Model based real-time control of sewer system using fuzzy-logic

8)

Pergamon

Waf. Sci. Tull. Vol. 36, No. 8-9. pp. 343-347.1997. Q 1997 IAWQ. Published by Elsev ier Science Ltd

Printed in Great Britain.

PH: S0273-1223(97)00575-1

0273-1223197 S J 7'00 + 0-00

MODEL BASED REAL-TIME CONTROL OF SEWER SYSTEM USING FUZZY-LOGIC L. Fuchs, T. Beeneken, P. Sponemann and C. Scheffer lnstitut fiir technisch-wissenschaftliche Hydrologie Engelbosteler Damm 22. D-30167 Hannover. Germany

ABSTRACT This paper describes the use of the sewermodelHYSTEM-EXTRAN in combination with a rule basedcontroldevice using fuzzy-logic to simulatethe real-timecontrolof a sewersystem. The rules for the controlof the system were set up with the helpof optimization procedures.Theadvantage of the procedure is provedby comparing the uncontrolled versus thecontrolled state in a simulatedmode for an existingsewer system.The final systemwas installedand tested within the sewer system. @ 1997IAWQ. Published by Elsevier Science Ud

KEYWORDS Real-time control, rule based system, fuzzy-logic TIlE SEWER SYSTEM FLENSBURG sOD The study was carried out for a part of the sewer system of the city of Flensburg, where runoff of rural areas drains into the sewer system. Within these small creeks detention basins have been built, to prevent the city flooding. In spite of these detention basins, flooding occurs frequently. During some of these events, the capacity of the detention basins was not exhausted. In a first step towards a real-time control system, this part of the sewer system was investigated in detail. The hydraulic behaviour of the drainage system Flensburg-SUd was analyzed with the hydrodynamic sewer system model HYSTEM·EXTRAN . The envisioned control occurs at selected nodes in the system based on water levels. For the control of the three detention basins, the following points are of critical importantance: a) The water levels in the detention basins, in order to obtain information about the remaining capacity. b) The hydraulic state of the downstream Miihlenstrom, in order to decide whether basins can be filled or emptied. The flow reduction at the outlet of the individual detention basins occurs in Flensburg by pipe throttles, which are equipped with sliding gates. Characteristic data of the detention basins are: - RRB Friesenlager: max. vol. 19200 m', • RRB Scherrebek: max. vol. 11200 m', - RRB Sophienhof: max. vol. 26000 m',

max. capacity 0.42 m '/s ., max. capactiy 1.45 m '/s ., max. capactiy 2.60 m 'Is.,

343

crest height 3.61 m; crest height 1.50 m; crest height 2.63 m;

344

L. FUCHS et al. I-

Measu rement

- Extran

Water levels from two different measurement stations are available for calibration of the model to the real system. In Fig. I the hydrographs of one of the 5 events used for verification is shown. An attempt has been made to adjust the two hydrographs from the measurement and the simulation with only one set of parameters. The graphs show, that the correspondence between measurements and simulations are satisfactory.

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The development of rules for the control of the three rainwater retention basins required investigations, which involve the following:

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a) Analysis of events, which were performed with a hydrological model and optimi-zation. b) Simulation of the current state of the Figure 1 Water level hydrograph measurement station Flensburg drainage system with the surface runoff MS 6, event on 24.06.1991 model HYSTEM and the hydrodynamic transport model EXTRAN. c) Creation of rules based upon the simulated present state and the study of regulating elements in the retention basins of the city of Flensburg (control goal). The rules are created for the rules interpreter. Simulation of controlled state. The transport model EXTRAN provides the rules interpreter with the water d) levels for defined points in defined intervals. The rules interpreter processes these values and returns new target values to EXTRAN. e) Comparison of the control results. f) Final evaluation of the rules. [hh .rnrn]

The examination of the current state, which was used as a comparision for the optimization, was done with the

hydrological model RHBSIM and the optimization model OPTIC. A target function is defined and minimized every time-step. In the preceding case, target levels were flooding within the drainage system, backwater in basins, diversion into collecting mains, emptying the system, etc .. All target levels were evaluated with a "costfactor" for each element of the drainage system to be examined. That means, floods were determined to be more critical than backwaters and these are higher than the diversion into collecting mains. Based on the optimization and further studies, simple rules for throttling the retention basins were developed. The control decision of the rules consists of an open or closed command for the restricting element dependent upon satisfaction of the conditions. Table I:

Possible control rules for the Friesenlager, Scherrebek and Sophienhof basins based on the optimization study

Basin

Condition

Friesenlager

Vol.(Fries.) < 30'11> IIIlI Vol.(MUhlensl.) > 40% 1lIVol.(MUhlensl.) ~ 100% VoUFries.1 > 80% and VoUMUhlenSl.1 < 50% or Vol.IMUhlenSl.1 < 40% Vol.(Soph.) < 30% IIIlI Vol.(Scherr.) > 50% 1lIVol.(Soph.)< 70% IIIlI Vol.(MUhlensl.l > 95%or Vol.IScherr.1 > 80% VoUSoph.1 > 95% and VoUScherr.) < 95% or Vol.IScherr.1 < 50% Vol.(Scherr.) < 60% IIIlIVol.(MUhlensl.) > 50%1lIVol.(MUhlensl.) ~ 100% Vol.(Scherr.)> 95% IIIlI Vol.(MUhlensl.) < 90% 1lIVol.(MUhlensl.) < 50%

Friesenlaaer Sophienhof Sophienhof Schembek Schembek

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345

Model based real-time control of sewer systems

Examples ofthe results ofthe simulated current state of the system are shown in Fig. 2 and Fig. 3. MS 5

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Water level hydrograph - measuring station MS 5. rainfall event No. 01. 25.06.1985

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Figure 3

Water level hydrographs of the three rainwater retention basins (RRB), rainfall event No. 01. 25.06.1985

Fig. 3 shows an overflow of the Scherrebek during Event No. 01 on 25.06.1985. The overflow volume of -31600 m' flows out over the emergency spillway. The hydrograph for measurement station MS 5 is shown in Fig. 3. As soon as the top of the railway embankment opening is reached, the water level rises to a critical level. If the water level exceeds this height, strong flooding takes place in this area. This station is thus an indicator for critical runoff situations. The clearly recognizable increase in the water level can be explained by the overflow of the Scherrebek basin upstream at this time. The water levels are similar during all simulated rainfall events, that is, the characteristics of the filling and discharging processes are the same. The following points can be listed, which are essential to the creation of rules for the group control: The Friesenlager basin has the highest backwater. Backwater capacity is still available.. The Sophienhofbasin still has sufficient retention capacity. At the highest water level the downstream basin Scherrebek overflows. The Scherrebek basin is very often overloaded. Retention capacity is rapidly exhausted during an event. An overflow affects MS5 with high water levels. The entire Mtihlenstrom did not overflow during the simulated rainfall events. Flooding in the inner city areas with these simulations during average water levels in the Flensburger Sound could not be demonstrated. The basins Friesenlager and Sophienhof do not overflow. The overflow volumes and the associated durations for the Scherrebek basin are listed for some events in Table 2.

PRODUCING THE RULE BASE An analysis of the current state and of the optimization simulation (Table 2) allows the creation of a rule base for the control of the Friesenlager, Scherrebek and Sophienhof basins. A study of the water level hydrographs (simulation of the current state) allows the following definition of a control goal: "Reduction of the overflow at the Scherrebek basin. If no overflow occurs at this basin. then there is a high probability that the hydraulic capacity of the Miihlenstrom is not endangered". The formulation of this goal is supported by the waterlevel hydrographs and the Scherrebek basin: Only if the emergency overflow of the Scherrebek basin becomes active,

L. FUCHS et al.

346

very high waterlevelsare causedby this additional runoff at the 'railway embankment bottleneck'. The creation of a rule base (IF... THEN...) should ensure, that this controlgoal is achieved. The controlactionsfor the regulatingelementson the retention basins are definedby 24 rules according to the requirements of the rules interpreter. If in a given time step no rule is applicable for a pump, then the pump is controlledby a pumpreferenceline. That meansthat the basin dischargeis not throttled, but is adjusted based on the local waterlevel in the basin. This rule has the following impact on the implementation of the controlin the drainagesystem: The sliding gate at the basin dischargemust be completely open. RESULTS WITHCONTROL Table 2 compares the overflowquantities in the uncontrolled state with the controlled state for the Scherrebek retention basin. A positive effectcan be clearly recognized on the overflowvolume,which was reducedby an average of 91%. The averageoverflowduration was reduced ca. 40 hours. The rapid rise in water level at the Scherrebekbasin • characteristic of the uncontrolled state - is no longer present. It can be assumed, that the MUhlenstrom as a whole has a reduced load due to the controls. As a conclusion ofthis examination the control goal can be said to be fulfilled ! Table 2: Overflow volumesof basin Scherrebeck in controlled and uncontrolled states Event No

uncontrolled Date

controlled Overflow

Duratien

[m~

Duration [hh:mml

Reduced Overflow Quantity

[m~

[hh:mml

[%1

Overflow

t

25.06 .85

31557

07:53

5754

04:58

82

2

12.09.88

25160

06 :06

3735

03:28

85

3

08.10.80

9697

05 :19

0

00 :00

100

4

31.07.72

23358

09:10

1609

02 :07

93

5

15.06.80

20527

05:24

19TI

02:16

90

6

21.07.80

1TI61

05 :03

1212

01 :41

93

7

25.07.81

25007

06:35

3243

03:08

87

8

16.07.73

15497

05:23

365

01:04

98

9

04.09.90

12473

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00 :00

100

10

13.07.88

9247

03:08

0

00:00

100

190285

58:01

17895

18:42

091

Totals

COMPARISION RULE BASEDCONTROL VERSUS OPTIMIZATION Based on the fact, that different modelswere used for the studies, the results of the optimization study can only be comparedwith the controlled results for tendencies. Both studiesshow a similarbehaviortendencyfor the three retention basins: The backwater volume (V ... =11200 m') in the Scherrebek basin is very rapidly exhausted, so that overflows occur here often.

Model based real-lime control of sewer systems

347

=

The Friesenlager basin (V ... 19200 m') maintainsa large potential backwater volume during rainfall events. This capacity was recognized in both control studies and used when needed by control actions. In the current state, this basin empties last. Control actions at the Sophienhofbasin (V ... = 26000 m') have the same goal: reduce the load on the Scherrebek basin downstream. This basin has the largest unused storage capacity in the current state. The behavior of the Mahlenstrom in the hydrological study can not be compared with the hydrodynamic simulation. In comparision the hydrodynamic simulationof the Miihlenstrom determined it to be free of overflow. Critical water levels have been eliminated by the controls. The contradictory conclusions (overflow H free of overflow)are explainedby the different models.. Usingreal-time control,both the hydrological and the hydrodynamic simulation models achieved a reduction of the overflow quantities. SUMMARY Target orientedinterventions in an ongoingrunoff processare consideredas controlactions. Amongothers global control representsan operationalconcept for goal oriented interventions.The global control was conceived,such that information about the state of the drainage system was processedcentrally by a rules interpreter.The rules interpreter fed a control strategy in the form of a rule base and reached a control decision based on the state information. The study and creation of the global control system required water level measurementstations and regulating elements at the basins to be defined in the equivalent system. For the processing of the rule base, a rules interpreterwas developed. The rules interpreterusesFuzzy-Logic (fuzzification, inference, defuzzification) and is set up in such a manner,that the requirements to be a control-decision-maker will be fulfilled. A rule base for the rules interpreterwas createdbased upon optimization calculations and the resultsof the simulatedcurrent state. The formulation of a control goal was necessaryfor the rule base. This controlgoal was formulated in such a way, that existing overflows of the Scherrebek retention basin should be reduced. Achievement of this goal reduces the critical hydraulic situation of the Milhlenstrom tributary. The result of the control study is, that the overflows of the Scherrebek basin could be reduced by 90%. Additionally,the Milhlenstromno longer reaches critical water levels, which can lead to flooding. REFERENCES BEENEKEN,T., FUCHS, L., SCHEFFER,C., SroNEMANN, P. (1994):Anwendungder Fuzzy-Logikin der AbfluBsteuerung, (Use of fuzzy-logic for real-time control), Zeitschrift fUr Stadtentwlisserung und Gewlisserschutz 26, p.65-127, SUG-Verlag Hannover, 1994. FUCHS, L., HURLEBUSCH, R. (1994): Steuerung von Regenrilckhaltebecken im Bereich der Stadt Flensburg (Real-time control of detention basins in the Flensburg area), Zeitschrift fur Stadtentwlisserung und Gewlisserschutz, No. 26, p. 33 - 63, SUG-Verlag Hannover, 1994. ITWH (1993): AbschluBbericht (Final Report), Elf-Pilot ProjectAensburger Forde - Sewer System Renovation, unpublished, 1993. ITWH (1993): Regelvorrichtungenan Regenrtlckhaltebecken (Regulating Elements in Retention Basins), EDPilot Project F1ensburger Porde- Sewer System Renovation, unpublished, 1993. KAHLERT, J., FRANK, H. (1993): Fuzzy-Logik und Fuzzy-Control, Eine anwendungsorientierte Einflihrung mit Begleitsoftware,Vieweg-Verlag, Braunschweig, 1993.