2018

Daniel Straub (TU Munich)

Eurocode provides the basis for the design of structures. It ensures a generally accepted level of safety throughout its domain of applicability. However, there are many instances of structures whose design is not fully covered by Eurocode; one example are lightweight structures subject to wind for which the simple load formulas given in Eurocode are not appropriate. When designing such structures, it is nevertheless desired that the overall safety of the structure is in accordance with Eurocode. In this talk, we address appropriate means to ensure this.
The lecture consists of two parts. First, we present a methodology for determining the relevant design parameters based on a limited set of response time-series from numerical simulations (or experiments). We show how the safety margin becomes a function of the amount of data available. This approach is demonstrated through application to a membrane structure analysed with fluid-structure interaction analysis.
The second part is looking at the issue that simple formulas given in Eurocode for establishing wind loads are based on conservative assumptions and parameter choices, i.e. the models contain “hidden safety”. As a consequence, even if advanced numerical models are more accurate than the Eurocode formulations, they can lead to reduced safety because they eliminate the conservative assumptions. To compensate, it can be necessary to employ additional safety factors. We make recommendations on these safety factors based on an analysis of a building portfolio.

Marianne Hörlesberger (Austrian Institute of Technology, Wien)

Textile reinforced polymer composites (TRPC) hold the promise for enhanced products featuring superior properties, such as light weight and high strength, with comparatively low material costs. This promising potential is nevertheless hindered by the lack of appropriate processing technologies to enable low-cost manufacturing of mass products with sufficient quality. The goal of the 3D-LightTrans project was to create a highly flexible manufacturing chain for low cost production of integral large scale 3D textile reinforced polymer composite parts and its integration in the complete supply chain. 3D-LightTrans manufacturing chains is based on hybrid yarn incorporating thermoplastic matrix material, processed to deep draped multilayer textiles and multifunctional 3D-textile constructions, which is fixed to dry pre-forms and finally, processed into composites by thermoforming. A model is presented for full automation (in nowadays mostly manually performed) complex handling operations.

Martin Schwarz (University of Innsbruck)

This talk addresses a novel for wave propagation in material with spatially varying random properties. The target model is the linear elastic wave equation in solids. We construct a deterministic Fourier integral operator to solve the problem. For modelling the uncertainty we
use a new approach:
The randomness is included into the solution operator rather than in the coefficients of the model. The solution can be represented by stochastic Fourier integral operators (sFIO), which
have nice computational properties for (numerical) simulations. Our model predicts the fully time dependent dynamic response of the structure, and its stochastic properties. Calibrating the sFIO to measurements can be used for both parameter estimation and damage detection.

Sebastian Nowotny (Deutsches Zentrum für Luft- und Raumfahrt e.V.)

This talk gives an overview of the current state for Laser Automated Tape Placement for thermoplastic composites at the DLR.
The process allows in-situ manufacturing of large-scale, complex structures. Using this tape placement facility, expensive and time-consuming manual processes such as preforming and vacuum bagging processes are not necessary. Furthermore, the process data acquisition and monitoring system allows the component to be analysed in-situ, reducing the costs of non-destructive testing. This facility has been used to produce structures from a number of thermoplastic materials, including PEEK, PEKK, and PPS, for both real-world applications and fundamental engineering material research. Ongoing projects at this facility include the in-situ integration of stiffening elements to aircraft skins, and research on additional welding and joining processes.

Martijn Schmeetz (INTALES GmbH)

Within the space industry there is a need for low mass structures in order to reduce costs of materials but also costs of fuel required to get these structures into space. In addition, novel manufacturing methods, like additive manufacturing, allow for the creation of more complex geometries which in turn require a more complex design process. Optimising such structures in terms of mass, while at the same time fulfilling all requirements regarding functionality and allowable values such as stresses, strains and displacements, poses a huge challenge. Gradient-based optimization strategies, but also evolutionary algorithms are characterized by the curse of dimensionality which leads to a large number of required model evaluations or to the situation where no global optimum can be identified.
For this reason, a novel approach is proposed where the optimization problem is tackled by a heuristic adaptation procedure on element level. During the FE-analysis, the structural requirements like allowable stresses or strains are checked and – if necessary – the thickness and/or material orientation of the element is updated. Access to the element routines in the FE-analysis is therefore a requirement for this strategy for which reason a number of state-of-the-art element routines have been developed and adopted as user element routines to be linked with the commercial FEM software ABAQUS. The optimization process is performed in an iterative manner, meaning that the external loading is applied in several load portions until the full force magnitudes are active. The main advantage of this approach is the applicability to large and complex FE-models, with the possibility of the structure having multiple local optimums. In addition, the strategy can be used for models involving different kinds of elements, like shell elements including layered composite, sandwich or isotropic (metallic) shell sections, and also fastener elements.
This approach by itself could lead to local concentrations of mass caused by high stresses concentrations. These stresses might be artificial, depending on the constitutive law used, and can occur near sharp corners, boundary conditions or load introduction areas. To reduce these peak masses a smoothing algorithm is developed which smooths the stress concentrations by averaging over multiple elements. The domain over which smoothing occurs for a specific element depends on a certain maximum distance from the element centroid and the similarity of neighbouring elements regarding how their stresses change with increasing load. Using this approach, artificial peak stresses can be smoothed out without the risk of over-smoothing and underestimation of stresses. Additionally, stiffness driven stresses can be smoothed or shifted as well with this algorithm.
In order to handle the large amount of data involved in the optimization process, SQLite-databases are used, which act as a means of exchanging information between the algorithms and the FE-software. With these databases the full optimization procedure remains traceable and, for example, the convergence behaviour of the process can be investigated. Also, it allows for the model itself and all of its properties and results to be visualized and filtered in an efficient manner. Finally, the layup stored in the database can easily be used for an automated model build, resulting in a complete and robust design/optimization work flow.
In this work, the theoretical backgrounds, the logic of the work flow and practical issues of the applications are discussed. An industrial example illustrates distinct features of the whole process and shows the advantages of the approach for industrial applications.

Thomas Zwanowetz (University of Innsbruck)

In order to determine the accuracy of finite element models, their predictions are compared to real world tests. If the results do not reach the desired level of consensus and these differences cannot be explained by engineering judgment alone, experimental data is used to upgrade the model. This step is known as parameter calibration.
Based on these results conclusions can be drawn to make further enhancements of the model. The presentation refers to a computational model of lightweight structures developed by the company INTALES GmbH Engineering solutions as well as its comparison with practical tests (loading) of the structure.
The presentation will include the following main topics:
● Full scale test and finite element model
● Parameter calibration with emphasis on the Nelder-Mead algorithm
● Adaptions of the model in particular the inclusion of friction

Daniel Sirianni (University of Innsbruck)

In this presentation a statistical approach towards inverse problems will be employed to determine specific material parameters based on experimental data. In statistical inverse problems the unknown parameters are modelled as random variables such that Bayes’ theorem can be used to obtain the posterior distribution of the parameters. A widely used method to solve statistical inverse problems is the Markov chain Monte Carlo method such as the Metropolis-Hastings algorithm. The Metropolis-Hastings algorithm produces a Markov chain whose equilibrium distribution is the sought after posterior distribution, realized asymptotically by the end pieces of the chain. This approach will be applied to a large scale finite element model, developed by INTALES. This model contains some poorly known material parameters such as damping and stiffness parameters. To determine these parameters the previously mentioned method is used. Once the empirical distribution of the parameters is known, one can perform a stochastic investigation of the deviation of measurement and prediction. Furthermore, statistical features of the parameters can be determined with the help of Monte Carlo methods.

Benoit Caillaud (University of Innsbruck)

The purpose of this study was to numerically investigate the influence of different snow conditions onto the structural behaviour of a snowboard undergoing the conditions of a carved turn. The properties of different types of snow were numerically idealized and the deformations and pressure distribution along the contact edge of a snowboard were observed, in an attempt to understand their sensitivity to the environmental parameters. A static load bench was developed in-house and a simplified snowboard prototype was manufactured in order to represent the in-situ conditions. The experimental set-up was idealized in a finite element model, representing the composite structure and its loading environment. A method for the validation of the numerical model was proposed, based on the comparison of the experimental and numerical displacement fields, and consisted in a best-fit algorithm to superimpose both deformed shapes. The congruence between the two deformed surfaces was expressed with statistical means, and constituted the target function for optimization frameworks. Additionally, the contact pressure at the interface was experimentally assessed with the use of pressure measurement tape, and compared with the numerical predictions. The results of the finite element simulation were then explored to give an insight into the influence of the snow properties onto the structural behaviour.

Jürgen Brandner, Manuel Schleiffelder (PTScientists GmbH)

PTScientists GmbH is an aerospace engineering company and unique in Europe as the only privately owned and funded SME that is developing a commercial lunar payload delivery system. The company was founded in 2008 and has been developing its spacecraft and lander concept, ALINA autonomous landing and navigation module, since 2010 with a goal of showing that lunar exploration is commercially viable. PTScientists is already working on a highly innovative technology demonstration mission that aims to be the first private mission to land on the Moon. “Mission to the Moon” will include several key proof-of-concept elements, with a view to developing a sustainable lunar transport and communications infrastructure, which may also be used to further humanity’s exploration ambitions. The company is headquartered in Berlin, Germany with 55 fixed employees and a team of part-time contributors. The team behind the mission also features some senior engineers of the original Apollo program such as Jack W. Crenshaw who was in charge of the flight trajectories for Apollo. Technical cooperation partners include Audi AG, Vodafone Germany and Nokia Bell Labs, the German Aerospace Center (DLR), the European Space Agency (ESA) as well as technical universities in Germany and Austria.