Redundancy in motion view
Hello i am new to motion view.
I have one doubt, in simulation model
1.how can we reduce redundancy in model? is there any specific methods?
2. In redundancy warning message of log file, some unknown id numbers shown(760000) in message which is not id number of any part in model. How to reduce Redundant constrains.
below is the image of the problem.
Best Answer
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Hi Tejas,
It is always recommended to minimize the number of redundant constraints as the solver will deactivate certain degrees of freedom from certain joints which can, in rare cases, negatively effect the overall motion of your system.
The Check Tool can display the current number of redundant constraints so you can view that information as you change your current constraints and reduce the total count.
However, it is very difficult to get the number of redundant constraints (especially for full vehicle models) to zero, and having redundant constraints does not necessarily mean there will be an issue.
For more on redundant constraints, please refer to our Intro to MotionView/MotionSolve eLearning, which discusses this topic.
https://learn.altair.com/enrol/index.php?id=496
Hope this helps!
Adam Reid
1
Altair EmployeeAnswers
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Hello Tejas,
I wouldn't say that there is an explicit way of reducing redundant constrains. Depending on your model there might be more than one way to do it. In general you need to avoid constraining a Degree of Freedom twice to avoid redundancy. MotionSolve's log file may help you locate these redundancies. For ID's that are not in the model tree I suggest that you search these ID numbers in the xml as they might refer to body markers or something similar.An easy exercise to practice is to create a 4-bar mechanism (Find attached 3 mdl files). You will see that by using just revolute joints (4-bar_revolute model) you will get a warning for redundant constrains which will be removed automatically by the solver. In this particular example you can either use a combination of ball and cylindrical and two revolute joints (4-bar-joint-combination model) or a 3 revolute and an inline joint (4-bar-inline model). You can search for Gruebler's equation to understand how the redundancy is calculated. As for the DOFs that a joint constrains you can refer to MotionView user manual Joints . As you are new to MotionView you may find some useful information in our MotionView eLearning. There is a joint dedicated chapter focusing on 4-bar mechanism example. Hope this helps!
Best regards,
Orestes.1 -
Hi Tejas,
It is always recommended to minimize the number of redundant constraints as the solver will deactivate certain degrees of freedom from certain joints which can, in rare cases, negatively effect the overall motion of your system.
The Check Tool can display the current number of redundant constraints so you can view that information as you change your current constraints and reduce the total count.
However, it is very difficult to get the number of redundant constraints (especially for full vehicle models) to zero, and having redundant constraints does not necessarily mean there will be an issue.
For more on redundant constraints, please refer to our Intro to MotionView/MotionSolve eLearning, which discusses this topic.
https://learn.altair.com/enrol/index.php?id=496
Hope this helps!
Adam Reid
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Adam Reid_21142 said:
Hi Tejas,
It is always recommended to minimize the number of redundant constraints as the solver will deactivate certain degrees of freedom from certain joints which can, in rare cases, negatively effect the overall motion of your system.
The Check Tool can display the current number of redundant constraints so you can view that information as you change your current constraints and reduce the total count.
However, it is very difficult to get the number of redundant constraints (especially for full vehicle models) to zero, and having redundant constraints does not necessarily mean there will be an issue.
For more on redundant constraints, please refer to our Intro to MotionView/MotionSolve eLearning, which discusses this topic.
https://learn.altair.com/enrol/index.php?id=496
Hope this helps!
Adam Reid
Hi Adam,
how much redundant constraints are allowed in model simulation. will they effect my answers such as angular velocity and timings of movement of links in fourbar?
suppose case 1- there are 90 parts and getting 10 redundant constraints it is ok ?
case2- parts in model 90 and getting 60 redundant constraints it is ok ?
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orestes said:
Hello Tejas,
I wouldn't say that there is an explicit way of reducing redundant constrains. Depending on your model there might be more than one way to do it. In general you need to avoid constraining a Degree of Freedom twice to avoid redundancy. MotionSolve's log file may help you locate these redundancies. For ID's that are not in the model tree I suggest that you search these ID numbers in the xml as they might refer to body markers or something similar.An easy exercise to practice is to create a 4-bar mechanism (Find attached 3 mdl files). You will see that by using just revolute joints (4-bar_revolute model) you will get a warning for redundant constrains which will be removed automatically by the solver. In this particular example you can either use a combination of ball and cylindrical and two revolute joints (4-bar-joint-combination model) or a 3 revolute and an inline joint (4-bar-inline model). You can search for Gruebler's equation to understand how the redundancy is calculated. As for the DOFs that a joint constrains you can refer to MotionView user manual Joints . As you are new to MotionView you may find some useful information in our MotionView eLearning. There is a joint dedicated chapter focusing on 4-bar mechanism example. Hope this helps!
Best regards,
Orestes.Thnak you orestes for your reply!
redundant constraints will effect my answers ?
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Tejas Milind Gangawane said:
Thnak you orestes for your reply!
redundant constraints will effect my answers ?
Hello Tejas,
As Adam mentions in the comment below, the solver may deactivate a constrain that is important to you. So in a way yes the answer / results will be affected if the dynamic behavior differs. The tool that Adam is mentioning can be activated if you search for options in the search bar and then select check model and check the degrees of freedom option.
With this you can check your model redundancy prior the simulation. You just have to click on Check Model and a report will appear. To check the specific redundancies though you will need to run the model and check the IDs in log file.
Hope this helps!
Orestes.1 -
Tejas Milind Gangawane said:
Hi Adam,
how much redundant constraints are allowed in model simulation. will they effect my answers such as angular velocity and timings of movement of links in fourbar?
suppose case 1- there are 90 parts and getting 10 redundant constraints it is ok ?
case2- parts in model 90 and getting 60 redundant constraints it is ok ?
Hi Tejas,
There is no rule for redundant constraints, the goal when building a model is to be mindful of them and try to build your model which minimizes them.
The solver will deactivate a redundant constraint because it has determined that it is redundant, and thus not needed to maintain the same degrees of freedom. It does not remove the entire constraint, just a single DOF from it.
Hope this helps!
Adam Reid
0