Numerical and experimental investigation on wave dynamic processes induced by high-speed trains entering railway tunnels are presented. Experiments were conducted by using a 1:250 scaled train-tunnel simulator. Numeri...Numerical and experimental investigation on wave dynamic processes induced by high-speed trains entering railway tunnels are presented. Experiments were conducted by using a 1:250 scaled train-tunnel simulator. Numerical simulations were carried out by solving the axisymmetric Euler equations with the dispersion-controlled scheme implemented with moving boundary conditions. Pressure histories at various positions inside the train-tunnel simulator at different distance measured from the entrance of the simulator are recorded both numerically and experimentally, and then compared with each other for two train speeds. After the validation of nonlinear wave phenomena, detailed numerical simulations were then conducted to account for the generation of compression waves near the entrance, the propagation of these waves along the train tunnel, and their gradual development into a weak shock wave. Four wave dynamic processes observed are interpreted by combining numerical results with experiments. They are: high-speed trains moving over a free terrain before entering railway tunnels; the abrupt-entering of high-speed trains into railway tunnels; the abrupt-entering of the tail of high-speed trains into railway tunnels; and the interaction of compression and expansion waves ahead of high-speed trains. The effects of train-tunnel configuration, such as the train length and the train-tunnel blockage ratio, on these wave processes have been investigated as well.展开更多
This paper studies the continuous evolution of breaking wave for the surface water waves propagating on a sloping beach. A Lagrangian asymptotic solution is derived. According to the solution coupled with the wave bre...This paper studies the continuous evolution of breaking wave for the surface water waves propagating on a sloping beach. A Lagrangian asymptotic solution is derived. According to the solution coupled with the wave breaking criteria and the equations of water particles motion, the wave deformation and the continuous wave breaking processes for the progressive water waves propagating on a sloping bottom can be derived. A series of experiments are also conducted to compare with the theoretical solution. The results show that the present solution can reasonably describe the plunging or spilling wave breaking phenomenon.展开更多
The new generation of gravity measurement satellites will use high-precision inter-satellite laser interferometry technology to measure the gravity field.The heat flow outside the satellite's orbit will act on the...The new generation of gravity measurement satellites will use high-precision inter-satellite laser interferometry technology to measure the gravity field.The heat flow outside the satellite's orbit will act on the optical bench(OB)through laser emission and reception apertures and introduce the temperature noise of the measurement signal.Based on modeling the orbital thermal environment at the incoming aperture and outgoing aperture of the laser designed on the spacecraft front panel,baffles are designed to reduce the heat flow from the apertures into the optical measurement system.The temperature noise of the optical bench caused by space radiation during on-orbit operation was analyzed using finite element simulation software.For the current design of the baffles,the temperature noise of the optical bench is lower than 0.1 K/Hz1/2@1 mHz when the direct solar radiation enters the apertures;when the apertures are in the light-blocking environment,the temperature noise of the optical bench is lower than 0.1 mK/Hz1/2@1 mHz,which meets the temperature noise requirement of a laser interferometer.The baffles are designed to achieve a stable shading period of up to 4 months in a year to facilitate the satellite to carry out ranging work.展开更多
Accurate thrust assessment is crucial for characterizing the performance of micro-thrusters.This paper presents a comprehensive evaluation of the thrust generated by a needle-type indium field emission electric propul...Accurate thrust assessment is crucial for characterizing the performance of micro-thrusters.This paper presents a comprehensive evaluation of the thrust generated by a needle-type indium field emission electric propulsion(In-FEEP)micro-thruster using three methods based on a pendulum:direct thrust measurement,indirect plume momentum transfer and beam current diagnostics.The experimental setup utilized capacitive displacement sensors for force detection and a voice coil motor as a feedback actuator,achieving a resolution better than 0.1μN.Key performance factors such as ionization and plume divergence of ejected charged particles were also examined.The study reveals that the high applied voltage induces significant electrostatic interference,becoming the dominant source of error in direct thrust measurements.Beam current diagnostics and indirect plume momentum measurements were conducted simultaneously,showing strong agreement within a deviation of less than 0.2N across the operational thrust range.The results from all three methods are consistent within the error margins,verifying the reliability of the indirect measurement approach and the theoretical thrust model based on the electrical parameters of In-FEEP.展开更多
The effect from the interaction of the alternating current(AC)magnetic field with kilogram-level test mass(TM)limits the detectivity of the TianQin space-based gravitational wave detection.The quantifed effect require...The effect from the interaction of the alternating current(AC)magnetic field with kilogram-level test mass(TM)limits the detectivity of the TianQin space-based gravitational wave detection.The quantifed effect requires the determination of the AC magnetic susceptibilityχ(f)of the TM.A torque method is proposed to measure theχ(f)of kg-level samples at the mHz band with a precision of 1×10^(-7).Combined with our previous work[Phys.Rev.Appl.18044010(2022)],the general frequency-dependent susceptibility of the alloy cube with side length L and electrical conductivityσis determined asχ(f)=χ0+(0.24±0.01)σμ0L^(2)f from 0.1 mHz to 1 Hz.The determination is helpful for the preliminary estimation of the in-band eddy current efect in the TianQin noise budget.The technique can be adopted to accurately measureχ(f)of the actual TM in other precision experiments,where the magnetic noise is a signifcant detection limit.展开更多
该文研究了LCLC谐振变换器在空间行波管放大器中的应用。基于电路分析的方法,研究了工作于零电压和零电流状态下的LCLC谐振电路的工作原理,并得到了各个工作模式的等效电路;基于该电路的工作原理,推导了该电路的参数;为验证分析的正确性...该文研究了LCLC谐振变换器在空间行波管放大器中的应用。基于电路分析的方法,研究了工作于零电压和零电流状态下的LCLC谐振电路的工作原理,并得到了各个工作模式的等效电路;基于该电路的工作原理,推导了该电路的参数;为验证分析的正确性,在PSIM仿真软件中对其进行仿真,并将仿真结果与计算结果进行了对比,仿真结果与分析结果高度一致;最后,设计了输入20 V,输出4600 V,开关频率200 k Hz,输出功率280W,效率高达93.38%的LCLC谐振变换器。仿真结果与实验结果都证实了分析的有效性。展开更多
The space-borne gravitational wave detectors will observe a large population of double white dwarf binaries in the Milky Way.However,the search for double white dwarfs in the gravitational wave data will be time-consu...The space-borne gravitational wave detectors will observe a large population of double white dwarf binaries in the Milky Way.However,the search for double white dwarfs in the gravitational wave data will be time-consuming due to the large number of templates involved and antenna response calculation.In this paper,we implement an iterative combinatorial algorithm to search for double white dwarfs in MLDC-3.1 data.To quickly determine the rough parameters of the target sources,the following algorithms are adopted in a coarse search process:(1)using the downsampling method to reduce the number of original data points;(2)using the undersampling method to speed up the generation of a single waveform template;(3)using the stochastic template bank method to quickly construct the waveform template bank while achieving high coverage of the parameter space;(4)combining the FFT acceleration algorithm with the stochastic template bank to reduce the calculation time of a single template.A fine search process is applied to further determine the parameters of the signals based on the coarse search,for which we adopt the particle swarm optimization.Finally,we detect O(10^(4))double white dwarf signals,validating the feasibility of our method.展开更多
When a block of dense sandy soil moves downhill, the shear-induced soil dilatancy along the basal shear boundary produces a negative value of excess pore pressure that increases the basal frictional resistance. Dilata...When a block of dense sandy soil moves downhill, the shear-induced soil dilatancy along the basal shear boundary produces a negative value of excess pore pressure that increases the basal frictional resistance. Dilatancy angle,Ψ, the degree to which the basal soil dilates due to the shear, normally evolves during slope failure. A study by other researchers shows that if Ψ is constant, the block of dense soil will remain stable(or unstable) sliding when the velocity-weakening rate of the basal friction coefficient of the block is small(or large) enough. Moreover, during unstable sliding processes, the block of dense soil exhibits "periodic" patterns of intermittent slipping. Here, we used a more efficient and accurate numerical scheme to revisit that study. We expanded their model by assuming Ψ evolves during slope failure. Consequently, we acquired completely different results. For instance, even though the velocity-weakening rate of the friction coefficient is fixed at the same smaller(or larger) value that those researchers use, the stable(or unstable) steady states of landslide they predict will inversely change to unstable(or stable) when Ψ decreases(or increases) with the increase of slide displacement to a value small(or large) enough. Particularly, in unstable processes, the soil block exhibits "aperiodic" styles of intermittent slipping, instead of "periodic". We found out that the stick states appearing later last longer(or shorter) in the case of decreasing(or increasing) Ψ. Moreover, because the basic states of landslides with impacts of dilatancy evolution are not steady nor periodic, traditional stability-analysis methods cannot be "directly" used to analyze the stability of such landslides. Here, we broke through this technical problem to a degree. We showed that combining a concept called "quasi-steady-state approximation" with a traditional stability-analysis technique can qualitatively predict the instability onset of the landslides. Through this study, we demonstrated that the combination of Chebyshev collocation(CC) and 4^(th)-order Runge-Kutta methods is more accurate and efficient than the numerical scheme those researchers use.展开更多
文摘Numerical and experimental investigation on wave dynamic processes induced by high-speed trains entering railway tunnels are presented. Experiments were conducted by using a 1:250 scaled train-tunnel simulator. Numerical simulations were carried out by solving the axisymmetric Euler equations with the dispersion-controlled scheme implemented with moving boundary conditions. Pressure histories at various positions inside the train-tunnel simulator at different distance measured from the entrance of the simulator are recorded both numerically and experimentally, and then compared with each other for two train speeds. After the validation of nonlinear wave phenomena, detailed numerical simulations were then conducted to account for the generation of compression waves near the entrance, the propagation of these waves along the train tunnel, and their gradual development into a weak shock wave. Four wave dynamic processes observed are interpreted by combining numerical results with experiments. They are: high-speed trains moving over a free terrain before entering railway tunnels; the abrupt-entering of high-speed trains into railway tunnels; the abrupt-entering of the tail of high-speed trains into railway tunnels; and the interaction of compression and expansion waves ahead of high-speed trains. The effects of train-tunnel configuration, such as the train length and the train-tunnel blockage ratio, on these wave processes have been investigated as well.
基金supported by the Research Grant Council of the Science Center,Taiwan,through Project Nos.NSC99-2923-E-110-001-MY3,NSC99-2221-E-110-087-MY3,and NSC102-2911-I-006-302
文摘This paper studies the continuous evolution of breaking wave for the surface water waves propagating on a sloping beach. A Lagrangian asymptotic solution is derived. According to the solution coupled with the wave breaking criteria and the equations of water particles motion, the wave deformation and the continuous wave breaking processes for the progressive water waves propagating on a sloping bottom can be derived. A series of experiments are also conducted to compare with the theoretical solution. The results show that the present solution can reasonably describe the plunging or spilling wave breaking phenomenon.
基金supported by the National Key R&D Program (2022YFC2204001)the National Natural Science Foundation of China (12005310)
文摘The new generation of gravity measurement satellites will use high-precision inter-satellite laser interferometry technology to measure the gravity field.The heat flow outside the satellite's orbit will act on the optical bench(OB)through laser emission and reception apertures and introduce the temperature noise of the measurement signal.Based on modeling the orbital thermal environment at the incoming aperture and outgoing aperture of the laser designed on the spacecraft front panel,baffles are designed to reduce the heat flow from the apertures into the optical measurement system.The temperature noise of the optical bench caused by space radiation during on-orbit operation was analyzed using finite element simulation software.For the current design of the baffles,the temperature noise of the optical bench is lower than 0.1 K/Hz1/2@1 mHz when the direct solar radiation enters the apertures;when the apertures are in the light-blocking environment,the temperature noise of the optical bench is lower than 0.1 mK/Hz1/2@1 mHz,which meets the temperature noise requirement of a laser interferometer.The baffles are designed to achieve a stable shading period of up to 4 months in a year to facilitate the satellite to carry out ranging work.
基金Project supported by the National Key Research and Development Program of China(Grant No.2020YFC2201001)the Guangdong Major Project of Basic and Applied Basic Research(Grant No.2019B030302001)+1 种基金the National Natural Science Foundation of China(Grant Nos.12105373,12105374,and 11927812)the Science and Technology Research Project of Jiangxi Provincial Department of Education(Grant No.GJJ2402105).
文摘Accurate thrust assessment is crucial for characterizing the performance of micro-thrusters.This paper presents a comprehensive evaluation of the thrust generated by a needle-type indium field emission electric propulsion(In-FEEP)micro-thruster using three methods based on a pendulum:direct thrust measurement,indirect plume momentum transfer and beam current diagnostics.The experimental setup utilized capacitive displacement sensors for force detection and a voice coil motor as a feedback actuator,achieving a resolution better than 0.1μN.Key performance factors such as ionization and plume divergence of ejected charged particles were also examined.The study reveals that the high applied voltage induces significant electrostatic interference,becoming the dominant source of error in direct thrust measurements.Beam current diagnostics and indirect plume momentum measurements were conducted simultaneously,showing strong agreement within a deviation of less than 0.2N across the operational thrust range.The results from all three methods are consistent within the error margins,verifying the reliability of the indirect measurement approach and the theoretical thrust model based on the electrical parameters of In-FEEP.
基金supported by the National Key R&D Program of China(Grant No.2020YFC2200500)the Key Laboratory of Tian Qin Project(Sun Yat-sen University),Ministry of Education+1 种基金the National Natural Science Foundation of China(Grant Nos.12075325,12005308,and 11605065)the Doctoral Research Foundation Project of Hubei University of Arts and Science(Grant No.kyqdf2059017)。
文摘The effect from the interaction of the alternating current(AC)magnetic field with kilogram-level test mass(TM)limits the detectivity of the TianQin space-based gravitational wave detection.The quantifed effect requires the determination of the AC magnetic susceptibilityχ(f)of the TM.A torque method is proposed to measure theχ(f)of kg-level samples at the mHz band with a precision of 1×10^(-7).Combined with our previous work[Phys.Rev.Appl.18044010(2022)],the general frequency-dependent susceptibility of the alloy cube with side length L and electrical conductivityσis determined asχ(f)=χ0+(0.24±0.01)σμ0L^(2)f from 0.1 mHz to 1 Hz.The determination is helpful for the preliminary estimation of the in-band eddy current efect in the TianQin noise budget.The technique can be adopted to accurately measureχ(f)of the actual TM in other precision experiments,where the magnetic noise is a signifcant detection limit.
文摘该文研究了LCLC谐振变换器在空间行波管放大器中的应用。基于电路分析的方法,研究了工作于零电压和零电流状态下的LCLC谐振电路的工作原理,并得到了各个工作模式的等效电路;基于该电路的工作原理,推导了该电路的参数;为验证分析的正确性,在PSIM仿真软件中对其进行仿真,并将仿真结果与计算结果进行了对比,仿真结果与分析结果高度一致;最后,设计了输入20 V,输出4600 V,开关频率200 k Hz,输出功率280W,效率高达93.38%的LCLC谐振变换器。仿真结果与实验结果都证实了分析的有效性。
基金supported by the Guangdong Major Project of Basic and Applied Basic Research(Grant No.2019B030302001)the National Natural Science Foundation of China(NSFC,Grant No.12173104)+2 种基金the fellowship of China Postdoctoral Science Foundation(Grant No.2021M703769)the Natural Science Foundation of Guangdong Province of China(Grant No.2022A1515011862)the support by National Supercomputer Center in Guangzhou。
文摘The space-borne gravitational wave detectors will observe a large population of double white dwarf binaries in the Milky Way.However,the search for double white dwarfs in the gravitational wave data will be time-consuming due to the large number of templates involved and antenna response calculation.In this paper,we implement an iterative combinatorial algorithm to search for double white dwarfs in MLDC-3.1 data.To quickly determine the rough parameters of the target sources,the following algorithms are adopted in a coarse search process:(1)using the downsampling method to reduce the number of original data points;(2)using the undersampling method to speed up the generation of a single waveform template;(3)using the stochastic template bank method to quickly construct the waveform template bank while achieving high coverage of the parameter space;(4)combining the FFT acceleration algorithm with the stochastic template bank to reduce the calculation time of a single template.A fine search process is applied to further determine the parameters of the signals based on the coarse search,for which we adopt the particle swarm optimization.Finally,we detect O(10^(4))double white dwarf signals,validating the feasibility of our method.
基金financial support with the Grant No. MOST 105-2911-I-006-301
文摘When a block of dense sandy soil moves downhill, the shear-induced soil dilatancy along the basal shear boundary produces a negative value of excess pore pressure that increases the basal frictional resistance. Dilatancy angle,Ψ, the degree to which the basal soil dilates due to the shear, normally evolves during slope failure. A study by other researchers shows that if Ψ is constant, the block of dense soil will remain stable(or unstable) sliding when the velocity-weakening rate of the basal friction coefficient of the block is small(or large) enough. Moreover, during unstable sliding processes, the block of dense soil exhibits "periodic" patterns of intermittent slipping. Here, we used a more efficient and accurate numerical scheme to revisit that study. We expanded their model by assuming Ψ evolves during slope failure. Consequently, we acquired completely different results. For instance, even though the velocity-weakening rate of the friction coefficient is fixed at the same smaller(or larger) value that those researchers use, the stable(or unstable) steady states of landslide they predict will inversely change to unstable(or stable) when Ψ decreases(or increases) with the increase of slide displacement to a value small(or large) enough. Particularly, in unstable processes, the soil block exhibits "aperiodic" styles of intermittent slipping, instead of "periodic". We found out that the stick states appearing later last longer(or shorter) in the case of decreasing(or increasing) Ψ. Moreover, because the basic states of landslides with impacts of dilatancy evolution are not steady nor periodic, traditional stability-analysis methods cannot be "directly" used to analyze the stability of such landslides. Here, we broke through this technical problem to a degree. We showed that combining a concept called "quasi-steady-state approximation" with a traditional stability-analysis technique can qualitatively predict the instability onset of the landslides. Through this study, we demonstrated that the combination of Chebyshev collocation(CC) and 4^(th)-order Runge-Kutta methods is more accurate and efficient than the numerical scheme those researchers use.
