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Using 2D In Vivo IVUS-Based Models for Human Coronary Plaque Progression Analysis and Comparison with 3D Fluid-Structure Interaction Models: A Multi-Patient Study
Get PDFComputational modeling has been used extensively in cardiovascular and biological research, providing valuable information. However, 3D vulnerable plaque model construction with complex geometrical features and multicomponents is often very time consuming and not practical for clinical implementation. This paper investigated if 2D atherosclerotic plaque models could be used to replace 3D models to perform correlation analysis and achieve similar results. In vivo intravascular ultrasound (IVUS) coronary plaque data were acquired from a patient follow-up study to construct 2D structure-only and 3D FSI models to obtain plaque wall stress (PWS) and strain (PWSn) data. One hundred and twenty-seven (127) matched IVUS slices at baseline and follow up were obtained from 3 patients. Our results showed that 2D models overestimated stress and strain by 30% and 33%, respectively, compared to results from 3D FSI models. 2D/3D correlation comparison indicated that 116 out of 127 slices had a consistent correlation between plaque progression (WTI) and wall thickness; 103 out of 127 slices had a consistent correlation between WTI and PWS; and 99 out of 127 slices had a consistent correlation between WTI and PWSn. This leads to the potential that 2D models could be used in actual clinical implementation where quick analysis delivery time is essential
Size-Dependent Diffusion of Dextrans in Excised Porcine Corneal Stroma
Get PDFDelivery of therapeutic agents to the eye requires efficient transport through cellular and extracellular barriers. We evaluated the rate of diffusive transport in excised porcine corneal stroma using fluorescently labeled dextran molecules with hydrodynamic radii ranging from 1.3 to 34 nm. Fluorescence correlation spectroscopy (FCS) was used to measure diffusion coefficients of dextran molecules in the excised porcine corneal stroma. The preferential sensitivity of FCS to diffusion along two dimensions was used to differentially probe diffusion along the directions parallel to and perpendicular to the collagen lamellae of the corneal stroma. In order to develop an understanding of how size affects diffusion in cornea, diffusion coefficients in cornea were compared to diffusion coefficients measured in a simple buffer solution. Dextran molecules diffuse more slowly in cornea as compared to buffer solution. The reduction in diffusion coefficient is modest however (67% smaller), and is uniform over the range of sizes that we measured. This indicates that, for dextrans in the 1.3 to 34 nm range, the diffusion landscape of corneal stroma can be represented as a simple liquid with a viscosity approximately 1.5 times that of water. Diffusion coefficients measured parallel vs. perpendicular to the collagen lamellae were indistinguishable. This indicates that diffusion in the corneal stroma is not highly anisotropic. Our results support the notion that the corneal stroma is highly permeable and isotropic to transport of hydrophilic molecules and particles with hydrodynamic radii up to at least 34 nm
Optimization of Forming Process of a U-rib by Gas Heating Based on Theoretical Prediction
Get PDFBending deformation of U-rib by gas heating is investigated using Thermal Elastic Plastic FEA employing an accurate heat source model. To validate our computational model, comparison between numerical analysis and experimental measurements are carried out. Good agreement is obtained for both temperature and deformation measurements. Inherent deformation method is employed to evaluate the overall behavior of U-rib under the influence of heating location and heating speed. Based on the prediction by FEA and using the inherent deformation method a new mathematical model describing the deformation of the U-rib is developed and evaluated for different combinations of heating conditions which can optimize the process of U-rib bending
An Explicit Time Marching Technique With Solution-Adaptive Time Integration Parameters
Get PDFIn this work, an explicit time marching procedure, with solution-adaptive time integration parameters, is introduced for the analysis of hyperbolic models. The proposed technique is conditionally-stable, second-order accurate and it has controllable algorithm dissipation, which locally adapts at each time step, according to the computed solution. Thus, spurious modes can be more effectively dissipated and accuracy is improved. Since this is an explicit time integration technique, the new procedure is very efficient, requiring no system of equations to be dealt with at each time-step. Moreover, the technique is simple and easy to implement, being based just on displacement-velocity relations, requiring no computation of accelerations. Numerical results are presented along the paper, illustrating the good performance of the new method, as well as its potentialities
Large Eddy Simulation Combined with Characteristic-Based Operator-Splitting Finite Element Method
Get PDFA numerical large eddy simulation (LES) method combined with the characteristic-based operator-splitting finite element method is proposed. The subgrid eddy viscosity model is used to calculate sub-grid stress in LES. In each time step, the governing equations are split into diffusive and convective parts. The convective part is first discretized by using the characteristic Galerkin method and then solved explicitly. The backward-facing step flow and the flow past a single cylinder are adopted to validate the model. Results agree with existing numerical results or experimental data. The flow past two cylinders in tandem arrangement is also studied at Re = 1000. The critical spacing is obtained in the range of 2.25D to 2.5D through the change characteristics of the streamlines and hydrodynamic forces as spacing. We further analyze the hydrodynamic forces at the critical spacing range
Solution of Fully Fuzzy System of Linear Equations by Linear Programming Approach
Get PDFFuzzy systems of linear equations play a vital role in various applications of engineering, science and finance problems. This paper proposes a new method for solving Fully Fuzzy System of Linear Equations (FFSLE) using the linear programming problem approach. There is no restriction on the elements of coefficient matrix. The proposed method is able to solve the system, when the elements of the fuzzy unknown vector are both non-negative and non-positive. Triangular convex normalized fuzzy sets are considered for the present analysis. Known example problems are solved and compared with the results of existing methods to illustrate the efficacy and reliability of the proposed method
Analysis of Square-shaped Crack in Layered Halfspace Subject to Uniform Loading over Rectangular Surface Area
Get PDFThis paper examines the problem of a square-shaped crack embedded in a layered half-space whose external surface is subject to a uniform loading over a rectangular area. Two novel numerical methods and the superposition principle in fracture mechanics are employed for the analysis of the crack problem. The numerical methods are based on the fundamental solution of a multilayered elastic medium and are, respectively, applied to calculate the stress fields of layered halfspace without cracks and the discontinuous displacements of crack surfaces in layered halfspace. The stress intensity factor (SIF) values are calculated using discontinuous displacements and the influence of material properties and crack positions on the SIF values is analyzed. Using the minimum strain energy density criterion and the SIF values, the minimum values of the strain energy density factor are calculated and the crack growth is analyzed. Results show that the heterogeneity of layered media exerts an obvious influence on the fracture properties of cracked layered elastic solids
Dynamics of Free Liquid Jets Affected by Obstructions at the Jet Entrance
Get PDFFree liquid jets are of great technical importance in a variety of applications like ink-jet printing, glass painting, spray coating and metal cutting. Here we consider the changes induced in the dynamics of such jets by the presence of obstructions at the tube exit. Using stainless steel bars of 1.5 mm diameter as obstruction objects and aqueous solutions of glycerol of varying concentrations as working fluids, we performed experiments for different configurations, including a single rod at the centre of the tube exit, two parallel rods equidistant from the centre of the tube, and a 10 mesh screen. Images of the jets coming through such restricted section were captured by high speed camera from two locations. We could observe a morphological change in the cross section of the liquid jet only for jets passing through a tube exit containing only one rod. The maximum expansion ratio of the jet decreased with the concentration of glycerol. Attempts were also made to correlate the characteristic jet diameter ratio with the Weber number. The findings discussed in the present work may provide a new direction for the design of new instruments for the measurement of surface tension or viscosity of liquids
Fluid dynamic analysis of different Yacht configurations with VOF method
Get PDFThis paper presents two applications of Computational Fluid Dynamics (CFD) to super and mega yacht design, based on the Volume of Fluid method. After an overview of recent literature on the subject, the analysis of the hydrodynamic performances of different hull configurations and of different appendage configurations is presented
The Influence of Gravitational Field on Generalized Thermoelasticity with Two-Temperature under Three-Phase-Lag Model
Get PDFThe problem of the generalized thermoelastic medium for three different theories under the effect of a gravitational field is investigated. The Lord- Shulman, Green-Naghdi III, three-phase-lag theories are discussed with twotemperature. The normal mode analysis is used to obtain the analytical expressions of the displacement components, force stress, thermodynamic temperature and conductive temperature. The numerical results are given and presented graphically, when the thermal force is applied. Comparisons are made with the results predicted by three-phase-lag model, Green-Naghdi III and Lord-Shulman theories in the presence and absence of gravity as well as two temperature