Catálogo de publicaciones - libros

One way to increase the robustness of soft sensors is to use ensembles of symbolic regression-based predictors. Ensembles can increase the robustness because it gives a more consistent estimate of the output, it allows the derivation a measure of confidence and it can be used for problem detection. In this paper we will demonstrate the robust soft sensor by using ensembles of symbolic regression-based predictors in an industrial application.

Large area uniform plasmas are essential in microelectronics processing. Motivated by this application, a macroscopic model is proposed as a framework for investigating the occurrence of instabilities in high frequency plasma discharges for parallel plate geometries. This paper will concentrate on the formation of stationary, spatially inhomogeneous patterns.

A simple mathematical model for the motion of a pipeline bundle being towed using the Controlled Depth Tow Method (CDTM) is constructed and analysed. When the forces exerted by the sea on the bundle are neglected the model predicts that the bundle is neutrally stable and that its motion involves two different timescales. When these forces are not neglected the model predicts that the bundle will always be stable if the tension in the bundle at its downstream end is sufficiently large.

In the design workflow, CAD models of complex components include more and more details. A transformation of such models into Finite Element (F.E.) models often generates a much too large number of elements to be used directly. Generally, the removal of shape details or idealization operations are required to prepare F.E. models. These modifications must preserve the analysis result and the user must control the process in order to ensure sufficient accuracy of the F.E. results. In accordance to the analysis problems, the simplification process generates different appropriate F.E. models. In this paper, we present different operators and criteria to prepare analysis models from CAD models.

In viscoelastic pipes, where the material properties depends on a complex bulk modulus as well as on a complex shear modulus, the sound field within the fluid is affected. Therefore, the dispersion of flexural waves occurs in the pipe, while the speed of flexural waves decreases due to the coupled fluid mass. Coupling between the pipe wall and the fluid also decreases the sound speed in the fluid. Likewise, the speed of sound in fluid is frequency-dependent, just as the group velocity of bending waves depends on the frequency. Wavelet transform of non-stationary sound signals was used to identify the frequency-dependent fluid sound speed. Measurement and analysis of non-stationary signals with the use of time-frequency method provides a view to frequency dependent transfer characteristics of fluid-pipe coupled system. The results also showed that, in the case of propagating small disturbances (such as acoustic waves), the pipe wall inertia has a minor influence on the wave propagation characteristics. The elastic reaction of the wall to expansion of the cross section greatly exceeds the inertial reactions.

In many science and engineering problems, one observes smooth behaviour on macroscopic space and time scales. However, sometimes only a microscopic evolution law is known. In such cases, one can approximate the macroscopic time evolution by performing appropriately initialized simulations of the available microscopic model in small portions of the space-time domain. This coarse-grained time-stepper can be used to perform time-stepper based numerical bifurcation analysis. We discuss our recent results concerning the accuracy of the proposed methods.

Molecular dynamics simulations are typically very costly. We investigate whether optimal prediction, a method to approximate the mean solution of a large system of ordinary differential equations by a smaller system, can in principle be applied to speed up computations. A one-dimensional, solely classical model problem, describing some aspects of coating a copper layer onto a silicon crystal, is considered. Asymptotic methods are employed to approximate the high-dimensional conditional expectations, which arise in optimal prediction. Results of a comparison of the thus derived smaller system with the original system are shown.

The chart surface approach, a variational grid generation method for surface grids, is applied to CAD models describing ship hulls and propellers.

Strongly damped mechanical systems arise, for example, in vehicle dynamics and in modelling joints in biomechanics. Standard explicit integrators become unstable unless very small time steps are chosen. We are interested in the numerical solution of such systems with step sizes that are independent of the damping parameter. The smooth motion of the mechanical system is expanded in terms of solutions of differential-algebraic systems of index 2. These results hold for analytical solutions as well as for numerical solutions of suitable methods such as Radau collocation. In the border case of big damping constants it turns out that the error of numerical solutions of the strongly damped mechanical system is bounded by errors for the differential algebraic systems.

This paper deals with Shape Memory Alloy (SMA) actuators for mechatronic applications. A mathematical model on the macroscopic level is discussed and a computational framework is introduced. The latter makes use of the method of lines and results in a system of differential-algebraic equations in time. Some first simulation results for a 1D wire in the isothermal case illustrate the approach.