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dandersonjr1-Visitor
1-Visitor
September 14, 2012
Question

Mechanica Assembly analysis including multiple hydraulic cylinders contacting single member?

Good Day All,


How would one setup an Mechanica assembly analysis where you have 2 cylinders in contactwith one structual member at different approach angles and the structual member deflects (bends) due to the load being applied in such a way that displacement at one cylinder causes the force at the other cylinder to increase while maintaining sytsem force balance?
The piston cavities of the cylinders are connected by hydraulic passages so when you push down on one cylinder rod the other cylinder rod extends. Cylinders do not have the samepistonareas.


Any ideas on how to go about setting this up in mechanica?
I'm not able to use mechanism analysis to do this asmechanism analysis only deals with rigid body members.
This member deflects (bending) under load.


Thanks for any help you can provide,
Don Anderson


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5 replies

randyspeed1-Visitor
1-Visitor
September 14, 2012
Don,

The first thought that comes to mind is this - consider using a
constraint rather than a load at the "other" location. Read the
reaction load at this location in the run summary file under the list
of measures at the bottom. Define a local (or user) measure at the
location before running.

Add a point-to-ground spring at this location and adjust it's K value
to achieve the desired reaction force. Since the run is linear static
(I assume), two runs will give you the information you need to shoot
and get it right on the final (third) run.

Without more details on the job, this is my best guess at some
techniques that may help.

Randy Speed
Speed Consulting, LLC
(800) 256-7140 ph and fax
www.speedconsulting.com



Quoting Donald Anderson <->:

> Good Day All,
> How would one setup an Mechanica assembly analysis where you have 2
> cylinders in contact with one structual member at different approach
> angles and the structual member deflects (bends) due to the load
> being applied in such a way that displacement at one cylinder causes
> the force at the other cylinder to increase while maintaining sytsem
> force balance?
> The piston cavities of the cylinders are connected by hydraulic
> passages so when you push down on one cylinder rod the other
> cylinder rod extends. Cylinders do not have the same piston areas.
> Any ideas on how to go about setting this up in mechanica?
> I'm not able to use mechanism analysis to do this as mechanism
> analysis only deals with rigid body members.
> This member deflects (bending) under load.
> Thanks for any help you can provide,
> Don Anderson
>
>
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randyspeed1-Visitor
1-Visitor
September 14, 2012
Tim,

Yes, I agree with the force relationships and had considered that as a
possible solution. However, I am not aware of a way to do that in
Mechanica Structure. You can define a load as a function of
coordinates but I don't believe as a function of measures, such as
displacement or reaction load. This is, however, possible in Mechanism
(Motion).

Randy Speed
Speed Consulting, LLC
(800) 256-7140 ph and fax
www.speedconsulting.com



Quoting Tim Biggs <->:

> --0__=09BBF0EADFE5BF048f9e8a93df938690918c09BBF0EADFE5BF04
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ChrisKaswer16-Pearl
16-Pearl
September 17, 2012

Don,


You can create a mechanism in MDO that can approximate the stiffness of your beam with your active cylinders. First, run a Mechanica analysis on the beam with its supports oriented as they are in the real system and measure the stiffness in the direction you're most concerned with. Here's the trick - approximate the stiffness in one of a couple ways, torsional or translational, based on how you'd like to simulate its behavior. Then break the beam into two pieces, or more,and connect them with ajoint that you can apply your stiffness value to as a spring (translational ortorsional) equal to what you found it is in Mechanica. The mechanism will behave as it would as a flexible system (to the extent you model its flexibility). I gave a paper that included this topicat thePTC/User Conference in 2004. This approach works very well, so long asthe representation of your stiffness is adequate to capture what's happening.


Chris

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randyspeed1-Visitor
1-Visitor
September 17, 2012
Don,

I thought about this over the weekend and believe the best path forward is to solve for a balanced force set using MDO. In MDO you would apply forces that are related to each other using the pressure equation for the force definition. This way the forces are applied correctly. Once you go through an MDO simulation, then transfer the load set (at a specific time punch) over to Structure fea. The loads will be balanced and have the correct magnitudes.

Randy Speed
(214) 213-4440 cell phone
Speed Consulting, LLC
(800) 256-7140 ph and fax
www.speedconsulting.com


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randyspeed1-Visitor
1-Visitor
September 17, 2012
I thought over weekend and believe the best path fwd is to use mdo to run simulation, applied forces linked by definition of pressure, then transfer balanced forces to structure fea.

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