JModelica---an Open Source Platform for Optimization of Modelica Models

Optimization is becoming a standard methodology in many engineering disciplines to improve products and processes. The need for optimization is driven by factors such as increased costs for raw materials and stricter environmental regulations as well as a general need to meet increased competition. As model-based design processes are being used increasingly in industry, the prerequisites for optimization are often fulfilled. However, current tools and languages used to model dynamic systems are not always well suited for integration with state of the art numerical optimization algorithms. As a result, optimization is not used as frequently as it could, or less efficient, but easier to use, algorithms are employed. This paper reports a new Modelica-based open source project entitled JModelica, targeted towards dynamic optimization. The objective of the project is to bridge the gap between the need for high-level description languages and the details of numerical optimization algorithms. JModelica is also intended as an extensible platform where algorithm developers, particularly in the academic community, may integrate new and innovative methods. In doing so, researchers gain access to a wealth of industrially relevant optimization problems based on existing Modelica models, while at the same time facilitating industrial use of state of the art algorithms. The JModelica project rests upon three pillars, namely a language extension of Modelica for optimization entitled Optimica, software tools, and applications. In this paper, these three topics will be highlighted

Moving Boundary Models for Dynamic Simulations of Two-Phase Flows

Two-phase flows are commonly found incomponents in energy systems such as evaporators and boilers. Theperformance of these components depends among others on thecontroller. Transient models describing the evaporation process areimportant tools for determining control parameters, and fast loworder models are needed for this purpose. This article describes ageneral moving boundary (MB) model for modeling of two-phase flows.The new model is numerically fast compared to discretized modelsand very robust to sudden changes in the boundary conditions. Themodel is a $7^th$ order model (7 state variables), which is asuitable order for control design. The model is also well suitedfor open loop simulations for systems design and optimization.It is shown that the average void fraction has a significant influenceon the system response. A new method to calculate the average voidfraction including the influence of the slip ratio is given. Theaverage void fraction is calculated as a symbolic solution to theintegral of the liquid fraction profile

Models of a post-combustion absorption unit for simulation, optimization and non-linear model predictive control schemes

An increasing demand on load flexibility in power supply networks is the motivation to look at flexible, and possibly optimal control systems for power plants with carbon capture units. Minimizing the energy demand for carbon dioxide removal under these circumstances reduces the cost disadvantage of carbon capture compared to conventional production. In this work a dynamic model in Modelica of a chemical absorption process run with an aqueous monoethanolamine (MEA) is developed, and used for solving optimal control problems. Starting from a rather detailed dynamic model of the process, model reduction is performed based on physical insight. The reduced model computes distinctly faster, shows similar transient behavior and reflects trends for optimal steady-state operations reported in the literature. The detailed model has been developed in Dymola, and the reduced model is used in JModelica.org, a platform supporting non-linear dynamic optimization. First results are shown on the dynamic optimization of the desorption column, the main cause of energy usage in the process

The Modelica Fluid and Media Library for Modeling of Incompressible and Compressible Thermo-Fluid Pipe Networks

The new library Modelica_Fluid is a free Modelica package providing components describing zero- and one-dimensional thermo-fluid components, which can be connected in arbitrary networks. The purpose of the library is to provide standard interfaces for thermo-fluid components, demonstrate how to build such models, and include a growing set of models of common use. The component equations are decoupled from the equations to compute the fluid properties, which are provided by the Modelica.Media library through standard interfaces; incompressible and compressible fluids, single or multiple substances, one- and multi-phase fluids can be used, where appropriate. Newly introduced features of the Modelica.Media library are briefly reviewed. After extensive testing by interested users, the library will be included in the Modelica standard library as Modelica.Fluid

Object-Oriented Modeling of Thermo-Fluid Systems

Modelica is used since 1998 to model thermo-fluid systems. At least eight different libraries in this field have been developed and are utilized in applications. In the last year the Modelica Association has made an attempt to standardize the most important interfaces, provide good solutions for the basic problems every library in this field have and supply sophisticated base elements, especially media descriptions. This paper summarizes the design, new Modelica language elements, new symbolic transformation algorithms and describes two new libraries ? for media description and for fluid base components ? that will be included in the Modelica standard library

Design and Implementation of Object-Oriented Model Libraries using Modelica

This thesis describes basic models for thermo-fluid systems and the implementation of the models using a flexible object-oriented structure in the ThermoFluid library. Model libraries provide an excellent way to package engineering knowledge of systems to be reused by non-experts. Many commercial simulation packages provide good model libraries, but they are usually domain specific and closed. Modelica(TM) is an open standard of an object-oriented modeling language for heterogeneous, multi-domain dynamic systems. Modelica combines the expressive power of equation based modeling with advanced object-oriented structuring features. A unique feature of Modelica are class parameters which allow a high-level parameterization of physical phenomena. The models are based on first principles. Control volumes contain the thermodynamic balance equations in lumped or one-dimensional discretized form. The library is built to be flexible: fluid property models in the control volume can be exchanged, single- or multi-component fluids are supported and the momentum balance submodel can be static or dynamic. Chemical reactions can be added to the model separately from other phenomena. Thermodynamic Jacobians are used to transform the dynamic equations into an efficient form. Low order moving boundary models for two phase flows are another result of the thesis. They make use of a novel approach for approximating the mean void fraction in the two phase region. The experiences from designing an object-oriented, reusable model library are summarized using design patterns. Design patterns are an attempt to describe "good practice" in modeling in a semi-formal way. The library has been used successfully for a broad range of industrial applications, among others modeling of micro gas turbine systems, carbon-dioxide based refrigeration systems, fuel cells, power plants and steam networks. The applications are briefly described in the thesis

Object-Oriented Modeling of Physical Systems, Part 12

Abstract not available

Object-Oriented Modeling of Physical Systems, Part 11

Abstract not available