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Study on the physics of sediment particle movement in micro scale is essential for better understanding sediment transport phenomenon and estimating the rate of sediment transport in rivers and marine environment. Sediment particles basically transport in two modes of bed and suspended load. Bed load takes place through sliding, rolling and saltation. Many parameters influence on this process, which their effects are not fully understood. In this research the influence of the affecting parameters on movement of sediment particles in saltation under unidirectional steady flow are investigated. First, a numerical model is developed to simulate the particle motion in bed load saltation. Then the influencing parameters such as particle shape and its position between other particles, upon the jump length and average velocity of the particles are studied. The result of the study improves our understanding and results in better estimation of sediment transport rate for engineering application.

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In this study, a two-dimensional, axisymmetric, computational Algorithm has been developed to simulate the plasma flowfield in a MPD thruster for the purpose of determining the flow behavior and electromagnetic characteristics distribution. The solution employs Roe’s flux vector difference method in combination with Powell’s characteristics-splitting scheme. To ensure the stable high-accuracy solution, new modification of MUSCL technique so called OMUSCL2 method is used. According to being supersonic strong gasdynamic expansion near the electrodes tip, HHT entropy correction is employed. Further improvements to the physical model, such as the inclusion of relevant classical transport properties, a real equation of state, multi-level equilibrium ionization models, anomalous transport, and multi-temperature effects, that are essential for the realistic simulation MPD flows, are implemented. Numerical results of a lab-scale thruster are presented, whereby comparison with experimental data shows good agreement between the predicted and measured enclosed current and electric potential.

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Study on the physics of sediment particle movement at grain scale is essential for better understanding sediment transport phenomenon and estimating the rate of sediment transport in rivers and marine environment. Sediment particles basically transport in two modes of bed and suspended load. Bed load takes place through sliding, rolling and saltation, from which the latter is dominant. Many parameters influence on saltation phenomenon, which their effects are not fully understood. These influencing parameters make the saltation a stochastic phenomenon. In the present article the influence of the affecting parameters on movement of sediment particles at saltation mode of transport under unidirectional steady flow are investigated. A numerical model is developed to simulate the particle motion in bed load saltation with considering the main contributor forces. Then the influencing parameters that effect on the jump length and average velocity of the particles are studied. Among them are the initial condition, the particle position between other particles and the shape of particles. The influence of the velocity profile on the jump length and average velocity of the particles are also studied. In summary, the change in the initial condition including the initial velocity and angle produces less than 10% variation on the particle jump length and velocity. On the other hand the position of the grain between the other particles is considerably influential with 40% change in the jump length and average velocity. The particle shape is most important parameter in term of the influence on the jump length and average velocity; there is a 50% difference between the jump length of spherical particles and flake-shape particles, for average velocity it is about 10%. The result of the study improves our understanding of particle motion at grain scale and ultimately results in the better estimation of sediment transport rate. 

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As the coefficient of performance and the cooling power of adsorption chillers are low, the irreversibility calculation can identify the sources which limit the increase of performance parameters and effectively be used in association with current performance improvement techniques. Adopting the numerical modeling and calculating the temporal distribution of temperature in adsorber elements, this study measures the exergy destruction in different parts and processes of the adsorbent bed. The results show the maximum exergy destruction rate in isosteric phases, yet the total exergy destruction is low due to the short phase times. The highest total exergy loss is observed in isobaric heating phase due to the high irreversibility of desorption process and also long phase duration. Furthermore the effects of fin height and fin spacing on the exergy destruction of adsorbent bed are investigated. The results show that increasing fin height and fin spacing increase the total exergy destruction; however the dependency of fin spacing on exergy destruction is relatively low.

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Due to the extreme increase in computational power over the recent years, numerical methods have gained the most proportion in analyzing composite structures and components because of the consideration complicated failure mechanisms such as delamination, fiber buckling and fiber breakage, matrix cracking, debonding ribs of skin and a combination of mentioned failure mechanisms. However exact three - dimensional modeling damages caused by impact phenomena is still a challenge. In present numerical work, the most advanced modeling techniques have been used to predict the behavior of composite structure under high velocity impact. The ribs and layers have been modeled using solid elements and a user defined material model with modified puck and Hashin (3D) failure criteria was implemented. Because these failure criteria do not exist in Commercial version of the Abaqus software, we have used Fortran software for writing these criteria so this capability was added to the software. Figures of velocity variations and force variations of projectile, damaged area, different mechanisms of fracture were reported as results and commented upon. In this study, The numerical results have been validated with experimental data and show very good agreement.

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Anchors play a special role in geotechnical structures such as excavations. The anchor section in soil is generally divided into five zones including reinforcement element, grout, grout and surrounding soil mixture, shear zone and soil media. The main objective of the present research is to determine the soil-anchor interaction parameters for numerical modeling of anchored wall using FLAC2D software. Basically, the injection area determining is the main challenge in the anchor force nomination. According to the proposed method, the diameter of the injected area is determined based on the injection pressure, grout volume, porosity and shear zone thickness. It is shown that the diameter of the injected area is approximately increased by 40% relatively to the drilling diameter. The diameter of the injected area in rock media, however, is equal to the drilling diameter. The other parameters are determined using equalization of rock media formulas for soil media. In order to ensure the validity of the proposed method, the pull-out test is numerically simulated in FLAC2D software. The numerical results have been then verified with anchor tension results in an excavation project. The results indicate that ultimate load of anchor calculated from the numerical model is comparable with equations proposed by many researches. Also, there is a negligible difference between the displacement obtained in numerical simulation and pull-out test results. This method is therefore can be used in numerical modeling of anchored wall in soil media with high precision. Anchors play a special role in geotechnical structures such as excavations. The anchor section in soil is generally divided into five zones including reinforcement element, grout, grout and surrounding soil mixture, shear zone and soil media. The main objective of the present research is to determine the soil-anchor interaction parameters for numerical modeling of anchored wall using FLAC2D software. Basically, the injection area determining is the main challenge in the anchor force nomination. According to the proposed method, the diameter of the injected area is determined based on the injection pressure, grout volume, porosity and shear zone thickness. It is shown that the diameter of the injected area is approximately increased by 40% relatively to the drilling diameter. The diameter of the injected area in rock media, however, is equal to the drilling diameter. The other parameters are determined using equalization of rock media formulas for soil media. In order to ensure the validity of the proposed method, the pull-out test is numerically simulated in FLAC2D software. The numerical results have been then verified with anchor tension results in an excavation project. The results indicate that ultimate load of anchor calculated from the numerical model is comparable with equations proposed by many researches. Also, there is a negligible difference between the displacement obtained in numerical simulation and pull-out test results. This method is therefore can be used in numerical modeling of anchored wall in soil media with high precision.

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Large amount of diesel engine waste heats make researchers design systems that utilize the engine waste heat to provide the cooling demand of the heavy-duty vehicles and improve the engine efficiency. Considerable advantages of adsorption cooling system lead to be nominated for this purpose. Coolant and exhaust gases are the main sources of waste heats of diesel engines and using each of them to drive the adsorption cooling system requires its own equipment and working pair. In this paper, a detailed numerical model has been developed and to examine the performance of the cooling system driven by the coolant waste heat with working pair of silica gel-water and also driven by exhaust waste heat with zeolite13x-water working pair. An identical absorbent bed and ambient conditions have been employed to compare the performance of both systems to identify the more appropriate system. The results show that exhaust driven adsorption cooling system has more capability to meet the vehicle cooling demand. Moreover, the performance of the both adsorption cooling systems were examined under variable ambient condition. Results indicate that increase in ambient temperature leads to almost a linear performance drop in both systems that is more considerable in the coolant- driven adsorption system.

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In the present study, for the first time, adsorbent bed of SWS-1L/water adsorption chiller with rectangular and trapezoidal finned flat-tube heat exchanger with has been simulated three dimensionally based on the distributed parameters model and finite volume method. Effects of some important parameters on the chiller performance such as bed averaged pressure, temperature and uptake variations with cycle time have been examined for better understanding of bed dynamic behavior. Also, a comparative study between two different configurations of adsorbent bed including rectangular and trapezoidal fins has been conducted based on identical adsorbent mass. For this purpose, bed temperature, uptake and pressure distributions as well as the vapor flow patterns at the end of heating cycle phases and also effects of fin height and spacing on the system performance have been studied. In this investigation at fixed bed length of 20mm, fin height and spacing variations have been examined in the range of 8-20mm and 3-12mm, respectively. Results indicated that the system performance with rectangular and trapezoidal adsorbent beds are almost similar except for those conditions which fin spacing is 3mm and fin height are 14, 20mm. For the mentioned dimensions, the specific cooling power (SCP) of rectangular beds are almost 5% and 17% (for fin heights of 14 and 20mm, respectively) better than those of trapezoidal beds. Maximum and minimum SCP of adsorption chiller with flat-tube heat exchanger were obtained about 882 and 163W/kg for the smallest and the largest bed geometry and operating conditions considered in this study.

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In this paper, flexural behavior of composite sandwich beams under four point bending loading has been studied experimentally and numerically. The skins and the core of the sandwich composite beam have been made of woven glass/epoxy composites and polyvinylchloride foam with 70 kg/m3 density, respectively. The experiments were performed on the beams with different lengths and two different types of layup sequence for the skins as 0/90 and ±45. Failure was initiated in the beams due to indentation of the foam and extended to the face sheet failure under the loading roller. Numerical simulation of the sandwich beam has been performed using ABAQUS commercial software to verify experimental results. During the numerical simulations, the nonlinear material models were employed for shear stress-strain behavior modeling of the foam and the face sheets. In addition, due to the large deformation during bending test geometrical nonlinearity assumption was used in FE analysis. Failure initiation was predicted in the face sheets using modified Hashin criteria. Nonlinear stress analysis and failure predictions in the face sheets and the foam were conducted using USDFLD subroutine in ABAQUS software. Also crushable foam model was employed to simulate the plastic behavior of the foam core. The load-displacement curves and failure mechanisms predicted by the numerical simulations illustrated good correlation with the experimental data.

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In the present study, adsorbent bed of an adsorption chiller with finned flat-tube heat exchanger has been simulated three dimensionally based on the heat and mass transfer model with finite volume method. To examine the inter-particle mass transfer resistance effects on the system performance parameters, two different configurations of adsorbent bed including rectangular and trapezoidal fins with identical length and adsorbent mass have been considered and the effects of bed length on the system performance for different fin height and fin pitch have been studied. Moreover, effects of bed length for different particle diameters and also heating source temperatures have been investigated. Results indicated that increasing of bed length (or in the other words increasing of inter-particle resistance) increases and decreases cycle time and specific cooling power, respectively, yet the coefficient of performance is not influenced. Also, increasing bed length reduces the difference between specific cooling power of rectangular and trapezoidal beds if there is any. Moreover it is clear that optimum particles size increase with bed length increase. Finally, it is shown that effect of higher heating fluid temperature on specific cooling power improvement for beds with smaller length is more significant than those with longer length.

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This study, deals with the investigation of the accuracy and performance of a novel method for simulation of oscillating wave surge converter (OWSC). The OWSC is an instrument with one degree freedom mounted in near shore areas which oscillates back and forth. This device is used to harvest sea wave energy. The developed model is based on the well-known volume of fluid (VOF) method. Due to the nature of the OWSC motion, the VOF method in conjunction with unstructured dynamical grid mesh has been used in the literature. But in this study, a structured grid mesh is employed which facilitates the numerical preparation and the speed of simulation process. The results are compared with the experimental data and the results of numerical method in the literature by dynamical grid mesh. This comparison shows the high accuracy of the developed model in this study. The model validation is performed in an extreme condition with steep waves which need an accurate numerical scheme. The external forces including power take off (PTO) forces are also simulated. The capture factor, energy absorption condition and the effect of PTO on angle, angular velocity and slamming of the OWSC are also investigated. Finally, the effect of wave height and the PTO stiffness on the capture factor and absorbed energy by the OWSC for waves with a specific period are investigated.

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This paper presented a numerical modeling of dew-point counter-flow indirect evaporative coolers as a potential alternative to the conventional cooling systems. Unlike the conventional method of assuming constant surface heat (mass) flux or constant surface temperature boundary condition on the separating wall, the present article calculated real boundary conditions. Real boundary conditions were obtained by simultaneous solving of momentum, energy and mass transfer equations of the two flows coupled on the wall. Calculating real boundary conditions lead to a real distribution of humidity ratio and temperature on the separating wall where at each point, the summation of heat fluxes from air streams in adjacent channels is equal to the latent heat of evaporation at that point. Moreover, the model accuracy was increased through considering hydrodynamic and thermal developing flows of two air streams. The model predicted supply air temperature under different conditions, and the results were compared against experimental data as well as previous numerical models. It was shown that the maximum deviation of the supply air temperature was under ±3.3%. Then, a parametric analysis was conducted, which studies the effects of the inlet air velocity, channel gap, channel length and returned air ratio on the supply air temperature, dew-point effectiveness, cooling capacity and pressure drop. The results indicated that increasing channel length and returned air ratio, and reducing channel gap and inlet air velocity improved the dew-point effectiveness but increased the initial cost and pressure drop and decreased the cooling capacity.

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Applying an Electric potential between two electrodes with different thicknesses will cause corona discharge if the electric field around the corona electrode is strong enough to ionize the surrounding gas and weak enough to avoid arcing. Corona discharge used to be known as an unpleasant phenomenon but it has lots of applications today including the ionic thrusters. In this research, the specifications of the flow resulted from corona discharge such as velocity, thrust, and temperature, electric current, flow streamlines and thrust effectiveness have been numerically studied. To do so, the electrostatic and Navier-Stokes equations have been coupled and solved by finite element method (FEM) using the COMSOL Multiphysics software version 5.2.Data validation shows that the maximum errors between the numerical and experimental results in computing thrust, current and thrust effectiveness are respectively below 2%, 14% and 6%. Also the results show that with rising the applied Voltage, the resulted thrust and electric current will increase and the thrust effectiveness decreases. Furthermore, by considering the effect of Ohmic heating in the energy equation, it has been found that the maximum temperature raise happens around anode.

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Determination of soil engineering properties such as shear strength is essential to analysis many geotechnical problems. Therefore, determination of the reliable values for this parameter is very important. For this purpose, direct shear test as one of the oldest test to examine the shear strength of soils, is conducted on soil samples. There are too many factors which could affect results of direct shear test. Laboratory tests are expensive, difficult and time consuming, hence using numerical method to simulate experimental test and study effective factors could be useful. In this paper direct shear test was numerically modeled using CA2 hybrid finite element-discrete element method code. CA2 solves explicitly equations of motion together with macro or micro-constitutive equations. In this study, shear box is modeled using finite element grids and a discrete element model is implemented for simulation of soil specimen within the box. Appropriate boundary conditions are assigned to the box, normal stress is applied to the specimen using finite element grid and shear velocity was finally applied to the model. Shear force is applied to the model by a constant velocity 4.5×10-9 meter/cycle. It should be noted that, shear velocity is applied to the upper part of shear box, and applied velocity is considered small enough to confirm that there is a quasi-static condition in numerical solution. In this study using numerical simulation, the effects of box dimension, genesis pressure, normal stress, shear velocity and box wall friction on shear strength of the soil specimen are investigated. Study of box dimension effect, shows that peak effective internal friction angle in small direct shear box and large direct shear box differs about 6°, and cohesion decreases by increasing box dimension but for box dimensions bigger than 20cm, changes in box dimension has no significant effect on resulted soil cohesions. Investigation of influence of genesis pressure shows that, incrementing genesis pressure, cohesion increases too, that can be attributed to the SOCPI model provided in CA2. In SOCPI model by increasing genesis pressure the overlap between cylinders increases. In SOCPI model by increasing overlap the cohesion increases but peak friction angel doesn’t change too much. Normal stress analysis shows that, increasing normal stress, interlocking between soil particle increases and more interlocking causes increasing cohesion of the soil model. Shear velocity is another parameter which is studied in this research. Results show that by increasing shear velocity, soil shear strength increases. It should be mentioned that shear velocity should be considered as small enough to result in a quasi-static solution; for velocity smaller than that model run time increases ineffectively. In this research, friction of shear box wall as one of the important parameters in study of soil shear strength is also investigated. When there is friction between box wall and soil particles, shear strength can be underestimated for contractant soils or overestimated for dilatant soils. In this paper, it is shown that if soil has no significant volume changes, peak shear strength is not affected by friction between soil particle and box wall.

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Studies have shown that compressible materials between a rigid retaining wall and backfill reduced static and dynamic forces on the wall. Nowadays, panels with low density are used. Expanded polystyrene, which is one of the geo-synthetic products known as geofoam, is a compressible material. Geofoam is one of the geo-synthetic materials that are made of foam. Geofoam is very practical in geotechnical engineering due to its low bulk weight versus soil bulk weight and high compressibility, rapid and simple implementation, thermal insulation, and resistance against water absorption. It can be used in retaining walls, road construction projects as light fillers, and to reduce stress due to vertical loads in the base and sub base layers. Geofoam is one of the geosynthetic product which is made of lightweight expanded polystyrene (EPS) or extruded polystyrene (XPS). EPS geofoam is a block or planar rigid cellular foamed polymeric material that can be used in geotechnical applications. Studies have been shown that geofoam placed directly against a rigid retaining wall can reduce static loads on the wall. This study employed a finite difference method program, FLAC (Itasca, 2007), with considering yielding and non-yielding states for retaining walls to evaluate the effectiveness of geofoam panels in improving the statically behavior of retaining walls. To determine the effects of geofoam in soil displacement and earth force acting on the rigid wall, parameters such as the height of retaining wall, density and thickness of geofoam, cross-sectional shape of geofoam panel behind the wall, and also using of two geofoam panels with four panel spacing (50, 100, 150, 200 cm) have been studied via static analysis. In this numerical study three gravity –type retaining walls at heights of 3, 6 and 9 meters and geofoam panels with densities of 15, 20 and 25 (kg/m3) at three relative thicknesses of t/H=0.05, 0.2 and 0.4, were modeled. According to the results using of EPS15 with density equal to 15(kg/m3) which has the lowest density among other geofoam panels has a significant role in reducing of lateral stresses. Although the performance of geofoam in non-yielding retaining walls is better than yielding retaining walls. The results of the present research are as follows: 1- According to results, increasing the geofoam thickness increases soil lateral displacement and reduces forces on gravity retaining walls. The same effect can be achieved by reduction of geofoam density with equal thickness. In other words, Forces on gravity retaining walls are reduced and soil lateral displacement is increased by a reduction of geofoam density with equal thickness. 2- Using two geofoam panels with distance of 50 cm, unlike 3-meter high wall, is proper in the 6 and 9 meters yielding retaining walls. 3- Trapezoidal geofoam increases soil lateral displacement and reduces forces on retaining walls compared to a rectangular geofoam panel with the same cross-sectional area. 4- Effect of geofoam on the reduction of forces on non-yielding gravity retaining walls is more than that on yielding walls. 5- According to results, stiffness of geofoam panel (K=E/t) has significant role in reducing of lateral forces acting on retaining walls. In this study, it was observed that K≤5 MN/m3 provide the most effective range for the design of these system to reduce static forces acting on yielding retaining walls.

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Layer structure of rural roads under heavy traffic has essential importance because of simultaneous observing of economic and technical issues. In this study with investigating a case study of a rural road, different structure models of layers a road under traffic Agricultural trailers have been investigated. To identify different models of the road of structure-traffic index (STI) is used. At first, it is specified that 12 wheels trailers with tridem axle have more destructive effect on the pavement relation to 18 wheels trailers with tandem axle, by the modeling of finite element software ABAQUS; and the Scania G400 placed for the base calculation as a critical trailer. Then different road models is investigated separate for fatigue and rutting distress under crossing of critical trailer. The modeling critical trailer load on the different road models show that there is a Exponential relationship between STI index and fatigue and rutting distress with acceptable accuracy. This relationship is indirect for the fatigue distress with changes constant equal to 13.76. In contrast, this relationship is direct for the rutting distress with changes constant equal to 135.31 that show rutting has more influence of STI index changes relation to fatigue. Also in this study, it is tried to investigate different layer efficiency of pavement in reducing agents related with rutting and fatigue damage that the most important matter is remarkable effect cold asphalt on the rutting reducing so that even cold asphalt layer is more effective to reduce rutting distress parameter relation to sub base and base layers with together. Layer structure of rural roads under heavy traffic has essential importance because of simultaneous observing of economic and technical issues. In this study with investigating a case study of a rural road, different structure models of layers a road under traffic Agricultural trailers have been investigated. To identify different models of the road of structure-traffic index (STI) is used. At first, it is specified that 12 wheels trailers with tridem axle have more destructive effect on the pavement relation to 18 wheels trailers with tandem axle, by the modeling of finite element software ABAQUS; and the Scania G400 placed for the base calculation as a critical trailer. Then different road models is investigated separate for fatigue and rutting distress under crossing of critical trailer. The modeling critical trailer load on the different road models show that there is a Exponential relationship between STI index and fatigue and rutting distress with acceptable accuracy. This relationship is indirect for the fatigue distress with changes constant equal to 13.76. In contrast, this relationship is direct for the rutting distress with changes constant equal to 135.31 that show rutting has more influence of STI index changes relation to fatigue. Also in this study, it is tried to investigate different layer efficiency of pavement in reducing agents related with rutting and fatigue damage that the most important matter is remarkable effect cold asphalt on the rutting reducing so that even cold asphalt layer is more effective to reduce rutting distress parameter relation to sub base and base layers with together.

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In this paper a modified Godunov-type wave propagation algorithm is utilised for the modelling of falling water wave over a dry bed. The defined numerical model is well-balanced and is capable to treat the influx/efflux source terms and also the friction term within the flux-differencing of the finite volume neighbouring cells. Additionally, the method employs a rather simple HLLE wave speed for the propagation over dry-state. First the efflux flow from the bed of a reservoir is analyzed. Then, the entrance of falling water wave from the middle and edge sides of the reservoir over a dry bottom is simulated. In order to validate the achieved numerical results for the non-hydrostatic pressure situations a dimensionless number based upon the inflow velocity, the slot length and the falling height is introduced. The obtained results of the defined numerical solver are then compared with the numerical prediction of the STAR-CD which is a commercial Navier-Stokes package. The numerical results demonstrate that the introduced flux-wave solver is able to simulate the falling water waves over the dry-state for a given range of the dimensionless number.

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In this paper, the issue of heat transfer in three-dimensional solid objects, a special form with cylindrical geometry, is investigated using the numerical finite element method by the commercial software Abaqus. Heating and cooling in food processing are common activities, heating food for a variety of purposes such as reducing microbial aggregation, inactivating enzymes, reducing the amount of nutrient water, modifying the functional properties of a particular compound, and cooking when heat transfer is performed. It plays a central role in all these operations. In this paper, a cylindrical geometry specimen with a temperature of 200 °C is used to investigate the temperature variations of potatoes in high-temperature oil. The results of numerical modeling of potato slices in high-temperature oil show that the rate of changes in the edges of the model is higher than in other parts of the model, which is a factor for the burns of potato edges. Also, the temperature variations in the center of the model have the lowest changes in the logarithmic distribution of heat transfer in the cylinder radius. In addition, with the increase in an exposure time of potato samples in high-temperature oil, almost all models reach the same temperature conditions.

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One of an effective and economical solution in order to weir efficiency is using nonlinear weirs, Which can cause  the increase of the flow over weir by changing in geometric plan and increasing in weirs length in fixed widths of the channel . in this research, the hydraulic performances of  the piano-key weirs has been simulated by FLOW-3D and also it has been validated by the laboratory data. In the following, the discharge coefficient (C_d) has been measured and evaluated with the creation of single and double circular orifice on the heel of weir ( , For the different water head and in relation to without dimension parameters    .
Findings shown with the expansion orifice diameter, discharge coefficient of combined weir -with the maximum opening  - is increasing between 0.5 to 6% in comparison to without orifice piano-key weir., besides, with the rise in the high of single orifice ,which has a fixed diameter, the discharge coefficient is reducing between 0.5 to 3%. From the other side, the usage of double orifices decreases the discharge coefficient in comparison to the single type at the same opening size, in a way that by increase in the distance of orifices, at first, it faces to the rising trend and then by reaching to   it starts revising. Finally, an equation is provided for the estimation of the discharge coefficient by benefiting without dimension parameters with   .