M.M. Heidari; S. Kouchakzadeh
Abstract
Introduction: Determination the hydraulic performance of an irrigation network requires adequate knowledge about the sensitivities of the network structures. Hydraulic sensitivity concept of structures and channel reaches aid network operators in identifying structures with higher sensitivities which ...
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Introduction: Determination the hydraulic performance of an irrigation network requires adequate knowledge about the sensitivities of the network structures. Hydraulic sensitivity concept of structures and channel reaches aid network operators in identifying structures with higher sensitivities which will attract more attention both during network operation and maintenance program. Sluice gates are frequently used as regulator and delivery structures in irrigation networks. Usually discharge coefficient of sluice gate is considered constant in the design and operation stage. Investigation of sensitivity of offtakes and cross-regulators has carried out by various researchers and some hydraulic sensitivity indicators have been developed. In the previous researches, these indexes were developed based on constant coefficient of discharge for free flow sluice gates. However, the coefficient of discharge for free flow sluice gates depend on gate opening and the upstream water depth. So, in this research, some hydraulic sensitivity indicators at structure based on variable coefficient of discharge for free flow sluice gates were developed and they were validated by using observed data.
Materials and Methods: An experimental setup was constructed to analyses the performance of the some hydraulic sensitivity. The flume was provided with storage reservoir, pumps, electromagnetic flowmeter, entrance tank, feeder canal, delivery canals, offtakes, cross-regulators, collector reservoir, piezometric boards. The flume is 60.5 m long and the depth of that is 0.25 m, of which only a small part close to offtake and Cross-regulators was needed for these tests. Offtakes and Cross-regulators are free-flowing sluice gates type. Offtakes were located at distances 20 m and 42.5 m downstream from the entrance tank, respectively. and, Cross-regulators were located 2 m downstream from each offtakes. The offtakes are 0.21 m and Cross-regulators are 0.29 m wide. The upstream and downstream water levels at gates were measured with piezometer taps. There is a collector reservoir downstream of each delivery canal that was equipped with a 135 V-notch weir as a measuring device. The flow was provided by a pump having maximum capacity 35 lit/s, and was measured by an electromagnetic flowmeter of 0.5% accuracy. The suction pipe of the upstream pump was connected to the storage reservoir and its discharge pipe delivered the water to an entrance tank located at the upstream side of the flume. The entrance take was equipped with a turbulence reduction system. Measured water entered to feeder canal and, after adjusting water depth by Cross-regulators, it moved to offtakes and the brink of the feeder canal. Underneath the downstream end of the feeder canal and delivery canals, a tank was installed to collect the water. Water accumulated at the collector tanks was pumped to the storage reservoir by using a pump to complete the water circulation cycle.
Results and Discussion: Discharge coefficient is the most important parameter that is effect on hydraulic indicators sensitivity. Therefore, coefficient of discharge for free flow sluice gates determined based on experimental data. Sluice-gate discharge coefficient is a function of geometric and hydraulic parameters. For free flow, it is related to upstream depth and gate opening. In this study, analytical relationships for various sensitivity indices for channel reach were developed, and the performance of the proposed relationships was verified with experimental data compiled during this research. It was shown that using constant discharge coefficient yields average error in the calculated sensitivity of the water depth upstream regulator to the inlet flow, and average error of calculated reach sensitivity indicator, as 16.6% and 5.8%, respectively. While those values for variable coefficient was 5.7% and 1.9%, respectively. Also, for 20% variation in reach inflow, the variable coefficient improved the calculated mean flow depth error upstream of a regulator drastically, i.e. the mentioned error using constant coefficient was 17% while that of variable one was 4.3%
Conclusion: In this research, Analytical relationships based on using variable discharge coefficient for Three sensitivity indicators for a canal reach, i.e. reach sensitivity indicator of water depth, reach sensitivity indicator for conveyance and delivery developed. Comparing reach canal sensitivity indicators and the structural sensitivities, i.e. sensitivity of delivery of offtake to absolute water depth deviation and water depth sensitivity to the discharge for regulator with experimental data, showed good agreement. Hence, the technique proved to be reliable in providing what is necessary for practical canal.
M.M. Heidari; S. Kouchakzadeh
Abstract
Introduction: Unsteady flow in irrigation systems is the result of operations in response to changes in water demand that affect the hydraulic performance networks. The increased hydraulic performance needed to recognize unsteady flow and quantify the factors affecting it. Unsteady flow in open channels ...
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Introduction: Unsteady flow in irrigation systems is the result of operations in response to changes in water demand that affect the hydraulic performance networks. The increased hydraulic performance needed to recognize unsteady flow and quantify the factors affecting it. Unsteady flow in open channels is governed by the fully dynamic Saint Venant equation, which express the principles of conservation of mass and momentum. Unsteady flow in open channels can be classified into two types: routing and operation-type problems. In the routing problems, The Saint Venant equations are solved to get the discharge and water level in the time series. Also, they are used in the operation problem to compute the inflow at the upstream section of the channel according to the prescribed downstream flow hydrographs. The Saint Venant equation has no analytical solution and in the majority cases of such methods use numerical integration of continuity and momentum equations, and are characterized by complicated numerical procedures that are not always convenient for carrying out practical engineering calculations. Therefore, approximate methods deserve attention since they would allow the solution of dynamic problems in analytical form with enough exactness. There are effective methods for automatic controller synthesis in control theory that provide the required performance optimization. It is therefore important to get simplified models of irrigation canals for control design. It would be even more interesting to have linear models that explicitly depend on physical parameters. Such models would allow one to, handle the dynamics of the system with fewer parameters, understand the impact of physical parameters on the dynamics, and facilitate the development a systematic design method. Many analytical models have been proposed in the literature, Most of them have been obtained in the frequency domain by applying Laplace transform to linearized Saint-Venant equations. The got transcendental function can then be simplified using various methods to get a model expressed as a rational function of s (the Laplace variable), possibly including a time delay. It is therefore important to develop simple analytical models able to accurately reproduce the dynamic behavior of the system in realistic conditions.
Materials and Methods: Changes in water demand can create transient flow in irrigation networks. The Saint Venant equations are the equations governing open channel flow when unsteady flow propagates. In this research, the finite volume method using the time splitting scheme was employed to develop a computer code for solving the one dimensional unsteady flow equations. Considering stationary regime and small variations around it, the Saint-Venant equations around initial condition was linearized.
The Laplace transform is applied to the linearized saint venant equations, leading to an ordinary differential equation in the space variable x and parameterized by the Laplace variable s. The integration of this equation lead to a transfer matrix, and gives the discharge Q*(x, s) at any location with respect for the upstream discharge. This matrix is coupled with the downstream boundary condition and developed an equation that solved using Simpson integration algorithm. It should be noted numerical solution of developed equation is easier than solving fully dynamic saint venant and is less sensitive to the spatial step and the researcher simply writing code.
Results and Discussion: Froud Number (F), variation of inflow discharge (ΔQ/Q), and dimensionless parameter of KF2 in which K is the kinematic flow number, are effective factors on accuracy of developed equation. In order to determine the effect of the factors on accuracy of presenting formula, several simulations were performed using numerical model. The presented formula and numerical model were compared for 10, 20 and 30 percent discharge variation and error calculated, the maximum error increases with increasing ΔQ/Q.
To assess the importance of Froud Number and KF2, also several simulations were carried out, the results showed that the maximum error in the development equation for various Froud Number and KF2>1, is less than 3.8 percent.
Conclusion: Using Laplace transform to the saint venant equations and with respect to upstream and downstream boundary a formula for routing discharge presented. Investigation of the applicability range of presenting formula and cognitive effective factors on accuracy is necessary. So, the finite volume method using the time splitting scheme was employed to develop a computer code for solving the one dimensional unsteady flow equation. Then some tests of unsteady flow were simulated and verified the equations. The results showed that the maximum error increases with decreasing KF2 and increasing the rate of sudden changes of discharge. The maximum error in the presented formula for all tests with KF2>1, less than 3.8 percent.
M. Bijankhan; S. Kochakzadeh
Abstract
Abstract
Accurate water measurement and delivery are basic issues in irrigation networks management and performance. In this regard, baffle modules have been considered as appropriate means for delivering almost constant discharge within a specific range of upstream water variation. The structure is ...
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Abstract
Accurate water measurement and delivery are basic issues in irrigation networks management and performance. In this regard, baffle modules have been considered as appropriate means for delivering almost constant discharge within a specific range of upstream water variation. The structure is meant for low discharge delivery and could be employed in farm irrigation. However, the design criteria still requires further improvements. In this paper, the hydraulic sensitivity concept was used to provide two design methods for a 2 baffles module. The results of the first method presented a structure with -13.62% deviation of design discharge. While the second method resulted in a design criteria for baffle sluice module with only 2 baffles which its performance is similar to a 3 baffles one.
Keywords: Baffle modules, Hydraulic sensitivity, Intake, Water measurement structure, Performance improvement
