Excavation of underground caverns,such as mountain tunnels and energy-storage caverns,may cause the damages to the surrounding rock as a result of the stress redistribution.In this influenced zone,new cracks and disco...Excavation of underground caverns,such as mountain tunnels and energy-storage caverns,may cause the damages to the surrounding rock as a result of the stress redistribution.In this influenced zone,new cracks and discontinuities are created or propagate in the rock mass.Therefore,it is effective to measure and evaluate the acoustic emission(AE)events generated by the rocks,which is a small elastic vibration,and permeability change.The authors have developed a long-term measurement device that incorporates an optical AE(O-AE)sensor,an optical pore pressure sensor,and an optical temperature sensor in a single multi-optical measurement probe(MOP).Japan Atomic Energy Agency has been conducting R&D activities to enhance the reliability of high-level radioactive waste(HLW)deep geological disposal technology.In a high-level radioactive disposal project,one of the challenges is the development of methods for long-term monitoring of rock mass behavior.Therefore,in January 2014,the long-term measurements of the hydro-mechanical behavior of the rock mass were launched using the developed MOP in the vicinity of 350 m below the surface at the Horonobe Underground Research Center.The measurement results show that AEs occur frequently up to 1.5 m from the wall during excavation.In addition,hydraulic conductivity increased by 2e4 orders of magnitude.Elastoplastic analysis revealed that the hydraulic behavior of the rock mass affected the pore pressure fluctuations and caused micro-fractures.Based on this,a conceptual model is developed to represent the excavation damaged zone(EDZ),which contributes to the safe geological disposal of radioactive waste.展开更多
Inspired by the demand of improving the riding comfort and meeting the lightweight design of the vehicle, an inerter-based X-structure nonlinear energy sink(IXNES) is proposed and applied in the half-vehicle system to...Inspired by the demand of improving the riding comfort and meeting the lightweight design of the vehicle, an inerter-based X-structure nonlinear energy sink(IXNES) is proposed and applied in the half-vehicle system to enhance the dynamic performance. The X-structure is used as a mechanism to realize the nonlinear stiffness characteristic of the NES, which can realize the flexibility, adjustability, high efficiency, and easy operation of nonlinear stiffness, and is convenient to apply in the vehicle suspension, and the inerter is applied to replacing the mass of the NES based on the mass amplification characteristic. The dynamic model of the half-vehicle system coupled with the IX-NES is established with the Lagrange theory, and the harmonic balance method(HBM) and the pseudo-arc-length method(PALM) are used to obtain the dynamic response under road harmonic excitation. The corresponding dynamic performance under road harmonic and random excitation is evaluated by six performance indices, and compared with that of the original half-vehicle system to show the benefits of the IX-NES. Furthermore, the structural parameters of the IX-NES are optimized with the genetic algorithm. The results show that for road harmonic and random excitation, using the IX-NES can greatly reduce the resonance peaks and root mean square(RMS) values of the front and rear suspension deflections and the front and rear dynamic tire loads, while the resonance peaks and RMS values of the vehicle body vertical and pitching accelerations are slightly larger.When the structural parameters of the IX-NES are optimized, the vehicle body vertical and pitching accelerations of the half-vehicle system could reduce by 2.41% and 1.16%,respectively, and the other dynamic performance indices are within the reasonable ranges.Thus, the IX-NES combines the advantages of the inerter, X-structure, and NES, which improves the dynamic performance of the half-vehicle system and provides an effective option for vibration attenuation in the vehicle engineering.展开更多
With its complex nonlinear dynamic behavior,the tristable system has shown excellent performance in areas such as energy harvesting and vibration suppression,and has attracted a lot of attention.In this paper,an asymm...With its complex nonlinear dynamic behavior,the tristable system has shown excellent performance in areas such as energy harvesting and vibration suppression,and has attracted a lot of attention.In this paper,an asymmetric tristable design is proposed to improve the vibration suppression efficiency of nonlinear energy sinks(NESs)for the first time.The proposed asymmetric tristable NES(ATNES)is composed of a pair of oblique springs and a vertical spring.Then,the three stable states,symmetric and asymmetric,can be achieved by the adjustment of the distance and stiffness asymmetry of the oblique springs.The governing equations of a linear oscillator(LO)coupled with the ATNES are derived.The approximate analytical solution to the coupled system is obtained by the harmonic balance method(HBM)and verified numerically.The vibration suppression efficiency of three types of ATNES is compared.The results show that the asymmetric design can improve the efficiency of vibration reduction through comparing the chaotic motion of the NES oscillator between asymmetric steady states.In addition,compared with the symmetrical tristable NES(TNES),the ATNES can effectively control smaller structural vibrations.In other words,the ATNES can effectively solve the threshold problem of TNES failure to weak excitation.Therefore,this paper reveals the vibration reduction mechanism of the ATNES,and provides a pathway to expand the effective excitation amplitude range of the NES.展开更多
Differences in forest attributes and carbon sequestration of each organ and layer between broadleaved and conifer forests of central and outer urban areas are not well-defined,hindering the precise management of urban...Differences in forest attributes and carbon sequestration of each organ and layer between broadleaved and conifer forests of central and outer urban areas are not well-defined,hindering the precise management of urban forests and improvement of function.To clarify the effect of two forest types with different urbanization intensities,we determined differences in vegetation composition and diversity,structural traits,and carbon stocks of 152 plots(20 m×20 m)in urban park forests in Changchun,which had the largest green quantity and carbon density effectiveness.We found that 1.1-fold thicker and healthier trees,and 1.6-to 2.0-fold higher,healthier,denser,and more various shrubs but with sparser trees and herbs occurred in the central urban forests(p<0.05)than in the outer forests.The conifer forests exhibited 30–70%obviously higher tree aboveground carbon sequestration(including stem and leaf)and 20%bigger trees,especially in the outer forests(p<0.05).In contrast,1.1-to 1.5-fold higher branch stocks,healthier and more diverse trees were found in broadleaved forests of both the inner and outer forests(p<0.05).Plant size and dominant species had similarly important roles in carbon stock improvement,especially big-sized woody plants and Pinus tabuliformis.In addition,a higher number of deciduous or needle species positively affected the broadleaved forest of the central urban area and conifer forest of the outer urban area,respectively.These findings can be used to guide precise management and accelerate the improvement of urban carbon function in Northeast China in the future.展开更多
With the widespread use of high-power and highly integrated insulated gate bipolar transistor(IGBT),their cooling methods have become challenging.This paper proposes a liquid cooling scheme for heavy-duty automated gu...With the widespread use of high-power and highly integrated insulated gate bipolar transistor(IGBT),their cooling methods have become challenging.This paper proposes a liquid cooling scheme for heavy-duty automated guided vehicle(AGV)motor driver in port environment,and improves heat dissipation by analyzing and optimizing the core component of finned heat sink.Firstly,the temperature distribution of the initial scheme is studied by using Fluent software,and the heat transfer characteristics of the finned heat sink are obtained through numerical analysis.Secondly,an orthogonal test is designed and combined with the response surface methodology to optimize the structural parameters of the finned heat sink,resulting in a 14.57%increase in the heat dissipation effect.Finally,the effectiveness of heat dissipation enhancement is verified.This work provides valuable insights into improving the heat dissipation of IGBT modules and heat sinks,and provides guidance for their future applications.展开更多
This study discusses the magnetohydrodynamic nanofluid flow over an inclined permeable surface influenced by mixed convection, and Cattaeo-Christov heat flux. The heat transfer analysis is performed in the presence of...This study discusses the magnetohydrodynamic nanofluid flow over an inclined permeable surface influenced by mixed convection, and Cattaeo-Christov heat flux. The heat transfer analysis is performed in the presence of a heat source/sink and thermal stratification. To gauge the energy loss during the process, an irreversibility analysis is also performed. A numerical solution to the envisaged problem is obtained using the bvp4c package of MATLAB. Graphs are drawn to assess the consequences of the arising parameters against the associated profiles. The results show that an augmentation in the magnetic field and nanomaterial volume fraction results in an enhancement in the temperature profile. A strong magnetic field can significantly reduce the fluid velocity. The behavior of the Skin friction coefficient against the different estimates of emerging parameters is discussed. .展开更多
In this paper, sinking and growth of apexes and mid-stems of Myriophyllum spicatum L., Hydrilla verticillata (L.f.) Royle and Ceratophyllum demersum L. in concrete ponds containing eutrophic water and sediment were ...In this paper, sinking and growth of apexes and mid-stems of Myriophyllum spicatum L., Hydrilla verticillata (L.f.) Royle and Ceratophyllum demersum L. in concrete ponds containing eutrophic water and sediment were investigated. Sinking rates of apexes and mid-stems reached 34.8% and 4.4% at the 6 th day and 91.1% and 66.7% at the 22 nd day for M. spicatum, 57.8% and 55.6% at the 6 th day and 100% and 97.8% at the 22 nd day for H. vertieillata, 18.9% and 86.7% at the 6 th day and 95.6% and 100% at the 22 nd day for C. demersum, respectively. Most sunken fragments established themselves successfully with significant growth. Total shoot length ofplantlets developed from apexes and mid-stems increased by 399% and 61% for M. spicatum, 593% and 256% for H. vertieillata and 114% and 104% for C. demersum, respectively. The results showed that it was feasible to establish submersed macrophytes via sinking and colonization of shoot fragments clipped off manually.展开更多
We measured the organic content and sinking velocities of biodeposits from two scallop species(Chlamys farreri,Patinopecten yessoensis) and abalone(Haliotis discus hannai) that were cultured on suspended long-lines.Me...We measured the organic content and sinking velocities of biodeposits from two scallop species(Chlamys farreri,Patinopecten yessoensis) and abalone(Haliotis discus hannai) that were cultured on suspended long-lines.Measurements were conducted every two months from April 2010 to February 2011.The shellfish were divided into three size groups(small,middle,and big sizes).At each sample point,we assessedbiodeposit organic content,average sinking velocity,the frequency distribution of sinkingvelocities,and the correlation between organic content and sinking velocity.The organic content of biodeposits varied significantly among months(P<0.05) and the pattern of change varied among species.Sinking velocities varied significantly,ranging from <0.5 cm/s to >1.9 cm/s.The sinking velocities of biodeposits from C.farreri and P.yessoensis were 0.5-1.5 cm/s and from H.discus hannai were <0.7 cm/s.The organic content was significantly negatively correlated to the sinking velocity of biodeposits in C.farreri(P<0.001) and P.yessoensis(P<0.05).展开更多
Artificial freezing of water-bearing soil layers composing a sedimentary deposit can induce frost heave and water migration that affect the natural stress-strain state of the soil layers and freezing process.In the pr...Artificial freezing of water-bearing soil layers composing a sedimentary deposit can induce frost heave and water migration that affect the natural stress-strain state of the soil layers and freezing process.In the present paper,a thermo-hydro-mechanical(THM)model for freezing of water-saturated soil is proposed to study the effects of frost heave and water migration in frozen soils on the formation of a frozen wall and subsequent excavation activity for sinking a vertical shaft.The governing equations of the model are formulated relative to porosity,temperature,and displacement which are considered as primary variables.The relationship between temperature,pore water,and ice pressure in frozen soil is established by the Clausius-Clapeyron equation,whereas the interaction between the stress-strain behavior and changes in porosity and pore pressure is described with the poromechanics theory.Moreover,constitutive relations for additional mechanical deformation are incorporated to describe volumetric expansion of soil during freezing as well as creep strain of soil in the frozen state.The ability of the proposed model to capture the frost heave of frozen soil is demonstrated by a comparison between numerical results and experimental data given by a one-sided freezing test.Also to validate the model in other freezing conditions,a radial freezing experiment is performed.After the validation procedure,the model is applied to numerical simulation of artificial freezing of silt and sand layers for shaft sinking at Petrikov potash mine in Belarus.Comparison of calculated temperature with thermal monitoring data during active freezing stage is presented.Numerical analysis of deformation of unsupported sidewall of a shaft inside the frozen wall is conducted to account for the change in natural stress-strain state of soil layers induced by artificial freezing.展开更多
Transparent exopolymer particles(TEPs)are ubiquitous throughout the oceans,and their sedimentation is considered an efficient biological carbon sink pathway.To investigate the role of coastal TEPs in sinking carbon fr...Transparent exopolymer particles(TEPs)are ubiquitous throughout the oceans,and their sedimentation is considered an efficient biological carbon sink pathway.To investigate the role of coastal TEPs in sinking carbon from the upper layer,samples were collected in the spring and summer of 2011 in the Changjiang River(Yangtze River)Estuary,a typical coastal water.The concentrations and sinking rates of TEPs were measured,and potential sedimentation flux of TEPs was estimated.TEPs concentrations ranged from 40.00μg/L to 1040.00μg/L(mean=(209.70±240.93)μg/L)in spring and 56.67μg/L to 1423.33μg/L(mean=(433.33±393.02)μg/L)in summer,and they were higher at bloom stations than at non-bloom stations during both cruises.A significant positive correlation between TEPs concentration and chlorophyll a(Chl a)concentration was detected,suggesting that phytoplankton was the primary source of TEPs in this area.TEPs sinking rates ranged from 0.08 m/d to 0.57 m/d with a mean of(0.28±0.14)m/d in spring and 0.10 m/d to 1.08 m/d with a mean of(0.34±0.31)m/d in summer.The potential sedimentation flux of TEP-C ranged from 4.95 mg/(m2·d)to 29.40 mg/(m2·d)with a mean of(14.66±8.83)mg/(m2·d)in spring and 6.80 mg/(m2·d)to 30.45 mg/(m2·d)with a mean of(15.71±8.73)mg/(m2·d)in summer,which was^17.81%to 138.27%(mean=65.15%±31.75%)of sedimentation flux of phytoplankton cells in the study area.Due to the increase of TEPs concentrations and their sinking rates,sedimentation fluxes of TEPs at the bloom station were obviously higher than at the non-bloom station during both cruises.This study indicates that TEPs serve as a carbon sink in the Changjiang River Estuary,especially during bloom events,and their sedimentation should be taken into account when we study the carbon sedimentation in the coastal sea.展开更多
In the process of oil field exploitation, radioactive isotope tracer water injection profile logging is a main method to determine the water-intake capacity of the target intervals. For those general water injection w...In the process of oil field exploitation, radioactive isotope tracer water injection profile logging is a main method to determine the water-intake capacity of the target intervals. For those general water injection wells, whose perforated intervals are beyond the tubing shoe, the sinking speed of isotope grains is related to the density and salinity of the injection water and the tubing dimension. We studied the motion of the isotope grains in the water injection wells by both theoretical calculation and field experiment. The result shows that if the water injection quantity is over 20 m&3/d, and the density of the isotope grains, whose diameter is 100-600 μm, is 1.06 g/cm^3, then the logging technique for this kind of water injection wells will be appropriate. Whether water injection profile logging is successful in the well, whose perforated intervals are beyond the tubing shoe, depends on the sinking speed of the tracer grains.展开更多
The rectification of eccentricity was revealed to be more effective in tube sinking than drawing with a mandrel.The ratio of thickness to diameter of tube blank on both sides of thick and thin wall seems to be the pri...The rectification of eccentricity was revealed to be more effective in tube sinking than drawing with a mandrel.The ratio of thickness to diameter of tube blank on both sides of thick and thin wall seems to be the principal influential factor in rectifying eccentricity.The greater the ini- tial outside diameter and the initial wall thickness difference are and the less the initial wall thickness of the tube blank is,the better the rectification is.展开更多
The method of random forest was used to classify the heavy mineral assemblages of 2 418 Jurassic samples in the southern Junggar Basin, and determine the distribution of the heavy mineral assemblages from the same pro...The method of random forest was used to classify the heavy mineral assemblages of 2 418 Jurassic samples in the southern Junggar Basin, and determine the distribution of the heavy mineral assemblages from the same provenance systems. Based on the analysis of heavy minerals assemblages, ZTR index, sedimentary characteristics, U-Pb zircon ages, whole-rock geochemical and paleocurrent direction analysis, the study reveals that five important provenances were providing sediments to the southern Junggar Basin in the Jurassic period: The North Tianshan(NTS), Central Tianshan(CTS), Bogda Mountains, Zhayier Mountains and Kalamaili Mountains. During the Early Jurassic, NTS-CTS, Kalamaili Mountains and Zhayier Mountains are primary provenances, Bogda Mountains started to uplift and supply clastic materials in the Middle Jurassic. There are three sedimentary area in the Jurassic of southern Junggar Basin: the western part, the central part and the eastern part. In the western part, the clastic materials of the Early Jurassic was mainly from NTS blocks and Zhayier Mountains, and the sediments were dominantly derived from the Zhayier Mountains during the Middle–Late Jurassic. In the central part, the main provenance of the Early Jurassic switched from NTS to CTS. In the Xishanyao Formation, the main source went back to NTS again. The NTS was the primary provenance during the sedimentary periods of Toutunhe Formation and Qigu Formation. In the eastern part, the contribution of CTS and Kalamaili Mountains were considered as major provenances in the Early Jurassic-Xishanyao Formation, small proportion of sediments were from NTS. The Bogda mountains uplifted and started to provide sediments to the Junggar Basin in the sedimentary period of Xishanyao Formation, and became the major source during the Toutunhe Formation period, with small amount of sediments from CTS. The provenance from CTS was hindered during the sedimentary period of Qigu Formation owing to the uplifting of the Bogda mountains, and the sediments were mainly from the Bogda mountains and NTS.展开更多
The average swelling height of Qinghai-Xizang Plateau(Tibet) is about 4.1 km.The area is about 2 300 000 km2.It is the highest and the largest plateau in the world.Mount Qomolangma,the highest peak in the world,is loc...The average swelling height of Qinghai-Xizang Plateau(Tibet) is about 4.1 km.The area is about 2 300 000 km2.It is the highest and the largest plateau in the world.Mount Qomolangma,the highest peak in the world,is located in the southern fringe of the plateau,and its height is still increasing.What is the driving force for the rising of the Qinghai-Xizang plateau?How high will the plateau still rise from now on? These questions are much concerned by people.In this paper the distribution of the pressure at different depths in the region of Qinghai-Xizang Plateau are derived according to the three-dimensional structures of the S-wave velocity in the crust and upper mantle.The crust and upper mantle structures of the Qinghai-Xizang Plateau is deliberated on the basis of the distribution with a comprehensive analysis on the rock types,earthquakes and the relative crust movements.Then the two questions raised above are discussed.展开更多
Community group buying is a brand-new retail model,and this retail model is not limited to the first-and second-tier cities in China,and has gradually penetrated into the sinking market.The sinking consumer market is ...Community group buying is a brand-new retail model,and this retail model is not limited to the first-and second-tier cities in China,and has gradually penetrated into the sinking market.The sinking consumer market is changing with each passing day,and community group buying will surely usher in more help in the promotion and application of sinking market areas.The network platform of community group buying also gives full play to the resource advantages of"internet plus",expands the sales of fresh agricultural products,and constantly improves logistics problems to meet the consumer demand of sinking market.This paper introduces the development status of community group buying in China's sinking market,analyzes the existing problems and puts forward corresponding suggestions,and then looks forward to the future development of the industry.Finally,the future development of community group buying platform in the sinking market is prospected.展开更多
Since China announced its goal of becoming carbon-neutral by 2060, carbon neutrality has become a major target in the development of China's urban agglomerations. This study applied the Future Land Use Simulation(...Since China announced its goal of becoming carbon-neutral by 2060, carbon neutrality has become a major target in the development of China's urban agglomerations. This study applied the Future Land Use Simulation(FLUS) model to predict the land use pattern of the ecological space of the Beibu Gulf urban agglomeration, in 2060 under ecological priority, agricultural priority and urbanized priority scenarios. The Integrated Valuation of Ecosystem Services and Trade-offs(In VEST) model was employed to analyse the spatial changes in ecological space carbon storage in each scenario from 2020 to 2060. Then, this study used a Geographically Weighted Regression(GWR) model to determine the main driving factors that influence the changes in land carbon sinking capacity. The results of the study can be summarised as follows: firstly, the agricultural and ecological priority scenarios will achieve balanced urban expansion and environmental protection of resources in an ecological space. The urbanized priority scenario will reduce the carbon sinking capacity. Among the simulation scenarios for 2060, carbon storage in the urbanized priority scenario will decrease by 112.26 × 10^(6) t compared with that for 2020 and the average carbon density will decrease by 0.96 kg/m^(2) compared with that for 2020. Carbon storage in the agricultural priority scenario will increase by 84.11 × 10^(6) t, and the average carbon density will decrease by 0.72 kg/m^(2). Carbon storage in the ecological priority scenario will increase by 3.03 × 10^(6) t, and the average carbon density will increase by 0.03 kg/m^(2). Under the premise that the population of the town will increases continuously, the ecological priority development approach may be a wise choice.Secondly, slope, distance to river and elevation are the most important factors that influence the carbon sink pattern of the ecological space in the Beibu Gulf urban agglomeration, followed by GDP, population density, slope direction and distance to traffic infrastructure.At the same time, urban space expansion is the main cause of the changes of this natural factors. Thirdly, the decreasing trend of ecological space is difficult to reverse, so reasonable land use policy to curb the spatial expansion of cities need to be made.展开更多
Fluid-conveying pipes are widely used to transfer bulk fluids from one point to another in many engineering applications.They are subject to various excitations from the conveying fluids,the supporting structures,and ...Fluid-conveying pipes are widely used to transfer bulk fluids from one point to another in many engineering applications.They are subject to various excitations from the conveying fluids,the supporting structures,and the working environment,and thus are prone to vibrations such as flow-induced vibrations and acoustic-induced vibrations.Vibrations can generate variable dynamic stress and large deformation on fluid-conveying pipes,leading to vibration-induced fatigue and damage on the pipes,or even leading to failure of the entire piping system and catastrophic accidents.Therefore,the vibration control of fluid-conveying pipes is essential to ensure the integrity and safety of pipeline systems,and has attracted considerable attention from both researchers and engineers.The present paper aims to provide an extensive review of the state-of-the-art research on the vibration control of fluid-conveying pipes.The vibration analysis of fluid-conveying pipes is briefly discussed to show some key issues involved in the vibration analysis.Then,the research progress on the vibration control of fluid-conveying pipes is reviewed from four aspects in terms of passive control,active vibration control,semi-active vibration control,and structural optimization design for vibration reduction.Furthermore,the main results of existing research on the vibration control of fluid-conveying pipes are summarized,and future promising research directions are recommended to address the current research gaps.This paper contributes to the understanding of vibration control of fluid-conveying pipes,and will help the research work on the vibration control of fluidconveying pipes attract more attention.展开更多
文摘Excavation of underground caverns,such as mountain tunnels and energy-storage caverns,may cause the damages to the surrounding rock as a result of the stress redistribution.In this influenced zone,new cracks and discontinuities are created or propagate in the rock mass.Therefore,it is effective to measure and evaluate the acoustic emission(AE)events generated by the rocks,which is a small elastic vibration,and permeability change.The authors have developed a long-term measurement device that incorporates an optical AE(O-AE)sensor,an optical pore pressure sensor,and an optical temperature sensor in a single multi-optical measurement probe(MOP).Japan Atomic Energy Agency has been conducting R&D activities to enhance the reliability of high-level radioactive waste(HLW)deep geological disposal technology.In a high-level radioactive disposal project,one of the challenges is the development of methods for long-term monitoring of rock mass behavior.Therefore,in January 2014,the long-term measurements of the hydro-mechanical behavior of the rock mass were launched using the developed MOP in the vicinity of 350 m below the surface at the Horonobe Underground Research Center.The measurement results show that AEs occur frequently up to 1.5 m from the wall during excavation.In addition,hydraulic conductivity increased by 2e4 orders of magnitude.Elastoplastic analysis revealed that the hydraulic behavior of the rock mass affected the pore pressure fluctuations and caused micro-fractures.Based on this,a conceptual model is developed to represent the excavation damaged zone(EDZ),which contributes to the safe geological disposal of radioactive waste.
基金Project supported by the National Natural Science Foundation of China (Nos. 12172153 and51805216)the China Postdoctoral Science Foundation (No. 2023M731668)the Major Project of Basic Science (Natural Science) of the Jiangsu Higher Education Institutions of China(No. 22KJA410001)。
文摘Inspired by the demand of improving the riding comfort and meeting the lightweight design of the vehicle, an inerter-based X-structure nonlinear energy sink(IXNES) is proposed and applied in the half-vehicle system to enhance the dynamic performance. The X-structure is used as a mechanism to realize the nonlinear stiffness characteristic of the NES, which can realize the flexibility, adjustability, high efficiency, and easy operation of nonlinear stiffness, and is convenient to apply in the vehicle suspension, and the inerter is applied to replacing the mass of the NES based on the mass amplification characteristic. The dynamic model of the half-vehicle system coupled with the IX-NES is established with the Lagrange theory, and the harmonic balance method(HBM) and the pseudo-arc-length method(PALM) are used to obtain the dynamic response under road harmonic excitation. The corresponding dynamic performance under road harmonic and random excitation is evaluated by six performance indices, and compared with that of the original half-vehicle system to show the benefits of the IX-NES. Furthermore, the structural parameters of the IX-NES are optimized with the genetic algorithm. The results show that for road harmonic and random excitation, using the IX-NES can greatly reduce the resonance peaks and root mean square(RMS) values of the front and rear suspension deflections and the front and rear dynamic tire loads, while the resonance peaks and RMS values of the vehicle body vertical and pitching accelerations are slightly larger.When the structural parameters of the IX-NES are optimized, the vehicle body vertical and pitching accelerations of the half-vehicle system could reduce by 2.41% and 1.16%,respectively, and the other dynamic performance indices are within the reasonable ranges.Thus, the IX-NES combines the advantages of the inerter, X-structure, and NES, which improves the dynamic performance of the half-vehicle system and provides an effective option for vibration attenuation in the vehicle engineering.
基金Project supported by the National Science Fund for Distinguished Young Scholars of China(No.12025204)the National Natural Science Foundation of China(No.12202038)。
文摘With its complex nonlinear dynamic behavior,the tristable system has shown excellent performance in areas such as energy harvesting and vibration suppression,and has attracted a lot of attention.In this paper,an asymmetric tristable design is proposed to improve the vibration suppression efficiency of nonlinear energy sinks(NESs)for the first time.The proposed asymmetric tristable NES(ATNES)is composed of a pair of oblique springs and a vertical spring.Then,the three stable states,symmetric and asymmetric,can be achieved by the adjustment of the distance and stiffness asymmetry of the oblique springs.The governing equations of a linear oscillator(LO)coupled with the ATNES are derived.The approximate analytical solution to the coupled system is obtained by the harmonic balance method(HBM)and verified numerically.The vibration suppression efficiency of three types of ATNES is compared.The results show that the asymmetric design can improve the efficiency of vibration reduction through comparing the chaotic motion of the NES oscillator between asymmetric steady states.In addition,compared with the symmetrical tristable NES(TNES),the ATNES can effectively control smaller structural vibrations.In other words,the ATNES can effectively solve the threshold problem of TNES failure to weak excitation.Therefore,this paper reveals the vibration reduction mechanism of the ATNES,and provides a pathway to expand the effective excitation amplitude range of the NES.
基金the Youth Growth Technology Project,Science and Technology Department of Jilin Province(20230508130RC)Bureau of Forestry and Landscaping of Changchun.
文摘Differences in forest attributes and carbon sequestration of each organ and layer between broadleaved and conifer forests of central and outer urban areas are not well-defined,hindering the precise management of urban forests and improvement of function.To clarify the effect of two forest types with different urbanization intensities,we determined differences in vegetation composition and diversity,structural traits,and carbon stocks of 152 plots(20 m×20 m)in urban park forests in Changchun,which had the largest green quantity and carbon density effectiveness.We found that 1.1-fold thicker and healthier trees,and 1.6-to 2.0-fold higher,healthier,denser,and more various shrubs but with sparser trees and herbs occurred in the central urban forests(p<0.05)than in the outer forests.The conifer forests exhibited 30–70%obviously higher tree aboveground carbon sequestration(including stem and leaf)and 20%bigger trees,especially in the outer forests(p<0.05).In contrast,1.1-to 1.5-fold higher branch stocks,healthier and more diverse trees were found in broadleaved forests of both the inner and outer forests(p<0.05).Plant size and dominant species had similarly important roles in carbon stock improvement,especially big-sized woody plants and Pinus tabuliformis.In addition,a higher number of deciduous or needle species positively affected the broadleaved forest of the central urban area and conifer forest of the outer urban area,respectively.These findings can be used to guide precise management and accelerate the improvement of urban carbon function in Northeast China in the future.
基金Supported by the National Key Research and Development Plan Program(No.2022YFB4701101)National Natural Science Foundation of Chi-na(No.U1913211)Natural Science Foundation of Hebei Province of China(No.F2021202062)。
文摘With the widespread use of high-power and highly integrated insulated gate bipolar transistor(IGBT),their cooling methods have become challenging.This paper proposes a liquid cooling scheme for heavy-duty automated guided vehicle(AGV)motor driver in port environment,and improves heat dissipation by analyzing and optimizing the core component of finned heat sink.Firstly,the temperature distribution of the initial scheme is studied by using Fluent software,and the heat transfer characteristics of the finned heat sink are obtained through numerical analysis.Secondly,an orthogonal test is designed and combined with the response surface methodology to optimize the structural parameters of the finned heat sink,resulting in a 14.57%increase in the heat dissipation effect.Finally,the effectiveness of heat dissipation enhancement is verified.This work provides valuable insights into improving the heat dissipation of IGBT modules and heat sinks,and provides guidance for their future applications.
文摘This study discusses the magnetohydrodynamic nanofluid flow over an inclined permeable surface influenced by mixed convection, and Cattaeo-Christov heat flux. The heat transfer analysis is performed in the presence of a heat source/sink and thermal stratification. To gauge the energy loss during the process, an irreversibility analysis is also performed. A numerical solution to the envisaged problem is obtained using the bvp4c package of MATLAB. Graphs are drawn to assess the consequences of the arising parameters against the associated profiles. The results show that an augmentation in the magnetic field and nanomaterial volume fraction results in an enhancement in the temperature profile. A strong magnetic field can significantly reduce the fluid velocity. The behavior of the Skin friction coefficient against the different estimates of emerging parameters is discussed. .
基金Supported by the National Natural Science Foundation of China (39925007)the High Technology Research and Development Program of China (2002AA60l021)the Knowledge Innovation Program Key Project of Chinese Academy of Sciences (KSCX2-SW-102)
文摘In this paper, sinking and growth of apexes and mid-stems of Myriophyllum spicatum L., Hydrilla verticillata (L.f.) Royle and Ceratophyllum demersum L. in concrete ponds containing eutrophic water and sediment were investigated. Sinking rates of apexes and mid-stems reached 34.8% and 4.4% at the 6 th day and 91.1% and 66.7% at the 22 nd day for M. spicatum, 57.8% and 55.6% at the 6 th day and 100% and 97.8% at the 22 nd day for H. vertieillata, 18.9% and 86.7% at the 6 th day and 95.6% and 100% at the 22 nd day for C. demersum, respectively. Most sunken fragments established themselves successfully with significant growth. Total shoot length ofplantlets developed from apexes and mid-stems increased by 399% and 61% for M. spicatum, 593% and 256% for H. vertieillata and 114% and 104% for C. demersum, respectively. The results showed that it was feasible to establish submersed macrophytes via sinking and colonization of shoot fragments clipped off manually.
基金Supported by the National Key Technology Research and Development Program of China(No.2011BAD13B06)the National Natural Science Foundation of China(No.41276172)the Special Scientific Research Funds For Central Non-Profit Institute,CAFS(No.2014A01YY01)
文摘We measured the organic content and sinking velocities of biodeposits from two scallop species(Chlamys farreri,Patinopecten yessoensis) and abalone(Haliotis discus hannai) that were cultured on suspended long-lines.Measurements were conducted every two months from April 2010 to February 2011.The shellfish were divided into three size groups(small,middle,and big sizes).At each sample point,we assessedbiodeposit organic content,average sinking velocity,the frequency distribution of sinkingvelocities,and the correlation between organic content and sinking velocity.The organic content of biodeposits varied significantly among months(P<0.05) and the pattern of change varied among species.Sinking velocities varied significantly,ranging from <0.5 cm/s to >1.9 cm/s.The sinking velocities of biodeposits from C.farreri and P.yessoensis were 0.5-1.5 cm/s and from H.discus hannai were <0.7 cm/s.The organic content was significantly negatively correlated to the sinking velocity of biodeposits in C.farreri(P<0.001) and P.yessoensis(P<0.05).
基金supported by 17-11-01204 project(Russian Science Foundation)。
文摘Artificial freezing of water-bearing soil layers composing a sedimentary deposit can induce frost heave and water migration that affect the natural stress-strain state of the soil layers and freezing process.In the present paper,a thermo-hydro-mechanical(THM)model for freezing of water-saturated soil is proposed to study the effects of frost heave and water migration in frozen soils on the formation of a frozen wall and subsequent excavation activity for sinking a vertical shaft.The governing equations of the model are formulated relative to porosity,temperature,and displacement which are considered as primary variables.The relationship between temperature,pore water,and ice pressure in frozen soil is established by the Clausius-Clapeyron equation,whereas the interaction between the stress-strain behavior and changes in porosity and pore pressure is described with the poromechanics theory.Moreover,constitutive relations for additional mechanical deformation are incorporated to describe volumetric expansion of soil during freezing as well as creep strain of soil in the frozen state.The ability of the proposed model to capture the frost heave of frozen soil is demonstrated by a comparison between numerical results and experimental data given by a one-sided freezing test.Also to validate the model in other freezing conditions,a radial freezing experiment is performed.After the validation procedure,the model is applied to numerical simulation of artificial freezing of silt and sand layers for shaft sinking at Petrikov potash mine in Belarus.Comparison of calculated temperature with thermal monitoring data during active freezing stage is presented.Numerical analysis of deformation of unsupported sidewall of a shaft inside the frozen wall is conducted to account for the change in natural stress-strain state of soil layers induced by artificial freezing.
基金Foundation item:The National Key Research and Development Project of China under contract No.2019YFC1407805the National Natural Science Foundation of China under contract Nos 41876134,91751202,31700425,41676112 and 41276124+1 种基金the Tianjin 131 Innovation Team Program under contract No.20180314the Changjiang Scholar Program of Chinese Ministry of Education(T2014253)to Jun Sun.
文摘Transparent exopolymer particles(TEPs)are ubiquitous throughout the oceans,and their sedimentation is considered an efficient biological carbon sink pathway.To investigate the role of coastal TEPs in sinking carbon from the upper layer,samples were collected in the spring and summer of 2011 in the Changjiang River(Yangtze River)Estuary,a typical coastal water.The concentrations and sinking rates of TEPs were measured,and potential sedimentation flux of TEPs was estimated.TEPs concentrations ranged from 40.00μg/L to 1040.00μg/L(mean=(209.70±240.93)μg/L)in spring and 56.67μg/L to 1423.33μg/L(mean=(433.33±393.02)μg/L)in summer,and they were higher at bloom stations than at non-bloom stations during both cruises.A significant positive correlation between TEPs concentration and chlorophyll a(Chl a)concentration was detected,suggesting that phytoplankton was the primary source of TEPs in this area.TEPs sinking rates ranged from 0.08 m/d to 0.57 m/d with a mean of(0.28±0.14)m/d in spring and 0.10 m/d to 1.08 m/d with a mean of(0.34±0.31)m/d in summer.The potential sedimentation flux of TEP-C ranged from 4.95 mg/(m2·d)to 29.40 mg/(m2·d)with a mean of(14.66±8.83)mg/(m2·d)in spring and 6.80 mg/(m2·d)to 30.45 mg/(m2·d)with a mean of(15.71±8.73)mg/(m2·d)in summer,which was^17.81%to 138.27%(mean=65.15%±31.75%)of sedimentation flux of phytoplankton cells in the study area.Due to the increase of TEPs concentrations and their sinking rates,sedimentation fluxes of TEPs at the bloom station were obviously higher than at the non-bloom station during both cruises.This study indicates that TEPs serve as a carbon sink in the Changjiang River Estuary,especially during bloom events,and their sedimentation should be taken into account when we study the carbon sedimentation in the coastal sea.
文摘In the process of oil field exploitation, radioactive isotope tracer water injection profile logging is a main method to determine the water-intake capacity of the target intervals. For those general water injection wells, whose perforated intervals are beyond the tubing shoe, the sinking speed of isotope grains is related to the density and salinity of the injection water and the tubing dimension. We studied the motion of the isotope grains in the water injection wells by both theoretical calculation and field experiment. The result shows that if the water injection quantity is over 20 m&3/d, and the density of the isotope grains, whose diameter is 100-600 μm, is 1.06 g/cm^3, then the logging technique for this kind of water injection wells will be appropriate. Whether water injection profile logging is successful in the well, whose perforated intervals are beyond the tubing shoe, depends on the sinking speed of the tracer grains.
文摘The rectification of eccentricity was revealed to be more effective in tube sinking than drawing with a mandrel.The ratio of thickness to diameter of tube blank on both sides of thick and thin wall seems to be the principal influential factor in rectifying eccentricity.The greater the ini- tial outside diameter and the initial wall thickness difference are and the less the initial wall thickness of the tube blank is,the better the rectification is.
基金Supported by the China National Science and Technology Major Project(2017ZX05008-001)
文摘The method of random forest was used to classify the heavy mineral assemblages of 2 418 Jurassic samples in the southern Junggar Basin, and determine the distribution of the heavy mineral assemblages from the same provenance systems. Based on the analysis of heavy minerals assemblages, ZTR index, sedimentary characteristics, U-Pb zircon ages, whole-rock geochemical and paleocurrent direction analysis, the study reveals that five important provenances were providing sediments to the southern Junggar Basin in the Jurassic period: The North Tianshan(NTS), Central Tianshan(CTS), Bogda Mountains, Zhayier Mountains and Kalamaili Mountains. During the Early Jurassic, NTS-CTS, Kalamaili Mountains and Zhayier Mountains are primary provenances, Bogda Mountains started to uplift and supply clastic materials in the Middle Jurassic. There are three sedimentary area in the Jurassic of southern Junggar Basin: the western part, the central part and the eastern part. In the western part, the clastic materials of the Early Jurassic was mainly from NTS blocks and Zhayier Mountains, and the sediments were dominantly derived from the Zhayier Mountains during the Middle–Late Jurassic. In the central part, the main provenance of the Early Jurassic switched from NTS to CTS. In the Xishanyao Formation, the main source went back to NTS again. The NTS was the primary provenance during the sedimentary periods of Toutunhe Formation and Qigu Formation. In the eastern part, the contribution of CTS and Kalamaili Mountains were considered as major provenances in the Early Jurassic-Xishanyao Formation, small proportion of sediments were from NTS. The Bogda mountains uplifted and started to provide sediments to the Junggar Basin in the sedimentary period of Xishanyao Formation, and became the major source during the Toutunhe Formation period, with small amount of sediments from CTS. The provenance from CTS was hindered during the sedimentary period of Qigu Formation owing to the uplifting of the Bogda mountains, and the sediments were mainly from the Bogda mountains and NTS.
文摘The average swelling height of Qinghai-Xizang Plateau(Tibet) is about 4.1 km.The area is about 2 300 000 km2.It is the highest and the largest plateau in the world.Mount Qomolangma,the highest peak in the world,is located in the southern fringe of the plateau,and its height is still increasing.What is the driving force for the rising of the Qinghai-Xizang plateau?How high will the plateau still rise from now on? These questions are much concerned by people.In this paper the distribution of the pressure at different depths in the region of Qinghai-Xizang Plateau are derived according to the three-dimensional structures of the S-wave velocity in the crust and upper mantle.The crust and upper mantle structures of the Qinghai-Xizang Plateau is deliberated on the basis of the distribution with a comprehensive analysis on the rock types,earthquakes and the relative crust movements.Then the two questions raised above are discussed.
文摘Community group buying is a brand-new retail model,and this retail model is not limited to the first-and second-tier cities in China,and has gradually penetrated into the sinking market.The sinking consumer market is changing with each passing day,and community group buying will surely usher in more help in the promotion and application of sinking market areas.The network platform of community group buying also gives full play to the resource advantages of"internet plus",expands the sales of fresh agricultural products,and constantly improves logistics problems to meet the consumer demand of sinking market.This paper introduces the development status of community group buying in China's sinking market,analyzes the existing problems and puts forward corresponding suggestions,and then looks forward to the future development of the industry.Finally,the future development of community group buying platform in the sinking market is prospected.
基金Under the auspices of National Natural Science Foundation of China (No. 52268008, 51768001)。
文摘Since China announced its goal of becoming carbon-neutral by 2060, carbon neutrality has become a major target in the development of China's urban agglomerations. This study applied the Future Land Use Simulation(FLUS) model to predict the land use pattern of the ecological space of the Beibu Gulf urban agglomeration, in 2060 under ecological priority, agricultural priority and urbanized priority scenarios. The Integrated Valuation of Ecosystem Services and Trade-offs(In VEST) model was employed to analyse the spatial changes in ecological space carbon storage in each scenario from 2020 to 2060. Then, this study used a Geographically Weighted Regression(GWR) model to determine the main driving factors that influence the changes in land carbon sinking capacity. The results of the study can be summarised as follows: firstly, the agricultural and ecological priority scenarios will achieve balanced urban expansion and environmental protection of resources in an ecological space. The urbanized priority scenario will reduce the carbon sinking capacity. Among the simulation scenarios for 2060, carbon storage in the urbanized priority scenario will decrease by 112.26 × 10^(6) t compared with that for 2020 and the average carbon density will decrease by 0.96 kg/m^(2) compared with that for 2020. Carbon storage in the agricultural priority scenario will increase by 84.11 × 10^(6) t, and the average carbon density will decrease by 0.72 kg/m^(2). Carbon storage in the ecological priority scenario will increase by 3.03 × 10^(6) t, and the average carbon density will increase by 0.03 kg/m^(2). Under the premise that the population of the town will increases continuously, the ecological priority development approach may be a wise choice.Secondly, slope, distance to river and elevation are the most important factors that influence the carbon sink pattern of the ecological space in the Beibu Gulf urban agglomeration, followed by GDP, population density, slope direction and distance to traffic infrastructure.At the same time, urban space expansion is the main cause of the changes of this natural factors. Thirdly, the decreasing trend of ecological space is difficult to reverse, so reasonable land use policy to curb the spatial expansion of cities need to be made.
基金Project supported by the China National Funds for Distinguished Young Scholars(No.12025204)the Shanghai Municipal Education Commission(No.2019-01-07-00-09-E00018)。
文摘Fluid-conveying pipes are widely used to transfer bulk fluids from one point to another in many engineering applications.They are subject to various excitations from the conveying fluids,the supporting structures,and the working environment,and thus are prone to vibrations such as flow-induced vibrations and acoustic-induced vibrations.Vibrations can generate variable dynamic stress and large deformation on fluid-conveying pipes,leading to vibration-induced fatigue and damage on the pipes,or even leading to failure of the entire piping system and catastrophic accidents.Therefore,the vibration control of fluid-conveying pipes is essential to ensure the integrity and safety of pipeline systems,and has attracted considerable attention from both researchers and engineers.The present paper aims to provide an extensive review of the state-of-the-art research on the vibration control of fluid-conveying pipes.The vibration analysis of fluid-conveying pipes is briefly discussed to show some key issues involved in the vibration analysis.Then,the research progress on the vibration control of fluid-conveying pipes is reviewed from four aspects in terms of passive control,active vibration control,semi-active vibration control,and structural optimization design for vibration reduction.Furthermore,the main results of existing research on the vibration control of fluid-conveying pipes are summarized,and future promising research directions are recommended to address the current research gaps.This paper contributes to the understanding of vibration control of fluid-conveying pipes,and will help the research work on the vibration control of fluidconveying pipes attract more attention.