Concept development of a fixed sonobuoy launcher : A study to examine the feasibility of applying concept development methodology to solve an industry related problem

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Linköping University | Department of Management and Engineering Master Thesis, 30 hp | Mechanical Engineering - Engineering Design and Product Development Spring Term 2019 | LIU-IEI-TEK-A--19/03476--SE

Concept development of a fixed

sonobuoy launcher

- A study to examine the feasibility of applying concept

development methodology to solve an industry related problem

Anton Dahlgren Bjuhr

Oskar Johansson

Supervisor: Simon Schütte Examiner: Mikael Axin

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Abstract

Is it possible to apply concept development methodology to solve a real industrial problem? This study will examine if this is possible. Saab has ordered a concept which allows launching of a sonobuoy from a pressurized aircraft cabin, this is a perfect opportunity to test this theory because it is a real system with technical demands to ensure robustness and safety. The system needs to be operated in tight areas which is the reason no launcher available will be used, they do not fulfill this demand. There are also a number of demands that the concept needs to fulfill which must be ensured during the concept process. It is not common when developing a component that a thorough and systematical concept development process is carried out at Saab. Therefor it was interesting to see how it would work with a Saab related product. The concept development process was carried out thoroughly by researching known methods within the subject. It was decided that the process would not follow a singular methodology because there where no process that suited this study perfectly. The process used was decided to be parts from different literature where methods that suited the concept at the current state would be used. This was performed differently depending on the current state of the concept. For example the product requirement process were established in a different way than the concept generation because they are different, one is mostly gathering facts while the other is mainly a creative phase. Regardless of the step in the concept development process the objective was to always use some sort help from the methodology.

A combination of lacking experience with the technical area and applying concept development methodology towards a industrial problem slowed down the process. The final concept were not as developed as the plan was from the start. To perform each step required more research than what was intended and some steps became an iterative process which also took time from the actual development. However, the actual process of setting up requirements, generating ideas and evaluating concepts should also be regarded as deliverable for this study. It is material that can be used for future development and this concept where never intended to be a finished design which mean it is useful material for the future.

To use concept development methodology for this kind of projects is recommended based on this study. Foremost when the experience of the system is limited, it ensures that the solution space and requirements are examined more than it would have without the process. It also helps with decision making and when discussing a concept within the group which could lead to an agreement which it might not would have without the methods.

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Acknowledgements

This master thesis has been the last and final step in our five year journey of becoming a fully fledged engineer within the subject of mechanical engineering. This master thesis was conducted at the department of airframe design at Saab in Linköping Sweden.

We would like to acknowledge every one involved in this master thesis in any way for making it possible to realize. We would like to thank our supervisor at Linköping University, Simon Schütte, for helping us answering all the questions regarding the structure and layout of the thesis. We would also like to thank our project owner at Saab, Mats Folkesson and our examiner at Linköping University, Mikael Axin. We would also like to thank our opponents for supporting us throughout the whole work with valuable feedback. We would like to give a special thanks Ingemar Arvidsson for giving us the opportunity to do our Master Thesis work at Saab at the airframe design division, and for managing all the things surrounding the work. Our research would have been impossible without the aid and support from our supervisor Joel Wallgård at Saab. We really appreciate the enthusiasm and interest you have shown for our work.

We would also like to thank every one at our office at Saab for all the support and for the amusing fika room discussions. And finally a big thanks to Johan Söderberg who shared room with us during the whole project, for answering our trivial questions and putting up with our chit chatting and bad jokes.

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2.4.2 Sonobuoy Separation Study . . . 21 2.4.3 Pressure Aspects . . . 22 2.4.4 Patent . . . 24 2.4.5 State of Art . . . 26 3 Method 28 3.1 Pre Study . . . 28 3.2 Product Requirements . . . 28 3.3 Concept Generation . . . 28 3.4 Concept Selection . . . 29 3.5 Concept Evaluation . . . 29 3.6 Concept Development . . . 29 4 Product Requirements 30 4.1 Product Requirement Process . . . 30

4.2 Problem Breakdown . . . 31

4.3 Benchmarking of Competitors . . . 31

4.4 Hazard Analysis . . . 32

4.5 Customer Needs . . . 33

4.5.1 Customer Statements and Needs . . . 33

4.5.2 Hierarchical List . . . 34 4.6 Product Characteristics . . . 36 4.6.1 Functionality . . . 36 4.6.2 Durability . . . 36 4.6.3 Quality . . . 37 4.6.4 Affordability . . . 37 4.6.5 Fabricability . . . 37 4.6.6 Installability . . . 37 4.6.7 Usability . . . 38 4.6.8 Maintainability . . . 38 4.6.9 Safety . . . 38 4.6.10 Marketability . . . 38 4.7 Product Requirements . . . 39 5 Concept Generation 40 5.1 Mind Map . . . 40

5.2 Brainstorming and Braindrawing . . . 42

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6 Concept Selection 47

6.1 Concept Screening and Scoring . . . 47

6.1.1 Development Priorities . . . 47

6.1.2 Ranked Morphological Matrix . . . 50

6.1.3 vALUe . . . 51

6.1.4 Final Screening and Scoring . . . 51

6.2 Concept Selection . . . 54 7 Concept Development 55 7.1 Design Plan . . . 55 7.2 Manufacturing Techniques . . . 56 7.3 Cross Section . . . 56 7.3.1 Feasibility Analysis . . . 57 7.3.2 Stress Analysis . . . 58 7.4 General Design . . . 60 7.4.1 Design Space . . . 60 7.4.2 Components . . . 60 7.4.3 Door Concept . . . 61 7.4.4 Lid Concept . . . 62 7.5 Design Parameters . . . 63 7.5.1 Cross Section . . . 64 7.5.2 Reinforcements . . . 64 7.6 Future Development . . . 65 8 Concept Design 67 8.1 Concept of Sonobuoy Launcher with Door . . . 67

8.1.1 General Design . . . 67

8.1.2 Pros and Cons . . . 68

8.2 Concept of Sonobuoy Launcher with Lid . . . 69

8.2.1 General Design . . . 69

8.2.2 Pros and Cons . . . 70

9 Discussion 72 9.1 Methodology Discussion . . . 72 9.1.1 Product Requirements . . . 72 9.1.2 Concept Generation . . . 72 9.1.3 Concept Selection . . . 73 9.2 Results . . . 73

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9.2.1 Development Process . . . 73

9.2.2 Concept Designs . . . 73

9.3 Reflections . . . 74

9.3.1 Ethical Aspects . . . 74

9.3.2 Information Gathering . . . 74

9.3.3 Time and Resources . . . 75

9.3.4 Recommendations for Future Development . . . 75

10 Conclusion 76 10.1 Research Question 1 . . . 76 10.2 Research Question 2 . . . 77 Bibliography 79 Appendix 81 A Launcher Benchmark . . . 81 B vALUe . . . 83

C Requirements List - Version 1 . . . 89

D Requirements List - Version 2 . . . 93

E Requirements List - Version 3 . . . 97

F Sketches . . . 101

G Morphological Matrices . . . 117

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List of Figures

1.1 The sonobuoy launcher sub-systems that are included in the study is marked with green and

the sub-systems not included is marked with red. . . 2

2.1 The process of diverging the solution space and reducing the number of solutions by Ulrich et al. [1]. . . 6

2.2 The process of diverging the solution space and reducing the number of solutions by Ulrich et al. [1]. . . 13

2.3 An example of how a mind-map can be designed [4]. . . 14

2.4 An example of how a morphological matrix can be designed [4]. . . 15

2.5 An example how the axis can be labeled when creating a C-box [4]. . . 16

2.6 The general structure of a Harris Profile [4]. . . 17

2.8 Basic sketch of a sonobuoy with a wind flap marked with orange. . . 18

2.9 Rotation of the wind flap after launch. . . 18

2.7 A collection of different sized sonobuoys manufactured by Ultra [9]. . . 19

2.10 The sonobuoy launching process from leaving the aircraft to impact with the water surface [12]. 20 2.11 Visualization of the elephant foot. . . 21

2.12 The launcher shown from the top-view with the loads. . . 22

2.13 Shows the difference in stress concentration between a spherical and a prismatic pressure vessel [17]. . . 24

2.14 Component with a small radius in the load path[18]. . . 25

2.15 Component with a larger radius in the load path [18]. . . 25

2.16 Section view of sonobuoy launcher[19]. . . 25

2.17 Components of sonobuoy launcher[19]. . . 25

4.1 The procedures used to acquire the product requirements. . . 30

4.2 The subdivisions of the system and the future problems to solve for each subdivision. . . 31

5.1 Mind map of the sonobuoy launcher housing sub-function and possible solutions. . . 41

5.2 Mind map of the sonobuoy launcher door and locking mechanism sub-function and possible solutions. . . 42

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5.4 First round of generating general sonobuoy launcher concepts. . . 44

5.5 Morphological matrix for the sonobuoy launcher door. Page 1. . . 45

5.6 Morphological matrix for the sonobuoy launcher door. Page 2. . . 46

6.1 From the original C-box shown in Figure 2.5, a decision was made in what direction the concept or concepts should be taken. . . 49

6.2 A page from the ranked morphological matrix where the components and ideas are ranked. . 50

6.3 General sketches of the two concepts that could be chosen if a simpler solution is decided as the best choice . . . 52

6.4 General sketch of the divided tube which could be a solution if it is decided a more advanced system is favourable. . . 53

7.1 Visual representation of the sonobuoy launcher cross section. . . 57

7.2 Approximate size of the sonobuoy launcher. . . 58

7.3 The design space where both of the fixed launcher should be fitted into. . . 61

7.4 The design parameters of the door concept. . . 62

7.5 The design parameters of the lid concept. . . 63

7.6 Sonobuoy launcher concept with a square cross section. Sonobuoy loaded into the launcher. . 64

7.7 Sonobuoy launcher concept with a circular cross section. Sonobuoy loaded into the launcher. 64 7.8 Reinforcements on the launcher with door. . . 65

8.1 Render of the final concept with door. Door closed. . . 68

8.2 Render of the final concept with door. Sonobuoy loaded into the launcher. . . 68

8.3 Render of the final concept with door. . . 69

8.4 Render of the final concept with door. Door closed. . . 70

8.5 Render of the final concept with door. Sonobuoy loaded into the launcher. . . 70

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List of Tables

2.1 Risk Ranking with regards to severity and frequency [5]. . . 9

2.2 An example of how the Weighted Objectives Method can be structured [4]. . . 18

2.3 Common sonobuoys sizes [8, 13, 14]. . . 20

4.1 Customer statements and needs [1]. . . 33

4.2 Customer statements and needs [1]. . . 34

4.3 Hierarchical list [1]. . . 35

4.4 The first part of the requirements list. . . 39

6.1 Table if the Weighted Objectives Method which gave a ranking value which could be used when making a decision. . . 53

7.1 Table that shows the maximum allowed buckling stress versus the expected stress for different thickness on the launcher. . . 59

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Chapter 1 Introduction

This master thesis is ordered by Saab Aeronautics and it will be written at their facility. The master thesis will focus on concept development where the theories and methods from earlier university studies will be used to solve the given problem.

Saab is a company that handles classified information. This classified information may under no circum-stances be shared with people outside Saab. The intention with this report is to be shared with people outside of Saab, therefore information associated with different products at Saab and other classified information will be left out in this report and other documents that will be shared. For example no product names will be mentioned in the report, however all specifications important to this project will still be discussed but not in a context connected to a specific product.

1.1 Background & Problem Formulation

Saab is always looking for new market sectors to expand their business into. One of these sectors that is quite similar to their current sectors is the maritime airspace. The maritime airspace includes areas such as maritime intelligence, surveillance and reconnaissance, anti-submarine warfare, long-range search and rescue, combat search and rescue and maritime counter terrorism. One important system for anti-submarine warfare is the sonobuoy launching system. A sonobuoy is a buoy which is dropped into the water from an aircraft to search for submarines. The sonobuoy is equipped with sensors that searches and monitors the close-by area with the help of sonar waves and sends the information back to the aircraft. To launch these sonobuoys from the aircraft there must exist a specialized launching system for sonobuoys in the aircraft.

The subject for this master thesis study is to develop one or a few concepts of a launcher, which is capable of launching sonobuoys and similar items from a pressurised airplane cabin. Currently there are no sonobuoy launching systems on the open market that fulfills the system requirements set by Saab.

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Saab has during their studies looked at implementing two different types of sonobuoy launchers in the aircraft. One variant that has a carousel magazine and can rotate and carry up to ten sonobuoys, this one is used at lower altitudes. The other one is a fixed pressurised launcher that only carries one sonobuoy at a time and is used at higher altitudes. This concept study will however only focus on the fixed launcher as there currently are no existing solutions available to purchase on the open market that will be possible to implement in the wanted Saab aircraft. The main issue with implementing any of the existing launchers is the limited vertical space where the launcher is supposed to be installed. The available launchers are top feed which means that the vertical space must be twice the size of the actual sonobuoy. Currently, there is not enough space in the intended location in the airplane to fit a launcher with the height of a sonobuoy and still have room to load a sonobuoy from the top. Therefore the new launcher design must be able to load a sonobuoy in a tight space.

1.2 Purpose

The main focus area for this study is the mechanical opening and locking, release mechanism and pressure transfer aspects of the sonobuoy launcher. The objective is by systematic concept development create concepts for a safe and robust fixed launcher, that is utilised at higher altitudes. A sonobuoy launcher can easily become an advanced system with plenty of technical areas included. This concept study has the purpose of only including the main sub-functions of the sonobuoy launcher, which is shown in green in Figure 1.1. These sub-functions include being able to open, close and lock the launcher when loading the sonobuoy into the launcher. A manual mechanism to release the sonobuoy when the launcher is locked and exposed to a differential air pressure between the atmosphere and the aircraft cabin. Also, solving the issues regarding the different pressures throughout the process of launching the sonobuoy. The objective from Saab’s perspective is that the concepts should have a simple design that shows the possibilities and difficulties with designing a launcher for the given purpose.

Figure 1.1: The sonobuoy launcher sub-systems that are included in the study is marked with green and the sub-systems not included is marked with red.

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1.3 Delimitations

Saab has limited this study by wanting a simple mechanical solution that consists of only a few components. The process of launching the sonobuoy can be divided into two areas as can be seen in Figure 1.1. The launcher can be seen as an external design that will be installed into the aircraft, but there has to be a part that is integrated with the aircraft as well. The components integrated with the aircraft are the launch tube and the ambient pressure valve marked with red in Figure 1.1, and they will not be included in this study. The majority of the launchers on the market today are equipped with a pneumatic system that adds a force to the sonobuoy to increase the speed at the launch moment. This will, according to the project description given by Saab, not be included in the study. The launcher will only use gravity to launch the sonobuoy. Included in this study is to design some sort of indicator that tells the current state of the launcher. The states to be monitored are if the ambient pressure valve is open or closed, what the inside pressure is and also if the launcher is loaded or empty. For this to be a functioning system there has to be multiple sensors and gauges within the launcher. Those measuring devices will not be included in the study, only the indicators on the outside of the launcher. Any other electrical interfaces will not be included in this study. This study will mostly focus on the mechanical aspects of designing a sonobuoy launcher, but there will still be a thought of where electrical sensors or electrical motors could be placed.

In a launcher of this kind, there is supposed to be two different release mechanisms. One automatic system that can be activated with a push of a button or from a control panel. The second one is a manual release mechanism which is mainly used when the automatic one is not working. In this study, only the manual release mechanism will be included. However, it is possible to develop a manual mechanism that has the capability to be transformed into an automatic mechanism.

1.4 Research Questions

From the purpose and the delimitations for this study, following research questions will be answered through-out the course of this study.

• Is it possible to develop a space efficient sonobuoy launcher that can launch sonobuoys from a pressur-ized aircraft cabin using only gravity?

• How did the concept development methodology support the concept development process?

1.5 Objectives

The objective with this study is to develop one or a few concepts that will solve the given problem. The concepts are not supposed to be finished designs ready for manufacturing. The objective is by using a preferable method of concept development to choose the best concepts for this particular case. The chosen concepts should then be developed and defined to show that they meet the requirements. The reason to develop more than one concept is because this study is considered to be a research study to use when developing this product in the future. When this will happen and by who is not determined which means a broader study could be more productive than a more detailed and narrow one. This means that components, possible issues, operating conditions and similar information may be important to include in this report even though they are not connected to the final concepts.

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1.6 Deliverables

The main deliverable will consist of conceptual 3D models of the sonobuoy launcher concepts. This includes 3D models of the general design of the concepts and will not go so much into the details of the design like machine elements or other smaller details.

Other than the conceptual 3D models, information about the different launcher concepts will also be part of the deliverable. The results from each process which can be used for further development will be handed over as it could be useful in the future. A general plan for the future steps and what should be developed as the next step according to this study will be delivered. There will also be some sort of general calculations to show that the concepts are viable. Calculations showing that they will be able to stand the different forces that will affect the launcher such as the differential pressure between the interior and the exterior at a high altitude.

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Chapter 2 Theory

The process of generating and selecting concepts is according to Ulrich et al. an iterative process [1]. The process is described graphically in Figure 2.1 and is trying to convey the importance of exploring the whole solution space to start with. It is good to include as many ideas as possible in the beginning of the concept generation process. Even though some concepts might seem bad at first, they might spark an idea for another improved solution. After the first step of diverging the solution space, the next step is concept screening. During the concept screening process the inferior concepts are sorted out, the concepts that does not fulfil the product requirements. The process of generating concepts and screening of the concepts are overlapping each other. After the first screening, more concepts are generated based on the concepts that made it through. These two steps are iterated until the number of concepts have been reduced to a manageable level. The next step after the concept screening is to rate the concepts based on the the product requirements in a step called concept scoring [1]. Both the concept screening and the concept scoring follows the same general composition which can be summarized with a six step process.

1. Prepare the selection matrix.

2. Rate the concepts.

3. Rank the concepts.

4. Combine and improve the concepts.

5. Select one or more concepts.

6. Reflect on the results and the process.

2.1 Defining Product Requirements

The product requirements are presented in a requirements list, which has two purposes, it gives guidelines for the product development process and it gives the information needed when evaluating the concepts [2]. The requirements list is updated throughout the process and gets more detailed when the product gets more detailed.

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Figure 2.1: The process of diverging the solution space and reducing the number of solutions by Ulrich et al. [1].

2.1.1 Problem Breakdown

The problem breakdown is a step to ensure no systems or components are missed out because that could create a significant problem during the later stages of development. This section goes through the methods to find all problems related to the concept.

Clarifying the Task

Designers must define the task so that amplifications and corrections during its subsequent elaboration can be confined to the most essentials [3]. A requirement list is essential to create.

A phase data collection should be carried out where the following questions should be answered [3]:

• What is the problem about?

• What implicit wishes and expectations are involved?

• Do the specified constraints exist?

• What paths are open for development?

It is not a good idea to have fixed solution ideas or make up the mind too early [3]. Only required functions and the inputs and outputs should be defined. To achieve this the following questions should be answered:

• What objectives is the intended solution expected to satisfy?

• What properties must it have?

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WWWWWH

It is important when analyzing a problem to divide the issue into several questions [4]. This makes it easier to review the problem and develop a set of priorities. One method of doing this is WWWWWH, which means asking the questions: Who? What? Where? When? Why? And How? This is carried out in the absolute beginning of the design project. This makes the problem much clearer, easier to understand and also gives an insight to what the underlying problems are.

Problem Definition

A problem is the result of dissatisfaction towards a certain situation [4]. The thing about this is that satisfaction is a relative concept, which means that problems are also that. This can be interpreted into the fact that a big problem for one person does not have to be that for another individual. A situation is also only a problem if the problem-owner wants to change it. This means that if the problem is something that could be tolerated, it should not be considered a problem.

The goal of this is to create explicit statements on the problem and give a direction for the idea generation [4]. It also helps to get this detailed and thought through because it helps sharing the understanding between everybody involved. When listing these problems, it creates the opportunity to discuss them and come to an agreement of the importance and relevance of the problem. It could also be a good idea to create a problem tree which breaks down the problems into smaller categories to get a better picture how problems relate to each other.

2.1.2 Benchmarking

To create a product that could compete on the market it is crucial to have a good understanding of how the competing products are designed and work [1]. The benchmarking is performed to support many of the activities early in the project. The benchmarking can also be a good source of inspiration for the product and product process design.

Usually information about competing products are gathered and shown in a chart. Each column in the chart corresponds to a different product and each row is corresponding to one of the metrics that were developed earlier in the product development process [1]. The concept of doing a benchmark of the competitors’ products is really simple. In practice, it is time consuming and not as easy as it sounds to benchmark competitive products. This process often includes to obtaining their products, test them and disassemble them. This time investment is however crucial for creating a competitive product.

2.1.3 Preliminary Hazard Analysis

This method is used in an early stage of development in order to identify, classify, asses and document the risks to a certain problem [5]. The objective for this is to create an assessment early on in order to locate possible hazards with the procedure. It is important to include every kind of risks to get the best result of the PHA.

PHA Prerequisites

Firstly, the prerequisites has to be established which is to define and describe the system to get a better understanding of the issue and all the surrounding aspects [5]. Start of with establishing system boundaries and description of subsystems, energy conversions, process flows, operations and environment. Also, collect information from related systems that might give an input to the hazard analysis.

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All possible accidental events must be identified which means it is important to consider all parts of the system, operational modes, maintenance operations, safety systems and so on [5]. All findings should be recorded regardless of how small or insignificant they are. Common sources of hazards are:

• Sources and propagation paths of stored energy in electrical, chemical or mechanical form.

• Mechanical moving parts.

• Material or system incompatibilities.

• Collisions and subsequent problems of survival and escape.

• Fire and explosion.

• Toxic and corrosive liquids and gases escaping from containers or being generated as a result of other incidents.

• Deterioration in long-term storage.

• Noise including sub-sonic and supersonic vibrations.

• Human error in operating, handling or moving near equipment of the system.

• Software error that can cause accidents.

Hazard Identification

To identify the hazards a number of steps can be followed to ensure that nothing is looked passed [5]. It is important to analyze previous systems that are in some way similar, also looking at the hazard analysis of these system if possible. Consider energy flows, materials, human interactions, environmental factors. Perform small scale testing and theoretical analysis, also thinking through a worst case scenario analysis.

Consequence and Frequency Analysis

The risk of a certain event is calculated with consideration to frequency of event and the severity of the consequences [5].

One accidental event could lead to number of different consequences where the severity also can vary from negligible to catastrophic [5]. Sometimes the average severity of an event is assessed. But it is probably more rewarding to consider all possible consequences, most important the worst foreseeable consequence. When executing this step in the analysis there are two graded scales that are used, the severity and frequency scale which are visualized below.

Severity scale [5]:

1. Minor - Failure results in minor system damage but does not cause injury to personnel, allow any kind of exposure to operational or service personnel or allow any release of chemicals into the environment.

2. Major - Failure results in a low level of exposure to personnel or activities facility alarm system.

3. Critical - Failure results in minor injury to personnel, personnel exposure to harmful chemicals or radiation or fire or a release of chemicals to the environment.

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Frequency scale [5]:

1. Very unlikely – Once per 1000 years or more.

2. Remote – Once per 100 years.

3. Occasional – Once per 10 years.

4. Probable – Once per year.

5. Frequent – Once per month or more often.

Table 2.1: Risk Ranking with regards to severity and frequency [5].

If the steps has been carried out there should now be a list with all the hazards possible with this future system [5]. They should also be ranked regarding to severity and frequency which shows which hazards that are the most critical.

2.1.4 Customer Needs

A key part to define the product requirements according to Ulrich et al. is to have the customer needs already documented [1]. Therefore, it is very important to do a comprehensive study of the needs before starting with the product requirements.

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Identifying Customer Needs

The goals of the method for identifying the customer needs are to [1]:

• Ensure that the products are focused on customer needs.

• Identify latent or hidden needs as well as explicit needs. • Provide a fact base for justifying the product specifications.

• Create an archival record of the need’s activity of the development process. • Ensure that no critical customer need is missed or forgotten.

• Develop a common understanding of customer needs among the development team.

The idea behind this method is to create a better connection between the people who will be using the product and with the designers and engineers that directly control the details of the product [1].

The step by step process that Ulrich and Eppinger recommends [1]:

• Gather raw data from the customer.

• Interpret the information in terms of customer needs. • Organize the needs into a hierarchy.

• Establish the relative importance of the needs. • Reflect on the results and the process.

Interpret Raw Data in Terms of Customer Needs

The raw data of the customers results in statements listed as customer needs [1]. This is an organized list of all the needs of the customers written in a clear way for the engineer to understand. These statements are then translated into “Interpreted needs” for the product which are technological problems to the customer statement. The problem should not be expressed as one solution because it limits the concept development stage.

Organize the Needs into a Hierarchy

When creating the list of customer needs it can get very large and difficult to understand and interpret [1]. Therefore, it is important to create a structure where the needs are listed in categories and rate the importance of each need. This is done in a hierarchy list which lists primary needs followed by secondary needs and rating all these needs by its importance. The primary needs are more general while the secondary needs are more detailed.

This method is most effective when doing it by the following steps, start off with writing the need statements on an individual note for each one [1]. This way it will generate more notes but some of them will be similar which means that the next step is to eliminate redundant statements. It is important to be sure these statements mean the same thing. Then group these statements into smaller groups that is considered to be similar. Similar can mean different things, for example similar technical problem. Ulrich et al. argues that the groups should consist of similar customer needs, not technical aspects or physical components. When this is done create labels for each group. The last step is to review and if needed, edit the groups. There is not really a correct answer to what should be included in what group so this could be a topic to discuss further during the product development process.

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2.1.5 Product Characteristics

To get a better understanding of the product that is to be designed, how it should work and behave, it is important to set up the characteristics for the product early in the engineering process. The product char-acteristics list is supposed to help the product developers and designers in the product development process and can be used as a checklist when developing the product. Each and every characteristic corresponds to different parts of the product life cycle. To help with identifying as many product characteristics as possible, a list of questions for product characteristics by Salustri [6] was followed. The list has a several questions for each characteristic to stimulate the thinking about product characteristics. It is just a guide and is therefore not a complete list of characteristics that should be included. The product characteristics and questions that are relevant for the product are selected.

2.1.6 Requirement List

It is important to state if the items on the list are demands or wishes [3]. Demands must be fulfilled and can be categorized into two different kind of demands, the ones that should achieve a purpose, i.e. waterproof and measurable demands which has a limit to achieve, i.e. maximum weight. Wishes should be considered when possible to improve the concepts, there should always be a trade-off for when it limits the quality of the demands. The wishes could be categorized depending on its importance. The items should also be categorized as either quantity or quality items. Quantity items are all items involving number and magnitudes while quality items are permissible variations or special demands such as waterproof or shock proof.

Identifying requirements can be difficult because they are not all clear and right in front of you [3]. It is important to systematically go through the following steps in order to minimize the risk of missing anything:

• Pay attention to the main headings of the checklist and determine the quantitative data.

• Ask:

– What objectives must the solution satisfy? – What properties must it have?

– What properties must it not have?

• Collect further information.

• Specify demands and wishes clearly.

• If possible, rank the wishes as being of major, medium or minor importance.

It is then important to arrange the requirements in a clear order to make it easy to understand the list [3]. This is done by defining the main objective and the main characteristics and creating sub-groups with less important requirements.

2.2 Concept Generation

The concept generation process is based on the earlier generated product requirements. The process of generating new concepts can according to Ulrich et al. be divided into five steps, see Figure 2.2 [1]. The first step is to clarify the problem. Break the problem down into smaller sub-problems to understand the problem better. Step two in the process is to do external searches about the problem to see if anyone has had the same problem before. These external searches include looking for relevant patents, searching for information

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in literature, benchmarking of the competitors’ products as well as talking with experts and with potential users. This step is a crucial step for the whole product development process because it is always cheaper to implement an existing solution than to create a new one. Step three in the process of generating ideas for new concepts is done in parallel with step two. Step three is searching internally for useful information. This is is where personal knowledge and creativity is used to come up with new solutions to the problem. The fourth step in the concept generation process is to explore systematically. The team have up until this step collected hundreds of ideas and fragments to possible solutions for the problem. All these ideas needs to be sorted and organized. The final step is to reflect on the solutions and on the process. Ulrich et al. recommends to ask the following questions during the whole process:

• Is the team developing confident that the solution space has been fully explored?

• Are there alternative function diagrams?

• Are there alternative ways to decompose the problem?

• Have external sources been thoroughly pursued?

• Have ideas from everyone been accepted and integrated in the process?

The concept generation process is a very iterative process according to Ulrich et al., both beginners as well as more experienced concept developers can benefit from following a structured method for concept generation. And usually the process is not a linear one and the same step is usually used more than one time.

2.2.1 Quality of the Best Idea

A study performed by Ulrich et al. aimed to find any patterns with generating ideas in groups [7]. Two different methods where tested when solving a problem and the results where compared to each other. The first method was to generate ideas to the problem in group through the whole process. The second method was to generate ideas individually the first half of the time then working together the second half, called hybrid process.

To evaluate the different methods the objective of the idea generation session must be defined [7]. In this study the objective was determined to be the quality of the best ideas. Another objective could be the amount of ideas or the quality of the average idea, but this study focused on the best ideas. It is considered that if two ideas are similar on the surface they are most likely to have similar quality.

Previous research suggest that more ideas are generated when working individually compared to when working as a group [7]. The literature lists three reasons behind this phenomenon. The first one is free riding, which means that some members of the group will rely on the rest to perform while they do nothing. This can also be the effect of too many members where some members do not get the task. The second reason is evaluation apprehension, which is the fear of negative response to the idea which results in that the idea might not be brought up. The final reason is production blocking, which is when more people want to express their ideas at the same time. This could lead to some ideas not getting attention or even mentioned, they just disappear because there is no room for them. However, it is most likely that the evaluation of the ideas are better when performed as a group task.

The result of this study was that the hybrid process generated better and more ideas generally [7]. The hybrid process generated three times more ideas than the group process. It was also considered that the quality of the best and average ideas of the hybrid process was better than the with the group process. Regardless of how good one idea might be it is never a certainty that it is successful [7]. There is no possible way to know if the idea will deliver on the market. Therefore it is normal for a company to invest in multiple ideas at the same time.

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Figure 2.2: The process of diverging the solution space and reducing the number of solutions by Ulrich et al. [1].

2.2.2 Brainstorming

Brainstorming is much more than people sitting around a table and discussing ideas [4]. Brainstorming is a specific method with a set of rules and a way of working for generating ideas. The main purpose of brainstorming is to come up with many ideas where no idea is too stupid or hard to realize to not be included in the idea generation. All ideas need to be brought up to stimulate the creativity. Criticism of the ideas should be postponed from the early steps of this method.

Roozenburg et al. argues that the process of brainstorming consists of three steps [4]. The first step of the process is all about diverging from the problem. The purpose of this step is to come up with as many different solutions as possible for the specific problem. Crazy and unique ideas are welcomed and appreciated.The next step in the brainstorming process is to evaluate and group the different ideas together. An overview of the solution space is created. Then in the third step the different concepts and ideas are screened. The best ideas are kept and the not so good ones that are hard to realize are thrown away.

There are different types of brainstorming [4]:

• Brainwriting Session - Usually only uses words and writing down the ideas.

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Brainstorming is suited for relatively simple problems. When the problems are larger it is a good idea to divide them into smaller sub-problems

2.2.3 Mind Map

A mind map is a graphical representation and overview of the solution space for a specific problem [4]. The mind map can be used both to show different solutions to the problem and to map their advantages or disadvantages. For larger problems, it is possible to divide it up into smaller problems and show the possible solutions for the respective sub-problem separately. The branches for the more important problems can be made thicker to differentiate them from the others. An example of a mind map can be seen in Figure 2.3.

Figure 2.3: An example of how a mind-map can be designed [4].

2.2.4 Morphological Chart

A morphological chart is used to generate ideas in a systematical way, usually by dividing the product into sub-functions [4]. The morphological matrix is divided up into the different sub-functions of the product, as seen in Figure 2.4. The idea is to come up with as many solutions to each sub-function as possible resulting in a chart full of solutions to each problem. The morphological matrix will give the product developer a better overview of the different sub-problem solutions. From this stage it is time to combine the different solutions from the sub-functions into complete concepts. Combining all the solutions for the sub-functions can be difficult because of the wast number of possible combinations, it is therefore crucial to leave out obvious bad combinations. It could also be a good idea to rank the sub-functions and solutions to easier see which combinations that looks better on paper.

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Figure 2.4: An example of how a morphological matrix can be designed [4].

2.3 Concept Evaluation and Selection

When the ideas and concepts are generated there need to be some sort of evaluation and selection process. The idea behind these methods is to structure the concepts and evaluating the pros and cons with each concept. This will help the selection process when ranking the different concepts.

2.3.1 C-box

A C-box is a 2x2 matrix with two axes with a criterion where all the ideas can be positioned [4]. Usually the criteria are innovativeness and feasibility. All the ideas that have been generated should be positioned in the matrix according to how innovative and feasible they are. It is important to discuss every idea within the group to get a fair position of each idea. An example of a C-box can be seen in Figure 2.5.

2.3.2 vALUe

This method is used to quickly evaluate a large set of ideas [4]. This is an inventorying method that allows the group to review and evaluate the ideas. It is named vALUe because the purpose is to find the Advantages, Limitations and Unique elements of the concepts. The process is to list the advantages, limitations and unique elements for each idea, this is done in a similar structure and vocabulary for each idea. This will make it easier to compare the ideas to each other and get a short documentation for each idea. The objective is to narrow down the amount of ideas by using this method.

2.3.3 Harris Profile

The Harris Profile, Figure 2.6, is created to make direct comparisons between different concepts [4]. The first step is to create a set of product criteria to evaluate the different concepts with. Then every concept will receive four boxes for each criterion which symbolizes -2, -1, 1 and 2 which is the rating system. Each

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Figure 2.5: An example how the axis can be labeled when creating a C-box [4].

system will be rated according to the scale which will give a visualization how the concepts compare against each other. This helps the decision making process even though it does not give a direct answer to which idea is the best.

2.3.4 Weighted Objectives Method

The Weighted Objective Method is used to compare different concepts by rating them on different criteria [4]. This method is best suited for a few concepts that has already been evaluated to some degree. The output from this method is an individual score for each concept which gives a direct indication of which concepts that are preferred. When the criteria are identified they are weighted depending on the importance of that criterion. The concepts are then rated for each criterion which gives a score depending on the weight of that criterion. In the end the scores are added together for each concept to give a final score which gives a clear visualization of how the concepts are rated against each other. An example of a weighted objective matrix can be seen in Table 2.2.

2.4 Pre Study

To get more familiar with sonbuoys and different types of launchers, a pre study was carried out. Several launchers and sonobuouys were examined to get different perspectives of the products. Theories of how to use sonobuoys as well as sonobuoy launchers was studied. Information about different pressure aspects to consider when designing a pressurised sonobuoy launcher was gathered.

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Figure 2.6: The general structure of a Harris Profile [4].

2.4.1 Sonobuoy

A sonobuoy is a cylindrical shaped capsule filled with electrical sensors [8]. The main purpose of the sonobuoy is to, with the help of the equipped sensors, provide the information required to detect and localize submerged submarines. Sonobuoys can also be used to determine environmental conditions in the waters or to communicate with friendly submarines. A selection of different sonobuoys with various sizes can be seen in Figure 2.7.

There are three main types of sonobuoys [8]. Active sonobuoys emits sonar sound waves in the water to generate an echo from any eventual nearby target. Passive sonobuoys listens for sonar sound waves emitted from the active buoys or for other acoustic sounds emitted from an eventual target. Lastly, there are special purpose buoys that can be adapted for different tasks such as collecting information about the water temperature or the ambient noise level. Sonar is a technique that simply put uses sound waves to detect and locate objects submerged in water in a nearby region [10].

Some sonobuoys have a wind flap on top of the launcher as visualized in Figure 2.8. This flap is armed when the sonobuoy is loaded upside down into the sonobuoy launcher. When the sonobuoy is launched and exits the aircraft through a hole under the aircraft the wind flap is flipped up with a spring, demonstrated in Figure 2.9, and gets caught by the passing air flow. The flap is in its turn disengaging a parachute. To get consistent launches and to be able to calculate where the sonobuoy will land, it is important to always load the sonobuoys in the same direction in the sonobuoy launcher.

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Table 2.2: An example of how the Weighted Objectives Method can be structured [4].

Figure 2.8: Basic sketch of a sonobuoy with a wind flap marked with orange.

Figure 2.9: Rotation of the wind flap af-ter launch.

Sonobuoy Usage

When dropping a sonobuoy from an aircraft on an anti-submarine mission, the aircraft has an target area which varies depending on what type of submarine are searched for [10]. The aircraft begins with scanning the waters for any surfaced submarine using on board sensors. If nothing is found the aircraft crew will start dropping sonobuoys into the water in a specific pattern. The sonobuoys is dropped in a predefined pattern to be able to precisely localize the target [11].

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Figure 2.7: A collection of different sized sonobuoys manufactured by Ultra [9].

The sonobuoys are dropped in a three staged process seen in Figure 2.10 [12]. The first step is launching the sonobuoy from the aircraft. The next step is stabilization of the sonobuoy. This is done by a drogue chute which is engaged soon after the launch. Directly after the sonobuoy leaves the airplane, the buoy releases a wind flap which is caught by the passing air flow. The wind flap is in its turn pulling out the drogue chute and the buoy begins a stabilized decent. The third step is retardation. The drogue chute is cut off and another larger reefed parachute is deployed at a predefined height to slow down the buoy before impact with the water surface.

The sonobuoys can be dropped from an altitude of up to 30,000 feet [11]. Once the sonobuoy touches the water, the buoy inflates a surface float with a radio transmitter for communication with the aircraft. The other part of the sonobuoy, the sensor equipment, descends below the surface to a predefined depth, which is set before the buoy is released from the aircraft. The equipment under the surface consists of a sail that stays just below the surface to keep the buoy stable [10]. The other part is the transducer which is the part that sink to the desired depth. The transducer converts acoustic sound waves in the water to electrical energy. The signal then gets passed on to the radio transmitter and then transferred via a RF antenna to the aircraft.

The information sent back to the aircraft will show up on the instruments and will then be compared and matched to a database [10]. If a match is found, it will be assumed that a submarine is in the near proximity of the sonobuoys. To be able to confirm the presence of a submarine, an active sonobuoy is dropped. The active sonobuoy emits sonar sound waves in all directions. If these sonar waves hit a submarine the waves will bounce of the submarine, create an echo and get picked up by the passive sonobuoys dropped earlier. The presence of a submarine can then be confirmed and pinpointed. The sonobuoys also help positioning the location of the submarine.

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Figure 2.10: The sonobuoy launching process from leaving the aircraft to impact with the water surface [12].

Sonobuoy Classes

Sonobuoys come in a lot of different size classes [8]. In Table 2.3 the most common sizes of sonobuoys with their associated diameters and lengths. The classes are named after letters A, B, C etc. with the A-class being one of the larger sizes and also one of the most common sizes. The diameter of the cylinder tube for the different classes are usually the same but the length differs. The A-class sonobuoy has a specified diameter of 4 7/8 inches which corresponds to 123.9 millimeters, which is the most common diameter for sonobuoys. The weight also varies between different sonobuoy sizes and manufacturers, but an A-class sonobuoy will not exceed a weight of 39 pounds or 17.69 kilograms.

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2.4.2 Sonobuoy Separation Study

Saab has conducted computer simulations regarding the launch of the sonobuoys [15]. They tested different scenarios to, if possible, draw conclusions of the separation when gravity launching the sonobuoy. The scenarios tested were velocity of aircraft, altitude of aircraft, load factor, falling distance inside the tube, sonobuoy mass and sonobuoy size. Also, simulations with a so called "elephant foot", seen in Figure 2.11, was performed because previous solutions had used this method. This means that the launch tube has a conical shape in the final section to create a smoother separation. One of the main concerns is that the sonobuoy will get stuck half way through the orifice due to the horizontal forces in the aircraft direction. The elephant foot is implemented to solve this issue.

The main function of the elephant foot is to prevent the sonobuoy from getting stuck in the launch tube. When long buoys like the A-class sonobuoy is launched, they have a risk of getting stuck in the launch tube when the air flow is hitting the bottom side of the buoy while the other side is still left inside the launch tube. The elephant foot seen in Figure 2.11 is a cone shaped hollow space connected to the launch tube that lets the sonobuoy pivot freely around the corner marked with the number 2.

Figure 2.11: Visualization of the elephant foot.

The conclusion from the simulation is that it is possible to launch the sonobuoy only using gravity [15]. However, there are some restrictions when doing so. The type of sonobuoy has a big significance, especially the weight of it. The A-sized buoy is the most difficult one because it is the longest and because it is exposed to horizontal forces for a longer duration than a shorter buoy. The length and large exposed area also contributes to higher levels of stress than with the other sonobuoys. The lightest sonobuoys of the A-size are therefore particularly difficult to launch because it does not reach the same velocity as the heavier ones while in the launch tube. However, with modifications to the aircraft and with the elephant foot it is possible. When testing the G-sized sonobuoys there were less issues which indicates that the size has an impact, not only the weight. It is important to have low friction between the buoy and the tube, 0.3 is the highest possible friction coefficient but 0.1 is preferable. The velocity of the aircraft has significance but the altitude of the aircraft do not has a significance. The falling distance inside the aircraft does not have a

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significance because there is not a big difference between the smallest and largest distance inside the aircraft. The most important conclusions from this study is the low friction coefficient that the system needs to have, this is more important for the parts not included in this study but there is still a good idea to look at it [15]. It is also good to know that the inside falling distance does not matter enough to be taken into consideration.

2.4.3 Pressure Aspects

The sonobuoy will be dropped at high altitudes with pressure differences between the aircraft cabin and the inside of the launcher. This will create pressure that acts on the launcher which needs to be taken in consideration when designing the launcher.

Buckling Stress for Circular Cylinders Under External Pressure

The analysis methodology of "Buckling stress for circular cylinders under external pressure" was investigated to see if it could help the design process [16]. This method was chosen using Saab data sheets and consulting with stress engineers at Saab. This specific stress case is used to figure out when the material starts to deform when exposed to an evenly distributed force acting radially inwards on the cylinder, as in Figure 2.12. The actual data sheets used are company restricted but the formulas used are generally known and can therefore be shown in this report. The equations are used to calculate the buckling constant, K, the maximum allowed stress and the expected stress the tube will endure with different thicknesses.

Figure 2.12: The launcher shown from the top-view with the loads.

L2 R × t > 5

R2

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K = 0.304L 2 R2 (2.2) σ(Buckling) = K × π × E 12 × (1 − v2₎  t L 2 (2.3) σ(tmax) = Pmax  R t (2.4)

Prismatic Pressure Vessels

Pressure vessels are used in a lot of different applications and use cases around the world such as nuclear reactors, storage vessels for gases and for pneumatic reservoirs [17]. Normally pressure vessels are made with a circular cross section because it is known to be one of the most efficient structural forms for pressure vessels in regards to its structural integrity. One of the big limitations with a cylindrical pressure vessel is its low volume efficiency of 25 to 50 % lower than a prismatic pressure vessel, depending on the installation. For pressure vessels with a circular cross section the membrane stress is the dominant force and the bending stress can be neglected [17]. The bending stress of a prismatic pressure vessel can however not be ignored. The total stress in a prismatic pressure vessel can be calculated as the sum of the membrane stress and the bending stress. A prismatic pressure vessel consists of six rectangular plates connected to each other to form a cuboid. The bending stress in a prismatic pressure vessel is inversely proportional to the square of the plate thickness. The bending stress is also proportional to the plate size of the prismatic pressure vessel. These two relations should therefore be considered when designing a prismatic pressure vessel. A simple comparison between a pressure vessel with a circular cross section and one with a square cross section can be sen in Figure 2.13. Both pressure vessels occupy the same space and are made of the same material and with the same material thickness. Both pressure vessels experience the same pressure force and it can be seen in Figure 2.13 that the prismatic pressure vessel experience a maximal force of up to 20 times higher at its peak compared to the highest stress in the cylindrical pressure vessel. Normally it is recommended that the prismatic pressure vessels are reinforced with either stiffeners or girders to be able to withstand high pressures.

Stress Concentration in Corners

A stress concentration is a local area that has a much higher concentration of material stress than the surrounding material [18]. These stress concentrations are generally found where the component experience some sort of abrupt change in the geometry like for example a sharp corner.

Finding an area with a high stress concentration is relatively easy [18]. They are generally found in areas with a small radius or in sharp corners located in the path of the load on the component. An example of a component with a high stress concentration can be seen in Figure 2.14. The component represents a truck commonly found on skateboards. It can be seen that the sharp corner with a radius of 0.01" experiences a high stress. If this radius is increased to 0.08" as seen in Figure 2.15, the stress is reduced from 14 419 psi to 3 873 psi. This is an extreme example of a stress concentration but it shows where stress concentrations are generally found and what can be done to prevent local areas with high stress.

Other things that can be done to improve the load ratings, the reliability and the fatigue life of a product is to avoid cyclic loads when incorporating a sharp corner in the product [18]. It is also good to remember that the stress is based on a ratio and not a magnitude, so the same radius does not work for all features.

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Figure 2.13: Shows the difference in stress concentration between a spherical and a prismatic pressure vessel [17].

2.4.4 Patent

A source of inspiration other than different products where different patents regarding sonobuoys. They where analyzed and if any information was of value it is listed in this chapter.

Sonobuoy Launcher - 1967

This design is the first relevant solution of a sonobuoy launcher because today’s solutions are refined from this product [19]. These are the relevant characteristics of the launcher which will help understanding how it works:

• The cross section of the capsule is hexagonal but the actual buoy is circular.

• The door is shown in Figure 2.17 as the left half of the hexagonal launch tube. To load the buoy the lever on the top left in Figure 2.16 is pulled down to remove the piston.

• Above the sonobuoy there is a piston that goes through several chambers. In 2 of these are springs located to force the piston to the correct position.

• Furthest down there is a latch that keeps the sonobuoy from falling.

• To launch the sonobuoy the device shown in Fig. 3 is used. To start the process the lid of the gas tube (82) is punctured. From this device there are two outlets, one is to a tube which leads to the top

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Figure 2.14: Component with a small radius in the load path[18].

Figure 2.15: Component with a larger radius in the load path [18].

of the piston which pushes the piston down with the pressure from the gas. The second outlet is to a piston which eventually removes the lock from the latch. This enables the sonobuoy to fall through and at the same time get added velocity from the force of the piston.

Figure 2.16: Section view of sonobuoy launcher[19].

Figure 2.17: Components of sonobuoy launcher[19].

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2.4.5 State of Art

Different sonobuoy launchers were analyzed in this chapter. One of them is public information while the rest are information given to Saab specifically which means that some information is company restricted. They can still be described in general but names and sources will be redacted.

Harris Corporation

Harris Corporation is one of the few companies on the sonobuoy launcher market where they offer both single and multiple launch configurations [20]. The systems are designed for maritime patrol and anti-submarine applications and are used in special mission air crafts, the American P-8A Poseidon for instance.

The single launch system is designed to hold one A-sized sonobuoy at a time and it is powered by a pneumatic system [20]. The launcher is mounted to the floor, however it is presumed that a portion of it is located beneath the floor. The launcher has an electrical interface to the aircraft which means it can be operated remotely.

Generic Launcher 1

Saab has received product specific material by the company who developed and owns the product. This material was given specific to Saab which means that it is restricted to Saab only [21].

The launcher is a tube that is divided into an upper and a lower part with support structure holding it still [21]. The upper part is fixed in a vertical position while the lower part has fixed location in the bottom but able to rotate which means that the bottom part can be tilted. When tilted the sonobuoy can be loaded then tilted back to vertical position to match the outline of the upper part of the launcher. This outline is covered with some form of sealing material to seal the inside of the launcher from the cabin, which enables the pressure change. A mechanical lock prevents the door from opening while the pressure inside the launcher is different from the cabin pressure.

Saab has also received material from another manufacturer, a smaller type of buoy launcher named Generic Launcher 2 in this study. The airplane where the Generic Launcher 2 is mounted is a smaller type of airplane with a passenger count of around 50 passengers in its original version [22].

The Generic Launcher 2 is a smaller type of launcher and is not capable of launching buoys of the same size as the launcher that will be developed during this project. The Generic Launcher 2 is a launcher developed for dropping smaller sensor buoys, but the design should be able to scale up to fit larger buoys.

The main function that differentiates this launcher from other launchers such as the pressurized single buoy launcher from Harris, is that this launcher is also gravitationally launched similarly to the Generic Launcher 1. This means that the launcher does not use any other energy source to launch the sonobuoy airplane other than gravity. It is just the mechanism that is holding the buoy that opens up.

The launcher is mounted very close to the outer shell of the airplane fuselage. This means that the dropped buoy will not reach as high velocity before it exits the plane.

The valve between the launcher and the outside atmosphere consists of a pendulum valve. This valve corresponds to the ambient pressure valve seen in picture 1.1. The valve is maneuvered with the help of pressurised air.

The launcher release mechanism is controlled by an electric solenoid. It is also possible to operate the release mechanism by hand with a handle connected to the solenoid via a wire.

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Generic Launcher 3 was developed by a public company but the document used for this study was given to Saab per request which means that it is a classified document. The document does not reveal any history, development or area of usage, only specific information about the product.

The launcher is primarily used to launch sonobuoys. The launch sequence is driven only by the gravity. The launcher is a square tube with a lid at the top where the launcher is loaded with the sonobuoy, which means that the launcher uses top-feeding. The lid seals the inside from the cabin enabling the possibility of high altitude launching. The product is equipped with a valve to equalize the pressure inside the launcher but specifics of that component is not mentioned in the document. The activation requires two steps by the operator, the first step is to open the bottom trap door which changes the inside pressure. When this is confirmed the operator activates the locking device which is otherwise locked by default. The trapdoor has an mechanical activation which consist of a handle and a lever. The locking device uses an electro-mechanical latching mechanism. The system is also equipped with sensors to monitor the different states of the launcher, the pressure, the trap door and if there is an object in the launcher.

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Chapter 3 Method

This chapter will describe the work process throughout this study of how to reach the objectives and how to verify that these objectives have been reached.

3.1 Pre Study

It is important to have a good foundation when defining this project, which is achieved by gathering infor-mation and knowledge that will be useful. This will mainly be achieved by a literature study which will include patent research, available information on current solutions, specification sheets of sonobuoys and information previous gathered by Saab. This will lead to an understanding of how launchers operate and a general knowledge of all things that needs to be considered when developing the concepts.

3.2 Product Requirements

The first step towards solving the problem and reach the objectives is to determine which characteristics the product must have. This step includes task clarification and problem breakdown to get a better un-derstanding of the prerequisites and get familiarized with the task. Other steps included in this procedure are costumer needs analysis, benchmarking, hazard analysis, product characteristics analysis. These steps are carried out to view the problem from different angles and easier motivate future decisions. The end product of this stage is a requirement lists, which lists all demands the product should satisfy. The list serves as a checklist throughout the concept development phase and should be updated when the task gets more specified.

3.3 Concept Generation

This is the first stage where the group members are allowed to be solution orientated. The objective is to come up with as many ideas as possible, there should not be any critical thinking in the beginning, quantity is preferred. The ideas can be generated with regards to the whole system, subsystems or individual components. Another strategy is to generate technical functions and their means to solving the chosen issue. This stage will include methods like mind maps, brainstorming, brain writing, problem statements, function analysis and morphological charts. The morphological chart allows concept generation by choosing different solutions to every subsystem and combining them into different concepts.

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3.4 Concept Selection

To select a few concepts to move on with there are different methods that compare them from different angles. It is a good idea to categorize the concepts to easier eliminate concepts that are similar. Creating a list with pros and cons can also be helpful in early stages of selection, this can be carried out by giving quick answers intuitively which saves time. Also, writing down unique elements to ideas can help in the choosing process. Other methods compare the concepts by listing demands and wishes from the requirements list and then evaluates every concept with regards to the requirements. This gives a visual presentation on how the concepts stands against each other and towards the objectives of the whole study. Methods that can be used for this step are Harris profile, datum method or weighted objectives method.

3.5 Concept Evaluation

This stage is where the performance and quality of the remaining concepts are evaluated using different methods. One important aspect is how the product is supposed to be operated and how it works. This can be evaluated by doing simulations and testing on prototypes. When there are only a few concepts it is a good idea to develop them further in order to describe them visually and functionally as much as possible. Explain the concepts in the group and evaluate them. It is also an option to perform a product usability evaluation where the usage of the product is determined and the concepts are evaluated with regards to that.

3.6 Concept Development

When the final concept or concepts are chosen, it is time for the final development which will also be the output from this study. The first step is to determine which stage of development that should be reached which depends on the amount of concepts and the number of weeks left. Also, determining how the output should be presented should be decided, some examples are physical prototype, sketches or 3D models in a CAD program. There are several aspects that can be included in the development and it will be decided which ones in the beginning of this phase. However, the design and assembly of all components will be the main output to deliver. Other aspects are materials, stress analysis, manufacturing, ergonomics, costs, environment and safety which will be considered for the development.

Concept development of a fixed sonobuoy launcher : A study to examine the feasibility of applying concept development methodology to solve an industry related problem