Viscoelastic Behavior of a Lung Alveolar Duct Model

1999 ◽  
Vol 122 (2) ◽  
pp. 143-151 ◽  
Author(s):  
E. Denny ◽  
R. C. Schroter
Keyword(s):  
Surface Tension ◽  
Tidal Volume ◽  
Viscoelastic Behavior ◽  
Surface Tension Force ◽  
Element Model ◽  
Lung Parenchyma ◽  
Oscillatory Behavior ◽  
Published Data ◽  
Elastic Model ◽  
Alveolar Duct

A study is conducted into the oscillatory behavior of a finite element model of an alveolar duct. Its load-bearing components consist of a network of elastin and collagen fibers and surface tension acting over the air–liquid interfaces. The tissue is simulated using a visco-elastic model involving nonlinear quasi-static stress–strain behavior combined with a reduced relaxation function. The surface tension force is simulated with a time- and area-dependent model of surfactant behavior. The model was used to simulate lung parenchyma under three surface tension cases: air-filled, liquid-filled, and lavaged with 3-dimethyl siloxane, which has a constant surface tension of 16 dyn/cm. The dynamic elastance Edyn and tissue resistance Rti were computed for sinusoidal tidal volume oscillations over a range of frequencies from 0.16–2.0 Hz. A comparison of the variation of Edyn and Rti with frequency between the model and published experimental data showed good qualitative agreement. Little difference was found in the model between Rti for the air-filled and lavaged models; in contrast, published data revealed a significantly higher value of Rti in the lavaged lung. The absence of a significant increase in Rti for the lavaged model can be attributed to only minor changes in the individual fiber bundle resistances with changes in their configuration. The surface tension was found to make an important contribution to both Edyn and Rti in the air-filled duct model. It was also found to amplify any existing tissue dissipative properties, despite exhibiting none itself over the small tidal volume cycles examined. [S0148-0731(00)00502-1]

A model for mechanical structure of the alveolar duct

1982 ◽  
Vol 52 (4) ◽  
pp. 1064-1070 ◽  
Author(s):  
T. A. Wilson ◽  
H. Bachofen
Keyword(s):  
Surface Tension ◽  
Lung Volume ◽  
Published Data ◽  
Scanning Electron Micrographs ◽  
Fiber System ◽  
Lung Capacity ◽  
Alveolar Duct ◽  
Tissue System ◽  
Line Elements ◽  
Air Liquid Interface

The appearance of the microstructure of the lung as revealed in transmission and scanning electron micrographs of perfusion-fixed air- and saline-filled lungs suggests the following model for the structure of the alveolar duct. There are two networks of force-bearing elements. The first is an interdependent part of the peripheral connective tissue system that starts from the pleura and extends into the interlobar and interlobular fissures. At the sublobular level, its geometry is not yet fully clear. This network is extended by changes in lung volume and is insensitive to surface tension. The second network is composed of the line elements that form the rims of the alveolar openings. This network is the terminal part of the axial fiber system that surrounds bronchi, bronchioli, and arteries. The line elements of this network are extended by the outward force of surface tension. The two-dimensional alveolar walls that form the alveoli are negligible mechanical components except as platforms for surface tension at the air-liquid interface. An analysis of the mechanics of this model yields relations among surface area, recoil pressure, lung volume, and surface tension that are consistent with published data for lung volumes below 80% of total lung capacity.

Effect of surface forces on oscillatory behavior of lungs

1995 ◽  
Vol 79 (5) ◽  
pp. 1578-1585 ◽  
Author(s):  
D. Stamenovic ◽  
G. M. Barnas
Keyword(s):  
Surface Tension ◽  
Airway Resistance ◽  
Surface Film ◽  
Oscillatory Behavior ◽  
Tissue Impedance ◽  
Dimethyl Siloxane ◽  
Tissue Resistance ◽  
Before And After ◽  
Alveolar Duct ◽  
The Difference

The effect of alveolar surface tension on lung dynamic behavior was investigated by measuring total lung and tissue impedances in excised rabbit lungs at breathing frequencies of 0.2–0.8 Hz and tidal volumes of 10, 20, and 30 ml before and after lavage with 3-dimethyl siloxane, which provided a constant surface tension of 16 dyn/cm. The lungs were oscillated around the mean deflation pressures of 5 (control) and 8 cmH2O (lavaged), i.e., lung volume of 60% of total lung capacity. The total lung impedance was calculated from measurements of pressure and airflow at the trachea, and tissue impedance was measured by the alveolar capsule technique. The airway contribution was obtained as the difference between total lung and tissue impedances. In the lavaged lungs, dynamic elastance (Edyn) decreased and tissue resistance (Rti) increased relative to the control values over the entire frequency range. Airway resistance increased at the higher flow rates only. The decrease in Edyn could be attributed to the absence of surface film elastance in the lavaged lungs. The increase in airway resistance could be attributed to accentuated flow dependence due to changes in airway geometry and residual lavage liquid. However, the most intriguing result was the increase in Rti in the lavaged lungs. It could be attributed to altered mechanics at the alveolar duct level after lavage. It is concluded that dissipative properties of lung tissue are major determinants of Rti, whereas elastic properties of both tissue and surface film are important determinants of Edyn.

Relationships Between Alveolar Size and Fibre Distribution in a Mammalian Lung Alveolar Duct Model

1997 ◽  
Vol 119 (3) ◽  
pp. 289-297 ◽  
Author(s):  
E. Denny ◽  
R. C. Schroter
Keyword(s):  
Static Pressure ◽  
Collagen Fibre ◽  
Element Model ◽  
Volume Density ◽  
Fibre Volume ◽  
Published Data ◽  
Liquid Interfaces ◽  
Tension Properties ◽  
Alveolar Duct ◽  
Mammalian Lung

A finite element model, comprising an assemblage of tetrakaidecahedra or truncated octahedra, is used to represent an alveolar duct unit. The dimensions of the elastin and collagen fibre bundles, and the surface tension properties of the air-liquid interfaces, are based on available published data. Changes to the computed static pressure-volume behavior with variation in alveolar dimensions and fibre volume densities are characterized using distensibility indices (K). The air-filled lung distensibility (Ka) decreased with a reduction in the alveolar airspace length dimensions and increased with a reduction of total fibre volume density. The saline-filled lung distensibility (Ks) remained constant with alveolar dimensions and increased with decreasing total fibre volume density. The degree of geometric anisotropy between the duct lumen and alveoli was computed over pressure-volume cycles. To preserve broadly isotropic behavior, parenchyma with smaller alveolar airspace length dimensions required higher concentrations of fibres located in the duct and less in the septa in comparison with parenchyma of larger airspace dimensions.

A Finite Element Model for Predicting the Collapse of Short and Large Two-Line Patterns During Drying Process in Photolithography

2010 ◽  
Author(s):  
Seyed Farshid Chini ◽  
Alidad Amirfazli
Keyword(s):  
Surface Tension ◽  
Finite Element ◽  
Surface Tension Force ◽  
Element Model ◽  
Fe Model ◽  
Interface Shape ◽  
Surface Evolver ◽  
Parallel Patterns ◽  
Line Parallel ◽  
Three Phase

Photolithography is one of the main mass nano-production processes. Smaller devices are always aimed to save material and energy. Manufacturing small devices by photolithography is a challenge, due to the risk of collapse of patterns during the drying of rinse liquid. One of the main pattern shapes is the two-line parallel. In our previous study, an analytical model was developed for predicting the collapse of large (L/d, LAR>20; see Fig. 1) two-line parallel patterns [1]. This model assumes the rinse interface shape is cylindrical. Knowledge of the rinse interface shape is needed to define the forces contribute to collapse, i.e. Laplace pressure and surface tension force at the three-phase line. In the current study, a Finite Element (FE) model is developed to predict the collapse of short (LAR<20) and large (LAR>20) two-line parallel patterns. Rinse liquid shape and its curvature are found using Surface Evolver (an interactive program for the study of surfaces shaped by surface tension, gravitational and other energies). Another finite element method (i.e. ANSYS 11.0) is used to find the pattern deformation. It was found that the pattern deformation decreases by decreasing the LAR value. It is important as for the cases that due to the design specifications, selection of the pattern material and rinse liquid is restricted, by changing the LAR value one may resolve the collapse problem.

A Finite Element Model for Macroscopic Deformation of the Lung

1980 ◽  
Vol 102 (1) ◽  
pp. 1-7 ◽  
Author(s):  
D. L. Vawter
Keyword(s):  
Surface Tension ◽  
Finite Element ◽  
Interfacial Tension ◽  
Finite Element Model ◽  
Element Model ◽  
Lung Parenchyma ◽  
Elastic Behavior ◽  
Incremental Approach ◽  
Macroscopic Deformation ◽  
Nonlinear Elastic

A finite element model is formulated for determining the macroscopic stress, strain and deformation of the lung parenchyma. The effects of nonlinear elastic behavior, finite deformation, and interfacial tension are included. An incremental approach is used. Illustrative results for deformation of the lung due to its weight are included. The necessity of including surface tension explicitly is demonstrated.

scholarly journals Comparison of Surface Tension Models for the Volume of Fluid Method

Processes ◽  
2019 ◽  
Vol 7 (8) ◽  
pp. 542 ◽  
Author(s):  
Kurian J. Vachaparambil ◽  
Kristian Etienne Einarsrud
Keyword(s):  
Surface Tension ◽  
Multiphase Flow ◽  
Capillary Rise ◽  
Surface Tension Force ◽  
Surface Force ◽  
Parallel Plates ◽  
Time Step ◽  
Mesh Resolution ◽  
Active Research ◽  
Spurious Currents

With the increasing use of Computational Fluid Dynamics to investigate multiphase flow scenarios, modelling surface tension effects has been a topic of active research. A well known associated problem is the generation of spurious velocities (or currents), arising due to inaccuracies in calculations of the surface tension force. These spurious currents cause nonphysical flows which can adversely affect the predictive capability of these simulations. In this paper, we implement the Continuum Surface Force (CSF), Smoothed CSF and Sharp Surface Force (SSF) models in OpenFOAM. The models were validated for various multiphase flow scenarios for Capillary numbers of 10 − 3 –10. All the surface tension models provide reasonable agreement with benchmarking data for rising bubble simulations. Both CSF and SSF models successfully predicted the capillary rise between two parallel plates, but Smoothed CSF could not provide reliable results. The evolution of spurious current were studied for millimetre-sized stationary bubbles. The results shows that SSF and CSF models generate the least and most spurious currents, respectively. We also show that maximum time step, mesh resolution and the under-relaxation factor used in the simulations affect the magnitude of spurious currents.

3-D Heterogeneous Elastic Crustal Structure for Deformation Models in the Hengill Area, SW Iceland

2021 ◽  
Author(s):  
Cécile Ducrocq ◽  
Halldór Geirsson ◽  
Alex Hobé ◽  
Gylfi Páll Hersir ◽  
Thóra Árnadóttir ◽  
...  
Keyword(s):  
Crustal Structure ◽  
Power Plants ◽  
Electrical Power ◽  
Element Model ◽  
Volcanic Complex ◽  
Elastic Model ◽  
Spatial Effects ◽  
Volcanic System ◽  
Shear Moduli ◽  
Deformation Models

&lt;p&gt;Crustal deformation in volcanic areas relates ground motions, measured by geodetic techniques, to physical (e.g. pressure or volumetric) changes of magmatic sources below the surface. These measurements contribute to studies of&lt;!-- this is not optimal, changing it might require rewriting the entire sentence. Perhaps you want to break this sentence into two. --&gt; ongoing processes at the source of possible unrest, and are thus key for hazard assessment in active volcanic areas around the globe. However, such assessments often rely on geodetic-based models with quite simplistic assumptions of the physical structure of the volcanic complex. Particularly, constant values of elastic parameters (e.g. Poisson&amp;#8217;s ratio and shear moduli) are commonly used for entire active volcanic areas, thus overlooking the spatial effects of lithological properties, depth-dependant compression and temperature variations on those parameters. These simplifications may lead to inaccurate interpretation of the location, shape, and volume change of deformation sources.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;In this study we ask how the 3-D heterogeneities of the elastic crustal structure beneath the Hengill volcanic system, SW Iceland, affects models of deformation sources in the area. The Hengill area hosts two active volcanic systems (Hengill and Hr&amp;#243;mundartindur), and two high-enthalpy geothermal power plants (Nesjavellir and Hellishei&amp;#240;i), which provide thermal and electrical power to Reykjav&amp;#237;k, the capital of Iceland, only 30 km away. To retrieve information on the spatial heterogeneities in the shear moduli and Poisson&amp;#8217;s ratio beneath the Hengill area, we first estimate the 3-D shallow density structure of the area using results from regional and local gravimetric surveys. We implement this structure, along with seismic tomographic studies of the SW Iceland, in a Finite Element Model to solve, using forward models, for the 3-D heterogeneities in the shear moduli and Poisson&amp;#8217;s ratio beneath the Hengill area.&lt;!-- This might be more effective if the order of these statements is changed, for example: To achieve [stated goal] we produce [FEM] using [results from geophysics]. --&gt; Furthermore, we discuss the difference between static and kinematic elastic moduli, which is important when building deformation models from seismic tomography.&lt;!-- My first reaction to this statement is: &quot;How do you address this?&quot; This could be answered directly, except if you think it detracts from the story. --&gt; The new 3-D inferred elastic model is then used to re-estimate parameters for different sources of deformation causing uplift and subsidence in the area in the past decades. This study shows the importance of accounting for heterogeneities in the crustal elastic structure to estimate with higher accuracy the sources of deformation in volcanic areas around the world.&lt;/p&gt;

FEBio finite element model of a pediatric cervical spine

2021 ◽  
pp. 1-7
Author(s):  
Sean M. Finley ◽  
J. Harley Astin ◽  
Evan Joyce ◽  
Andrew T. Dailey ◽  
Douglas L. Brockmeyer ◽  
...  
Keyword(s):  
Finite Element ◽  
Cervical Spine ◽  
Finite Element Model ◽  
Material Properties ◽  
Surgical Simulation ◽  
Element Model ◽  
Axial Stiffness ◽  
Published Data ◽  
Axial Tension ◽  
Flexion Extension

OBJECTIVE The underlying biomechanical differences between the pediatric and adult cervical spine are incompletely understood. Computational spine modeling can address that knowledge gap. Using a computational method known as finite element modeling, the authors describe the creation and evaluation of a complete pediatric cervical spine model. METHODS Using a thin-slice CT scan of the cervical spine from a 5-year-old boy, a 3D model was created for finite element analysis. The material properties and boundary and loading conditions were created and model analysis performed using open-source software. Because the precise material properties of the pediatric cervical spine are not known, a published parametric approach of scaling adult properties by 50%, 25%, and 10% was used. Each scaled finite element model (FEM) underwent two types of simulations for pediatric cadaver testing (axial tension and cardinal ranges of motion [ROMs]) to assess axial stiffness, ROM, and facet joint force (FJF). The authors evaluated the axial stiffness and flexion-extension ROM predicted by the model using previously published experimental measurements obtained from pediatric cadaveric tissues. RESULTS In the axial tension simulation, the model with 50% adult ligamentous and annulus material properties predicted an axial stiffness of 49 N/mm, which corresponded with previously published data from similarly aged cadavers (46.1 ± 9.6 N/mm). In the flexion-extension simulation, the same 50% model predicted an ROM that was within the range of the similarly aged cohort of cadavers. The subaxial FJFs predicted by the model in extension, lateral bending, and axial rotation were in the range of 1–4 N and, as expected, tended to increase as the ligament and disc material properties decreased. CONCLUSIONS A pediatric cervical spine FEM was created that accurately predicts axial tension and flexion-extension ROM when ligamentous and annulus material properties are reduced to 50% of published adult properties. This model shows promise for use in surgical simulation procedures and as a normal comparison for disease-specific FEMs.

Microscopic vs. macroscopic deformation of the pulmonary alveolar duct

1992 ◽  
Vol 72 (4) ◽  
pp. 1348-1354 ◽  
Author(s):  
D. Yager ◽  
H. Feldman ◽  
Y. C. Fung
Keyword(s):  
Human Lung ◽  
Lung Parenchyma ◽  
Stretch Ratio ◽  
Area Ratio ◽  
Force Balance ◽  
Load Carrying ◽  
Macroscopic Deformation ◽  
Alveolar Duct ◽  
Deformed State ◽  
Length And Area

The stretch of the perimeters of alveolar ducts was measured at the surface of saline-filled specimens of human and dog lung parenchyma that were stretched biaxially. The microscopic stretch of these ducts was measured at several levels of isotropic biaxial macroscopic stretch of the parenchyma with stretch ratio (lambda x = lambda y) in the range of 1.20–1.40, which roughly corresponds to tidal breathing in humans and dogs. Alveolar walls were found to be load-carrying elements in the saline-filled lung, as seen by their straightness at all levels of stretch. Quantitatively, let l, A, L, and S denote, respectively, the duct perimeter length and area and the parenchymal target perimeter and area in the deformed state and lo, Ao, Lo, and So the corresponding variables in the undeformed state. The microscopic stretch ratio of the ducts (l/lo) was found to be approximately 4% larger than the macroscopic stretch ratio (L/Lo) in human lung and approximately 10% larger in dog lung. The microscopic area ratio of the ducts (A/Ao) was found to be approximately 10% larger than the macroscopic area ratio (S/So) in human lung and approximately 22% larger in dog lung. Ducts within human parenchyma were seen to be about twice as stiff as ducts within dog parenchyma over the range of macroscopic stretch studied. This correlates with the volume fractions of collagen and elastin being higher in the human lung than in dog lung. The observed nonuniformity in strain field at the microstructural level suggests the need to include a force balance between alveolar ducts and septal walls when modeling the mechanics of saline-filled parenchyma.

scholarly journals Viscoelastic behavior of a casing material and its utilization in premium connections in high-temperature gas wells

2018 ◽  
Vol 10 (12) ◽  
pp. 168781401881745 ◽  
Author(s):  
Ying Zhang ◽  
Zhanghua Lian ◽  
Mi Zhou ◽  
Tiejun Lin
Keyword(s):  
High Temperature ◽  
Contact Pressure ◽  
Viscoelastic Model ◽  
Viscoelastic Behavior ◽  
Element Model ◽  
Gas Production ◽  
Prony Series ◽  
Gas Well ◽  
Gas Leakage ◽  
High Temperature Gas

At the high or extra-high temperatures in a natural gas oilfield, where the premium connection is employed by casing, gas leakage in the wellbore is always detected after several years of gas production. As the viscoelastic material’s mechanical properties change with time and temperature, the relaxation of the contact pressure on the connection sealing surface is the main reason for the gas leakage in the high-temperature gas well. In this article, tension-creep experiments were conducted. Furthermore, a constitutive model of the casing material was established by the Prony series method. Moreover, the Prony series’ shift factor was calculated to study the thermo-rheological behavior of the casing material ranging from 120°C to 300°C. A linear viscoelastic model was implemented in ABAQUS, and the simulation results are compared to our experimental data to validate the methodology. Finally, the viscoelastic finite element model is applied to predict the relaxation of contact pressure on the premium connections’ sealing surface versus time under different temperatures. And, the ratio of the design contact pressure and the intending gas sealing pressure is recommended for avoiding the premium connections failure in the high-temperature gas well.

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