Channel Cross-section Profiles Research Articles

Influence of manufacturing technique and autoclaving curing rate on the non-linear behaviour of thin-walled, GFRP channel columns – Experimental studies

The target of this research is to investigate the influence of manufacturing technique and autoclaving process parameters on the buckling and post-buckling behaviour of thin-walled, GFRP laminates. We investigated the compression of channel cross-section profiles with the following dimensions of the inner perimeter: (web × flange × length of the profile): 80 mm × 38 mm × 240 mm. The nominal wall thickness of the columns was equal to 1.2 mm. The inner radius at the web-flange junction was equal to 2 mm. The material used to produce the samples was eight-layered pre-preg tape with an angle-ply, symmetric layer arrangement: [45/−45/45/−45]s. The columns were manufactured using two different techniques. The first technique was to form the channel cross-section profile by draping over an aluminium mandrel, while the second was to form square cross-section profiles, by winding around an aluminium mandrel, which are then cut into two channel-cross sections. Moreover, two curing process types were applied. The first is a nominal (suggested by the pre-preg producer) curing cycle on a hollow section aluminium mandrel, while the second is a modified curing cycle on a solid aluminium mandrel. In total, four different sets of specimens were produced and subjected to static compression. Higher buckling strength (denoting critical loads and post-buckling behaviour) is shown to be a result of internal, after curing stresses in the composite – the highest buckling resistance is achieved for the columns manufactured as square hollow sections and machined into channel sections. This solution is the most economically efficient. Additionally, the samples were 3D scanned in order to assess post-manufacturing distortions and the deviations from the nominal geometry.

Modulated vibration texturing of hierarchical microchannels with controllable profiles and orientations

Hierarchical microchannels, which consist of the primary channel formation and superimposed secondary nanostructures, are attracting ever-increasing attention due to their unique capacity to enhance and modify the surface characteristics and functional performance. The mechanical machining methods for microchannel fabrication, such as micro-milling and diamond turning, can achieve high material removal rates without changing material properties. However, they have limited capacity to control the channel cross-section profiles and shapes due to the relative size between the channel dimension and tool geometry. This study proposes a new cutting-based approach for the fast and cost-effective fabrication of hierarchical microchannels with controllable profiles and orientations by utilizing modulated elliptical vibration texturing. The modulation motion is adopted to form the primary channel in an incremental approach, while the elliptical vibration texturing is utilized to create micro/nano-scale secondary textures. By controlling the tool modulation trajectory, hierarchical dimple arrays with controllable cross-section profiles are first demonstrated. Then, by programming the layout of dimples to adjust the overlapping ratio between each cut, channels can be formed with arbitrary cross-section profiles and orientations. The efficacy of the proposed process has been demonstrated through numerical simulation and experimental results. Hierarchical microchannels with straight and curving shapes, as well as different cross-section profiles (sinusoidal, triangular, trapezoidal), have been presented.

Inertial microfluidics: A method for fast prediction of focusing pattern of particles in the cross section of the channel

Inertial microfluidics is utilized as a powerful passive method for particle and cell manipulation, which uses the hydrodynamic forces of the fluid in the channel to focus particles in specific equilibrium positions in the cross section of the channel. To achieve high performance manipulation, knowledge of focusing pattern of particles in the cross section of channel is essential. In this paper, we propose a method to address this important issue. To this end, firstly inertial microfluidics is analyzed in rectangular cross section channels. The results indicate that fluid flow velocity and channel's cross-sectional profiles have great impacts on the forces exerted on particles. Next, these results are utilized to propose a method to predict equilibrium positions in non-rectangular cross section channels through some simple calculations. This method is based on approximating the velocity profile of a non-rectangular cross section channel by utilizing portions of velocity profiles of different rectangular cross section channels. To analyze the method's performance, results obtained from the proposed method are compared with Direct Numerical Simulation (DNS) and experimental studies of seven non-rectangular channels. It is observed that the proposed approach accurately predicts particles trajectories and their equilibrium positions in the cross section of channels.

A 1D numerical model for the simulation of unsteady and highly erosive flows in rivers

This work is focused on a numerical finite volume scheme for the coupled shallow water-Exner system in 1D applications with arbitrary geometry. The mathematical expressions modeling the hydrodynamic and morphodynamic components of the physical phenomenon are treated to deal with cross-section shape variations and empirical solid discharge estimations. The resulting coupled equations can be rewritten as a non-conservative hyperbolic system with three moving waves and one stationary wave to account for the source terms discretization. Moreover, the wave celerities for the coupled morpho-hydrodyamical system depend on the erosion-deposition mechanism selected to update the channel cross-section profile. This influence is incorporated into the system solution by means of a new parameter related to the channel bottom variation celerity. Special interest is put to show that, even for the simplest solid transport models as the Grass law, to find a linearized Jacobian matrix of the system can be a challenge in presence of arbitrary shape channels. In this paper a numerical finite volume scheme is proposed, based on an augmented Roe solver, first order accurate in time and space, dealing with solid transport flux variations caused by the channel geometry changes. Channel cross-section variations lead to the appearance of a new solid flux source term which should be discretized properly. The stability region is controlled by wave celerities together with a proper reconstruction of the approximate local Riemann problem solution, enforcing positive values for the intermediate states of the conserved variables. Comparison of the numerical results for several analytical and experimental cases demonstrates the effectiveness, exact well-balancedness and accuracy of the scheme.

Analysis of river rehabilitation success, Pipers River, Tasmania

Rivers provide a range of ecosystem services, habitats for rare and endangered species, and water for use by human communities. In the last 200 years, rivers have become degraded by human impacts, necessitating large investments in rehabilitation and restoration, which have been little evaluated for their long term success. Australian rivers have undergone more rapid recent degradation than Europe, and this study assessed change of the Pipers River in Tasmania from 2000 to 2016, during which time the community undertook major rehabilitation efforts, including willow removal, riparian fencing and native vegetation replanting. River hydraulics and channel geomorphology were assessed by comparing channel cross-sectional profiles and hydraulic data from before and after. Historical photographs and site descriptions were assessed for river change, including channel features and vegetation condition. Results demonstrated the resilience of a bedrock confined reach to degradation pressure, and recovery from erosion trajectories at a rehabilitated floodplain reach, with natural vegetation regeneration. Two previously unstable eroding reaches after rehabilitation showed stabilized conditions and hydraulic values, with reduction in turbulent and critical flow. This study demonstrates that catchment rehabilitation activities have a positive effect on stabilizing and recovery from channel erosion. The long term outcomes of river rehabilitation initiatives in reducing channel degradation is little researched previously, and this assessment has shown community investment to be largely successful. This geomorphic and hydraulic evidence contributes to existing understanding from water quality and aquatic biotic surveys, that investment in river rehabilitation has long-term positive benefits.

A three-dimensional FEM model of channel machining by scanning micro electrochemical flow cell and jet electrochemical machining

In this research, a three-dimensional (3D) finite element method (FEM) model based on Faraday’s law and moving mesh technique is proposed to simulate the channel machining process in Scanning Micro Electrochemical Flow Cell (SMEFC) and jet electrochemical machining (jet-ECM). The scarcity of available FEM models for the channel fabrication by electrochemical machining (ECM) with confined electrolyte is identified through a brief review of ECM simulation with moving electrode. The detailed information on the model establishment is then presented, including the fundamental principle, the way to construct the geometrical model of the moving electrolyte droplet during the machining process, the boundary settings and some key assumptions. Thanks to the introduction of the virtual electrolyte layer and the moving mesh technique, confined machining of channels by SMEFC can be simulated. In the experimental validation phase, species of the electrolyte (NaNO3 and NaCl), the dimension of the hollow electrodes and the electrochemical equivalent of the workpiece, the machining voltages and feed rates are compared in terms of the channel cross-sectional profiles and errors. The flow field and heat transfer still need to be considered in order to simulate the case with NaNO3 electrolyte in the future. This proposed 3D simulation model can improve the understanding and applicability of channel machining by SMEFC, since the current density distribution and the change of workpiece shape can be calculated simultaneously. With some modifications, this method can be as well extended to the channel machining by jet-ECM. Two case studies of micro scale and meso scale jet-ECM are simulated respectively. The proposed simulation method is a potential way to understand and improve the channel machining process by ECM with confined electrolyte.

Coupled method for the numerical simulation of 1D shallow water and Exner transport equations in channels with variable cross-section

This work is focused on the a numerical finite volume scheme for the resulting coupled shallow water-Exner system in 1D applications with arbitrary geometry. The mathematical expression modeling the the hydrodynamic and morphodynamic components of the physical phenomenon are treated to deal with cross-section shape variations and empirical solid discharge estimations. The resulting coupled system of equations can be rewritten as a nonconservative hyperbolic system with three moving waves and one stationary wave to account for the source terms discretization. But, even for the simplest solid transport models as the Grass law, to find a linearized Jacobian matrix of the system can be a challenge if one considers arbitrary shape channels. Moreover, the bottom channel slope variations depends on the erosion-deposition mechanism considered to update the channel cross-section profile. In this paper a numerical finite volume scheme is proposed, based on an augmented Roe solver (first order accurate in time and space) and dealing with solid transport flux variations caused by the channel geometry changes. Channel crosssection variations lead to the appearance of a new solid flux source term which should be discretized properly. Comparison of the numerical results for several analytical and experimental cases demonstrate the effectiveness, exact wellbalanceness and accuracy of the scheme.

Buckling strength improvements for Fibre Metal Laminates using thin-ply tailoring

The buckling response and load carrying capacity of thin-walled open cross-section profiles made of Fibre Metal Laminates, subjected to static axial compression loading are considered. These include thin-walled Z-shape and channel cross-section profiles adopting a 3/2 FML lay-up design, made of 3 aluminium layers. The objective of the investigation is the comparison of standard thickness Fibre Reinforced Plastic layers versus thin-ply material technology. Whilst thin ply designs differ only by the layer thickness, they offer an exponential increase in stacking sequence design freedoms, allowing detrimental coupling effects to be eliminated. The benefit of different hybrid materials are also considered. The comparisons involve semi-analytical and finite element methods, which are validated against experimental investigations.

The effect of temperature on the cryogenic abrasive jet micro-machining of polytetrafluoroethylene, high carbon steel and polydimethylsiloxane

A previously developed cryogenic abrasive jet micro-machining apparatus was used to machine polytetrafluoroethylene (PTFE), high carbon steel, and polydimethylsiloxane (PDMS) at temperatures between −182°C and 17°C. As the machining temperature was lowered, the maximum erosion rate of PTFE increased five-fold and was found to occur at progressively higher angles of attack, shifting from 15° to 90°, although the angular dependence weakened and the maximum became less pronounced. This was similar to the behavior of PDMS observed in an earlier study [1]. The dependence of the erosion rate on angle of attack in high carbon steel, a useful masking material, was found to be insensitive to temperature, but the erosion rate increased approximately two-fold as the temperature decreased from 17°C to −182°C. The cross-sectional profiles of masked, machined micro-channels in PDMS and PTFE had relatively steep sidewalls compared to glass channels, even at the lowest temperature of −182°C, which indicates erosion was still not fully brittle. Predictions of the evolution of the channel cross-sectional profiles generally agreed well with experiments, although the channel width in PDMS at −182°C was under-predicted, most likely due to thermal effects. None of the materials exhibited an erosion incubation period, and there was minimal particle embedding in the samples machined below room temperature.

Opening Barrier Renormalization by Membrane Local Curvature Fluctuations around the Mechanosensitive Channel: Analytical Expression

We calculate renormalization of the opening energy barrier of mechanosensitive channel by local curvature fluctuations: U= U0 +Ufl, Eq. (1), P0(z) and P1(z,H) are lateral pressure profiles in the flat and curved bilayer respectively, H and A(z) are local mean curvature and the difference between open/closed channel cross-section profiles. Function P1(z,H) was derived in [1] analytically using flexible strings model of lipid chains [2]. The average over fluctuations of the membrane's shape h(x,y) in the Monge representation [3] uses Boltzmann factor of a curved conformation exp(-F(H)/T) with elastic free energy functional F(H) taken in the Helfrich form, Eq. (3); k and r are bending rigidity and surface tension. Comparing our results with molecular dynamics data [4] for curved bilayers, we estimate relative importance of the contributions of the lipid tails and phospholipid headgroups to the energy barrier U.

River channel response to short-term human-induced change in landscape connectivity in Andean ecosystems

The drainage basin of the Deleg River (88 km 2), located in the southern Ecuadorian Andes, was studied to assess the geomorphic and hydrologic response of a fluvial system to human-induced environmental change in its contributing area. Historical data on land use, channel morphology and sedimentology were collected, based on a spatial analysis of aerial photographs (1963–1995) and a field survey (2002). Analysis of channel cross-sectional profiles and sedimentological data revealed a major change in morphology and sedimentology of the Deleg River during the past four decades: (i) the active river channel narrowed by over 45%, (ii) the riverbed incised on average by over 1.0 m and (iii) the median grain size of the bed surface decreased from 13.2 cm to 4.7 cm. The spatial pattern of land cover within the Deleg catchment also changed considerably: highly degraded agricultural land in the low-lying areas was abandoned and partially afforested for timber and wood production, whereas secondary upland forest was increasingly cleared for expansion of cropland and pastures. Notwithstanding large changes in the spatial organization of land use within the catchment, the overall land use did not change significantly during the past four decades. This suggests that the response of the Deleg River to land-use change not only depends on the overall land-use change, but also on the spatial pattern of land-use/cover change within the catchment. Although forestation and regeneration of bare gully slopes and floors throughout the catchment only represented a minor part of the total land-use change, these land-use/cover changes had a major impact on the hydrological and sediment connectivity in the landscape.