Anders Buen

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About Anders Buen

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  • Birthday 06/03/1970

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    Oslo, Norway
  • Interests
    Violin-, Hardanger- fiddle-, room- and architectural acoustics.

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  1. Thanks Marty, good to know. Maybe the most important effect then.
  2. Thanks for the referene. I may write him. He has a nice website on his current activites.
  3. That was a brilliant estimation! Redistributing the numbers into displacement makes them even smaller. 0,02mm @ 25 Hz for the ship at 3mm/s. And about 1 micro m for the violin also at about 3 mm/s, equivalent to 1 g if the math is sound.
  4. Thanks for sharing your experience and thoughts, David! I know you have long experience as a restorer of fine violins as well as deep knowledge on humidity and wood issues. (Maybe even using this in the making, I guess, with those shaped maple backs). :-) Basically I think the museum representatives and their supporting experts do share your and Dons opinion on this. The humidity variations, shape changes and stress gradient variations are much more important than vibrations for degradation of the ships. For the most brittle alum treated "hard bread" like objects maybe the story is more complex? They do run research on this, but mainly on humidity and chemical changes I believe, indicating the same as above. Personally I am a bit surprised by our opinions on the effect of vibration. I thought it did play a role in crack formation in violins, especially around the wings and holes. But this is also a region where the wood will dry out faster or moist up faster and form tension and humidity gradients. The wings are also easily bent under tension, maybe inside cases while closing them, or similar. Just a misplaced thumb while lifting the instrument. I had the idea to count repairs like eyebrows and wing cleats in violins as repairs of vibration caused cracks, but I guess that is not the case.
  5. If we think about bending the wood until it cracks, I would believe the amplitude has to be pretty large before it happens. We hear the cracks form. Maybe a thinner sample can take more bending than a thicker? A violin plate can be bent quite a lot. A cm or even more. But with not perfectly squared samples the cracks may come at lower bending amplitudes. Brittle wood with cracks in them already may take less bending. I guess the humidity content might have an influence too. Drier samples probably crack easier. Letting the wood stay outdoor a couple days making it softer and more moist make it easier to cut with a knife or V-shaped tool.
  6. From the excavation: There are some cracks..
  7. Do any of you have an idea what the amplitudes typically are in a violin top, bridge top, or wings, while playing? Just for the reference: They go for a vibration limit of 1 mm/s for the ships and exhibition objects, with an upper limit of 3 mm/s I think. 1 mm/s is about what the ships do experience from walking activity in the museum. The strongest vibration modes are around 25 Hz, close to a resonance in the floor. The front dragon head swing forward and backward in that mode. The concrete floor is rather thin and supported by a fairly dense grid of thin concrete columns, so the floor span freely and are not on ground. The column "sing" beautifully when hit at the sides.
  8. Yes, the ships were not treated with alum. But the rest of the wooden objects did. I think. they have a research project on how to keep these alum treated objects best over time. Humidity cycling tests etc. The Wasa ship in Stockholm is alum treated, I believe. Looks like waxed wood from the outside. Some of the objects, at least one sledge, is mounted on a metal frame holding the pieces in place with almost invisible "fishlines". Some of the objects are partly in pieces, just mounted togheter. The wagon here is one example: The outside is intact while the inside of the wood is degraded by sulphuric acid, I believe. I think the ships are better off than these.
  9. Parts looks like burnt wood. The dried mud picture makes sense. The old boards here have been buried in mud, maybe being exposed to weter and not depending on the water level in the soil. The nails must be new.
  10. Yes, those are iron nails. Sure. And it is a lot of them, about 270 kg, I believe. The supports and their supporting bands shaped to follow each board almost perfectly are also iron. They weighed one of the ships the other year with force cells on each support. They know the moisture content variations in the ship from those weigh measurements and the climate logging they do. There are some cracked lines in the boat sides from the earth movement while they were buried in clay. I am not sure how they do hold these in shape. Maybe more nails and some supporting wood. I think they did bend some of the old boards too with steam like the new boards to get the exhibited shape. A copy did not work well at sea, so the exhibited ship shape is not correct for a sea worthy ship. One needs to sail them to figure out, I guess. We do have some copes that does sail.
  11. Another fun pic is this difference plot between laser lidar shape measurements 5 yrs apart. The museum claim that the difference seen here are creep. While my hypothesis is that this can be the difference between two humidity conditions, the latter measurement with a little higher avereage moisture content in the wood than the first. Blue is narrower (from us) and red hot is wider (towards us). It was presented in the Norwegian media in an attempt to speed up the decision to found a new museum building. I do not think there is an english page available.
  12. Just for the reference, some pics from the museum. Some of the upper boards is new wood, as you may see. From the excavation:
  13. Many thanks! Also for the book reference which looks relevant and like a good source. :-) I assume models for metal fatigue and cracks do follow a certain vibration amplitude and/or repeated bending adding up risk for crack formation. I did learn that metal do contain dislocations like spaghetti moving around and causing the work hardening whern they meet. The hardening can be fixed by glowing the metal. An iron thread can be bent enough to give in, after some work hardening. I can see that wood may not behave like that with its completely different cellular and long chain molecule structure. Although I would guess that rattling the egyptian mumies too much could lead to some parts coming loose. Paper, degraded cellulosis, or nature based textiles. Less stable structures than wood, even if the wood is old. I guess your prolonged vibration tests on a violin or wood samples did not change the wooden properties? If any cracks do appear it would probably affect the crossgrain properties most.
  14. And in which museum is it displayed? Thanks!