PPI SyEN 80 – 19 August 2019
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2.1 MBSE Integration with Mechanical Design
Jose L. Fernandez
Aeronautical Engineer, PhD in Computer Science, and MBSE Methodologist
Copyright © 2019 by Jose L. Fernandez. All rights reserved.
Editor’s note: A book entitled Practical Model-Based Systems Engineering by Jose L. Fernandez (the author of this article) and Carlos Hernandez has just been released. It is highlighted in the Systems Engineering Publications Section of this issue of PPI SyEN.
This paper describes the challenges identified in the integration of MBSE, methods, notation, tools and people, with mechanical design, particularly Computer Aided Design (CAD) tools. Searching the literature and attending to Systems Engineering conferences, the author found some interesting approaches to bridge systems engineering models represented in SysML notation and CAD models developed with commercial CAD tools.
The author summarizes and references here some of the Model Based Systems Engineering and Mechanical Design integration approaches, so that the interested reader may plan his/her roadmap to apply them.
One of the main concerns of Model Based Engineering (MBE) is the integration of disparate models from diverse specialties. That is the case of mechatronic systems (Bishop, 2016), such as robotic applications, where we have to integrate system, software, mechanical, and electrical models frequently developed by different people with different tools.
Below there is a summary of the challenges identified in the integration of Model Based Systems Engineering (MBSE), methods, notation, tools, and people, with mechanical design, particularly Computer Aided Design (CAD) tools. Following, some interesting approaches to bridge systems engineering models represented in SysML notation and CAD models developed with commercial CAD tools are described as well.
II. Main challenges of the integration
The main challenges of the integration of Model Based Systems Engineering and Mechanical Design are the following:
Differences in the abstraction levels of the systems engineering models, frequently represented in SysML notation and the CAD tools models for mechanical design. These differences make it difficult to establish associations between both types of models.
The visualization of a CAD model in a SysML Block Definition Diagram is very different from the views with which a mechanical engineer is accustomed to working.
SysML limitation in representing physical system structures that may change over time.
These different views need to be consistent and linked together with dependency links supported by tools.
Some MBSE methodologies represent functionality as scenario-based or service request-based. The lack of a functional hierarchy representation is an impediment to create dependencies between system and mechanical models when both may be functions-based (Mhenni et al., 2014).
The solution neutral functions identified for the system need to include those functions that may be implemented by mechanical parts.
Engineers from different disciplines have to work together on a holistic system model to manage the dependencies between disciplines.
Top-down and sequential approaches for engineering are no longer adequate because engineers need to explore design details in early stages of the project.
III. Diverse approaches for the integration
Considering the extended use of SysML notation and its supporting tools in MBSE, we found some approaches for their integration with CAD models that are summarized below. Some of these approaches are functionally oriented and are based on the system functional hierarchy so we think that they can be integrated with the ISE&PPOOA MBSE method presented in our recently published methodology book (Fernandez and Hernandez, 2019).
These approaches are based either in the extension of SysML notation, the transformation of metamodels from MBSE to CAD or the use of a Domain Specific Language (DSL). See Figure 1. Examples of these approaches are described in the next section.
Figure 1: MBSE (SysML) – CAD Integration Approaches
IV. Examples of integration alternatives
One approach proposed by Grundel and Abulawi proposes the extension of the SysML blocks, adding a block compartment where they represent sketches that are less detailed engineering representations than CAD models. Sketches facilitate the communication of design ideas and allow evolving them. Grundel and Abulawi developed the so called SkiPo (Sketch and Port) model. In SkiPo, a block contains diverse compartments: one for the functional description, another for the sketch area including sketches or pictures, and a third one, the block area where the solution can be specified by describing specific properties or decomposing it into subordinate blocks (Grundel and Abulawi, 2016).
A sketch always contains geometry details but other types of constraints can be documented as well, such as materials specifications and joining techniques.
Alberts and Zingel propose an extended SysML profile based on the Contact&Channel-Approach (C&C2-A) for integrated modeling of functions and including physical properties of physical systems. One of the rules for the consistent application of this approach states that every system and subsystem can be described by the basic elements Work Surface Pair (WSP) for two elements being in contact, Channel and Support Structure (CSS) and Connector (C). From functional flows represented by activity diagrams with partitions, the CSSs are generated automatically by a plugin of the prototype tool they developed. When the CSS are created, the structure can be modeled using SysML Internal Block Diagrams with stereotyped SysML connectors to network WSs (Alberts and Zingel, 2013). They propose to apply C&C2-A combined with the Functional Architectures for Systems (FAS) MBSE method (Lamm and Weilkiens, 2010).
Other approaches are based on metamodel transformation. A metamodel would be a textual, graphical, and/or formal representation of the modeling concepts used by a tool and how they are linked. It is known that SysML/UML are defined by a metamodel; the MOF 2.5 specification provides the basis for metamodel definition in OMG’s family of modeling languages including the UML and is based on a simplification of UML 2’s class modeling capabilities. CAD tools such as Solid Edge have metamodels supporting the modeling concepts which are generally supported by mechanical CAD tools. As is represented in Figure 2, if it is possible to create a map between metamodel concepts, then a transformation language and a transformation tool between models can be developed. We applied this approach for the use of the Cheddar tool for performance assessment of the PPOOA software architecture models as described in a previous paper (Fernandez and Marmol, 2008). Qamar proposes a metamodel transformation approach to be applied to transform Solid Edge CAD models into SysML models. To facilitate the mapping, they extended SysML, because it lacks formal and detailed semantics needed to build the mapping relations with sufficient semantic depth. The created SysML profile for Solid Edge is used to model dependencies between the SysML and the Solid Edge models. The Atlas Transformation Language (ATL) is used to read the model conforming to the Solid Edge metamodel and writes the target model conforming to SysML profile for Solid Edge (Quamar et al., 2015).
Scheffler et al propose using metamodels to allow export CAD models transformed into an XMI format of a SysML model (Scheffler, R. et al., 2016).
In some cases, as described by Qamar, the dependencies captured by modeling the correspondence relationships between models as described above, do not provide information about the type of dependency and when it is applicable. So they propose an approach where they use a Domain Specific Modeling Language to provide the necessary dependency modeling features. A dependency here is a causal relationship between two or more properties. They model two types of dependencies: synthesis dependency whose outputs are synthesis properties, and analysis dependency whose outputs are analysis properties. As soon as a design concept is captured, dependencies between the views are captured inside the dependency model (Qamar et al., 2015).
Similar approaches as those described above are to be taken for the Electrical Computer Aided Design (ECAD) where a SysML profile for ECAD modeling is proposed, where concepts such as black box, cable, conductor, connector, cavity, contact, and tool are considered (Cabot, 2018).
Figure 2: Metamodel-based Transformation of Models
Summary and Conclusions
One of the main concerns of Model Based Engineering is the integration of disparate models from diverse specialties.
There are differences in the abstraction levels of the systems engineering models, frequently represented in SysML notation and the CAD tools models for mechanical design. These differences make it difficult to establish associations between both types of models.
A literature search identified three main groups of integration approaches. These approaches are based either in the extension of SysML notation, the transformation of metamodels from MBSE to CAD, or the use of Domain Specific Languages (DSL).
Considering the differences between these integration approaches and the tools supporting them, the interested reader may plan his/her roadmap to apply them.
List of Acronyms Used in this Paper
ATL Atlas Transformation Language
CAD Computer Aided Design
C&C2– A Contact&Channel-Approach
CSS Channel and Support Structure
DSL Domain Specific Language
ECAD Electrical Computer Aided Design
MBE Model Based Engineering
MBSE Model Based Systems Engineering
MOF Meta Object Facility
ISE&PPOOA Integrated Systems Engineering and Pipelines of Processes in Object Oriented Architectures
OMG Object Management Group
SkiPo Sketch and Port
SysML Systems Modeling Language
UML Unified Modeling Language
WS Working Surface
WSP Work Surface Pair
XMI XML Metadata Interchange
XML Extensible Markup Language
Albers A. and C. Zingel , “Extending SysML for Engineering Designers by Integration of the Contact & Channel – Approach (C&C2-A) for Function-Based Modeling of Technical Systems,” Procedia Computer Science, Volume 16, 2013, Pages 353-362, ISSN 1877-0509, https://doi.org/10.1016/j.procs.2013.01.037.
Bishop, R.H. (Ed). Mechatronics. An Introduction. Taylor & Francis Group, Boca Raton, FL, 2016.
Cabot, J. SysML extension for ECAD (Electrical Computer-aided Design). https://modeling-languages.com/sysml-extension-ecad-electrical-cable-design/ (accessed June 25, 2019).
Fernandez, J.L. and C. Hernandez. Practical Model-Based Systems Engineering. Artech House, Nordwood, MA, 2019.
Fernandez J.L. and G. Marmol, “An Effective Collaboration of a Modeling Tool and a Simulation and Evaluation Framework”. INCOSE International Symposium, 18: 1509-1522. doi:10.1002/j.2334-5837.2008.tb00896.x.
Grundel, M. and J. Abulawi, “SkiPo – a sketch and flow based model to develop mechanical systems.” INCOSE International Symposium, 26: 399-414. doi:10.1002/j.2334-5837.2016.00168.x.
Lamm, J.G. and T. Weilkiens, “Functional Architectures in SysML.” Proceedings of the Tag des Systems Engineering (TdSE ’10). Munich, Germany, 2010.
Mhenni, F. et al., “A SysML-based methodology for mechatronic systems architectural design,” Advanced Engineering Informatics. (2014), http://dx.doi.org/10.1016/j.aei.2014.03.006.
Qamar, A., Wikander, J. and C. During. “Managing dependencies in mechatronic design: a case study on dependency management between mechanical design and system design.” Engineering with Computers (2015) 31: 631. https://doi.org/10.1007/s00366-014-0366-x.
Scheffler, R. et al., “Graphical Modelling of a Meta‐Model of CAD Models for Deep Drawing Tools.” INCOSE International Symposium, 26: 1090-1104. doi:10.1002/j.2334-5837.2016.00213.x.
About the Author
Jose L. Fernandez has a PhD in Computer Science, and an Engineering Degree in Aeronautical Engineering, both by the Universidad Politecnica de Madrid (UPM,) Spain. He has over 30 years of experience in industry as system engineer, project leader, researcher, department manager, and consultant. He was involved in projects dealing with software development and maintenance of large systems, specifically real-time systems for air traffic control, power plants Supervisory Control and Data Acquisition (SCADA), avionics and cellular phone applications.
Jose was associate professor at the E.T.S. Ingenieros Industriales, Universidad Politecnica de Madrid. His areas of interest were systems engineering, real-time systems, software engineering, CASE tools, and project management. He is the methodologist of the PPOOA architectural framework for real-time systems and ISE&PPOOA, an integrated systems and software MBSE methodology for complex systems.
Jose has more than 50 publications in international journals and conference proceedings, mainly in the fields of systems engineering, software development, real-time systems, and project management. He is senior member of the IEEE (Institute of Electric and Electronics Engineering) and member of INCOSE (International Council on Systems Engineering), participating in the software engineering body of knowledge, systems engineering body of knowledge, and requirements engineering working groups of these associations. He is a member of the PMI (Project Management Institute), participating as reviewer of the PMBoK 6th Edition, 2017 and the Requirements Management Practice Guide, 2016.
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