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    Wyświetlanie 1-4 z 4
    Tytuł:
    Skinfold creep under load of caliper. Linear visco- and poroelastic model simulations
    Autorzy:
    Nowak, J.
    Nowak, B.
    Kaczmarek, M.
    Powiązania:
    https://bibliotekanauki.pl/articles/306928.pdf
    Data publikacji:
    2015
    Wydawca:
    Politechnika Wrocławska. Oficyna Wydawnicza Politechniki Wrocławskiej
    Tematy:
    symulacja komputerowa
    tkanka miękka
    lepkosprężystość
    modelowanie
    computer simulations
    soft tissue
    lymphoedema
    viscoelasticity
    poroelasticity
    modeling
    Opis:
    Purpose: This paper addresses the diagnostic idea proposed in [11] to measure the parameter called rate of creep of axillary fold of tissue using modified Harpenden skinfold caliper in order to distinguish normal and edematous tissue. Our simulations are intended to help understanding the creep phenomenon and creep rate parameter as a sensitive indicator of edema existence. The parametric analysis shows the tissue behavior under the external load as well as its sensitivity to changes of crucial hydro-mechanical tissue parameters, e.g., permeability or stiffness. Methods: The linear viscoelastic and poroelastic models of normal (single phase) and oedematous tissue (twophase: swelled tissue with excess of interstitial fluid) implemented in COMSOL Multiphysics environment are used. Simulations are performed within the range of small strains for a simplified fold geometry, material characterization and boundary conditions. The predicted creep is the result of viscosity (viscoelastic model) or pore fluid displacement (poroelastic model) in tissue. Results: The tissue deformations, interstitial fluid pressure as well as interstitial fluid velocity are discussed in parametric analysis with respect to elasticity modulus, relaxation time or permeability of tissue. The creep rate determined within the models of tissue is compared and referred to the diagnostic idea in [11]. Conclusions: The results obtained from the two linear models of subcutaneous tissue indicate that the form of creep curve and the creep rate are sensitive to material parameters which characterize the tissue. However, the adopted modelling assumptions point to a limited applicability of the creep rate as the discriminant of oedema.
    Źródło:
    Acta of Bioengineering and Biomechanics; 2015, 17, 4; 39-48
    1509-409X
    2450-6303
    Pojawia się w:
    Acta of Bioengineering and Biomechanics
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Measurement and analysis of the air pressure curve on the rigid lenses by use of ocular response analyzer
    Autorzy:
    Kasprzak, H.
    Mazur, E.
    Widlicka, M.
    Powiązania:
    https://bibliotekanauki.pl/articles/307438.pdf
    Data publikacji:
    2014
    Wydawca:
    Politechnika Wrocławska. Oficyna Wydawnicza Politechniki Wrocławskiej
    Tematy:
    okulistyka
    ciśnienie śródgałkowe
    lepkosprężystość
    ORA
    ocular viscoelasticity
    intraocular pressure
    air pressure curve
    Opis:
    Purpose: Pressure curves obtained from Ocular Response Analyzer (ORA) differ for the same patient in form and height. In some cases measurements on the subject show significant differences between recorded pressure curves. The purpose of the paper is to examine if the differences result from the corneal properties or from the device operation. Methods: Examination of air pressure curves was carried out on four plano-convex glass lenses with radii of curvature close to the central corneal radius. Lenses were mounted in front of the air jet of the ORA analyzer. Series of 30 measurements on each lenses were recorded with 20s and 60s time interval between measurements. Results were exported to computer and analyzed numerically Results: Results show much higher reproducibility of pressure curves in every series of measurements in comparison to pressure curves recorded on the patients eye. This demonstrates that ORA produces air pulses with high reproducibility. Conclusions: Differences in air pressure pulses for the real eye can indicate the dynamics of ocular properties during measurements. Obtained pressure curves are not symmetrical and not well fitted by Gaussian curve. Type of asymmetry of air pressure curves may be explained by viscoelasticity of air.
    Źródło:
    Acta of Bioengineering and Biomechanics; 2014, 16, 4; 117-121
    1509-409X
    2450-6303
    Pojawia się w:
    Acta of Bioengineering and Biomechanics
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Non-integer viscoelastic constitutive law to model soft biological tissues to in-vivo indentation
    Autorzy:
    Demirci, N.
    Tönük, E.
    Powiązania:
    https://bibliotekanauki.pl/articles/307448.pdf
    Data publikacji:
    2014
    Wydawca:
    Politechnika Wrocławska. Oficyna Wydawnicza Politechniki Wrocławskiej
    Tematy:
    rachunek niecałkowitego rzędu
    tkanka miękka
    lepkosprężystość
    fractional calculus
    indentation tests
    inverse finite element analysis
    soft tissue constitutive relation
    viscoelasticity
    Opis:
    Purpose: During the last decades, derivatives and integrals of non-integer orders are being more commonly used for the description of constitutive behavior of various viscoelastic materials including soft biological tissues. Compared to integer order constitutive relations, non-integer order viscoelastic material models of soft biological tissues are capable of capturing a wider range of viscoelastic behavior obtained from experiments. Although integer order models may yield comparably accurate results, non-integer order material models have less number of parameters to be identified in addition to description of an intermediate material that can monotonically and continuously be adjusted in between an ideal elastic solid and an ideal viscous fluid.Methods: In this work, starting with some preliminaries on non-integer (fractional) calculus, the “spring-pot”, (intermediate mechanical element between a solid and a fluid), non-integer order three element (Zener) solid model, finally a user-defined large strain non-integer order viscoelastic constitutive model was constructed to be used in finite element simulations. Using the constitutive equation developed, by utilizing inverse finite element method and in vivo indentation experiments, soft tissue material identification was performed. Results: The results indicate that material coefficients obtained from relaxation experiments, when optimized with creep experimental data could simulate relaxation, creep and cyclic loading and unloading experiments accurately.Conclusions: Non-integer calculus viscoelastic constitutive models, having physical interpretation and modeling experimental data accurately is a good alternative to classical phenomenological viscoelastic constitutive equations.
    Źródło:
    Acta of Bioengineering and Biomechanics; 2014, 16, 4; 13-21
    1509-409X
    2450-6303
    Pojawia się w:
    Acta of Bioengineering and Biomechanics
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Mechanical guidelines on the properties of human healthy arteries in the design and fabrication of vascular grafts: experimental tests and quasi-linear viscoelastic model
    Autorzy:
    Faturechi, Rahim
    Hashemi, Ata
    Abolfathi, Nabiollah
    Solouk, Atefeh
    Powiązania:
    https://bibliotekanauki.pl/articles/307007.pdf
    Data publikacji:
    2019
    Wydawca:
    Politechnika Wrocławska. Oficyna Wydawnicza Politechniki Wrocławskiej
    Tematy:
    elastyczność
    model konstytutywny
    tętnica
    elasticity
    constitutive model
    human artery
    artificial artery
    quasi-linear viscoelasticity
    Opis:
    Knowledge of mechanical behavior of healthy human arteries as the guidelines to target properties of vascular grafts deserves special attention. There is a lack of mathematical model to characterize mechanical behavior of biomaterial while many mathematical models to reflect mechanics of human arteries have been proposed. The objective of this paper was set to measure mechanical properties of healthy human arteries including Common Carotid Artery (CCA), Abdominal Aorta Artery (AAA), Subclavian Artery (SA), Common Iliac Artery (CIA) and Right and Left Iliac Artery (RIA and LIA) and compare them to those of commercial ePTFE and Dacron®. Methods: Series of stress relaxation and strain to failure tests vere performed on all samples. The experimental data was utilized to develop quasi-linear viscoelastic (QLV) model of both natural and artificial arteries. Results: ePTFE is the stiffest sample, while the CCA is the most compliant one among all. RIA and CIA are more viscous than the other natural arteries, while AA and CCA are less viscous. The proposed model demonstrated an accurate fit to the experimental results, a proof of its ability to model both nonlinear elasticity and viscoelasticity of the human arteries and commercial ones. Conclusions: ePTFE and Dacron® are much stiffer than human arteries that may lead to the disruption of blood hemodynamic and may not be biomechanically feasible as a replacement.
    Źródło:
    Acta of Bioengineering and Biomechanics; 2019, 21, 3; 13-21
    1509-409X
    2450-6303
    Pojawia się w:
    Acta of Bioengineering and Biomechanics
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
      Wyświetlanie 1-4 z 4

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