Hans-Günther Reimerdes

Finite Element for the Static and Stability Analysis of Sandwich Plates

A finite element for the static and stability analysis of sandwich plates is formulated based on a three-layer sandwich model and its underlying differential equations. The Kirchhoff-Love hypothesis is assumed for the face sheets. The core is modelled by a three-dimensional material law neglecting the in-plane core stiffnesses. A stability analysis is performed on the basis of the geometric stiffness matrix considering the membrane prestresses of the face sheets.

Dynamic aero-structural response of an elastic wing model

Abstract A highly elastic rectangular wing model with a supercritical airfoil was designed and manufactured to study aero-structural equilibrium configurations and aerodynamic damping at various speeds in a subsonic wind tunnel. The supporting structure is a cross-shaped spar. A foam with negligible stiffness is used to provide the aerodynamic surface of the wing. Experimental data are used to examine a coupled algorithm for simulating fluid–structure interaction which simultaneously solves the Euler or Navier–Stokes equations and the structural dynamics equations in the time domain. The elastic wing is modelled by a generalized Timoshenko-type beam with six degrees of freedom for a material cross-section. Correct reproduction of the aero-structural equilibrium shape of the wing model and the deflection under zero lift and nonzero lift conditions, time consistency of unsteady deformations and pressure fluctuations are examined by comparing numerical and experimental results.

Imperfection Sensitivity of Circular Cylindrical Shells of Varying Length Subjected to Axial Compression

Within the first half of the last century, a significant deviation between theoretical buckling loads of thin-walled shell structures and the buckling load determined experimentally was identified. The reason for this discrepancy is explained by the presence of imperfections having a degrading effect on the load carrying capacity of shell structures. To investigate the influence of imperfections on the real buckling load, different imperfection modelling approaches are developed. Within this paper the imperfection sensitivity of unstiffened circular cylindrical shell structures is investigated with the Single Perturbation Load Approach as well as the axis-symmetric imperfection modelling. Thereby, the influence of geometrical relations of the shell structures on the imperfection sensitivity is investigated. The achieved results are compared to empirical findings reported in literature.

Structural Concept and Design for Modular and Serviceable Spacecraft Systems

The performance of spacecraft systems can be improved significantly by a modular and serviceable design approach. Maintenance operations as well as system upgrades in context of On-Orbit Servicing (OOS) become feasible. To enable autonomous maintenance and reconfiguration operations in orbit, one major challenge is the development of a suitable structural concept. The general idea to achieve a modular design is based on the fragmentation of common satellite systems into standardized building blocks. This paper depicts the design process of the primary structural components and the required docking interface. Different concepts for both parts are presented, designed and finally assessed by multiple criteria.

Aero-structural Dynamics Experiments at High Reynolds Numbers

The elastic wing model, its excitation and comprehensive high frequency measuring equipment for the High Reynolds Number Aero-Structural Dynamics (HIRENASD) tests in the European Transonic Windtunnel (ETW) are shortly described. Some of the stationary polars are presented in terms of wing deformation, as well as aerodynamic coefficients and pressure distributions. Then unsteady processes observed in the measurements of static aerodynamic coefficients, are regarded with focus on small amplitude pressure waves travelling upstream from the trailing edge and triggering periodically break-down and redeployment of the local supersonic domains with transonic shock waves to run upstream and to disappear. Another focus is on stochastic vibrations excitation while moving forward during nominally static experiments. Emphasis is put on measured variations of pressure distribution on the wing surface caused by defined vibration excitation applying internal force couples at the wing root, whereby the exciter frequencies were chosen close to natural frequencies of the wing model. Phase and magnitude of measured local lift fluctuations as well as real and imaginary parts of pressure distributions are presented.

Design, Qualification and Experimental Investigation on Flexible Wind Tunnel Wing Models

The purpose of this work on highly flexible wing models is the validation of the numerical direct simulation, developed in the Collaborative Research Center SFB 401. The first step in the validation process is the investigation of a flexible straight wing model in the subsonic region. The design and construction of this wing model will be described under consideration of aerodynamic and structural constraints. A short introduction in the measurement techniques and the tests under wind-off and windon conditions will be given. Different data reduction methods to obtain the frequency and the damping factor during wind tunnel tests will be introduced. Some experiments under steady state and transient flow conditions will be presented for validation of the numerical calculations.

Structural Idealization of Flexible Generic Wings in Computational Aeroelasticity

In the present contribution concepts of reduced structural models for Computational Aero-Elastic simulation (CAE) on aircraft wings are presented. Here the idealization approach relies on analytical methods with the aim to shorten in comparison to a typical finite element method computational cost and time, by preserving nearly the same accuracy. Prior to more detailed investigations using higher order models, these simplified models allow an earlier access of insight regarding the aeroelastic and structural behavior of the wing at the very beginning of the design process. At first a one-dimensional idealization that extends the Timoshenko beam by taking into account additional effects due to warpings is developed. To better describe the influence of swept, a three dimensional idealization is derived. Both idealizations yield good agreements in results concerning the global static deformation and the modal behavior of the wing.

Finite Element for Sandwich Panels Based on Analytical Solution of Constitutive Equations

Sandwich structures with low strength honeycomb or foam cores are being used due to their high bending stiffness to weight ratio in many structural applications. Because of their high flexibility, the deformation field of these core materials show a nonlinear pattern in the through-thickness direction as well as in the core in-plane which can affect significantly the local as well as the global structural behaviour of sandwich panels.