Although there are many studies in the literature concerning viscoelastic fluids, it remains a challenging subject in the field of polymer rheology to determine which is the most appropriate model and parameter set to describe the rheological behavior of a given viscoelastic fluid under real flow. The aim of this work is to present an optimization procedure for the estimation of nonlinear parameters of the viscoelastic constitutive equations implemented in the viscoelasticFluidFoam solver available in the OpenFOAM software. The code allows simultaneous fitting of experimental data of two rheological properties: (i) shear viscosity, obtained by rotational and capillary rheometers and (ii) principal stress difference, determined by the flow induced birefringence images obtained during the flow of melt polymer sample in multipass rheometer. In order to illustrate the methodology, a polyethylene sample was characterized at 140°C in the multipass rheometer MPR5S through a slit-die at 0.1 and 0.5 mm/s. The results using multi-mode Giesekus and EPTT constitutive equations showed that the models with the parameters estimated by the proposed methodology were able to satisfactorily represent the shear thinning, observed in the experiments of conventional rheometry, and the stress field determined using birefringence images.

尽管在文献中有许多关于粘弹性流体的研究，但是在聚合物流变学领域中确定哪种是最合适的模型和参数集来描述给定粘弹性流体在实际流动下的流变行为仍然是一个具有挑战性的课题。这项工作的目的是为OpenFOAM软件中提供的粘弹性流体泡沫求解器中实现的粘弹性本构方程的非线性参数估计提供一种优化程序。该代码允许同时拟合具有两种流变特性的实验数据：（i）通过旋转流变仪和毛细管流变仪获得的剪切粘度，以及（ii）由在多道次熔融聚合物样品流动过程中获得的流动诱发双折射图像确定的主应力差流变仪。为了说明该方法，在多通道流变仪MPR5S中以0.1和0.5 mm / s的狭缝模头在140°C下对聚乙烯样品进行了表征。使用多模式Giesekus和EPTT本构方程的结果表明，具有通过所提出方法估算的参数的模型能够令人满意地表示在常规流变学实验中观察到的剪切稀化，以及使用双折射图像确定的应力场。