Utilisation des moyens modernes de calcul pour l'établissement des avant-projets et projets de réseaux d'irrigation par aspersion

Abstract

Modern collective irrigation system design calculations are apt to be complicated and long drawn-out by conventional methods, and modern computer facilities offer attractive possibilities in this connection. The Standard Network Programme described considerably reduces calculation times, and thus enables the actual construction work to commence much sooner than used to be possible ; it also makes for much more accurate design. The two main phrases of the programme are 1.) discharge and duct diameter calculation, and 2.) preparation of design documents. Discharge and duct diameter calculation : The positions and characteristics of distribution points are determined by conventional design office methods and give the general duct layout. The necessary data are then fed into the machine from a data sheet prepared by the designer, the first part of which refers to the entire system (assumed basic data, principle of flow rate summation, rates considered for cost optimisation), and the second part of which defines all the individual duct sections ant the necessary hydraulic characteristics. Rates of flow are computed automatically, with statistical weighting (Clement's formula) and allowance for possible concentration of irrigation. Duct diameters are defined either by applying an "economic diameter" to each flow, or by normal optimisation based on applicable unit costs. The "economic diameter" is defined by statistical interpretation of a large number of normal optimisation procedures. The flow and duct diameter calculations usually take place as a coherent sequence, their results being printed as a single list of specifications for all the individual duct sections. If necessary, the calculation can be run for a range of delivery heads, so as to "optimise" these in terms of distribution network and pumping plant cost. Network cost calculation is provided for in the programme. Preparation of design documents : Design documents necessary for tendering procedure include longitudinal profiles, bills of quantities and detailed cost estimates. Longitudinal profiles are established from designer's data sheets giving full definitions of the stresses for which the structures are to be designed. With this information, the programme then records full numerical longitudinal profile data on a tape. The bill of quantities is produced on the strength of information already supplied, and is as detailed as required for the considered job. The programme then enables quantities to be determined by structural units and categories. The cost estimate is produced automatically from the unit rates list for the considered scheme. Items costed are ducts, special components, excavation work, structures and equipment. The programme can also provide for phasing of the construction work, with that required to meet initial users' requirements being carried out in the first phase, and extension of the system to its final capacity being completed in subsequent phases. The printed data include a distinction between initial and subsequent-phase work items. Conclusion : The Standard Network Programme has given satisfactory results for several preliminary and final designs and is now being modified and improved in the light of this initial experience. It nevertheless already provides the designer with a self-contained instrument, which it is claimed offers the following advantages over proven conventional methods : (i) Exceptional rapidity and reliability-both assets for big projects. (ii) It leaves the designer free to concentrate on really important creative work without having to bother with tedious menial jobs. (iii) By the inescapable logic and standardisation associated with computers, the programme ensures full rigour and clarity of the calculations and the presentation of results.