During the continuous casting process of low carbon steel,the solidified hook formed in the mold has great effects on the surface quality of the cast slab.Some factory experiments have been conducted to investigate th...During the continuous casting process of low carbon steel,the solidified hook formed in the mold has great effects on the surface quality of the cast slab.Some factory experiments have been conducted to investigate the microscopic characteristics and reveal the influence of process parameters on solidified hooks.The depth of the hooks showed a positive correlation with the deflection angle,length,and oscillation mark(OM)depth,which indicates that the OM depth can serve as an approximate indicator for evaluating the depth of the solidified hooks.On the wide and narrow faces of the cast slab,the depth of the solidified hooks and the temperature distribution in the mold show opposite trends,with lower depths of solidified hooks at positions with higher temperatures.In addition,the influence of process parameters on solidified hooks was analyzed.With the increase in superheat,not only the depth of solidified hooks gradually decreases,but also the ratio of depression-typed marks increases.Increasing casting speed and decreasing immersion depth of the submerged entry nozzle will both lead to a decrease in the depth of the solidified hook.展开更多
We present a compact optical delay line(ODL)with wide-range continuous tunability on thin-film lithium niobate platform.The proposed device integrates an unbalanced Mach-Zehnder interferometer(MZI)architecture with du...We present a compact optical delay line(ODL)with wide-range continuous tunability on thin-film lithium niobate platform.The proposed device integrates an unbalanced Mach-Zehnder interferometer(MZI)architecture with dual tunable couplers,where each coupler comprises two 2×2 multimode interferometers and a MZI phase-tuning section.Experimental results demonstrate continuous delay tuning from 0 to 293 ps through synchronized control of coupling coefficients,corresponding to a 4 cm path difference between interferometer arms.The measured delay range exhibits excellent agreement with theoretical predictions derived from ODL waveguide parameters.This result addresses critical challenges in integrated photonic systems that require precise temporal control,particularly for applications in optical communications and quantum information processing,where a wide tuning range is paramount.展开更多
Most studies on solute transport in coastal aquifers affected by tides focus on the transport of instantaneous released solute,and there are few studies on continuously released solute affected by tides.In this study,...Most studies on solute transport in coastal aquifers affected by tides focus on the transport of instantaneous released solute,and there are few studies on continuously released solute affected by tides.In this study,the image monitoring method is used to establish the quantitative relationship between the concentration of the colored tracer and the hue value of the image,and the digital image is used to determine the tracer concentration distribution.Using image monitoring method laboratory experiments,quantitative analysis of the characteristics of continuously released solute transport in coastal unconfined aquifers under the tidal influence.Experiments show that the high tide inhibits the increase in the concentration of each point in the aquifer.Under the influence of tides,the solute plume retreats towards the land.During the low tide period,the solute plume migrates toward the sea again.And the solute plume will maintain a relatively stable shape after entering the aquifer for a long enough time.Ignoring the tidal effect seems to have little effect on the estimation of the position of the solute plume,but ignoring the tidal effect has a certain influence on the estimation of the dispersion range of the solute plume.No matter whether considering the tidal action,the final dispersion range of the solute plume is almost the same.But before the solute plume reaches a stable state,ignoring the tidal effect will lead to a smaller dispersion range of the solute plume.展开更多
Strengthened directivity with higher-order side lobes can be generated by the transducer with a larger radius at a higher frequency. The multi-annular pressure distributions are displayed in the cross-section of the a...Strengthened directivity with higher-order side lobes can be generated by the transducer with a larger radius at a higher frequency. The multi-annular pressure distributions are displayed in the cross-section of the acoustic vortices(AVs)which are formed by side lobes. In the near field, particles can be trapped in the valley region between the two annuli of the pressure peak, and cannot be moved to the vortex center. In this paper, a trapping method based on a sector transducer array is proposed, which is characterized by the continuously variable topological charge(CVTC). This acoustic field can not only enlarge the range of particle trapping but also improve the aggregation degree of the trapped particles. In the experiments, polyethylene particles with a diameter of 0.2 mm are trapped into the multi-annular valleys by the AV with a fixed topological charge. Nevertheless, by applying the CVTC, particles outside the radius of the AV can cross the pressure peak successfully and move to the vortex center. Theoretical studies are also verified by the experimental particles trapping using the AV with the continuous variation of three topological charges, and suggest the potential application of large-scale particle trapping in biomedical engineering.展开更多
To address the incompatibility between high environmental adaptability and deep subwavelength characteristics in conventional local resonance metamaterials,and overcome the deficiencies in the stability of existing ac...To address the incompatibility between high environmental adaptability and deep subwavelength characteristics in conventional local resonance metamaterials,and overcome the deficiencies in the stability of existing active control techniques for band gaps,this paper proposes a design method of pure metal vibration damping metamaterial with continuously tunable stiffness for wideband elastic wave absorption.We design a dual-helix narrow-slit pure metal metamaterial unit,which possesses the triple advantage of high spatial compactness,low stiffness characteristics,and high structural stability,enabling the opening of elastic flexural band gaps in the low-frequency range.Similar to the principle of a sliding rheostat,the introduction of continuously sliding plug-ins into the helical slits enables the continuous variation of the stiffness of the metamaterial unit,achieving a continuously tunable band gap effect.This successfully extends the effective band gap by more than ten times.The experimental results indicate that this metamaterial unit can be used as an additional vibration absorber to absorb the low-frequency vibration energy effectively.Furthermore,it advances the metamaterial absorbers from a purely passive narrowband design to a wideband tunable one.The pure metal double-helix metamaterials retain the subwavelength properties of metamaterials and are suitable for deployment in harsh environments.Simultaneously,by adjusting its stiffness,it substantially broadens the effective band gap range,presenting promising potential applications in various mechanical equipment operating under adverse conditions.展开更多
The exponential stability of a class of neural networks with continuously distributed delays is investigated by employing a novel Lyapunov-Krasovskii functional. Through introducing some free-weighting matrices and th...The exponential stability of a class of neural networks with continuously distributed delays is investigated by employing a novel Lyapunov-Krasovskii functional. Through introducing some free-weighting matrices and the equivalent descriptor form, a delay-dependent stability criterion is established for the addressed systems. The condition is expressed in terms of a linear matrix inequality （LMI）, and it can be checked by resorting to the LMI in the Matlab toolbox. In addition, the proposed stability criteria do not require the monotonicity of the activation functions and the derivative of a time-varying delay being less than 1, which generalize and improve earlier methods. Finally, numerical examples are given to show the effectiveness of the obtained methods.展开更多
Continuously rotating detonation engine （CRDE） is a focus for concern in the field of aerospace propulsion. It has several advantages, including one-initiation, high thermal efficiency and simple structure. Due to t...Continuously rotating detonation engine （CRDE） is a focus for concern in the field of aerospace propulsion. It has several advantages, including one-initiation, high thermal efficiency and simple structure. Due to these characteristics, it is expected to bring revolutionary advance- ments to aviation and aerospace propulsion systems and now has drawn much attention throughout the world. In this paper, an overview of the development of CRDE is given from several aspects： basic concepts, applications, experimental studies, numerical simulations, and so on. Representative results and outstanding contributions are summarized and the unresolved issues for further engi- neerin~ applications of CRDE are 13rovided.展开更多
Considering arch rib, lateral brace, suspender, girder, pier and track position, the model for the interaction between long-span tied arch continuous bridge and multiple tracks was established by using steel-concrete ...Considering arch rib, lateral brace, suspender, girder, pier and track position, the model for the interaction between long-span tied arch continuous bridge and multiple tracks was established by using steel-concrete composite section beam element to simulate concrete-filled steel tube(CFST) arch rib, using the beam element with rigid arm to simulate the prestressed concrete girder and using nonlinear bar element to simulate longitudinal constraint between track and bridge. Taking a(77+3×156.8+77) m tied arch continuous bridge with four tracks on the Harbin-Qiqihar Passenger Dedicated Line as an example, the arrangement of continuously welded rail(CWR) was explored. The longitudinal force in CWR on the tied arch continuous bridge, the pier top horizontal force and torque due to the unbalance load case, were analyzed under the action of temperature, vertical live load, train braking and wind load.Studies show that, it can significantly reduce track displacement to set the track expansion devices at main span arch springing on both sides; the track stress due to arch temperature variation can reach 40.8 MPa; the track stress, pier top horizontal force and torque are related to the number of loaded tracks and train running direction, and the bending force applied to unloaded track is close to the loaded track, while the braking force applied to unloaded track is 1/4 to 1/2 of the loaded track; the longitudinal force of track due to the wind load is up to 12.4 MPa, which should be considered.展开更多
A proven beam-track contact model was used to analyze the track-structure interaction of CWR (continuously welded track) on bridge. Considering the impact of adjacent bridges, the tower-cable-track-beam-pier-pile fini...A proven beam-track contact model was used to analyze the track-structure interaction of CWR (continuously welded track) on bridge. Considering the impact of adjacent bridges, the tower-cable-track-beam-pier-pile finite element model of the cable-stayed bridge was established. Taking a bridge group including 40-32m simply-supported beam and (32+80+112)m single-tower cable-stayed bridge and 17-32m simply-supported beam on the Kunming-Shanghai high-speed railway as an example, the characteristics of CWR longitudinal force on the cable-stayed bridge were studied. It is shown that adjacent bridges must be considered in the calculation of the track expansion force and bending force on cable-stayed bridge. When the span amount of adjacent bridges is too numerous, it can be simplified as six spans; the fixed bearing of adjacent simply-supported beams should be placed on the side near the cable-stayed bridge; the track expansion device should be set at the bridge tower to reduce the track force near the bridge abutment.展开更多
Abstract The continuously rotating detonation engine （CRDE） is a new concept of engines for air- craft and spacecraft. Quasi-stable continuously rotating detonation （CRD） can be observed in an annular combustion c...Abstract The continuously rotating detonation engine （CRDE） is a new concept of engines for air- craft and spacecraft. Quasi-stable continuously rotating detonation （CRD） can be observed in an annular combustion chamber, but the sustaining, stabilizing and adjusting mechanisms are not yet clear. To learn more deeply into the CRDE, experimental studies have been carried out to inves- tigate hydrogen-oxygen CRDE. Pressure histories are obtained during each shot, which show that stable CRD waves are generated in the combustor, when feeding pressures are higher than 0.5 MPa for fuel and oxidizer, respectively. Each shot can keep running as long as fresh gas feeding main- tains. Close-up of the pressure history shows the repeatability of pressure peaks and indicates the detonation velocity in hydrogen-oxygen CRD, which proves the success of forming a stable CRD in the annular chamber. Spectrum of the pressure history matches the close-up analysis and confirms the CRD. It also shows multi-wave phenomenon and affirms the fact that in this case a single detonation wave is rotating in the annulus. Moreover, oscillation phenomenon is found in pressure peaks and a self-adjusting mechanism is proposed to explain the phenomenon.展开更多
The effects of continuously regenerating diesel particulate filter （CRDPF） systems on regulated gaseous emissions, and number-size distribution and mass of particles emanated from a diesel engine have been investiga...The effects of continuously regenerating diesel particulate filter （CRDPF） systems on regulated gaseous emissions, and number-size distribution and mass of particles emanated from a diesel engine have been investigated in this study. Two CRDPF units （CRDPF-1 and CRDPF-2） with different specifications were separately retrofitted to the engine running with European steady-state cycle （ESC）. An electrical low pressure impactor （ELPI） was used for particle number-size distribution measurement and mass estimation. The conversion/reduction rate （RcR） of hydrocarbons （HC） and carbon monoxide （CO） across CRDPF-1 was 83% and 96.3%, respectively. Similarly, the RCR of HC and CO and across CRDPF-2 was 91.8% and 99.1%, respectively. The number concentration of particles and their concentration peaks; nuclei mode, accumulation mode and total particles; and particle mass were highly reduced with the CRDPF units. The nuclei mode particles at downstream of CRDPF-1 and CRDPF-2 decreased by 99.9% to 100% and 97.8% to 99.8% respectively; and the particle mass reduced by 73% to 92.2% and 35.3% to 72.4%, respectively, depending on the engine conditions. In addition, nuclei mode particles increased with the increasing of engine speed due to the heterogeneous nucleation initiated by the higher exhaust temperature, while accumulation mode particles were higher at higher loads due to the decrease in the air-to-fuel ratio （A/F） at higher loads.展开更多
Two continuously regenerating diesel particulate filter （CRDPF） with different configurations and one particles oxidation catalyst （POC） were employed to perform experiments in a controlled laboratory setting to e...Two continuously regenerating diesel particulate filter （CRDPF） with different configurations and one particles oxidation catalyst （POC） were employed to perform experiments in a controlled laboratory setting to evaluate their effects on NO2, smoke and particle number emissions. The results showed that the application of the after-treatments increased the emission ratios of NO2/NOx significantly. The results of smoke emissions and particle number （PN） emissions indicated that both CRDPFs had sufficient capacity to remove more than 90% of total particulate matter （PM） and more than 97% of solid particles. However, the POC was able to remove the organic components of total PM, and only partially to remove the carbonaceous particles with size less than 30 nm. The negligible effects of POC on larger particles were observed due to its honeycomb structure leads to an inadequate residence time to oxidize the solid particles or trap them. The particles removal efficiencies of CRDPFs had high degree of correlations with the emission ratio of NO2/NOx. The PN emission results from two CRDPFs indicated that more NO2 generating in diesel oxidation catalyst section could obtain the higher removal efficiency of solid particles. However this also increased the risk of NO2 exposure in atmosphere.展开更多
The quality of central equiaxed grain zone （CEGZ） of GCr15 bearing steel billets was investigated at different superheats （20, 25 and 35 ℃ by experimental observations and a finite element model in order to optimi...The quality of central equiaxed grain zone （CEGZ） of GCr15 bearing steel billets was investigated at different superheats （20, 25 and 35 ℃ by experimental observations and a finite element model in order to optimize superheat in continuous casting process. Several GCrl5 billets were collected from the continuous casting shop, and the same CEGZ was chosen for comparison of internal quality of GCrl5 billets. Considering the limitation of segregation index at some points, two- dimensional segregation ratio in CEGZ was introduced. Firstly, the segregation ratio and the area of center large dark points in CEGZ obtain the minimum at 25 ℃ superheat, which indicates that the quality of CEGZ at 25 ~C superheat is improved compared with those at 20 and 35 ℃ superheats for corresponding continuously cast billets. The highest superheat and the lowest superheat are not beneficial for improving the central zone quality in the billets. Secondly, the quality of CEGZ of GCr15 billets increases with a decrease in the secondary dendrite arm spacing of CEGZ. Finally, according to the established finite element model, it is deduced that the secondary dendrite arm spacing of CEGZ is closely related to its later solidifica- tion time at solid fraction of 0.5-1.0, and the former will be decreased when decreasing the latter.展开更多
The current research on pulse continuously variable transmission（CVT） is mainly focused on reducing the pulse degree and making pulse degrees a constant value. Current research mainly confined to find out new design...The current research on pulse continuously variable transmission（CVT） is mainly focused on reducing the pulse degree and making pulse degrees a constant value. Current research mainly confined to find out new design parameters by using the method of optimization, and reduce the pulse degree of pulse CVT and its range of variation. But the fact is that the reduction of the pulse degree is not significant. This article presents a new structure of mechanical pulse CVT--the rotational swashplate pulse CVT with driven by helical gear axial meshing. This transmission is simple and compact in structure and low in pulsatile rate （it adopts 6 guide rods）, and the pulsatile degree is irrelevant to the transmission ratio. Theoretically, pulsatile rate could be reduced to zero if appropriate curved surface of the swashplate is used. Compared with the connecting rod pulse CVT, the present struc^tre uses helical gear mechanism as transmission part and it avoids unbalanced inertial force in the former model. This paper analyzes the principle of driving of this transmission, presents its mechanical structure, and discusses its motion characteristics. Experimental prototype of this type of CVT has been manufactured. Tests for the transmission efficiency（when the rotational speed of the output shaft is the maximum） and the angular velocity of the output shaft have been carried out, and data have been analyzed. The experimental results show that the speed of the output shaft for the experimental prototype is slightly lower than the theoretical value, and the transmission efficiency of the experimental prototype is about 70%. The pulse degree of the CVT discussed in this paper is less than the existing pulse CVT of other types, and it is irrelevant to the transmission ratio of the CVT. The research provides the new idea to the CVT study.展开更多
A numerical model of heat transfer was developed to investigate the heat transfer of continuously cast billet with the aid of surface temperature tests by ThermaCAMTM researcher and nail shooting experiments. The effe...A numerical model of heat transfer was developed to investigate the heat transfer of continuously cast billet with the aid of surface temperature tests by ThermaCAMTM researcher and nail shooting experiments. The effects of secondary cooling practice and casting speed on the solidification process and central segregation of carbon were investigated as well with the actual central segregation tests. The results show that the surface center and billet center temperatures exhibit a different pattern during solidification, and the solidified shell thickness is presented as an ＂S＂ type. With the increase of secondary cooling intensity and the decrease of casting speed, the end points of the solidus line and the liquidus line move forward, and the central segregation level of carbon decreases. The optimal casting condition is suggested for continuously cast high carbon billet with F-EMS （final electromagnetic stirring）.展开更多
The automatic control of clutch starting in car with a metal pushingbelt-planetary gear continuously variable transmission (CVT) is a complex problem. A suited controlstrategy is required to realize quick and smooth s...The automatic control of clutch starting in car with a metal pushingbelt-planetary gear continuously variable transmission (CVT) is a complex problem. A suited controlstrategy is required to realize quick and smooth start. A simulation state space equation isestablished on clutch staring control of a car with CVT by bond graph theory. According to the fuzzycontrol method with the expert system, a fuzzy control system of car starting process to weaken thejerk motion is introduced. The simulation results indicate that the jerk motion of clutch startingis below 10 m/s^3.展开更多
We prepare a new type of patented biodegradable biomedical Mg-Nd-Zn-Zr(JDBM)alloy system and impose double continuously extrusion(DCE)processing.The lowest processing temperature is 250℃for JDBM-2.1Nd and 310℃for JD...We prepare a new type of patented biodegradable biomedical Mg-Nd-Zn-Zr(JDBM)alloy system and impose double continuously extrusion(DCE)processing.The lowest processing temperature is 250℃for JDBM-2.1Nd and 310℃for JDBM-2.8Nd,which increases with the Nd concentration.The highest yield strength of 541 MPa is achieved in JDBM-2.1 Nd samples when extruded at 250℃and the elongation is about 3.7%.Moreover,the alloy with a lower alloying element content can reach a higher yield strength while that with a higher alloying element content can reach a larger elongation after DCE processing.However,when extruded under the same conditions,the alloy with a higher alloying contents exhibits better tensile properties.展开更多
A new mechanics model, which reveals additional longitudinal force transmission between the continuously welded rails and the bridges, is established on the fact that the influence of the mutual relative displacement ...A new mechanics model, which reveals additional longitudinal force transmission between the continuously welded rails and the bridges, is established on the fact that the influence of the mutual relative displacement (among) the rail, the sleeper and the beam is taken into account. An example is presented and numerical results are compared. The results show that the additional longitudinal forces calculated with the new model are less than those of the previous, especially in the case of the flexible pier bridges. The new model is also suitable for the analysis of the additional longitudinal force transmission between rails and bridges of ballastless track with small resistance fasteners without taking the sleeper displacement into account, and compared with the ballast bridges, the ballastless bridges have a much stronger additional longitudinal force transmission between the continuously welded rails and the bridges.展开更多
The most remarkable characteristic of a metal belt-planetary gearcontinuously variable transmission is a wider ratio range and a bigger torque capacity than aconventional metal pushing belt continuously variable trans...The most remarkable characteristic of a metal belt-planetary gearcontinuously variable transmission is a wider ratio range and a bigger torque capacity than aconventional metal pushing belt continuously variable transmission. A parallel hybrid car with thistransmission system not only can reduce fuel consumption and pollutant emission at a ECE city cycle,but also can keep the motor working in the most efficiency area and can be started by a lower powermotor by oneself. At the same time, the continuously variable transmission system can realize thesmooth switch between the motor and the engine.展开更多
基金the financial support of National Key Research and Development Plan(No.2021YFB3702000)National Natural Science of China(Nos.52074076,52174306 and U20A20272)Fundamental Research Funds for the Central Universities(Nos.N2225023 and N2425006).Author information。
文摘During the continuous casting process of low carbon steel,the solidified hook formed in the mold has great effects on the surface quality of the cast slab.Some factory experiments have been conducted to investigate the microscopic characteristics and reveal the influence of process parameters on solidified hooks.The depth of the hooks showed a positive correlation with the deflection angle,length,and oscillation mark(OM)depth,which indicates that the OM depth can serve as an approximate indicator for evaluating the depth of the solidified hooks.On the wide and narrow faces of the cast slab,the depth of the solidified hooks and the temperature distribution in the mold show opposite trends,with lower depths of solidified hooks at positions with higher temperatures.In addition,the influence of process parameters on solidified hooks was analyzed.With the increase in superheat,not only the depth of solidified hooks gradually decreases,but also the ratio of depression-typed marks increases.Increasing casting speed and decreasing immersion depth of the submerged entry nozzle will both lead to a decrease in the depth of the solidified hook.
基金supported by the National Natural Science Foundation of China(Grant Nos.12192251,12334014,12404378,92480001,12134001,12174113,12174107,12474325,12404379,and 12474378)the Innovation Program for Quantum Science and Technology(Grant No.2021ZD0301403)+1 种基金Shanghai Municipal Science and Technology Major Project(Grant No.2019SHZDZX01)Fundamental Research Funds for the Central Universities,the Engineering Research Center for Nanophotonics&Advanced Instrument,Ministry of Education,East China Normal University(Grant No.2023nmc005).
文摘We present a compact optical delay line(ODL)with wide-range continuous tunability on thin-film lithium niobate platform.The proposed device integrates an unbalanced Mach-Zehnder interferometer(MZI)architecture with dual tunable couplers,where each coupler comprises two 2×2 multimode interferometers and a MZI phase-tuning section.Experimental results demonstrate continuous delay tuning from 0 to 293 ps through synchronized control of coupling coefficients,corresponding to a 4 cm path difference between interferometer arms.The measured delay range exhibits excellent agreement with theoretical predictions derived from ODL waveguide parameters.This result addresses critical challenges in integrated photonic systems that require precise temporal control,particularly for applications in optical communications and quantum information processing,where a wide tuning range is paramount.
基金supported by the National Natural Science Foundation of China(No.42172281)the Opening Fund of the State Key Laboratory of China University of Geosciences(Wuhan)(No.SKJ2018055)。
文摘Most studies on solute transport in coastal aquifers affected by tides focus on the transport of instantaneous released solute,and there are few studies on continuously released solute affected by tides.In this study,the image monitoring method is used to establish the quantitative relationship between the concentration of the colored tracer and the hue value of the image,and the digital image is used to determine the tracer concentration distribution.Using image monitoring method laboratory experiments,quantitative analysis of the characteristics of continuously released solute transport in coastal unconfined aquifers under the tidal influence.Experiments show that the high tide inhibits the increase in the concentration of each point in the aquifer.Under the influence of tides,the solute plume retreats towards the land.During the low tide period,the solute plume migrates toward the sea again.And the solute plume will maintain a relatively stable shape after entering the aquifer for a long enough time.Ignoring the tidal effect seems to have little effect on the estimation of the position of the solute plume,but ignoring the tidal effect has a certain influence on the estimation of the dispersion range of the solute plume.No matter whether considering the tidal action,the final dispersion range of the solute plume is almost the same.But before the solute plume reaches a stable state,ignoring the tidal effect will lead to a smaller dispersion range of the solute plume.
基金Project supported by the National Key R&D Program of China(Grant No.2023YFE0201900)。
文摘Strengthened directivity with higher-order side lobes can be generated by the transducer with a larger radius at a higher frequency. The multi-annular pressure distributions are displayed in the cross-section of the acoustic vortices(AVs)which are formed by side lobes. In the near field, particles can be trapped in the valley region between the two annuli of the pressure peak, and cannot be moved to the vortex center. In this paper, a trapping method based on a sector transducer array is proposed, which is characterized by the continuously variable topological charge(CVTC). This acoustic field can not only enlarge the range of particle trapping but also improve the aggregation degree of the trapped particles. In the experiments, polyethylene particles with a diameter of 0.2 mm are trapped into the multi-annular valleys by the AV with a fixed topological charge. Nevertheless, by applying the CVTC, particles outside the radius of the AV can cross the pressure peak successfully and move to the vortex center. Theoretical studies are also verified by the experimental particles trapping using the AV with the continuous variation of three topological charges, and suggest the potential application of large-scale particle trapping in biomedical engineering.
基金supported by the National Natural Science Foundation of China(No.52250287)the Outstanding Youth Science Fund Project of Shaanxi Province of China(No.2024JC-JCQN-49)。
文摘To address the incompatibility between high environmental adaptability and deep subwavelength characteristics in conventional local resonance metamaterials,and overcome the deficiencies in the stability of existing active control techniques for band gaps,this paper proposes a design method of pure metal vibration damping metamaterial with continuously tunable stiffness for wideband elastic wave absorption.We design a dual-helix narrow-slit pure metal metamaterial unit,which possesses the triple advantage of high spatial compactness,low stiffness characteristics,and high structural stability,enabling the opening of elastic flexural band gaps in the low-frequency range.Similar to the principle of a sliding rheostat,the introduction of continuously sliding plug-ins into the helical slits enables the continuous variation of the stiffness of the metamaterial unit,achieving a continuously tunable band gap effect.This successfully extends the effective band gap by more than ten times.The experimental results indicate that this metamaterial unit can be used as an additional vibration absorber to absorb the low-frequency vibration energy effectively.Furthermore,it advances the metamaterial absorbers from a purely passive narrowband design to a wideband tunable one.The pure metal double-helix metamaterials retain the subwavelength properties of metamaterials and are suitable for deployment in harsh environments.Simultaneously,by adjusting its stiffness,it substantially broadens the effective band gap range,presenting promising potential applications in various mechanical equipment operating under adverse conditions.
基金The National Natural Science Foundation of China (No60574006)
文摘The exponential stability of a class of neural networks with continuously distributed delays is investigated by employing a novel Lyapunov-Krasovskii functional. Through introducing some free-weighting matrices and the equivalent descriptor form, a delay-dependent stability criterion is established for the addressed systems. The condition is expressed in terms of a linear matrix inequality （LMI）, and it can be checked by resorting to the LMI in the Matlab toolbox. In addition, the proposed stability criteria do not require the monotonicity of the activation functions and the derivative of a time-varying delay being less than 1, which generalize and improve earlier methods. Finally, numerical examples are given to show the effectiveness of the obtained methods.
基金co-supported by the Aeronautical Science Foundation of China(No.2008ZH71006)the National Natural Science Foundation of China(No.91441110)the Aerospace Innovation Fund of China(No.SY41YYF2014009)
文摘Continuously rotating detonation engine （CRDE） is a focus for concern in the field of aerospace propulsion. It has several advantages, including one-initiation, high thermal efficiency and simple structure. Due to these characteristics, it is expected to bring revolutionary advance- ments to aviation and aerospace propulsion systems and now has drawn much attention throughout the world. In this paper, an overview of the development of CRDE is given from several aspects： basic concepts, applications, experimental studies, numerical simulations, and so on. Representative results and outstanding contributions are summarized and the unresolved issues for further engi- neerin~ applications of CRDE are 13rovided.
基金Project(51378503)supported by the National Natural Science Foundation of ChinaProject(2014M552158)supported by China Postdoctoral Science Foundation
文摘Considering arch rib, lateral brace, suspender, girder, pier and track position, the model for the interaction between long-span tied arch continuous bridge and multiple tracks was established by using steel-concrete composite section beam element to simulate concrete-filled steel tube(CFST) arch rib, using the beam element with rigid arm to simulate the prestressed concrete girder and using nonlinear bar element to simulate longitudinal constraint between track and bridge. Taking a(77+3×156.8+77) m tied arch continuous bridge with four tracks on the Harbin-Qiqihar Passenger Dedicated Line as an example, the arrangement of continuously welded rail(CWR) was explored. The longitudinal force in CWR on the tied arch continuous bridge, the pier top horizontal force and torque due to the unbalance load case, were analyzed under the action of temperature, vertical live load, train braking and wind load.Studies show that, it can significantly reduce track displacement to set the track expansion devices at main span arch springing on both sides; the track stress due to arch temperature variation can reach 40.8 MPa; the track stress, pier top horizontal force and torque are related to the number of loaded tracks and train running direction, and the bending force applied to unloaded track is close to the loaded track, while the braking force applied to unloaded track is 1/4 to 1/2 of the loaded track; the longitudinal force of track due to the wind load is up to 12.4 MPa, which should be considered.
基金Project(51178469) supported by the National Natural Science Foundation of China
文摘A proven beam-track contact model was used to analyze the track-structure interaction of CWR (continuously welded track) on bridge. Considering the impact of adjacent bridges, the tower-cable-track-beam-pier-pile finite element model of the cable-stayed bridge was established. Taking a bridge group including 40-32m simply-supported beam and (32+80+112)m single-tower cable-stayed bridge and 17-32m simply-supported beam on the Kunming-Shanghai high-speed railway as an example, the characteristics of CWR longitudinal force on the cable-stayed bridge were studied. It is shown that adjacent bridges must be considered in the calculation of the track expansion force and bending force on cable-stayed bridge. When the span amount of adjacent bridges is too numerous, it can be simplified as six spans; the fixed bearing of adjacent simply-supported beams should be placed on the side near the cable-stayed bridge; the track expansion device should be set at the bridge tower to reduce the track force near the bridge abutment.
基金supported by the National Natural Science Foundation of China(No.91441110)
文摘Abstract The continuously rotating detonation engine （CRDE） is a new concept of engines for air- craft and spacecraft. Quasi-stable continuously rotating detonation （CRD） can be observed in an annular combustion chamber, but the sustaining, stabilizing and adjusting mechanisms are not yet clear. To learn more deeply into the CRDE, experimental studies have been carried out to inves- tigate hydrogen-oxygen CRDE. Pressure histories are obtained during each shot, which show that stable CRD waves are generated in the combustor, when feeding pressures are higher than 0.5 MPa for fuel and oxidizer, respectively. Each shot can keep running as long as fresh gas feeding main- tains. Close-up of the pressure history shows the repeatability of pressure peaks and indicates the detonation velocity in hydrogen-oxygen CRD, which proves the success of forming a stable CRD in the annular chamber. Spectrum of the pressure history matches the close-up analysis and confirms the CRD. It also shows multi-wave phenomenon and affirms the fact that in this case a single detonation wave is rotating in the annulus. Moreover, oscillation phenomenon is found in pressure peaks and a self-adjusting mechanism is proposed to explain the phenomenon.
基金supported by the National Natural Science Foundation of China (No. 40805053)
文摘The effects of continuously regenerating diesel particulate filter （CRDPF） systems on regulated gaseous emissions, and number-size distribution and mass of particles emanated from a diesel engine have been investigated in this study. Two CRDPF units （CRDPF-1 and CRDPF-2） with different specifications were separately retrofitted to the engine running with European steady-state cycle （ESC）. An electrical low pressure impactor （ELPI） was used for particle number-size distribution measurement and mass estimation. The conversion/reduction rate （RcR） of hydrocarbons （HC） and carbon monoxide （CO） across CRDPF-1 was 83% and 96.3%, respectively. Similarly, the RCR of HC and CO and across CRDPF-2 was 91.8% and 99.1%, respectively. The number concentration of particles and their concentration peaks; nuclei mode, accumulation mode and total particles; and particle mass were highly reduced with the CRDPF units. The nuclei mode particles at downstream of CRDPF-1 and CRDPF-2 decreased by 99.9% to 100% and 97.8% to 99.8% respectively; and the particle mass reduced by 73% to 92.2% and 35.3% to 72.4%, respectively, depending on the engine conditions. In addition, nuclei mode particles increased with the increasing of engine speed due to the heterogeneous nucleation initiated by the higher exhaust temperature, while accumulation mode particles were higher at higher loads due to the decrease in the air-to-fuel ratio （A/F） at higher loads.
基金supported by the National Natural Science Foundation of China (No. 50876013)
文摘Two continuously regenerating diesel particulate filter （CRDPF） with different configurations and one particles oxidation catalyst （POC） were employed to perform experiments in a controlled laboratory setting to evaluate their effects on NO2, smoke and particle number emissions. The results showed that the application of the after-treatments increased the emission ratios of NO2/NOx significantly. The results of smoke emissions and particle number （PN） emissions indicated that both CRDPFs had sufficient capacity to remove more than 90% of total particulate matter （PM） and more than 97% of solid particles. However, the POC was able to remove the organic components of total PM, and only partially to remove the carbonaceous particles with size less than 30 nm. The negligible effects of POC on larger particles were observed due to its honeycomb structure leads to an inadequate residence time to oxidize the solid particles or trap them. The particles removal efficiencies of CRDPFs had high degree of correlations with the emission ratio of NO2/NOx. The PN emission results from two CRDPFs indicated that more NO2 generating in diesel oxidation catalyst section could obtain the higher removal efficiency of solid particles. However this also increased the risk of NO2 exposure in atmosphere.
基金The authors are very grateful for National Natu- ral Science Foundation of China （No. 51504047） and Fundamental Research Funds for the Central Universities （No. CDJPY 14130001 ）. Meanwhile, the authors acknowledge very valuable discussion with Prof. Guang-hua Wen and Prof. Ping Tang from Chongqing University.
文摘The quality of central equiaxed grain zone （CEGZ） of GCr15 bearing steel billets was investigated at different superheats （20, 25 and 35 ℃ by experimental observations and a finite element model in order to optimize superheat in continuous casting process. Several GCrl5 billets were collected from the continuous casting shop, and the same CEGZ was chosen for comparison of internal quality of GCrl5 billets. Considering the limitation of segregation index at some points, two- dimensional segregation ratio in CEGZ was introduced. Firstly, the segregation ratio and the area of center large dark points in CEGZ obtain the minimum at 25 ℃ superheat, which indicates that the quality of CEGZ at 25 ~C superheat is improved compared with those at 20 and 35 ℃ superheats for corresponding continuously cast billets. The highest superheat and the lowest superheat are not beneficial for improving the central zone quality in the billets. Secondly, the quality of CEGZ of GCr15 billets increases with a decrease in the secondary dendrite arm spacing of CEGZ. Finally, according to the established finite element model, it is deduced that the secondary dendrite arm spacing of CEGZ is closely related to its later solidifica- tion time at solid fraction of 0.5-1.0, and the former will be decreased when decreasing the latter.
基金supported by Beijing Municipal Natural Science Foundation of China(Grant No. 3123036)Science and Technology Project of Beijing Municipal Education Commission of China(Grant No.KM200911417010)
文摘The current research on pulse continuously variable transmission（CVT） is mainly focused on reducing the pulse degree and making pulse degrees a constant value. Current research mainly confined to find out new design parameters by using the method of optimization, and reduce the pulse degree of pulse CVT and its range of variation. But the fact is that the reduction of the pulse degree is not significant. This article presents a new structure of mechanical pulse CVT--the rotational swashplate pulse CVT with driven by helical gear axial meshing. This transmission is simple and compact in structure and low in pulsatile rate （it adopts 6 guide rods）, and the pulsatile degree is irrelevant to the transmission ratio. Theoretically, pulsatile rate could be reduced to zero if appropriate curved surface of the swashplate is used. Compared with the connecting rod pulse CVT, the present struc^tre uses helical gear mechanism as transmission part and it avoids unbalanced inertial force in the former model. This paper analyzes the principle of driving of this transmission, presents its mechanical structure, and discusses its motion characteristics. Experimental prototype of this type of CVT has been manufactured. Tests for the transmission efficiency（when the rotational speed of the output shaft is the maximum） and the angular velocity of the output shaft have been carried out, and data have been analyzed. The experimental results show that the speed of the output shaft for the experimental prototype is slightly lower than the theoretical value, and the transmission efficiency of the experimental prototype is about 70%. The pulse degree of the CVT discussed in this paper is less than the existing pulse CVT of other types, and it is irrelevant to the transmission ratio of the CVT. The research provides the new idea to the CVT study.
基金Sponsored by National Natural Science Foundation of China(50925415)Fundamental Research Funds for Central University of China(N100102001)
文摘A numerical model of heat transfer was developed to investigate the heat transfer of continuously cast billet with the aid of surface temperature tests by ThermaCAMTM researcher and nail shooting experiments. The effects of secondary cooling practice and casting speed on the solidification process and central segregation of carbon were investigated as well with the actual central segregation tests. The results show that the surface center and billet center temperatures exhibit a different pattern during solidification, and the solidified shell thickness is presented as an ＂S＂ type. With the increase of secondary cooling intensity and the decrease of casting speed, the end points of the solidus line and the liquidus line move forward, and the central segregation level of carbon decreases. The optimal casting condition is suggested for continuously cast high carbon billet with F-EMS （final electromagnetic stirring）.
基金National Natural Science Founda-tion of China (No.59835160).
文摘The automatic control of clutch starting in car with a metal pushingbelt-planetary gear continuously variable transmission (CVT) is a complex problem. A suited controlstrategy is required to realize quick and smooth start. A simulation state space equation isestablished on clutch staring control of a car with CVT by bond graph theory. According to the fuzzycontrol method with the expert system, a fuzzy control system of car starting process to weaken thejerk motion is introduced. The simulation results indicate that the jerk motion of clutch startingis below 10 m/s^3.
基金support by the national key research and development plan(No.2016YFC1102100)the National Natural Science Founda-tion of China(Nos.51501110,51728202,11332013 and 51501115)+1 种基金the Natural Science Foundation of Shang-hai(15ZR1422600)the Shanghai Jiao Tong University Medical-engineering Cross Fund(No.YG2015MS66 and No.YG2014MS62).
文摘We prepare a new type of patented biodegradable biomedical Mg-Nd-Zn-Zr(JDBM)alloy system and impose double continuously extrusion(DCE)processing.The lowest processing temperature is 250℃for JDBM-2.1Nd and 310℃for JDBM-2.8Nd,which increases with the Nd concentration.The highest yield strength of 541 MPa is achieved in JDBM-2.1 Nd samples when extruded at 250℃and the elongation is about 3.7%.Moreover,the alloy with a lower alloying element content can reach a higher yield strength while that with a higher alloying element content can reach a larger elongation after DCE processing.However,when extruded under the same conditions,the alloy with a higher alloying contents exhibits better tensile properties.
文摘A new mechanics model, which reveals additional longitudinal force transmission between the continuously welded rails and the bridges, is established on the fact that the influence of the mutual relative displacement (among) the rail, the sleeper and the beam is taken into account. An example is presented and numerical results are compared. The results show that the additional longitudinal forces calculated with the new model are less than those of the previous, especially in the case of the flexible pier bridges. The new model is also suitable for the analysis of the additional longitudinal force transmission between rails and bridges of ballastless track with small resistance fasteners without taking the sleeper displacement into account, and compared with the ballast bridges, the ballastless bridges have a much stronger additional longitudinal force transmission between the continuously welded rails and the bridges.
基金This project is supported Fok Yingtung Education Foundation(No.81070)and National Natural Science Foundation of China(No.50005026).
文摘The most remarkable characteristic of a metal belt-planetary gearcontinuously variable transmission is a wider ratio range and a bigger torque capacity than aconventional metal pushing belt continuously variable transmission. A parallel hybrid car with thistransmission system not only can reduce fuel consumption and pollutant emission at a ECE city cycle,but also can keep the motor working in the most efficiency area and can be started by a lower powermotor by oneself. At the same time, the continuously variable transmission system can realize thesmooth switch between the motor and the engine.
