Modeling Patient-Specific Periaortic Interactions with Static and Dynamic Structures Using a Moving Heterogeneous Elastic Foundation Boundary Condition

In this paper, we consider the influence of the conditions for fixing a wavy plate lying on an elastic foundation on its stressed-deformed state. The profiled plates are widely used in construction practice as fencing structures, for siding works, for roofing and others. The stress-strain state of the wavy plates varies depending on geometry, materials mechanical properties, foundation characteristics and boundary condition. Steel with polymer coatings, which make the sheets a decorative material, is increasingly used in individual and low-rise buildings. The elastic foundation is considered as Winkler base, so we suppose that the reaction of the base is directly proportional to the deflection of the plate at each point. The Bubnov-Galerkin method is used to determine the stress-strain state of the plate. To solve the problem, we use special orthogonal Legendre polynomials satisfying the boundary conditions: simply supported and clamped edges. The results of the calculations were compared for different types of fixation.

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Mechanics Mechanism Analysis of Concrete Pavement Resonant Rubblization

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.667.365 ◽

2015 ◽

Vol 667 ◽

pp. 365-369

Author(s):

Peng Chen ◽

Xin Qiu ◽

Qing Zhu ◽

Chan Chan Ouyang

Keyword(s):

Boundary Condition ◽

Natural Frequency ◽

Elastic Foundation ◽

Thin Plate ◽

Natural Frequencies ◽

Excitation Frequency ◽

Concrete Pavement ◽

Mechanism Analysis ◽

Vibration Theory ◽

Fundamental Natural Frequency

Based on the assumption of thin plate of elastic foundation and vibration theory, a method for calculating the fundamental natural frequency of cement slab is presented and the certain relationship between the fundamental natural frequency of cement slab and cement slab boundary condition is discussed. As well, according to the analysis results of fundamental natural frequencies of the typical cement pavements of China, the selected proposals of the excitation frequency of the resonant rubblization machine are presented .The research results provide a theory support to popularize resonant rubblization technology in overlaying and rebuilding engineering of the existed cement pavements in China.

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An Outflow Boundary Condition Model for Noninvasive Prediction of Fractional Flow Reserve in Diseased Coronary Arteries

Journal of Biomechanical Engineering ◽

10.1115/1.4038250 ◽

2018 ◽

Vol 140 (4) ◽

Author(s):

Iyad A. Fayssal ◽

Fadl Moukalled ◽

Samir Alam ◽

Hussain Isma'eel

Keyword(s):

Boundary Condition ◽

Coronary Arteries ◽

Fractional Flow Reserve ◽

Physiological Parameters ◽

Arterial System ◽

Patient Specific ◽

Fractional Flow ◽

Condition Model ◽

Flow Reserve ◽

Boundary Condition Model

This paper reports on a new boundary condition formulation to model the total coronary myocardial flow and resistance characteristics of the myocardial vascular bed for any specific patient when considered for noninvasive diagnosis of ischemia. The developed boundary condition model gives an implicit representation of the downstream truncated coronary bed. Further, it is based on incorporating patient-specific physiological parameters that can be noninvasively extracted to account for blood flow demand to the myocardium at rest and hyperemic conditions. The model is coupled to a steady three-dimensional (3D) collocated pressure-based finite volume flow solver and used to characterize the “functional significance” of a patient diseased coronary artery segment without the need for predicting the hemodynamics of the entire arterial system. Predictions generated with this boundary condition provide a deep understanding of the inherent challenges behind noninvasive image-based diagnostic techniques when applied to human diseased coronary arteries. The overall numerical method and formulated boundary condition model are validated via two computational-based procedures and benchmarked with available measured data. The newly developed boundary condition is used via a designed computational methodology to (a) confirm the need for incorporating patient-specific physiological parameters when modeling the downstream coronary resistance, (b) explain the discrepancies presented in the literature between measured and computed fractional flow reserve (FFRCT), and (c) discuss the current limitations and future challenges in shifting to noninvasive assessment of ischemia.

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Accurate Simulation of Light Propagation in Complex Skin Tissues Using an Improved Tetrahedron-Based Monte Carlo Method

Applied Sciences ◽

10.3390/app11072998 ◽

2021 ◽

Vol 11 (7) ◽

pp. 2998

Author(s):

Hao Jia ◽

Bin Chen ◽

Dong Li

Keyword(s):

Boundary Condition ◽

Monte Carlo ◽

Energy Deposition ◽

Laser Energy ◽

Patient Specific ◽

Computational Domain ◽

Photon Propagation ◽

Cross Bridge ◽

Diffused Light ◽

Mc Method

Understanding light transportation in skin tissues can help improve clinical efficacy in the laser treatment of dermatosis, such as port-wine stains (PWS). Patient-specific cross-bridge PWS vessels are structurally complicated and considerably influence laser energy deposition due to shading effects. The shading effect of PWS vessels is investigated using a tetrahedron-based Monte Carlo (MC) method with extended boundary condition (TMCE). In TMCE, body-fitted tetrahedra are generated in different tissues, and the precision of photon–surface interaction can be considerably improved via mesh refinement. Such improvement is difficult to achieve with the widely used voxel-based MC method. To fit the real physical boundary, the extended boundary condition is adapted by extending photon propagation to the semi-infinite tissue layers while restricting the statistics of photon propagation in the computational domain. Results indicate that the shading parameters, such as the cross angle, vessel distance, and geometric shadow (GS), of cross-bridge blood vessel pairs determine the peak characteristics of photon deposition in deep vessels by affecting the relative deposition of collimated and diffused light. Collimated light is shaded, attenuated, and partially transformed into diffused light due to the increase in vessel distance and GS of vessel pairs, resulting in difficulty in treating deep and shallow vessels with one laser pulse. The TMCE method can be used for the individualized and precise forecasting of laser energy deposition based on the morphology and embedding characteristics of vascular lesions.

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MRI-Based Inflow Boundary Conditions for Patient Specific Fluid Structure Interaction Modeling of Abdominal Aortic Aneurysms

ASME 2012 Summer Bioengineering Conference, Parts A and B ◽

10.1115/sbc2012-80463 ◽

2012 ◽

Author(s):

Santanu Chandra ◽

Samarth Raut ◽

Anirban Jana ◽

Robert W. Biederman ◽

Mark Doyle ◽

...

Keyword(s):

Boundary Condition ◽

Boundary Conditions ◽

Wall Thickness ◽

Wall Stress ◽

Patient Specific ◽

Structure Interaction ◽

Outflow Boundary Conditions ◽

Abdominal Aortic ◽

Outflow Boundary ◽

Fully Coupled

Rupture of abdominal aortic aneurysm (AAA) is the 10th leading cause of death for men over age of 50 in US. The decision for surgical intervention is currently based on aneurysm diameter or its expansion rate. However, the use of these criteria for all patients is debatable. For example, small aneurysms do rupture or become symptomatic before reaching the critical diameter. Computationally predicted mechanical wall stress is considered a viable alternative criterion for rupture risk assessment. Hence, it is important to evaluate the effect of different modeling approaches on the accuracy of the predicated AAA wall stress. For computational solid stress (CSS) analysis or finite element analysis (FEA), a uniform static or transient intraluminal pressure is generally applied on the wall-lumen surface whereas in fluid-structure interaction (FSI) modeling the wall-lumen surface experiences transient and non-uniform fluid stress. An earlier comparison on idealized AAA models [1] revealed that static and transient CSS underestimate the peak wall stress (PWS) by an average 20–30% for variable wall thickness and 10% for uniform wall thickness when compared to fully coupled FSI. However, FSI-predicted stresses and strains were observed to be sensitive to inflow and outflow boundary conditions, warranting further study on a more accurate approach for FSI modeling. Though significant work has been performed on modeling outflow boundary conditions [2], studies on the sensitivity of computed stress or strain to the type of FSI inflow boundary condition is scarce [2–4]. We hypothesize that a FSI framework with a patient specific velocity boundary condition derived from magnetic resonance imaging (MRI) data applied to patient specific AAA geometry would provide better accuracy of PWS calculations compared to a FEA model. In this work, we present a framework where the AAA geometry is reconstructed from computed tomography (CT) images, on which FSI simulations were performed with inlet velocity components extracted from patient MR images of the abdominal aorta. Fully coupled FSI simulations were performed and results were compared with CSS simulations with uniform transient pressure boundary conditions.

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A Numerical Analysis of the Hemodynamic Functionality of Human Coronary Stenosis Under Different Physiologic Conditions and Boundary Condition Formulations

Volume 2: Computational Fluid Dynamics ◽

10.1115/ajkfluids2019-4820 ◽

2019 ◽

Author(s):

Iyad Fayssal ◽

Fadl Moukalled

Keyword(s):

Boundary Condition ◽

Boundary Conditions ◽

Functional Significance ◽

Diffusion Flux ◽

Computational Effort ◽

Patient Specific ◽

Computational Domain ◽

Artery Disease ◽

Outflow Boundary

Abstract Coronary artery disease (CAD) is among the foremost causes for human death worldwide. This study aims at investigating the performance of different boundary condition model types to characterize CAD functional significance. In addition, alternate models to estimate FFR using any different combination of boundary conditions at inlet and outlet were analyzed. In the first type of boundary condition, an outflow resistance model is used combined with a fixed pressure at inlet. In the second model of boundary conditions, constant pressure values are imposed at the domain inlet and outlet/s sections. In the third model, a zero diffusion flux is applied at outlet with a pre-specified flow rate at inlet. Numerical simulations performed on healthy and stenosed idealized and physiological arterial models revealed the superiority of the first type of boundary condition to directly capture the level of ischemia in diseased arteries. However, in this model, special numerical treatment at the outflow boundary is needed to dampen pseudo numerical reflections entering the computational domain. Alternative simple methods are developed to tackle the problem incurred in the second and third types of boundary condition types. The alternate models are effective for carrying extensive parametric studies with minimal computational effort. The new developed methods allow results generated via generic simulations under any specified boundary condition type to correctly estimate CAD functional significance. The obtained surrogate models account for the effects of the patient-specific physiologic parameters and can be easily incorporated without modifying existing CFD codes. Moreover, where it is unfeasible to experimentally incorporate the downstream effects of a given diseased arterial segment, an important aspect the alternative models provide is that they can be easily adopted by experimentalists through building in-vitro arterial models to assess the functional significance of the obstruction caused by the disease and its relation to any given patient specific physiologic parameter.

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Variational Principles for Some Nonstandard Elastic Problems

Journal of Applied Mechanics ◽

10.1115/1.3173114 ◽

1987 ◽

Vol 54 (4) ◽

pp. 768-771 ◽

Cited By ~ 2

Author(s):

R. T. Shield

Keyword(s):

Boundary Condition ◽

Elastic Foundation ◽

Variational Principles ◽

Rigid Punch ◽

Elastic Bodies ◽

Smooth Contact ◽

Nonstandard Problems

Variational principles are derived for some nonstandard problems involving elastic bodies in smooth contact. For these problems, the portions of the surfaces where one boundary condition holds rather than another must be determined as part of the solution to the problem. Cases considered include a body containing a crack or delamination, indentation by a rigid punch, and contact with an elastic foundation.

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