Table of Content

25 July 2016, Volume 44 Issue 7

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Mechanical Engineering

Vision-Based Welding Deviation Detection for CO₂ Arc Welding

GUO Bo SHI Yong-hua

2016, 44(7):  1-8.  doi:10.3969/j.issn.1000-565X.2016.07.001

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Capturing high-quality welding images and extracting deviation information are two important steps of welding deviation detection.In this paper,on the basis of imaging characteristics analysis in the process CO₂ arc welding,real-time welding images were acquired clearly and steadily by using a wide dynamic range camera.Then,according to the characteristics of welding images,an improved Canny algorithm was developed to detect groove edges,and both Hough transform and prior knowledge were used to connect these edges.Moreover,in order to fit out the edge of weld pool,a differential evolution ellipse detection algorithm on the basis of condition restric- tion was proposed,with which welding deviation can be successfully calculated.Experimental results show that the proposed algorithm possesses strong robustness and high precision,so that it meets the requirements of seam track- ing and welding automation well.

FPGA Fixed-Point Technology of Exponential Function Achieved by CORDIC Algorithm

TANG Wen-ming LIU Gui-xiong

2016, 44(7):  9-14.  doi:10.3969/j.issn.1000-565X.2016.07.002

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Although CORDIC algorithm has been widely used in various transcendental functions,its general itera- tive algorithm is inefficient in using FPGA (Field Programmable Gate Array) to solve the exponential function in a wide-range domain.In order to solve this problem,an FPGA fixed-point technology,which expands the conver- gence region and optimizes the iteration structure to implement CORDIC algorithm solver,is designed.In the inves- tigation,firstly,range compression method is employed to realize the convergence domain expansion of exponential function achieved by CORDIC algorithm.Secondly,the iteration structure of CORDIC algorithm is optimized.Then,the exponential function achieved by CORDIC algorithm is analyzed in a simulative way and implemented in FPGA.Finally,a 15-grade pipeline structure as well as a hyperbolic method is used to implement the expansion in convergence domain of CORDIC algorithm.Simulated and experimental results show that,in comparison with the general CORDIC algorithm,the proposed algorithm saves about 1/3 hardware resources,uses only two DSP multi- plexer units,expands the convergence domain from［－1.1182,1.1182］to［－6,6］,and achieves a relative er- ror low to 10^-3 .

A Probe into Life of Hydraulic Ｒubber Hose in Strong Vibration Environment

YANG Zhong-jiong GAO Yu ZHOU Li-qiang WANG Hui

2016, 44(7):  15-21.  doi:10.3969/j.issn.1000-565X.2016.07.003

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In the process of rock cutting using hard-rock tunnel boring machines,vibration loads may occur,and alternating stress may load on hydraulic rubber hose under the action of vibration load and internal pressure.When the alternating stress exceeds the fatigue limit,fatigue damage may occur.In this paper,on the basis of composite material mechanics and materials mechanics,a mathematical model of hydraulic rubber hose is established.Then,the effects of vibration parameters,oil pressure and hose structure parameters on the life of hose are analyzed through simulation and experiments.The results show that (1) when the excitation frequency of vibration load is close to hose's natural frequency,the hose life reaches the minimum; (2) with the increase of vibration load ampli- tude,the life of rubber hose decreases; (3) at a middle-lower pressure,the change of oil pressure has little effect on the stress loaded on steel wire; and (4) bigger bending radius of hose may result in lower stress.

Transfer Function Representation of Dynamic Circulating Flow Rate of Torque Converter

2016, 44(7):  22-28.  doi:10.3969/j.issn.1000-565X.2016.07.004

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In order to rapidly solve the dynamic response of circulating flow rate of torque converter,a transfer functions representation method for dynamic circulating flow rate is proposed.In this method,through the derivation on the basis of one-dimension flow theory,a torque converter with certain structure is selected as the research ob- ject,and dynamic circulating flow rate is regarded as a first-order linear system's response with the input of static circulating flow rate.Then,the transfer function of dynamic circulating flow system is constructed according to the static and dynamic CFD (Computational Fluid Dynamics) simulation data under simple working conditions in torque converter's common working range.Simulated results show that the proposed method helps achieve a fit goodness of 0.987 for dynamic circulating flow rate prediction in common working range,and a fit goodness of 0.95 for input and output shafts' dynamic torque prediction; and that,in comparison with CFD simulation,the proposed method greatly increases the calculation speed only with a slight decrease in calculation accuracy,so that it is effec- tive in rapidly solving the dynamic response of torque converter.

Control of Shape Deviation for Multi-Point Stretch Bending Profiles

LIANG Ji-cai LI Yi

2016, 44(7):  29-33.  doi:10.3969/j.issn.1000-565X.2016.07.005

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Firstly,the basic formation principle of multi-point stretch bending profiles was expounded,and the cau- ses as well as the influence factors of shape deviation and surface indentation defect for multi-point stretch bending profiles were analyzed.Secondly,by taking into consideration the limitations of conventional profile compensation optimization methods,a new optimization method to control shape deviation and avoid indentation defect was pro- posed.Then,an iterative model of multi-point stretch bending profiles was constructed.Finally,some experiments were carried out to verify the effectiveness of the proposed model.The results indicate that,after the iterative opti- mization of die shape and location,the shape deviation decreases greatly from the maximum 2.32mm to 0.61mm,and the surface indentation defect is controlled effectively.

Bond Graph Model and Simulation of Coaxial Dual-Output Reducer

LIN Chao HUANG Chao CAI Zhi-qin

2016, 44(7):  34-40,54.  doi:10.3969/j.issn.1000-565X.2016.07.006

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In this paper,firstly,the conditions for two output shafts with opposite but uniform speed are analyzed.Secondly,a bond graph model of coaxial dual-output reducer is established on the basis of bond graph theory,in which such factors as average mesh stiffness,rotational inertia and damping are considered.Then,according to the causality and power flow in bond graph,the corresponding equation of state is derived,and a system simulation is conducted to discover the variations of system variables with time and to explore the transmission performance and dynamic characteristics of the system.Moreover,the influences of various parameters on system's dynamic charac- teristics are analyzed by comparing the response curves of output shaft speed at different parameters.Finally,a sim- plified model of coaxial dual-output reducer is established,a virtual prototype experiment is made,and the results are compared with those obtained by bond graph method.It is found that the bond graph theory is effective in the dynamic simulation of coaxial dual-output reducer.

Analysis of Dynamic Characteristics of Hydraulic Torque Converter Applied to Wheel Loader

WANG Zhen-bao QIN Si-cheng

2016, 44(7):  41-46.  doi:10.3969/j.issn.1000-565X.2016.07.007

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In order to analyze the dynamic characteristics of hydraulic torque converter applied to wheel loader,firstly,the original steady performance of hydraulic torque converter was discovered through a bench test.Second- ly,the V-shaped shovel and transport operations of ZL50 wheel loader were tested.Then,on the basis of test data,the distributions of engine torque were analyzed.Moreover,a mathematical model of hydraulic torque converter was established according to Newton's law of motion and used to investigate the dynamic characteristics of hydraulic torque converter in the two above-mentioned working conditions.Finally,a comparison is made between the dyna- mic test values of torque ratio and the static ones.The results show that the dynamic performance of torque converter can be replaced by the steady one when wheel loader is in transport condition.However,as the fluctuation range of angular acceleration is too large in V-shaped shovel operation，the dynamic characteristics must be considered.

Kinematic Calibration of 3-RRR Parallel Mechanism Considering Reducer Backlash

ZHANG Xian-min ZENG Lei

2016, 44(7):  47-54.  doi:10.3969/j.issn.1000-565X.2016.07.008

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In order to improve the positioning accuracy of macro parallel platforms,firstly,an error model of 3- RRR parallel mechanism,which takes into consideration the reducer backlash,is derived,and the effectiveness of the proposed model is verified through a comparison with the error model without considering the reducer backlash.Secondly,an experiment is carried out to measure the attitude error of end-effector and to identify the parameters of the two above-mentioned models.Then,IDWM is employed to realize spatial interpolation and error compensation,followed with a kinematic calibration.Finally,the inverse kinematic model is corrected according to kinematic cali- bration results.It is found from the measured posture error distribution of end-effector that the proposed error model considering reducer backlash is superior to that without considering the backlash.The kinematic calibration conside- ring reducer backlash enhances the positioning accuracy of parallel mechanism and provides a theoretical foundation for the development of high-precision macro-micro parallel mechanisms.

Calculation Model of Friction Force of Nano-Scale Rough Surface on the Basis of LJ Potential and Stochastic Processes

ZHU Sheng-guang HUANG Ping

2016, 44(7):  55-60,69.  doi:10.3969/j.issn.1000-565X.2016.07.009

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On the basis of the potential barrier of contact surfaces and the stochastic properties of contact surface morphology,a new calculation model of sliding friction force loaded on nano-scale rough surface is established.Then,the model is used to numerically calculate the sliding friction force of the same material friction pair with rig- orous stationary process.The results show that the normal load is linear to the mean sliding friction force obtained by the presented model and is exponential to the average surface separation; and that the average normal force in- creases linearly with the standard deviation of roughness height distribution at the same average surface separation.In addition,the calculation results are consistent with the existing research conclusions,which means that the pres- ented model is effective and feasible.With this model,the mean sliding friction force can be predicted according to the distribution parameters of contact interface morphology,material parameters and normal load.

A Probe into Active-Passive Compliant Device for Robotic Peg-in-Hole Assembly

OUYANG Fan ZHANG Tie CHEN Yang

2016, 44(7):  61-69.  doi:10.3969/j.issn.1000-565X.2016.07.010

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In this paper,the conditions for the jamming-free peg-in-hole assembly of holes with coarse internal sur- face are analyzed,and a magnetic force-based active-passive compliant device is designed to avoid the jamming.In this device,a passive compliant section connected by repulsive magnetic force is used to separate the shaft from the end-effector in the process of assembly.Thus,both resistance and resistance moment significantly decrease.After that,a rotational push-pull active compliant section connected by magnetic force is employed to generate a torque for the escape of shaft from jamming point.In addition,a three-axis motion platform with open-structured motion control card and a one-dimension force sensor are deployed to conduct experiments for four pairs of shaft and hole with different diameters.The results indicate that the designed active-passive compliant device can effectively avoid the jamming in the assembly process of holes with coarse internal surface,and that the assembly can be finished within 10 seconds,which means that the proposed device and the corresponding damping control algorithm are both effective.

Measurement of Micro Drill Web Thickness on the Basis of Image Processing

ZHANG Wu-jie NIE Xin-qiao HE Guang-dong

2016, 44(7):  70-76,89.  doi:10.3969/j.issn.1000-565X.2016.07.011

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As the traditional instruments for web thickness measurement is inefficient for the micro drills with an outer diameter of less than 0.30mm,a novel method on the basis of image processing is proposed.In order to im- prove the instrument accuracy,a comparison is made among three subpixel edge detection algorithms,and the gray moment algorithm is selected as the subpixel edge detection algorithm by comprehensively considering the error and time consumption.Then,two micro drills respectively with the diameters of 0.40mm and 0.25mm are used to veri- fy the proposed method.The results show that，for the micro drill with a diameter of 0.40mm,the proposed method on the basis of image processing presents a repeatability of 1μm,which is higher than that of the traditional contact measuring method; and that the repeatability keeps 1μm even for the micro drill with a diameter of 0.25mm,which means that the proposed method is effective in measuring the web thickness of micro drill with a diameter being less than 0.30mm.

Grinding and Meshing Performance of Offset Face Gear Modified with Disk Wheel

FU Xue-zhong FANG Zong-de LI Jian-hua HOU Xiang-ying

2016, 44(7):  77-82.  doi:10.3969/j.issn.1000-565X.2016.07.012

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Firstly,an offset face gear was generated by using a disk wheel,and the topological modification of the gear was achieved through disk wheel's profile modification and center movement control.Secondly,the coordinate systems for grinding and meshing were established,and tooth surface equations of the gear were deduced.Then,by taking into consideration misalignment and topological modification,computational models for tooth contact analysis and loaded tooth contact analysis of the offset face gear pairs were established,and the corresponding computer pro- gram was developed.Finally,some examples were given.The results show that (1) the method of grinding offset face gear with disk wheel is feasible; (2) the tooth surface of the offset face gear is geometrically asymmetrical,and the offset value has an effect on contact patch as well as loaded transmission error but has little influence on transmission error; and (3) the meshing performance of offset face gear pairs can be effectively improved by means of topological modification of the offset face gear.

Architecture & Civil Engineering

A Probe into Nonlinear Stability of Single-Layer Reticulated Shells by Means of Random Imperfection Modal Method

WEI De-min TU Jia-ming

2016, 44(7):  83-89.  doi:10.3969/j.issn.1000-565X.2016.07.013

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The nonlinear stability of Kiewitt-Lamella single-layer reticulated shells is analyzed by means of random imperfection modal method,and the stable ultimate load of the reticulated shell structure,which is affected by both the spatial sample number of random defect and the rise-span ratio,is investigated.Then,a comparison of calcu- lated results is made between random imperfection modal method and consistent imperfection modal method.The results show that (1) the spatial sample number of random defect should be not less than 90 for the stability analy- sis of structures via statistical method; (2) for the reticulated shell structure with large rise-span ratio,the probabi- listic reliability to calculate the critical load via consistent imperfection modal method is rather low,so that it is nece- ssary to verify the critical load with the help of random imperfection modal method; and (3) when the rise-span ra- tio of a single-layer reticulated shell is less than 1/6,the calculated stable bearing capacities obtained by the two a- bove-mentioned initial defect distribution methods are nearly equal.

Accuracy Comparison Between Two Sound Intensity Arrays in Plane Wave and the Corresponding Numerical Analysis

WANG Hong-wei ZHANG Long

2016, 44(7):  90-95,101.  doi:10.3969/j.issn.1000-565X.2016.07.014

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On the basis of the theoretical derivation of three-dimension sound intensity arrays in plane wave,firstly,the sound pressure and the particle velocity are estimated,and the sound intensity spectrum is calculated.Then,a comparison of amplitude bias and directional bias is made between a tetrahedral microphones system and a six-mi- crophone system.Finally,the numerical simulation results are verified through experiments in an anechoic cham- ber.It is found that (1) the magnitude bias expands exponentially as frequency increases; (2) the amplitude bia- ses of the two systems are both less than 0.5dB within the range from 0Hz to 4kHz,which means that the systems both meet the accuracy requirements; (3) the tetrahedral microphones system is superior to the six-microphone sys- tem; and (4) the directional bias of six-microphone system is close to 6° at a frequency of 8kHz,while that of tetra- hedral approach is only 1° and increases slowly in the whole frequency domain,which means that the tetrahedral microphones system exhibits higher directional accuracy than the six-microphone system.

Application of Heterogeneous PV Panels Arranged with Gaps to Top Daylighting of Buildings

BIAN Yu MA Yuan

2016, 44(7):  96-101.  doi:10.3969/j.issn.1000-565X.2016.07.015

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The structure of PV panels arranged with gaps is appropriate for the top daylighting of buildings thanks to its performances of shading,daylighting and power generation.In this paper,by taking into consideration the cli- mate condition in Guangzhou area,4 types of PV structures with various parameters were investigated in a compara- tive way,and an optimized layout scheme of PV panels was selected by comprehensively considering both dayligh- ting performance and power generation capability,namely,constructing a tilt angle of 60° between the PV panel and the horizontal plane to ensure good daylighting performance and provide strong power generation capability,Moreover,the optimized scheme was analyzed in terms of daylighting performance and power generation capability through a building design case.The results show that the presented PV structure possesses good shading perfor- mance,and that it helps achieve an average daylighting factor of 4.9% on the ground being 10m lower the PV structure and an annual power generation capability of 61.8kW·h/m 2 .

Numerical Stimulation of Interface Delamination Failure for Prefabricated Slab Ballastless Track

DAI Gong-lian SU Miao

2016, 44(7):  102-107,122.  doi:10.3969/j.issn.1000-565X.2016.07.016

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Firstly,the failure mode and adhesive mechanism of interface between different layers of ballastless track were analyzed by simplifying temperature load into the shear load of track slab.Then,on the basis of constructive cohesive force model and experimental bond strength parameters of cement asphalt mortar,an interface finite ele- ment model of ballastless track structure was established.Finally,the evolution rules of interfacial stress,interfa- cial bond bearing capacity,interfacial relative displacement and interfacial cracks under the action of shear load were investigated.The results show that (1) both interfacial shear stress and normal stress distribute unevenly and achieve their maximums at the ends of track slab,and interfacial normal stress may result in a tension of track slab at two ends of the slab; (2) under the action of shear load,the interface fails gradually as a result of the interfacial shear stress exceeding the maximum bond strength,and the maximum interfacial bond bearing capacity is 264.8kN; (3) the longitudinal displacement of track slab relatively to mortar-filling layer increases continuously with the shear load and then longitudinal cracks appear; and (4) the relative vertical opening displacement decreases after the in- terface has been cracked,followed with an interfacial shear fracture which may result in the delamination of ballast- less tracks.

Stochastic Process Model of Sulfuric Acid-Caused Corrosion Depth of Concrete

XIAO Jie QU Wen-jun ZHU Peng ZHU Yan-juan

2016, 44(7):  108-115.  doi:10.3969/j.issn.1000-565X.2016.07.017

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Firstly,an accelerated corrosion test was conducted with 6 groups of concrete cylinder specimens to simu- late the sulfuric acid corrosion environment with interrupted corrosion layer.Secondly,the corrosion depths of cor- roded specimens were measured by using a three-dimension (3D) laser scanner and a vernier caliper,respectively.Then,an objective function was proposed with the help of least square cylinder,and the 3D point coordinates ob- tained with 3D laser scanner were treated with Matlab to calculate the corrosion depth of each point on cylinder sur- face.Finally,the corrosion depth was statistically analyzed.The results indicate that the corrosion depth can be ex- pressed as a Gaussian random process with normal distribution; and that both mean value and standard deviation of the depth approximately increase with corrosion time in a linear way.Moreover,it is found that the mean corrosion depth measured with vernier caliper is slightly less than that obtained with 3D laser scanner,while the correspond- ing standard deviation measured with vernier caliper is obviously less than that obtained with 3D laser scanner.As the amount of data obtained with 3D laser scanner is tens of thousands of times as such as that obtained with vernier caliper,it is more reliable to calculate corrosion depth with Gaussian random process model.

Triaxial Tests of Deformation Characteristics of Bottom Ash from Municipal Solid Waste Incineration

SONG Dan-qing XIANG Guo-sheng

2016, 44(7):  116-122.  doi:10.3969/j.issn.1000-565X.2016.07.018

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In order to discover the deformation characteristics of MSWI (Municipal Solid Waste Incineration) bot- tom ash,the material characteristics were analyzed,and consolidated triaxial draining compression tests were car- ried out for the samples with various particle size distribution and immersion time as well as for the remoulded sam- ples after destruction.Thus,the stress-strain curves and effective stress ratio curves of MSWI bottom ash at diffe- rent confining pressures were obtained.The results show that (1) particle size distribution and immersion time are two important factors influencing the deformation characteristics of MSWI bottom ash; (2) for the samples with a particle size being less than 2mm,the strength decreases as the content of large-size particles increases and slightly decreases with the prolonging of immersion time; (3) the strength of remoulded MSWI bottom ash decreases after the destruction; and (4) in comparison with that of the standard sand,the peak of stress-strain curve of MSWI bot- tom ash appears relatively faster.

Integration Methods of Green Building Techniques for Campus in Macau Climatic Region and Corresponding Application

HUANG Jun LIN Yan WANG Shi-xiao

2016, 44(7):  123-129,146.  doi:10.3969/j.issn.1000-565X.2016.07.019

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Macau is located in an area with typical subtropical monsoon climate.It possesses the climate characte- ristics of high temperature,abundant sunshine,high average wind speed,high humidity and plenty of rainfall.The integration methods of green building techniques in Macau should possess an overall goal,diverse means，integrated modules,systematic application and high operation efficiency.In this paper,by systematically investigating the first local building to win the Three-Star Green Certificate,namely the Student Center of the University of Macau,the application of integration methods of green building techniques for campus buildings is illustrated through a practical example.In response to the favorable sunshine and natural ventilation in Macau climatic region,the designers adopts a systematic method integrating passive green building techniques assisted by active green building techniques to realize an organic integration between campus architectures and green building techniques.

Physics

Effects of Noise and Reverberation on Children's Visual Short-Term Memory

PENG Jian-Xin JIANG Peng

2016, 44(7):  130-134.  doi:10.3969/j.issn.1000-565X.2016.07.020

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Visual short-term memory behaviors for Chinese bi-syllable phrases were tested on Grades 3 and 6 chil- dren under the conditions of two different reverberation times and three different interference noise levels,and the effects of noise and reverberation time on the visual short-term memory for Chinese phases of children with different ages were investigated.Then,the differences between auditory memory and visual memory behaviors of children in reverberation and noise environments were analyzed in a comparative way.The results show that (1) both interfer- ence noise level and age have significant effects on the visual short-term memory of children in classroom; (2) with the decrease of interference noise level,the shortening of reverberation time and the increase of children's age,the visual short-term memory scores of children for Chinese phrases increase; and (3) the effects of noise and reverber- ation time on auditory memory behavior are greater than those on visual memory,and the difference in scores be- tween the auditory and visual memory behavior decreases with the decrease of noise level and with the shortening of reverberation time.

Measurement of Individual Pinna Rotation Angle and Customization of Head-Related Transfer Functions

YU Guang-zheng HE Ying-yang LI Zhe-lin

2016, 44(7):  135-141.  doi:10.3969/j.issn.1000-565X.2016.00.021

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The measured value of pinna rotation angle depends on subject's original head position,and the corre- sponding measurement methods of pinna rotation angle may affect the distribution of individual head-related transfer functions (HRTFs) in various elevations.In this paper,both face-based vertical reference plane and Frankfurt refe- rence plane are used to measure and compare the pinna rotation angles of 60 human subjects,and a mean diffe- rence of about 5° is obtained.Then,in order to discover the effect of pinna rotation angle on the spatial distribution of individual HRTFs,the left pinna is rotated on the same ellipsoidal head model with an interval of 5°,and three calculation models respectively corresponding to the pinna rotation angles of 16°,11° and 6° are obtained.Moreo- ver,the HRTFs of the three coupling models are calculated and analyzed by means of the fast multi-pole boundary element method (FM-BEM). The results show that the frequency discrepancy of the pinna notches at high frequen- cies reaches about 1.0kHz,and that the magnitude difference even reaches about 10dB in some directions.In ad- dition,from the individual HRTFs customized via spatial coordinate transformation,it is found that the frequencies and magnitude of pinna notches of the customized HRTFs are similar to those of directly-calculated HRTFs,which means that the proposed individual customization method for individual pinna rotation angle is effective.

A Probe into Characteristics of Acoustic Cavitation Bubbles in Supercritical Fluid

LU Yi-Gang CAI Miao

2016, 44(7):  142-146.  doi:10.3969/j.issn.1000-565X.2016.07.022

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Firstly,according to the physical parameters of substance's critical point,the principles and methods for artificial implantation of cavitation nuclei in supercritical fluid are proposed.Secondly,by analyzing the physical characteristics of supercritical fluid,such as high hydrostatic pressure,low surface tension and no steam inside cavi- tation bubbles,the cavitation threshold of supercritical fluid is derived with the help of Rayleigh model.Then,by comprehensively taking into consideration the strong compressibility and physical characteristics of supercritical fluid,a simplified Gilmore equation for the calculation and analysis of supercritical fluid cavitation is given.More- over,according to the experimental data provided by the American National Standards Institute,density-pressure relationship and sound speed-pressure relationship of supercritical CO₂ fluid are fitted to solve the Gilmore equa- tion.Finally,the effects of initial radius,fluid temperature,sound pressure amplitude and ultrasonic frequency on the ultrasonic cavitation process are analyzed.The results indicate that the threshold of supercritical fluid is similar to hydrostatic pressure; and that,when ultrasonic sound pressure is greater than cavitation threshold,the movement of bubbles under the action of ultrasonic is similar to that of conventional liquids,such as water.