A Complexity Metric forPractical Ship Design

1

Jean-David Caprace

ANAST – University of Liège – Belgium

PRADS – September 2010

• Boundaries – What, How and Why?• Background• How to measure the ship complexity• Presentation of the test case on a passenger ship• Conclusion

2

OutlineOf this presentation

3

Boundaries – What, How and Why?

• Ship designer problem selection of the best design alternative

• Evaluation of the design alternative many attributes (economic, technical, environmental, safety)

• Every design change impact on how much producing/maintaining the ship will cost

• Understand the impact every time the designer make a change

4

BoundariesWhat? – Selection of the best design alternative

• Complex design– Are more fragile– Leads to more surprises (always bad)– Leads to longer development schedule– Causes costly late design modification– Fosters suboptimal tradeoffs between

competing goals– Makes follow-up of design more difficult

5

BoundariesWhat? – Selection of the best design alternative

How well you handle your

design comes down to how

well you handle complexity!

• To give a quantitative and objective metric for the designer – Design evaluation tool

• To find an alternative to the cost evaluation during the design– Expected to be faster– Easier to implement– “Real time”

6

BoundariesHow? – Reduction of the product complexity

• Design for X Optimize total benefits– Design for production– Design for assembly– Design to cost– Design for safety– Design for environment– Design for maintenance– Design for simplicity

7

BoundariesWhy? – To optimize the life cycle of the product

Design for life cycle

• Very hard to find a formal definition of complex systemcomplex system

• Complexity often implies– Many parts with a lot of redundancy– Many relationships/interactions among the

parts– Combination effects that are not easily

predicted– A form of a hierarchy

• If complexity increase LCCost increase

8

BackgroundWhat is a complex system?

• Engineers are using everyday the word “complexity”• Sometimes it is easy to feel the complexity …

9

Complexity evaluationWhat is a complex system?

• Engineers are using everyday the word “complexity”• Sometimes not …

10

Complexity evaluationWhat is a complex system?

11

How to measure the ship complexity

• Complexity affects design, manufacturing, assembly operations, maintenance, dismantling, etc.

• Difficult to measure each factors involved in complexity assessment– Number of components– Number of connections– Number of assembly– Geometry and shape– Production processes– Density– Etc.

12

Complexity evaluationA challenge

• Industry has already attempted to measure complexity– Using empirical measures– Problem proliferation of possible measures

• number of item, production sequence and assemblies, etc.

– So many metrics • how to select the most appropriate indicators ?• do you have the sufficient accuracy ?• how can you tell if the overall complexity is bring reduced if one

measure falls but another rises ?

13

Complexity evaluationA challenge

• Complexity related to …– Number of parts/connections– Complexity of each parts

• Different complexities– Manufacturing complexity– Assembly complexity– Process complexity– Maintenance complexity– Etc.

• Study limited to steel structure

14

Complexity evaluationTheoretical consideration

• Steel structure complexity– Shape complexity (Csh)

– Assembly complexity (Cas)

– Material complexity (Cmt)

Complexity evaluationDifferent factors

• Shape complexity (Csh)– Ability to perform the

manufacturing of individual parts of the product

– Based on sphericity of the product components –

16

Complexity evaluationDifferent factors

Csh= 0

Csh= 0.194

Csh= 0.329

17

Complexity evaluationDifferent factors

• Shape complexity (Csh)

Similar to the material density Reduce number of part and reduce the Csh of each part

• Assembly complexity (Cas)– Ability to easily assemble the

components of a product– Based on a recursive

formulation similar to the Shannon Entropy

– n non-isomorphic sub-trees

Complexity evaluationDifferent factors

simple complex

19

Complexity evaluationDifferent factors

20

Complexity evaluationDifferent factors

• Assembly complexity (Cas)

Lifts and stairs high assembly complexity Use concepts of modularity and use standardization

• Material complexity (Cmt)– Ability to use different types

of material and scantling in a product Standardization

– Based on the number of different material and scantling used in the product

Complexity evaluationDifferent factors

22

Complexity evaluationDifferent factors

• Material complexity (Cmt)

Material and scantling standardization is required

23

Complexity evaluationDifferent factors

• Global complexity

– Weighted Sum– Minimization of the

correlation coefficient– Production time vs

Complexity– R² = 0.76

24

Complexity evaluationOverall complexity

• Design manager Define upper and lower limits

25

Conclusion and recommendations

• It’is always possible to design something so complicated that you can never get it right!• This methodology provides:

– An aid for the designers compare different design alternatives– A monitoring of the sources of complexity which helps to determine the

consequences of decision making– A spotting of the sources of complexity and cost which helps to reduce design

effort– An objective, quantifiable, unambiguous metrics of complexity

• Results:– Reduction of lead time and life cycle cost

26

Conclusion and recommendationsOf this presentation

• This research have been limited to:– Ship’s structure (i.e. mainly steel parts and not outfitting)– Complexity evaluation during production (i.e. not on maintenance

or dismantling)– Large passenger ships

• Additional researches are thus required– Outfitting components (HVAC, pipes, electrical cables, etc.)– Take into account of maintenance and dismantling stage– To test the methodology on other types of ships

27

Future workOf this presentation

28

Thank you for your attentionAs Einstein said, everything should be as simple as possible

But not simpler !