Vadim Engelson

Modelica - A Unified Object-Oriented Language for System Modelling and Simulation

A new language called Modelica for hierarchical physical modeling is developed through an international effort. Modelica 1.0 [http:// www.Dynasim.se/Modelica] was announced in September 1997. It is an object-oriented language for modeling of physical systems for the purpose of efficient simulation. The language unifies and generalizes previous object-oriented modeling languages. Compared with the widespread simulation languages available today this language offers three important advances: 1) non-causal modeling based on differential and algebraic equations; 2) multidomain modeling capability, i.e. it is possible to combine electrical, mechanical, thermodynamic, hydraulic etc. model components within the same application model; 3) a general type system that unifies object-orientation, multiple inheritance, and templates within a single class construct.

Lossless compression of high-volume numerical data from simulations

Summary form only given. We propose a lossless algorithm of delta compression (a variant of predictive coding) that attempts to predict the next point from previous points using higher-order polynomial extrapolation. In contrast to traditional predictive coding our method takes into account varying (non-equidistant) domain (typically, time) steps. To save space and guarantee lossless compression, the actual and predicted values are converted to 64-bit integers. The residual (difference between actual and predicted values) is computed as difference of integers. The unnecessary bits of the residual are truncated, e.g., 1111110101 is replaced by 10101. The length of the bit sequence (5/sub 10/=(000101)/sub 2/) is prepended.

A design, simulation and visualization environment for object-oriented mechanical and multi-domain models in Modelica

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 the system models in textual form, whereas CAD systems are convenient tools for this purpose. We have designed an environment that supports the translation from CAD models to standard Modelica notation. This notation is then used for simulation and visualization. Assembly information is extracted from the CAD models, from which a Modelica model is generated. By solving equations expressed in Modelica, the system is simulated. A 3D visualization tool based on OpenGL visualizes expected and actual model behavior, as well as additional parameters. The environment has been applied for robot and flight simulation.

Automatic Generation of User Interfaces From Data Structure Specifications and Object-Oriented Application Models

Applications in scientific computing operate with data of complex structure and graphical tools for data editing, browsing and visualization are necessary.

Variant Handling, Inheritance and Composition in the ObjectMath Computer Algebra Environment

ObjectMath is a high-level programming environment and modeling language for scientific computing which supports variants and graphical browsing in the environment and integrates object-oriented constructs such as classes and single and multiple inheritance within a computer algebra language. In addition, composition of objects using the part-of relation and support for solution of systems of equations is provided. This environment is currently being used for industrial applications in scientific computing. The ObjectMath environment is designed to handle realistic problems. This is achieved by allowing the user to specify transformations and simplifications of formulae in the model, in order to arrive at a representation which is efficiently solvable. When necessary, equations can be transformed to C++ code for efficient numerical solution. The re-use of equations through inheritance in general reduces models by a factor of two to three, compared to a direct representation in the Mathematica computer algebra language. Also, we found that multiple inheritance from orthogonal classes facilitates re-use and maintenance of application models.

SIE Method of Analysing Microwave Fields of a 3D Heart Model

The Singular Integral Equations Method (SIE) used in this article allowed us to solve Maxwells Equations for a Three-Dimensional (3D) asymmetric heart model when a microwave catheter (MC) was placed inside the model and radiated microwaves. Here we explain the main idea of our SIE method. We first separated the solution of equations from satisfying the boundary conditions. For this purpose, we found the solution of the differential equations having a point source. This fundamental solution is used in our integral representation of a problem. The integral representation automatically satisfied the differential equations but has an unknown density function which must be found from the boundary conditions. The solution of the differential equations, obtained by our SIE method, was rigorous, that is it satisfied the differential equations and all boundary conditions. The false roots did not occur when applying our SIE method.All surfaces of the heart model were defined as a triangular mesh covering the 3Dheart surfaces. The heart model consisted of cardiac muscle and the right and left atriums with ventricles which were filled with blood. In this article we presented our calculations of the microwave electric field inside of a heart model. We have seen that our SIE method enabled one to optimal the size and shape of a MC when used to remove abnormal tissue in a heart model. We discovered that the electric field distribution most suitable for microwave ablation was a curved microwave catheter pressed against the lateral surface of heart atrium.

Singular integral equations method for computations of the scattering characteristics of a model heart exposed to electromagnetic radiation

The singular integral equations method elaborated in this paper allows us to solve accurately the Maxwells equations for a three-dimensional (3D) model heart exposed to electromagnetic radiation in the frequency range SHF and EHF. To test our algorithm we have computed the back scattering cross-section for a metal disc. Our computations are in good agreement with experiment given in literature. To demonstrate the usefulness of the algorithm we have computed the scattering characteristics of a simplified model of the human heart. This model is composed of the myocardium, the right and left atria and ventricles. All surfaces of the model are defined a triangular mesh in 3D covering the heart surfaces and normals n-> to the triangles.

The computation of electrical fields on a heart model with a microwave catheter

In our paper, we calculated the distribution of an electric field modulus at several parallel cross-sections of a model heart (with a catheter inside of its right atrium). The catheter was created out of dielectric or metal material. The frequency of the microwave signal was f = 10 GHz. The distribution of the electric field modulus has resonance peaks. The electric field could be concentrated in different places of the heart depending on weather the material of the catheter was dielectric or metal.

Microwave scattering by a three-dimensional model human heart

In this paper we report on computations of the scattered plane electromagnetic (EM) field by a model human heart at selected incidence polar /spl theta/ and azimuthal /spl phi/ angles of the microwaves. The heart model is composed of the myocardium as well as the right and left atria with ventricles. The 3D surface model of the heart has been created in 3D StudioMAX. The method of singular integral equations (SIE) was applied. For verification of the SIE algorithm we compared our computational results with experimental data for a metal disk.

Generating Efficient 3D Graphics Animation Code WithOpenGL From Object Oriented Models In Mathematica

Traditionally 3D plots of parametric functions expressed in Mathematica are computed interpretively and saved in a static form before display. This causes low graphic performance. In this paper we describe an approach to generate efficient C++/Fortran90 code from such functions. This code is linked together with a powerful 3D browsing environment and uses OpenGL with possible hardware support. Thus flexibility of interactive exploration of 3D scenes and animation options become available for the end-user. 1 Introduction 1.1 The visualization problem Numerical experiments based on mathematical models is one of the most prevalent classes of applications of high performance computers and workstations. A common problem is however to interpret and make use of numerical data produced from such experiments. High performance numerical programs usually generate vast amounts of data (in our applications 1-2 Gbyte or more).