Modelica Standard Library Research Articles

Dynamic Modeling of a Thermochemical System for Solar Fuel Production Based on an Open-Source Framework

This paper describes the dynamic process model for a solar fuels synthesis plant currently being built in Germany. The open-source, equation-based modelling language Modelica is used as the foundation. In this plant, biogas and steam are reformed, producing synthesis gas and subsequently turned into synthetic crude oil. This work contains the necessary model setups for the thermal energy storage, solar-absorbing gas receiver and reforming reactor to consider the thermohydraulic, thermochemical and radiative interactions occurring in the process. The remaining infrastructure is modeled with the Modelica Standard Library. A way to fit these models with experimental data for validation is also outlined.

A fast and accurate modeling approach for water and steam thermodynamics with practical applications in district heating system simulation

In U.S. district heating (DH) systems, steam is the most common heat transport medium. Industry demand for new advanced modeling capabilities of complete steam DH systems is increasing; however, the existing models for water/steam thermodynamics are too slow for large system simulations because of computationally expensive algebraic loops that require the solution to nonlinear systems of equations. For practical applications, this work presents a novel split-medium approach that implements numerically efficient liquid water models alongside various water/steam models, breaking costly algebraic loops by decoupling mass and energy balance equations. New component models for steam DH systems are also presented. We implemented the models in the equation based Modelica language and evaluated accuracy and computing speed across multiple scales: from fundamental thermodynamic properties to complete districts featuring 10 to 200 buildings. Compared to district models with the IF97 water/steam model and equipment models from the Modelica Standard Library, the new implementation improves the scaling rate for large districts from cubic to quadratic with negligible compromise to accuracy. For an annual simulation with 180 buildings, this translates to a computing time reduction from 33 to 1–1.5 h. These results are critically important for industry practitioners to simulate steam DH systems at large scales.

Development of an object-oriented, thermal-hydraulics model for ARC FLiBe loop safety assessment

The development of new fusion reactor concepts is a challenging task for designers and safety analysts. Little information is usually available from previous experiences or experimental campaigns, especially when the design is innovative. Hence, system modeling is of fundamental importance. A proper system model should allow the investigation of different design options, and a preliminary assessment of the relative safety features. Anticipated or accidental transients can be studied, exploring the design space and highlighting possible criticalities. Object-oriented modeling is extremely advantageous to carry out this task. ARC pre-conceptual design (MIT-PSFC) may greatly benefit from this kind of analysis. A 1-D system-level, thermal-hydraulics model of ARC FLiBe loop developed in Modelica language is presented in this work. Because of the innovative nature of ARC design, most of the components are not available in the Modelica standard library. Thus, the key components of the loop are defined and modeled. No experimental results are currently available for model validation; therefore, the model consistency is assessed by verification and benchmark against analytical and numerical models. A Python wrapper is developed to explore multiple transient conditions by automating pre-processing and post-processing. Component failures are injected in the thermal-hydraulics model by a Monte Carlo routine. It is found that the model can efficiently describe different transients, with a low error on key parameters (pressure drop, fluid temperature). Furthermore, the model can be easily adapted to different design, thanks to the modular structure of object-oriented models. Similarly, it can be implemented in broader applications for safety analysis by coupling with suitable soft computing techniques.

DhcSim — A Modelica library for simple modeling of complex DHC systems

District heating and cooling systems play an important role in future energy infrastructure by accessing local energy potentials, reducing temperature levels and exploiting synergies between energy systems. Therefore, a transition to next generation heating and cooling networks is needed, which can be realized by multi-level design, bidirectional usage of production and consumption or combined heating and cooling systems. This will increase the complexity of network design which may be hard to analyze and assess without the support of a system simulation. The following paper presents the dhcSim Modelica library which can be used to model complex district heating and cooling networks within a multi-level network structure. The library was developed as extension to the Modelica Buildings library and Modelica Standard library and provides a clear and easy to use model structure. This structure distinguishes between two-, four and multi-port-models which allows the modeling of highly complex multi-level DHC systems. The library provides models for both district heating and cooling and can be easily adapted to individual user cases. To illustrate the implementation of the library and how it can be used, a case study of a three-level district heating network is presented. Using the network simulation of the introduced example, it could be shown that the supply temperature requirements of some consumers could not be achieved by the proposed network and thus further action is needed.

Port-Hamiltonian Modeling of Thermofluid Systems and Object-Oriented Implementation With Modelica I: Thermodynamic Part

In this paper, we present the physical foundations and the development of the thermodynamic part of a Modelica library with the fundamental components for modeling thermofluid systems. We have chosen Modelica because it is an object-oriented modeling language that allows an elegant design of the library, with a top-down conception that starts from very general components where we model the thermodynamic properties common to all simple substances and descend by inheritance to model the properties of each particular substance. To model the behavior of each component, we have used: classical thermodynamics to define the equilibrium states, the local equilibrium hypothesis of Classical Irreversible Thermodynamics to model the changes of state, and the port-Hamiltonian approach to obtain the equations of the system dynamics. With this formulation, we implement the thermodynamic behavior of ideal gases (including monatomic gases as a particular case), the 2073 substances defined for the CEA (Chemical Equilibrium with Applications) NASA Glenn computer program, the IAPWS Formulation 1995 for the Thermodynamic Properties of Water Substance for General and Scientific Use, and the Syltherm 800 HTF (Heat Transfer Fluid). We also define graphical symbols for each library component that facilitate modeling complex systems with simple drag-and-drop manipulations, component connection, and parameter selection. These symbols are a slightly modified version of those used in bond graphs to facilitate their reading and the representation of the structure of complex systems. We also show the modeling, simulation, and comparison for accuracy, performance, and scalability of some thermodynamic systems implemented with the Modelica Standard Library (MSL) and the proposed library.

Hybrid Gearbox Modeling Using Modelica4.0

Gearbox modeling with mixed continuous and discrete events has been studied for long time. The gearbox power loss depends on the angular velocity and load. In this report, the LossyGear model of the Modelica standard library was constructed with a new configuration from the viewpoint of system engineering utilizing the synchronous feature of Modelica Standard Library 4.0. The proposed method can also be regarded as a case study for general cyber-physical modeling approach.

DC-DC Linearized Converter Model for Faster Simulation of Lightweight Urban Electric Vehicles

The aim of this paper is to present a new bidirectional DC-DC linearized converter model for use in power demand and recovery units mainly used in Lightweight Electric Vehicle applications. The model significantly reduces the simulation time of the experiments performed, with up to a 4450-fold decrease in simulation times with respect to the original switched DC-DC topology. The study begins with a literature review of available switched converters, after which the presented topology is selected. The object-oriented modeling language Modelica ® is used to implement the converter in the Dymola ® modeling environment. Components and base classes from the Modelica Standard Library and VehicleInterfaces library are mainly used for better interoperability. Because of the intensive use of converters in the whole vehicle and the time consumed by the converter simulations due to high frequency commutation, a linearized DC-DC converter model is proposed. Comparison tests are performed between the reference switched models and the proposed linearized models in Dymola ® tool to validate the linearized model behaviour. Nearly identical responses are obtained for both models, while simulation times are reduced as much as 1/4450 for the linearized converter. Furthermore, validation tests are carried out between the proposed linearized model in Dymola ® and a reference switched model in LTspice ® specific purpose simulation package for switched electronic circuits. Excellent agreement in the responses of both models is observed.

Predesign of a flexible multibody system excited by moving load using a mechatronic system approach

In this paper, a new analytical approach to object oriented modeling is presented for the predesign of a multibody system. We investigate the dynamic behavior of a system of interconnected components using the modeling language Modelica. In engineering, beam-masses are often used as design models. In fact, the considered system is composed of a flexible beam subjected to a moving load and supporting one or more translating elastic subsystems. Each subsystem is controlled by a vibration absorber and the structure is affected dynamically only through the moving character of the load. The problem of calculation of the dynamic response of this system is very important in many engineering applications such as in the predesign and analysis of a robotic portal systems, machine tools and bridge crane systems. The object oriented modeling approach will be presented to demonstrate the importance of this approach to parametric investigation. It will illustrate how subsystems from Modelica Standard Library can be connected to the developed structure in order to study the vibrational behavior of such a system. For validation purpose, results are compared with those reported in the literature.

Modelado de baterías para aplicación en vehículos urbanos eléctricos ligeros

<p>En este artículo se propone un modelo dinámico de batería que permite simular el comportamiento de distintos tipos de baterías para su aplicación en vehículos eléctricos urbanos ligeros. El modelo es fácilmente parametrizable a partir de las curvas de descarga experimentales del equipo real y se ajusta adecuadamente al comportamiento particular de la curva de carga/descarga de las baterías de Litio-Ferrofosfato (LiFePo4). Se han utilizado los datos obtenidos sobre una instalación experimental para la calibración del modelo propuesto y se presentan resultados de la validación del mismo. El modelo se ha implementado en el lenguaje de modelado orientado a objetos Modelica reutilizando clases de su librería estándar Modelica Standard Library. La calibración y validación se ha realizado con la herramienta de modelado Dymola.</p>

Diagnosis Analysis of Modelica Models

To leverage on model based engineering for fault diagnosis, it is useful to be able to do direct analysis of general purpose modelling languages for engineering systems. In this work, it is demonstrated how non-trivial Modelica models, for example utilizing the Modelica standard library, can be automatically transformed into a format where existing fault diagnosis analysis techniques are applicable. The procedure is demonstrated on a model of an air cooling system in the Gripen fighter aircraft developed by Saab, Sweden. It is discussed why the Modelica language is well suited for diagnosability analysis, and a number of non-trivial diagnosability analysis shows the efficacy of the approach. The methods extract the model structure, which gives additional insight into the system, e.g., highlighting model connections and possible model decompositions.

Dynamic equation-based thermo-hydraulic pipe model for district heating and cooling systems

Simulation and optimisation of district heating and cooling networks requires efficient and realistic models of the individual network elements in order to correctly represent heat losses or gains, temperature propagation and pressure drops. Due to more recent thermal networks incorporating meshing decentralised heat and cold sources, the system often has to deal with variable temperatures and mass flow rates, with flow reversal occurring more frequently. This paper presents the mathematical derivation and software implementation in Modelica of a thermo-hydraulic model for thermal networks that meets the above requirements and compares it to both experimental data and a commonly used model. Good correspondence between experimental data from a controlled test set-up and simulations using the presented model was found. Compared to measurement data from a real district heating network, the simulation results led to a larger error than in the controlled test set-up, but the general trend is still approximated closely and the model yields results similar to a pipe model from the Modelica Standard Library. However, the presented model simulates 1.7 (for low number of volumes) to 68 (for highly discretized pipes) times faster than a conventional model for a realistic test case. A working implementation of the presented model is made openly available within the IBPSA Modelica Library. The model is robust in the sense that grid size and time step do not need to be adapted to the flow rate, as is the case in finite volume models.

Dynamic Simulations supporting the Design Process of a real Combined Heat and Power Application in Switzerland

In many European countries the production of combined heat and power based on renewable energies is well established though the efficient and economical operation of such plants remains a challenging task. This also applies to the existing district heating network at Baden-Dättwil (Switzerland) where a conventional gas boiler is substituted by a wood-fired boiler comprising an Organic Rankine Cycle. An overall control strategy that allows fully exploring governmental incentives is therefore of paramount importance. In addition, the highly fluctuating heat demands combined with the thermal inertia of the different plant components impose demanding requirements to the control system to guarantee a stable as well as highly efficient operation.The overall control concept is successfully tested and verified by means of dynamic simulations of the overall plant with a simplified model for the district heating network. The models are implemented using the object oriented modeling language Modelica. The overall model is based on open source Modelica libraries such as ThermoCycle, Modelica Standard Library and StateGraph2 as well as on own Modelica models.The overall model is prepared to be coupled to the real plant control system which will allow virtual commissioning in the next step. This allows pre-tuning of control parameters as well as a weakness analysis which again helps to speed up the commissioning process. In General, the dynamic simulations proved to be a useful tool that deepened the insight and understanding of the plant operation at an early project phase and therefore greatly supported the making of design decisions. After commissioning, the calibrated simulation models will be used for monitoring purposes.

An acoustics library for the Modelica multidomain modeling language

The Modelica® modeling language is especially well-suited for modeling the complicated electrical, mechanical, magnetic, and acoustical connections within an acoustic transducer or other acoustic system. The Modelica Standard Library includes many of the components that are needed for modeling electromechanical systems, but does not include piezoelectric or acoustical components. This paper describes methods and modeling code to provide an acoustical domain and several methods to include piezoelectric length expander pieces in the Modelica language.

A model for the transient performance simulation of solar cavity receivers

In this paper, a detailed model for the transient simulation of solar cavity receivers for concentrating solar power plants is presented. The proposed model aims to consider all the major phenomena influencing the performance of a cavity receiver, including radiation, convection and conduction heat transfer mechanisms. For the radiation heat exchange within the cavity, the radiosity method is implemented, where the view factor calculation for all the active and passive surfaces is performed by a ray tracing algorithm programmed in a free software environment for statistical computing, namely R. A one-dimensional modeling approach is used for the tubes constituting the receiver active panels, through which the heat transfer fluid (HTF) is pumped. The governing partial differential equations are solved numerically by applying the finite volume method. Convective heat losses are modeled through different correlations for natural and forced convection heat losses from the specific literature. Once the thermal behavior has been characterized, the geometry of the model is later fixed to check the consistency of the model and to study its dynamic characteristics. A specific 51.6MWth, PS10 like receiver is used in this paper, although the implemented model has the flexibility to allow a variable number of panels and geometric configurations. At last, an adaptive neural controller, designed and trained offline, controls the outlet temperature of the molten salts to the desired operating value. Results for transient simulations are shown in the paper, demonstrating the plausibility of the estimations obtained with the developed model. The proposed model has been implemented in the Modelica language and based on the Modelica Standard Library (MSL) modeling approach.

Using a Discrete-Event System Specifications (DEVS) for designing a Modelica compiler

We introduce a new architecture for the design of a tool for modeling and simulation of continuous and hybrid systems. The environment includes a compiler based on Modelica, a modular and a causal standard specification language for physical systems modeling (the tool supports models composed using certain component classes defined in the Modelica Standard Library, and the instantiation, parameterization and connection of these MSL components are described using a subset of Modelica). Models are defined in Modelica and are translated into DEVS models. DEVS theory (originally defined for modeling and simulation of discrete event systems) was extended in order to permit defining these of models. The different steps in the compiling process are show, including how to model these dynamic systems under the discrete event abstraction, including examples of model simulation with their execution results.

The early implementation of failure modes into existing component model libraries

This research addresses a need in systems engineering to verify that a system can meet performance requirements; this is done by integrating failure behavior into the system’s nominal model during the initial stages of design. In general, failure behavior is not used in early assessments, lending toward increased uncertainty in the model’s validity. Current libraries do not model failures and thus cannot confidently address how a design will function in the intended operational environments. Since failures occur from effects on the environment, they should be included during verification and validation efforts. Current approaches capture off-nominal behavior using parameter variation where flow variables and parameters are varied to measure the system-level effect. This approach is ad hoc and does not accurately capture failure mode behavior. To address this limitation, an approach is developed to understand and implement failure mode behavior into nominal models. The Modelica Standard Library (MSL) is used as an example for the component library of nominal models. MSL has a significant amount of basic nominal component behavior and therefore is desirable for this research. Two approaches are developed to implement failure mode behavior; the first uses transfer function and use case graphs, and the second uses existing literature. In addition, complex systems often have a large number of components and an even larger number of failure modes. Since the goal is to limit the development time, we generate an approach to identify high-risk failure modes. This captures an early system-level effect of each failure mode and uses an occurrence to calculate risk. To show the usefulness of each method, two examples are provided including a vehicle drivetrain subsystem with a variety of failures and a diesel engine with fuel injector and valve failures.

Convenient Model Inversion by means of Object-Oriented Modeling for a Parallel Kinematic Robot

AbstractThe paper presents the capability of object-oriented modeling languages to obtain inverse plant models almost automatically by means of Modelica and the simulation tool Dymola. Based on an available plant model in Modelica the construction of its inverse model is shown with focus on new blocks from the free Modelica Standard Library (Version 3.2). This method is applied to a model of a six degrees of freedom (DOF) parallel kinematic robot that should be implemented in a so called inverse disturbance observer (IDOB) control architecture.

Simulation of Electric Drive System Faults in Hybrid Electric Vehicles

With the increased number of electric drive systems in hybrid electric vehicles also the probability of electric faults within those systems rises. We have developed a Modelica® library to simulate fieldoriented drive systems, including faults. The library is called freeFOClib (short for “free Field-Oriented Control library”) and can be used to build a field-oriented control system for existing machine models from the Modelica Standard Library, investigate the impact of electric faults (e.g., battery faults, inverter faults, machine faults) on a electric drive system, and run simulations to estimate the fuel consumption of hybrid electric vehicles. This paper will show how to model and simulate a faulty electric drives systems in combination with a hybrid electric vehicle.