Object-oriented Modeling Language Research Articles

The use of physical knowledge to guide formula manipulation in system modelling

Very often, systems consist of subsystems which may be independently described. Object oriented modelling languages, as Dymola and Omola, allow models to be structured in independent submodels as systems are structured in subsystems. However, it is not an easy task to derive a mathematical model, suitable for simulation environments, from such a representation. Algebraic problems arise when the modelling tool attempts to solve the computational causality assignment in the equations. This paper discusses the advantages of physical causality analysis in object oriented modelling. A new representation, which adds a layer of physical knowledge, is proposed in order to analyze the physical behaviour of models described in a modular way. The physical interactions in the model are derived before computational causality assignment is undertaken. An automated procedure to find the adequate mathematical representation of coupling phenomena is developed by means of a symbolic formula manipulation kernel. The proposed methodology allows object oriented and modular modelling, preserving the system model structure analogy. The algorithms developed could be applied to support well established object oriented modelling languages as Dymola and Omola.

Object-oriented modelling of thermal power plants

This paper presents a set of model libraries, called K2, for modelling of thermal power plants. The models are based on first principles and describe mainly the dynamic mass and energy properties of the modelled system. The K2 models are described in the object-oriented modelling language OMOLA and the libraries are organized in an OMOLA model database. The libraries are grouped into three different sets, namely unit libraries, subunit libraries and model component libraries. The unit models are used to build up plant system models, which are application dependent. The units are composed of subunits. The subunits describe different physical phenomena and a set of subunits build up the behaviour of the unit model. Model components are used to facilitate the development of new units and subunits. OMOLA models can be simulated in the OMSIM simulation environment and the K2 model database has been used in a case study of the dynamics in an HRSG plant.

97/03872 Biomass and natural gas as co-feedstocks for production of fuel for fuel-cell vehicles

Object-oriented modelling languages have become in recent years a very attractive choice for the control-oriented, dynamic modelling of power plants, due to their ease of development, flexibility, and reusability features. The paper describes a hierarchical modelling framework for thermal power plants, based on the Modelica language and on an existing library of elementary models, with particular emphasis on combined-cycle plants. The design criteria of the framework are discussed, and demonstrated by examples. The implications for the modelling of advanced power plants of the future, such as IGCC plants, integrated fuel-cell and combined cycle plants, and plants with CO2 capture capabilities are finally discussed.

Modelica — A unified object-oriented language for physical systems modeling

Modelica — A unified object-oriented language for physical systems modeling

Implementing inheritance in operational graphical languages

System engineering development methods and automation techniques are required to manage the complexity inherent in the design of large computer based systems and to provide an efficient means for reusing the system by means of inheritance.Growing interest is being shown in operational models, i.e. models that can be executed using a suitable support environment. Most operational models are graphical and can be considered as high-level programs which are developed using high-level modeling languages. Generally speaking, while the OO approach has reached a good maturity at the programming level (although differences in individual languages are not negligible) there is no clear consensus on how it can be extended to the design and analysis phases.These artificial discontinuities can be eliminated if a single modeling language is used which is operational. The operational approach eliminates the scope and semantic discontinuities in the development process by using a single, integrated, formal set of modeling abstractions to create a given executable model.It was to address these problems and provide advanced software architectural features, that O 3 ML was developed by us. Combining the concept of Operational, OO and Modeling we get a modeling language which we refer to as Operational Object-Oriented Modeling Language ( O 3 ML) that provides the basic vocabulary used to express both domain knowledge and prototyping ideas.

Static, dynamic and run-time modeling of compound classes

Automation techniques are required to manage the complexity inherent in the design of large computer based systems and to provide an efficient means for using the services present in other system.Operational models often allow timing constraints to be expressed and, consequently, a discrete-event simulation of the model can be performed. In this way, statistical estimates of the system's parameters can be collected in order to support decision making. When a formal proof would be too expensive, such statistics can confidently be used to determine some properties of the system. O 3 ML (Operational Object-Oriented Modeling Language) is a graphical language develped by us, to model complex operational software system, which is centered upon the creation of a system prototype providing the feature to dynamically generate actors and establish connection during run time. The developed models can be evaluated it in a controlled simulation framework.In O 3 ML actors can be assembled into complex structures forming composite actors, by establishing connection using connectors. In a more abstract view, these networked structures can be interpreted as entity-relationship models. Such aggregation of actors is always encapsulated within a higher-level composite actor specification. An actor class can, thus, encapsulate an actor (which is a composite actor). This would make the actor structure recursive so that arbitrary complex hierarchical actor structures can be constructed.

Simulation of a Power Plant Using an Object-Oriented Model Database

An object-oriented approach to modelling and simulation of a Heat Recovery Steam Generation plant, HRSG, using a model database called K2 is presented. This database is a set of model libraries for modelling of thermal power plants described in the object-oriented modelling language Omola. The models in the database are based on first principles and describe mainly the dynamic behaviour in the water/steam cycle. The plant studied in this paper is the HRSG side of a combined cycle power plant. Using the object-oriented methodology supported by Omola and K2 the HRSG plant is decomposed in its sections and these sections are in turn built by assembling unit models taken from the unit libraries. The HRSG model has subsequently been used in a simulation study to evaluate different control strategies.

Modeling of multibody systems with the object-oriented modeling language Dymola

The object-oriented modeling language Dymola allows the physical modeling of large interconnected systems based on model components fromdifferent engineering domains. It generatessymbolic code for different target simulators. In this paper, a Dymola class library for the efficient generation of the equations of motion for multibody systems is presented. The library is based on aO(n) algorithm which is reformulated in an objectoriented way. This feature can also be interpreted as a bond graph oriented modeling of multibody systems. Furthermore a new algorithm for a certain class ofvariable structure multibody systems, such as systems with Coulomb friction, is presented, which allows the generation of efficient symbolic code.

A knowledge-based approach to production scheduling for batch processes

Scheduling problem solving has escaped its initial attention on mathematical programming approaches and it is gaining benefits from other fields such as Discrete-Event simulation and Artificial Intelligence (AI). The AI community has investigated the problem and most of its research focuses on the use of dispatching heuristic rules and constraint-satisfaction. This paper presents a different perspective. The similarities between the design and the multiproduct batch plant scheduling problems are analyzed, stressed and exploited; and a methodology based on a task-oriented approach is introduced. The scheduler is viewed as the “designer” of a production plan. Similar to the design problem, the “final artifact” is not known in advance and the complexity of the overall problem is tackled by means of decomposition. To accomplish it, the structure of the solution methodology is identified and explicitly conceptualized. The approach relies on the appropriate modeling of the scheduling scenario. An object-oriented modeling language is presented.

ANDECS Robot-Trajectory Optimization for State-Constrained Time-Optimal Control and Minimum Power Consumption

The robot trajectory optimization features of the ANDECS environment are described. Robot trajectory optimization problems are formulated as multi-objectives parameter optimization problems in search for a good compromise among conflicting criteria, such as “minimal” time and “minimal” power consumption. For that the robot dynamics is analyzed by time-simulation of a robot model with variable structure, which is generated by the object-oriented modeling language Dymola.

A role for goal-oriented autonomous agents in modeling people-environment interactions in forest recreation

Increased demand by the public for diverse and quality recreation opportunities has placed considerable pressure on the natural resource and its management. This problem is compounded by a general lack of understanding of interactions between people and forest recreation environments that result in wide variations in perceptions, expectations, and patterns of choice and use. Emerging technologies, such as distributed artificial intelligence, provide a mechanism to integrate advances in recreation research with a Geographic Information Systems (GIS) based environment. Distributed artificial intelligence provides the foundation for a modeling system to simulate the interactions between recreators and their environment. Despite the work done by many researchers in the development of object-oriented modeling and simulation languages, GIS, nonhuman agent design and simulations, no single system has been constructed to handle the complexity of goal-oriented autonomous human agents seeking recreational opportunities in natural environments. This paper describes a theoretical framework and a model for simulating hiker behavior in a natural environment using intelligent agents, discrete event simulation (DEVS) and GIS data. The results of hiker interactions are summarized to provide feedback on the implications for alternative recreation management planning.

Modeling of Process Control Systems in Omola

In this paper an object-oriented approach to modeling of process control systems is discussed. Many control methodologies uses a limitied number of primitives as building blocks which are based on a mathematical framework using equations and events. In Omola, an object-oriented modeling language, model entities are defined as classes. A class is composed of attributes which are definitions of model components. A class inherits attributes form its super class. The paper conclude that Omola can describe integrated control systems. The paper also conclude that there is a need of additional structuring principles and hierarchical control methodologies.

Modelling of Combined Discrete Event and Continuous Time Dynamical Systems

A language for describing combined discrete event and continuous time dynamical systems is presented. The language is an extension of Omola which is an object-oriented modelling and simulation language based on differential and algebraic equations. The discrete event concepts and the simulation procedure are discussed in some detail. Examples of how combined models are used to represent physical systems are provided.

Automated formula manipulation supports object-oriented continuous-system modeling

Digital continuous-system simulation languages are discussed. It is demonstrated how sophisticated automated formula manipulation can be used to automatically generate state-space models from an object-oriented description of a physical system. The two major complications, algebraic loops and structural singularities, occur frequently as a consequence of couplings between submodels (objects), and these difficulties can often be dealt with by automated formula manipulation. A software tool, Dymola, in which the various formula manipulation techniques have been implemented, is presented. Dymola is an object-oriented continuous-system modeling language and a model manipulator that can be used to generate models in several simulation languages. >

An Incorporated Use of Fuzzy Logic Toolbox and Modelica Library to Design SSSC Damping Controller

ObjectStab is a general purpose simulation tool for power system stability studies developed by Modelica which is an object-oriented modeling language. It provides enough modeling flexibility to allow addition or modification of new power system components. This paper describes an incorporated use of fuzzy logic toolbox in Matlab/Simulink and Object-Stab library to enhance the application of this library into fuzzy control design environment. The example provided here is the modeling of the static synchronous series compensator (SSSC) which is the new device developed in the ObjectStab. In addition, the interface of ObjectStab with Matlab/Simulink for an SSSC damping controller design by fuzzy logic toolbox is explained step by step. Simulation studies in a multi-machine power system confirm the effectiveness of the designed fuzzy controller.

Transients in thin-film RC networks : F. A. Lindholm and W. W. Happ. Electro-Technology (August 1965), p. 38

Packed beds serve as thermal energy storages (TES) and heat exchangers (HEX) in different technological applications. In this paper, a general heterogeneous model of heat transfer in packed beds is developed. It is implemented by lumped element formulation in object-oriented modeling language Modelica and is successful validated with data sets taken from two different experiments reported in literature.The main advantages of the introduced model are the general, theory-based approach and the lumped element formulation in Modelica. The first point mentioned above should allow to simulate a packed bed TES/HEX without the necessity applying measured data for model calibration or to apply specific heat transfer correlations with restricted application. The second point establishes the possibility to integrate the TES/HEX model within plant models of larger scale without increasing the simulation time drastically.