共查询到18条相似文献,搜索用时 78 毫秒
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用动态流体双折射法对三种有代表性的心血管模型(模拟大血管、动脉狭窄和人造心脏瓣膜)中的脉动血流间隙测试,得出速度剖面,剪应力分布,压力和流量之间的相位关系。结果说明本文所描述的双折射液和模拟血管是适用于心血管内流场的高质量模拟实验的,动态流体双折射方法及简化的光-力学关系是适用于低频脉动模拟血流的定量分析的。 相似文献
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本文系统地讨论了以动态流体双折射方法实现心血管内流场的高质量模拟测试的基本理论和实用分析方法。首先,分析了稳态流动和振荡剪切流中光-力学关系的差异,提出了脉动流中简化的光-力学关系假设,然后给出了其适用于低频脉动流动的实验验证。 相似文献
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本文重点介绍用于心血管内流场的高质量模拟的动态流体双折射实验技术和系统。首先制备了两种仿血双折射液和一种弹性透明的硅橡胶模拟血管,有关参数测定表明它们适用于模拟血流和血管。其次,为了消除光线穿过圆管产生的图象畸变,用光线追迹法推导出消畸方程并选用最佳匹配浸渍液消畸。最终设计建立了一台由微机控制的集流动、光学、图象与数据采集处理和同步控制子系统于一体的新型测量系统。 相似文献
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本文系统地讨论了以动态流体双折射方法实现心血管内流场的高质量模拟测试的基本理论和实用分析方法。首先,分析了稳态流动和振荡剪切流中光──力学关系的差异,提出脉动流中简化的光──力学关系假设,然后给出其适用于低频脉动流动的实验验证。为使医学和生物力学研究人员易于掌握,又提出一种简单新颖的局域分析法。 相似文献
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Flow induced crystallization of high density polyethylene has been studied in a two-phase flow system using low density polyethylene as the carrier phase. Extensional stresses were generated under slow flow conditions by either of two methods: one involving flow past a stationary seed, the other involving a droplet deformation and bursting mechanism. In both cases, oriented, fibrillar crystallization of the high density phase was observed optically and correlated with calculations indicating the presence of flow-induced extensional gradients. Morphological, thermal, and birefringence data indicate that the crystalline fibers produced are oriented and superheatable, and consist of a multifibrillar substructure. For fibers produced by the droplet bursting process a semi-quantitative agreement was found between fiber melting point and birefringence based on a simplified analysis for the bursting induced extensional flow. These results demonstrate that two-phase flows of crystallizable systems are a convenient means for studying the phenomenon of flow induced crystallization in polymer melts. 相似文献
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Philip Harrison Luc J. P. Janssen Vincent P. Navez Gerrit W. M. Peters Frank P. T. Baaijens 《Rheologica Acta》2002,41(1-2):114-133
The stress-optical rule relates birefringence to stress. Consequently, measurement of flow birefringence provides a non-intrusive
technique of measuring stresses in complex flows. In this investigation we explore the use of an axisymmetric geometry to
create a uniaxial elongational flow in polymer melts. In axisymmetric flows both birefringence and orientation angle change
continuously along the path of the propagating light. The cumulative influence of the material's optical properties along
the light's integrated path makes determination of local birefringence in the melt impossible. One can nevertheless use birefringence
measurements to compare with predictions from computer simulations as a means of evaluating the constitutive equations for
the stress. More specifically, in this investigation we compare the light intensity transmitted through the experimental set-up
vs entry position, with the theoretically calculated transmitted intensity distribution as a means of comparing experiment
and simulation. The main complication in our experiments is the use of a flow cell that necessarily consists of materials
of different refractive indices. This introduces refraction and reflection effects that must be modeled before experimental
results can be correctly interpreted. We describe how these effects are taken into account and test the accuracy of predictions
against experiments. In addition, the high temperatures required to investigate polymer melts mean that a further complication
is introduced by thermal stresses present in the flow cell glass. We describe how these thermal-stresses are also incorporated
in the simulations. Finally, we present some preliminary results and evaluate the success of the overall method.
Received: 2 April 2001 Accepted: 27 August 2001 相似文献
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The rheology of dilute, colloidal suspensions in polymeric suspending fluids can be studied with simultaneous dichroism and birefringence measurements. The dichroism provides a direct measure of the particle dynamics, but the birefringence is a composite property with independent contributions from the suspended particles and the polymer molecules. For suspensions where the contribution from the particles is significant, the composite birefringence must be decoupled in order to analyze the dynamics of the polymeric suspending fluid. A method to perform the decoupling is derived and then demonstrated through transient shear flow experiments with dilute suspensions ofFeOOH particles in semi-dilute, xanthan gum suspending fluids. The birefringence of the xanthan gum suspending fluid is calculated from experimental measurements of the composite birefringence and the dichroism of the suspension. To gather information on particle/polymer interactions, the calculated birefringence is compared to the birefringence of xanthan gum solutions containing no suspended particles and the dirchoism is compared to that of a suspension in a Newtonian fluid. 相似文献
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Flow birefringent method and its data processing was reviewed and a new hybrid method of flow birefringence and boundary integration
was introduced. The basic equations and boundary conditions suitable to the hybrid method were derived, and a comparison of
the hybrid and other classical methods was given. Finally as an example, the flow in a step converging tube was analyzed by
the given method.
The project supported by National Natural Science Foundation of China (NSFC) 相似文献
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Summary Investigation of time dependent behaviour of a polystyrene melt is carried out with the aid of a new apparatus for biaxial extension. Use is made of the method of two impinging fluid streams guided by lubricated trumpet shaped metal walls. The flow birefringence is measured in the plane of symmetry and, at the same time, the force is measured which tends to separate the trumpets. The linear stress-optical relation turns out to be valid in this new flow geometry. An accurate value for the stress-optical coefficient can be determined from the relaxation experiments. The stress build-up as calculated from the optical measurements, is compared with the pertinent result of the theory of linear viscoelasticity. For the desired interconversion of dynamic moduli use is made of the approximation by Schwarzl and Struik. The steady state measurements are checked by the results of the non-linear model of Acierno et al.With 16 figures and 2 tables 相似文献
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A novel approach is presented to study the benchmark problem of flow around spheres in model dilute solutions of monodisperse samples of atactic polystyrene in di-octyl phthalate. Spheres are held stationary on flexible cantilevers of known spring-constant, k, while the polymer solutions are pumped past at controlled flow rates, allowing access to a wide range of Deborah number. In this way the non-Newtonian forces experienced by the spheres can be measured as a function of Deborah number, while detailed observations and measurements of birefringence are made, enabling assessment of macromolecular strain and orientation. In addition the flow field around a sphere has been measured in an a-PS solution. Experiments have been performed on a single sphere and on two spheres axially aligned in the direction of flow. The extensional flow around the downstream stagnation point of the single sphere is found to play a pivotal role in the development of molecular strain and stress, resulting in flow modification and subsequent non-Newtonian behaviour. The flow birefringence in the wake is found to modify severely the flow around a second, downstream, sphere, affecting the non-Newtonian forces encountered by the second sphere. This provides an explanation for the time interval dependent terminal velocity often observed when two spheres follow the same path through viscoelastic liquids. 相似文献