In this study the effect of chute bed roughness height on energy dissipation has been investigated. First effective parameters were identified and then a general dimensionless relationship was developed. A series of tests were conducted by a physical model using the bed slopes of 25 and 35 degrees and four different uniform roughness heights (3. 38, 7, 12. 7 and 38. 1 mm) having uniform particle sizes on the bed. Total of 80 tests were conducted with flow discharges range between 4 and 40 L s-1 and Froude number between 4. 5 and 9. A relationship was developed for prediction of energy slope on this type roughened bed chutes and the results obtained were compared with the results of previous works. Energy dissipation per unit length of the roughened chute was 7 to 38% greater than that of the smooth chute (without roughness).

In this study the effect of chute bed roughness height on energy dissipation has been investigated. To do so first general non dimensional relationship was developed. Then series of experimental tests were conducted in a physical model using three different bed slopes (15, 22.5 and 30 degrees) and three different uniform roughness heights (1.1, 1.43 and 2.1 cm). Total of 48 tests were conducted with flow discharges ranged between 15 and 45 lit/sec. Results show that in comparison with the smooth bed, nearly 12 to 48 percent of the flow energy was dissipated on the roughened bed chute. Maximum energy dissipation occurred for slope of 22.5 degrees and the minimum energy was dissipated on 30 degrees chute. A relationship was developed for prediction of energy slope on this type roughened bed chutes and the results obtained were compared with the results of previous works.

Along with the numerous developments and facilities for constructing large dams, there is a need for developing design and construction methods for systems that can correctly discharge the floods. Weirs refer to any barrier across a channel that raises the flow level and accelerates the flow when flowing over it (Abrishami and Hoseini, 2011). Piano key weirs are the newest type of long-crest weirs and one of the best solutions for modifying the existing weirs. Reducing the energy of the flow over the weirs before their transfer downstream is a solution for preventing possible damage to the structure itself and downstream structures as well as the excess costs incurred by the builders of hydraulic structures due to constructing strong protective structures (Katourani, 2012). Lempè riè re and Ouamane (2003) described the piano key weirs and stated their advantages compared to other conventional nonlinear weirs as the ability to place the weir in the crest of the reservoir dam and thus increasing the specific flow rate. Erpicum and Machieles (2011) compared the energy dissipation between two different geometries for a piano key weir and a spillway weir. Concerning the application of a block, the tests and results obtained by the US Land Renewal Organization indicate that using large blocks that separate the flow jet and create turbulence can effectively dissipate the kinetic energy of the current...

Flow with intermediate relative roughness (the ratio of roughness height to water depth higher than 1/80 and lower than 1/40) is common in most of mountainous streams. Despite this fact and numerous studies on flow with intermediate relative roughness, it is still unclear that how profile of the streamwise velocity varies along water depth. In this study, instantaneous velocity of flow in an open-channel with rough bed has been measured using Particle Image Velocimetry (PIV). In order to analyze profile of streamwise velocity, double averaging method (spatial averaging of time-averaged values in a thin slab parallel to the channel bed) is used. It was observed that near the rough bed, vectors of instantaneous velocity showed strong spatial variations that makes extraction of unique behavior for velocity profile impossible without double averaging. Results also showed that values of double averaged velocity is not sensitive to priority in averaging (i. e. time and then spatial averaging or spatial and then time averaging),thus double averaging regardless of priority can be used. To investigate double averaged velocity profile, three approaches including logarithmic profile with variable parameter, linear profile and mixing layer profile were employed. Results showed that all three profiles could be fitted properly to our experimental data. However, logarithmic profile with variable Von-Karman constant and integration constant which is supported by strong scientific background is the most suitable profile and is therefore recommended.

In the present study, a solar air heater U shaped turbulators integrated on the absorber plate with artificial roughness has been subjected to computational fluid dynamics (CFD) analysis. For simulation, Renormalization group (RNG) k- ɛ model has been used to investigate several fluid flow properties such as flow behaviour, temperature distribution along absorber plate, and velocity distribution. By taking into account the relative roughness height (e/D) varies from 0.018 to 0.038 and a turbulence intensity of 5%, the aforementioned fluid flow properties have been investigated. Reynolds' number has a value varied in between 3800 to 18000. Also, it has been discovered that effective efficiency reaches a maximum value of around 0.7396 for relative roughness height of 0.038 at Reynolds' number of 16000. Further, results obtained from simulation suggested that there has been a considerable rise of about 22°C in temperature of air after passing through the roughened solar air heater.

In this research the effect of roughness for different bed slopes on the control of sedimentary density current in subcritical conditions was investigated. The results showed that for each bed slope increasing the roughness height had considerable effect on reducing the load discharge of density current front (from 40% to 70% for concentration of 10 g L-1 and 35% to 55% for concentration of 20 g L-1). Also the amount of water entrainment rate reduced with increasing the roughness height (from 50% to 60% for concentration of 10 g L-1 and 48% to 60% for concentration of 20 g L-1). Finally, an equation for predicting water entrainment as a function of Richardson Number and relative roughness was presented. Sensitivity analysis of the proposed equation in this research showed that the effect of Richardson number on estimation of the water entrainment is much more than the effect of relative roughness on it.

One of the most popular additive manufacturing techniques is called laser powder bed fusion. Several parameters are involved in this method and four of the most important factors are laser power, scanning speed, infill pattern angle, and hatch space. Change in this parameter has a direct effect on defects and fabricated parts quality. Post-processing treatment such as heat treatment was cared out in order to improve part property and applications. Built time and costs reduce significantly by suitable choice of process parameters and post-processing treatments. In this article genetic algorithm cared out to highest relative density and lowest surface roughness and best value of each parameter presented. The results showed that the best output could achieve by using 102-105 Watt of laser power, 623-630 mm.s-1 scan speed, 73-76 µm of hatch space, and 638-640 °C of heat treatment temperature.

In the present study, the aim is to investigate the effect of roughness and the change in their height and distance on the characteristics of the hydraulic jump in the downstream stilling basin of the ogee spillway. For this purpose, numerical simulation of the flow pattern and analysis of the geometric characteristics of the ogee spillway with the gate were performed using the Fluent software. The simulation method used in this study is the volume of fluid (VOF) method, which is used to model multiphase flows. The results showed that the use of roughness in the channel bottom has a significant effect on reducing the length and secondary depth of the hydraulic jump. In particular, with increasing roughness height, the ratio of secondary depth to primary depth decreases, which is due to the shortening of the hydraulic jump length and the closer proximity of the primary and secondary depths due to the flow encountering the roughness. On the other hand, increasing roughness height leads to greater flow deflection in the channel bottom. Based on the results, the best spacing for the roughness’s is 2 cm between them, which provides optimal performance in terms of reducing the hydraulic jump length and regulating the flow. The results clearly show that changes in the roughness parameters, especially their height and spacing, play an important role in improving the performance of the stilling basin and controlling the hydraulic jump.

Identifying the constraining factors of production and yield gap is very important. Therefore; this research was performed to identify the production constraining factors of local rice cultivars. All management practices from nursery preparation to harvesting stages for 100 paddy fields of local rice cultivars were recorded through field studies, in Sari, from 2015-2016. In the CPA, the actual and calculated potential yield were 4495 and 5703 kg/ha, respectively and the gap was 1221 kg/ha. The yield gap caused by number of top-dressing variables was 324 kg/ha, equal to 27% of the total yield gap. The yield gap related to previous year of legumes cultivation was 218 kg ha-1, equal to 18% of the total yield variation. Among the 10 variables entered in the CPA model, the effects of top-dress fertilizer application and its application frequency and foliar application were remarkable, which could compensate a significant part of the yield gap (444 kg/ha, 37% of total) in the farmers’ fields by managing these variables. According to boundary line analysis (BLA) finding, actual yield mean on the basis of optimal limit related to 12 variables under study was 5369 kg/ha, with 881 kg/ha yield gap . Mean relative yield and relative yield gap for 12 variables (transplanting date, seedling age, number of seedlings per hill, planting density, nitrogen and phosphorous per hectare, nitrogen before transplanting, harvesting date, lodging problem, pest problem, diseases problem and weeds problem) were 83.64 and 16.35 kg/ha, respectively. Based on the finding, it can be stated that the model precision is appropriate and can be applied for both estimation of the quantity of yield gap and determining the portion of each restricting yield variables.

In all river engineering projects, determination of flow resistance is essential. Most commonly, the Manning roughness coefficient, n, is used to describe the flow resistance or relative roughness of main channel or flood plane. Over the past decades little or no study has been conducted to investigate the effects of particle shapes on Manning roughness coefficient. Therefore, it is the purpose of this study to see how and by what extend, the particle shape can affect the Manning’s coefficient. To do so three different sediment shapes (angle rounded particles and crushed particles and spherical artificial particles); each in 11 different sizes were collected and tested under different flow conditions. Tests conducted in a flume of 10 meter long, 25 cm wide, 50 cm height and constant bed slope of 0.0005. The results show that the effect of particle shape in larger particle size is less compare to the smaller particle size. As in sediments with size of 11 mm, values of Manning roughness coefficient (n) for sediment particles shows great difference and in 21mm and 27mm sediment particles, the Manning roughness coefficient (n) in angle rounded and spherical artificial particles are equal nearly as the average difference between Manning's coefficient (n) of these particles are found to be in the order of +1.65 percent and values of Manning roughness coefficient (n) for crushed particles in 21mm and 27mm sediment particles shows little difference with other sediment particles. The average difference between Manning's coefficient (n) of crushed particles with natural rounded particles are found to be in the order of -6.2 percent.