Keynote Lectures

Social Simulations for Policy Making: Experiences from the COVID Crisis
Frank Dignum, Umeå University, Sweden, Sweden

Seamless Coupling of PDE-based Simulations with the Coupling Library preCICE
Benjamin Uekermann, University of Stuttgart, Germany, Germany

M&S and MBSE: Individual Challenges and Mutual Opportunities
Andrea D'Ambrogio, Università di Roma "Tor Vergata", Italy, Italy

Abstract
Although social simulations have been used for quite some time now, they seem to be primarily an academic tool to investigate social phenomena. Decision makers could profit from having ways to investigate what are the possible effects of new regulations. This is especially true in times of crisiswhen decisions have to be made quick and consequences are often difficult to envisage. In this presentation I will discuss the possibility to support decision makers in crisis situations based on our experiences during the covid crisis. I will discuss both the advantages, but also the limitations on the current software and theories to support this work.

Abstract
As pointed out in multiple keynote presentations at previous SIMULTECH conferences, interoperability of simulation models and software is an important success factor of simulations in general. The FMI standard, today's most popular co-simulation concept, realizes such interoperability by treating simulation models as libraries (FMUs). A "coupler" then calls and orchestrates these models. This is easily possible for simple models, such as ODE-based ones. More accurate models with space resolution – PDE-based models – however, cannot always be easily converted into libraries adhering to a pre-defined API. In fact, such models are often implemented in legacy software, which is the result of decades of work. A natural wish is to couple such software in a minimally-invasive way instead. This can be realized if we turn things around: if the coupling software instead becomes the library, which is then called by the model software.

PDE-based simulations also come with another challenge: They are typically very expensive to solve. Large compute clusters are often needed to solve a single model and large amounts of (space-dependent) data need to be communicated to couple models to one another. If all coupling data is orchestrated by a single coupling process, this process quickly becomes a severe performance bottleneck. To handle this challenge, a peer-to-peer coupling approach can be very helpful.

In this presentation, I introduce the basic concepts behind the open-source coupling library preCICE (https://precice.org/) – the library concept and the peer-to-peer concept. preCICE thus allows researchers to seamlessly plug together PDE-based simulation software for partitioned multi-physics and multi-scale simulations. For the actual coupling, preCICE offers methods for fixed-point acceleration (quasi-Newton acceleration), fully parallel communication (MPI or TCP/IP), data mapping (radial-basis function interpolation), and time interpolation (waveform relaxation). Today, although being an academic software project at heart, preCICE is used by more than 100 research groups in both academia and industry. Ready-to-use adapters for many popular PDE-based simulation software packages are available, e.g. OpenFOAM, SU2, CalculiX, FEniCS, or deal.II. The wide variety of application fields ranges from aerodynamics to astronautics, automotive manufacturing, wind energy, biomechanics, biomimetics, marine engineering, nuclear fusion, reactor safety, geophysical systems, and many more.

Abstract
Modeling and Simulation (M&S) and Systems Engineering (SE) disciplines have evolved in different contexts, with long lasting examples of close and effective interaction. The introduction of Model Based Systems Engineering (MBSE), which refers to the formalized application of modeling to support system development activities, has provided a significant step forward in the SE field and naturally leads to a more integrative approach between M&S and SE. The talk illustrates the main challenges that can be addressed by exploiting the opportunities of such an integrative approach. The mutual benefits that can be achieved are illustrated and discussed in terms of M&S Based Systems Engineering, which promotes executable models and proposes simulation as the native mechanisms to address measures of performance and effectiveness throughout the systems life cycle, and simulation systems engineering, which proposes the execution of an interdisciplinary MBSE process for developing, maintaining, and employing simulations.