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Evaluation of contact definitions in a Finite Element model of the human cervical musculature
KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
2012 (English)Independent thesis Advanced level (degree of Master (One Year)), 20 credits / 30 HE creditsStudent thesisAlternative title
Icke-linjär och dynamisk modelering av nackens muskelatur. (Swedish)
Abstract [en]

The human neck is especially vulnerable to severe injuries why it is of interest to gain a better understanding of the injury mechanisms involved. A 3D Finite Element (FE) model including the geometry of the individual neck muscles has been developed at Kungliga Tekniska Högskolan (KTH) and gives the possibility to study the strains inside the muscles. However, in this model the muscles are only hindered to interpenetrate and can glide relative each other with a roughly estimated coefficient of friction. The focus of this thesis has been to modify the FE-model in order to model the connectivity on a physiological basis using methods available in the used FE-software. The main reason for this was to get a more realistic muscle displacement without separations that are present in the current model. The connective tissue surrounding and connecting the muscles was modeled with two principal approaches. The first was based on a combination of FE-contacts where the material properties were contacts. The other approach was based on a new element type called Smoothed Particle Hydrodynamics (SPH) elements in combination with FE-contacts. Both approaches showed that the structural stiffness did not increase significantly, but the strain levels where somewhat elevated. Stability issues arouse with deleted elements and negative element volumes causing the FE‐contact based approach to fail prematurely. The SPH‐based approach had fewest deleted elements and completed the simulation but increased the calculation time with approximately 50 %. It was concluded that the implementation of a connection between the muscles had a relatively low influence on the strains and kinematics of the neck and could be used to avoid muscle separations. The influence on stability of the model was however more evident and the most stable result increased the calculation time significantly.

Abstract [sv]

Den mänskliga nacken är en väldigt sårbar del av kroppen och det är därför av stort intresse att lära sig mer om de olika skademekanismerna inblandade. På Kungliga Tekniska Högskolan (KTH) har en 3D Finita Element (FE) modell utvecklats som inkluderar musklernas geometri och ger möjlighet att studera töjningarna inuti musklerna. Men i denna modell hindras musklerna endast från penetration och kan glida relativt varandra med en grovt uppskattad friktionskoefficient. I detta examensarbete har fokus legat på att modifiera FEM‐modellen för att modellera sammanbindningen mellan musklerna på en fysiologisk basis med hjälp av tillgängliga metoder i den använda FEM‐mjukvaran. Huvudmålet med detta var att uppnå mer realistiska muskelrörelser utan separationer som uppstår i den befintliga modellen.

Den bindvävnad som omger och binder samman musklerna modellerades med två grundstrategier. Den första var baserad på en kombination av FEM‐kontakter där materialegenskaperna kopplades till styvheten i FEM-kontakterna. Den andra strategin baserades på en ny elementtyp kallad Smoothed Particle Hydrodynamics (SPH) i kombination med FEM‐kontakter. Båda strategierna visade att den strukturella styvheten inte ökade med några signifikanta nivåer, men töjningsnivåerna ökade något mer. En del stabilitets problem uppstod som gav raderade element och negativa elementvolymer vilket ledde till att den FEM‐kontakt baserade strategin kraschade innan simuleringen slutförts. Den SPH‐baserade strategin resulterade i minst antal raderade element och slutförde simuleringen men ökade beräkningstiden med c.a. 50 %.

Det fastställdes att implementeringen av de nya metoderna hade en relativt liten påverkan på töjningar och kinematiken hos nacken och kan användas för att undvika muskelseparationer. Inverkan på stabiliteten hos modellen var dock mer märkbart och det stabilaste resultatet ökade beräkningstiden betydligt.

Place, publisher, year, edition, pages
2012. , 69 p.
National Category
Applied Mechanics
Identifiers
URN: urn:nbn:se:kth:diva-92631OAI: oai:DiVA.org:kth-92631DiVA: diva2:514154
Subject / course
Solid Mechanics
Uppsok
Technology
Supervisors
Examiners
Available from: 2016-01-27 Created: 2012-04-05 Last updated: 2016-01-27Bibliographically approved

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