Metamaterials can control and manipulate acoustic/elastic waves on a subwavelength scale using cavities or additional components.However,the large cavity and weak stiffness components of traditional metamaterials may ...Metamaterials can control and manipulate acoustic/elastic waves on a subwavelength scale using cavities or additional components.However,the large cavity and weak stiffness components of traditional metamaterials may cause a conflict between vibroacoustic reduction and load-bearing capacity,and thus limit their application.Here,we propose a lightweight multifunctional metamaterial that can simultaneously achieve low-frequency sound insulation,broadband vibration reduction,and excellent load-bearing performance,named as vibroacoustic isolation and bearing metamaterial(VIBM).The advent of additive manufacturing technology provides a convenient and reliable method for the fabrication of VIBM samples.The results show that the compressive strength of the VIBM is as high as 9.71 MPa,which is nearly 87.81%higher than that of the conventional grid structure(CGS)under the same volume fraction.Moreover,the vibration and sound transmission are significantly reduced over a low and wide frequency range,which agrees well with the experimental data,and the reduction degree is obviously larger than that obtained by the CGS.The design strategy can effectively realize the key components of metamaterials and improve their application scenarios.展开更多
The application of multi-material topology optimization affords greater design flexibility compared to traditional single-material methods.However,density-based topology optimization methods encounter three unique cha...The application of multi-material topology optimization affords greater design flexibility compared to traditional single-material methods.However,density-based topology optimization methods encounter three unique challenges when inertial loads become dominant:non-monotonous behavior of the objective function,possible unconstrained characterization of the optimal solution,and parasitic effects.Herein,an improved Guide-Weight approach is introduced,which effectively addresses the structural topology optimization problem when subjected to inertial loads.Smooth and fast convergence of the compliance is achieved by the approach,while also maintaining the effectiveness of the volume constraints.The rational approximation of material properties model and smooth design are utilized to guarantee clear boundaries of the final structure,facilitating its seamless integration into manufacturing processes.The framework provided by the alternating active-phase algorithm is employed to decompose the multi-material topological problem under inertial loading into a set of sub-problems.The optimization of multi-material under inertial loads is accomplished through the effective resolution of these sub-problems using the improved Guide-Weight method.The effectiveness of the proposed approach is demonstrated through numerical examples involving two-phase and multi-phase materials.展开更多
A non-contact low-frequency(LF)method of diagnosing the plasma surrounding a scaled model in a shock tube is proposed.This method utilizes the phase shift occurring after the transmission of an LF alternating magnetic...A non-contact low-frequency(LF)method of diagnosing the plasma surrounding a scaled model in a shock tube is proposed.This method utilizes the phase shift occurring after the transmission of an LF alternating magnetic field through the plasma to directly measure the ratio of the plasma loop average electron density to collision frequency.An equivalent circuit model is used to analyze the relationship of the phase shift of the magnetic field component of LF electromagnetic waves with the plasma electron density and collision frequency.The applicable range of the LF method on a given plasma scale is analyzed.The upper diagnostic limit for the ratio of the electron density(unit:m^(-3))to collision frequency(unit:Hz)exceeds 1×10^(11),enabling an electron density to exceed 1×10^(20)m^(-3)and a collision frequency to be less than 1 GHz.In this work,the feasibility of using the LF phase shift to implement the plasma diagnosis is also assessed.Diagnosis experiments on shock tube equipment are conducted by using both the electrostatic probe method and LF method.By comparing the diagnostic results of the two methods,the inversion results are relatively consistent with each other,thereby preliminarily verifying the feasibility of the LF method.The ratio of the electron density to the collision frequency has a relatively uniform distribution during the plasma stabilization.The LF diagnostic path is a loop around the model,which is suitable for diagnosing the plasma that surrounds the model.Finally,the causes of diagnostic discrepancy between the two methods are analyzed.The proposed method provides a new avenue for diagnosing high-density enveloping plasma.展开更多
The static sealing of underground gas storage(UGS),including the integrity of cap rocks and the stability of faults,is analyzed from a macro perspective using a comprehensive geological evaluation method.Changes in po...The static sealing of underground gas storage(UGS),including the integrity of cap rocks and the stability of faults,is analyzed from a macro perspective using a comprehensive geological evaluation method.Changes in pore structure,permeability,and mechanical strength of cap rocks under cyclic loads may impact the rock sealing integrity during the injection and recovery phases of UGS.In this work,the mechanical deformation and failure tests of rocks,as well as rock damage tests under alternating loads,are conducted to analyze the changes in the strength and permeability of rocks under multiple-cycle intense injection and recovery of UGS.Additionally,this study proposes an evaluation method for the dynamic sealing performance of UGS cap rocks under multi-cycle alternating loads.The findings suggest that the failure strength(70%)can be used as the critical value for rock failure,thus providing theoretical support for determining the upper limit of operating pressure and the number of injection-recovery cycles for the safe operation of a UGS system.展开更多
The authors show the results of a study conducted on a joint connecting a concrete column to a composite steel concrete floor,subjected to tension on the beams as a result of the decomposition of sagging bending momen...The authors show the results of a study conducted on a joint connecting a concrete column to a composite steel concrete floor,subjected to tension on the beams as a result of the decomposition of sagging bending moment.The beam to column connection is achieved by means of headed studs welded to the beam and embedded in the concrete cast.Five different configurations have been tested at failure and the results are compared to formulae proposed in literature.Different degrees of ductility,reliability and strength have been obtained varying geometry and reinforcement ratio on the joints tested.展开更多
Microgrid stability analysis is a critical issue especially due to the inverters’low-inertia nature.The voltage and current control loops influences on stability are researched frequently most of which focus on mediu...Microgrid stability analysis is a critical issue especially due to the inverters’low-inertia nature.The voltage and current control loops influences on stability are researched frequently most of which focus on medium and high-frequency characteristic.Although the complete state-space model aims at low-frequency characteristic,it is too complicated and the calculation amount is huge with the scale of the microgrid increasing.One available reduced-order model of an inverter is simple,but it is suitable for only single inverter without network dynamic in microgrid.To fill in these gaps,a novel modeling method is proposed in this paper to investigate the low-frequency instability phenomenon and describe the whole DG connected system including network.In consideration of the high penetration level of induction motor(IM)loads and constant power(CP)loads in practical applications,the low-frequency mathematical model of IM and CP loads on the basis of static load is also built in this paper.Simulation and experimental results verify the effectiveness of the proposed model.展开更多
During large-scale hydraulic fracturing in shale gas horizontal wells,a cement sheath easily loses its integrity due to thefluctuation and continuous change of wellbore temperature and pressure and the cyclic loading ...During large-scale hydraulic fracturing in shale gas horizontal wells,a cement sheath easily loses its integrity due to thefluctuation and continuous change of wellbore temperature and pressure and the cyclic loading and unloading,which will threaten wellbore integrity.In order tofigure out the failure mechanism of cement sheath integrity under strong alternating thermal loads and prevent the failure of cement sheath barriers during large-scale hydraulic fracturing in shale gas horizontal wells,this paper adopted the independently developed experimental device to test and evaluate the sealing integrity and mechanical integrity of the full-scale combination of production casing,cement sheath and intermediate casing under strong alternating thermal loads.And the integrity experimental results of two kinds of full-scale cement sheaths(conventional and high-strength cement sheaths)under three kinds of strong alternating thermal loads(cycle number for the occurrence of discontinuous CO_(2) bubble:4 and 14;cycle number for the occurrence of continuous CO_(2) bubble:5 and 15;alternating thermal load:30-120℃ and 30-150℃)were obtained.And the following research results were obtained.First,alternating thermal load has a significant negative impact on the integrity of cement sheath,and with the increase of alternating temperature and temperature difference,the thermal cycle number characterizing the sealing integrity of cement sheath reduces sharply.Second,the interfacial mechanical property indicators that characterize the shearing force between cement sheath and casing and the axial and radial bonding strength decrease with the increase of the alternating temperature.Third,the micro annulus in cement sheath is mainly caused by discordant deformation between the casing and the cement sheath materials,and the mechanical degradation and deterioration of the set cement induced by the alternating thermal load aggravate the failure of the sealing integrity of cement sheath to a certain degree.In conclusion,the research results can provide a reference for the design of large-scale fracturing in deep shale gas horizontal wells.展开更多
The morphological changing trend of the Yangtze Estuary, the largest estuary of Asia, has become a focus of research in recent years. Based on a long series of topographic data from 1950 to 2015, this paper studied th...The morphological changing trend of the Yangtze Estuary, the largest estuary of Asia, has become a focus of research in recent years. Based on a long series of topographic data from 1950 to 2015, this paper studied the erosion-deposition pattern of the entire Yangtze Estuary. An alternation between erosion and deposition was found during the past 65 years, which was in correspondence to the alternation between flood and dry periods identified by multi-year average duration days of high-level water flow (defined as discharge ≥ 60,000 m<sup>3</sup>/s, namely, D<sub>≥60,000</sub>) from the Yangtze River Basin. A quantitative relationship was further developed between the erosional/depositional rate of the Yangtze Estuary and the interpreting variables of yearly water discharge, D<sub>≥60,000</sub> and yearly river sediment load, with contributing rates of 1%, 59% and 40%, respectively. Mechanism behind the alternate erosion and deposition pattern was analyzed by examining residual water surface slope and the corresponding capacity of sediment transport in flood and dry periods. In flood periods, a larger discharge results in steeper slope of residual water level which permits a greater capacity of sediment transport. Therefore, more bed materials can be washed to the sea, leading to erosion of the estuary. In contrast, flatter slope of residual water level occurs in dry periods, and deposition dominates the estuarine area due to the decreased capacity of sediment transport and the increased backwater effect of flood-tide. Coastal dynamics and estuarine engineering projects alter the local morphological changes, but slightly affect the total erosional/depositional rate of the whole estuarine region. Heavy sedimentation within the Yangtze Estuary after the impoundment of the Three Gorges Dam can be attributed to the reduced occurrence frequency of flood years due to water regulation by the dam, and largely (at least 36%-52%) sourced from the sea. Deposition is still possible to occur in the Yangtze Estuary in the future, because the multi-year average D<sub>≥60,000</sub> is unlikely to exceed the critical value of 14 days/yr which corresponds to the future equilibrium state of the Yangtze Estuary, under the water regulation of the large cascade dams in the upper Yangtze. Nevertheless, the mean depositional rate will not surpass the peak value of the past years, since the total sediment load entering the Yangtze Estuary has presented a decreasing trend.展开更多
针对液压挖掘机减速机构快速启动时冲击载荷过大,制动时出现摆尾现象以及齿轮断齿或输出轴损坏的故障现象,基于定轴转动刚体的冲量矩定理,通过启动过程、制动过程故障现象分析表明,启动过程采用控油策略,可降低启动冲击;制动过程采用平...针对液压挖掘机减速机构快速启动时冲击载荷过大,制动时出现摆尾现象以及齿轮断齿或输出轴损坏的故障现象,基于定轴转动刚体的冲量矩定理,通过启动过程、制动过程故障现象分析表明,启动过程采用控油策略,可降低启动冲击;制动过程采用平压策略,可避免摆尾现象。采用增设压力变送器、回转缓冲阀等液压元器件,研发一种控流平压液压系统,降低启动时回转马达的流量,提高制动时回转马达进口侧的工作压力,实现回转液压系统的优化。通过试验验证,优化后的液压系统启动(制动)过程用时由4 s (5 s)延长至5 s (5.5 s),延长了1 s (0.5 s),减轻了启动(制动)冲击;制动结束时液压系统回转马达出口与进口压力未出现交替增大现象,其最大压差Δp由3.8 MPa减低至2 MPa,降低了制动冲击,避免平台摆尾部现象的产生;延长了其使用寿命,系统已经无故障记录持续工作5 368 h。展开更多
基金Project supported by the National Natural Science Foundation of China(Nos.11991032 and 52241103)the Hunan Province Graduate Research Innovation Project of China(No.KY0409052440)。
文摘Metamaterials can control and manipulate acoustic/elastic waves on a subwavelength scale using cavities or additional components.However,the large cavity and weak stiffness components of traditional metamaterials may cause a conflict between vibroacoustic reduction and load-bearing capacity,and thus limit their application.Here,we propose a lightweight multifunctional metamaterial that can simultaneously achieve low-frequency sound insulation,broadband vibration reduction,and excellent load-bearing performance,named as vibroacoustic isolation and bearing metamaterial(VIBM).The advent of additive manufacturing technology provides a convenient and reliable method for the fabrication of VIBM samples.The results show that the compressive strength of the VIBM is as high as 9.71 MPa,which is nearly 87.81%higher than that of the conventional grid structure(CGS)under the same volume fraction.Moreover,the vibration and sound transmission are significantly reduced over a low and wide frequency range,which agrees well with the experimental data,and the reduction degree is obviously larger than that obtained by the CGS.The design strategy can effectively realize the key components of metamaterials and improve their application scenarios.
基金supported by the National Natural Science Foundation of China(Grant No.52172356)the Hunan Provincial Natural Science Foundation of China(Grant No.2022JJ10012).
文摘The application of multi-material topology optimization affords greater design flexibility compared to traditional single-material methods.However,density-based topology optimization methods encounter three unique challenges when inertial loads become dominant:non-monotonous behavior of the objective function,possible unconstrained characterization of the optimal solution,and parasitic effects.Herein,an improved Guide-Weight approach is introduced,which effectively addresses the structural topology optimization problem when subjected to inertial loads.Smooth and fast convergence of the compliance is achieved by the approach,while also maintaining the effectiveness of the volume constraints.The rational approximation of material properties model and smooth design are utilized to guarantee clear boundaries of the final structure,facilitating its seamless integration into manufacturing processes.The framework provided by the alternating active-phase algorithm is employed to decompose the multi-material topological problem under inertial loading into a set of sub-problems.The optimization of multi-material under inertial loads is accomplished through the effective resolution of these sub-problems using the improved Guide-Weight method.The effectiveness of the proposed approach is demonstrated through numerical examples involving two-phase and multi-phase materials.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.52107162 and 12202479)the Science and Technology Projects of Shaanxi Province,China(Grant Nos.2022CGBX-12 and 2022KXJ-57)the Science and Technology Projects of Xi’an City,China(Grant Nos.23KGDW0023-2022 and 23GXFW0011)。
文摘A non-contact low-frequency(LF)method of diagnosing the plasma surrounding a scaled model in a shock tube is proposed.This method utilizes the phase shift occurring after the transmission of an LF alternating magnetic field through the plasma to directly measure the ratio of the plasma loop average electron density to collision frequency.An equivalent circuit model is used to analyze the relationship of the phase shift of the magnetic field component of LF electromagnetic waves with the plasma electron density and collision frequency.The applicable range of the LF method on a given plasma scale is analyzed.The upper diagnostic limit for the ratio of the electron density(unit:m^(-3))to collision frequency(unit:Hz)exceeds 1×10^(11),enabling an electron density to exceed 1×10^(20)m^(-3)and a collision frequency to be less than 1 GHz.In this work,the feasibility of using the LF phase shift to implement the plasma diagnosis is also assessed.Diagnosis experiments on shock tube equipment are conducted by using both the electrostatic probe method and LF method.By comparing the diagnostic results of the two methods,the inversion results are relatively consistent with each other,thereby preliminarily verifying the feasibility of the LF method.The ratio of the electron density to the collision frequency has a relatively uniform distribution during the plasma stabilization.The LF diagnostic path is a loop around the model,which is suitable for diagnosing the plasma that surrounds the model.Finally,the causes of diagnostic discrepancy between the two methods are analyzed.The proposed method provides a new avenue for diagnosing high-density enveloping plasma.
文摘The static sealing of underground gas storage(UGS),including the integrity of cap rocks and the stability of faults,is analyzed from a macro perspective using a comprehensive geological evaluation method.Changes in pore structure,permeability,and mechanical strength of cap rocks under cyclic loads may impact the rock sealing integrity during the injection and recovery phases of UGS.In this work,the mechanical deformation and failure tests of rocks,as well as rock damage tests under alternating loads,are conducted to analyze the changes in the strength and permeability of rocks under multiple-cycle intense injection and recovery of UGS.Additionally,this study proposes an evaluation method for the dynamic sealing performance of UGS cap rocks under multi-cycle alternating loads.The findings suggest that the failure strength(70%)can be used as the critical value for rock failure,thus providing theoretical support for determining the upper limit of operating pressure and the number of injection-recovery cycles for the safe operation of a UGS system.
文摘The authors show the results of a study conducted on a joint connecting a concrete column to a composite steel concrete floor,subjected to tension on the beams as a result of the decomposition of sagging bending moment.The beam to column connection is achieved by means of headed studs welded to the beam and embedded in the concrete cast.Five different configurations have been tested at failure and the results are compared to formulae proposed in literature.Different degrees of ductility,reliability and strength have been obtained varying geometry and reinforcement ratio on the joints tested.
基金This work was supported by the National key research and development plan 2016YFB0900300National Natural Science Foundation of China under Grant51677162Natural Science Foundation of Hebei Province E2017203337。
文摘Microgrid stability analysis is a critical issue especially due to the inverters’low-inertia nature.The voltage and current control loops influences on stability are researched frequently most of which focus on medium and high-frequency characteristic.Although the complete state-space model aims at low-frequency characteristic,it is too complicated and the calculation amount is huge with the scale of the microgrid increasing.One available reduced-order model of an inverter is simple,but it is suitable for only single inverter without network dynamic in microgrid.To fill in these gaps,a novel modeling method is proposed in this paper to investigate the low-frequency instability phenomenon and describe the whole DG connected system including network.In consideration of the high penetration level of induction motor(IM)loads and constant power(CP)loads in practical applications,the low-frequency mathematical model of IM and CP loads on the basis of static load is also built in this paper.Simulation and experimental results verify the effectiveness of the proposed model.
基金Project supported by the National Natural Science Foundation of China“Study on Casing-Cement Sheath-Formation Integrity under Alternating Temperature,Pressure and Their Coupling Effects”(No.:51904261)China Postdoctoral Science Foundation(No.:2019M653478)。
文摘During large-scale hydraulic fracturing in shale gas horizontal wells,a cement sheath easily loses its integrity due to thefluctuation and continuous change of wellbore temperature and pressure and the cyclic loading and unloading,which will threaten wellbore integrity.In order tofigure out the failure mechanism of cement sheath integrity under strong alternating thermal loads and prevent the failure of cement sheath barriers during large-scale hydraulic fracturing in shale gas horizontal wells,this paper adopted the independently developed experimental device to test and evaluate the sealing integrity and mechanical integrity of the full-scale combination of production casing,cement sheath and intermediate casing under strong alternating thermal loads.And the integrity experimental results of two kinds of full-scale cement sheaths(conventional and high-strength cement sheaths)under three kinds of strong alternating thermal loads(cycle number for the occurrence of discontinuous CO_(2) bubble:4 and 14;cycle number for the occurrence of continuous CO_(2) bubble:5 and 15;alternating thermal load:30-120℃ and 30-150℃)were obtained.And the following research results were obtained.First,alternating thermal load has a significant negative impact on the integrity of cement sheath,and with the increase of alternating temperature and temperature difference,the thermal cycle number characterizing the sealing integrity of cement sheath reduces sharply.Second,the interfacial mechanical property indicators that characterize the shearing force between cement sheath and casing and the axial and radial bonding strength decrease with the increase of the alternating temperature.Third,the micro annulus in cement sheath is mainly caused by discordant deformation between the casing and the cement sheath materials,and the mechanical degradation and deterioration of the set cement induced by the alternating thermal load aggravate the failure of the sealing integrity of cement sheath to a certain degree.In conclusion,the research results can provide a reference for the design of large-scale fracturing in deep shale gas horizontal wells.
基金Youth Project of National Natural Science Foundation of China,No.41601275Open Research Fund of Key Laboratory of Water-Sediment Sciences and Water Disaster Prevention of Hunan Province,No.2019SS06Scientific Research Key Project in Hunan Province Education Department,No.2014A006。
文摘The morphological changing trend of the Yangtze Estuary, the largest estuary of Asia, has become a focus of research in recent years. Based on a long series of topographic data from 1950 to 2015, this paper studied the erosion-deposition pattern of the entire Yangtze Estuary. An alternation between erosion and deposition was found during the past 65 years, which was in correspondence to the alternation between flood and dry periods identified by multi-year average duration days of high-level water flow (defined as discharge ≥ 60,000 m<sup>3</sup>/s, namely, D<sub>≥60,000</sub>) from the Yangtze River Basin. A quantitative relationship was further developed between the erosional/depositional rate of the Yangtze Estuary and the interpreting variables of yearly water discharge, D<sub>≥60,000</sub> and yearly river sediment load, with contributing rates of 1%, 59% and 40%, respectively. Mechanism behind the alternate erosion and deposition pattern was analyzed by examining residual water surface slope and the corresponding capacity of sediment transport in flood and dry periods. In flood periods, a larger discharge results in steeper slope of residual water level which permits a greater capacity of sediment transport. Therefore, more bed materials can be washed to the sea, leading to erosion of the estuary. In contrast, flatter slope of residual water level occurs in dry periods, and deposition dominates the estuarine area due to the decreased capacity of sediment transport and the increased backwater effect of flood-tide. Coastal dynamics and estuarine engineering projects alter the local morphological changes, but slightly affect the total erosional/depositional rate of the whole estuarine region. Heavy sedimentation within the Yangtze Estuary after the impoundment of the Three Gorges Dam can be attributed to the reduced occurrence frequency of flood years due to water regulation by the dam, and largely (at least 36%-52%) sourced from the sea. Deposition is still possible to occur in the Yangtze Estuary in the future, because the multi-year average D<sub>≥60,000</sub> is unlikely to exceed the critical value of 14 days/yr which corresponds to the future equilibrium state of the Yangtze Estuary, under the water regulation of the large cascade dams in the upper Yangtze. Nevertheless, the mean depositional rate will not surpass the peak value of the past years, since the total sediment load entering the Yangtze Estuary has presented a decreasing trend.
文摘针对液压挖掘机减速机构快速启动时冲击载荷过大,制动时出现摆尾现象以及齿轮断齿或输出轴损坏的故障现象,基于定轴转动刚体的冲量矩定理,通过启动过程、制动过程故障现象分析表明,启动过程采用控油策略,可降低启动冲击;制动过程采用平压策略,可避免摆尾现象。采用增设压力变送器、回转缓冲阀等液压元器件,研发一种控流平压液压系统,降低启动时回转马达的流量,提高制动时回转马达进口侧的工作压力,实现回转液压系统的优化。通过试验验证,优化后的液压系统启动(制动)过程用时由4 s (5 s)延长至5 s (5.5 s),延长了1 s (0.5 s),减轻了启动(制动)冲击;制动结束时液压系统回转马达出口与进口压力未出现交替增大现象,其最大压差Δp由3.8 MPa减低至2 MPa,降低了制动冲击,避免平台摆尾部现象的产生;延长了其使用寿命,系统已经无故障记录持续工作5 368 h。
