Porous Wall Model Research Articles

Haemodynamic Effects on the Development and Stability of Atherosclerotic Plaques in Arterial Blood Vessel.

Studying the formation and stability of atherosclerotic plaques in the hemodynamic field is essential for understanding the growth mechanism and preventive treatment of atherosclerotic plaques. In this paper, based on a multiplayer porous wall model, we established a two-way fluid-solidinteraction with time-varyinginlet flow. The lipid-rich necrotic core (LRNC) and stress in atherosclerotic plaque were described for analyzing the stability of atherosclerotic plaques during the plaque growth by solving advection-diffusion-reaction equations with finite-element method. It was found that LRNC appeared when the lipid levels of apoptotic materials (such as macrophages, foam cells) in the plaque reacheda specified lowerconcentration, and increased with the plaque growth. LRNC was positively correlated with the blood pressure and was negatively correlated with the blood flow velocity. The maximum stress wasmainlylocatedat the necrotic core and graduallymovedtoward the left shoulder of the plaque with the plaque growth, which increases the plaque instability and the risk of the plaque shedding. The computational model may contribute to understanding the mechanisms of early atherosclerotic plaque growth and the risk of instability in the plaque growth.

Study on sliding stability of porous-concrete retaining wall model test subjected to rainfall infiltration

The common disadvantage of a conventional retaining wall is a heavy object as a block that is difficult to lift and handle conveniently. A drainage pipe is commonly used to displace water from the backfill. In areas with high annual rainfall, the soil could be saturated in a short time and added lateral load significantly. In this study, porous concrete was utilized as a retaining wall material with the advantages of the lighter weight of the block and additional drainage capability due to its high void ratio. A set of a laboratory-scale retaining walls using conventional and porous concrete walls was investigated through three different rainfall modes. To initiate the instability condition, a vertical load was applied then the lateral moving was recorded using LVDT sensors. Soil moisture content sensors recorded hydrologic responses of the saturation process. The loading test results showed that the porous concrete wall model was being displaced less than experienced by the conventional concrete wall. It shows that the porous concrete wall model can withstand the load as the additional lateral load from infiltrated rainwater dissipates rapidly. Therefore, the porous concrete wall has the advantage of being used as a Retaining Wall Material.

CFD/CSD-based flutter prediction method for experimental models in a transonic wind tunnel with porous wall

To predict the flutter dynamic pressure of a wind tunnel model before flutter test, an accurate Computational Fluid Dynamics/Computational Structural Dynamics (CFD/CSD)-based flutter prediction method is proposed under the conditions of a 2.4 m × 2.4 m transonic wind tunnel with porous wall. From the CFD simulations of the flows through an inclined hole of this wind tunnel, the Nambu’s linear porous wall model between the flow rate and the differential pressure is extended to the porous wall with inclined holes, so that the porous wall can be conveniently modeled as a boundary condition. According to the flutter testing approach for the current wind tunnel, the steady CFD calculation is conducted to achieve the required inlet Mach number. A time-domain CFD/CSD method is then employed to evaluate the structural response of the experimental model, and the critical flutter point is obtained by increasing the dynamic pressure step by step at a fixed Mach number. The present method is applied to the flutter calculations for a vertical tail model and an aircraft model tested in the current transonic wind tunnel. For both models, the computed flutter characteristics agree well with the experimental results.

Long time error estimates of IFE methods for the unsteady multi-layer porous wall model

In this paper, we study the immersed finite element (IFE) method for the multi-layer porous wall model for the drug-eluting stents. Firstly, under some realistic assumptions on the initial data and the body force, we deduce the long time priori stability for the variational problem for all t∈R+. Then, based on these results, the uniform optimal error estimates for both the semi-discrete IFE method and the fully discrete Euler IFE method are proved. Finally, some numerical experiments are performed to verify the theoretical predictions.

Long‐time stability and asymptotic analysis of the IFE method for the multilayer porous wall model

In this article, we study the long‐time stability and asymptotic behavior of the immersed finite element (IFE) method for the multilayer porous wall model for the drug‐eluting stents. First, with the IFE method for the spatial descretization, and the implicit Euler scheme for the temporal discretization, respectively, we deduce the global stability of fully discrete solution. Then, we investigate the asymptotic behavior of the discrete scheme which reveals that the multilayer porous wall model converges to the corresponding elliptic equation if approaches to a steady‐state in both and norms as . Finally, some numerical experiments are given to verify the theoretical predictions.

A Physiologic Model for the Problem of Blood Flow through Diseased Blood Vessels

This study focuses on the behavior of blood flow through diseased artery in the presence of porous effects. The laminar, incompressible, fully developed, non-Newtonian in an artery having axially non-symmetric but radially symmetric stenosis is numerically studied. Here blood is represented as Herschel-Bulkley fluid model and flow model is shown by the Navier-Stokes and the continuity equations. Using appropriate boundary conditions, numerical expression for volumetric flow rate, pressure drop and wall shear stress have been derived. The expressions are computed numerically and results are presented graphically. The effects of porous parameter on wall shear stress, stenosis length, stenosis size and stenosis shape parameter are discussed. The wall shear stress increases as the porous parameter, stenosis size and stenosis length increases, but as the stenosis shape parameter increases, the wall shear stress decreases. The work shows that the results obtained from the porous wall model are significantly different from those obtained by the rigid wall model.

Numerical Validation of a Time Domain Perforated Plate Model with Nonlinear and Inertial Effects

A time domain perforated plate model based on the "homogenization" concept is presented; the dynamic porous wall model. This model takes into account linear and nonlinear losses as well as inertial effects due to the unsteady flow in the vicinity of the holes. A numerical validation of the dynamic porous wall model is performed via the computation of the impedance versus frequency for an acoustic liner consisting of a solid wall back sheet and a perforated face sheet, separated by a given distance. Two types of unsteady flow are considered; firstly 3D LES in which the holes in the perforated face sheet are fully resolved, and secondly 2D URANS simulations in which the dynamic porous wall model is used to include the effects of the perforated face sheet. Comparisons of the results show that the new dynamic porous wall model captures both nonlinear and inertial effects well.

Evaluation of Wall-Interference Correction Method Using Numerical Analysis and Porous Wall Model

Evaluation of the conventional linear wall-interference correction method is conducted using flows around a two-dimensional airfoil in a wind tunnel computed by computational fluid dynamics and a porous wall model. First, the computational results are validated by comparison with wind-tunnel test measurements. Then, the wall-interference effect is discussed using these results. Porous walls are effective for reducing blockage, which change the Mach number around the airfoil. However, high wall porosity causes large downwash, which changes the flow angle. In this paper, Mokry’s method, which is one of the linear wall-interference correction methods, is evaluated quantitatively using computational fluid dynamics. Computational result with wind-tunnel walls are corrected by Mokry’s method, and the corrected result is compared with the one without wind-tunnel walls. Mokry’s method shows high accuracy in subsonic and no-stall conditions, which satisfy the requirement of the small-perturbation potential equation. Its accuracy is also high even if the model is large relative to the wind-tunnel size. However, an error of about 10 drag counts is caused due to a shock wave in transonic flow conditions, and accuracy rapidly degrades around the stall condition, where an error exceeding 100 counts is caused by flow separation.

Effect of porous media of the stenosed artery wall to the coronary physiological diagnostic parameter: A computational fluid dynamic analysis

Functional assessment of a coronary artery stenosis severity is generally assessed by fractional flow reserve (FFR), which is calculated from pressure measurements across the stenosis. The purpose of this study is to investigate the effect of porous media of the stenosed arterial wall on this diagnostic parameter.To understand the role of porous media on the diagnostic parameter FFR, a 3D computational simulations of the blood flow in rigid and porous stenotic artery wall models are carried out under steady state and transient conditions for three different percentage area stenoses (AS) corresponding to 70% (moderate), 80% (intermediate), and 90% (severe). Blood was modeled as a non Newtonian fluid. The variations of pressure drop across the stenosis and diagnostic parameter were studied in both models.The FFR decreased in proportion to the increase in the severity of the stenosis. The relationship between the percentage AS and the FFR was non linear and inversely related in both the models. The cut-off value of 0.75 for FFR was observed at 81.89% AS for the rigid artery model whereas 83.61% AS for the porous artery wall model. This study demonstrates that the porous media consideration on the stenotic arterial wall plays a substantial role in defining the cut-off value of FFR. We conclude that the effect of porous media on FFR, could lead to misinterpretation of the functional severity of the stenosis in the region of 81.89 %–83.61% AS.

Analysis, simulation and impedance operator of a nonlocal model of porous medium for acoustic control

The problem under consideration relates to a model of a porous wall devoted to aircraft motor noise reduction. For such a medium, the parameters of the propagation equation depend on the frequency. Then, the corresponding time model involves nonrational convolution operators, which make the model complex from both the analysis and the simulation points of view. In this paper, based on the so-called diffusive representation of convolution operators, a time-local formulation of the porous wall model, well adapted to analysis and numerical simulation, is established and analyzed. Then its associated impedance operator is computed. Finally some numerical results relating to the simulation of the porous wall and to the one of its impedance operator are given to highlight the theoretical part.

A multi-layer porous wall model for coronary drug-eluting stents

An analytical solution for solving the transient drug diffusion in adjoining porous wall layers faced with a drug-eluting stent is presented. The endothelium, intima, internal elastic lamina and media are all treated as homogeneous porous media and the drug transfer through them is modelled by a set of coupled partial differential equations. The classical separation of variables method for a multi-layer configuration is used. The model addresses the concept of penetration depth for multi-layer solids that is useful to treat the wall thickness by estimating a physical bound for mass diffusion. Drug concentration level and mass profiles in each layer at various times are given and discussed.

Formulation différentielle dissipative d'un modèle de paroi absorbante en aéroacoustique

The problem under consideration relates to a particular model of porous wall devoted to aircraft motor noise reduction. Because parameters of the propagation equation are frequency dependent, the time-model of such a medium involves convolution operators. We introduce a new formulation of these operators based on their symbols, both time-local and dissipative. The coupling of this so-obtained model with a standard aeroacoustic one then leads to a time-local system whose analysis is simplified thanks to the existence of an energy functional in the sense of which the global dissipativity is insured. To cite this article: C. Casenave et al., C. R. Mecanique 336 (2008).

Dissipative state formulations and numerical simulation of a porous medium for boundary absorbing control of aeroacoustic waves

The problem under consideration relates to a model of porous wall devoted to aircraft motors noise reduction. For such a medium, the parameters of the propagation equation depend on the frequency, so the corresponding time-model involves non rational convolution operators. Consequently, the impedance of the wall is a non rational function of the frequency. On the basis of complex analysis and causality properties, we introduce infinite dimensional state formulations of these operators. The coupling of the so-obtained model with a standard aeroacoustic one then leads to a time-local system whose analysis is simplified thanks to the existence of an energy functional in the sense of which the global dissipativity is insured. Some numerical results are given to illustrate the theoretical results.