Online Publikations-Server der FH Aachen
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Any Cargo: Das Fahrrad als Hauptverkehrsmittel in der Stadt
No full textDurch die Urbanisierung, wird es in Städten immer enger und der Verkehr nimmt zu. Das hat hohe Emissionen und Platzmangel zur Folge. In der Masterarbeit wurde die Abhängigkeit zum Auto in der Stadt hinterfragt und ein Konzept erarbeitet, welches die Autonutzung und den Autobesitz ablöst. Dabei entstand ein neuer Fahrradanhänger, der eine multifunktionale Nutzung zulässt und einen elektrischen Antrieb besitzt. Dadurch bietet er einen komfortablen Support im Alltag. Zudem wurde ein Geschäftskonzept entwickelt, welches ermöglicht, den Anhänger mit einem digitalen Ausleihsystem unter Nachbarn oder Freunden zu teilen. Ein wichtiges Kriterium für das Produkt und den Service war, dass die Mobilität der Zukunft nicht nur nachhaltig sein soll, sondern auch Laune machen muss
Experimental and numerical investigation on the effect of pressure on micromix hydrogen combustion
No full textThe micromix (MMX) combustion concept is a DLN gas turbine combustion technology designed for high hydrogen content fuels. Multiple non-premixed miniaturized flames based on jet in cross-flow (JICF) are inherently safe against flashback and ensure a stable operation in various operative conditions.
The objective of this paper is to investigate the influence of pressure on the micromix flame with focus on the flame initiation point and the NOx emissions. A numerical model based on a steady RANS approach and the Complex Chemistry model with relevant reactions of the GRI 3.0 mechanism is used to predict the reactive flow and NOx emissions at various pressure conditions. Regarding the turbulence-chemical interaction, the Laminar Flame Concept (LFC) and the Eddy Dissipation Concept (EDC) are compared. The numerical results are validated against experimental results that have been acquired at a high pressure test facility for industrial can-type gas turbine combustors with regard to flame initiation and NOx emissions.
The numerical approach is adequate to predict the flame initiation point and NOx emission trends. Interestingly, the flame shifts its initiation point during the pressure increase in upstream direction, whereby the flame attachment shifts from anchoring behind a downstream located bluff body towards anchoring directly at the hydrogen jet. The LFC predicts this change and the NOx emissions more accurately than the EDC. The resulting NOx correlation regarding the pressure is similar to a non-premixed type combustion configuration
Virgin passive colon biomechanics and a literature review of active contraction constitutive models
No full textThe objective of this paper is to present our findings on the biomechanical aspects of the virgin passive anisotropic hyperelasticity of the porcine colon based on equibiaxial tensile experiments. Firstly, the characterization of the intestine tissues is discussed for a nearly incompressible hyperelastic fiber-reinforced Holzapfel–Gasser–Ogden constitutive model in virgin passive loading conditions. The stability of the evaluated material parameters is checked for the polyconvexity of the adopted strain energy function using positive eigenvalue constraints of the Hessian matrix with MATLAB. The constitutive material description of the intestine with two collagen fibers in the submucosal and muscular layer each has been implemented in the FORTRAN platform of the commercial finite element software LS-DYNA, and two equibiaxial tensile simulations are presented to validate the results with the optical strain images obtained from the experiments. Furthermore, this paper also reviews the existing models of the active smooth muscle cells, but these models have not been computationally studied here. The review part shows that the constitutive models originally developed for the active contraction of skeletal muscle based on Hill’s three-element model, Murphy’s four-state cross-bridge chemical kinetic model and Huxley’s sliding-filament hypothesis, which are mainly used for arteries, are appropriate for numerical contraction numerical analysis of the large intestine
Unsteady shallow meandering flows in rectangular reservoirs: a modal analysis of URANS modelling
No full textShallow flows are common in natural and human-made environments. Even for simple rectangular shallow reservoirs, recent laboratory experiments show that the developing flow fields are particularly complex, involving large-scale turbulent structures. For specific combinations of reservoir size and hydraulic conditions, a meandering jet can be observed. While some aspects of this pseudo-2D flow pattern can be reproduced using a 2D numerical model, new 3D simulations, based on the unsteady Reynolds-Averaged Navier-Stokes equations, show consistent advantages as presented herein. A Proper Orthogonal Decomposition was used to characterize the four most energetic modes of the meandering jet at the free surface level, allowing comparison against experimental data and 2D (depth-averaged) numerical results. Three different isotropic eddy viscosity models (RNG k-ε, k-ε, k-ω) were tested. The 3D models accurately predicted the frequency of the modes, whereas the amplitudes of the modes and associated energy were damped for the friction-dominant cases and augmented for non-frictional ones. The performance of the three turbulence models remained essentially similar, with slightly better predictions by RNG k-ε model in the case with the highest Reynolds number. Finally, the Q-criterion was used to identify vortices and study their dynamics, assisting on the identification of the differences between: i) the three-dimensional phenomenon (here reproduced), ii) its two-dimensional footprint in the free surface (experimental observations) and iii) the depth-averaged case (represented by 2D models)
Solar sail dynamics and control
No full textSolar sails are large and lightweight reflective structures that are propelled by solar radiation pressure. This chapter covers their orbital and attitude dynamics and control. First, the advantages and limitations of solar sails are discussed and their history and development status is outlined. Because the dynamics of solar sails is governed by the (thermo-)optical properties of the sail film, the basic solar radiation pressure force models have to be described and compared before parameters to measure solar sail performance can be defined. The next part covers the orbital dynamics of solar sails for heliocentric motion, planetocentric motion, and motion at Lagrangian equilibrium points. Afterwards, some advanced solar radiation pressure force models are described, which allow to quantify the thrust force on solar sails of arbitrary shape, the effects of temperature, of light incidence angle, of surface roughness, and the effects of optical degradation of the sail film in the space environment. The orbital motion of a solar sail is strongly coupled to its rotational motion, so that the attitude control of these soft and flexible structures is very challenging, especially for planetocentric orbits that require fast attitude maneuvers. Finally, some potential attitude control methods are sketched and selection criteria are given
Performance requirements for near-term interplanetary solar sailcraft missions
No full textSolar sailcraft provide a wide range of opportunities for high-energy low-cost missions. To date, most mission studies require a rather demanding performance that will not be realized by solar sailcraft of the first generation.
However, even with solar sailcraft of moderate performance, scientifically relevant missions are feasible. This is demonstrated with a Near Earth Asteroid sample return mission and various planetary rendezvous missions
Mission performance evaluation for solar sails using a refined SRP force model with variable optical coefficients
No full textSolar sails provide ignificant advantages over other low-thrust propulsion systems because they produce thrust by the momentum exchange from solar radiation pressure (SRP) and thus do not consume any propellant.The force exerted on a very thin sail foil basically depends on the light incidence angle. Several analytical SRP force models that describe the SRP force acting on the sail have been established since the 1970s. All the widely used models use constant optical force coefficients of the reflecting sail material. In 2006,MENGALI et al. proposed a refined SRP force model that takes into account the dependancy of the force coefficients on the light incident angle,the sail’s distance from the sun (and thus the sail emperature) and the surface roughness of the sail material [1]. In this paper, the refined SRP force model is compared to the previous ones in order to identify the potential impact of the new model on the predicted capabilities of solar sails in performing low-cost interplanetary space missions. All force models have been implemented within InTrance, a global low-thrust trajectory optimization software utilizing evolutionary neurocontrol [2]. Two interplanetary rendezvous missions, to Mercury and the near-Earth asteroid 1996FG3, are investigated. Two solar sail performances in terms of characteristic acceleration are examined for both scenarios, 0.2 mm/s2 and 0.5 mm/s2, termed “low” and “medium” sail performance. In case of the refined SRP model, three different values of surface roughness are chosen, h = 0 nm, 10 nm and 25 nm. The results show that the refined SRP force model yields shorter transfer times than the standard model
Large lightweight deployable structures for planetary defence: solar sail propulsion, solar concentrator payloads, large-scale photovoltaic power
No full textRadiation pressure force model for an ideal laser-enhanced solar sail
No full textThe concept of a laser-enhanced solar sail is introduced and the radiation pressure force model for an ideal laser-enhanced solar sail is derived. A laser-enhanced solar sail is a “traditional” solar sail that is, however, not solely propelled by solar radiation, but additionally by a laser beam that illuminates the sail. The additional laser radiation pressure increases the sail's propulsive force and can give, depending on the location of the laser source, more control authority over the direction of the solar sail’s propulsive force vector. This way, laser-enhanced solar sails may augment already existing solar sail mission concepts and make novel mission concepts feasible
Music of the Spheres : der Klang der Planeten
No full text"Die Bachelorarbeit “Music of the Spheres” soll wissenschaftliche und künstlerische Elemente zum Thema “Klang der Planeten” in Form einer populärwissenschaftlichen Publikation versammeln. Seit Beginn der Menschheit fasziniert uns der Blick in den nächtlichen Sternenhimmel. Einher geht die Sehnsucht des Unbekannten, die unsere Fantasie beflügelt. Als auf die Erde gebundenen Lebewesens treibt uns der Drang, mehr über das Universum da draußen herauszufinden. Dieses Spannungsfeld zwischen Wissensdrang und Fantasie ist eine interessante Grundlage für die geplante Bachelorarbeit.
In der Bachelorarbeit sollen unsere Emotionen mit wissenschaftlichen Erkenntnissen verbunden werden. Für das menschliche Ohr ist die Klangwelt des Weltalls, verursacht durch die sich bewegenden Planeten, ohne Hilfsmittel nicht hörbar. Nach unseren bekannten physikalischen Erkenntnissen ist es im Weltraum komplett still, aufgrund des im All vorherrschenden Vakuums. Der Schall kann sich nicht wie auf der Erde über Schallwellen ausbreiten. In der Publikation soll der Klang der Planeten beschrieben bzw. dargestellt werden. Die wissenschaftshistorische Dimension soll aufgezeigt werden. So hat man sich zum Beispiel in der Antike musikalische und lyrische Bilder davon gemacht, wie sich der Klang des Weltalls und der Planeten anhören könnte. Weiterhin faszinierte diese Frage Künstler unterschiedlicher Epochen und Stilrichtungen, und ist bis heute ein Thema das Anlaß zu künstlerischem Schaffen gibt.
In Form einer Printpublikation soll die Bachelorarbeit historische Thesen und aktuelle wissenschaftliche Texte, Forschungsberichte und Klangdokumente zusammenbringen, literarische und musikalische Umsetzungen zum Thema aufzeigen, und mit wissenschaftlichem und künstlerisch-interpretativem Bildmaterial vereinen.
Um das Thema visuell zu veranschaulichen, sollen die Texte durch Bilder und Siebdrucke ergänzt werden. Selbst erstellte Siebdruck Experimente könnten mit- und ineinander verknüpft werden. Die Publikation weißt ein durchgehendes Gestaltungskonzept auf, welches Texte, Illustrationen und Bildmaterial als Einheit verknüpfen und wiedererkennbar machen. Ebenfalls ist die Auswahl der verwendeten Materialien und Verarbeitungstechniken, wie Druck, Bindung und Papier zu beachten. Neben dem Text- und Bildmaterial werden Klang-Beispiele eingebunden durch QR Codes. So kann der Leser den QR Code der Siebdrucke scannen, um den von der US-Weltraumorganisation NASA erstellten Klang des Planeten anzuhören. Oder ausgehend von wissenschaftlichem Bildmaterial kann der Leser per Scan eine musikalische Partition zum entsprechenden Planeten anhören.
Die angestrebte Zielgruppe besteht aus Wissenschafts- und Designaffinen Personen, die sich insbesondere für den Weltraum interessieren. Entsprechend soll die Gestaltung informativ und gleichzeitig zeitgenössisch sein, um Aufmerksamkeit zu erregen. Mit dem Inhalt der Publikation soll dem Leser gleichzeitig auch der Klang der Planeten hörbar zugänglich gemacht werden