With the development of the dense array,the surface wave velocity and azimuthal anisotropy under the array can be directly obtained by beamforming the noise cross-correlation functions(NCFs). However, the retrieval of...With the development of the dense array,the surface wave velocity and azimuthal anisotropy under the array can be directly obtained by beamforming the noise cross-correlation functions(NCFs). However, the retrieval of the Green’s function by cross-correlating the seismic noise requires that the noise source has a uniform distribution. For the case with uneven noise source, the azimuthal dependence on the sources in the expression for the spatial coherence function, which corresponds to the NCF in the time domain,has the same form as the azimuthal dependence of the surface wave velocity in weakly anisotropic media. Therefore, the uneven noise source will affect the surface wave anisotropy extraction. In this study, three passive seismic methods, i.e.,beamforming, SPAC(spatial autocorrelation), and NCF, are compared to demonstrate that an uneven source distribution and uneven station distribution have equivalent effects on the outcome from each method. A beamforming method is proposed to directly extract the velocity and azimuthal anisotropy of surface waves. The effect of uneven noise source and/or station distribution on estimating the azimuth anisotropy of surface waves was investigated using data from the ChinArray Phase Ⅱ. A method for correcting the apparent anisotropy in beamforming results caused by an uneven station distribution is suggested.展开更多
Visual odometry is critical in visual simultaneous localization and mapping for robot navigation.However,the pose estimation performance of most current visual odometry algorithms degrades in scenes with unevenly dist...Visual odometry is critical in visual simultaneous localization and mapping for robot navigation.However,the pose estimation performance of most current visual odometry algorithms degrades in scenes with unevenly distributed features because dense features occupy excessive weight.Herein,a new human visual attention mechanism for point-and-line stereo visual odometry,which is called point-line-weight-mechanism visual odometry(PLWM-VO),is proposed to describe scene features in a global and balanced manner.A weight-adaptive model based on region partition and region growth is generated for the human visual attention mechanism,where sufficient attention is assigned to position-distinctive objects(sparse features in the environment).Furthermore,the sum of absolute differences algorithm is used to improve the accuracy of initialization for line features.Compared with the state-of-the-art method(ORB-VO),PLWM-VO show a 36.79%reduction in the absolute trajectory error on the Kitti and Euroc datasets.Although the time consumption of PLWM-VO is higher than that of ORB-VO,online test results indicate that PLWM-VO satisfies the real-time demand.The proposed algorithm not only significantly promotes the environmental adaptability of visual odometry,but also quantitatively demonstrates the superiority of the human visual attention mechanism.展开更多
An experimental study was conducted to investigate the properties of stratified regular or wavy two-phase flow in two parallel separators located after a manifold.A total of 103 experiments with various gas and liquid...An experimental study was conducted to investigate the properties of stratified regular or wavy two-phase flow in two parallel separators located after a manifold.A total of 103 experiments with various gas and liquid velocity combinations in three inlet pipes were conducted,including 77 groups of outlet pipe resistance symmetry and 26 groups of outlet pipe resistance asymmetry trials.The experimental results have revealed that when the gas-liquid flow rate is low,the degree of uneven splitting is high,and“extreme”conditions are attained.When the superficial gas velocity is greater than that established in the extreme case,the direction of the liquid-phase displacement is reversed,while that of the gas remains unchanged.Thus,the degree of gas phase bias tends to be mitigated with an increase in the gas velocity,while the uneven splitting degree of liquid approaches 10%.Finally,varying the gas-phase outlet pipe resistance is shown to effectively change the gas-liquid two-phase flow distribution.展开更多
To design a more effective blade pitch adjustment mechanism,research was done on changes to the hydrodynamic characteristics of VVPs(Variable Vector Propeller) caused by different rules for changing pitch angle. A mat...To design a more effective blade pitch adjustment mechanism,research was done on changes to the hydrodynamic characteristics of VVPs(Variable Vector Propeller) caused by different rules for changing pitch angle. A mathematical method for predicting the hydrodynamic characteristics of a VVP under unsteady conditions is presented based on the panel method. Mathematical models for evaluation based on potential flow theory and the Green theorem are also presented. The hydrodynamic characteristics are numerically predicted. To avoid gaps between panels,hyperboloidal quadrilateral panels were used. The pressure Kutta condition on the trailing edge of the VVP blade was satisfied by the Newton-Raphson iterative procedure. The influence coefficients of the panels were calculated by Morino's analytical formulations to improve numerical calculation speed,and the method developed by Yanagizawa was used to eliminate the point singularity on derivation calculus while determining the velocities on propeller surfaces. The calculation results show that it's best for the hydrodynamic characteristics of the VVP that pitch angle changes follow the sine rule.展开更多
A leaching experiment on simulated rare earth ore pillars with uneven grade distribution was conducted because of the readsorption of rare earth elements in the in situ leaching process of ion-adsorption-type rare ear...A leaching experiment on simulated rare earth ore pillars with uneven grade distribution was conducted because of the readsorption of rare earth elements in the in situ leaching process of ion-adsorption-type rare earth ore.Results show that the readsorption of rare earth elements in the barren layer is the main reason for the decrease in rare earth concentration in the leachate,decrease in rare earth recovery and extension of the leaching process.This limitation could be affected by the concentration of rare earth of the influent flow passing through the barren ore layer,and pH value of leaching agents shows minimal effect during leaching.The magnesium sulfate leaching process requires higher liquid-tosolid ratio than the ammonium sulfate leaching process.The former also has lower peak value of rare earth concentration and more significant tailing in the leaching curve.The readsorption of rare earth elements in the barren layer is more severe in magnesium sulfate leaching than in ammonium sulfate leaching.Thus,areas without ore belts should be avoided when magnesium sulfate is used for leaching.展开更多
To address the scale variance and uneven distribution of objects in scenarios of object-counting tasks,an algorithm called Refinement Network(RefNet) is exploited.The proposed top-down scheme sequentially aggregates m...To address the scale variance and uneven distribution of objects in scenarios of object-counting tasks,an algorithm called Refinement Network(RefNet) is exploited.The proposed top-down scheme sequentially aggregates multiscale features,which are laterally connected with low-level information.Trained by a multiresolution density regression loss,a set of intermediate-density maps are estimated on each scale in a multiscale feature pyramid,and the detailed information of the density map is gradually added through coarse-to-fine granular refinement progress to predict the final density map.We evaluate our RefNet on three crowd-counting benchmark datasets,namely,ShanghaiTech,UCFC0,and UCSD,and our method achieves competitive performances on the mean absolute error and root mean squared error compared to the state-of-the-art approaches.We further extend our RefNet to cell counting,illustrating its effectiveness on relative counting tasks.展开更多
Energy piles are a new type of heat exchange systems with buried pipes in a pile foundation,which optimize a ground source heat pump system for the utilization of shallow geothermal energy.In this study,based on the p...Energy piles are a new type of heat exchange systems with buried pipes in a pile foundation,which optimize a ground source heat pump system for the utilization of shallow geothermal energy.In this study,based on the principle of similarity,the thermo-mechanical behavior of the model energy pile with a large cross-section in saturated sandy soil was experimentally evaluated.The pre-cast model concrete pile with a diameter of 0.2 m and length of 1.5 m was buried in saturated sand in a steel box with dimensions of 2.5 m×2.5 m×2.0 m(length×width×height).The pile was heated using water in the polyethylene(PE)pipe,which was connected to a water cycle temperature controller.At a constant inlet water temperature of 55℃,three thermal cycles were carried out with the same heating and cooling periods and different water flow rates.The temperature distributions in the pile and soil,in addition to the pore pressure,soil pressure,and displacement of the pile,were monitored to clarify the thermo-mechanical behavior of the pile and soil.The heat transfer efficiency was analyzed based on the temperature difference and water flow rates.The measured strain at different locations in the pile under cyclic thermal loading revealed that the uneven strain that developed in a pile body should be considered for its long-term application.Furthermore,focus should be directed toward the long-term unrecoverable displacement of the energy pile due to the thermal plastic strain and thermal consolidation of the soil.展开更多
基金supported by the National Key R&D Program of China (No. 2017YFC1500200)National Natural Science Foundation of China (Nos. 41674062 and 41174041)China National Special Fund for Earthquake Scientific Research of Public Interest (No. 201308011)
文摘With the development of the dense array,the surface wave velocity and azimuthal anisotropy under the array can be directly obtained by beamforming the noise cross-correlation functions(NCFs). However, the retrieval of the Green’s function by cross-correlating the seismic noise requires that the noise source has a uniform distribution. For the case with uneven noise source, the azimuthal dependence on the sources in the expression for the spatial coherence function, which corresponds to the NCF in the time domain,has the same form as the azimuthal dependence of the surface wave velocity in weakly anisotropic media. Therefore, the uneven noise source will affect the surface wave anisotropy extraction. In this study, three passive seismic methods, i.e.,beamforming, SPAC(spatial autocorrelation), and NCF, are compared to demonstrate that an uneven source distribution and uneven station distribution have equivalent effects on the outcome from each method. A beamforming method is proposed to directly extract the velocity and azimuthal anisotropy of surface waves. The effect of uneven noise source and/or station distribution on estimating the azimuth anisotropy of surface waves was investigated using data from the ChinArray Phase Ⅱ. A method for correcting the apparent anisotropy in beamforming results caused by an uneven station distribution is suggested.
基金Supported by Tianjin Municipal Natural Science Foundation of China(Grant No.19JCJQJC61600)Hebei Provincial Natural Science Foundation of China(Grant Nos.F2020202051,F2020202053).
文摘Visual odometry is critical in visual simultaneous localization and mapping for robot navigation.However,the pose estimation performance of most current visual odometry algorithms degrades in scenes with unevenly distributed features because dense features occupy excessive weight.Herein,a new human visual attention mechanism for point-and-line stereo visual odometry,which is called point-line-weight-mechanism visual odometry(PLWM-VO),is proposed to describe scene features in a global and balanced manner.A weight-adaptive model based on region partition and region growth is generated for the human visual attention mechanism,where sufficient attention is assigned to position-distinctive objects(sparse features in the environment).Furthermore,the sum of absolute differences algorithm is used to improve the accuracy of initialization for line features.Compared with the state-of-the-art method(ORB-VO),PLWM-VO show a 36.79%reduction in the absolute trajectory error on the Kitti and Euroc datasets.Although the time consumption of PLWM-VO is higher than that of ORB-VO,online test results indicate that PLWM-VO satisfies the real-time demand.The proposed algorithm not only significantly promotes the environmental adaptability of visual odometry,but also quantitatively demonstrates the superiority of the human visual attention mechanism.
基金supported by the National Science and Technology Major Project of China(No.2016ZX05028-004-003).
文摘An experimental study was conducted to investigate the properties of stratified regular or wavy two-phase flow in two parallel separators located after a manifold.A total of 103 experiments with various gas and liquid velocity combinations in three inlet pipes were conducted,including 77 groups of outlet pipe resistance symmetry and 26 groups of outlet pipe resistance asymmetry trials.The experimental results have revealed that when the gas-liquid flow rate is low,the degree of uneven splitting is high,and“extreme”conditions are attained.When the superficial gas velocity is greater than that established in the extreme case,the direction of the liquid-phase displacement is reversed,while that of the gas remains unchanged.Thus,the degree of gas phase bias tends to be mitigated with an increase in the gas velocity,while the uneven splitting degree of liquid approaches 10%.Finally,varying the gas-phase outlet pipe resistance is shown to effectively change the gas-liquid two-phase flow distribution.
文摘To design a more effective blade pitch adjustment mechanism,research was done on changes to the hydrodynamic characteristics of VVPs(Variable Vector Propeller) caused by different rules for changing pitch angle. A mathematical method for predicting the hydrodynamic characteristics of a VVP under unsteady conditions is presented based on the panel method. Mathematical models for evaluation based on potential flow theory and the Green theorem are also presented. The hydrodynamic characteristics are numerically predicted. To avoid gaps between panels,hyperboloidal quadrilateral panels were used. The pressure Kutta condition on the trailing edge of the VVP blade was satisfied by the Newton-Raphson iterative procedure. The influence coefficients of the panels were calculated by Morino's analytical formulations to improve numerical calculation speed,and the method developed by Yanagizawa was used to eliminate the point singularity on derivation calculus while determining the velocities on propeller surfaces. The calculation results show that it's best for the hydrodynamic characteristics of the VVP that pitch angle changes follow the sine rule.
基金financially supported by the National Natural Science Foundation of China (No.5177041221)。
文摘A leaching experiment on simulated rare earth ore pillars with uneven grade distribution was conducted because of the readsorption of rare earth elements in the in situ leaching process of ion-adsorption-type rare earth ore.Results show that the readsorption of rare earth elements in the barren layer is the main reason for the decrease in rare earth concentration in the leachate,decrease in rare earth recovery and extension of the leaching process.This limitation could be affected by the concentration of rare earth of the influent flow passing through the barren ore layer,and pH value of leaching agents shows minimal effect during leaching.The magnesium sulfate leaching process requires higher liquid-tosolid ratio than the ammonium sulfate leaching process.The former also has lower peak value of rare earth concentration and more significant tailing in the leaching curve.The readsorption of rare earth elements in the barren layer is more severe in magnesium sulfate leaching than in ammonium sulfate leaching.Thus,areas without ore belts should be avoided when magnesium sulfate is used for leaching.
文摘To address the scale variance and uneven distribution of objects in scenarios of object-counting tasks,an algorithm called Refinement Network(RefNet) is exploited.The proposed top-down scheme sequentially aggregates multiscale features,which are laterally connected with low-level information.Trained by a multiresolution density regression loss,a set of intermediate-density maps are estimated on each scale in a multiscale feature pyramid,and the detailed information of the density map is gradually added through coarse-to-fine granular refinement progress to predict the final density map.We evaluate our RefNet on three crowd-counting benchmark datasets,namely,ShanghaiTech,UCFC0,and UCSD,and our method achieves competitive performances on the mean absolute error and root mean squared error compared to the state-of-the-art approaches.We further extend our RefNet to cell counting,illustrating its effectiveness on relative counting tasks.
基金This work was supported by the national Natural Science Foundation of China[Grant No(s).5137215551678369]the Technical Innovation Foundation of Shenzhen[Grant No.JCYJ20170302143610976].
文摘Energy piles are a new type of heat exchange systems with buried pipes in a pile foundation,which optimize a ground source heat pump system for the utilization of shallow geothermal energy.In this study,based on the principle of similarity,the thermo-mechanical behavior of the model energy pile with a large cross-section in saturated sandy soil was experimentally evaluated.The pre-cast model concrete pile with a diameter of 0.2 m and length of 1.5 m was buried in saturated sand in a steel box with dimensions of 2.5 m×2.5 m×2.0 m(length×width×height).The pile was heated using water in the polyethylene(PE)pipe,which was connected to a water cycle temperature controller.At a constant inlet water temperature of 55℃,three thermal cycles were carried out with the same heating and cooling periods and different water flow rates.The temperature distributions in the pile and soil,in addition to the pore pressure,soil pressure,and displacement of the pile,were monitored to clarify the thermo-mechanical behavior of the pile and soil.The heat transfer efficiency was analyzed based on the temperature difference and water flow rates.The measured strain at different locations in the pile under cyclic thermal loading revealed that the uneven strain that developed in a pile body should be considered for its long-term application.Furthermore,focus should be directed toward the long-term unrecoverable displacement of the energy pile due to the thermal plastic strain and thermal consolidation of the soil.
