A posteriori error estimation for extended finite elements by an extended global recovery

in International Journal for Numerical Methods in Engineering (2008), 76(8), 1123-1138

This contribution presents an extended global derivative recovery for enriched finite element methods (FEMs), such as the extended FEM along with an associated error indicator. Owing to its simplicity ... [more ▼]

This contribution presents an extended global derivative recovery for enriched finite element methods (FEMs), such as the extended FEM along with an associated error indicator. Owing to its simplicity, the proposed scheme is ideally suited to industrial applications. The procedure is based on global minimization of the L2 norm of the difference between the raw strain field (C-1) and the recovered (C0) strain field. The methodology engineered in this paper extends the ideas of Oden and Brauchli (Int. J. Numer. Meth. Engng 1971; 3) and Hinton and Campbell (Int. J. Numer. Meth. Engng 1974; 8) by enriching the approximation used for the construction of the recovered derivatives (strains) with the gradients of the functions employed to enrich the approximation employed for the primal unknown (displacements). We show linear elastic fracture mechanics examples, both in simple two-dimensional settings, and for a three-dimensional structure. Numerically, we show that the effectivity index of the proposed indicator converges to unity upon mesh refinement. Consequently, the approximate error converges to the exact error, indicating that the error indicator is valid. Additionally, the numerical examples suggest a novel adaptive strategy for enriched approximations in which the dimensions of the enrichment zone are first increased, before standard h- and p-adaptivities are applied; we suggest to coin this methodology e-adaptivity. Copyright © 2008 John Wiley & Sons, Ltd. [less ▲]

Potentials for Realising a Consistent Transition Between Function Modelling with the IFM Framework and Early System Simulation

in Proceedings of 19th International Conference on Engineering Design (2013)

Conceptual design is considered one of the most demanding design tasks requiring a joint effort of the involved designers, particularly in interdisciplinary design. Sound decision-making across ... [more ▼]

Conceptual design is considered one of the most demanding design tasks requiring a joint effort of the involved designers, particularly in interdisciplinary design. Sound decision-making across disciplines on alternative solution concepts may be considerably facilitated through early system simulation. A consistent transition of the available information in function modelling to early system simulation may thus support designers in this task. The IFM framework intends to support cross-disciplinary collaboration of involved designers by providing an integrated function modelling approach. In the paper it is analysed in how far a consistent transition from the IFM framework to established modelling techniques for simulation may be realised. The paper compares the information required for early system simulation in an interdisciplinary design context to the specific information conveyed in the different views of the IFM framework. The analysis identifies specific potentials and barriers for a consistent transition between them. Finally, the implications of the derived insights are discussed. [less ▲]

Practising circles: Studying institutional change and circular economy practice

in Journal of Cleaner Production (2019), 237

Preface

in Lausen, Berthold; Krolak-Schwerdt, Sabine; Böhmer, Matthias (Eds.) Data Science, Learning by Latent Structures, and Knowledge Discovery (2015)

Presentation of work in social network analysis

Presentation (2018)

Principles for setting single line and multiline control based on network characteristics

Scientific Conference (2019, September)

Principles of Persuasion in Social Engineering and Their Use in Phishing

in T. Tryfonas, I. Askoxylakis (Ed.) Human Aspects of Information Security, Privacy, and Trust Third International Conference, HAS 2015 (2015)

Research on marketing and deception has identified principles of persuasion that in influence human decisions. However, this research is scattered: it focuses on specific contexts and produces different ... [more ▼]

Research on marketing and deception has identified principles of persuasion that in influence human decisions. However, this research is scattered: it focuses on specific contexts and produces different taxonomies. In regard to frauds and scams, three taxonomies are often referred in the literature: Cialdini's principles of influence, Gragg's psychological triggers, and Stajano et al. principles of scams. It is unclear whether these relate but clearly some of their principles seem overlapping whereas others look complementary. We propose a way to connect those principles and present a merged and reviewed list for them. Then, we analyse various phishing emails and show that our principles are used therein in specific combinations. Our analysis of phishing is based on peer review and further research is needed to make it automatic, but the approach we follow, together with principles we propose, can be applied more consistently and more comprehensively than the original taxonomies. [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 ▲]

Proceedings of the BIVEC-GIBET Transport Research Days 2013

Book published by University Press (2013)

Process Reference Model "IT Grundschutz"

Report (2006)