Computer simulations of blood flow with mass transport through the carotid artery bifurcation

The current paradigm for clinical diagnostic for the treatment of vascular disease relies exclusively on diagnostic imaging data to define the present state of the patient, empirical data to evaluate the efficacy of prior treatments for similar patients. These techniques are insufficient to predict the outcome of a given treatment for an individual patient. We here propose a new paradigm of predictive medicine where physician could use computational simulation to construct and evaluate a specific geometrical/anatomical model to predict the outcome for an individual patient. For this purpose it is necessary to develop a complex software system which combines user friendly interface, automatic solid modeling, automatic finite mesh generation, computational fluid dynamics and post-processing visualization. The flow dynamics is defined according to the incompressible Navier-Stokes equations for Newtonian and non-Newtonian fluids. Mass transport of oxygen and macromolecules is modeled by the convection diffusion equation and coupled with flow dynamics. The computer simulations are based upon finite element analysis where the new computer methods for coupling oxygen transport and fluid flow are described. The comparison results shows a good agreement between clinical observation for critical zones of flow separation, flow recirculation, low wall shear stresses which may contribute to the development of atherosclerotic diseases.

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Assessment of flow within developing chicken vasculature and biofabricated vascularized tissues using multimodal imaging techniques

Scientific Reports ◽

10.1038/s41598-021-97008-w ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Prasanna Padmanaban ◽

Ata Chizari ◽

Tom Knop ◽

Jiena Zhang ◽

Vasileios D. Trikalitis ◽

...

Keyword(s):

Fluid Flow ◽

Imaging Techniques ◽

Dark Field ◽

Flow Dynamics ◽

Laser Speckle ◽

Shear Stresses ◽

Imaging Data ◽

Contrast Imaging ◽

Flow Shear ◽

Engineered Tissues

AbstractFluid flow shear stresses are strong regulators for directing the organization of vascular networks. Knowledge of structural and flow dynamics information within complex vasculature is essential for tuning the vascular organization within engineered tissues, by manipulating flows. However, reported investigations of vascular organization and their associated flow dynamics within complex vasculature over time are limited, due to limitations in the available physiological pre-clinical models, and the optical inaccessibility and aseptic nature of these models. Here, we developed laser speckle contrast imaging (LSCI) and side-stream dark field microscopy (SDF) systems to map the vascular organization, spatio-temporal blood flow fluctuations as well as erythrocytes movements within individual blood vessels of developing chick embryo, cultured within an artificial eggshell system. By combining imaging data and computational simulations, we estimated fluid flow shear stresses within multiscale vasculature of varying complexity. Furthermore, we demonstrated the LSCI compatibility with bioengineered perfusable muscle tissue constructs, fabricated via molding techniques. The presented application of LSCI and SDF on perfusable tissues enables us to study the flow perfusion effects in a non-invasive fashion. The gained knowledge can help to use fluid perfusion in order to tune and control multiscale vascular organization within engineered tissues.

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Finite Element Analysis of Tire/Rim Interface Forces Under Braking and Cornering Loads

Tire Science and Technology ◽

10.2346/1.2139512 ◽

1992 ◽

Vol 20 (2) ◽

pp. 83-105 ◽

Cited By ~ 5

Author(s):

J. P. Jeusette ◽

M. Theves

Keyword(s):

Finite Element ◽

Shear Stress ◽

Contact Pressure ◽

Element Model ◽

Shear Stresses ◽

Detailed Knowledge ◽

Stress Distributions ◽

Element Analysis ◽

Plane Shear ◽

Normal Contact

Abstract During vehicle braking and cornering, the tire's footprint region may see high normal contact pressures and in-plane shear stresses. The corresponding resultant forces and moments are transferred to the wheel. The optimal design of the tire bead area and the wheel requires a detailed knowledge of the contact pressure and shear stress distributions at the tire/rim interface. In this study, the forces and moments obtained from the simulation of a vehicle in stationary braking/cornering conditions are applied to a quasi-static braking/cornering tire finite element model. Detailed contact pressure and shear stress distributions at the tire/rim interface are computed for heavy braking and cornering maneuvers.

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Effects of Loading and Boundary Conditions on the Performance of Ultrasound Compressional Viscoelastography: A Computational Simulation Study to Guide Experimental Design

Materials ◽

10.3390/ma14102590 ◽

2021 ◽

Vol 14 (10) ◽

pp. 2590

Author(s):

Che-Yu Lin ◽

Ke-Vin Chang

Keyword(s):

Boundary Conditions ◽

Simulation Study ◽

Viscoelastic Properties ◽

Measurement Accuracy ◽

Computational Simulation ◽

Vertical Direction ◽

Fixation Method ◽

Element Analysis ◽

Sample Container

Most biomaterials and tissues are viscoelastic; thus, evaluating viscoelastic properties is important for numerous biomedical applications. Compressional viscoelastography is an ultrasound imaging technique used for measuring the viscoelastic properties of biomaterials and tissues. It analyzes the creep behavior of a material under an external mechanical compression. The aim of this study is to use finite element analysis to investigate how loading conditions (the distribution of the applied compressional pressure on the surface of the sample) and boundary conditions (the fixation method used to stabilize the sample) can affect the measurement accuracy of compressional viscoelastography. The results show that loading and boundary conditions in computational simulations of compressional viscoelastography can severely affect the measurement accuracy of the viscoelastic properties of materials. The measurement can only be accurate if the compressional pressure is exerted on the entire top surface of the sample, as well as if the bottom of the sample is fixed only along the vertical direction. These findings imply that, in an experimental validation study, the phantom design should take into account that the surface area of the pressure plate must be equal to or larger than that of the top surface of the sample, and the sample should be placed directly on the testing platform without any fixation (such as a sample container). The findings indicate that when applying compressional viscoelastography to real tissues in vivo, consideration should be given to the representative loading and boundary conditions. The findings of the present simulation study will provide a reference for experimental phantom designs regarding loading and boundary conditions, as well as guidance towards validating the experimental results of compressional viscoelastography.

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Behavior of Offshore Pile in Calcareous Sand—Case Study

Journal of Marine Science and Engineering ◽

10.3390/jmse9080839 ◽

2021 ◽

Vol 9 (8) ◽

pp. 839

Author(s):

Tarek N. Salem ◽

Nadia M. Elkhawas ◽

Ahmed M. Elnady

Keyword(s):

Load Capacity ◽

High Stress ◽

Embedment Depth ◽

Shear Stresses ◽

Northern Coast ◽

Compression Tests ◽

Calcareous Sand ◽

Element Analysis ◽

Mixing Ratios

The erosion of limestone and calcarenite ridges that existed parallel to the Mediterranean shoreline forms the calcareous sand (CS) formation at the surface layer of Egypt's northern coast. The CS is often combined with broken shells which are considered geotechnically problematic due to their possible crushability and relatively high compressibility. In this research, CS samples collected from a site along the northern coast of Egypt are studied to better understand its behavior under normal and shear stresses. Reconstituted CS specimens with different ratios of broken shells (BS) are also investigated to study the effect of BS ratios on the soil mixture strength behavior. The strength is evaluated using laboratory direct-shear and one-dimensional compression tests (oedometer test). The CS specimens are not exposed to significant crushability even under relatively high-stress levels. In addition, a 3D finite element analysis (FEA) is presented in this paper to study the degradation offshore pile capacity in CS having different percentages of BS. The stress–strain results using oedometer tests are compared with a numerical model, and it gave identical matching for most cases. The effects of pile diameter and embedment depth parameters are then studied for the case study on the northern coast. Three different mixing ratios of CS and BS have been used, CS + 10% BS, CS + 30% BS, and CS + 50% BS, which resulted in a decrease of the ultimate vertical compression pile load capacity by 8.8%, 15%, and 16%, respectively.

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Fractographical Analysis and Biomechanical Considerations of a Tooth Restored With Intracanal Fiber Post: Report of the Fracture and Importance of the Fiber Arrangements

Operative Dentistry ◽

10.2341/15-262-s ◽

2016 ◽

Vol 41 (5) ◽

pp. E149-E158 ◽

Cited By ~ 4

Author(s):

VF Wandscher ◽

CD Bergoli ◽

IF Limberger ◽

TP Cenci ◽

P Baldissara ◽

...

Keyword(s):

Finite Element Analysis ◽

Finite Element ◽

Glass Fiber ◽

Shear Stresses ◽

Fiber Post ◽

Element Analysis ◽

Parallel Fibers ◽

Tooth Structure ◽

Anterior Teeth ◽

Compressive Stresses

SUMMARY Objective: This article aims to present a fractographic analysis of an anterior tooth restored with a glass fiber post with parallel fiber arrangement, taking into account force vectors, finite element analysis, and scanning electron microscopy (SEM). Methods: A patient presented at the Faculty of Dentistry (Federal University of Santa Maria, Brazil) with an endodontically treated tooth (ETT), a lateral incisor that had a restorable fracture. The treatment was performed, and the fractured piece was analyzed using stereomicroscopy, SEM, and finite element analysis. Results: The absence of remaining coronal tooth structure might have been the main factor for the clinical failure. We observed different stresses actuating in an ETT restored with a fiber post as well as their relationship with the ultimate fracture. Tensile, compression, and shear stresses presented at different levels inside the restored tooth. Tensile and compressive stresses acted together and were at a maximum in the outer portions and a minimum in the inner portions. In contrast, shear stresses acted concomitantly with tensile and compressive stresses. Shear was higher in the inner portions (center of the post), and lower in the outer portions. This was confirmed by finite element analysis. The SEM analysis showed tensile and compression areas in the fiber post (exposed fibers=tensile areas=lingual surface; nonexposed fibers=compression areas=buccal surface) and shear areas inside the post (scallops and hackle lines). Stereomicroscopic analysis showed brown stains in the crown/root interface, indicating the presence of microleakage (tensile area=lingual surface). Conclusion: We concluded that glass fiber posts with parallel fibers (0°), when restoring anterior teeth, present a greater fracture potential by shear stress because parallel fibers are not mechanically resistant to support oblique occlusal loads. Factors such as the presence of remaining coronal tooth structure and occlusal stability assist in the biomechanical equilibrium of stresses that act upon anterior teeth.

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Failure analysis of simple overlap bonding joints and numerical investigation of the adhered tip geometry effect on the joint strength

Materials Testing ◽

10.1515/mt-2021-0035 ◽

2021 ◽

Vol 63 (11) ◽

pp. 1007-1011

Author(s):

İsmail Saraç

Keyword(s):

Finite Element Analysis ◽

Experimental Study ◽

Finite Element ◽

Reference Model ◽

Lap Joints ◽

Shear Stresses ◽

Element Analysis ◽

Single Lap Joints ◽

Failure Loads ◽

Previous Experimental Study

Abstract This study was carried out in two stages. In the first step, a numerical study was performed to verify the previous experimental study. In accordance with the previous experimental study data, single lap joints models were created using the ANSYS finite element analysis program. Then, nonlinear stress and failure analyses were performed by applying the failure loads obtained in the experimental study. The maximum stress theory was used to find finite element failure loads of the single lap joints models. As a result of the finite element analysis, an approximate 80 % agreement was found between experimental and numerical results. In the second step of the study, in order to increase the bond strength, different overlap end geometry models were produced and peel and shear stresses in the adhesive layer were compared according to the reference model. As a result of the analyses, significant strength increases were calculated according to the reference model. The strength increase in model 3 and model 5 was found to be 80 % and 67 %, respectively, relative to the reference model.

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Quantitative Analysis of Reynolds and Navier–Stokes Based Modeling Approaches for Isothermal Newtonian Elastohydrodynamic Lubrication

Journal of Tribology ◽

10.1115/1.4050272 ◽

2021 ◽

Vol 143 (12) ◽

Author(s):

Leoluca Scurria ◽

Tommaso Tamarozzi ◽

Oleg Voronkov ◽

Dieter Fauconnier

Keyword(s):

High Speed ◽

Stokes Equations ◽

Thickness Distribution ◽

Elastohydrodynamic Lubrication ◽

Lubricant Film ◽

Secondary Flows ◽

Navier Stokes ◽

Shear Stresses ◽

Low Viscosity ◽

Fluid Film Thickness

Abstract When simulating elastohydrodynamic lubrication, two main approaches are usually followed to predict the pressure and fluid film thickness distribution throughout the contact. The conventional approach relies on the Reynolds equation to describe the thin lubricant film, which is coupled to a Boussinesq description of the linear elastic deformation of the solids. A more accurate, yet a time-consuming method is the use of computational fluid dynamics in which the Navier–Stokes equations describe the flow of the thin lubricant film, coupled to a finite element solver for the description of the local contact deformation. This investigation aims at assessing both methods for different lubrication conditions in different elastohydrodynamic lubrication (EHL) regimes and quantify their differences to understand advantages and limitations of both methods. This investigation shows how the results from both approaches deviate for three scenarios: (1) inertial contributions (Re > 1), i.e., thick films, high speed, and low viscosity; (2) high shear stresses leading to secondary flows; and (3) large deformations of the solids leading to inaccuracies of the Boussinesq equation.

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The Unified Theory of Tubesheet Design - Part III: Comparison with ASME Method and Case Study

Journal of Pressure Vessel Technology ◽

10.1115/1.4051797 ◽

2021 ◽

Author(s):

Hong-Song Zhu ◽

Jinguo Zhai ◽

Guo-Yan Zhou

Keyword(s):

Heat Exchangers ◽

Numerical Comparison ◽

Unified Theory ◽

Element Analysis ◽

Theoretical Comparison ◽

Comparison Results ◽

Different Types ◽

Special Case ◽

Simplified Mechanical Model

Abstract Based on the unified theory of tubesheet (TS) design for fixed TS heat exchangers (HEX), floating head and U-tube HEX presented in Part I and Part II, theoretical and numerical comparisons with ASME method are performed in this paper as Part III. Theoretical comparison shows that ASME method can be obtained from the special case of the simplified mechanical model of the unified theory. Numerical Comparison results indicate that predictions given by the unified theory agree well with finite element analysis (FEA), while ASME results are not accurate or not correct. Therefore, it is concluded that the unified theory deals with different types of HEX in equal detail with confidence to predict design stresses.

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MOCVD Equipment for Recent Developments towards the Blue and Green Solid State Laser

MRS Internet Journal of Nitride Semiconductor Research ◽

10.1557/s1092578300001988 ◽

1996 ◽

Vol 1 ◽

Cited By ~ 4

Author(s):

H. Jürgensen ◽

D. Schmitz ◽

G. Strauch ◽

E. Woelk ◽

M. Dauelsberg ◽

...

Keyword(s):

Heat Transfer ◽

Growth Rate ◽

Mass Transport ◽

Stokes Equations ◽

Chemical Species ◽

Heterogeneous Reactions ◽

Radiative Properties ◽

Coupled Flow ◽

Device Structure ◽

Group Iii

For the growth of an electrically pumped lasing nitride emitter, the development of the MOCVD equipment and the process are mutually dependent. Most important is the implementation of the rapid temperature changes that are required between the growth of the different layers of a device structure. Equally important is to provide a reaction chamber that develops a stable gas phase at all growth temperatures used in the process. In this paper we will give insight in the technology and the relationship between processes and equipment. The development of the reation chamber was supported by mathematical modeling that formed the basis for the selection of appropriate process parameters for growth of group-III nitrides. The modeling consists of the numerical solution of the Navier-Stokes equations coupled with heat transfer and mass transport of the chemical species. The modeling of radiative heat transfer takes into account the effect of changing surface radiative properties. These changes result from the coating of the reactor inner surfaces during the growth run. Coupled flow dynamics and chemistry including homogeneous and heterogeneous reactions play an important role for predicting growth rate distributions on the susceptor area. At the practically used high temperatures, group-III metalorganics turn out to be almost entirely decomposed and it is the mass transport of these decomposition products to the growing layer that is assumed to control the growth rate in accordance with experimental observations.AIXTRON GmbH

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