arXiv subjects

Antti Stenvall

Publications and source records attributed to Antti Stenvall.

4 recordsLinked to original sources

arXiv2019

Semantics of HTS AC loss modelling: Theories, models and experiments

Computer-assisted modelling is an essential approach to design new devices. It speeds up the process from the initial idea to an actual device and saves resources by reducing the number of built prototypes. This is also a significant practical motivator behind scientific research in contemporary high-temperature superconductor (HTS) AC loss modelling. However, in the scientific literature in this field, consistent practices about modelling terminology have not been established. Then, it is up to the reader to decide, what is the true intent and meaning of the authors. Consequently, the interpretation of such literature might be very much reader-dependent. Moreover, an inseparable part of the whole modelling process is the development of modelling approaches and numerical methods and comparing the predictions obtained via modelling to experimentally achieved results: It is commonplace to discuss the accuracy of modelling results or the validation of a model. In this paper, we discuss the terminology related to theories, models and experiments in the context of HTS AC loss modelling. We discuss the recursive nature of theories and models in this context, discuss the compatibility of discrete formulations of physics utilized in our field with the corresponding continuum descriptions, as well as with intuition, and interpret the perceived meaning of validation of a self-consistent model, shedding light on the relationships between theories, models and measurements. We present our view on understanding these relations in the familiar context of AC losses in HTS. As a result, we end this paper with four conjectures describing our views.

physics.gen-ph↗

arXiv2018

Open Material Property Library With Native Simulation Tool Integrations -- MASTO

Reliable material property data is crucial for trustworthy simulations throughout different areas of engineering. Special care must be taken when materials at extreme conditions are under study. Superconductors and devices assembled from superconductors and other materials, like superconducting magnets, are often operated at such extreme conditions: at low temperatures under high magnetic fields and stresses. Typically, some library or database is used for getting the data. We have started to develop a database for storing all kind of material property data online called Open Material Property Library With Native Simulation Tool Integrations -- MASTO. The data that can be imported includes, but is not limited to, anisotropic critical current surfaces for high temperature superconducting materials, electrical resistivities as a function of temperature, RRR and magnetic field, general fits for describing material behaviour etc. Data can also depend on other data and it can be versioned to guarantee permanent access. The guiding idea in MASTO is to build easy-to-use integration for various programming languages, modelling frameworks and simulation software. Currently, a full-fledged integration is built for MATLAB to allow users to fetch and use data with one-liners. In this paper we briefly review some of the material property databases commonly used in superconductor modelling, present a case study showing how selection of the material property data can influence the simulation results, and introduce the principal ideas behind MASTO. This work serves as the reference document for citing MASTO when it is used in simulations.

cond-mat.mtrl-sci↗

arXiv2016

Towards a unified framework for decomposability of processes

The concept of process is ubiquitous in science, engineering and everyday life. Category theory, and monoidal categories in particular, provide an abstract framework for modelling processes of many kinds. In this paper, we concentrate on sequential and parallel decomposability of processes in the framework of monoidal categories: We will give a precise definition, what it means for processes to be decomposable. Moreover, through examples, we argue that viewing parallel processes as coupled in this framework can be seen as a category mistake or a misinterpretation. We highlight the suitability of category theory for a structuralistic interpretation of mathematical modelling and argue that for appliers of mathematics, such as engineers, there is a pragmatic advantage from this.

math.CT↗

arXiv2013

Computation of Losses in HTS Under the Action of Varying Magnetic Fields and Currents

Numerical modeling of superconductors is widely recognized as a powerful tool for interpreting experimental results, understanding physical mechanisms and predicting the performance of high-temperature superconductor (HTS) tapes, wires and devices. This is especially true for ac loss calculation, since a sufficiently low ac loss value is imperative to make these materials attractive for commercialization. In recent years, a large variety of numerical models, based on different techniques and implementations, have been proposed by researchers around the world, with the purpose of being able to estimate ac losses in HTSs quickly and accurately. This article presents a literature review of the methods for computing ac losses in HTS tapes, wires and devices. Technical superconductors have a relatively complex geometry (filaments, which might be twisted or transposed, or layers) and consist of different materials. As a result, different loss contributions exist. In this paper, we describe the ways of computing such loss contributions, which include hysteresis losses, eddy current losses, coupling losses, and losses in ferromagnetic materials. We also provide an estimation of the losses occurring in a variety of power applications.

cond-mat.supr-con↗