| 1. |
- Dabbaghchian, Saeed, et al.
(författare)
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Reconstruction of vocal tract geometries from biomechanical simulations
- 2018
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Ingår i: International Journal for Numerical Methods in Biomedical Engineering. - : John Wiley & Sons. - 2040-7939 .- 2040-7947.
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Tidskriftsartikel (refereegranskat)abstract
- Medical imaging techniques are usually utilized to acquire the vocal tract geometry in 3D, which may then be used, eg, for acoustic/fluid simulation. As an alternative, such a geometry may also be acquired from a biomechanical simulation, which allows to alter the anatomy and/or articulation to study a variety of configurations. In a biomechanical model, each physical structure is described by its geometry and its properties (such as mass, stiffness, and muscles). In such a model, the vocal tract itself does not have an explicit representation, since it is a cavity rather than a physical structure. Instead, its geometry is defined implicitly by all the structures surrounding the cavity, and such an implicit representation may not be suitable for visualization or for acoustic/fluid simulation. In this work, we propose a method to reconstruct the vocal tract geometry at each time step during the biomechanical simulation. Complexity of the problem, which arises from model alignment artifacts, is addressed by the proposed method. In addition to the main cavity, other small cavities, including the piriform fossa, the sublingual cavity, and the interdental space, can be reconstructed. These cavities may appear or disappear by the position of the larynx, the mandible, and the tongue. To illustrate our method, various static and temporal geometries of the vocal tract are reconstructed and visualized. As a proof of concept, the reconstructed geometries of three cardinal vowels are further used in an acoustic simulation, and the corresponding transfer functions are derived.
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| 2. |
- Dabbaghchian, Saeed, et al.
(författare)
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Simulation of vowel-vowel utterances using a 3D biomechanical-acoustic model
- 2021
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Ingår i: International Journal for Numerical Methods in Biomedical Engineering. - Wiley : Wiley-Blackwell. - 2040-7939 .- 2040-7947. ; 37:1
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Tidskriftsartikel (refereegranskat)abstract
- A link is established between biomechanical and acoustic 3D models for the numerical simulation of vowel-vowel utterances. The former rely on the activation and contraction of relevant muscles for voice production, which displace and distort speech organs. However, biomechanical models do not provide a closed computational domain of the 3D vocal tract airway where to simulate sound wave propagation. An algorithm is thus proposed to extract the vocal tract boundary from the surrounding anatomical structures at each time step of the transition between vowels. The resulting 3D geometries are fed into a 3D finite element acoustic model that solves the mixed wave equation for the acoustic pressure and particle velocity. An arbitrary Lagrangian-Eulerian framework is considered to account for the evolving vocal tract. Examples include six static vowels and three dynamic vowel-vowel utterances. Plausible muscle activation patterns are first determined for the static vowel sounds following an inverse method. Dynamic utterances are then generated by linearly interpolating the muscle activation of the static vowels. Results exhibit nonlinear trajectory of the vocal tract geometry, similar to that observed in electromagnetic midsagittal articulography. Clear differences are appreciated when comparing the generated sound with that obtained from direct linear interpolation of the vocal tract geometry. That is, interpolation between the starting and ending vocal tract geometries of an utterance, without resorting to any biomechanical model.
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| 3. |
- Feng, Xianhui, et al.
(författare)
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Study on fracture behavior of molars based on three‐dimensional high‐precision computerized tomography scanning and numerical simulation
- 2022
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Ingår i: International Journal for Numerical Methods in Biomedical Engineering. - : John Wiley & Sons. - 2040-7939 .- 2040-7947. ; 38:3
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Tidskriftsartikel (refereegranskat)abstract
- A series of three-dimensional (3D) numerical simulations are conducted to investigate the gradual failure process of molars in this study. The real morphology and internal mesoscopic structure of a whole tooth are implemented into the numerical simulations through computerized tomography scanning, digital image processing, and 3D matrix mapping. The failure process of the whole tooth subject to compressions including crack initiation, crack propagation, and final failure pattern is reproduced using 3D realistic failure process analysis (RFPA3D) method. It is concluded that a series of microcracks are gradually initiated, nucleated, and subsequently interconnect to form macroscopic cracks when the teeth are under over-compressions. The propagation of the macroscopic cracks results in the formation of fracture surfaces and penetrating cracks, which are essential signs and manifestations of the tooth failure. Moreover, the simulations reveal that, the material heterogeneity is a critical factor that affects the mechanical properties and fracture modes of the teeth, which vary from crown fractures to crown-root fractures and root fractures depending on different homogeneity indices.
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| 4. |
- Funke, Simon Wolfgang, et al.
(författare)
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Variational data assimilation for transient blood flow simulations: Cerebral aneurysms as an illustrative example
- 2019
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Ingår i: International Journal for Numerical Methods in Biomedical Engineering. - : Wiley. - 2040-7939 .- 2040-7947. ; 35:1
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Tidskriftsartikel (refereegranskat)abstract
- Several cardiovascular diseases are caused from localised abnormal blood flow such as in the case of stenosis or aneurysms. Prevailing theories propose that the development is caused by abnormal wall shear stress in focused areas. Computational fluid mechanics have arisen as a promising tool for a more precise and quantitative analysis, in particular because the anatomy is often readily available even by standard imaging techniques such as magnetic resonance and computed tomography angiography. However, computational fluid mechanics rely on accurate initial and boundary conditions, which are difficult to obtain. In this paper, we address the problem of recovering high-resolution information from noisy and low-resolution physical measurements of blood flow (for example, from phase-contrast magnetic resonance imaging [PC-MRI]) using variational data assimilation based on a transient Navier-Stokes model. Numerical experiments are performed in both 3D (2D space and time) and 4D (3D space and time) and with pulsatile flow relevant for physiological flow in cerebral aneurysms. The results demonstrate that, with suitable regularisation, the model accurately reconstructs flow, even in the presence of significant noise.
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| 5. |
- Gasser, T. Christian, et al.
(författare)
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A quarter of a century biomechanical rupture risk assessment of abdominal aortic aneurysms. Achievements, clinical relevance, and ongoing developments
- 2022
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Ingår i: International Journal for Numerical Methods in Biomedical Engineering. - : Wiley. - 2040-7939 .- 2040-7947.
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Tidskriftsartikel (refereegranskat)abstract
- Abdominal aortic aneurysm (AAA) disease, the local enlargement of the infrarenal aorta, is a serious condition that causes many deaths, especially in men exceeding 65 years of age. Over the past quarter of a century, computational biomechanical models have been developed towards the assessment of AAA risk of rupture, technology that is now on the verge of being integrated within the clinical decision-making process. The modeling of AAA requires a holistic understanding of the clinical problem, in order to set appropriate modeling assumptions and to draw sound conclusions from the simulation results. In this article we summarize and critically discuss the proposed modeling approaches and report the outcome of clinical validation studies for a number of biomechanics-based rupture risk indices. Whilst most of the aspects concerning computational mechanics have already been settled, it is the exploration of the failure properties of the AAA wall and the acquisition of robust input data for simulations that has the greatest potential for the further improvement of this technology.
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| 6. |
- 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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| 7. |
- Jansson, Johan, et al.
(författare)
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Adaptive unified continuum FEM modeling of a 3D FSI benchmark problem
- 2017
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Ingår i: International Journal for Numerical Methods in Biomedical Engineering. - : Wiley-Blackwell. - 2040-7939 .- 2040-7947. ; 33:9
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we address a 3D fluid-structure interaction benchmark problem that represents important characteristics of biomedical modeling. We present a goal-oriented adaptive finite element methodology for incompressible fluid-structure interaction based on a streamline diffusion–type stabilization of the balance equations for mass and momentum for the entire continuum in the domain, which is implemented in the Unicorn/FEniCS software framework. A phase marker function and its corresponding transport equation are introduced to select the constitutive law, where the mesh tracks the discontinuous fluid-structure interface. This results in a unified simulation method for fluids and structures. We present detailed results for the benchmark problem compared with experiments, together with a mesh convergence study.
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| 8. |
- 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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| 9. |
- Naseri, Hosein, 1987, et al.
(författare)
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A numerical study on the safety belt-to-pelvis interaction
- 2022
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Ingår i: International Journal for Numerical Methods in Biomedical Engineering. - : Wiley. - 2040-7939 .- 2040-7947. ; 38:4
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Tidskriftsartikel (refereegranskat)abstract
- The slide of the lap belt over the iliac crest of the pelvis during vehicle frontal crashes can substantially increase the risk of some occupant injuries. A multitude of factors, related to occupants or the design of belt, are associated with this phenomenon. This study investigates safety belt-to-pelvis interaction and identifies the most influential parameters. It also explores how initial lap belt position influences the interaction between lap belt and pelvis. A finite element model of the interaction between lap belt with pelvis through a soft tissue part was created. Belt angle, belt force, belt loading rate and belt-to-body friction as belt design parameters, and pelvis angle, constitute parameters of soft tissue, and soft tissue-to-pelvis friction as occupant parameters were inspected. For the soft tissue part, subcutaneous adipose tissue with different thicknesses was created and the effect initial lap belt position may have on lap belt-to-pelvis interaction was investigated. The influential parameters have been identified as: the belt angle and belt force as belt design parameters and the pelvis angle and compressibility of soft tissue as occupant parameters. The risk for the slide of lap belt over the iliac crest of the pelvis was predicted higher as the initial lap belt positions goes superior to the pelvis. Of different submarining parameters, the lap belt angle represents the most influential one. The lap belt-to-pelvis interaction is influenced by the thickness of subcutaneous adipose tissue between lap belt and pelvis indicating a higher risk for obese occupants.
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| 10. |
- 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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