| 1. |
- Hansbo, Peter F G, 1959
(författare)
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A discontinuous finite element method for elasto-plasticity
- 2010
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Ingår i: International Journal for Numerical Methods in Biomedical Engineering. - : Wiley. - 2040-7939 .- 2040-7947. ; 26:6, s. 780-789
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Tidskriftsartikel (refereegranskat)abstract
- We propose an interior penalty discontinuous finite element method for small strain elasto-plasticity using triangular or tetrahedral meshes. A new penalty formulation suitable for plasticity, in particular allowing for inter-element slip, is introduced. The method is also locking free, which is crucial as the plastic zone may exhibit an incompressible response. Numerical results are presented.
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| 2. |
- Johansson, Håkan, 1979, et al.
(författare)
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Application-specific error control for parameter identification problems
- 2011
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Ingår i: International Journal for Numerical Methods in Biomedical Engineering. - : Wiley. - 2040-7939 .- 2040-7947. ; 27:4, s. 608-618
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Tidskriftsartikel (refereegranskat)abstract
- An often occurring scenario in the mathematical modeling of physical phenomena is that of a two-step computation consisting of, first, identifying a relevant parameter set from experiments (such as material parameters) and, second, carrying out a subsequent simulation using these parameters. In order to ensure the quality of the results from the simulation, the different sources of errors, for example, from discretization and inexact solution, must be traced and properly reduced. In this paper, a previously developed method for goal-oriented a posteriori error estimation for identification problems is extended to accommodate the combined identification and subsequent simulation. © 2009 John Wiley & Sons, Ltd.
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| 3. |
- Ngoc Vinh, Phan, et al.
(författare)
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Analytical solutions to two- and three-dimensional periodic flows for numerical model testing
- 2010
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Ingår i: International Journal for Numerical Methods in Biomedical Engineering. - : Wiley. - 2040-7947 .- 2040-7939. ; 26:2, s. 190-204
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Tidskriftsartikel (refereegranskat)abstract
- Analytical solutions to 2D depth-averaged (external mode) and fully 3D (internal mode) periodic flows for numerical model testing are presented in this paper. These solutions take into account the effects of the bottom friction, the horizontal turbulent viscosity, and the vertical turbulent viscosity for the case of 3D flow. The key linkage for the modes is the relationship between the bottom friction coefficients in the 2D and 3D solutions. In the analytical solutions, two parameters are introduced concerning the periodic flows studied, namely, the rate of the horizontal turbulent viscosity and a dimensionless number given by the ratio of this rate to the wave celerity. The effects of the horizontal turbulent viscosity on the wave amplitude and the phase are significant if the square of this number is not much smaller than one. Three cases for numerical model testing are developed according to three different chosen values of the complex wave number. Various results illustrating the solutions to these test cases are also presented. Copyright (C) 2008 John Wiley & Sons. Ltd.
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| 4. |
- Alsafadie, Rabe, et al.
(författare)
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Efficient local formulation for elasto-plastic corotational thin-walled beams
- 2011
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Ingår i: The International Journal for Numerical Methods in Biomedical Engineering. - : Wiley. - 2040-7939. ; 27:4, s. 498-509
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Tidskriftsartikel (refereegranskat)abstract
- A local elasto-plastic formulation, based on a low-order nonlinear strain expression using Bernoulli beam kinematics, is presented in this paper. This element, together with the corotational framework proposed in (Comput. Meth. Appl. Mech. Eng. 2002; 191(17): 1755-1789) can be used to analyze the nonlinear buckling and postbuckling of thin-walled beams with arbitrary cross-section. The formulation captures both the Saint-Venant and warping torsional effects of open cross-sections. Numerical examples show that this local formulation is more efficient than the one proposed in (Comput. Meth. Appl. Mech. Eng. 2002; 191(51):5811-5831) based on a Timoshenko beam assumption.
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| 5. |
- Eriksson, T. S. E., et al.
(författare)
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Modeling the dispersion in electromechanically coupled myocardium
- 2013
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Ingår i: International Journal for Numerical Methods in Biomedical Engineering. - : Wiley. - 2040-7939. ; 29:11, s. 1267-1284
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Tidskriftsartikel (refereegranskat)abstract
- We present an approach to model the dispersion of fiber and sheet orientations in the myocardium. By utilizing structure parameters, an existing orthotropic and invariant-based constitutive model developed to describe the passive behavior of the myocardium is augmented. Two dispersion parameters are fitted to experimentally observed angular dispersion data of the myocardial tissue. Computations are performed on a unit myocardium tissue cube and on a slice of the left ventricle indicating that the dispersion parameter has an effect on the myocardial deformation and stress development. The use of fiber dispersions relating to a pathological myocardium had a rather big effect. The final example represents an ellipsoidal model of the left ventricle indicating the influence of fiber and sheet dispersions upon contraction over a cardiac cycle. Although only a minor shift in the pressure-volume (PV) loops between the cases with no dispersions and with fiber and sheet dispersions for a healthy myocardium was observed, a remarkably different behavior is obtained with a fiber dispersion relating to a diseased myocardium. In future simulations, this dispersion model for myocardial tissue may advantageously be used together with models of, for example, growth and remodeling of various cardiac diseases.
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| 6. |
- Henderson, Leon, 1986, et al.
(författare)
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The use of pseudo-inertia in asymptotic modelling of constraints in boundary value problems
- 2011
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Ingår i: International Journal for Numerical Methods in Biomedical Engineering. - 2040-7947. ; 27:1, s. 59-68
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Tidskriftsartikel (refereegranskat)abstract
- In recent publications, the validity of using positive and negative inertial penalty parameters and the advantage of this approach over the conventional positive penalty function approach have been established for linear eigenvalue problems. This paper shows how this method may be applied to solve a boundary value problem. A steady-state 2-D heat transfer problem is used to demonstrate the method. First, the governing partial differential equation is modified by adding a pseudo-inertial term that results in an equation, which is mathematically identical to the equation governing the free vibration of a membrane. The essential boundary conditions of zero temperature along a specified line are imposed using inertial penalty parameters. The characteristic vibration modes found in this way are used to generate the complementary function to the heat transfer problem. This solution satisfies all natural boundary conditions (adiabatic) and zero temperature conditions using the inertial penalty parameter. To satisfy any additional temperature distribution imposed on the system, two sets of corrector terms are superimposed resulting in the final solution. The results are compared with constrained solutions obtained using the Lagrangian multiplier method and the ordinary penalty method.
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| 7. |
- Pierce, D. M., et al.
(författare)
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Modeling sample/patient-specific structural and diffusional responses of cartilage using DT-MRI
- 2013
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Ingår i: International Journal for Numerical Methods in Biomedical Engineering. - : Wiley. - 2040-7939. ; 29:8, s. 807-821
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Tidskriftsartikel (refereegranskat)abstract
- We propose a new 3D biphasic constitutive model designed to incorporate structural data on the sample/patient-specific collagen fiber network. The finite strain model focuses on the load-bearing morphology, that is, an incompressible, poroelastic solid matrix, reinforced by an inhomogeneous, dispersed fiber fabric, saturated with an incompressible fluid at constant electrolytic conditions residing in strain-dependent pores of the collagen-proteoglycan solid matrix. In addition, the fiber network of the solid influences the fluid permeability and an intrafibrillar portion that cannot be 'squeezed out' from the tissue. We implement the model into a finite element code. To demonstrate the utility of our proposed modeling approach, we test two hypotheses by simulating an indentation experiment for a human tissue sample. The simulations use ultra-high field diffusion tensor magnetic resonance imaging that was performed on the tissue sample. We test the following hypotheses: (i) the through-thickness structural arrangement of the collagen fiber network adjusts fluid permeation to maintain fluid pressure (Biomech. Model. Mechanobiol. 7: 367-378, 2008); and (ii) the inhomogeneity of mechanical properties through the cartilage thickness acts to maintain fluid pressure at the articular surface (J. Biomech. Eng. 125: 569-577, 2003). For the tissue sample investigated, both through-thickness inhomogeneities of the collagen fiber distribution and of the material properties serve to influence the interstitial fluid pressure distribution and maintain fluid pressure underneath the indenter at the cartilage surface. Tissue inhomogeneity appears to have a larger effect on fluid pressure retention in this tissue sample and on the advantageous pressure distribution.
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| 8. |
- Valentin, A., et al.
(författare)
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A finite element-based constrained mixture implementation for arterial growth, remodeling, and adaptation : Theory and numerical verification
- 2013
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Ingår i: International Journal for Numerical Methods in Biomedical Engineering. - : Wiley. - 2040-7939. ; 29:8, s. 822-849
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Tidskriftsartikel (refereegranskat)abstract
- We implemented a constrained mixture model of arterial growth and remodeling in a nonlinear finite element framework to facilitate numerical analyses of diverse cases of arterial adaptation and maladaptation, including disease progression, resulting in complex evolving geometries and compositions. This model enables hypothesis testing by predicting consequences of postulated characteristics of cell and matrix turnover, including evolving quantities and orientations of fibrillar constituents and nonhomogenous degradation of elastin or loss of smooth muscle function. The nonlinear finite element formulation is general within the context of arterial mechanics, but we restricted our present numerical verification to cylindrical geometries to allow comparisons with prior results for two special cases: uniform transmural changes in mass and differential growth and remodeling within a two-layered cylindrical model of the human aorta. The present finite element model recovers the results of these simplified semi-inverse analyses with good agreement.
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