7 research outputs found
Numerical simulations of a sphere settling in simple shear flows of yield stress fluids
We perform D numerical simulations to investigate the sedimentation of a
single sphere in the absence and presence of a simple cross shear flow in a
yield stress fluid with weak inertia. In our simulations, the settling flow is
considered to be the primary flow, whereas the linear cross shear flow is a
secondary flow with amplitude of the primary flow. To study the effects
of elasticity and plasticity of the carrying fluid on the sphere drag as well
as the flow dynamics, the fluid is modeled using the elastovisco-plastic (EVP)
constitutive laws proposed by \cite{saramito2009new}. The extra non-Newtonian
stress tensor is fully coupled with the flow equation and the solid particle is
represented by an immersed boundary (IB) method. Our results show that the
fore-aft asymmetry in the velocity is less pronounced and the negative wake
disappears when a linear cross shear flow is applied. We find that the drag on
a sphere settling in a sheared yield stress fluid is reduced significantly as
compared to an otherwise quiescent fluid. More importantly, the sphere drag in
the presence of a secondary cross shear flow cannot be derived from the pure
sedimentation drag law owing to the non-linear coupling between the simple
shear flow and the uniform flow. Finally, we show that the drag on the sphere
settling in a sheared yield-stress fluid is reduced at higher material
elasticity mainly due to the form and viscous drag reduction.Comment: 41 pages, 24 figure
Regional temperature control in ceramic injection moulding: an approach based on cooling rate optimisation
The injection moulding of ceramic components with uneven wall thickness presents challenges due to differential cooling rates developing in the injected parts, which cause premature solidification of the feedstock at thin features and lead to detrimental defects , worsening in components from green to sintered states. To cope with this, suitable mould thermal control approaches have to be selected and validated, as current control methods are based on the achievement of a uniform cavity surface temperature, which is not tailored to such complex geometries. In this work, a novel thermal control system is proposed, based on regional mould temperatures, implemented with the use of Peltier modules, which locally and independently heat and cool different cavity features according to their thickness. The regional temperature profiles are optimised over time with the use of a coupled Finite Element-Particle Swarm Optimisation (FE-PSO), to achieve uniform cooling rates throughout the moulded components. The performance of this approach is compared to both constant ambient mould temperature and Rapid Heat Cycle Moulding (RHCM) techniques, which instead aim at achieving uniform temperatures throughout the mould cavity surface. Results show that the novel proposed method, based on regional temperature control and uniform cooling rates, promotes the simultaneous solidification of features with a 10-times difference in surface-to-volume ratio. Due to this, in terms of components quality, the novel method brings the advantages 1 of higher dimensional control and reduction of differential shrinkage compared to the other analysed approaches, thus increasing the capability to use injection moulding to manufacture ceramic components characterised by non-uniform wall thickness
Numerical modelling of fibre suspensions in newtonian and non-newtonian fluids
Ph.DDOCTOR OF PHILOSOPH
Chinese Physics A NONLINEAR ANALYTICAL AND NUMERICAL STUDY FOR AN OPEN SYSTEM WITH COHERENT OFF-RESONANCE FIELDS *
An exact nonlinear analytical solution of an open V-type inversionless lasing system with two incoherent pump fields, off-resonant driving and probe fields is given. Through qualitative and quantitative comparison of the gain, dispersion and population differences of the linear and nonlinear cases, some conclusions concerning the Rabi frequencies of the driving and the probe fields are drawn and discussed in detail