Rosic B.V.,TU Braunschweig |
Rosic B.V.,Institute of Scientific Computing |
Diekmann J.H.,German Aerospace Center |
Diekmann J.H.,Institute of Flight Systems
Journal of Aircraft | Year: 2015
The paper deals with the propagation of uncertainty in input parameters through the aircraft model in clean cruise configuration triggered by the elevator pulse. Assuming aerodynamic coefficients as random variables and processes, the evolution of uncertainties in the aircraft state is estimated with the help of efficient nonintrusive procedures-stochastic collocation and the nonintrusive Galerkin approaches, here contrasted to the slow convergent Monte Carlo integration. These numerical methods are implemented by using the flight simulator in a black-box manner. In this way, the set of samples of aircraft states is simply obtained by solving the corresponding systems of deterministic ordinary differential equations. Additionally, the paper provides the variance-based sensitivity analysis of a flight model carried out with the help of the polynomial-chaos approach. © 2014 by the authors. Published by the American Institute of Aeronautics and Astronautics, Inc.
Rosic B.,Institute of Scientific Computing |
Matthies H.G.,Institute of Scientific Computing |
Litvinenko A.,Institute of Scientific Computing |
Pajonk O.,Institute of Scientific Computing |
And 3 more authors.
ECCOMAS Thematic Conference - ADMOS 2011: International Conference on Adaptive Modeling and Simulation, An IACM Special Interest Conference | Year: 2012
The description of heterogenous material is here given within the probabilistic framework, where uncertain material properties in time and/or space are represented by stochastic processes and fields. For material with uncertain structure such as quarry, masonry etc., we study the coupled heat and moisture trasnport modelled by the Künzel equations. The transport coefficients defining the material behavior are nonlinear functions of structural responses - the temperature and moisture fields - and material properties. In order to closely determine the mentioned parameters of such system we focus our attention on the solution of inverse problem via direct, non-sampling Bayesian update methods which combine the a priori information with the measurment data for the description of the posterior distribution of parameters. Namely, we consider material parameters, observations and forward operator as random. Since the measurments are always polluted by some kind of measurment error we modell it here by a Gaussian distribution. The new approach has shown to be effective and reliable in comparison to most methods, which take the form of integrals over the posterior and compute them by sampling, e.g. Markov chain Monte Carlo (MCMC). In addition, we compare our method with this and other Bayesian update methods.
Krosche M.,TU Braunschweig |
Krosche M.,Institute of Scientific Computing |
Heinze W.,TU Braunschweig |
Heinze W.,Institute of Aircraft Design and Lightweight Structures
Journal of Aircraft | Year: 2015
As part of the Collaborative Research Center 880, preliminary aircraft design activities are carried out for a new class of low-noise cruise-efficient short takeoff and landing (CESTOL) transport aircraft.Acorresponding aircraft is quite different from a state-of-the-art commercial aircraft because of the use of a high-lift system with active flow control. The fact that new technologies are not sufficiently understood yet in combination with the assumption of common design data and the use of classical calculation methods expresses itself in uncertainties that are of epistemic character. The robustness of a deterministicCESTOLaircraft design toward parameters such as the necessary engine thrust, direct operating costs, and the maximum takeoff and landing distances is investigated here concerning the mentioned uncertainties. For this purpose, a stochastic description of parameter variations of the design is formulated. Stochastic quantities are computed by Monte Carlo sampling to rate the robustness. A distributed component-based software implementation is used to perform the Monte Carlo sampling. The software system is installed on a Linux cluster with several multi-CPU computers; a deterministic sample is simulated through the design program PrADO. © 2014 by the authors. Published by the American Institute of Aeronautics and Astronautics, Inc.
Lorenz P.,Leibniz Institute of Surface Modification |
Kloppel M.,Institute of Scientific Computing |
Smausz T.,University of Szeged |
Csizmadia T.,University of Szeged |
And 3 more authors.
Materials Research Express | Year: 2015
Nanostructures are of increasing importance in manifold application fields such as electronics, optics and beyond. However, the fast and cost-effective production of nanostructures is a big technological challenge for laser machining. One promising approach is laser irradiation of thin metal layers, which allows the fabrication of metal nanostructures induced by a melting and transformation process. The influence of laser parameters (laser fluence, laser pulse number) on the morphology of the nanopatterned film and the dynamics of the nanostructure formation during excimer laser irradiation of a 20 nmchromium film on fused silica were studied. The dynamics of nanopatterning, comprising hole and droplet formation, were investigated by time-dependent reflection and transmission measurements as well as time-dependent optical microscopy. The resulting patterns were investigated by optical and scanning electron microscopy (SEM). However, for an optimization of this process a better underst and ing of the underlying physical phenomena is necessary. Therefore, experimental data of laser-induced nanopatterning were compared with results of physical simulations that consider the heat equation (laser-solid interaction including melting and evaporation) and the Navier-Stokes equation (transformation processes of the molten phase). The simulations, making use of laser fluence-dependent effective material parameters (surface tension and viscosity), are in good agreement with the experimental results. © 2015 IOP Publishing Ltd.