A reconfigurable compact small size multiband meander line power divider with low insertion loss using two varactor diodes is presented in this paper. Design methods along with analysis equations are provided. The reconfigurable responses are realized by tuning the controlling voltages of the two varactor diodes thereby resulting compact size and less loss. One diode is used to tune the return loss of the input port and the other diode is utilized to tune the return loss of the two output ports and the isolation between the two ports. The tuning frequency range is from 0.8 GHz to 1.2 GHz. By tuning the bias voltages of the diodes, power divider can operate in 0.8 GHz to 1.2 GHz frequency bands.  A reconfigurable power divider is designed, fabricated and measured to validate the proposed methods. The power divider has the merits of compactness, low insertion loss, good isolation between two output ports, good return loss, and only two varactor diodes.

Geomorphology of the river, a term used to check the river system. Zohreh river is one of the rivers in Khuzestan that consisted from 2 arm Fahlian and Kheyrabad it flow to Persian gulf at the end of Hendijan flat. To accomplish this study topographic maps, remote sensing data, including: Landsat satellite images, Landsat TM and ETM + collected from the Geological Survey of America (Earth Explorer), aerial photographs taken in 1334 of National Geography Organization is used. Next, aerial photos of 1334 as the base image and satellite image of Landsat 8 (2015) were selected as the data terminal. The future direction of the river in 2030 (1409) is plotted and compared with other periods. In this interval is 2 Meander complained. The findings suggest that during the period under review trends in three periods studied are quite different in the river, so in terms of reducing the length, intervals 7, experiences the lowest decline while interval 2 experience biggest decline in three visits. In terms of increasing the length, intervals 7, experiences the lowest increase and intervals 8, had the largest increase. The findings indicate that during the three periods under review, the river changes in the periods studied are quite different. The results show that in 1955 10 cases of amputation has occurred in the river channel and along the river has become 3, 653 km shorter. Even though at intervals of 1 to 5 we except villages along the way, there is no human factor; But in the interval of 6 industries are seen. Interval 7 in the northern part of the land is under irrigated agriculture. But in the southern part are bare. In the interval of 8, lands under the tide, and asphalt and dirt roads are important feature.

Natural channels always form meanders along their path, and it is important to consider the effect of this meander on the flow characteristics pattern. When a flood occurs, the water level crosses the main section of the river and enters its floodplains. In this case, the river crossing becomes a compound cross-section. In this study, using the Flow3D software (powerful software in the field of computational fluid dynamics), the vortex rotational power and transverse flow in the meandering compound channel under the influence of relative depth and Sinusoidal Change were investigated. For this purpose, six channels with different sinuosity and three relative depths were used. The results of the numerical simulation showed that the maximum rotational power of vortices increased with an average of about 195% by increasing the sinusoidal rate from 1 to 1. 209. The maximum rotational strength of the vortices and the transverse flow rate occurred at a 45-degree angle to the central arc and a sinusoidal value of 1. 209. In the main cross-section of the meandering compound channel, for all sinusoidal values, by decreasing the relative depth, the vortex and transverse rotation strengths increased and the rate of change in transverse current power relative to relative depth changes decreased with increasing sinusoidal rate.

Natural debris floods travel in straight and meandering courses. The flow behaviour greatly depends on the volume fractions of solid and fluid, as well as on their dynamic interactions with the channel geometry. For the quasi three-dimensional simulations of flow dynamics and mass transport of these floods through meandering and straight channels, we employ a two-phase debris flow model to carry out simulations for debris floods within straight and sine-generated meandering channels of different amplitudes. The results for different sinuous meandering paths are compared with that in the straight one in terms of phase velocity, downslope advection and dispersion, depths of the maxima, deposition of mass, position of front and rear parts of the solid and fluid phases, and also the flow dynamics out of the conduits. The results reveal the slowing of the flow and increase of momentary deposition of the mixture mass in the vicinity of the bends along with the increasing sinuosity. The numerical experiments are useful to better understand the dynamics of debris floods down meandering channels as seen in the natural paths of the rivers as well as already existing channels like episodic rivers in hilly regions. The results can be extended to propose some appropriate mitigation strategies.

A series of experiments was performed in a laboratory flume to determine the threshold of meandering and braiding of river patterns. For the 4, purpose, of modeling, an alluvial reach of Ghezol Ozan (a meandering river in central north of Iran) was selected and using reasonable values of  geometric, hydraulic and bed material properties of  this river, a physical model with horizontal scale of 1: 400 and vertical scale of 1:40 was constructed. After performing several laboratory tests it was found that discharge and slope were closely related to the threshold values of channel patterns. Also based on regression analysis of experimental, results a number of analytical relationships were obtained for determining the threshold of meandering and braiding patterns. The proposed relationships are between the channel longitudinal slope and discharge and between the non dimensional unit stream power (NUSP) and shields parameter. The later is a new and interesting relationship in river morphology. Several diagrams were made to show that under what initial" conditions the meandering and braiding patterns are established. The laboratory observations of this research have indicated that at very low NUSP, the 4.channel remains straight, but at NUSP of 5.5 to 6.5 a meandering channel is formed and as NUSP increases to 12-22 a braided channel is formed.

Secondary currents are important mechanisms in open channels, having major contribution in flow field and its corresponding parameters including boundary shear stress and depth-averaged velocity. Compound open channels involve extra plan form vortices in the flow field. Curved open channels generate especial vortices due to the effects of centrifugal force. Precise modeling of secondary currents in curves and meanders is a very important issue in practical applications. Using open source ``OpenFOAM'' software, the flow field in a meandering channel with compound cross section is simulated herein. Reynolds averaged Navier-Stocks equations (RANS) are solved. Applying appropriate boundary conditions over the free-surface, the simpleFoam solver has been used to model the two-phase air-water flow interface, assuming a steady flow condition, and a symmetry boundary condition. The experimental data from FCF belonging to University of Birmingham is selected for verification and validation of the present numerical results. Two turbulent models of Realizable k− varepsilon and SST k− omega are applied. Lateral velocity profiles at the cross sections indicate that at each wave-length of a meander, a vortex forms in the main channel at the apex, directing towards the outer bank near the bed and towards the inner bank near the water free-surface. The secondary current patterns, achieved for curved compound open channels differ from those of the simple channels. This is partly due to the interaction of shear stresses occurring at the interfaces between the main channel and the floodplains. Deviation of paths of the main channel and floodplains, downstream of each apex, results in entering the flow from inner bank to the main channel and exiting the flow from the main channel to the outer bank. These flow patterns shift the flow from inner-to the outer bank, downstream of each apex. Therefore, a helicoidally secondary current pattern forms, growing in size and strength farther downstream of the apex region.

The existence of bridge pier in streamflow causes a complex 3D flow formation, which also causes the scouring around bridge pier. Since rivers are usually curved, it is necessary to investigate the impact of change in flow patterns caused by passage of flow through the curve on the scouring around bridge pier. By developing Computational Fluid Dynamics (CFD), there is a possibility to simulate the flow pattern around the bridge piers. Therefore, the purpose of this research is modeled a 3D flow stream near the bridge piers in a curved channel. For this purpose a fluent model software was employed, and solved by stream equations using finite volume method of centralism. For discretization of Navier Stocks equation, three turbulence models of K-e, K-w, and RSM were used. In order to consider free surface, Fluid Volume Method was applied. The numerical model was validated with measured experimental data around the bridge piers in the meandering flume with 5 sequential curve paths. The results showed that the RSM turbulence model performed well compared to the other two models. When comparing the flow of upstream to downstream of bridge piers it can be observed that the placement of bridge piers in the middle of curved shape channel may lead secondary flow towards the inner curve of a channel. Also, the resulted vortex continues with a 150 degree curve.

Meandering has attracted the attention of scientists and engineers since a long time. In river bend, high variations of flow depth, velocity and shear stress across the river produce a spiral flow and hence, bank erosion in outer bank and sedimentation in inner bank. Such situation is very complicated in rivers with floodplains. In this condition, flood flow enters the floodplains and changes the direction of secondary flow because of momentum transfer between main channel and floodplains. In this paper, using a quasi-two dimensional mathematical model, the lateral distribution of velocity in overbank meandering rivers is simulated. This mathematical model combined with dimensionless relationships for secondary flow term is solved numerically in curvilinear system. The most important result of this research indicates that the maximum and minimum magnitudes of velocity are occurred in inner and outer banks, respectively, which is in the opposite sense with the flow structure at the inbank meandering channels. This finding agrees well with the experimental data in overbank meandering channels. Furthermore, the numerical results have higher accuracy compared with Ervine et. al. method. The mean relative error of proposed and Ervine et al. methods for predicting the main channel velocity are 6 and 10 percents, respectively.