Tài liệu HD4-1 Control Structure pdf

MIKE 11 HD EXERCISE 4 CONTROL STRUCTURES INTRODUCTION What Is MIKE11 CS The MIKE 11Control Structures module should be used whenever the flow through a structure is to be regulated by th

MIKE 11 HD EXERCISE 4 CONTROL STRUCTURES INTRODUCTION

What Is MIKE11 CS

The MIKE 11Control Structures module should be used whenever the flow through a structure is to be regulated by the operation of a movable gate or the flow is controlled directly as in the case of a pump MIKE 11 CS has four control types:

 Underflow Gate (Sluice Gate)

 Overflow Gate (Weirs or Inflatable Dams)

 Radial Gates (Dam spillways)

 Discharge Control (pumps)

What is this session?

This session will guide you step by step through the basic features of MIKE 11 CS When working with the examples, you will become familiar with the most important features of the control structure module

With the help of the MIKE 11 Reference Manual and the MIKE 11 on-line Help you will be able to work carry out most control structure operations

Before You Begin

Even though MIKE 11 CS contains a user-friendly interface and on-line help you will require an understanding of the respective hydraulic engineering principles In addition to the help menus some additional information about controllable structures is detailed in the Appendix We recommend that you read this information particularly if carrying out PID control

CONTROL STRATEGY

The Control Strategy is the sequence of commands or rules that determine the way a structure in MIKE11 can be operated For the purposes of the following descriptions we will assume that the structure in question is a Sluice Gate However, the principles are applicable to all types of structures and/or pumps For all a sluice gate the set level is determined by a control strategy A control strategy describes how the gate level is set when a condition is met at a control point

For a specific gate it is possible to have any number of control strategies by using a sequence (or list) of

`IF' statements which are evaluated as TRUE or FALSE consecutively Each ‘IF’ statement can have any number of conditions that all must be evaluated to TRUE for the `IF'-condition to be evaluated as TRUE

A control strategy is defined by two conditions:

1 The condition that must be evaluated as TRUE or FALSE

2 The control that is to be applied to the structure (gate level)

The control to be applied to a structure is a relationship between an independent variable and a dependent variable The independent variable is the value of a control point such as a water level upstream of a gate and a dependent variable is the value of the target point such as the level of the gate

The Control Strategy Dialog

1 The control strategy for a structure is set using

the Control Definitions dialog on the tabular

view of the network editor Any number of

Control Definitions can be entered for a

particular structure and in combination they

are referred to as the control strategy

2 The Control Definitions are evaluated

consecutively starting with 1 through to the

last (Number 4 in the example shown here The control definitions are evaluated sequentially until a definition is evaluated as TRUE The last

control definition is always assumed to be

TRUE if all definitions are FALSE ) Explore

various control definitions available

3 For each Control Definition you must define

the Calculation Mode that the strategy will

operate with and the type of Control and

Target point If you wish to scale the Target

points you must also specify the type of

scaling The available Calculation Modes are:

 Direct Gate Operation The Direct Gate

Operation is the most commonly applied

mode In this mode the gate level is set

directly by the rule

 PID Solution Under PID solution the gate

levels will be set using a PID algorithm

that will calculate the gate position based

on the control variable

 Momentum Equation If the Momentum

equation option is chosen then the

structure will be removed and the Fully

Dynamic Equation will be solved This is

useful for the simulation of inflatable

fabridams after deflation

 Iterative Solution The iterative solution method allows you to specify and hydraulic condition that must be met MIKE11 will then iterate

each simulation time step to find a gate

position that will achieve the required target

4 The Control Type can be selected as any state

variable from a MIKE11 HD, AD or WQ

simulation There are also a range of specific

control types that are computed from the state

variables Explore the various types of Control

Variables

5 A scaling factor can also be introduced to scale the

target point

values The

target point can

be scaled by a

time series

(created by the

user) or a

computational

variable at some

point in the

solution

Scaling variable

allows the user

to define an operating rule that may change slightly depending on the conditions A typical case would be the seasonal variation of a gate or the setting of a gate level as a function of the water level

Control

Definitions have

been defined the

user can set the

evaluation rules

by selecting the

‘Details…’

button in the

Control

Definition

dialog Select

the Details button and explore the Definitions Dialog

7 On the Control and Target point Tab of the Details window you should first define the location of the Control Point and the Target Point If you are using Direct Gate operation then you will not have to define a Target Point as it is automatically set to Gate level and to the branch and chainage points of the structure However, if you are using the iterative solution then you will have to specify the target point where you would like to achieve a particular condition

8 On the Control

Strategy tab you

set the Control

Point values and

the

corresponding

Target Point

values

MIKE11 will

use this table to

determine what

the target point

should be for

any given Control point value For a simple underflow gate you would typically set the Control point

as the upstream water level and the Target Point as the gate level Notice that when you move the mouse over the Values table that the type of variable and the units for the variable will be displayed in

a fly out dialog

9 The Logical

Operands tab is

logical

statements that

must evaluate as

TRUE for the

control strategy

to be applied

You can enter

any number of

logical statements The statements are evaluated consecutively using the AND logical join In other words, all the logical statement must evaluate to TRUE for the control strategy to be implemented The statements read from right to left The example statement shown is read as follow: The water level (H) on the Branch called River at chainage 180 is greater than > 36.5 If the ‘’ Use TS value switch is set to on then the values are taken from a Time series file that is specified Note that the grey fields change depending on the setting selected for the control rule Investigate the various Logical Operand Types (LO Types) and the various sign types available If a logical type such as dH is chosen you will have to enter two Branch Name and Chainage locations which will first be used to calculate the dH variable before the logical expression is evaluated

10 The iteration/PID tab allows you to enter the parameters for controlling the PID algorithm or the iterative solution In the iterative solution you have to set the convergence criteria The criteria can be set as absolute or as relative If absolute is used then the iteration will achieve convergence if the difference between the target point and its desired value are within the limits specified If the Relative convergence criteria is used the Values in the criteria represent the fraction of the desired target value (ie 0.1 represents a value that is within 10% of the target value) We will not cover the PID control

in this course but for more information on the PID control please take the time to read the Appendix document

11 The Control Structure module can be used to build up extremely complex rules and is a very powerful tool for dam operation and optimization, irrigation system control and other applications that require control To become completely comfortable with the operation of the system you need to use the system and implement a control rule You should try the following problems to familiarize yourself with the system

Controlling a Sluice Gate

This exercise will involve you setting up a simple sluice gate in a channel and changing the gate level at a specified time This is the simplest form of control structure and is good for introducing you to the concepts of the control structure In practice much more complex control algorithms are used

1 To start this exercise you need to first develop a single branch irrigation channel model The irrigation canal has a constant cross-section as shown below with the following geometric parameters:

 The channel is 10 km long

 The channel has a constant slope of 0.02%

 Channel roughness of 0.02 Mannings’n

 The upstream end channel invert is 2.0m above datum

2 Now we will insert a sluice gate structure in to the

canal The gate (underflow structure) is constructed 7.5

km from the upstream end with the following geometry:

 The gate width is 25m

 The sill level + 0.5m

 The inflow head loss coef is 0.1

 Initially the gate level is 3.0m

Note you will have to insert two cross sections immediately upstream and downstream of the structure You can insert these structures using the automatic interpolation of cross sections facility in the Cross Section Editor

3 Apply the following boundary conditions to the model:

 At the upstream end, a constant discharge of Q = 125 m3/s

 At the downstream end, a Q-h relation has been provided below

0 20 50 100 250 500

0 0.98 1.71 2.61 4.59 7.06

4 Use the "Control Structures", investigate the effect of closing the gate from +3.0m to +1.25 m over a

15 minute period What is the rise in water level upstream?

5 Add a Secondary canal to the above model setup at 7.4 km (i.e 100m upstream of the sluice) This canal has the same slope and roughness as the main canal The length is 2.5 km In the Secondary canal at a point 100m downstream of the bifurcation, insert a gate (Sill level=+0.5m, Width = 15 m) Set the inflow head loss coef to 0.1

The Secondary canal has a similar cross-section to the main canal, except that the canal bottom width

is b = 15m The Q-h relation to be applied at the downstream boundary of the Secondary canal is;

0 20 50 100 250

0 1.51 2.66 4.09 7.19

6 Now try to operate the gate in the secondary canal to restrict the increase in water level caused by closing the main gate to a maximum level of 4 m Implement the following rule:

IF

(WL u/s Main Gate > 4.0m) THEN (Raise gate 0.1m, to a maximum level of 6.5m)

ELSE IF

(WL u/s Main Gate< 3.0 m) THEN (Lower gate 0.1m)

ELSE

(Do nothing)

7 How far does the gate in the secondary canal need to be raised?

Controlling a Dam Spillway Using Radial

Gates

This exercise will involve you setting up a simple

simulation of a river channel with a small flood

control and water supply dam at the headwaters

You must control the water level in the reservoir

to prevent overtopping using a set of Radial Gates

on the spillway The control of the gates is based

on two conditions; the inflow into the reservoir

and the water level downstream of the dam If the

inflow increases, water must be released to

prevent overtopping but you must also maintain

water levels down stream below critical thresholds

to prevent flooding

1 To start this exercise you need to first develop a single branch river channel model The channel has a constant cross-section as shown below with the following geometric parameters:

 The channel is 50 km long (chainage 0 to 50000)

 The channel has a constant slope of 0.02% (0.0002m/m)

 Channel roughness of 0.03 Mannings’n

 The down stream end invert of the channel is 0.0m above datum

2 We will locate the dam structure 200m (chainage 200m) from the upstream model boundary and include the dam storage as additional storage area in the processed data of the cross section data The Storage relationship for the Dam is given below

3 The spillway has 5 radial gates with the following geometry

 The gate width is 3m

 The sill level is 35.0m

 The radius of the gates is 2m

 The Trunnion height is 2m

 Gate height is 4.2m

 We will assume that the reservoir is initially at full supply level of 35m

4 The downstream tail water level is constant at 5m above datum and the upstream inflow hydrograph is given below

Discharge (m3/s)

1/06/2001 00:00 0 1/06/2001 06:00 100 1/06/2001 12:00 100 1/06/2001 18:00 100 2/06/2001 00:00 100 2/06/2001 06:00 100 2/06/2001 12:00 100 2/06/2001 18:00 100 3/06/2001 00:00 100 3/06/2001 06:00 100 3/06/2001 12:00 100 3/06/2001 18:00 50 4/06/2001 00:00 50 4/06/2001 06:00 50 4/06/2001 12:00 50 4/06/2001 18:00 0 5/06/2001 00:00 0 5/06/2001 06:00 0

5 Implement a control of the dam spillway such that the following rules are maintained

 The gates must be fully closed if the level is below 35 m

 If the reservoir level exceed 35m then open the gates to 35.2m

 If the reservoir level exceeds 35.5 m the gates shall be operated to minimize flooding down stream at 25000 The flooding level at chainage 25000m must be maintained below 18m as long as possible before the flood and as soon as possible after the flood inflow abates

 If the water level is greater than 36.5m (37m is overtopping) then the gates must be fully opened (37m) for inflows greater than 50m3/s For inflow less than 50 m3/s the gates should

be set at 36.5m

APPENDIX

WHAT IS PID Control

Engineering Applications

Engineers often concern themselves with how to control things Often we take this concept of control for granted, and don't even consider that anything is really happening at all The cruise control on a car is very familiar and easy to overlook, but the exact method by which the car is able to maintain a constant (or almost constant) speed can be mysterious Along the same lines, how does your refrigerator keep your food at a constant cold temperature no matter how your house temperature may change How do modern radio receivers lock onto radio stations and adjust the tuning as we drive, keeping our music playing cleanly All of these are control systems, and require a good understanding of engineering principles to understand fully

On/Off Control

As an introduction to the concept of a control

system, we'll start with a basic and familiar

example Consider the furnace in your house

If you return from vacation, you've probably

had the house set at a low temperature, say

60°F As soon as you walk in, you say to

yourself "BRRRRR!", and immediately turn

the thermostat up to 70°F But, it takes a while

for your house to warm up What is

happening?

In your house, the thermostat is connected to

the furnace and acts as a switch Your familiar

with how it works If the temperature you've

set in the thermostat is less than the actual

temperature in the house, the thermostat turns the furnace on to add heat to your house In our example, when you turned the thermostat setting up to 70°F, the furnace kicked on because the actual temperature in the house was lower (60°F) As the house warms up, the temperature rises (DUH!) When the temperature in the house finally passes 70°F, the thermostat automatically shuts off the furnace Then the thermostat waits until the temperature drops a couple of degrees below the 70°F you set when you walked in the door When the temperature drops enough, around 68°F, the thermostat once again kicks on the furnace and the cycle repeats

This type of control is called On/Off control No surprise there This type of control system works

by adjusting a controlled variable (in our example the furnace changing the air temperature) to achieve a setpoint (70°F) It does it by simply turning on the furnace if it is too cold, or by turning

off the furnace when it warms up

Graphically, we can look at it this way When you get home you changed the furnace setpoint to 70°F, and the furnace turned on You should note that the temperature DOES NOT HOLD PRECISELY AT 70°F It oscillates around the setpoint

This oscillatory nature is the problem with On/Off control While it is OK in your house there are many instances where we would simply not put up with this kind of control

Proportional Control

Now let's consider a slightly more complex example Think of a basic automobile cruise control (A cruise control will attempt to keep a car driving at a constant speed automatically) If we were to design a cruise control using the On/Off control scheme, no one would like it The car would be