A three dimensional model including a non-rotational symmetry keyhole of which the geometry is calculated base on the energy balance at keyhole wall is created to simulate the heat transfer and fluid flow within the m...A three dimensional model including a non-rotational symmetry keyhole of which the geometry is calculated base on the energy balance at keyhole wall is created to simulate the heat transfer and fluid flow within the molten pool during laser full penetration welding of titanium alloy plate.In order to take into account the effects of multiple reflections within the keyhole,a ray tracing method is employed and the coordinate dependent heat flux obtained is exerted on keyhole wall during the simulation on the heat transfer and fluid flow within molten pool.Furthermore,the computed weld cross sectional profile is compared with the experimental result to verify the model and it is fond that the simulation result is consists with experimental result.展开更多
A novel technique of electroforming with orbital moving cathode was carried out for the fabrication of non-rotating thin-walled parts.This technique features a large number of insulating and insoluble hard particles a...A novel technique of electroforming with orbital moving cathode was carried out for the fabrication of non-rotating thin-walled parts.This technique features a large number of insulating and insoluble hard particles as a real-time polishing to the cathode.When cathode moves,hard particles polish its surface and provide the nickel non-rotating parts with near-mirror finishing.Morphology,microstructure,surface roughness and micro hardness of deposits fabricated by novel method were studied in contrast with the sample produced by traditional electroforming methods.Theoretical analysis and experimental results showed that the novel technique could effectively remove the hydrogen bubbles and nodules,disturb the crystal nucleation,and refine the grains of layer.The mechanical properties were significantly improved over traditional method.The micro-hardness of the layer was in a uniform distribution ranging from 345 HV to 360 HV.It was confirmed that this technique had practical significance to non-rotating thin-walled parts.展开更多
It is generally accepted that the interaction between a bridge and its abutment＇s backfill soil is highly nonlinear, especially under a strong earthquake loading that contains a velocity pulse. For bridges with skew ...It is generally accepted that the interaction between a bridge and its abutment＇s backfill soil is highly nonlinear, especially under a strong earthquake loading that contains a velocity pulse. For bridges with skew abutments, the superstructure-abutment interaction can dominate the overall bridge performance. This study puts forth a new approach for predicting the lateral capacity of a skew abutment using verified high-fidelity three-dimensional continuum finite element （FE） models. The core idea is that the lateral capacity of a straight abutment is bounded from above and below by that of the abutment of a skew bridge that has the same deck-width, and that of another skew bridge （with the same angle） that has the same backwall length as the original/straight bridge, respectively. This postulation is then used in reverse to estimate the lateral capacity of a skew abutment, given the capacity of a straight but otherwise identical one with an arbitrary length. In prior research, the latter information had already been obtained in closed-form expressions that use physical parameters, such as backfill cohesion, internal friction angle and density, backwall height, and backwall-backfill friction angle. The approach presented here is constrained by the assumption that bridge deck will not rotate during loading. While this assumption is generally violated in a strong earthquake--because a skew bridge will tend to rotate, especially if its in-plane torsional rigidity is low, the model presented does serve as an anchor for parameterizing more advanced （e.g., macro-element plasticity） models that allow rotation, and also as fully parametric lateral response models for torsionally stiff （ile., multi-span, multi-bent） skew bridges.展开更多
Recently, a new definition, called Rortex, was proposed to quantify the purely rotational motion of fluids. In this work, based on the DNS data, the Rortex is used to assess and visualize the rotational motion and str...Recently, a new definition, called Rortex, was proposed to quantify the purely rotational motion of fluids. In this work, based on the DNS data, the Rortex is used to assess and visualize the rotational motion and structure of the vortex in swirling jets in comparison with other kinds of vortex criteria, including Q , λ2,vorticity and Ω criteria. The Rortex vector,Ω, Q and criteria are found to be better than the vorticity criterion for the vortex core identification. The vector triangle formed by the Rortex R , the nonrotational shear S , and the vorticity R is analyzed to give mechanical explanations, especially of the effect of the non-rotational shear on the rotation of fluids. In addition, the probability density distributions (PDF) of the Rortex R , the nonrotational shear S, and the vorticity R are computed. The peak value of the PDF of the vorticity could be used to explain the pure rigid rotation effect and the combination effects of the rigid rotation and the non?rotational shear.展开更多
Most of the times pumps operate off best point states.Reasons are changes of operating conditions,modifications,pollution and wearout or erosion.As consequences non-rotational symmetric flows,transient operational con...Most of the times pumps operate off best point states.Reasons are changes of operating conditions,modifications,pollution and wearout or erosion.As consequences non-rotational symmetric flows,transient operational conditions,increased risk of cavitation,decrease of efficiency and unpredictable wearout can appear.Especially construction components of centrifugal pumps,in particular intake elbows,contribute to this matter.Intake elbows causes additional losses and secondary flows,hence non-rotational velocity distributions as intake profile to the centrifugal pump.As a result the impeller vanes experience permanent changes of the intake flow angle and with it transient flow conditions in the blade channels.This paper presents the first results of a project,experimentally and numerically investigating the consequences of non-rotational inflow to leading edge flow conditions of a centrifugal pump.Therefore two pumpintake-elbow systems are compared,by only altering the intake elbow geometry:a common single bended 90°elbow and a numerically optimized elbow(improved regarding rotational symmetric inflow conditions and friction coefficient).The experiments are carried out,using time resolved stereoscopic PIV on a full acrylic pump with refractions index matched(RIM)working fluid.This allows transient investigations of the flow field simultaneously for all blade leading edges.Additional CFD results are validated and used to further support the investigation i.e.for comparing an analog pump system with ideal inflow conditions.展开更多
基金Foundation item:NSFC(No.50875200 and 50845011)Research Fund for the Doctoral Program of Higher Education of China(No.20090201120014 and 20070698088)Fundamental Research Funds for the Central Universities
文摘A three dimensional model including a non-rotational symmetry keyhole of which the geometry is calculated base on the energy balance at keyhole wall is created to simulate the heat transfer and fluid flow within the molten pool during laser full penetration welding of titanium alloy plate.In order to take into account the effects of multiple reflections within the keyhole,a ray tracing method is employed and the coordinate dependent heat flux obtained is exerted on keyhole wall during the simulation on the heat transfer and fluid flow within molten pool.Furthermore,the computed weld cross sectional profile is compared with the experimental result to verify the model and it is fond that the simulation result is consists with experimental result.
基金Funded partly by the National Natural Science Foundation of China(No.50975143)the Aviation Science Funds,China (No.2009ZE52048)
文摘A novel technique of electroforming with orbital moving cathode was carried out for the fabrication of non-rotating thin-walled parts.This technique features a large number of insulating and insoluble hard particles as a real-time polishing to the cathode.When cathode moves,hard particles polish its surface and provide the nickel non-rotating parts with near-mirror finishing.Morphology,microstructure,surface roughness and micro hardness of deposits fabricated by novel method were studied in contrast with the sample produced by traditional electroforming methods.Theoretical analysis and experimental results showed that the novel technique could effectively remove the hydrogen bubbles and nodules,disturb the crystal nucleation,and refine the grains of layer.The mechanical properties were significantly improved over traditional method.The micro-hardness of the layer was in a uniform distribution ranging from 345 HV to 360 HV.It was confirmed that this technique had practical significance to non-rotating thin-walled parts.
文摘It is generally accepted that the interaction between a bridge and its abutment＇s backfill soil is highly nonlinear, especially under a strong earthquake loading that contains a velocity pulse. For bridges with skew abutments, the superstructure-abutment interaction can dominate the overall bridge performance. This study puts forth a new approach for predicting the lateral capacity of a skew abutment using verified high-fidelity three-dimensional continuum finite element （FE） models. The core idea is that the lateral capacity of a straight abutment is bounded from above and below by that of the abutment of a skew bridge that has the same deck-width, and that of another skew bridge （with the same angle） that has the same backwall length as the original/straight bridge, respectively. This postulation is then used in reverse to estimate the lateral capacity of a skew abutment, given the capacity of a straight but otherwise identical one with an arbitrary length. In prior research, the latter information had already been obtained in closed-form expressions that use physical parameters, such as backfill cohesion, internal friction angle and density, backwall height, and backwall-backfill friction angle. The approach presented here is constrained by the assumption that bridge deck will not rotate during loading. While this assumption is generally violated in a strong earthquake--because a skew bridge will tend to rotate, especially if its in-plane torsional rigidity is low, the model presented does serve as an anchor for parameterizing more advanced （e.g., macro-element plasticity） models that allow rotation, and also as fully parametric lateral response models for torsionally stiff （ile., multi-span, multi-bent） skew bridges.
基金National Natural Science Foundations of China(Grant No.51576211)the Science Fund for Creative Research Groups of National Natural Science Foundation of China(Grant No.51621062)+1 种基金the National High Technology Research and Development Program of China(863 Program,Grant No.2014AA052701)the Foundation for the Author of National Excellent Doctoral Dissertation of China(FANEDD,Grant No.201438).
文摘Recently, a new definition, called Rortex, was proposed to quantify the purely rotational motion of fluids. In this work, based on the DNS data, the Rortex is used to assess and visualize the rotational motion and structure of the vortex in swirling jets in comparison with other kinds of vortex criteria, including Q , λ2,vorticity and Ω criteria. The Rortex vector,Ω, Q and criteria are found to be better than the vorticity criterion for the vortex core identification. The vector triangle formed by the Rortex R , the nonrotational shear S , and the vorticity R is analyzed to give mechanical explanations, especially of the effect of the non-rotational shear on the rotation of fluids. In addition, the probability density distributions (PDF) of the Rortex R , the nonrotational shear S, and the vorticity R are computed. The peak value of the PDF of the vorticity could be used to explain the pure rigid rotation effect and the combination effects of the rigid rotation and the non?rotational shear.
文摘Most of the times pumps operate off best point states.Reasons are changes of operating conditions,modifications,pollution and wearout or erosion.As consequences non-rotational symmetric flows,transient operational conditions,increased risk of cavitation,decrease of efficiency and unpredictable wearout can appear.Especially construction components of centrifugal pumps,in particular intake elbows,contribute to this matter.Intake elbows causes additional losses and secondary flows,hence non-rotational velocity distributions as intake profile to the centrifugal pump.As a result the impeller vanes experience permanent changes of the intake flow angle and with it transient flow conditions in the blade channels.This paper presents the first results of a project,experimentally and numerically investigating the consequences of non-rotational inflow to leading edge flow conditions of a centrifugal pump.Therefore two pumpintake-elbow systems are compared,by only altering the intake elbow geometry:a common single bended 90°elbow and a numerically optimized elbow(improved regarding rotational symmetric inflow conditions and friction coefficient).The experiments are carried out,using time resolved stereoscopic PIV on a full acrylic pump with refractions index matched(RIM)working fluid.This allows transient investigations of the flow field simultaneously for all blade leading edges.Additional CFD results are validated and used to further support the investigation i.e.for comparing an analog pump system with ideal inflow conditions.
