single man sleeping cabin for submarines · submarines for future demands are designed to be...

Division of Mechanics Division of Machine Design

ISRN LUTFD2/TF.ME--07/5002--SE (1-75)

Single Man Sleeping Cabin for Submarines

Master’s Thesis by Almo Omerovic & Christer Millrud

Supervisors

Solveig Melin, Div. of Mechanics

Per-Erik Andersson, Div. of Machine Design

Johan Jensen, Kockums AB Malmö

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Preface This Master’s Thesis has been done at the Division of Mechanics and the Division of Machine Design at Lund Institute of Technology during winter and spring of 2007 in cooperation with Kockums AB in Malmö. The objective of this thesis is to design a single man cabin for a submarine, to be put into use when the submarine has extra personnel onboard, and the design should be such that the cabin fulfills required strength conditions. We would like to thank our supervisors, Professor Solveig Melin and University lecture Per-Erik Andersson, for many valuable discussions and good advices. We would also like to thank Naval Architect Johan Jensen, Constructor Kenneth Pikulik, M.Sc Anders Melander and M.Sc Jan Stenvall for sharing their knowledge of submarines with us. At last special thank to Mr. Richard Weston for his expertise in Ansys. Lund, May 2007 Almo Omerovic & Christer Millrud

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Abstract This thesis is done in cooperation with Kockums AB in Malmö and the objective is to design a single man cabin for a submarine. The cabin shall be designed in such way that several single man cabins can be connected to each other, and so that the cabin can withstand a static shock load of 15g. Since the cabin only will be used when the submarine has extra personnel on board, it is important that the cabin is quickly and easily assembled/disassembled. As the cabin shall fulfil several different functions, the design procedure is divided into sub-problems that holds one or more functions. In order to find solutions to sub-problems, both a brainstorming within the group and market research for already existing solutions are performed. Each solution is evaluated against its own selection criteria, and only those solutions that give the best results are taken into account for further development. One of the sub-problems is to design and evaluate the frame that shall carry all loads. In order to do this, three different suggestions were first modelled in Pro Engineer [1] and, then, exported to the FEM program Ansys [2] for stress analysis. The frame suggestion that had the lowest stress levels in these analyses was chosen for further development. The main focus has been on the design of the cabin in such way that it is as light as possible without loosing strength. The results from Ansys show that the frame can withstand the required shock load level. Further more, solutions for all other requested features have been taken into account and evaluated.

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Sammanfattning Detta examensarbete har gjorts i samarbete med Kockums AB i Malmö där målet är att designa en flexibel enmanshytt. Hytten skall designas på så sätt att den skall kunna kopplas samman med flera hytter och den skall också kunna tåla en statisk stötlast på 15g. Hytten skall bara användas när det finns extrapersonal ombord, därför är det viktigt att den enkelt och snabbt kan uppmonteras/nedmonteras. Eftersom hytten skall uppfylla flera olika funktioner, delas designproceduren i olika delproblem som var och en innehåller en eller flera funktioner. För att hitta lösningar till de olika delproblemen, har både brainstorming inom gruppen och en undersökning av markanden efter redan existerande lösningar utförts. Varje lösning utvärderas med hänsyn till sina egna utvärderingskriterier och bara de lösningar som ger bästa resultat tas till vidare utveckling. Ett av delproblem är att designa och utvärdera den lastbärande ramen. För att kunna göra detta, modelleras först tre olika ramdesignförslag i Pro Enginner som sedan exporteras till FEM programmet Ansys för en spänningsanalys. Ramdesignförslaget som har de lägsta spänningarna tas till vidareutveckling. Under designarbetet har huvudfokus varit att designa hytten så att den väger så lite som möjligt utan att förlora sina hållfasthetsegenskaper. Resultaten från Ansys visar att ramen tål den givna statiska stötlasten. Lösningar till alla andra delproblem har också presenterats och utvärderats.

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Table of contents Preface ...................................................................................................................................... iii Abstract ..................................................................................................................................... v Sammanfattning ..................................................................................................................... vii Table of contents ...................................................................................................................... ix 1 Introduction ........................................................................................................................... 1 2 Thesis objective ...................................................................................................................... 2 3 Methodology .......................................................................................................................... 3 4 Establish target specifications .............................................................................................. 4

4.1 Customer needs ................................................................................................................ 4 4.2 Metrics list ........................................................................................................................ 6 4.3 The market ........................................................................................................................ 7

5 Concept generation ............................................................................................................... 9

5.1 Clarify the problem .......................................................................................................... 9 5.2 Internal search ................................................................................................................ 10 5.3 External search ............................................................................................................... 11 5.4 Explore systematically ................................................................................................... 12

6 Concept selection ................................................................................................................. 21 7 Design and analyses of frames ............................................................................................ 29

7.1 Frame with rectangular support ...................................................................................... 30 7.2 Frame with crossing bars ................................................................................................ 33 7.3 Frame with poles ............................................................................................................ 35 7.4 Reflections and discussion ............................................................................................. 37

8 Presentation and analysis of the concept ........................................................................... 38

8.1 Presentation of solutions to the sub-problems ................................................................ 38 8.2 Test of Concept .............................................................................................................. 44

Test 1 ................................................................................................................................ 46 9. Final solution ...................................................................................................................... 56

9.1 Set final specifications ................................................................................................... 56 9.2 Presentation of final solution .......................................................................................... 57

10. Conclusions and remarks ................................................................................................ 58 11. Future work ...................................................................................................................... 59 12. Summary ........................................................................................................................... 60

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References ............................................................................................................................... 61 Appendix A- Drawings ........................................................................................................... 62

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1 Introduction Kockums AB has since 1914 been in the industry of designing submarines. Today’s design of a submarine from Kockums AB is shown in figure 1.1.

Figure 1.1. Schematic of a submarine.

Submarines for future demands are designed to be flexible in the sense that they must be able to perform a large variety of missions. For instance, sometimes the submarine has extra personnel on board. The submarine has a limited number of cabins, see figure 1.1, so the extra personnel can not be accommodated in regular spacing. In such situations every available free space needs to be taken into use and, therefore, the storage space is used to put up a number of temporary cabins, designed for one person each.

Figure 1.2. Regular sleeping cabin.

Today a temporary cabin is much like a bed, with walls to shut noise out when used for sleeping or resting. For the next generation of submarines, Kockums AB wants to upgrade temporary cabins in order to make them more comfortable for the user, and also include more comforting functions.

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2 Thesis objective The thesis objective is to design a single man cabin for a submarine, to be put into use when the submarine has extra, temporary, personnel onboard. The cabin will be placed in the storage space. The design of the cabin must be flexible so that several single man cabins easily can be connected to each other. Since the cabin only will be used when the submarine has extra personnel on board, it is important that the cabin is quickly and easily assembled/ disassembled. The cabin shall fulfil the existing environmental requirements as regards ventilation, temperature, noise level and illumination. Beside the cabin, there will be a small storage space for personal belongings. If possible, some comfort functions, like access to audio and TV, should be included. The main objective is to develop a principle design drawing for the cabin, which fulfils required strength conditions.

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3 Methodology For the design phase of this master thesis, the methodology in [3] is adopted in applicable phases. The concept development phase’s scheme is illustrated in figure 3.1, and shows the primary steps of concept development. However, the chapter where the customer needs are identified by interviews with users of the product is inhibited because Kockums already possess a list of target specifications. It is not often the design process proceed in a sequential fashion as shown in figure 3.1 only, with a completed stage before moving on to the next phase. The dashed arrows indicate that, sometimes, it is necessary to retard a step and redo the entire process. Because of new information becoming available, it may show that some former decisions were not so good, and a rethinking might be necessary. All steps in the development phases shown in figure 3.1 will be described in detail in following chapters. As concerns the mechanical properties, these are investigated using the commercial computer programs Pro Engineer and Ansys during the phase denoted Test Product Concept in figure 3.1.

Figure 3.1. Concept development phases.

Identify Customer Needs

Establish Target Specifications

Generate Product Concepts

Select Product Concept(s)

Test Product Concept(s)

Set final specifications

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4 Establish target specifications In this step the customer needs are defined and specified as precise, measurable details of what the product has to perform. These measurable details are named specifications. A specification consists of a metric and a value. For example, “weight of the cabin” is a metric, whereas “less than 70 kg” is the value of this metric. An analysis of the market will also be undertaken to see if there are any existing products available. From this research, target values for all the metrics are created.

4.1 Customer needs As the Kockums staff already has identified the customer needs, the information below is retrieved from interviews with employees at Kockums. It is requested that the storage space shall fit a maximum of 24 cabins. When the storage space is used for carrying torpedoes it is occupied as shown in figure 4.1. The space available for cabins is shown by a red area in figure 4.2, which shows the section of the space in figure 4.1 within the frame.

Figure 4.1. Weapon storage space. Figure 4.2. Placement space. The volume where the cabins are allowed to be placed within the storage space is 7330x5037x1250 mm (LxWxH) with L denoting the length, W the width and H the height of the of available storage space. Each cabin is maximized to a volume of 2124x770x625 mm (LxWxH), allowing all together 24 cabins to be fit in. In figure 4.3 the placement of all 24 cabins is shown.

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Figur 4.3. Placement of the cabins

Ordinary crewmembers have a minimum bed volume of 2000x700x600 mm (LxWxH). But since the maximum allowed height H is 625 mm for each cabin, this condition will not be met for the extra cabins. In the storage space, the locker for personal belongings with a minimum volume of 100 litres, also needs to be fitted in. The cabin shall be attached to either the accommodation platform (the ceiling) or to the torpedo handling platform (the floor) of the storage space, see figure 4.4. This is because the torpedo handling platform and the accommodation platform are individually resiliently mounted. The cabin shall also be designed in such way that it can be attached to the bottom of another cabin. In order to be able to move the torpedo rails without interference of the cabin, the best solution would be if it is attached to the accommodation platform. This is only a request and not a constraint, so if the cabin can not be attached to the accommodation platform, the torpedo handling platform is an option.

Figure 4.4. Platforms.

Various machines placed in the storage space produce low-level noise, and, additionally, activities are going on in the cabin vicinity. Thus, a person using a cabin shall have a possibility to shut these noises out. The temperature in the submarine is about 18 to 20 ºC. For comfort in the cabin it shall be possible to control temperature via a ventilation hole, connected to the submarine ventilation system. A reading lamp and an entertainment panel should also be possible to install. It is desirable that the entertainment panel supports functions as TV and audio, and also holds a network connection.

Accommodation platform

Torpedo handling platform

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The cabin is taken on board to the storage space through a torpedo hatch, which is one meter in diameter. That means that the cabin also has to be disassembled in a way to fit the hatch. When the cabin is out of use, it will be stored on board, or in a container on land. In order to save space, the cabin shall be possible to disassemble. The cabin should also have low enough weight to be easily carried by two persons.

4.2 Metrics list The metrics list is created to make it easier to evaluate the customer needs. In Table 4.1 such a list is presented for this specific task. Every metric is quantified with either a demanded (D) or a wished (W) value. This list will make it possible to compare and evaluate suggested design proposals. Table 4.1. List of metrics. D=demanded value, W=wished value Metric No Metric Value Unit 1 Bed volume 2000x700x600 (W) 3mm 2 Mattress thickness 70 (W) mm 3 Noise isolation 30 (W) dB 4 Cabin volume 2124x770x625 (D) 3mm 5 Weight of the cabin <70 (W) kg 6 Static chock load 15g (D) 2sm 7 Time to assemble/disassemble < 15 (W) min 8 Flame protected material Yes (D) Yes/No 9 Storage compactability Yes (D) Yes/No 10 Price < 10 000 (W) SEK 11 Storage size (height) < 200 (W) mm 12 Fall-out protection Yes (D) Yes/No 13 Entertainment panel Yes (W) Yes/No Below the metrics are explained:

1. Bed volume. The volume of air inside the cabin. This inflicts on the comfort of the person using the cabin.

2. Mattress thickness. The mattress must be as thin as possible to save bed volume but thick enough to be comfortable to use.

3. Noise insulation. It is important to choose materials that are noises reducing. 4. Cabin volume. The cabin volume is restricted by the demand to fit 24 cabins within

the storage space. 5. Weight of the cabin. It should be light enough for two persons to carry. 6. Static chock load. In consultation with the Structural department at Kockums AB the

mechanical properties of the cabin are tested for a static chock load with an acceleration of 15g. It shall also be tested for transverse and longitudinal shocks.

7. Time to assemble/disassemble. The cabin should be simple and quick to assemble/disassemble. It should contain few loose parts.

8. Flame protected materials. The materials used must comply with given fire regulation restrictions as specified by the International Maritime Organization IMO, cf. [4].

9. Storage compactability. When the cabin is disassembled it should occupy as little space as possible and be easy to stack.

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10. Price. Comfort and safety for the person using the cabin have higher priority than the price of the components comprising the cabin.

11. Storage size (height). The disassembled cabin should not exceed a height of 200 mm. 12. Fall-out protection. There shall be an open section on the cabin for entrance. When the

person is sleeping, a fall out protection shall be put up so that the person is prevented from falling out of the cabin.

13. Entertainment panel. There shall be some sort of entertaining functions so that the cabin can be used for more than just sleeping. An entertainment panel is included and shall have functions as light, ventilation, audio, TV and a network connection.

4.3 The market A market analysis to compare how other products fulfill the specifications is difficult simply because of the fact that there is no open market. How other countries develop their submarines, and the interior of these, are usually restricted information. One product that can be compared with the cabin developed in this thesis is a single man cabin used today in Swedish submarines. This cabin goes under the name “Puda’s crate”. It is a wooden design attached to a torpedo channel according to figure 4.5. The entertainment panel in this cabin contains only a reading lamp, and there are no possibilities to regulate the ventilation. The personal belongings are stored in the thin, metal locker seen in figure 4.6. Disassembling of the cabin is effectuated using hinges. The metrics for the “Puda’s crate” are seen in Table 4.2. However, values for metrics 3, 6, 9, 12 could not be found.

Figure 4.5. The Puda’s crate. [5] Figure 4.6. Thin, metal locker. [5]

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Table 4.2. List of metrics for the Puda’s crate. Metric No Metric Value Unit 1 Bed volume 1890x590x410 2 Mattress thickness 130 mm 3 Noise isolation - dB 4 Cabin volume 2140x640x540 5 Weight of the cabin 40 Kg 6 Different loads - N 7 Time to assemble/disassemble < 15 min 8 Flame protected material Yes Yes/no 9 Storage compactability Yes Yes/no 10 Price < 10 000 SEK 11 Storage size (height) - mm 12 Fall-out protection No Yes/No 13 Entertainment panel No Yes/No An alternative approach to the problem was taken in 2004 by a couple Industrial design students from LTH at an assignment to design a temporary sleeping compartment []. The solution to their assignment can be seen in figure 4.7. It is a tent-like structure that rests on the floor and is fixed to its surrounding by hooks according to figure 4.8. A metrics list for this sleeping compartment is, however, not included in their report and can, thus, not be presented in this thesis.

Figure 4.7. Sleeping compartment. [5]

Figure 4.8. Attachments to floor and ceiling. [5]

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5 Concept generation This chapter presents a brief description of the technique and working principles for the design, together with a layout of the cabin. This complex task is here divided into simpler sub-problems, and these are evaluated according to the scheme of the four steps of the concept generation method illustrated in figure 5.1.

Figure 5.1. The four step concept generation method.

5.1 Clarify the problem The cabin is a complex product with many desired functions. In order to make the cabin easier to develop, the task is decomposed into sub-problems. Each sub-problem comprises one or more functions of the cabin. The sub-problems are as follows:

1. Assembling/Disassembling method. The cabin needs to be compact to save space when it is stored within the submarine, or on land. This method describes how the cabin will be assembled/disassembled.

2. Frame. The frame has two main functions. It will carry most of the loads and it will work as an attachment position to a majority of the parts that the cabin consists of.

3. Wall. The main functions of the walls are to reduce noise and to prevent people from falling out of the cabin. If possible, it should assist in carrying some load as well. However, walls should weigh as little as possible but still fulfil requested functions.

4. Attachment. The cabin is attached to the accommodation platform, other cabins and the personal storage space. These parts, as it appears, will connect the cabin to the

1. Clarify the problem.

- Understanding - Problem

decomposition - Focus on critical

sub-problems

2. Search externally

- Lead users - Experts - Patents - Literature - Benchmarking

3. Search internally

- Individual - Group

4. Explore systematically

- Descriptions of the solutions for each sub-problem.

Sub-problems

Existing Concepts New Concepts

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accommodation platform, cabin to cabin and the personal storage space to the accommodation platform. It is requested that all connections are of the same type to avoid any problems if the cabin is mounted either on top or down under.

5. Mattress. The person using the cabin must be able to rest comfortable. This comfort is provided by putting a mattress at the bottom of the cabin.

6. Fall-out protection. There will be an open section on the cabin for entrance. When the person is sleeping, a fall-out protection can be put up so that the person is prevented from falling out of the cabin.

7. Entertainment panel. There must be some sorts of entertaining functions so that the cabin can be used for more than just sleeping. An entertainment panel is included and can have functions as light, ventilation, audio, TV and a network connection.

8. Personal storage space. There is no space to put personal belongings inside the cabin. Therefore, a personal storage space needs to be attached near the cabin.

9. Sound and light insulation on open part. Because one side of the cabin is open, some kind of sound and light barrier should be mounted so that the person inside the cabin can have some privacy.

5.2 Internal search Internal search is based on personal knowledge and creativity within the company or group to generate different solution concepts. In this project an internal search is undertaken prior to an external search. This is because looking into others ideas first might limit ones own creativity. After the external search is completed, the internal search is repeated to see if some new ideas have been generated in the light of others solutions. In order to generate ideas, the brain storming method was used to find different solutions to all sub-problems. Only relevant ideas are presented below, in terms of notes: 1. Assembling/Disassembling method

• Screws • Hinge • Spring mechanism • Ikea mechanism • Scissor mechanism • Telescope mechanism

2. Frame

• The frame it self carries the entire load • Wall helps in load carrying

3. Wall

• Soft walls • Rigid walls • Rigid-soft walls

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4. Attachments • Wedge • Rail • Screw • Spring mechanism

5. Mattress

• With inherent stiffness • Soft mattress

6. Fall-out protection

• Net • Straps • Board

7. Entertainment panel • Contains a lamp, ventilation, audio, TV and network connection.

8. Personal storage space • Locker • Drawer • Storage compartment of fabric.

9. Sound and light insulation on open part

• Curtain • Adjustable screen

5.3 External search An external search was made to find existing solutions to each sub-problem. This is an important step because it saves a lot of time if there is an already existing solution to a specific problem. In the search of solutions, experts at Kockums AB have been interviewed. Products from different manufacturers have been looked into, both in catalogues and on internet. The outcome of the investigation is summarized below. 1. Assembling/Disassembling method

• Screws • Hinge

2. Frame

• Because design of cabins is rare, it is difficult to find existing solutions applying to a frame hanging. The solutions that are used in boats, trains and caravans are not designed for hanging and, therefore, can not be considered in this case.

3. Wall

• Promat • Euro Insulite • Norac • Paroc

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4. Attachments • Screw • Spring mechanism • Ikea mechanism • Container lock • Keyhole lock

5. Mattress

• Tempur • DUX • Aurora Marine mattress

6. Fall-out protection

• Board 7. Entertainment panel

• Bus panel with light, ventilation and radio • Airplane panel with light, ventilation, radio and TV

8. Personal storage space

• Locker • Drawer

9. Sound and light insulation on open part

• Curtain • Adjustable screen

5.4 Explore systematically From the results presented in the Internal and External search section 5.2 and 5.3, various suggestions are chosen to be further developed. Below follows a more detailed description of the suggested solution to each sub-problem. 1. Assembling/Disassembling method Different parts of the cabin are clamped to each other by one of the following ways: A) Spring mechanism. The walls are attached to the frame by some sort of spring mechanism according to figure 5.1.

Figure 5.1. Spring mechanism.

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B) Ikea mechanism. The cabin is assembled/disassembled by using a solution developed by Ikea. A pin is inserted into a hole, where a screw to lock it according to figure 5.2 is presented.

C) Screw. The walls can be attached to the frame by screws as shown in figure 5.3. The holes in the bottom frame are threaded, so there is no need for nuts, and the screws are permanently mounted onto the side of the frame.

Figure 5.2. Ikea mechanism. Figure 5.3. Screw mechanism. D) Hinge. The walls and the bottom frame are connected by hinges so that the cabin can be smoothly folded into a compact package, see figure 5.4. E) Telescope mechanism. Assembling method is to elevate or lower the telescope arms, see figure 5.5. Poles are made like telescopes and attached to the bottom frame as shown in figure 5.9.

Figure 5.4. Hinge mechanism. Figure 5.5. Telescope mechanism.

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2. Frame The frames presented below are only basic designs. The bottom design of the frame can vary, depending on which type of mattress that is going to be used, whereas the design of the poles assisting the walls depends on which assembling/disassembling method that is going to be used. A) Frame with rectangular support, see figure 5.6. Both soft and stiff walls can be attached. Assembling method can be screw, hinge, Ikea or spring mechanism.

B) Frame with crossing bars, see figure 5.7. Both soft and stiff walls can be attached. Assembling method can be screw, hinge, Ikea or spring mechanism.

Figure 5.6. Frame with rectangular support. Figure 5.7. Frame with crossing bars. C) Frame with poles, see figure 5.8. This frame is designed for a stiff wall. Assembling method can be screw, hinge, Ikea or spring mechanism. D) Frame with telescope poles. This frame is designed for a soft wall. In order to make it stiff, the cabin is reinforced with horizontal bars according to figure 5.9.

Figure 5.8. Frame with poles. Figure 5.9. Frame with telescope poles.

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3. Wall Walls will cover three sides of the cabin and will be attached to the frame. One side is open so that a person can enter the cabin easily. A) Soft wall made of tarpaulin that damps noise and shuts light out. Soft in this context means that it does not carry any loads. B) Paroc [6] is involved in manufacturing, developing and distributing stone wool products used in buildings and in various industrial applications. Their wall panels are composites with a core of structural stone wool and with an outer casing of thin metal sheet, see figure 5.10. This material is non-combustible.

Figure 5.10. Paroc wall panel.

C) Promat [7] is a part of the Etex Group of companies, based in over 30 countries world-wide. They manufacture, design and develop fire protected wall panels and systems. Material used in their panels is PROMAXON, a man-made calcium silicate. It provides far better fire resistance with less material than conventionally mined calcium silicate. Figure 5.11 shows a design of a wall panel produced by Promat.

Figure 5.11. Promat wall panel.

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4. Attachments The cabin can be attached to the accommodation platform, other cabins and the locker by: A) Screw. The plate to the left in figure 5.12 holds the screws permanently, and the plate on the right in figure 5.12 has threaded holes, implying that there is no need for nuts.

. Figure 5.12. Attachment by screw.

B) Ikea mechanism. A pin is inserted into a hole, where there is a screw to lock it according to figure 5.2. C) Spring mechanism. Some sort of spring mechanism connects the different parts according to figure 5.1. D) Wedge. A wedge-like device that consists of two parts can be used as an attachment. When the parts are put together, they are locked by a pin according to figure 5.13.

Figure 5.13. Attachment by wedge.

E) Container lock. Consists of two parts according to figure 5.14. The device is locked when the oval part is inserted into the cylindrical part and turned 90 degrees.

F) Keyhole lock. This mechanism consists of two parts, where the pin is inserted into the hole and, then, pushed horizontally as shown in figure 5.15. A sprint is used to assure that the mechanism is locked.

Figure 5.14. Attachment by container lock. Figure 5.15. Attachment by keyhole lock.

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5. Mattress A mattress will be put on the bottom of the cabin. The options are listed below. A) Tempur [8] is a company that produces soft mattresses. The material used in a mattress is a relieve pressure material forming after the body shape as shown in figure 5.16. It was developed by NASA for the American space program. This mattress will need a resting support. B) Dux [9] is Swedish mattress manufacturer. Their mattresses have a built in spiral system that makes the mattress mold itself after the body shape as shown in figure 5.17. Dux can manufacture mattresses with or without an inherent stiffness. If the mattress has inherent stiffness, it do not need as much of a resting support as a soft mattress.

. Figure 5.16. Tempur mattress. Figure 5.17. Dux mattress. C) Aurora Marine [10] sells mattresses designed for marine applications. The method they use to design a mattress provides a unique built-in ventilation system, created by glass fibre reinforced cylindrical springs according to figure 5.18. The mattress molds itself after the body shape, and because it does not contain any metal parts, its weight is low. This is a soft mattress and needs a resting support.

Figure 5.18. Aurora-marine mattress.

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6. Fall-out protection The fall-out protection will be fastened in front of the open part of the cabin. Possible solutions are: A) Straps as illustrated in figure 5.19. Two straps prevent a person from falling out of the cabin. These straps can also be used to secure loose parts when the cabin is disassembled.

Figure 5.19. Straps.

B) Net, see figure 5.20. A net is attached to the cabin.

Figure 5.20. Net.

C) Board, see figure 5.21. This is a board similar to the fall-out protection that can be found attached to commonly used beds such as bunk beds.

Figure 5.21. Board.

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7. Entertainment panel Panel with light, ventilation, audio, internet and TV screen as illustrated in figure 5.22 can be intergraded in one of the walls.

Figure 5.22. Entertainment panel.

8. Personal storage space The person using the cabin should have the possibility to store personal belongings close to the compartment. This can be achieved in one of the following ways. Additionally, there will be some kind of small storage in terms of i.e. a net shelf inside the cabin, mounted on a wall. A) Locker, see figure 5.23. B) Drawer, see figure 5.24.

Figure 5.23. Locker. Figure 5.24. Drawer. C) Storage compartment of fabric, see figure 5.25.

Figure 5.25. Ikeas storage compartment of fabric.

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9. Sound and light insulation on open part The open part, where a person enters the cabin, shall have a removable sound and light insulation. Suggestions for solutions are: A) Curtain, see figure 5.26. A thick curtain with sound and light insulation properties covers the opening of the cabin. It is attached to a wire that is fastened between the walls.

B) Adjustable screen, see figure 5.27. A screen with sound and light insulation properties covers the opening to the cabin. It is attached to a track that leaps between the walls.

Figure 5.26. Curtain. Figure 5.27. Adjustable screen.

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6 Concept selection In this chapter different concepts for each sub-problem are compared and evaluated against each other in view of the selection criteria for each particular sub-problem. The selection criteria differ between sub-problems because each sub-problem is dedicated to a specific function. One or more concepts for each sub-problem are selected for further evaluation. Further on, the different concepts of the sub-problems are combined and improved in order to arrive at different cabin designs. The design suggestions are then compared and evaluated towards each other so that only one or two cabin concepts are chosen for further analyses. For each sub-problem where it is possible to do so, a matrix with selection criteria is set up in order to make evaluation of each sub-problem easier. The evaluations of the concepts using such a matrix are performed by choosing a reference concept and, then, compare all other concepts to this chosen one. The comparison is executed by employing a relative score of “better than” (+), “same as” (0) and “worse than” (-) for each item. Sub-problem 1. Assembling/Disassembling method The screws are chosen as a reference because it is a well known procedure. This makes it easier to compare different alternatives. Selection criteria and evaluation of the solutions are listed in Table 6.1. Below follows a discussion on which of the solutions that is finally judged the best. A. Spring mechanism B. Ikea C. Screw D. Hinge E. Telescope mechanism Table 6.1. Assembling/Disassembling method. Selection criteria

A

B

C

D

E

Time to assemble Easy to use Durability and strength Already existing solution Compact/Easy to store

+ + 0 - 0

+ + 0 0 0

0 0 0 0 0

+ + 0 0 +

+ + - - +

Sum +’s Sum 0’s Sum –‘s

2 3 1

2 3 0

0 5 0

3 1 0

3 0 2

Net score Rank Continue

1 3

No

2 2

Yes

0 5

No

3 1

Yes

1 3

No Alternative A: Spring mechanism Spring mechanism is simple to use and the assembling/disassembling time is short. Also, the mechanism has good durability and strength. Because no such existing solution has been

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found on the market, it would take much time to develop and test it. Therefore, this solution is not further considered in this thesis. However, such a solution is something to consider for future development. Alternative B: Ikea The Ikea solution is found to be easier to use and has same durability and strength as the screw. Time to assemble/disassemble the cabin is also considerably shorter when this solution is applied. With the Ikea solution the cabin becomes more compact and has less loose parts when disassembled. Alternative C: Screw The screw takes a long time to assemble/disassemble and is also difficult to use because the persons attaching the cabin must hold the cabin while getting the screws into the correct positions. Alternative D: Hinge Using hinges as assembling/disassembling method gives the same advantages as the Ikea solution. It is further easier to assemble/disassemble because of the absence of loose parts. Alternative E: Telescope mechanism Telescope mechanism is a complex device and no existing solution can be found on the market. It would take time and resources to develop and test this kind of device and, thus this solution might not be worth considering for further development. With regard to Table 6.1 and the discussions above, the hinge and the Ikea solutions will be further evaluated. Sub-problem 2. Frame A. Frame with rectangular support B. Frame with crossing bars C. Frame with poles D. Frame telescope poles In evolution of frame alternatives, the selection criteria table is not used because the choice depends on the outcome of the solutions for the other sub-problems, i.e. wall, mattress, attachments and choice of material. All the alternatives, apart from alternative D, are selected for further development. This is because alternative D is more complex than the others, and no existing solutions have been found on the market for this alternative. Sub-problem 3. Wall The Paroc wall is chosen as reference. A. Soft wall B. Paroc C. Promat A soft wall material is lighter than a solid one and can further more offer as good noise insulation as a solid wall. Despite of this, it is not desirable to use, because these kinds of materials do not posses the same durability and strength as rigid walls. They further do not give good enough protection against impact and, even though they might be flame protected,

23

they burn faster than solid materials. Because of these negative properties, soft walls are not further evaluated. Selection criteria for the other suggestions can be seen in Table 6.2. Table 6.2. Wall.

Selection criteria

B

C

Weight Sound reducing properties Fire resistance Already existing solution

0 0 0 0

+ 0 - 0


0 4 0

1 2 1


0 1

No

0 1

Yes Alternative B: Paroc The Paroc wall is 53mm thick and weighs 16 2mkg . It consists of incombustible material that can withstand fire for 3 hours. Alternative C: Promat The Promat wall is 19 mm thick and weighs 11 2mkg . Promat has 30 minutes fire resistance. With regards to Table 6.2 the Promat wall is chosen. It is lighter and thinner than the Paroc wall, which saves weight and space. It is not as fire resistant as the Paroc wall but can withstand fire for an acceptable length of time. Sub-problem 4. Attachments The screw is chosen as reference because it is a well known product. Selection criteria and evaluation of the solutions are listed in Table 6.3. A. Screw B. Ikea C. Spring mechanism D. Wedge E. Container lock F. Keyhole lock

24

Table 6.3. Attachments. Selection criteria

A

B

C

D

E

F

Time to attach Easy to use Already existing solution

0 0 0

+ 0 0

+ + -

+ + -

+ 0 -

+ + -


0 3 0

1 2 0

2 0 1

2 0 1

1 1 1

2 0 1


0 5

No

1 1

No

1 1

No

1 1

No

0 5

No

1 1

Yes Alternative A: Screw The screw takes a long time to assemble/disassemble and is also difficult to use because the persons attaching the cabin must hold the cabin while getting the screws into the correct positions. Alternative B: Ikea The Ikea solution offers a faster way to assemble/disassemble than the screw solution. But the screw that holds the pin needs to be twisted in order to lock. This makes it almost as difficult to use as the screw because the person holding the cabin must hold it and lock the mechanism simultaneously. Alternative C: Spring mechanism The spring mechanism is faster to attach as compared to the screw. It is also easier to use because no tool is needed in the mounting. Because no existing solution can be found on the market, it would take time to develop and test this alternative. But this solution is something to consider for the future. Alternative D: Wedge A wedge is fast to attach and easy to use because there is no need for tools. The disadvantage is that it has to be custom made for this special application. Alternative E: Container lock The container lock is fast to attach. But the oval part needs to be twisted to lock, which makes it difficult to use because the mounting personal must hold the cabin and lock the mechanism at the same time. Alternative F: Keyhole lock This solution gives the best result as regards both simplicity and time to attach. The only disadvantage with this solution is that it has to be custom made for this specific application. With consideration of to Table 6.3 and the discussion above the keyhole lock is chosen.

25

Sub-problem 5. Mattress The Dux mattress is chosen as reference for this sub-problem. Selection criteria and evaluation of the solutions are listed in Table 6.4. A. Tempur B. Dux C. Aurora Marine In order increase the bed volume as much as possible, the mattresses presented below are the thinnest ones that could be found, still considered comfortable enough. Table 6.4. Mattress. Selection criteria

A

B

C

Comfort Thickness Weight Fire resistance Price

0 - + 0 -

0 0 0 0 0

0 - + 0 -


1 2 2

0 5 0

1 2 2


-1 2

No

0 1

Yes

-1 2

Yes Alternative A: Tempur A mattress from Tempur with size 2000x700x150 mm (LxWxH), weighs around 14 kg and will cost approximately 5800 SEK. There is a mattress that is thinner but its comfort is lost if it is used without the support of another mattress. The mattress is flame protected according to IMO standards, but in case it starts burning, this mattress emits toxic gases. Alternative B: Dux A mattress from Dux with size 2000x700x100 mm (LxWxH ), weighs around 16 kg and will cost approximately 2500 SEK. This is a soft mattress and will need a support to rest on. It is flame protected according to IMO standards. Alternative C: Aurora Marine A mattress from Aurora Marine with size 2000x700x120 mm (LxWxH ), weighs approximately 9 kg and will cost around 4500 SEK. This mattress and belonging textiles meets IMO standards for flammability, smoke and toxicity. With regards to Table 6.4 both the Dux and the Aurora Marine mattresses are candidates for the cabin.

26

Sub-problem 6. Fall-out protection The board is chosen as reference for this sub-problem. Selection criteria and evaluation of the solutions are listed in Table 6.5. A. Belt B. Net C. Board Table 6.5. Fallout protection.

Selection criteria

A

B

C

Safe Easy to use Weight Multitasking Already existing solution

0 0 + + 0

0 0 + 0 0

0 0 0 0 0


2 3 0

1 3 0

0 5 0


2 1

Yes

1 2

No

0 3

No Alternative A: Belt The belt is lighter than the board and can be used to secure the walls of the cabin when disassembled. Alternative B: Net The net is as light as a belt but it can not be used to secure the walls of the cabin when disassembled. Alternative C: Board The board is heavy and takes relatively much space when stored. It can not be used for multitasking, i.e. securing, the walls when stored. With regard to Table 6.5 and the discussion above, the belt solution is chosen. Sub-problem 7. Entertainment panel In evaluation of this sub-problem, selection criteria tables do not give any assistance. All the suggested functions are available on the market today. So, what kinds of functions that are included in the entertainment panel depend on how much money the customer wants to spend.

27

Sub-problem 8. Personal storage The locker is chosen as reference for this sub-problem. Selection criteria and evaluation of the solutions are listed in Table 6.6. A. Locker B. Drawer C. Storage compartment of fabric Table 6.6. Personal storage.

Selection criteria

A

B

C

Weight Size Helps in carrying the load Durability Lockable Already existing solution

0 0 0 0 0 0

0 0 - 0 0 0

+ + - - - 0


0 6 0

0 5 1

2 1 3


0 1

Yes

-1 2

No

-1 2

No Alternative A: Locker The locker can help to stabilize the cabin, is lockable and durable. Alternative B: Drawer The drawer can not help to stabilize the cabin and is not an as effective storage space as a locker. Alternative C: Storage compartment of fabric The storage made of fabric has a plus on size because it can be folded when no longer in use. But it can not support in carrying loads and the durability is less than for the locker. Furthermore, it can not be locked. With regard to Table 6.6 and the discussion above, the locker is chosen.

28

Sub-problem 9. Sound and light insulation on open part The curtain is chosen as reference for this sub-problem. Selection criteria and evaluation of the solutions are listed in Table 6.7. A. Curtain B. Adjustable screen Table 6.7. Sound and light insulation on open part.

Selection criteria

A

B

Weight Durability Complexity Already existing solution

0 0 0 0

- 0 - 0


0 4 0

0 2 2


0 1

Yes

-2 2

No Alternative A: Curtain A curtain is easy to use, has good insulation properties and is, further, compact when stored. Alternative B: Adjustable screen When employing the screen, a track must be mounted between the walls. This makes the screen more complex to provide for, and it is further heavier than the curtain. With regards to Table 6.7 and the discussion above the curtain is chosen.

29

7 Design and analyses of frames Here the three different frame types: frame with rectangular support, frame with crossing bars and frame with poles, as described under section 5.4.2, are analyzed systematically to determine which of the alternatives that is best suited for further development. The frame is modelled as one solid part, without respect to assembling/disassembling method. Each frame is given the same restriction of outer dimensions of 2124x770x625 mm (LxWxH). Pro Engineer and Ansys Workbench are used as analyses tools. The frames are modelled in Pro Engineer and exported to Ansys Workbench for a FEM analysis. The von Mises effective stress effσ according to equation (7.1) is calculated and plotted in Ansys Workbench for each frame type, and further used as dimensioning parameter in design of the frames with respect to the structural behavior.

[ ] 21213

223

212113333222211

233

222

211 333 σσσσσσσσσσσσσ +++−−−++=eff (7.1)

The stress components of equation (7.1) are defined in figure 7.1.

Figure 7.1. Definition of stress components on an infinitesimal volume element Each frame type is separately analyzed for static shock load, with an acceleration of 15g in three orthogonal directions. Static shock load is modelled by the Ansys Workbench routine as an acceleration load, working on all nodes of the structure. Because analyses shall be executed for three orthogonal directions, separate analyses corresponding to the three different directions must be carried out for each frame type. Shock load is, in reality, a transient load. In consultation with Structural department at Kockums AB a static shock load is applied because it leads to simpler calculations and the outcome of the analysis is more conservative than if applying transient loads.

30

The durability of the frames when a submarine longitudes and transverses 90 degrees with an acceleration of 1g, i.e. earth’s gravity, should also be analyzed. But two of the directions in the shock test coincide with the longitudinal and the transverse direction, respectively, for which the acceleration is 15 times larger. This makes the longitudinal respective transverse analysis unnecessary. The analysis is preformed for the worst case scenario, i.e. when the two cabins are attached to each other, and, then, together, attached to the accommodation platform. A person using each cabin is idealized as a mass of 100 kg, attached to the bottom of each frame. This is modelled in Ansys Workbench by loading the surfaces that belong to the bottom of the frame with the load of 15gx100 N. The cabin is clamped to the accommodation platform by the four keyhole attachments, and these are implemented in Ansys Workbench as boundary conditions. This is done by locking the nodes that belong to the surface where the keyhole attachments are located in all degrees of freedom. Material used is steel SS 355 with the following material properties: Density 3m/kg7850=ρ Modulus of elasticity 210=E MPa Yield strength 355=sσ MPa Fracture strength 630490 −=Bσ MPa Each frame is analyzed in Ansys Workbench, using solid tetrahedral elements of the second order. The tetrahedral elements consist of 10 nodes, where every node has three degrees of freedom.

7.1 Frame with rectangular support This frame type is made of 3 mm thick sheet metal as illustrated in figure 7.2. The mesh is also shown in figure 7.2. Number of elements used in the analysis is 12 758. The weight of the frame is 44 kg. In figure 7.3 the boundary conditions and the forces acting on the frame are shown together with the loading directions. The boundary conditions are marked “Fixed support”, the persons using the cabins are marked “Force” and “Force 2” and the body acceleration force is marked “Acceleration”.

Figure 7.2. Geometry and mesh of frame with rectangular support.

31

Figure 7.3. Boundary conditions and body forces.

The variation of the von Mises effective stress (7.1) from the shock load analysis in longitudinal-, transverse-, and vertical directions can be seen in figures 7.4, 7.5 and 7.6. Numerical singularities are found in the structure as extreme amplitudes of stress distributions and marked by red arrows in the figures 7.4, 7.5. In figure 7.6 the red arrow only marks where the highest stress appears. The singularities are, however ignored since they are products of modelling draw-backs. They arise from the model geometry in one node only, due to implementation of the boundary conditions and do not exist in reality. Below the maximum values of the von Mises effective stress are given for each direction, disregarding singularities: Longitudinal 180=effσ MPa Transverse 165=effσ MPa Vertical 185=effσ MPa

Vertical

Longitudinal

Transverse

32

Figure 7.4. Shock in longitudinal direction. Figure 7.5. Shock in transverse direction.

Figure 7.6. Shock in vertical direction.

33

7.2 Frame with crossing bars This frame type consists of 3 mm thick bottom made of sheet metal, four 50x30x3 mm profiles and 3 mm thick crossing bars made of sheet metal as illustrated in figure 7.7. The mesh is also shown in figure 7.7. Number of elements used in the analysis is 13 394. The weight of the frame is 38 kg. In figure 7.8 the boundary conditions and the forces acting on the frame are shown. The boundary conditions are marked “Fixed support”, the persons using the cabins are marked “Force” and “Force 2” and the body acceleration force is marked “Acceleration”.

Figure 7.7. Geometry and mesh of frame with crossing bars.


Bottom

Profile

Crossing bars

Profile

34

The variation of the von Mises effective stress from the shock test in longitudinal-, transverse-, and vertical directions can be seen in figures 7.9, 7.10 and 7.11. Here a singularity emerges in the shock test in transverse direction. Below the maximum values of the von Mises effective stress, extracted from figures 7.9, 7.10 and 7.11, are given for each load direction, stress values of singularities disregarded: Longitudinal 109=effσ MPa Transverse 187=effσ MPa Vertical 120=effσ MPa



35

7.3 Frame with poles This frame type consists of 3 mm thick bottom made of sheet metal and four 50x30x3 mm profiles as illustrated in figure 7.12.The mesh is also shown in figure 7.12. Number of elements used in the analysis is 12 332. The weight of the frame is 34 kg. In figure 7.13 the boundary conditions and the forces acting on the frame are shown. The boundary conditions are marked “Fixed support”, the persons using the cabins are marked “Force” and “Force 2” and the body acceleration force is marked “Acceleration”.

Figure 7.12. Geometry and mesh of frame with poles.


Bottom

Profile

36

The variation of the von Mises effective stress from the shock test in longitudinal-, transverse-, and vertical directions can be seen in figures 7.14, 7.15 and 7.16. Below the maximum values of the von Mises effective stress, extracted from figures 7.14, 7.15 and 7.16, are given for each direction: Longitudinal 373=effσ MPa Transverse 355=effσ MPa Vertical 124=effσ MPa



37

7.4 Reflections and discussion The analyses in this chapter have been performed to compare the frame structures and to decide on the best alternative. Therefore meshing of the frames was not so carefully done. Some of the elements have sharp angels and this leads to high aspect ratios. This results in that the stress levels for each shock test is only approximate. But the results are comparable and enough to determine which frame structure that has the best strength properties. During the analysis of the frame with rectangular support, extremes in the von Mises stress are found in individual nodes. These can be ignored since they are products of modelling draw-backs due to the boundary condition implementation and do not exist in reality. The frame with crossing bars gives the lowest stress levels out of the three frame types, assuming the same applied static chock load. It is 4 kg heavier than the frame with poles, but the maximum stress levels for the frame with poles are more than 2 times higher in two of the shock tests. The frame with rectangular support has maximum stress levels somewhere in between the other two, and its weight of 44 kg makes it the heaviest of all the here investigated frames. From these arguments the frame with crossing bars is chosen to be further developed. The investigated frame shape is only a basic concept and, thus, it may be advantageous to modify it so that all other solutions to the separate sub-problems can be included in the best possible way. In the analysis of the frame with crossing bars, large deflections of the crossing bars on the long side were discovered. The bars are made of sheet metal and in one of the directions in the shock test there is a compressive load on them. Because they are so long, together with that sheet metal is week in compression, large deflections occur. This phenomenon is known as buckling. To avoid buckling the sheet metal is replaced by a 30x20x2 mm rectangular profile, with a much higher buckling load. A short support, made of a 30x20x2 mm rectangular profile, is also added on the opposite long side where support was not present during the analysis, cf. figure 7.17.

Figure 7.17. Reinforced frame.

Long crossing bar

Short support

38

8 Presentation and analysis of the concept In this chapter the final solution to the different sub-problems is presented and assembled to the cabin. The final FEM analysis of the cabin is also presented in this chapter and is performed using Ansys.

8.1 Presentation of solutions to the sub-problems In each sub-problem focus has been on to minimize number of loose parts so that the cabin will be easily assembled/disassembled. As the cabin will hang from the accommodation platform and two persons should be able to carry it, effort has been made to find solutions that are light but still strong enough to carry all loads. 1. Assembling/Disassembling method As an assembling/disassembling method the hinge solution is chosen because the cabin is more compact and has less loose parts when disassembled with hinge solution than with the Ikea solution. It consists of three different parts according to the figure 8.1, for an exploded view see figure 8.2.

Figure 8.1. Hinge solution Figure 8.2. Hinge solution, exploded view The hinge is integrated with the rest of the cabin in such way that the green and red parts of the hinge are welded to the rectangular profiles, respectively, and connected with each other by the pin as illustrated in figure 8.3. The red and green parts are made of aluminium, and the pin is made of stainless steel.

Figure 8.3. The hinge integrated with the cabin

39

2. Frame According to the arguments discussed in chapter 7 the frame with crossing bars is chosen, and a model of this frame can been seen in figure 8.4. The bottom of the frame is manufactured by bending a sheet metal, while the vertical poles are standard profiles connected to each other the by hinge solution according to figure 8.3. Reinforcement on the short sides of frame is introduced by welding the crossing bars made of sheet metal. The FEM analysis described in chapter 7 further shows that the long side of the frame aimed at entering the cabin has to be reinforced by crossing bars made of rectangular profiles together with a short support. When calculating the weight of the cabin it is found that, if the frame is made of steel, the total weight will be around 90 kg. This is too heavy if two persons shall be able to carry it. Therefore the material of the frame is changed to aluminum. This saves 25 kg of weight on the frame with the present design. But because strength of aluminum is less than for steel the frame probably will have to be made of profiles with larger cross section, which will increase the weight somewhat.

Figure 8.4. Frame with crossing bars

In order to be able to fold the cabin the crossing bars on the long side needs to be taken away. This is done by welding an attachment, made of aluminium, between the long crossing bars and the vertical poles as illustrated in figure 8.5. The attachment consists of two main parts, where part 1 is welded to the end of the long crossing bars, see figure 8.6. On the vertical pole part 2 is attached so the long crossing bars can be mounted. Both parts 1 and 2 hold a hole, where a pin spring locks the attachment on place.

Figure 8.5. The attachment Figure 8.6. The attachment, exploded view

Part 2

Part 1

40

3. Wall The wall of the cabin is divided into one long section and two shorter sections. They are Paroc walls, as chosen in the concept selection chapter. Long wall The long section wall is placed on one of the long sides of the cabin. It is shown in figure 8.7 and the rectangular hole in the wall is cut out to make place for the entertainment panel. There are also three masked red sections in figure 8.7. These are tracks that are cut out in the wall, seen in the enlargement in figure 8.8. Spline joints, which are attached to the frame, are going to be inserted into the tracks in order to keep the wall in place.

Figure 8.7. Long wall

Figure 8.8. Spline joint track

Short wall The short wall is shown in figure 8.9. The two short walls are identical, and the red markings are tracks that are cut out in the wall. The tracks are identical to the tracks on the long wall and keep the walls in place.

Figure 8.9. Short wall

Spline joint track

Spline joint track

41

4. Attachment The attachment is a keyhole lock that was chosen in the concept selection chapter. It can be seen in figure 8.10 and consist of an upper part, a pin spring, a bolt and a plate. For an exploded view, see figure 8.11. The upper part is attached to the accommodation platform and to the bottom of the frame. The pin spring is attached on the upper part and works as lock to secure that the bolt stays in the right position. It also has a function so that it can stay in an unlocked position so people mounting the cabin do not need to hold the pin. The bolt will be inserted into the accommodation platform and is attached to the plate with a screw. The plate is welded to the frame. Stainless steel is used for the pin spring, the bolt and the upper part that is attached to the accommodation platform and the locker. Aluminium is used for the upper part that is attached to the frame, and for the plate. Stainless steel is used to minimize wear of the bolt, and it is no problem using stainless steel together with aluminium. It is not recommended to weld aluminium to steel, though. Therefore the bolt is attached with a screw to the aluminium plate. The same reasoning applies to the upper part that is welded to the accommodation platform and the locker, both made of steel.

Figure 8.10. Attachment. Figure 8.11. Attachment, exploded view.

5. Mattress The mattress from Dux is placed on the bottom of the frame and the shape of the mattress is shown in figure 8.12.

Figure 8.12. Mattress

Support to the mattress is given by a product called Alucore. Eight plates made of Alucore are placed across the bottom of the frame according to figure 8.13. Alucore is a very stiff and light material because of the special structure seen in figure 8.14. One Alucore plate that is used here is 685x130x10 mm and weights 4.7 2mkg .

Upper part

Pin spring

Bolt

Plate

42

Figure 8.13. Alucore placed in the frame

Figure 8.14. Alucore structure

6. Fall-out protection The straps that were chosen in the concept selection chapter will be fastened in front of the open part of the cabin according to figure 8.15, which is the same as figure 5.19 repeated here for convenience. Two straps made of flame protected fabric prevent a person from falling out of the cabin. They can also be used when the cabin is disassembled to secure loose parts.

Figure 8.15. Straps.

43

7. Entertainment panel The entertainment panel includes lamp, fan, TV, audio, network connection and buttons to control different functions. Figure 8.16 shows the entertainment panel with the parts marked.

Figure 8.16. Entertainment panel.

8. Personal storage space The personal storage space is made of 2 mm thick steel and has the dimensions 476x770x490 mm (LxWxH). With these dimensions the personal storage space can fit approximately 170 litres of equipment. It is shown in figure 8.17, and in 8.18 in an exploded view. This suggestion is only included to visualise how the personal storage space might look like. It is recommended that the personal storage space shall be bought pre-made and the attachments welded to the locker. There is need for some sort of distance between the cabin and the personal storage space to avoid noise when the two surfaces move relatively to each other.

Figure 8.17. Personal storage space. Figure 8.18. Personal storage space, exploded view.

Lamp TV

Fan Button

Audio

Network Connection

44

9. Sound and light insulation on open part On the open part there will be a curtain with light and sound reducing properties. It is shown in figure 8.19, which is the same figure as 5.26, repeated here for convenience. The curtain is made of flame protected fabric and is attached to a wire that is fastened between the walls.

Figure 8.19. Curtain.

8.2 Test of Concept For the final analysis the model of the cabin is simplified in the respect that only the frame of the cabin is modelled. This is because the frame is supposed to carry the entire load. The analyses here are preformed similar to the analyses in chapter 7. The frame is analyzed for a static shock load of 15 g in three orthogonal directions. The static shock load of 15g is modelled by the Ansys routine inertia load as an acceleration force applied on all nodes of the structure. The worst case scenario is considered here, when two cabins are attached to each other as illustrated in figure 8.20.

Figure 8.20. Two cabins attached to each other.

As mentioned in chapter 8.1, the cabin is rigidly attached to the accommodation platform by the four keyhole attachments. These are modelled in Anasys as boundary conditions by locking the nodes that belong to surfaces VB, VF, HB and HF, shown in figure 8.20, in all degrees of freedom. Because the frame geometry is very complex, the hinge solution is modelled in a simplified manner as shown in figure 8.21.

Simplified model of hinge

VB

VF

HB

HF

45

Figure 8.21. Simplified model of hinge The weight of all cabin components and a person lying in the bottom of the cabin is simulated by increasing the density of the frame so that the total weight of the frame becomes 160 kg. This is done in consultation with the Structural department at Kockums AB. When the analysis of the final frame is preformed, it is very important that the results are as correct as possible. That is why a shell model is created and analyzed in Ansys 11.0 instead of using Ansys Workbench 11.0. This is done in order to get a better mesh and avoid improper aspect ratio of the elements. A shell model is a copy of the geometry of the solid model but it lacks thickness. It is created in ProEngineer 2.0, saved as an iges-file and then imported in Ansys 11.0, where all FEM analysis is preformed. Elements used in the analysis are first order triangular shell elements called shell63. The element has three nodes and six degrees of freedom at each node: translations in the nodal x, y, and z directions and rotations about the nodal x, y, and z -axes. Higher order shell elements could not be used because of lack of computational power. The final frame type is evaluated with respect to the deflections and the effective von Mises stress distribution. All frame parts are made of aluminium SS 4212 with the material properties listed below: Density 3mkg2700=ρ Modulus of elasticity E 70= MPa Yield strength 245sσ = MPa Fracture strength 290Bσ = MPa

46

Test 1 The mesh of the shell model of the frame and the loading directions are shown in figure 8.22. Number of elements used in the analysis is 12 208 and the weight of the connected frames are 320 kg.

Figure 8.22. Shell model and its mesh

The distributions of the von Mises effective stress in MPa during the shock test in longitudinal-, transverse-, and vertical directions are illustrated in figures 8.23, 8.24 and 8.25 below:

Figure 8.23. Distribution of von Mises stress during shock test in longitudinal direction.

A

B

Longitudinal

Vertical

Transverse

47

Figure 8.24. Distribution of von Mises stress during shock test in transverse direction.

Figure 8.25. Distribution of von Mises stress during shock test in vertical direction.

C D

E

F

48

The maximum values of the von Mises effective stress and maximum deflections are extracted from figures 8.23, 8.24 and 8.25, for each direction and shown in Table 8.1: Table 8.1. Maximum values of the von Mises effective stress and deflections. For positions, see figures 8.23, 8.24 and 8.25

Shock load direction von Mises effective stress Maximum deflection Longitudinal MPa488eff =σ , A 139=xu mm, B

Transverse MPa268eff =σ ,C 41=yu mm, D

Vertical MPa219eff =σ , E 43=zu mm, F Conclusions The levels of the von Mises effective stress in longitudinal direction in the short crossing bars are up to 488 MPa, which is considerably higher than the yield strength of 245 MPa of aluminium. The high stress occurs because of buckling, described in the discussion in chapter 7. This applies to the long crossing bars before they where replaced by rectangular profiles. It can be seen in figure 8.24 that the buckling problem can be avoided by rectangular profiles instead of sheet metal. So, to avoid buckling, the short crossing bars are also replaced by 20x10x2 mm rectangular profiles. It also can be seen from Table 8.1 that during the shock in the transverse and the vertical directions large deflections in the L-profile on the long side of the frame are detected. To decrease these deflections a 30x30x5 mm profile is welded to the long profile to give extra support. This reinforced shell model of the frame is shown in figure 8.26 and is further on analyzed in test 2.

Figure 8.26. Reinforced shell model of the frame

Rectangular profiles

L-profile

49

Test 2 Here the reinforced frame according to figure 8.26 is analyzed and the mesh together with the loading directions can be seen in figure 8.27. Number of elements used in the analysis is 13 240 and the mass of the connected frames are 320 kg.

Figure 8.27. Mesh of reinforced shell model of the frame

The distributions of the von Mises effective stress, in MPa, within the material during the shock test in longitudinal-, transverse-, and vertical directions are illustrated in figures 8.28, 8.29 and 8.30 below:

Figure 8.28. Distribution of von Mises stress during shock test in longitudinal direction.

A

B

Vertical

Longitudinal

Transverse

50

Figure 8.29. Distribution of von Mises stress during shock test in transverse direction.

Figure 8.30. Distribution of von Mises stress during shock test in vertical direction.

C D

E F

51

In Table 8.2 the maximum values of the von Mises effective stress and maximum deflections are extracted from figures 8.28, 8.29 and 8.30, for each direction: Table 8.2 Maximum values of the von Mises effective stress and deflections. For positions, see figures 8.28, 8.29 and 8.30.

Shock load direction von Mises effective stress Maximum deflection Longitudinal MPa242eff =σ , A 14=xu mm, B

Transverse MPa256eff =σ , C 28=yu mm, D

Vertical MPa227eff =σ , E 30=zu mm, F Conclusion The effect of changing the short crossing bars to rectangular profiles for shock load in a longitudinal direction is shown in figure 8.28, and it can be seen that effective von Mises stress levels have decreased considerably. Deflections in longitudinal direction are also reduced, from 139 mm to 14 mm. Table 8.2 also shows that deflections in transverse respectively vertical directions are lower than the deflections for same directions in Table 8.1. When figures 8.24 and 8.29 of the von Mises effective stress distribution for shock load in transverse direction are compared, it can be seen that stress levels are reduced when the frame is reinforced with rectangular profiles and L-profiles. Maximum von Mises effective stress for shock in transverse direction is decreased somewhat as illustrated in figure 8.31, but is still above allowed yield strength.

Figure 8.31. Area of maximum von Mises effective stress for shock in transverse direction

For a shock load in vertical direction the overall distribution of von Mises effective stress is lowered when the frame is reinforced, as can be seen from figure 8.30. Maximum von Mises effective stress is somewhat higher when frame is reinforced as illustrated in figure 8.32, but is still below the yield strength. The highest stress is, further more, obtained at a position which is complicated to mesh and is therefore probably a numerical artifact.

52

Figure 8.32. Area of maximum von Mises effective stress for shock in vertical direction

As it can also be seen in figures 8.31 and 8.32, the maximum values of von Mises effective stress for the shock load in transverse and vertical directions are located in the same areas of the frame. This area represents the hinge that is used to assemble and disassemble the cabin, but in reality the hinge is much thicker and the bolt that connects the hinge is made of stainless steel with yield strength 640 MPa. These are the reasons why those maximum stress levels should not be taken into consideration. In order to check the convergence of the results an analysis with a finer mesh is preformed and the differences in results were found to be around five percent, which is fully acceptable.

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Test 3 In order to analyze the attachment in figure 8.10 the highest reaction forces and moments from the nodes belonging the surfaces where the boundary conditions are applied were considered. These quantities are: Reaction forces Reaction moments

57818−=xF N 471.67−=xM Nm 838.1906=yF N 578.24113=yM Nm

46.27217=zF N 674.206−=zM Nm These values are recorded during the shock load in the longitudinal direction on the surface VB, cf. figure 8.20, and are the sum of the reaction forces and moments from all nodes belonging to that surface. From the reaction forces and moments the normal and shear stresses are calculated according to formulas found in [11] for the smaller part of the bolt, used in the attachment as shown in figure 8.33.

Figure 8.33. Bolt used in attachment

From [11]:

bWM

AN+=σ (8.1)

ATµτ = (8.2)

with ( )4

2 3dWbπ

= , 4

2dA π= and

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=µ for the circular cross-section.

The resulting force in the x, y-plane is. 6461822 =+= yxxy FFF N

Also:

( )8.71

42578.13241

4

46.2721732 =+=+=

ddWM

AF

b

yz

ππσ MPa

54

1.79

4

6461834

2 ===dA

Fxy

πµτ MPa

The von Mises effective stress according to equation (7.1) is.

7.1541.79*38.71 22 =+=effσ MPa Conclusion Both xF and yF are located in the surface and together they form a resultant xyF according to figure 8.34.

Figure 8.34. Forces located in surface

xyF is used in equation (8.2) to calculate the shear stress. This method to calculate the shear

stress is conservative because equation (8.2) calculates the shear stress in centre of gravity, in this case in the middle of the circular cross-section, where the shear stress has its maximum value. When the normal stress is calculated, plane bending is assumed because yM is much larger than xM . The twisting moment zM is not taken into consideration because the bolt is able to rotate freely around its symmetry line. The bolt is made of stainless steel with yield strength of 640 MPa and the calculated von Mises effective stress is only 154.7 MPa.

xF

yF xyF

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Test 4 Here the hinge solution is analyzed with respect to the bearing pressure between hinge and support. The figures 8.35 and 8.36 show the geometry of the hinge. The analysis is preformed to ensure that the bolt of stainless steel holding the hinge does not tear on the rest of the material. This is done in following manner.

Figure 8.35. The geometry of the hinge Figure 8.36. Bearing pressure area

The loading force F is with kg the weight of two cabins attached to

each other and the weight of two persons lying in the bottom of each cabin.

N

The area A to distribute this force over is seen in figure 8.36 as shadowed and is

Finally MPa

Conclusion This analysis is conservative because the force used in the calculation of the pressure is one forth of the total shock load. In reality this force is much smaller. The hinge is made of aluminum with the yield stress 245 MPa, and the calculated pressure is well below this value.

A

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9. Final solution In this chapter the final specifications are set and the cabin is assembled from all the solutions to the sub-problems.

9.1 Set final specifications Now when the details of the cabin are ready and a durability test has been performed, the final specifications are ready to be set. They are seen in Table 9.1, where the row ‘Target value’ is the values from Table 4.1, repeated here for convenience. Table 9.1. List of metrics. D=demanded value, W=whished value Metric No Metric Value Target value Unit 1 Bed volume 2060x685x492 2000x700x600 (W) 3mm 2 Mattress thickness 100 70 (W) mm 3 Noise insulation - 30 (W) dB 4 Cabin volume 2124x770x625 2124x770x625 (D) 3mm 5 Weight of the cabin 59 <70 (W) kg 6 Static chock load 15g 15g (D) 2sm 7 Time to

assemble/disassemble - < 15 (W) min

8 Flame protected material Yes Yes (D) Yes/No 9 Storage compactability Yes Yes (D) Yes/No 10 Price - < 10 000 (W) SEK 11 Storage size (height) 200 < 200 (W) mm 12 Fall-out protection Yes Yes (D) Yes/No 13 Entertainment panel Yes Yes (W) Yes/No As seen in Table 9.1 there are no values for noise insulation, time to assemble/disassemble and price included. Since the cabin solution only is in the concept phase, noise insulation and time to assemble/disassemble can not be measured. Which production methods that are going to be used when producing the cabin have not been looked into. Therefore it is hard to predict a price for the cabin. But all solutions are designed, where it is possible, with standardized dimensions of goods.

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9.2 Presentation of final solution All solutions to the sub-problems that are described in chapter 8.1 are here assembled to one part. The cabin and some of its parts dimensions are showed in figure 9.1 and Table 9.2. For more detailed parts descriptions and dimensions see drawings in Appendix A

Figure 9.1. The cabin.

Table 9.2. Dimensions of cabin parts Name Quantity Dimension Unit 1 Vertical profiles 4 60x40x3 mm 2 Crossing bars on short side 2 20x10x2 mm 3 Crossing bars on long side 1 30x20x2 mm 4 Support on the open part 2 30x20x3 mm 5 Wall on the short side 2 644x577x19 mm 6 Wall on the long side 2 2038x577x19 mm 7 Mattress 2 2058x685x100 mm 8 Alucore plate 8 685x130x10 mm 9 Entertainment panel 1 400x200x30 mm

1

2

3

4

5

6 7

8 9

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10. Conclusions and remarks The main effort has been put on the design of the cabin in such a way that it is as light as possible without sacrificing strength. With a total weight of 59 kg it can be carried by two persons a short distance. If it is too heavy to be carried as one unit it can be carried in parts instead, i.e. the mattress and the walls are detachable from the frame. The cabin can be lifted to position for attaching it to the accommodation platform without having the mattress in it. This makes a total weight of 41 kg for the cabin. If it is still found too heavy to lift, some device must be developed to aid in lifting it. The results from Ansys show that the frame can withstand the shock load of 15 g. In the simplified model used for the analysis, the details, as attachments and bolts, are not included. But the analytical calculations show that these parts endure required stress levels. Further more, the cabin contains solutions for all requested features as to be quickly and easily assembled/ disassembled, have modular design, ventilation, noise level reduction, illumination and an entertainment panel with requested functions. Some of these functions, such as ventilation and noise level reduction, have however not been tested because the cabin only is in the concept phase.

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11. Future work As mentioned the main objective has been to make the basic design so that the cabin fulfils the required strength conditions. In the strength analyses, the weldings have not been considered. Strength analysis of the attachments of the long crossing bars and the Alucore boards that support the mattress have not been made, because no major stress is detected in those areas. This is only a concept design of the cabin and some functions that can be desirable to include have not been designed yet. For instance, when the cabin shall be carried in its disassembled form it would be convenient to have some sort of handles to hold on to. Which kind of curtain that shall give noise and light insulation needs to be determined. The parts that shall be in the entertainment panel also needs to be determined. Ventilation and noise reduction also need to be closely investigated, because this is not included in this Master Thesis.

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12. Summary This thesis is done for Kockums AB in Malmö and the objective is to design a single man cabin for a submarine. It shall be designed so that several single man cabins can be connected to each other. Since the cabin only will be used when the submarine has extra personnel on board, it is important that the cabin is quickly and easily assembled/ disassembled. It shall also fulfil the existing environmental requirements as regards ventilation, temperature, noise level and illumination. Beside the cabin, a small storage space for personal belongings shall be designed. If possible, some comfort functions, like access to audio and TV, should be included. As the cabin shall fulfil several functions, the design is divided into sub-problems that contain one or more functions. This is done to make it easier to design and evaluate a solution that fulfils each specific function. To find solutions for all the sub-problems, both a brainstorm session and a market search for already existing solutions are preformed. A first selection is made to sort out a few promising suggestions for further development. After being further investigated, a second selection is made. This time the selection is more careful, and a selection matrix is created where the suggestions are evaluated against specific, important functions that the sub-problem shall meet. One of the sub-problems is the design of the frame that is the load carrying structure. To evaluate the suggestions different frames are modelled as solids in Pro Engineer and the geometry exported to a FEM program for stress analysis. Ansys Workbench is used for this evaluation because it gives a quick overview of the stress levels. The frame that gave the lowest stress levels in the analysis is chosen for further development. The selected frame is modelled as a shell in Pro Engineer and the geometry exported to Ansys for an analysis to determine the structural dimensions needed. Ansys gives more detailed results than Ansys Workbench due to better control of meshing, and it can also deliver forces in the nodes. A shell model is used because the geometry is so thin that using solid element will give bad aspect ratios of the elements. The main effort has been put on the design of the cabin in such way that it is as light as possible without sacrificing strength. The results from Ansys show that the frame can withstand a shock load of 15 g. Further more the cabin contains solutions for all requested features such that it shall be quickly and easily assembled/ disassembled, have a modularity design and meet ventilation and noise level requirements, include illumination and contain an entertainment panel with requested functions. Some of these functions have not been tested within this concept phase.

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References [1] Pro Engineer Wildfire 2.0, Educational edition. [2] Ansys and Ansys Workbench 11.0, University Advanced. [3] Ulrich K.T & Eppinger S.D. (2003). Product Design and Development. [4] International Maritime Organization, International code for Application of Fire Test Procedures. [5] Berggren B., Eriksson E., Krajewski M., Maltesson L. & Viitasalo J. (2004). Temporary sleeping compartment. [6] http://www.paroc.com [7] http://www.promat.com [8] http://www.tempur.se [9] http://www.dux.se [10] http://www.aurora-marine.com [11] Sundström B. (1998). Handbok och formelsamling i hållfasthetslära.

http://www.paroc.com/

http://www.promat.com/

http://www.tempur.se/

http://www.dux.se/

http://www.aurora-marine.com/

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Appendix A- Drawings

single man sleeping cabin for submarines · submarines for future demands are designed to be...

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