Preserving the Vasa ship - https ://uu.diva-portal.org

http://www.diva-portal.org

This is the published version of a paper presented at 29th Annual International SICOMPconference on Manufacturing and Design of Composites, Luleå, 2018..

Citation for the original published paper:

Gamstedt, E K., Afshar, R., Ahlgren, A. (2018)Preserving the Vasa ship – Research and development of a new support structureIn:

N.B. When citing this work, cite the original published paper.

Permanent link to this version:http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-367292

Preserving the Vasa ship – Research and development of a support structure

Kristofer Gamstedt

Reza Afshar

Anders Ahlgren

Link to composites

• Wood is a polymer composite

Harrington, 1996

• Composites to support aging structures in cultural heritage

• Sustainable methods to extend lifetime of aging infrastructures

The 17th century warship ”Vasa” Sank on its maiden voyage 1628 Raised in 1961 1.3 millions visitors/year 1000 tonnes displacement Aging and creeping…

Background • 1964: Simple cradle with 8 supports

• 1990: Increasing deformations → more supports

• 2000-: Geodetic measurements: increasing deformation

Need to design an improved support system: Minimize the risk for collapse and achieve dimensional stability

”Support Vasa” Project, 2012-2017 and beyond

Uppsala: A. Vorobyev, R. Afshar, N. van Dijk, I. Hassel, I. Bjurhager, D. Wu, K. Gamstedt Students: F. Bommier, F. Garnier, N. Alavyoon, E. Luari SLU: G. Almkvist; Vasa museum: A. Ahlgren, E. + F. Hocker, L. Malmberg, M. Olofsson

Position measurements logged since year 2000

Measurements at 400 locations

Geodetic measurements

Creep strain measurements Average creep strain in elements

𝜀𝑖𝑗 =1

2

𝜕𝑢𝑖𝜕𝑥𝑗

+𝜕𝑢𝑗

𝜕𝑥𝑖

𝜀 = 𝑛𝑖𝜀𝑖𝑗𝑛𝑗

van Dijk, N., Gamstedt, E.K. and Bjurhager, I., Journal of Cultural Heritage, 17 (2016), 102-113.

Maximum principal strain, portside

(van Dijk et al., 2016)

Structure and geometry

Creep: material, beams, joints

FE simulations Validation: positions motion

Destructive mechanical characterization of Vasa oak Limited amounts of (in)valuable material

Vorobyev, A., van Dijk, N. P. and Gamstedt, E. K., “Orthotropic creep in polyethylene glycol impregnated archaeological oak from the Vasa ship”, Mechanics of Time-Dependent Materials, in press, 2018. DOI: 10.1007/s11043-018-9382-3.

Radial compression: ―――― Recent oak ―――― Vasa oak

2 ×

Static

Creep

Recent oak Vasa oak

Creep rate > 10 × for Vasa oak

Vorobyev, A., Arnould, O., Laux, D., Longo, R., van Dijk, N.P. and Gamstedt, E.K., Holzforschung, 70 (2015), 457-465.

Micromechanics: cell wall to clear wood

Young’s moduli Poisson’s ratios Shear moduli Viscous properties

Microfibril angle Density PEG/moisture

Wagner, L., Almkvist, G., Bader, T.K., Bjurhager, I., Rautkari, L. and Gamstedt E.K., “Influence of chemical degradation and polyethylene glycol on moisture-dependent cell wall properties of archaeological wooden objects: a case study of the Vasa shipwreck”, Wood Science and Technology, 50 (2016), 1103-1123.

Vorobyev, A., Almkvist, G., van Dijk, N.P. and Gamstedt, E.K., “Effects of density, polyethylene glycol treatment and moisture content on stiffness properties of waterlogged archaeological wood”, Holzforschung, ”, 71 (2017), 327-335.

Effects of the joints on the global deformation

Representative joint

(1) Global FE – Whole ship

(2) Detailed FE model – Joint

FE model of the ship

Mechanical testing of joints in a wall-section replica

Afshar, R., van Dijk, N.P., Bjurhager, I. and Gamstedt, E.K., “Comparison of experimental testing and finite element modelling of a replica of a section of the Vasa warship to identify the behaviour of structural joints”, Engineering Structures, 147 (2017), 62-76.

A big test sample… Construction of 10 tonnes replica

Mechanical testing at KTH Lightweight Structures

Testing of replica

Deformation: laser scanning, DSP

Vorobyev, A., Garnier, F., van Dijk, N. P., Hagman, O. and Gamstedt, E. K., “Evaluation of displacements in wooden replica of the hull part of the Vasa ship by means of a 3D laser scanner”, Digital Applications in Archaeology and Cultural Heritage, 2018

Rotational stiffness

Combined bending and compression

Fixed to the testing frame

Fixed to the testing frame

In-plane shear stiffness

Comparison of FE beam model with experimental results: Spring constants

Comparisons FEM-Experiments Spring constants

Ship geometry

Laser scanning

Segmentation

Splines along cross-sections

Division into cross-section and spline interpolation from frame model

Schematic of a cross-section

Creo model

(1)

(2)

(3)

(4)

(5)

Inner Outer

Different zone of the hull

Division into zones...

Top view

A cross-section: inner and outer planks

Division into zones

CAD and meshed FE model

• Solid shell: hull • Shell: decks,

aft side (gallery), beck

• Beam: decks, cloumns, masts, stiffeners

• Solid: keel • Spring: joint

stiffness

Meshed model (ANSYS) • Orthotropic solid shell elements

• Shell-beam-spring connections

• Loads from eigenweight and wiring

• Static and generalized to creep

From a validated global FE model, provide a tool to bring forth an optimized support structure Target: Relieve highly stressed regions, limit creep deformation

? ? ? ? ? ? ? ? ? ? ? ? ? ? ?

Concept #1 Current support

Concept #2

Internal support structure

Comparison of designs: • displacement • stress distribution • reaction forces at the

support locations

Concept #2

Concept 2 Current support

Port

Starboard Hull only Hull only

Concept 2 better than current support

Less displacement More symmetric

Concept 2 Concept 1

Port

Starboard Hull only Hull only

Concept 2 better than concept 1

Less displacement! Same trends for maximum stress and reaction loads

Not only Vasa… • Oseberg and Gokstad viking ships

• HMS Victory

• Cutty Sark

• SS Great Britain

• Fregatten Jylland

• Bremer Cog

• Mary Rose

• Roman ships of Pisa

• Wooden buildings…?

(Craig A. Shutt, 2009)

Experiences from concrete bridges

Final remarks • Composite mechanics useful in design support

structure of wooden objects (cultural heritage+) • A sensitivity study can show which parameters

are important than others • Next step: Verification by static tests • Future: Control climate to reduce deformation • Sustainable engineering: Not always build new,

also extend lifetime of old