TY - JOUR A1 - Kezerashvili, Roman Ya A1 - Dachwald, Bernd T1 - Preface: Solar sailing: Concepts, technology, and missions II JF - Advances in Space Research Y1 - 2021 U6 - https://doi.org/10.1016/j.asr.2021.01.037 SN - 0273-1177 VL - 67 IS - 9 SP - 2559 EP - 2560 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Thoma, Andreas A1 - Thomessen, Karolin A1 - Gardi, Alessandro A1 - Fisher, A. A1 - Braun, Carsten T1 - Prioritising paths: An improved cost function for local path planning for UAV in medical applications JF - The Aeronautical Journal N2 - Even the shortest flight through unknown, cluttered environments requires reliable local path planning algorithms to avoid unforeseen obstacles. The algorithm must evaluate alternative flight paths and identify the best path if an obstacle blocks its way. Commonly, weighted sums are used here. This work shows that weighted Chebyshev distances and factorial achievement scalarising functions are suitable alternatives to weighted sums if combined with the 3DVFH* local path planning algorithm. Both methods considerably reduce the failure probability of simulated flights in various environments. The standard 3DVFH* uses a weighted sum and has a failure probability of 50% in the test environments. A factorial achievement scalarising function, which minimises the worst combination of two out of four objective functions, reaches a failure probability of 26%; A weighted Chebyshev distance, which optimises the worst objective, has a failure probability of 30%. These results show promise for further enhancements and to support broader applicability. KW - Path planning KW - Cost function KW - Multi-objective optimization Y1 - 2023 U6 - https://doi.org/10.1017/aer.2023.68 SN - 0001-9240 (Print) SN - 2059-6464 (Online) IS - First View SP - 1 EP - 18 PB - Cambridge University Press CY - Cambridge ER - TY - JOUR A1 - Havermann, Marc A1 - Seiler, F. A1 - Georges, A. A1 - Srulijes, J. T1 - Progress in Doppler picture velocimetry (DPV) / Seiler, F. ; George, A. ; Srulijes, J. ; Havermann, M. JF - Experiments in Fluids. 44 (2008), H. 3 Y1 - 2008 SN - 1432-1114 SP - 389 EP - 395 PB - - ER - TY - JOUR A1 - Blome, Hans-Joachim A1 - Seboldt, Wolfgang A1 - Dachwald, Bernd A1 - Richter, Lutz T1 - Proposal for an integrated European Space Exploration Study JF - Space Debris and Space Traffic Management Symposium 2004 : proceedings of the International Academy of Astronautics Space Debris and Space Traffic Management Symposium, held in conjunction with the 55th International Astronautical Congress (IAC), October 4 - 8, 2004, Vancouver, British Columbia, Canada / ed. by Joerg Bendisch Y1 - 2004 SN - 0-87703-523-7 N1 - Proceedings IAC-2004-IAA, 3.6.1.06; Space Debris and Space Traffic Management Symposium <2004, Vancouver, British Columbia> ; International Academy of Astronautics PB - Univelt CY - San Diego, Calif. ER - TY - JOUR A1 - Blome, Hans-Joachim A1 - Mashhoon, B. T1 - Quasi-normal oscillations of a Schwarzschild black hole JF - Physics Letters A. 100 (1984), H. 5 Y1 - 1984 SN - 0375-9601 SP - 231 EP - 234 ER - TY - JOUR A1 - Christen, Marc A1 - Kowalski, Julia A1 - Bartelt, Perry T1 - RAMMS: Numerical simulation of dense snow avalanches in three-dimensional terrain JF - Cold Regions Science and Technology N2 - Numerical avalanche dynamics models have become an essential part of snow engineering. Coupled with field observations and historical records, they are especially helpful in understanding avalanche flow in complex terrain. However, their application poses several new challenges to avalanche engineers. A detailed understanding of the avalanche phenomena is required to construct hazard scenarios which involve the careful specification of initial conditions (release zone location and dimensions) and definition of appropriate friction parameters. The interpretation of simulation results requires an understanding of the numerical solution schemes and easy to use visualization tools. We discuss these problems by presenting the computer model RAMMS, which was specially designed by the SLF as a practical tool for avalanche engineers. RAMMS solves the depth-averaged equations governing avalanche flow with accurate second-order numerical solution schemes. The model allows the specification of multiple release zones in three-dimensional terrain. Snow cover entrainment is considered. Furthermore, two different flow rheologies can be applied: the standard Voellmy–Salm (VS) approach or a random kinetic energy (RKE) model, which accounts for the random motion and inelastic interaction between snow granules. We present the governing differential equations, highlight some of the input and output features of RAMMS and then apply the models with entrainment to simulate two well-documented avalanche events recorded at the Vallée de la Sionne test site. KW - RAMMS KW - snow KW - avalanche Y1 - 2010 U6 - https://doi.org/10.1016/j.coldregions.2010.04.005 SN - 1872-7441 VL - 63 IS - 1-2 SP - 1 EP - 14 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Götten, Falk A1 - Havermann, Marc A1 - Braun, Carsten A1 - Gomez, Francisco A1 - Bil, Cees T1 - RANS Simulation Validation of a Small Sensor Turret for UAVs JF - Journal of Aerospace Engineering N2 - Recent Unmanned Aerial Vehicle (UAV) design procedures rely on full aircraft steady-state Reynolds-Averaged-Navier-Stokes (RANS) analyses in early design stages. Small sensor turrets are included in such simulations, even though their aerodynamic properties show highly unsteady behavior. Very little is known about the effects of this approach on the simulation outcomes of small turrets. Therefore, the flow around a model turret at a Reynolds number of 47,400 is simulated with a steady-state RANS approach and compared to experimental data. Lift, drag, and surface pressure show good agreement with the experiment. The RANS model predicts the separation location too far downstream and shows a larger recirculation region aft of the body. Both characteristic arch and horseshoe vortex structures are visualized and qualitatively match the ones found by the experiment. The Reynolds number dependence of the drag coefficient follows the trend of a sphere within a distinct range. The outcomes indicate that a steady-state RANS model of a small sensor turret is able to give results that are useful for UAV engineering purposes but might not be suited for detailed insight into flow properties. Y1 - 2019 U6 - https://doi.org/10.1061/(ASCE)AS.1943-5525.0001055 SN - 1943-5525 VL - 32 IS - 5 PB - ASCE CY - New York ER - TY - JOUR A1 - Dachwald, Bernd A1 - Mengali, Giovanni A1 - Quarta, Alessandro A. A1 - Circi, Christian T1 - Refined Solar Sail Force Model with Mission Application / Giovanni Mengali ; Alessandro A. Quarta , Christian Circi ; Bernd Dachwald JF - Journal of Guidance, Control, and Dynamics. 30 (2007), H. 2 Y1 - 2007 SN - 0162-3192 N1 - 2. ISBN: 0731-5090 SP - 512 EP - 520 ER - TY - JOUR A1 - Mertens, Josef T1 - Required technologies for supersonic aircraft JF - Fluid dynamics research on supersonic aircraft : this report is a compilation of the edited proceedings of the special course on "Fluid dynamic research on supersonic aircraft" held at the Karman Institute for Fluid Dynamics (VKI) in Rhode-Saint-Genese, Belgium, 25-29 May 1998 Y1 - 1998 SN - 92-837-1007-X N1 - (RTO educational notes ; 4) SP - 5.1 EP - 5.16 PB - Research and Technology Organization CY - Neuilly-sur-Seine ER - TY - JOUR A1 - Smith, Wayne A1 - Kotliar, Konstantin A1 - Lammertyn, Leandi A1 - Ramoshaba, Nthai E. A1 - Vilser, Walthard A1 - Huisman, Hugo W. A1 - Schutte, Aletta E. T1 - Retinal vessel caliber and caliber responses in true normotensive black and white adults: The African-PREDICT study JF - Microvascular Research N2 - Purpose Globally, a detrimental shift in cardiovascular disease risk factors and a higher mortality level are reported in some black populations. The retinal microvasculature provides early insight into the pathogenesis of systemic vascular diseases, but it is unclear whether retinal vessel calibers and acute retinal vessel functional responses differ between young healthy black and white adults. Methods We included 112 black and 143 white healthy normotensive adults (20–30 years). Retinal vessel calibers (central retinal artery and vein equivalent (CRAE and CRVE)) were calculated from retinal images and vessel caliber responses to flicker light induced provocation (FLIP) were determined. Additionally, ambulatory blood pressure (BP), anthropometry and blood samples were collected. Results The groups displayed similar 24 h BP profiles and anthropometry (all p > .24). Black participants demonstrated a smaller CRAE (158 ± 11 vs. 164 ± 11 MU, p < .001) compared to the white group, whereas CRVE was similar (p = .57). In response to FLIP, artery maximal dilation was greater in the black vs. white group (5.6 ± 2.1 vs. 3.3 ± 1.8%; p < .001). Conclusions Already at a young age, healthy black adults showed narrower retinal arteries relative to the white population. Follow-up studies are underway to show if this will be related to increased risk for hypertension development. The reason for the larger vessel dilation responses to FLIP in the black population is unclear and warrants further investigation. Y1 - 2020 U6 - https://doi.org/10.1016/j.mvr.2019.103937 SN - 0026-2862 VL - 128 IS - Article 103937 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Wittmann, Klaus A1 - Feuerbacher, B. A1 - Ulamec, S. A1 - Rosenbauer, H. (u.a.) T1 - Rosetta Lander - In Situ Characterisation of a Comet Nucleus JF - Acta Astronautica. 45 (1999), H. 4-9 Y1 - 1999 SN - 0094-5765 SP - 389 EP - 395 ER - TY - JOUR A1 - Wittmann, Klaus A1 - Ulamec, S. A1 - Feuerbacher, B. A1 - Rosenbauer, H. (u.a.) T1 - Rosetta Lander - In Situ Investigation of a Cometary Nucleus JF - Lunar and Planetary Science. 28 (1997) Y1 - 1997 SN - 0270-9511 N1 - Proceedings of the 28th Annual Lunar and Planetary Science Conference, March 17-21, 1997, Houston, Texas SP - 1461 EP - 1462 ER - TY - JOUR A1 - Bühler, Yves A1 - Christen, Marc A1 - Kowalski, Julia A1 - Bartelt, Perry T1 - Sensitivity of snow avalanche simulations to digital elevation model quality and resolution JF - Annals of Glaciology N2 - Digital elevation models (DEMs), represent the three-dimensional terrain and are the basic input for numerical snow avalanche dynamics simulations. DEMs can be acquired using topographic maps or remote-sensing technologies, such as photogrammetry or lidar. Depending on the acquisition technique, different spatial resolutions and qualities are achieved. However, there is a lack of studies that investigate the sensitivity of snow avalanche simulation algorithms to the quality and resolution of DEMs. Here, we perform calculations using the numerical avalance dynamics model RAMMS, varying the quality and spatial resolution of the underlying DEMs, while holding the simulation parameters constant. We study both channelized and open-terrain avalanche tracks with variable roughness. To quantify the variance of these simulations, we use well-documented large-scale avalanche events from Davos, Switzerland (winter 2007/08), and from our large-scale avalanche test site, Valĺee de la Sionne (winter 2005/06). We find that the DEM resolution and quality is critical for modeled flow paths, run-out distances, deposits, velocities and impact pressures. Although a spatial resolution of ~25 m is sufficient for large-scale avalanche modeling, the DEM datasets must be checked carefully for anomalies and artifacts before using them for dynamics calculations. KW - snow KW - avalanche Y1 - 2011 SN - 1727-5644 VL - 52 IS - 58 SP - 72 EP - 80 PB - Cambridge University Press CY - Cambridge ER - TY - JOUR A1 - Kowalski, Julia A1 - McElwaine, Jim N. T1 - Shallow two-component gravity-driven flows with vertical variation JF - Journal of Fluid Mechanics Y1 - 2013 SN - 0022-1120 VL - 714 SP - 434 EP - 462 PB - Cambridge Univ. Press CY - Cambridge ER - TY - JOUR A1 - Havermann, Marc A1 - Ende, H. A1 - Seiler, F. A1 - Schwenzer, M. T1 - Shock tunnel measurement of the interaction amplification factor for a hot gas side jet in a supersonic cross flow / Havermann, M. ; Ende, H. ; Seiler, F. ; Schwenzer, M. 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 - 113 EP - 118 PB - Springer CY - Berlin ER - TY - JOUR A1 - Thoma, Andreas A1 - Ravi, Sridhar T1 - Significance of parallel computing on the performance of Digital Image Correlation algorithms in MATLAB N2 - Digital Image Correlation (DIC) is a powerful tool used to evaluate displacements and deformations in a non-intrusive manner. By comparing two images, one of the undeformed reference state of a specimen and another of the deformed target state, the relative displacement between those two states is determined. DIC is well known and often used for post-processing analysis of in-plane displacements and deformation of specimen. Increasing the analysis speed to enable real-time DIC analysis will be beneficial and extend the field of use of this technique. Here we tested several combinations of the most common DIC methods in combination with different parallelization approaches in MATLAB and evaluated their performance to determine whether real-time analysis is possible with these methods. To reflect improvements in computing technology different hardware settings were also analysed. We found that implementation problems can reduce the efficiency of a theoretically superior algorithm such that it becomes practically slower than a suboptimal algorithm. The Newton-Raphson algorithm in combination with a modified Particle Swarm algorithm in parallel image computation was found to be most effective. This is contrary to theory, suggesting that the inverse-compositional Gauss-Newton algorithm is superior. As expected, the Brute Force Search algorithm is the least effective method. We also found that the correct choice of parallelization tasks is crucial to achieve improvements in computing speed. A poorly chosen parallelisation approach with high parallel overhead leads to inferior performance. Finally, irrespective of the computing mode the correct choice of combinations of integerpixel and sub-pixel search algorithms is decisive for an efficient analysis. Using currently available hardware realtime analysis at high framerates remains an aspiration. Y1 - 2019 SP - 1 EP - 17 ER - TY - JOUR A1 - Dachwald, Bernd A1 - Wi, Bong T1 - Solar Sail Kinetic Energy Impactor Trajectory Optimization for an Asteroid-Deflection Mission JF - Journal of Spacecraft and Rockets. 44 (2007), H. 4 Y1 - 2007 SN - 0022-4650 N1 - 2. ISSN: 1533-6794 SP - 755 EP - 764 ER - TY - JOUR A1 - Dachwald, Bernd A1 - Seboldt, Wolfgang A1 - Lämmerzahl, W. T1 - Solar Sail Propulsion: An Enabling Technology for Fundamental Physics Missions JF - Lasers, Clocks and Drag Free Control : Exploration of Relativistic Gravity in Space / by Hansjörg Dittus ..., eds. - ( Astrophysics and Space Science Library ; 349) Y1 - 2008 SN - 978-3-540-34376-9 SP - 379 EP - 398 PB - Springer CY - Berlin [u.a.] ER - TY - JOUR A1 - Dachwald, Bernd A1 - Wie, Bong T1 - Solar Sail Trajectory Optimization for Intercepting, Impacting, and Deflecting Near-Earth Asteroids JF - AIAA Guidance, Navigation and Control Conference and Exhibit - AIAA Modeling and Simulation Technologies Conference and Exhibit - AIAA Atmospheric Flight Mechanics Conference and Exhibit : [San Francisco, California, 15 - 18 August 2005 ; papers]. - (AIAA meeting papers on disc ; [10.]2005,16-17) Y1 - 2005 SN - 1-56347-765-3 N1 - American Institute of Aeronautics and Astronautics ; AIAA Guidance, Navigation, and Control Conference and Exhibit <2005, San Francisco, Calif.> ; AIAA paper number: AIAA-2006-6176 PB - American Institute of Aeronautics and Astronautics CY - Reston, Va. ER - TY - JOUR A1 - Dachwald, Bernd A1 - Ohndorf, A. A1 - Wie, Bong T1 - Solar Sail Trajectory Optimization for the Solar Polar Imager (SPI) Mission JF - AIAA Guidance, Navigation, and Control Conference & Exhibit - AIAA Atmospheric Flight Mechanics Conference & Exhibit - AIAA Modeling and Simulation Technologies Conference & Exhibit - AIAA/AAS Astrodynamics Specialist Conference & Exhibit : [21 - 24 August 2006, Keystone, Colorado ; papers]. - (AIAA meeting papers on disc ; [11.]2006,19-20 ) Y1 - 2006 SN - 1-56347-802-1 N1 - American Institute of Aeronautics and Astronautics ; American Astronautical Society ; AIAA/AAS Astrodynamics Specialist Conference & Exhibit <2006, Keystone, Colo.> ; AIAA paper number: AIAA-2006-6177 PB - American Institute of Aeronautics and Astronautics CY - Reston, Va. ER -