Are 'flexible bodies' what once were known as 'substructures?' If so you can include  nonlinear elements with substructures to simulate such things as uplifting displacements from compression-only supports or contact between such things as adjoining objects which might rock towards each other and make contact. In a (long) past life I did a lot of transient analysis using substructures to model free-standing spent nuclear fuel storage racks. I only mention this as a sort of warning that convergence in this sort of analysis can be mighty slow—tiny changes have big effects. Rigid body motion (at least at the time) was really a huge pain in the butt, and I've always suspected that solutions for that sort of analysis weren't unique. Minor changes to check convergence produced all sorts of results. I've always likened it to trying to reproduce the motion of a ball bearing dropped on a concrete floor—tiny changes to such things as interface stiffness or gap opening made for wildly varying results. And the more cases you ran to hunt around for a converged solution the more different converged solutions you got. Just like real life.

I saw an analysis once to calculate the path of a moving bicycle starting with no steering input. Every run was different. Just like real life.

Christopher Wright P.E. (ret'd) |"They couldn't hit an elephant at
chrisw@skypoint.com | this distance" (last words of Gen.
http://www.skypoint.com/members/chrisw/ | John Sedgwick, Spotsylvania (1864)

'Flexible bodies' are an ADAMS thing where you replace a normally rigid body with a stiffness/mass/modal representation of the part.  Being a Component Modal Synthesis representation, the body must be linear.  The interfaces with said body can be nonlinear.  The approach greatly extends the use of a traditional multibody dynamics solver.

A caution to James on the bonded contact; be wary of the stiffness of the bonded contact.  I have seen errors in a clamped-clamped beam that was held together ~L/3 by bonded contact.  Long story for why we did that ...  The model's first bending mode was not the correct traditional first bending mode but was an S-shaped mode because the stiffness of the bonding elements tying the beam was abnormally high.  Perhaps multiple issues in one example - but, something to consider.

Alan Baker
Sr. Manager, T55 Growth Mechanical Systems, Shafting, and Dynamics
Engine Systems & Component Analysis
Honeywell | Aerospace
Office:  480.293.2059
alan.baker2@honeywell.com

ns.

Sounds like a substructure including he limitations.

Christopher Wright P.E. (ret'd) |"They couldn't hit an elephant at
chrisw@skypoint.com | this distance" (last words of Gen.
http://www.skypoint.com/members/chrisw/ | John Sedgwick, Spotsylvania (1864)

Dear Mr. Wright,
the flexible bodies are built in Adams following the Craig-Bampton method. The first trials were made at the end of the 20th century; I was part of one of the teams who were trying to find a good method to incorporate bodies with distributed flexibility into ADAMS. We started with a pure modal superposition approach, but the modal basis, even if it was quite large, failed to properly represent the body's deformed shape when it was subject to quasi-static loading and its interface points were constrained. So we added a set of "constrained" modes to the basis, obtained by constraining all the dofs at the interfaces except one, where a unit generalized displacement was applied. The resulting deformed shape was called the "constrained" or "static" mode. Repeating the process for each other dof at the interfaces, we got the set of static modes to add to the "traditional" ones. That "hybrid" basis proved to be far better than the original one. That's how flexible bodies are described in ADAMS; in fact, the method has some other numerical tricks to make it more accurate and efficient, but the core elements are the ones I mentioned.

Best regards
Riccardo Testi

Development and Strategies
2 Wheeler Engines Technical Centre
Piaggio & C. S.p.A
Viale Rinaldo Piaggio, 25
56025 Pontedera (Pisa) - ITALY
Phone:  +39 0587 272850
Fax:        +39 0587 272010
Mobile: +39 339 7241918
E-mail:    riccardo.testi@piaggio.com

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Subject: [Xansys] Re: [External] Re: ANSYS to ADAMS with Bonded Contact..

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ns.

Sounds like a substructure including he limitations.

Christopher Wright P.E. (ret'd)                        |"They couldn't hit an elephant at
chrisw@skypoint.com                                    | this distance" (last words of Gen.
https://urlsand.esvalabs.com/?u=http%3A%2F%2Fwww.skypoint.com%2Fmembers%2Fchrisw%2F&e=d76018bd&h=f18423fd&f=y&p=y      | John Sedgwick, Spotsylvania (1864)

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