10 research outputs found
The Suborbital Particle Aggregation and Collision Experiment (SPACE): Studying the Collision Behavior of Submillimeter-Sized Dust Aggregates on the Suborbital Rocket Flight REXUS 12
The Suborbital Particle Aggregation and Collision Experiment (SPACE) is a
novel approach to study the collision properties of submillimeter-sized, highly
porous dust aggregates. The experiment was designed, built and carried out to
increase our knowledge about the processes dominating the first phase of planet
formation. During this phase, the growth of planetary precursors occurs by
agglomeration of micrometer-sized dust grains into aggregates of at least
millimeters to centimeters in size. However, the formation of larger bodies
from the so-formed building blocks is not yet fully understood. Recent
numerical models on dust growth lack a particular support by experimental
studies in the size range of submillimeters, because these particles are
predicted to collide at very gentle relative velocities of below 1 cm/s that
can only be achieved in a reduced-gravity environment.
The SPACE experiment investigates the collision behavior of an ensemble of
silicate-dust aggregates inside several evacuated glass containers which are
being agitated by a shaker to induce the desired collisions at chosen
velocities. The dust aggregates are being observed by a high-speed camera,
allowing for the determination of the collision properties of the
protoplanetary dust analog material. The data obtained from the suborbital
flight with the REXUS (Rocket Experiments for University Students) 12 rocket
will be directly implemented into a state-of-the-art dust growth and collision
model
Determination of measurement uncertainty by Monte Carlo simulation
Modern coordinate measurement machines (CMM) are universal tools to measure
geometric features of complex three-dimensional workpieces. To use them as
reliable means of quality control, the suitability of the device for the
specific measurement task has to be proven. Therefore, the ISO 14253 standard
requires, knowledge of the measurement uncertainty and, that it is in
reasonable relation with the specified tolerances. Hence, the determination of
the measurement uncertainty, which is a complex and also costly task, is of
utmost importance. The measurement uncertainty is usually influenced by several
contributions of various sources. Among those of the machine itself, e.g.,
guideway errors and the influence of the probe and styli play an important
role. Furthermore, several properties of the workpiece, such as its form
deviations and surface roughness, have to be considered. Also the environmental
conditions, i.e., temperature and its gradients, pressure, relative humidity
and others contribute to the overall measurement uncertainty. Currently, there
are different approaches to determine task-specific measurement uncertainties.
This work reports on recent advancements extending the well-established method
of PTB's Virtual Coordinate Measuring Machine (VCMM) to suit present-day needs
in industrial applications. The VCMM utilizes numerical simulations to
determine the task-specific measurement uncertainty incorporating broad
knowledge about the contributions of, e.g., the used CMM, the environment and
the workpiece
Microgravity experiments on the collisional behavior of Saturnian ring particles
In this paper we present results of two novel experimental methods to
investigate the collisional behavior of individual macroscopic icy bodies. The
experiments reported here were conducted in the microgravity environments of
parabolic flights and the Bremen drop tower facility. Using a cryogenic
parabolic-flight setup, we were able to capture 41 near-central collisions of
1.5-cm-sized ice spheres at relative velocities between 6 and . The analysis of the image sequences provides a uniform distribution
of coefficients of restitution with a mean value of and values ranging from to 0.84. Additionally, we
designed a prototype drop tower experiment for collisions within an ensemble of
up to one hundred cm-sized projectiles and performed the first experiments with
solid glass beads. We were able to statistically analyze the development of the
kinetic energy of the entire system, which can be well explained by assuming a
granular `fluid' following Haff's law with a constant coefficient of
restitution of . We could also show that the setup is
suitable for studying collisions at velocities of
appropriate for collisions between particles in Saturn's dense main rings.Comment: Accepted for publication in the Icarus Special Issue "Cassini at
Saturn
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Experimental studies on the aggregation properties of ice and dust in planet-forming regions
To investigate the second stage of formation of protoplanets up to kilometre size which is still not understood, we built a setup for collision experiments with millimetre-sized, highly porous dust aggregates. The experiments, which were successfully conducted at ambient temperature during ESA’s 45th Parabolic Flight Campaign, are the first in a series of at least three parabolic flight campaigns. The recent experiment probed the sticking and collision behaviour of dust aggregates (composed of 1.5 μm-sized monodisperse SiO 2 grains) from which planetesimals and cometary nuclei are considered to have formed. In the parabolic flights, pairs of fragile dust aggregates were collided under microgravity conditions at relative velocities between � 25 cm/ s and � 40 cm/s using a set of pistons driven at constant acceleration. Additionally, fragile aggregates were impacted on a dusty target screen, simulating protoplanetary collisions with larger bodies. The collision events happened at random impact angle and were recorded by ESA’s IMPACT Camera and Digital Recording System, a high–speed, high–resolution digital camera.
The majority of both the particle-target and aggregate-aggregate collisions showed a quasi-elastic rebounding behaviour. Whereas � 10% of the particle-target collisions
resulted in sticking (of sub-millimetre-sized fragments only), the other key effect in � 10% of the aggregate-aggregate collisions was fragmentation. The measured coefficient of
restitution for the bouncing collisions indicates that the residual translational energy is � 5% of the primal energy of the aggregates’ motion for central collisions and increases
with increasing impact parameter.
During future Parabolic Flight Campaigns, the experimental work will be extended to collisions of dust aggregates at lower temperatures (80 − 220 K) and of solid ice particles and icy aggregates at cryogenic temperatures (below � 140 K) corresponding to the conditions found in the outer solar nebula at 5 − 30 AU
Methodology to Evaluate the Performance of Portable Photogrammetry for Large-Volume Metrology
The increased relevance of large-volume metrology (LVM) in industrial applications entails certain challenges: measurements must be cost-efficient and the technologies must be easy to use while ensuring accuracy and reliability. Portable photogrammetry shows great potential to overcome such challenges, but industrial users do not yet rely on its accuracy for large scenarios (3 to 64 m), especially when mass-market cameras are not conceived of as industrial metrology instruments. Furthermore, the measurement results might also depend on the operator’s skills and knowledge of the key process variables. In this work, a methodology was designed so that the measurement uncertainty of portable photogrammetry can be evaluated under controlled conditions for LVM. To do so, PTB’s reference wall, which was designed to assess laser-based methods applied to large volumes, was used as a reference artefact to study the measurement performance under different conditions, enabling an analysis of the relative influence of two process variables: the spatial arrangement of the optical instruments on the scene, and the relative camera poses for an accurate triangulation. According to these variables, different measuring conditions were designed (Monte Carlo analysis), and experimentally evaluated and reported (LME, length measuring errors), analysing the performance figures expected from both unskilled and expert users
GUM-Compliant Uncertainty Evaluation Using Virtual Experiments
A virtual experiment simulates a real measurement process by means of a numerical model. The numerical model produces virtual data whose properties reflect those of the data observed in the real experiment. In this work, we explore how the results of a virtual experiment can be employed in the context of uncertainty evaluation for a corresponding real experiment. The uncertainty evaluation was based on the Guide to the Expression of Uncertainty in Measurement (GUM), which defines the de facto standard for uncertainty evaluation in metrology. We show that, under specific assumptions about model structure and variance of the data, virtual experiments in combination with a Monte Carlo method lead to an uncertainty evaluation for the real experiment that is in line with Supplement 1 to the GUM. In the general case, a GUM-compliant uncertainty evaluation in the context of a real experiment can no longer be based on a corresponding virtual experiment in a simple way. Nevertheless, virtual experiments are still useful in order to increase the reliability of an uncertainty analysis. Simple generic examples as well the case study of a virtual coordinate measuring machine are presented to illustrate the treatment