Poster: Global energy minimization for multi-crack growth in linear elastic fracture using the extended finite element method

Presentation (2014, January 17)

A posteriori error estimation for finite element approximations of fractional Laplacian problems and applications to poro–elasticity

Doctoral thesis (2022)

This manuscript is concerned with a posteriori error estimation for the finite element discretization of standard and fractional partial differential equations as well as an application of fractional ... [more ▼]

This manuscript is concerned with a posteriori error estimation for the finite element discretization of standard and fractional partial differential equations as well as an application of fractional calculus to the modeling of the human meniscus by poro-elasticity equations. In the introduction, we give an overview of the literature of a posteriori error estimation in finite element methods and of adaptive refine- ment methods. We emphasize the state–of–the–art of the Bank–Weiser a posteriori error estimation method and of the adaptive refinement methods convergence results. Then, we move to fractional partial differential equations. We give some of the most common discretization methods of fractional Laplacian operator based equations. We review some results of a priori error estimation for the finite element discretization of these equations and give the state–of–the–art of a posteriori error estimation. Finally, we review the literature on the use of the Caputo’s fractional derivative in applications, focusing on anomalous diffusion and poro-elasticity applications. The rest of the manuscript is organized as follow. Chapter 1 is concerned with a proof of the reliability of the Bank–Weiser estimator for three–dimensional problems, extending a result from the literature. In Chapter 2 we present a numerical study of the Bank–Weiser estimator, provide a novel implementation of the estimator in the FEniCS finite element software and apply it to a variety of elliptic equations as well as goal-oriented error estimation. In Chapter 3 we derive a novel a posteriori estimator for the L2 error induced by the finite element discretization of fractional Laplacian operator based equations. In Chapter 4 we present new theoretical results on the convergence of a rational approximation method with consequences on the approximation of fractional norms as well as a priori error estimation results for the finite element discretization of fractional equations. Finally, in Chapter 5 we provide an application of fractional calculus to the study of the human meniscus via poro-elasticity equations. [less ▲]

Practical error bounds in energy norm based on a recovered displacement field

in Pimienta, P M (Ed.) 10th World Congress on Computational Mechanics (WCCM 2012) (2012)

Prediction of nocturnal hypoglycemia by an aggregation of previously known prediction approaches: proof of concept for clinical application

in Computer Methods & Programs in Biomedicine (2016), 134

Presentation in Computational Sciences PhD Presentation Day

Presentation (2022, March 22)

Primary energy used in centralized and decentralized ventilation systems measured in field tests in residential buildings

in Proceedings of the 26th AIVC Conference, Effective Ventilation in high performance buildings (2015, September)

Ventilation systems can save heat energy by using heat recovery, but consume electrical energy to power the fans. In practice, the energy efficiency of those systems can be lower than expected, when ... [more ▼]

Ventilation systems can save heat energy by using heat recovery, but consume electrical energy to power the fans. In practice, the energy efficiency of those systems can be lower than expected, when compared to the nominal values provided by the manufacturer. In this paper, results of a comprehensive field tests with 20 centralized and 60 decentralized ventilation systems for residential buildings and the calculation of the primary energy savings of those devices are presented. Factors like volume flow unbalances, shortcuts, temperature change rates and specific fan power have been addressed by tracer gas technology and other means and been used as input factors to calculate the primary energy balance of those devices. Every system showed positive primary energy savings. The mean value for centralized systems was 2.92 Wh/m3 with a high standard deviation of 2.23 Wh/m3, while the decentralized systems showed higher savings of around 4.75 Wh/m3 with a standard deviation of 0.01 to 0.15 Wh/m3. In general, the calculated savings in field tests were significantly lower compared to the case of using nominal values as input parameters. [less ▲]

Principles for setting single or multiline control based on network characteristics

Poster (2021, January)

Privacy and Transparency in CBDCs: A Regulation-by-Design AML/CFT Scheme

in Proceedings of the 2021 IEEE International Conference on Blockchain and Cryptocurrency (ICBC) (2021, May)

Central banks and governments all over the world are increasingly exploring digital versions of fiat money, known as retail Central Bank Digital Currencies (CBDCs). Most initiatives rely on Distributed ... [more ▼]

Central banks and governments all over the world are increasingly exploring digital versions of fiat money, known as retail Central Bank Digital Currencies (CBDCs). Most initiatives rely on Distributed Ledger Technologies and are presented as alternatives to physical cash. Consequently, anonymity-related regulatory questions arise in terms of Anti-Money Laundering and Counter-Terrorist Financing compliance. Against this backdrop, this paper provides a techno-legal taxonomy of approaches to balance privacy and transparency in CBDCs without thwarting accountability, but it also underlines cross-sectoral impacts. The contribution heeds regulation-by-design as its core methodological foundation, with Privacy-Enhancing Technologies as the relevant use case. Thus, it highlights that not only technology aids legal purposes, but also that some regulatory requirements ought to be designed into technology for one to reach agreed-upon results and/or standards. [less ▲]

Privacy in Cross-border Digital Currency. A Transatlantic Approach

in Frankfurt Forum on US-European GeoEconomics (2022, September)

As a growing number of countries explore Central Bank Digital Currencies (CBDCs) for the domestic context, multi-country cross-border CBDCs pilots are also proliferating. Cross-border CBDCs could make ... [more ▼]

As a growing number of countries explore Central Bank Digital Currencies (CBDCs) for the domestic context, multi-country cross-border CBDCs pilots are also proliferating. Cross-border CBDCs could make cross-border payments faster, cheaper, and simpler. However, for any cross-border CBDC to unlock these benefits and be widely adopted, it must address key concerns, chief among them risks around privacy and transparency of data. This article illustrates how various technical design choices can affect the privacy and transparency of cross-border CBDCs. For instance, architectural choices about the structure of a cross-border CBDC and representational choices about how transactions are encoded in the underlying software can have far-reaching implications for privacy and transparency—both in a domestic context and for cross-border transactions. Many of the cross-border CBDC pilot studies to date have (understandably) adopted the technical designs provided by enterprise distributed ledger platforms. However, some of these designs make tradeoffs regarding privacy, efficiency, and/or security. Whether these tradeoffs are acceptable is a matter of policy, and requires coordination between different regulators and central banks. In view of these implications—and some of the corresponding tensions that arise—we argue that the US and the EU should work together alongside other partners to create the technological and regulatory environment to enable privacy-preserving cross-border CBDCs. The US and the EU should seize the emergence of CBDCs as an opportunity to finally establish a transatlantic privacy framework, and clarify its interplay with the prevention of money laundering and financing of terrorism (AML/CFT/CPF). More broadly, both should harness the clout of their combined financial systems to develop digital asset regulation and standards with a global reach and democratic values. These regulatory developments would not only streamline regulatory guidelines, but they could also directly impact and ease the technical development of a cross-border CBDC. [less ▲]

Probabilistic multiconstraints optimization of cooling channels in ceramic matrix composites

in Composites. Part B, Engineering (2015), 81

This paper presents a computational reliable optimization approach for internal cooling channels in Ceramic Matrix Composite (CMC) under thermal and mechanical loadings. The algorithm finds the optimal ... [more ▼]

This paper presents a computational reliable optimization approach for internal cooling channels in Ceramic Matrix Composite (CMC) under thermal and mechanical loadings. The algorithm finds the optimal cooling capacity of all channels (which directly minimizes the amount of coolant needed). In the first step, available uncertainties in the constituent material properties, the applied mechanical load, the heat flux and the heat convection coefficient are considered. Using the Reliability Based Design Optimization (RBDO) approach, the probabilistic constraints ensure the failure due to excessive temperature and deflection will not happen. The deterministic constraints restrict the capacity of any arbitrary cooling channel between two extreme limits. A “series system” reliability concept is adopted as a union of mechanical and thermal failure subsets. Having the results of the first step for CMC with uniformly distributed carbon (C-) fibers, the algorithm presents the optimal layout for distribution of the C-fibers inside the ceramic matrix in order to enhance the target reliability of the component. A sequential approach and B-spline finite elements have overcome the cumbersome computational burden. Numerical results demonstrate that if the mechanical loading dominates the thermal loading, C-fibers distribution can play a considerable role towards increasing the reliability of the design. [less ▲]