Multibody Free Software for Teaching PurposesGiuseppe Quaranta, Marco Morandini and Pierangelo Masarat i

Dipart imento di Ingegneria Aerospaziale

Multibody Dynamics 2005, June 21- 24 Madrid, Spain

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Multibody Dynamics 2005

Outlook

➢ Introduction & Motivat ions➢ Status & requirements of MBD Teaching

➢A special case MBD for aerospace engineering f ield➢ Teaching through software development & applicat ion➢ A case study: MBDyn a DIAPM software

➢Mult idisciplinary approach➢Open Source software➢ Object Oriented programming

➢ Experience gained ➢ Conclusions & future developments

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Multibody Dynamics 2005

Introduction & Motivations

➢ Strong nonlinearit ies lead toward an higher degree of complex ity of classical linear FEM models

➢ Users must possess strong foundations in➢ MATHEMATICS ➢ NUMERICS ➢ PHYSICS

Applicat ion of lessons learned on realist ic models is a must to reach a deep understanding

MBD

NL Finite Elements

Computat ional

Mathematics

System Dynamics

ClassicalMechanics

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Multibody Dynamics 2005

Introduction & Motivations (Cont.)➢ Simple adoption of commercial, “black box” codes, may

not help students to understand main crit ical points➢ It is unrealist ic to expect student to write even a trivial

MBD software from scratch➢ A good compromise is represented by the adoption of

MBDyn an Open Source analysis software for➢ new physical problems➢ new mathematical formats➢ new numerical recipes ➢ more ....

➢ Students may focus on realist ic problems with a signif icant scient if ic contents, and at the same t ime:➢ do not “reinvent the wheel” every t ime➢ learn from predecessors ➢ acquire a global vision of the interconnect ions

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Multibody Dynamics 2005

MBD Teaching: Status and Requirements

➢ Students have to deal with an high level of complex ity ➢ A “proper” MBD user must possess the capability to

dist inguish when an analysis failure is due to:➢ improper modelling of physical phenomena➢ inaccuracies of input data➢ numerical failures➢wrong dynamic formulat ion➢ physical pathological behaviours

➢ The main university commitment must be to transfer to future engineers awareness of possible pit fall more than practice in the usage of a specif ic commercial GUI

➢ Simple and accessible GUI, at f irst stages of learning, may give the misleading impression of utmost simplicity

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Multibody Dynamics 2005

MBD for Aerospace Engineers

➢ Typical applicat ion of MBD to aerospace engineering are naturally mult idisciplinary➢ helicopters and t ilt rotors➢ landing gear systems➢ ....

➢ f luid dynamics forces, hydraulic components, controls and so on

➢ Users need to develop/ use non standard modules

➢ numerical modelling knowledge to create interacting mult idisciplinary elements is needed

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Multibody Dynamics 2005

MBDyn a multibody code

➢ Open Source MBD project developed at DIAPM➢ Mult idisciplinary

➢mechanical elements➢ kinematically perfect constraints➢ deformable nonlinear elements➢ electric, hydraulic, aerodynamic & control elements

➢ Interconnected to other software for concurrent simulat ions➢MATLAB/ Simulink (Scilab/ Scicos)➢Aerodynamic codes for Fluid- Structure Interact ions

➢ Real- Time capabilit ies when connected with RTAI (Real Time Applicat ion Interface) Linux OS

MBDynMBDyn

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Multibody Dynamics 2005

MBDyn: Open Source

If the source code of a software package is available to experienced and motivated users, those who really need a feature, will succeed in modifying the code, making their improvements available to the whole community. ➢ Successful stories

Linux OS

➢ ... and for scientif ic software

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Multibody Dynamics 2005

MBDyn: Open Source (Cont.)

How openness helps teaching/ learning MBD?Free access to the whole software source code gives the

opportunity to➢ learn about the structure and the key parts of a MBD

code ➢ learn from solut ions implemented by predecessors➢ experiment and compare new elements, new

formulat ions, and so on without start ing every t ime from scratch

➢work on realist ic (complex) test cases and not on simple examples

➢ interact with a community of users/ developers

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Multibody Dynamics 2005

MBDyn: Object Oriented Programming

➢ The object oriented structure, based on the adoption of C+ + , is one of the main strength of MBDyn for teaching purposes

➢ It allows to ident ify easily the principal operat ions which must be executed during every mult ibody simulat ion: modularity and standardization are exploited

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Multibody Dynamics 2005

MBDyn: OO Programming (Cont.)

Principal advantages of OO programming➢ definit ion of object with a common external interface

which hides the technical details of the real implementat ion➢ in this way it is possible to interact with all the

modules without knowing the internals➢ Operator overloading capability

➢ possibility to def ine a new object with the same external interface but with a completely dif ferent technical implementat ion

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Multibody Dynamics 2005

Experience gained

➢ The possibility to learn with the hands direct ly on the core of a MBD tool is a prof icient method to transfer knowledge

➢ A lot of interest ing features have been developed with the help of, or under the pressure of student projects➢ electro- elast ic behaviour of piezo- electric embedded

elements➢ parallel algorithms➢ a library of hydraulic components➢ f lex ible slider joint➢ Fluid- Structure interaction simulat ions with MBD codes

and CFD codes➢ extraction of stability information using POD➢ and many more...

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Multibody Dynamics 2005

Conclusions

➢ The experience gained by the MBDyn developing team in teaching MBD using code programming, developing and employment has been presented

➢ Specif ic aerospace applicat ions often require the capability to interact with commercial codes to develop specif ic new features

➢ the experience up to now is very posit ive and increases the self- conf idence of new MBD software users

➢ We think the experience can be spread to others, either by the adoption of MBDyn by more students for development and test ing of new ideas or techniques, or by start ing a new common Open Source product to be adopted for this purpose by the mult ibody research community