A massive parallel aeroelastic simulation platform has been built to investigate the first1.5-stage fan of an aeroengine at rotating stall.The Computational Fluid Dynamics(CFD)solver and Computational Structural Dynam...A massive parallel aeroelastic simulation platform has been built to investigate the first1.5-stage fan of an aeroengine at rotating stall.The Computational Fluid Dynamics(CFD)solver and Computational Structural Dynamics(CSD)solver are coupled directly by non-matching mesh interfaces.The unsteady rotor/stator interaction is solved by the Sliding Mesh Interface method.The original rotor blades are shrouded by the midspan shrouds.An unshrouded fan is also created to investigate the effects of the midspan shrouds.Both the shrouded fan and unshrouded fan have stable aeroelasticity at the designed state.At rotating stall,the stalled region rotates at 30%of the rotor speed on the absolute reference frame.The energy spectrum of the rotating stalled flow is measured quantitatively.It shows that the first two order excitations are much stronger than the higher order excitations.In the flow of rotating stall,the fifth backward travelling wave mode of shrouded fan is resonated by the fifth excitation of the rotational stalled flow because the rotational speed of the stalled region coincides with the modal rotational speed,while for the unshrouded fan,the first bending mode is resonated by the second excitation of the rotational stalled flow,forming two waves in the circumference of the annulus blades.At rotating stall,the vibration of the shrouded blades is still under control but the vibration of the unshrouded blades is diverged and out of control.A novel tool,i.e.,resonance map,is proposed to predict the resonance.It provides a perspective to explain the effects of midspan shrouds at a theoretical level,and it would also be helpful in the structural design of blades.展开更多
Bridges are a part of vital infrastructure,which should operate even after a disaster to keep emergency services running.There have been numerous bridge failures during major past earthquakes due to liquefaction.Among...Bridges are a part of vital infrastructure,which should operate even after a disaster to keep emergency services running.There have been numerous bridge failures during major past earthquakes due to liquefaction.Among other categories of failures,mid span collapse(without the failure of abutments)of pile supported bridges founded in liquefiable deposits are still observed even in most recent earthquakes.This mechanism of collapse is attributed to the effects related to the differential elongation of natural period of the individual piers during liquefaction.A shake table investigation has been carried out in this study to verify mechanisms behind midspan collapse of pile supported bridges in liquefiable deposits.In this investigation,a typical pile supported bridge is scaled down,and its foundations pass through the liquefiable loose sandy soil and rest in a dense gravel layer.White noise motions of increasing acceleration magnitude have been applied to initiate progressive liquefaction and to characterize the dynamic features of the bridge.It has been found that as the liquefaction of the soil sets in,the natural frequency of individual bridge support is reduced,with the highest reduction occurring near the central spans.As a result,there is differential lateral displacement and bending moment demand on the piles.It has also been observed that for the central pile,the maximum bending moment in the pile will occur at a higher elevation,as compared to that of the interface of soils of varied stiffness,unlike the abutment piles.The practical implications of this research are also highlighted.展开更多
文摘A massive parallel aeroelastic simulation platform has been built to investigate the first1.5-stage fan of an aeroengine at rotating stall.The Computational Fluid Dynamics(CFD)solver and Computational Structural Dynamics(CSD)solver are coupled directly by non-matching mesh interfaces.The unsteady rotor/stator interaction is solved by the Sliding Mesh Interface method.The original rotor blades are shrouded by the midspan shrouds.An unshrouded fan is also created to investigate the effects of the midspan shrouds.Both the shrouded fan and unshrouded fan have stable aeroelasticity at the designed state.At rotating stall,the stalled region rotates at 30%of the rotor speed on the absolute reference frame.The energy spectrum of the rotating stalled flow is measured quantitatively.It shows that the first two order excitations are much stronger than the higher order excitations.In the flow of rotating stall,the fifth backward travelling wave mode of shrouded fan is resonated by the fifth excitation of the rotational stalled flow because the rotational speed of the stalled region coincides with the modal rotational speed,while for the unshrouded fan,the first bending mode is resonated by the second excitation of the rotational stalled flow,forming two waves in the circumference of the annulus blades.At rotating stall,the vibration of the shrouded blades is still under control but the vibration of the unshrouded blades is diverged and out of control.A novel tool,i.e.,resonance map,is proposed to predict the resonance.It provides a perspective to explain the effects of midspan shrouds at a theoretical level,and it would also be helpful in the structural design of blades.
文摘Bridges are a part of vital infrastructure,which should operate even after a disaster to keep emergency services running.There have been numerous bridge failures during major past earthquakes due to liquefaction.Among other categories of failures,mid span collapse(without the failure of abutments)of pile supported bridges founded in liquefiable deposits are still observed even in most recent earthquakes.This mechanism of collapse is attributed to the effects related to the differential elongation of natural period of the individual piers during liquefaction.A shake table investigation has been carried out in this study to verify mechanisms behind midspan collapse of pile supported bridges in liquefiable deposits.In this investigation,a typical pile supported bridge is scaled down,and its foundations pass through the liquefiable loose sandy soil and rest in a dense gravel layer.White noise motions of increasing acceleration magnitude have been applied to initiate progressive liquefaction and to characterize the dynamic features of the bridge.It has been found that as the liquefaction of the soil sets in,the natural frequency of individual bridge support is reduced,with the highest reduction occurring near the central spans.As a result,there is differential lateral displacement and bending moment demand on the piles.It has also been observed that for the central pile,the maximum bending moment in the pile will occur at a higher elevation,as compared to that of the interface of soils of varied stiffness,unlike the abutment piles.The practical implications of this research are also highlighted.
