A review on design criteria for vortex tubes

In this study, the past investigations of the design criteria of vortex tubes were overviewed and the detailed information was presented on the design of them. Vortex tubes were classified and the type of them was described. All criteria on the design of vortex tubes were given in detail using experimental and theoretical results from the past until now. Finally, the criteria on the design of them are summarized.     

力学复合环境下挠性陀螺仪的动力学分析

为研究分析挠性陀螺仪在过载振动复合环境下附加误差形成的机理和建立误差补偿模型,从结构分析入手,采用有限元分析软件ANSYS建立陀螺仪的实体模型和有限元模型,计算陀螺仪的章动频率,并与实验测量值进行比较,验证了模型的正确性;对挠性陀螺仪在过载-振动复合环境中的动力学特性进行分析研究,得到了各节点轴向位移,结合施加的载荷即可以计算得到陀螺仪的漂移角速度;同时通过模态分析计算得到陀螺仪的固有频率及相应振型.     

Effect of Laminar Orthotropic Myofiber Architecture on Regional Stress and Strain in the Canine Left Ventricle

Recent morphological studies have demonstrated a laminar (sheet) organization of ventricular myofibers. Multiaxial measurements of orthotropic myocardial constitutive properties have not been reported, but regional distributions of three-dimensional diastolic and systolic strains relative to fiber and sheet axes have recently been measured in the dog heart by Takayama et al. [30]. A three-dimensional finite-deformation, finite element model was used to investigate the effects of material orthotropy on regional mechanics in the canine left ventricular wall at end-diastole and end-systole. The prolate spheroidal model incorporated measured transmural distributions of fiber and sheet angles at the base and apex. Compared with transverse isotropy, the orthotropic model of passive myocardial properties yielded improved agreement with measured end-diastolic strains when: (1) normal stiffness transverse to the muscle fibers was increased tangent to the sheets and decreased normal to them; (2) shear coefficients were increased within sheet planes and decreased transverse to them. For end-systole, orthotropic passive properties had little effect, but three-dimensional systolic shear strain distributions were more accurately predicted by a model in which significant active systolic stresses were developed in directions transverse to the mean fiber axis as well as axial to them. Thus the ventricular laminar architecture may give rise to anisotropic material properties transverse to the fibers with greater resting stiffness within than between myocardial laminae. There is also evidence that intact ventricular muscle develops significant transverse stress during systole, though it remains to be seen if active stress is also orthotropic with respect to the laminar architecture. This revised version was published online in July 2006 with corrections to the Cover Date.     

性能增强再生混凝土梁受弯性能试验研究

设计并完成了6根再生混凝土梁试件,其中1根普通再生混凝土梁,3根不同硅粉掺量再生混凝土梁,2根子午线钢纤维与尼龙纤维组成的混杂纤维再生混凝土梁。对该6根梁进行了抗弯性能试验,探讨了普通及性能增强再生混凝土梁受力变形机理及破坏特征。试验结果表明：普通及性能增强再生混凝土梁受力过程仍具有较为明显的弹性、开裂、屈服、极限四个过程;其受力过程基本符合平截面假定,能够按照混凝土结构设计规范(GB50010-2010)进行结构设计;相较于普通再生混凝土,性能增强再生混凝土梁在抗开裂及极限承载力等性能方面更为优异,能够应用于工程实际。最后利用ABAQUS有限元软件对试验梁试件进行了有限元分析,结果表明有限元分析所获得的受弯过程与试验过程吻合较好,验证了试验的正确性。     

The Discrete Models on a Frictional Single Degree of Freedom System

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Stresses in hollow hexagons under external pressure

A two-dimensional photoelastic study was made of the stresses produced in a regular hexagon with a central, circular hole when subjected to external pressure. Four sizes of the hole were tested, and three types of loading were used. This paper describes the pressure-loading fixtures and the procedure which was used to calibrate them. An experimental confirmation of the theoretical solution of Kawaguchi¹ is given, and typical stress patterns and boundary stress distributions are included.     

一种计算三维裂纹应力强度因子的新方法

构造了一种新的三维奇异单元,提出了一种有效计算三维裂纹应力强度因子新的数值方法。该方法的计算结果与理论解和Newman解结果一致;与Panson等方法相比所使用的自由度数大大减小。结果表明该方法是一种高效、稳定可靠的计算方法。     

爆炸载荷作用下具有可折叠芯层夹芯梁的动态响应

基于目前研究最广泛的刚性折纸(Tachi-origami)样式,通过改变其初始折叠角度构建出4种不同的蜂窝胞元,并且通过排列分布将其组成夹芯梁。采用商用有限元软件Abaqus/explicit对准静态和爆炸载荷作用下可折叠芯层夹芯梁的力学响应进行研究,分析可折叠芯层的泊松比变化规律、夹芯梁背板挠度以及能量吸收机理;并将夹芯梁与等质量的实体梁进行对比。采用后面板最大挠度作为抗爆性能的评价,结果发现:可折叠芯层在准静态载荷下具有一定的负泊松比效应;夹芯梁的抗爆性能优于实体梁,曲边蜂窝的初始折角对其作为芯层夹芯梁的抗爆性能有较大影响,随着初始折角的逐渐增大,其抗爆性能逐渐下降;当初始折角为直角时对应于方孔直边蜂窝,其抗爆性能最差。     

Crack energy density in arbitrary direction for piezoelectrics and its characteristic features in electromechanical mixed mode crack

The concepts of crack energy density (CED) and its derivatives in arbitrary direction were established for piezoelectric material and, keeping their application to mixed mode fracture in mind, the characteristic features of them as fracture parameters were investigated based on the approximate equations for CED and its derivatives. That is, CED and its derivatives in arbitrary direction are defined first and separation into their each mode contribution is made. Subsequently, path independent integral expressions of them are derived, and then using them, approximate equations of each mode contribution of CED are obtained concretely for the case where linear singular solution is known. The resulting equations are then used to investigate the effects of electric field and electrical boundary condition on CED and its derivatives. An infinite piezoelectric plane with a crack inclined with respect to the poling direction is considered as a numerical example. Mode I contribution of mechanical CED is mainly employed as a possible fracture parameter for the study and it was shown that applied electric field significantly influences on fracture parameters especially for the impermeable crack perpendicular to the poling direction. The effect of electric field has the tendency to decrease as crack inclination angle increases. It was also found that, even for the impermeable crack perpendicular to the poling direction, crack propagation could be deviated from self-similar direction under a strong negative electric field, and this fact is qualitatively consistent with an existing experimental observation. For the ideally sharp crack with no width, impermeable and Hao and Shen type boundary conditions are admissible showing qualitative agreement with experimental results, but exact boundary condition is not suitable and finally consistent with permeable boundary condition.     

Distribution of Friction Heat Between a Stationary Pin and Rotating Ring

The analysis of the heat distribution between a stationary pin and rotating ring was considered. To solution of the governing quasi-stationary heat conductivity equation the finite Fourier transform was used. The convective cooling from outer and internal surface of the ring as the boundary conditions were considered. The ring surface temperature, the average temperature on the ring surface and the heat distribution coefficient for the studied system were determined. The numerical results for the temperatures and heat distribution coefficient which demonstrated the effects of the Biot number and internal radius of the ring on them, were presented.