... | ... | @@ -50,6 +50,8 @@ __In the case of high quality pictures__ (resolution and contrast), a $`G^2_i`$ |
|
|
|
|
|
__In the case of low quality pictures__, each possible combination of active contact is provided to the optimization procedure. The sum of the contact force magnitude is equally distributed over the active contacts. This approach is slower than the previous one and only gives good results when the contact force are almost equally distributed over the active contacts. To overcome the second drawback the fitting procedure will consider all the granular media to propagate the fitted forces on the adjacent disk when the optimization procedure succeed (PhD Thesis of O. Lantsoght, currently defending).
|
|
|
|
|
|
>JK: I'm currently trying an idea to use betweenness centrality as an initial guess (based on https://pubs.rsc.org/en/content/articlepdf/2018/sm/c8sm01372a ) maybe I can add an outlook here...
|
|
|
|
|
|
### 2.3 Optimization procedure
|
|
|
|
|
|
The optimization procedure uses the forces magnitude and orientation as parameters and try to minimize the difference between the computed photoelastic signal and the picture of disk. Different methods exist to compare two images, among them we have the Mean Squared Error (MSE) or the Structural Similarity Index (SSIM) [3,4]. The main advantage of the MSE is the speed of computation but it considers the image globally. On the opposite he SSIM is slower but considers region of the image to take into account its structure. Presently, for this application, both comparison criteria are similar, they are globally good but for some case failed to detect that the images do not match at all.
|
... | ... | @@ -65,6 +67,8 @@ In the case of low quality pictures, the initial guess of the forces distributio |
|
|
To improve the initial guess of the forces provided to the optimizer, the forces identified on some disks are applied on the adjacent disk using the Newton's third law. Then the optimization procedure is called with all possible combination of active contact (the propagated contact force being always active). If an optimization procedure succeed, the newly identified forces are propagated to they neighbors.
|
|
|
|
|
|
> I have to work on the following images to explain propagation steps with particle 139 and/or 480.
|
|
|
> JK: Maybe a smaller crop just showing the affected particle and its neighbour would give a clearer view on what is happening ?
|
|
|
|
|
|
<img src="uploads/cadedc89a2659bbcb5d0d927d5767e85/Picture.png" width="250">
|
|
|
<img src="uploads/093ba577f1853595e148c32d324fb0da/synthetic0.png" width="250">
|
|
|
<img src="uploads/7ec3e96162cda9ad086b560426877142/synthetic1.png" width="250">
|
... | ... | |