Journal of Northeastern University(Natural Science)

Grid Signal Synchronization Method by Using Cascaded Filter Phase-Locked Loop

WANG An-na， TANG Ai-bo， LIU Yu-ning， SONG Chong-hui

2020, 41 (4): 457-463. DOI: 10.12068/j.issn.1005-3026.2020.04.001

Abstract ( 684 )

HTML

PDF (871KB) ( 811 )

In the case of grid fault conditions， the traditional SRF-PLL has large frequency and phase signal detection errors when performing grid signal synchronization， and a grid signal synchronization method based on cascaded filter phase-locked loop was proposed. In QT1-PLL， the cascaded filtering structure was used to improve the filtering performance and the response speed of the system. The effect of grid frequency offset on phase-locked results can be eliminated by adding phase and amplitude compensation links in the phase-locked loop. Simulation and experimental results showed that accurate frequency and phase detection can be achieved in 1.5 grid periods when the voltage signal has a 20° phase step and 4 Hz frequency step. When the frequency and phase overshoot are 0.5 Hz and 4°， respectively， it can meet the fast and accurate requirements of the grid-connected system， and verify the correctness and effectiveness of the proposed theory.

References | Related Articles | Metrics

Structure Learning Algorithm of Bayesian Networks Based on Markov Blanket

ZHAO Jian-zhe， WU Chen-ni， WANG Xing-wei， PEI Li-ya

2020, 41 (4): 464-470. DOI: 10.12068/j.issn.1005-3026.2020.04.002

Abstract ( 672 )

HTML

PDF (446KB) ( 883 )

The automatic learning of Bayesian network graph structure is a challenge in machine learning. Aiming at the problems of low learning efficiency of traditional algorithm， difficulty in removing redundant edges and determining the direction of the edges in the structure， a Bayesian network structure learning algorithm based on Markov blanket was proposed. The proposed algorithm improves the classical Markov blanket learning algorithm， reduces the number of conditional independent inspections， and is more suitable for Bayesian network structure learning in the subsequent determination of directed structures. At the same time， a general solution for determining the direction of two directed edges was given， which effectively improves the learning efficiency of the learning algorithm. Finally， the Bayesian network-based interconnected cloud QoE evaluation model was established， and the simulation experiment was carried out. The results showed that the improved learning algorithm is superior to the traditional algorithm in prediction accuracy and learning efficiency.

References | Related Articles | Metrics

Fast Segmentation Algorithm of 3D Lung Parenchyma Based on Continuous Max-Flow

ZHAO Hai， ZHOU Bing-ling， ZHU Hong-bo， DOU Sheng-chang

2020, 41 (4): 470-474. DOI: 10.12068/j.issn.1005-3026.2020.04.003

Abstract ( 594 )

HTML

PDF (866KB) ( 713 )

Pulmonary nodules are the main form of lung cancer， which has complex shape and structure and is easy to adhere to normal tissues， making it difficult to segment. A three-dimensional lung parenchyma segmentation method based on spatial constraints was proposed to achieve segmentation of lung parenchyma tissue and acquisition of target regions.First， the SLIC method was used to construct a two-dimensional CT sequence image into a superpixel image matrix， and the matrix was thinned to reduce the dimension of the matrix. Then the nodes between adjacent slices were connected to construct a three-dimensional structure of the lung parenchyma. Finally， the continuous max-flow method was used to segment the constructed three-dimensional lung structure. The experimental results showed that the proposed algorithm can quickly and accurately segment three-dimensional lung parenchyma tissue， and obtain good results for segmentation of different types of lung nodules， which has certain clinical application value.

References | Related Articles | Metrics

Newsvendor Model with Overconfidence Behavior Under CVaR Criterion

CHEN Ke-gui， HUANG Min， WANG Xin-yu

2020, 41 (4): 475-481. DOI: 10.12068/j.issn.1005-3026.2020.04.004

Abstract ( 630 )

HTML

PDF (637KB) ( 613 )

In order to study the ordering strategy of risk-aversion retailers when they have overconfident behaviors in their beliefs in random market demand， CVaR was used as a risk measurement criterion， and an overconfident newsvendor model under CVaR was established. The effect of risk-aversion and overconfidence on retailer’s optimal ordering decision and corresponding conditional risk value was discussed. And the belief condition risk value and actual condition risk value of over confident retailers and fully rational retailers were analyzed. The results showed that overconfidence causes retailer to reduce the risk value of the condition and the order quantity deviates from full rational. Numerical examples verified the validity of the model and provided theoretical support for retailers’ ordering decisions in reality.

References | Related Articles | Metrics

Image Denoising and Enhancement Algorithm Based on Median Filtering and Fractional Order Filtering

ZHANG Xue-feng， YAN Hui

2020, 41 (4): 482-487. DOI: 10.12068/j.issn.1005-3026.2020.04.005

Abstract ( 738 )

HTML

PDF (1573KB) ( 1024 )

In order to avoid the blurring of image by classical median filter， a noise detection model was established. A switching filter was designed by detecting noise. When the detection point is noisy， the median filter was used for denoising. When the detection point is non-noisy point， the fractional differential filter was used to enhance the image. The proposed algorithm can not only effectively remove the salt and pepper noise in the image， but also enhance the image， so that the image retains the details intact when the edge is protruding. Selecting “Lena” and other classic images for multiple experiments and analysis， the results showed the effectiveness of the proposed algorithm in image denoising and enhancement.

References | Related Articles | Metrics

Global Chaotic Bat Optimization Algorithm

CUI Xue-ting， LI Ying， FAN Jia-hao

2020, 41 (4): 488-492. DOI: 10.12068/j.issn.1005-3026.2020.04.006

Abstract ( 658 )

HTML

PDF (370KB) ( 735 )

In order to improve the accuracy of feature selection of bat algorithm， a global chaotic bat optimization algorithm(GCBA) was proposed. Firstly， GCBA adopts chaotic mapping method to enable the initialization of the population to traverse the entire solution space， obtain the optimal position of the bat， and make it more abundant. It solved the problem of initial population randomness. At the same time， GCBA introduces the optimal solution of the current particle and the optimal solution of the current population to jump out of local optimal solutions， which can effectively avoid the premature and improve the global search ability of the algorithm. The results of the bat algorithm(BA)， particle swarm optimization(PSO) and genetic algorithm(GA) on 10 data sets showed that the proposed algorithm has higher classification accuracy and stronger ability to jump out of local optimum.

References | Related Articles | Metrics

Online Estimation Method for State of Health of Electric Vehicle Power Battery

LIU Fang， LIU Xin-yi， SU Wei-xing， LIN Hui

2020, 41 (4): 492-498. DOI: 10.12068/j.issn.1005-3026.2020.04.007

Abstract ( 1058 )

HTML

PDF (767KB) ( 833 )

An effective estimation method for online operation of electric vehicle power battery SOH was proposed. The advantage is that it only relies on the voltage and current data measured by the battery management system in real time， without the need of offline battery life decay curve and the initial state of the battery. Therefore， it is more in line with the actual needs of electric vehicles for SOH estimation. Based on the Thevenin and OCV-SOC models， a battery model with time and SOH as hidden variables was constructed in the battery constant-current charging mode. Based on this battery model， a fast solving algorithm based on NLS(nonlinear least square) initialization GA search range was proposed for online parameter identification， and the real-time SOH estimation value of electric vehicle was obtained. The verification results showed that the SOH estimation algorithm has good practicability and high estimation accuracy.

References | Related Articles | Metrics

Effect of Aging Temperatures on Microstructure and Mechanical Properties of 890MPa Grade Copper-Bearing Steel

KAN Li-ye， YE Qi-bin， WANG Yi-min， WANG Zhao-dong

2020, 41 (4): 499-504. DOI: 10.12068/j.issn.1005-3026.2020.04.008

Abstract ( 613 )

HTML

PDF (5630KB) ( 602 )

According to nano-precipitates strengthening mechanism， an ultra-high strength steel for marine engineering(NEU890) was designed with yield strength of 890MPa. Under the same solid solution conditions， the effects of aging temperature on microstructure， tensile property at room temperature and Charpy impact at -40℃ were studied. The distribution of nano-sized precipitates was analyzed by transmission electron microscopy and the strengthening contribution was estimated. The results showed that the yield strength of the solid solution sample is 852MPa， and the aging yield strength at 500℃ can reach the peak value of 1026MPa， which is achieved by a typical aging precipitation strengthening. The brittle aging temperature range of NEU890 steel is 300~500℃. When the aging temperature is 550~600℃， the yield strength becomes 994~910MPa and the impact energy at -40℃ is 108~166J， which can meet the tensile and impact requirements of EQ91 steel.

References | Related Articles | Metrics

Nitrogen Control Process of COST-FB2 Rotor Steel for Ultra-supercritical Thermal Power Station

PENG Lei-zhen， JIANG Zhou-hua， GENG Xin， LI Xiao-kai

2020, 41 (4): 505-510. DOI: 10.12068/j.issn.1005-3026.2020.04.009

Abstract ( 611 )

HTML

PDF (662KB) ( 577 )

The gas phase nitriding process of COST-FB2 steel was studied by conducting the gas phase nitriding experiment and thermodynamic calculation under different nitrogen partial pressure and nitriding time in a 30kg vacuum induction furnace. The optical emission spectrometer ARL 4460， gas analyzer of TC-500 and infrared analyzer HIR-944B were used to analyze the content in the middle part of ingot sample. The results showed that the calculated data is in a good agreement with the experimental one when the nitriding pressure is ≤20kPa. Since gas phase nitriding is a first-order reaction， the nitrogen content in the tested steel can reach the equilibrium value with the nitriding time of 15min. When the partial pressure of nitrogen is 1.5~6kPa，the mass fraction of nitrogen in COST-FB2 steel can be controlled between 0.015%~0.03%. In order to avoid the formation of porosity defects inside the ingot during casting， pressure casting should be preferred to use with a pressure of at least 20kPa. Moreover， the mass fraction of nitrogen in steel should be controlled between 0.015%~0.02% and the nitrogen partial pressure should be 1.5~3kPa during smelting so that the formation of large particle BN in the tested steel can be avoided.

References | Related Articles | Metrics

Molecular Dynamics Study on Effect of CaF₂ on Melt Structure of CaO-Al₂O₃-CaF₂

ZHANG Xiao-bo， LIU Cheng-jun， JIANG Mao-fa

2020, 41 (4): 510-515. DOI: 10.12068/j.issn.1005-3026.2020.04.010

Abstract ( 618 )

HTML

PDF (1275KB) ( 789 )

In CaO-Al₂O₃-CaF₂ ternary slag system， the variations of the melt structures including the short-range and medium-range structure， and bond-angle change of the slag with different CaF₂ content were studied using molecular dynamics(MD)method. The results showed that the average bond lengths of Ca—F， Al—F， Ca—O and Al—O are 0.2345， 0.1895， 0.2325 and 0.1745nm，respectively. With the addition of CaF₂， there is a dynamic equilibrium between Ca²⁺and the coordination anions(O^2- and F^-)， and the total coordination number(CN)is maintained between 6 and 7. The Al—O tetrahedral structure in the system can be transformed from the complex(Q⁴ and Q³)to simple(Q² and Q¹)structure and from the Al—O tetrahedral［AlO₄］^5- to［AlO₃F］^4- structure， resulted to depolymerize the network structure of the melt. These observations from atomic scale well explain that the addition of CaF₂ can improve the fluidity of CaO-Al₂O₃-CaF₂ slag. The bond angle analysis indicates that the F^- in the system is more likely to replace the original O^2- position and the network structure with the Al³⁺ core has still be a tetrahedral structure， which does not cause a large-scale atomic rearrangement.

References | Related Articles | Metrics

Numerical Simulation of Oxygen Generation Characteristics of Ω-Shaped Step Radial Flow Pressure Swing Adsorbent Bed

FENG Ming-jie， XU Feng-sen， ZHOU Shuai-lei

2020, 41 (4): 516-520. DOI: 10.12068/j.issn.1005-3026.2020.04.011

Abstract ( 629 )

HTML

PDF (1291KB) ( 527 )

In order to improve the performance of PSA oxygen production equipment， an Ω-shaped step radial flow adsorption bed was designed. Using Fluent 16.0 software， the change rule of the flow field， concentration field， oxygen production characteristics and bed penetration time of the adsorption bed were studied by numerical simulations， which were further compared with those in the traditional Π radial flow adsorption bed. The results showed that the penetration time of the Ω-shaped step radial flow adsorption bed is significantly longer than that of the Π-shaped one under the same conditions and the flow unevenness area is greatly reduced. Moreover， for the Ω-shaped bed， the O₂ molar fraction of the production gas can reach 91.8%， which is only 87.1% for the Π-shaped one. There is a great difference in the shape of the high molar fraction O₂ zone in the two types of adsorption beds during adsorption stage. The high molar fraction O₂ zone moves forward in a near cup shape in the Ω-shaped bed， while it becomes a long cone shape in the Π-shaped one.

References | Related Articles | Metrics

Optimal Design of Interval Reliability for Uncertain Structures

WANG Xin-gang， XU Pei-xi， LI Shang-jie， MA Rui-min

2020, 41 (4): 521-527. DOI: 10.12068/j.issn.1005-3026.2020.04.012

Abstract ( 610 )

HTML

PDF (959KB) ( 614 )

The interval reliability for uncertain structures was studied and an optimal design model based on interval reliability was established. By using the model of nested genetic algorithm and radial basis function neural network， the direct optimization of the interval was carried out， which solves the problem of the optimal design based on the interval reliability and avoids the complicated transformation process of the indirect model. The disturbance of the design vector in actual engineering was fully considered， and the constraint of the objective function fluctuation in this case was proposed， so that the objective function and the constraint function still meet the reliability requirements under disturbance. The numerical examples verified the validity and superiority of the model. The proposed model was applied to the optimization of driving slabs with interval uncertain parameters， whose results verified its feasibility and engineering effectiveness.

References | Related Articles | Metrics

Thermal Error Modeling of Machining Center Spindle Based on Physical Modeling Method

KANG Cheng-ming， ZHAO Chun-yu， FU Li-xin

2020, 41 (4): 528-533. DOI: 10.12068/j.issn.1005-3026.2020.04.013

Abstract ( 564 )

HTML

PDF (1533KB) ( 741 )

Aiming at the problem that the thermal error of spindles has a serious impact on the accuracy of machine tools， a thermal error prediction model based on heat transfer theory and thermal deformation mechanism was proposed. Firstly， the real-time temperature field model of the spindle system was derived from an analysis of the heat transfer mechanism. Then， the mechanism of the thermal deformation of the main shaft was analyzed according to the size of the machine tool， and the relationship between the temperature field and the thermal error was obtained with the physical modeling method. Finally， the thermal error simulation and experimental verification of the spindle were carried out on two vertical machining centers of the same type. The results showed that the average prediction accuracy of the spindle thermal error model reaches 95.0%， which proves that the model has high precision and robustness.

References | Related Articles | Metrics

Effect of Different Postures on Burst Fracture of Thoracolumbar Segment

LI Wu-jie， GUO Li-xin

2020, 41 (4): 534-540. DOI: 10.12068/j.issn.1005-3026.2020.04.014

Abstract ( 646 )

HTML

PDF (1381KB) ( 506 )

Based on the statistical results of clinical medicine， a complete and detailed spine finite element model of the T12-L2 thoracolumbar segment was established， and the nonlinear material properties with failure criteria were given to the model to study the biomechanism of spinal burst fractures in different postures. The vertical compressive load was generated by a rigid ball vertically colliding with the thoracolumbar model. Before the collision， the thoracolumbar model was in the upright， forward flexion， and backward extension postures， thereby obtaining the fracture process in three postures and the evaluation parameters of longitudinal height， lateral width， and articular process contact force to evaluate the degree of burst fracture. It was found that in the backward extension posture， the canal stenosis was the most serious in burst fracture.

References | Related Articles | Metrics

Laser-Assisted Grinding Mechanism of Al₂O₃ Ceramics

MA Zhe-lun， YU Kui-dong， DONG Jin-long， YU Tian-biao

2020, 41 (4): 541-546. DOI: 10.12068/j.issn.1005-3026.2020.04.015

Abstract ( 711 )

HTML

PDF (2607KB) ( 1018 )

Aiming at the problems of difficult processing of alumina ceramics and poor surface quality， laser-assisted heating grinding was studied. According to the thermophysical performance parameters of alumina ceramics， the laser-assisted heating grinding mechanism was analyzed， a laser-assisted heating grinding experimental system was built， laser-assisted heating grinding and conventional grinding experiments were performed. The scanning electron microscopy(SEM) and laser confocal analysis were used to analyze the processed workpiece surfaces. The results showed that alumina ceramics can change the material removal method and make the ceramic brittle removal into plastic removal by using the laser-assisted heating grinding. Compared with conventional grinding， the morphology of the processed surface has less brittle fracture， lower surface roughness value， better surface quality and longer service life of the grinding wheel.

References | Related Articles | Metrics

Effect of Pre-stress Time-Characteristics on Grinding Strengthened Surface Stress

NIU Yi-jing， SUN Cong， PANG Gang， XIU Shi-chao

2020, 41 (4): 546-550. DOI: 10.12068/j.issn.1005-3026.2020.04.016

Abstract ( 552 )

HTML

PDF (1913KB) ( 597 )

In order to obtain the residual stress value and martensite content of the hardened layer with different pre-stress unloading times， a pre-stress hardening grinding experiment was carried out. The pre-stress grinding was simulated to obtain the temperature change of the surface layer of the workpiece and the influence of the pre-stress unloading time on the surface’s mechanical thermal stress. Combining the experimental data and simulation， the effects of pre-stress time-characteristics on phase transformation and phase transformation stress were discussed. The results showed that the pre-stress has certain time-characteristics in 7 seconds. With the increase of unloading time， the grain boundary of the crystal is elongated， the content of martensite increases， and the residual compressive stress of the machined surface increases.

References | Related Articles | Metrics

Temperature Field and Stress Field Simulation of Titanium Alloy Laser Fuse Additive Manufacturing

REN Zhao-hui， LIU Zhen， ZHOU Shi-hua， DUAN Jing-xi

2020, 41 (4): 551-556. DOI: 10.12068/j.issn.1005-3026.2020.04.017

Abstract ( 611 )

HTML

PDF (2014KB) ( 944 )

Complex thermal cycling and residual stress distribution during the laser fuse additive forming can cause large deformation or even cracking of the deposited layer. ABAQUS software was used to establish a fully thermo-mechanical coupled finite element model. The mobile heat source subroutine was used to simulate laser loading， and the life-and-death unit technology was used to simulate the addition of materials. The thermal cycle characteristics and residual stress distribution of Ti-6Al-4V titanium alloy’s single-channel multi-layer thin-walled parts during the deposition were studied by considering the latent heat of fusion， convective/radiation heat transfer boundary conditions and material nonlinearity with temperature. The results showed that the deposition process has experienced the rapid heating and rapid cooling. With the increase of the number of layers， the thermal accumulation effect is enhanced. The sedimentary layer is in the tensile stress state and is prone to cracks and other defects.

References | Related Articles | Metrics

Micro-scale Grinding Force of Dental Zirconia Ceramics

ZHOU Yun-guang， DONG Biao， YUE Xin-wei， TAN Yan-qing

2020, 41 (4): 557-562. DOI: 10.12068/j.issn.1005-3026.2020.04.018

Abstract ( 639 )

HTML

PDF (704KB) ( 605 )

Based on the assumption that the shape of conical abrasive with circular edge angles and the protrusion height follow Rayleigh distribution， a mathematical model of undeformed cutting thickness of a single abrasive was established. According to three different sources of the micro-grinding force， a single abrasive was taken as the research object， and a theoretical model of cutting deformation force， plough force and friction force of single abrasive during the grinding process was established. A theoretical model of micro-grinding force was established by combining the number of abrasive per unit area. The verification results of tangential grinding force and normal grinding force prediction models showed that the average error between theoretical and experimental values of tangential grinding force is 7.32%， and the maximum error is less than 10%. The average error of normal grinding force is 8.18%， and the maximum error is less than 20%.

References | Related Articles | Metrics

Magnetite Quartz Pre-treatment Using High Voltage Pulse

GAO Peng， HAN Li-ren， YUAN Shuai， CHEN Hong-yun

2020, 41 (4): 563-568. DOI: 10.12068/j.issn.1005-3026.2020.04.019

Abstract ( 627 )

HTML

PDF (1668KB) ( 711 )

A new type of laboratory high-voltage pulse(HVP) pretreatment technology and a pretreatment-crushing-grinding-weak magnetic separation process were used to investigate the effect of HVP pretreatment technology on the pulverized products of Dagushan magnetite quartzite and on the grade of magnetic separation concentrate.The test results showed that the grade of pretreatment concentrate increases by 7.26%when the grinding concentration，the grinding time， the magnetic field strength and the magnetic separation time are 70%， 3min， 111.4 kA/m and 3min respectively. The analysis of liberation degree showed that the particle size distribution of the pretreated products is more uniform， and the liberation degree of the useful mineral is increased by 17.78%(-0.50mm grain size). The microstructure observed by SEM showed that the cracks inside the pretreated crushed product mainly generate and develop between the adjacent mineral interfaces. The HVP pretreatment technology can reduce the grinding time thus decreasing the energy consumption by promoting the generation and development of microcracks along different mineral grain boundaries within the ore.

References | Related Articles | Metrics

Heavy Metal Pollution and Potential Risk Assessment of Soil in Fushun Western Open-Pit Mining Area

JIANG Bin-hui， ZHANG Bo， WANG Xue-feng， JIANG Qi

2020, 41 (4): 568-574. DOI: 10.12068/j.issn.1005-3026.2020.04.020

Abstract ( 698 )

HTML

PDF (558KB) ( 814 )

By measuring the heavy metal content in the typical area of the mining area， it is found that Cd is the characteristic element of the heavy metal pollution in the mining area. The pollution degree and the potential ecological risk caused by the heavy mental pollution were evaluated by using the single factor pollution index method， the Nemero pollution index method and the potential hazard index method respectively. The results showed that the average values of single element pollution index and Nemero pollution index of Cd are 4.06 and 5.32， respectively， both indicate a heavy pollution. The Nemero pollution index of the three ecological restoration areas are 2.07~4.57， among which the south natural ecological restoration(SNER) area is heavy pollution and the other areas are moderate pollution. The potential ecological risk index of heavy metals in the mining area is 98.62~224.55， the SNER area reaches the medium hazard level， and the remaining areas are evaluated as mild ecological hazards.

References | Related Articles | Metrics

Experimental Study and Numerical Analysis on Flexural Behavior of Flange-Channel Steel Roof Specimen

ZHAO Wen， ZHANG Chao-zhe， WANG Zhi-guo， JIA Peng-jiao

2020, 41 (4): 575-580. DOI: 10.12068/j.issn.1005-3026.2020.04.021

Abstract ( 620 )

HTML

PDF (1037KB) ( 687 )

Based on the flexural tests on the FCSR(flange-channel steel roof) specimens， the working mechanism and failure mode of the specimens were investigated. In order to study the influence of the key parameters， including the tube thickness， the flange thickness， the compressive strength of the concrete and the spacing between the tubes on the flexural behavior of the specimens， finite element models of FCSR specimens were established by using the ABAQUS software. The results indicated that the lateral stiffness of the specimen is high and the failure mode is obvious ductile failure. The wall thickness of the steel pipe and the concrete strength may have certain influence on the bearing capacity of the specimen， while the thickness of the flange plate has no obvious influence on it. It is also found that the spacing of the steel pipe can affect the bearing capacity obviously. The research results may provide some basis for the application of the new pipe roof structure.

References | Related Articles | Metrics

Synergies in Early Hydration Reaction of Slag-Steel Slag-Gypsum System

LI Ying， WU Bao-hua， NI Wen， MU Xin-li

2020, 41 (4): 581-586. DOI: 10.12068/j.issn.1005-3026.2020.04.022

Abstract ( 759 )

HTML

PDF (2643KB) ( 914 )

The reaction process of slag-steel slag-gypsum system in early stage of hydration was studied with a focus on the types， production time， relative production and micromorphology of early hydration products under the single variable conditions. The results showed that both gypsum and steel slag can stimulate the hydration of slag. In early hydration process of slag-steel slag-gypsum cementitious material system， the synergies of slag， steel slag and gypsum can be driven by the formation of ettringite， and the main hydration products are ettringite and C-S-H gel. The very early hydration rate of steel slag and mixture of steel slag and gypsum is fast， which has great significance to adjusting the setting time of slag-steel slag-gypsum cementitious material system.

References | Related Articles | Metrics

Throttling and Acoustic Characteristics of Throttling Orificeplate with Different Configurations

XIE Hui， GE Xi-yun， LIU Jian， LIU Shuai

2020, 41 (4): 587-593. DOI: 10.12068/j.issn.1005-3026.2020.04.023

Abstract ( 693 )

HTML

PDF (1278KB) ( 884 )

In order to explore the effect of hole shape and the structure of the throtting orificeplate on the pressure drop of pipelines and the noise generated by the vibration of the pipeline， the vibration and sound pressure level of four different throtting orificeplate in an anechoic chamber were studied. The mechanism of throtting orificeplate with different configurations were analyzed by numerical simulation. The results show that the mechanical energy loss of flow in throttle pipe with square hole shape is the largest， whose pressure drop is 12.6kPa bigger than that in the pipe with circular hole shape and the same opening. The stress amplitude and the sound pressure level of that pipe are both obviously higher than that of other three pipes. The throttling orificeplate with stepped hole can effectively raises the local minimum pressure of the fluid in the pipe and reduces the occurrence of cavitation， so the radiated sound pressure level of the pipe is the smallest.

References | Related Articles | Metrics

Multifractal Volatility Modeling of Stock Market Considering Jumps and Leverage Effects

ZHANG Tong-hui， YUAN Ying， ZHUANG Xin-tian

2020, 41 (4): 594-598. DOI: 10.12068/j.issn.1005-3026.2020.04.024

Abstract ( 612 )

HTML

PDF (371KB) ( 606 )

Considering the jumping behaviors and leverage effects in the stock market， a new multifractal volatility model was constructed based on the HAR model. Taking 5min high-frequency data of Shanghai composite index and Shenzhen component index as the research samples and using the test method of “model confidence set”(MCS)， the prediction ability of each volatility model to China’s stock market in the two sub-samples of high volatility and low volatility was empirically compared. The results showed that the proposed multifractal volatility measure index and its measurement model have a good predictive function， especially in the period of high(extreme) volatility. The results are expected to provide new ideas and methods for the management and control of financial risks， in particular extreme risks.

References | Related Articles | Metrics

Evaluation of Technological Innovation Capability in China’s Provinces Based on Structural Equation

CHEN Yang， YI Ping-tao， LI Wei-wei

2020, 41 (4): 599-604. DOI: 10.12068/j.issn.1005-3026.2020.04.025

Abstract ( 488 )

HTML

PDF (431KB) ( 571 )

Selecting indicators from the three dimensions of innovation environment， innovation investment and innovation output， an evaluation index system for technological innovation capability was constructed. Aiming at the problem that the index system is characterized by hierarchical structures and has existing correlations， a SEM-G evaluation model was proposed for the indirect importance of the fusion index， and the technological innovation capability of 30 provinces in China from 2009 to 2017 was evaluated and analyzed. It was found that the technological innovation capability of 30 provinces in China is relatively weak， and the development of technological innovation capability in most provinces is insufficient. The level gap between innovation environment，innovation investment and innovation output is significant， and the balance between different innovation elements is low. On this basis， corresponding suggestions were given.

References | Related Articles | Metrics

Positive Solutions of Second-Order Boundary Value Problems with Sign-Changing Green’s Function

ZHANG Guo-wei， QU Xue-bing

2020, 41 (4): 604-608. DOI: 10.12068/j.issn.1005-3026.2020.04.026

Abstract ( 533 )

HTML

PDF (361KB) ( 576 )

The existence of positive solutions for a class of second-order boundary value problems with a sign-changing Green’s function was studied， and the sign-changing Green’s function was caused by different values of coefficients in boundary value conditions， which is different from that the change of the coefficient of the first order of the unknown function usually leads to the change of the Green’s function. When there is no non-negative limitation of nonlinear term， the existence of positive solutions for second-order boundary value problems was proved by giving constraints to the positive and negative parts of Green’s function. The validity of the theoretical results was illustrated by two concrete examples， in which the coefficients of boundary value condition include both positive and negative cases. In addition， two different boundary conditions were explained.

References | Related Articles | Metrics

Archive