Exact calculations of the static earth pressure from a thick alluvium require accurate/Co values. These calculations influence the sinking cost and the safety of the freezing method. The static earth pressure coeffici...Exact calculations of the static earth pressure from a thick alluvium require accurate/Co values. These calculations influence the sinking cost and the safety of the freezing method. The static earth pressure coefficient （K0） of thick and deep soil was analyzed using laboratory tests. The results show that the static earth pressure coefficient of thick and deep soils is nonlinear and different from that of superficial soils. The constant of superficial soils is usually invariant and the total stress or incremental stress definitions used in traditional geo-meehanics give the same value. The influence of load increments when calculating for superficial soil is ignored. The difference in values of K0 for thick alluvium defimed by the total stress or the incremental stress methods is over 10%. The effects of the thick alluvium on K0 should be considered during the design of frozen shaft projects. Such things as the frozen shaft thickness and the excavated section height should be chosen to assure the rationality of the design and to avoid potential faults and accidents.展开更多
The static earth pressure coefficient of soils is,approximately,considered to be a constant in the view of clas-sical soil mechanics. This is supported by many research results. The high pressure experimental research...The static earth pressure coefficient of soils is,approximately,considered to be a constant in the view of clas-sical soil mechanics. This is supported by many research results. The high pressure experimental research and analysis of remolding deep soil described herein indicate that the static earth pressure of thick overburden has a notable non lin-ear characteristic. It also appears larger than that of superficial soils. It is necessary for deep coal mine design and con-struction to consider this particularity of soil pressure so as to avoid engineering accidents and heavy loss of life and property.展开更多
The physical layer key generation technique provides an efficient method,which utilizes the natural dynamics of wireless channel.However,there are some extremely challenging security scenarios such as static or quasi-...The physical layer key generation technique provides an efficient method,which utilizes the natural dynamics of wireless channel.However,there are some extremely challenging security scenarios such as static or quasi-static environment,which lead to the low randomness of generated keys.Meanwhile,the coefficients of the static channel may be dropped into the guard space and discarded by the quantization approach,which causes low key generation rate.To tackle these issues,we propose a random coefficient-moving product based wireless key generation scheme(RCMP-WKG),where new random resources with remarkable fluctuations can be obtained by applying random coefficient and by moving product on the legitimate nodes.Furthermore,appropriate quantization approaches are used to increase the key generation rate.Moreover,the security of our proposed scheme is evaluated by analyzing different attacks and the eavesdropper’s mean square error(MSE).The simulation results reveal that the proposed scheme can achieve better performances in key capacity,key inconsistency rate(KIR)and key generation rate(KGR)compared with the prior works in static environment.Besides,the proposed scheme can deteriorate the MSE performance of the eavesdropper and improve the key generation performance of legitimate nodes by controlling the length of the moving product.展开更多
The static and dynamic diffusion coefficients are important coefficients to describe the moisture transfer processes in particleboard. In this paper, the formula of culculating the static and dynamic diffusion coeffic...The static and dynamic diffusion coefficients are important coefficients to describe the moisture transfer processes in particleboard. In this paper, the formula of culculating the static and dynamic diffusion coefficients were deduced. At first, the static diffusion coefficients of four kinds of particleboards were determined by using diffusion cup method. The results demonstrated that the static diffusion coefficients parallel to panel surface were 10-20 times as large as that of perpendicular to panel surface for test boards. To determine both dynamic diffusion coefficients and surface emission coefficients of moisture in particleboards in one experimental period, specimens in four different thicknesses of each kind of particleboard were used in the experiment. Then the method of regression was used and the dynamic diffusion coefficients and surface emission coefficients were determined based on the slope and intercept of the regressive line.展开更多
Many analytical methods have been adopted to estimate the slope stability by providing various stability numbers,e.g.static safety of factor(static FoS)or the critical seismic acceleration coefficient,while little att...Many analytical methods have been adopted to estimate the slope stability by providing various stability numbers,e.g.static safety of factor(static FoS)or the critical seismic acceleration coefficient,while little attention has been given to the relationship between the slope stability numbers and the critical seismic acceleration coefficient.This study aims to investigate the relationship between the static FoS and the critical seismic acceleration coefficient of soil slopes in the framework of the upper-bound limit analysis.Based on the 3D rotational failure mechanism,the critical seismic acceleration coefficient using the pseudo-static method and the static FoS using the strength reduction technique are first determined.Then,the relationship between the static FoS and the critical seismic acceleration coefficient is presented under considering the slope angleβ,the frictional angleφ,and the dimensionless coefficients B/H and c/γH.Finally,a fitting formula between the static FoS and the critical seismic acceleration coefficient is proposed and validated by analytical and numerical results.展开更多
Typical rotors such as those on steam turbine or generator are often supported by two bearings with two balance planes at both ends.Vibrations are monitored by a pair of proximity probes at each bearing.There are two ...Typical rotors such as those on steam turbine or generator are often supported by two bearings with two balance planes at both ends.Vibrations are monitored by a pair of proximity probes at each bearing.There are two approaches to reduce 1X vibration due to unbalance at both ends via balancing with influence coefficient method.The first approach is to treat it as a multiple-plane balancing problem involving 2x2 matrix of complex influence coefficients.The second approach is to treat it as two single-plane balance problems using static(in-phase)and couple(180 degree out-of-phase)components,respectively.Conversion equations of influence coefficients between these two approaches have been found previously by the author.The corresponding spreadsheets that convert influence coefficients between these two formats are presented in the current paper.The paper shows effectiveness of these conversion equations in dealing with real balancing problems in the field.A detailed balance case is presented to demonstrate how the conversion equations are used to reduce vibration effectively.展开更多
One of the most important issues in geotechnical engineering is excess pore pressure caused by clay soil loading and consolidation. Regarding uncertainties and complexities, this issue has long been the subject of att...One of the most important issues in geotechnical engineering is excess pore pressure caused by clay soil loading and consolidation. Regarding uncertainties and complexities, this issue has long been the subject of attention of many researchers. In this work, a one-dimensional consolidation apparatus was equipped in a way that pore water pressure and settlement could be continuously read and recorded during consolidation process under static loading. The end of primary consolidation was obtained using water pressure changes helping to present a new method for determining the end of primary consolidation and consolidation coefficient. This method was then compared with two classical theory methods of lg t and t. Using Terzaghi's theory, the way of pore pressure dissipation for lg t, t and the new method was found and compared with experimental results. It is concluded that the new method has better results.展开更多
This article lists all possible conversion equations of influence coefficients(ICs)with different formats when some of these are known to handle two-plane balancing tasks with no or less trial weight runs.There are tw...This article lists all possible conversion equations of influence coefficients(ICs)with different formats when some of these are known to handle two-plane balancing tasks with no or less trial weight runs.There are two approaches for two-plane balancing.One can treat it as a multi-plane balance problem involving a 2×2 matrix of complex ICs where two direct ICs along with two cross-effect ICs are generated so that correction weights at one or two balance planes can be determined.One can also apply a static pare(in-phase)and/or couple pair(180 degrees out-of-phase)weights for balancing.The latter approach has been used quite often in the field,especially on steam turbine and generator rotors.Dependent on vibration mode shapes and combinations as well as balance plane accessibility,sometimes applying static or couple pair weights can be a wise choice;other times weights at one or two end planes are needed.There are totally 4 possible sets of IC data due to weights at plane 1,plane 2,static pair,and couple pair.IC data would typically be obtained by applying trial weights followed by trial weight runs.It is found,however,that all these IC data can be converted easily without trial weight runs once any two of 4 sets are known.The above findings and conversion equations have been obtained analytically and verified by experimental results.Real cases are given to demonstratetheirapplications.展开更多
To enhance the gas-damping effect and improve the bearing performance,a restricted layer is applied on the surface of aerostatic porous bearings.Based on the gas lubrication theory,a mathematical model of an aerostati...To enhance the gas-damping effect and improve the bearing performance,a restricted layer is applied on the surface of aerostatic porous bearings.Based on the gas lubrication theory,a mathematical model of an aerostatic porous bearing with a restricted layer is established,and two proportional coefficients,a permeability ratio δ and a thickness ratioγ,are proposed.Critical values of δ and γ are determined through sensitivity analyses of complex restriction-layer parameters.The static characteristics of aerostatic porous bearings with a restricted layer or an unrestricted layer are comparatively analyzed by using Fluent simulation.The results show that when δ≈0.005 and γ≈0.010,the load capacity and static stiffness of the restricted-layer aerostatic porous bearing are high;compared with the unrestricted-layer aerostatic porous bearing,the restricted-layer aerostatic porous bearing has a lower sensitivity to changes in the air supply area.The existence of the restricted layer not only enhances the throttling effect and reduces the mass flow rate,but also effectively improves the static stiffness of the bearing.展开更多
With increasingly stringent requirements for the airtightness of high-speed train bodies,determining appropriate airtightness levels has become critically important.To calculate the airtightness of high-speed train bo...With increasingly stringent requirements for the airtightness of high-speed train bodies,determining appropriate airtightness levels has become critically important.To calculate the airtightness of high-speed train bodies more accurately,based on one-dimensional isentropic flow theory,this study derives cabin pressure calculation models for both positive and negative pressure conditions during static airtightness tests of high-speed train bodies.Since the flow coefficient,which is closely related to the leakage characteristics of the carriage,is influenced by multiple factors including operating pressure conditions(positive/negative),leakage path cross-sectional shape,and size,a flow coefficient calibration method is proposed to achieve high-precision and efficient calibration of the flow coefficient for trains with varying leakage properties.This method generates a series of flow coefficient values for circular and square cross-sectional shapes under both positive and negative pressure conditions across various cross-sectional areas.Furthermore,functional relationships between flow coefficient and leakage path area under positive/negative pressure are established through curve fitting.Using these functional relationships and the cabin pressure calculation model,the pressure variation curves for a static airtightness test are simulated.Specifically,for circular cross-sectional shapes,the theoretical curves under positive and negative pressure conditions exhibited R^(2) values of 0.9936 and 0.9931,respectively,when compared to experimental data,and for square cross-sectional shapes,the corresponding R^(2) values are 0.9928 and 0.9932,validating the accuracy of the proposed theoretical model.The proposed theoretical model effectively evaluates the airtightness of high-speed train bodies with varying performance levels during static airtightness tests,providing a robust theoretical reference for optimizing high-speed train airtightness design.展开更多
The flow and mixing behavior of two miscible liquids has been studied in an innovative static mixer by using CFD,with Reynolds numbers ranging from 20 to 160.The performance of the new mixer is compared with those of ...The flow and mixing behavior of two miscible liquids has been studied in an innovative static mixer by using CFD,with Reynolds numbers ranging from 20 to 160.The performance of the new mixer is compared with those of Kenics,SMX,and Komax static mixers.The pressure drop ratio(Z-factor),coefficient of variation(CoV),and extensional efficiency(α)features have been used to evaluate power consumption,distributive mixing,and dispersive mixing performances,respectively,in all mixers.The model is firstly validated based on experimental data measured for the pressure drop ratio and the coefficient of variation.CFD results are consistent with measured data and those obtained by available correlations in the literature.The new mixer shows a superior mixing performance compared to the other mixers.展开更多
A new structural damage identification method using limited test static displacement based on grey system theory is proposed in this paper. The grey relation coefficient of displacement curvature is defined and used t...A new structural damage identification method using limited test static displacement based on grey system theory is proposed in this paper. The grey relation coefficient of displacement curvature is defined and used to locate damage in the structure, and an iterative estimation scheme for solving nonlinear optimization programming problems based on the quadratic programming technique is used to identify the damage magnitude. A numerical example of a cantilever beam with single or multiple damages is used to examine the capability of the proposed grey-theory-based method to localize and identify damages. The factors of meas-urement noise and incomplete test data are also discussed. The numerical results showed that the damage in the structure can be localized correctly through using the grey-related coefficient of displacement curvature, and the damage magnitude can be iden-tified with a high degree of accuracy, regardless of the number of measured displacement nodes. This proposed method only requires limited static test data, which is easily available in practice, and has wide applications in structural damage detection.展开更多
A weak transverse static magnetic field(WTSMF,0–0.5 T)is applied to the directional solidification process of a DD3 Ni-based SX superalloy,aiming to tailor the microstructure and microsegregation of alloys.The mechan...A weak transverse static magnetic field(WTSMF,0–0.5 T)is applied to the directional solidification process of a DD3 Ni-based SX superalloy,aiming to tailor the microstructure and microsegregation of alloys.The mechanisms of microstructural refinement and microsegregation distribution caused by a WTSMF during directional solidification are discussed.It is shown that the primary dendrite arm spacing is rapidly reduced from 181 to 143μm,and the average size ofγ′phase is significantly refined from 0.85 to 0.25μm as the magnetic field increases from 0 to 0.5 T.At the same time,the volumefractions ofγ/γ′eutectic and the segregation coefficient are also gradually decreased.The 3D numerical simulations of the multiscale convection in liquid phase show that the modifications of the microstructure and microsegregation in DD3 are mainly attributed to the enhanced liquid flow caused by thermoelectric magnetic convection(TEMC)at dendrite/sample scale under the WTSMF.The maximum of the TEMC increases with increasing the magnetic field intensity.This work paves a simple way to optimize the microstructure and microsegregation in directionally solidified Ni-based SX superalloys without changing the processing parameters and composition.展开更多
The proper selection of a relevant mixer generally requires an effective assessment of several models against theapplication requirements. This is a complex task, as traditional evaluation methods generally focus only...The proper selection of a relevant mixer generally requires an effective assessment of several models against theapplication requirements. This is a complex task, as traditional evaluation methods generally focus only on a single aspect of performance, such as pressure loss, mixing characteristics, or heat transfer. This study assesses aurea-based selective catalytic reduction (SCR) system installed on a ship, where the installation space is limitedand the distance between the urea aqueous solution injection position and the reactor is low;therefore, the staticmixer installed in this pipeline has special performance requirements. In particular, four evaluation indices areused in this study: The B value, C value, pressure loss correction factor (Z′), and the ratio of the required distanceto the equivalent diameter of the pipe (LV/D) when the velocity field after the mixer attains uniformity. Six typesof static mixers were simulated with varying concentrations, flow speeds, and positions. A fuzzy comprehensiveevaluation method was introduced to evaluate and compare the related advantages and disadvantages. The resultsshowed that 1) mixing performance was related to the shape of the mixer and had no direct relationship with flowvelocity. 2) For the same mixer position, the lower the urea concentration, the greater the difficulty of evenly mixing the solution. 3) At a constant urea concentration, the mixing performance improved when the mixer was closer to the injection inlet. 4) The installation of a GK mixer in the SCR system of a 9L20C diesel engine was best.展开更多
According to the relationship between load and response, the equivalent static wind load(ESWL) of a structure can be estimated by load-response correlation(LRC) method, which can be accurately used to estimate the bac...According to the relationship between load and response, the equivalent static wind load(ESWL) of a structure can be estimated by load-response correlation(LRC) method, which can be accurately used to estimate the background ESWL of a structure. The derivation of the classical expression of LRC formula is based on a specific command response at a critical position, and the ESWL distribution has only one form in this case. In this paper, a general expression of LRC formula is derived based on a specific command response at all positions. For the general expression, ESWLs can be expressed by load-response correlation coefficients, response-response correlation coefficients, RMS values of the fluctuating wind loads, and peak factor in the form of matrices. By comparing the expressions of LRC method, it was found that the classical expression was only one form of the general one. The general expression which introduces the response-response correlation coefficients provided more options for structural engineers to estimate ESWLs and offered further insights into the LRC method. Finally, a cable-stayed bridge, a rigid three span continuous girder bridge, and a suspension bridge were used to verify the correctness of the general expression of LRC method.展开更多
Now,the static push-the-bit rotary steerable system(SRSS)developed in China is being put into field tests and primary applications.During its normal drilling,higher frictional forces generated by the static pushing fo...Now,the static push-the-bit rotary steerable system(SRSS)developed in China is being put into field tests and primary applications.During its normal drilling,higher frictional forces generated by the static pushing forces of the rotary ribs on the wellbore wall influence the weight-on-bit(WOB)transmission efficiency and the rate of penetration(ROP).In this paper,analytical models of the WOB transmission efficiency were established for the wellbore wall with and without ladders respectively based on the structure and working principle of the SRSS.And the variation rules of the WOB transmission efficiency with the nominal WOB,the frictional coefficient of wellbore wall,the pushing force and the front chamfer of the steerable rib were analyzed.And the following research results were obtained.First,the nominal WOB of this SRSS has to satisfy the minimum requirement and it is conducive to the increase of WOB transmission efficiency by increasing the nominal WOB appropriately.Second,whether there are ladders on the wellbore wall or not,the WOB transmission efficiency decreases as the total pushing forces of steerable ribs and the frictional coefficient of wellbore wall increase.And the WOB transmission efficiency in the case of wellbore wall with ladders is much lower than that without ladders.Third,if there are ladders on the wellbore wall,the front chamfer of steerable rib has a significant effect on the WOB transmission efficiency.The larger the front chamfer is,the lower the WOB transmission efficiency is(even self-locking).In conclusion,the research results play an important role in guiding the rational selection and control of the WOB at drilling site.展开更多
The Republic of Serbia is characterized by an unsatisfactory macroeconomic environment. Under the conditions of an evident shortage of liquid assets, the financial capital has moved from real to the financial sector, ...The Republic of Serbia is characterized by an unsatisfactory macroeconomic environment. Under the conditions of an evident shortage of liquid assets, the financial capital has moved from real to the financial sector, which led companies to over-indebtedness and shutdown of their own capacities. Therefore, capital investments largely depend on internal financing sources and the ability of companies to internally generate funds for investments. In this regard, an emphasis is placed on the difference in the assessment of the company＇s investment capacity based on internal financing sources, which are measured using static and dynamic indicators in order to prove the necessity of applying dynamic coefficients, which are unfortunately not present in our domestic practice. The paper examines and proves the advantages of the use of the dynamic approach for such analyses using the example of energy sector, which is one of the most important branches in Serbian economy.展开更多
基金Project BK2007040 supported by the Provincial Natural Science Foundation of Jiangsu, China
文摘Exact calculations of the static earth pressure from a thick alluvium require accurate/Co values. These calculations influence the sinking cost and the safety of the freezing method. The static earth pressure coefficient （K0） of thick and deep soil was analyzed using laboratory tests. The results show that the static earth pressure coefficient of thick and deep soils is nonlinear and different from that of superficial soils. The constant of superficial soils is usually invariant and the total stress or incremental stress definitions used in traditional geo-meehanics give the same value. The influence of load increments when calculating for superficial soil is ignored. The difference in values of K0 for thick alluvium defimed by the total stress or the incremental stress methods is over 10%. The effects of the thick alluvium on K0 should be considered during the design of frozen shaft projects. Such things as the frozen shaft thickness and the excavated section height should be chosen to assure the rationality of the design and to avoid potential faults and accidents.
基金Project 50534040 supported by the National Natrual Science Foundation of China
文摘The static earth pressure coefficient of soils is,approximately,considered to be a constant in the view of clas-sical soil mechanics. This is supported by many research results. The high pressure experimental research and analysis of remolding deep soil described herein indicate that the static earth pressure of thick overburden has a notable non lin-ear characteristic. It also appears larger than that of superficial soils. It is necessary for deep coal mine design and con-struction to consider this particularity of soil pressure so as to avoid engineering accidents and heavy loss of life and property.
基金supported in part by the National Natural Science Foundation of China(Numbers 62171445,62471477 and 62201592).
文摘The physical layer key generation technique provides an efficient method,which utilizes the natural dynamics of wireless channel.However,there are some extremely challenging security scenarios such as static or quasi-static environment,which lead to the low randomness of generated keys.Meanwhile,the coefficients of the static channel may be dropped into the guard space and discarded by the quantization approach,which causes low key generation rate.To tackle these issues,we propose a random coefficient-moving product based wireless key generation scheme(RCMP-WKG),where new random resources with remarkable fluctuations can be obtained by applying random coefficient and by moving product on the legitimate nodes.Furthermore,appropriate quantization approaches are used to increase the key generation rate.Moreover,the security of our proposed scheme is evaluated by analyzing different attacks and the eavesdropper’s mean square error(MSE).The simulation results reveal that the proposed scheme can achieve better performances in key capacity,key inconsistency rate(KIR)and key generation rate(KGR)compared with the prior works in static environment.Besides,the proposed scheme can deteriorate the MSE performance of the eavesdropper and improve the key generation performance of legitimate nodes by controlling the length of the moving product.
文摘The static and dynamic diffusion coefficients are important coefficients to describe the moisture transfer processes in particleboard. In this paper, the formula of culculating the static and dynamic diffusion coefficients were deduced. At first, the static diffusion coefficients of four kinds of particleboards were determined by using diffusion cup method. The results demonstrated that the static diffusion coefficients parallel to panel surface were 10-20 times as large as that of perpendicular to panel surface for test boards. To determine both dynamic diffusion coefficients and surface emission coefficients of moisture in particleboards in one experimental period, specimens in four different thicknesses of each kind of particleboard were used in the experiment. Then the method of regression was used and the dynamic diffusion coefficients and surface emission coefficients were determined based on the slope and intercept of the regressive line.
基金Project(2017YFB1201204)supported by the National Key R&D Program of ChinaProject(1053320190957)supported by the Fundamental Research Funds for the Central Universities,China。
文摘Many analytical methods have been adopted to estimate the slope stability by providing various stability numbers,e.g.static safety of factor(static FoS)or the critical seismic acceleration coefficient,while little attention has been given to the relationship between the slope stability numbers and the critical seismic acceleration coefficient.This study aims to investigate the relationship between the static FoS and the critical seismic acceleration coefficient of soil slopes in the framework of the upper-bound limit analysis.Based on the 3D rotational failure mechanism,the critical seismic acceleration coefficient using the pseudo-static method and the static FoS using the strength reduction technique are first determined.Then,the relationship between the static FoS and the critical seismic acceleration coefficient is presented under considering the slope angleβ,the frictional angleφ,and the dimensionless coefficients B/H and c/γH.Finally,a fitting formula between the static FoS and the critical seismic acceleration coefficient is proposed and validated by analytical and numerical results.
文摘Typical rotors such as those on steam turbine or generator are often supported by two bearings with two balance planes at both ends.Vibrations are monitored by a pair of proximity probes at each bearing.There are two approaches to reduce 1X vibration due to unbalance at both ends via balancing with influence coefficient method.The first approach is to treat it as a multiple-plane balancing problem involving 2x2 matrix of complex influence coefficients.The second approach is to treat it as two single-plane balance problems using static(in-phase)and couple(180 degree out-of-phase)components,respectively.Conversion equations of influence coefficients between these two approaches have been found previously by the author.The corresponding spreadsheets that convert influence coefficients between these two formats are presented in the current paper.The paper shows effectiveness of these conversion equations in dealing with real balancing problems in the field.A detailed balance case is presented to demonstrate how the conversion equations are used to reduce vibration effectively.
文摘One of the most important issues in geotechnical engineering is excess pore pressure caused by clay soil loading and consolidation. Regarding uncertainties and complexities, this issue has long been the subject of attention of many researchers. In this work, a one-dimensional consolidation apparatus was equipped in a way that pore water pressure and settlement could be continuously read and recorded during consolidation process under static loading. The end of primary consolidation was obtained using water pressure changes helping to present a new method for determining the end of primary consolidation and consolidation coefficient. This method was then compared with two classical theory methods of lg t and t. Using Terzaghi's theory, the way of pore pressure dissipation for lg t, t and the new method was found and compared with experimental results. It is concluded that the new method has better results.
文摘This article lists all possible conversion equations of influence coefficients(ICs)with different formats when some of these are known to handle two-plane balancing tasks with no or less trial weight runs.There are two approaches for two-plane balancing.One can treat it as a multi-plane balance problem involving a 2×2 matrix of complex ICs where two direct ICs along with two cross-effect ICs are generated so that correction weights at one or two balance planes can be determined.One can also apply a static pare(in-phase)and/or couple pair(180 degrees out-of-phase)weights for balancing.The latter approach has been used quite often in the field,especially on steam turbine and generator rotors.Dependent on vibration mode shapes and combinations as well as balance plane accessibility,sometimes applying static or couple pair weights can be a wise choice;other times weights at one or two end planes are needed.There are totally 4 possible sets of IC data due to weights at plane 1,plane 2,static pair,and couple pair.IC data would typically be obtained by applying trial weights followed by trial weight runs.It is found,however,that all these IC data can be converted easily without trial weight runs once any two of 4 sets are known.The above findings and conversion equations have been obtained analytically and verified by experimental results.Real cases are given to demonstratetheirapplications.
文摘To enhance the gas-damping effect and improve the bearing performance,a restricted layer is applied on the surface of aerostatic porous bearings.Based on the gas lubrication theory,a mathematical model of an aerostatic porous bearing with a restricted layer is established,and two proportional coefficients,a permeability ratio δ and a thickness ratioγ,are proposed.Critical values of δ and γ are determined through sensitivity analyses of complex restriction-layer parameters.The static characteristics of aerostatic porous bearings with a restricted layer or an unrestricted layer are comparatively analyzed by using Fluent simulation.The results show that when δ≈0.005 and γ≈0.010,the load capacity and static stiffness of the restricted-layer aerostatic porous bearing are high;compared with the unrestricted-layer aerostatic porous bearing,the restricted-layer aerostatic porous bearing has a lower sensitivity to changes in the air supply area.The existence of the restricted layer not only enhances the throttling effect and reduces the mass flow rate,but also effectively improves the static stiffness of the bearing.
基金Projects(52372402,U2568224)supported by the National Natural Science Foundation of China。
文摘With increasingly stringent requirements for the airtightness of high-speed train bodies,determining appropriate airtightness levels has become critically important.To calculate the airtightness of high-speed train bodies more accurately,based on one-dimensional isentropic flow theory,this study derives cabin pressure calculation models for both positive and negative pressure conditions during static airtightness tests of high-speed train bodies.Since the flow coefficient,which is closely related to the leakage characteristics of the carriage,is influenced by multiple factors including operating pressure conditions(positive/negative),leakage path cross-sectional shape,and size,a flow coefficient calibration method is proposed to achieve high-precision and efficient calibration of the flow coefficient for trains with varying leakage properties.This method generates a series of flow coefficient values for circular and square cross-sectional shapes under both positive and negative pressure conditions across various cross-sectional areas.Furthermore,functional relationships between flow coefficient and leakage path area under positive/negative pressure are established through curve fitting.Using these functional relationships and the cabin pressure calculation model,the pressure variation curves for a static airtightness test are simulated.Specifically,for circular cross-sectional shapes,the theoretical curves under positive and negative pressure conditions exhibited R^(2) values of 0.9936 and 0.9931,respectively,when compared to experimental data,and for square cross-sectional shapes,the corresponding R^(2) values are 0.9928 and 0.9932,validating the accuracy of the proposed theoretical model.The proposed theoretical model effectively evaluates the airtightness of high-speed train bodies with varying performance levels during static airtightness tests,providing a robust theoretical reference for optimizing high-speed train airtightness design.
文摘The flow and mixing behavior of two miscible liquids has been studied in an innovative static mixer by using CFD,with Reynolds numbers ranging from 20 to 160.The performance of the new mixer is compared with those of Kenics,SMX,and Komax static mixers.The pressure drop ratio(Z-factor),coefficient of variation(CoV),and extensional efficiency(α)features have been used to evaluate power consumption,distributive mixing,and dispersive mixing performances,respectively,in all mixers.The model is firstly validated based on experimental data measured for the pressure drop ratio and the coefficient of variation.CFD results are consistent with measured data and those obtained by available correlations in the literature.The new mixer shows a superior mixing performance compared to the other mixers.
基金Project supported by the Natural Science Foundation of China(No. 50378041) and the Specialized Research Fund for the Doc-toral Program of Higher Education (No. 20030487016), China
文摘A new structural damage identification method using limited test static displacement based on grey system theory is proposed in this paper. The grey relation coefficient of displacement curvature is defined and used to locate damage in the structure, and an iterative estimation scheme for solving nonlinear optimization programming problems based on the quadratic programming technique is used to identify the damage magnitude. A numerical example of a cantilever beam with single or multiple damages is used to examine the capability of the proposed grey-theory-based method to localize and identify damages. The factors of meas-urement noise and incomplete test data are also discussed. The numerical results showed that the damage in the structure can be localized correctly through using the grey-related coefficient of displacement curvature, and the damage magnitude can be iden-tified with a high degree of accuracy, regardless of the number of measured displacement nodes. This proposed method only requires limited static test data, which is easily available in practice, and has wide applications in structural damage detection.
基金financially supported by the National Natural Science Foundation of China(Nos.51690163,52130204,52174376,51822405)the Science and Technology Innovation Team Plan of Shaan Xi Province(No.2021TD-17)+3 种基金the Joint Research Funds of the Department of Science&Technology of Shaanxi Province and NPU(No.2020GXLH-Z-024)the Fundamental Research Funds for the Central Universities(No.D5000210902)the Key R&D Program of ShaanXi Province(No.2019ZDLGY 04-04)the Research Fund of the State Key Laboratory of Solidification Processing(NPU)(No.2019-QZ-02)。
文摘A weak transverse static magnetic field(WTSMF,0–0.5 T)is applied to the directional solidification process of a DD3 Ni-based SX superalloy,aiming to tailor the microstructure and microsegregation of alloys.The mechanisms of microstructural refinement and microsegregation distribution caused by a WTSMF during directional solidification are discussed.It is shown that the primary dendrite arm spacing is rapidly reduced from 181 to 143μm,and the average size ofγ′phase is significantly refined from 0.85 to 0.25μm as the magnetic field increases from 0 to 0.5 T.At the same time,the volumefractions ofγ/γ′eutectic and the segregation coefficient are also gradually decreased.The 3D numerical simulations of the multiscale convection in liquid phase show that the modifications of the microstructure and microsegregation in DD3 are mainly attributed to the enhanced liquid flow caused by thermoelectric magnetic convection(TEMC)at dendrite/sample scale under the WTSMF.The maximum of the TEMC increases with increasing the magnetic field intensity.This work paves a simple way to optimize the microstructure and microsegregation in directionally solidified Ni-based SX superalloys without changing the processing parameters and composition.
基金wasfinancially aided by the National Natural Science Foundation of China(52276122).
文摘The proper selection of a relevant mixer generally requires an effective assessment of several models against theapplication requirements. This is a complex task, as traditional evaluation methods generally focus only on a single aspect of performance, such as pressure loss, mixing characteristics, or heat transfer. This study assesses aurea-based selective catalytic reduction (SCR) system installed on a ship, where the installation space is limitedand the distance between the urea aqueous solution injection position and the reactor is low;therefore, the staticmixer installed in this pipeline has special performance requirements. In particular, four evaluation indices areused in this study: The B value, C value, pressure loss correction factor (Z′), and the ratio of the required distanceto the equivalent diameter of the pipe (LV/D) when the velocity field after the mixer attains uniformity. Six typesof static mixers were simulated with varying concentrations, flow speeds, and positions. A fuzzy comprehensiveevaluation method was introduced to evaluate and compare the related advantages and disadvantages. The resultsshowed that 1) mixing performance was related to the shape of the mixer and had no direct relationship with flowvelocity. 2) For the same mixer position, the lower the urea concentration, the greater the difficulty of evenly mixing the solution. 3) At a constant urea concentration, the mixing performance improved when the mixer was closer to the injection inlet. 4) The installation of a GK mixer in the SCR system of a 9L20C diesel engine was best.
基金Sponsored by the National Natural Science Foundation of China(Grant No.51508107)the China Postdoctoral Science Foundation(Grant No.2016M590592)the Natural Science Foundation of Fujian Province(Grant No.2015J05098)。
文摘According to the relationship between load and response, the equivalent static wind load(ESWL) of a structure can be estimated by load-response correlation(LRC) method, which can be accurately used to estimate the background ESWL of a structure. The derivation of the classical expression of LRC formula is based on a specific command response at a critical position, and the ESWL distribution has only one form in this case. In this paper, a general expression of LRC formula is derived based on a specific command response at all positions. For the general expression, ESWLs can be expressed by load-response correlation coefficients, response-response correlation coefficients, RMS values of the fluctuating wind loads, and peak factor in the form of matrices. By comparing the expressions of LRC method, it was found that the classical expression was only one form of the general one. The general expression which introduces the response-response correlation coefficients provided more options for structural engineers to estimate ESWLs and offered further insights into the LRC method. Finally, a cable-stayed bridge, a rigid three span continuous girder bridge, and a suspension bridge were used to verify the correctness of the general expression of LRC method.
基金Project supported by the National Research Council of Science and Technology Major Project“Rotary Steering System Research and Development”(No.:2016ZX05022-002)the Surface Project of the National Natural Science Foundation of China“Study on Borehole Collission Prevention Mechanism Based on Magnetic Field Distribution and Passive Magnetic Ranging of Downhole Casing String”(No.:51674284)the Changjiang Scholars and Innovative Team Development Program of the Ministry of Education of the People's Republic of China.
文摘Now,the static push-the-bit rotary steerable system(SRSS)developed in China is being put into field tests and primary applications.During its normal drilling,higher frictional forces generated by the static pushing forces of the rotary ribs on the wellbore wall influence the weight-on-bit(WOB)transmission efficiency and the rate of penetration(ROP).In this paper,analytical models of the WOB transmission efficiency were established for the wellbore wall with and without ladders respectively based on the structure and working principle of the SRSS.And the variation rules of the WOB transmission efficiency with the nominal WOB,the frictional coefficient of wellbore wall,the pushing force and the front chamfer of the steerable rib were analyzed.And the following research results were obtained.First,the nominal WOB of this SRSS has to satisfy the minimum requirement and it is conducive to the increase of WOB transmission efficiency by increasing the nominal WOB appropriately.Second,whether there are ladders on the wellbore wall or not,the WOB transmission efficiency decreases as the total pushing forces of steerable ribs and the frictional coefficient of wellbore wall increase.And the WOB transmission efficiency in the case of wellbore wall with ladders is much lower than that without ladders.Third,if there are ladders on the wellbore wall,the front chamfer of steerable rib has a significant effect on the WOB transmission efficiency.The larger the front chamfer is,the lower the WOB transmission efficiency is(even self-locking).In conclusion,the research results play an important role in guiding the rational selection and control of the WOB at drilling site.
文摘The Republic of Serbia is characterized by an unsatisfactory macroeconomic environment. Under the conditions of an evident shortage of liquid assets, the financial capital has moved from real to the financial sector, which led companies to over-indebtedness and shutdown of their own capacities. Therefore, capital investments largely depend on internal financing sources and the ability of companies to internally generate funds for investments. In this regard, an emphasis is placed on the difference in the assessment of the company＇s investment capacity based on internal financing sources, which are measured using static and dynamic indicators in order to prove the necessity of applying dynamic coefficients, which are unfortunately not present in our domestic practice. The paper examines and proves the advantages of the use of the dynamic approach for such analyses using the example of energy sector, which is one of the most important branches in Serbian economy.
