Applying Set-Based Design in Submarine
Design
by
R.C. Rutten
December 2, 2015
Supervisors
Delft University of Technology Prof. Ir. J.J. Hopman
Ir. P. de Vos
Nevesbu
Ing. W.P.H.M. Schiks Ir. C.I.M van Roosmalen
Thesis for the degree of MSc in Marine Technology in specialization of
Design of Ships
Applying Set-Based Design in
Submarine Design
By
R.C. Rutten
Performed at
Nevesbu
This thesis SDPO.15.031.m is classified as confidential in accordance with
the genereal conditions for projects performed by the TU Delft.
15 December 2015
Company supervisors
Responsible supervisor: Ing. W.P.H.M. Schiks
E-mail: W.P.H.M.Schiks@nevesbu.com Daily Supervisors: Ir. C.I.M. van Roosmalen
E-mail: C.I.M.vanRoosmalen@nevesbu.com Thesis exam committee
Chair/Responsible Professor: Prof. ir. J.J. Hopman Staff Member: Ir. P. de Vos
Staff Member: Dr. ir. S.A. Miedema Company Member: Ing. W.P.H.M. Schiks Company Member: Ir. C.I.M. van Roosmalen Author Details
Studynumber: 4025814
PREFACE
About two years ago the Dutch ministry of defence confirmed the need for the replacement of the current Walrus class submarines in 2025. Since then the replacement program is accelerating which makes the design process of submarines a trending research topic. Globally the market is even bigger with the replacement programmes of the diesel electric submarines of the Norwe-gian, Swedish and Australia’s navy. The complexity of the submarine design is exemplified by Navantia, which have major weight problems with their S-80 submarine design for the Spanish Navy.
This thesis was carried out for the degree of MSc in Marine Technology in specialization of Design of Ships at Delft University of Technology. This thesis was performed at Nevesbu a company which is involved in the design and engineering of submarines since its foundation in 1935.
For the readers which are interested in design methods part 1 of this thesis is recommended. The second part of this thesis treats the characteristics of submarine design. Part three include a case study of the implementation of Set-Based Design for a submarine HVAC system.
Firstly, I would like to thank Nevesbu and in particular Wahyu Schiks and Kees van Roosmalen for the opportunity to get a look behind the scenes of submarine design and the assistance during the project. Secondly, I would like to thank Hans Hopman and Peter de Vos for their critical look and assistance during my graduation project.
ABSTRACT
About two years ago the Dutch ministry of defence confirmed the need for the replacement of the current Walrus class submarines in 2025. Since then the replacement program is accelerating which makes the design process of submarines a trending research topic. The complexity of the submarine design is exemplified by Navantia, which have major weight problems with their S-80 submarine design for the Spanish Navy. A “new” design methodology Set-Based Design (SBD) was developed by Toyota in the ’60s. This methodology has been called promising but actual applications are still rare.
The design practice at Nevesbu tends to quickly converge on a solution, a point in the solution space. This point is than customized in order to fulfil all design requirements. Most of the time these requirements are based on educated guesses or ideas. The consequences of these guesses and ideas are unclear or doubtful. Some requirements may have a great impact on the design, which is undesirable, or the combination of requirements which were set do not result in a fea-sible solution. This fast convergence seems to be efficient, but when the starting point is weak substantial iterations are needed before all requirements are met.
The first goal is to have a better understanding of SBD and what the advantages and disad-vantages are of this methodology. The core principles behind SBD should be discussed and compared with other design methods. The other design methods in this thesis are the Design Spiral (DS), used by Nevesbu and others, and System Engineering (SE) which is also a commonly used design method. The second goal is to prove the improvement of the SBD methodology in the design process of a submarine. The research question of this thesis is:
“How can the application of the Set-Based Design methodology be an improvement for the future submarine design process? ”
Traditionally ships are designed using the Design Spiral of Evans. In this spiral design issues are evaluated and solved to meet the requirements. This evaluation is done in several iterations to meet an optimal solution. Another design method is SE. SE focuses on defining customer needs and required functionalities then proceeding with design synthesis and system validation while considering the complete problem. Both methods have as disadvantage that the quality of the design is greatly dependent on the starting point of the design.
SBD is a design methodology where the design is kept flexible during the design process. This flexibility can be seen in the minimal constraints which are set a the beginning of the design. This flexibility is applied because in the initial phase the consequences of design decisions are still unknown. With the flexibility the decision making is delayed in order to evaluate the con-sequence of the fixation of specific requirements. The concon-sequence is that the a lot of concepts must be evaluated in a early stage. The consequences on the flexibility of the requirements lead to a product which fulfils the needs from the customer better. Because the designer can show the customer the consequences of specific requirements. So when the requirements are eventually set the customer has a better view on what the consequences are. Another advantage of this delay in decision making is that the an unfeasible set of requirements is avoided. This flexibility
Abstract
also increases the evaluation of innovative ideas which can be beneficial for the design but, are not conform the current boundaries. Because of the broad and general studies the knowledge gathered from one project could be better used for new projects.
Submarines must be able to attack, protect and provide surveillance without being noticed by anyone. These special operations result in a difficult and long design process approximately be-tween 10-15 years. The most difficult parts of designing a submarine keep the balance bebe-tween weight, space and energy right. Another difficult part is a optimal integration of all systems. This is difficult because the margins in the design are smaller than those of surfaced ships be-cause of the limited space available.
Because of the small margins in the design a change in the design can have major consequences. With a broader evaluation of the design space these consequences are better known. This high complexity with small design margins are favourable for the application of SBD. Because only limited submarines will be actual built the design could not be gradually fine tuned during the built. Because a weaker performance of the first submarine will not be tolerated. At last the de-lay in decision making cause a more up to date design compared with the current design method. This flexibility is gradually reduced with the foundation of studies. By eliminating the worst solutions and keeping a set of best solutions, instead of choosing only the best, the flexibility for changes in the requirements is accomplished. With SBD the work could increase because a broader range of studies and research is necessary. This extra work in comparison with the current design methods could still lead to a lower lead time by achieving a higher efficiency by reducing the rework and iterations in a later phase. The SBD philosophy avoids the iteration by the convergence and gradually increasing the boundaries of the design space. This gradually reducing of the design space can be done by the individual functional groups if the foundation behind the restriction is correct. Below some criteria for SBD are presented:
• Flexibility
– Work with sets and range – Minimal constraints – Avoid single solutions • Convergence
– Feasibility before commitment – Decision making based on knowledge – Stay in the design space
• Knowledge Management
– Establish the reuse of knowledge gathered
The major difference between current design methods and SBD is that a single point in the design space is avoided. The constraints at the start of the design process are flexible and not fixed as common in the current design methods. With the evaluation of sets of solution the flex-ibility increases to adopt changes in the requirements or systems without major consequences. Convergence to the final solution is done by gradually decreasing the feasible design space by adding new boundaries, or from conclusions based on more detailed analysis. With the the DS the final design is a modification after several iterations from a specified starting point, often a previous design. Also SE iterates constantly to balance the design and to check the feasibility of the design. In the figure below a schematic overview of the different design methods is presented. From a practical application in the form of a case study these improvements could confirmed.
Abstract
Figure: schematic drawing of the different design processes
SBD methodology a more fundamental background is created. This could be dedicated to the minimal constraints at the start of the design. This can be confirmed by figure 9.1 in this figure there can be seen that with the current design criteria the compromise will be a sub optimal point for both the crew and the CO2 scrubber. With SBD the fixation of temperature and
hu-midity criteria is delayed. Already in this case study the improvement could be seen by this delay. The more extensive research in the actual loads of the crew on the submarine will also lead to a better design. Because of this research the criteria for curtain areas can be better addressed. This will lead to a better optimized HVAC system and work environment for the crew. In the MORAY designs every Watt of heat produced by a light bulb is taken into account but, the heat production of the crew is generalized and not compensated for the work intensity.
CONTENTS
Preface . . . v
Abstract . . . ix
List of Figures . . . xvi
List of Tables . . . xvii
Nomenclature . . . xix Symbols . . . xix Abbreviations . . . xx 1. Introduction . . . 1 1.1 Problem . . . 1 1.2 Goal . . . 2 1.3 Structure . . . 4
Part I Design Methods 5 2. Current Submarine Design Methods . . . 7
2.1 Ship Design Spiral . . . 7
2.2 System Engineering . . . 8
3. Set-Based Design . . . 11
3.1 Principles of Set-Based Design . . . 12
3.2 Ship to Shore Connector Application of SBD . . . 14
3.3 Submarine Application of SBD . . . 15
3.4 Comparison of DS, SE and SBD . . . 17
3.5 Criteria for a SBD Process . . . 19
Part II Submarine Design Process 21 4. Submarine Design . . . 23
4.1 Naval Ship Design . . . 23
4.2 Submarine Operations . . . 24
4.3 Design Process . . . 24
4.4 Challenges in Submarine Design . . . 25
4.5 Suitability of SBD in Submarine Design . . . 27
5. Design process Moray class submarine . . . 29
5.1 Research focus . . . 29
Contents
6. How to apply Set-Based Design . . . 33
6.1 Submarine Functions . . . 34
6.2 Mapping the Design Space . . . 34
6.3 Reducing the Design Space . . . 35
6.4 Knowledge Management . . . 36
Part III Application of Set-Based Design 39 7. Scenario of Case Study . . . 41
7.1 Aim . . . 41
7.2 Choice of HVAC System . . . 41
7.3 Process Boundaries . . . 41
7.4 Design Boundaries . . . 42
7.5 Study Setup . . . 42
8. HVAC Design Process . . . 45
8.1 Mapping the Design Space . . . 45
8.2 Reducing the Design Space . . . 47
8.3 Knowledge Management . . . 48
9. Evaluation of Case Study . . . 51
9.1 Level of “Set-Based” . . . 51
9.2 Comparison Current Submarine HVAC Systems . . . 52
9.3 HVAC Studies Sketch Design . . . 52
9.4 Discussion . . . 54 10. Conclusion . . . 57 11. Recommendations . . . 59 Appendix 65 A. Set of Solutions . . . 67 A.1 Goal . . . 67
A.2 Heating Solutions . . . 67
A.3 Ventilation Solutions . . . 69
A.4 CO2 Solutions . . . 70
A.5 O2 Solutions . . . 72
A.6 Humidity Solutions . . . 73
B. Submarine HVAC Systems Evaluation . . . 75
B.1 HVAC Requirements . . . 75
B.2 Heating/Cooling System . . . 76
B.3 Ventilation System . . . 78
B.4 Air conditioning . . . 80
B.5 HVAC system loads . . . 81
C. Human influence on environmental conditions . . . 85
C.1 Goal . . . 85
Contents D. Configuration study . . . 89 D.1 Goal . . . 89 D.2 Study Setup . . . 89 D.3 Results . . . 91 D.4 Conclusion . . . 94
E. Environmental influence on the HVAC system . . . 97
E.1 Goal . . . 97
E.2 CO2 scrubbers . . . 97
E.3 Heating . . . 98
E.4 Conclusions . . . 99
F. Energy, volume and weight of the HVAC system . . . 101
F.1 Goal . . . 101
F.2 O2 generator . . . 101
F.3 CO2 scrubber . . . 103
F.4 Conclusion . . . 104
LIST OF FIGURES
1.1 Scope of research of this thesis [1] . . . 3
2.1 Design Spiral [2] . . . 7
2.2 System Engineering in Naval Ship Design [1] . . . 9
3.1 Set-Based Process [3] . . . 12
3.2 Ship-to-Shore Connector of the US Navy [4] . . . 14
3.3 SSC Set Reduction Process [5] . . . 14
3.4 Influence decision delay. [6]. . . 17
3.5 schematic drawing of the different design processes . . . 18
4.1 Estimation of number of FTE to design a conventional submarine. [7] . . . 24
6.1 Flowchart for Set-Based Design . . . 33
6.2 Efficiency vs. ship speed [8] . . . 37
7.1 Set-Based Process [3] . . . 43
8.1 Intersection analysis of Temperature and humidity requirements . . . 49
9.1 Comparison between system requirements and design criteria . . . 53
A.1 Working principle of water chiller [9] . . . 68
A.2 Performance characteristics of different types of fans [10] . . . 70
A.3 Difference between absorption and adsorption [11] . . . 71
A.4 Example of a CO2 absorption canister for the RNLN [12] . . . 71
A.5 Regenerable chemical absorbent CO2 scrubber [13] . . . 71
A.6 Mollier diagram [11] . . . 73
B.1 Location of cooling and heating equipment . . . 77
B.2 Air flows and equipment of ventilation system . . . 79
B.3 Location of the minimal heat load in the submarine . . . 81
B.4 Location of the maximal heat load in the submarine . . . 82
B.5 Location of crew in submarine . . . 83
C.1 Human tolerance to O2 [14] . . . 86
C.2 Human tolerance to Temperature [14] . . . 87
C.3 Human performance dependency on temperature [15] . . . 87
C.4 Human dependency on temperature and humidity . . . 88
D.1 3 HVAC test configurations . . . 90
D.2 Difference room temperature variation configuration 1 . . . 92
D.3 Begin temperature variation configuration 1 . . . 92
D.4 Difference room temperature variation configuration 2 . . . 92
D.5 Begin temperature variation configuration 2 . . . 92
List of Figures
D.7 Begin temperature variation configuration 3 . . . 92
D.8 Mass flow variation configuration 1 . . . 93
D.9 Heat load variation configuration 1 . . . 93
D.10 Mass flow variation configuration 2 . . . 93
D.11 Heat load variation configuration 2 . . . 93
D.12 Mass flow variation configuration 3 . . . 93
D.13 Heat load variation configuration 3 . . . 93
E.1 Absorption capacity of Ca(OH)2 canisters [12] . . . 97
E.2 Absorption capacity LiOH [16] . . . 98
F.1 Volume comparison oxygen storage [17] . . . 101
F.2 Oxygen Generator [13] . . . 102
F.3 Volume comparison oxygen source . . . 102
F.4 Influence of submarine size and maximal CO2 level on volume and weight . . . . 103
F.5 Influence of crew size, crew load and maximal CO2 level on mass flow . . . 103
LIST OF TABLES
3.1 Initial design factors of the hull design group. [18] . . . 16
3.2 Key design factors. [18] . . . 16
4.1 Difference Commercial & Naval Ships[1] . . . 23
A.1 Chemical properties absorbent [19] . . . 71
B.1 HVAC requirements reference submarines . . . 75
B.2 Heating and Cooling systems reference submarines . . . 76
B.3 Equalizing ventilation and water circulation system reference submarines . . . 78
B.4 Air conditioning system reference submarines . . . 80
C.1 Environmental limitation due to human presence . . . 88
E.1 Canister properties [16] . . . 98
F.1 Oxygen storage properties . . . 102
F.2 Technical specification oxygen generation system . . . 102
NOMENCLATURE Symbols ∆T change in temperature K ∆t time step s 5 displacement tonnes hemispherical emissivity −
ω rotational speed rad/s
φ relative humidity %
ρ density kg/m3
σ Stefan-Boltzmann constant W/m2K4
A object’s surface m2
C concentration kg/kg
Cp heat capacity at constant pressure J/kgK
D diameter m
h heat transfer coefficient W/m2K
k thermal conductivity W/mK L load kg/s M mass kg ˙ m mass flow kg/s n mole mol P power W p pressure kg/ms2 Q heat flux W/m2 q volume flow m/s
R ideal gas constant −
r evaporation heat J/kg
T temperature K
V volume m3
v velocity m/s
Abbreviations
Abbreviations
ACGIH The American Conference of Governmental Industrial Hygienists ACU Air Conditioning Unit
AIP Air Independent Propulsion
ASHRAE American Society of Heating, Refrigerating and Air-Conditioning Engineers
C Carbon Ca(OH)2 Calciumhydroxide CE Concurrent Engineering CH4 Methane CO Carbon Monoxide CO2 Carbon Dioxide
CoB Centre of Buoyancy CoG Centre of Gravity DS Design Spiral
H2 Hydrogen
H2O Water
HCl Hydrogen Chloride HF Hydrogen Fluoride
HVAC Heating, Ventilation and Air Conditioning INCOSE International Council on System Engineering IVHHN International Volcanic Health Hazard Network LCAC Landing Craft Air Cushion
LEP Life Extension Programme LiOH Lithiumhydroxide
LOx Liquid Oxygen
MARIN Martitime Research Insstitute Netherelands M EA Ethanolamine
MEM Main Electric Motor
MIT Massachusetts Institute of Technology
MORAY Multi Operational Requirement Affected Yield N aClO3 Natriumchloraat
N aHCO3 Sodium Bicarbonate
N aOH Sodium Hydroxide
Abbreviations
O2 Oxygen
OSHA Occupational Safety and Health Administration RDM Rotterdamsche Droogdok Maatschappij
RNLN Royal Netherlands Navy SBD Set-Based Design
SE System Engineering SSC Ship-to-Shore Connector
SSK Diesel-electric partrol submarine UDT Undersea Defence Technology UK United Kingdom
US United States WWII Second World War
1. INTRODUCTION
Nevesbu provides multidisciplinary services in naval architecture, structural & marine engineer-ing and marine design. In the submarine market they can offer a wide range of services, rangengineer-ing from specific study assignments to complete basic and detail design and engineering projects. Since its foundation 80 years ago Nevesbu is designing submarines. Starting with the design of the export submarines Sep and Orzel for the Polish Navy. In the ’70 and ’80 Nevesbu was responsible for design of the current submarines of the Royal Netherlands Navy (RNLN) the Walrus class. Some recent work is the Life Extension Programme (LEP) for the Walrus class and Sonar replacement on the Walrus class.
Because of the search for improvement, Nevesbu is interested in Set-Based Design (SBD) for future design processes. Especially when taking into account that the RNLN is planning to commission the successor of the Walrus class by 2025. With a production process of approxi-mately 10 years the design process should start soon. Because of the history between RNLN and Nevesbu the involvement of Nevesbu is likely. The “new” design methodology Set-Based Design was developed by Toyota in the ’60s. This methodology has been called promising but actual applications are still rare. So what is SBD and what are the possible improvements for the application in the future submarine design process?
1.1 Problem
In the present design methods the requirements are set at an early stage in the design process. Most of the time these requirements are based on educated guesses or ideas. The consequences of these guesses and ideas are unclear or doubtful. Some requirements may have a great impact on the design, which is undesirable, or the combination of requirements which were set do not result in a feasible solution. These problems will get clear during the design process and create a lot of design rework to fix the changes. These uncertainties during the design process lead to an inefficient design process.
The design practice at Nevesbu tends to quickly converge on a solution, a point in the solu-tion space. This point is than customized in order to fulfil all design requirements. This fast convergence seems to be efficient, but when the starting point is weak substantial iteration is needed to be executed before the requirements are met. So the efficiency and the quality of the end product are greatly depending on the choice and quality of the initial starting point of the design. In a early phase of the design process the knowledge is neither well defined, developed or understood. Because of this the risk for a weak starting point is high. With a weak starting point the design can be stuck at a local optimum instead of the global optimum. The process can even be started all over again when no feasible solution is found. So the end product is dependent on the choice of the initial starting point. This potential suboptimal design is un-wanted in the search of the best design. Also there is no theoretical guarantee that the process will ever converge to meet all requirements.
The lead time in a submarine design process is 10-15 years. This is long in comparison with other ship types due to the complexity of the submarine. The complexity is mostly caused by the
1. INTRODUCTION
small margins on volume, weight and energy in combination with the interdependencies between systems. Also the interaction between the various systems on board means that late changes have a major impact on the design process resulting in potential delays. The changes occur by a change in the requirements caused by unrealistic boundaries or optimistic estimations on new developments. With SBD these potential delays are potentially avoided.
At the Undersea Defence Technology (UDT) conference in 2015 rear admiral Matt Parr stated that the a new Astute class submarine was already outdated before any mission was completed [20]. This is caused by the rapid development in product technology in combination with early choice of components in the relative long design process.
In 1959 the Design Spiral (DS) gave a formal description on how to design a ship. For System Engineering (SE) INCOSE has developed a SE handbook to help implementing SE. However a formal description or handbook for SBD is not available. When can you call a design process ”Set-Based”? The principles of SBD are discussed by Sobek [21] but a guideline to fully im-plement SBD in the design process has yet to be developed. So a good understanding on the theory behind SBD is essential before the possible improvements are investigated.
1.2 Goal
The first goal is to have a better understanding of SBD and what the advantages and disad-vantages are of this methodology. The core principles behind SBD should be discussed and compared with other design methods. The other design methods in this thesis are the Design Spiral, used by Nevesbu and others, and System Engineering which is also a commonly used design method. After this study a framework could be presented on how SBD should be applied. The second goal is to prove the improvement of the SBD methodology in the design process of a submarine. For this investigation the characteristics of submarine design must be evaluated. Also the current submarine design process is evaluated in order to give a well founded conclusion about the possible improvements.
Research question
How can the application of the Set-Based Design methodology be an improvement for the future submarine design process?
Sub questions • What is the Set-Based Design philosophy? • When is a design process Set-Based?
• What are the differences between current design methods and Set-Based Design? • What is the current design process of a submarine at Nevesbu?
• Is the application of Set-Based Design possible for Submarine design?
• Will Set-Based Design reduce the lead-time of the design process of a submarine? • Will Set-Based Design increase the quality of the submarine design?
Hypothesis
The hypothesis of this report is that a SBD methodology can be an improvement in terms of quality of future submarine designs. For an improvement in the lead time the SBD method-ology should be developed and fine tuned in order to be beneficial over the current design process.
1. INTRODUCTION The quality of the design will increase because of the flexible design space. This flexibility in the design space results in a evaluation of wider set of solutions during the design process. Also the flexibility delays the convergence to the final solution. Because of the delay the knowledge of the trade-offs between systems is better known so the decision could be made with more foundation. The improvement on the lead-time will greatly depend on the deviations in the requirements of the design compared with a previous design. If only minor deviations are required a DS will produce, based on the quality, an equivalent design in less time. Secondly, a submarine is replaced once every 25-30 years, with an update about half its life time. With the use of SBD, the knowledge gathered in previous designs can be better applied on future designs. When only once in the 30 years a design is made this advantage of better mapping the knowledge gathered is favourable. As can be seen at the moment at Nevesbu most of the people who worked on the Walrus class are retired. This means that also their knowledge is lost and retrieving this lost knowledge takes time. So when the knowledge is better documented less time is lost in retrieving the lost knowledge and speed up the design process.
Boundaries
This research focuses on the application of SBD in submarine design. The choice of submarine design is made firstly because of the nature of Nevesbu. Secondly, with a lead time of 10-15 years and the complexity of the systems, a submarine is at first sight promising for the use of SBD.
Because of the design period of several years a validation off a total submarine design will take many years to complete. When the method is proven for the design of the HVAC system, it is assumed that it can be extended to the complete submarine design. With the duration of this thesis in mind the practical validation is limited to the HVAC system of a submarine.
Figure 1.1: Scope of research of this thesis [1]
It can be argued that the design process is started with the idea for a new design and ended just before the first mission. The scope of this thesis is based on the involvement of Nevesbu in the design of submarines. The designer has limited options to set the requirements for the new submarine because the mission and the functional requirements of the submarine are put together by the navy in question. For this reason the scope of this thesis is limited to start after the requirements are set. The consequence of this is that the functional requirements are assumed to be available. In this thesis the building phase of the submarine is neglected. This is also done because the MORAY design, which is used as reference, is never built so no comparison could be made for that phase. For these reasons, the scope of this thesis is limited to this part of the design process, see figure 1.1.
1. INTRODUCTION
1.3 Structure
In the first part of this thesis the different design approaches are treated. Chapter 2 describes two Point-Based Design method namely the Design Spiral and System Engineering. The third method, discussed in chapter 3, is Set-Based Design. The second part of this thesis describes submarine design. The specific characteristics of a submarine design process can be found in chapter 4. In chapter 5 the MORAY design process is analysed. This second part is concluded with a framework for the application of SBD in a submarine design process. In order to put the theory in practise a case study is presented in part three of this thesis.
Part I
2. CURRENT SUBMARINE DESIGN METHODS
Currently new submarines are designed as evolutions of their predecessors. This means that the new design has the previous design as a starting point and is than adopted for the new operational requirements and fitted with modern technology. First the Design Spiral (DS) is treated and secondly System Engineering (SE) is discussed.
2.1 Ship Design Spiral
The traditional design method follows the Design Spiral of Evans [2]. The starting point of the design spiral is often an existing design which is most compatible with the new requirements and operational use of the new ship. In this method, the design issues, as stated in figure 2.1, are evaluated to meet the requirements. Because all the issues are dependent on each other the cycle must be repeated until a solid design is formed which meets all separate requirements. Because the information is growing each cycle, the level of detail should also be increased every cycle.
Figure 2.1: Design Spiral [2]
The advantage of this method is that the design process is organised. A clear structure in the design process is made and the progress can be monitored easily. This method is widely used which results in a good implementation of the design method in the current design processes. In every cycle the integration of all systems is accomplished. A continuing cycle of integration is favourable for a designs which require a high level of integration such as submarines.
A disadvantage of this method is the dependency on the initial starting design. If the initial starting point is weak, the new design may not be optimal too. Secondly, in the case of great deviations in the requirements between the previous and the new design, the number of iter-ations to accomplish a suitable solution is large. Due to these numerous iteriter-ations the design process becomes time consuming. A third disadvantage is the sequential working method. The calculations are made sequentially which results in a longer design process. Because of the time
2. CURRENT SUBMARINE DESIGN METHODS
constraints given often only a few iterations are performed to realize the design on time. The absence of enough iterations causes a possible suboptimal solution. A final disadvantage is the uncertainty of the number of iterations necessary to come to a optimal design. Unforeseen it-erations can cause delays or the limited number of itit-erations performed can be leading to an undesirable design.
In general there will be changes in the design requirements during the design process. For every change in the requirements some extra iterations of the design spiral has to be made. This makes the design spiral inflexible to changes in the design requirements. In order to get a feasi-ble design without delays at some point design concessions must be made.
An improvement to the DS is Concurrent Engineering (CE). By evaluating the design issues concurrently the lead time of the design process is reduced. This is accomplished by simulta-neously working on the design issues. By working this way the man-hours stay the same but the lead time is reduced. Still iterations must be made to create an optimal design. Serial engi-neering is fraught with shortcomings due to the delayed feed-back loops. As usually practiced, CE attempts to bring more feedback upstream earlier, generally through face-to-face meetings. Since this is done early, changes to the design are relatively easy and inexpensive, and ideally, the design team soon arrives at a solution that will satisfy all parties. While an improvement over se-rial engineering, the basic picture remains the same: the design team is iterating on one solution. The DS design methodology is used by several countries and companies, including Nevesbu, for new designs, e.g. for the Moray class an export model of the Dutch Walrus class. Another example is the conceptual design of the Class 210mod from ThyssenKruppis here the 209, 212, 214 and ULA-Class submarine of the Royal Norwegian Navy were used as starting point. In the new 210mod proven concepts of the submarine designs stated above were implemented in the design [22].
2.2 System Engineering
“System Engineering is an interdisciplinary approach and means to enable the realization of successful systems. It focuses on defining customer needs and required functionality early in the development cycle, documenting requirements, then proceeding with design synthesis and system validation while considering the complete problem: Operations, Cost & Schedule, Performance, Training & Support, Test, Disposal and Manufacturing. Systems Engineering considers both the business and the technical needs of all customers with the goal of providing a quality product that meets the user needs.” [23]
Because of the rapidly evolution of technology this century also the ship design become more and more complex. This complexity increase the natural tendency toward a specialization within the engineering. This means that engineers are specialist in one or two systems with less knowledge from other systems. SE is a design method which incorporate these specializations by only con-strain the system design by some requirements within these requirements the system engineer gets freedom to design the optimal system. The requirements should be selected in order to integrate all system successfully. So are the needs and demands translated in requirements also more general system characteristics such as weight and volume are bound by the requirements. Another characteristic property of SE is the broader look of the design factors. The idea is to look at the whole life cycle performance of the ship. An example is that the performance is tested on the full life cycle of the ship and not based on the performance after the delivery.
2. CURRENT SUBMARINE DESIGN METHODS but also the different sailing modes are evaluated. In figure 2.2 an schematic example is given of SE. As discussed above in SE the functions and performance are broader evaluated in the design process compared with other design methods. In other design methods the functions and performance are only used as in and output of the design.
Figure 2.2: System Engineering in Naval Ship Design [1]
The beneficial part of SE is that the design is optimized for the life cycle of the ship and not only optimized at the requirements presented. Because of the specialization of the engineers the quality of the individual systems will increase. Also on the lead-time SE can be beneficial because the work can be done more concurrent and independent from work on other systems, if the requirements are set correctly.
A disadvantage of SE is that in the design process iteration steps are necessary to balance the design. As mentioned in section 2.1, this makes the design method inflexible and potentially time consuming. SE is focussing on translating the requirements to the systems and when the system designs are finished all systems are integrated in the total design. The quality of the design after integration of all systems is depending on the initial requirements set for the sys-tem. So only at the begin and end the integration between the systems is accomplished. For the design of a submarine this can cause problem because of the high level of integration and small design margins. In order to reduce the risk at wrong estimation in the initial design phases the requirements are set with enough margin. In a submarine design this may cause major design problems because these margins are not available in a submarine design. These submarine char-acteristics are further discussed in chapter 4.
For the building of new submarines the Australian and Swedish navy are investigating the use SE for the design process[24][25]. A design tool which facilitates the implementation of SE is done by Andrews for a UK submarine design. His Design Building Block approach is an good example of the design tool for the implementation of SE in concept design phase of a naval ship [26]. A similar design tool is developed by the US Navy [27] and the Royal Netherlands Navy [28].
3. SET-BASED DESIGN
In search for a faster design process the rarely used design methodology Set-Based Design (SBD) is evaluated. SBD is a design methodology based on the design process of Toyota. Toyota is able to produce high quality cars within a relatively short lead time. In the 60’s Toyota started with a concurrent design approach. This approach gradually evolved into a design process defined as SBD by Sobek [21]. With SBD the work is not only done concurrent but additionally the work is done more independently as before. SBD is argued as a promising method for designing a high quality product[21][3][29]. However the application of this method is still rare. Besides Toyota the US Navy has used SBD to generate and select a concept design for the Ship-to-Shore Con-nector, see section 3.2.[29] Further applications in other markets can be found by Raudberget[3] and at Schlumberger.[30] A definition of SBD as presented by Sobek is as follows:
”Design participants reason about, develop, and communicate sets of solutions in parallel and relatively independently. As the design progresses, they gradually narrow their respective sets of solutions based on additional information from development, testing, their customer, and other participants sets. As designs converge, participants commit to staying within the set(s), barring extreme circumstances, so that others can rely on their communication.”[21]
In the following section this definition is further explored but in order to get a better under-standing of SBD some specific terms are defined first.
Design factors
Design factors are parametric units which have influence on the design of a submarine. Some important submarine design factors are maximal diving depth, underwater speed or indiscretion ratio. But they can also be less explicit like propeller efficiency or crew comfort.
Set of solutions
Most of the time multiple design solutions (often called concepts) exist, for example single or double hull. Both solution have some variance for example in diameter, thickness or frame dis-tance. Al those solutions give a continues set of feasible solutions.
The design space
The design space is a multidimensional parametric set which includes all feasible design solu-tions. The design space is a summary of the feasible range of all design factors and sets of solutions together. In some figures the design space is shown as a two dimensional space this is done just to visualise some ideas or principles. In reality the design space is a multi dimensional space which is hard to visualise.
Functional groups
Functional groups are groups which are specialised on a function. Some examples on functional groups in the design process of a submarine are: Hull, propulsion, Command and Surveillance and auxiliary systems. Each functional group can be further divided in sub functions e.g outer hull and pressure hull or command centre and radio room or HVAC and fresh water system.
3. SET-BASED DESIGN
3.1 Principles of Set-Based Design
In this section some specific characteristics of SBD a mentioned. These principles will help to understand what Set-Based Design is. For an accurate application of the SBD methodology these principles must be taken into account. The three SBD Principles are explained below.
Principle 1: Map the Design Space
The first principle is all about gathering design knowledge to understand which set of design solutions are possible. Analysis of feasibility, relative benefit or cost and other trade-offs will increase the understanding of this design space. This multidimensional parametric set, the design space, includes all feasible design solutions. For each function the relevant parameters or concepts are studied by specialist. These studies are done by the functional departments in parallel and relatively independently. Based on their past experience, analysis, experimentation and testing or outside information they define feasible regions from their perspective. On the top of figure 3.1 a representation of this feasible area for some functional groups are shown.
Figure 3.1: Set-Based Process [3]
This knowledge generated in an early phase of the design process is very useful in order to make the design decisions better founded and not based on assumptions or educated guesses. This broad exploration and research on the feasibilities of design solution and understanding of the relationships between different parameters or solutions seems inefficient. But the idea is that this knowledge will pay off in the certainty that the solution is the best solution. Or indirectly in reduced research studies in future projects because only the design space must be updated with new design possibilities.
Principle 2: Integrate by intersection
Integration of subsystems into a system is a compromised workable solution for all subsys-tems. This can also be expressed as the intersection of the design spaces of all subsystems, see figure 3.1. The optimal system can be found in the overlapping of the design spaces of all sub-systems. Finding intersections can only be accomplished when the developers of the indi-vidual sub-systems communicate with each other. Through the communication the indiindi-vidual designers will adapt the design space to get to the workable solution. This way of integration of all systems will avoid the challenge to marry independently optimized components or systems. Secondly, the communications between different functional groups is easier and so more efficient. This is because the both engineers is well prepared because a broader set is investigated instead of just one or two options. With SBD there is more knowledge gathered of trade-offs between systems, components or design parameters.
3. SET-BASED DESIGN Instead of moving from point to point in the design space the design space itself is gradually reduced. This convergence of the design space delays the decision making for one solution. This way every decision is made with certainty and based on funded reasoning instead of educated guesses. This is contradictory with the philosophy of a design spiral method were the decisions are made as early as possible to avoid confusion between functional groups.
At the start of the design the constraints of the project are low. This allows the designers to explore the total size of the design space and show that there is not just one solution to solve the problem. This gives the opportunity for innovation in the design. When the level of constraints increases, the design space becomes more and more limited. By limiting the design space the weaker concepts are excluded and the promising, better, solutions are kept. Instead of searching for the best concepts within the set, SBD rejects the worst concepts out of the set. This is because the consequence of not rejecting the worst concept is less critical than not selecting the best concept. Hence the selection of the best concept is done according to SBD with the highest level of knowledge. This results in a robust and flexible process for selecting the best concept. This selection method lowers the influence of the decisions made in the early stages of the design. Also the decision to converge to a single solution is postponed.
Another part of successful integration is to seek for conceptual robustness in the set of design solutions. If a solution is independently of other functional groups or is suitable for all the solutions in other functional groups conceptual robustness is found. When this conceptual robustness is found the solution can be explored in further detail. This conceptual robustness is more applicable on products with multiple end products, series of designs. In submarines this is rather rare but the MORAY class with three variants, the 1100, 1400 and 1800 tonnes solution, is a good example. Also with the flexible A26 design of Kockums this conceptual robustness can decrease development time and increase the serviceability.
Principle 3: Establish feasibility before commitment
At some point the set must converge to a single design. The trade-off between further investiga-tion and narrowing the set is of crucial concern for the efficiency of the design process. When the set is narrowed too early, the optimal solution could be lost. Waiting with narrowing however, can increase the workload and therefore be inefficient. The reduction of the design space must be based on additional information and not on arbitrary decisions.
When the decision is made to narrow the set, all team members should stay in the narrowed set. This must be done to avoid unnecessary iteration steps and miscommunication between team members. When a team member is designing outside of a determined set the design process is slowed down by back-tracking and rework. By only narrowing the set when enough knowledge is gathered, the robustness of the set is increased. When the designers stays in the committed set of solutions all decisions and conclusion remain valid during the entire design process. This will improve the quality of the end product and reduce the amount of rework. The robustness of the set guarantees that there is always a feasible design in the set. Gathering and exchanging the knowledge of the separate team members on a regular basis also lowers the risk for unnecessary iterations. Iansiti claims that a flexible approach will lead to an overall system optimization because all the possibilities and interactions are understood before you commit to a particular design [31].
At last an important part for successful implementation of SBD is the control and managing of uncertainties of the design process. The uncertainties are in the convergence rate of the design space and the depth of research which is needed to properly reduce the set. Some functional groups need more research than other this must be managed and controlled by the managers.
3. SET-BASED DESIGN
3.2 Ship to Shore Connector Application of SBD
Figure 3.2: Ship-to-Shore Connector of the US Navy [4]
In the US Navy, a well documented example of the application of SBD is the Ship-to-Shore Connector (SSC), see figure 3.2. The design of the SSC is the first application of SBD in ship design. The reason of the choice of the set-based methodology was to test the advantages of SBD. The main advantage which the US Navy wanted to test was the ability to docu-ment design decisions. The reason behind this interest was the long design process of com-plex naval ships. Since the design process can easily exceed 10 years the personnel turnover might be substantial. Without proper doc-umenting of the design decisions, the design knowledge and rationale gathered in the early stages is lost or forgotten in later stages [5].
Execution
The SBD methodology is used in the preliminary design phase. In six steps the initial design space was reduced to come to a single concept design with some backups designs. The first step of reducing the design factors was by excluding the design factors which have low or no impact on the total ship design. This was done by experts in each functional group. Secondly, the non-dominating options are excluded. An option is called non-dominating when another option is better i every case. Thirdly, the design factors were combined and all the infeasible combinations were excluded. Next an integrated design was made of the possible combinations. When it was not possible to balance a solution, it failed and was dropped. At last a selection was made based on the score of the concept. In figure 3.3 a schematic overview of this reduction method is presented.
3. SET-BASED DESIGN Set-Based Design process evaluation
The SSC is an evolution of its predecessor: the Landing Craft Air Cushion (LCAC). The new SSC did not require major changes and the design space was highly constrained. This makes the design process of the SSC not ideal for testing the benefits of the SBD design philosophy. A complex ship type with a lot of additional requirements lends itself better to show the benefits of SBD.
The process was led by professor Singer who did some research on SBD. His expertise was nec-essary to run the process smoothly, because the organization structure was not used to apply a SBD methodology. Due to the lack of specific process or execution strategies the process can be inefficient. In the case of the SSC it was concluded by the naval sea systems command that, in a future execution, significantly more energy must be dedicated to the preparations for applying SBD. [32]
One might discuss how “Set-Based” this application is. Because of the lack of actual formal description of SBD questions can be placed on its level of “Set-Based”. McKenny rated the level of “Set-Based” of the application of the SSC design with the help of his standards presented on the 2012 international marine design conference [33]. The score based on these standards was 9 out of 15 [5]. Only on the part of mapping the design space high scores were achieved. Low scores were achieved on communication and facilitation. An explanation could be the lack of formal negotiation related to integration. Based on the score of McKenney the label of SBD application must be taken with a grain of salt. Not achieving a truly unique and unexpected solution was not surprising, mainly because of the tight constraints placed on the design. These include the readiness of usable technologies, schedules, and dimensional restrictions of the deck. When thoroughly evaluating the principles of SBD, as discussed in section 3.1, the standard presented by McKenney does not cover all principles. The reduction of the design space was based on the educated guesses of experienced designers concerning the key design parameters, rather than research. By only looking at some key design parameters, other design factors are excluded. This means that a part of the design space is not taken to account during the convergence to a single solution. By excluding these design factors the design reduction is based on less knowledge. For SBD the reduction must applied to the sets of solutions and the range of the design factors. Secondly, the final solution is determined by scoring the remaining concepts. Where SBD principles subscribe that the weaker solution must be excluded instead of searching for the best solution.
3.3 Submarine Application of SBD
A second application of SBD found in the literature is by Frye at MIT. Frye put some theoretical effort in mapping the design space of a submarine [18]. Frye developed a framework for the first principle defined by Sobek: Map the design space. The framework starts with the development of a design space. Next, this set is reduced by searching the feasible regions in the set.
Set Development
By the development of sets, five functional groups are defined: hull, performance, power & propulsion, auxiliary and payloads. For every functional group the key design parameters are mapped. A design parameter can be discrete, for example only a integer, types of which material are available, or the parameter can be continuous like the L/D ratio which is not bound to a specific number. In table 3.1 a clear visualisation is presented of the the design space concerning the hull design by Frye.
3. SET-BASED DESIGN
Table 3.1: Initial design factors of the hull design group. [18]
Narrowing the set
The method used for narrowing the set is corresponding to the SSC visualised in figure 3.3. The defined set is broad so for narrowing the set some reduction methods are used. The first reduction method is the Factor/Option screening method. In this method a design factor is eliminated if it presents a dominated solution, is insignificant at the ship level (is not something that affects the combination screening), or is a variable that will have no impact on assessing the whole ship level.[18] After this reduction method only 10 design factors remain, see table 3.2.
Table 3.2: Key design factors. [18]
The second part of narrowing the set is done by systematically varying the key design pa-rameters listed in table 3.2. With the help of parametric equations, in this case pre-sented by Burcher and Rydill [34], other de-sign parameters can be calculated. So can the L/D ratio be calculated with these paramet-ric equations from the following design factors: diameter, endurance, crew size and payload volume. Now a selection is made by eliminat-ing the concepts where the calculated design parameters are not in the initial range of a pa-rameter. The criteria for the selection is that the L/D ratio must be between 6 to 11 meters, as presented in table 3.1.
When evaluating the level of “Set-Based” on the application on submarines. The same conclusion can be drawn as done previously case of the SSC. Additionally, the reduction to a single concept, with some backups, is done with a low level of detail. Only some basic parametric equations are used, so the level of detail is not increased with reduction of the design space. Narrowing the
3. SET-BASED DESIGN
3.4 Comparison of DS, SE and SBD
The initial phase of all the design methods is to set the functional needs of a new design. Then these functional needs are translated into design requirements and concepts. The first deviations between the design methods can be seen in the fixation of these requirements. To explore a more flexible set of requirements SBD, evaluates sets and ranges of design factors in some isolation from a principle design. By avoiding fixation of design parameters up front, the design process is more flexible to cater for changes in the design development later on. In SE and the DS these design requirements are fixed in an early design phase which limit the flexibility in the design process. In these design methods early constraints must be placed in order to proceed with the design at a sub-system level. Consequently, these constraints and the design decisions made with them are made without detailed information and based on educated guesses. However, with SBD some decision on specific design requirements are postponed until all consequence of the decision are known.
Figure 3.4: Influence decision delay. [6]
This flexibility of SBD seems to increase the amount of work, because of the set of possibil-ities which must be evaluated. However, the flexibility allows changes in the requirements without extra work during the process. Be-cause of the flexibility, the management influ-ence on design decision and selection of re-search areas extends over the length of the process compared with the DS,as can be seen in figure 3.4. Secondly, because of the delay in decision making the decisions are made with more knowledge. A second effect of the de-lay in decision making is that the committed costs are postponed, see figure 3.4. If the line of SE must be drawn in figure 3.4 it will be between the lines of SBD and DS. Although the requirements of the system are fixed in an early stage in SE the form of the system is still flexible.
With the DS the starting point is a single design solution mostly based on a previous design. The starting point of SBD is set of feasible solutions. In order to get to a final solution with the DS the design point is modified until all requirements are met. In SE the boundaries of the systems are set and fixed in a early stage. But the form of systems is converging gradually but the feasibility of the design is constantly checked by iterations of all systems. In a SBD process the design space is gradually narrowed until a single solution is found. The difference between the design methods are presented in figure 3.5. If the starting point of the DS is close to the final design the efficiency is high because the final solution can be found with a limited number of iterations. If the boundaries in SE are set correctly the iterations and design progress are fast. Although this high efficiency could not be guaranteed with certainty.
With the use of the DS, the functional groups are dependent on new information on other func-tional groups. If the necessary design information could not be delivered on time delays occur. With SE this risk is smaller because the boundaries of each functional group are set, and when you design within these boundaries the work can be done independently. Although the initial de-velopment of these boundaries require a lot of communication between functional groups. Only when the boundaries are made with wrong estimates some delays occur when the boundaries are 17
3. SET-BASED DESIGN
Figure 3.5: schematic drawing of the different design processes
changed. SBD covers this by evaluating ranges of design factors and converging the boundaries in time which makes SBD the most independent design process of the three. This flexibility of SBD makes it possible to start earlier for some functional groups like the production groups. As mentioned before, the integration of all systems are a major challenge in submarine design. In the DS the integration is done by evaluating the design requirements in every design cycle. This iterative process continues until all requirements are obtained. In the SE methodology the integration is done by setting boundaries for the systems. The integration will be successful when the design is kept within these boundaries. In SBD methodology the integration is done by searching for the intersection of the design spaces of all systems.
The optimal solution found with the DS is the solution which meets all requirements. Because of the fixed starting point this optimal solution could be a local optimum. By evaluating the total set of solutions SBD optimizes with the same principle, but lowers the risk to be trapped in a local optimum. SE optimizes the design by optimizing every system separately. The risk of this method is that the optimal solution of all systems separately is not by all means the best total solution.
With the SBD a robust design process is developed by making the decisions when enough knowledge is gathered. This robustness lowers the risk of bottlenecks on the design. Avoiding bottlenecks decreases the delays by redesigning or iterations. Because of the fixation in an early stage in the design process the consequences of bottlenecks are more severe in the conventional design methods.
With the DS no assurance can be given that the final solution is the best design solution. With SE there can be assured that the systems are the best solution within the boundaries set at start of the project. But no assurance can be given that the total design is optimal. Because SBD evaluates the total design space in combination with the increase of knowledge at the time of crucial design decision makes the design more defensible to be the best design.
Because the research is done systematically over a range of the specific parameters the design knowledge gathered could be reused in new projects if everything is documented properly. In the case of the current design methods only the calculation methods could be reused. But most of the reasoning behind design decisions is lost. The data gathered from previous projects only give specific data point instead of the broader range. In the current design methods most knowledge transfer is exchanged due to verbal communication from the more experienced to the
3. SET-BASED DESIGN
3.5 Criteria for a SBD Process
In section 3.2 & 3.3 the level of ”Set-Based” is questioned. In this section some criteria and guidlines are presented in order to prevent a process to diverge from the SBD methodology. Three key elements of SBD are: flexibility, convergence and knowledge management. In the following subsections these key elements are further defined.
Flexibility
This flexibility starts already with the creation of the functional description of the submarine. The constraints of functional requirements of the submarine must be kept at a minimum in the initial phase of the design process. An minimum constraint functional description is necessary for a total exploration of the design space. If the design requirements are bounded at a high level, some direction is given to the design. The consequence is that a part of the design space is excluded before the feasibility of that area is checked. The flexibility is reached by evaluating sets of solutions and ranges of design factors. The flexibility is kept by having more than one design solution in the design space. Highly bound functional requirements can cause the designer to look outside the design space.
Convergence
The second unique and key element of SBD is the convergence of the design space. For the convergence knowledge is most important. All the decision making in the reduction of the de-sign space must be done with enough knowledge. The weaker solutions are excluded when in all situations other solution are preferable or when enough knowledge is gathered to exclude the solution based on founded reasoning.
Secondly, the solution will be found in the shared solution of all feasible solution together. This is why the interdependencies are important, to keep the feasibility of the total solution. Inde-pendent from the importance of the function an overlap between the functions as can be seen in figure 3.1, must be found. This can cause that, on a system level, a not preferred solution should stay in the set. Because an optimal solution evaluated in the isolation of specific func-tional group only, can be an suboptimal solution for the total design because of the influence on other functional groups.
The last important point for a successful and efficient convergence is that when the design space is reduced you should stay in this new design space. When designing inside the design space all conclusions stay valid during the design process. But when the designer gets outside of the design space this can not be guaranteed. So keeping in the design space is essential for the robustness of the design process and end product.
Knowledge Management
Knowledge is the foundation of a design in a SBD process. For a better efficiency in future projects knowledge, must not be lost or dependable on one person or a previous design. When doing the necessary studies for the design the whole set must be evaluated, not just one point or part, to check the feasibility. This increases the efficiency by avoiding rework of studies with only other values for input parameters. This element of SBD prevents designers to copy previous designs without understanding of the reasoning behind the solution. The knowledge gathered by previous projects should be used as an input and not the solution itself.
As will be discussed in chapter 5 in the current design process most documentation is based on how component sizes is calculated. In those documents little to no attention is given on the 19
3. SET-BASED DESIGN
decision making or considerations which leads to a design decision. Working with sets makes it possible to work concurrent and independently from other functional groups.
Part II
4. SUBMARINE DESIGN
Sailing around all oceans and seas without being noticed: that is the principle task of a subma-rine. How this is possible and how such a vessel is designed is discussed in this chapter. First, the design of naval ships is briefly discussed, followed with the requirements and operational tasks of a submarine. Thirdly, the design process of a submarine is thoroughly discussed. The next two sections are about the unique characteristics and the design challenges of a submarine. Finally, the suitability of SBD in submarine design is discussed.
4.1 Naval Ship Design
The design process of a naval ship deviates greatly in comparison to a commercial ship. Com-mercial ships are designed for the lowest cost and with fixed requirements. Naval ships on the other hand are designed for fixed cost to negotiable requirements. The goal of a naval ship is performance driven instead of profit driven. Because of the performance driven design the tech-nology level is high, which results in a high complexity and cost. Secondly, a naval vessel is not an off the shelf product: every design deviates from it’s predecessor because of the in-service-life time of 25-30 years. Commercial ships have the same in-service-life time but the ships are more frequently built. Also, the changing goals and preferable functions cause an one off design. The difference between a commercial and naval ship is summarized in table 4.1.
Table 4.1: Difference Commercial & Naval Ships[1]
Commercial Naval Owner Private Enterprise Government Goal Private Service Public Service
Profit-driven Performance-driven Function Transport/Tool Weapon
Regulatory body Classification Society Navy Rules
Risk Insured Uninsured
Funding Shareholders/Loans Taxes Technology Proven Prototyping
Medium Tech High Tech In-service-life 6-12 Years 25-30 Years Development 3-4 Years 8-12 Years Complexity Low-Medium High
Costs 1-100 M Euro’s 10-1000 M Euro’s Equipment COTS COTS/MOTS/Special
4. SUBMARINE DESIGN
4.2 Submarine Operations
A submarine is a sophisticated vessel with a wide range of capabilities. A submarine on the other hand must be able to execute numerous types of operations, listed below. A submarine must be able to attack and defend others and itself. Secondly, a lot of surveillance and intelligence operations are executed. And most important all must be done without being noticed.
• Anti-Submarine Warfare • Anti-Surface Warfare • Mine Warfare
• Cruise Missile Strike Capability • Sea Control
• Search and Rescue
• Intelligence, Surveillance, and reconnaissance • Strategic Deterrence
• Battle Group Support
• Landing of special operations forces • Transportation of personnel and cargo
All those operations bring special requirements on the vessel. For operations with special forces escape hatches and deployment facilities must be developed. In the early stage of a submarine design, the operations which must be executed must be determined. The list of operational requirements will lead to technical requirements for the submarine. These requirements can then be translated to actual systems that must be implemented.
4.3 Design Process
The design process of a submarine takes approximately 10-15 years. This is mostly caused by the complexity and level of detail. In the design process of a submarine limited to no space for change. The different phases of the design process are discussed below.[7][35] Typically the level of detail is increased with every new design. In figure 4.1 the work load of a submarine design is presented [7]. This example is from a feasibility study for the new submarine for the Australian Navy. The data is gathered by estimations of experienced submarine designers. To deal with the uncertainties a high and a low estimation are presented.
4. SUBMARINE DESIGN Concept Design
In the concept design stage no limitations are yet given. This create a great design freedom. In this phase the needs and the operational characteristics of the future submarine are formulated. The level of detail is low in this phase. The purpose of this stage is to evaluate different concept to operate a submarine to accomplish the operational tasks. In this phase the possible level of innovation is highest and the interaction between systems is explored. An example of an operational characteristic decided, in this phase, is the number of submarines that are necessary. Another operational decision could be the unconventional unmanned submarine instead of the conventional manned submarines. After this phase it is still possible to have several design options.
Preliminary Design
After the concepts are formulated, a feasibility study is done in the preliminary design phase. For the innovative designs, feasibility of the necessary technology is investigated. Also the first constraints are set by the customer, such as budget. The potential of the design is analysed. The end product of this phase should be a robust design which is tested on its feasibility. The work load is increased in comparison with the concept design. The specific properties are tested on their feasibility by experts in their field.
Contract Design
During the Contract design the detail of the design is increased. All contract specifications are developed and drawings are made in this phase. In this phase the integration of all subsystems is presented. After this stage the start of the production can begin on the yard. After this phase the flexibility is minimal.
Detail Design
As the name suggests, in the detail design phase attention is given to detail. The level of detail is increased for every component. Also the detailed construction drawings are made, with all the bolts drawn. During the production problems will occur. Designing solutions for these problems is also done during the detail phase. Because of the support to fabrication this phase can stretch up to 10 years. Because of the great detail the work load of the engineers is highest at this point. The work load is further increased because several tasks are concurrent: drawing, engineering and construction are execute on the same time.
4.4 Challenges in Submarine Design
The operational philosophy of Navies is changing over time. These operational philosophy changes result in design changes. The submarines in the WWII period were designed to attack in order to defend territorial waters or destroy enemy supply lines. After the WWII period, submarines were still able to attack hostile ships but gathering intelligence was a new major function of the submarine. In the current RNLN’s philosophy, the focus is more on global mis-sion instead of operating close to our own borders.
The operational philosophy will probably change within the design process of approximately 10 years. In SBD the commitment to a fully specified operational function is set at a later phase. This gives the navy in question the possibility to fully specify the functions more in line with the than current operational philosophy.
