Stepped spillways for significant energy dissipation along the chute have gained interest; popularity among researchers; dam engineers. Due to the complexity of air-water two-phase flow over stepped spillways, the fin...Stepped spillways for significant energy dissipation along the chute have gained interest; popularity among researchers; dam engineers. Due to the complexity of air-water two-phase flow over stepped spillways, the finite volume computational fluid dynamics module of the FLUENT software was used to simulate the main characteristics of the flow. Adopting the RNG k- turbulence model, the mixture flow model for air-water two-phase flow was used to simulate the flow field over stepped spillway with the PISO arithmetic technique. The numerical result successfully reproduced the complex flow over a stepped spillway of an experiment case, including the interaction between entrained air bubbles; cavity recirculation in the skimming flow regime, velocity distribution; the pressure profiles on the step surface as well. The result is helpful for understanding the detailed information about energy dissipation over stepped spillways.展开更多
A novel oscillator structure, bimorph piezoelectric cantilever beam with two-stepped variable thicknesses,is proposed to improve the energy harvestingperformance of the vibration energy harvester (VEH) under low-frequ...A novel oscillator structure, bimorph piezoelectric cantilever beam with two-stepped variable thicknesses,is proposed to improve the energy harvestingperformance of the vibration energy harvester (VEH) under low-frequency vibration environment. Firstly, the piezoelectric cantilever is segmented to obtain the energy functions based on the Euler-Bernoulli beam assumptions, and the Galerkin approach is utilized to discretize the energy functions. Applying boundary conditions and continuity conditions enforced at separation locations, the electromechanical coupled governing equations for the piezoelectric energy harvesterareintroduced by means of the Lagrange equations. Furthermore, the steady state response expressions are obtained for harmonic base excitations at arbitrary frequencies. Numerical results are computed and the effects ofthe lengths-ratio, thicknesses-ratio,end thicknessand load resistance on the output voltage, harvested power and power density are discussed. Moreover, to verify thecorrectness ofanalytical results, the finite element method (FEM)simulationis also conducted to analyze performance of the proposed VEH, where a good agreement is presented. All the results show thatthe present oscillator structureis moreefficient than the conventional uniform beam structure, specifically, for vibration energy harvesting in low-frequency environment.展开更多
The Jiaodong Peninsula in Shandong Province,China is the world’s third-largest gold metallogenic area,with cumulative proven gold resources exceeding 5000 t.Over the past few years,breakthroughs have been made in dee...The Jiaodong Peninsula in Shandong Province,China is the world’s third-largest gold metallogenic area,with cumulative proven gold resources exceeding 5000 t.Over the past few years,breakthroughs have been made in deep prospecting at a depth of 500‒2000 m,particularly in the Sanshandao area where a huge deep gold orebody was identified.Based on previous studies and the latest prospecting progress achieved by the project team of this study,the following results are summarized.(1)3D geological modeling results based on deep drilling core data reveal that the Sanshandao gold orefield,which was previously considered to consist of several independent deposits,is a supergiant deposit with gold resources of more than 1200 t(including 470 t under the sea area).The length of the major orebody is nearly 8 km,with a greatest depth of 2312 m below sea level and a maximum length of more than 3 km along their dip direction.(2)Thick gold orebodies in the Sanshandao gold deposit mainly occur in the specific sections of the ore-controlling fault where the fault plane changes from steeply to gently inclined,forming a stepped metallogenic model from shallow to deep level.The reason for this strong structural control on mineralization forms is that when ore-forming fluids migrated along faults,the pressure of fluids greatly fluctuated in fault sections where the fault dip angle changed.Since the solubility of gold in the ore-forming fluid is sensitive to fluid pressure,these sections along the fault plane serve as the target areas for deep prospecting.(3)Thermal uplifting-extensional structures provide thermodynamic conditions,migration pathways,and deposition spaces for gold mineralization.Meanwhile,the changes in mantle properties induced the transformation of the geochemical properties of the lower crust and magmatic rocks.This further led to the reactivation of ore-forming elements,which provided rich materials for gold mineralization.(4)It can be concluded from previous research results that the gold mineralization in the Ji展开更多
The effects of journal misalignment on a journal bearing caused by an asymmetric rotor structure are presented in this study.A new model considering the asymmetric deflection is applied.Also,the thermo-hydrodynamic of...The effects of journal misalignment on a journal bearing caused by an asymmetric rotor structure are presented in this study.A new model considering the asymmetric deflection is applied.Also,the thermo-hydrodynamic of the oil film in the journal bearing and straightforward elasticity theory are considered in the analysis.Based on the structure stiffness equivalent characteristic,a simple stepped shaft can reflect the entire complex structure model.The existing lubrication model,which does not consider this angle component,is not very precise for journal bearings.Film pressure,misalignment angle,velocity field,oil leakage,and temperature field were calculated and compared in the journal bearing analysis.The results indicate that bearing performances are greatly affected by misalignment caused by the asymmetric structure.A simple stepped shaft can effectively represent a misaligned journal bearing in a rotor-bearing system.展开更多
In this paper, the k ε turbulence model is used to simulate the three dimensional turbulence flow over the stepped spillway at the Yubeishan reservoir. In order to solve the curved free water surface and to handl...In this paper, the k ε turbulence model is used to simulate the three dimensional turbulence flow over the stepped spillway at the Yubeishan reservoir. In order to solve the curved free water surface and to handle the complex boundary conditions, the fractional Volume Of Fluid (VOF) model that is applicable to the solution of the stratified two phase flow is introduced along with k ε turbulence model and the unstructured grid is used for the discretization of the irregular simulation domain. By these methods, the turbulence flow field of the stepped spillway is simulated successfully. The location of the free surface along the spillway, the magnitude and distribution of the velocity, the pressure on the step surface, the turbulence kinetic energy and turbulence dissipation rate are obtained by simulation. The changes and distributions of these characteristics along the width of the spillway are also obtained. The energy dissipation ratio of the stepped spillway is calculated according to the upstream and downstream water depth and velocities展开更多
Stepped frequency radar is a well known scheme to generate high range resolution profile （HRRP） of targets. Through appropriate radar parameter design, the radar enables both unambiguous velocity measurement and hig...Stepped frequency radar is a well known scheme to generate high range resolution profile （HRRP） of targets. Through appropriate radar parameter design, the radar enables both unambiguous velocity measurement and high resolution ranging within a single dwell in a high pulse repetition frequency （HPRF） mode. This paper analyzes in detail the design principle of the HPRF stepped frequency radar system, the solution to its ambiguity issue, as well as its signal processing method. Both theoretical analysis and simulation results demonstrate that the proposed radar scheme can work independently to solve the problem of motion compensation, and is therefore highly applicable to many new types of radar.展开更多
Numerical simulation of stepped channel flow was conducted using turbulence models based on the VOF technique. Stepped channel flow is a complicated air-water two-phase flow with free surface, which can be divided int...Numerical simulation of stepped channel flow was conducted using turbulence models based on the VOF technique. Stepped channel flow is a complicated air-water two-phase flow with free surface, which can be divided into three flow regimes： skimming flow, nappe flow and transition flow. The characteristics of skimming flow over mild stepped channel was investigated, including friction factors, air concentration profiles velocity field, clear-water and bulked depths, static pressure, etc. Smooth channel flow was also simulated to compare the hydraulic characteristics of the stepped channel flow with the smooth one. Comparisons between the computed and the measured were made. Furthermore, comparison of the computed air concentration with Straub and Anderson＇s data was also performed. The Fluent 6.1 software was employed to conduct this numerical simulation work.展开更多
Radio frequency observations of cloud-to-ground lightning (CG) were made in 1999 in Guangdong Province with the broadband lightning interferometer. In this paper, radiation source locations and electric field waveform...Radio frequency observations of cloud-to-ground lightning (CG) were made in 1999 in Guangdong Province with the broadband lightning interferometer. In this paper, radiation source locations and electric field waveforms are analyzed for different types of breakdown events, including the preliminary breakdown of in-cloud activities, the stepped leaders of initial strokes to ground and activities during and following return strokes. It is shown that the structure and development of lightning discharges and associated breakdown processes can be reconstructed by using this new type of lightning radiation source location system. The detectable radiation of lightning was primarily produced by the negative breakdown process. The channel was concentrated with few branches during the preliminary breakdown stage of CG lightning flashes. The radiation sources appeared generally at the tip of the channel. During the late period of the stepped leader, the radiation sources were dispersed with branches extended away from the main channel. The radiation sources were in a certain length segment of the channel and the altitude of the segment descended along with the propagation of the leader to the ground. During the preliminary breakdown and the stepped leader of initial strokes to the ground, a sequence of fast negative streamers were observed to start continually from or farther away the lightning-initiated region and propagate along the developed leader channel, which may supply negative charge that assisted the leader's development. The progression speed of fast negative streamers was about ten times faster than the average speed of lightning channel.展开更多
In this paper, the k-ε two-equation turbulence model was used to simulatethe three-dimensional turbulent flow of the stepped spillway at the Yubeishan reservoir. In order tosolve the curved free water surface and to ...In this paper, the k-ε two-equation turbulence model was used to simulatethe three-dimensional turbulent flow of the stepped spillway at the Yubeishan reservoir. In order tosolve the curved free water surface and to handle the complex boundary conditions, the fractionalVolume Of Fluid (VOF) model that is applicable to the solution of the stratified two-phase flow wasintorduced to the k-ε turbulence model and the unstructured grid was used for the discretization ofthe irregular simulation domain. By these methods, the turbulent flow field of the stepped spillwaywas simulated successfully. The location of the free surface along the spillway, the magnitude anddistribution of the velocity, the pressure distribution on the step surface, the turbulence kineticenergy and turbulence dissipation rate were obtained by simulation. The changes and distributions ofthese characteristics along the width of the spillway were also obtained. The energy dissipationratio of the stepped spillway was calculated according to the upstream and downstream water depthand velocities.展开更多
The free flow on the step surfaces has received much attention for its representative body type,flow structure,water-air two phase flow,cavitation,and many complex issues.The experiments about the time-averaged pressu...The free flow on the step surfaces has received much attention for its representative body type,flow structure,water-air two phase flow,cavitation,and many complex issues.The experiments about the time-averaged pressure and aeration concentration distribution on the step surface show that the vertical plane of steps will inevitably experience negative pressure,which must rely on adequate aeration concentration to avoid cavitation damage.However,the self-aerated flow at the head section has a relatively low aeration concentration,and the concentration of the entire steps decreases with the increasing of weir head,the minimum appears in the vicinity of the corner,and the location is close to the minimum pressure.Thus,it is necessary to set aerator in the upstream end of the step surfaces to avoid cavitation damage.展开更多
The numerical thermal mechanical simulation of radial forging process of steel H13 stepped shaft with GFM(Gesellschaft fur Fertigungstechnik und Maschinenbau) forging machine was carried out by three-dimensional finit...The numerical thermal mechanical simulation of radial forging process of steel H13 stepped shaft with GFM(Gesellschaft fur Fertigungstechnik und Maschinenbau) forging machine was carried out by three-dimensional finite element code DEFORM 3D.According to the effective plastic strain,the mean stress and the mean plastic strain distribution of the radial forging,the forging penetration efficiency(FPE) was studied throughout each operation.The results show that the effective plastic strain in the center of the forging is always greater than zero for the desirable larger axial drawing velocity.The mean stress in the center of the workpiece is proposed to describe hydrostatic pressure in this paper.There is compressive strain layer beneath the surface of the workpiece to be found,while there is tensile strain core in the center of the workpiece.These results could be a valuable reference for designing the similar forging operations.展开更多
This study systematically introduces the development of the world’s first full-link and full-system ground demonstration and verification system for the OMEGA space solar power satellite(SSPS).First,the OMEGA 2.0 inn...This study systematically introduces the development of the world’s first full-link and full-system ground demonstration and verification system for the OMEGA space solar power satellite(SSPS).First,the OMEGA 2.0 innovation design was proposed.Second,field-coupling theoretical models of sunlight concentration,photoelectric conversion,and transmitting antennas were established,and a systematic optimization design method was proposed.Third,a beam waveform optimization methodology considering both a high beam collection efficiency and a circular stepped beam shape was proposed.Fourth,a control strategy was developed to control the condenser pointing toward the sun while maintaining the transmitting antenna toward the rectenna.Fifth,a high-efficiency heat radiator design method based on bionics and topology optimization was proposed.Sixth,a method for improving the rectenna array’s reception,rectification,and direct current(DC)power synthesis efficiencies is presented.Seventh,high-precision measurement technology for high-accuracy beam-pointing control was developed.Eighth,a smart mechanical structure was designed and developed.Finally,the developed SSPS ground demonstration and verification system has the capacity for sun tracking,a high concentration ratio,photoelectric conversion,microwave conversion and emission,microwave reception,and rectification,and thus satisfactory results were obtained.展开更多
基金supported by the National Natural Science Foundation of China(Grant No.50609011).
文摘Stepped spillways for significant energy dissipation along the chute have gained interest; popularity among researchers; dam engineers. Due to the complexity of air-water two-phase flow over stepped spillways, the finite volume computational fluid dynamics module of the FLUENT software was used to simulate the main characteristics of the flow. Adopting the RNG k- turbulence model, the mixture flow model for air-water two-phase flow was used to simulate the flow field over stepped spillway with the PISO arithmetic technique. The numerical result successfully reproduced the complex flow over a stepped spillway of an experiment case, including the interaction between entrained air bubbles; cavity recirculation in the skimming flow regime, velocity distribution; the pressure profiles on the step surface as well. The result is helpful for understanding the detailed information about energy dissipation over stepped spillways.
基金The authors gratefully acknowledge the support of the National Natural Science Foundation of China (Grants 11672008 and 11272016).
文摘A novel oscillator structure, bimorph piezoelectric cantilever beam with two-stepped variable thicknesses,is proposed to improve the energy harvestingperformance of the vibration energy harvester (VEH) under low-frequency vibration environment. Firstly, the piezoelectric cantilever is segmented to obtain the energy functions based on the Euler-Bernoulli beam assumptions, and the Galerkin approach is utilized to discretize the energy functions. Applying boundary conditions and continuity conditions enforced at separation locations, the electromechanical coupled governing equations for the piezoelectric energy harvesterareintroduced by means of the Lagrange equations. Furthermore, the steady state response expressions are obtained for harmonic base excitations at arbitrary frequencies. Numerical results are computed and the effects ofthe lengths-ratio, thicknesses-ratio,end thicknessand load resistance on the output voltage, harvested power and power density are discussed. Moreover, to verify thecorrectness ofanalytical results, the finite element method (FEM)simulationis also conducted to analyze performance of the proposed VEH, where a good agreement is presented. All the results show thatthe present oscillator structureis moreefficient than the conventional uniform beam structure, specifically, for vibration energy harvesting in low-frequency environment.
基金by the NSFC-Shandong Joint Fund Program entitled“Control Mechanisms of Faults on Deep Gold Deposits in Jiaodong Peninsula”(U2006201).
文摘The Jiaodong Peninsula in Shandong Province,China is the world’s third-largest gold metallogenic area,with cumulative proven gold resources exceeding 5000 t.Over the past few years,breakthroughs have been made in deep prospecting at a depth of 500‒2000 m,particularly in the Sanshandao area where a huge deep gold orebody was identified.Based on previous studies and the latest prospecting progress achieved by the project team of this study,the following results are summarized.(1)3D geological modeling results based on deep drilling core data reveal that the Sanshandao gold orefield,which was previously considered to consist of several independent deposits,is a supergiant deposit with gold resources of more than 1200 t(including 470 t under the sea area).The length of the major orebody is nearly 8 km,with a greatest depth of 2312 m below sea level and a maximum length of more than 3 km along their dip direction.(2)Thick gold orebodies in the Sanshandao gold deposit mainly occur in the specific sections of the ore-controlling fault where the fault plane changes from steeply to gently inclined,forming a stepped metallogenic model from shallow to deep level.The reason for this strong structural control on mineralization forms is that when ore-forming fluids migrated along faults,the pressure of fluids greatly fluctuated in fault sections where the fault dip angle changed.Since the solubility of gold in the ore-forming fluid is sensitive to fluid pressure,these sections along the fault plane serve as the target areas for deep prospecting.(3)Thermal uplifting-extensional structures provide thermodynamic conditions,migration pathways,and deposition spaces for gold mineralization.Meanwhile,the changes in mantle properties induced the transformation of the geochemical properties of the lower crust and magmatic rocks.This further led to the reactivation of ore-forming elements,which provided rich materials for gold mineralization.(4)It can be concluded from previous research results that the gold mineralization in the Ji
基金Project supported by the National Natural Science Foundation of China (No. 60879002)the Tianjin Support Plan of China(No. 10ZCKFGX03800)
文摘The effects of journal misalignment on a journal bearing caused by an asymmetric rotor structure are presented in this study.A new model considering the asymmetric deflection is applied.Also,the thermo-hydrodynamic of the oil film in the journal bearing and straightforward elasticity theory are considered in the analysis.Based on the structure stiffness equivalent characteristic,a simple stepped shaft can reflect the entire complex structure model.The existing lubrication model,which does not consider this angle component,is not very precise for journal bearings.Film pressure,misalignment angle,velocity field,oil leakage,and temperature field were calculated and compared in the journal bearing analysis.The results indicate that bearing performances are greatly affected by misalignment caused by the asymmetric structure.A simple stepped shaft can effectively represent a misaligned journal bearing in a rotor-bearing system.
文摘In this paper, the k ε turbulence model is used to simulate the three dimensional turbulence flow over the stepped spillway at the Yubeishan reservoir. In order to solve the curved free water surface and to handle the complex boundary conditions, the fractional Volume Of Fluid (VOF) model that is applicable to the solution of the stratified two phase flow is introduced along with k ε turbulence model and the unstructured grid is used for the discretization of the irregular simulation domain. By these methods, the turbulence flow field of the stepped spillway is simulated successfully. The location of the free surface along the spillway, the magnitude and distribution of the velocity, the pressure on the step surface, the turbulence kinetic energy and turbulence dissipation rate are obtained by simulation. The changes and distributions of these characteristics along the width of the spillway are also obtained. The energy dissipation ratio of the stepped spillway is calculated according to the upstream and downstream water depth and velocities
基金Supported by the fund of National Defense Industry Innovative Team
文摘Stepped frequency radar is a well known scheme to generate high range resolution profile （HRRP） of targets. Through appropriate radar parameter design, the radar enables both unambiguous velocity measurement and high resolution ranging within a single dwell in a high pulse repetition frequency （HPRF） mode. This paper analyzes in detail the design principle of the HPRF stepped frequency radar system, the solution to its ambiguity issue, as well as its signal processing method. Both theoretical analysis and simulation results demonstrate that the proposed radar scheme can work independently to solve the problem of motion compensation, and is therefore highly applicable to many new types of radar.
文摘Numerical simulation of stepped channel flow was conducted using turbulence models based on the VOF technique. Stepped channel flow is a complicated air-water two-phase flow with free surface, which can be divided into three flow regimes： skimming flow, nappe flow and transition flow. The characteristics of skimming flow over mild stepped channel was investigated, including friction factors, air concentration profiles velocity field, clear-water and bulked depths, static pressure, etc. Smooth channel flow was also simulated to compare the hydraulic characteristics of the stepped channel flow with the smooth one. Comparisons between the computed and the measured were made. Furthermore, comparison of the computed air concentration with Straub and Anderson＇s data was also performed. The Fluent 6.1 software was employed to conduct this numerical simulation work.
基金This work was supported by the National Natural Science Foundation of China (Grant No.49975003), the Chinese Academy of Sciences (Grant No.Kzcx2-201) the Cold and Anal Regions Environmental and Engineering Research Institute, the Chinese Academy
文摘Radio frequency observations of cloud-to-ground lightning (CG) were made in 1999 in Guangdong Province with the broadband lightning interferometer. In this paper, radiation source locations and electric field waveforms are analyzed for different types of breakdown events, including the preliminary breakdown of in-cloud activities, the stepped leaders of initial strokes to ground and activities during and following return strokes. It is shown that the structure and development of lightning discharges and associated breakdown processes can be reconstructed by using this new type of lightning radiation source location system. The detectable radiation of lightning was primarily produced by the negative breakdown process. The channel was concentrated with few branches during the preliminary breakdown stage of CG lightning flashes. The radiation sources appeared generally at the tip of the channel. During the late period of the stepped leader, the radiation sources were dispersed with branches extended away from the main channel. The radiation sources were in a certain length segment of the channel and the altitude of the segment descended along with the propagation of the leader to the ground. During the preliminary breakdown and the stepped leader of initial strokes to the ground, a sequence of fast negative streamers were observed to start continually from or farther away the lightning-initiated region and propagate along the developed leader channel, which may supply negative charge that assisted the leader's development. The progression speed of fast negative streamers was about ten times faster than the average speed of lightning channel.
文摘In this paper, the k-ε two-equation turbulence model was used to simulatethe three-dimensional turbulent flow of the stepped spillway at the Yubeishan reservoir. In order tosolve the curved free water surface and to handle the complex boundary conditions, the fractionalVolume Of Fluid (VOF) model that is applicable to the solution of the stratified two-phase flow wasintorduced to the k-ε turbulence model and the unstructured grid was used for the discretization ofthe irregular simulation domain. By these methods, the turbulent flow field of the stepped spillwaywas simulated successfully. The location of the free surface along the spillway, the magnitude anddistribution of the velocity, the pressure distribution on the step surface, the turbulence kineticenergy and turbulence dissipation rate were obtained by simulation. The changes and distributions ofthese characteristics along the width of the spillway were also obtained. The energy dissipationratio of the stepped spillway was calculated according to the upstream and downstream water depthand velocities.
基金The National Basic Research Program of China("973"Project)(Grant No.2013CB035905)The National Natural Science Foundation of China(Grant No.51179114)
文摘The free flow on the step surfaces has received much attention for its representative body type,flow structure,water-air two phase flow,cavitation,and many complex issues.The experiments about the time-averaged pressure and aeration concentration distribution on the step surface show that the vertical plane of steps will inevitably experience negative pressure,which must rely on adequate aeration concentration to avoid cavitation damage.However,the self-aerated flow at the head section has a relatively low aeration concentration,and the concentration of the entire steps decreases with the increasing of weir head,the minimum appears in the vicinity of the corner,and the location is close to the minimum pressure.Thus,it is necessary to set aerator in the upstream end of the step surfaces to avoid cavitation damage.
文摘The numerical thermal mechanical simulation of radial forging process of steel H13 stepped shaft with GFM(Gesellschaft fur Fertigungstechnik und Maschinenbau) forging machine was carried out by three-dimensional finite element code DEFORM 3D.According to the effective plastic strain,the mean stress and the mean plastic strain distribution of the radial forging,the forging penetration efficiency(FPE) was studied throughout each operation.The results show that the effective plastic strain in the center of the forging is always greater than zero for the desirable larger axial drawing velocity.The mean stress in the center of the workpiece is proposed to describe hydrostatic pressure in this paper.There is compressive strain layer beneath the surface of the workpiece to be found,while there is tensile strain core in the center of the workpiece.These results could be a valuable reference for designing the similar forging operations.
文摘This study systematically introduces the development of the world’s first full-link and full-system ground demonstration and verification system for the OMEGA space solar power satellite(SSPS).First,the OMEGA 2.0 innovation design was proposed.Second,field-coupling theoretical models of sunlight concentration,photoelectric conversion,and transmitting antennas were established,and a systematic optimization design method was proposed.Third,a beam waveform optimization methodology considering both a high beam collection efficiency and a circular stepped beam shape was proposed.Fourth,a control strategy was developed to control the condenser pointing toward the sun while maintaining the transmitting antenna toward the rectenna.Fifth,a high-efficiency heat radiator design method based on bionics and topology optimization was proposed.Sixth,a method for improving the rectenna array’s reception,rectification,and direct current(DC)power synthesis efficiencies is presented.Seventh,high-precision measurement technology for high-accuracy beam-pointing control was developed.Eighth,a smart mechanical structure was designed and developed.Finally,the developed SSPS ground demonstration and verification system has the capacity for sun tracking,a high concentration ratio,photoelectric conversion,microwave conversion and emission,microwave reception,and rectification,and thus satisfactory results were obtained.
