([X Y Z],'first','rows'); %here I noticed that there were some duplicate data points which I removed

No, that takes unique rows of X Y Z combinations, but scatteredInterpolant() and griddata() want unique X Y combinations. You should change to

[~, I, ~] = unique([X Y],'first','rows'); 

[Muhammad Atif]

Hi Walter,

Thank you so much for your quick reply here and thank you for highlighting the problem. I tried your suggestion and the duplicate point warning is over now but there is no improvement in the picture quality. I tried different levels of contour(0:1:20/0:0.1:20/0:0.1:100 etc). but nothing has improved. Is there something I am missing. Last time when I was trying on 2D data, I had this issue when I was only using resultant of x-velocity and y-velocity but later I added w-velocity and it worked fine. But here I tried all combination but no success. I have attached my recent picture of contour.

I highly appriciate your help.

Thanks

[Muhammad Atif]

I also tried X and Y only in scatter interpolant but still same result.

U2 = scatteredInterpolant(X1, Y1, U1);

Answer 2

[darova]

There is something wrong with the data

D = importdata('data.txt');
 X = D.data(:,2);
 Y = D.data(:,3);
 Z = D.data(:,4);
 plot3(X,Y,Z,'.')

[Muhammad Atif]

Hi Darova, Thanks for your comment.

I am not sure what you mean by something wrong with the data. I have exported this data from Ansys Fluent. I have tried to visualise this data in PARAVIEW software and when I plotted points I could see these points making trailer body. Even in matlab I am getting the shape but the data U,V and W which set background of the graph is not showing the results properly.

Any suggestion on data? At the mement I exported data in ASCII fromat and it was undefined extension and I converted it into text data. I dont know if this could be an issue. I did this with another 2D data file which does not show any problem.

Please advise me something that I could try as a check.

Thanks

[Muhammad Atif]

HI Darova,

I have also plotted these points using scatter3 plot and you can see in the attached pictures they exactly look like what I had in Ansys. X Y Z are creating flow domain and tractor trailer body. I dont see any issue with data, If you have any suggestionin your mind please share with me.

thanks

[Muhammad Atif]

@Star Strider@Walter Roberson

Any chance you could help me on this issue.

thanks

[darova]

Do you have any data for eges or faces? How to separate regions truck-air?

[Muhammad Atif]

Can you tell me a way to get this from ansys. I could get that data.

[darova]

Upload STL model of a region you want to plot