PERFORMANCES
TYPES OF NODES
Nodes where the total head is imposed.
Dam: Given steady free surface height.
Pressure Node: Given steady level and pressure head.
Reservoir: Established in terms of capacity (volume stored according to level) for a minimum of three levels, floor level and initial level. In the analysis of networks with simulation over time, GESTAR 2010 will calculate the evolution of the level and volume stored over time.
Nodes where the demand is imposed.
Known Consumption Nodes: Consumption is known, and independent of local pressure. The maximum supply and momentary demand are specified. Optionally, if dealing with an irrigation hydrant, the data for the plot being supplied (surface area, fictitious continuous flow rate, pressure set point) and the network (irrigation times) can be loaded, obtaining the probability of opening and the degree of freedom of demand. Alternatively the degree of freedom of demand can be set, and the supply required obtained. If consumption is not on demand but rotational and based on established turns, the node can be assigned to a given turn.
Junction node: There is no consumption.
Nodes where demand depends on local pressure:
Emitters All types of components with an emitted flow, Q, depending on the pressure head, H, according to the relationship . In particular the values of K and N for sprinklers selected from the corresponding database, in the form of tables, flow emitted/pressure, are calculated automatically. If this database contains information on the reach of the emitter according to pressure, the corresponding reach of the calculated pressure can be evaluated and represented as a graph. The properties of an associated feeder conduit can be added, with all the characteristics of the pipe-type elements. If consumption is based on established turns, the node can be assigned to a given turn.
Regulating Hydrants These have a hybrid behaviour, combining the behaviour of the Known Consumption Node when pressure is above a certain threshold (pressure set point), with that of the Emitter Node when pressure drops lower than the pressure set point. If consumption is not on demand but rotational and based on established turns, the node can be assigned to a given turn.
Sprinklers: These constitute a particular type of emitter in which the point of emission is represented in the node where the emitter joins the network, the junction node, facilitating its representation and configuration in the design of irrigation in plots with hundreds or thousands of components.
TYPES OF ELEMENTS
Pipes: Conduits with a constant cross-section, with options to incorporate singular head losses and throttle valves. The values of Interior Diameter and Roughness can be loaded in the Pipes Database, according to manufacturer, Material and pressure rating, or imposed by the user. Optionally for each pipe an arbitrary number of accessories and a throttle valve (or retention valve) can be incorporated, with a variable degree of opening with single losses of the type and generalised single losses formulated . The coefficients k of the singular losses in accessories is automatically communicated from the databases parameterised according to the type of singular element. In the case of valves the values of k are computed as: the discharge coefficient being included in the interval (0.1), and being a function of the degree of opennessa and valve type. is loaded from the valve databases. Alternatively, the values of K and N, reproducing the dissipation of total head in any devices, must be supplied by the user in the corresponding dialogue boxes, with utilities for adjusting to experimental data. Each pipe admits logical retention and independent closure devices and registers the design flow rate (equipped for the sizing phase) and speed in order to facilitate the migration of the results to transient analysis packages.
Pumps: Discharge elements defined in terms of increasing height through energy according to the flow rate, optionally considering total power consumption (or efficiency) and the NPSHR. The performance curves of the Element can be loaded using tabular values defined by the user, or automatically from the pump databases, which provide additional resources for choosing pumps adapted to a nominal point. Each pump incorporates a logical retention device. The performance curves are modelled using splines, permitting a precise fit throughout the range of flow rates for any type of geometry of the curve (maximums, minimums, inflection points). Thanks to this, GESTAR 2010 can exclusively offer a simple form of detailed modelling of the functioning of pumping stations as a whole, defining a pseudo-pump which takes as performance curves the conjoined curves of height-flow rate and power-flow rate, which GESTAR 2010 supplies directly in the “Pumping stations” module, according to the system curve, type and number of groups, and type of regulation.
Automatic regulating valves: Pressure reducing valves, pressure sustaining valves, flow limiting valves and acceptable combinations of these, configured by algorithms which enable a correct implementation of the operational states and limits of all of them in numerous contexts, including their placement in branches. The head loss coefficients K, for totally open positions, can be introduced manually or from the database of regulating valves.
Emitter Lines Pipes with a continuous flow emitted by unit of length q, where the flow rate emitted is not constant, but dependent on local pressure through relationships of the type: .
An integro-differential model is applied which enables the calculation of pressure and flow rate distributions throughout the Emitter line and evaluates locally emitted flow rates. When the Emitter lines have a closed end, the definition is admitted of various sub-sections with homogeneous properties as to the type of emitter and spacing, slope, Interior diameter and Roughness. If the end has another type of connexion (for example, to another Emitter line or pipe) only one section is admitted, and it will be automatically detected if there is a feed at one or both ends, and in this last case, the emitter behaviour will be simulated, detecting the internal point of zero velocity (neutral).
GRAPHICAL INTERFACE
Interactive configuration: Graphic and interactive “click & drop” configuration of networks, “point and click” input/output in intuitive, user-friendly windows, scale reproduction of the network layout, diagrams, dialogue windows, help menus, tables, graphs, error management, etc.
Working with UTM co-ordinates: Origin and scale (proportional to the screen resolution or set by the user) configurable for adjusting maps and orthophotos used as background.
Inserting images: As auxiliary cartographic backgrounds for layouts or in bmp, jpg, or gif format.
Consultation and documentation of data and results: Editing windows, colour codes, map of numerical values, pop-up window with data on the selected component, tables of results, export of ACCESS and EXCEL database text files. Graphs of evolution over time.
Configurable graphic parameters: Default values, prefix of identifiers, colour coding and visualization format in the map of numerical values, appearance of map background, Nodes and Elements, visualisation/hiding symbols of Nodes and Elements, direction arrows, number of digits in visualised data.
Rectangular and irregular polygonal section: For cutting, copying, pasting, moving, deleting, calculating cost and assigning parameters to all selected components.
Dividing a pipe into two stretches: At the point selected by the cursor on an existing Pipe, enabling the introduction of an intermediate Node, interpolating its elevation and the lengths of the two resulting stretches.
Joining networks: Merging two independent *.network files into a single output file in order to join partial networks in a larger system, with optional assignation of different prefixes to the components of each network and overlapping shared connection Nodes (co-ordinate and ID).
Zoom In/out: Zoom in to enlarge and zoom to half size, selection of initial zoom level set in Scale options.
Scrolling: Navigation around the network map using horizontal and vertical scroll bars.
Searching for nodes/elements: Directly locating Nodes and Elements by ID and by comments field, with signing on the map or automatic drop-down windows to edit data.
Inserting images: Informative text added to the network map with configurable format.
TOOLS FOR OPTIMUN SIZING OF BRANCHING NETWORKS
In the case of networks configured as strictly branching with predetermined design flow rates and layout, GESTAR provides the sizing tool which includes economic optimisation criteria; this can find the combination of Pipes to meet the imposed pressure requirements for Design flow rates, with a minimum overall cost, or very close to the overall minimum. We present below the main features and resources of the optimisation module.
Calculation of Design Flow Rates: through accumulation of open intakes in turn-based irrigation or by the Clement formulation for on-demand irrigation, with different levels of guaranteed supply, gradable according to the number of intakes. Design flow rates can be adjusted by the user in the module itself or by editing the Pipes.
Sizing Pipes for on-demand networks: For branching networks with a known total head (with direct feed or through interposed pumping) with given layouts, Design flow rates and pressure set points, through economic optimization techniques.
Sizing Pipes for rotational networks, with specified turns, using economic optimization criteria, for branching networks with a known total head (with direct feed or through an intermediate pump) with a given layout and pressure set points.
Inclusion of single and distributed losses: The effect of single losses can be studied through their equivalent length, distributed uniformly throughout as a percentage of the length of each conduit, either specifically or stretch by stretch.
Imposed pipelines: Stretches of pipelines can also be defined whose properties are imposed and are not altered during optimisation.
Optimum nominal discharge height: In the case of networks with direct pumping, for design flow rates in the network, giving the weighted efficiency of the pump, the annual volumes served, the unit costs of the contracted power supply, and the applicable surcharges or discount rates, if any, it also gives the height which will optimise power and amortisation costs.
Adjustment of parameters: Various adjustments and optimisation options which enable sizing to be refined and additional costs to be assessed are now user-configurable and accessible.
Express resizing: Starting from a binary file or text file generated in a previous sizing procedure, containing the complete description of the network to be optimised and the established restrictions, individual values can be easily adjusted or systematic tests carried out with the help of the sizing assistant.
Guide to refining design. Options about the most critical Nodes, whose pressure requirements raise the costs of conduits the most, so that pressure requirements on them can be reduced in a rational and orderly manner, in order to lower system costs.
Assignements by sections of overpressure due to transients , enabling pipe costs to be adjusted by reusing the results of the analysis of transients to judge the correct pressure rating for each section, adjusted for calculated overpressure rather than a single overall value.
Assignements by sectionsof maximum acceptable speeds , in order to adjust costs by reusing the results of the analysis of transients to judge the maximum acceptable speed suited to each section, adjusted for local conditions rather than a single overall value.
HYDRAULIC SIMULATION MODULE CHARACTERISTICS
The most relevant numerical aspects related to the hydraulic solver are listed below:
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Cuasi steady hydraulic solver uses a evolved Nodal Head type method, combined with Newton Raphson algorithm, for solving the system of non linear equations, with several extensions to handle with the specific irrigation network components, (Aliod and Gonzalez 2007).
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Unknowns, either node heads or flow rate, are computed coupled and relaxed at each iteration step.
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Jacobian matrix computed for general non linear elements constitutive equations.
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Solution convergence control by two independent criteria: maximum average flow residue at the nodes, respect the average flow rate in the elements, and maximum difference between the value of the head in the nodes, or the relative flow rate in elements, between two consecutive iterations.
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Regulation valves simulation by direct calculation of their operational parameters coupled with the whole equation system.
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Dual modeling of hydrants depending on the pressure level on the network: when the pressure rises above the hydrant pressure setting, the node is modeled as a pressure independent flow demand, but when the network pressure falls below that level, the node demand is modeled as an emitter.
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Pressure dependent continuous-like flow emissions (for modelling drip irrigation tubing) are links modelled by means of a generalization (Aliod and González, 2007), of the integrodifferential approach of Warrick and Yitayew (1988).
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Inverse analysis allows the direct computation of unknown control parameters at node or elements, and computation of a common roughness or diameter for a group of elements, using a modified system of equations (Aliod and González. 2007).
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Cubic spline fitting of characteristic curves (head, power, NPSHR) of pumps vs flow rate, and of curves describing the reservoirs volume vs level.
HYDRAULIC ANALYSIS TOOLS
CONFIGURATION OF DETERMINIST SCENARIOS
Stationary scenario: Opening/closing Known Consumption Nodes and regulating hydrants by point and click or by order executed by identifier.
Table of programming in quasi-stationary evolution over time: specification of the time interval of opening of each Node with flow demand, sprinklers and pipe elements, and pumping groups. Intervals and duration configurable by time lapse (or number of intervals) and length of interval.
Programming shifts: Specification of the number of turns, duration of each of them and definition of Nodes (Known Consumption, Hybrid, Sprinkler) belonging to the turn. Extension of the table of programming over time to programme the start of each turn.
Logical instructions in quasi-stationary evolution over time: Control orders, complementary to programming tables qualifying the opening/closing of Nodes with demand, pipes and pumps, according to the value of the characteristic variables (pressure or flow rate) regarding control values in Nodes and Elements.
Factors modulating demand: For each demand node it is possible to define factors modulating the assigned resources, to reproduce the operation of shared hydrants, seasonal variations, etc.
Generator of energy prices. As many prices and price bands can be generated as desired (by day of the week, by month, by season, etc) with 24 periods of discrimination for each of them, both in terms of energy consumed and of available power, specifying the maximum power to be contracted in each period.
CONFIGURATION OF RANDOM SCENARIOS.
Generation of random demand scenarios: Distributions of demand nodes open or closed at random, satisfying a pre-established percentage of open intakes and including the probability of opening of each intake.
Assignation of non-conditional demand status: Opened or closed status can be set which are not affected by the generation of random demand status, making it possible to analyse mixed scenarios combining determinist (turns) and random demand conditions.
Network analyst: By generating a high number of random scenarios (with restrictions marked by the Nodes in non-conditional demand status) the maximum, minimum and average values are determined for all variables. Optionally, scenarios which generate alarms can be separated and saved individually for later analysis.
ALARMS AND REPORTS
Configuration of alarms: Options for setting a range of acceptable values for the variables: speed in pipes, aspiration in pumps, in valves, in emitter lines, head losses per unit of length, pressure in demand nodes, in junction nodes, and flow rate in hydrants. Threshold alarms can also be defined: maximum - minimum levels exceeded in reservoirs, pump cavitation, contracted power exceeded, negative pressures at any point and pressure in Hydrants below the Pressure set point (with adjustable tolerance). If an alarm is triggered, the component is marked graphically and noted in a report.
Alarm report: Exhaustive list of alarms (exportable to ACCESS file) generated in successive scenarios of evolution over time or random, indicating the scenario number, the component which generated the alarm, value of the variable producing the alarm and units of the variable. Includes a summary of the number of breaches per component (Element or Node) and percentage of pressure breaches in demand nodes.
TOOLS FOR MODELLING, REGULATING AND OPTIMISING PUMPING STATIONS
Shown below are the main features and resources available in GESTAR 2010 for modelling, regulating and optimising pumping stations, by obtaining System Curves, Operation Curves and Probability Density Function of flow rates (PDF), which together establish energy costs for a certain period.
Pump Selection: Automatic incorporation of the performance curves of discharge equipment from databases of pumps, by direct search by model or search for the pump which best suits a determined nominal functioning point.
Estimation of simplified performance curves: Parabolic type curves are determined for a pump type adapted to a nominal functioning point according to basic parameters.
Obtaining maximum, average and recommended System Curves: Given an arbitrary network with one or more points of known total head, the maximum, minimum and recommended system curves are determined for any pumping station feeding the network through a simulation of multiple random states for each flow demand percentage in the pumping station.
Obtaining System Curves of a given reliability. The information needed to build various system curves for a determined degree of reliability can be extracted from the process of simulating multiple random states.
Pumping station Operation Curves: Calculation of head-flow rate, power-flow rate, efficiency-flow rate, and spin speed-flow rate curves, and stop-start transition points for pump groups with arbitrary compositions of fixed pumps and variable speed pumps, of the same or different kinds.
Determining the PDF of flow occurrence: For on-demand irrigation conditions, in branching irrigation networks fed from one point, the Probability Density Function of the flow rate at the feed point for an irrigation campaign. Possibility of dividing by low demand, shoulder and peak demand bands.
Set demand curves: Introduction by the user of estimated or experimental demand probability density curves.
Determination of energy consumption: Combining the curves of the pumping station (head-flow rate and power-flow rate) and the Probability Density Function of the flow rates (with option to split into low, shoulder and peak) a calculation is obtained of energy costs reflecting the dependence of the results on the performance curves of the pumps, the number and size of the equipment, the regulation strategies used and the network system curve.
Energy cost*: Computes spending in energy supply in terms of electricity fares, kwh of energy consumption and and kw of power contracted.
TOOLS FOR INVERSE HYDRAULIC ANALYSIS
The number of duplicate requirements in target nodes must be the same as the number of degrees of control freedom (not to be confused with the degree of freedom of demand in an irrigation hydrant) available for adjustment.
NOTE: Arbitrarily imposed duplicate requirements may not be consistent, leading to badly constructed problems, without a solution in the space of physically viable solutions.
Double Condition Nodes: Nodes simultaneously specifying demand and pressure conditions to be met simultaneously in an operating network. These constitute the restrictive conditions to meet which the parameters of degrees of freedom for control must be adjusted in other free nodes and free elements, or free pipe sets.
Free node: Degree of freedom for control associated with point values which will determine the pressure and flow rate which should be supplied to the node in question in order to meet the requirements imposed by double condition nodes.
Free element: Degree of freedom for control associated with elements where the necessary energy jump and circulating flow to meet the requirements imposed by double condition nodes will end. If the resulting element is passive, it will be calculated as a dimensional coefficient of losses (or if two of the three parameters, length, interior diameter and roughness are supplied, the remainder will be determined) and if the element is active, the functioning point of the required discharge group will be calculated.
Free pipe sets: Group of connected or unconnected pipes sharing: either Interior Diameter or Roughness. The shared diameter or roughness is the degree of freedom for control which is adjusted to meet the requirements imposed by double condition nodes. Utility for the calibration of models, determination of unknown properties of pipes, adjustment to existing networks. Badly formed problems (physically impossible conditions) should be avoided.