WO2002008975A2 - Pipe network optimisation - Google Patents
Pipe network optimisation Download PDFInfo
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- WO2002008975A2 WO2002008975A2 PCT/GB2001/003349 GB0103349W WO0208975A2 WO 2002008975 A2 WO2002008975 A2 WO 2002008975A2 GB 0103349 W GB0103349 W GB 0103349W WO 0208975 A2 WO0208975 A2 WO 0208975A2
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- pipe
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- pipes
- flow
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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06F—ELECTRIC DIGITAL DATA PROCESSING
- G06F30/00—Computer-aided design [CAD]
- G06F30/10—Geometric CAD
- G06F30/13—Architectural design, e.g. computer-aided architectural design [CAAD] related to design of buildings, bridges, landscapes, production plants or roads
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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06F—ELECTRIC DIGITAL DATA PROCESSING
- G06F2113/00—Details relating to the application field
- G06F2113/14—Pipes
Definitions
- the present invention relates to a method of optimising a pipe network.
- the invention relates to the optimisation of a pipe rehabilitation strategy for a pipe network such as a water supply network. More particularly still, the invention can provide a "least cost" acceptable strategy for the rehabilitation of a selection of pipes within a water supply network.
- a water mains network will typically be divided into a number of separate district meter areas (DMAs) which will be separately modelled within the network model as a whole.
- DMAs district meter areas
- a typical network will have half a dozen or so DMAs each having a designated source, which may be a real source such as a service reservoir, or a pseudo-source such as a trunk main. Alternatively, sources may be located further back upstream on trunk mains, with the modelled DMAs being supplied via branch mains off the trunk mains.
- nodes Within the network, and within each DMA, the network model will identify "nodes". The concept of nodes will be familiar to those skilled in the art of network analysis. Nodes are designated by the network model builder, or the original geographical survey of the physical network on which the model is based, and includes such things as pipe junctions, pressure points, and demand points (typically models for residential areas will have 20 to 30 houses allocated to each node). The points where individual service pipes for single properties branch from the network would not generally be considered as network nodes (although there may be exceptions to this, for instance for models that cover sparsely populated rural areas). The information provided by a network model can be used in the analysis of the performance of the network.
- One of the functions that conventional network analysis tools can provide is to predict the effect on a network (or on a DMA or part of a DMA) of changes made to certain elements within that network.
- network analysis tools can be used when planning a rehabilitation strategy.
- the network planner will have a number of performance constraints which must be accommodated, such as ensuring that rehabilitated pipes do not introduce an unacceptable steep hydraulic gradient (i.e. too much loss of pressure per unit length along a pipe line) but within those constraints the planner will be able to make a number of choices on rehabilitation technique, and the size of any new pipe or pipe lining that might be installed to rehabilitate the existing pipe.
- the network planner will have details of contractors which offer appropriate rehabilitation services and associated costs.
- Costs will typically vary not just with the rehabilitation technique, and size of any rehabilitated pipe, but also with location and ground conditions. For instance, it will be more expensive to dig up a main road than a side road etc.
- the network planner will be constrained to select from a pre-agreed list of preferred contractors which have submitted acceptable tenders. This information is referred to hereinafter as a contractor "cost table" (regardless of whether or the information is in fact tabulated).
- the planner will want to determine the cheapest acceptable strategy by reference to the relevant cost table. Where a single pipe or pipe element is to be rehabilitated performance predictions, and therefore design choices, are easily made. However, the process can be extremely complex where a number of changes are to be made at different parts of a network, many of which will impact on each other and on other parts of the network. It is therefore an object of the present invention to provide a method of optimising a pipe network. In particular, it is an object of the invention to provide a method of determining a "least cost" acceptable solution when planning a pipe network rehabilitation strategy. The method according to the present invention is not, however, limited to optimising by reference to cost, but could be adapted to provide optimisation on the basis of other criteria. In addition, the invention is not limited in application to rehabilitation of existing networks but can be used to aid in the planning of a new network.
- a method of optimising a model of a pipe network with respect to a predetermined criteria comprising modifying a starting proposal for a list of pipes within the network model which may be modified by performing the following operations: i) selecting a first pipe from the pipe list which may be considered for modification;
- a method of determining the hydraulic significance of each of a list of pipes within a model of a pipe network comprising: i) performing a network analysis on the network model to determine the flow patterns through the network at a given time; ii) counting the number of instances of each pipe occurring in a flow path between a source node defined by the network model and the boundary of the network model, and using the instance count for each pipe as the indication of the hydraulic significance of that pipe within the network, such that pipes with a higher instance count are considered to more hydraulically significant than pipes with a lower instance count.
- a third aspect of the present invention there is provided a method of determining peak flow rate demands on pipes within a model of a pipe network, the method comprising:
- the invention has a number of novel aspects which are combined in preferred embodiments but which can also be utilised independently.
- Figure 1 is a flow diagram illustrating the steps of an iterative optimisation method according to the present invention
- Figure 2 is a flow diagram illustrating the steps of a method for determining the hydraulic significance of pipes within a pipe network in accordance with the present invention
- Figure 3 a is a schematic illustration of a simple pipe network
- Figure 3b is a table presenting the results of an hydraulic significance determination made in accordance with the method of Figure 2.
- Figures 4a and 4b are further schematic illustrations of the simple pipe network of Figure 3 a used to illustrate a method of performing a peak flow analysis in accordance with the present invention.
- Figure 5 is a flow diagram illustrating the steps of a method for deriving a start strategy for the iterative method illustrated in Figure 1.
- the rehabilitation method of the present invention will be one part of a system additionally comprising a computer model of the network under consideration, a hydraulic solving engine for performing hydraulic calculations and predicting the effect of changes to the network, and suitable interface and reporting facilities.
- additional software analysis tools required will be readily apparent to the skilled reader by the references that are made to the required functionality.
- Such additional software tools may be entirely conventional and thus no description of appropriate tools will be made apart from references to the required functionality.
- the invention requires reference to a contractor cost table in which the various rehabilitation options open to the planner, and associated costs, are listed.
- the concept of a contractor cost table is discussed above.
- the cost table should be represented in a database from which information can readily be extracted. If the network planner does not have an appropriate database one can be constructed and indeed the system according to the present invention may incorporate a database into which relevant information can be input by the planner. As such, the system could guide the planner as to the information required.
- a maximum acceptable hydraulic gradient will normally be specified. That is, there will be a maximum permissible head loss per unit length of pipe within the network to ensure demand can be met.
- Minimum and maximum permissible pressures may be specified for each node, or selected nodes, within the network. For instance, it is often necessary to maintain particular nodes above a minimum pressure to avoid adverse effects on downstream pressures or flow rates and also meet levels of service criteria.
- Minimum tank levels may be specified for reservoirs etc.
- operating limits may be defined by the network model, the network planner or may be default parameters provided by the system according to the invention (or indeed a combination of the two).
- operating limits may be referred to generally hereinafter as "operating limits”.
- optimisation method of the present invention is an iterative routine which takes a "start" rehabilitation strategy for a number of pipes and modifies the strategy to produce an optimum "least cost” strategy (by reference to the appropriate user provided cost table) whilst ensuring that operating limits are not violated.
- a list of the pipes to be rehabilitated must be provided together with a suggested rehabilitation option for each pipe.
- the selected pipes incorporating the proposed rehabilitation (which may for instance be pipe lining or replacement ) are referred to hereinafter "rehab.pipes”.
- the planner may manually select the pipes to be rehabilitated from the network model, or use an appropriate filter (for instance selecting all cast iron pipes above a certain diameter), and may then select a "safe" strategy from the available rehabilitation options as the start strategy for the iterative routine. For instance, such a "safe" strategy may be to replace existing pipes with new pipes of similar size and flow characteristics, or a size larger than the existing pipes. Preferred methods for ordering the list of the pipes to be rehabilitated, and generating an appropriate start strategy for the iterative routine, will be described further below.
- the iterative routine according to the present invention may be operated as follows.
- the first step is to select a first rehab.pipe from the pipe list.
- the next step is to consult the appropriate cost table and "step down" the initially proposed rehabilitation method for the selected rehab.pipe.
- This is a step down in cost which can be determined from the appropriate cost table and will generally entail stepping down the size of the pipe to the next size down, but may also entail changing the material of the pipe or rehabilitation technique.
- a network analysis is performed to determine whether or not any of the predefined operating limits are violated as a result of the change to the selected pipe.
- This part of the routine requires calling upon network analysis tools (such as an hydraulic engine etc) to perform the necessary calculations on the network (modified by the rehabilitation strategy including the stepped down rehab.pipe) which are then compared with the predefined limits.
- network analysis tools such as an hydraulic engine etc
- the network analysis methods and tools which may be used to perform the calculations and make the necessary determination may be entirely conventional and thus will not be described here.
- the above test can result in one of two outcomes: either that there are no operating limit violations or that there are operating violations. If there are no operating limit violations the iterative routine moves on to select the next rehab.pipe from the pipe list and repeats the process of stepping down the selected rehab.pipe and determining whether this results in any operatmg limit violations.
- the iterative routine has completed its first iteration, and each rehab.pipe in the pipe list has been selected once, some rehab.pipes will have been stepped down whereas others will have been locked in their previous rehabilitation proposal (which after the first iteration will of course be the start proposal).
- the routine then returns to the start of the pipe list and selects the first un-locked rehab.pipe from the list.
- the selected pipe is then again stepped down and a determination is made as to whether or not any operating limit violations result. If there are no operating limit violations the routine moves on to the next unlocked pipe in the pipe list. If there are operating limit violations the selected pipe is stepped back up to its previous rehabilitation proposal and locked.
- the routine is continuously iterated, making as many passes as necessary through the rehab.pipe list, until all pipes in the pipe list have been locked. This results in a rehabilitation strategy which meets the predefined operating requirements but which is cheaper to implement than the start strategy. This optimised strategy may then be reported as the "least cost” acceptable rehabilitation strategy.
- block 1 represents the starting point of the routine which is the provision of a rehab pipe list in accordance with a start rehabilitation strategy. This is discussed in general terms above.
- Block 2 ensures that all rehab.pipes in the pipe list are un-locked (the significance of which will be apparent from the above description of the iterative routine).
- Block 3 sets the un-locked rehab.pipe count designated, i, to 0.
- Block 4 determines whether all of the pipes in the rehab.pipe list are locked. If all the rehab.pipes are locked the program exits the iterative routine and proceeds to a reporting stage. If there are any unlocked pipes the process proceeds to block 5.
- the selected pipe i is stepped down as explained above by reference to the appropriate cost table.
- a network analysis is instigated to calculate the effect of stepping down pipe i on the predefined operational parameters of the network.
- the selected pipe i is stepped back up to its previous rehabilitation condition, i.e. returned to the condition it was in prior to being stepped down at block 8.
- pipe i (having been stepped up at block 11) is locked against further modification.
- the routine then returns to block 4.
- the program cycles through the iteration routine until the determination at block 4 finds that all pipes have been locked in a final rehabilitation strategy which is then passed on to a reporting routine, via any further analysis that may be deemed desirable (a preferred analysis is described further below).
- the order in which the iterative routine passes through the list of pipes to be rehabilitated may have a bearing on the optimised rehabilitation strategy arrived at by the routine.
- the pipe ordering is a reverse of the hydraulic significance of each pipe. In other words, the least hydraulically significant pipes are considered before the most hydraulically significant pipes.
- the determination of the hydraulic significance in accordance with the present invention is essentially a flow path analysis performed on the network model determining how many times each pipe occurs in flow paths between the source node and boundaries of the network (or DMA etc).
- the routine for determining the hydraulic significance of the selected pipes must be made by reference to an appropriate network model which has the necessary information. Because water supply and/or distribution systems are dynamic and water demand patterns vary over time, a typical network model will comprise a number of "snap shots" of the flow conditions at various time intervals over a given time period. For instance, the direction of water flow through some pipe elements may change over a 24 hour period as demand patterns change.
- the first step in the procedure is to build a pipe list.
- This may either be a list of every pipe within the network (or the portion of the network (DMA etc) under consideration) or only of those pipes selected for rehabilitation. The latter would streamline the process.
- the pipes may be listed in any order.
- the preferred routine for determining the hydraulic significance of pipes illustrated in Figure 2 considers the network flow at 30 minute intervals throughout a 24 hour period, although it will be appreciated that other time intervals/periods could be selected. Thus, at block 14 time is set to 0 and is an advanced to the first time interval at block 15.
- the network model must be balanced.
- the hydraulic engine must determine the flow patterns through the network at the selected time interval. This is a conventional operation and is a basic facility provided by conventional network analysis tools.
- the node count is set to 0.
- the network nodes are identified by the network model.
- the node count is incremented to the next node.
- the order in which the nodes are considered is not important.
- the program operates to trace the flow path from the selected node back to the source. There may be a number of different flow paths between the selected node and the source.
- an increment is made in an instance count for each pipe in the pipe list which appears in a flow path from the currently selected node to the source (for further details see the description of Figure 3 given below).
- the pipe list is sorted and ranked on the basis of the instance count for each pipe . Pipes with the highest instance count are considered to be the most hydraulically significant. The result is that each selected pipe is ordered in accordance with its hydraulic significance and this order can be used for the iterative routine described above.
- Fig. 3 a is a schematic diagram of a simple pipe network and Fig. 3b is a table illustrating incrementation of the pipe count for each pipe in the network to arrive at a figure representative of each pipe's hydraulic significance.
- the illustrated network comprises a source S, eight pipes P1-P8, and six network nodes, N1-N6 respectively.
- each node is considered in turn and the flow paths to that node via the pipe or pipes terminated or converging at that node are traced having regard to the flow directions determined by the network analysis performed to balance the network (as mentioned above).
- Flow directions are indicated in Figure 3a by arrows associated with each pipe.
- Each pipe converging at the selected node is considered in turn and every flow path from the source to that pipe is traced. Any pipe occurring at least once in one or more of the flow paths to the pipe under consideration receives an instance count of 1.
- node Nl is fed directly by a single pipe PI.
- pipe PI There are however three separate flow paths to node Nl via pipe PI, namely: P8/P6/P3/P1; P8/P7/P5/P3/P1; and P8/P7/P4/P1.
- node N3 this is fed directly by two separate pipes, P3 and P4, each of which must be considered separately.
- P8/P6/P3 and P8/P7/P5/P3.
- P6/P7 and P8 receive an instance count of 1.
- P4 which also converges at node N3
- P7 and P8 receive an instance count.
- the hydraulic significance count represented by Figs. 3a and 3b represents the process made at a given time.
- the flow directions through the network can change over a period of time. For instance, should the flow direction through pipe element 5 reverse, the hydraulic significance of pipes 6 and 7 under that particular flow condition would also reverse. Thus to obtain a more representative indication of hydraulic significance the same process is repeated for each time period under consideration.
- the overall hydraulic significance for each pipe is taken as the sum of the counts made at each of the time intervals considered (in the example set out above this is every 30 mins over a 24 hour period).
- the total hydraulic significance count of pipe element P7 would be greater than for pipe P6.
- the overall result is that a hydraulic significance is attached to each pipe within the pipe list which can then be ordered accordingly.
- This ordering can be used to determine the order in which pipe elements are considered by the iterative routine of Fig. 1.
- the invention has been found to give good results when the pipes are considered by the iterative routine in an order which is the reverse of the relative hydraulic significance of the pipe elements.
- the iteration routine of Fig. 1 must take as its starting point a start rehabilitation strategy.
- the start strategy selected may have a bearing on the final outcome although it is expected that, whatever the starting strategy, the iterative routine will provide a good solution. Nevertheless, a preferred scheme for settling on a start strategy for the iterative routine will now be described.
- the pipes to be rehabilitated must be selected by the network planner, i.e. a pipe list must be constructed as mentioned above.
- the network planner can then determine the least expensive option for rehabilitating each pipe by reference to an appropriate cost table. Once the least expensive option has been selected, a determination may be made as to whether any of the predefined operating limits are violated by the strategy proposed. If the answer is no, then this least expensive option may be taken as the solution and there is no need to run the iterative routine at all. Such a solution can be considered as a lower bound solution and is not likely to occur very often.
- the present invention proposes a scheme for modifying the initial strategy to produce a start strategy for the iterative routine. Since the iterative routine will generally improve upon whatever start strategy is selected, the present invention contemplates a routine which represents a pragmatic approach to the selection of a start strategy. If the initial least cost option causes operating limit violations it will be necessary to increase the size of at least some of the rehab.pipes. In accordance with the preferred method of the present invention, this is done by again referring to the hydraulic significance of the selected pipes (preferably determined in accordance with the method described above). All the rehab.pipes are then increased in size but not all rehab.pipes are increased by the same amount.
- the amount by which each rehab.pipe or group of pipes is increased in size is determined by relation to the hydraulic significance of that rehab.pipe or group of pipes.
- the invention proposes taking a select group of the most hydraulically significant rehab.pipes and increasing the size of these pipes by three sizes larger than that proposed in the initial solution and then increasing the size of the remaining pipes to one size larger than that proposed in the initial solution.
- the selection of the "most significant" pipes can be made on a number of bases, for instance this could be the top few percent of pipes in the list, the top specified number of pipes in the hydraulic significance order, or pipes with a hydraulic significance above a lower limit.
- the principle of the invention is to provide a simple approach which whilst being pragmatic has some reference to the relative importance of pipes in the network and thus the effect that changes of sizes of particular pipes or groups of pipes in the network may have on the network as a whole.
- the starting strategy option is, once again, to set all rehab pipes to the maximum possible size offered as an option from the associated contractor cost charts.
- This final modified strategy is then used as the start strategy for the iterative routine. It has also been found that the iterative solution finding stage of the current invention can be significantly shortened if a step is taken that presupposes that all the existing ferrous mains to be rehabilitated already exhibit hydraulic frictions normally associated with the much smoother plastic mains used for rehabilitation).
- each rehab.pipe within the network is capable of meeting peak flow demands without unacceptable pressure losses per unit length of pipe, i.e. without the hydraulic gradient increasing above a predefined maximum limit.
- Conventional water supply network analysis will provide estimates of the flow rate expected through each pipe in the network. This conventional "network analysis flow" can be used in determination of the limit violations.
- a method of determining the peak flow requirement of each pipe in a pipe network which improves upon the results obtained by conventional network analysis by taking into account variations in the local water supply demand across the network and the effect that this may have on the total demand placed on individual pipes within the network.
- the present invention provides a method of estimating peak flow which combines both an estimate of local demand determined in a novel way together with peak flow through the network calculated by conventional network analysis processes (which will be referred to hereinafter as "network analysis peak flow").
- the local demand flow is calculated on the basis of flow procedures similar to those normally applied to determine flow rates to service pipes on a spur of a pipe network, but applied across the network as a whole.
- the invention introduces the concept of "pseudo-spurs".
- the preferred way for separating the network into pseudo-spurs is to first identify each source or pseudo source within the network and also each node which receives convergent inflows from two or more pipes of the network.
- Each of the nodes/sources identified in this way is then considered to be the origin of one or more downstream pseudo-spurs. Where two or more pseudo-spurs have a common origin, they may collectively be viewed as a "pipe tree".
- the pseudo-spurs (which are effectively branches of a pipe-tree) and pipe-trees are identified by reference to the network analysis flow patterns (i.e. flow directions) through the various pipe elements of the network. To determine local demands at the peak flow condition, this is done by reference to the network analysis peak flow pattern.
- the network analysis flow component of the resultant peak flow determined can be calculated by any conventional network analysis technique. No particular technique will therefore be described for calculating the network analysis flow.
- the preferred manner in which the local demand is accounted for by the present invention will now be described with reference to Figures 4a and 4b which reproduce the simple network of Figure 3.
- each node is considered to be supplying domestic properties only, i.e. 50 houses are supplied by each of nodes Nl and N2, 200 houses are supplied by node N3, 150 houses are supplied by node N4 and 100 houses are supplied by node N5. There is no local demand at node N6.
- a convergent node is a pipe junction at which flow converges from two or more separate pipes. It will be appreciated that any particular node may be a convergent node at some parts of the day but not at others. Since the object here is to determine peak flow demands, the convergent nodes are identified by reference to the network analysis peak flow pattern. In this case (assuming the flow pattern illustrated to be the peak flow pattern as determined by network analysis) there is a single source S and two convergent nodes, i.e. nodes N3 and N4. A determination is then made of the pseudo-spurs originating at each of the convergent nodes and the source.
- the pipe tree which has its origin at the source S comprises three separate pseudo-spurs.
- a first pseudo-spur comprises pipes P8 and P6 and terminates at downstream conversion node N4.
- a second pseudo-spur comprises pipes P8, P7 and P5 and again terminates at downstream convergent node N4.
- the third pseudo- spur comprises pipe elements P8, P7 and P4 and terminates at downstream convergent node N3.
- the pipe tree which has its origin at this node comprises only a single pseudo-spur which terminates at downstream convergent node N3 and comprises the single pipe P3.
- the pipe tree which has its origin at this node comprises two pseudo-spurs each of which consists of a single pipe PI and P2 respectively.
- the network as a whole there are three pipe trees and six pseudo- spurs. It will be seen that some pipes, namely pipes P7 and P8, occur in more than one pseudo-spur.
- the next stage is to consider the number of users (in this case houses) supplied by each pipe to determine a local demand loading for each pipe.
- An assumption is made that the local domestic demand (houses) at a convergent node is supplied equally from the converging pipes.
- the part that pipe plays in supplying downstream properties supplied by all pseudo-spurs of which that pipe is an element must be considered.
- pipe PI this occurs in only a single pseudo-spur and moreover is the only pipe in that particular pseudo-spur.
- the local loading of pipe PI is the 50 houses located at node Nl.
- pipe P2 which also has a local loading of 50 houses.
- Pipe P6 is part of a single pseudo-spur P8/P6 which has its origin at source S and its termination at convergent node N4. Therefore, the local loading applied to pipe element P6 comprises the 75 houses supplied at node N4.
- pipe element P7 this is part of two pseudo-spurs both of which have their origin at the source S but which have different terminations.
- the first of these is pseudo-spur P8/P7/P5 which terminates at node N4.
- the second is P8/P7/P4 which terminates at node N3.
- the total local loading applied to pipe P7 s considered to comprise a contribution from its function in both of these pseudo-spurs.
- pipe P7 is considered to supply all 100 houses at node N5, 75 of the houses at node N4 (via pipe P5), and 100 of the houses at node N3 (via pipe P4), giving a total loading for pipe P7 of 275 houses.
- the total local demand loading for pipe element P7 may be arrived at by summing the direct local demand loadings of pipe P7 with that of each of the downstream pipes in the same pipe tree, i.e. pipes P4 and P5 which have direct loadings of 100 and 75 houses respectively. This gives the total of 275 house for pipe P7.
- pipe P8 is part of three different pseudo-spurs all having their origin at source S. Two of these terminate at node N4, namely pseudo-spur P8/P6 and pseudo- spur P8/P7/P5. The third is pseudo-spur P8/P7/P4 which converges at node N3.
- the total loading for pipe P8 comprises a contribution from its function in each of its pseudo-spurs.
- the total local loading for pipe P8 can be arrived at by summing the direct local loading of pipe P8 with the direct local loadings for each of the pipes downstream of pipe P8 within the same pipe tree (which will of course be all pipes downstream of pipe P8 within each pseudo-spur of which pipe P8 is an element).
- the total local loading for pipe P8 is the sum of the direct local loading for pipe P8 (which is 0), the direct local loading for pipe P7 (which is 100 houses), the direct local loading for pipe P5 (which is 75 houses), the direct local loading for pipe P6 (which is 75 houses) and the direct local loading for pipe P4 (which is 100 houses), which gives a total of 350 houses.
- An alternative way of arriving at the total local loading for pipe P8 is simply to sum the total local loadings for each of the pipes immediately downstream of pipe P8 within the same pipe tree. In other words totalling the previously calculated total local loadings of pipes P6 and P7. This same method can be applied throughout the network.
- the associated local demand must be determined. This may be done by estimating the local demand per house and then calculating the local demand for each pipe (as a simple multiple of the total local loading for that pipe and the estimated local demand per house). Alternatively an appropriate formula may be applied to the total house loading for each pipe.
- Local demand conditions are conventionally determined by an empirical formula. For instance, one such formula provided by the Foundation for Water Research applicable to domestic properties is as follows:
- N number of houses
- A a power term, taken to be 0.78
- houses are categorised as one of two types each having a different value for k (0.067 and 0.107 respectively).
- This formula then provides an estimate of the local demand at different locations across a network by applying the formula to the two groups of properties. Applying the above formula to, for instance, pipe P7, and assuming in this example that 75% of the houses are type 1 and the others type 2, gives a total local demand flow for pipe P7 of 6.16 litres per second.
- the next step is to calculate a throughflow component of the peak pipe flow for each pipe in the network. This is done by estimating the flow to be provided
- the network downstream of the pipe tree on the basis of the conventional network analysis flow rates by determining the contribution made to the network downstream of each pseudo-spur containing the pipe in question.
- the throughflow for each pseudo-spur is determined and the throughflows for each individual pipe is taken to be the sum of the throughflow through each of the pipe spurs including that pipe.
- the flow figures for the through flow calculation may be taken from a conventional network analysis, i.e. may be conventional network analysis peak flows.
- Figure 4b shows the results of such a conventional network analysis on the basis of a normal (house) demand flow of 0.0045 litres per second and a peaking factor of 2.
- a normal (house) demand flow of 0.0045 litres per second and a peaking factor of 2.
- the network analysis then apportions this to each pipe element in accordance with conventional methods and the relevant flows are listed.
- the peak flow through pipe element P7 for example, would be assumed to be 2.7 litres per second.
- pseudo-spur P8 P7/P5 which terminates at node N4. Only a single pipe is immediately downstream of node N4, i.e. pipe P3. Pseudo-spur P8/P7/P5 does not however provide all the flow for pipe P3 since pseudo-spur P8/P6 also terminates at node N4. Thus, the contribution made by pseudo-spur P8/P7/P5 to the network analysis flow through pipe P3 is taken as the ratio of the flow through the downstream pipe of the spur, i.e. pipe P5, to the total network flow converging at node N4. Thus, the through flow through pseudo-spur P8/P7/P5 is determined by the calculation: where q n is the network analysis flow in pipe n
- the total through flow for pipe P7 is then the sum of the through flows through each of the pseudo-spurs P8/P7/P5 and P8 P7/P4, i.e. 0.14 + 0.5 litres per second, which gives 0.64 litres per second.
- the total peak design flow demand for pipe P7 is then the sum of the through flow component and the local demand component calculated above, i.e. 0.64 + 6.16 litres per second, giving a total of 6.8 litres per second.
- the peak design flow calculated in accordance with the present invention which takes account of local demand, is much higher than the network analysis peak flow for pipe P7 of 2.7 litres per second.
- the same process can be applied to each pipe within the network.
- Fig. 5 is a flow diagram illustrating how determination of peak flow requirements in accordance with the above outlined procedure can be incorporated in a preferred routine for establishing a start rehabilitation strategy for the iterative routine of Figure 1.
- block 23 represents the initial stage of selecting the least expensive rehabilitation option for all pipes selected for rehabilitation. This will be done by the network planner as mentioned above. Rather than advancing immediately to a determination of whether any operating limits are violated, the next stage at block 24 is to apply the peak flow analysis described above.
- the rehab proposal is automatically adjusted by upsizing the rehab.pipe in question to the minimum required size to accommodate the peak flow (or by changing the material of the pipe to a material which provides higher flow rates).
- a selection of the most hydraulically significant pipes are set to three size larger than initially proposed in the least expensive strategy.
- the selection of the most hydraulically significant pipes can be made on a number of basis as mentioned above. Making the pipes three sizes larger is to some extent arbitrary adjustment but one which has been found to provide satisfactory results.
- the peak flow analysis is applied once more.
- the peak flow analysis is provided at this stage in the routine on the assumption of resizing of pipes in blocks 28 and 29 such that hydraulically significant pipes are three times larger than the minimum rehab.pipes and all other rehab.pipes are one size larger than the smallest rehab.pipe option.
- the reason for doing this is that increasing the size of some pipes may mean that the flow pattern for the network is affected so that other pipes no longer need to have as large a minimum size as previously required when the peak flow analysis was conducted at block 24. It will be appreciated that each time the peak flow analysis is performed there must first be a conventional network analysis of the flow through the network based on the modified pipe sizes.
- the iterative routine has been described above at some length in relation to Figure 1. It will be appreciated that an early step in the procedure is to unlock all of the pipes (i.e. block 2 of Figure 1). This will include unlocking any pipes which have been resized by application of peak flow analysis at block 30. This is desirable because increasing the size of some pipes within the network may allow the minimum acceptable size of other pipes to be reduced. However, an effect of this may be that as a result of the iterative routine some pipes are reduced to below the minimum size that might be dictated by the peak flow analysis calculations.
- the peak flow analysis may be performed a further time and any pipes which are found to be below the minimum size suggested by the peak flow analysis can be increased in size accordingly.
- This is a relatively pragmatic post optimisation procedure. It is conceivable that as a result of such resizing, the maximum default pressure or some internal pipe pressure threshold may possibly be exceeded. However, it is considered that this will be negligible in practice.
- the above example of the present invention provides a method of optimising a pipe network rehabilitation strategy in a novel way and which further includes novel methods for determining the hydraulic significance of pipes within a pipe network and the required peak flow capacity of any particular pipe within the network.
- the network planner may place a mimmum permissible size for pipes within the network not withstanding that the optimisation process might suggest that smaller pipes would meet flow demands etc.
- the planner may limit the reduction in size of the rehab.pipe compared with the original pipe to just one or maybe two sizes below the original pipe size.
- the planner may require certain pipe rehabilitation techniques or pipe materials to be used in certain parts of the network. The manner in which these, and other conditions, could be included in the process will be clear to the skilled reader.
- the invention is not limited to the optimisation of the networks during a rehabilitation process. For instance, this same procedure could be used as one step in the design process for a new network.
- optimisation may be performed by reference to factors other than costs simply by replacing the cost table with any appropriate "preference" list.
Abstract
Description
Claims
Priority Applications (3)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
AU2001278574A AU2001278574A1 (en) | 2000-07-25 | 2001-07-25 | Pipe network optimisation |
US10/088,831 US6829566B2 (en) | 2000-07-25 | 2001-07-25 | Pipe network optimization |
EP01956650A EP1303826A2 (en) | 2000-07-25 | 2001-07-25 | Pipe network optimisation |
Applications Claiming Priority (2)
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GB0018158.6 | 2000-07-25 | ||
GBGB0018158.6A GB0018158D0 (en) | 2000-07-25 | 2000-07-25 | Pipe network optimisation |
Publications (2)
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WO2002008975A2 true WO2002008975A2 (en) | 2002-01-31 |
WO2002008975A3 WO2002008975A3 (en) | 2002-05-30 |
Family
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Family Applications (1)
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PCT/GB2001/003349 WO2002008975A2 (en) | 2000-07-25 | 2001-07-25 | Pipe network optimisation |
Country Status (5)
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US (1) | US6829566B2 (en) |
EP (1) | EP1303826A2 (en) |
AU (1) | AU2001278574A1 (en) |
GB (1) | GB0018158D0 (en) |
WO (1) | WO2002008975A2 (en) |
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WO2007106873A3 (en) * | 2006-03-15 | 2007-11-01 | Autodesk Inc | Synchronized physical and analytical flow system models |
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US7856342B1 (en) | 2006-10-02 | 2010-12-21 | Autodesk, Inc. | Automatic reinforcement modeling |
Also Published As
Publication number | Publication date |
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US20030033117A1 (en) | 2003-02-13 |
WO2002008975A3 (en) | 2002-05-30 |
EP1303826A2 (en) | 2003-04-23 |
AU2001278574A1 (en) | 2002-02-05 |
US6829566B2 (en) | 2004-12-07 |
GB0018158D0 (en) | 2000-09-13 |
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