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This paper describes an inexpensive, non-invasive, and highly adaptable surface reconstruction device for opaque liquids. The instrument was developed to study the lateral sloshing of ferrofluids in microgravity as part of the UNOOSA DropTES 2019 StELIUM project. Its design is driven by the geometrical and mechanical constraints imposed by ZARM’s d...
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... representative example consisting on a video camera and a laser line is first depicted in Fig. 2. The line is treated as a set of points, and so the discussion is focused on the reconstruction of point P. Since P is defined by the intersection of the laser position vector and the visual line , the geometrical ...
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... Different areas of research, such as oceanology, 1 spacecraft, 2,3 and spray systems, 4,5 rely on understanding the dynamics of liquid surfaces. In oceanology, small waves created by wind 6,7 as well as tsunamis 8 are analyzed through scaled-up experimental measurements. ...
Analyzing the deformation of liquid surfaces to better understand, for example, wave generation in oceanology or the formation of industrial spray systems, requires a series of three-dimensional snapshots that temporally resolve such events. This requirement is challenging, especially when applied to transient liquid surfaces that deform rapidly. A technique called Fringe Projection-Laser Induced Fluorescence (FP-LIF), developed by the authors, generates three-dimensional surface reconstructions of irregular liquid structures using snapshots recorded via a single camera only. In this article, FP-LIF is associated, for the first time, with a high-speed detection system, allowing the three-dimensional visualization of liquid surface deformation and breakups at a kHz frame rate. The technique is applied here at 20 kHz for imaging the complete development of a wide hollow-cone water spray and analyzing, in detail, the transition from early injection to stabilization. The three-dimensional image series covered a total time window of 300 ms (6000 frames). It is observed during the first 100 ms that the initial liquid jet deforms into a stable tulip shaped sheet. Then, between 100 and 180 ms, the tulip shape gradually grows until its stabilization corresponds to the final conical shaped sheet. Once the stabilization is reached, the fluctuation of the final spray-angle-ranging from 40 to 50 degrees is extracted by post-processing 1000 consecutive three-dimensional images, providing a detailed analysis of the radial symmetry of the spray over time and three-dimensional space. The results provided in this article are relevant for the validation of Computational Fluid Dynamics spray models.
... An exception is the European Space Agency (ESA) Drop Your Thesis! 2017 The Ferros project, that studied the axisymmetric sloshing of water-based ferrofluids when subjected to an inhomogeneous magnetic field in microgravity [39][40][41]. Although the axisymmetric and lateral sloshing of ferrofluids were also studied during the United Nations Office for Outer Space Affairs (UNOOSA) DropTES 2019 experiment StELIUM [42][43][44], statistical significance was not achieved for the axisymmetric modes [45]. Therefore, the configuration of the Drop Your Thesis! 2017 experiment is adopted in this work. ...
... with ⋅ ± = − 0 2 ( ± ) 2 + ± ± (43) and being the external normal vector at . According to Gauss's law, the normal component of the induction field is continuous through ( + = − = ). ...
A coupled ferrohydrodynamic interface-tracking model is introduced for the analysis of the equilibrium, linear stability, and modal response of magnetic liquid interfaces in surface tension-dominated axisymmetric multiphase flows. The incompressible viscous mass and momentum balances are solved together with the steady-state Maxwell equations by following a monolithic solution scheme. The method is fully implicit, allowing to reach a steady-state solution in a single time step. In addition, the time-dependent evolution of the interface subject to variable external inputs can also be simulated. The geometry is particularized for the study of the free surface oscillations of a ferrofluid in a cylindrical tank under the influence of an inhomogeneous magnetic field in microgravity. Five regions are used to discretize the simulation domain, which combines analytical and elliptic mappings. Magnetic field-free results are validated by the literature. The modal response of the fluid-magnetic system agrees with measurements from the European Space Agency (ESA) Drop Your Thesis! 2017 The Ferros experiment and improves previous quasi-analytical estimations. This new framework of analysis can be applied to the study of a wide variety of microfluidic and low-gravity fluid systems.
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... Subsequent publications presented refined numerical models and numerical results of technical relevance [154,[164][165][166][167][168][169][170][171]. The axisymmetric and lateral sloshing of water-based ferrofluids was characterized in microgravity when subjected to an inhomogeneous magnetic field as part of the ESA Drop Your Thesis! 2017 [77,172,173] and UNOOSA DropTES 2019 [174][175][176][177] campaigns reported in Chapter 9. ...
The commercialization of the sub-orbital environment, the ambition to make humans a multi-planetary species, and the urgent need for sustainable space operations are driving the development of a new generation of space systems. The use of electromagnetic forces (and electromagnetism, in general) is proposed in this dissertation to enable mid-distance, contactless actuation and sensing for space technology development. Following this paradigm, two applications are explored: electron-based touchless spacecraft potential sensing, and low-gravity magnetohydrodynamics.
The electron-based touchless potential sensing method was recently introduced to characterize the electrostatic state of non-cooperative objects in GEO and deep space. Applications span from arcing prevention to space debris removal. Although the fundamentals of this approach were studied in previous works, several open questions remained regarding the effect of complex geometries and differential charging on the sensing process. Such questions are here addressed with efficient numerical tools and vacuum chamber experiments, providing key insights into the behavior of realistic spacecraft formations. In addition, new active photoelectron-based sensing strategies are proposed that overcome some of the challenges of previous implementations.
The concept of low-gravity magnetohydrodynamics is also introduced as a way to actuate low-gravity fluid mechanics systems using magnetic forces. The theoretical foundations of the field are established from the analytical, numerical, and experimental perspectives with particular attention to the equilibrium, stability, and modal response of gas-liquid interfaces. Specific features of bubbles and droplets are also explored. Finally, the use of magnetic polarization and Lorentz forces in low-gravity fluid systems is discussed together with some of their applications, which include phase separation, magnetic positive positioning, and low-gravity electrolysis. The development of such technologies is initiated with support from microgravity research campaigns at ZARM's drop tower and Blue Origin's New Shepard suborbital rocket.
... DropTES 2019 StELIUM experiment, whose design is described in Refs. [39][40][41], was subsequently launched at the ...
... Further details on the design and operation of the detection system can be found in Refs. [40,41]. ...
... In the first part of this paper [42], a novel surface reconstruction approach is described and tested on ground. The system correlates the observations of a projected laser pattern with the height of an opaque fluid surface. ...
... The need for an inexpensive, non-invasive, highly adaptable, and reliable surface reconstruction system motivates the design of the SDS in the first part of this paper [42]. Its operation is based on the projection of a laser pattern over the opaque ferrofluid surface and the triangulation of such pattern with camera measurements. ...
... The GoPro Hero 5 Session camera is placed at the center of the structure and works at 4K resolution and 30 fps frame rate. The resulting video measurements are processed by adopting the theoretical framework described in Ref. 42. ...
This paper addresses the operation in microgravity of the surface reconstruction device whose design is detailed in the first part of the manuscript. The system, employed during the drop tower campaign of the UNOOSA DropTES 2019 StELIUM experiment, studies the axisymmetric and lateral oscillations of a ferrofluid solution in microgravity. The free liquid surface is reconstructed in a cylindrical tank and relevant metrics of the magnetic sloshing problem, such as contact angles, hysteresis parameters, natural oscillation frequencies, or damping ratios, are derived. The result is a rich and unique database where several phenomena of scientific and technological interest are reported for the first time. The dependence of the fundamental axisymmetric and lateral modal frequencies with the applied magnetic field is consistent with the literature and past experiments. Although the detection system was designed and built using low-cost hardware, high-quality results are obtained.
