Structural Design & Optimization

Today's structures demand more than ever an optimized design considering the load and weight requirements for an eventual reduction in cost of manufacturing and/or operation. Therefore varied optimization processes play an important role in the design cycle of complex structures.

Current projects

OptiFee - Layout - Topology optimization of unconventionally stiffened CFRP structures considering manufacturability criteria

Funding: DFG

Duration: 2021-2024

Team: L. Reichert, P. Horst, S. Heimbs

In the topology optimization of stiffened lightweight structures, such as an aircraft fuselage, individual stiffener layouts are evaluated with respect to their mass and manufacturing costs. For this evaluation, detailed structural data is required as a basis, which is not available without high computational effort. This is especially the case for unconventional topologies, deviating from a conventional stringer-frame design. In addition, unconventional topologies face greater constraints due to manufacturability aspects and challenges in cost determination. Unconventional stiffening topologies, at least partially employed, promise advantages in terms of mass, but these may come hand in hand with cost disadvantages.

The OptiFee project follows the research hypothesis that unconventionally stiffened structures can be evaluated in terms of mass, manufacturing costs and manufacturability even without a detailed structural design, thus making the use of layout topology optimization possible for the first time in preliminary design. Derived from this, the main objective of the project is the development of a two-step, integrated method for the evaluation of unconventional stiffening topologies with respect to their mass and manufacturing costs under consideration of manufacturability criteria. For this purpose, structures made of carbon fiber reinforced plastic (CFRP) are to be considered. Due to the high manufacturing costs in this area, the optimization of structures in terms of mass and cost is particularly relevant. An aircraft fuselage structure will serve as an application example. The aim is to gain knowledge of the relationships and interactions between stiffener layouts that have not been designed in detail in the early preliminary design and their structural mass, manufacturing costs and manufacturability.

DFG database

Completed projects

Wandstärkenverteilung eines Flügelkastens mit Absenkung für die Integration eines Absaugpanels

Funding: DFG (Exzellenzcluster)

Duration: 2019 - 2022

Team: L. Lobitz, P. Horst, S. Heimbs

Active laminar flow control by means of boundary layer suction is a promising approach to reduce aircraft drag. In this context, the subproject B3.1 of the Cluster of Excellence SE2A deals with the structural design of a suction panel and its integration into the wing.

The global wing design aims to enable high laminar run lengths while minimizing structural mass. Based on the resulting requirements, a detailed concept for suction panels for active laminar flow control is developed. Here, novel technologies such as plastic and metal 3D printing offer great potential in terms of functional integration and high component complexity. In order to benefit from this extended design freedom, it is investigated whether it is possible to manufacture both the porous suction skin and the core structure of the suction panels using 3D printing.

The suction panels must be removably connected to the wing's primary structure for maintenance and repair. In order to prevent a transition from laminar to turbulent flow at these interfaces in the wing skin, tight tolerances must be kept with regard to component joints, steps and surface waviness.

Funding: EFRE

Duration: 2018 - 2022

Team: L. Nagel, L. Reichert, A. Herwig, F. Runge

The main goal of the JoinTHIS project is to develop, implement and evaluate a manufacturing methodology based on AFP and welding technologies for thermoplastics, enabling the autoclave-free production of thermoplastic CFRP structures for the next aircraft generation. The new manufacturing method ensures an economically implementation of large-scale structural lightweight construction concepts for aircraft fuselages based on thermoplastic fiber-reinforced materials. The combination of procedural advantages of AFP (high degree of automation, flexible component geometries) with the advantages of thermoplastic matrix materials over thermoset systems (in situ consolidation, weldability and recyclability) leads to greatly reduced cycle times, thus achieving high production rates in aircraft construction (> 100 pcs / month). Due to an increasing production and resource efficiency as well as reducing CO2 emissions, the new manufacturing method is making a significant contribution to a sustainable mobility strategy as presented by the European Commission's FlightPath 2050.

Focus of research:

Modeling of residual stresses and evaluating their influence on components and assemblies.
Designing a detailed multiscale model of the AFP and welding process.
Development and research of thermoplastic laying and process monitoring technology.

JoinTHIS_Bild1 — Strength and stability analysis depending on geometry deviations

JoinTHIS_Bild2 — Temperature and pressure influence as a subject of investigation in the process

JoinTHIS_Bild3 — Schematic representation of the consolidation zone

Funding: DFG

Duration: 2011 - 2014 (1^st Funding period); 2015 - 2018 (2^nd Funding period) & 2019

Team: K. Sommerwerk, F. Runge, M. Rohdenburg

A full analysis of today's commercial aircrafts has shown a substantial need for high lift devices, which will not be covered by the predominant technology evolution. This is true in particular in the domains of noise reduction and enhanced scalability of the performance parameters of high lift device during take-off and landing.

In the long term, these requirements lead to the development of the technological fundamentals for a new segment of low noise commercial aircrafts capable of short take-offs and landings, which allow for better integration in the cities of industrialized societies. The realization of this vision of new means of transport requires technologies based on aeroacoustics, aerodynamics and flight dynamics, which surpasses the available methods and knowledge by far.

The subproject C3 "Structural Design and Aeroelasticity" focuses on the requirements of the structural design of the aircraft taking into account the general aeroelastic effects of the wing and the special effects created by the blown flap. New flap designs will be evaluated within this context.

SFB880 C3 - Animation of skin thickness distribution change — Optimisation of thickness distributions

SFB880 C3 - Animation of element stress x distribution change — local element stress in spanwise direction

Team: L. Reichert, P.Horst

This project pursues the establishment of an interdisciplinary research focus "individualized CFRP light-weight structures with the aid of flexible manufacturing technologies". Overall, this research group is based on fundamental research projects as well as application-based research projects with industrial partners. This project is the second step of this local strategy and addresses the area of "local variant flexibility"

Within the interdisciplinary development process, the implementation of Continuous Wet Draping (CWD) and its assessment is carried out.

The project "FlexProCFK" is a cooperation between the Institute of Production Engineering and Machine Tools (IFW) of the Leibniz Universität Hannover, the Institute of Aircraft Design and Lightweight Structures (IFL) of the Technische Universität Braunschweig und the Institute of Polymer Materials and Plastics Engineering (PuK) of the Clausthal University of Technology. The aim of the project is to design and implement an innovative flexible manufacturing technology for the production of individualized CFRP structures. Within the project, Continuous Wet Draping is developed as a new production technology in carbon fiber fabrics are individually impregnated with resin and subsequently draped into complex geometries.

The specific tasks to be developed or researched by the different partners are therefore derived from the expertise of the respective partner:

Development of a method for the implementation of individualization into the integrated structure and production design process (IFL)
Development and research of a method and a module for the targeted application of matix systems onto carbon fiber fabrics (PuK)
Evaluation of the novel CWD technology for flexible production of inidviualized stiffening structures in the context of the integrated design process of structure and production (IFL)
Reasearch and specific manipulation of the draping behavior of carbon fiber fabrics with locally variable properties on complexly curved surfaces (PuK)
Development and research of a method and modules for draping variable carbon fiber fabrics on arbitrary and variable profiles (IFW)
Development and research of a method and its modules for the flexible stocking and on-line assembly of semi-finished CFRP products for flexible draping (IFW)

Further information

Team: H. Sommerwerk

The certification requirements of commercial aircrafts specify safe operation under continuous and recurrent icing conditions. Nevertheless several accidents a year are due to icing problems. Especially water droplets larger than 50 μm diameter (supercooled large droplets) has potential for critical icing conditions and are not considered in CS 25.

The main focus of the IFL is the research and testing of new and innovative deicing systems under conditions of supercooled large droplets. In addition to icing and deicing tests in a climatic chamber this work is about the development of methods to simulate the structure behaviour in deicing processes.

Team: T. Fabel

Ziel dieses Projektes ist es, zwei Konzepte zum Ausblasen von Luft aus einer Klappenoberfläche zu entwickeln. Dabei sind die Entwicklung/Konzepte der Auslässe in die übrigen Klappenstruktur zu integrieren. Dabei haben die Projektpartner folgende Aufgaben:

Management: IFL der TU Braunschweig (Ehemalige IFL-Leitung: Prof. Horst)
Erstellen von Strukturkonzepten: ILR der TU Dresden (Prof. Wolf), EADS IW
Materialinformationen bzw. Auswahl der Materialien: IFL
Ausblaskonzepte und Integration in die Klappe: ILK der TU Dresden (Prof. Hufenbach), IFL, ILR, EADS IW
Fertigen der Coupon-Prüfkörper: ILK, EADS IW
Testen der Prüfkörper: IFL, IL

Team: M. Pietrek

The research project "Bürgernahes Flugzeug" of the TU Braunschweig, DLR and LU Hannover is following a vision of inter-European air transportation of the future, with small airports close to cities providing efficient point-to-point connections. At the same time, the project is developing the basic technology such a vision would require.

The research in work package 2000 focuses on asymmetric sandwich constructions of the fuselage. Especially the numerical simulations of these structures are very important. Undamaged fuselage sections as well as damaged structures, e.g. by impacts, are analysed to detect minimal dimensions and critical load cases. Experimental analyses with coupon specimens of damaged sandwich shells are necessary to identify failure modes of these structures and to validate numerical simulations.