Hydraulic falls under a floating ice plate due to submerged obstructions

AbstractSteady two-dimensional nonlinear flexural–gravity hydraulic falls past a submerged obstruction on the bottom of a channel are considered. The fluid is assumed to be ideal and is covered above by a thin ice plate. Cosserat theory is used to model the sheet of ice as a thin elastic shell, and boundary integral equation techniques are then employed to find critical flow solutions. By utilising a second obstruction, solutions with a train of waves trapped between two obstructions are investigated.</jats:p

Time dependent hydraulic falls and trapped waves over submerged obstructions

We consider the classical problem of a free surface flowing past one or more disturbances in a channel. The fluid is assumed to be inviscid and incompressible, and the flow, irrotational. Both the effects of gravity and surface tension are considered. The stability of critical flow steady solutions, which have subcritical flow upstream of the disturbance and supercritical flow downstream, is investigated. We compute the initial steady solution using boundary integral equation techniques based on Cauchy integral formula and advance the solution forward in time using a mixed Euler-Lagrange method along with Adams-Bashforth-Moulton scheme. Both gravity and gravity-capillary critical flow solutions are found to be stable. The stability of solutions with a train of waves trapped between two disturbances is also investigated in the pure gravity and gravity-capillary cases

Forced and Unforced Flexural-gravity Solitary Waves

Flexural-gravity waves beneath an ice sheet are investigated. Forced waves generated by a moving load as well as freely propagating solitary waves are considered for the nonlinear problem as proposed by Plotnikov and Toland [2011]. In the unforced case, a Hamiltonian reformulation of the governing equations is presented in three dimensions. A weakly nonlinear analysis is performed to derive a cubic nonlinear Schrödinger equation near the minimum phase velocity in two dimensions. Both steady and time-dependent fully nonlinear computations are presented in the two-dimensional case, and the influence of finite depth is also discussed

Deformation of an elastic cell in a uniform stream and in a circulatory flow

The deformation of a circular, inextensible elastic cell is examined when the cell is placed into two different background potential flows: a uniform stream and a circulatory flow induced by a point vortex located inside the cell. In a circulatory flow a cell may deform into a mode m shape with m-fold rotational symmetry. In a uniform stream, shapes with two-fold rotational symmetry tend to be selected. In a weak stream a cell deforms linearly into an ellipse with either its major or its minor axis aligned with the oncoming flow. This marks an interesting difference with a bubble with constant surface tension in a uniform stream, which can only deform into a mode 2 shape with its major axis perpendicular to the stream (Vanden-Broeck & Keller, 1980b). In general, as the strength of the uniform stream is increased from zero, solutions emerge continuously from the cell configurations in quiescent fluid found by Flaherty et al. (1972). A richly populated solution space is described with multiple solution branches which either terminate when a cell reaches a state with a point of self-contact or loop round to continuously connect cell states which exist under identical conditions in the absence of flow

Solitary interfacial hydroelastic waves

Solitary waves travelling along an elastic plate present between two fluids with different densities are computed in this paper. Different two-dimensional configurations are considered: the upper fluid can be of infinite extent, bounded by a rigid wall or under a second elastic plate. The dispersion relation is obtained for each case and numerical codes based on integro-differential formulations for the full nonlinear problem are derived

Ethnic Communities in the Danube Delta. A Cultural Dialogue

Ethnographic research in the Danube Delta reveals particular features of traditional cultureand way of life in the area, pointing out to the importance of the human factor in shaping the specificcharacter of the Delta habitat. As anywhere else, humans have engaged into a dialogue with nature,ready to adapt to the environment and to relate to it. The Danube Delta appears as an interethnichabitat. The way of life and the system of beliefs and customs prove that the Danube Delta areashares the coordinates of coethnicity with Dobrudja region with certain differences determined byhabitat on one hand and by particular features of the ethnic groups living in the area on the otherhand

Process related impurity breakthrough from depth filtration during monoclonal antibody purification

Upstream advances have led to increased mAb titers above 5g/L in 14-day fed-batch cultures. This is accompanied by higher cell densities and process-related impurities such as DNA and Host Cell Protein (HCP), which have caused challenges for downstream operations. Depth filtration remains a popular choice for harvesting CHO cell culture. However, manufacturers are looking to move away from natural materials such as cellulose and Diatomaceous Earth (DE) for better filter consistency and security of supply. This thesis investigates the impact of high cell density (30-40 million cells/ml) feed material on traditional cellulose and DE filters compared to synthetic polyacrylate + silica depth filters. The study focuses on the retention of process-related impurities such as DNA and HCP through breakthrough studies and a novel confocal microscopy method for imaging foulant in-situ. Further investigation is carried out to understand the effects on Protein A chromatography. In a 2:1 primary: secondary depth filter scale-down model, it was found that the primary filter was the limiting step in terms of pressure and that soluble impurities were mostly removed by the secondary filters. A direct comparison of secondary synthetic and cellulose/DE filters was performed by scaling up the primary depth filter. The viability of the cell culture, and hence DNA concentration at input, was an important factor for DNA retention. HCP was not significantly removed by the depth filtration train. The confocal imaging of the secondary filter showed that cell debris and DNA foulant were distributed differently based on viability and filter type, leading to differences in the pressure profile and impurity retention. In order to gain a deeper understanding of process interaction, three different depth filtration trains were compared where the variables were filter materials and loading. The filtrate was used in a scale-down Protein A chromatography lifetime study and a low pH hold with 0.2μm filtration. Results show that a 36% loading increase in the primary synthetic filter negatively. affected DNA retention in the secondary filter. Confocal imaging of the depth filters showed that the foulant was pushed down through the filter with higher loading. The additional two layers in the primary synthetic filter led to better pressure profiles in both primary and secondary filters but did not help to retain HCP or DNA. Increased solids in the filtrate were associated with the synthetic filter trains, as was precipitation in the Protein A column feed. Confocal imaging of resin after 100 cycles showed that DNA build-up around the outside of the bead was associated with synthetic filter trains, leading to potential mass transfer problems

The non-local AFM water-wave method for cylindrical geometry

We develop an AFM (Ablowitz-Fokas-Musslimani) method applicable to studying water waves in a cylindrical geometry. As with the established AFM method for two-dimensional and three-dimensional water waves, the formulation involves only surface variables and is amenable to numerical computation. The method is developed for a general cylindrical surface, and we demonstrate its use for numerically computing fully nonlinear axisymmetric periodic and solitary waves on a ferrofluid column