In this context,a testing system to understand rock fracturing processes induced by different dynamic disturbances under true triaxial compression was developed.The system is mainly composed of a static loading subsys...In this context,a testing system to understand rock fracturing processes induced by different dynamic disturbances under true triaxial compression was developed.The system is mainly composed of a static loading subsystem,a dynamic loading subsystem,a specimen box subsystem,and a data measurement subsystem.The static loading subsystem uses low stiffness loss frame structure technology,which greatly improves the frame stiffness in the three principal stress directions(up to 20 GN/m)and ensures the demand of the disturbance experiment in both the prepeak and postpeak stages.The disturbance loads with frequency of 0e20 Hz and stress level of 0e30 MPa were applied using large flow parallel oil source technology characterized with high heat dissipation efficiency.For the disturbance loads with frequency of 100e500 Hz and stress level of 0e30 MPa,they were realized by using high-frequency and centimeter-per-second-scale low-speed disturbance rod technology.Three rigid self-stabilizing specimen boxes were utilized to provide support for the specimen and deformation sensors,ensuring the stability and accuracy of the data obtained.To verify the performance of the true triaxial test system,disturbance experiments were conducted on granite specimens.The results show that the experimental device satisfies the requirements of original design,with an excellent repeatability and reliable testing results.展开更多
This study numerically investigates the aeromechanic behavior of a transonic fan model with a flat tip-leading-edge on the NASA rotor 67 test case.Single-passage unsteady calculations at a near stall operating point o...This study numerically investigates the aeromechanic behavior of a transonic fan model with a flat tip-leading-edge on the NASA rotor 67 test case.Single-passage unsteady calculations at a near stall operating point of 82%design speed show that the dominant frequencies of mass flow were not the harmonics of the rotor rotational frequency.A full-annulus fluid–structure interaction analysis was subsequently carried out to examine the unsteady flows and their interactions with blade vibrations.The results show that the modal displacement of the backward traveling seventh nodal diameter of the second torsion mode grew exponentially,which reveals that the blade vibration was non-synchronous.The vibration pattern indicates that the aerodynamic mode was resonant with the structural vibration mode.Around the rotor tip,the circumferential vortical propagation induced by interactions among the main flow,tip leakage flow,and tip clearance vortex was the source of aerodynamic excitation.To clarify the mechanism of the non-synchronous vibration,the coupling between aerodynamic disturbance and structural response,i.e.,aliasing,was summarized.The frequency spectra of the fluctuating pressure show that an aerodynamic Back-ward Traveling Wave(BTW)was co-aliased to a structural BTW due to the propagation of the cir-cumferential vortex.The correlation between the frequency and free convective speed of the aerodynamic disturbance determined the directions of aliasing.展开更多
The surrounding rock of underground space is always affected by external dynamic disturbance from the side position,such as blasting vibration from a stope at the same level or seismic waves from adjacent strata.A ser...The surrounding rock of underground space is always affected by external dynamic disturbance from the side position,such as blasting vibration from a stope at the same level or seismic waves from adjacent strata.A series of laboratory tests,numerical simulations and theoretical analyses were carried out in this study to disclose the sliding mechanism of roof rock blocks under lateral disturbance.Firstly,the experiments on trapezoidal key block under various clamping loads and disturbance were conducted,followed by numerical simulations using the fast Lagrangian analysis of continua(FLAC3D).Then,based on the conventional wave propagation model and the classical shear-slip constitutive model,a theoretical model was proposed to capture the relative displacement between blocks and the sliding displacement of the key block.The results indicate that the sliding displacement of the key block increased linearly with the disturbance energy and decreased exponentially with the clamping load when the key block was disturbed to slide(without instability).Meanwhile,when the key block was disturbed to fall,two types of instability process may appear as immediate type or delayed type.In addition,the propagation of stress waves in the block system exhibited obvious low-velocity and lowfrequency characteristics,resulting in the friction reduction effect appearing at the contact interface,which is the essential reason for the sliding of rock blocks.The results can be applied to practical underground engineering and provide valuable guidance for the early detection and prevention of rockfalling disasters.展开更多
Soil disturbance includes the change of stress state and the damage of soil structure.The field testing indices reflect the combined effect of both changes and it is difficult to identify the soil structure disturbanc...Soil disturbance includes the change of stress state and the damage of soil structure.The field testing indices reflect the combined effect of both changes and it is difficult to identify the soil structure disturbance directly from these indices.In the present study,the small-strain shear modulus is used to characterize soil structure disturbance by normalizing the effective stress and void ratio based on Hardin equation.The procedure for evaluating soil sampling disturbance in the field and the further disturbance during the subsequent consolidation process in laboratory test is proposed,and then validated by a case study of soft clay ground.Downhole seismic testing in the field,portable piezoelectric bender elements for the drilled sample and bender elements in triaxial apparatus for the consolidated sample were used to monitor the shear wave velocity of the soil from intact to disturbed and even remolded states.It is found that soil sampling disturbance degree by conventional thin-wall sampler is about 30%according to the proposed procedure,which is slightly higher than that from the modified volume compression method proposed by Hong and Onitsuka(1998).And the additional soil disturbance induced by consolidation in laboratory could reach about 50%when the consolidation pressure is far beyond the structural yield stress,and it follows the plastic volumetric strain quite well.展开更多
The oscillatory response of multiple shock waves to downstream perturbations in a supersonic flow is studied numerically in a rectangular duct.Multiple shock waves are formed inside the duct at a shock Mach number of ...The oscillatory response of multiple shock waves to downstream perturbations in a supersonic flow is studied numerically in a rectangular duct.Multiple shock waves are formed inside the duct at a shock Mach number of 1.75.The duct has an exit height of H,and the effect of duct resonance on multiple shock oscillations is investigated by attaching exit ducts of lengths 0H,50H,and 150H.The downstream disturbance frequency varied from 10 Hz to 200 Hz to explore the oscillation characteristics of the multiple shock waves.The oscillatory response of shock waves under self-excited and forced oscillation conditions are analyzed in terms of wall static pressure,shock train leading-edge location,shock train length,and the size of the separation bubble.The extent of the initial shock location increases with an increase in exit duct length for the self-excited oscillation condition.The analysis of the shock train leading edge and the spectral analysis of wall static pressure variations are conducted.The variation in the shock train length is analyzed using the pressure ratio method for self-excited as well as forced oscillations.The RMS amplitude of the normalized shock train length(ζ_(ST))increases with an increase in the exit duct length for the self-excited oscillation condition.When the downstream perturbation frequency is increased,ζ_(ST)is decreased for exit duct configurations.For all exit duct designs and downstream forcing frequencies,the size of the separation bubble grows and shrinks during the shock oscillations,demonstrating the dependence on duct resonance and forced oscillations.展开更多
Slug flow or high GVF(Gas Volume Fraction)conditions can cause pressure disturbance waves and alternating loads at the boundary of mechanical seals for multiphase pumps,endangering the safety of multiphase pump units....Slug flow or high GVF(Gas Volume Fraction)conditions can cause pressure disturbance waves and alternating loads at the boundary of mechanical seals for multiphase pumps,endangering the safety of multiphase pump units.The mechanical seal model is simplified by using periodic boundary conditions and numerical calculations are carried out based on the Zwart-Gerber-Belamri cavitation model.UDF(User Define Function)programs such as structural dynamics equations,alternating load equations,and pressure disturbance equations are embedded in numerical calculations,and the dynamic response characteristics of mechanical seal are studied using layered dynamic mesh technology.The results show that when the pressure disturbance occurs at the inlet,as the amplitude and period of the disturbance increase,the film thickness gradually decreases.And the fundamental reason for the hysteresis of the film thickness change is that the pressure in the high-pressure area cannot be restored in a timely manner.The maximum value of leakage and the minimum value of axial velocity are independent of the disturbance period and determined by the disturbance amplitude.The mutual interference between enhanced waves does not have a significant impact on the film thickness,while the front wave in the attenuated wave has a promoting effect on the subsequent film thickness changes,and the fluctuation of the liquid film cavitation rate and axial velocity under the attenuated wave condition deviates from the initial values.Compared with pressure disturbance conditions,alternating load conditions have a more significant impact on film thickness and leakage.During actual operation,it is necessary to avoid alternating load conditions in multiphase pump mechanical seals.展开更多
An experimental study on the breakup of a conical liquid sheet from a pressure swirl atomizer was conducted by using a Particle Image Velocimetry (PIV) system. The variation of wavelength, wave speed and amplitude of ...An experimental study on the breakup of a conical liquid sheet from a pressure swirl atomizer was conducted by using a Particle Image Velocimetry (PIV) system. The variation of wavelength, wave speed and amplitude of wave versus liquid pressure was obtained. The results indicate that the cone half angle increases with liquid pressure. The stripped half wavelength liquid fragment seems to break into a series of drops immediately and no obvious contraction from liquid fragment to ligament is seen. The recorded images also show that both short and long wavelength waves exist simultaneously, and influence the breakup of the conical liquid sheet. The result of this study is useful for the purpose of developing and verifying the atomization model of spray produced by a pressure swirl atomizer.展开更多
基金This study was financially supported by the National Natural Science Foundation of China(Grant No.51839003),for which we are grateful.
文摘In this context,a testing system to understand rock fracturing processes induced by different dynamic disturbances under true triaxial compression was developed.The system is mainly composed of a static loading subsystem,a dynamic loading subsystem,a specimen box subsystem,and a data measurement subsystem.The static loading subsystem uses low stiffness loss frame structure technology,which greatly improves the frame stiffness in the three principal stress directions(up to 20 GN/m)and ensures the demand of the disturbance experiment in both the prepeak and postpeak stages.The disturbance loads with frequency of 0e20 Hz and stress level of 0e30 MPa were applied using large flow parallel oil source technology characterized with high heat dissipation efficiency.For the disturbance loads with frequency of 100e500 Hz and stress level of 0e30 MPa,they were realized by using high-frequency and centimeter-per-second-scale low-speed disturbance rod technology.Three rigid self-stabilizing specimen boxes were utilized to provide support for the specimen and deformation sensors,ensuring the stability and accuracy of the data obtained.To verify the performance of the true triaxial test system,disturbance experiments were conducted on granite specimens.The results show that the experimental device satisfies the requirements of original design,with an excellent repeatability and reliable testing results.
基金co-supported by the National Science and Technology Major Project,China(No.2017-Ⅱ-0009-0023).
文摘This study numerically investigates the aeromechanic behavior of a transonic fan model with a flat tip-leading-edge on the NASA rotor 67 test case.Single-passage unsteady calculations at a near stall operating point of 82%design speed show that the dominant frequencies of mass flow were not the harmonics of the rotor rotational frequency.A full-annulus fluid–structure interaction analysis was subsequently carried out to examine the unsteady flows and their interactions with blade vibrations.The results show that the modal displacement of the backward traveling seventh nodal diameter of the second torsion mode grew exponentially,which reveals that the blade vibration was non-synchronous.The vibration pattern indicates that the aerodynamic mode was resonant with the structural vibration mode.Around the rotor tip,the circumferential vortical propagation induced by interactions among the main flow,tip leakage flow,and tip clearance vortex was the source of aerodynamic excitation.To clarify the mechanism of the non-synchronous vibration,the coupling between aerodynamic disturbance and structural response,i.e.,aliasing,was summarized.The frequency spectra of the fluctuating pressure show that an aerodynamic Back-ward Traveling Wave(BTW)was co-aliased to a structural BTW due to the propagation of the cir-cumferential vortex.The correlation between the frequency and free convective speed of the aerodynamic disturbance determined the directions of aliasing.
基金This work was financially supported by National Key Research and Development Program of China(Grant No.2022YFC2903903)National Natural Science Foundation of China(Grant No.52304132)Yunnan Major Scientific and Technological Projects(Grant No.202202AG050014).These support is gratefully acknowledged.
文摘The surrounding rock of underground space is always affected by external dynamic disturbance from the side position,such as blasting vibration from a stope at the same level or seismic waves from adjacent strata.A series of laboratory tests,numerical simulations and theoretical analyses were carried out in this study to disclose the sliding mechanism of roof rock blocks under lateral disturbance.Firstly,the experiments on trapezoidal key block under various clamping loads and disturbance were conducted,followed by numerical simulations using the fast Lagrangian analysis of continua(FLAC3D).Then,based on the conventional wave propagation model and the classical shear-slip constitutive model,a theoretical model was proposed to capture the relative displacement between blocks and the sliding displacement of the key block.The results indicate that the sliding displacement of the key block increased linearly with the disturbance energy and decreased exponentially with the clamping load when the key block was disturbed to slide(without instability).Meanwhile,when the key block was disturbed to fall,two types of instability process may appear as immediate type or delayed type.In addition,the propagation of stress waves in the block system exhibited obvious low-velocity and lowfrequency characteristics,resulting in the friction reduction effect appearing at the contact interface,which is the essential reason for the sliding of rock blocks.The results can be applied to practical underground engineering and provide valuable guidance for the early detection and prevention of rockfalling disasters.
基金This study is partly supported by the National Natural Science Foundation of China(Grant Nos.51978613,52278374 and 51988101).All these funding grants are greatly acknowledged.
文摘Soil disturbance includes the change of stress state and the damage of soil structure.The field testing indices reflect the combined effect of both changes and it is difficult to identify the soil structure disturbance directly from these indices.In the present study,the small-strain shear modulus is used to characterize soil structure disturbance by normalizing the effective stress and void ratio based on Hardin equation.The procedure for evaluating soil sampling disturbance in the field and the further disturbance during the subsequent consolidation process in laboratory test is proposed,and then validated by a case study of soft clay ground.Downhole seismic testing in the field,portable piezoelectric bender elements for the drilled sample and bender elements in triaxial apparatus for the consolidated sample were used to monitor the shear wave velocity of the soil from intact to disturbed and even remolded states.It is found that soil sampling disturbance degree by conventional thin-wall sampler is about 30%according to the proposed procedure,which is slightly higher than that from the modified volume compression method proposed by Hong and Onitsuka(1998).And the additional soil disturbance induced by consolidation in laboratory could reach about 50%when the consolidation pressure is far beyond the structural yield stress,and it follows the plastic volumetric strain quite well.
基金supported by Basic Science Research Program through the National Research Foundation of Korea(NRF)funded by the Ministry of Education(NRF-2021R1I1A3044216)。
文摘The oscillatory response of multiple shock waves to downstream perturbations in a supersonic flow is studied numerically in a rectangular duct.Multiple shock waves are formed inside the duct at a shock Mach number of 1.75.The duct has an exit height of H,and the effect of duct resonance on multiple shock oscillations is investigated by attaching exit ducts of lengths 0H,50H,and 150H.The downstream disturbance frequency varied from 10 Hz to 200 Hz to explore the oscillation characteristics of the multiple shock waves.The oscillatory response of shock waves under self-excited and forced oscillation conditions are analyzed in terms of wall static pressure,shock train leading-edge location,shock train length,and the size of the separation bubble.The extent of the initial shock location increases with an increase in exit duct length for the self-excited oscillation condition.The analysis of the shock train leading edge and the spectral analysis of wall static pressure variations are conducted.The variation in the shock train length is analyzed using the pressure ratio method for self-excited as well as forced oscillations.The RMS amplitude of the normalized shock train length(ζ_(ST))increases with an increase in the exit duct length for the self-excited oscillation condition.When the downstream perturbation frequency is increased,ζ_(ST)is decreased for exit duct configurations.For all exit duct designs and downstream forcing frequencies,the size of the separation bubble grows and shrinks during the shock oscillations,demonstrating the dependence on duct resonance and forced oscillations.
基金the support of the National Natural Science Foundation of China(52372368)。
文摘Slug flow or high GVF(Gas Volume Fraction)conditions can cause pressure disturbance waves and alternating loads at the boundary of mechanical seals for multiphase pumps,endangering the safety of multiphase pump units.The mechanical seal model is simplified by using periodic boundary conditions and numerical calculations are carried out based on the Zwart-Gerber-Belamri cavitation model.UDF(User Define Function)programs such as structural dynamics equations,alternating load equations,and pressure disturbance equations are embedded in numerical calculations,and the dynamic response characteristics of mechanical seal are studied using layered dynamic mesh technology.The results show that when the pressure disturbance occurs at the inlet,as the amplitude and period of the disturbance increase,the film thickness gradually decreases.And the fundamental reason for the hysteresis of the film thickness change is that the pressure in the high-pressure area cannot be restored in a timely manner.The maximum value of leakage and the minimum value of axial velocity are independent of the disturbance period and determined by the disturbance amplitude.The mutual interference between enhanced waves does not have a significant impact on the film thickness,while the front wave in the attenuated wave has a promoting effect on the subsequent film thickness changes,and the fluctuation of the liquid film cavitation rate and axial velocity under the attenuated wave condition deviates from the initial values.Compared with pressure disturbance conditions,alternating load conditions have a more significant impact on film thickness and leakage.During actual operation,it is necessary to avoid alternating load conditions in multiphase pump mechanical seals.
基金Aeronautical Science Foundation of China (99C5 10 91)
文摘An experimental study on the breakup of a conical liquid sheet from a pressure swirl atomizer was conducted by using a Particle Image Velocimetry (PIV) system. The variation of wavelength, wave speed and amplitude of wave versus liquid pressure was obtained. The results indicate that the cone half angle increases with liquid pressure. The stripped half wavelength liquid fragment seems to break into a series of drops immediately and no obvious contraction from liquid fragment to ligament is seen. The recorded images also show that both short and long wavelength waves exist simultaneously, and influence the breakup of the conical liquid sheet. The result of this study is useful for the purpose of developing and verifying the atomization model of spray produced by a pressure swirl atomizer.
