Bulk flow model with perturbation simplification has been used to calculate rotordynamic coefficients in annular seals which have significant influences on the dynamic behavior of rotors in turbomachinery. In this wor...Bulk flow model with perturbation simplification has been used to calculate rotordynamic coefficients in annular seals which have significant influences on the dynamic behavior of rotors in turbomachinery. In this work, a transient bulk flow model with arbitrary rotor motion is developed, and the boundary conditions and friction factor in the model are calibrated with steady Computational Fluid Dynamics（CFD） analysis. The numerical solution scheme is developed based on the finite element method to obtain the transient reaction force in the seal clearance. With a periodic circular rotor orbit, the transient forces at multiple whirling frequencies are used to evaluate the rotordynamic coefficients. The leakage flowrate of CFD analysis has good agreement with experimental results and the calibrated parameters in bulk flow model are dependent on operating conditions. Although CFD calibration improves the accuracy of the perturbed bulk flow model, the direct damping is overestimated and the cross-coupled damping is underestimated. Compared with the perturbed model, the predictions of the transient bulk flow model are more agreeable with the experiment.展开更多
Water quality within water distribution system may vary with both location and time. Water quality models are used to predict the spatial and temporal variation of water quality throughout water system. A model of res...Water quality within water distribution system may vary with both location and time. Water quality models are used to predict the spatial and temporal variation of water quality throughout water system. A model of residual chlorine decay in water pipe has been developed, given the consumption of chlorine in reactions with chemicals in bulk water, bio films on pipe wall, in corrosion process, and the mass transport of chlorine from bulk water to pipe wall. Analytical methods of the flow path from water sources to the observed point and the water age of every observed node were proposed. Model is used to predict the decay of residual chlorine in an actual distribution system. Good agreement between calculated and measured values was obtained.展开更多
为揭示再生水和多泥沙质河水中的悬浮固体颗粒对土壤水分入渗性能的影响,该文通过室内灌水入渗试验,研究了灌溉水悬浮固体浓度(0、1.0、5.0和10.0 g/L)、灌水频率(1 d 1次、2 d 1次、4d 1次)、含悬浮固体灌溉水-清水交替灌溉模式(纯含...为揭示再生水和多泥沙质河水中的悬浮固体颗粒对土壤水分入渗性能的影响,该文通过室内灌水入渗试验,研究了灌溉水悬浮固体浓度(0、1.0、5.0和10.0 g/L)、灌水频率(1 d 1次、2 d 1次、4d 1次)、含悬浮固体灌溉水-清水交替灌溉模式(纯含悬浮固体灌溉水灌溉、含悬浮固体灌溉水-清水交替灌溉)条件下受灌土壤容重、孔隙率、悬浮固体沉积量、地表入渗性能以及入渗水流运动非均匀特征的变化规律。结果表明,当灌水中的悬浮固体浓度由0增大到10.0 g/L时,受灌土壤容重增大、孔隙率减小、地表入渗能力降低,优先流通道整体弯曲系数由4.31增大到11.18;灌溉定额相同条件下,当灌水频率由1d 1次下降到4 d 1次时,表层土壤容重增大、孔隙率降低,诱发土壤分层,优先流通道整体弯曲系数由7.78增大到12.12;含悬浮固体灌溉水-清水交替灌溉可降低土壤容重、增大孔隙率、减小悬浮固体沉积量、提高地表入渗能力、降低入渗水流运动的非均匀性,但高频率的清水淋洗作用仅使悬浮固体的最大迁移深度增加了5 cm。研究成果对再生水和多泥沙质河水农田灌溉制度设计具有参考价值。展开更多
Vegetation is of great significance in river ecosystems in terms of hydrodynamics,water environment and ecology.The question of how to predict the bulk velocity in channel flow through submerged vegetation is currentl...Vegetation is of great significance in river ecosystems in terms of hydrodynamics,water environment and ecology.The question of how to predict the bulk velocity in channel flow through submerged vegetation is currently a hot topic in hydraulics research.The present study addresses this question.The various formulae used for bulk velocity estimation in previous work were reviewed and compared.The main novelty of this paper is that a new expression of friction factor is proposed as a function of two dimensionless factors,and the number of tuning parameters is less than that in previous work.A comparison of measured and calculated data was conducted for flow through submerged rigid and flexible vegetation.The comparison showed that the proposed new model can make more accurate predictions than previous models.It is envisaged that the proposed formulation can be usefully employed in eco-hydraulics predictions.展开更多
Fully amorphous Zr_(52.5)Cu_(17.9)Ni_(14.6)Al_(10)Ti_(5) bulk metallic glass(BMG) samples with a relative density exceeding 98% were fabricated via selective laser melting(SLM).High fracture stresses of around1700 MPa...Fully amorphous Zr_(52.5)Cu_(17.9)Ni_(14.6)Al_(10)Ti_(5) bulk metallic glass(BMG) samples with a relative density exceeding 98% were fabricated via selective laser melting(SLM).High fracture stresses of around1700 MPa and a reproducible plastic strain of about 0.5% were obtained for cylindrical SLM samples.The analysis of the observed serrations during compressive loading implies that the shear-band dynamics in the additively manufactured samples distinctly differ from those of the as-cast glass.This phenomenon appears to originate from the presence of uniformly dispersed spherical pores as well as from the more pronounced heterogeneity of the glass itself as revealed by instrumented indentation.Despite these heterogeneities,the shear bands are straight and form in the plane of maximum shear stress.Additive manufacturing,hence,might not only allow for producing large BMG samples with complex geometries but also for manipulating their deformation behaviour through tailoring porosity and structural heterogeneity.展开更多
Interstitial fluid movement in the brain parenchyma has been suggested to contribute to sustaining the metabolism in brain parenchyma and maintaining the function of neurons and glial cells.The pulsatile hydrostatic p...Interstitial fluid movement in the brain parenchyma has been suggested to contribute to sustaining the metabolism in brain parenchyma and maintaining the function of neurons and glial cells.The pulsatile hydrostatic pressure gradient may be one of the driving forces of this bulk flow.However,osmotic pressure- related factors have not been studied until now.In this prospective observational study,to elucidate the relationship between osmolality (mOsm/kg) in the serum and that in the cerebrospinal fluid (CSF),we simultaneously measured the serum and CSF osmolality of 179 subjects with suspected neurological conditions.Serum osmolality was 283.6 ± 6.5 mOsm/kg and CSF osmolality was 289.5 ± 6.6 mOsm/kg.Because the specific gravity of serum and CSF is known to be 1.024–1.028 and 1.004–1.007,respectively,the estimated average of osmolarity (mOsm/L) in the serum and CSF covered exactly the same range (i.e.,290.5–291.5 mOsm/L).There was strong correlation between CSF osmolality and serum osmolality,but the difference in osmolality between serum and CSF was not correlated with serum osmolality,serum electrolyte levels,protein levels,or quotient of albumin.In conclusion,CSF osmolarity was suggested to be equal to serum osmolarity.Osmolarity is not one of the driving forces of this bulk flow.Other factors such as hydrostatic pressure gradient should be used to explain the mechanism of bulk flow in the brain parenchyma.This study was approved by the Institutional Review Board of the Tohoku University Hospital (approval No.IRB No.2015-1-257) on July 29,2015.展开更多
基金supported by the National Natural Science Foundation of China(No.11176010)
文摘Bulk flow model with perturbation simplification has been used to calculate rotordynamic coefficients in annular seals which have significant influences on the dynamic behavior of rotors in turbomachinery. In this work, a transient bulk flow model with arbitrary rotor motion is developed, and the boundary conditions and friction factor in the model are calibrated with steady Computational Fluid Dynamics（CFD） analysis. The numerical solution scheme is developed based on the finite element method to obtain the transient reaction force in the seal clearance. With a periodic circular rotor orbit, the transient forces at multiple whirling frequencies are used to evaluate the rotordynamic coefficients. The leakage flowrate of CFD analysis has good agreement with experimental results and the calibrated parameters in bulk flow model are dependent on operating conditions. Although CFD calibration improves the accuracy of the perturbed bulk flow model, the direct damping is overestimated and the cross-coupled damping is underestimated. Compared with the perturbed model, the predictions of the transient bulk flow model are more agreeable with the experiment.
基金TheNationalNaturalScienceFoundationofChina (No .5 96 780 18)
文摘Water quality within water distribution system may vary with both location and time. Water quality models are used to predict the spatial and temporal variation of water quality throughout water system. A model of residual chlorine decay in water pipe has been developed, given the consumption of chlorine in reactions with chemicals in bulk water, bio films on pipe wall, in corrosion process, and the mass transport of chlorine from bulk water to pipe wall. Analytical methods of the flow path from water sources to the observed point and the water age of every observed node were proposed. Model is used to predict the decay of residual chlorine in an actual distribution system. Good agreement between calculated and measured values was obtained.
文摘为揭示再生水和多泥沙质河水中的悬浮固体颗粒对土壤水分入渗性能的影响,该文通过室内灌水入渗试验,研究了灌溉水悬浮固体浓度(0、1.0、5.0和10.0 g/L)、灌水频率(1 d 1次、2 d 1次、4d 1次)、含悬浮固体灌溉水-清水交替灌溉模式(纯含悬浮固体灌溉水灌溉、含悬浮固体灌溉水-清水交替灌溉)条件下受灌土壤容重、孔隙率、悬浮固体沉积量、地表入渗性能以及入渗水流运动非均匀特征的变化规律。结果表明,当灌水中的悬浮固体浓度由0增大到10.0 g/L时,受灌土壤容重增大、孔隙率减小、地表入渗能力降低,优先流通道整体弯曲系数由4.31增大到11.18;灌溉定额相同条件下,当灌水频率由1d 1次下降到4 d 1次时,表层土壤容重增大、孔隙率降低,诱发土壤分层,优先流通道整体弯曲系数由7.78增大到12.12;含悬浮固体灌溉水-清水交替灌溉可降低土壤容重、增大孔隙率、减小悬浮固体沉积量、提高地表入渗能力、降低入渗水流运动的非均匀性,但高频率的清水淋洗作用仅使悬浮固体的最大迁移深度增加了5 cm。研究成果对再生水和多泥沙质河水农田灌溉制度设计具有参考价值。
基金Supported by the National Key Research and Development Program of China(Grant No.2019YFD1100205)the National Natural Science Foundation of China(Grant Nos.51809286,51809288).
文摘Vegetation is of great significance in river ecosystems in terms of hydrodynamics,water environment and ecology.The question of how to predict the bulk velocity in channel flow through submerged vegetation is currently a hot topic in hydraulics research.The present study addresses this question.The various formulae used for bulk velocity estimation in previous work were reviewed and compared.The main novelty of this paper is that a new expression of friction factor is proposed as a function of two dimensionless factors,and the number of tuning parameters is less than that in previous work.A comparison of measured and calculated data was conducted for flow through submerged rigid and flexible vegetation.The comparison showed that the proposed new model can make more accurate predictions than previous models.It is envisaged that the proposed formulation can be usefully employed in eco-hydraulics predictions.
基金support from the China Scholarship Council(CSC)the support from DFG under grant nos.PA 2275/4-1,PA 2275/6-1,KU 1974/11-1 and KO 5571/1-1。
文摘Fully amorphous Zr_(52.5)Cu_(17.9)Ni_(14.6)Al_(10)Ti_(5) bulk metallic glass(BMG) samples with a relative density exceeding 98% were fabricated via selective laser melting(SLM).High fracture stresses of around1700 MPa and a reproducible plastic strain of about 0.5% were obtained for cylindrical SLM samples.The analysis of the observed serrations during compressive loading implies that the shear-band dynamics in the additively manufactured samples distinctly differ from those of the as-cast glass.This phenomenon appears to originate from the presence of uniformly dispersed spherical pores as well as from the more pronounced heterogeneity of the glass itself as revealed by instrumented indentation.Despite these heterogeneities,the shear bands are straight and form in the plane of maximum shear stress.Additive manufacturing,hence,might not only allow for producing large BMG samples with complex geometries but also for manipulating their deformation behaviour through tailoring porosity and structural heterogeneity.
文摘Interstitial fluid movement in the brain parenchyma has been suggested to contribute to sustaining the metabolism in brain parenchyma and maintaining the function of neurons and glial cells.The pulsatile hydrostatic pressure gradient may be one of the driving forces of this bulk flow.However,osmotic pressure- related factors have not been studied until now.In this prospective observational study,to elucidate the relationship between osmolality (mOsm/kg) in the serum and that in the cerebrospinal fluid (CSF),we simultaneously measured the serum and CSF osmolality of 179 subjects with suspected neurological conditions.Serum osmolality was 283.6 ± 6.5 mOsm/kg and CSF osmolality was 289.5 ± 6.6 mOsm/kg.Because the specific gravity of serum and CSF is known to be 1.024–1.028 and 1.004–1.007,respectively,the estimated average of osmolarity (mOsm/L) in the serum and CSF covered exactly the same range (i.e.,290.5–291.5 mOsm/L).There was strong correlation between CSF osmolality and serum osmolality,but the difference in osmolality between serum and CSF was not correlated with serum osmolality,serum electrolyte levels,protein levels,or quotient of albumin.In conclusion,CSF osmolarity was suggested to be equal to serum osmolarity.Osmolarity is not one of the driving forces of this bulk flow.Other factors such as hydrostatic pressure gradient should be used to explain the mechanism of bulk flow in the brain parenchyma.This study was approved by the Institutional Review Board of the Tohoku University Hospital (approval No.IRB No.2015-1-257) on July 29,2015.
