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## Re: [ontolog-forum] Theory of properties - stress tensor

 To: "[ontolog-forum]" David Leal Mon, 11 Jul 2011 09:16:06 +0100 <20110711081635.376F1138CC5@xxxxxxxxxxxxxxxxx>
 ```Dear Doug,    (01) >The answer to the first question would depend upon how the ontology >defined "quantity". So long as the ontology accepts matricies as >Quantities, then the tensor could be regarded as a quantity.    (02) But a stress tensor IS NOT A MATRIX !!!! :) It is a function, which can be encoded as a matrix, and for which an evaluation can be calculated by matrix operations. So are we happy that some quantities are functions?    (03) > > ... Is a von Mises's equivalent stress regarded as a "property" > of a stress tensor? > >Yes, it should be.    (04) With a very loose RDF-type meaning of "property", this use of the term is OK. But is we think of physical properties that are measurable aspects of physical objects, then the use of the term is not. A von Mises's equivalent stress may be a physical property of a body B at a point P, but it is surely not a physical property of the stress tensor. Instead it is derivable from the stress tensor by a mathematical operation. It so happens that this derived quantity has a physical meaning - it is a predictor of plastic flow.    (05) Best regards, David    (06) At 05:51 11/07/2011, doug foxvog wrote: >On Sun, July 10, 2011 16:47, David Leal said: > >[Question extracted from email]: > > > It is not clear to me, how a stress tensor would be included in an > > ontology for properties. Is a stress tensor regarded as a "quantity", > > like a mass? > >The answer to the first question would depend upon how the ontology >defined "quantity". So long as the ontology accepts matricies as >Quantities, then the tensor could be regarded as a quantity. > > > ... Is a von Mises's equivalent stress regarded as a > > "property" of a stress tensor? > >Yes, it should be. > >-- doug f > > > Dear Azamat and others, > > > > A theory of properties is interesting to me, and it may help to look > > in detail at a property which mentioned by Azamat. > > > > A small region of solid matter can have a property that is its stress > > tensor. A stress tensor is a single thing, and should not be thought > > of as a "compound property" or a "property of properties". The > > following points should be noted about a stress tensor: > > > > 1) Inevitably stress varies from position to position within a solid > > object. Sometimes when we choose a small enough neighbourhood of a > > point P within a solid object, the stress within that neighbourhood > > varies by only a small amount, so that we can say "Body B in the > > neighbourhood of point P has stress S". But if the neighbourhood is > > too small, then there is no concept of stress and instead only > > molecular bonds. Hence sometimes, we cannot say that "Body B in the > > neighbourhood of point P has stress S", because by the time we have > > shrunk the neighbourhood sufficiently to get a stress value that does > > not vary too much within the neighbourhood, the concept of stress has > > disappeared. This situation can occur at a crack tip - a location of > > particular interest to engineers. > > > > Density is also a property that can only apply to "Body B in the > > neighbourhood of a point P", if the neighbourhood is of a sufficient > > size. If some neighbourhoods have one molecule in them and others > > have two, then the variation of density from point to point is > > somewhat extreme. :) > > > > 2) A stress tensor can be thought of as bilinear function from pairs > > of direction vectors to force per unit area. The function can be > > encoded as a matrix of force per unit area values. However, this > > encoding is not the thing itself. The encoding depends upon the > > coordinate system used to express the directions. If the coordinate > > system is not Cartesian, then there are alternative co-variant and > > contra-variant matrix encodings. > > > > 3) A stress tensor has "invariants". These are quantities that are > > derived from the tensor, where the quantity is not dependent upon the > > coordinate system chosen to encode the stress tensor. An example is > > von Mises's equivalent stress. > > > > It is not clear to me, how a stress tensor would be included in an > > ontology for properties. Is a stress tensor regarded as a "quantity", > > like a mass? Is a von Mises's equivalent stress regarded as a > > "property" of a stress tensor? > > > > Best regards, > > David > > > > At 19:44 07/07/2011, AzamatAbdoullaev wrote: > >>AA: Again, we need to start from classification - what kinds of > >>properties exist: formal properties (attributes and predicates) or > >>substantial properties (real properties); intrinsic, mutual, > >>permanent, transient, emergent, simple, complex properties, or > >>compound properties as property of properties, like "stress tensor". > >>By default, in any sound classification, the property to be used is > >>a simple or basic property. The more basic property the more common > >>it is. A theory of properties is better to develop as a theory of > >>state space, an aggregate of properties. > > > > > > ============================================================ > > David Leal > > CAESAR Systems Limited > > registered office: 29 Somertrees Avenue, Lee, London SE12 0BS > > registered in England no. 2422371 > > tel: +44 (0)20 8857 1095 > > mob: +44 (0)77 0702 6926 > > e-mail: david.leal@xxxxxxxxxxxxxxxxxxx > > web site: http://www.caesarsystems.co.uk > > ============================================================ > > > > > > _________________________________________________________________ > > Message Archives: http://ontolog.cim3.net/forum/ontolog-forum/ > > Config Subscr: http://ontolog.cim3.net/mailman/listinfo/ontolog-forum/ > > Unsubscribe: mailto:ontolog-forum-leave@xxxxxxxxxxxxxxxx > > Shared Files: http://ontolog.cim3.net/file/ > > Community Wiki: http://ontolog.cim3.net/wiki/ > > To join: http://ontolog.cim3.net/cgi-bin/wiki.pl?WikiHomePage#nid1J > > > > > > >============================================================= >doug foxvog doug@xxxxxxxxxx http://ProgressiveAustin.org > >"I speak as an American to the leaders of my own nation. The great >initiative in this war is ours. The initiative to stop it must be ours." > - Dr. Martin Luther King Jr. >============================================================= > > >_________________________________________________________________ >Message Archives: http://ontolog.cim3.net/forum/ontolog-forum/ >Config Subscr: http://ontolog.cim3.net/mailman/listinfo/ontolog-forum/ >Unsubscribe: mailto:ontolog-forum-leave@xxxxxxxxxxxxxxxx >Shared Files: http://ontolog.cim3.net/file/ >Community Wiki: http://ontolog.cim3.net/wiki/ >To join: http://ontolog.cim3.net/cgi-bin/wiki.pl?WikiHomePage#nid1J >    (07) ============================================================ David Leal CAESAR Systems Limited registered office: 29 Somertrees Avenue, Lee, London SE12 0BS registered in England no. 2422371 tel: +44 (0)20 8857 1095 mob: +44 (0)77 0702 6926 e-mail: david.leal@xxxxxxxxxxxxxxxxxxx web site: http://www.caesarsystems.co.uk ============================================================    (08) _________________________________________________________________ Message Archives: http://ontolog.cim3.net/forum/ontolog-forum/ Config Subscr: http://ontolog.cim3.net/mailman/listinfo/ontolog-forum/ Unsubscribe: mailto:ontolog-forum-leave@xxxxxxxxxxxxxxxx Shared Files: http://ontolog.cim3.net/file/ Community Wiki: http://ontolog.cim3.net/wiki/ To join: http://ontolog.cim3.net/cgi-bin/wiki.pl?WikiHomePage#nid1J    (09) ```
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