Effects of Different Viscometer Test on Stencil Printing Process for CFD Simulation

This study discusses the use of different spindle type for the testing of lead-free solder paste by using Computational Fluid Dynamics (CFD) simulation. The study focuses on measuring the volume of solder paste deposition on the solder pad. Parallel-plate (PP) and Cone-plate (CP) spindle were used with five different tests consist of different spindle type and setting. The Volume of Fluid (VOF) method was used for the simulation while Cross model was applied as viscosity model for the solder paste. SAC305 type 3 lead-free solder paste was used in this study as it is mostly popular used by the industries nowadays. The solder paste filled the volume under different squeegee speeds and aperture size was compared between experiments and simulations. For different squeegee speed, PP 0.5 mm gap obtained the lowest average discrepancy value between simulation and experimental results. At different aperture size, all test show similar trend line and about the same value of average discrepancy with CP1° while PP 0.5 mm gap showed the lowest average discrepancy. At small aperture volume, all tests performed shows similar value of filled volume except PP 0.5 mm which exhibit the lowest percentage difference when compared with the experimental values at a bigger aperture volume.

Shear Characteristics of the Interface between Recycled Concrete Aggregates and Various Geosynthetics

To investigate the interface shear characteristics between various geosynthetics and recycled concrete aggregate (RCA), 30 large-scale monotonic direct shear tests were conducted. The main work was to analyse the effect of a biaxial polypropylene geogrid, a glass fiber geogrid, a warp-knitted polyester geogrid, a woven geotextile, and geonet on the interface shear properties of RCA. The test results show that adding a biaxial polypropylene geogrid or a geonet to RCA can improve its interface shear strength. The inclusion of glass fiber geogrids, warp-knitted polyester geogrids, and woven geotextiles decrease the interface shear strength of RCA. The reinforcing RCA with geosynthetics can effectively suppress its shear dilation, and the change in internal friction angle is consistent with the change law of the material interface enhancement coefficient. Finally, the aperture size of a geogrid has a significant effect on the mechanical properties of the geogrid-RCA interface. The interface shear strength increases first and then decreases with an increase in the ratio between aperture size and median particle diameter. It is concluded that there is an optimal range of aperture ratio between a geogrid and RCA.

Natural Rock Fractures: From Aperture to Fluid Flow

Fractures provide preferential flow paths and establish the internal “plumbing” of the rock mass. Fracture surface roughness and the matedness between surfaces combine to delineate the fracture geometric aperture. New and published measurements show the inherent relation between roughness wavelength and amplitude. In fact, data cluster along a power trend consistent with fractal topography. Synthetic fractal surfaces created using this power law, kinematic constraints and contact mechanics are used to explore the evolution of aperture size distribution during normal loading and shear displacement. Results show that increments in normal stress shift the Gaussian aperture size distribution toward smaller apertures. On the other hand, shear displacements do not affect the aperture size distribution of unmated fractures; however, the aperture mean and standard deviation increase with shear displacement in initially mated fractures. We demonstrate that the cubic law is locally valid when fracture roughness follows the observed power law and allows for efficient numerical analyses of transmissivity. Simulations show that flow trajectories redistribute and flow channeling becomes more pronounced with increasing normal stress. Shear displacement induces early aperture anisotropy in initially mated fractures as contact points detach transversely to the shear direction; however, anisotropy decreases as fractures become unmated after large shear displacements. Radial transmissivity measurements obtained using a torsional ring shear device and data gathered from the literature support the development of robust phenomenological models that satisfy asymptotic trends. A power function accurately captures the evolution of transmissivity with normal stress, while a logistic function represents changes with shear displacement. A complementary hydro-chemo-mechanical study shows that positive feedback during reactive fluid flow heightens channeling.

Analysis of the physical properties of spindle seeds for seed sorting operations

The relationships between the basic physical properties of seeds of selected spindle species were evaluated for the needs of seed sorting operations. Physical properties were measured in the seeds of five spindle species, and the presence of relationships between these attributes was determined in correlation and regression analyses. The average values of the evaluated parameters were determined in the following range: terminal velocity—from 9.2 to 10.3 m s−1, thickness—from 2.57 to 3.26 mm, width—from 2.87 to 3.74 mm, length—from 3.94 to 5.52 mm, angle of external friction—from 20.7° to 24.6°, mass—from 16.5 to 33.8 mg. Spindle seeds were arranged in the following ascending order based on their geometric mean diameter: winged spindle, Hamilton’s spindle, large-winged spindle, broadleaf spindle and European spindle. Spindle seeds should be separated in a sieve equipped with at least two mesh screens with slotted apertures. Depending on the processed spindle species, aperture size should range from ≠ 2.7 to ≠ 3.5 mm in the top screen, and from ≠ 2.4 to ≠ 3.0 mm in the bottom screen.

MULTIPLE DIRECTION INTERFERENCE SUPPRESSION BY UNIFORM LINEAR PHASED ARRAY SIDELOBE EFFICIENT CANCELLER

Background. For radar systems, the beam pattern of a uniform linear array (ULA) is synthesized to ensure signal selectivity by direction. A specific ULA sidelobe is cancelled by rescaling the beam weights. In particular, this is done by increasing the number of sensors and shortening the scanning step. However, a noticeable limitation is a loss of the transmitted power. Therefore, the problem is to optimally balance the number of sensors versus effective ULA sidelobe cancellation. Objective. In order to ensure multiple direction interference suppression, the goal is to find an optimal number of ULA radar sensors for the beam pattern synthesis. The criterion is to determine such a minimum of these sensors at which mainlobes towards useful signal directions are evened as much as possible. Methods. To achieve the said goal, the ULA sidelobe cancellation is simulated. The simulation is configured and carried out by using MATLAB® R2020b Phased Array System ToolboxTM functions based on an algorithm of the sidelobe cancellation. Results. By increasing the number of ULA sensors, the beam pattern lobes are not only thinned but also change in their power. In particular, the interference direction sidelobes become relatively stronger. The number of sensors is limited by the three influencing factors: the thinned-array curse transmitted power loss, the aperture size, and the sidelobes intensification. Conclusions. An optimal number of ULA radar sensors for the beam pattern synthesis can be found when the scanning step is equal to the least distance between adjacent interference directions. At the start, the number of sensors is set at the number of useful signal directions. If the mainlobes towards useful signal directions are not evened enough, the set of interference directions is corrected. Keywords: radar phased array; beam pattern; interference direction; sidelobe cancellation; aperture size.

Physico-Chemical, Functional and Proximate Properties of Standardised Millet Flakes

Millets are the 5th most important cereals in the world after wheat, maize, rice and barley. It is a minor cereal containing abundant of nutrients but its consumption is lacking to a certain extent mainly due to the lack of ready-to-cook or ready-to-eat products and processing of millet to prepare ready to cook (RTC) foods can increase its economic and nutritional value. The processing, physical, chemical and nutritional aspects were analysed against the commercially available foxtail and proso flakes to standardise. The decorticated grains were steeped in 5 L of potable water at ambient conditions (30 ± 2ºC) for 10 hr, autoclaved at 180ºC under the pressure of 20 to 24 lbs/psi for 10 min dried at 50ºC in a mechanical dryer to 18 ± 1% moisture content. The processed grains were rolled to flakes in a heavy-duty roller flakes machine with an aperture size of 0.25 mm. The commercial foxtail and proso flakes had higher values for all physical parameters than standardised ones.