Mounting of Inner Support Structure on the Swedish Warship Vasa: Product Development

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Mounting of Inner Support Structure on the Swedish Warship Vasa

Product Development

Infästning av inre stödstruktur till regalskeppet Vasa Produktutveckling

Camilla Granbom

Faculty of Health, Science and Technology

Degree Project for Master of Science in Engineering, Mechanical Engineering 30 hp

Supervisor: Reza Karimi Examiner: Jens Bergström Date: 2020-06-16

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ABSTRACT

The master’s thesis is focused around the mounting of an inner support structure to the Swedish warship Vasa and was given by Camatec Industriteknik AB. The Swedish warship Vasa is one of the greatest national treasures of Sweden. The ship was built high and narrow, therefore a small gust of wind made her capsize during her maiden journey. Today it is the world’s best- preserved ship from the 17th century and has been on display for the public at the Vasa museum since the year 1990.

The purpose of the master’s thesis was to generate and evaluate concepts for the mounting of the inner support structure to the Swedish warship Vasa. The master’s thesis had the following goals:

• To generate and analyse possible concepts regarding the mounting.

• Final proposals of the mounting created in CAD.

• FEM calculations of the final proposals to ensure that they handle the load conditions properly.

The master’s thesis followed the methodical process of product development with the steps:

pilot study, concept generation, concept selection and concept evaluation.

Three concepts were selected for further analysis. Two concepts involved a timber tong around the hanging knees. One fastened in a present structure of the ship (concept Y2.1) and the other one attached clamping force created by a spring in the construction (concept Y2.2). The third concept was a metal sheet between the main wales at the outside of the ship (concept G5).

The concept Y2.1 was eliminated due to high local stress concentrations at the attachment in the ship. The concept Y2.2 showed some desirable features, including visual representation if tension was present. However, it was not ensured that the concept can keep the surface pressure below the maximum 0.15 MPa. Another uncertainty with the concept was the behaviour of the timber tongs if movement of the hull occurred. Therefore, the concept Y2.2 needs additional work before it can be continued or eliminated. The concept G5 handled the loading case without exceeding the required surface pressure. However, a decision whether the metal sheets would be to visible for visitors needs to be taken before continuing with or eliminate the concept.

In summary, the concepts need further analysing before a final concept selection can be done.

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SAMMANFATTNING

Examensarbetet har fokuserat på infästningen av en inre stödstrukturen till regalskeppet Vasa och har utförts tillsammans med Camatec Industriteknik AB. Vasaskeppet är idag en av Sveriges största nationalskatter. Skeppet byggdes högt och smalt, således fick en mild bris henne att kantra under sin jungfruresa. Det är idag världens mest bevarade skepp från 1600- talet och har funnits på utställning sen 1990.

Syftet med examensarbetet var att generera och utvärdera koncept för infästningen av den inre stödstrukturen till regalskeppet Vasa. Målen med examensarbetet var:

• Att generera och analysera möjliga koncept till infästningen.

• Modellera de valda koncepten i CAD.

• Utföra FEM- simuleringar på de valda koncepten för att säkerställa att lasterna fördelas rätt.

Examensarbetet följer produktutvecklingsprocessen och har behandlat följande steg: förstudie, konceptgenerering, konceptval samt konceptutvärdering.

Tre koncept valdes att tas vidare för djupare analys. Två koncept involverade en timmersax runt knäna på skeppet. Ett som fästes i skeppets befintliga struktur (koncept Y2.1) medans det andra fäste enbart med klämkraft som uppkom tack vare en fjäder i konstruktionen (koncept Y2.2).

Det tredje konceptet var en plåt mellan berghultarna på utsidan av skeppet (koncept G5).

Konceptet Y2.1 eliminerades på grund av de lokalt höga spänningskoncentrationer som uppkom. Konceptet Y2.2 visade upp önskvärda funktioner, såsom att visuellt påvisa drag. Dock är det inte säkerställt att konceptet genererar ett yttryck under det maximala trycket på 0.15 MPa. Ytterligare är timmersaxens beteende vid rörelse av skrovet osäkert. Således krävs fortsatt arbete med konceptet Y2.2 innan det kan tas vidare eller elimineras. Konceptet G5 hanterade lasterna utan att överskrida den maximala gränsen för yttrycket. Däremot måste ett beslut fattas, angående om plåtarna mellan berghultarna är för synlig eller inte, innan konceptet kan tas vidare eller elimineras.

Sammanfattningsvis behöver vidare analys av koncepten ske innan ett slutligt konceptval kan fattas.

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ACKNOWLEDGEMENTS

I would like to express my sincerest gratitude to my supervisor Michael Larsson at Camatec Industriteknik AB for his continuous support and help throughout the project. Additionally, I wish to thank the entire ‘Vasa project group’ at Camatec, for welcoming me and helping me with the project. I address a special thanks to Michael Olofsson for his enthusiastic help with my simulations in Ansys. Finally, I would like to give my appreciation to Reza Karimi for his input on my report. Thank you.

Camilla Granbom June 4^th, 2020

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Background

1.1 The Swedish warship Vasa

The Swedish warship Vasa is one of the greatest national treasures of Sweden. The ship is mainly constructed of heartwood from Pedunculate oak (Quercus robur) [1]. It is 69 m long, 50 m high (from keel to mainmast) and was launched in the year 1628 [2]. Her maiden journey lasted for only 1 300 metres due to a lack of stability in the construction. The part of the ship submerged under water was too small relative to the part above it. Hence a small gust of wind made it capsize. The ship quickly sank to the bottom of the sea, where it was forgotten for more than 300 years, until finally being salvaged in the year 1961. Today it is the world’s best- preserved ship from the 17th century and has been on display for the public at the Vasa museum since 1990. The goal is to preserve the Vasa for at least an additional 1000 years.

However, the carpenters of the Vasa museum have noted that the timber of the ship is being deformed at the hull [3]. Additionally, the ship is tilted to the portside and the angle increases over time. The ship is therefore in need of aligning as well as a new support structure.

The Vasa is currently mounted much like a sailboat, with keel blocks and support along the sides. The present support structure is from the 1960’s and was further improved in the 1990’s.

However, the current structure is inadequate at reducing the ongoing motion and deformation over time and consequently insufficient to secure a long-lasting preservation of the Swedish warship Vasa. Therefore, the Vasa ship needs a new support to secure long-term preservation.

As a result of gravity and deformation the hull is moving downward [3]. The new support structure therefore needs to distribute forces gently on the ship, to ensure that the hull maintains its shape. Consequently, the motion of the hull, creep and crack formation need to be controlled and minimized.

Additionally, studies have concluded that the ship would benefit of a new outer support along with a new ‘skeleton’ in form of an inner support system. The inner support structure is intended to stop the movement of the hull and guide forces from the ship to the outer support structure.

The inner support structure therefore needs to be mounted in the ship in order to lead forces from the ship to the outer support structure.

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2 1.1.1 Relevant anatomy of wooden ships

The hanging knees are a structure at the inside of the ship which in this thesis is seen as vertical beams on the inside [4]. The main wales are horizontal beams on the outside of the ship in a larger dimension than the surrounding ones.

1.2 Camatec Industriteknik AB

The master’s thesis project was performed at Camatec Industriteknik AB. Camatec is an engineering agency with offices in Karlstad, Västerås and Töcksfors. The company provides technical solutions for problems in various business areas, with the aim to design easy to manufacture products, which can hit the market rapidly.

1.3 Problem description

The master’s thesis is focused around the mounting of an inner support structure to the Vasa ship. Because the ship is composed of old timber the surface pressure needs to stay below 0.15 MPa in order to avoid deformation by creep [4]. The mounting should avoid unnecessarily invasive procedures such as drilling or nailing. In addition, the material in contact with the ship should not be harmful.

Another challenge for the mounting is the upcoming alignment of the ship, since it may create a different loading case than the present. The mounting is intended to prevent outwards and inwards movement of the hull. Moreover, the design of the mounting is not allowed to disturb the experience for the visitors.

1.4 Purpose and goals

The purpose of the master’s thesis was to generate and evaluate concepts for the mounting of an inner support structure to the Swedish warship Vasa.

The following goals that of the thesis were:

• To generate and analyse possible concepts regarding the mounting.

• Final proposals of the mounting created in CAD.

• FEM calculations of the final proposals to ensure that it handles the load conditions properly.

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1.5 Limitations and delimitations

The master’s thesis will be limited to 30 hp, which corresponds to one semester’s full-time work, hence time is the constraining currency.

Another limit around the master’s thesis is the confidential agreement of the project, which limits some details disclosed in the report. This includes the exact whereabouts of the mounting and specifics around it.

The work of the mounting is delimited by:

• The focus is on the mounting of an inner support structure to the ship, not of the functionality of the inner or outer support structure.

• No prototype of the mounting will be created.

• No experimental tests will be conducted of the final design of the mounting.

1.6 Product development

Product development is the methodical process of developing new products or improve existing ones [5]. In today’s climate of high consumption and fast exchange, companies need to continuously improve their products to stay current and keep the customers pleased. The process of product development is a well-established theoretical process, and a tool to ensure that the development and improvement of products are done methodically and efficiently.

During product development different steps is applied to ensure a successful process, and can generally be divided into the three steps listed below [5]:

• Problem analysis: Identifying the problem and its requirements.

• Synthesis: To identify solutions that meet the needs.

• To analyse the solutions: Evaluating the solutions according to the requirements.

The process is iterative. If none of the generated solutions meet the requirements step 1 and/or step 2 is repeated. The solution that best fulfil the needs is considered the final alternative. A general rule is that construction problems do not have only one right solution, but several.

Another important consideration to keep in mind is that the first solution rarely is the best one.

Typically, an idea that in the beginning sounds, absurd, can with some effort become the final alternative. It is therefore profitable that the synthesis phase has a quantity focus.

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Methodology

2.1 Pilot study

At the problem analysis phase, a pilot study was carried out to collect additional information about the project [6]. As a part of the pilot study, a project plan was created to further define the project.

The project plan answers the questions: ‘what is the problem to be solved?’, ‘How is the project is meant to be carried out?’ and ‘What time frame does the project have?’. As part of the project plan a work breakdown structure (WBS) and a time schedule in form of a Gantt-chart were created.

The WBS is a breakdown of the project to create an overview of the problem whilst identifying which activities needs to be carried out [6]. The activities identified in the WBS are the base of the Gantt-chart. In a Gantt-chart the activities are given a timeframe for when they need to be completed. This creates an outline of the dependency of activities. It identifies which activities that can be carried out simultaneously and the ones dependent on the completion of another activity.

2.2 Design specification

The design specification is also a part of the problem analysis [5]. Additional information other than the problem formulation is gathered and translated into requirements. The design specification is created to make the requirements for the product more concrete. This is done to further clarify the meaning of the project and to make sure that the full lifecycle of the product and all stakeholders are considered.

The requirements are produced by using Olsson’s requirement matrix, see Table 2.1.The requirements should be formulated in a measurable way, and each requirement are intended to be unique. The needs are then categorised into demands and wishes, where demands must be fulfilled, and wishes are more of a request. The wishes are then weighted from 1-5, where 5 represents the most important wishes, practically considered demands.

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5 Table 2.1: Olsson’s requirement matrix

Aspect

Lifecycle phase Process Environment Human Economy

Production 1.1 1.2 1.3 1.4

Manufacturing 2.1 2.2 2.3 2.4

Distribution 3.1 3.2 3.3 3.4

Consumption 4.1 4.2 4.3 4.4

Removal 5.1 5.2 5.3 5.4

A design specification has the following purpose [5]:

• Concretise the problem formulation further.

• Make sure that all aspects, lifecycle phases and stakeholders are considered.

• Create a unified vision for those committed to the project.

• Make the management of the project easier.

• Support and direct the search for solutions.

• Create a foundation for adjustment of requirements.

A well-produced design specification is expected to contribute with the following advantages:

• Shorter development time, due to less adjustments.

• Reduced development cost.

• Better quality and thus more competitive products.

• Transmit knowledge to the next generation of products.

2.3 Concept generation

In the concept generation phase creativity is an important tool. The concept generation phase is part of the synthesis step [5]. The aim of the concept generation is to produce ideas, which meet the requirements of the design specification. Models and methodical work support the creative processes.

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6 The following steps implemented a systematic search for solutions:

1. Reformulate the problem in a broader, more abstract and solution independent form.

2. Do a function analyse to divide the function of the product into subfunctions.

3. Search for solutions to the subfunctions.

4. Combine solutions for subfunctions into total solutions.

5. Gather the potentially acceptable total solutions.

2.3.1 Reformulating the problem description

The purpose of the reformulation is to find more universally acceptable ideas from a wider perspective, instead of problem specific solutions obtained from a restricted problem description [5]. This is done by reformulating the functional requirements from the design specification in a more abstract way. The reformulations are then combined to create a broader and more abstract formulation of the problem.

2.3.2 Functional analysis

The aim of the functional analyse is to set up a structure of functions that the product is intended to carry out [5]. The basis of the functional analysis is the reformulation of the functional requirements done in the previous step. The result is a functional structure where the complex total function of the product is divided to simpler subfunctions. The intention is to find sub- solutions that fulfils the needs of each subfunction. An advantage of the functional analyse is that it is generally easier to find solutions for the subfunctions than for the complex total function.

2.3.3 Creative methods

In the concept generation phase, creativity is an important tool. As a creative method brainwriting was used to generate a significant number of concepts. A session was conducted with a group of participants from Camatec. The group was composed of a variety of engineers with little to no prior background information of the project. The participants were chosen to be of different experience levels and from different fields to gain a wide diversity of perspectives.

At the beginning of the brainwriting a small presentation with some background information of the problem was given. The problem formulation ‘How should a mounting between an inner support structure and the Vasa ship be constructed?’ was stated. The participants were also presented with the following restrictions:

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• The surface pressure is not allowed to exceed the maximum surface pressure.

• The mounting should be adjustable.

• After the assembly or an adjustment, a fastening of the mounting should be possible.

• At the interface there should be room for a deformable material.

• There should be room for an eventual extra support structure at the mounting.

• It should be possible to place a sensor device on the mounting.

During the brainwriting each participant were given a sheet of paper [7]. For the first five minutes the ambition was to individually come up with ideas and communicate them onto the sheet in any way; drawing, by text or another preferred way. After five minutes, the papers were shifted one step. The participants then got five more minutes to either integrate the former person’s ideas or ignore them and create new additional ideas. The exercise was continued until the worksheets has circled a whole lap.

2.3.4 Creating concepts

To create concepts the generated solutions to the subfunctions was combined into total solutions by the help of a morphological matrix [5]. It is done in the following stages:

1. Put subfunctions and their corresponding part solutions into a morphologic matrix 2. Create total solutions by drawing polygons in the matrix

3. Distinguish total solutions which fulfils all demands in the design specification and have geometrically and physically compatible part solutions

4. Remove the obviously unreasonable total solutions

The procedure of combining subfunctions to total solutions can be seen in Figure 2.1.

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Subfunction Subfunction solution

Function 1 Solution 1 Solution 2 Solution 3 Solution 4 Function 2 Solution 5 Solution 6 Solution 7 Solution 8 Function 3 Solution 9 Solution 10 Solution 11 Solution 12 Function 4 Solution 13 Solution 14 Solution 15 Solution 16

Figure 2.1: How to combine solutions in a morphological matrix [5].

2.4 Concept evaluation and selection

Evaluation of the generated concepts is achieved by analysing each concept on their quality relative the demands and wishes in the design specification [5]. The selection is then based on a comparison between the results to decide which concept has the best quality. This may seem straightforward, nevertheless it is related to the following difficulties:

• The quality of a solution is affected by several properties.

• Various properties have dissimilar significance.

• Various stakeholders value properties differently.

• There is generally insufficient information of the concepts when a decision needs to be made.

To ensure a systematically approach to evaluate the quality of the concepts the process is executed in the following steps, which is illustrated in Figure 2.2 [5].

1. Eliminate concepts that does not fulfil the demands.

2. Concept screening with an elimination matrix.

3. Concept scoring with a weighted relative decision matrix.

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9 Figure 2.2: The evaluation process according to Ulrich and Eppinger. [5]

2.4.1 Concept screening

The concept screening process starts parallel with the concept generation phase [5]. Concepts are eliminated before the evaluation begins, based on not fulfilling the demands for the total solution. The basis of the evaluation is to make sure that the concept:

• Solves the main problem

• Fulfils the demands in the design specification

• Are realizable

• Are within the cost range

• Are safe and ergonomic

• Suits the company

The concepts which meets the requirements presented above are continued in the process.

Moreover, concepts which require additional information are also continued for further evaluation [5]. As a support for this initial evaluation an elimination matrix is used, see in Table 2.2.

Elimination of bad concepts

Decision matrix Elimination matrix

Evaluation Search for solutions

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10 Table 2.2: Elimination matrix according to Pahl and Beitz [5]

Elimination matrix for: Elimination requirements:

Concept Solves the main problem Fulfils all demands Realizable Within the cost range Safe and ergonomic Suits the company Enough information

(+) Yes (–) No

(?) Requires more info Decision:

(+) Complete concept (–) Eliminate concept (?) Search for additional info

Comments Decision

1 + + + + + + + +

2 + + – –

3 + + ? + + + + ?

4 5 6

Every requirement is considered for each concept [5]. If a requirement is fulfilled a (+) is put in the box. If more information about a concept is needed for a requirement a (?) is put in the box. If the requirement is not fulfilled a (–) is put in the box. After the evaluation of requirements, a decision whether the concept should be completed, eliminated or if a search for more information is needed, is taken. When a concept is completed, it directly moves on to the next evaluation process and is marked with (+). A concept where a search for additional information required is marked with (?). Eliminated concepts are marked with (–) and are removed from the process.

2.4.2 Concept scoring

The next step of the evaluation process is the weighted relative decision matrix [5]. It has the purpose to rank concepts based on requirements from the design specification. Concepts that does not meet the requirements in an agreeable way are eliminated. However, combining the existing concepts in this step could lead to newer promising alternatives.

In the weighted relative decision matrix, the selection is based on the relative comparison between the concepts. Therefore, it is important to consider the following factors [5]:

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• The requirements are based on the demands and wishes of the design specification.

• Cover all relevant aspects, however the focus should be on the critical main problem.

• Formulate a maximum of 15-20 requirements.

• Combine related requirements if needed.

Additionally, the weighted relative decision matrix considers the weight factor for each requirement. The matrix can be seen in Table 2.3.

Table 2.3: The weighted relative decision matrix according to Pugh [5]

Requirement Concept

1 (ref) 2 3 4

Wish A (w = 5)

D A T U M

– – 0

Wish B (w = 4) 0 – +

Wish C (w = 3) – 0 +

Demand D (w = 5) – + 0

Wish F (w = 3) – – –

Sum + 0 5 7

Sum 0 1 1 1

Sum – 16 12 3

Net value 0 –16 –7 +4

Ranking 2 4 3 1

Development Yes No No Yes

The requirements along with their weight factor and the alternative concepts are shown in the matrix [5]. A reference concept (DATUM) is chosen. Any of the concepts can be the reference, however generally a well-known concept such as the current one is chosen. Each concept is then evaluated and scored according to the reference concept.

At every requirement a decision must be made whether the concept fulfils the requirement better than (+), as good as (0) or worse than (–) the reference concept [5].

The result of the comparison (+, 0, –) is placed in the corresponding box in the matrix. The weight factor is multiplied with the result of the comparison (+, 0, –) then a summation of the result is done. A net value and ranking are then computed based on the results of the summation.

A decision of which concept to proceed with is then made based on the relation between the net values and ranking.

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12 Before next evaluation, existing concepts must be analysed in order to explore the possibility of new better concepts generated by:

• Modifying already strong concepts to eliminate drawbacks.

• Combining concepts with different advantages to create solutions with several positive assessments.

After the assessment, a new matrix is created with the highest ranked concept as a reference.

Selected concepts, which proceeded the previous screening, are placed in a new matrix, along with any new concepts. The iterative process with the weighted relative decision matrix is continued until a final decision has been made [5].

2.5 Product design and calculations

A more detailed design and construction of the concepts which are chosen for further evaluation are specified in CAD, with the help of the software Creo 5. However, a completely detailed construction is not performed. The CAD-model is used to further develop the concepts and to analyse the arising surface pressures with the use of the FEM-simulation software Ansys. To obtain stresses at critical parts of the mounting calculations with Equation 2-1 was performed.

𝜎 =

^𝐹

𝐴 (2-1)

where, A – the area

F – the applied force σ – the obtained stress.

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Results

In this chapter some results have been censored due to confidentiality. This limits the disclosure about the exact whereabouts and specific details of the mounting.

3.1 Pilot study

The pilot study resulted in a project plan. The following results were generated by the project plan:

• A clear view of the problem definition, purpose and goals.

• A WBS of the planned activities.

• A time plan in form of a Gantt-chart.

The WBS and Gantt-chart can be seen in Appendix A (Figure A.1 and Figure A.2 respectively).

3.2 Design specification

The design specification resulted in a list of demands and wishes, which can be seen in Table 3.1 with the following labels; demands (D), wishes (W), functional requests (F) and limiting requests (L).

The cell number corresponds to the cells in Olsson’s requirement matrix, see Table 2.1.

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14 Table 3.1: Table over the list of requirements

Require nr.

Cell Requirements Demand = D

Wish = W

Fnc. = F Lim. = L 1 1.1 The surface pressure does not exceed 0.15

MPa

D L

2 1.1 The design follows Eurocode 3 D L

3 1.2 The materials are environmentally friendly W, 3 L 4 2.3 The parts have low weight, construction

inside the ship should be possible

W, 3 L

5 2.4 Production cost do not exceed x SEK W, 3 L

6 3.2 Minimally invasive procedures in the ship D L 7 4.1 Carry loads from the ship to the inner

support structure

D F

8 4.1 Fastens the ship D F

9 4.1 Fastens the inner support structure D F

10 4.1 The mounting can be adjusted, if the ship behaves different over time

D F

11 4.1 The mounting can be fixed after adjustment D F 12 4.1 At the interface between ship and mounting

there is space for additional material which deforms before the ship

D F

13 4.1 Mounting of additional structure is possible, if more support is needed over

time

W, 4 F

14 4.2 The materials do not damage the ship D L

15 4.3 The mounting does not affect the experience for the visitors

W, 5 L

16 5.1 Easy to exchange, in case of fracture, dismantling should be easy

D L

17 5.1 The material at the interface between mounting and ship is easy to exchange

D L

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3.3 Concept generation

The brainwriting session resulted in several concepts, these are listed and explained below. In Figure 3.1 – 3.9 visualizations of some concepts can be seen. Numerous concepts are attached in a present structure of the ship, this is not further explained due to confidentiality. The concepts that were eliminated in Table 3.2 are listed and explained in Appendix B.

1. Plates on the outside of the hanging knees mounted in a present structure of the ship and a horizontal plate between the knees.

Figure 3.1: Illustration of concept 1.

2. Clamp with two contact areas around the hanging knees.

3. Clamp with three contact areas around the hanging knees.

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16 4. Plates on the outside of the hanging knees mounted in a present structure of the ship and a horizontal plate between the knees. Clamp with several contact areas (like spider legs) around the hanging knees.

5. Timber tongs around the hanging knee. The pressure around the knee increases the more the tongs are pulled out.

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17 6. Sheet of metal on the front of the hanging knee, attached by a present structure of the ship.

7. Sheet of metal between the hanging knees, attached by a present structure of the ship.

8. One Christmas tree stand like structure inside the ship attached by stretching out and securing the legs.

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18 9. Two Christmas tree stand like structures inside the ship attached by stretching out and

securing the legs in a present structure of the ship.

10. Metal sheet between the main wales on the outside of the ship.

11. Bike tyre: a steel rim and closest to the ship a rubber “tyre” with air pumped into it.

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19 The concepts that generated in the creative phase were sorted into an elimination matrix where a first elimination of unreasonable concepts was done, which can be seen in Table 3.2.

Table 3.2: First elimination of concepts by an elimination matrix

Elimination matrix for: Elimination requirements:

Concept Solves the main problem Fulfils all demands Realizable Within the price range Safe and ergonomic Suits the company Enough information

(+) Yes (–) No

(?) Requires more info Decision:

(+) Complete concept (–) Eliminate concept (?) Search for additional info

Comments Decision

1 + ? + + + + ? Might exceed 0.15 MPa in

tension ?

2 + ? + + + + ? Might exceed 0.15 MPa ?

3 + ? + + + + ? Might exceed 0.15 MPa ?

4 + ? + ? + + ? Might exceed 0.15 MPa

and/or price range ?

5 + ? + + + + ? Might exceed 0.15 MPa ?

tension ?

8 + ? + + + + ? Difficulties if tension arises ?

10 + ? + + + + ? Visible from the outside ?

12 + + – –

13 + + – –

14 + – –

15 + – –

16 + – –

17 + – –

18 + – –

19 + – –

20 + – –

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20 Those concepts which required additional information for more accurate assessment were placed for further evaluation. The subfunctions of these concepts were sorted into a morphological matrix. This can be seen in Table 3.3. The subfunction is a result of the functional analysis.

Table 3.3: Morphological matrix over subfunctions and sub-solution alternative

Subfunction Sub-solution alternative

Increase area Christmas tree

stand Metal sheet Spider legs Length

adjustment Spring Turnbuckle Hydraulic

Attachment to

the ship Clamp

A present structure of the

ship

Screw Timber tongs

Placement in the

ship Knee Between knees Between main

wales

A present structure of the

ship

The work with the morphological matrix resulted in numerous concepts sorted in colour categories below. Many of the concepts can also be varied by length adjustment however, it is not done in this study.

Blue:

B1. Clamp with two contact areas around the knee.

B2. Clamp with three contact areas around the knee.

B3. Clamp with several (spider legs) contact areas around the knee.

B4. Clamp around the knee with a supportive metal sheet closest to the knee.

B5. Clamp with several (spider legs) contact areas around the knee, with a supportive metal sheet closest to the knee.

B6. Timber tongs around the knee. The pressure around the knee increases the more the tongs are pulled out.

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21 Green:

G1. Metal sheet between the main wales, attached in a present structure of the ship.

G2. Plates on the outside of the knees and metal plate horizontal between. Attached in a present structure of the ship.

G3. Bent metal sheet between the knees, attached in a present structure of the ship.

G4. Bent metal sheet at the front of the knees, attached in a present structure of the ship.

G5. Metal sheet between the main wales attached in a present structure of the ship, pressure plates at the inside of the ship attached to the inner support structure.

G6. One Christmas tree stand like structure inside the ship attached by stretching out and securing the legs in a present structure of the ship.

G7. Two Christmas tree stand like structure inside the ship attached by stretching out and securing the legs in a present structure of the ship.

Yellow:

Y1. Attachment by a present structure of the ship and clamp around the knees and metal plate horizontal between knees.

Y2. Attachment by a present structure of the ship and timber tongs around the knee. The pressure around the knee increases the more the tongs are pulled out.

Red:

R1. A steel rim and closest to the ship a rubber “tyre” with air pumped into it to attach it by pressure.

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3.4 Concept selection

A concept selection was performed with help of weighted relative decision matrices. The matrices can be seen below in Table 3.4 – 3.7.

Table 3.4: Weighted relative decision matrix of the concepts B1-B6

B1 B2 B3 B4 B5 B6

Minimizes surface pressure (w = 5)

D A T U M

+ + + + +

Distributes forces

evenly (w = 5) 0 0 + + 0

Low weight (w =

3) – – – – +

Low cost (w = 3) – – – – 0

Additional

structure (w = 4) 0 0 0 0 0

Do not disturb

visitors (w = 5) 0 0 0 0 0

Easy to dismantle

(w = 5) 0 0 – – 0

Easy to exchange interface material (w = 5)

0 0 – – +

Adjustable structure (w = 5)

0 + 0 0 +

Sum + 5 10 10 10 18

Sum 0 6 5 3 3 6

Sum – 6 6 16 16 0

Net value 0 –6 4 –6 –6 18

Ranking 2 4 3 4 4 1

Development No No No No No Yes

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23 Table 3.5: Weighted relative decision matrix of the concepts G1-G7

G1 G2 G3 G4 G5 G6 G7

D A T U M

0 0 0 + – –

Distributes forces evenly (w

= 5)

0 0 0 + – –

Low weight (w

= 3) 0 0 0 – 0 0

Low cost (w = 3) – – – – – –

Additional

structure (w = 4) + + + + + +

Do not disturb

visitors (w = 5) + + + 0 + +

Easy to dismantle (w = 5)

0 0 0 0 0 0

Easy to exchange interface material (w = 5)

0 0 0 0 0 0

Adjustable structure (w = 5)

0 0 0 0 + +

Sum + 9 9 9 14 14 14

Sum 0 6 6 6 4 3 3

Sum – 3 3 3 6 13 13

Net value 0 6 6 6 8 1 1

Ranking 7 2 2 2 1 5 5

Development No No No No Yes No No

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24 Table 3.6: Weighted relative decision matrix of the concepts Y1, Y2 and R1

Y1 Y2 R1

D A T U M

+ +

Distributes forces evenly (w = 5) 0 +

Low weight (w = 3) + –

Low cost (w = 3) 0 –

Additional structure (w = 4) 0 –

Do not disturb visitors (w = 5) 0 0

Easy to dismantle

(w = 5) 0 –

Easy to exchange interface material

(w = 5)

+ 0

Adjustable structure

(w = 5) + 0

Sum + 18 10

Sum 0 4 3

Sum – 0 15

Net value 0 18 –5

Ranking 2 1 3

Development Yes Yes No

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25 Table 3.7: Weighted relative decision matrix of the developed concepts Y1, Y2, G5 and B6

Y1 Y2 G5 B6

D A T U M

+ + –

Distributes forces evenly

(w = 5) 0 + –

Low weight (w = 3) + – +

Low cost (w = 3) 0 + +

Additional structure (w =

4) 0 + –

Do not disturb visitors (w

= 5) 0 – 0

Easy to dismantle

(w = 5) 0 0 0

Easy to exchange interface material

(w = 5)

+ – +

Adjustable structure

(w = 5) + + +

Sum + 18 22 16

Sum 0 4 1 2

Sum – 0 13 14

Net value 0 18 9 2

Ranking 3 1 2 4

Development No Yes Yes No

The concepts Y2 and G5 scored highest and were therefore chosen for further development.

This is done by specifying their design and construction in CAD.

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26

3.5 Product design and calculations

The concepts Y2 and G5 received the highest score in the evaluation and were then continued for further development.

3.5.1 Concept Y2

The concept Y2 was modelled in CAD. It is based on the principle of timber tongs. The timber tongs are placed on the inside of the ship in a structure called hanging knees. If the tongs are elongated the clamping force around the knee increases. This is intended to stop the movement of the hull.

During the evaluation of concept design and construction the concept Y2 got divided into two concepts. Y2.1 where the timber tong is attached by a present structure of the ship and Y2.2 where the timber tong is attached by an initial clamping force due to a spring in the construction.

The two concepts can be seen Figure 3.10 and Figure 3.11 respectively. The divide was implemented because the attachment in a present structure of the ship may lead to high stresses locally.

Figure 3.10: Concept Y2.1, timber tongs attached by a present structure of the ship.

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27 Calculations based on Equation 2-1 were computed to investigate the obtained stresses in concept Y2.1. When applying the force F and area A, the surface pressure of 6 MPa was calculated. The result greatly exceeds the maximally allowed surface pressure σmax = 0.15 MPa. Hence, concept Y2.1 was eliminated.

Figure 3.11: Concept Y2.2, timber tongs attached by initial clamping force created by springs, the yellow lines represent the springs.

In Figure 3.11 the pressure plates in front of the knees are fixed by turnbuckles, which can be adjusted to the appropriate length, connected to the inner support structure. The pressure plates are intended to stop the hull from moving inwards.

Figure 3.12 and Figure 3.13 illustrates parts of the concept Y2.2 in more details.

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28

Figure 3.12: a) Arm of concept Y2.2 b) Tongs of concept Y2.2.

Figure 3.13: a) Contact material of Y2.2 b) Plate of Y2.2.

a) b)

a)

b)

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29 Simulations on the timber tongs was done in Ansys. Four situations were simulated:

Case 1: Short arms, fixed knee and a force in the timber tongs.

Case 2: Short arms, fixed tongs and a force in the knee.

Case 3: Long arms, fixed knee and a force in the timber tongs.

Case 4: Long arms, fixed timber tongs and a force in the knee.

For all simulations, the friction coefficient between the knee and the contact material was set to μ = 0.3. Case 1 and case 3 corresponds to a movement of the inner support structure, while case 2 and case 4 corresponds to a movement of the of the shipside.

In each case two steps were implemented, in the first step a spring with the force Fs was applied (see Figure 3.11 for location of the spring). In the second step the force F was applied at either the timber tongs or the knee, depending on which case.

In Figure 3.14 and Figure 3.15 the short timber tongs and the long timber tongs are presented.

The arm length for the short timber tong is 300 mm for the tongs and 350 for the arm, which results in a total arm length of 650 mm. For the long timber tongs, the matching lengths are 800 mm respective 1000 mm which gives a total arm length of 1800 mm.

Figure 3.16 and Figure 3.17 illustrates the equivalent von Mises stress for case 1 and case 2, with F = 1000 N and Fs = 10 000 N in the spring. Figure 3.18 and Figure 3.19 presents the equivalent von Mises stress for case 3 and case 4 with F = 6000 N and Fs = 100 N in the spring.

In Figure 3.20 – 3.23 the simulations of contact pressure in the contact interface is shown for case 1 – case 4. The images show both plates (one on each side of the knee) of the timber tongs for each case. Note that the patterns for case 1 and case 3 are similar while case 2 and case 4 correspond to each other. This is due to the similarities considered in boundary condition between these cases. In Figure 3.21 and Figure 3.23 when the force is applied in the knee, sliding of the plates seems to have occurred. This is visible since the maximum pressure is not concentrated in the centre, but instead the maximum pressure arises on one corner of the plates.

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30 Figure 3.14: Visual representation of the timber tongs with short arms simulated in Ansys.

Figure 3.15: Visual representation of the timber tongs with long arms simulated in Ansys.

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31 Figure 3.16: The equivalent stress in case 1, F = 1000 N in the tongs and Fs = 10 000 N in

the spring.

Figure 3.17: The equivalent stress in case 2, F = 1000 N in the knee and Fs = 10 000 N in the spring.

Figure 3.18: The equivalent stress in case 3, F = 6000 N in the tongs and Fs = 100 N in the spring.

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32 Figure 3.19: The equivalent stress in case 4, F = 6000 N in the knee and Fs = 100 N in the

spring.

Figure 3.20: The contact pressure for case 1, F = 1000 N in the tongs and Fs = 10 000 N in the spring.

Figure 3.21: The contact pressure for case 2, F = 1000 N in the knee and Fs = 10 000 N in the spring.

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33 Figure 3.22: The contact pressure for case 3, F = 6000 N in the knee and Fs = 100 N in the

spring.

Figure 3.23: The contact pressure for case 4, F = 6000 N in the knee and Fs = 100 N in the spring.

Table 3.8 and Table 3.9 summarize the results from the simulations of case 1 – case 4 can be seen. The tables present the reaction force after 1 and 2 seconds along with the contact pressure in the knee at various forces and spring forces. The spring force was chosen to generate sufficient initial clamp force for the timber tongs to hold on to the knee.

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34 Table 3.8: Table over the results of the simulations for case 1 and case 2

Boundary conditions

Spring force Fs

(N)

Force F (N)

Reaction force after 1 s

(N)

Contact pressure in

knee (MPa)

Case 1

10 000 500 4000 4690 0,11

10 000 1000 4000 5390 0,14

20 000 500 8000 8680 0,20

20 000 1000 8000 9390 0,23

Case 2

10 000 500 940 1205 5,2*10^–2

10 000 1000 940 1470 8,5*10^–2

20 000 500 1880 2150 7,3*10^–2

20 000 1000 1880 2410 0,10

Table 3.9: Table over the results of the simulations for case 3 and case 4

Boundary conditions

Spring force Fs

(N)

Force F (N)

(N)

Contact pressure in

knee (MPa)

Case 3

100 1000 97 3120 8,4*10^–2

100 6000 97 18 250 0,50

1000 1000 970 3990 9,5*10^–2

1000 6000 970 19 120 0,48

Case 4

100 1000 57 2010 8,2*10^–2

100 6000 57 11 760 0,49

1000 1000 570 2520 8,1*10^–2

1000 6000 570 12 170 0,45

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35 3.5.2 Concept G5

The concept G5 was modelled in CAD approximately, due to the simplicity of the concept. The concept idea is to place a steel sheet between the main wales on the outside of the ship. The steel sheet is, by a present structure, connected to the pressure plates placed on the inside of the ship.

The pressure plates are attached to the inner support structure. If an inward movement of the ship side occurs the pressure plates would prevent this movement. However, if an outward movement of the shipside would occur the steel sheets on the outside hinder this movement, because of the connection between the steel sheets and the inner support structure.

A part of the outside of the ship with steel sheets between the main wales were modelled in CAD, shown in Figure 3.24. It must be noted that neither the colours nor the dimensions in the pictures correspond to the actual situation.

The part of the concept regarding the connection with the inner support structure and the inside of the ship is not modelled, due to confidentiality. It was assumed that this part of the concept can handle the applied load successfully.

Figure 3.24: Concept G5 the steel sheets between the main wales at the outside of the ship.

Calculations with Equation 2-1 was computed on the metal sheets in concept G5 to ensure that the limit σmax = 0.15 MPa was not exceeded. The force F per metal sheet and area A was

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36 used. This resulted in a surface pressure significantly below the maximally allowed surface pressure.

In order to investigate the distribution of the loads, another simulation was performed on concept G5. The Ansys simulation was computed with F = 45 kN on each metal sheet, which is a larger load than the real case. It resulted in a surface pressure of σ = 0.14 MPa and is illustrated in Figure 3.25.

Figure 3.25: Concept G5 with F = 45 kN per steel sheet.

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37

Discussion

The process and results of the master’s thesis is discussed below. The project successfully fulfilled its purpose and goals. Possible concepts of the mounting were generated, modelled in CAD and evaluated by FEM.

4.1 Design specification and concept generation

The design specification is intended to consider all aspects, lifecycle phases and stakeholders of the product. However, the design specification created in this project may not achieve this completely. There are more needs to be found regarding the allowed size of the mounting as well as manufacturing. Although, being sufficient for this part of the project, the design specification may need an update for future work with the mounting.

In the brainwriting session discussion between the members occurred. The main benefit of brainwriting over brainstorming is that every idea is documented, not only the ideas of the loudest person. It can also be easier for shy individuals to communicate their ideas on a paper instead of to the whole group. However, a drawback is that it can be hard to motivate creativity in silence.

The morphological matrix presents an overview of possible sub-solutions and their combinations. During the work a restriction was set against concepts with screws. The screws are too invasive and were therefore eliminated as a sub-solution. Hence, concepts with screws are not presented since they did not satisfy all demands of the product specification.

However, screws were still sorted as a sub-solution in the morphological matrix as a documentation for the future. If more invasive procedures are necessary in the future the morphological matrix can be revisited and a new iterative process of product development can begin with the advantage of a head start.

The length variation for the different concepts was not considered in the morphological matrix due to the number of concepts that would arise if every length variation was considered for each concept. Additionally, an initial concept with turnbuckles fulfilled the length variations.

It was therefore deemed inefficient to develop an already working function, since turnbuckles can be implemented on the generated concepts. Although, agreeing with the previous discussion, the sub-solutions generated was still introduced in the matrix.

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4.2 Concept selection

Initially two rather different concepts were chosen in order to give Camatec a wide evaluation base for a final concept selection. The concepts for further evaluation were chosen so parts of them could be combined to create new concepts if the evaluation deemed it necessary or beneficial, this to ensure a wide selection for the company.

During the evaluation process the concept Y2 was divided into two separate sub-concepts. The third concept G5 was a bit disregarded by this, since the workload increased with the separation of Y2. Due to the similarities it was considered more important to evaluate Y2.1 and Y2.2 together and assess G5 further if time allowed it.

The requirements in the weighted decision matrices were chosen to take different parts of the mounting as well as different phases of its lifecycle in consideration. However, if other requirements had been chosen the outcome of the weighted decision matrices might have changed.

This is important to considerate when handling the matrices, and thus objectively choose requirements for the matrix. Additionally, it is important to correctly evaluate the result of the matrices. If two concepts get the same score it is important to examine the ratio of their minus, plus and zero signs and their meaning. For example, a concept with no zeros but with a variety of plus and minus may be better than a concept with only zeros.

The concepts G5 and Y2 scored highest in the weighted decision matrices. Hence, they were chosen for further evaluation. Another important factor in the choice were the concepts ability to solve the mounting in dissimilar ways.

An outcome of this is various pros and cons for the two concepts respectively. The visual representation that the timber tongs offer, if tension arises, is a great advantage for them compared to other concepts. However, they have higher stress levels than G5 and possibly does not distribute the pressure as effective.

Since the metal sheet is placed along with the ship, G5 distributes the pressure effective. It also provides an infinite number of attachment points, which makes it possible to attach additional support structures if necessary.

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4.3 Product design and current numbers

The concept Y2 was divided into two concepts due to possibly high local stress levels in an attachment of a present structure of the ship. Therefore, a separate concept of Y2 was developed to remove the attachment in the present structure from the mounting.

Calculation showed that, locally, at the attachment in the present structure the surface pressure was 6 MPa. The accepted stress level is 0.15 MPa. Although the timber tongs may reduce the stress, it is unlikely that the stress can be reduced to the accepted level. Therefore, Concept Y2.1 was eliminated and no further evaluation of the concept was performed.

In Table 3.8 the reaction force for case 1 and case 2 is presented. Table 3.9 presents the corresponding for case 3 and case 4. In the first step, after 1 s, only the force of the spring is applied. In the second step, after 2 s, both forces are applied. The exchange for the spring, how much applied force relative the reaction force at the plates, can be computed by the force from this first step. For case 1 the exchange is 0.4 and for case 2 it is 0.094. For case 3 the exchange is 0.97 and 0.57 for case 4. It is evident that the exchange is higher for the long-armed timber tongs than for the short-armed. This is due to an increase in lever that the long arms provide. It is also shows that the cases where a force is applied to the timber tongs have significantly higher exchange than the cases with a force applied to the knee. After the load in step 2 is applied the exchange increases. For case 1 the exchange goes from 0.4 to 1.39. For case 2 the exchange goes from 0.094 to 0.53. For case 3 the exchange goes from 0.97 to 3.02. For case 4 the exchange goes from 0.57 to 1.95. This indicates that the timber tongs are working as anticipated, since the exchange of force increases when the tongs are elongated. Hence, an elongation of the tongs results in a clamping force.

Although the clamping force increases when the short-armed timber tong is elongated, it requires a large spring force to generate sufficient clamping force initially. A spring force of 20 000 N could not hold on to the knee at the required maximum force. Whilst the long-armed timber tongs could withstand the maximum force with a spring force of 100 N. However, the long-armed construction is too large, and the arms would need to be thicker and wider to avoid buckling or breaking. An optimization of the arms therefore needs to be performed to understand weather it can fit whilst withstanding the required loading case.

The contact pressure for case 1 and case 3 display similar patterns in, see Figure 3.20 and Figure 3.22 respectively. Correspondingly, the pattern of contact pressure for case 2 and case 4 are alike, this is illustrated in Figure 3.21 and Figure 3.23 respectively. Evidently, the contact

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40 pressure is dependent on boundary conditions and not arm`s length. For case 2 and case 4 sliding are displayed, the maximum contact pressure is shifted from the middle to one side of the plate.

This behaviour is not presented for case 1 and case 3. However, in all four cases it is obvious that only a minority of the contact material’s area are in contact. Ideally, the total area would be in contact, which would result in a lower and more well-distributed contact pressure. The contact area would probably increase if the plate was stiffer, this could be done by making the steel plate thicker.

The contact pressure in the knee differs between case 1 and case 2. The contact pressure is higher for case 1 than for case 2. Sliding probably occurs in case 2, which results in lower pressure. The clamp force is probably just enough to hold on to the knee without letting it slip away. This behaviour is also presented in case 4 when both the applied loads, F and Fs, are low.

When, instead, a large force is applied to the knee the timber tong elongates more, which results in a higher surface pressure.

If Fs is high the initial clamping force between the knee and the contact material increases which gives less slip. The magnitude of the force required for the spring to give an enough clamping force for the timber tongs to hold on to the knee and elongate differs with arm length, due to the increase in lever related to increasing arm length.

The concept G5 was only modelled partly in CAD due to the simplicity of the concept and a lack of time, see Figure 3.24. The outside was modelled so calculations in Ansys could be carried out. The concept G5 can withstand the maximal load without exceeding the accepted surface pressure. A simulation with a higher load than the maximally expected was computed in Ansys, this is illustrated in Figure 3.25.

This resulted in a surface pressure below the maximally allowed. However, a steel sheet between the main wales may be to visible from the outside and thus disturb visitors. Therefore, the visibility must be investigated before the concept can be either continued or eliminated.

The inside of concept G5 was assumed to handle the loading case without exceeding the maximum surface pressure. However, this must be properly investigated to validate the assumption.

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41

Conclusions

In this project, concepts for the mounting of the inner support structure to the Swedish warship Vasa were generated and evaluated. The project fulfilled the goals set in the background; to generate concepts, model selected concepts and simulate the selected concepts to the mounting.

However, there are still work left before a final concept for the mounting can be chosen.

The concept Y.2.2 showed some desirable features, however it is still unclear if it can be implemented whilst keeping the surface pressure below 0.15 MPa. Another uncertainty with the concept is the behaviour of the timber tongs if the ship moves outwards. Therefore, the concept Y2.2 needs additional work before a final choice of concept can be done.

Concept G5 stays below the required surface pressure. However, a decision whether the metal sheets would be too visible needs to be taken before moving forward with the concept.

5.1 Future work

The future work required for the mounting of the inner support structure to the Vasa ship are:

• Further evaluate Y2.2 in Ansys to make sure it handles the loads properly.

• Take a decision about concept G5’s visibility for visitors.

• Do a final concept selection.

• Detailed construction of the final concept.

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42

References

[1] I. Bjurhager and et al., “State of Degradation in Archeological Oak from the 17th Century Vasa Ship: Substantial Strength Loss Correlates with Reduction in (Holo)Cellulose Molecular Weight,” Biomacromolecules, 6 July 2012.

[2] Vasamuseet, “Vasamuseet.se,” 16 November 2018. [Online]. Available:

https://www.vasamuseet.se/vasas-historia/tidslinje. [Accessed 24 January 2020].

[3] Vasamuseet, “Vasamuseet,” 15 January 2020. [Online]. Available:

https://www.vasamuseet.se/forskning/stottning. [Accessed 21 January 2020].

[4] M. Larsson, Private communication, 2020.

[5] H. Johannson and et al., Produktutveckling - effektiva metoder för konstruktion och design, Stockholm: Liber AB, 2004.

[6] M. Eriksson and J. Lilliesköld, Handbok för mindre projekt, Stockholm: Liber AB, 2004.

[7] M. Litcanu and et al., “Brain-Writing Vs. Brainstorming Case Study For Power

Engineering Education,” Procedia - Social and Behavioral Sciences, pp. 387-390, 2 June 2015.

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43

Appendices

Appendix A – WBS and Gantt-chart

Figure A.1: WBS of the project

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44 Figure A.2: Gantt-chart of the project

Mounting of Inner Support Structure on the Swedish Warship Vasa: Product Development