Modelica Tools Research Articles

Hybrid wind-wave systems: The case of the VolturnUS-S semi-submersible platform

Wind-wave hybrid floating systems are subject to active research and development in academia and industry. Industrialization of hybrid wind-wave energy systems will benefit from modular designs, allowing floating platforms to be used with or without wave energy converters (WECs). This work explores the design process to use oscillating water column (OWC) WECs as modular add-on features to existing semi-submersible floating platform designs. As the base case design, the IEA 15 MW offshore reference wind turbine with the VolturnUS-S floating platform designed by the University of Maine was used. A design approach was proposed, which involved various tools, such as OpenFAST developed by NREL, and the OWC Modelica tool developed at IST/ULisboa. Aero-hydro-servo-elastic simulations were performed to analyze the influence of the wind turbine energy generation design modifications and damage equivalent loads (DELs). The hybrid platform was modeled in the OWC Modelica tool to assess the wave energy conversion and the interaction between OWCs and the floating platform. The investigated hybrid design did not significantly increase DELs of the wind turbine in aero-hydro-servo-elastic simulations. The hybrid system does not decrease the LCOEcompared to a standalone floating wind turbine. The main cost driver was identified to be the material of the OWCs' ducts. Furthermore, the coupling forces between OWCs and the floating platform were found to be in the same order of magnitude as the wave excitation and radiation forces. The possibilities of including these forces in OpenFAST and the challenges for this are discussed.

Design optimization and energy performance evaluation of a dedicated outdoor air system with dual cooling sources

Dedicated outdoor air systems can save cooling energy and improve thermal comfort compared to conventional air-conditioning systems. Although many studies have investigated the energy performance of dedicated outdoor air systems for a certain application, there is a lack of a modeling resource to investigate with how the designs of the system are coordinated with control strategies aiming to improve its energy efficiency. This paper aims to optimize dedicated outdoor air system designs and develop a flexible model to evaluate the performance of the system. First, two innovative energy-saving designs of dedicated outdoor air system with dual cooling sources were proposed. Alternative design 1 optimizes the structure of the fresh air unit, while alternative design 2 builds on alternative design 1 by coupling it with a heat recovery system. Then, the two innovative systems and a baseline design were modeled using the equation-based Modelica tool. Finally, the energy performance of the three systems was evaluated under a hot and humid climate. Results showed that the Modelica-based models are able to capture the transient control strategy details. Alternative design 2 was found to be the optimal design among the three designs, with the highest energy efficiency ratio of chiller plants at 5.3. Moreover, it can reduce the cooling load supply by 9.3% and save about 7.4% on the energy consumption of chiller plants compared to the baseline design. In addition, alternative design 2 has a payback period of only 2.7 years, compared to the baseline design. It reveals the benefit of the heat recovery system in reducing the energy consumption and the cost of the cooling system. The developed dedicated outdoor air system simulation model can provide an evaluation for further improving the system optimization design, control strategy, and equipment configuration in engineering applications.

Algorithms for the Structural Analysis of Multimode Modelica Models

Since its 3.3 release, Modelica offers the possibility to specify models of dynamical systems with multiple modes having different DAE-based dynamics. However, the handling of such models by the current Modelica tools is not satisfactory, with mathematically sound models yielding exceptions at runtime. In this article, we propose several contributions to this multifaceted issue, namely: an efficient and scalable multimode extension of the structural analysis of Modelica models; a systematic way of rewriting a multimode Modelica model, based on this analysis, so that the rewritten model is guaranteed to be correctly compiled by state-of-the-art Modelica tools; a proposal for the handling of the consistent initialization of multimode models; multimode structural analysis algorithms that handle both multiple modes and mode change events in a unified framework, coupled with a compile-time algorithm for identifying and quantifying impulsive behaviors at mode changes. Our approach is illustrated on relevant example models, and the performance of our implementations is assessed on a variable dimension large-scale model.

A Modular, Extensible, and Modelica-Standard-Compliant OpenModelica Compiler Framework in Julia Supporting Structural Variability

Nowadays, industrial products are getting increasingly complex, and time-to-market is significantly shorter. Modeling and simulation tools for cyber-physical systems need to keep up with the increased complexity. This paper presents OpenModelica.jl, a modular and extensible Modelica compiler framework in Julia targeting ModelingToolkit.jl and supporting Variable Structured Systems. We extended the Modelica language with three new operators to support continuous-time mode-switching and reconfiguration via recompilation at runtime. Therefore, our compiler supports the Modelica language and variable structure systems via the aforementioned extensions. To our knowledge, there are no other Modelica tools available that support both standard Modelica and variable structure systems. We evaluated our framework using a standardized benchmark suite, in terms of simulation, compilation and recompilation performance. The results concerning compilation and simulation time performance were compared with the results of running the existing OpenModelica compiler with the same set of models. A custom benchmark was devised to estimate the cost in terms of recompilation when simulating variable structure systems. The performance experiments showed that OpenModelica.jl is currently about four times slower in terms of compilation time when compiling a transmission line model with tens of thousands of equations and variables. The difference in simulation performance between the two compilers was negligable. Furthermore, the impact of recompilation during the simulation was usually small compared with the simulation time for long simulations. The results are promising for a prototype, and we outline approaches to further improve both compilation and simulation performance as future research.

Cyber–physical system modeling with Modelica using message passing communication

Modelica is an object-oriented modeling language whose design and features facilitate the description of cyber–physical systems (CPS). Message passing communication (MPC), seen as the transmission of impulses of information between model components, eases the description of the discrete-event parts of CPS models. However, Modelica does not currently supports MPC. Modelica supports an equation-based component connection rationale, where Modelica tools automatically transform component connections into model equations, following a physical modeling approach. The differences between MPC and Modelica connections are analyzed. A proposal for supporting MPC in Modelica is presented, inspired by the coupled PDEVS model communication approach. The presented MPC proposal is based on the definition of structures to manage messages, named buffers, interface ports and communication channels. Also, an implementation of the proposed MPC mechanism in the form of a new free Modelica library, named MSGLib, is presented. MSGLib includes functionality to manage and dynamically store messages, and describe component communications. Two examples, a pick and place system and a robotic arm, are presented to demonstrate the use of the library, and its combination with other Modelica models.

Modelica-based simulation of electromagnetic transients using Dynaωo: Current status and perspectives

This paper presents the current status, the open challenges, and perspectives for Modelica-based simulation of Electromagnetic Transient (EMT) using Dynaωo environment. The simulation efficiency in native Modelica environments requires improvements for larger-scale systems, as they have been primarily developed and used for complex but small problems. This paper investigates the use of Dynaωo, an open-source hybrid C++/Modelica tool originally developed for large-scale electromechanical transient studies, for electromagnetic transient simulations. It demonstrates that its approach manages to bring improvements in terms of performances while keeping the flexibility, accuracy, and robustness of full Modelica tools, but that there is still room for further improvements.

Study of the Thermal Comfort of a Building that does not Comply with Construction Standards in Madagascar: Experimentation and Simulation with OMEdit

A very large number of buildings in developing countries are far from complying with the standards of housing. This paper presents the subjective study of the thermal comfort of a building that does not comply with construction standards or thermal regulations, located in Madagascar. Modeling was done using the Modelica tool, especially its BuildSysPro library. In order to minimize the inaccuracies, a step of an experimental adjustment of the developed numerical model was also carried out usingexperimental reference data that were obtained from the temperaturemeasurementsof the studied building elements as well as the wind speed and the received solar radiation flux. It was found that despite the obvious non-compliance with building standards and thermal regulations, the building has an acceptable thermal environment vis-à-vis its occupant.

Study of the Thermal Comfort of a Building that does not Comply with Construction Standards in Madagascar: Experimentation and Simulation with OMEdit

A very large number of buildings in developing countries are far from complying with the standards of housing. This paper presents the subjective study of the thermal comfort of a building that does not comply with construction standards or thermal regulations, located in Madagascar. Modeling was done using the Modelica tool, especially its BuildSysPro library. In order to minimize the inaccuracies, a step of an experimental adjustment of the developed numerical model was also carried out usingexperimental reference data that were obtained from the temperaturemeasurementsof the studied building elements as well as the wind speed and the received solar radiation flux. It was found that despite the obvious non-compliance with building standards and thermal regulations, the building has an acceptable thermal environment vis-à-vis its occupant.

Assessing scalability of a low-voltage distribution grid co-simulation through functional mock-up interface

State-of-the-art Modelica tools for modelling and simulating multi-physical systems have reached certain maturity among the building physics community. Hence, simulation is widely used for control, sizing and performance assessment of energy systems. However, serious efficiency issues arise for large-scale models. This article proposes a practical application of co-simulation methods on detailed district energy systems. The aim of this study is to assess performance and scalability of co-simulation through functional mock-up interfaces on a detailed and multi-physical district model. In particular, we propose a comparative analysis between classical simulation and co-simulation methods and a scalability analysis on a growing number of buildings. The models have been implemented using Modelica language and the OpenIDEAS library. A decomposition approach is taken for modelling the entire system, while stochasticity in the inputs is taken into account. Results are presented for various integration scenarios, including a classical integrated simulation for reference and co-simulations involving different master-algorithms within Dymola and DACCOSIM 2017. Scenarios are compared in terms of speed-up and accuracy of principal physical quantities representing key performance indicators such as indoor temperature, current and voltage at building's connection. The analysis shows that co-simulation can run up to 90 times faster than the integrated simulation for 24 buildings, while ensuring acceptable accuracy.

Applying Modelica Tools to System Dynamics Based Learning Games: Project Management Game

Learning simulation games are interactive simulations with game characteristics. This paper presents a learning simulation game for EPCM (engineering, procurement, and construction management) project management training. The simulation model utilises system dynamics, which is a methodology for understanding the behaviour of dynamic complex systems of different domains using modelling and simulation. The system dynamics model in turn uses the equation-based Modelica modelling language: a system dynamics model created with the graphical user interface is converted to a pure Modelica model. Two Modelica environments, namely, OpenModelica and the custom Modelica solver, have been used to simulate the generated Modelica model. The focus of this article is on how generic systems modelling and simulation platforms such as Modelica based environments can be utilised in developing a learning simulation game: what benefits do they bring and what disadvantages do they have? On the one hand, it is evaluated how the Modelica language as such is suitable for being used in a learning game development. On the other hand, the suitability of the selected implementation environments, that is, OpenModelica, the custom Modelica solver, Simantics, and Simupedia, is evaluated. The paper also shortly presents how the project management game was received by its players.

Function Inlining in Modelica Models

AbstractThe equation-based Modelica language allows the modeller to specify custom functions. The body of a function is an algorithm that contains procedural code to be executed when the function is called. This language feature is useful for many applications; however, the insertion of a function often prevent model optimizations that require the model to be formulated in purely declarative form by equations only. This paper discusses several non-trivial cases in which the function call and the corresponding algorithmic code can be transformed into an equivalent purely equation-based model, thus allowing further optimization. The inlining algorithms presented in the paper go well beyond the state of the art in commercial and open-source Modelica tools.