Libraries for Model-Based Mechatronic
Concept Design in SysML
Benjamin Kruse
Engineering Design and Computing Laboratory, ETH Zurich
Benjamin Kruse
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Agenda
 Motivation & Introduction
 Functional Modeling Library in SysML
 Library Definition and Usage
 User Study for Library Evaluation




Amesim Simulation Library in SysML
Component Modeling Library in SysML
Outlook
Summary
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Motivation: Rising Complexity
Benjamin Kruse
Systems Engineering Vision 2025 Project Team.
“A World in Motion – Systems Engineering Vision
2025.” International Council on Systems
Engineering. 2014.
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State of the Art in Research & Industry
 Functional Architectures in SysML1 (FAS)
 Method for obtaining functional architectures
for systems in block-oriented form
 By using heuristics for grouping functions
and allocating them to functional blocks
 State of usage of SysML2
 Functional modeling has the
most added value for users
 Needed improvements:
 Usability of SysML needs to be improved
 Modeling methods and guidelines are needed
1) Lamm, J. G., and Weilkiens, T. “Method for Deriving Functional Architectures from Use Cases.” Systems Engineering,
2014; 17:2, p. 225-236.
2) Albers, A., and Zingel, C. “Challenges of Model-Based Systems Engineering: A Study Towards Unified Term
Understanding and the State of Usage of SysML.” Smart Product Engineering, Springer, 2013.
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Vision 2025 & Evolving MBSE
 SE Vision 20251
 Formal systems modeling
 Composable design: A key to productivity
 By combining formal models from libraries
 Evolving SysML2
 Include precise semantics
that avoid ambiguity
 Be usable for multiple application domains
 Integrate across discipline-specific
engineering tools
 Primary consideration: Usability!
1) Systems Engineering Vision 2025 Project Team. “A World in Motion – Systems
Engineering Vision 2025.” International Council on Systems Engineering. 2014.
2) Friedenthal, S. and Burkhart, R. “Evolving SysML and the System Modeling
Environment to Support MBSE.” in: Insight, INCOSE, 2015, 18:2, p.39-41
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Approach for Mechatronic Concept Generation
Formal &
Standardized
Language
Task
Specification
Mechanical
Electrical
…
Mechatronic
Concept Models
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Engineering Design + Computing Laboratory
Model
Generation
Generic
Multi-Disciplinary
Model Libraries
Model
Simulation
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Hirtz, J., Stone, R. B., Mcadams, D. A.,
Szykman, S., and Wood, K. L. A: “Functional
Basis for Engineering Design: Reconciling
and Evolving Previous Efforts.” No. 1447,
USA: NIST. 2002.
NIST Functional Basis (FB)
 Established collection of operators and flows to be
combined into elementary functions of engineering systems
i.e. braking of electric car
Decrease. To reduce a flow in response to a
control signal. Example: Closing the value further
decreases the flow of propane to the gas grill.
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Rotational energy. Energy that
results from a rotation or a virtual
rotation. Example: …
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Functional Modeling Library in SysML
 ElementaryFunction: FB operator as SysML activity
 BasicFlow: SysML block to define object flows
Kruse, Münzer, et al.:
“Workflow and Modeling
Conventions for Function
and Product Structure
Modeling of Mechatronic
Systems in SysML using
Libraries”. Mechatronics
2012, Linz, Austria, 2012
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Functional Modeling
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electric car main function
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Functional Decomposition
Step-by-step functional
decomposition, until
elementary functions
Overall Function:
e.g. Control Motion
from library are used
User-Defined Function:
e.g. Recuperate Braking Energy
Elementary Function:
e.g. ElectricalEnergy : Store
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Function Library Evaluation
 Common advantages of reuse in
software development1 and engineering design2:
 Better understanding of a system
built from building blocks
 Higher model and system quality
 Faster development
 Achievable through Function Library?
 Experiment Hypotheses:
 Using the library leads to better models
 Using the library leads to reduced workload
1) Chughtai, A., and Oliver V. "Software-Wiederverwendung-Theoretische Grundlagen, Vorteile und realistische Beurteilung."
in: Software-Management: Beherrschung des Lifecycles. Editor: Versteegen, G., Springer, 2002.
2) Duffy, A. H. B., and Ferns, A. F. “An Analysis of Design Reuse Benefits.” Proceedings of the 12th International Conference
on Engineering Design (ICED ’99). 1998; p. 799-804.
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User Study for Library Evaluation
 Measurements for model quality:
 More functionalities covered (compared to master models)
to access task completion
 Higher relative number of functions of the Functional Basis
 Not: bigger model size (because not corresponding to model quality)
 Measurements for modeling workload (Better Usability?):
 TLX1 test to measure the perceived workload of participants
(Established test by NASA)
 ETH tools course for functional modeling & SysML:
 11 participants (inexperienced students)
 3 afternoon sessions
1) Hart, S. G. & Staveland, L. E.: “Development of NASA-TLX (Task Load Index): Results of empirical and theoretical
research.” in: Human Mental Workload. Amsterdam: North Holland Press. 1988.
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Experiment Plan
 Factor:
 With SysML library:
Functional Basis
incorporated
in SysML
 Without SysML library:
Functional Basis
given on paper
 Tasks: Creating
functional models
of a coffee maker
 Task 1:
Brewing coffee
 Task 2: Grinding
coffee beans
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Rating
70
Results: TLX (NASA)
100
60
50
40
Overall Perceived Workload
90
Day 3-1 Workload (without library)
30
20
80
10
70
0
60
Importance Weight
50
3-2: with
library
10
3-1: no
library
20
1: no
library
30
2: with
library
Mental
40
0
Rating
70
Physical
Temporal
Performance
Effort
Frustration
Day 3-2 Workload (with library)
60
50
Day 1 (without SysML library)
Day 2 (with SysML library)
40
Day 3-1 (without SysML library)
Day 3-2 (with SysML library)
30
20
 Results:
10
 Learning effect
 Library increased workload!
0
Mental
Importance Weight
Physical
Temporal
Performance
Effort
Frustration
(0 = minimum workload, 100 = maximum workload)
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Results: Questionnaire & Comments
 Questionnaire:
 “Modeling with the library in SysML improved the resulting model /
modeling process compared to not having the library.”
 Approval rating: 59 – 60 (0 = completely disagree, 100 = completely agree)
 Comments about library usage:
“library forces you to break down the activity further”
Productivity
“triggers my thought process”
Increased workload & comments:
Results of using Functional Basis
“resulting model is
“having to look
upNOT
functions,
and
directly of using the library
decide which are appropriate”
more fundamental”
“very limited by the functions of the library”
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Time
S. Rifkin: “Why new
software processes are
not adopted”, Advances
in Computers, (59). 2003
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Results: Library & FB Acceptance
 Library & FB acceptance:
 Library used
when available
(good user acceptance)
 Functional Basis
barely used
without library
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Relative # of FB functions
 Significant correlation (p < 0.001) between availability of library
and the number of functions from library
 Significant correlation
(p < 0.001) between
availability of library and
relative number of
FB functions
No SysML Library
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With SysML Library
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Results: Task Completion
 Significant correlation
(p < 0.018) between
availability of library and
ratio of covered
functionalities
 Significant correlation
(p < 0.021) between
ratio of FB functions and
ratio of covered functionalities
Relative # of functionalities
 Grade of task completion1:
No SysML Library
With SysML Library
 Having the library (and therefore using the Functional Basis)
leads to a broader coverage of the necessary functionalities
1) Annett, J.: “Hierarchical Task Analysis”. In: Hollnagel, E., Ed., Handbook of Cognitive Task Design, Lawrence Erlbaum
Assoc. Inc., Mahwah. 2003. 17-35.
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User Study – Summary
Higher usage of
formal FB terms
More functionalities
covered
Reuse benefits?
Better understanding
of a system
Higher model /
Increased workload
(Due to usage of FB,
not due to the library)
Experiment assumption
of general usage of FB
not applicable
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system quality
Faster development
Better & more
formal models
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Further development process
…
Structure
Behavior
Functions
Function
Library
Use Cases
Behavior
Library
Requirements
Task
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(FBS)
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Component
Library
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Amesim Simulation Library in SysML
 Incorporation of Amesim library into SysML
Library (SysML)
Library
(Amesim)
Model (SysML)
Model (Amesim)
 Model transformations between SysML IBDs & Amesim models
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Component Modeling Library in SysML
 Structural Components:
Library
 (Mostly) Physical entity or module
 Following eCl@ss standard
 Model:
 Block with attributes (e.g. weight, etc)
 Interfaces:
 Ports with additional information
(e.g. type, etc) and flow types
corresponding to function library
Model
Image source: http://www.cross-morse.co.uk/timing_belt.asp
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Allocation Matrix: Usage-to-Definition
column: elementary functions
as actions (operator & flow)
row: (mostly physical)
components from library
ElectricalEnergy:Store
(for recuperation)
is allocated to
the component
“Car Battery”
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Library Summary
 Function Library




Based on the defined terms of the Functional Basis
Increased workload for inexperienced users
Higher usage of FB terms
Better & more formal
More functionalities covered
functional models
 Amesim Simulation Library
 Corresponding to Amesim
simulation elements
Composing traceable partial
simulation models in SysML
 Component Modeling Library
 Based on eCl@ss standard
 For reusing common elements
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Composing configurations
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Outlook
 Combination of model-based libraries in SysML
and automated design synthesis
 Model transformation for solution space exploration
using boolean satisfiability1
 Model transformations for system behavior simulation
 Automated synthesis & evaluation of SysML models
 Further testing and validation with industry
1) Münzer, C., Helms, B., and Shea, K. “Automatically Transforming Object-Oriented Graph-Based Representations into
Boolean Satisfiability Problems for Computational Design Synthesis.” Journal of Mechanical Design, 2013; 135:10
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Automated Design Synthesis
Problem
System
Boundary
Gear
System Boundary
System Boundary
Engine rpm
System Boundary
R
Acceleration
CombustionCombustion
Brakes and
R Gearbox
Acceleration
Motion
R
T
T
junction Engine
Gearbox
Engine R
Wheels
R
T
Combustion R
R
Acceleration
R
Planetary
R
junction
Gearbox
R
Engine
T
Combustion R R DriveGearbox RR
R
Acceleration
Wheels
Electric
R
Electric
R
R
Battery
R
junction
Engine
and
Machine
T
Brake
Machine R
T
Wheels
R
Vehicle
R
Battery
Electric
and
T
Machine R
Wheels
Vehicle
R
Battery
and
T
Vehicle
Münzer, C., Helms, B., and Shea, K. “Automatically Transforming Object-Oriented Graph-Based Representations into
Boolean Satisfiability Problems for Computational Design Synthesis.” Journal of Mechanical Design, 2013; 135:10
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Automated Simulation
Problem
System
Boundary
Combustion
Engine
R
Gearbox
R
R
R
Brakes and
Wheels
T
T
 Automated map between elements
and corresponding simulation models
 Enables quantitative feedback on
generated concepts and optimization
Münzer, C. and Shea, K.: “A Simulation-based CDS Approach:
Automated Generation Of Simulation Models Based From
Generated Concept Model Graphs”, Proceedings of the ASME
IDETC/CIE 2015, DETC2015-47353
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integrated error ei [m]
Simulated vs. Optimized Solutions
Münzer, C. and Shea, K.: ASME IDETC/CIE 2015
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Engineering Design + Computing Laboratory
total CO2 emissions [g]
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Summary
SysML Model
(FBS)
Function
Library
•
•
Operator & Flow
Behavior
Library
•
Amesim
component
Component •
Library
Functional Basis
Physical entity
or module
Image source: http://www.cross-morse.co.uk/timing_belt.asp
Solution Space Explorer
System Boundary
R
Benjamin Kruse
Electrical
Machine 1
Planetary R
Drive 2 R
R
Combustion
Engine
using Boolean Satisfiability
Simulation
Electric
System BoundaryElectrical R
Junction
Machine 2
R
Combustion
Engine
R
Planetary R
Drive 2 R
R
R
Combustion
Engine
Electric
System BoundaryElectrical RR Planetary R
Junction
Machine 2 R Drive 1
Electrical
R
Machine 1
R
R
Electric
Junction
R
Combustion
Engine
R
R
Planetary R
Drive 2 R
R
Wheels 1 T
Electric
System BoundaryElectrical RR Planetary R
Junction
Machine 2 R Drive 1
Electrical
Machine 1
Planetary R
Drive 2 R
Electrical
Machine 1
R
T
Wheels 1 T
Electrical R Planetary
R
Machine 2 R Drive 1 R
R
R
R
T
Wheels 1 T
Planetary
R
Drive 1
R
T
Wheels 1 T
T
Model
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Thank you for your attention!
Benjamin Kruse
Engineering Design and Computing Laboratory, ETH Zurich
CLA F 32.2, Tannenstrasse 3, 8092 Zurich, Switzerland
http://www.edac.ethz.ch
bkruse@ethz.ch
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