scholarly journals Cavitation onset caused by acceleration

2017 ◽  
Vol 114 (32) ◽  
pp. 8470-8474 ◽  
Author(s):  
Zhao Pan ◽  
Akihito Kiyama ◽  
Yoshiyuki Tagawa ◽  
David J. Daily ◽  
Scott L. Thomson ◽  
...  
Keyword(s):  
High Speed ◽  
Equation Of Motion ◽  
Cavitation Number ◽  
High Speed Photography ◽  
Impulsive Force ◽  
Research Groups ◽  
Independent Research ◽  
Series Of Experiments ◽  
Intuitive Interpretation ◽  
Dimensionless Term

Striking the top of a liquid-filled bottle can shatter the bottom. An intuitive interpretation of this event might label an impulsive force as the culprit in this fracturing phenomenon. However, high-speed photography reveals the formation and collapse of tiny bubbles near the bottom before fracture. This observation indicates that the damaging phenomenon of cavitation is at fault. Cavitation is well known for causing damage in various applications including pipes and ship propellers, making accurate prediction of cavitation onset vital in several industries. However, the conventional cavitation number as a function of velocity incorrectly predicts the cavitation onset caused by acceleration. This unexplained discrepancy leads to the derivation of an alternative dimensionless term from the equation of motion, predicting cavitation as a function of acceleration and fluid depth rather than velocity. Two independent research groups in different countries have tested this theory; separate series of experiments confirm that an alternative cavitation number, presented in this paper, defines the universal criteria for the onset of acceleration-induced cavitation.

scholarly journals Experimental Study on the Relationship Between Cavitation and Lift Fluctuations of S-Shaped Hydrofoil

2021 ◽  
Vol 9 ◽  
Author(s):  
Haiyu Liu ◽  
Pengcheng Lin ◽  
Fangping Tang ◽  
Ye Chen ◽  
Wenpeng Zhang ◽  
...  
Keyword(s):  
High Speed ◽  
Developmental Process ◽  
Angle Of Attack ◽  
Cavitation Number ◽  
High Speed Photography ◽  
Cloud Cavitation ◽  
Cavitation Inception ◽  
Sheet Cavitation ◽  
Hydraulic Machinery ◽  
Stall Angle

In order to study the energy loss of bi-directional hydraulic machinery under cavitation conditions, this paper uses high-speed photography combined with six-axis force and torque sensors to collect cavitating flow images and lift signals of S-shaped hydrofoils simultaneously in a cavitation tunnel. The experimental results show that the stall angle of attack of the S-shaped hydrofoil is at ±12° and that the lift characteristics are almost symmetrical about +1°. Choosing α = +6° and α = −4° with almost equal average lift for comparison, it was found that both cavitation inception and cloud cavitation inception were earlier at α = −4° than at α = +6°, and that the cavitation length at α = −4° grew significantly faster than at α = +6°. When α = +6°, the cavity around the S-shaped hydrofoil undergoes a typical cavitation stage as the cavitation number decreases: from incipient cavitation to sheet cavitation to cloud cavitation. However, when α = −4°, as the cavitation number decreases, the cavitation phase goes through a developmental process from incipient cavitation to sheet cavitation to cloud cavitation to sheet cavitation to cloud cavitation, mainly because the shape of the S-shaped hydrofoil at the negative angle of attack affects the flow of the cavity tails, which is not sufficient to form re-entrant jets that cuts off the sheet cavitation. The formation mechanism of cloud cavitation at the two different angles of attack (α = +6°、−4°) is the same, both being due to the movement of the re-entrant jet leading to the unstable shedding of sheet cavity. The fast Fourier analysis reveals that the fluctuations of the lift signals under cloud cavitation are significantly higher than those under non-cavitation, and the main frequencies of the lift signals under cloud cavitation were all twice the frequency of the cloud cavitation shedding.

scholarly journals On compression and damage evolution in two thermoplastics

2017 ◽  
Vol 473 (2197) ◽  
pp. 20160495 ◽  
Author(s):  
N. K. Bourne ◽  
S. C. Garcea ◽  
D. S. Eastwood ◽  
S. Parry ◽  
C. Rau ◽  
...  
Keyword(s):  
High Speed ◽  
Deformation Behaviour ◽  
Three Dimensional ◽  
Spatial And Temporal Variation ◽  
High Speed Photography ◽  
Radial Deformation ◽  
X Ray Imaging ◽  
Series Of Experiments ◽  
The Impact ◽  
Continuous Range

The well-known Taylor cylinder impact test, which follows the impact of a flat-ended cylindrical rod onto a rigid stationary anvil, is conducted over a range of impact speeds for two polymers, polytetrafluoroethylene (PTFE) and polyetheretherketone (PEEK). In previous work, experiments and a model were developed to capture the deformation behaviour of the cylinder after impact. These works showed a region in which spatial and temporal variation of both longitudinal and radial deformation provided evidence of changes in phase within the material. In this further series of experiments, this region is imaged in a range of impacted targets at the Diamond synchrotron. Further techniques were fielded to resolve compressed regions within the recovered polymer cylinders that showed a fracture zone in the impact region. The combination of macroscopic high-speed photography and three-dimensional X-ray imaging has identified the development of failure with these polymers and shown that there is no abrupt transition in behaviours but rather a continuous range of responses to competing operating mechanisms. The behaviours noted in PEEK in these polymers show critical gaps in understanding of polymer high strain-rate response.

The role of rapidly compressed gas pockets in the initiation of condensed explosives

1974 ◽  
Vol 340 (1620) ◽  
pp. 113-128 ◽  
Keyword(s):  
High Speed ◽  
Thermal Contact ◽  
Gas Bubbles ◽  
Lead Azide ◽  
High Speed Photography ◽  
Water Tank ◽  
Minimum Volume ◽  
Specific Heats ◽  
Series Of Experiments ◽  
Minimum Volumes

The mechanism of initiation of explosion by the rapid compression of gas spaces has been studied by means of high-speed photography at framing rates up to 10 7 frames s -1 . Single crystals of silver azide, lead azide and PETN were mounted in a water tank and gas bubbles of chosen composition and size (diameter in the range 50 μm to 1 mm) collapsed on to them by water shocks of strength about 0.1 GPa (1 kbar). The gas bubbles collapsed to minimum volumes in times of the order of 1 μs (depending on the initial bubble size). Initiation of fast reaction occurred in the azides within ca . 5 × 10 -8 s of the bubble reaching minimum volume provided the bubble made thermal contact with the explosive. During the collapse, the bubble involuted to form a jet of velocity of a few 100 ms -1 , and after reaching minimum volume, expanded giving an expansion shock. The importance of these phenomena in the initiation of explosion, as well as possible initiation by shock perturbation, was assessed in a series of experiments designed to separate the various possible mechanisms. The conclusion is that adiabatic heating of the gas in the bubble was the prime cause for initiation. Calculations, and experiments with gases such as argon and helium (high value of γ ; the ratio of the specific heats) and butane (low γ ) supported this conclusion. Finally, the relevance to other explosive situations is discussed.

The Structure of Wiggins' Interpersonal Circumplex: Cross-Cultural Studies

1999 ◽  
Vol 15 (3) ◽  
pp. 196-205 ◽  
Author(s):  
Rosario Martínez-Arias ◽  
Fernando Silva ◽  
Ma Teresa Díaz-Hidalgo ◽  
Generós Ortet ◽  
Micaela Moro
Keyword(s):  
Cultural Studies ◽  
Cross Cultural ◽  
The Other ◽  
Spanish Version ◽  
Interpersonal Circumplex ◽  
Research Groups ◽  
Independent Research ◽  
Research Results ◽  
Cross Cultural Studies

Summary: This paper presents the results obtained in Spain with The Interpersonal Adjective Scales of J.S. Wiggins (1995) concerning the variables' structure. There are two Spanish versions of IAS, developed by two independent research groups who were not aware of each other's work. One of these versions was published as an assessment test in 1996. Results from the other group have remained unpublished to date. The set of results presented here compares three sources of data: the original American manual (from Wiggins and collaborators), the Spanish manual (already published), and the new IAS (our own research). Results can be considered satisfactory since, broadly speaking, the inner structure of the original instrument is well replicated in the Spanish version.

Crack divergence phenomena in tempered glass

2020 ◽  
Vol 13 (3) ◽  
pp. 115-129
Author(s):  
Shin’ichi Aratani
Keyword(s):  
Optimal Design ◽  
High Speed ◽  
Glass Plate ◽  
Acute Angle ◽  
Divergence Angle ◽  
High Speed Photography ◽  
Tempered Glass ◽  
Thick Glass

High speed photography using the Cranz-Schardin camera was performed to study the crack divergence and divergence angle in thermally tempered glass. A tempered 3.5 mm thick glass plate was used as a specimen. It was shown that two types of bifurcation and branching existed as the crack divergence. The divergence angle was smaller than the value calculated from the principle of optimal design and showed an acute angle.

Experimental Measurement of In-Plane Rolling Nonpneumatic Tire Vibrations Using High-Speed Imaging

2019 ◽  
Vol 47 (3) ◽  
pp. 196-210
Author(s):  
Meghashyam Panyam ◽  
Beshah Ayalew ◽  
Timothy Rhyne ◽  
Steve Cron ◽  
John Adcox
Keyword(s):  
High Speed ◽  
Image Correlation ◽  
Dynamic Mode Decomposition ◽  
Dynamic Mode ◽  
High Speed Imaging ◽  
Correlation Algorithm ◽  
Mode Decomposition ◽  
Series Of Experiments ◽  
Plane Deformations ◽  
Dominant Frequencies

ABSTRACT This article presents a novel experimental technique for measuring in-plane deformations and vibration modes of a rotating nonpneumatic tire subjected to obstacle impacts. The tire was mounted on a modified quarter-car test rig, which was built around one of the drums of a 500-horse power chassis dynamometer at Clemson University's International Center for Automotive Research. A series of experiments were conducted using a high-speed camera to capture the event of the rotating tire coming into contact with a cleat attached to the surface of the drum. The resulting video was processed using a two-dimensional digital image correlation algorithm to obtain in-plane radial and tangential deformation fields of the tire. The dynamic mode decomposition algorithm was implemented on the deformation fields to extract the dominant frequencies that were excited in the tire upon contact with the cleat. It was observed that the deformations and the modal frequencies estimated using this method were within a reasonable range of expected values. In general, the results indicate that the method used in this study can be a useful tool in measuring in-plane deformations of rolling tires without the need for additional sensors and wiring.

Experimental study of hydrodynamic effects in the inverse water hydrocarbon emulsions flow in microchannels

2016 ◽  
Vol 11 (1) ◽  
pp. 30-37 ◽  
Author(s):  
A.A. Rakhimov ◽  
A.T. Akhmetov
Keyword(s):  
High Speed ◽  
Petroleum Industry ◽  
Chemical Compounds ◽  
High Viscosity ◽  
Blocking Effect ◽  
High Speed Photography ◽  
Simple Chemical ◽  
Reported Study ◽  
Dynamic Blocking ◽  
Hydrodynamic Effects

The paper presents results of hydrodynamic and rheological studies of the inverse water hydrocarbon emulsions. The success of the application of invert emulsions in the petroleum industry due, along with the high viscosity of the emulsion, greatly exceeding the viscosity of the carrier phase, the dynamic blocking effect, which consists in the fact that the rate of flow of emulsions in capillary structures and cracks falls with time to 3-4 orders, despite the permanent pressure drop. The reported study shows an increase in viscosity with increasing concentration or dispersion of emulsion. The increase in dispersion of w/o emulsion leads to an acceleration of the onset of dynamic blocking. The use of microfluidic devices, is made by soft photolithography, along with high-speed photography (10,000 frames/s), allowed us to see in the blocking condition the deformation of the microdroplets of water in inverse emulsion prepared from simple chemical compounds.

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