4.5. Boundary Conditions

4.5.1. BOUNDH (class)

Fig. 4.5.1 Pressure head boundary condition

Supplier type

type label	description	active
BOUNDH (reservoir)	Constant or time dependent head	Yes

4.5.1.1. Mathematical model

A BOUNDH prescribes the head in a certain point of the system.

(4.5.1)\[H=f(t)\]

The head specified is the total energy head and, because the velocity in the reservoir is zero, equal to the hydraulic head and equal to the level in the reservoir. The head is constant during the steady state calculation. During the unsteady state calculation the head can vary in time according to a table specified by the user or specified by a Control Component. To achieve the specified head the BOUNDH has to supply or consume fluid to or from the system. The discharge will be determined by the continuity equation for the H-node the BOUNDH is connected to. When a BOUNDH is located between two pipes it actually decouples the system: the pipes are behaving independently of each other and waterhammer waves will reflect fully (reflection factor -1).

Entrance losses

The entrance losses are not accounted for in the BOUNDH (class). The entrance losses can be modeled with RESIST (class) elements, which is adviced if the velocity at the reservoir becomes significant.

4.5.2. BOUNDH (reservoir)

4.5.2.1. Hydraulic specifications

description	input	unit	range	default	remarks
Head at t = 0	Real	[m]

See also “Mathematical model” on page 224.

4.5.2.2. Component specific output

None

4.5.2.3. H-actions

In unsteady state the head can vary in time using the action table. An example is given below:

BOUNDH Action table HTIME

Time [s]	Head [m]
0.0	10.0
0.99	10.0
1.0	20.0
1.99	20.0
2.00	0.0
2.99	0.0
3.00	20.0
10.00	20.0

The table must always start at t = 0. The value of the property “head at t = 0” is synchronized automatically by the user interface with the steady state value (value at t = 0) specified in the action table.

In this example the head remains at the steady state value until 0.99 s. At t = 1.0 s the head suddenly rises to 20.0 m and keeps that value until 1.99 s. At t = 2.00 s the head falls stepwise to 0 m etc. Wanda will interpolate the values in the action table to find the correct value for the current timestep.

4.5.2.4. Component messages

None

4.5.3. BOUNDQ (class)

Fig. 4.5.2 Discharge (or flow) boundary condition

Supplier type

type label	description	active
BOUNDQ (reservoir)	Constant or time dependent discharge	yes

4.5.3.1. Mathematical model

A BOUNDQ prescribes the discharge in a certain point of the system.

(4.5.2)\[Q=f(t)\]

Sign convention:

• into the system

• out of the system.

The component BOUNDQ supplies discharge (called the delivery rate) to the system. For the steady state calculation the discharge is constant. For the unsteady state calculation the discharge can vary in time according to a user-specified table or a Control Component. The component BOUNDQ can be very helpful in modelling a branched system or a reciprocating pump.

Entrance losses

The entrance losses are not accounted for in the BOUNDQ (class). The entrance losses can be modeled with RESIST (class) elements, which is adviced if the velocity at the reservoir becomes significant.

4.5.4. BOUNDQ (reservoir)

4.5.4.1. Hydraulic specifications

Description	input	unit	range	default	remarks
Discharge at t = 0	real	[m3/s]

See also “Mathematical model” on page 226.

4.5.4.2. Component specific output

None

4.5.4.3. H-actions

In unsteady state the discharge can vary in time. The time variation must be defined in menu ‘Hydraulic actions’ via a specified table.

An example is given below:

BOUNDQ Action table QTIME

Time [s]	Discharge [m3/h]
0.0	0.0
1.00	200.0
10.00	20.0

The table must always start at t = 0. The value of the head at t = 0 must match with the steady state value given in the template of component BOUNDQ.

In the example the rate is zero at steady state. It rises linearly in 1 s to 200 m³/h. After 1 s the rate decreases linearly in 9 s to 20 m³/h.

4.5.4.4. Component messages

None