Numerical Methods for Simulation and Optimization of Chemically Reacting Flows in Catalytic Monoliths

The aim of this work is to develop numerical methods and software for simulation and optimization of complex processes in catalytic monoliths to achieve better understanding of the physic-chemical processes in catalytic reactors. The fluid dynamics are modelled by the boundary layer equations (BLEs), which are a large system of parabolic partial differential equations (PDEs) with highly nonlinear boundary conditions arising from the coupling of surface processes with the flow field inside the channel. The BLEs are obtained by simplifying the comprehensive model described by the Navier-Stokes equations and applying the boundary approximation theory. The surface and gas-phase chemical reactions are described by detailed models. The PDEs are semi-discretized using the method of lines leading to a structured system of differential-algebraic equations (DAEs). The DAEs are integrated by an implicit method, based on backward differentiation formulas (BDF). We develop a new BDF code with tailored efficient and robust numerical methods by exploiting the structure, and by an appropriate scaling for ill-conditioned iteration matrices, and by computing consistent initial values. Efficient methods for computation of partial derivatives in the framework of automatic differentiation and of finite differences are introduced and compared. Our newly developed simulation tool is more stable than the existing simulation tool, and faster than by a factor of ten to more than 60, depending on the applications. To improve the performance of catalytic reactors (e.g., maximizing gas conversion or selectivity) we can control certain process conditions, such as temperature at the catalyst wall or the ratio of catalytic active surface area to the geometric surface area or the gas composition, the temperature, or the velocity at the inlet of the catalyst. It is the first time that this problem is generally formulated as an optimal control problem constrained by a system of PDEs describing the chemical fluid dynamics process and additional constraints. The direct shooting approach in combination with sequential quadratic programming (SQP) method is used for solving the resulting optimal control problem. An efficient numerical method for computation of the derivatives required by the SQP method is introduced. In addition, error analysis for the numerical Newton method is investigated in detail. We introduce a new error model. Based on our error model and analysis, the limiting accuracy of the solution of nonlinear equations by the numerical Newton method can be obtained. Our newly developed software package for simulation and optimization can be applied to different reaction mechanisms and channel settings with different initial/boundary conditions. This software is applied to two practical applications: catalytic combustion of methane and conversion of ethane to ethylene. The numerical results are presented. The simulation software provides a useful tool for the validation of reactions mechanisms. The software package allows, e.g., for a better design and operation of the conversion of natural gas to higher hydrocarbons or the improvement of exhaust treatment in cars

Procedure for making flat thermoplastic composite plates by Automated Fiber Placement and their mechanical properties

Automated Fiber Placement (AFP) is one of the new manufacturing processes for composites that has many advantages such as fast rate of material deposition, repeatability, and reduction of material waste. Thermoplastic composites compared with thermoset composites show a lot of advantages such as higher impact resistance, recyclability etc. and they are very suitable for primary structures of an aircraft. However, manufacturing of thermoplastic composites requires more efforts because of the very high viscosity of thermoplastic resin. This study proposed a manufacturing procedure to make flat thermoplastic laminates with different layup sequences by using a heated mandrel during layup process with AFP. It is shown that using a mandrel heated to a temperature higher than glass transition can make flat laminates. Processing parameters which consist of hot gas temperature, compaction force, layup speed, mandrel temperature, were found for different laminates. Moreover, repass after material deposition helps to reduce void content inside the laminates. The obtained flat laminates show the crystallized thermoplastic resin. The high degree of crystallinity is recommended to have good mechanical properties. Tensile, compression and in-plane shear tests were carried out to determine mechanical properties of the laminates made by AFP. Results are compared with those made by autoclave. Test results show that laminates made by AFP have higher tensile modulus, higher compression modulus, similar tensile strength, and almost equal of shear modulus. However, a reduction in compression strength is observed

Investigation on the effect of cross beams in single span bridges under dynamic aspect by using finite element method

In the 1980s and 1990s, most bridges in Vietnam employed simple beam for short-span river crossings that did not need navigation and mainly used the reinforced concrete T-beams or pre-stressed concrete. While the T-frame structure that has hang single span is widely applied for rivers that require navigation...The single girder is a basic span made of pre-stressed reinforced concrete T or I cross section, with spacing ranging from 2.2m to 2.6m, and the absence of diaphragms was a common feature of bridges built during this time period. All horizontal crashes almost have happened on the spans that did not have diaphragms. As a result, the impact force is concentrated mostly on the lateral girders, leading to total damage. Thus, researches to evaluate the effect of diaphragms in the distribution of horizontal impact forces as well as minimizing the damage in the span structures are crucial. This study focuses on simulating and studying the influence of the number and position of the diaphragms in terms of stress, deformation and damage when a collision occurs in order to propose additional and repair solutions to enhance the horizontal resistance of span

Persistent Test-time Adaptation in Episodic Testing Scenarios

Current test-time adaptation (TTA) approaches aim to adapt to environments that change continuously. Yet, when the environments not only change but also recur in a correlated manner over time, such as in the case of day-night surveillance cameras, it is unclear whether the adaptability of these methods is sustained after a long run. This study aims to examine the error accumulation of TTA models when they are repeatedly exposed to previous testing environments, proposing a novel testing setting called episodic TTA. To study this phenomenon, we design a simulation of TTA process on a simple yet representative $\epsilon$-perturbed Gaussian Mixture Model Classifier and derive the theoretical findings revealing the dataset- and algorithm-dependent factors that contribute to the gradual degeneration of TTA methods through time. Our investigation has led us to propose a method, named persistent TTA (PeTTA). PeTTA senses the model divergence towards a collapsing and adjusts the adaptation strategy of TTA, striking a balance between two primary objectives: adaptation and preventing model collapse. The stability of PeTTA in the face of episodic TTA scenarios has been demonstrated through a set of comprehensive experiments on various benchmarks

Establishment of the human cardiac models using gene editing and reprogramming in Human Pluripotent Stem Cells to understand the putative functions of the G-protein coupled receptor kinase 5 polymorphism (GRK5-L41)

A nonsynonymous single polymorphism (SNP) in G protein-coupled receptor kinase 5 (GRK5) was discovered in 2008 that changes the amino acid at the position 41 from Glutamine (Q) into Leucine (L) (Liggett et al., 2008). The putative functions of the GRK5-L41 polymorphism were reported to be involved in faster desensitisation of both b1 and b2 adrenergic receptors in vitro and the cardiac protective functions by improving the survival rate of patients with heart failure conditions or transplantation in vivo. Nevertheless, the mechanisms underlying these processes are still poorly understood, which is the purpose of this thesis. This thesis presents the establishment of the first human cardiac models of GRK5- L41 polymorphism using human pluripotent stem cells (hPSCs) and their derived cardiomyocytes (CMs). The thesis is distributed into four main themes, containing (1) the formulation of monolayer cardiac differentiation protocols; (2) the establishment of human induced pluripotent stem cells from lymphoblastoid cell lines bearing the GRK5- L41 sequence; (3) the development of footprint-free and shortcut CRISRP/Nickase approach that allowed generating the gene-edited human embryonic stem cells expressing GRK5-Q41, GRK5-Q/L41, and GRK5-L41; and (4) the evaluation of GRK5- L41 functions using cardiac functional analysis assays. Relating to disease modelling and cardiovascular biomedical research, the ability to differentiate the hPSCs into CMs plays a critical role by providing an unlimited resource of human CMs for in vitro testing and experiments. Here, three main monolayer cardiac differentiation protocols, including E8-AB, mTeSR-AB, and mTeSR-CHIR, were described in details and proven to be highly consistent, efficient, robust, and reproducible. Additionally, these protocols have been ascertained to be effective in more than 27 hPSC lines routinely maintained in the lab regardless of the culture conditions (non-defined vs. defined culture conditions), cell types (human embryonic stem cells vs. human induced pluripotent stem cells), reprogramming methods, and somatic cell sources (in the case of induced pluripotent stem cells). Indeed, by using the E8-AB protocol, more than 1x107 CMs/line have been produced in this thesis, providing enough resource for functional assay analysis and mechanistic studies of GRK5-L41. Furthermore, two independent approaches were made to create the human cardiac model of GRK5-L41 polymorphism, involving the establishment of GRK5-L41 bearing hiPSCs from lymphoblastoid cell lines, and simultaneously introducing the GRK5-L41 sequence to the HUES7 genome to create the Q/L41, and L41 expressing HUES7 lines. In general, four hPSC lines were successfully generated in this thesis, including hiPSC-GRK5-L41, hiPSC-GRK5-Q41, HUES7-GRK5-Q/L41, and HUES7- GRK5-L41. The H-Fib-hiPSC, cell lines generated from HUES7-derived fibroblast, was the additional line obtained after testing the effectiveness of episomal plasmid. All cell lines were able to differentiate into CMs at high purity, approximately 85%, and were used for the development of functional assays. Four main functional experiments were developed focusing on the GRK5-related functions in the heart, consisting of contractility and hypertrophic response to catecholamine induction, especially during the chronic response. The effects of catecholamine, in this case, Isoprenaline (ISO), on the contractility of the CMs were measured by two assays, the CardioExcyte96 platform detecting the contraction rate and beating pattern in real-time, and the LANCE Ultra cAMP assay assessing the production of cAMP. These results indicated that extended culture of CMs in ISO (>30h) introduced the detrimental effects on the contractility and beating pattern of the CMs in vitro, generating the arrhythmias in GRK5-Q41 CMs. Interestingly, the GRK5-L41 CMs exhibited a high level of the beat rate in response to ISO and maintained it constantly during prolonged exposure to ISO similar to that of b-blocker treatments in GRK5-Q41 CMs. The Western Blot analysis of the cellular distribution of GRK5 spotted the localisation of GRK5 during ISO treatment for 72h. Further characterisation using immunofluorescence analysis of chronic exposure to ISO demonstrated the elevation of BNP level, a hypertrophic marker, indicating that ISO treatment duration (>30h) induced the hypertrophic response of hPSC-CMs in vitro. Taken together, the findings within this thesis has been the first step in a discovery process of the cardiac protective functions of GRK5-L41 polymorphism during heart failure. Despite the presence of limitation and difficulty, it manages to provide sufficient information to explore further the interrelationship between nuclear accumulation of GRK5, hypertrophic response, and contractility regulation mediated by either GRK5-Q41 and GRK5-L41 in hPSC-CMs in vitro

A Regularization of the Backward Problem for Nonlinear Parabolic Equation with Time-Dependent Coefficient

We study the backward problem with time-dependent coefficient which is a severely ill-posed problem. We regularize this problem by combining quasi-boundary value method and quasi-reversibility method and then obtain sharp error estimate between the exact solution and the regularized solution. A numerical experiment is given in order to illustrate our results

Some algorithms related to consistent decision table

Rough set theory is useful mathematical tool developed to deal with vagueness and uncertainty. As an important concept of rough set theory, an attribute reduct is a subset of attributes that are jointly sufficient and individually necessary for preserving a particular property of the given information table. Rough set theory is also the most popular for generating decision rules from decision table. In this paper, we propose an algorithm finding object reduct of consistent decsion table. On the other hand, we also show an algorithm to find some attribute reducts and the correctness of our algorithms is proof-theoretically. These our algorithms have polynomial time complexity. Our finding object reduct helps other algorithms of finding attribute reducts become more effectively, especially as working with huge consistent decision table