Session 3. Hydraulic Design and Analysis of Microirrigation Systems (I)
An Improved Finite Element Model for the Analysis of Microirrigation Systems
V. F. Bralts, P. J. Gerrish and R. Yue
An interactive microcomputer program which uses the finite element method to analyze the hydraulic design of microirrigation systems was developed. A partial differential equation was developed which satisfies the conservation of mass in a generalized pipe element. The finite element method was then used to solve the partial differential equation. The virtual node concept was used to modify the "DESIGNER" software to allow the analysis of large, 10,000 or more emitter, microirrigation systems in a fast, efficient and accurate manner.
Keywords: Microirrigation, Finite element, Hydraulics
Abstract taken from paper found on pages 60 to 67 in Proceedings of 5th International Microirrigation Congress, April 2-6, 1995, Orlando, Florida. American Society of Agricultural Engineers, 2950 Niles Road, St. Joseph, Michigan 49085-9659, USA. Phone: 616-429-0300 FAX: 616-429-3852 EMAIL: HQ@ASAE.ORG
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Computer Modeling and Simulation of Microirrigation Subunits
J. Rodrigo and F. Bonnet
A mathematical model has been developed to calculate emitter flow rates in a microirrigation subunit using the Darcy-Weisbach formula with the Colebrook equation to determine head losses. The installation of the emitters is stochastically simulated assuming a normal distribution for the manufacturer's coefficient of variation of the emitters. Both the mathematical model and the stochastic system have been developed using QuickBasic software and is designed for maximum flexibility to allow its use in rectangular and non-rectangular subunits with uniform and non-uniform slopes. The program can be used to calculate empirically the emitter flow rates and the subunit irrigation emission uniformity of a hypothetical case. These results can then be compared with those obtained by the field methods of Merriam and Keller (1978) and ASAE EP 458. This program can be a very powerful tool to define a microirrigation subunit's design criteria that take into consideration the emitter coefficient of manufacturing variation.
Keywords: Microirrigation, Simulation model, Emitter flow, Coefficient of uniformity
Abstract taken from paper found on pages 67 to 73 in Proceedings of 5th International Microirrigation Congress, April 2-6, 1995, Orlando, Florida. American Society of Agricultural Engineers, 2950 Niles Road, St. Joseph, Michigan 49085-9659, USA. Phone: 616-429-0300 FAX: 616-429-3852 EMAIL: HQ@ASAE.ORG
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Friction Head Losses in Drip Irrigation Manifolds for Trapezoidal Shaped Subunits
J. L. De Paco
The shapes of the areas to which a manifold supplies water in a drip irrigation system are very different. The trapezoidal ones can be considered as a base from which rectangular and triangular forms are particular cases.
The friction head loss in a pipe with decreasing flow depends on the discharge distribution along its length, which varies with the shape of the irrigation subunit. In the present paper, two simplified solutions are obtained for hydraulic calculation of manifolds irrigating subunits of trapezoidal shapes with a large number of laterals. The solutions are then particularized for rectangular and triangular shaped subunits.
Keywords: Friction head loss, Manifold pipes, Drip irrigation
Abstract taken from paper found on pages 74 to 79 in Proceedings of 5th International Microirrigation Congress, April 2-6, 1995, Orlando, Florida. American Society of Agricultural Engineers, 2950 Niles Road, St. Joseph, Michigan 49085-9659, USA. Phone: 616-429-0300 FAX: 616-429-3852 EMAIL: HQ@ASAE.ORG
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Hydraulic Analysis of Microirrigation System by Unsteady Flow Approach
Soichi Nishiyama, Tosio Cho, Hiroshi Kawano and Kazuto Ishizaki
The pressure distribution in a microirrigation system was analyzed using a new method. The results were compared with field data and shown to be quite accurate.
To achieve the uniform application of water, it is necessary to analyze the water pressure distribution in the field. Because the discharge from the riser or emitter is a function of water pressure, it is important to know the pressure distribution along the lateral line. There are many methods developed to analyze the pressure distribution.
In this paper, the hydraulic transient approach is presented to analyze the pressure distribution in a microirrigation system. Using a computer, the new analysis method was shown to be very accurate.
The characteristics of the new method are: (1) the whole irrigation system can be analyzed; (2) in the analysis, there is no assumption, therefore, the accuracy is very high; and (3) it is possible to provide the necessary information for evaluation of uniformity of fertigation or chemigation.
Keywords: Microirrigation, Pressure distribution, Unsteady flow
Abstract taken from paper found on pages 80 to 83 in Proceedings of 5th International Microirrigation Congress, April 2-6, 1995, Orlando, Florida. American Society of Agricultural Engineers, 2950 Niles Road, St. Joseph, Michigan 49085-9659, USA. Phone: 616-429-0300 FAX: 616-429-3852 EMAIL: HQ@ASAE.ORG
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Finite Element Analysis of Large Scale Microirrigation System
Yaohu Kang, Soichi Nishiyama and Hiroshi Kawano
It is very important to analyze the hydraulics of microirrigation systems. The purpose of this research is to find a method for analysis of hydraulics of large microirrigation systems by applying the finite element method. Some equations are developed using the equivalent length principle to consider the minor losses when the head losses due to emitter connections, tees or bends are significant. Where these equations are used, there is no need to increase the numbers of nodes. A lateral discharge equation is provided to express the relationship between the total lateral discharge and inlet pressure head of the lateral. By using the lateral discharge equation, a lateral line can be considered as an emitter and a submain line as a lateral. The inlet pressure heads of the laterals can be determined first and the pressure head distribution along each lateral can then be obtained easily. By implementing this method, the hydraulics of a large microirrigation system even with millions of emitters can be analyzed easily using personal computer. The analytical procedure is simple, and the accuracy is very high.
Keywords: Microirrigation, Hydraulics, Lateral discharge equation, Finite element analysis
Abstract taken from paper found on pages 84 to 90 in Proceedings of 5th International Microirrigation Congress, April 2-6, 1995, Orlando, Florida. American Society of Agricultural Engineers, 2950 Niles Road, St. Joseph, Michigan 49085-9659, USA. Phone: 616-429-0300 FAX: 616-429-3852 EMAIL: HQ@ASAE.ORG
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Finite Element Analysis of Drip Irrigation System
C. Chatterjee and K. N. Tiwari
A finite element model developed to analyze drip irrigation takes into account the minor losses due to bends, tees and barbs. An iterative procedure is used to solve a set of linearized flow equations. A computer code is developed to determine pressures at various nodes for a given inlet pressure. Both Darcy-Weisbach and Hazen-Williams equations can be used to calculate the friction losses. The results obtained from the proposed finite element model were experimentally verified and found to have close agreement.
Keywords: Drip irrigation, Finite element method, Minor losses
Abstract taken from paper found on pages 91 to 96 in Proceedings of 5th International Microirrigation Congress, April 2-6, 1995, Orlando, Florida. American Society of Agricultural Engineers, 2950 Niles Road, St. Joseph, Michigan 49085-9659, USA. Phone: 616-429-0300 FAX: 616-429-3852 EMAIL: HQ@ASAE.ORG
