Collapse-type shrinkage is one of highly refractory drying defects inlow-medium density plantation-grown eucalypt wood used as solid wood products. Basic density (BD),microfibril angle (MFA), double fibre cell wall th...Collapse-type shrinkage is one of highly refractory drying defects inlow-medium density plantation-grown eucalypt wood used as solid wood products. Basic density (BD),microfibril angle (MFA), double fibre cell wall thickness (DWT), proportion of ray parenchyma (RP),unit cell wall shrinkage, total shrinkage and residual collapse, which are associated withcollapse-type shrinkage characteristics, were investigated by using simple regression method forthree species of collapse-susceptible Eucalyptus urophyll,, E. grandis and E. urophyllaxE.grandis,planted at Dong-Men Forest Farm in Guangxi autonomous region, China. The results indicated that:unit cell wall shrinkage had a extremely strong positive correlation with BD, moderately strongpositive correlation with DWT, and a weakly or moderately negative correlation with RP and MFA;total shrinkage was positively correlated with BD, DWT and RP and negatively related to MFA, but notable to be predicted ideally by any examined factors alone owing to lower R^2 value (R^2≤0.5712);residual collapse was negatively correlated with BD and DWT, linearly positively correlated withMFA, and had strongly positive linear correlation with RP. It is concluded that BD can be used assingle factor (R^2≥ 0.9412) to predicate unit cell wall shrinkage and RP is the relatively soundindicator for predicting residual collapse展开更多
Longitudinal and transverse mechanical properties and energy absorption properties of foam-filled square tubes under quasi-static loading conditions were studied.The foam-filled thin-walled square tube was fabricated ...Longitudinal and transverse mechanical properties and energy absorption properties of foam-filled square tubes under quasi-static loading conditions were studied.The foam-filled thin-walled square tube was fabricated with aluminum tube as its shell and closed-cell Al-Mg alloy foam as its core.The results indicated that the plateau region of the load-displacement curve exhibited a marked fluctuant serration which was clearly related to the formation of folds.The longitudinal deforming mode of foam-filled square tube was the same as that of the empty tube,but the fold number of foam-filled square tube was more than that of the empty tube.The longitudinal compression load and energy absorption value of foam-filled square tube were higher than the sum of that of aluminum foam (alone) and empty tube (alone) due to the interaction between tube and filler.In transverse direction,the compression load and energy absorption ability of foam-filled square tubes were significantly lower than those in longitudinal direction.展开更多
目的:观察天灸法对内脏高敏性肠易激综合征(IBS)小鼠结肠组织5-羟色胺(5-HT)及其受体蛋白表达的影响,探讨天灸法治疗IBS的作用机制。方法:将40只SPF级新生昆明小鼠随机分为正常组、模型组、拮抗组和天灸组,每组10只。造模前拮抗组于侧...目的:观察天灸法对内脏高敏性肠易激综合征(IBS)小鼠结肠组织5-羟色胺(5-HT)及其受体蛋白表达的影响,探讨天灸法治疗IBS的作用机制。方法:将40只SPF级新生昆明小鼠随机分为正常组、模型组、拮抗组和天灸组,每组10只。造模前拮抗组于侧脑室注射0.2m L对氯苯丙氨酸(PCPA),模型组、拮抗组和天灸组小鼠应用直肠内冰乙酸刺激结合夹尾刺激制备内脏高敏性IBS模型。造模后,天灸组小鼠行天灸法干预,穴取“中脘”“天枢”“足三里”,每周各穴贴药1次,每次贴药2 h,共3周。采用腹壁回缩反射(AWR)评分和腹壁肌电波幅评价小鼠内脏高敏状态;HE法观察小鼠结肠组织形态变化;免疫组化法检测小鼠结肠组织5-HT及其受体蛋白表达。结果:与正常组比较,20、40 mm Hg(1 mm Hg=0.133 kPa)压力下模型组腹壁肌电波幅升高(P<0.05),60、80 mm Hg压力下模型组AWR评分及腹壁肌电波幅均升高(P<0.05);与模型组比较,20 mm Hg压力下天灸组腹壁肌电波幅降低(P<0.05),40 mm Hg压力下天灸组与拮抗组AWR评分均升高(P<0.05),60、80 mm Hg压力下天灸组与拮抗组AWR评分及腹壁肌电波幅均降低(P<0.05)。与正常组比较,模型组黏膜上层结构轻度紊乱,黏膜下层可见中度炎性细胞;与模型组比较,天灸组与拮抗组黏膜上层固有腺体形状规则,可见少量炎性细胞。与正常组比较,模型组结肠组织5-HT及5-羟色胺受体3(5-HT3R)蛋白平均阳性面积率增加、5-羟色胺受体4(5-HT4R)蛋白平均阳性面积率降低(P<0.05);与模型组比较,天灸组和拮抗组结肠组织5-HT及5-HT3R蛋白平均阳性面积率降低(P<0.05)。结论:天灸法可改善内脏高敏性IBS小鼠内脏高敏状态,可能与5-HT信号通路介导的肠脑轴的调节有关。展开更多
Classical Mach-number(M) scaling in compressible wall turbulence was suggested by van Driest(Van Driest E R.Turbulent boundary layers in compressible fluids.J Aerodynamics Science,1951,18(3):145-160) and Huang et al.(...Classical Mach-number(M) scaling in compressible wall turbulence was suggested by van Driest(Van Driest E R.Turbulent boundary layers in compressible fluids.J Aerodynamics Science,1951,18(3):145-160) and Huang et al.(Huang P G,Coleman G N,Bradshaw P.Compressible turbulent channel flows:DNS results and modeling.J Fluid Mech,1995,305:185-218).Using a concept of velocity-vorticity correlation structure(VVCS),defined by high correlation regions in a field of two-point cross-correlation coefficient between a velocity and a vorticity component,we have discovered a limiting VVCS as the closest streamwise vortex structure to the wall,which provides a concrete Morkovin scaling summarizing all compressibility effects.Specifically,when the height and mean velocity of the limiting VVCS are used as the units for the length scale and the velocity,all geometrical measures in the spanwise and normal directions,as well as the mean velocity and fluctuation(r.m.s) profiles become M-independent.The results are validated by direct numerical simulations(DNS) of compressible channel flows with M up to 3.Furthermore,a quantitative model is found for the M-scaling in terms of the wall density,which is also validated by the DNS data.These findings yield a geometrical interpretation of the semi-local transformation(Huang et al.,1995),and a conclusion that the location and the thermodynamic properties associated with the limiting VVCS determine the M-effects on supersonic wall-bounded flows.展开更多
In this paper,several exact expressions for the mean heat flux at the wall(qw)for the compressible turbulent channel flows are derived by using the internal energy equation or the total energy equation.Two different r...In this paper,several exact expressions for the mean heat flux at the wall(qw)for the compressible turbulent channel flows are derived by using the internal energy equation or the total energy equation.Two different routes,including the FIK method and the RD method,can be applied.The direct numerical simulation data of compressible channel flows at different Reynolds and Mach numbers verify the correctness of the derived formulas.Discussions related to the different energy equations,and different routes are carried out,and we may arrive at the conclusion that most of the formulas derived in the present work are just mathematical ones and that they generally are lacking in clear physical interpretation in our opinion.They can be used to estimate qw,but might not be suitable for exploring the underlying physics.展开更多
The major source of loss in modem compressors is the secondary loss. Non-axisymmetric endwall profile contouring is now a well established design methodology in axial flow turbines. However, flow development in axial ...The major source of loss in modem compressors is the secondary loss. Non-axisymmetric endwall profile contouring is now a well established design methodology in axial flow turbines. However, flow development in axial compressors is differ from turbines, the effects of non-axisymmetric endwall to axial compressors requires flow analysis in detail. This paper presents both experimental and numerical data to deal with the application of a non-axisymmetric hub endwall in a high-subsonic axial-flow compressor. The aims of the experiment here were to make sure the numerically obtained flow fields is the physical mechanism responsible for the improvement in efficiency, due to the non-axisymmetric hub endwall. The computational results were first compared with avail- able measured data of axisymmetric hub endwall. The results agreed well with the experimental data for estima- tion of the global performance. The coupled flow of the compressor rotor with non-axisymmetric hub endwall was simulated by a state-of-the-art multi-block flow solver. The non-axisymmetric hub endwall was designed for a subsonic compressor rotor with the help of sine and cosine functions. This type of non-axisymmetric hub end- wall was found to have a significant improvement in efficiency of 0.45% approximately and a slightly increase for the total pressure ratio. The fundamental mechanisms of non-axisymmetric hub endwall and their effects on the subsonic axial-flow compressor endwall flow field were analyzed in detail. It is concluded that the non-axisymmetric endwall profiling, though not optimum, can mitigate the secondary flow in the vicinity of the hub endwall, resulting in the improvement of aerodynamic performance of the compressor rotor.展开更多
Direct numerical simulations are carried out to assess the potential drag reduction of compressible turbulent flow between isothermal walls.For the sake of achieving drag reduction,the flow is actively controlled by d...Direct numerical simulations are carried out to assess the potential drag reduction of compressible turbulent flow between isothermal walls.For the sake of achieving drag reduction,the flow is actively controlled by deformable dimples lying on the bottom wall of the channel.The first stage of the procedure consists in assessing the optimum geometry of the dimples.In this regard,the lower wall is allowed to freely deform itself according to the loop of control.This method is called the smart wall approach in this paper.By an analysis of the typical shape of the wall deformation thus obtained,it is found that dimples should be thinner than or comparable to the width of streaky structures in the spanwise direction and elongated in the streamwise direction.With active dimples as the wall-deformation actuators,a 15% drag reduction is obtained for the flow at Mam = 0.35 while the drag reduction rate is about 12% for the flow at Mam = 1.5.The fundamental mechanism of the drag reduction is then discussed in this paper.The drag reduction is believed to result from two aspects:the reduction of the mean streamwise velocity gradient near the deformable wall and the suppression of the turbulent fluctuations.展开更多
基金This work was supported by both the project ( No. 30170754)from Chinese National Natural Science Fund and the national significant fundamental research 'Ascending Plan' program (No.95- 07) authorized by Ministry of Science and Technology, China. And was partly presented at the 54th Annual Meeting of the Japan Wood Research Society in Hokkaido, Japan and at the 7th Pacific Rim Bio-based Composites Symposium in Nanjing, P. R. China.
文摘Collapse-type shrinkage is one of highly refractory drying defects inlow-medium density plantation-grown eucalypt wood used as solid wood products. Basic density (BD),microfibril angle (MFA), double fibre cell wall thickness (DWT), proportion of ray parenchyma (RP),unit cell wall shrinkage, total shrinkage and residual collapse, which are associated withcollapse-type shrinkage characteristics, were investigated by using simple regression method forthree species of collapse-susceptible Eucalyptus urophyll,, E. grandis and E. urophyllaxE.grandis,planted at Dong-Men Forest Farm in Guangxi autonomous region, China. The results indicated that:unit cell wall shrinkage had a extremely strong positive correlation with BD, moderately strongpositive correlation with DWT, and a weakly or moderately negative correlation with RP and MFA;total shrinkage was positively correlated with BD, DWT and RP and negatively related to MFA, but notable to be predicted ideally by any examined factors alone owing to lower R^2 value (R^2≤0.5712);residual collapse was negatively correlated with BD and DWT, linearly positively correlated withMFA, and had strongly positive linear correlation with RP. It is concluded that BD can be used assingle factor (R^2≥ 0.9412) to predicate unit cell wall shrinkage and RP is the relatively soundindicator for predicting residual collapse
基金Project (200412) supported by the Nippon Sheet Glass Foundation,Japan
文摘Longitudinal and transverse mechanical properties and energy absorption properties of foam-filled square tubes under quasi-static loading conditions were studied.The foam-filled thin-walled square tube was fabricated with aluminum tube as its shell and closed-cell Al-Mg alloy foam as its core.The results indicated that the plateau region of the load-displacement curve exhibited a marked fluctuant serration which was clearly related to the formation of folds.The longitudinal deforming mode of foam-filled square tube was the same as that of the empty tube,but the fold number of foam-filled square tube was more than that of the empty tube.The longitudinal compression load and energy absorption value of foam-filled square tube were higher than the sum of that of aluminum foam (alone) and empty tube (alone) due to the interaction between tube and filler.In transverse direction,the compression load and energy absorption ability of foam-filled square tubes were significantly lower than those in longitudinal direction.
文摘目的:观察天灸法对内脏高敏性肠易激综合征(IBS)小鼠结肠组织5-羟色胺(5-HT)及其受体蛋白表达的影响,探讨天灸法治疗IBS的作用机制。方法:将40只SPF级新生昆明小鼠随机分为正常组、模型组、拮抗组和天灸组,每组10只。造模前拮抗组于侧脑室注射0.2m L对氯苯丙氨酸(PCPA),模型组、拮抗组和天灸组小鼠应用直肠内冰乙酸刺激结合夹尾刺激制备内脏高敏性IBS模型。造模后,天灸组小鼠行天灸法干预,穴取“中脘”“天枢”“足三里”,每周各穴贴药1次,每次贴药2 h,共3周。采用腹壁回缩反射(AWR)评分和腹壁肌电波幅评价小鼠内脏高敏状态;HE法观察小鼠结肠组织形态变化;免疫组化法检测小鼠结肠组织5-HT及其受体蛋白表达。结果:与正常组比较,20、40 mm Hg(1 mm Hg=0.133 kPa)压力下模型组腹壁肌电波幅升高(P<0.05),60、80 mm Hg压力下模型组AWR评分及腹壁肌电波幅均升高(P<0.05);与模型组比较,20 mm Hg压力下天灸组腹壁肌电波幅降低(P<0.05),40 mm Hg压力下天灸组与拮抗组AWR评分均升高(P<0.05),60、80 mm Hg压力下天灸组与拮抗组AWR评分及腹壁肌电波幅均降低(P<0.05)。与正常组比较,模型组黏膜上层结构轻度紊乱,黏膜下层可见中度炎性细胞;与模型组比较,天灸组与拮抗组黏膜上层固有腺体形状规则,可见少量炎性细胞。与正常组比较,模型组结肠组织5-HT及5-羟色胺受体3(5-HT3R)蛋白平均阳性面积率增加、5-羟色胺受体4(5-HT4R)蛋白平均阳性面积率降低(P<0.05);与模型组比较,天灸组和拮抗组结肠组织5-HT及5-HT3R蛋白平均阳性面积率降低(P<0.05)。结论:天灸法可改善内脏高敏性IBS小鼠内脏高敏状态,可能与5-HT信号通路介导的肠脑轴的调节有关。
基金supported by the National Nature Science Foundation of China (Grant Nos.90716008,10572004 and 11172006)the National Basic Research Program of China (Grant No.2009CB724100)
文摘Classical Mach-number(M) scaling in compressible wall turbulence was suggested by van Driest(Van Driest E R.Turbulent boundary layers in compressible fluids.J Aerodynamics Science,1951,18(3):145-160) and Huang et al.(Huang P G,Coleman G N,Bradshaw P.Compressible turbulent channel flows:DNS results and modeling.J Fluid Mech,1995,305:185-218).Using a concept of velocity-vorticity correlation structure(VVCS),defined by high correlation regions in a field of two-point cross-correlation coefficient between a velocity and a vorticity component,we have discovered a limiting VVCS as the closest streamwise vortex structure to the wall,which provides a concrete Morkovin scaling summarizing all compressibility effects.Specifically,when the height and mean velocity of the limiting VVCS are used as the units for the length scale and the velocity,all geometrical measures in the spanwise and normal directions,as well as the mean velocity and fluctuation(r.m.s) profiles become M-independent.The results are validated by direct numerical simulations(DNS) of compressible channel flows with M up to 3.Furthermore,a quantitative model is found for the M-scaling in terms of the wall density,which is also validated by the DNS data.These findings yield a geometrical interpretation of the semi-local transformation(Huang et al.,1995),and a conclusion that the location and the thermodynamic properties associated with the limiting VVCS determine the M-effects on supersonic wall-bounded flows.
基金the National Natural Science Foundation of China(Grant Nos.11822208,11772297,and 91852205)Guangdong provincial Key Laboratory(Grant No.2019B20203001).
文摘In this paper,several exact expressions for the mean heat flux at the wall(qw)for the compressible turbulent channel flows are derived by using the internal energy equation or the total energy equation.Two different routes,including the FIK method and the RD method,can be applied.The direct numerical simulation data of compressible channel flows at different Reynolds and Mach numbers verify the correctness of the derived formulas.Discussions related to the different energy equations,and different routes are carried out,and we may arrive at the conclusion that most of the formulas derived in the present work are just mathematical ones and that they generally are lacking in clear physical interpretation in our opinion.They can be used to estimate qw,but might not be suitable for exploring the underlying physics.
基金Financial supports for the work presented are provided by National Natural Science Foundation of China (Project No: 50806073)China Postdoctoral Science Foundation (Project No: 20070420068)K C Wong Education Foundation, these supports are greatly appreciated
文摘The major source of loss in modem compressors is the secondary loss. Non-axisymmetric endwall profile contouring is now a well established design methodology in axial flow turbines. However, flow development in axial compressors is differ from turbines, the effects of non-axisymmetric endwall to axial compressors requires flow analysis in detail. This paper presents both experimental and numerical data to deal with the application of a non-axisymmetric hub endwall in a high-subsonic axial-flow compressor. The aims of the experiment here were to make sure the numerically obtained flow fields is the physical mechanism responsible for the improvement in efficiency, due to the non-axisymmetric hub endwall. The computational results were first compared with avail- able measured data of axisymmetric hub endwall. The results agreed well with the experimental data for estima- tion of the global performance. The coupled flow of the compressor rotor with non-axisymmetric hub endwall was simulated by a state-of-the-art multi-block flow solver. The non-axisymmetric hub endwall was designed for a subsonic compressor rotor with the help of sine and cosine functions. This type of non-axisymmetric hub end- wall was found to have a significant improvement in efficiency of 0.45% approximately and a slightly increase for the total pressure ratio. The fundamental mechanisms of non-axisymmetric hub endwall and their effects on the subsonic axial-flow compressor endwall flow field were analyzed in detail. It is concluded that the non-axisymmetric endwall profiling, though not optimum, can mitigate the secondary flow in the vicinity of the hub endwall, resulting in the improvement of aerodynamic performance of the compressor rotor.
基金supported by the National Natural Science Foundation of China (Grant Nos.10932005 and 50910222)
文摘Direct numerical simulations are carried out to assess the potential drag reduction of compressible turbulent flow between isothermal walls.For the sake of achieving drag reduction,the flow is actively controlled by deformable dimples lying on the bottom wall of the channel.The first stage of the procedure consists in assessing the optimum geometry of the dimples.In this regard,the lower wall is allowed to freely deform itself according to the loop of control.This method is called the smart wall approach in this paper.By an analysis of the typical shape of the wall deformation thus obtained,it is found that dimples should be thinner than or comparable to the width of streaky structures in the spanwise direction and elongated in the streamwise direction.With active dimples as the wall-deformation actuators,a 15% drag reduction is obtained for the flow at Mam = 0.35 while the drag reduction rate is about 12% for the flow at Mam = 1.5.The fundamental mechanism of the drag reduction is then discussed in this paper.The drag reduction is believed to result from two aspects:the reduction of the mean streamwise velocity gradient near the deformable wall and the suppression of the turbulent fluctuations.
