This study presents an analytical solution of thermal and mechanical displacements, strains, and stresses for a thick-walled rotating spherical pressure vessel made of functionally graded materials (FGMs). The pressur...This study presents an analytical solution of thermal and mechanical displacements, strains, and stresses for a thick-walled rotating spherical pressure vessel made of functionally graded materials (FGMs). The pressure vessel is subject to axisymmetric mechanical and thermal loadings within a uniform magnetic field. The material properties of the FGM are considered as the power-law distribution along the thickness. Navier’s equation, which is a second-order ordinary differential equation, is derived from the mechanical equilibrium equation with the consideration of the thermal stresses and the Lorentz force resulting from the magnetic field. The distributions of the displacement, strains, and stresses are determined by the exact solution to Navier’s equation. Numerical results clarify the influence of the thermal loading, magnetic field, non-homogeneity constant, internal pressure, and angular velocity on the magneto-thermo-elastic response of the functionally graded spherical vessel. It is observed that these parameters have remarkable effects on the distributions of radial displacement, radial and circumferential strains, and radial and circumferential stresses.展开更多
目的通过体素水平静息态功能MRI(resting state functional MRI,rs-fMRI)序列探索脑小血管病相关轻度认知障碍(mild cognitive impairment associated with cerebral small vessel disease,CSVD-MCI)患者早期认知障碍的机制,并分析其与...目的通过体素水平静息态功能MRI(resting state functional MRI,rs-fMRI)序列探索脑小血管病相关轻度认知障碍(mild cognitive impairment associated with cerebral small vessel disease,CSVD-MCI)患者早期认知障碍的机制,并分析其与临床神经心理学指标的相关性。材料与方法筛选临床及常规MRI检查符合CSVD-MCI诊断标准的受试者21例,并挑选与其年龄、性别及受教育年限相匹配的健康对照(health control,HC)20例,所有被试都接受rs-fMRI检查,计算全脑度中心度(degree centrality,DC)值,将两组DC值差异显著团块的峰值蒙特利尔神经病学研究所(Montreal Neurological Institute,MNI)坐标作为种子点,与全脑其他体素进行功能连接(functional connection,FC)分析,两组脑功能存在差异脑区的DC及FC值与蒙特利尔认知评估量表(Montreal Cognitive Assessment,MoCA)评分进行相关性分析,并进一步分析CSVD总负荷评分与MoCA评分,以及CSVD总负荷评分与各认知域评分的相关性。结果与HC组相比,CSVD-MCI组左侧内侧额上回/左侧前扣带回、左侧角回/左侧缘上回、右侧内侧额上回/右侧额中回、左侧小脑及右侧小脑DC值减低,左侧前扣带回与左侧颞中下回、双侧楔前叶、双侧中扣带回FC值减低。白质高信号评分、CSVD总负荷评分与MoCA评分呈显著负相关(r_(s)=−0.461,P=0.036;r_(s)=−0.458,P=0.037);CSVD总负荷评分与视空间和执行功能评分呈负相关(r_(s)=−0.473,P=0.030),与其他认知域评分无显著相关性。CSVD-MCI组左侧前扣带回-右侧楔前叶FC值与MoCA评分呈显著正相关(r=0.565,P=0.018)。结论常规MRI可以显示CSVD特征性影像学病灶,rs-fMRI序列可以早期发现DC及FC减低脑区,CSVD评分及DC、FC值与临床神经心理学评分呈明显相关,可作为CSVD-MCI患者的潜在影像学标志物,揭示其认知功能减退的潜在机制。展开更多
This paper studies optimal shape design of pressure vessel head subject to internal uniform pressure.The optimization aims at minimizing its maximum stress while the volume of the vessel head remains no less than the ...This paper studies optimal shape design of pressure vessel head subject to internal uniform pressure.The optimization aims at minimizing its maximum stress while the volume of the vessel head remains no less than the standard ellipsoidal head.Super-ellipse curve is selected to describe the middle surface shape of the vessel head because it represents a large family of curves with only two or three parameters and makes the design and manufacture easy.The performance of different elements and element sizes of FEM modeling is carefully studied in view of computational cost,accuracy and noises of von Mises stress.The response surface of the maximum stress vs.shape design parameters is approximated by a Kriging surrogate model with EI criterion for sampling adding,based on the parameter optimization which is carried out to search the optimal shape.Finally,it is shown by numerical comparison that the super-ellipsoidal head is better than the standard ellipsoidal head and the other vessel heads in the literature.展开更多
文摘This study presents an analytical solution of thermal and mechanical displacements, strains, and stresses for a thick-walled rotating spherical pressure vessel made of functionally graded materials (FGMs). The pressure vessel is subject to axisymmetric mechanical and thermal loadings within a uniform magnetic field. The material properties of the FGM are considered as the power-law distribution along the thickness. Navier’s equation, which is a second-order ordinary differential equation, is derived from the mechanical equilibrium equation with the consideration of the thermal stresses and the Lorentz force resulting from the magnetic field. The distributions of the displacement, strains, and stresses are determined by the exact solution to Navier’s equation. Numerical results clarify the influence of the thermal loading, magnetic field, non-homogeneity constant, internal pressure, and angular velocity on the magneto-thermo-elastic response of the functionally graded spherical vessel. It is observed that these parameters have remarkable effects on the distributions of radial displacement, radial and circumferential strains, and radial and circumferential stresses.
基金Sponsored by the National Natural Science Foundation of China(Grant No.9121620111128205)+1 种基金the National Program on Key Basic Research Project(Grant No.2011CB610304)the Fundamental Research Funds for the Central Universities(Grant No.DUT 11 ZD(G)04)
文摘This paper studies optimal shape design of pressure vessel head subject to internal uniform pressure.The optimization aims at minimizing its maximum stress while the volume of the vessel head remains no less than the standard ellipsoidal head.Super-ellipse curve is selected to describe the middle surface shape of the vessel head because it represents a large family of curves with only two or three parameters and makes the design and manufacture easy.The performance of different elements and element sizes of FEM modeling is carefully studied in view of computational cost,accuracy and noises of von Mises stress.The response surface of the maximum stress vs.shape design parameters is approximated by a Kriging surrogate model with EI criterion for sampling adding,based on the parameter optimization which is carried out to search the optimal shape.Finally,it is shown by numerical comparison that the super-ellipsoidal head is better than the standard ellipsoidal head and the other vessel heads in the literature.
