A New Framework for the Simulation of Equation-Based Models with Variable Structure

Many modern models contain changes that affect the structure of their underlying equation system, e.g. the breaking of mechanical devices or the switching of ideal diodes. The modeling and simulation of such systems in current equation-based languages frequently poses serious difficulties. In order to improve the handling of variable-structure systems, a new modeling language has been designed for research purposes. It is called Sol and it caters to the special demands of variable-structure systems while still representing a general modeling language. This language is processed by a new translation scheme that handles the differential-algebraic equations in a highly dynamic fashion. In this way, almost arbitrary structural changes can be processed. In order to minimize the computational effort, each change is processed as locally as possible, preserving the existing computational structure as much as possible. Given this methodology, truly object-oriented modeling and simulation of variable-structure systems is made possible. The corresponding process of modeling and simulation is illustrated by two examples from different domains

Trust in government and fiscal adjustments : [Version 4 June 2013]

The paper looks at the determinants of fiscal adjustments as reflected in the primary surplus of countries. Our conjecture is that governments will usually find it more attractive to pursue fiscal adjustments in a situation of relatively high growth, but based on a simple stylized model of government behavior the expectation is that mainly high trust governments will be in a position to defer consolidation to years with higher growth. Overall, our analysis of a panel of European countries provides support for this expectation. The difference in fiscal policies depending on government trust levels may help explaining why better governed countries have been found to have less severe business cycles. It suggests that trust and credibility play an important role not only in monetary policy, but also in fiscal policy

К вопросу о философском осмыслении экологических проблем

Вопросы по охране окружающей среды стали актуальной темой для обсуждения на протяжении последних 20-30 лет. Глобальная экологическая ситуация заметно ухудшается. Для философии проблемы взаимодействия человека, общества и природы, их единения видятся в духовном постижении человеком самого себя и природы. Поэтому, появившиеся новые экологические проблемы ставят перед философами задачу поиска новых гармоничных способов восстановления отношений человека с естественной средой. Один из них - понимание модели дальнейшего устройства социума как эколого-информационной культуры. Questions on environmental protection became a hot topic for discussion for the past 20-30 years. The global environmental situation is deteriorating significantly. For the philosophy of the problem of interaction between man, society and nature, their unity seen in the spiritual comprehension of the man himself and nature. Therefore, new environmental problems pose philosophers the task of finding new ways to restore the harmonious human relationships with the natural environment. One of them - the understanding of the model of society as a device to further environmental information culture

Key Technologies for hybrid electric flight

This is a short presentation of the current technology assumptions behind the project IMOTHEP and future technology potential

Object-Oriented Formulation and Simulation of Models using Linear Implicit Equilibrium Dynamics

New robust and yet powerful Modelica libraries as the DLR ThermoFluid Stream library or the introduction of dialectic mechanics use a special modeling approach that uses linear implicit equilibrium dynamics. In this paper, we study the basic motivation of this approach, its benefits and drawbacks before finally showing how to get from the models to applicable simulation code

Regularization of the Logarithmic Mean for Robust Numerical Simulation

To calculate the driving temperature difference between the hot and the cold side of a heat exchanger, the use of the logarithmic mean temperature difference is common practice. To provide high robustness in complex dynamic system models, a robust formulation of the logarithmic mean (logmean) function becomes vital. As the analytic definition of the logmean function naturally comes along with singularities and limitations for specific input conditions, it is essential to extend and modify it for heat exchanger modeling. This paper proposes how the logmean function can be extended to be valid in all four quadrants of the Cartesian coordinate system and how to bridge the resulting definition gaps. Special focus lies on the robust formulation in such a way that it can be easily handled by numerical solvers. This includes the numerical approximation of the logmean by use of its integral form by implicit ODE solvers with variable step width. Furthermore a way is presented to flatten the naturally steep gradients in the vicinity of the x- and y-axes without manipulating the function in the uncritical regions. All the modifications on the logmean are finally applied in a simple simulation model written in the object-oriented programming language Modelica to examine the robustness of the approach

Introducing Dialectic Mechanics

This paper introduces a new method for mechanical systems with its own interface that enables the object-oriented formulation of very stiff contacts. It thereby suppresses high frequencies and yields stable replacement dynamics leading to an equivalent steady state. Potential applications are the efficient modeling and simulation of robotic manipulation or the easier handling of what formerly have been variable-structure systems

Effects of Event-Free Noise Signals on Continuous-Time Simulation Performance

Generating stochastic input signals such as noise in physical systems is traditionally implemented using discrete random number generators based on discrete time-events. Within the Modelica community, random number generators free of time-events have recently been proposed in order to increase the performance of system simulations. However, the impact of such signals on commonly used solvers, such as DASSL or Radau IIA, is still under discussion. In order to provide better understanding for modeling practitioners, we examine the influence of event-free noise models on simulation performance. To this end, we conduct practical simulation experiments with systems of three sizes, two solvers, and different parameters. Results indicate that step-size control can handle event-free noise generators well and that they outperform sampled generators. The findings can be related to other time-dependent system inputs

Dialectic Mechanics: Extension for Real-Time Simulation

Dialectic mechanics was introduced as an approximative modeling alternative to the classic Newtonian formulation of mechanics. It allows for additional freedom in placing a systems eigenvalues to facilitate simulation of systems, that are not suitable for most integration methods, when modeled according to the classic approach. The original idea of dialectic mechanics enables the suppression of high frequencies, but may still yield very stiff systems unsuitable for explicit integration methods. An additional term is added to enable real-time simulation with explicit methods. The goal of this paper is an analysis of the resulting equations and a comparison to the classic Newtonian formulation, aiming for an understanding of which applications most benefit from using dialectic mechanics

Robust Modeling of Volumes for Dynamic Simulations of Thermo-Fluid Stream Networks

Modeling of complex thermo-fluid systems often leads to either many states or large non-linear systems of equations, which are both undesirable especially for real-time applications. Both of these issues can be solved by our algebraic stream-dominated approach to build hard real-time capable simulations. In this approach volume elements play a central role as boundaries and loop-breakers for fluid streams. In this paper, we first derive a lumped state standard volume model from first principle and then several specialized volumes for different applications. We regularize the models to perform robustly, even in degenerated operating conditions that might appear in dynamic simulations. While doing so, we show all approximations and assumptions used to arrive at the final models. Finally, we present some application examples showcasing the use of the different volumes for dynamic simulations. Alongside the models developed in this paper these examples are part of our open-source Modelica library and their implementation is therefore available