TY - CHAP A1 - Götten, Falk A1 - Havermann, Marc A1 - Braun, Carsten A1 - Gomez, Francisco A1 - Bil, Cees T1 - On the Applicability of Empirical Drag Estimation Methods for Unmanned Air Vehicle Design Read More: https://arc.aiaa.org/doi/10.2514/6.2018-3192 T2 - 2018 Aviation Technology, Integration, and Operations Conference, AIAA AVIATION Forum Y1 - 2018 U6 - https://doi.org/10.2514/6.2018-3192 SN - 1533-385X N1 - AIAA 2018-3192 SP - Article 3192 ER - TY - CHAP A1 - Möhren, Felix A1 - Bergmann, Ole A1 - Janser, Frank A1 - Braun, Carsten T1 - On the determination of harmonic propeller loads T2 - AIAA SCITECH 2023 Forum N2 - Dynamic loads significantly impact the structural design of propeller blades due to fatigue and static strength. Since propellers are elastic structures, deformations and aerodynamic loads are coupled. In the past, propeller manufacturers established procedures to determine unsteady aerodynamic loads and the structural response with analytical steady-state calculations. According to the approach, aeroelastic coupling primarily consists of torsional deformations. They neglect bending deformations, deformation velocities, and inertia terms. This paper validates the assumptions above for a General Aviation propeller and a lift propeller for urban air mobility or large cargo drones. Fully coupled reduced-order simulations determine the dynamic loads in the time domain. A quasi-steady blade element momentum approach transfers loads to one-dimensional finite beam elements. The simulation results are in relatively good agreement with the analytical method for the General Aviation propeller but show increasing errors for the slender lift propeller. The analytical approach is modified to consider the induced velocities. Still, inertia and velocity proportional terms play a significant role for the lift propeller due to increased elasticity. The assumption that only torsional deformations significantly impact the dynamic loads of propellers is not valid. Adequate determination of dynamic loads of such designs requires coupled aeroelastic simulations or advanced analytical procedures. Y1 - 2023 U6 - https://doi.org/10.2514/6.2023-2404 N1 - AIAA SCITECH 2023 Forum, 23-27 January 2023, National Harbor, Md & Online PB - AIAA ER - TY - JOUR A1 - Götten, Falk A1 - Finger, Felix A1 - Havermann, Marc A1 - Braun, Carsten A1 - Gomez, Francisco A1 - Bill, C. T1 - On the flight performance impact of landing gear drag reduction methods for unmanned air vehicles JF - Deutscher Luft- und Raumfahrtkongress 2018 N2 - The flight performance impact of three different landing gear configurations on a small, fixed-wing UAV is analyzed with a combination of RANS CFD calculations and an incremental flight performance algorithm. A standard fixed landing gear configuration is taken as a baseline, while the influence of retracting the landing gear or applying streamlined fairings is investigated. A retraction leads to a significant parasite drag reduction, while also fairings promise large savings. The increase in lift-to-drag ratio is reduced at high lift coefficients due to the influence of induced drag. All configurations are tested on three different design missions with an incremental flight performance algorithm. A trade-off study is performed using the retracted or faired landing gear's weight increase as a variable. The analysis reveals only small mission performance gains as the aerodynamic improvements are negated by weight penalties. A new workflow for decision-making is presented that allows to estimate if a change in landing gear configuration is beneficial for a small UAV. Y1 - 2018 U6 - https://doi.org/10.25967/480058 PB - DGLR CY - Bonn ER - TY - JOUR A1 - Möhren, Felix A1 - Bergmann, Ole A1 - Janser, Frank A1 - Braun, Carsten T1 - On the influence of elasticity on propeller performance: a parametric study JF - CEAS Aeronautical Journal N2 - The aerodynamic performance of propellers strongly depends on their geometry and, consequently, on aeroelastic deformations. Knowledge of the extent of the impact is crucial for overall aircraft performance. An integrated simulation environment for steady aeroelastic propeller simulations is presented. The simulation environment is applied to determine the impact of elastic deformations on the aerodynamic propeller performance. The aerodynamic module includes a blade element momentum approach to calculate aerodynamic loads. The structural module is based on finite beam elements, according to Timoshenko theory, including moderate deflections. Several fixed-pitch propellers with thin-walled cross sections made of both isotropic and non-isotropic materials are investigated. The essential parameters are varied: diameter, disc loading, sweep, material, rotational, and flight velocity. The relative change of thrust between rigid and elastic blades quantifies the impact of propeller elasticity. Swept propellers of large diameters or low disc loadings can decrease the thrust significantly. High flight velocities and low material stiffness amplify this tendency. Performance calculations without consideration of propeller elasticity can lead to decreased efficiency. To avoid cost- and time-intense redesigns, propeller elasticity should be considered for swept planforms and low disc loadings. KW - Propeller KW - Finite element method KW - Blade element method KW - Propeller elasticity KW - Aeroelasticity Y1 - 2023 U6 - https://doi.org/10.1007/s13272-023-00649-y SN - 1869-5590 (Online) SN - 1869-5582 (Print) N1 - Corresponding author: Felix Möhren VL - 14 SP - 311 EP - 323 PB - Springer Nature CY - Berlin ER - TY - JOUR A1 - Bergmann, Ole A1 - Möhren, Felix A1 - Braun, Carsten A1 - Janser, Frank T1 - On the influence of elasticity on swept propeller noise JF - AIAA SCITECH 2023 Forum N2 - High aerodynamic efficiency requires propellers with high aspect ratios, while propeller sweep potentially reduces noise. Propeller sweep and high aspect ratios increase elasticity and coupling of structural mechanics and aerodynamics, affecting the propeller performance and noise. Therefore, this paper analyzes the influence of elasticity on forward-swept, backward-swept, and unswept propellers in hover conditions. A reduced-order blade element momentum approach is coupled with a one-dimensional Timoshenko beam theory and Farassat's formulation 1A. The results of the aeroelastic simulation are used as input for the aeroacoustic calculation. The analysis shows that elasticity influences noise radiation because thickness and loading noise respond differently to deformations. In the case of the backward-swept propeller, the location of the maximum sound pressure level shifts forward by 0.5 °, while in the case of the forward-swept propeller, it shifts backward by 0.5 °. Therefore, aeroacoustic optimization requires the consideration of propeller deformation. Y1 - 2023 U6 - https://doi.org/10.2514/6.2023-0210 N1 - Session: Propeller, Open Rotor, and Rotorcraft Noise II AIAA SCITECH 2023 Forum, 23-27 January 2023, National Harbor, MD & Online PB - AIAA CY - Reston, Va. ER - TY - JOUR A1 - Blome, Hans-Joachim A1 - Chu, Y. A1 - Hoell, J A1 - Priester, W. T1 - On the observational discrimination of Friedmann-Lemaître models JF - Large Scale Structures of the Universe: Proceedings of the 130th Symposium of the International Astronomical Union, dedicated to the memory of Marc A. Aaronson (1950-1987) held in Balatonfured, Hungary, June 15-20, 1987. Edited by Jean Audouze, Marie-Christine Pelletan and Sandor Szalay. Y1 - 1988 SN - 90-277-2742-2 N1 - International Astronomical Union. Symposium no. 130 SP - 517 PB - Kluwer Academic Publishers CY - Dordrecht ER - TY - CHAP A1 - Baader, Fabian A1 - Keller, Denis A1 - Lehmann, Raphael A1 - Gerber, Lukas A1 - Reiswich, Martin A1 - Dachwald, Bernd A1 - Förstner, Roger T1 - Operating melting probes for ice penetration under sublimation conditions and in reduced gravity on a sounding rocket T2 - Proceedings of the 24th ESA Symposium on European Rocket and Balloon Programmes and related Research Y1 - 2019 SN - 0379-6566 N1 - 24th PAC Symposium 2019 ER - TY - JOUR A1 - Havermann, Marc A1 - Seiler, F. A1 - Boller, F. A1 - Mangold, P. T1 - Operation of the ISL transonic shock tube in a high subsonic flow regime / Seiler, F. ; Havermann, M. ; Boller, F. ; Mangold, P. ; Takayama K. JF - Shock Waves : Proceedings of the 24th International Symposium on Shock Waves Beijing, China July 11-16, 2004 / edited by Z. Jiang Y1 - 2005 SN - 978-3-540-22497-6 SP - 307 EP - 312 PB - Springer CY - Berlin ER - TY - CHAP A1 - Neu, Eugen A1 - Janser, Frank A1 - Khatibi, Akbar A. A1 - Orifici, Adrian C. T1 - Operational modal analysis of a cantilever in a wind tunnel using optical fiber bragg grating sensors T2 - 6th International Operational Modal Analysis Conference. IOMAC´15. 2015 May 12-14 Gijon - Spain Y1 - 2015 U6 - https://doi.org/10.13140/RG.2.1.3753.0324 ER - TY - JOUR A1 - Neu, Eugen A1 - Janser, Frank A1 - Khatibi, Akbar A. A1 - Braun, Carsten A1 - Orifici, Adrian C. T1 - Operational Modal Analysis of a wing excited by transonic flow JF - Aerospace Science and Technology N2 - Operational Modal Analysis (OMA) is a promising candidate for flutter testing and Structural Health Monitoring (SHM) of aircraft wings that are passively excited by wind loads. However, no studies have been published where OMA is tested in transonic flows, which is the dominant condition for large civil aircraft and is characterized by complex and unique aerodynamic phenomena. We use data from the HIRENASD large-scale wind tunnel experiment to automatically extract modal parameters from an ambiently excited wing operated in the transonic regime using two OMA methods: Stochastic Subspace Identification (SSI) and Frequency Domain Decomposition (FDD). The system response is evaluated based on accelerometer measurements. The excitation is investigated from surface pressure measurements. The forcing function is shown to be non-white, non-stationary and contaminated by narrow-banded transonic disturbances. All these properties violate fundamental OMA assumptions about the forcing function. Despite this, all physical modes in the investigated frequency range were successfully identified, and in addition transonic pressure waves were identified as physical modes as well. The SSI method showed superior identification capabilities for the investigated case. The investigation shows that complex transonic flows can interfere with OMA. This can make existing approaches for modal tracking unsuitable for their application to aircraft wings operated in the transonic flight regime. Approaches to separate the true physical modes from the transonic disturbances are discussed. Y1 - 2016 U6 - https://doi.org/10.1016/j.ast.2015.11.032 SN - 1270-9638 VL - 49 SP - 73 EP - 79 PB - Elsevier CY - Amsterdam ER - TY - CHAP A1 - Dachwald, Bernd A1 - Mengali, Giovanni A1 - Quarta, Alessandro A A1 - Macdonald, Malcolm A1 - McInnes, Colin R T1 - Optical solar sail degradation modelling T2 - 1st International Symposium on Solar Sailing N2 - We propose a simple parametric OSSD model that describes the variation of the sail film's optical coefficients with time, depending on the sail film's environmental history, i.e., the radiation dose. The primary intention of our model is not to describe the exact behavior of specific film-coating combinations in the real space environment, but to provide a more general parametric framework for describing the general optical degradation behavior of solar sails. Y1 - 2007 N1 - 1st International Symposium on Solar Sailing 27–29 June 2007, Herrsching, Germany SP - 1 EP - 27 ER - TY - JOUR A1 - Dachwald, Bernd T1 - Optimal Solar Sail Trajectories for Missions to the Outer Solar System JF - Journal of guidance, control, and dynamics. 28 (2005), H. 6 Y1 - 2005 SN - 0162-3192 N1 - 2. ISSN: 0162-3192. - 3. ISSN: 0731-5090 SP - 1187 EP - 1193 ER - TY - JOUR A1 - Dachwald, Bernd T1 - Optimal Solar Sail Trajectories for Missions to the Outer Solar System JF - 22nd AIAA Applied Aerodynamics Conference and Exhibit - AIAA/AAS Astrodynamics Specialist Conference and Exhibit - AIAA Guidance, Navigation, and Control Conference and Exhibit - AIAA Modeling and Simulation Technologies Conference and Exhibit - AIAA Atmospheric Flight Mechanics Conference and Exhibit : 16 - 19 August 2004, Providence, Rhode Island / American Institute of Aeronautics and Astronautics. - (AIAA meeting papers on disc ; 2004,14-15) Y1 - 2004 N1 - American Institute of Aeronautics and Astronautics ; AIAA/AAS Astrodynamics Specialist Conference and Exhibit <2004, Providence, RI> ; AIAA paper number: AIAA-2004-5406 PB - American Inst. of Aeronautics and Astronautics CY - Reston, Va. ER - TY - CHAP A1 - Wahle, Michael T1 - Optimale Auslegung von Schwingungsdämpfern zur Schwingungsberuhigung elastischer Strukturen T2 - Dämpfung von Schwingungen bei Maschinen und Bauwerken : Tagung Nürnberg, 9. u. 10. April 1987. - (VDI-Berichte ; 627) Y1 - 1987 SN - 3-18-090627-8 SP - 355 EP - 373 PB - VDI-Verl. CY - Düsseldorf ER - TY - JOUR A1 - Dachwald, Bernd A1 - Ohndorf, A. A1 - Seboldt, Wolfgang T1 - Optimierung der Lageregelung von Raumfahrzeugen mit Niedrigschubantrieb mittels evolutionärer neuronaler Regler / A. Ohndorf ; B. Dachwald ; W. Seboldt JF - Deutscher Luft- und Raumfahrtkongress 2005 : Friedrichshafen, 26. bis 29. September 2005, Motto: Luft- und Raumfahrt - Grenzen überwinden, Horizonte erweitern / Deutsche Gesellschaft für Luft- und Raumfahrt - Lilienthal-Oberth e.V. (DGLR). [Red.: Peter Brandt (verantwortlich)]. Bd. 3. - (Jahrbuch ... der Deutschen Gesellschaft für Luft- und Raumfahrt Y1 - 2005 N1 - Deutscher Luft- und Raumfahrt-Kongress <2005, Friedrichshafen> ; Deutsche Gesellschaft für Luft- und Raumfahrt - Lilienthal-Oberth ; Dokumentnr: DGLR-2005-224 SP - 1971 EP - 1978 PB - DGLR CY - Bonn ER - TY - BOOK A1 - Funke, Harald T1 - Optimierung und Miniaturisierung der Mikro-Misch-Diffusionsverbrennung von Wasserstoff zur potentiellen Anwendung in einer Ultra-Gasturbine. Schlussbericht. Y1 - 2008 N1 - Förderkennzeichen: 1729X05 PB - Fachhochschule Aachen CY - Aachen ER - TY - CHAP A1 - Schoutetens, Frederic A1 - Dachwald, Bernd A1 - Heiligers, Jeannette T1 - Optimisation of photon-sail trajectories in the alpha-centauri system using evolutionary neurocontrol T2 - 8th ICATT 2021 N2 - With the increased interest for interstellar exploration after the discovery of exoplanets and the proposal by Breakthrough Starshot, this paper investigates the optimisation of photon-sail trajectories in Alpha Centauri. The prime objective is to find the optimal steering strategy for a photonic sail to get captured around one of the stars after a minimum-time transfer from Earth. By extending the idea of the Breakthrough Starshot project with a deceleration phase upon arrival, the mission’s scientific yield will be increased. As a secondary objective, transfer trajectories between the stars and orbit-raising manoeuvres to explore the habitable zones of the stars are investigated. All trajectories are optimised for minimum time of flight using the trajectory optimisation software InTrance. Depending on the sail technology, interstellar travel times of 77.6-18,790 years can be achieved, which presents an average improvement of 30% with respect to previous work. Still, significant technological development is required to reach and be captured in the Alpha-Centauri system in less than a century. Therefore, a fly-through mission arguably remains the only option for a first exploratory mission to Alpha Centauri, but the enticing results obtained in this work provide perspective for future long-residence missions to our closest neighbouring star system. Y1 - 2021 N1 - 8th ICATT (International Conference on Astrodynamics Tools and Techniques), 23 - 25 June 2021, Virtual SP - 1 EP - 15 ER - TY - THES A1 - Börner, Sebastian T1 - Optimization and testing of a low NOx hydrogen fuelled gas turbine Y1 - 2013 N1 - Zugl.: Bruxelles, Université libre, Diss., 2013 PB - Université Libre de Bruxelles CY - Bruxelles ER - TY - THES A1 - Keinz, Jan T1 - Optimization of a Dry Low NOx Micromix Combustor for an Industrial Gas Turbine Using Hydrogen-Rich Syngas Fuel Y1 - 2018 N1 - Dissertation submitted for the degree of Doctor of Engineering Sciences and Technology ; in Cooperation with Aachen university of Applied Sciences, Department Aerospace Technology; Thesis director: Prof. P. Hendrick; Thesis co-director: Prof. H. Funke PB - Université Libre de Bruxelles - Brussels School of Engineering Aero-Thermo-Mechanics CY - Brüssel ER - TY - JOUR A1 - Dachwald, Bernd A1 - Seboldt, Wolfgang T1 - Optimization of Interplanetary Rendezvous Trajectories for Solar Sailcraft Using a Neurocontroller JF - A collection of technical papers / AIAA Astrodynamics Specialist Conference : Monterey, California, 5 - 8 August 2002. - Vol. 2 Y1 - 2002 SN - 1-56347-549-9 N1 - Astrodynamics Specialist Conference <2002, Monterey, Calif.> American Institute of Aeronautics and Astronautics ; AIAA paper number: AIAA-2002-4989 SP - 1263 EP - 1270 PB - American Institute of Aeronautics and Astronautics CY - Reston, Va. ER -