1,720,976 research outputs found
A parametric study for the design of an optimized ultrasonic-percussive planetary drill tool
Full text linkTraditional rotary drilling for planetary rock sampling, in situ analysis, and sample return are challenging because the axial force and holding torque requirements are not necessarily compatible with lightweight spacecraft architectures in low-gravity environments. This paper seeks to optimize an ultrasonic percussive drill tool to achieve rock penetration with lower reacted force requirements, with a strategic view toward building an ultrasonic planetary core drill (UPCD) device. The UPCD is a descendant of the ultrasonic/sonic driller/corer technique. In these concepts, a transducer and horn (typically resonant at around 20 kHz) are used to excite a toroidal free mass that oscillates chaotically between the horn tip and drill base at lower frequencies (generally between 10 Hz and 1 kHz). This creates a series of stress pulses that is transferred through the drill bit to the rock surface, and while the stress at the drill-bit tip/rock interface exceeds the compressive strength of the rock, it causes fractures that result in fragmentation of the rock. This facilitates augering and downward progress. In order to ensure that the drill-bit tip delivers the greatest effective impulse (the time integral of the drill-bit tip/rock pressure curve exceeding the strength of the rock), parameters such as the spring rates and the mass of the free mass, the drill bit and transducer have been varied and compared in both computer simulation and practical experiment. The most interesting findings and those of particular relevance to deep drilling indicate that increasing the mass of the drill bit has a limited (or even positive) influence on the rate of effective impulse delivered
Preliminary testing of the European Ultrasonic Planetary Core Drill (UPCD) in simulated permafrost terrain as a precursor to arctic field trials
No full textPlanetary drilling technologies which have been optimized for the exploration of the Polar Regions of Mars and the Moon must be equipped with the capability to operate in ice-bound terrain. This paper shall discuss the preliminary work of the authors in investigating the capability of a new ultrasonic/percussive drilling system in simulated permafrost, accomplished through a series of laboratory experiments. The results obtained have allowed the authors to conclude that the drill system is capable of drilling to the required depths in representative ice-bound materials, though particular care must be taken to avoid incidents involving the melting of liquid volatiles, bound within the simulated permafrost, and the subsequent seizing of the drill string which can result
Push-and-twist drillstring assemblies
No full textDeep drilling using a rigid drillstring requires the assembly and disassembly of multiple drill pipes. The interfaces between these pipes provide a challenge for automation because they must transmit large drilling forces and movements while, at the same time, minimize the actions and forces that are needed to make or break the interface. A geometry which can address these requirements has been suggested by the authors. This approach would use a push-and-twist bayonet system to engage drill pipes, with torque transmission through the bayonet studs. A variety of L-shaped and T-shaped bayonet paths have been proposed to ensure that separation of specific drill pipes can be achieved through a combination of clockwise and counter-clockwise rotation and single-point clamping. Sustained drills into a variety of media are used to show that percussive impulses are transmitted across the interface, whilst ensuring that the drill interface is able to withstand the shock loading associated with hammer-drilling. These tests are repeated and contrasted to control experiments using a single-piece control drillstring, which allows the performance of the interface and any degradation over time to be quantified. Results suggest that the bayonet-style connection performs well with no significant performance losses encountered or structural degradation noted
The Development of the European Ultrasonic Planetary Core Drill (UPCD)
No full textFuture exploration missions to rocky bodies within the Solar System may wish to utilize drill systems on
landed vehicles which simply cannot deliver the weight on bit, or accommodate the mass and volume levels
which are required for the use of existing drill technology. This issue is being tackled by the development of
the Ultrasonic Planetary Core Drill (UPCD) project. This paper shall detail the development effort of this
drill to date, describing how lessons learned from early technology have informed the current design. Details
of the Concept of Operations, the routine by which the drill samples and caches rocks for later analysis will
also be presented, with an emphasis on the effect that the refinement of this process has had on the overall
design
A Motion Control System Design for an Ultrasonic Planetary Core Drill (UPCD) Unit
No full textA prototype of a motion control system for an Ultrasonic Planetary Core Drill (UPCD)
tool is presented. This system is designed to maintain a consistent dynamic behavior in the
ultrasonic horn/free-mass/drill bit stack during ultrasonic-percussive drilling into a range of
non-homogeneous rocks. The control system is a simple negative feedback loop which
employs the output of the P100 control unit (manufactured by Sonic Systems Ltd) that
powers the ultrasonic transducer, ensuring that the drill tool is advanced while a steady
ultrasonic vibration level is maintained. This paper describes the mechanical design of the
test rig, the control system design and an evaluation of its performance
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Ultrasonically-assisted penetration of granular and cemented materials
No full textGranular material can often be penetrated by the application of high-frequency vibrations. This effect may be seen in loosely packed granular material, in permafrost where the discrete grains exist in an icy matrix, and even where those grains have been compacted and cemented to form a sedimentary rock. For space applications, the vibrations may be reasonably generated by a Langevin transducer and their energy delivered to the target material by a number of different mechanisms, depending on the nature of the target and the depth or bore diameter of the desired drill campaign. The application of such vibrations is generally associated with reductions in weight-on-bit and power requirements when compared to more traditional techniques
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