1,725,819 research outputs found
Investigation into the Strouhal numbers associated with vortex shedding from parallel-plate thermoacoustic stacks in oscillatory flow conditions
No full textThis paper investigates vortex shedding processes occurring at the end of a stack of parallel plates, due to an oscillating flow induced by an acoustic standing wave. Here the hot-wire anemometry measurement technique is applied to detect the velocity fluctuations due to vortex shedding near the end of the stack. The hot-wire fast time response enables detailed frequency spectra of the velocity signal to be obtained, which can be used for identifying the dominant frequencies associated with vortex shedding, and thus allow calculation of the corresponding Strouhal numbers. By varying the stack configuration (the plate thickness and spacing) and the acoustic excitation level (the so-called drive ratio), the impact of the stack blockage ratio and the Reynolds number on the Strouhal number has been studied in detail. Furthermore, in the range of Reynolds numbers between 200 and 5000 a correlation between the Strouhal number and Reynolds number has been obtained and compared with analogous relationships in the steady flow. Particle Image Velocimetry (PIV) is also used to visualize the vortex shedding processes within an acoustic cycle, phase-by-phase, in particular during the part of the cycle when the fluid flows out of the stack—selected cases are shown for comparisons with hot-wire measurements
Ueber den Einfluss der Härte des Stahls auf dessen Magnetisirbarkeit
No full textvon V. Strouhal und C. BarusEnth.: Ueber den Einfluss des Anlassens auf die Haltbarkeit der Magnete / von V. Strouhal und C. Baru
Moserius Strouhal 1940
No full textGenus <i>Moserius</i> Strouhal, 1940 <p> TYPE SPECIES. — <i>Moserius percoi</i> Strouhal, 1940 by monotypy.</p>Published as part of <i>Taiti, Stefano & Montesanto, Giuseppe, 2018, New species of subterranean and endogean terrestrial isopods (Crustacea, Oniscidea) from Tuscany (central Italy), pp. 197-226 in Zoosystema 40 (11)</i> on page 202, DOI: 10.5252/zoosystema2018v40a11, <a href="http://zenodo.org/record/3741502">http://zenodo.org/record/3741502</a>
Finding Aid for the George Strouhal Papers
No full textThe George Strouhal Papers is composed of NASA corporate contractor records and reports, reports, white papers and papers, manuals, research binders, memorandums, brochures, booklets, a poster, college course lecture notes, course assignment records, and miscellaneous materials, created and used by George Strouhal during his career working at NASA’s Manned Spacecraft Center (later Johnson Space Center) between the 1960s and 1970s. Strouhal was a mechanical engineer known for his work focusing on thermal protection systems for the Apollo Program and Space Shuttle Program. The bulk of the collection is composed of Strouhal’s copies of official NASA corporation contractors’ reports, papers, records, and other materials, from the 1950 through 1970s. There are miscellaneous NASA, contractors, and various organizations’ aerospace research materials that he retained while working at NASA. The collection includes course notes kept by Strouhal during his undergraduate and other educational course work in the 1950s and 1960s
Analysis and Experiment of an Ultra-light Flapping Wing Aircraft
No full textII
Inspired by flying animals in nature especially birds, human has designed and attempted
to achieve man-powered flapping wing aircraft in very early aviation history. Limited by
the understanding of the aerodynamic theory and materials in practise, the bird-like
aircraft remains as a dream and ambition for over a contrary. As the relevant knowledge
and technology are fast developing in the last decade, the research topic becomes
attractive again with encouraging results from a few full scale aircraft flight tests.
Although it is suspected that a manned scale flapping wing may not be as efficient as
fixed wing, the unique advantages of high manoeuvrability and short take-off and
landing capability will keep flapping wing as one of the most potential type of personal
and aerobatic aircraft in the future market.
The aim of this project is to investigate into the feasibility and development of a
bio-inspired bird-like man-powered ultra-light flapping wing aircraft (ULFWA). The
project is based on analytical and experimental study of a scaled model taking an
existing hang glider as the baseline airframe. Based on the characteristics of flying
animals in nature and manmade hang glider properties, this thesis focuses its study on
evaluating the feasibility and analysis of primarily a human powered aircraft. For this
purpose, there are four main features as guidance in the ULFWA design. Firstly the
flapping frequency was limited to below 2Hz. Secondly the hang glider airframe was
adapted with a simple flapping mechanism design. Thirdly the flapping wing stroke and
kinematics has been kept with the simplest and resonant movement to achieve high
mechanical efficiency. Finally the wing structure has flexible rib of chord wise
unsymmetrical bending stiffness to offset the aerodynamic lift loss in upstroke. An
engine powered mechanism design was also studied as additional option of the ULFWA.
The initial design and aerodynamic calculation of the ULFWA was based on the hang
glider data including dimensions, MTOW (226 kg) and cruising speed. The unsteady
aerodynamic lift and thrust forces were calculated based on Theodorsen’s theory and
unsteady panel method in 2D and extended to 3D using strip theory. A set of optimal
flapping kinematic parameters such as amplitude and combination of the heaving and
pitching motion of the 2D wing section were determined by calculation and comparison
in the limited range. Considering the maximum power and lag motion that human could
achieve, the flapping frequency in the ULFWA design is limited to 1Hz. This slow motion
leads to a much lower propulsive efficiency in terms of the optimum Strouhal Number
(St=0.2-0.4), which was used as the design reference. Mechanism and structure design
with inertia force calculation was then completed based on the kinematics. This led to
the evaluation of power requirement, which was divided into two components, drag and
inertia forces. The results show that the ULFWA needs minimum 2452.25W (equals to
3.29Bhp) to maintain sustainable cruise flight.
In order to demonstrate the ULFWA flapping mechanism and structure design, a 1:10
scaled model with two pairs of wings of different stiffness were built for testing and
measurement. Two servomotors were used as to simulate human power actuation. With
this model, simplified structure and one of mechanism designs was shown. Four
experiments were carried out to measure the model’s lift and thrust force. Because of
the limited response of the servo motors, the maximum flapping frequency achieved is
only 0.75 Hz in the specified flapping amplitude which is close to reality and has
improvement margin. By reducing the flapping amplitude, the frequency can be
increased to gain higher thrust. Although it is fund that the result from scaled model test
is a little lower than theoretical result, it has demonstrated the feasibility and potential
of human powered flapping wings aircraft
Materialien über die Ökologie und Biologie von \u3cem\u3eSphaeromides bureschi\u3c/em\u3e Strouhal
No full textThe acquatic cave Isopod Sphaeromides bureschi Strouhal was discovered by I. Buresch in the underground water of two caves in western Stara-Planina. In this paper the author describes a new station, a spring, in the same region and then exposes the results of ecological and biological observations on this species (biotope, temperature, sex-ratio, feeding regime, locomotion)
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe 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
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