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Eine Phasenfeldmethode für zwei-skalige Topologieoptimierung
No full textTopology optimization is the search for an ideal structural design for a given physical setting. In additive manufacturing a higher part complexity produces almost no additional costs. This design freedom allows for structural optimization on multiple scales. We model the material distribution via the phase-field method, which leads to a concise problem formulation and opens up the possibility for a functional analytical examination and a simple implementation. The coupling of meso- and macroscale structures is achieved via a local volume constraint, where two parameters govern the porosity of the arising designs. In [1] these constraints are enforced in order to create the bone-like infill structures, but the local volumes stay fixed throughout the runtime of the algorithm. Here we are defining novel stress-adaptive local volumes. In our meso-macro coupling we are using a penalty approach instead of a constrained formulation. We are able to prove the existence of a solution of the arising optimal control problem. Pseudo-timestepping is used to solve the problem and we show the existence of a solution for this method. As far as we are aware, this analysis has not been conducted before. Lastly, the optimal control problem is solved. The major numerical difficulty is the computational bottleneck of calculating the local volumes. Therefore we are applying multiprocessing, which we have not seen in other research work in this realm. We can see the benefits of the new stress-dependent local volume constraints: Where local stresses are high, more material is placed and the part becomes stiffer. In less critical areas the porosity is higher, saving weight as well as costs.Topologieoptimierung ist die Suche nach einer idealen Struktur für eine gegebene physikalische Problematik. In der additiven Fertigung erhöht die Bauteilkomplexität kaum die Produktionskosten. Diese Gestaltungsfreiheit ermöglicht es uns die Struktur auf mehreren Skalen zu optimieren. Wir modellieren die Materialverteilung mittels der Phasenfeldmethode, was zu einer präzisen Problemformulierung führt und die Möglichkeit einer funktionalanalytischen Untersuchung und einer einfachen Implementierung eröffnet. Die Kopplung von meso- und makroskaligen Strukturen wird über eine lokale Volumenbeschränkung erreicht, wobei zwei Parameter die Porosität der entstehenden Designs steuern. In [1] werden diese Nebenbedingungen verwendet um die knochenähnlichen Füllstrukturen zu erzeugen, aber die lokalen Volumina ändern sich nicht während der Laufzeit des Algorithmus. Hier definieren wir neuartige spannungsabhängige lokale Volumina. Für die Meso-Makro-Kopplung benutzen wir einen Strafterm anstatt einer restringierten Formulierung. Die Existenz einer Lösung für das entstehende Optimalsteuerungsproblem können wir beweisen. Wir verwenden ein numerisches Zeitschrittverfahren und zeigen die Existenz einer Lösung für diesen Ansatz. Soweit uns bekannt ist, wurde diese funktionalanalytische Untersuchung bisher noch nicht durchgeführt. Abschließend berechnen wir die optimalen Strukturen, wobei der größte numerische Aufwand bei der Berechnung der lokalen Volumina liegt. Deshalb setzen wir Multiprocessing ein, was wir in anderen Forschungsarbeiten auf diesem Gebiet noch nicht gesehen haben. Wir sehen die Vorteile der neuen spannungsabhängigen lokalen Volumenbeschränkungen: Wo die lokalen Spannungen hoch sind, wird mehr Material angebracht und das Baueil wird stabiler. In weniger kritischen Bereichen ist die Porosität höher, was sowohl Gewicht als auch Kosten spart
On a two-scale phasefield model for topology optimization
Get PDFIn this article, we consider a gradient flow stemming from a problem in two-scale topology optimization. We use the phase-field method, where a Ginzburg--Landau term with obstacle potential is added to the cost functional, which contains the usual compliance but also an additional contribution including a local volume constraint in a penalty term. The minimization of such an energy by its gradient-flow is analyzed in this paper. We use an regularization and discretization of the associated state-variable to show the existence of weak solutions to the considered system. Download Document
Two-scale topology optimization with heterogeneous mesostructures based on a local volume constraint
Get PDFA new approach to produce optimal porous mesostructures and at the same time optimizing the macro structure subject to a compliance cost functional is presented. It is based on a phase-field formulation of topology optimization and uses a local volume constraint (LVC). The main novelty is that the radius of the LVC may depend both on space and a local stress measure. This allows for creating optimal topologies with heterogeneous mesostructures enforcing any desired spatial grading and accommodating stress concentrations by stress dependent pore size. The resulting optimal control problem is analysed mathematically, numerical results show its versatility in creating optimal macroscopic designs with tailored mesostructures
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On a two-scale phasefield model for topology optimization
No full textIn this article, we consider a gradient flow stemming from a problem in two-scale topology optimization. We use the phase-field method, where a Ginzburg--Landau term with obstacle potential is added to the cost functional, which contains the usual compliance but also an additional contribution including a local volume constraint in a penalty term. The minimization of such an energy by its gradient-flow is analyzed in this paper. We use an regularization and discretization of the associated state-variable to show the existence of weak solutions to the considered system
On a Two-Scale Phasefield Model for Topology Optimization
No full textIn this article, we consider a gradient flow stemming from a problem in two-scale topology optimization. We use the phase-field method, where a Ginzburg–Landau term with obstacle potential is added to the cost functional, which contains the usual compliance but also an additional contribution including a local volume constraint in a penalty term. The minimization of such an energy by its gradient-flow is analyzed in this paper. We use an regularization and discretization of the associated state-variable to show the existence of weak solutions to the considered system
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Variations on the Author
Get PDF“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
Get PDFWe 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
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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