Current Issue : October - December Volume : 2015 Issue Number : 4 Articles : 4 Articles
As result of increase of customers� demands, products becomemore complexes and dynamics control increased its role into product\ndevelopment. As example, clothing washing machines use LeBlanc balancers in order to reduce vibration issues. Nevertheless, the\nbehaviour of such apparatus is still hard to describe and the numerical simulation of this sort of vibration control is based on\nball rings. The main goal of this work is to define and characterize a numerical model that describes the hydrodynamics balance\nring in the transient state in addition to steady state models. As consequence, the behaviour of balance ring was identified in a\ncomputational fluid dynamics tool and an equation that describes restoration forces, unbalance, force phase, and eccentricity was\nfound....
Background: We propose an a posteriori estimator of the error of hyper-reduced\npredictions for elastoviscoplastic problems. For a given fixed mesh, this error estimator\naims to forecast the validity domain in the parameter space, of hyper-reduction\napproximations. This error estimator evaluates if the simulation outputs generated by\nthe hyper-reduced model represent a convenient approximation of the outputs that\nthe finite element simulation would have predicted. We do not account for the\napproximation error related to the finite element approximation upon which the\nhyper-reduction approximation is introduced.\nMethods: We restrict our attention to generalized standard materials. Upon use of\nincremental variational principles, we propose an error in constitutive relation. This error\nis split into three terms including a tailored norm of the hyper-reduction approximation\nerror. This error norm is defined by using the convexity of an incremental potential\nintroduced to state the constitutive equations. The second term of the a posteriori error\nis related to the stress recovery technique that generates stresses fulfilling the finite\nelement equilibrium equations. The last term is a coupling term between the hyper reduction\napproximation error at each time step and the errors committed before this\ntime step. Unfortunately, this last term prevents error certification. In this paper, we\nrestrict our attention to outputs extracted by a Lipschitz function of the displacements.\nResults: In the proposed numerical examples, we show very good preliminary results\nin predicting the validity domain of hyper-reduction approximations. The average\ncomputational time of the predictions obtained by hyper reduction, is accelerated by a\nfactor of 6 compared to that of finite element simulations. This speed-up incorporates\nthe computational time devoted to the error estimation.\nConclusions: The numerical implementation of the proposed error estimator is\nstraightforward. It does not require the computation of the incremental potential. In\nthe numerical results, the estimated validity domain of hyper-reduced approximations\nis inside the reference validity domain. This paper is a first attempt for a posteriori error\nestimation of hyper-reduction approximations....
In spite of the industrial significance, molecular mechanism of the strain hardening\nsaliently observed in bidisperse polymeric liquids has not been elucidated yet. In this\nstudy, the multi-chain slip-link simulation (called primitive chain network simulation)\nwas performed for the bidisperse polystyrene blends for which experimental data for\nelongational viscosity have been reported earlier. The simulation reasonably reproduced\nlinear viscoelasticity and transient and steady uniaxial elongational viscosities.\nIt has been confirmed that the long chain stretch dominates the stress at the strain\nhardening as already demonstrated earlier via the tube model. The molecular analysis\nemploying the decoupling approximation revealed for the first time that there exist\ntwo molecular mechanisms to induce strain hardening in bidisperse blends. The\nmechanism switches depending on the Weissenberg number with respect to the\nRouse relaxation time of the long chain, WiRL. At WiRL < 1, the simultaneous increase of\nthe long chain orientation and stretch with increasing WiRL lifts the viscosity beyond\nthe Trouton�s viscosity. At WiRL ? 1, the isotropic short chain suppresses the stretch/\norientation-induced reduction of friction to enhance the stretch of long chain....
Background: The flow of suspensions through bifurcations is encountered in several\napplications. It is known that the partitioning of particles at a bifurcation is different\nfrom the partitioning of the suspending fluid, which allows particle separation and\nfractionation. Previous works have mainly investigated the dynamics of particles suspended\nin Newtonian liquids.\nMethods: In this work, we study through 2D direct numerical simulations the partitioning\nof particles suspended in non-Newtonian fluids flowing in a T-junction. We\nadopt a flow configuration such that the two outlets are orthogonal, and their flow\nrates can be tuned. A fictitious domain method combined with a grid deformation\nprocedure is used. The effect of fluid rheology on the partitioning of particles between\nthe two outlets is investigated by selecting different constitutive equations to model\nthe suspending liquid. Specifically, an inelastic shear-thinning (Bird-Carreau) and a\nviscoelastic shear-thinning (Giesekus) models have been chosen; the results are also\ncompared with the case of a Newtonian suspending liquid.\nResults: Simulations are carried out by varying the confinement, the inlet flow rate\nand the relative weight of the two outlet flow rates. For each condition, the fluxes of\nparticles through the two outflow channels are computed. The results show that shear thinning\ndoes not have a relevant effect as compared to the equivalent Newtonian\ncase, i.e., with the same choice of the relative outlet flow rates. On the other hand, fluid\nelasticity strongly alters the fraction of particles exiting the two outlets as compared to\nthe inlet. Such effect is more pronounced for larger particles and inlet flow rates.\nConclusions: The results illustrated here show the feasibility to efficiently separate/\nfractionate particles by size, through the use of viscoelastic suspending liquids....
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