Showing papers by "Andrea Walther published in 2017"
TL;DR: This paper presents a meta-modelling framework that automates the very labor-intensive and therefore time-heavy and therefore expensive and expensive process of numerical optimization of shapes immersed in fluids.
Abstract: Numerical optimization is becoming an essential industrial method in engineering design for shapes immersed in fluids. High-fidelity optimization requires fine design spaces with many desig...
19 citations
04 Jul 2017
TL;DR: The paper motivates the exploitation of algorithmic differentiation and proposes an extension of FMI for the evaluation of adjoint directional derivatives, which avoids compilation of the target language that often takes a large fraction of the overall simulation time.
Abstract: Algorithmic differentiation has proven to be an efficient method for evaluating derivative information for implementations of mathematical functions. In the context of the Functional Mockup Interface (FMI) the reverse mode of algorithmic differentiation shows immense promise. FMI is increasingly used for model-based applications, such as parameter estimation or optimal control. The paper motivates the exploitation of algorithmic differentiation and proposes an extension of FMI for the evaluation of adjoint directional derivatives. Attempts to interface algorithmic differentiation libraries with Modelica tools have been made. Instead of generating code for the target language which is instrumented with algorithmic differentiation library API and then compiled, in this new approach the intermediate representation used by the library is generated directly. This avoids compilation of the target language that often takes a large fraction of the overall simulation time. It also avoids model execution in order to create such an internal representation at runtime. The initial results are presented here.
2 citations
01 Jan 2017
TL;DR: In this article, a triple-ring-electrode set-up is presented that is optimised to balance the sensitivity of the frequency dependent impedance for the full set of material parameters.
Abstract: A complete characterisation of piezo ceramic materials typically requires several differently processed specimen. Since the results of all these measurements are combined to form one single set of material parameters, inconsistencies occur naturally. The problem when considering only one specimen is the lack of sensitivity for several material parameters. Therefore, a triple-ring-electrode set-up is presented that is optimised to balance the sensitivity of the frequency dependent impedance for the full set of material parameters. This specific set-up is designed to characterise the material properties using only one specimen, hence reaching consistent material parameters while still aiming to be sufficiently sensitive to each parameter. This more complex set-up calls for a FEM-based inverse problem, that makes it possible to find parameters that fit the measured impedance. The whole optimisation procedure is described exemplarily for one specimen of PIC255 (PI ceramic, Lederhose, Germany) leading to feasi...
1 citations