Rule Based Control

Rule-based Controls are statements of the form:

RULE ruleID

IF condition_1

AND condition_2

OR condition_3

AND condition_4

etc.
THEN action_1

AND action_2

etc.

ELSE action_3

AND action_4

etc.

PRIORITY priority

where

ruleID	=	an ID label assigned to the rule
conditon_n	=	a condition clause
action_n	=	an action clause
priority	=	a priority value (e.g., a number from 1 to 5)

The following conventions apply to rule statements:

1. Only the RULE, IF and THEN portions of a rule are required; the other portions are optional.

2. Any number and combination of AND and OR clauses can be used in a rule.

3. When mixing AND and OR clauses, the OR operator has higher precedence than AND, i.e.,

IF A or B and C

is equivalent to

IF (A or B) and C.

If the interpretation was meant to be IF A or (B and C)then this can be expressed using two rules as in

Rule 1: IF A THEN ...

Rule 2: IF B and C THEN ...

4. The PRIORITY value is used to determine which rule applies when two or more rules require that conflicting actions be taken on a link. The higher the value the higher the priority. A rule without a priority value always has a lower priority than one with a value. For two rules with the same priority value, the rule that appears first is given the higher priority.

5. There is no limit on the number of rule statements that can be added to a project.

A condition clause in a Rule-Based Control takes the form of: object id attribute relation value where

object	=	a category of network object
id	=	the object's ID label
attribute	=	an attribute or property of the object
relation	=	a relational operator
value	=	an attribute value

Some example conditional clauses are:

    JUNCTION 23 PRESSURE > 20

    TANK T200 FILLTIME BELOW 3.5

    LINK 44 STATUS IS OPEN

    SYSTEM DEMAND >= 1500

    SYSTEM CLOCKTIME = 7:30 AM



The Object keyword can be any of the following:

    NODE           LINK   SYSTEM

    JUNCTION   PIPE

    RESERVOIR   PUMP

    TANK   VALVE

When SYSTEM is used in a condition no ID is supplied.

The following attributes can be used with Node-type objects:

    DEMAND

    HEAD

    PRESSURE

The following attributes can be used with Tanks:

   LEVEL

   FILLTIME (hours needed to fill a tank)

   DRAINTIME (hours needed to empty a tank)

These attributes can be used with Link-Type objects:

   FLOW

   STATUS (OPEN, CLOSED, or ACTIVE)

   SETTING (Pump speed or Valve setting)

The SYSTEM object can use the following attributes:

   DEMAND (total system demand)

   TIME (hours from the start of the simulation)

   CLOCKTIME (24-hour clock time with AM or PM appended)

Relation operators consist of the following:

   = IS

   <> NOT

   < BELOW

   > ABOVE

   <= >=

An action clause in a Rule-Based Control takes the form of:

object id STATUS/SETTING IS value

where

object	=	LINK, PIPE, PUMP, or VALVE keyword
id	=	the object's ID label
value	=	a status condition (OPEN or CLOSED), pump speed setting, or valve setting

Some example action clauses are:

  LINK 23 STATUS IS CLOSED

  PUMP P100 SETTING IS 1.5

  VALVE 123 SETTING IS 90

Here are several examples of Rule-Based Controls.

Example 1:

This set of rules shuts down a pump and opens a by-pass pipe when the level in a tank exceeds a certain value and does the opposite when the level is below another value.

RULE 1

IF TANK 1 LEVEL ABOVE 19.1

THEN PUMP 335 STATUS IS CLOSED

AND PIPE 330 STATUS IS OPEN

RULE 2

IF TANK 1 LEVEL BELOW 17.1

THEN PUMP 335 STATUS IS OPEN

AND PIPE 330 STATUS IS CLOSED



Example 2:

These rules change the tank level at which a pump turns on depending on the time of day.

RULE 3

IF SYSTEM CLOCKTIME >= 8 AM

AND SYSTEM CLOCKTIME < 6 PM

AND TANK 1 LEVEL BELOW 12

THEN PUMP 335 STATUS IS OPEN

RULE 4

IF SYSTEM CLOCKTIME >= 6 PM

OR SYSTEM CLOCKTIME < 8 AM

AND TANK 1 LEVEL BELOW 14

THEN PUMP 335 STATUS IS OPEN

Rule-Based Controls are applied after an initial hydraulic state of the network is computed (i.e., after time zero). They are evaluated over the course of a hydraulic simulation as follows:

1. The rules are evaluated at a sub-hydraulic time step equal to 1/10 of the normal hydraulic time step (e.g., if hydraulics are updated every hour, then rules are evaluated every 6 minutes).

2. Over this sub-hydraulic time step, clock time is updated as are the water levels in storage tanks (based on the last set of pipe flows computed).

3. If a rule's conditions are satisfied, then its actions are added to a list. If an action conflicts with one for the same link already on the list then the action from the rule with the higher priority stays on the list and the other is removed. If the priorities are the same then the original action stays on the list.

4. If the list is not empty, then the new actions are taken. If this causes the status of one or more links to change then a new hydraulic solution is computed.

5. The action list is cleared and the next sub-hydraulic time step is checked.