Hello Nico! Bilingual report from the research project Support Vasa part II: Vasa's body language

Guest blogger Nico van Dijk from Delft, The Netherlands, postdoctoral researcher specialized in mechanics at Uppsala University and in the Support Vasa project. Here, Nico reports in his native language and English on his work on simulations of the Vasa that will aid in the design of a new support structure for the ship:

Vasa’s lichaamstaal

Ontmoeting met de Vasa

Iets meer dan twee jaar geleden wist ik niets van het oorlogsschip Vasa. Ik wist überhaupt niet zoveel van Zweden, hoewel Nederland, waar ik vandaan kom, helemaal niet zo ver weg ligt. Het is bijzonder dat iets kleins (of iets groots) je leven zo kan veranderen.

Na mijn promotie aan de TU Delft in Nederland was ik op zoek naar een mogelijkheid mijn academische loopbaan voort te zetten in een ander land. Na wat rondkijken vond ik een vacature bij de universiteit van Uppsala bij de Toegepaste Mechanica groep: Postdoctoral position for structural optimization of the support structure of the Vasa.

Ik werd uitgenodigd om bij de Vasa in Stockholm een kijkje te nemen. In mei 2012 stapte ik voor het eerst door de deuren van het Vasa museum. Hoewel ik al wel foto’s gezien had, was ik overdonderd door de ontzettende grootte van het schip. Het voelde alsof ik terug in de tijd keek.

Anders Ahlgren en Fred Hocker namen ons mee op een rondleiding door het museum en zelfs aan boord van het schip. We keken hoe het schip in elkaar zat en onderzochten, natuurlijk, de draagconstructie waar ik me in mijn onderzoek mee bezig zou gaan houden. Tijdens het bezoek aan het museum werd het voor me duidelijk dat het niet zomaar een academisch onderzoek zou zijn. Nee, een grote verantwoordelijkheid rustte op de schouders van zowel het onderzoeksteam als het personeel van het museum: het behouden van de Vasa voor de komende 1000 jaar. 

Vasa’s body language

Meeting the Vasa

A little over two years ago, I knew nothing of the Vasa. In fact, my knowledge of Sweden was very limited even though my home country The Netherlands is not very far away. It is amazing how small things (or big things) can change our lives.

After my PhD studies at Delft University of Technology in The Netherlands, I was looking for an opportunity to continue my academic career in another country. After some searching I found a vacancy at Uppsala University in the Applied Mechanics group: Postdoctoral position for structural optimization of the support structure of the Vasa.

I was invited to take a look at the Vasa ship in Stockholm. In May 2012 I first stepped through the doors of the Vasa museum. Even though I did see some pictures before that, I was amazed by the sheer size of the ship. It felt like looking back into the distant past.

Anders Ahlgren and Fred Hocker took us on a tour through the museum and even on board the ship. We looked at the construction of the ship and, of course, at the support structure that would be the subject of my research. During this visit to the museum it dawned on me that this was not going to be just another academic study. No, a large responsibility rested upon the shoulders of both the research team as well as the personnel at the museum: to preserve the Vasa for 1000 years to come.

 

De Vasa beweegt. The Vasa is moving.

De Vasa beweegt

De Vasa ligt al sinds 1988 ogenschijnlijk roerloos in het huidige Vasa museum. Elk jaar verplaatsen echter verschillende delen van het schip zich ten opzichte van elkaar. Bij het museum realiseren ze zich goed dat het schip beweegt en houden ze haar voortdurend in de gaten door middel van regelmatige metingen aan een groot aantal locaties op de romp. Deze metingen geven ons een idee hoe het schip zich aan het bewegen en deformeren is. We proberen de lichaamstaal van de Vasa te lezen.

De verzameling ribben met gelijke tussenruimten die de huidige draagconstructie vormen zijn verre van ideaal. Ze ondersteunen het schip niet waar dat het meest nodig is en kunnen zelfs de oorzaak zijn van sommige plaatselijke vervormingen in de romp van het schip. De ingenieurs bij het museum zijn voortdurend bezig de wiggen tussen de metalen ribben en de romp van het schip te controleren en te verstellen om deze plaatselijke vervormingen te minimaliseren. Het project “Support Vasa” is tot stand gekomen om deze vervormingen in het schip te onderzoeken en een verbeterde draagconstructie te ontwerpen.

The Vasa is moving

The Vasa ship has been residing in the current Vasa museum seemingly motionless since 1988. However, every year different parts of the ship are displaced a couple of millimeters. At the museum they are well aware that the ship is moving and constantly busy to keep an eye on her by means of regular measurements of a large number of points on the hull. These measurements give us an idea of how the ship is moving and deforming. We try to read the body language of the Vasa.

The set of equally spaced ribs that is now the support structure is far from ideal. It does not support the ship where it is most needed and may even cause some local deformations of the hull of the ship. Engineers at the museum are constantly checking and adjusting the wedges between the metal ribs and the hull of the ship to minimize these local deformations. The project “Support Vasa” was started to investigate the deformations of the Vasa and to design an improved support structure.

Verstelbare wiggen ondersteunen de Vasa. Adjustable wedges support the Vasa.

Vasa-eikenhout imiteren

Het is natuurlijk erg belangrijk om in de gaten te houden wat de Vasa ons op dit moment vertelt met haar bewegingen, maar we zouden ook graag willen weten wat er met haar gaat gebeuren in de toekomst. In deze moderne tijd proberen ingenieurs het gedrag van constructies zoals de Vasa te voorspellen met behulp van computermodellen. Deze modellen zijn natuurlijk pas nauwkeurig wanneer de daadwerkelijke eigenschappen van het materiaal worden gebruikt als input. Een simpel voorbeeld: Als we willen weten hoeveel een veer uitrekt als we er een gewicht aan hangen, dan moeten we de stijfheid en lengte van de veer weten en hoeveel gewicht we eraan hangen.

Op dezelfde manier moeten we de eigenschappen weten van het eikenhout dat gebruikt is om de Vasa te bouwen. Jammer genoeg is Vasa-eikenhout een erg complex materiaal; het heeft verschillende eigenschappen in verschillende richtingen (probeer maar eens hout in de verkeerde richting te spijten), op verschillende plekken (probeer maar eens hout te hakken bij een knot) en deze eigenschappen hangen af van de tijd, de temperatuur en vochtgehalte (hout snijden wordt makkelijker als je het nat maakt). Maar het is nog lastiger, want Vasa-eikenhout is niet ‘normaal’ hout, maar archeologisch (oud), doordrenkt (voorheen lag het onder water) and geïmpregneerd (behandeld om scheuren te voorkomen tijdens het drogen) wat allemaal invloed heeft op de eigenschappen.

Het eikenhout van de Vasa is een zo ingewikkeld materiaal dat de beste manier om alle eigenschappen te verkrijgen waarschijnlijk is om het te imiteren - er een computermodel van te maken. We weten veel over hoe Vasa-eikenhout eruit ziet tot in de microscopisch kleine details. Door van deze kennis  gebruik te maken zijn wij op dit moment bezig de (gemiddelde) eigenschappen van Vasa-eikenhout te reproduceren met verschillende modellen van de microstructuur.

Deze eigenschappen kunnen dan gebruikt worden om te voorspellen wat er gaat gebeuren met de Vasa en een draagconstructie te ontwerpen die precies voldoet aan haar behoeftes. Ons team van onderzoekers is hard aan het werk om te begrijpen wat de Vasa ons wil vertellen en zo te zorgen dat de volgende generaties ook de kans krijgen om terug te kijken in ons verre verleden.

We simuleren eikenhout van de Vasa. We simulate Vasa oak.

Imitating Vasa oak

Of course it is extremely important to keep track of what the Vasa is telling us with her movements right now, but we would also like to know what will happen to her in the future. In this modern age, engineers try to predict the behavior of structures such as the Vasa ship by creating computer models. Of course these models are only accurate when accurate properties of the material are used as input. A simple example: If we want to know how much a spring extends when we hang a weight from it, we need to know the stiffness and length of the spring and how much weight we hang from it.

In the same way, we need to know the properties of the oak wood that has been used to build the Vasa ship. Unfortunately, Vasa oak is a very complex material; it has different properties in different directions (try splitting wood in the wrong direction), in different places (try cutting wood where there is a knot) and depending on time, temperature and moisture (carving wood becomes easier when you make it wet). But it is even more difficult, since Vasa oak is not ‘normal’ wood, but archaeological (old), waterlogged (previously submersed in water) and impregnated (treated to avoid cracking during drying) which all affect its properties.

Vasa oak is so complex that probably the best way to obtain all necessary properties is to imitate it - to create a computer model. We know a lot about what Vasa oak looks like down to the microscopic scale. Using this knowledge, we are currently working on reproducing the (average) properties of Vasa oak with different models of its microstructure.  

These properties can then be used to predict what will happen to the Vasa ship and to design a support structure that is tailored specifically to her needs. Our team of researchers is hard at work to understand what the Vasa wants to tell us and ensure that the coming generations also have an opportunity to look back into our distant past.

 

Guest Post: An Investigation of Vasa's Human Remains

Diver holding a cranium during excavation

 

It is believed that around 30 people went down with Vasa when she sank. When the ship was raised and excavated in the 1960s, over 1,500 human bones were recorded and cataloged, and these bones are currently believed to represent 15 individuals. Unfortunately, some of these bones have lost their find numbers and therefore their find location. In some cases even the individual to which they belong has been lost as well. This has become the current crux of my research at the museum– sorting through the records and the bones. I started out with many hours spent in front of a computer looking at what is recorded in the online database. I then moved onto more hands-on work. I spent time down in the magazine getting acquainted with the individuals there, and then moved on to the individuals on display in the Face to Face exhibit.

I have been working under the guidance of the museum’s Director of Research, Fred Hocker, and every day for a couple of weeks we would remove one individual from display to be studied. On a typical day, we would head to the exhibit first thing in the morning, lift the glass from the individual display and carefully remove each bone, taking care to put each piece in archival boxes laced with tissue paper. This was the exciting bit, and it always attracted a crowd. Inevitably, someone would always ask, “Are they real?” The reply that they were, in fact, real, then drew one of two responses – a look of horror or an excited, “Can I touch them?” It seemed the children were especially keen to touch the bones, or perhaps they were just bold enough to ask.

Once the bones were removed and the display glass put back in place, we would take the individual back to the conservation workshop so I could spend the day with them. We don’t know the names of the people who died on the ship, but they have all been assigned names from the Swedish phonetic alphabet (Adam, Beata, Cesar, David, etc.). I try to refer to them by these names as often as I can because it helps me to remember that they are people rather than mere objects. As I examined the bones, I would find myself talking out loud to the person they belonged to. This had the combined effect of not only making me feel a bit crazy, but also further reminding me that these were once people, with whole lives, families, and friends of their own, not just a collection of artifacts in a museum. I generally spent only one day with each individual, so Fred and I would head back to the exhibit in the afternoon to return them to their display case. A crowd would once again form, often larger than in the morning, but just as curious and intrigued as the morning’s crowd had been. Now, I spend my days in front of a computer again sorting through all of the information I have gathered. Though not as exciting as working hands-on with the bones, it is just as important and will eventually help us to discover more about who these people really were.

Allison Miller is currently a graduate student in the Program in Maritime Studies at East Carolina University. She has joined us for a few weeks this summer to work with and study the skeletons found aboard Vasa. 

Hello Alexey! Bilingual report from the research project Support Vasa part I: Time dependent experiments

Guest blogger Alexey Vorobyev from Kazan, Russia, researcher on mechanical behaviour of archaeological wood in the Support Vasa project and PhD candidate in Applied Mechanics, Uppsala university, reports in his native language and English:

Эксперименты по ползучести археологической древесины в Музее Ваза.

Археологическая древесина корабля Ваза – материал со сложной внутренней структурой. Корабль пролежал на дне Стокгольмской гавани 333 года. После обнаружения и подъема корабля корпус Вазы был пропитан полиэтиленгликолем и высушен. Несомненно все эти модификации влияют на статическое поведение корпуса корабля.

The material Vasa is made of is very complex. Initially Vasa material was just oak and due to historical circumstances spent 333 years at the bottom of Stockholm harbour. After the ship was salvaged, Vasa was impregnated with polyethylene glycol and dried. All those modifications are undoubtedly affecting the mechanical response of the Vasa.

Археологическая древесина Ваза кубический образец. Vasa material cube sample.

Для прогнозирования деформаций и перемещений конструкции мы проводим эксперименты по ползучести древесины. Одна из особенностей этих экспериментов - это их зависимость от времени. В качестве образцов мы используем не только материал корабля, но и сухие образцы свежего дуба (Quercus Robur).

In order to predict deformations and displacements of the ship structure in the future, we are performing time dependent experiments with Vasa material. However it is not only archaeological material that is tested, we compare our results with reference material, which is a dried recent oak (Quercus Robur).

Весь эксперимент состоит из трех инсталяций. В первой мы замеряем изменение веса наших образцов в зависимости от времени и микроклимата в музее. Во второй мы замеряем ползучесть в планках из археологической древесины Ваза. Параметры прогиба, веса, толщины принимаются во внимание. Наконец в третьей инсталяции мы делаем упор на измерение ползучести под непосредственной нагрузкой в материале Ваза и свежего дуба для последующего сравнения. Нагрузка прикладывается на кубические образцы со стороной 25 мм в направлении древесных волокон.

Time dependent tests are consisting of three different installations. In the first we are measuring the change of weight of our samples with time, depending on museum climate. The second installation is measuring creep of planks. Here we are measuring parameters such as plank deflection, change in weight and in thickness with time and climate at the museum. The third installation is measuring deformation on Vasa wood and reference material. In detail, we are using cubic samples with a side of 25 mm and applying force in the longitudinal or axial direction.

Установка измерения ползучести в балках. Plank installation for measuring creep, with applied load.

 

Установка измерения ползучести в образцах обыкновенного дуба и материала Ваза. Rig for measuring creep in Vasa cubic samples under permanent load in axial direction. 

Результаты экспериментов предполагается использовать в качестве начальных параметров для общей статической модели поведения корпуса корабля под собственным весом. Мы надеемся, что текущая работа позволит нам понять, предсказать и избежать в будущем ненужных деформаций в корпусе корабля Ваза

The results of the experiments will be an input for a general mechanical model that will be used for prediction of the structural behavior of the ship.

We believe this will help us to predict, understand and avoid the unwanted deformations of the ship hull.

 Алексей Воробьев,

Казань, Российская Федерация

Докторант по направлению прикладная механика (Инженерная физика), Уппсальский Университет,

Специализация в области проектирования материалов и конструкций,

Тема проекта докторской диссертации: Исслелование статического и динамического поведения археологической древесины под действием нагрузки с течением времени (вязкоупругость, ползучесть).

Проект: ”Support Vasa”

                                                                                                                                                                                                                                       

Fotografering

Summer is kicking into high gear here in Stockholm, as evidenced by the lines stretching out and away down the sidewalk in front of the museum. Even from below in the magazines, through all the rebar and concrete of the excavation pontoon, there has been a noticable increase in the volume of foot traffic overhead. For the last few weeks, I've been keeping busy in the basement studio, photographing the tools. (And occasionally a few other fun things on request - see mystery object below)

 

Object photo of a small decorative animal

 

The goal is for the photos to look highly standardized; museum-style photographic documentation of artifacts requires a systematic and studied approach. For each object, we take six plan view shots (from all four sides, top and bottom - see example above) with a scaled ruler and the object number, two perspective views ("glamour shots" - see below) and finally any detail shots necessary. This adds up to a bare minimum of eight photographs in total per object, though usually more.

 

Perspective view of small animal figurine

Any guesses as to what sort of creature this may be? The missing face calls for some interpretation...


After processing, the objects float in clean white space, and the photos look straightforward and almost clinical. Simple, right?

 

Perspective view of small animal figurine

 

In reality, the process requires a fair amount of fussing and creative thinking, because there is so much variation in the objects themselves. It involves a lot of very careful object handling, some very delicate and considered supporting and propping up with slivers and wedges of white gum eraser, and lots of balancing off ladders and holding-of-breath to get clear shots with the least amount of lens distortion possible. Also plenty of cajoling and trickery to convince the lighting set up and external flashes to cooperate (it's somewhat advanced in years). I'm about two thirds of the way through photographing the roughly 230 or so charges in my care.

 

Taking photos of taking photos

A rare glimpse of the photographer in her natural habitat- shot of shooting shots above, courtesy of Irene!


As with all of this fiddly work though, time seems to pass quickly, and I enjoy the attention to detail it requires. I'm starting to see further connections between objects as I go through them one by one for a second time. It's heartening to follow along with catalog records and drawings done six months ago and realize how much I have learned about the collection since then in the process.