An Inverse POD-RBF Network Approach to Parameter Estimation in Mechanics

An inverse approach is formulated using proper orthogonal decomposition (POD) integrated with a trained radial basis function (RBF) network to estimate various physical parameters of a specimen with little prior knowledge of the system. To generate the truncated POD-RBF network utilized in the inverse problem, a series of direct solutions based on FEM, BEM or exact analytical solutions are used to generate a data set of temperatures or deformations within the system or body, each produced for a unique set of physical parameters. The data set is then transformed via POD to generate an orthonormal basis to accurately solve for the desired material characteristics using the Levenberg-Marquardt (LM) algorithm to minimize the objective least squares functional. While the POD-RBF inverse approach outlined in this paper focuses primarily in application to conduction heat transfer, elasticity, and fracture mechanics, this technique is designed to be directly applicable to other realistic conditions and/or relevant industrial problems

Red blood cells tracking and cell-free layer formation in a microchannel with hyperbolic contraction: a CFD model validation

Background and Objective: In recent years, progress in microfabrication technologies has attracted the attention of researchers across disciplines. Microfluidic devices have the potential to be developed into powerful tools that can elucidate the biophysical behavior of blood flow in microvessels. Such devices can also be used to separate the suspended physiological fluid from whole in vitro blood, which includes cells. Therefore, it is essential to acquire a detailed description of the complex interaction between erythrocytes (red blood cells; RBCs) and plasma. RBCs tend to undergo axial migration caused by occurrence of the Fåhræus-Lindqvist effect. These dynamics result in a cell-free layer (CFL), or a low volume fraction of cells, near the vessel wall. The aim of the paper is to develop a numerical model capable of reproducing the behavior of multiphase flow in a microchannel obtained under laboratory conditions and to compare two multiphase modelling techniques Euler-Euler and Euler-Lagrange. Methods: In this work, we employed a numerical Computational Fluid Dynamics (CFD) model of the blood flow within microchannels with two hyperbolic contraction shapes. The simulation was used to reproduce the blood flow behavior in a microchannel under laboratory conditions, where the CFL formation is visible downstream of the hyperbolic contraction. The multiphase numerical model was developed using Euler-Euler and hybrid Euler-Lagrange approaches. The hybrid CFD simulation of the RBC transport model was performed using a Discrete Phase Model. Blood was assumed to be a nonhomogeneous mixture of two components: dextran, whose properties are consistent with plasma, and RBCs, at a hematocrit of 5% (percent by volume of RBCs). Results: The results show a 5 μm thick CFL in a microchannel with a broader contraction and a 35 μm thick CFL in a microchannel with a narrower contraction. The RBC volume fraction in the CFL is less than 2%, compared to 7–8% in the core flow. The results are consistent for both multiphase simulation techniques used. The simulation results were then validated against the experimentally-measured CFL in each of the studied microchannel geometries. Conclusions: Reasonable agreement between experiments and simulations was achieved. A validated model such as the one tested in this study can expedite the microchannel design process by minimizing the need to prefabricate prototypes and test them under laboratory conditions.The work was partially supported by the Faculty of Energy and Environmental Engineering, Silesian University of Technology (SUT) within Ministry of Education and Science (Poland) statutory research funding scheme (MG, ZO) and by the Silesian University of Technology rector’s pro-quality grants No. 02/040/RGJ21/1011 (SS) and 08/060/RGJ21/1017 (ZO) and National Center of Science (Poland) No. 2017/27/B/ST8/01046 (BM). Rui Lima and João M. Miranda were partially funded by Portuguese national funds of FCT/MCTES (PIDDAC) through the base funding from the following research units: UIDB/00532/2020 (Transport Phenomena Research Center CEFT) and UIDB/04077/2020 (MEtRICs)

IRT research on influence of long-term loads on defects in FRP strengthened RC beams

It has been more than two decades, since FRP strengthening method was first time used in Poland. Therefore there is a natural need to develop an efficient quality assessment technique to verify design assumptions of strengthening in existing structures after many years. One of the promising non-destructive method of quality assessment is infrared thermography (IRT). In this paper, an initial study on recognition of delamination mainly in CFRP laminates using IRT was conducted as well as the influence of long-term loads on defects in CFRP strengthened RC beams was presented

Porównanie trzech modeli in silico wymiany ciepła w ciele ludzkim podczas ochładzania

The comparison of three numerical models of skin undergoing thermal stimulation in a human forearm is presented. Small brass compress is used to cool tissues, followed by the analysis of the skin temperature recovery process. In silico generated results are validated against in vivo measurements on 8 male adults.W pracy przedstawiono porównanie trzech modeli numerycznych tkanek przedramienia poddanych stymulacji termicznej. Chłodzenie skóry zrealizowano za pomocą mosiężnego kompresu. Analizowano proces powrotu schłodzonej skóry do warunków równowagi termicznej. Wyniki symulacji in silico porównano z pomiarami in vivo wykonanymi dla grupy 8 dorosłych mężczyznach

Application Of The Proper Orthogonal Decomposition In Steady State Inverse Problems

This chapter provides an overview of an inverse analysis technique for retrieving unknown boundary conditions. The first step of this approach is to solve a sequence of forward problems made unique, by defining the missing boundary condition as a function of some unknown parameters. Several combinations of values of these parameters that produce a sequence of solutions are considered. These combinations are then sampled at a predefined set of points. Proper Orthogonal Decomposition (POD) is used to produce a truncated sequence of orthogonal basis function. The solution of the forward problem is written as a linear combination of the basis vectors. The unknown coefficients of this combination are evaluated by minimizing the discrepancy between the measurements and the POD approximation of the field. The chapter also discusses numerical examples to show the robustness and numerical stability of the proposed scheme. © 2003 Elsevier B.V. All rights reserved

Coupling Bem, Fem And Analytic Solutions In Steady-State Potential Problems

Problems solved by using different steady-state solution techniques in adjacent subregions are discussed. The computational domain typically consists of two subregions, with a linear boundary value problem in one of them. BEM or analytical methods are used to solve the problem in this subregion. Static condensation of the off-interfacial degrees of freedom in this subdomain produces a linear set of equations linking nodal potentials and fluxes on the interface. This set of equations is generated by solving a sequence of boundary value problems in the linear subregion. Access to the source version of the software used to solve these boundary value problems is not required. Thus, the condensation can be accomplished using any commercial BEM code. The resulting set of equation is then treated as a boundary condition attached to the second subregion. In the latter, any numerical technique can be used and both linear and nonlinear problems may be considered. The paper addresses coupling of BEM and FEM, BEM and BEM and analytical solutions with BEM and FEM. Numerical examples are included. © 2002 Elsevier Science Ltd. All rights reserved

Estimation Of Constant Thermal Conductivity By Use Of Proper Orthogonal Decomposition

An inverse approach is developed to estimate the unknown heat conductivity and the convective heat transfer coefficient. The method relies on proper orthogonal decomposition (POD) in order to filter out the higher frequency error. The idea is to solve a sequence of direct problems within the body under consideration. The solution of each problem is sampled at a predefined set of points. Each sampled temperature field, known in POD parlance as a snapshot, is obtained for an assumed value of the retrieved parameters. POD analysis, as an efficient mean of detecting correlation between the snapshots, yields a small set of orthogonal vectors (POD basis), constituting an optimal set of approximation functions. The temperature field is then expressed as a linear combination of the POD vectors. In standard applications, the coefficients of this combination are assumed to be constant. In the proposed approach, the coefficients are allowed to be a nonlinear function of the retrieved parameters. The result is a trained POD base, which is then used in inverse analysis, resorting to a condition of minimization of the discrepancy between the measured temperatures and values calculated from the model. Several numerical examples show the robustness and numerical stability of the scheme. © Springer-Verlag 2005

An Inverse POD-RBF Network Approach to Parameter Estimation in Mechanics

An inverse approach is formulated using proper orthogonal decomposition (POD) integrated with a trained radial basis function (RBF) network to estimate various physical parameters of a specimen with little prior knowledge of the system. To generate the truncated POD-RBF network utilized in the inverse problem, a series of direct solutions based on FEM, BEM or exact analytical solutions are used to generate a data set of temperatures or deformations within the system or body, each produced for a unique set of physical parameters. The data set is then transformed via POD to generate an orthonormal basis to accurately solve for the desired material characteristics using the Levenberg-Marquardt (LM) algorithm to minimize the objective least squares functional. While the POD-RBF inverse approach outlined in this paper focuses primarily in application to conduction heat transfer, elasticity, and fracture mechanics, this technique is designed to be directly applicable to other realistic conditions and/or relevant industrial problems

IRT research on influence of long-term loads on defects in FRP strengthened RC beams

It has been more than two decades, since FRP strengthening method was first time used in Poland. Therefore there is a natural need to develop an efficient quality assessment technique to verify design assumptions of strengthening in existing structures after many years. One of the promising non-destructive method of quality assessment is infrared thermography (IRT). In this paper, an initial study on recognition of delamination mainly in CFRP laminates using IRT was conducted as well as the influence of long-term loads on defects in CFRP strengthened RC beams was presented

An Inverse Pod-Rbf Network Approach To Parameter Estimation In Mechanics

An inverse approach is formulated using proper orthogonal decomposition (POD) integrated with a trained radial basis function (RBF) network to estimate various physical parameters of a specimen with little prior knowledge of the system. To generate the truncated POD-RBF network utilized in the inverse problem, a series of direct solutions based on the finite element method, the boundary element method or exact analytical solutions are used to generate a data set of temperatures or deformations within the system or body, each produced for a unique set of physical parameters. The data set is then transformed via POD to generate an orthonormal basis to accurately solve for the desired material characteristics using the Levenberg-Marquardt algorithm to minimize the objective least-squares functional. While the POD-RBF inverse approach outlined in this article focuses primarily in application to conduction heat transfer, elasticity and fracture mechanics, this technique is designed to be directly applicable to other realistic conditions and/or relevant industrial problems. © 2012 Copyright Taylor and Francis Group, LLC