Entrance pressure instability of LLDPE and its composites

RSC Advances ◽  
2016 ◽  
Vol 6 (85) ◽  
pp. 81703-81711 ◽  
Author(s):  
Haiqing Hu ◽  
Jie Liu ◽  
Tongjie Sun ◽  
Jian Zhao ◽  
Xin Wang ◽  
...  
Keyword(s):  
Pressure Fluctuation ◽  
The Relationship ◽  
Entrance Pressure

The relationship between entrance pressure fluctuation and perturbation of the extrudates was elaborated experimentally.

scholarly journals Investigation into the Relationship between Super-Knock and Misfires in an SI GDI Engine

Energies ◽  
2021 ◽  
Vol 14 (8) ◽  
pp. 2099
Author(s):  
Jian Gao ◽  
Anren Yao ◽  
Yeyi Zhang ◽  
Guofan Qu ◽  
Chunde Yao ◽  
...  
Keyword(s):  
Pressure Fluctuation ◽  
Direct Injection ◽  
Exhaust Valve ◽  
Gasoline Direct Injection ◽  
Exhaust Pipe ◽  
Pressure Transducers ◽  
Spark Plug ◽  
Si Engines ◽  
Gdi Engine ◽  
The Relationship

The super-knock poses new challenges for further increasing the power density of spark ignition (SI) engines. The critical factors and mechanism connecting regarding the occurrence of super-knock are still unclear. Misfire is a common phenomenon in SI engines that the mixture in cylinder is not ignited normally, which is often caused by spark plug failure. However, the effect of misfire on engine combustion has not been paid enough attention to, particularly regarding connection to super-knock. The paper presents the results of experimental investigation into the relationship between super-knock and misfires at low speed and full load conditions. In this work, a boosted gasoline direct injection (GDI) engine with an exhaust manifold integrated in the cylinder head was employed. Four piezoelectric pressure transducers were used to acquire the data of a pressure trace in cylinder. The spark plugs of four cylinders were controlled manually, of which the ignition system could be cut off as demanded. In particular, a piezoelectric pressure transducer was installed at the exhaust pipe before the turbocharger to capture the pressure traces in the exhaust pipe. The results illustrated that misfires in one cylinder would cause super-knock in the other cylinders as well as the cylinder of itself. After one cylinder misfired, the unburned mixture would burn in the exhaust pipe to produce oscillating waves. The abnormal pressure fluctuation in the exhaust pipe was strongly correlated with the occurrence of super-knock. The sharper the pressure fluctuation, the greater the intensity of knock in the power cylinder. The cylinder whose exhaust valve overlapped with the exhaust valve of the misfired cylinder was prone to super-knock.

scholarly journals State-of-the Art-Powerhouse, Dam Structure, and Turbine Operation and Vibrations

2020 ◽  
Vol 12 (4) ◽  
pp. 1676 ◽  
Author(s):  
Zaher Mundher Yaseen ◽  
Ameen Mohammed Salih Ameen ◽  
Mohammed Suleman Aldlemy ◽  
Mumtaz Ali ◽  
Haitham Abdulmohsin Afan ◽  
...  
Keyword(s):  
Pressure Fluctuation ◽  
Draft Tube ◽  
Hydropower Plant ◽  
Francis Turbine ◽  
Future Research ◽  
Research Directions ◽  
Operation Costs ◽  
Hydropower Plants ◽  
Future Research Directions ◽  
The Relationship

Dam and powerhouse operation sustainability is a major concern from the hydraulic engineering perspective. Powerhouse operation is one of the main sources of vibrations in the dam structure and hydropower plant; thus, the evaluation of turbine performance at different water pressures is important for determining the sustainability of the dam body. Draft tube turbines run under high pressure and suffer from connection problems, such as vibrations and pressure fluctuation. Reducing the pressure fluctuation and minimizing the principal stress caused by undesired components of water in the draft tube turbine are ongoing problems that must be resolved. Here, we conducted a comprehensive review of studies performed on dams, powerhouses, and turbine vibration, focusing on the vibration of two turbine units: Kaplan and Francis turbine units. The survey covered several aspects of dam types (e.g., rock and concrete dams), powerhouse analysis, turbine vibrations, and the relationship between dam and hydropower plant sustainability and operation. The current review covers the related research on the fluid mechanism in turbine units of hydropower plants, providing a perspective on better control of vibrations. Thus, the risks and failures can be better managed and reduced, which in turn will reduce hydropower plant operation costs and simultaneously increase the economical sustainability. Several research gaps were found, and the literature was assessed to provide more insightful details on the studies surveyed. Numerous future research directions are recommended.

Large eddy simulation of turbulent cavitating flow in a Venturi-type section with special emphasis on LES errors and pressure fluctuation analyses

2021 ◽  
Vol 35 (26) ◽  
pp. 2150440
Author(s):  
Linfeng Deng ◽  
Yun Long ◽  
Bin Ji ◽  
Xinping Long
Keyword(s):  
Large Eddy Simulation ◽  
Pressure Fluctuation ◽  
Cavitating Flow ◽  
Numerical Results ◽  
Fluctuation Analysis ◽  
Simulation Accuracy ◽  
Modified Model ◽  
Eddy Simulation ◽  
Large Eddy ◽  
The Relationship

In this study, large eddy simulation (LES) coupled with the homogeneous cavitation model is used to simulate the turbulent cavitating flow in the venturi with special emphasis on LES errors and pressure fluctuation analysis. The numerical results accurately predict the quasi-periodic behavior and frequency characteristics of the cavitation by comparing them with the experimental observations. The modified one-dimensional model is utilized here to figure out the relationship between cavitation and pressure fluctuation. A good coincidence between the predicted and monitored pressure is obtained to validate the consideration of the geometric and flow factors in the modified model. Further analysis indicated that the cavity volume acceleration is the main source of cavitation excited pressure fluctuation. Moreover, LES Verification and Validation (V&V) are involved to quantify the errors and uncertainties of the numerical results. It is found that the large magnitude of the errors often emerges in the region where the re-entrant jet and shedding cavity occurs, which demonstrates the influence of cavitation on the simulation accuracy. The modeling error has a larger magnitude than the numerical error and both often show opposite signs. To better understand the influence of cavitation on LES V&V, the interaction between cavitation and vortex is also discussed further.

Numerical Simulation and Experimental Study of the Pressure Fluctuation in Water Turbines

2010 ◽  
Author(s):  
Ru-Zhi Gong ◽  
Hong-Jie Wang ◽  
Wan-Jiang Liu ◽  
Da-Qing Qin ◽  
Feng-Chen Li
Keyword(s):  
Pressure Fluctuation ◽  
Large Scale ◽  
Pressure Pulsation ◽  
Low Frequency ◽  
Hydraulic Turbine ◽  
Experimental Conditions ◽  
Runner Blade ◽  
Water Turbine ◽  
Water Turbines ◽  
The Relationship

Pressure fluctuation is a common problem in large-scale hydraulic turbine, which will affect the performance of the water turbines, such as negatively affecting the efficiency, increasing the damage of related components and decreasing the life span, bringing up great potential troubles to the operation safety of large-scale water turbines. The mechanism how the pressure fluctuation appears is due to the low-frequency pressure pulsation in the draft tube and the mid-frequency pressure pulsation generated by dynamic and static interferences before the runner transmit upstream, and the low-frequency and mid-frequency pressure pulsation in the front of the runner, guide vanes, fixed vanes and the inlet of the volute. To study the relationship between the capacity and the pressure fluctuation of the water turbine, the CFD calculation was performed on the water turbine and the results of the calculation were compared with the measurements in this study. The model of water turbine studied in this paper is Baihetan HEC_1014-type. The computations were carried out in the whole runner blade passage and the boundary conditions were set as the same as the experimental conditions. The unsteady state flow of the turbine was computed. The effects of turbulence were modeled with standard κ-ε turbulence model. The inner flow field and the pressure fluctuation were obtained from the calculation using the solver of Fluent. And the results of simulation are compared with the experimental results.

Interstellar gas in the central region of the Galaxy

1967 ◽  
Vol 31 ◽  
pp. 239-251 ◽  
Author(s):  
F. J. Kerr
Keyword(s):  
Central Region ◽  
Galactic Plane ◽  
Neutral Hydrogen ◽  
Continuum Emission ◽  
Galactic Centre ◽  
Interstellar Gas ◽  
Hydrogen Recombination ◽  
The Galaxy ◽  
Centre Region ◽  
The Relationship

A review is given of information on the galactic-centre region obtained from recent observations of the 21-cm line from neutral hydrogen, the 18-cm group of OH lines, a hydrogen recombination line at 6 cm wavelength, and the continuum emission from ionized hydrogen.Both inward and outward motions are important in this region, in addition to rotation. Several types of observation indicate the presence of material in features inclined to the galactic plane. The relationship between the H and OH concentrations is not yet clear, but a rough picture of the central region can be proposed.

The relationship of the scleractinian corals to the rugose corals

Paleobiology ◽  
1980 ◽  
Vol 6 (02) ◽  
pp. 146-160 ◽  
Author(s):  
William A. Oliver
Keyword(s):  
Critical Points ◽  
Scleractinian Corals ◽  
Convincing Evidence ◽  
Early Triassic ◽  
Rugose Corals ◽  
History Of ◽  
The Subject ◽  
Relationship Of ◽  
The Relationship ◽  
Biologic Factors

The Mesozoic-Cenozoic coral Order Scleractinia has been suggested to have originated or evolved (1) by direct descent from the Paleozoic Order Rugosa or (2) by the development of a skeleton in members of one of the anemone groups that probably have existed throughout Phanerozoic time. In spite of much work on the subject, advocates of the direct descent hypothesis have failed to find convincing evidence of this relationship. Critical points are:(1) Rugosan septal insertion is serial; Scleractinian insertion is cyclic; no intermediate stages have been demonstrated. Apparent intermediates are Scleractinia having bilateral cyclic insertion or teratological Rugosa.(2) There is convincing evidence that the skeletons of many Rugosa were calcitic and none are known to be or to have been aragonitic. In contrast, the skeletons of all living Scleractinia are aragonitic and there is evidence that fossil Scleractinia were aragonitic also. The mineralogic difference is almost certainly due to intrinsic biologic factors.(3) No early Triassic corals of either group are known. This fact is not compelling (by itself) but is important in connection with points 1 and 2, because, given direct descent, both changes took place during this only stage in the history of the two groups in which there are no known corals.

Choosing a Markov blanket

2020 ◽  
Vol 43 ◽  
Author(s):  
Thomas Parr
Keyword(s):  
Markov Blanket ◽  
Target Article ◽  
The Relationship

Abstract This commentary focuses upon the relationship between two themes in the target article: the ways in which a Markov blanket may be defined and the role of precision and salience in mediating the interactions between what is internal and external to a system. These each rest upon the different perspectives we might take while “choosing” a Markov blanket.

Tinkering with cognitive gadgets: Cultural evolutionary psychology meets active inference

2019 ◽  
Vol 42 ◽  
Author(s):  
Paul Benjamin Badcock ◽  
Axel Constant ◽  
Maxwell James Désormeau Ramstead
Keyword(s):  
Evolutionary Psychology ◽  
Research Program ◽  
Active Inference ◽  
Innovative Research ◽  
Cognitive Faculties ◽  
Cultural Evolutionary ◽  
The Relationship

Abstract Cognitive Gadgets offers a new, convincing perspective on the origins of our distinctive cognitive faculties, coupled with a clear, innovative research program. Although we broadly endorse Heyes’ ideas, we raise some concerns about her characterisation of evolutionary psychology and the relationship between biology and culture, before discussing the potential fruits of examining cognitive gadgets through the lens of active inference.

Radiation Damage, Contrast and Statistics in High Resolution Biological Electron Microscopy

1970 ◽  
Vol 28 ◽  
pp. 260-261
Author(s):  
Robert M. Glaeser
Keyword(s):  
High Resolution ◽  
Particle Flux ◽  
Unit Area ◽  
Signal To Noise ◽  
Resolution Image ◽  
High Resolution Image ◽  
Pass Through ◽  
Counting Statistics ◽  
The Relationship ◽  
Picture Element

It is well known that a large flux of electrons must pass through a specimen in order to obtain a high resolution image while a smaller particle flux is satisfactory for a low resolution image. The minimum particle flux that is required depends upon the contrast in the image and the signal-to-noise (S/N) ratio at which the data are considered acceptable. For a given S/N associated with statistical fluxtuations, the relationship between contrast and “counting statistics” is s131_eqn1, where C = contrast; r2 is the area of a picture element corresponding to the resolution, r; N is the number of electrons incident per unit area of the specimen; f is the fraction of electrons that contribute to formation of the image, relative to the total number of electrons incident upon the object.

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