# Rock cutting process **URL:** \ **Category:** PFC\ **Created:** [September 7, 2022, 1:19pm UTC](https://forum.itascainternational.com/t/rock-cutting-process/741 "2022-09-07T13:19:40Z")\ **Posts on this page:** 8\ **Page:** 1
**Author:** ![mehrgini](https://avatars.discourse-cdn.com/v4/letter/m/b2d939/32.png) [@mehrgini](https://forum.itascainternational.com/u/mehrgini)\ **Post date:** [September 7, 2022, 1:19pm UTC](https://forum.itascainternational.com/t/rock-cutting-process/741/1 "2022-09-07T13:19:40Z")
Hello everyone, I am trying to simulate bit-rock interactions, like cutting a rock sample with a blade. the bit rotates and hits the rock from the top part and cuts it. I have two main questions that would be very great if you can help me to resolve them: 1- I want to have viscous damping once the bit hits the rock, how can I add it? 2- When the bit hits the rock, some of the balls enter into the bit boundary. Normally that should not happen but I do not know why it is happening. I tried wall resolution and wall attribute cutoff-angle commands, but they were not helpful (see the attached photo). Thank you so much for your help. Behzad ![1](https://canada1.discourse-cdn.com/flex031/uploads/itasca/original/1X/7a70f6160e91352c11cf9b9fed5ccf7f3104171e.png) ---
**Author:** ![dblanksma](https://avatars.discourse-cdn.com/v4/letter/d/858c86/32.png) [@dblanksma](https://forum.itascainternational.com/u/dblanksma)\ **Post date:** [September 8, 2022, 2:31pm UTC](https://forum.itascainternational.com/t/rock-cutting-process/741/2 "2022-09-08T14:31:58Z")
Hello Behzad, 1. Depending on the contact model you are using, you can use viscous dashpot damping with the contact properties `dp_nratio` or `dp_sratio`. More information on the dashpot damping can be found in the contact model docs (i.e. for [Linear Model](http://docs.itascacg.com/flac3d700/common/contactmodel/linear/doc/manual/cmlinear.html?node5332) see section Properties - Dashpot Group). 2. This can be caused by a variety of things; contact stiffness or two small, velocity of the wall is too high, or the timestep is not sufficiently small enough. If only a few balls are penetrating through the walls I would not worry too much about it, and just delete them. ---
**Author:** ![mehrgini](https://avatars.discourse-cdn.com/v4/letter/m/b2d939/32.png) [@mehrgini](https://forum.itascainternational.com/u/mehrgini)\ **Post date:** [September 8, 2022, 4:05pm UTC](https://forum.itascainternational.com/t/rock-cutting-process/741/3 "2022-09-08T16:05:14Z")
Hello Derrick, Thank you so much for your reply. I have already applied the dashpot damping parameters, I was wondering if there are other types of adjustments or if I am on the right track. For the second one, that is perfect, I will try adjusting these parameters to see their impacts. Thanks indeed, Behzad ---
**Author:** ![mehrgini](https://avatars.discourse-cdn.com/v4/letter/m/b2d939/32.png) [@mehrgini](https://forum.itascainternational.com/u/mehrgini)\ **Post date:** [September 19, 2022, 3:57pm UTC](https://forum.itascainternational.com/t/rock-cutting-process/741/4 "2022-09-19T15:57:53Z")
Hi Derrick, I have one question regarding the problem that I am trying to simulate. After the cutting process, I want to count the number of balls that they have lost their bonds. I am using “ball.isbonded” command, but I am not sure if it is considering the whole balls or just the balls with active contact, how I can fix it, etc. I really appreciate your valuable help. Thanks, Behzad ---
**Author:** ![dblanksma](https://avatars.discourse-cdn.com/v4/letter/d/858c86/32.png) [@dblanksma](https://forum.itascainternational.com/u/dblanksma)\ **Post date:** [September 19, 2022, 4:21pm UTC](https://forum.itascainternational.com/t/rock-cutting-process/741/5 "2022-09-19T16:21:59Z")
The `ball.isbonded` _FISH_ function will check all _active_ contacts on the ball provided to the function. As described [here](http://docs.itascacg.com/flac3d700/pfc/pfcmodule/doc/manual/ball_manual/ball_fish/ball_intrinsics/fish_ball.isbonded.html?node4863) in the documentation. If any of the active contacts are bonded the function will return true. ---
**Author:** ![mehrgini](https://avatars.discourse-cdn.com/v4/letter/m/b2d939/32.png) [@mehrgini](https://forum.itascainternational.com/u/mehrgini)\ **Post date:** [September 19, 2022, 4:40pm UTC](https://forum.itascainternational.com/t/rock-cutting-process/741/6 "2022-09-19T16:40:51Z")
Thanks for your quick reply, Derrick. So, is there any way to be able to count all balls that are single with no bond? Is there a function for that? Can I use the ball.isbonded function for that? Thanks indeed for your time and help. Behzad ---
**Author:** ![dblanksma](https://avatars.discourse-cdn.com/v4/letter/d/858c86/32.png) [@dblanksma](https://forum.itascainternational.com/u/dblanksma)\ **Post date:** [September 19, 2022, 6:39pm UTC](https://forum.itascainternational.com/t/rock-cutting-process/741/7 "2022-09-19T18:39:53Z")
There is not a built-in function to find the number of unbonded balls. You can define a FISH function, something similar to this: ```auto > fish define CountUnbondedBalls > local count_ = 0 > loop foreach local ball ball.list() > if (ball.isbonded(ball) == false) > count_ += 1 > endif > endloop > CountUnbondedBalls = count_ > end > [CountUnbondedBalls] ``` or a more efficient way could be accomplished with splitting and list filtering: ```auto > [UnbondedBallList = list(ball.list)(ball.isbonded(::ball.list) # true)] > [NumUnbondedBalls = list.size(UnbondedBallList) ``` ---
**Author:** ![mehrgini](https://avatars.discourse-cdn.com/v4/letter/m/b2d939/32.png) [@mehrgini](https://forum.itascainternational.com/u/mehrgini)\ **Post date:** [September 19, 2022, 7:23pm UTC](https://forum.itascainternational.com/t/rock-cutting-process/741/8 "2022-09-19T19:23:33Z")
Thank you so much, Derrick, I really appreciate it. Your help was really valuable. Thanks again for your time, Behzad