1,721,016 research outputs found
Driving bifurcating parametrized nonlinear PDEs by optimal control strategies: Application to Navier-Stokes equations with model order reduction
Full text linkThis work deals with optimal control problems as a strategy to drive bifurcating solution of nonlinear parametrized partial differential equations towards a desired branch. Indeed, for these governing equations, multiple solution configurations can arise from the same parametric instance. We thus aim at describing how optimal control allows to change the solution profile and the stability of state solution branches. First of all, a general framework for nonlinear optimal control problem is presented in order to reconstruct each branch of optimal solutions, discussing in detail the stability properties of the obtained controlled solutions. Then, we apply the proposed framework to several optimal control problems governed by bifurcating Navier-Stokes equations in a sudden-expansion channel, describing the qualitative and quantitative effect of the control over a pitchfork bifurcation, and commenting in detail the stability eigenvalue analysis of the controlled state. Finally, we propose reduced order modeling as a tool to efficiently and reliably solve parametric stability analysis of such optimal control systems, which can be challenging to perform with standard discretization techniques such as Finite Element Method
POD-based reduced order methods for optimal control problems governed by parametric partial differential equation with varying boundary control
Full text linkIn this work we propose tailored model order reduction for varying boundary
optimal control problems governed by parametric partial differential equations.
With varying boundary control, we mean that a specific parameter changes where
the boundary control acts on the system. This peculiar formulation might
benefit from model order reduction. Indeed, fast and reliable simulations of
this model can be of utmost usefulness in many applied fields, such as
geophysics and energy engineering. However, varying boundary control features
very complicated and diversified parametric behaviour for the state and adjoint
variables. The state solution, for example, changing the boundary control
parameter, might feature transport phenomena. Moreover, the problem loses its
affine structure. It is well known that classical model order reduction
techniques fail in this setting, both in accuracy and in efficiency. Thus, we
propose reduced approaches inspired by the ones used when dealing with
wave-like phenomena. Indeed, we compare standard proper orthogonal
decomposition with two tailored strategies: geometric recasting and local
proper orthogonal decomposition. Geometric recasting solves the optimization
system in a reference domain simplifying the problem at hand avoiding
hyper-reduction, while local proper orthogonal decomposition builds local bases
to increase the accuracy of the reduced solution in very general settings
(where geometric recasting is unfeasible). We compare the various approaches on
two different numerical experiments based on geometries of increasing
complexity
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
POD-Galerkin model order reduction for parametrized nonlinear time-dependent optimal flow control: An application to shallow water equations
No full textIn the present paper we propose reduced order methods as a reliable strategy to efficiently solve parametrized optimal control problems governed by shallow waters equations in a solution tracking setting. The physical parametrized model we deal with is nonlinear and time dependent: this leads to very time consuming simulations which can be unbearable, e.g., in a marine environmental monitoring plan application. Our aim is to show how reduced order modelling could help in studying different configurations and phenomena in a fast way. After building the optimality system, we rely on a POD-Galerkin reduction in order to solve the optimal control problem in a low dimensional reduced space. The presented theoretical framework is actually suited to general nonlinear time dependent optimal control problems. The proposed methodology is finally tested with a numerical experiment: the reduced optimal control problem governed by shallow waters equations reproduces the desired velocity and height profiles faster than the standard model, still remaining accurate
A MILP Formulation for an Automated Guided Vehicle Scheduling Problem with Battery Constraints
No full textNowadays, AGVs are frequently used in industries for the internal transportation of goods or pallets. The aim of an AGV-based internal transportation system is to transfer the right amount of the right material to the right place at the right time. Therefore, the determination of a good scheduling of the AGV tasks is essential to overcome delays in production and material handling processes. In this work, we study a scheduling problem arising from an internal transportation system of a company operating in the manufacturing field where AGVs subject to battery constraints are used for horizontal movement of materials. The aim of this work is to highlight the impact of the AGV battery recharge times on the completion time of the material handling process. To this aim, we propose an original mixed integer linear programming (MILP) formulation to optimally solve the addressed problem. The proposed model is validated on test instances built from real data comparing its results with those obtained disregarding the battery constraints. The results show the effectiveness of the proposed solution method and the impact of the AGV charging time on the handling process completion time
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Mutation analysis of the RPGR gene reveals novel mutations in south European patients with X-linked retinitis pigmentosa.
No full text- …
