# mbd Giving Forces in MBD

## Recommended Posts

Hi, I have few doubts on Force Entity in MBD. I am listing out. Please Explain me.

1. if have a force vs degree curve to give as input, What should be the independent Variable for the interpolation?

2. When I created a force element, why 6 arrows are created?I am really confused. Please help me.

3. How to measure angle between two markers which the help of motion solve functions?

Thanks

##### Share on other sites

Hello Sai - Let me answer the questions in a different order

2. What you have shown here is an Action-Reaction force, that means, the force is acting between 2 bodies - 1) referred as an action body (Body 1 in the force panel) and 2) the reaction body (Body 2 on the force panel. The 3 "arrows" in blue are being applied on the action body while the 3 arrows in pink are acting on the reaction body.

3) MotionSolve has functions such as AX(), AY(), AZ() to measure the angle between 2 markers in radians depending upon about which direction the angles need to be measured. From the Expression builder in MotionView, you may click on MotionSolve Functions help to learn more about these functions at https://2020.help.altair.com/2020/hwsolvers/ms/topics/chapter_heads/functions.htm

e.g AZ(mrk1_id, mrk2_id) measures the angle about Z between marker with id mrk1_id with respect to marker with id mrk2_id

1) You might have to provide a function such as described above in 3) as an independent variable.

MotionView provides some easy means to define rotation between markers that belong to a joint/force/bushing etc.. For e.g if there is a joint with varname j_0, the expression `{j_0.AZ}` would provide the expression AZ() that measures angle between the I marker and J marker of the joint.

Note - a) These function return angle in radians. You may use RTOD to convert into degrees. b)  Also these functions measures the angle continuously and does not reset to 0 deg after the 360 deg rotation. You would have to wrap this function with a MOD function

e.g. `MOD(AZ(mrk1, mrk2)*RTOD, 360)`

Hope this helps

Regards

praful

Chris Coker likes this

##### Share on other sites

Hi Praful,

Thank you so much for clear explanation

##### Share on other sites

Hi,

I tried with your suggestion, but looks like my force is not acting w.r.t angle

##### Share on other sites

Would you be able to share the model ? - regards, praful

##### Share on other sites

Sorry Sir I cant share the model as it is confidential.

Can you help me with this problem.

Instead of Force vs Angle, I am trying to speed(mm) vs Angle(Deg) as I am having velocity of door w.r.t to angle.

So this is a Door slam simulation model.

the velocity should be given at door handle and Angle is measure w.r.t to hinges.

It would be great if you help e with this

Thanks

##### Share on other sites

Can you explain why you need this is a bit more detail, in the context of a door slam simulation?

Note, speed is expressed in mm/sec, not mm.  mm would be displacement.

Also note, the units of rotation in MotionView/MotionSolve are in radians, not degrees.

You really cannot define a rotation (angle) with respect to speed (mm/sec), as the units are not consistent.

So, you need to explain in more detail your goals for the simulation, and what you are trying to achieve.