Introduction:During floods in many Rivers, the flow exits its main section and inundates the vicinity floodplains. The hydraulic flow in compound sections differs significantly from single channels. In such conditions, due to the change in flow section shape and the roughness difference between the main channel and floodplains, the flow structure in compound channels becomes highly complex (Yang et al., 2007; 2013). Vegetation in natural rivers is typically classified into rigid (trees) and flexible (grasses) plant. The stems of flexible plants can change shape with the movement of water flow, whereas the trunks of rigid trees remain unchanged against the flow without deformation (Terrier, 2010). The vegetation of floodplain is one of the main components that can influence the velocity distribution in compound channels (samadi Rahim et al., 2021; Hamidifar et al., 2016). this study, has investigated the flow field and the formation of secondary currents resulting from rigid and flexible vegetation in divergence compound channels with a mobile bed.Methodology:In order to investigate the effect of the vegetation of floodplain on the flow structure and the formation of secondary currents, solid cylindrical plastic rods with a diameter (D) of 10 mm were used to model the vegetation of trees and artificial grass with a height of 3 cm as flexible vegetation on They were placed in floodplains with a width of 0.36 cm. The distance between the rows of rods (lx) was considered constant and equal to 75 mm. While in order to change the vegetation density, the transverse distance between two rods (ly) was set at three distances of 50, 75 and 100 mm. In the main channel with a width of 0.24 meters and a height of 0.15 meters, siliceous sediments with a mean diameter (D50) of 1 mm created a mobile bed. In the floodplain, three divergence angles of 3.8, 5.7 and 11.3 degrees were set in such a way that in three relative depths of flow equal to 0.25, 0.35 and 0.45 and three densities of vegetation with the space ratio to 5, 7.5 and 10 were performed in a total of 36 experiments. The components of the local velocity of the flow in the middle section and at the end of the divergence of floodplain were measured by the 3D velocimeter of the Vectrino Profiler.Results and Discussion:In the non-prismatic compound channels with vegetation, the vertical isovelocity in the common area between the main channel and the floodplain indicates a strong velocity gradient in this area and confirms the formation of a free shear layer due to the Kelvin-Helmholtz phenomenon. Due to the presence of grass vegetation in the floodplain bed, the flow in floodplain is divided into two separate regions: the flow within the grass vegetation and the flow top of the grass vegetation. In divergent compound sections without vegetation, the transverse velocity of the flow in the main channel and the floodplain is significant and its positive. In the presence of vegetation, because the crest of the dune has reached the middle range of the divergence reach, the vertical component of the velocity in the main channel has become negative. As the distance from the floodplain bed increases, the drag force caused by the trees dominates and the contribution of the bed roughness in controlling the flow decreases. Therefore, the velocity profile in floodplain does not follow the logarithmic distribution and almost assumes an S shape. Vegetation has caused the formation of very weak secondary currents in the floodplain, especially in the reach of the end of the divergence. Also, the increase in vegetation density has caused the strength of eddies to decrease in the the main channel. The transverse gradient shows that the greatest effect of the secondary currents was in the common area between the main channel and floodplain, so that the increase in vegetation density confirms the formation of a stronger shear layer in this area. Vegetation on the floodplain weakens the secondary currents in this area. These results agree well with the studies of researchers such as Yang et al. (2007), Hamidifar et al. (2016) and Samadi Rahim et al. (2023). Also, the movement of eddies direction is constantly changing and the flow is very complicated. Therefore, local erosion is observed in the bed of the main channel and close to the common side wall, and on the other side, the height of the dune is increased. While in the main channel, there are two eddies in opposite directions. Conclusion:The Kelvin-Helmholtz instability causes the generation of a free shear layer in the intersection area. Also, the formation of points with a velocity close to zero on the floodplains shows the existence of excessive resistance of flexible and rigid vegetation compared to literature. The periodic positive and negative values of the transverse flow velocity in the floodplain range indicate the interference of Von Kàrmàn vortex streets in the space between the two vegetation elements. In the divergent compound channel with the vegetated floodplain, too weak secondary currents are generated, especially in the end of the divergence reach.

In the present study, flow characteristics in compound meandering channels under the changes of building arrangement in the floodplains were investigated using a numerical simulation. A constant sinuosity factor of 1.21 and relative flow depths (Dr) of 0.29 to 0.49 were considered to illustrate the effect of the hydraulic parameters on the variations of the velocity components. Three types of building arrangements, including structural obstacles perpendicular to the flow of the floodplain (MHT, density=18.5%), structural obstacles parallel to the flow of the floodplain (MGT, density=23.7%), and checkered structural obstacles (MFT, density=23.7%), were used. The simulated data were in good agreement with the experimental data indicating the proper ability of the numerical model in simulation. The result reveals that in the concave arc of sections CS1 and CS7 (apex sections), changing the building arrangements has a negligible effect on the change of transverse and secondary flows due to the parallelism of the main channel flow and the floodplain flow as well as the insignificant effect of the floodplain flow on the main channel. But near the convex arc, these changes are more significant. Hence in section CS4, with the increase of the Dr from 0.29 to 0.49, for cases MAT, MGT, and MHT, the maximum value of depth-averaged transverse flow strength increases by 61%, 91%, and 41%, respectively. In section CS1, the secondary flow cells created in the case of MGT1 cover the entire section; however, in cases of MFT1 and MHT1, the size of the cell is small and is located on the left side of the section. In mid-sections, a small secondary cell in the same direction as the transverse flow (clockwise) is formed in the right corner near the bottom of the channel and gradually grows in the mid-sections and reaches its maximum size in section CS7. Along with the building arrangements of cases MFT1 and MHT1, the transverse component of the floodplain flow velocity (at the entrance of the floodplain flow to the main channel y/h=5) is weakened in the middle sections (CS3, CS4, and CS5). The dimensions of the secondary flow cell increase in the next sections and reach its largest value in section CS7.

Secondary breakup of Newtonian droplet into continuous air jet was numerically studied. A coupled Large Eddy Simulation (LES)/ Volume of Fluid (VOF) technique was used in this investigation. Dynamic adaptive mesh was also employed. To this end, the open source CFD package, Open FOAM, was used to perform the numerical study and was modified to meet the needs of the problem. In order to reduce the error, resulting from the spurious currents, Laplacian smoothing filter was used, which transforms the volume fraction into a smoother volume fraction. This filtering process also helped to obtain a sharp fluid interface. The smoothing has qualitatively and quantitatively improved the simulation results in bag breakup regime. Comparing the results of the RNG k-e turbulence model and LES model showed the great influence of LES model to improve results. The detailed physics of two different breakup regimes, i.e. bag and multimode (streamer) were investigated. The numerical drop breakup regimes showed appropriate agreement with experimental observation. According to the analogy between the secondary and primary atomization, the outcomes can be used for development of the atomization models.

Purpose: Managers are one of the important elements of an organization, for this reason, in order to draw the future of the organization, it is necessary for the planners to specify the conditions of their selection and appointment. Therefore, the current research has been done with the aim of identifying and analyzing the components of selecting future principals.Method: In this research, comparative and benchmarking method is used as a prospective approach. This approach is based on the belief that today's advanced organizations/countries can be considered as a model for the future of another organization/countries in their respective subjects. For this, first, the fields of comparison and benchmarking were determined using Brody's four-step comparison method; then the countries of Canada, Finland, Australia, South Africa, and Japan were selected according to the qualitative balance value in the international advanced TEAMS test, human development index, life quality index(health, instruction, and welfare), education quality index, and other scientific-scholarly indexes; finally, by extracting the criteria for the selection and appointment of principals through content analysis and comparison with Iran, the proposed framework for Iran has been presented.Findings: A total of 61 components for the selection of secondary school principals were identified from among the studies conducted in the selected countries in this article. By extracting the commonalities and differences of each of the components among the countries, it was found that the highest index of manager selection and appointment belongs to Japan and the lowest one is related to Finland.Conclusion: There are similarities between the components of selection of principals of secondary schools in Iran and selected countries. In Iran, special attention should be paid to important components such as adherence to religious principles, appropriate personality traits, creativity and innovation, motivation to develop capabilities, professional growth, power of supervision and accountability, social image, leader skills, and purposefulness and foresight.

In this paper, the effect of installation of a triangular vane attached to the bank on the transverse mixing and reduction of pollutant concentrations has been investigated. Triangular vanes are environment friendly structures and used for river sediment management. By generating secondary currents, these vanes can create transverse mixing in a shorter distance and help the river self-purification. The experiments were conducted in a flume 80 cm wide and 10 m long. A triangular vane with an effective length of 30 % of the channel width and an angle of 45 ° relative to the mainstream was installed at 50 cm downstream of the source of the tracer. Water and salt solution was used as a tracer. The concentration was measured by 96 sensors at each transverse section and in the four downstream sections of the tracer. In addition, around the vane, the 3D velocity pattern was also recorded. The results showed that the presence of the vane causes an increase in the amount of transverse velocity and their direction indicating the presence of secondary currents which resulted in a 30% increase in the variance of the concentration distribution. Also, the existence of this structure has led to the uniformity of concentration distribution and decrease of concentration of 80 % of the concentration at the maximum point of the concentration distribution at the center of the channel relative to the no vane condition.