scholarly journals Observations on Cavitation Damage in a Flowing System

1963 ◽  
Vol 85 (3) ◽  
pp. 347-356 ◽  
Author(s):  
F. G. Hammitt
Keyword(s):  
Fluid Dynamic ◽  
Material Strength ◽  
Cavitation Damage ◽  
Maximum Test ◽  
Bubble Density ◽  
Specimen Material ◽  
Short Period ◽  
Flowing System ◽  
Very High ◽  
Additional Exposure

Cavitation damage to specimens of stainless steel, carbon steel, aluminum, and plexiglas, placed in a cavitating venturi using water and mercury as test fluids is mostly in the form of irregularly shaped pits which do not change with additional exposure to the cavitating field within the limited durations utilized. The rate of damage is very high initially, decreases for a relatively short period of time, then increases again up to the maximum test durations of 150 hours with water and 270 hours with mercury. Observation of damage effects by several independent techniques, using a variety of specimen materials, with two different fluids under various fluid dynamic conditions, leads to a suggested correlating model in terms of the cavitation bubble density and energy and specimen material strength.

scholarly journals Modeling heavy metal release in the epiphytic lichen Evernia prunastri

2021 ◽  
Author(s):  
Andrea Vannini ◽  
Luca Paoli ◽  
Riccardo Fedeli ◽  
Sharon Kwambai Kangogo ◽  
Massimo Guarnieri ◽  
...  
Keyword(s):  
Heavy Metal ◽  
Remote Area ◽  
Metal Release ◽  
Evernia Prunastri ◽  
Epiphytic Lichen ◽  
Pollution Levels ◽  
Short Period ◽  
High Pollution ◽  
Heavy Metal Release ◽  
Very High

AbstractIn this study, the release of Cu2+ and Zn2+ was investigated and modeled in the epiphytic lichen Evernia prunastri. Samples were incubated with solutions containing these metals at ecologically relevant concentrations (10 and 100 μM) and then transplanted to a remote area and retrieved after 1, 2, 3, 6, 12, and 18 months. The results showed that, after 12 months, all samples faced similar metal reductions of ca. 80–85%, but after this period, all the involved processes seem to be no longer capable of generating further reductions. These results suggest that the lichen E. prunastri can provide information about environmental improvements after exposure to high or very high pollution levels in a relatively short period of time.

scholarly journals Achieving High-Speed Retraction in a Stretchable Hydrogel

2020 ◽  
Author(s):  
Rosa Maria Badani Prado ◽  
Satish Mishra ◽  
Buckston Morgan ◽  
Rangana Wijayapala ◽  
Seyed Meysam Hashemnejad ◽  
...  
Keyword(s):  
High Speed ◽  
Biological Tissues ◽  
Biological Species ◽  
Vital Role ◽  
Polypropylene Glycol ◽  
Glycol Diacrylate ◽  
Mantis Shrimp ◽  
Power Amplification ◽  
Short Period ◽  
Very High

Many biological species apply the power amplification mechanism for locomotion, feeding, and protection. In power amplification, a biological system rapidly releases stored-energy by achieving a very high velocity over a short period of time, resulting in high power output. Such power amplification allows insects such as locust to jump and Mantis shrimp to kill prey by its appendage strike. Biological elastomeric polymers such as resilin play a vital role in the power amplification process because of their high stretchability and resilience. In synthetic materials, although<br>crosslinked rubbers display high stretchability and resilience, such is difficult to achieve in the water-containing systems such as in hydrogels, commonly considered materials for mimicking biological tissues. Here, we have used a simple free-radical polymerization of acrylic acid (AAc), methacrylamide (MAAm), and polypropylene glycol diacrylate (PPGDA) to obtain hydrogels. In these gels, the polymerized AAc and MAAm act as hydrophilic blocks and PPG as hydrophobic, and the gel structure resemble that of resilin consisting of hydrophilic and hydrophobic components. The bioinspired gels display very high stretchability, as high as eight times the original length, and greater than 90% resilience. In addition, the gel samples can reach a retraction velocity of 16 m/s with an acceleration of 4X10^3 m/s2. These values are similar or better than those observed in water containing biological systems, such as appendage strikes in Mantis shrimp, etc. To the best of our knowledge, such performance has not been reported in the<br>literature for any water containing networks.

Research Protocols and Ethical Considerations in Indigenous Knowledge Systems

2019 ◽  
pp. 714-730
Author(s):  
Mogege David Mosimege
Keyword(s):  
South Africa ◽  
Indigenous Knowledge ◽  
Ethical Issues ◽  
Research Community ◽  
Knowledge Systems ◽  
Ethical Considerations ◽  
Short Period ◽  
Indigenous Knowledge Systems ◽  
Protection Mechanisms ◽  
Very High

Research in Indigenous Knowledge Systems (IKS) in South Africa has grown at a very high pace in a relatively short period of time. The growth thereof has presented researchers and the knowledge holders with challenges that have never faced them in the same way before. It has necessitated a review of how researchers interact with those who hold the knowledge and has required that protection mechanisms be implemented to safeguard the misuse and misappropriation of the indigenous knowledge. This Chapter outlines the focus on IKS in South Africa since 1995 and reflects on the challenges related to this focus. Specifically the Chapter looks at the challenges related to the recognition of knowledge holders, the ethical issues facing both researchers and knowledge holders, and the protocols that have been designed and used in South Africa and other places. It concludes by indicating the challenges that still remain and how these can be explored further by the research community.

Air Ingress Analysis: Computational Fluid Dynamics Models

2010 ◽  
Author(s):  
Chang H. Oh ◽  
Eung S. Kim
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
High Temperature ◽  
Fluid Dynamic ◽  
Department Of Energy ◽  
Validation Data ◽  
The Core ◽  
Air Ingress ◽  
Dynamics Models ◽  
Very High

Idaho National Laboratory (INL), under the auspices of the U.S. Department of Energy (DOE), is performing research and development that focuses on key phenomena important during potential scenarios that may occur in very high temperature reactors (VHTRs). Phenomena identification and ranking studies to date have ranked an air ingress event, following on the heels of a VHTR depressurization, as important with regard to core safety. Consequently, the development of advanced air-ingress-related models and verification and validation data are a very high priority. Following a loss of coolant and system depressurization incident, air will enter the core of the High Temperature Gas Cooled Reactor through the break, possibly causing oxidation of the core and reflector graphite structure. Simple core and plant models indicate that, under certain circumstances, the oxidation may proceed at an elevated rate with additional heat generated from the oxidation reaction itself. Under postulated conditions of fluid flow and temperature, excessive degradation of lower plenum graphite can lead to a loss of structural support. Excessive oxidation of core graphite can also lead to a release of fission products into the confinement, which could be detrimental to reactor safety. Computational fluid dynamics models developed in this study will improve our understanding of this phenomenon. This paper presents two-dimensional (2-D) and three-dimensional (3-D) computational fluid dynamic (CFD) results for the quantitative assessment of the air ingress phenomena. A portion of the results from density-driven stratified flow in the inlet pipe will be compared with the experimental results.

scholarly journals Very-High-Eccentricity Librations at Some Higher Order Resonances

1992 ◽  
Vol 152 ◽  
pp. 153-158 ◽  
Author(s):  
J.C. Klafke ◽  
S. Ferraz-Mello ◽  
T. Michtchenko
Keyword(s):  
Phase Space ◽  
Numerical Integration ◽  
Higher Order ◽  
Planar Problem ◽  
High Eccentricity ◽  
Disturbing Potential ◽  
Numerical Exploration ◽  
Numerical Integrations ◽  
Short Period ◽  
Very High

Motions near the 3:1, 4:1 and 5:2 resonances with Jupiter are studied by means of numerical integrations of a semi-analytically averaged Sun-Jupiter-asteroid planar problem. In order to have a model including the very-high-eccentricity regions of the phase space, we adopted a set of local expansions of the disturbing potential, adequate to perform the numerical exploration of regions in the phase space with eccentricities higher than 0.9 (Ferraz-Mello and Klafke, 1991). Individual solutions and qualitative results thus obtained are completely reproduced by numerical integration of the complete equations by filtering off the short-period components of these solutions.

Disorder Induced IR Anomaly in Hexagonal AlGaN Short-Period Superlattices and Alloys

1999 ◽  
Vol 572 ◽  
Author(s):  
A. M. Mintairov ◽  
A. S. Vlasov ◽  
J. L. Merz ◽  
D. Korakakis ◽  
T. D. Moustakas ◽  
...  
Keyword(s):  
Theoretical Study ◽  
Lattice Instability ◽  
Disorder Effects ◽  
Reflectivity Spectra ◽  
Damping Parameter ◽  
Short Period ◽  
Short Period Superlattices ◽  
Bulk Gan ◽  
Ternary Nitride ◽  
Very High

ABSTRACTWe report an experimental (infrared reflectance spectroscopy) and theoretical study of the polar optical phonons in hexagonal ternary nitride compounds: AlNm/GaNn (n=2-8, m=4, 8) superlattices (SL) and spontaneously ordered AlxGa1−xN (x=0.08–0.55) alloys. In infrared (IR) reflectivity spectra we revealed two modes having strong LO-TO splitting (20–150 cm−1), and several modes, having a small (1–3 cm−1) LO-TO splitting. All modes have a very high damping parameter ≥20 cm−1. The unusual observation is the negative value of the oscillator strength for the weak IR mode at ∼690 cm−1, suggesting possible lattice instability, consistent with high damping observed. We found from lattice dynamical calculations that weak IR active modes correspond to modes localized at GaN-AlN interfaces. Our analysis has shown that an anomalous mode is induced by the disorder effects and arises due to strong overlapping of the LO-TO phonon branches of the bulk GaN and AlN. In SL samples the anomalous mode corresponds to phonons localized on interface inhomogenities.

Numerical Simulation of Radiation Losses in a Decaying Laser Spark Using LBL Method

2015 ◽  
Vol 789-790 ◽  
pp. 287-295
Author(s):  
Ankit Sharma ◽  
Ankit Bansal ◽  
Anil Kishan ◽  
Ratan Joarder
Keyword(s):  
Energy Deposition ◽  
Laser Energy ◽  
Fluid Dynamic ◽  
Dynamic Effects ◽  
Radiation Model ◽  
Radiation Losses ◽  
Laser Spark ◽  
Deposited Energy ◽  
Reported Data ◽  
Very High

An investigation has been done to numerically simulate the radiation losses which occur due to laser energy deposition in a domain. Although the fluid dynamic effects due to laser energy deposition has been studied by a number of researchers independently but the effect of radiation has either been neglected or has not been highlighted effectively. When laser energy is deposited in a domain, very high temperatures are reached. At such high temperature, the diatomic air species may become highly dissociated and emission from the resulting two mono atomic species N and O cannot be neglected and is the major source of radiation loss. An Open Source CFD software Open Foam has been used to study the above effects. P1 radiation model along with radiation Line by Line method has been used to calculate the radiation losses. Radiation losses obtained are20 timeshigher as compared to the only one past reported data but still are negligible as compared to the deposited energy. Hence our study validates the assumption of neglecting radiation losses, which was assumed earlier in all previous studies without any proper validation, using the most accurate LBL method.

Research Protocols and Ethical Considerations in Indigenous Knowledge Systems

2017 ◽  
pp. 156-172
Author(s):  
Mogege David Mosimege
Keyword(s):  
South Africa ◽  
Indigenous Knowledge ◽  
Ethical Issues ◽  
Research Community ◽  
Knowledge Systems ◽  
Ethical Considerations ◽  
Short Period ◽  
Indigenous Knowledge Systems ◽  
Protection Mechanisms ◽  
Very High

Research in Indigenous Knowledge Systems (IKS) in South Africa has grown at a very high pace in a relatively short period of time. The growth thereof has presented researchers and the knowledge holders with challenges that have never faced them in the same way before. It has necessitated a review of how researchers interact with those who hold the knowledge and has required that protection mechanisms be implemented to safeguard the misuse and misappropriation of the indigenous knowledge. This Chapter outlines the focus on IKS in South Africa since 1995 and reflects on the challenges related to this focus. Specifically the Chapter looks at the challenges related to the recognition of knowledge holders, the ethical issues facing both researchers and knowledge holders, and the protocols that have been designed and used in South Africa and other places. It concludes by indicating the challenges that still remain and how these can be explored further by the research community.

Increasing Performance of Plasma Spray Formed Components

1998 ◽  
Author(s):  
J.S. O’Dell ◽  
T.N. Mckechnie ◽  
R.R. Holmes
Keyword(s):  
Plasma Spray ◽  
Heat Treating ◽  
Spray Forming ◽  
Material Strength ◽  
Thermal Treatments ◽  
Alloying Additions ◽  
Near Net Shape ◽  
Material Utilization ◽  
Very High ◽  
Strength And Ductility

Abstract Near net shape spray forming of components significantly simplifies and reduces cost of fabricating some structures. Material utilization is very high, and laborious machining can be avoided. As-spray formed components have been tested and found to perform adequately. However, improvements in alloying, thermal treatment and coating have been demonstrated to add increased performance to spray formed components. In fabricating tungsten components alloying additions of rhenium, nickel or iron have made significant increases in material strength and ductility. Thermal treatments such as heat treating and HIPing change and densify the microstructures. Coating the internal and external surfaces of components improves environmental compatibility. Increased performance of plasma spray formed refractory metal components is presented.

Slugging Fatigue Assessment for Steel Lazy Wave Risers

2021 ◽  
Author(s):  
Brad Campbell ◽  
Puneet Agarwal ◽  
Christopher Curtis ◽  
Guangqiang Yang ◽  
Angshuman Singha ◽  
...  
Keyword(s):  
Time Series ◽  
High Amplitude ◽  
Spatial And Temporal Variability ◽  
Full Time ◽  
Spatial Integration ◽  
Local Weight ◽  
Long Period ◽  
Global Weight ◽  
Bubble Density ◽  
Short Period

Abstract The objective of this paper is to introduce a new analysis methodology for assessment of riser fatigue due to slugging. Under certain flow regimes, a multiphase (oil-gas-water) flow can result in slug flow, in which a sequence of relatively high density slugs and relatively low density bubbles propagate along the flowline and the riser. The variation of slug and bubble density at a location with time is random, and slug characteristics can also change significantly along the riser length. Due to local and global weight variations, the riser undergoes cycles of bending which cause fatigue. By explicitly modeling full spatial and temporal variability and randomness of slugs, the new analysis method is significantly more accurate than other methods and it captures physics of riser's slugging response. The slugging fatigue of a steel lazy wave riser was analyzed in Orcaflex software by modeling a repeating pair of slug and bubble with constant slug and bubble densities and associated lengths over the 3-hour simulation time. A separate slug train was propagated in five sub-segments of the riser. To model a more accurate and realistic representation of slugging behavior, the time series of density was extracted at each node from the multiphase flow simulator Olga. Statistical and spectral analysis of the Olga output showed that assumptions of constant slug-bubble density, and of slug behavior being uniform over long segments of riser are too simplistic. Therefore, full time series of density at each node was input into the riser analysis using the existing capabilities of Orcaflex software. As the Orcaflex slug form approach was computationally expensive, we also developed an extrenal slug loader, which provides same level of accuracy while being computationally fast and full automated. The new method shows that the cyclic riser response at the touchdown point (TDP) is composed of two parts. One is the relatively short period (~20-60 seconds) fluctuations that occur because of local weight variations as a slug-bubble passes a riser node. The other is the relatively long period (~10-30 minutes) fluctuations that occur due to global weight variations, which are due to spatial integration of density time series over the lower catenary. These long period fluctuations drive the TDP fatigue. Preliminary field measurements with an ROV, while inducing temporary slugging in the riser, confirmed analytical predictions of long period and high amplitude motions at hog bend. This paper presents a new and significantly more accurate method for analyzing riser fatigue due to slugging. Previously unknown behavior of very long period and high amplitude riser motions is identified and explained. SLWR response to slugging can be an important contributor to the overall fatigue design budget especially at the TDP. This work reflects ExxonMobil's on-going efforts to ensure that we maintain safe designs as we adopt systems new to us in new and challenging environments.

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