Hyperstatic balance of a simple beam

Stéphane C.

Hello,

I am new to MotionSolve and it seems fantastic.

I am mostly interested in forces balance of mechanisms.

I tried a simple example (attached), with a bar with 2 ball joints at its extremities, and a loading of 1000N in axial direction at its center.

What type of analysis could lead to a "good" physical result for forces at extremities?

Static analysis leads to 1000N at one extremity and 0 N at other. I would expect 500 N at both wouldn't you?

Thanks a lot!

AnanthK

Hello Stephane, 

Your model is over-constrained. When this happens, Motionsolve randomly removes constraints in order to proceed with the solution, which means that you get unrealistic results. 

If you open the .log file from the results, you see this: 

______________________________________________________________

WARNING: Row Deficiency Detected!

This may indicate a kinematic or over-constrained model.
Program will continue with redundant constraints removal.

WARNING: The following redundant constraints were removed:
-------------------------------------------------
(1) Joint/301002 : SPH_X between Part/30102 & Part/30101
-------------------------------------------------
NOTE: DOT1 is the perpendicular constraint between two axes.
DOT2 is the perpendicular constraint between an axis and a vector rj->ri.
SPH_X(or Y,Z) is the coincidental constraint between the X(or Y,Z) of two points.
DIST is the distance constraint between two points.
The existence of redundant constraints may indicate potential modeling errors.
See Users Manual for further info and remarks.

______________________________________________________________

 

Please see this article on how to resolve redundant constraints: https://2020.help.altair.com/2020.1/hwsolvers/ms/topics/solvers/ms/modeling_constraints.htm

You need the right combination of constraints to solve the problem, which means

 

1) some thought applied to how the mechanism (or beam) would be constrained in the physical world. 

2) Choose the right joint, or combinations of joints that give you the correct number of constraints, using the help article: https://2020.help.altair.com/2020.1/hwdesktop/mv/topics/motionview/joints_r.htm?zoom_highlightsub=joints

AnanthK

Hello Stephane, 

Your model is over-constrained. When this happens, Motionsolve randomly removes constraints in order to proceed with the solution, which means that you get unrealistic results. 

If you open the .log file from the results, you see this: 

______________________________________________________________

WARNING: Row Deficiency Detected!

This may indicate a kinematic or over-constrained model.
Program will continue with redundant constraints removal.

WARNING: The following redundant constraints were removed:
-------------------------------------------------
(1) Joint/301002 : SPH_X between Part/30102 & Part/30101
-------------------------------------------------
NOTE: DOT1 is the perpendicular constraint between two axes.
DOT2 is the perpendicular constraint between an axis and a vector rj->ri.
SPH_X(or Y,Z) is the coincidental constraint between the X(or Y,Z) of two points.
DIST is the distance constraint between two points.
The existence of redundant constraints may indicate potential modeling errors.
See Users Manual for further info and remarks.

______________________________________________________________

 

Please see this article on how to resolve redundant constraints: https://2020.help.altair.com/2020.1/hwsolvers/ms/topics/solvers/ms/modeling_constraints.htm

You need the right combination of constraints to solve the problem, which means

 

1) some thought applied to how the mechanism (or beam) would be constrained in the physical world. 

2) Choose the right joint, or combinations of joints that give you the correct number of constraints, using the help article: https://2020.help.altair.com/2020.1/hwdesktop/mv/topics/motionview/joints_r.htm?zoom_highlightsub=joints

Stéphane C.

Thank you!