Systematic assessment of local & global signal control policies: A methodological perspective

in Proceedings of 2015 International Conference on Models and Technologies for Intelligent Transportation Systems, MT-ITS 2015 (2015)

Traffic control performance on networks depends on the flow response to the policy adopted, which in turn contributes to determine the optimal signal settings. This paper focuses on the relationship ... [more ▼]

Traffic control performance on networks depends on the flow response to the policy adopted, which in turn contributes to determine the optimal signal settings. This paper focuses on the relationship between local and network wide traffic control policies within the combined traffic control and assignment problem. Through a full exploration of the solution space, an in depth cross comparison is performed between the well-known local policies P0 and Equisaturation, versus the global policies Maximum Throughput and Minimum Delay, to verify how the two local policies approximate the optimal settings for signalized intersections. Realistic traffic dynamics, such as congestion, multiple controllers and spillback are considered, to empirically determine the conditions under which the local policies are able to approximate global performances. After presenting the different local and global control policies, experiments are performed on simple toy networks. The complexity of the underlying network and, therefore, of the problems' boundary conditions is then increased, allowing us to showcase how the different metrics perform in different situations. Finally, conclusions on the results are drawn. © 2015 BME. [less ▲]

Systems Engineering, Systems Thinking, and Learning: a Case Study in Space Industry

Doctoral thesis (2013)

Systems thinking is a prerequisite of systems engineering, which is performed in multi-disciplinary teams, i.e. software engineers, mechanical engineers, electronic engineers, and others, work together to ... [more ▼]

Systems thinking is a prerequisite of systems engineering, which is performed in multi-disciplinary teams, i.e. software engineers, mechanical engineers, electronic engineers, and others, work together to develop, build, and test technical systems such as space systems. The more team members consider a systems perspective the less rework is expected and the less effort of systems engineers is required. How systems thinking evolves in practice is not sufficiently understood. Therefore, work activity of multi-disciplinary teams has been studied in an empirical study. Data from multiple sources and of different temporal resolution has been collected over four years in four studies in space systems engineering. These studies are a concept exploration project in a summer school, two concept exploration projects in a concurrent design facility, and five projects in several lifecycle stages in a small space systems company. An analytical framework has been developed based on an activity-theoretical analysis and a theme-and-key-event analysis. Contradicting multiple roles, differences in parameter definition and impact, differences in work approaches and ways of interacting, contradicting work standards, trust and doubts in extra-disciplinary decisions, awareness of diversity and orientation towards extra-disciplinary interactors, and velocity and availability of information are identified contradictions with learning potential. These contradictions provoke initiators of multi-disciplinary interaction. These are proactive provision of extra-disciplinary advice and three types of questions: critical questioning across disciplinary boundaries, asking for extra-disciplinary advice, and questioning the current work approach. The contradictions prompt the selection of themes that comprise several key events. These themes and key events are analysed on three levels (macro, meso, and micro) with a focus on systems thinking content and discourse features. Systems thinking evolves in interaction within a broad temporal range, from minutes to years. It evolves vertically, i.e. within a discipline, and horizontally, i.e. across disciplines. The evolution of systems thinking is influenced by the multi-disciplinary quality of interaction. This quality is defined by the diversity or multi-disciplinarity of the interaction, the awareness of the diversity, the orientation towards extra-disciplinary interactors, the differences in interactional responsiveness, and the cohesion of interaction. Improving the multi-disciplinary quality of interaction to foster the evolution of systems thinking is the major goal of the developed WAVES (Work Activity for a Versatile Evolution of Systems engineering and thinking) strategy. The WAVES strategy comprises two paths. The first path focuses on the introduction of employees into professional life, (space) industry, a company, a team, and a task. The second path focuses on the continuous improvement of the work activity. The implementation and evaluation of WAVES in a small space system company is the basic contribution to industry. The implementation within systems engineering departments of large space organisations has been prepared. The developed analytical framework contributes a new approach to analyse work activity in practice. Finally, the answers to the first part of the main research question contribute to a better understanding of systems engineering, systems thinking, and its learning in practice. [less ▲]

Taylor-Series Expansion Based Numerical Methods: A Primer, Performance Benchmarking and New Approaches for Problems with Non-smooth Solutions

in Archives of Computational Methods in Engineering (2019)

We provide a primer to numerical methods based on Taylor series expansions such as generalized finite difference methods and collocation methods. We provide a detailed benchmarking strategy for these ... [more ▼]

We provide a primer to numerical methods based on Taylor series expansions such as generalized finite difference methods and collocation methods. We provide a detailed benchmarking strategy for these methods as well as all data files including input files, boundary conditions, point distribution and solution fields, so as to facilitate future benchmarking of new methods. We review traditional methods and recent ones which appeared in the last decade. We aim to help newcomers to the field understand the main characteristics of these methods and to provide sufficient information to both simplify implementation and benchmarking of new methods. Some of the examples are chosen within a subset of problems where collocation is traditionally known to perform sub-par, namely when the solution sought is non-smooth, i.e. contains discontinuities, singularities or sharp gradients. For such problems and other simpler ones with smooth solutions, we study in depth the influence of the weight function, correction function, and the number of nodes in a given support. We also propose new stabilization approaches to improve the accuracy of the numerical methods. In particular, we experiment with the use of a Voronoi diagram for weight computation, collocation method stabilization approaches, and support node selection for problems with singular solutions. With an appropriate selection of the above-mentioned parameters, the resulting collocation methods are compared to the moving least-squares method (and variations thereof), the radial basis function finite difference method and the finite element method. Extensive tests involving two and three dimensional problems indicate that the methods perform well in terms of efficiency (accuracy versus computational time), even for non-smooth solutions. [less ▲]

Temperature Fields Induced by Low Power Focused Ultrasound in Soft Tissues During Gene Therapy. Numerical Predictions and Experimental Results

in Archives of Acoustics (2009), 34(4), 445459

Textual Inference with Deep Learning Technique

in Proceedings of the 28th Annual Benelux Conference on Artificial Intelligence (BNAIC2016). (2016)

Thermo-mechanical coupling and part-level analysis for additive manufacturing processes

Scientific Conference (2021, January 13)

[1] Hussein, A. and Hao, L. and Yan, C. and Everson, R. Finite element simulation of the temperature and stress fields in single layers built without-support in selective laser melting. Materials & Design ... [more ▼]

[1] Hussein, A. and Hao, L. and Yan, C. and Everson, R. Finite element simulation of the temperature and stress fields in single layers built without-support in selective laser melting. Materials & Design (1980-2015), (2013), 52:638–647. [2] Bangerth, W. and Hartmann, R. and Kanschat, G. deal.II – a General Purpose Object Oriented Finite Element Library. ACM Trans. Math. Softw.(2007), Vol. 33., 4:24/1–24/27. [less ▲]

Thermodynamically constrained averaging theory for cancer growth modelling

in IFAC-PapersOnLine (2016), 49(26), 289-294

In Systems Biology, network models are often used to describe intracellular mechanisms at the cellular level. The obtained results are difficult to translate into three-dimensional biological systems of ... [more ▼]

In Systems Biology, network models are often used to describe intracellular mechanisms at the cellular level. The obtained results are difficult to translate into three-dimensional biological systems of higher order. The multiplicity and time dependency of cellular system boundaries, mechanical phenomena and spatial concentration gradients affect the intercellular relations and communication of biochemical networks. These environmental effects can be integrated with our promising cancer modelling environment, that is based on thermodynamically constrained averaging theory (TCAT). Especially, the TCAT parameter viscosity can be used as critical player in tumour evolution. Strong cell-cell contacts and a high degree of differentiation make cancer cells viscous and support compact tumour growth with high tumour cell density and accompanied displacement of the extracellular material. In contrast, dedifferentiation and losing of cell-cell contacts make cancer cells more fluid and lead to an infiltrating tumour growth behaviour without resistance due to the ECM. The fast expanding tumour front of the invasive type consumes oxygen and the limited oxygen availability behind the invasive front results automatically in a much smaller average tumour cell density in the tumour core. The proposed modelling technique is most suitable for tumour growth phenomena in stiff tissues like skin or bone with high content of extracellular matrix. [less ▲]

Three-Dimensional Crack Propagation with Global Enrichment XFEM and Vector Level Sets

Scientific Conference (2015)

Three-dimensional non-linear fracture mechanics by enriched meshfree methods without asymptotic enrichment

in Proceedings of the IUTAM Symposium on Discretization Methods for Evolving Discontinuities (2007)

This paper presents a three-dimensional, extrinsically enriched meshfree method for initiation, growth and coalescence of an arbitrary number of cracks in non-linear solids including large deformations ... [more ▼]

This paper presents a three-dimensional, extrinsically enriched meshfree method for initiation, growth and coalescence of an arbitrary number of cracks in non-linear solids including large deformations, for statics and dynamics. The novelty of the methodology fashioned in this work is that only an extrinsic discontinuous enrichment and no near-tip/asymptotic enrichment is required. Instead, a Lagrange multiplier field is added along the crack front to close the crack along the front. This decreases the computational cost and removes difficulties involved with a branch enrichment. Numerical examples treated include the pull-out of a reinforcement bar from a concrete block, and a Taylor bar impact with very large deformation and fragmentation. The results are compared to experimental results, and other simulations from the literature, which shows the robustness and accuracy of the method. © 2007 Springer. [less ▲]

Time and frequency domain analysis of piezoelectric energy harvesters by monolithic finite element modeling

in International Journal for Numerical Methods in Engineering (2017)

The successful design of piezoelectric energy harvesting devices relies upon the identification of optimal geometrical and material configurations to maximize the power output for a specific band of ... [more ▼]

The successful design of piezoelectric energy harvesting devices relies upon the identification of optimal geometrical and material configurations to maximize the power output for a specific band of excitation frequencies. Extendable predictive models and associated approximate solution methods are essential for analysis of a wide variety of future advanced energy harvesting devices involving more complex geometries and material distributions. Based on a holistic continuum mechanics modeling approach to the multi-physics energy harvesting problem, this article proposes a monolithic numerical solution scheme using a mixed-hybrid 3-dimensional finite element formulation of the coupled governing equations for analysis in time and frequency domain. The weak form of the electromechanical/circuit system uses velocities and potential rate within the piezoelectric structure, free boundary charge on the electrodes, and potential at the level of the generic electric circuit as global degrees of freedom. The approximation of stress and dielectric displacement follows the work by Pian, Sze, and Pan. Results obtained with the proposed model are compared with analytical results for the reduced-order model of a cantilevered bimorph harvester with tip mass reported in the literature. The flexibility of the method is demonstrated by studying the influence of partial electrode coverage on the generated power output. [less ▲]