期刊文献+
共找到237篇文章
< 1 2 12 >
每页显示 20 50 100
A Study on the Performances of Solar Air Collectors Having a Hemispherical Dimple on the Absorber Plate
1
作者 Shuilian Li Fan Zeng Xinli Wei 《Fluid Dynamics & Materials Processing》 EI 2024年第5期939-955,共17页
In order to increase the efficiency of solar air collectors,a new variant with a protrusion is proposed in this study,and its performances are analyzed from two points of view,namely,in terms of optics and thermodynam... In order to increase the efficiency of solar air collectors,a new variant with a protrusion is proposed in this study,and its performances are analyzed from two points of view,namely,in terms of optics and thermodynamics aspects.By comparing and analyzing the light paths of the protrusion and the dimple,it can be concluded that when sunlight shines on the dimple,it is reflected and absorbed multiple times,whereas for the sunlight shining on the protrusion,there is no secondary reflection or absorption of light.When the lighting area and the properties of the surfaces are the same,the absorption rate of the dimple is 10.3 percentage points higher than that of the protrusion.In the range of Reynolds number from 3000 to 11000,numerical simulations about the effects of the relative height(e/Dh=0.033–0.1)and relative spacing(p/e=4.5–8.5)of protrusions on air heat transfer and flow resistance show that,in terms of comprehensive evaluation coefficient(PF),the best relative height is 0.085,when the relative spacing is 5.A correlation of Nu and f with Re,e/Dh and p/e is obtained by linear regression of the results,in order to provide a useful reference for the design and optimization of this kind of solar air collector. 展开更多
关键词 Heat transfer hemispherical protrusion DIMPLE solar air collector CORRELATION
下载PDF
The Contribution of Hemispherical Photographs to Understand Natural Forest Regeneration in the AKAK Forest Area
2
作者 Agbor James Ayamba Nkwatoh Athanasius Fuashi Kamah Pascal Bumtu 《Open Journal of Forestry》 2024年第3期313-326,共14页
Examining the contribution of hemispherical photographs in the understanding of Natural forest regeneration is very important in estimating the future forest structure, composition and to enforce conservation regulati... Examining the contribution of hemispherical photographs in the understanding of Natural forest regeneration is very important in estimating the future forest structure, composition and to enforce conservation regulations. This study sets out to examine the interaction between stump sprouting, LAI, site and canopy openness for the entire AKAK forest area and for the logging compartments;2013, 2015 and 2017 respectively. 49 sprouted stump were identified randonly. 20 m × 20 m plots were demarcated along a canopy gaps for each sprouted stump, the plots were established in such a manner that the sprouted stumps will be in the middle. For each of the selected 49 sprouted stump, indirect measurements of canopy cover were performed in the 49 plots of 20 m × 20 m (0.04 ha), giving a total of 1.96 ha of land covered. Galaxy S3 smartphone with a built-in Infinix ZERO 4 fish-eye lens with 198˚ view angle equidistant projection was used to take photos. The fish-eye lens was mounted on the phone camera and photograph were taken at a fixed height of 1.3 m. Results revealed that, the combine Principal Component Factor Analysis (2013, 2015 and 2017) of the correlation matrix for Sprout, Years, LAI 4%, LAI 5%, Canopy and Site openness, shows that factor 1 explained 62.6% of total variance while factor 2 explained 17.9% together explain 80.05% Communalities. For the year 2013, 2015 and 2017 respectively shows that there is a very strong correlation (p p < 0.0005) between LAI4 and LAI5. 展开更多
关键词 hemispherical Photographs Natural Forest Regeneration AKAK Forest
下载PDF
Heavy Metal Detection in Soils by Laser Induced Breakdown Spectroscopy Using Hemispherical Spatial Confinement 被引量:6
3
作者 孟德硕 赵南京 +5 位作者 马明俊 王寅 胡丽 余洋 方丽 刘文清 《Plasma Science and Technology》 SCIE EI CAS CSCD 2015年第8期632-637,共6页
Spatial confinement has great potential for Laser Induced Breakdown Spectroscopy (LIBS) instruments after it has been proven that it has the ability to enhance the LIBS signal strength and repeatability. In order to... Spatial confinement has great potential for Laser Induced Breakdown Spectroscopy (LIBS) instruments after it has been proven that it has the ability to enhance the LIBS signal strength and repeatability. In order to achieve in-situ measurement of heavy metals in farmland soils by LIBS, a hemispherical spatial confinement device is designed and used to collect plasma spectra, in which the optical fibers directly collect the breakdown spectroscopy of the soil samples. This device could effectively increase the stability of the spectrum intensity of soil. It also has other advantages, such as ease of installation, and its small and compact size. The relationship between the spectrum intensity and the laser pulse energy is studied for this device. It is found that the breakdown threshold is 160 cm-2, and when the laser fluence increases to 250 J/cm2, the spectrum intensity reaches its maximum. Four different kinds of laser pulse energy were set up and in each case the limits of detection of Cd, Cu, Ni, Pb and Zn were calculated. The results show that when the laser pulse fluence was 2.12 GW/cm2, we obtained the smallest limits of detection of these heavy metals, which are all under 10 mg/kg. This device can satisfy the needs of heavy metal in-situ detection, and in the next step it will be integrated into a portable LIBS instrument. 展开更多
关键词 laser induced breakdown spectroscopy hemispherical spatial confinement laser fiuence limit of detection
下载PDF
AN ANALYTICAL SOLUTION FOR THREE-DIMENSIONAL DIFFRACTION OF PLANE P-WAVES BY A HEMISPHERICAL ALLUVIAL VALLEY WITH SATURATED SOIL DEPOSITS 被引量:2
4
作者 Zhao Chenggang Dong Jun Gao Fuping 《Acta Mechanica Solida Sinica》 SCIE EI 2006年第2期141-151,共11页
An analytical solution for the three-dimensional scattering and diffraction of plane P-waves by a hemispherical alluvial valley with saturated soil deposits is developed by employing Fourier-Bessel series expansion te... An analytical solution for the three-dimensional scattering and diffraction of plane P-waves by a hemispherical alluvial valley with saturated soil deposits is developed by employing Fourier-Bessel series expansion technique. Unlike previous studies, in which the saturated soil deposits were simulated with the single-phase elastic theory, in this paper, they are simulated with Biot's dynamic theory for saturated porous media, and the half space is assumed as a single-phase elastic medium. The effects of the dimensionless frequency, the incidence angle of P-wave and the porosity of soil deposits on the surface displacement magnifications of the hemispherical alluvial valley are investigated. Numerical results show that the existence of a saturated hemispherical alluvial valley has much influence on the surface displacement magnifications. It is more reasonable to simulate soil deposits with Biot's dynamic theory when evaluating the displacement responses of a hemispherical alluvial valley with an incidence of P-waves. 展开更多
关键词 Biot's dynamic theory three-dimensional scattering hemispherical alluvial valley analytical solution
下载PDF
Seismic responses of a hemispherical alluvial valley to SV waves: a three-dimensional analytical approximation 被引量:1
5
作者 Chenggang Zhao Jun Dong +1 位作者 Fuping Gao D.-S. Jeng 《Acta Mechanica Sinica》 SCIE EI CAS CSCD 2006年第6期547-557,共11页
Abstract An analytical solution to the three-dimen-sional scattering and diffraction of plane SV-waves by a saturated hemispherical alluvial valley in elastic half-space is obtained by using Fourier-Bessel series expa... Abstract An analytical solution to the three-dimen-sional scattering and diffraction of plane SV-waves by a saturated hemispherical alluvial valley in elastic half-space is obtained by using Fourier-Bessel series expan-sion technique. The hemispherical alluvial valley with saturated soil deposits is simulated with Biot's dynamic theory for saturated porous media. The following conclusions based on numerical results can be drawn: (1) there are a significant differences in the seismic response simulation between the previous single-phase models and the present two-phase model; (2) the nor-malized displacements on the free surface of the alluvial valley depend mainly on the incident wave angles, the dimensionless frequency of the incident SV waves and the porosity of sediments; (3) with the increase of the incident angle, the displacement distributions become more complicated; and the displacements on the free surface of the alluvial valley increase as the porosity of sediments increases. 展开更多
关键词 Biot's dynamic theory Saturated porous media Three-dimensional scattering hemispherical alluvial valley
下载PDF
Global and Hemispherical Interannual Variation of Total Column Ozone from TOMS and OMI Data 被引量:2
6
作者 José Luis Pinedo-Vega Mario Molina-Almaraz +2 位作者 Carlos Ríos-Martínez Fernando Mireles-García J. Ignacio Dávila-Rangel 《Atmospheric and Climate Sciences》 2017年第3期247-255,共9页
Daily Total Column Ozone (TCO) measurements compiled from Total Ozone Mapping Spectrometer (TOMS) and Ozone Monitoring Instruments (OMI) were used to analyze the global and hemispherical TCO interannual variations. Tw... Daily Total Column Ozone (TCO) measurements compiled from Total Ozone Mapping Spectrometer (TOMS) and Ozone Monitoring Instruments (OMI) were used to analyze the global and hemispherical TCO interannual variations. Two periods of TCO measurements were analyzed separately covering full years. For the 1978-1994 period, the TCO showed a global decade decrease rate of 13.45 DU (about -4.3%). For the Northern Hemisphere(NH) the decade decrease rate was of 12.96 DU (-4.0%), while in the Southern Hemisphere (SH) was of 13.57 DU (-4.5%). These decreases in ozone trends, using the totality of TOMS and OMI satellite measurements, are greater than those reported in literature. The 1998-2014 period global TCO decade decrease rate was of 1.56 DU, corresponding 0.94 DU and 0.138 DU for the NH and SH, respectively. The global TCO variations must show a double annual periodicity, the first one with maxima in March due to the Northern Hemisphere (NH) and the second one during September due to the Southern Hemisphere (SH). However, the maxima due to SH TCO interannual variations have gradually vanished. A disturbance in the SH TCO interannual variations has appeared since 1980;graphically the periodicity brakes down and transforms to a double peak from 1985 and on. This effect can be attributed to the hemispheric impact of the ozone hole at the South Pole. Between October 1, 2004 and December 14, 2005 TOMS and OMI have recorded this disturbance unequivocally. We conclude that the disturbance in SH TCO has an irreversible character. 展开更多
关键词 GLOBAL and hemispherical OZONE Trends Total Column OZONE Interannual Variation TOMS DATA OMI DATA
下载PDF
Evaluating the impact of sampling schemes on leaf area index measurements from digital hemispherical photography in Larix principis-rupprechtii forest plots
7
作者 Jie Zou Wei Hou +5 位作者 Ling Chen Qianfeng Wang Peihong Zhong Yong Zuo Shezhou Luo Peng Leng 《Forest Ecosystems》 SCIE CSCD 2020年第4期686-703,共18页
Background:Digital hemispherical photography(DHP)is widely used to estimate the leaf area index(LAI)of forest plots due to its advantages of high efficiency and low cost.A crucial step in the LAI estimation of forest ... Background:Digital hemispherical photography(DHP)is widely used to estimate the leaf area index(LAI)of forest plots due to its advantages of high efficiency and low cost.A crucial step in the LAI estimation of forest plots via DHP is choosing a sampling scheme.However,various sampling schemes involving DHP have been used for the LAI estimation of forest plots.To date,the impact of sampling schemes on LAI estimation from DHP has not been comprehensively investigated.Methods:In this study,13 commonly used sampling schemes which belong to five sampling types(i.e.dispersed,square,cross,transect and circle)were adopted in the LAI estimation of five Larix principis-rupprechtii plots(25m×25 m).An additional sampling scheme(with a sample size of 89)was generated on the basis of all the sample points of the 13 sampling schemes.Three typical inversion models and four canopy element clumping index(Ωe)algorithms were involved in the LAI estimation.The impacts of the sampling schemes on four variables,including gap fraction,Ωe,effective plant area index(PAIe)and LAI estimation from DHP were analysed.The LAI estimates obtained with different sampling schemes were then compared with those obtained from litter collection measurements.Results:Large differences were observed for all four variable estimates(i.e.gap fraction,Ωe,PAIe and LAI)under different sampling schemes.The differences in impact of sampling schemes on LAI estimation were not obvious for the three inversion models,if the fourΩe algorithms,except for the traditional gap-size analysis algorithm were adopted in the estimation.The accuracy of LAI estimation was not always improved with an increase in sample size.Moreover,results indicated that with the appropriate inversion model,Ωe algorithm and sampling scheme,the maximum estimation error of DHP-estimated LAI at elementary sampling unit can be less than 20%,which is required by the global climate observing system,except in forest plots with extremely large LAI values(~>6.0).However,obtaining an LAI from DHP with an estimation error lower than 5%is impossible regardless of which combination of inversion model,Ωe algorithm and sampling scheme is used.Conclusion:The LAI estimation of L.principis-rupprechtii forests from DHP was largely affected by the sampling schemes adopted in the estimation.Thus,the sampling scheme should be seriously considered in the LAI estimation.One square and two transect sampling schemes(with sample sizes ranging from 3 to 9)were recommended to be used to estimate the LAI of L.principis-rupprechtii forests with the smallest mean relative error(MRE).By contrast,three cross and one dispersed sampling schemes were identified to provide LAI estimates with relatively large MREs. 展开更多
关键词 Sampling scheme Elementary sampling unit Clumping index Leaf area index Digital hemispherical photography FOREST LARIX
下载PDF
Anisotropic exciton Stark shift in hemispherical quantum dots
8
作者 Shu-Dong Wu 《Chinese Physics B》 SCIE EI CAS CSCD 2021年第5期338-347,共10页
The exciton Stark shift and polarization in hemispherical quantum dots(HQDs)each as a function of strength and orientation of applied electric field are theoretically investigated by an exact diagonalization method.A ... The exciton Stark shift and polarization in hemispherical quantum dots(HQDs)each as a function of strength and orientation of applied electric field are theoretically investigated by an exact diagonalization method.A highly anisotropic Stark redshift of exciton energy is found.As the electric field is rotated from Voigt to Faraday geometry,the redshift of exciton energy monotonically decreases.This is because the asymmetric geometric shape of the hemispherical quantum dot restrains the displacement of the wave function to the higher orbital state in response to electric field along Faraday geometry.A redshift of hole energy is found all the time while a transition of electron energy from this redshift to a blueshift is found as the field is rotated from Voigt to Faraday geometry.Taking advantage of the diminishing of Stark effect along Faraday geometry,the hemispherical shapes can be used to improve significantly the radiative recombination efficiency of the polar optoelectronic devices if the strong internal polarized electric field is along Faraday geometry. 展开更多
关键词 anisotropic Stark shift EXCITON hemispherical quantum dots electric field
原文传递
ON FLEXURAL VIBRATION OF HEMISPHERICAL SHELL
9
作者 樊尚春 刘广玉 王振均 《Applied Mathematics and Mechanics(English Edition)》 SCIE EI 1991年第10期1023-1030,共8页
This paper makes detailed analyses tor the flexural vibration (frequency) of the hemispherical shell and presents the varying laws of frequency with the rarving boundary angles and the wall thickness of the above shel... This paper makes detailed analyses tor the flexural vibration (frequency) of the hemispherical shell and presents the varying laws of frequency with the rarving boundary angles and the wall thickness of the above shell, It is an important value to develop the instrument, such as hemispherical resonator gyro (HRG), whose sensing component is a hemispherical shell. 展开更多
关键词 hemispherical shell fletural vibration resonant frequency resonator gyro
下载PDF
Working Principle and Error Analysis for Hemispherical Resonator Gyro under Force-rebalance Mode
10
作者 Hong-Bo Zhao Shun-Qing Ren 《Journal of Harbin Institute of Technology(New Series)》 EI CAS 2013年第1期75-80,共6页
The two control methods, namely the general-control and the quadrature-control modes for HRG under force-rebalance mode were introduced firstly. Then the azimuth of antinode on the hemispherical resonator was deduced.... The two control methods, namely the general-control and the quadrature-control modes for HRG under force-rebalance mode were introduced firstly. Then the azimuth of antinode on the hemispherical resonator was deduced. The dynamics equations of resonator under the nonuniformity of density distribution were established by way of Bubonov-Galerkin method which is commonly used for solution of differential equations, and the state equation was established through the dynamics equations. The analytic solutions of the vibration displacement and the velocity were achieved by solving the state equation, and then the ratio of rebalance excitation to primary excitation was derived under the two working modes, thus the estimation of input angular rate of HRG were obtained. By comparing and calculating these two modes, the error caused by resonator's machining defects can be greatly inhibited under quadrature-control, and the fourth harmonic density error's tolerance were calculated to ensure the accuracy of HRG under these two modes. 展开更多
关键词 hemispherical resonator gyro force-rebalance mode quadrature-control density distribution nonuniformity
下载PDF
The Gravitational Attraction between Hemispherical Masses
11
作者 Jonathan D. Weiss 《Applied Mathematics》 2017年第6期820-834,共15页
This paper is a study of the gravitational attraction between two uniform hemispherical masses aligned such that the pair is cylindrically symmetric. Three variations are considered: flat side to flat side, curved sid... This paper is a study of the gravitational attraction between two uniform hemispherical masses aligned such that the pair is cylindrically symmetric. Three variations are considered: flat side to flat side, curved side to curved side, and flat side to curved side. Expressions for the second and third variation are derived from the first, with the use of superposition and the well-known gravitational behavior of a spherical mass as equivalent to a point mass at its center. The study covers two masses of equal diameter and of different diameters, such that one is four times that of the other. Calculations are done for separations from zero to fifty times the radius of the larger of the two, which is effectively the asymptotic limit. It is demonstrated that at any separation, the force can be expressed as if the two hemispheres were point masses separated by a certain distance. Expressions for that distance and the location of the (fictitious) point masses within each hemisphere are presented. Unlike the case of two spherical masses, the location within their respective hemisphere is not necessarily the same for each point and both are dependent upon the separation between the two hemispheres. The calculation for the first variation is done in two ways. The first is a “brute force” multi-dimensional integral with the help of Wolfram Mathematica. The second is an axial expansion for the potential modified for off-axis locations by Legendre polynomials. With only a few terms in the expansion, the results of the second method are in extremely good agreement with those of the first. Finally, an interesting application to a split earth is presented. 展开更多
关键词 GRAVITATIONAL ATTRACTION hemispherical Solids LEGENDRE POLYNOMIALS Split Earth
下载PDF
New Methods to Quantify Canopy Structure of Leafless Boreal Birch Forest from Hemispherical Photographs
12
作者 T. D. Reid R. L. H. Essery 《Open Journal of Forestry》 2013年第2期70-74,共5页
Hemispherical photography has been used for many years to measure the physical characteristics of forests, but most related image processing work has focused on leafy canopies or conifers. The boreal forest contains l... Hemispherical photography has been used for many years to measure the physical characteristics of forests, but most related image processing work has focused on leafy canopies or conifers. The boreal forest contains large areas of deciduous trees that remain leafless for over half the year, influencing surface albedo and snow dynamics. Hemispherical photographs of these sparse, twiggy canopies are difficult to acquire and analyze due to bright bark and reflections from snow. This Note presents new methods for producing binary images from hemispherical photographs of a leafless boreal birch forest. Firstly, a thresholding method based on differences between colour panes provides a quick way to remove bright sunlit patches on vegetation. Secondly, an algorithm for joining up fragmented pieces of tree after thresholding ensures a continuous canopy. These methods reduce the estimated hemispherical sky view fraction by up to 6% and 3%, respectively. Although the processing remains subjective to some degree, these tools help to standardize analysis and allow the use of some photographs that might have previously been considered unsuitable for scientific purposes. 展开更多
关键词 hemispherical PHOTOGRAPHY Image Processing Leafless CANOPIES BOREAL FOREST Snow Abisko
下载PDF
Draping Behavior of Carbon Non-Crimp Fabrics and Its Effects on Mechanical Performance of the Hemispherical Composites
13
作者 李龙 肇研 +3 位作者 LIU Gang ZHAO Xiaoran SONG Jiupeng GONG Ming 《Journal of Wuhan University of Technology(Materials Science)》 SCIE EI CAS 2018年第3期720-728,共9页
In order to investigate the draping behavior of non-crimp fabrics(NCFs), two types of carbon NCFs with tricot-chain stitches or chain stitches were formed on a hemispherical mould via a stretch forming process. The ... In order to investigate the draping behavior of non-crimp fabrics(NCFs), two types of carbon NCFs with tricot-chain stitches or chain stitches were formed on a hemispherical mould via a stretch forming process. The shear angle and forming defects of the fabrics were measured on the hemisphere, under different blank holder forces(BHFs). The results showed that increasing BHF could enhance the shear angle slightly, reduce the asymmetry for the deformation of the fabrics, and change the main type of the process-induced defects. Besides, compression tests were performed on the corresponding composite components. By analyzing the change of fiber volume fraction and structural parameters of the textile reinforcements, the effects of draping behavior of NCFs on the mechanical performance of the composites were studied. The results reveal that draping process has distinguishable impacts on the mechanical properties of the final components, which is closely related to the stitching pattern of the NCFs. 展开更多
关键词 non-crimp fabric hemispherical forming shear deformation mechanical properties liquid composite molding
原文传递
Hemispherical resonator with low subsurface damage machined by small ball-end fine diamond grinding wheel:A novel grinding technique 被引量:1
14
作者 Biao QIN Henan LIU +5 位作者 Jian CHENG Jinchuan TIAN Jiangang SUN Zihan ZHOU Chuanzhen MA Mingjun CHEN 《Chinese Journal of Aeronautics》 SCIE EI CAS CSCD 2024年第5期570-585,共16页
As for the ultra-precision grinding of the hemispherical fused silica resonator,due to the hard and brittle nature of fused silica,subsurface damage(SSD)is easily generated,which enormously influences the performance ... As for the ultra-precision grinding of the hemispherical fused silica resonator,due to the hard and brittle nature of fused silica,subsurface damage(SSD)is easily generated,which enormously influences the performance of such components.Hence,ultra-precision grinding experiments are carried out to investigate the surface/subsurface quality of the hemispherical resonator machined by the small ball-end fine diamond grinding wheel.The influence of grinding parameters on the surface roughness(SR)and SSD depth of fused silica samples is then analyzed.The experimental results indicate that the SR and SSD depth decreased with the increase of grinding speed and the decrease of feed rate and grinding depth.In addition,based on the material strain rate and the maximum undeformed chip thickness,the effect of grinding parameters on the subsurface damage mechanism of fused silica samples is analyzed.Furthermore,a multi-step ultra-precision grinding technique of the hemispherical resonator is proposed based on the interaction influence between grinding depth and feed rate.Finally,the hemispherical resonator is processed by the proposed grinding technique,and the SR is improved from 454.328 nm to 110.449 nm while the SSD depth is reduced by 94%from 40μm to 2.379μm.The multi-step grinding technique proposed in this paper can guide the fabrication of the hemispherical resonator. 展开更多
关键词 Fused silica Ultra-precision grinding hemispherical resonator Subsurface damage Grinding technique
原文传递
Experimental investigation about the incipient velocity of spherical particles on a hemispherical bed surface
15
作者 Chuannan Li Jie Chen +2 位作者 Changbo Jiang Xie Li Zhiyuan Wu 《Particuology》 SCIE EI CAS CSCD 2024年第5期49-61,共13页
The sediment particles play a huge role in shaping the bed load transport.In this research,240 water-tunnel experiments are carried out to investigate the incipient velocity of the observation particles in two particl... The sediment particles play a huge role in shaping the bed load transport.In this research,240 water-tunnel experiments are carried out to investigate the incipient velocity of the observation particles in two particle arrangements.To accurately predict the incipient velocity of the observation particles,the equation is conceived by the rolling instability mechanism.The incipient velocity equations and experimental data are used to analyze the trend of dispersive pressure and the effect of arrangement position on velocity.We find that it is appropriate to choose the coefficient of drag as 0.261 and the coefficient of lift as 0.198 for the incipient velocity equation of spherical particles on the hemispherical bed surface.Furthermore,the dispersive pressure is closely related to the flow state,particle size,and particle arrangement,which leads to the incipient velocity of the observation particle being at a minimum when the interference particle angle is 45°.Finally,the particle spacing and the projected area changed with the arrangements,directly affecting the incipient velocity of the observed particle.The analysis of four aspects for the coefficients,dispersive pressure,different particle spacing,and projected area will facilitate the prediction of particle incipient velocity,especially on hemispherical beds. 展开更多
关键词 hemispherical bed surface Observed particle Interference particle Dispersive pressure Incipient velocity
原文传递
A novel method of water bath heating assisted small ball-end magnetorheological polishing for hemispherical shell resonators
16
作者 Jinchuan TIAN Mingjun CHEN +1 位作者 Jian CHENG Henan LIU 《Chinese Journal of Aeronautics》 SCIE EI CAS CSCD 2023年第12期451-460,共10页
Hemispherical shell resonator(HSR)is the core component of hemispherical resonator gyro.It is aφ-shaped small-bore complex component with minimum curvature radius less than 3 mm.Thus,traditional polishing methods are... Hemispherical shell resonator(HSR)is the core component of hemispherical resonator gyro.It is aφ-shaped small-bore complex component with minimum curvature radius less than 3 mm.Thus,traditional polishing methods are difficult to polish it.Small ball-end magnetorheological polishing method can polish the small components with complicated three-dimensional surface and obtain non-destructive surface.Therefore,this method is suitable for polishing HSR.However,the material removal rate of the ordinary small ball-end magnetorheological polishing is low,leading to long polishing time and low output of HSR.To solve this problem,a water bath heating assisted small ball-end magnetorheological polishing method is proposed in this research.The influence rule of processing parameters on the material removal rate is studied experimentally.A set of optimal processing parameters is obtained to maximize the material removal rate.Compared with the ordinary method,the material removal rate of the new method can be improved by 143%.Subsequently,an HSR is polished by the new method.The results show that the polishing time can be reduced by 55%,and the polished surface roughness can reach 7.7 nm.The new method has the great potential to be used in actual production to improve the polishing efficiency of HSR. 展开更多
关键词 hemispherical shell resonator Magnetorheological fluid temperature Material removal rate Optimization Small ball-end magnetorheological polishing
原文传递
Study of the Effect of Acetic Acid and Phosphate on Copper Corrosion by Immersion Tests
17
作者 Yuna Yamaguchi Kaho Sugiura +4 位作者 Toyohiro Arima Fuka Takahashi Itaru Ikeda Yutaka Yamada Osamu Sakurada 《Materials Sciences and Applications》 2024年第1期15-23,共9页
It was reported that hemispheric corrosion occurred in copper tubes in an acetic acid environment. When hemispheric corrosion occurred, corrosion could easily progress if water then flowed into the copper pipe, and co... It was reported that hemispheric corrosion occurred in copper tubes in an acetic acid environment. When hemispheric corrosion occurred, corrosion could easily progress if water then flowed into the copper pipe, and countermeasures were needed. Therefore, we studied the copper corrosion caused by acetic acid. The present work investigated the relationship between the corrosion form of copper and acetic acid concentration using phosphorous-deoxidized copper, and reported that hemispherical corrosion was observed at acetic acid concentrations of 0.01 to 1 vol.% (0.002 to 0.2 mol·L<sup>-1</sup>) in the immersion test. In this study, the effects of acetic acid and phosphate on copper corrosion were examined using oxygen-free copper in immersion tests. The results suggested that different concentrations of phosphate in acetic acid solutions and the presence or absence of acetic acid and phosphate affected the corrosion of copper, resulting in different corrosion forms and corrosion progress. 展开更多
关键词 Acetic Acid PHOSPHATE Oxygen-Free Copper hemispherical Corrosion Ant-Nest Corrosion
下载PDF
Motion equations of hemispherical resonator and analysis of frequency split caused by slight mass non-uniformity 被引量:8
18
作者 Yan HUO Shunqing REN +1 位作者 Guoxing YI Changhong WANG 《Chinese Journal of Aeronautics》 SCIE EI CAS CSCD 2020年第10期2660-2669,共10页
The mass non-uniformity of hemispherical resonator is one of reasons for frequency split,and frequency split can cause gyroscope to drift.Therefore,it is of great significance to analyze the relationship between mass ... The mass non-uniformity of hemispherical resonator is one of reasons for frequency split,and frequency split can cause gyroscope to drift.Therefore,it is of great significance to analyze the relationship between mass non-uniformity and frequency split,which can provide a theoretical basis for mass balance of imperfect resonator.The starting point of error mechanism analysis for gyroscope is the motion equations of resonator.Firstly,based on the Kirchhoff-Love hypothesis in the elastic thin shell theory,the geometric deformation equations of resonator are deduced.Secondly,the deformation energy equation of resonator is derived according to the vibration mode and relationship between the stress and strain of hemispherical thin shell.Thirdly,the kinetic energy equation of resonator is deduced by the Coriolis theorem.Finally,the motion equations of resonator are established by the Lagrange mechanics principle.The theoretical values of precession factor and natural frequency are calculated by the motion equations,which are substantially consistent with the ones by the finite element method and practical measurement,the errors are within a reasonable range.Simultaneously,the varying trend of natural frequency with respect to the geometrical and physical parameters of resonator by the motion equations is consistent with that by the finite element analysis.The above conclusions prove the correctness and rationality of motion equations.Similarly,the motion equations of resonator with mass non-uniformity are established by the same modeling method in case of ignoring the input angular rate and damping,and the state equations with respect to the velocity and displacement of vibration system are derived,then twonatural frequencies are solved by the characteristic equation.It is concluded that one of reasons for frequency split is the 4 th harmonic of mass non-uniformity,and thus much attention should be paid to minimizing the 4 th harmonic of mass non-uniformity in the course of mass balancing for imperfect resonator. 展开更多
关键词 hemispherical resonator Lagrange mechanics principle Theory of elastic thin shell Motion equations Mass non-uniformity Frequency split
原文传递
An experimental investigation of transient cavitation control on a hydrofoil using hemispherical vortex generators 被引量:5
19
作者 Ebrahim Kadivar Takaho Ochiai +1 位作者 Yuka Iga Ould el Moctar 《Journal of Hydrodynamics》 SCIE EI CSCD 2021年第6期1139-1147,共9页
Unsteady cavitation causes noise,damage,and performance decline in the marine engineering and fluid machinery systems.Therefore,finding a method to control the cavitation and its destructive effects is important for t... Unsteady cavitation causes noise,damage,and performance decline in the marine engineering and fluid machinery systems.Therefore,finding a method to control the cavitation and its destructive effects is important for the industrial applications.In this work,we proposed a passive method to control the unsteady behavior of transient cavitation at the medium Reynolds number.For this aim,we performed an experimental study using a high-speed camera to analyze the effects of hemispherical vortex generators(VGs)on the cavitation dynamics around a hydrofoil surface.In addition,the pressure pulsations induced by the collapse of the cavity structures in the wake region of the hydrofoil were captured with a pressure transducer mounted on the wall downstream of the hydrofoil.The results showed that the instability behaviors of the cavity structures on the hydrofoil were mitigated using the proposed cavitation passive control method.In addition,the pressure pulsations in the wake region of the hydrofoil were reduced significantly.It can be concluded that the suppression of cavitation instabilities can improve the operating life and reliability of the marine and hydraulic systems. 展开更多
关键词 Hydrodynamic cavitation cavitation passive control hemispherical vortex generators pressure pulsations high speed observation
原文传递
Standing wave drift of hemispherical resonator with quality factor non-uniformity under a ring electrode excitation 被引量:1
20
作者 Yan HUO Zeyu WANG +3 位作者 Shunqing REN Zhennan WEI Guoxing YI Changhong WANG 《Chinese Journal of Aeronautics》 SCIE EI CAS CSCD 2022年第1期160-172,共13页
Hemispherical Resonator Gyroscope(HRG)is a classical high precision Coriolis Vibration Gyroscope(CVG),which performs attitude estimation of carrier by detecting the precession of standing wave of resonator,thus,the dr... Hemispherical Resonator Gyroscope(HRG)is a classical high precision Coriolis Vibration Gyroscope(CVG),which performs attitude estimation of carrier by detecting the precession of standing wave of resonator,thus,the drift of standing wave of resonator has a great influence on the output accuracy of gyroscope,where the quality factor non-uniformity of resonator is one of main error sources.Ring electrode is a classical excitation structure of HRG because the standing wave can precess freely under its excitation,which makes the gyroscope have more accurate scale factor,larger measurement range and better dynamic characteristics.In this paper,the equations of motion of an ideal resonator excited by a ring electrode are derived by the elastic thin shell theory and Lagrange mechanical principle,then the corresponding equivalent mechanical model is established.According to the“average method”,it can be seen that the ideal resonator excited by the ring electrode works in integral mode,and any position in the circumferential direction of resonator can be a working point,which means that the quality factor non-uniformity has a great effect on the drift of standing wave.Therefore,the equations of motion of resonator with quality factor non-uniformity under the ring electrode excitation are deduced by the equivalent mechanical model,and the drift model of standing wave is established by the“average method”,it can be found that both the amplitude of quality factor non-uniformity and angle between the“inherent damping axis”and antinode axis of standing wave can affect the drift rate of standing wave.Moreover,the drift model indicates that if the input angular rate does not reach the threshold,the precession angular rate of standing wave will appear“self-locking”phenomenon,that is,the gyroscope will lose the integral effect. 展开更多
关键词 hemispherical resonator Theory of elastic thin shell Motion equations Average method Quality factor non-uniformity “Self-locking”phenomenon
原文传递
上一页 1 2 12 下一页 到第
使用帮助 返回顶部