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  • Research
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  • Clusters of Excellence at TU Braunschweig
  • SE²A - Sustainable and Energy-Efficient Aviation
  • Research
  • ICA B "Flight Physics and Vehicle Systems"
Logo Sustainable and Energy Efficient Aviation of TU Braunschweig
B2.1 - Load reduction potential of nonlinear stiffness and damping technologies
  • ICA B "Flight Physics and Vehicle Systems"
    • B5.2 - Application of physics-based finite-element tools in stiffness tailored structures for cryogenic hydrogen storage for improved mechanical and thermo-mechanical response
    • B4.2 - Consistent Multilevel Model Coupling and Knowledge Representation in Multidisciplinary Analysis and Design
    • B4.1- Collaborative Multidisciplinary Structural Design and Thermal Management for Electric Aircraft
    • B3.5 - Production technologies for hybrid suction designs - Bonding of micro-perforated sheets for hybrid laminar flow control suction panels
    • B3.2 - Advancing the additive xHLFC suction panel concept towards wind-tunnel readiness
    • B3.1 - Protective, multifunctional suction shells for hybrid laminar flow control: Design, integration, simulation and testing
    • B2.5 - EverScale - Enhancement and verification of load alleviation technologies by subscale flight testing
    • B2.4- Hybrid load alleviation by fluidic/reversed control and nonlinear structures
    • B2.3 - ARGO2 - Integrated design of control methods for stability of elastic aircraft
    • B1.9 - Validation of turbulent boundary layer-induced sound transmission through a fuselage section
    • B1.8 - Wind-tunnel experiments of advanced design of swept-wing with suction surfaces
    • B1.7 - Extension of Correlation-based Transition Transport Models for Laminar Aircraft Design
    • B1.6 - Effective Design Methods and Design Exploration for Laminar Wing and Fuselage
    • B1.5 - Sensitivities of Laminar Suction Boundary Layers for Large Reynolds Numbers
    • B1.3- Physics of broadband noise of sound sources from installed propulsors
    • JRG-B1 - Physics of Laminar Wing and Fuselage
    • JRG-B2 - Flow Physics of Load Reduction
    • B1.1 - Propeller and wing aerodynamics of distributed propulsion
    • B1.2 - Aerodynamic analysis of partly embedded boundary layer ingesting propulsors
    • B1.3 - Fast non empiric prediction of propulsion installation related noise
    • B1.4 - Transition Prediction and Design of Hybrid Laminar Flow Control on Blended Wing Bodies Based on 3D Parabolized Stability Equations
    • B2.1 - Load reduction potential of nonlinear stiffness and damping technologies
    • B2.2 - Structural technologies enabling load alleviation
    • B2.3 - Active load Reduction for enabling a 1-G wing using fOrward-looking and distributed sensors (ARGO)
    • B2.4 - Morphing structures for the 1g-wing
    • B3.1 - Global and Local Design Methodology for Laminar Flow Control
    • B3.2 - Process simulation and multiscale manufacturing of suction panels for laminar flow control
    • B3.3 - Thin Plies in Application for Next Generation Aircraft (TANGA)
    • B3.4 - New methods for failure and fatigue analysis of suction panels for laminar flow control
    • B5.1 - ADEMAO: Aircraft Design Engine based on Multidisciplinary Analysis and Optimization
    • JRG-B5 - Long-Range Aircraft Configurations and Technology Analyses
    • JRP - Permeation assessment for cryogenic applications by means of Fiber Bragg Grating sensors
    • ⯇ back to research

B2.1 - Load reduction potential of nonlinear stiffness and damping technologies

Nonlinear Stiffness Design

Stiffness curves
Typical nonlinear stiffness relations

The aim of the project is to create passive load alleviation with nonlinear elastic materials. The idea is increasing the performance during low load cases around cruise and decreasing the loading of high load cases. In other words, the wing shall be stiff during cruise and gets more flexible at high loading cases.
To examine this, an iterative process computes trimmed, quasi-steady manoeuvres. In doing so, the process considers the aeroelastic coupling. It iteratively calculates loads and deformations, using the vortex lattice method for the aerodynamic analysis and a finite element model for the nonlinear structural analysis.

Viscoelastic Damping Design

An essential requirement of aeronautic structures is their lightweight design. Such characteristic yields a considerable susceptibility to vibrations, affecting the controllability of an aircraft. In order to encounter transient events, such as gust encounter or landing impact, a rapid decay of vibrations achieved with proper placement of dampers would help to passively alleviate dynamic loads. Based on finite element modelling, tools will be developed that enable the damping analysis of vibrating structures supplemented with local viscoelastic dampers. Additionally, an optimization algorithm will be evolved, focusing on the integration positions to achieve maximum damping increase for loads critical modes with minimal impact on structural weight.

Implementation of an iterative eigenvalue solver

viscoelastic material
Loss factor of a viscoelastic material in dependence of frequency and temperature

A special property of viscoelastic materials is the frequency and temperature dependence of their material parameters. One rheological model which describes the mechanical behavior of viscoelasticity is the generalized Maxwell model. At different excitation frequencies, both the stiffness and the damping capability of the material can vary significantly. Therefore, to evaluate the influence of local viscoelastic elements on a global structure regarding eigenfrequencies and damping ratios, it is necessary to solve an eigenvalue problem with frequency dependent stiffness and damping matrices. The frequency dependence avoids a direct calculation and requires an iterative solution algorithm.

Modeling of viscoelastic shear-layer dampers

viscoelastic layer
Forced shear deformation of a viscoelastic layer in a Constrained Layer Damping treatment

Procedures for an increase of the damping effectiveness include the deliberate generation of shear strain in viscoelastic materials. A common application for vibration damping which utilizes this effect is the Constrained Layer Damping treatment (CLD), where a viscoelastic core layer is constrained between the stiffer base structure and a stiffer face layer. Occurring bending vibrations force the viscoelastic layer under shear strain. Since aircraft vibrations cover a wide range of different frequency and temperature ranges during operation, the damping material has to cope with the corresponding influences. Due to the dependence on frequency and temperature of viscoelastic material properties, the damping performance will also vary during operation.

Optimization tool for optimal damping design

One of the main challenges in aeronautic manufacturing is to design structures which comply with stiffness requirements and maximum mass limits at the same time. Therefore, the overall objective in terms of viscoelastic damping design will be to develop an optimization tool which aims to deliver highest damping with lowest mass increase. The optimization tool will optimize several design variables like the positioning or the topology of the viscoelastic and face layer, in order to create a tailored geometry for particular mode damping.

Mitglieder

Kjell Bramsiepe

Martin Gröhlich

Contact

Project lead

Prof. Dr.-Ing. Lorenz Tichy

Institute of Aeroelasticity
+49 551 709-2341

 

Organisation

Institute of Aeroelasticity

German Aerospace Center (DLR)
Bunsenstr. 10
37073 Göttingen

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Cluster of Excellence SE²A –
Sustainable and Energy-Efficient Aviation
Technische Universität Braunschweig
Hermann-Blenk-Str. 42
38108 Braunschweig

se2a(at)tu-braunschweig.de
+49 531 391 66661

 

 

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