@article {25513,
	title = {Contributions of prestrains, hyperelasticity, and muscle fiber activation on mitral valve systolic performance},
	journal = { International Journal for Numerical Methods in Biomedical Engineering},
	volume = {33},
	number = {4},
	year = {2017},
	publisher = {John Wiley \& Sons},
	abstract = {The present study addresses the contributions of prestrains and muscle fiber activation to the global response of the mitral valve during systole. A finite element model of a porcine mitral valve is created using anatomical measurements and 3D echocardiographic recordings. The passive behavior of the leaflets is modeled using a transversely isotropic hyperelastic constitutive model, and we assume orthotropic muscle activations in the anterior leaflet. A simple approach to incorporate prestrains in the mitral valve apparatus is used by expanding the mitral annulus before applying the ventricular pressure to the mitral leaflets. Several finite element analyses are run with or without muscle activation and with or without prestrains. The analysis results are compared at peak systole with the echocardiograpic recordings. The case where prestrains and activation are accounted for simultaneously is the most efficient to approach the physiological flat shape of the closed valve observed in the echocardiograpic measurements. These results suggest that the active components present in the mitral leaflets and the presence of prestrains contribute to the physiological deformations of the mitral valve at peak systole and that material models based on\&nbsp;in vitro\&nbsp;mechanical testing are not sufficient for numerical studies of the mitral apparatus.\&nbsp;},
	author = {Victorien Emile {Prot} and Bj{\o}rn H. {Skallerud}}
}
@article {25514,
	title = {Nanoindentation and finite element modelling of chitosan{\textendash}alginate multilayer coated hydrogels},
	journal = {Soft Matter},
	volume = {12},
	number = {35},
	year = {2017},
	pages = {7338-7349},
	publisher = {Royal Society of Chemestry},
	abstract = {Composite soft materials are used as compounds for determining the effects of mechanical cues on cell behavior and cell encapsulation and for controlling drug release. The appropriate composite soft materials are conventionally prepared by selective deposition of polymers at the surface of an ionic hydrogel. In the present study we address the impact of a mechanically stratified two-layer structure of these materials on their overall mechanical characterization by applying a combination of nanoindentation, confocal microscopy and finite element modelling. We prepare covalent cross-linked hydrogels based on acrylamide (AAM) and including an anionic group, and impregnate them using a multilayer deposition strategy of alternating exposure to cationic chitosan and anionic alginate. The thickness of the chitosan{\textendash}alginate layer on the hydrogels was determined to be 0.4 {\textpm} 0.05 μm for 4 bilayers, and 0.7 {\textpm} 0.1 μm for the 8 bilayer deposition procedure employing a fluorescently labelled chitosan and confocal microscopy. The force{\textendash}indentation data for the AAM gels were highly reproducible, whereas 77\% and 50\% of the force{\textendash}indentation data were reproducible following the 4 and 8 bilayer deposition. The main trends in the reproducible force{\textendash}distance data were found to yield an apparent increased Young{\textquoteright}s modulus after the deposition. Finite element modelling showed that adaption of a homogeneous Young{\textquoteright}s modulus for the specimens with deposited layers yields approximately three times too low stiffness compared to the estimate of the mechanical properties of the outer part in the two-layered mechanical model. The thickness of the multilayer region determined by confocal microscopy was used in the model. This study shows that the mechanical layered property needs to be included in the interpretation of the nanoindentation data when there is a significant mechanical contrast.},
	author = {Victorien Emile {Prot} and Bj{\o}rn Torger {Stokke} and Maurstad, Gjertrud and Sherstova, Tatyana and Bj{\o}rn H. {Skallerud}}
}
@article {24007,
	title = {Tension behaviour of HNBR and FKM elastomers for a wide range of temperatures},
	journal = {Journal of Polymer Testing},
	volume = {49},
	year = {2016},
	month = {02/2016},
	pages = {128-136},
	publisher = {Elsevier},
	abstract = {This article presents uniaxial tension tests of three different elastomer compounds commonly applied as seal materials in the oil and gas industry. The tests were performed at five different temperatures, ranging from\&nbsp;-20 to 150\&nbsp;{\textdegree}C. Optical measurements were used to ensure high quality stress{\textendash}strain data. The material samples were exposed to a cyclic deformation history, enabling the viscoelastic behaviour to be explored. A considerable effect of temperature changes was found, with a pronounced increase of stiffness and viscosity for the lowest temperatures. A dip in the stress{\textendash}strain curve was seen for one of the hydrogenated nitrile butadiene rubbers tested at low temperatures. Matrix-particle debonding simulations qualitatively described this stress dip. For the tests performed at the highest temperatures, a considerable number encountered material failure.},
	keywords = {Elastomers, Failure, Relaxation, Temperature effects, Uniaxial tension},
	doi = {10.1016/j.polymertesting.2015.11.017},
	author = {Ilseng, A. and Bj{\o}rn H. {Skallerud} and A. H. {Clausen}}
}
@inproceedings {24010,
	title = {Case study of elastomer seals using FEM},
	journal = {MekIT{\textquoteright}15  8th National Conference on Computational Mechanics, Trondheim, Norway},
	year = {2015},
	month = {11/2015},
	publisher = {International Center for Numerical Methods in Engineering (CIMNE)},
	address = {Barcelona, Spain},
	isbn = {97884944244-96},
	author = {Ilseng, A. and Bj{\o}rn H. {Skallerud} and Clausen, A.}
}
@misc {24013,
	title = {Contributions of residual strains, hyperelasticity models, and muscle fiber activation on mitral valve systolic performance},
	howpublished = {9. European Solid Mechanics Conference, Madrid, 2015},
	year = {2015},
	type = {Keynote},
	author = {Bj{\o}rn H. {Skallerud} and Victorien Emile {Prot}}
}
@book {24008,
	title = {Proceedings of the MekIT{\textquoteright}15 Eighth National Conference on Computational Mechanics.},
	year = {2015},
	publisher = {International Center for Numerical Methods in Engineering (CIMNE).},
	address = {Barcelona, Spain},
	isbn = {97884944244-96},
	editor = {Bj{\o}rn H. {Skallerud} and H. I. {Andersson}}
}
@inproceedings {24009,
	title = {Volumetric compression of HNBR and FKM elastomers},
	journal = {9. European Conference on Constitutive Models for Rubbers IX, Prague, Chech Republic, 2015},
	year = {2015},
	month = {10/2015},
	pages = {235-241},
	publisher = {CRC Press},
	isbn = {978-1-138-02873-9},
	doi = {10.1201/b18701-42},
	author = {Ilseng, A. and Bj{\o}rn H. {Skallerud} and A. H. {Clausen}}
}
@inproceedings {Simula.simula.2460,
	title = {Effect of Oscillatory Cerebrospinal Fluid Pressure on Fluid Movement in the Spinal Cord},
	journal = {Seventh National Conference on Computational Mechanics (MekIT{\textquoteright}13)},
	year = {2013},
	publisher = {Tapir Akademisk Forlag},
	type = {Conference},
	author = {St{\o}verud, Karen-Helene and Mardal, Kent-Andre and Hans Petter {Langtangen}},
	editor = {Bj{\o}rn H. {Skallerud} and Helge I. {Andersson}}
}
@article {Simula.simula.1828,
	title = {A Fast Strong Coupling Algorithm for the Partitioned Fluid-Structure Interaction Simulation of BMHVs},
	journal = {Computer Methods in Biomechanics and Biomedical Engineering},
	volume = {15},
	number = {12},
	year = {2013},
	pages = {1281-1312},
	publisher = {Elsevier},
	author = {Annerel, Sebastiaan and Degroote, Joris and Claessens, T. and Sigrid Kaarstad {Dahl} and Bj{\o}rn H. {Skallerud} and Leif Rune {Hellevik} and Van Ransbeeck, Peter and Seegers, P. and Verdonck, P. and Vierendeels, Jan}
}
@inproceedings {feinberg-mekit-2013,
	title = {Uncertainty Quantification of Diffusion in Layered Media by a New Method Based on Polynomial Chaos Expansion},
	journal = {Seventh National Conference on Computational Mechanics MekIT{\textquoteright}13},
	year = {2013},
	publisher = {Akademika Publishing},
	type = {Conference},
	abstract = {We address uncertainty quantification of diffusion processes in layered media, where the properties of the layers and their locations are uncertain and therefore described as stochastic quantities. The method of generalized polynomial chaos expansions is attractive for uncertain quantification in computational mechanics because of its fast convergence. However, the jumps associated with layered media slow down the convergence significantly. In this paper we describe a new technique to circumvent the convergence problem, however this technique requires an extension of the classical polynomial chaos method to handle dependent random variables. We develop a convenient computational way of incorporating dependent random variables in polynomial chaos expansions. Numerical investigations involving porous media flow through two layers demonstrate that the new method can effectively deal with stochastic permeabilities and stochastic location of the permeability jumps. Comparisons with existing methods show a significant increase in the convergence rate.},
	keywords = {Conference},
	author = {Feinberg, Jonathan and Hans Petter {Langtangen}},
	editor = {H. I. {Andersson} and Bj{\o}rn H. {Skallerud}}
}
@article {Simula.simula.2394,
	title = {Velocity Profiles in the Human Ductus Venosus: a Numerical Fluid Structure Interaction Study},
	journal = {Biomechanics and Modeling in Mechanobiology},
	volume = {12},
	number = {5},
	year = {2013},
	pages = {1019-1035},
	author = {Paul Roger {Leinan} and Degroote, Joris and Kiserud, Torvid and Bj{\o}rn H. {Skallerud} and Vierendeels, Jan and Leif Rune {Hellevik}}
}
@article {Simula.simula.1824,
	title = {Application of a Strong FSI Coupling Scheme for the Numerical Simulation of Bileaflet Mechanical Heart Valve Dynamics: Study of Wall Shear Stress on the Leaflets},
	journal = {Progress in Computational Fluid Dynamics},
	volume = {12},
	number = {2-3},
	year = {2012},
	pages = {68-80},
	author = {Annerel, Sebastiaan and Degroote, Joris and Vierendeels, Jan and Claessens, T. and Van Ransbeeck, Peter and Sigrid Kaarstad {Dahl} and Bj{\o}rn H. {Skallerud} and Leif Rune {Hellevik} and Segers, P. and Verdonck, P.}
}
@inproceedings {Simula.simula.1830,
	title = {Effects of an Orthogonal Contractile System in the Anterior Leaflet on the Systolic Mitral Valve Response: a Nonlinear Finite Element Study},
	journal = {10th Internation Symposium, Computational Methods in Biomechanics and Biomedical Engineering},
	year = {2012},
	type = {Conference},
	author = {Victorien Emile {Prot} and Bj{\o}rn H. {Skallerud}}
}
@article {Simula.simula.1822,
	title = {FSI-Simulation of Asymmetric Mitral Valve Dynamics During Diastolic Filling},
	journal = {Computer Methods in Biomechanics and Biomedical Engineering},
	volume = {15},
	number = {2},
	year = {2012},
	pages = {121-130},
	publisher = {Taylor \& Francis Online},
	author = {Sigrid Kaarstad {Dahl} and Vierendeels, Jan and Degroote, Joris and Annerel, Sebastiaan and Leif Rune {Hellevik} and Bj{\o}rn H. {Skallerud}}
}
@article {Simula.simula.1820,
	title = {Impact of Pulmonary Venous Locations on the Intra-Atrial Flow and Mitral Plane Velocity Profile},
	journal = {Cardiovascular Engineering and Technology},
	volume = {3},
	number = {3},
	year = {2012},
	pages = {2069-281},
	author = {Sigrid Kaarstad {Dahl} and Thomassen, E. and Leif Rune {Hellevik} and Bj{\o}rn H. {Skallerud}}
}
@article {Simula.simula.1826,
	title = {Muscle Fibers in the Human Mitral Valve: Extent of Smooth Muscle and Implications for Dynamic Modelling},
	journal = {APMIS},
	volume = {120},
	number = {6},
	year = {2012},
	pages = {484-494},
	author = {I. S. {Nordrum} and Bj{\o}rn H. {Skallerud}}
}
@inproceedings {Simula.simula.1214,
	title = {A Biomechanical Model for Human Umbilical Veins and Wharton{\textquoteright}s Jelly},
	journal = {8th International Conference on Computational Fluid Dynamics in the Oil \& Gas, Metallurgical and Process Industries},
	year = {2011},
	type = {Conference},
	author = {Paul Roger {Leinan} and Victorien Emile {Prot} and C. N. {van den Broek} and Kiserud, T. and Bj{\o}rn H. {Skallerud} and Leif Rune {Hellevik} and F. N. {van de Vosse}}
}
@inproceedings {Simula.simula.1030,
	title = {CBC.RANS - a New Flexible, Programmable Software Framework for Computational Fluid Dynamics},
	journal = {Sixth national conference on Computational Mechanics (MekIT{\textquoteright}11)},
	year = {2011},
	publisher = {Tapir Academic Press},
	type = {Conference},
	author = {Mortensen, Mikael and Hans Petter {Langtangen} and Myhre, J.},
	editor = {Bj{\o}rn H. {Skallerud} and H. I. {Andersson}}
}
@inproceedings {Simula.simula.638,
	title = {On the Complexity of Stationary Flow in Patient-Specific Aneurysms},
	journal = {MekIT{\textquoteright}11 Sixth national conference on Computational Mechanics},
	year = {2011},
	pages = {379-392},
	publisher = {tapir academic press},
	type = {Conference},
	abstract = {Summary Sound or bruits in the vasculatory system at the range of 1Hz-1kHz is known to occur, and frequency peaks at high frequencies are associated with sick blood vessels. The exact reason for these sounds are not known, but the sound may be generated by turbulence. Turbulence generated sound is typically associated with high frequencies but also with low energy levels. Unfortunately, most blood flow simulations are performed with space and time resolutions where rapid fluctuations typ- ically associated with non-laminar flow cannot be captured. Complex non-laminar flow and the subsequent oscillatory wall stresses can po- tentially be of importance in understanding aneurysm rupture through the local arterial wall response. To investigate the possible presence of complex non-laminar blood flow in intracranial aneurysms, we per- formed high resolution computational fluid dynamics (CFD) simulations for patient specific middle cerebral artery (MCA) aneurysms with sta- tionary inflow conditions. The current study confirms, through high resolution simulations, that complex oscillatory flow may occur in in- tracranial aneurysms. CFD practitioners should therefore be aware of the potentially strong demands to space-time computational resolution in blood flow simulations.},
	isbn = {978-82-519-2798-7},
	author = {Valen-Sendstad, Kristian and Mardal, Kent-Andre and Mortensen, Mikael and Bj{\o}rn Anders Petterson {Reif} and Hans Petter {Langtangen}},
	editor = {Bj{\o}rn H. {Skallerud} and Helge I. {Andersson}}
}
@inproceedings {Simula.simula.630,
	title = {The Effect of Varying Cross-Sectional Areas on Cerebrospinal Fluid Flow and Pressure in the Cervical Spine},
	journal = {MekIT{\textquoteright}11. Sixth national conference on Computational Mechanics},
	year = {2011},
	publisher = {Tapir Academic Press},
	type = {Conference},
	abstract = {The aim of this study was to determine CSF pressure and velocities in idealized geometries representing the stenosed spinal canal found in Chiari patients.We applied the Navier-Stokes equation to simulate the cyclic CSF flow during one cardiac cycle. Hereby, we have illuminated a well-established medical hypothesis for the relation between the Chiari I malformation and syringomyelia: namely that spinal cord cysts are caused by the so-called Venturi effect (predicted by Bernoulli\&$\#$39;s law) appearing in fluids that flow through obstructed areas. The results showed that the pressure gradient in geometries with obstructions comparable to Chiari patients may be 10 times as high as under normal flow conditions. The results also showed that the pressure gradients at the level of an obstruction may be twice as large as that predicted from steady flow or Bernoulli\&$\#$39;s law.},
	isbn = {978-82-519-2798-7},
	author = {St{\o}verud, Karen-Helene and Mardal, Kent-Andre and Hans Petter {Langtangen} and Haughton, Victor},
	editor = {Bj{\o}rn H. {Skallerud} and Andersson, H.I.}
}
@misc {Simula.simula.1184,
	title = {Finite Element Analysis of the Mitral Valve With Active Muscle Fibres},
	howpublished = {SIAM CSE Reno, Nevada, USA},
	year = {2011},
	author = {Victorien Emile {Prot} and Bj{\o}rn H. {Skallerud}}
}
@inproceedings {Simula.simula.1024,
	title = {Flow Patterns and Aerosol Dispersion Inside an Aerosol Test Chamber},
	journal = {Sixth national conference on Computational Mechanics (MekIT{\textquoteright}11)},
	year = {2011},
	publisher = {Tapir Academic Press},
	type = {1},
	author = {Hannibal E. {Fossum} and Bj{\o}rn Anders Petterson {Reif} and Skogan, Gunnar},
	editor = {Bj{\o}rn H. {Skallerud} and H. I. {Andersson}}
}
@inproceedings {Simula.simula.1032,
	title = {Large Eddy Simulations of the Release of Liquified Chlorine From a Pressurized Tank Into the Atmosphere},
	journal = {Sixth national conference on Computational Mechanics (MekIT{\textquoteright}11)},
	year = {2011},
	publisher = {Tapir Academic Press},
	type = {Conference},
	author = {Vik, Thomas and Bj{\o}rn Anders Petterson {Reif}},
	editor = {Bj{\o}rn H. {Skallerud} and H. I. {Andersson}}
}
@article {24487,
	title = {Modeling active muscle contraction in mitral valve leaflets during systole: A first approach},
	journal = {Biomechanics and Modeling in Mechanobiology},
	volume = {10},
	year = {2011},
	pages = {11-26},
	publisher = {Springer},
	author = {Bj{\o}rn H. {Skallerud} and Victorien Emile {Prot} and I. S. {Nordrum}}
}
@inproceedings {Simula.simula.1022,
	title = {Modeling the Dispersion and Transport of Aerosols Emitted From Industrial Facility During 2005 and 2008 Outbreaks of Legionnaire{\textquoteright}s Disease in Norway},
	journal = {Sixth national conference on Computational Mechanics (MekIT{\textquoteright}11)},
	year = {2011},
	publisher = {Tapi Academic Press},
	type = {Conference},
	author = {Hannibal E. {Fossum} and Tutkun, Murat and Bj{\o}rn Anders Petterson {Reif} and Andreassen, {\O}yvind},
	editor = {Bj{\o}rn H. {Skallerud} and H. I. {Andersson}}
}
@inproceedings {Simula.simula.1216,
	title = {A Strong Coupling FSI Scheme for Simulating BMHV Dynamics},
	journal = {8th International Conference on CFD in Oil \& Gas, Metallurgical and Process Industries},
	year = {2011},
	type = {Conference},
	author = {Annerel, Sebastiaan and Degroote, Joris and Claessens, T. and Sigrid Kaarstad {Dahl} and Bj{\o}rn H. {Skallerud} and Leif Rune {Hellevik} and Van Ransbeeck, Peter and Segers, P. and Verdonck, P. and Vierendeels, Jan}
}
@inproceedings {Simula.simula.1026,
	title = {Verification of Markovian Properties of Turbulent Boundary Layer at High Reynolds Number},
	journal = {Sixth national conference on Computational Mechanics (MekIT{\textquoteright}11)},
	year = {2011},
	publisher = {Tapir Academic Press},
	type = {1},
	author = {Fredbo, M. and Tutkun, Murat},
	editor = {Bj{\o}rn H. {Skallerud} and H. I. {Andersson}}
}
@misc {Simula.sc.864,
	title = {Effect of Mitral Valve Shape on Flow Dynamics During Left Ventricular Contraction},
	howpublished = {World Congress in Biomechanics, Singapore},
	year = {2010},
	month = {August},
	author = {Sigrid Kaarstad {Dahl} and Bj{\o}rn H. {Skallerud}}
}
@inproceedings {Simula.simula.80,
	title = {FSI Simulation of the Mitral Valve With Contact and Active Anisotropic Material Models},
	journal = {6th World Congress of Biomechanics},
	year = {2010},
	pages = {266},
	type = {Conference},
	author = {Leif Rune {Hellevik} and Astorino, M. and Moireau, P. and Victorien Emile {Prot} and Bj{\o}rn H. {Skallerud} and Gerbeau, Jean-Fr{\`e}d{\`e}ric}
}
@inproceedings {Simula.simula.82,
	title = {Initial Study on Material Modeling of Umbilical Veins in Fetal Sheep},
	journal = {6th World Congress of Biomechanics},
	year = {2010},
	pages = {361},
	type = {Conference},
	author = {Paul Roger {Leinan} and Leif Rune {Hellevik} and Victorien Emile {Prot} and Kiserud, T. and Bj{\o}rn H. {Skallerud}}
}
@article {Simula.simula.42,
	title = {Modeling Active Muscle Contraction in Mitral Valve Leaflets During Systole: a First Approach},
	journal = {Biomechanics and Modeling in Mechanobiology},
	volume = {10},
	year = {2010},
	pages = {11-26},
	publisher = {Springer},
	abstract = {The present study addresses the effect of muscle activation contributions to mitral valve leaflet response during systole. State-of-art passive hyperelastic material modeling is employed in combination with a simple active stress part. Fiber families are assumed in the leaflets: one defined by the collagen and one defined by muscle activation. The active part is either assumed to be orthogonal to the collagen fibers or both orthogonal to and parallel with the collagen fibers (i.e. an orthotropic muscle fiber model). Based on data published in the literature and information herein on morphology, the size of the leaflet parts that contain muscle fibers is estimated. These parts have both active and passive materials, the remaining parts consist of passive material only. Several solid finite element analyses with different maximum activation levels are run. The simulation results are compared to corresponding echocardiography at peak systole for a porcine model. The physiologically correct flat shape of the closed valve is approached as the activation levels increase. The non-physiological bulging of the leaflet into the left atrium when using passive material models is reduced significantly. These results contribute to improved understanding of the physiology of the native mitral valve, and add evidence to the hypothesis that the mitral valve leaflets not are just passive elements moving as a result of hemodynamic pressure gradients in the left part of the heart.},
	doi = {10.1007/s10237-010-0215-9},
	author = {Bj{\o}rn H. {Skallerud} and Victorien Emile {Prot} and Nordrum, I.}
}
@article {Simula.SC.662,
	title = {On Modelling and Analysis of Healthy and Pathological Human Mitral Valves: Two Case Studies},
	journal = {Journal of the Mechanical Behavior of Biomedical Materials},
	volume = {3},
	number = {2},
	year = {2010},
	month = {February},
	pages = {167-177},
	abstract = {Biomechanical data and related constitutive modelling of the mitral apparatus served as a basis for finite element analyses to better understand the physiology of mitral valves in health and disease. Human anterior and posterior leaflets and chordae tendinae from an elderly heart showing no disease and a hypertrophic obstructive cardiomyopathic heart (HOCM) were mechanically tested by means of uniaxial cyclic extension tests under quasi-static conditions. Experimental data for the leaflets and the chordae tendinae showed highly nonlinear mechanical behaviours and the leaflets were anisotropic. The mitral valve from the HOCM heart exhibited a significantly softer behaviour than the valve from the healthy one. A comparison with porcine data was included because many previous mitral modelling studies have been based on porcine data. Some differences in mechanical response were observed. Material parameters for hyperelastic, transversely isotropic constitutive laws were determined. The experimental data and the related model parameters were used in two finite element studies to investigate the effects of the material properties on the mitral valve response during systole. The analyses showed that during systole the mitral valve from the HOCM heart bulged into the left atrium by taking on the shape of a balloon, whereas the anterior leaflet of the healthy valve remained in the left ventricle.},
	doi = {10.1016/j.jmbbm.2009.05.004},
	author = {Victorien Emile {Prot} and Bj{\o}rn H. {Skallerud} and Sommer, Gerhard and Gerhard A. {Holzapfel}}
}
@inbook {Simula.simula.74,
	title = {The Optics of Bruising},
	booktitle = {Optical-Thermal Response of Laser-Irradiated Tissue},
	year = {2010},
	month = {December},
	publisher = {Springer},
	organization = {Springer},
	edition = {second},
	chapter = {22},
	isbn = {978-90-481-8830-7},
	author = {L. L. {Randeberg} and Bj{\o}rn H. {Skallerud} and N. E. {Langlois} and O. A. {Haugen} and L. O. {Svaasand}},
	editor = {Ashley J. {Welch} and Martin J.C. {van Gemert}}
}
@article {Simula.simula.54,
	title = {Void Coalescence With Or Without Prestrain},
	journal = {International Journal of Damage Mechanics},
	volume = {19},
	year = {2010},
	pages = {153-174},
	author = {Z. L. {Zhang} and Bj{\o}rn H. {Skallerud}}
}
@article {Simula.simula.44,
	title = {Wire Tension Versus Wire Frequency: an Experimental Ilizarov Frame Study},
	journal = {Journal of Biomechanics},
	volume = {43},
	number = {12},
	year = {2010},
	pages = {2327-2331},
	abstract = {Stability of an Ilizarov frame highly depends on maintenance of adequate tension in the wires. Wire tension should be measured accurately in experimental laboratory studies when new types of wire fixators are tested. In this study, 20 wires were tested using two different wire fixators. The wires were sequentially tensioned from 0 to 1275N in 50N intervals. For each tension value, corresponding vibration frequency was recorded. We then described the relationship between wire tension and wire vibration frequency in an empirical equation (R2=99.8). Wire vibration frequency can also be described theoretically by the Euler-Bernoulli equation for a thin beam. Theoretical frequencies were calculated and compared with corresponding experimental frequencies. A close agreement was found (95\% limits of agreement, \pm3.2Hz). This empirical equation represents a simple tool, applicable when investigating the effect of new wire fixators, pre-tensioning and frame constructions on wire tension.},
	doi = {10.1016/j.jbiomech.2010.04.029},
	author = {La Russa, Valentina and Bj{\o}rn H. {Skallerud} and Klaksvik, Jomar and Olav A. {Foss}}
}
@inproceedings {Simula.sc.1180,
	title = {Alternative Elasticity Modeling Approaches for Mitral Valve Analysis: Consequences for Stress and Deformation Prediction},
	journal = {Proceeding of the 22nd Nordic Seminar on Computational Mechanics},
	year = {2009},
	type = {Conference},
	isbn = {1901-7278},
	author = {Bj{\o}rn H. {Skallerud} and Victorien Emile {Prot}},
	editor = {Damkilde, L. and Andersen, L. and Kristensen, A.S. and Lund, E.}
}
@misc {Simula.sc.1142,
	title = {Alternative Elasticity Modeling Approaches for Mitral Valve Analysis: Consequences for Stress and Deformation Prediction},
	howpublished = {Talk at the 22nd Nordic seminar on Computational Mechanics, Aalborg, Denmark, October 22-23 2009},
	year = {2009},
	month = {October},
	author = {Bj{\o}rn H. {Skallerud} and Victorien Emile {Prot}}
}
@article {Simula.sc.986,
	title = {Comments on the Evaluation of the Stress Intensity Factor for a General Re-Entrant Corner in Anisotropic Bi-Materials},
	journal = {Engineering Fracture Mechanics},
	volume = {76},
	number = {9},
	year = {2009},
	month = {June},
	pages = {1373-1379},
	abstract = {This paper illustrates an efficient contour integral procedure to obtain stress intensity factors in combination of the asymptotic analysis with finite element analysis. Note that this set-up is very general: the material can be anisotropic elastic, and the specimen can be built as a bi-material system, notches of arbitrary opening angle can be analyzed (\gamma = 0 \rightarrow crack, \gamma = 180{\textdegree} \rightarrow free edge). The purpose of this technical note is to comment on three issues in the notch mechanics: the interpretation of the eigenvalue equation, the definition of stress intensity factors, and the effect of the outer contour location on H-integral evaluations.},
	doi = {10.1016/j.engfracmech.2009.01.012},
	author = {L. Y. {Shang} and Z. L. {Zhang} and Bj{\o}rn H. {Skallerud}}
}
@article {Simula.sc.964,
	title = {Cyclic Plasticity Modelling for ANDES Thin Shell and Line-Spring Finite Elements},
	journal = {International Journal of Applied Mechanics},
	volume = {1},
	number = {1},
	year = {2009},
	pages = {201-233},
	abstract = {This paper presents a proposed methodology to account for cyclic plastic response of the thin shell ANDES and line-spring finite elements. A through thickness integration scheme is employed for the shell element and stress resultant plasticity is used for the line-spring element. A simplified contact formulation to account for crack closure in the line-spring element is also presented. Numerical comparisons between the proposed models and detailed 3D analyses (pipes) are carried out and presented herein. A comparison between the present implementation and large scale experiment of a surface cracked pipe subjected to large cyclic plastic strains is also presented. The purpose of the presented implementation is to account for cyclic loading in pipeline technology where significant amount of plasticity in the loading cycles occurs.},
	doi = {10.1142/S1758825109000101},
	author = {Berg, Espen and Kjell H. {Holthe} and Bj{\o}rn H. {Skallerud}}
}
@article {Simula.sc.988,
	title = {Evaluation of Fracture Mechanics Parameters for Free Edges in Multi-Layered Structures With Weak Singularities},
	journal = {International Journal of Solids and Structures},
	volume = {46},
	number = {5},
	year = {2009},
	month = {March},
	pages = {1134-1148},
	abstract = {This study focuses on the stress intensity factors for free edges in multi-layered structural components. The effects of elastic constants of various material combinations on the weak singularity at free edges are analyzed. Using the H-integral approach, the effects of elastic mismatch parameters, the bond area and the thickness of the thin metal layer on the stress intensity factor are quantified and the results are compared with detailed finite element solutions. A good agreement between numerical predictions obtained from the H-integral and the detailed FE results is achieved, showing the applicability of this approach. Similar to a crack problem, the singular elastic field dominates in an annular region adjacent to the notch tip. The relationship between the valid range of the K-dominated field and the thin-film thickness is then demonstrated. Furthermore, the competition of crack initiation between the free edge interface (180{\textdegree} opening angle) and a 90{\textdegree} notch interface in a generic specimen is investigated, in order to find out which is the prevailing failure mode. Comparison between isotropic Si and anisotropic Si substrate is also illustrated. Anisotropy of the Si substrate has a significant influence on the stress intensity factor when combined with an Au or Al metal layer but not with a Cu layer. Additionally, standardized numerical formulae of the dimensionless stress intensity factor have been derived to guide the engineering application.},
	doi = {10.1016/j.ijsolstr.2008.10.018},
	author = {L. Y. {Shang} and Z. L. {Zhang} and Bj{\o}rn H. {Skallerud}}
}
@article {Simula.sc.832,
	title = {Finite Element Analysis of the Mitral Apparatus: Annulus Shape Effect and Chordal Force Distribution},
	journal = {Biomechanics and Modeling in Mechanobiology},
	volume = {8},
	number = {1},
	year = {2009},
	pages = {43-55},
	author = {Victorien Emile {Prot} and Rune, Haaverstad and Bj{\o}rn H. {Skallerud}}
}
@inproceedings {Simula.SC.584,
	title = {Implementing a K-E Turbulence Model in the FEniCS Finite Element Programming Environment},
	journal = {MekIT{\textquoteright}09.~~Fifth~~national~~conference~~on~~Computational~~Mechanics},
	year = {2009},
	publisher = {Tapir},
	type = {Conference},
	isbn = {9788251924214},
	author = {Valen-Sendstad, Kristian and Mortensen, Mikael and Hans Petter {Langtangen} and Bj{\o}rn Anders Petterson {Reif} and Mardal, Kent-Andre},
	editor = {Bj{\o}rn H. {Skallerud} and Andersson, Helge}
}
@inproceedings {Simula.sc.692,
	title = {Implicit Interaction of Two Rigid Mitral Leaflets in a Partitioned Fluid-Structure Approach},
	journal = {MekIT{\textquoteright}09. Fifth~~national~~conference~~on~~Computational~~Mechanics},
	year = {2009},
	month = {May},
	pages = {135-149},
	publisher = {NTNU},
	type = {Conference},
	address = {Trondheim},
	abstract = {The aim of our study was twofold. First, to develop an implicit algorithm accounting for interaction of two rigid, asymmetric mitral leaflets in a partitioned, fluid-structure interaction simulation. Second, to study the impact of the imposed inlet conditions on the mitral valve movement during diastolic filling. Two-dimensional simulations with a transient patient-specific left ventricle geometry were carried out to test the algorithm, to introduce a higher degree of physiological realism in the simulations, and to reduce the computational cost. Two different inlet configurations were tested. The results indicate that the inlet configuration has significant impact on intramitral flow and the movement of the mitral leaflets during diastole.},
	isbn = {978-82-519-2421-4},
	author = {Sigrid Kaarstad {Dahl} and Vierendeels, Jan and Degroote, Joris and Annerel, Sebastiaan and Bj{\o}rn H. {Skallerud} and Leif Rune {Hellevik}},
	editor = {Bj{\o}rn H. {Skallerud} and H. I. {Andersson}}
}
@misc {Simula.sc.708,
	title = {Implicit Interaction of Two Rigid Mitral Leaflets in a Partitioned Fluid-Structure Approach},
	howpublished = {Talk at MekIT{\textquoteright}09, Trondheim, May 27th},
	year = {2009},
	month = {May},
	abstract = {The aim of our study was twofold. First, to develop an implicit algorithm accounting for interaction of two rigid, asymmetric mitral leaflets in a partitioned, fluid-structure interaction simulation. Second, to study the impact of the imposed inlet conditions on the mitral valve movement during diastolic filling. Two-dimensional simulations with a transient patient-specific left ventricle geometry were carried out to test the algorithm, to introduce a higher degree of physiological realism in the simulations, and to reduce the computational cost. Two different inlet configurations were tested. The results indicate that the inlet configuration has significant impact on intramitral flow and the movement of the mitral leaflets during diastole.},
	author = {Sigrid Kaarstad {Dahl} and Vierendeels, Jan and Degroote, Joris and Annerel, Sebastiaan and Bj{\o}rn H. {Skallerud} and Leif Rune {Hellevik}}
}
@inproceedings {Simula.sc.1124,
	title = {Large Eddy Simulations of the Evaporation From a Liquid Pool Beneath a Turbulent Air Flow},
	journal = {MekIT{\textasciiacute}09. Fifth national conference on Computational Mechanics},
	year = {2009},
	note = {Listed in the 2009 annual report as "Numerical Simulation of the Evaporation From a Liquid Pool Beneath a Turbulent Boundary layer"},
	publisher = {Tapir akademisk forlag},
	type = {Conference},
	isbn = {9788251924214},
	author = {Vik, Thomas and Bj{\o}rn Anders Petterson {Reif}},
	editor = {Bj{\o}rn H. {Skallerud} and Andersson, H.I.}
}
@inproceedings {Simula.sc.834,
	title = {On Material Modelling of Umbilical Vein},
	journal = {Fifth National Conference on Computational Mechanics (MekIT{\textasciiacute}09)},
	year = {2009},
	pages = {281-295},
	publisher = {Tapir Akademisk Forlag},
	type = {Conference},
	isbn = {978-82-519-2421-4},
	author = {Paul Roger {Leinan} and Leif Rune {Hellevik} and Victorien Emile {Prot} and Kiserud, Torvid and Bj{\o}rn H. {Skallerud}},
	editor = {Bj{\o}rn H. {Skallerud} and Andersson, H.I.}
}
@book {Simula.sc.1022,
	title = {MekIT{\textasciiacute}09. Fifth National Conference on Computational Mechanics},
	year = {2009},
	month = {June},
	publisher = {Tapir Academic Press},
	isbn = {9788251924214},
	author = {Bj{\o}rn H. {Skallerud} and H. I. {Andersson}}
}
@article {Simula.sc.972,
	title = {The Modified Cam Clay Model for Constrained Compression of Human Morsellised Bone: Effects of Porosity on the Mechanical Behaviour},
	journal = {Journal of the Mechanical Behavior of Biomedical Materials},
	volume = {2},
	number = {1},
	year = {2009},
	month = {January},
	pages = {43-50},
	abstract = {Morsellised cortico-cancellous bone (MCB) is often used in revision surgery for filling skeletal defects. The MCB porosity is found to influence the degree of bone ingrowth. Thus expressing a material model in terms of porosity may be attractive from a clinical point of view. We analysed the moisture content and performed constrained compression testing of human impacted and unimpacted MCB, in order to determine material parameters for the common constitutive soil model: modified cam clay. The model seemed to be suitable for the unimpacted pellets with a logarithmic bulk modulus {\k a}ppa=0.059\pm0.0019 and a logarithmic hardening constant {\l}ambda=0.36\pm0.014. This model, relating the specific volume (and porosity) to the logarithm of stress, may be suited to find the best compromise of stiffness and porosity for MCB.},
	doi = {10.1016/j.jmbbm.2008.02.004},
	author = {Knut B. {Lunde} and Bj{\o}rn H. {Skallerud}}
}
@article {Simula.SC.474,
	title = {Nonlinear Solid Finite Element Analysis of Mitral Valves With Heterogeneous Leaflet Layers},
	journal = {Computational Mechanics},
	volume = {43},
	number = {3},
	year = {2009},
	pages = {353-368},
	author = {Victorien Emile {Prot} and Bj{\o}rn H. {Skallerud}}
}
@inproceedings {Simula.sc.1014,
	title = {Numerical Modeling of Aerosol Dispersion Inside a Rotating Aerosol Chamber},
	journal = {MekIT{\textasciiacute}09. Fifth national conference on Computational Mechanics},
	year = {2009},
	month = {June},
	publisher = {Tapir akademisk forlag},
	type = {1},
	isbn = {9788251924214},
	author = {Vartdal, M. and Bj{\o}rn Anders Petterson {Reif}},
	editor = {Bj{\o}rn H. {Skallerud} and Andersson, H.I.}
}
@inproceedings {Simula.SC.568,
	title = {On the Performance of an Algebraic Multigrid Preconditioner for the Pressure Equation With Highly Discontinuous Media},
	journal = {MekIT{\textquoteright}09.~~Fifth~~national~~conference~~on~~Computational~~Mechanics},
	year = {2009},
	month = {May},
	pages = {191-204},
	publisher = {NTNU},
	type = {Conference},
	abstract = {We study the performance of an algebraic multigrid (AMG) preconditioner combined with conjugate gradient-type methods for the pressure equation in the presence of strong discontinuity of the permeability. Such discontinuities are problematic for iterative solvers, due to the dependence of the condition number of the discretized linear system of equations on the magnitude of the discontinuities. We identify two separate causes of such ill-conditioning, and assess how well the AMG preconditioner handles these. For the more difficult problems, we discuss techniques to modify the model to allow iterative solutions.},
	isbn = {978-82-519-2421-4},
	author = {Joachim Berdal {Haga} and Hans Petter {Langtangen} and Nielsen, Bj{\o}rn Fredrik and Osnes, Harald},
	editor = {Bj{\o}rn H. {Skallerud} and H. I. {Andersson}}
}
@inproceedings {Simula.sc.1002,
	title = {Predicting Particle Deposition in the Human Airways With RANS},
	journal = {MekIT{\textasciiacute}09. Fifth national conference on Computational Mechanics},
	year = {2009},
	note = {Listed in 2009 annual report as "A comparison of RANS Turbulence Models for Simulation of Flow in the Human Respiratory System"},
	month = {June},
	publisher = {Tapir akademisk forlag},
	type = {Conference},
	isbn = {9788251924214},
	author = {H. E. {Fossum} and Bj{\o}rn Anders Petterson {Reif}},
	editor = {Bj{\o}rn H. {Skallerud} and H. I. {Andersson}}
}
@inproceedings {Simula.sc.1122,
	title = {Proper Orthogonal Decomposition of Velocity and Scalar Fields in Shear Generated Turbulence},
	journal = {MekIT{\textasciiacute}09. Fifth national conference on Computational Mechanics},
	year = {2009},
	note = {Is registered in the 2009 annual report as "Low order Dynamical System Modelling of StratifiedHear Turbulence"},
	publisher = {Tapir akademisk forlag},
	type = {Conference},
	isbn = {9788251924214},
	author = {Tutkun, Murat and Bj{\o}rn Anders Petterson {Reif} and Peter B. V. {Johansson} and Werne, J.},
	editor = {Bj{\o}rn H. {Skallerud} and Andersson, H.I.}
}
@inproceedings {Simula.sc.698,
	title = {Simulating Heart Valve Dynamics in FEniCS},
	journal = {MekIT{\textasciiacute}09. Fifth National Conference on Computational Mechanics},
	year = {2009},
	pages = {411-419},
	publisher = {Tapir Akademisk Forlag},
	type = {1},
	isbn = {978-82-519-2421-4},
	author = {Selim, Kristoffer and Logg, Anders},
	editor = {Bj{\o}rn H. {Skallerud} and H. I. {Andersson}}
}
@misc {Simula.sc.1148,
	title = {Subject Specific Finite Element Analysis of a Callus Distraction - a Preliminary Study},
	howpublished = {Talk at MekIT{\textquoteright}09: Fifth National Conference on Computational Mechanics, Trondheim, May 26-27},
	year = {2009},
	author = {Sune Hansborg {Pettersen} and Aamodt, A. and Olav A. {Foss} and Bj{\o}rn H. {Skallerud}}
}
@inproceedings {Simula.sc.1006,
	title = {Subject Specific Finite Element Analysis of Callus Distraction - a Preliminary Study},
	journal = {Fifth national conference on Computational Mechanics (MekIT{\textasciiacute}09)},
	year = {2009},
	month = {June},
	publisher = {Tapir akademisk forlag},
	type = {Conference},
	isbn = {9788251924214},
	author = {Sune Hansborg {Pettersen} and Aamodt, A. and Olav A. {Foss} and Bj{\o}rn H. {Skallerud}},
	editor = {Bj{\o}rn H. {Skallerud} and H. I. {Andersson}}
}
@article {Simula.sc.980,
	title = {Subject Specific Finite Element Analysis of Implant Stability for a Cementless Femoral Stem},
	journal = {Clinical Biomechanics},
	volume = {24},
	number = {6},
	year = {2009},
	month = {July},
	pages = {480-487},
	abstract = {BACKGROUND: The primary stability of a cementless implant is crucial to ensure long term stability through osseointegration. In the present study we have examined how subject specific finite element models can be used to evaluate the stability of a cementless femoral stem. METHODS: Micromotion on the bone-implant interface of a cementless stem was measured experimentally in six human cadaver femurs. Subject specific finite element models were built from computed tomography of the same femurs, and used to simulate the same load scenario used experimentally. FINDINGS: Both experimental measurements and numerical analyses showed a tendency of increased rotational stability for bigger implants. Good correlation was found between measurements and calculated values of axial rotation (R(2)=0.74, P@article {Simula.sc.982,
	title = {Subject Specific Finite Element Analysis of Stress Shielding Around a Cementless Femoral Stem},
	journal = {Clinical Biomechanics},
	volume = {24},
	number = {2},
	year = {2009},
	month = {February},
	pages = {196-202},
	abstract = {{Background Stress shielding around a femoral stem is usually assessed experimentally using composite or human cadaver femurs. In the present study we have explored the feasibility of using subject specific finite element models to determine stress shielding in operated femurs. Methods Cortical strain was measured experimentally on seven human cadaver femurs, intact and implanted with a straight cementless prosthesis. Two load configurations were considered: single leg stance and stair climbing. Subject specific finite element models derived from computed tomography of the same femurs were analysed intact and with an implant. Principal cortical strain was used to validate the finite element models. Stress shielding was defined as the change in equivalent (von Mises) strain between pre- and post-operative femurs. Findings Cortical strain predicted by the finite element analyses showed to be close to unity with the experimental observations for both intact (R2=0.94},
	doi = {10.1016/j.clinbiomech.2008.11.003},
	author = {Sune Hansborg {Pettersen} and Tina S. {Wik} and Bj{\o}rn H. {Skallerud}}
}
@inproceedings {Simula.sc.1178,
	title = {Tissue Fiber Families in the Mitral Valve - Constitutive Modelling Numerical Analysis and Potential Clinical Application},
	journal = {Proceeding of the 22nd Nordic Seminar on Computational Mechanics},
	year = {2009},
	type = {Conference},
	isbn = {1901-7278},
	author = {Bj{\o}rn H. {Skallerud}},
	editor = {Damkilde, L. and Andersen, L. and Kristensen, A.S. and Lund, E.}
}
@misc {Simula.sc.1140,
	title = {Tissue Fiber Families in the Mitral Valve - Constitutive Modelling Numerical Analysis and Potensial Clinical Application},
	howpublished = {Invited keynote talk at the 22nd Nordic Seminar on Computational Mechanics, Aalborg, Denmark, October 22-23 2009},
	year = {2009},
	month = {October},
	author = {Bj{\o}rn H. {Skallerud}}
}
@inproceedings {Simula.sc.1128,
	title = {Unsteady RANS Modelling of Pollutant Dispersion in an Idealized Urban Area},
	journal = {MekIT{\textasciiacute}09. Fifth national conference on Computational Mechanics},
	year = {2009},
	note = {Is listed in the 2009 annual report as "CFD Modeling of Pollutant Dispersion in an Idealized Urban Area"},
	publisher = {Tapir akademisk forlag},
	type = {Conference},
	isbn = {9788251924214},
	author = {E. M. M. {Wingstedt} and Bj{\o}rn Anders Petterson {Reif}},
	editor = {Bj{\o}rn H. {Skallerud} and Andersson, H.I.}
}
@inproceedings {Simula.SC.578,
	title = {Using Cython to Speed Up Numerical Python Programs},
	journal = {MekIT{\textasciiacute}09.~~Fifth~~national~~conference~~on~~Computational~~Mechanics},
	year = {2009},
	pages = {495-512},
	publisher = {NTNU},
	type = {Conference},
	abstract = {The present study addresses a series of techniques for speeding up numerical calculations in Python programs. The techniques are evaluated in a benchmark problem involving finite difference solution of a wave equation. Our aim is to find the optimal mix of user-friendly, high-level, and safe programming in Python with more detailed and more error-prone low-level programming in compiled languages. In particular, we present and evaluate Cython, which is a new software tool that combines high- and low-level programming in an attractive way with promising performance. Cython is compared to more well-known tools such as F2PY, Weave, and Instant. With the mentioned tools, Python has a significant potential as programming platform in computational mechanics.},
	isbn = {978-82-519-2421-4},
	author = {Wilbers, Ilmar and Hans Petter {Langtangen} and {\O}deg{\r a}rd, {\r A}smund},
	editor = {Bj{\o}rn H. {Skallerud} and H. I. {Andersson}}
}
@misc {Simula.SC.242,
	title = {A 2D Patient-Specific FSI Assessment of Mitral Valve Dynamics During Diastolic Filling},
	howpublished = {Presented at 8th.World Congress on Computational Mechanics (WCCM8)/5th European Congress on Computational Methods in Applied Sciences and Engineeering (ECCOMAS 2008), Venice, Italy},
	year = {2008},
	month = {June},
	author = {Sigrid Kaarstad {Dahl} and Leif Rune {Hellevik} and Bj{\o}rn H. {Skallerud}}
}
@inproceedings {Simula.sc.954,
	title = {A 2D Patient-Specific FSI Assessment of Mitral Valve Dynamics During Diastolic Filling},
	journal = {8th world Congress on Computational Mechanics/5th European Congress on Computational Methods in Applied sciences and Engineering, Venice, Italy},
	year = {2008},
	type = {Conference},
	author = {Sigrid Kaarstad {Dahl} and Leif Rune {Hellevik} and Bj{\o}rn H. {Skallerud}}
}
@article {Simula.sc.940,
	title = {On the Applicability of Bovine Morsellized Cortico-Cancellous Bone As a Substitute for Human Morsellized Cortico-Cancellous Bone for in Vitro Mechanical Testing},
	journal = {Journal of Biomechanics},
	volume = {41},
	number = {16},
	year = {2008},
	month = {December},
	pages = {3469-3474},
	abstract = {Morsellized cortico-cancellous bone (MCB) is frequently used in orthopaedic revision surgery to restore lost bone stock. In this study, we examine the validity of using bovine MCB as a substitute for human MCB in in vitro mechanical testing of bone grafts. The paper describes the fat and water content of impacted and unimpacted human and bovine MCB. During this work we applied constrained compression testing to describe the elastic, plastic and time dependent response. Nearly all parameters were found to be significantly different and were influenced differently by impaction for the two types of MCB. The denser trabecular structure, higher fat content of bovine MCB and higher stiffness and compressive strength of cortical bovine bone may explain the differences observed. Consequently we are not confident about the applicability of bovine MCB as a substitute for human MCB for in vitro mechanical testing.},
	doi = {10.1016/j.jbiomech.2008.08.030},
	author = {Knut B. {Lunde} and Olav A. {Foss} and Bj{\o}rn H. {Skallerud}}
}
@inproceedings {Simula.sc.1102,
	title = {On the Biomechanical Analysis of Bruises},
	journal = {21st Nordic Seminar on Computational Mechanics},
	year = {2008},
	type = {Conference},
	author = {Bj{\o}rn H. {Skallerud} and Winnem, A. and L. L. {Randeberg} and Svaasand, L.},
	editor = {K. M. {Mathisen} and Kvamsdal, T. and Pettersen, B.}
}
@article {Simula.sc.938,
	title = {Constitutive Models for Constrained Compression of Unimpacted and Impacted Human Morselized Bone Grafts},
	journal = {Journal of Biomechanical Engineering},
	volume = {130},
	number = {6},
	year = {2008},
	month = {December},
	pages = {61014},
	abstract = {Morselized corticocancellous bone (MCB) is widely used in revision surgery with and without impaction. In the current study material parameters for the nonlinear viscoelastic and plastic responses of impacted and unimpacted human MCBs were determined during constrained compression. These models may be useful in finite element analyses of surgical constructs involving impacted and unimpacted MCBs. MCB is impacted layer by layer in the femoral canal during revision surgery. The influence of different layers on the mechanical properties was therefore also examined by comparing the relaxation strength and elastic and plastic strains for bone pellets impacted in one and two layers during constrained compression of human MCB. The relaxation strength was found to increase significantly by 14\% for two layer pellets compared to one layer pellets, and the plastic strains decreased significantly by 15\%, while the elastic strains were similar.},
	doi = {10.1115/1.2979878},
	author = {Knut B. {Lunde} and Olav A. {Foss} and Fosse, Lars and Bj{\o}rn H. {Skallerud}}
}
@inproceedings {Simula.sc.1038,
	title = {Effect of Embedded Defects in Pipelines Subjected to Plastic Strains During Operation},
	journal = {Proceedings of the Eighteenth (2008) International Offshore and Polar Engineering Conference},
	year = {2008},
	type = {Conference},
	abstract = {Recent research has shown that the effect of internal pressure can be detrimental to the fracture response of pipelines with circumferential flaws subjected to bending or tensile loading. In addition, recent work at SINTEF indicates that embedded defects under certain circumstances can be more critical than surface cracks with the same height and length. This is contrary to the common practice in ECA analyses of assuming that the results for surface cracks can be conservatively applied also to embedded defects given that the ligament height (distance from defect to pipe surface) is at least half of the defect height. Today{\textquoteright}s analytical equations that are the basis for most engineering critical assessments are not capable of accounting for the effect of internal pressure, and the industry does not have a common recognized practice for assessing the integrity of pipelines for longitudinal strains in the plastic range during operation. Finite element methods, however, can be used to accurately simulate the effect of biaxial loading. A finite element model with shell and line spring elements that incorporate the effect of internal pressure has been employed to efficiently investigate the fracture integrity of a pipeline during operation. The model is capable of analyzing surface cracks on both the inner and outer pipe surfaces under biaxial loading, as well as embedded defects with various ligament heights. The pipe model has been subjected to tensile loading while under internal pressure, and embedded defects have been compared to surface cracks of similar size. The results illustrate that embedded defects can cause a reduction in the strain capacity as compared to surface cracks.},
	isbn = {978-1-880653-70-8},
	author = {Ols{\o}, Erlend and Berg, Espen and Kjell H. {Holthe} and Nyhus, B{\r a}rd and Bj{\o}rn H. {Skallerud} and Thaulow, Christian and {\O}stby, Erling}
}
@article {Simula.sc.942,
	title = {The Fluid Phase of Morsellized Bone: Characterization of Viscosity and Chemical Composition},
	journal = {Journal of the Mechanical Behavior of Biomedical Materials},
	volume = {1},
	number = {2},
	year = {2008},
	pages = {199-205},
	abstract = {Morsellized bone is widely used in orthopaedics to fill skeletal defects. The material behaviour is highly time-dependent, due to the liquid consisting of fat and water present in the impacted graft layer. In this study this fluid was characterized with respect to viscosity and chemical composition. Bovine bone was ground in a bone mill, transferred to tubes and centrifuged. This procedure allowed to successfully extract the fluid present inside the ground bone. The fluid was found to have similar composition to yellow bone marrow and a temperature dependent viscosity that could be described by Andrade{\textquoteright}s equation with coefficients A = 1.3 * 10^-4 Pa s and B = 3950 C. The viscosity data can be used in quantitative modelling based on a mixture theory approach to simulate the mechanical behaviour of the graft during packing and cement filling in the femur.},
	doi = {10.1016/j.jmbbm.2007.10.001},
	author = {Knut B. {Lunde} and Sletmoen, Marit and Bj{\o}rn Torger {Stokke} and Bj{\o}rn H. {Skallerud}}
}
@article {Simula.sc.948,
	title = {Fracture of Anodic-Bonded Silicon-Thin Film Glass-Silicon Triple Stacks},
	journal = {Engineering Fracture Mechanics},
	volume = {75},
	number = {5},
	year = {2008},
	month = {March},
	pages = {1064-1082},
	abstract = {In this study we focus on the fracture behavior of two types silicon-thin film glass-silicon (Si-Glass-Si) triple stacks specimens with a sharp corner. We determine the notch stress intensity factor Kn for both specimens using a combination of the Williams eigenfunction expansion method, Stroh{\textquoteright}s sextic formalism, finite element analysis, and the path-independent H-integral. Empirical solutions of dimensionless stress intensity factors are proposed for two typical specimens, and the dependence of geometry is analyzed. Furthermore, the effect of glass thickness on stress intensity is explored for anodic-bonded Si-Glass-Si triple stacks. We discuss the feasibility of using a critical value of Kn to correlate the failure results for both specimens with various bond area and glass thickness.},
	doi = {10.1016/j.engfracmech.2007.04.030},
	author = {L. Y. {Shang} and Z. L. {Shang} and Bj{\o}rn H. {Skallerud}}
}
@misc {Simula.sc.1052,
	title = {Solid Versus Membrane Finite Elements in Analysis of the Mitral Valve: a Case Study},
	howpublished = {Talk at the 6th International Conference on Computation of Shell \& Spatial Structures},
	year = {2008},
	author = {Victorien Emile {Prot} and Bj{\o}rn H. {Skallerud}}
}
@misc {Simula.sc.1110,
	title = {Surface and Embedded Crack in the Offshore Pipelines Subjected to Plastic Strains},
	howpublished = {Talk at the 6th international Conference on Computation of Shell and Spatial Structures},
	year = {2008},
	author = {Berg, E. and Bj{\o}rn H. {Skallerud} and Kjell H. {Holthe}}
}
@article {Simula.sc.952,
	title = {Surface Roughness Characterization for Fatigue Life Predictions Using Finite Element Analysis},
	journal = {International Journal of Fatigue},
	volume = {30},
	number = {12},
	year = {2008},
	month = {Deecember},
	pages = {2200-2209},
	abstract = {Fatigue cracks usually initiate at the surface in homogenous materials, thus the surface state has a high influence on fatigue life. The most important surface parameters are surface roughness, residual stress, and microstructure. Methods for determining residual stresses and microstructure are well established, whereas surface roughness cannot readily be characterized in terms of fatigue life. Common methods employing reduction factors and roughness parameters are notoriously inaccurate, leading to large safety factors and overly conservative designs. A new method is proposed, in which microscopic surface measurements are used to create finite element models of surface topography. The influence of surface roughness on fatigue life can then be based on stress solutions instead of empirically derived reduction factors.},
	doi = {10.1016/j.ijfatigue.2008.05.020},
	author = {Sigmund Kyrre {{\r A}s} and Bj{\o}rn H. {Skallerud} and B{\r a}rd Wathne {Tveiten}}
}
@article {Simula.sc.918,
	title = {Two-Parameter Fracture Mechanics and Circumferential Crack Growth in Surface Cracked Pipelines Using Line-Spring Elements},
	journal = {Engineering Fracture Mechanics},
	volume = {75},
	number = {1},
	year = {2008},
	month = {January},
	pages = {17-30},
	publisher = {Elsevier},
	doi = {10.1016/j.engfracmech.2007.03.023},
	author = {Berg, E. and Bj{\o}rn H. {Skallerud} and Thaulow, Christian}
}
@article {Simula.sc.920,
	title = {Ultimate Fracture Capacity of Pressurized Pipes With Defects - Comparisons of Large Scale Testing and Numerical Simulations},
	journal = {Engineering Fracture Mechanics},
	volume = {75},
	number = {8},
	year = {2008},
	month = {May},
	pages = {2352-2366},
	doi = {10.1016/j.engfracmech.2007.09.004},
	author = {Berg, E. and {\O}stby, Erling and Thaulow, Christian and Bj{\o}rn H. {Skallerud}}
}
@inproceedings {Simula.SC.22,
	title = {Application of Symbolic Finite Element Tools to Nonlinear Hyperelasticity},
	journal = {Fourth national conference on Computational Mechanics (MekIT{\textquoteright}07)},
	year = {2007},
	month = {May},
	pages = {87-101},
	publisher = {Tapir Academic Press},
	type = {Conference},
	address = {NO-7005 Trondheim},
	abstract = {The present paper addresses the use of high level languages, symbolic mathematical tools and code generation in an implementation of the finite element method, using a nonlinear hyperelasticity equation as example. Advantages of the software development method that will be demonstrated include closeness to the mathematics, enabling high human efficiency with easy to use high level languages, while still keeping a high computational efficiency by generating tailored inner loop code for the problem at hand. The application we have in mind for the equations presented here is the simulation of the passive elastic properties of heart and blood vessel tissue.},
	isbn = {978-82-519-2235-7},
	author = {Martin Sandve {Aln{\ae}s} and Mardal, Kent-Andre and Sundnes, Joakim},
	editor = {Bj{\o}rn H. {Skallerud} and Andersson, H.I.}
}
@inproceedings {Simula.SC.36,
	title = {Benchmark of a Tsunami Run-Up Code},
	journal = {MekIT{\textquoteright}07. Fourth National Conference on Computational Mechanics},
	year = {2007},
	month = {May},
	pages = {127-134},
	publisher = {Tapir Academic Press 2007},
	type = {Conference},
	isbn = {978-82-519-2235-7},
	author = {Rolv Erlend {Bredesen} and Hans Petter {Langtangen} and Pedersen, Geir},
	editor = {Bj{\o}rn H. {Skallerud} and H. I. {Anderson}}
}
@misc {Simula.sc.910,
	title = {Effects on Connective Tissue Pathologies on Mitral Valve Response},
	howpublished = {Talk at the Conference on Modeling of heterogeneous materials with application in construction and biomedical engineering, Prague},
	year = {2007},
	month = {June},
	author = {Victorien Emile {Prot} and Bj{\o}rn H. {Skallerud} and Gerhard A. {Holzapfel}}
}
@inproceedings {Simula.SC.54,
	title = {Efficient Representation of Computational Meshes},
	journal = {MekIT{\textquoteright}07. Fourth National Conference on Computational Mechanics},
	year = {2007},
	publisher = {Tapir Akademisk Forlag},
	type = {Conference},
	isbn = {9788259122357},
	author = {Logg, Anders},
	editor = {Bj{\o}rn H. {Skallerud} and H. I. {Andersson}}
}
@inproceedings {Simula.SC.77,
	title = {A First-Approach Towards Patient-Specific 2D FSI-Simulation of Mitral Valve Dynamics During Diastolic Filling},
	journal = {MekIT-07, Fourth national conference on Computational Mechanics},
	year = {2007},
	pages = {175-184},
	publisher = {Tapir Academic Press},
	type = {Conference},
	address = {Trondheim},
	abstract = {The mitral valve controls the flow of blood into the ventricle during diastole and prevents backflow into the atrium in systole. The two mitral valve leaflets have significantly different geometries. The dynamics of the leaflets and their influence on the transmitral and intraventricular flow is a controversial topic. In this paper we report results from work in progress on fluid structure interaction simulations of the mitral leaflets during left ventricular filling. The aim of the present study was to assess the impact of left ventricular initial pressures and vortices on the mitral leaflet dynamics. An explicitly coupled fluid structure interaction scheme was utilized for the numerical simulations. A 2D transient representation of the left ventricular wall movement was imposed as boundary conditions for the simulations. The left ventricular wall was rendered by ultrasound recordings, and speckle tracking was used for transient tracking of the wall movement during diastole. Thus, the structural calculations are simplified and involve only the mitral valves. The ultrasound measurements were used both for validation/comparison with the simulated mitral valve dynamics as well as for imposition of the left ventricular wall movement. Our simulations show that the initial pressure configuration in the left heart is significant for the mitral valve dynamics. The simulations also indicate that the mitral valve flutter has important bearings on the vortex formation in the vicinity of the mitral valves.},
	isbn = {978-82-519-2235-7},
	author = {Leif Rune {Hellevik} and Sigrid Kaarstad {Dahl} and Bj{\o}rn H. {Skallerud}},
	editor = {Bj{\o}rn H. {Skallerud} and H. I. {Andersson}}
}
@inproceedings {Simula.SC.20,
	title = {Lattice Boltzmann Method and Turbidity Flow Modeling},
	journal = {MekIT{\textquoteright}07 : Fourth National Conference in Computational Mechanics},
	year = {2007},
	month = {May},
	pages = {213-228},
	publisher = {Tapir Academic Press},
	type = {Conference},
	abstract = {We discuss the Lattice Boltzmann method (LBM), which provides a new way of thinking on complex, multiphase fluid flow problems. We present the basics of the LBM as well as its origins in the Cellular Automata. The particle-based nature of the LBM makes it well suited to study fluid-boundary interfaces. We then commence to sketch advanced applications like particle suspension problems and we show how the LBM can be applied on turbidity currents, a challenging fluid flow problem. We show that the LBM has a good deal of versatility in modeling physical systems.},
	isbn = {978-82-519-2235-7},
	author = {Al-Khayat, Omar and Are Magnus {Bruaset} and Hans Petter {Langtangen}},
	editor = {Bj{\o}rn H. {Skallerud} and H. I. {Andersson}}
}
@misc {Simula.sc.912,
	title = {Modeling of the Mitral Valve in the Heart},
	howpublished = {Talk at CBC Workshop on Biomedical Computing, Simula},
	year = {2007},
	month = {June},
	author = {Bj{\o}rn H. {Skallerud}}
}
@inproceedings {Simula.SC.18,
	title = {Parallelisation and Numerical Performance of a 3D Model for Coupled Deformation, Fluid Flow and Heat Transfer in Sedimentary Basins},
	journal = {MekIT{\textquoteright}07. Fourth National Conference on Computational Mechanics},
	year = {2007},
	month = {May},
	pages = {151-162},
	publisher = {Tapir Academic Press},
	type = {Conference},
	address = {Trondheim},
	abstract = {In this paper, we present some parallel performance results for a 3D simulator of coupled deformation, fluid flow and heat transfer in sedimentary basins. The model parameters are derived from an industry simulator, with realistic material properties and complex irregular grids of up to 1.5 million nodes with 7.3 million degrees of freedom. We have performed parallelisation on the linear algebra level using the ML algebraic multigrid preconditioner with iterative methods in the Diffpack finite element framework. Implementation and speedup results are presented.},
	isbn = {978-82-519-2235-7},
	author = {Joachim Berdal {Haga} and Are Magnus {Bruaset} and Cai, Xing and Hans Petter {Langtangen} and Osnes, Harald and Skogseid, Jakob},
	editor = {Bj{\o}rn H. {Skallerud} and H. I. {Andersson}}
}
@article {Simula.sc.876,
	title = {Transversely Isotropic Membrane Shells With Application to Mitral Valve Mechanics. Constitutive Modelling and Finite Element Implementation},
	journal = {International Journal for Numerical Methods in Engineering},
	volume = {71},
	number = {8},
	year = {2007},
	month = {August},
	pages = {987-1008},
	doi = {10.1002/nme.1983},
	author = {Victorien Emile {Prot} and Bj{\o}rn H. {Skallerud} and Gerhard A. {Holzapfel}}
}
@inproceedings {Staff.2005.1,
	title = {The Accuracy of the Velocity Approximation With Respect to the Pressure Approximation for Incompressible Fluid Flow},
	journal = {Third National Conference on Computational Mechanics (MekIT 05)},
	year = {2005},
	month = {May},
	pages = {297-311},
	publisher = {Tapir Academic Press},
	type = {1},
	edition = {first},
	address = {Trondheim, May 11-12},
	abstract = {We consider the accuracy of the velocity approximation with respect to the pressure approximation using various standard finite element methods for incompressible fluid flow. Of particular interest is the case where the hydrostatic part of the pressure is dominating, which implies that the pressure may be large relative to the velocity. Some standard mixed elements like the Mini element and the Taylor-Hood element handle this case well, while others like the P\_2-P\_0 element and the Crouzeix-Raviart element do not. This seems to be related to the fact that the Taylor-Hood and the Mini elements yield a stable approximation of the mixed Poisson problem.},
	author = {Gunnar Andreas {Staff} and Mardal, Kent-Andre},
	editor = {Bj{\o}rn H. {Skallerud} and Helge I. {Andersson}}
}
@inproceedings {Linge.2005.2,
	title = {Biology and Modelling of Cardiovascular Tissue Dynamics},
	journal = {Third National Conference on Computational Mechanics (MekIT 05)},
	year = {2005},
	month = {May},
	pages = {211-225},
	publisher = {Tapir Academic Press},
	type = {1},
	address = {Trondheim, Norway May 11-12},
	abstract = {It is well known that shape and function of heart and blood vessels are influenced by blood flow and pressure. The heart muscle grows to cope with the demands of a sportsman, the inner diameter of vessels increases with increased shear stress from blood flow, and vessel walls themselves get thicker with elevated blood pressure. Such effects are observed in healthy people with varying activity levels, and also in patients with different malfunctions. Modelling and simulating the function and the adaptation of heart and blood vessels to mechanical load is needed to fully understand the complex relations involved. A thorough understanding of these mechanisms is fundamental for good patient diagnosis and treatment planning. Also, simulations will reduce the need for time consuming and stressful invasive measurements. In this brief review, we present some of the relevant biology, and address important modelling approaches of cardiovascular functioning and adaptation.},
	author = {Linge, Svein},
	editor = {Bj{\o}rn H. {Skallerud} and Helge I. {Andersson}}
}
@inproceedings {Thorvaldsen.2005.2,
	title = {A Mixed Formulation for Modeling the Mechanical Bahavior of the Heart},
	journal = {MekIt05 - Third national conference om Computational Mechanics, Trondheim May 11-12},
	year = {2005},
	month = {May},
	pages = {327-341},
	publisher = {Tapir Academic Press},
	type = {1},
	abstract = {In this paper we present a mixed finite element formulation for modeling the mechanical behavior of the cardiac tissue. The modeling may be divided into a passive and an active part. The passive properties are in this work described by a transversely isotropic, hyperelastic material model. Moreover, the myocardium is assumed to be almost incompressible. In advanced models the active contraction is strongly connected to electro-physiological processes in the muscle cells. In this paper we simplify the active stress contribution by modeling it as a linear function in time. Due to the fact that the heart muscle undergoes large deformations during contraction, both material and geometrical non-linearities must be taken into account in the analysis. Numerical results are presented for different activation patterns applied to a box-shaped test specimen, which represents a piece of the myocardial wall. The proposed mixed method offers reasonable results in the modeling of the mechanical behavior of the test specimen.},
	author = {Thorvaldsen, Tom and Sundnes, Joakim and Osnes, Harald},
	editor = {Bj{\o}rn H. {Skallerud} and Helge I. {Andersson}}
}
@inproceedings {Hanslien.2005.2,
	title = {Numerical Simulations of Cardiac Arrhythmias and Defibrillation},
	journal = {MekIT{\textquoteright}05 - Third national conference on Computational Mechanics, Trondheim, Norway May 11-12},
	year = {2005},
	pages = {135-144},
	publisher = {Tapir Academic Press},
	type = {1},
	address = {Trondheim},
	isbn = {82-519-2052-3},
	author = {Hanslien, Monica and Sundnes, Joakim and Glenn T. {Lines}},
	editor = {Bj{\o}rn H. {Skallerud} and Helge I. {Andersson}}
}
@inproceedings {SC.6.Mardal.2003,
	title = {Error Estimates for the Linear Navier-Stokes Equations},
	journal = {Proceedings of the Second National Conference on Computational Mechanics (MekIT{\textquoteright}03)},
	year = {2003},
	pages = {225-237},
	publisher = {Tapir Academic Press},
	type = {1},
	isbn = {9788251918688},
	author = {Mardal, Kent-Andre and Hans Petter {Langtangen} and Winter, R.},
	editor = {Bj{\o}rn H. {Skallerud} and Andersson, H.I.}
}
@inproceedings {SC.5.Langtangen.2001,
	title = {Propagation of Large Destructive Waves},
	journal = {Computational Mechanics (MekIT{\textquoteright}01)},
	year = {2001},
	publisher = {Tapir},
	type = {1},
	author = {Hans Petter {Langtangen} and Pedersen, G.},
	editor = {H. I. {Andersson} and Bj{\o}rn H. {Skallerud}}
}
