Tidal waves,intermittent rainfall,and fluctuations in water levels,which create cyclic hydraulic gradients,can exacerbate the migration of fine particles within soils and lead to deterioration in stability.However,mac...Tidal waves,intermittent rainfall,and fluctuations in water levels,which create cyclic hydraulic gradients,can exacerbate the migration of fine particles within soils and lead to deterioration in stability.However,macroscale experimental methods struggle to capture the microscopic deformations that occur during seepage-induced erosion.Therefore,this study,which is based on the coupled computational fluid dynamics–discrete element method(CFD–DEM)coupling method,investigates the contact mechanical mechanisms that induce macroscopic deformation under cyclic hydraulic gradients by considering the effects of different amplitudes and frequencies.The results show that the erosion mass of fine particles increases in a stepwise manner,with a multipeak variation in the erosion rate,and both the erosion amount and intensity are greater under constant gradient conditions.Fine particles erode primarily near the contact surface and,after migration,accumulate mainly in the coarse particle layers close to the contact surface.Increasing the amplitude and frequency of the cyclic hydraulic gradient leads to more fine particle blockages within the coarse particle layer.The cyclic hydraulic gradient causes the contact force chain network to repeatedly break and reorganize,reducing the shear strengths of the soil and resulting in more pronounced anisotropy in the contact force distribution.展开更多
Stony debris flows,characterized by coarse boulders embedded in a sediment-laden matrix,greatly amplify destructive potential by altering flow dynamics and impact forces.Conventional single-phase particle-fluidmixture...Stony debris flows,characterized by coarse boulders embedded in a sediment-laden matrix,greatly amplify destructive potential by altering flow dynamics and impact forces.Conventional single-phase particle-fluidmixture models often struggle to capture the complexities introduced by coarse boulders and multi-phase interactions,while strong-coupling methods can be computationally prohibitive for practical hazard assessments.In this study,we propose a semi-hybrid,fully resolved coupling numerical framework for modeling boulder-laden debris flows.This framework conceptualizes debris flows as a composite system comprising a continuous viscous fluidphase(including finesediments)and a discrete phase of arbitrarily shaped coarse particles.The continuous phase is treated as a generalized nonlinear Coulomb-viscoplastic fluidusing the smoothed particle hydrodynamics(SPH)method,while coarse particles are modeled via the distributed contact discrete element method(DCDEM).These two phases are coupled through an efficienttwo-way resolved scheme,ensuring accurate simulation of flow-boulder interactions within a unifiedtimeframe.We validate the proposed method against two physical experiments:(1)gravity-driven concrete flows and(2)debris flowinteracting with slit-type barriers.Results confirmthe method's robustness in accurately capturing fluid-solid-structureinteractions and deposition processes.Its capabilities are further showcased through the simulation of a stony debris-flowevent inWenchuan County,China,highlighting its promise for real-world engineering applications and validating the effectiveness of the existing cascade dam system in mitigating debrisflowimpact and energy dissipation.展开更多
基于计算流体力学-离散元耦合方法(computational fluid dynamics-discrete element method,CFD-DEM),运用STAR-CCM+软件,对船舶在浮冰区航行过程中的冰阻力特性与破冰机理开展了系统的数值模拟分析。为保证模拟结果的数值可靠性,首先...基于计算流体力学-离散元耦合方法(computational fluid dynamics-discrete element method,CFD-DEM),运用STAR-CCM+软件,对船舶在浮冰区航行过程中的冰阻力特性与破冰机理开展了系统的数值模拟分析。为保证模拟结果的数值可靠性,首先完成了网格收敛性验证,并通过多尺度网格加密及敏感性分析,确定了兼顾计算效率与模拟精度的最优数值模型。研究重点考察了船舶航速与浮冰厚度两个关键参数对冰阻力的非线性影响规律,揭示了船-冰相互作用中冰阻力变化与破碎能量耗散的内在机制。进一步从应力波传播、断裂模式、动能转化等角度,对不同工况下浮冰的破碎程度、裂纹扩展路径及碎冰堆积形态进行了定量评估与定性分析。该研究深化了对船-冰-水多相耦合动力学行为的理解,并为极地船舶冰区航行性能优化与抗冰结构设计提供了可靠的数值分析方法与工程参考。展开更多
In this paper,a high-fidelity computational fluid dynamics(CFD)and rigid body dynamics(RBD)coupled platform for virtual flight simulation is developed to investigate the flight stability of fixed canard dual-spin proj...In this paper,a high-fidelity computational fluid dynamics(CFD)and rigid body dynamics(RBD)coupled platform for virtual flight simulation is developed to investigate the flight stability of fixed canard dual-spin projectile.The platform's reliability is validated by reproducing the characteristic resonance instability of such projectiles.By coupling the solution of the Unsteady Reynolds-Averaged Navier-Stokes equations and the seven-degree-of-freedom RBD equations,the virtual flight simulations of fixed canard dual-spin projectiles at various curvature trajectories are achieved,and the dynamic mechanism of the trajectory following process is analyzed.The instability mechanism of the dynamic instability during trajectory following process of the fixed canard dual-spin projectile is elucidated by simulating the rolling/coning coupled forced motion,and subsequently validated through virtual flight simulations.The findings suggest that an appropriate yaw moment can drive the projectile axis to precession in the tangential direction of the trajectory,thereby enhancing the trajectory following stability.However,the damping of the projectile attains its minimum value when the forward body equilibrium rotational speed(-128 rad/s)is equal to the negative of the fast mode frequency of the projectile.Insufficient damping leads to the fixed canard dual-spin projectile exiting the dynamic stability domain during the trajectory following,resulting in weakly damped instability.Keeping the forward body not rotating or increasing the spin rates to-192 rad/s can enhance the projectile's damping,thereby improving its dynamic stability.展开更多
絮团分形结构特征对絮团沉降和压密脱水行为有着重要的影响,目前传统实验方法难以精确解析微观絮凝过程。为了克服这一局限性难题,基于计算流体力学-离散元法(Computational Fluid Dynamic-Discrete Element Method,CFD-DEM)耦合,在实...絮团分形结构特征对絮团沉降和压密脱水行为有着重要的影响,目前传统实验方法难以精确解析微观絮凝过程。为了克服这一局限性难题,基于计算流体力学-离散元法(Computational Fluid Dynamic-Discrete Element Method,CFD-DEM)耦合,在实验验证基础上建立了絮团分形成长数值模型。应用所建立的数值模型,对实验型絮凝搅拌器典型区域内微细矿物颗粒絮凝行为进行了数值模拟研究。通过考察不同搅拌转速条件下颗粒配位数统计量、絮团的空隙率、絮团的有效密度等重要参数,揭示絮团的分形成长演变规律、运动变化规律以及沉降机制。结果表明:固定搅拌转速下且颗粒配位数小于3时,颗粒配位数和搅拌转速总体呈正相关性;颗粒配位数大于5时,颗粒配位数和搅拌转速呈负相关性;在研究搅拌转速范围内(250~450 r/min),絮团平均粒径随搅拌转速增加而降低,空隙率随絮团中子颗粒数的增加而增加,而有效密度与絮团等效直径呈幂减函数关系。研究结果不仅为深入理解絮团分形成长机制以及过程调控提供理论依据,同时对絮凝工艺过程强化提供技术指导。展开更多
For accurate aeroelastic analysis,the unsteady rotor flowfield is solved by computational fluid dynamics(CFD)module based on RANS/Euler equations and moving-embedded grid system,while computational structural dynamics...For accurate aeroelastic analysis,the unsteady rotor flowfield is solved by computational fluid dynamics(CFD)module based on RANS/Euler equations and moving-embedded grid system,while computational structural dynamics(CSD)module is introduced to handle blade flexibility.In CFD module,dual time-stepping algorithm is employed in temporal discretization,Jameson two-order central difference(JST)scheme is adopted in spatial discretization and B-L turbulent model is used to illustrate the viscous effect.The CSD module is developed based on Hamilton′s variational principles and moderate deflection beam theory.Grid deformation is implemented using algebraic method through coordinate transformations to achieve deflections with high quality and efficiency.A CFD/CSD loose coupling strategy is developed to transfer information between rotor flowfield and blade structure.The CFD and the CSD modules are verified seperately.Then the CFD/CSD loose coupling is adopted in airloads prediction of UH-60A rotor under high speed forward flight condition.The calculated results agree well with test data.Finally,effects of torsional stiffness properties on airloads of rotors with different tip swept angles(from 10° forward to 30° backward)are investigated.The results are evaluated through pressure distribution and airloads variation,and some meaningful conclusions are drawn the moderated shock wave strength and pressure gradient caused by varied tip swept angle and structural properties.展开更多
基金financially supported by the Natural Science Foundation of China(Grant Nos.52425805 and U2569208)Development Fund of Tunnel and Underground Engineering Research Center of Jiangsu Province(Grant No.2021-SDJJ-04).
摘要Tidal waves,intermittent rainfall,and fluctuations in water levels,which create cyclic hydraulic gradients,can exacerbate the migration of fine particles within soils and lead to deterioration in stability.However,macroscale experimental methods struggle to capture the microscopic deformations that occur during seepage-induced erosion.Therefore,this study,which is based on the coupled computational fluid dynamics–discrete element method(CFD–DEM)coupling method,investigates the contact mechanical mechanisms that induce macroscopic deformation under cyclic hydraulic gradients by considering the effects of different amplitudes and frequencies.The results show that the erosion mass of fine particles increases in a stepwise manner,with a multipeak variation in the erosion rate,and both the erosion amount and intensity are greater under constant gradient conditions.Fine particles erode primarily near the contact surface and,after migration,accumulate mainly in the coarse particle layers close to the contact surface.Increasing the amplitude and frequency of the cyclic hydraulic gradient leads to more fine particle blockages within the coarse particle layer.The cyclic hydraulic gradient causes the contact force chain network to repeatedly break and reorganize,reducing the shear strengths of the soil and resulting in more pronounced anisotropy in the contact force distribution.
基金supported by the Japan Society for the Promotion of Science(JSPS)KAKENHI(Grant Nos.JP23KK0182,JP23K26356,and JP24K00971).
摘要Stony debris flows,characterized by coarse boulders embedded in a sediment-laden matrix,greatly amplify destructive potential by altering flow dynamics and impact forces.Conventional single-phase particle-fluidmixture models often struggle to capture the complexities introduced by coarse boulders and multi-phase interactions,while strong-coupling methods can be computationally prohibitive for practical hazard assessments.In this study,we propose a semi-hybrid,fully resolved coupling numerical framework for modeling boulder-laden debris flows.This framework conceptualizes debris flows as a composite system comprising a continuous viscous fluidphase(including finesediments)and a discrete phase of arbitrarily shaped coarse particles.The continuous phase is treated as a generalized nonlinear Coulomb-viscoplastic fluidusing the smoothed particle hydrodynamics(SPH)method,while coarse particles are modeled via the distributed contact discrete element method(DCDEM).These two phases are coupled through an efficienttwo-way resolved scheme,ensuring accurate simulation of flow-boulder interactions within a unifiedtimeframe.We validate the proposed method against two physical experiments:(1)gravity-driven concrete flows and(2)debris flowinteracting with slit-type barriers.Results confirmthe method's robustness in accurately capturing fluid-solid-structureinteractions and deposition processes.Its capabilities are further showcased through the simulation of a stony debris-flowevent inWenchuan County,China,highlighting its promise for real-world engineering applications and validating the effectiveness of the existing cascade dam system in mitigating debrisflowimpact and energy dissipation.
摘要基于计算流体力学-离散元耦合方法(computational fluid dynamics-discrete element method,CFD-DEM),运用STAR-CCM+软件,对船舶在浮冰区航行过程中的冰阻力特性与破冰机理开展了系统的数值模拟分析。为保证模拟结果的数值可靠性,首先完成了网格收敛性验证,并通过多尺度网格加密及敏感性分析,确定了兼顾计算效率与模拟精度的最优数值模型。研究重点考察了船舶航速与浮冰厚度两个关键参数对冰阻力的非线性影响规律,揭示了船-冰相互作用中冰阻力变化与破碎能量耗散的内在机制。进一步从应力波传播、断裂模式、动能转化等角度,对不同工况下浮冰的破碎程度、裂纹扩展路径及碎冰堆积形态进行了定量评估与定性分析。该研究深化了对船-冰-水多相耦合动力学行为的理解,并为极地船舶冰区航行性能优化与抗冰结构设计提供了可靠的数值分析方法与工程参考。
基金supported by the National Natural Science Foundation of China(Grant Nos.U2141254 and U23B6009)。
摘要In this paper,a high-fidelity computational fluid dynamics(CFD)and rigid body dynamics(RBD)coupled platform for virtual flight simulation is developed to investigate the flight stability of fixed canard dual-spin projectile.The platform's reliability is validated by reproducing the characteristic resonance instability of such projectiles.By coupling the solution of the Unsteady Reynolds-Averaged Navier-Stokes equations and the seven-degree-of-freedom RBD equations,the virtual flight simulations of fixed canard dual-spin projectiles at various curvature trajectories are achieved,and the dynamic mechanism of the trajectory following process is analyzed.The instability mechanism of the dynamic instability during trajectory following process of the fixed canard dual-spin projectile is elucidated by simulating the rolling/coning coupled forced motion,and subsequently validated through virtual flight simulations.The findings suggest that an appropriate yaw moment can drive the projectile axis to precession in the tangential direction of the trajectory,thereby enhancing the trajectory following stability.However,the damping of the projectile attains its minimum value when the forward body equilibrium rotational speed(-128 rad/s)is equal to the negative of the fast mode frequency of the projectile.Insufficient damping leads to the fixed canard dual-spin projectile exiting the dynamic stability domain during the trajectory following,resulting in weakly damped instability.Keeping the forward body not rotating or increasing the spin rates to-192 rad/s can enhance the projectile's damping,thereby improving its dynamic stability.
摘要For accurate aeroelastic analysis,the unsteady rotor flowfield is solved by computational fluid dynamics(CFD)module based on RANS/Euler equations and moving-embedded grid system,while computational structural dynamics(CSD)module is introduced to handle blade flexibility.In CFD module,dual time-stepping algorithm is employed in temporal discretization,Jameson two-order central difference(JST)scheme is adopted in spatial discretization and B-L turbulent model is used to illustrate the viscous effect.The CSD module is developed based on Hamilton′s variational principles and moderate deflection beam theory.Grid deformation is implemented using algebraic method through coordinate transformations to achieve deflections with high quality and efficiency.A CFD/CSD loose coupling strategy is developed to transfer information between rotor flowfield and blade structure.The CFD and the CSD modules are verified seperately.Then the CFD/CSD loose coupling is adopted in airloads prediction of UH-60A rotor under high speed forward flight condition.The calculated results agree well with test data.Finally,effects of torsional stiffness properties on airloads of rotors with different tip swept angles(from 10° forward to 30° backward)are investigated.The results are evaluated through pressure distribution and airloads variation,and some meaningful conclusions are drawn the moderated shock wave strength and pressure gradient caused by varied tip swept angle and structural properties.