An Effect of Air Content on the Occurrence of Cavitation

1960 ◽  
Vol 82 (4) ◽  
pp. 941-945 ◽  
Author(s):  
J. W. Holl
Keyword(s):  
Pressure Coefficient ◽  
Cavitation Number ◽  
Experimental Results ◽  
Simultaneous Occurrence ◽  
Minimum Pressure ◽  
Air Content ◽  
The Difference ◽  
Dissolved Air

The simultaneous occurrence of vaporous and gaseous cavitation on hydrofoils is considered. The experimental results show that gaseous cavitation occurs at much higher ambient pressures than that for the vaporous cavitation resulting in desinent-cavitation numbers twice the minimum-pressure coefficient of the hydrofoil. The analysis indicates that the difference between the desinent-cavitation number for the gaseous cavitation and that for the vaporous cavitation is proportional to the dissolved air content and inversely proportional to the square of the velocity.

The Onset of Bubble-Ring Cavitation on Hemispherical Headforms

1982 ◽  
Vol 104 (1) ◽  
pp. 115-122
Author(s):  
B. R. Parkin
Keyword(s):  
Pressure Coefficient ◽  
Reynolds Numbers ◽  
Present Theory ◽  
Cavitation Number ◽  
Approximate Theory ◽  
Freestream Velocity ◽  
Laminar Separation ◽  
Air Bubble ◽  
Air Content ◽  
Good Agreement

An approximate theory is developed to predict the onset of cavitation on hemispherical headforms for Reynolds numbers at which laminar separation is known to occur. Insofar as it is possible, the theory is based upon first principles. Fairly good agreement is obtained between the cavitation desinence trends recently measured by Holl and Carroll and the present theory. It is also found that the onset cavitation number should be less than the magnitude of the pressure coefficient at the laminar separation point and that the cavitation number increases with freestream velocity. As long as there is an appreciable concentration of dissolved air in the water, it is also found, in agreement with experiment, that the onset of bubblering cavitation is practically independent of air content. Moreover, the observed occurrence of a lowest speed for “bubble-ring” cavitation, which is the only cavitation form considered here, and the range of “cutoff” speeds predicted by the present asymptotic theory show very encouraging agreement. The present theory suggests that this cutoff speed and its accompanying cutoff cavitation number can also depend on the temperature of the water, provided that the initial size attributed to a “typical” spherical free-stream air bubble nucleus also varies with the temperature. At 80° F (26.6°C) it is estimated that the typical nucleus from which bubble-ring cavitation originates has a radius of about seven μm. At higher temperatures the nucleus radius decreases from this value while at lower temperatures the initial radius exceeds the value noted.

scholarly journals Plastic failure zone characteristics and stability control technology of roadway in the fault area under non-uniformly high geostress: A case study from Yuandian Coal Mine in Northern Anhui Province, China

2020 ◽  
Vol 12 (1) ◽  
pp. 406-424 ◽  
Author(s):  
Yaoguang Huang ◽  
Aining Zhao ◽  
Tianjun Zhang ◽  
Weibin Guo
Keyword(s):  
Numerical Methods ◽  
Numerical Solutions ◽  
Stress Test ◽  
Pressure Coefficient ◽  
Stability Control ◽  
Failure Zone ◽  
Plastic Failure ◽  
Comparison Results ◽  
High Geostress ◽  
The Difference

AbstractIn order to explore the effective support method for deep broken roadway, based on the in situ stress test results, the analytical and numerical solutions of the stress and the range of plastic failure zone (PFZ) in a circular roadway subjected to non-uniform loads were obtained using analytical and finite difference numerical methods based on the elastoplastic theory, respectively. Their comparison results show that the analytical and numerical methods are correct and reasonable. Furthermore, the high geostress causes the stress and range of PFZ in roadway roof and floor to increase sharply while those in roadway ribs decrease. Moreover, the greater the difference of horizontal geostress in different horizontal directions is, the larger the range of PFZ in roadway roof and floor is. The shape of PFZ in roadway varies with the ratio of horizontal lateral pressure coefficient in x-direction and y-direction. Finally, according to the distribution characteristics of PFZ and range of PFZ under the non-uniformly high geostress, this paper has proposed a combined support scheme, and refined and optimized supporting parameters. The field monitoring results prove that the roadway deformation and fracture have been effectively controlled. The research results of this paper can provide theoretical foundation as well as technical reference for the stability control of deep broken roadway under non-uniformly high geostress.

Simulation and experimentation of a magnetorheological brake with adjustable gap

2016 ◽  
Vol 28 (12) ◽  
pp. 1614-1626 ◽  
Author(s):  
Wan-Li Song ◽  
Dong-Heng Li ◽  
Yan Tao ◽  
Na Wang ◽  
Shi-Chao Xiu
Keyword(s):  
Magnetorheological Fluid ◽  
Structure Design ◽  
Experimental Results ◽  
Wear Property ◽  
Braking Performance ◽  
Braking Torque ◽  
The Difference ◽  
The Impact ◽  
Theoretical Analyses ◽  
Magnetostatic Simulation

The aim of this work is to investigate the effect of the small magnetorheological fluid gap on the braking performance of the magnetorheological brake. In this article, theoretical analyses of the output torque are given first, and then the operating principle and design details of the magnetorheological brake whose magnetorheological fluid gap can be altered are presented and discussed. Next, the magnetic circuit of the proposed magnetorheological brake is conducted and further followed by a magnetostatic simulation of the magnetorheological brakes with different sizes of fluid gap. A prototype of the magnetorheological brake is fabricated and a series of tests are carried out to evaluate the braking performance and torque stability, as well as the verification of the simulation results. Experimental results show that the braking torque increases with the increase in the current, and the difference for the impact of the fluid gap on braking performance is huge under different currents. The rules, which the experimental results show, have an important significance on both the improvement of structure design for magnetorheological brake and the investigation of the wear property under different fluid gaps.

Study on Simulation Experiment with Universal Pass Rolling Deformation for Heavy Rail

2012 ◽  
Vol 430-432 ◽  
pp. 525-529 ◽  
Author(s):  
Lin Chen ◽  
Ke Xin Bi
Keyword(s):  
Finite Element ◽  
Pressure Coefficient ◽  
Small Deformation ◽  
Dimensional Accuracy ◽  
Research Unit ◽  
Finite Element Software ◽  
Universal Mill ◽  
The Difference ◽  
Rolling Deformation ◽  
Heavy Rail

Using the finite element software ANSYS/LS-DYNA for the universal rolling machine to simulate,research unit of the universal rolling deformation etc, and the use of universal mill for heavy rail rolling to simulate of lead samples, study of both. By comparing experimental results, the results show rolling simulation of laboratory lead samples and finite element simulations of computer are basically the same, use the universal pass, the difference of pressure coefficient for the rail head and rail base and rail back that work on the workpiece at the universal pass is small, deformation of workpiece is uniformity, it ensure the dimensional accuracy of the finished rail on the rail section.

Effect of Saturation Degree on Concrete Deterioration due to Freeze-Thaw Action

2011 ◽  
Vol 477 ◽  
pp. 404-408 ◽  
Author(s):  
Wen Cui Yang ◽  
Yong Ge ◽  
Bao Sheng Zhang ◽  
Jie Yuan
Keyword(s):  
Frost Resistance ◽  
Water Pressure ◽  
High Water ◽  
Frost Damage ◽  
Critical Value ◽  
Cold Weather ◽  
Saturation Degree ◽  
Freeze Thaw ◽  
Air Content ◽  
The Difference

Freezing-thawing durability of cement concrete is extremely important in cold weather, to better understand mechanism of frost damage and air-entraining，saturation degree of pores in concrete and its relation with frost resistance were studied in this paper. Concrete specimens with different saturation degree from 0 to 100% were prepared used a sealed tin with a high water pressure pump. Then these specimens were subjected to six freezing-thawing cycles and the relative dynamic modulus of elasticity was examined. The results showed that critical saturation degree of concrete with water- binder ratio of 0.30 and 0.47, air content of 1%, 4% and 6% were from 0.60 to 0.80. When its saturation degree exceeded the critical value, concrete was deteriorated significantly after only six freeze-thaw cycles. The critical saturation degree was mainly related to the air content of concrete mixture, and it decreased with the increasing of air content. The difference between the saturation degree and the critical value can be used to evaluate potential frost resistance of concrete, and its result was consistent with the result of frost tests very well.

Determination of Incompressible Flow Friction in Smooth Circular and Noncircular Passages: A Generalized Approach Including Validation of the Nearly Century Old Hydraulic Diameter Concept

1988 ◽  
Vol 110 (4) ◽  
pp. 431-440 ◽  
Author(s):  
N. T. Obot
Keyword(s):  
Reynolds Number ◽  
Friction Factor ◽  
Critical Reynolds Number ◽  
Pressure Coefficient ◽  
Hydraulic Diameter ◽  
Length Scale ◽  
The Difference ◽  
Friction Method ◽  
Reduced Data

It has been demonstrated conclusively that the widely observed differences in data for frictional pressure coefficient between circular and noncircular passages derive from the inseparably connected effects of transition and the choice of a length scale. A relatively simple approach, the critical friction method (CFM), has been developed and when applied to triangular, rectangular, and concentric annular passages, the reduced data lie with remarkable consistency on the circular tube relations. In accordance with the theory of dynamical similarity, it has also been shown that noncircular duct data can be reduced using the hydraulic diameter or any arbitrarily defined length scale. The proposed method is what is needed to reconcile such data with those for circular tubes. With the hydraulic diameter, the critical friction factor almost converges to a universal value for all passages and the correction is simply that required to account for the difference in critical Reynolds number. By contrast, with any other linear parameter, two corrections are needed to compensate for variations in critical friction factor and Reynolds number. Application of the method to roughened passages is discussed.

The Effect of Turning Angle on the Loss Generation of LP Turbines

2017 ◽  
Author(s):  
Diego Torre ◽  
Guillermo Garcia-Valdecasas ◽  
David Cadrecha
Keyword(s):  
High Speed ◽  
Pressure Coefficient ◽  
Experimental Results ◽  
Cfd Simulations ◽  
Airfoil Surface ◽  
High Lift ◽  
Turning Angle ◽  
Pressure Losses ◽  
Coefficient Distribution ◽  
Inlet Angle

The effect of turning angle on the loss generation of Low Pressure (LP) Turbines has been investigated experimentally in a couple of turbine high-speed rigs. Both rigs consisted of a rotor-stator configuration. All the airfoils are high lift and high aspect ratio blades that are characteristic of state of the art LP Turbines. Both rigs are identical with exception of the stator. Therefore, two sets of stators have been manufactured and tested. The aerodynamic shape of both stators has been designed in order to achieve the same spanwise distribution of Cp (Pressure coefficient) over the airfoil surface, each one to its corresponding turning angles. Exit angle in both stators is the same. Therefore the change in turning is obtained by a different inlet angle. The aim of this experiment is to obtain the sensitivity of profile and endwall losses to turning angle by means of a back-to-back comparison between both sets of airfoils. Because the two sets of stators maintain the same pressure coefficient distribution, Reynolds number and Mach number, each one to its corresponding velocity triangles, one can state that the results are only affected by the turning angle. Experimental results are presented and compared in terms of area average, radial pitchwise average distributions and exit plane contours of total pressure losses. CFD simulations for the two sets of stators are also presented and compared with the experimental results.

scholarly journals Experimental Study of Vibrational Acceleration Spread and Comparison Using Three Citrus Canopy Shaker Shaking Tines

2017 ◽  
Vol 2017 ◽  
pp. 1-9 ◽  
Author(s):  
Tian-Hu Liu ◽  
Reza Ehsani ◽  
Arash Toudeshki ◽  
Xiang-Jun Zou ◽  
Hong-Jun Wang
Keyword(s):  
Experimental Study ◽  
Experimental Results ◽  
Average Decrease ◽  
Vibrational Acceleration ◽  
The Difference ◽  
Canopy Shaker

The goal of this article is to experimentally study how the vibrational acceleration spreads along the branch shaken by PVC tine, steel tine, and nylon tine for citrus canopy shaking harvesting and to compare the difference. PVC tine and steel tine have potential to be used as shaking rod for citrus canopy shaking harvesting. Nylon tine is a commonly used shaking rod. A tractor-mounted canopy shaker was developed to do the trial. The shaking frequency was set at 2.5 and 5 Hz. Experimental results showed that the vibrational acceleration at the shaking spot is not the highest. Spreading from shaking spot to the stem, it increases evidently. When spreading from stems of the outside subbranch to stems of the nearest inside subbranch, its average decrease percentage is 42%. The overall vibrational acceleration of shaking at 5 Hz is 1.85 times as high as shaking at 2.5 Hz. The overall vibrational acceleration exerted by straight PVC tine and steel tine is 1.77 and 1.97 times as high as that exerted by straight nylon tine, respectively. It is indicated that replacing nylon tine with steel tine or PVC tine helps remove the fruits inside the canopy. Replacing with steel tine is more effective than with PVC tine.

Object Detection Via Flexible Anchor Generation

2021 ◽  
Author(s):  
Pengxin Ding ◽  
Huan Zhou ◽  
Jinxia Shang ◽  
Xiang Zou ◽  
Minghui Wang
Keyword(s):  
Object Detection ◽  
Detection Performance ◽  
Experimental Results ◽  
Object Size ◽  
The Difference ◽  
Simple Network

This paper designs a method that can generate anchors of various shapes for the object detection framework. This method has the characteristics of novelty and flexibility. Different from the previous anchors generated by a pre-defined manner, our anchors are generated dynamically by an anchor generator. Specially, the anchor generator is not fixed but learned from the hand-designed anchors, which means that our anchor generator is able to work well in various scenes. In the inference time, the weights of anchor generator are estimated by a simple network where the input is some hand-designed anchor. In addition, in order to make the difference between the number of positive and negative samples smaller, we use an adaptive IOU threshold related to the object size to solve this problem. At the same time, we proved that our proposed method is effective and conducted a lot of experiments on the COCO dataset. Experimental results show that after replacing the anchor generation method in the previous object detectors (such as SSD, mask RCNN, and Retinanet) with our proposed method, the detection performance of the model has been greatly improved compared to before the replacement, which proves our method is effective.

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