Soichi Nishiyama

Analysis of Microirrigation Systems Using a Lateral Discharge Equation

Our objective was to develop an accurate, simple and quick method for analyzing the hydraulics of microirrigation submain units using the finite element method. A lateral discharge equation was developed to express the relationship between the discharge and pressure head at the inlet of a lateral. The lateral discharge equation allows a lateral to be represented as a point sink and the submain as a lateral. The methodology we used provides a symmetrical tridiagonal stiffness matrix which is easy to solve and requires minimum computer memory. Initially all nodal pressures are set equal to the inlet pressure head of the submain. The pressure head distribution along the submain is then determined. The pressure head distribution along each lateral is next obtained since the inlet pressure head is already known. By implementing this procedure, the hydraulics of any submain unit, even if it has many emitters (four millions emitters or more), can be analyzed using a personal computer.

Hydraulic Analysis of Microirrigation Submain Units

A simple method was developed for hydraulic analysis of a microirrigation submain unit. The lateral discharge equation is used to express the relationship between the inlet discharge and the inlet pressure head of a lateral. This equation allows for considering a submain as a lateral and a lateral as an emitter. The back step method was applied for calculating pressure distribution along the submain line. The golden section search was used to find the optimal estimate of pressure head at the end of the submain. The forward step method was used for determining distributions of the pressure head and the emitter discharge along each lateral. A flowchart for calculation on a personal computer is included. It was found that any microirrigation submain unit can be analyzed using this method. The analytical procedure is simple, accurate, and fast.

Design of microirrigation laterals at minimum cost

Abstract Based on the design methods of finite elements and golden-section searches, a method was developed for designing microirrigation laterals at minimum cost. Characteristics of water application uniformity as affected by lateral diameters and lengths were analyzed. When the required average emitter discharge is known, the relationships of water application uniformity, best submain position (paired laterals), and operating pressure head as a function of the lateral diameter and length can be accurately determined using a personal computer. The lateral diameter and length can then be determined from a contour map representing water application uniformity as a function of the lateral diameter and length (computer calculation). The best submain position and operating pressure head for this lateral diameter and length is then determined by computer calculation. This method is suitable for designing microirrigation laterals on both uniformly and nonuniformly sloping fields.

Design of microirrigation laterals on nonuniform slopes

Abstract A method for designing microirrigation laterals on nonuniform slopes was developed using the finite element method. Six representative nonuniform slope patterns were discussed in detail. The design principle was implemented based on the results of computer simulations. It was found that a single lateral is suitable for Pattern I while paired laterals are better for Patterns II ∼ VI in most cases. The diameter of a single lateral or paired laterals may have two solutions for a required uniformity of water application and the length may have multiple solutions. When the required average emitter discharge, required uniformity of water application, and one parameter (either length or diameter) of a single lateral or paired laterals are given, the unknown parameter, best submain position (paired laterals) and operating pressure head can be accurately designed using personal computers. The design procedures are described.