1. Review and comparison of the modeling approaches and risk analysis methods for complex ship system.
Author: Sunil Basnet

2. Outline Introduction Methodology Case study with RR Conclusions
Future research

3. Aim of the research
Review and comparison of safety engineering techniques:
Risk analysis methods:
For identifying and mitigating risks in a system.
Modeling approaches:
For presenting a graphical model of the structural composition and behavior of a system.

4. “ Safety is more important than convenience”- Don Hambidge
Motivation
“ Safety is more important than convenience”- Don Hambidge
Autonomous projects – unavailability of data for probabilistic methods.
Development of advanced technologies – need to focus on new types of risks. i.e. software errors,design errors and risks due to unsafe interactions.
Dominant risk analysis methods:
Failure Mode and effects analysis (1949)
Fault Tree Analysis (1962)
Image: Rolls- Royce

5. Key concern: Research questions:
Can these traditional methods , developed for simpler systems, co-op with the issues due to rapid technological change? OR
Should we implement modern tools and methods developed for complex systems?
Research questions:
Which approach is suitable for modeling a complex ship system?
Which method is suitable at identifying risks in a complex ship system?
Can the risk analysis method identify increasing emergent failures such as component interaction issues?

6. Research limitations:
Probabilistic methods are not considered due to unavailability of the data about system failure and risks.
To limit the scope, only one widely used traditional method (from the methods implemented in R-R) are reviewed and assessed against one modern method.

7. Methodology: Initial literature review for selection of methods.
Detailed review of Modeling approaches (Tree structure method and System Modeling Language) and risk analysis methods (Fault Trees Analysis and Systems-Theoretical Process Analysis).
Case Study for analysis with experts of Rolls-Royce

8. Modelling approaches Tree structure method:
Presents structural composition of a system in a hierarchial approach.
Simple method but it is limited on the representation of component interactions.
System Modeling Language (SysML):
Developed in 2006
A graphical modeling language that presents the structural composition, behavior, and requirements of a system.
Aims to support the analysis, specification, design, and validation of complex systems.

9. Type of diagrams in SysML Block definition diagram
Internal block diagram
Activity diagram
Requirement diagram
Parametric diagram
Package diagram
Image: SysML TM.

10. Risk analysis methods Fault Trees Analysis
An approach to identify risks in a system in sequential events.
Uses boolean logic gates and symbols to denote the combination.

11. Risk analysis methods STPA
A systemic and systematic approach for identifying risks in a complex system
Implementation procedure:
Accident definition
Hazard identification
Develop safety constraints
Create a control structure
Identify unsafe control actions
Redefine safety constraints
Safety Control Structue

12. Case study ( )
Case: Implementation of methods in some parts of Azimuth thruster. Location: Rolls-Royce research and development center, Turku, Finland Aim: Test and evaluation of the methods with experts in R-R. Tools: Edraw Max ( Tree structure method and Fault Trees Analysis) RMStudio (STPA) Modelio / Astah SysML (SysML)
Image: Edraw
Image: RM Studio
Image: SysML TM.

13. Description of the case
The methods were implemented to model and identify risks in a part of the azimuth thruster.
Experts of Rolls-Royce (with diverse backgrounds) and familiar to the functionality of the azimuth thruster (R-R AZ123) implemented the methods.
Image: Azimuth thurster Rolls-Royce

14. Modeling approaches
Tree structure method

15. SysML
Package diagram
A tool to manage or group the diagrams and it’s elements.
Package can be created on multiple ways.
By diagram kind (e.g. behavior, requirements)
By system hierarchy (e.g. enterprise, system, component)

16. SysML Activity diagram
Presents the interactions among components when executing a certain activity.

17. SysML Requirement diagram Presents the requirements for the system

18. SysML Block definition diagram
Presents the structural composition of the system.
Can also include properties of the components.

19. SysML Internal Block diagram
Presents a layout of the interconnection between the components inside the system

20. SysML Parametric diagram
A tool for conducting efficiency, stress analysis and other engineering analysis

21. Risk analysis methods
Fault Tree Analysis

22. STPA ID Accident Description A1 Loss of the azimuth thruster.
The azimuth thruster gets detached from the vessel. A2
Failure of the azimuth thruster.
The azimuth thruster fails. ID
Hazard
Description
Relationship H1
Vessel grounding.
Grounding of vessel occurs.
A1, A2 H2
Vessel collision
Vessel collides with an object.
Hazards
Safety Constraints
H1. Vessel grounding.
SC1. The vessel should be designed to withstand harsh weather conditions.
SC2. Proper routing and constant weather and sea state monitoring.
SC3. Hardware and software redundancy.
SC4. Intensive software testing.
H2. Vessel collision.
SC2. Object detection sensor and radars redundancy.
SC3. Intensive testing of sensors and radars.

23. Control Structure

24. Identification of potentially unsafe control actions.
Not providing the action causes a hazard
Providing the action causes a hazard.
Providing the action too late causes a hazard
Provided the action too early causes a hazard
Operator:
Change speed
Not reducing the speed when needed.
Increasing speed without vessel’s surrounding awareness.
Reducing speed too late.
Change direction
Not changing direction when needed.
Changing direction without vessel’s surrounding awareness.
Changing direction too late.
Start Lubrication
Not lubricating the bearings and components
Identification of potentially unsafe control actions.
Analysing how these actions could occur.
Define requirements to prevent them.

25. Evaluation

26. Systems Modeling Language Systems Modeling Language
Expert’s Evaluation: Modelling Approaches
0 – 1.0
Poor
1.1 – 2.0
Satisfactory
2.1 – 3.0
Average
3.1 – 4.0
Good
4.1 – 5.0
Excellent
Tree structure method
Criteria's
Expert 1
Expert 2
Expert 3
Expert 4
Expert 5
Average rating
Method complexity 5 4
4.2
Modeling time 3
3.6
System's structural modeling 2
2.8
System's behavior modeling 1
1.6
Functionality
2.6
Systems Modeling Language
Criteria's
Expert 1
Expert 2
Expert 3
Expert 4
Expert 5
Average rating
Method complexity 2 3
2.4
Modeling time 1
2.0
System's structural modeling 5 4
4.2
System's behavior modeling
4.0
Functionality
3.6
Criteria's
Average Rating
Tree structure method
Systems Modeling Language
Method complexity
4.2
2.4
Modeling time
3.6
2.0
System's structural modeling
2.8
System's behavior modeling
1.6
4.0
Functionality
2.6
SysML involves more detailed modeling of the system. Thus, it is more complex and time consuming than Tree structure method.
However, SysML presents component interconnection, interactions, requirements and tool for analysis of the system which is not modeled in Tree structure method.

27. Systems-Theoretical Process Analysis
Expert’s Evaluation: Risk analysis methods
0 – 1.0
Poor
1.1 – 2.0
Satisfactory
2.1 – 3.0
Average
3.1 – 4.0
Good
4.1 – 5.0
Excellent
Fault Trees Analysis
Criteria's
Expert 1
Expert 2
Expert 3
Expert 4
Average rating
Method complexity 4 5
4.3
Analysis time 3
Risk Identification 2
3.3
Risk Mitigation 1
2.0
Structure of the model
4.0
Systems-Theoretical Process Analysis
Criteria's
Expert1
Expert 2
Expert 3
Expert 4
Average rating
Method complexity 3 2
2.5
Analysis time
2.8
Risk Identification 4
3.5
Risk Mitigation
3.3
Structure of the model
Criteria's
Average Rating
FTA
STPA
Method complexity
4.3
2.5
Analysis time
2.8
Risk Identification
3.3
3.5
Risk Mitigation
2.0
Structure of the model
4.0
FTA is simpler and faster to implement than STPA.
However, STPA is better at identifying risks related to component interactions and human errors than FTA.
The structure of the model prepared using FTA is easier to follow and understand than the model using STPA.

28. Conclusions

29. Modeling approaches Tree structure method SysML
Complexity of the method
Low
High
Time consumption
Very high
Level of detail for presenting structural composition
Level of detail for presenting component interactions
None
Level of detail for presenting requirements of a system
Level of support for conducting an engineering analysis
Suitability of the method for modeling a complex ship system

30. Risk analysis methods FTA STPA Complexity of the method Average High
Time consumption
Very high
Level of effectiveness for identifying component failures
Level of effectiveness for identifying unsafe component interactions
Level of effectiveness for identifying human errors
None
Level of support for a systemic and systematic analysis
Suitability for analyzing risks in a complex ship system (functionality)
Suitability for analyzing risks in a complex ship system (available resources and complexity)

31. Detected limitation in the modern methods and proposed solution
Modern methods are complex and require higher resources implementation.
A proposed solution:
Create a code template to generate diagrams instead of graphical interface. (graphviz)

32. Future research
Review considering the effectiveness of methods at initial design phase.
Review of methods with a proper weight factor assigned to each criterion.
Implementation study of the modern methods to develop a framework for safety assessment of autonomous vessels.

33. Thank you