| 1. |
- Engelson, Vadim
(author)
-
3D graphics and Modelica : an integrated approach
- 2000
-
In: Linköping Electronic Articles in Computer and Information Science. - : Linköping University Electronic Press. - 1401-9841. ; 5:9
-
Journal article (peer-reviewed)abstract
- The Modelica standard library and available Modelica tools contain some facilities for specification of 3D geometry and 3D graphics. Geometry and graphics is associated with physical objects included in simulated Modelica models. However, important graphics properties are missing from this model. In particular, physical objects cannot change their shape (geometry) and rendering features (graphics) dynamically. The physics of simulation, is often not affected by geometry of physical objects. For instance, a body is often approximated by its center of mass under certain conditions. Either simple predefined shapes or specifications of geometry via external files are used. The last facility leads to separation between the model and the corresponding graphics and geometry. Our proposal is to integrate 3D geometric and graphical features with Modelica models of physical objects. The 3D graphics information is specified explicitly via annotations containing certain graphics primitives or using instances from a specially designed geometry class library. The motivation, syntax and implementation outline for this approach are discussed in this report.
|
|
| 2. |
- Engelson, Vadim
(author)
-
Integration of collision detection with the multibody system library in Modelica
- 2000
-
In: Linköping Electronic Articles in Computer and Information Science. - : Linköping University Electronic Press. - 1401-9841. ; 5:10
-
Journal article (peer-reviewed)abstract
- Collision detection and response is one of the most difficult areas in simulation of multibody systems. Two known approaches, the impulse-based method and the force-based (penalty) method, can be applied for multibody simulation in Modelica. The impulse-based method requires instantaneous modification of some variables, but such modification is not always possible in Modelica. The force-based method leads to stiff ODE, which can be handled by solvers used with Modelica. We suggest a new way to express the penalty coefficients. The force-based method, however, requires computation of penetration depth which is time-consuming.We also suggest a method that combines the distance between bodies and the penetration depth into a single quantity used for force computation.Calling external functions is a preferable method integrate collision detection algorithms with practical physical models, since body geometry is stored externally. We describe an interface with collision detection tool SOLID.
|
|
| 3. |
- Engelson, Vadim
(author)
-
ObjectMath inheritance and composition diagram editor
- 2000
-
In: Linköping Electronic Articles in Computer and Information Science. - Linköping : Linköpings Universitet. - 1401-9841. ; 5:6
-
Journal article (peer-reviewed)abstract
- ObjectMath is a new object-oriented modeling language for scientific computing. The major innovation of this language is the introduction of object-oriented structure into a computer algebra language making it possible to group equations and formulae into classes. ObjectMath contains three object-oriented structuring constructs (class, instance and part) providing classes, single and multiple inheritance and composition of parts. Typical models in ObjectMath include between 10 and 30 such constructs. Inheritance and composition relationships are established between them. The problem is how to inspect, browse, and modify these relations in a convenient way. Our solution to this problem is using a graphical two-dimensional diagram editor connected to a text editor. An integrated programming environment for ObjectMath includes this editor. The report describes how object-oriented constructs of ObjectMath are mapped to their graphical representation. The ObjectMath syntax rules are mapped to diagram editor operations so that only syntactically correct models can be created.
|
|
| 4. |
- Engelson, Vadim
(author)
-
Simulation and visualization of autonomous helicopter and service robots
- 2000
-
In: Linköping Electronic Articles in Computer and Information Science. - : Linköping University Electronic Press. - 1401-9841. ; 5:8
-
Journal article (peer-reviewed)abstract
- To decrease the costs and the time it takes to develop and test new products, computer simulations are very helpful. Product models can be simulated, and their behavior can be examined. This applies not only to hardware, but even to software products that are composed of several components, so that their cooperative behaviour is simulated in a virtual environment. Some components of this environment can later be replaced by physical, real world devices. Some other components can be just prototypes, which are later replaced by more complex and realistic software components. In any case the idea is to construct a model and simulate both software and hardware before the actual production starts. In the WITAS project there is a need to develop a system which contains helicopters, robots and various control software and hardware. In particular there is a need to simulate the dynamic behavior of an autonomous aircraft within a virtual environment. There is a need to simulate a service environment, where robots can interact with the landed helicopter.In this report a study of object-oriented modeling of mechanical systems using Modelica is presented with applications to autonomous helicopters and robots. Mechanical features of an autonomous helicopter have been modeled in order to verify the control system. As the result the control system has been tested and tuned. However, the flight still is not stable in the cases when flight mission directions change too often.A robot which is able to grab, move, and release objects using automatic or manual control have been modeled. The problem of inverse geometry (and inverse kinematics) can be solved for robots using our approach. The robot models can be controlled interactively.The geometry and dynamic structure of these systems has been designed in CAD tools and later integrated with control systems for steering these devices. The simulation has been performed in Modelica.
|
|
| 5. |
- Engelson, Vadim
(author)
-
Tools for design, interactive simulation and visualization for dynamic analysis of mechanical models
- 2000
-
In: Linköping Electronic Articles in Computer and Information Science. - : Linköping University Electronic Press. - 1401-9841. ; 5:7
-
Journal article (peer-reviewed)abstract
- The complexity of mechanical and multi-domain simulation models is rapidly increasing. Therefore new methods and standards are needed for model design. A new language, Modelica, has been proposed by an international design committee as a standard, object-oriented, equation-based language suitable for description of the dynamics of systems containing mechanical, electrical, chemical and other types of components. However, it is complicated to describe system models in textual form, whereas CAD systems are convenient tools for this purpose. Therefore we have designed an environment that supports the translation from CAD models to standard Modelica representation. This representation is then used for simulation and visualization. Assembly information is extracted from CAD models, from which a Modelica model is generated. By solving equations expressed in Modelica, the system is simulated. We have designed several interactive 3D visualization tools which display expected and actual model behavior, as well as additional graphical elements for the purpose of engineering visualization. We applied this environment for robot movement and helicopter flight simulation.
|
|
| 6. |
- Ahrenberg, Lars, 1948-, et al.
(author)
-
Automatic Processing of Parallel Corpora: A Swedish Perspective
- 1999
-
Reports (other academic/artistic)abstract
- As empirical methods have come to the fore in multilingual language technology and translation studies, the processing of parallel texts and parallel corpora have become a major research area in computational linguistics. In this article we review the state of the art in alignment and data extraction techniques for parallel texts, and give an overview of current work in Sweden in this area. In a final section, we summarize the results achieved so far and make some proposals for future research.
|
|
| 7. |
- Ahrenberg, Lars, 1948-, et al.
(author)
-
Customizing Interaction for Natural Language Interfaces
- 1996
-
Reports (other academic/artistic)abstract
- Habitability and robustness have been noted as important qualities of natural-language interfaces. In this paper we discuss how these requirements can be met, in particular as regards the system's ability to support a coherent and smooth dialogue. The discussion is based on current work on customizing a dialogue system for three different applications. We adopt a sublanguage approach to the problem and propose a method for customization combining bottom-up use of empirical data with a global pragmatic analysis of a given application. Finally, we suggest three design principles that have emerged from our work called the sublanguage principle, the asymmetry principle and the quantity principle.
|
|
| 8. |
- Alferes, José Júlio, et al.
(author)
-
Dynamic Logic Programming
- 1997
-
Reports (other academic/artistic)abstract
- In this paper we investigate updates of knowledge bases represented by logic programs. In order to represent negative information, we use generalized logic programs which allow default negation not only in their bodies but also in their heads. We start by introducing the notion of an update $P \oplus U$ of a logic program $P$ by another logic program $U$. Subsequently, we provide a precise semantic characterization of $P \oplus U$, and study some basic properties of program updates. In particular, we show that our update programs generalize the notion of interpretation update. We then extend this notion to sequences of logic programs updates $P_1 \oplus P_2 \oplus \dots$, defining dynamic program updates, thereby introducing the paradigm of dynamic logic programming. This paradigm significantly facilitates modularization of logic programming, and thus modularization of non-monotonic reasoning as a whole. Suppose that we are given a set of logic program modules, each describing a different state of our knowledge of the world. Different states may represent different time points or different sets of priorities or perhaps even different viewpoints. Consequently, program modules may contain mutually contradictory as well as overlapping information. The role of the dynamic program update is to use the mutual relationships existing between different states to precisely determine, at any given state, the declarative and the procedural semantics of the combined program, resulting from all these modules.
|
|
| 9. |
- Amir, Eyal
(author)
-
Object-Oriented First-Order Logic
- 1999
-
Reports (other academic/artistic)abstract
- This paper describes a novel logic that extends First-Order Logic (FOL) to create counterparts of the Object-Oriented paradigm. We call it Object-Oriented First-Order Logic (OOFOL). FOL provides richness of representation, but is unwieldy in modeling large, complex tasks. On the other hand, the Object-Oriented paradigm has been successful at treating large, complex tasks in both software and knowledge engineering.In OOFOL, objects are theories that are connected via interface vocabularies to other objects, classes are used to provide a reusable logical template, and inheritance is used to adapt classes to specialized tasks. We show that such a logic can be given simple semantics using FOL. A variant of the logic that allows links between the objects to be unidirectional is also examined. This variant is called Directed Object-Oriented First-Order Logic (Directed OOFOL). We show that such a system can be given semantics using Circumscription.Our new tools facilitate the object-oriented design of theories. We demonstrate this through a few applications taken from model-based reasoning, theories of action and cognitive robotics. These examples also demonstrate the use of the object-oriented methodology and tools for the construction of first-order theories. We conclude with proposed inference algorithms for these logics.
|
|
| 10. |
- Andersson, Jörgen
(author)
-
Processorientering i offentlig verksamhet
- 1997
-
Reports (other academic/artistic)abstract
- Att anlägga ett processorienterat synsätt på en verksamhet har hittills mest behandlats i samband med privata företag. I artikeln presenteras hur en offentlig myndighet har gått tillväga för att förändra sin verksamhet i riktning mot processorientering. Försäkringskassan Östergötland har bland annat utnyttjat Total Quality Management och processledning för att öka kvaliteten i verksamheten samtidigt som besparingskrav från regering och riksdag har minskat de ekonomiska resurserna avsevärt. Erfarenheterna från Försäkringskassan Östergötland visar att förändringsarbete är en tidskrävande process som bland annat måste omfatta en förändring av organisationskulturen. Detta blir särskilt tydligt i detta fall då Försäkringskassan av tradition är en ”handboksstyrd” verksamhet med ett omfattande regelverk. Att då införa begrepp som TQM och kundorientering mm, som i första hand förknippas med den tillverkande privata industrin är en stor omställningsprocess. Vidare krävs ett stort engagemang både från personer i ledande befattningar och den operativa personalen vilket också har varit fallet i Försäkringskassan Östergötland. Det är också en bidragande orsak till varför förändringsarbetet hittills fallit väl ut. De ekonomiska konsekvenserna av förändringen märks tydligast genom en minskad administration där man har kunnat minska denna med en tredjedel. Ett pro-blem i arbetet har varit att man inte har haft kontroll över sina informationssystem. Nödvändiga förändringar har inte blivit gjorda eftersom man inte kunnat påverka informationssystemens utformning. Rapporten ingår som en del av forskningsprojektet ”Business Modelling”. Projektet bedrivs som ett konsortium mellan Handelshögskolan i Stockholm, Kungliga Tekniska Högskolan i Stockholm och Linköpings universitet. I projektet studeras bland annat förändringsarbete i praktiken där vi hittills har samarbetat med Ericsson Radio, Posten och Försäkringskassan Östergötland. Projektet ”Business Modelling” finansieras av Närings- och teknikutvecklingsverket, NUTEK.
|
|
