tunnel#
A pressurized tunnel object that can couple reservoirs and hydropower plants. The flow in the tunnel is calculated based on the pressure and mass balance in the tunnel network
Input connections |
reservoir, plant, discharge_group, tunnel, interlock_constraint |
Output connections |
tunnel, plant, reservoir, river, interlock_constraint, discharge_group |
License |
SHOP_OPEN |
Release version |
13.5.1.a |
Introduction#
The tunnel module can be used to model both single tunnels between reservoirs and complex tunnel systems leading in and out of hydropower plants. The main assumption is that flow in a tunnel can be determined by the pressure difference between inlet and outlet, and the head loss due to friction inside the tunnel. Tunnels are also allowed to have gates inside them to control the water flow.
Physical properties#
It is possible to input several physical properties of each tunnel. The start_height and end_height are used to determine whether the tunnel openings are submerged or not. This influences whether the reservoir level is high enough to allow water flowing through the tunnel, and the counterpressure at the far end for water flowing through the tunnel. Diameter and length are currently not in use for the optimization, but reserved for more detailed simulation of pressure wave propagation in the tunnel system. The loss_factor is multiplied with the square of the flow in the tunnel to obtain the pressure loss in the direction of the flow.
time_delay is currently put on the tunnel object for backwards compatibility, but no pressurized tunnel should have any meaningful time delay. Time delay should be placed on a river object for improved consistency and flexibility when defining delays.
Optimization properties#
For a single tunnel#
The gate_opening_curve XY-table is the basis for optimization of gates inside tunnels. If a tunnel does not have a gate inside it, this data is not needed. Note that this is not related to the old gate object in SHOP, which should not be used in favour of tunnels and rivers. The X-values represent an arbitrary position given by increasing numbers. The Y-values represent the corresponding opening factor for each position. In the simplest case, a binary gate can be described by the X-values [0,1] and Y-values [0,1]. This means that position “0” has an opening factor of 0. SHOP interprets an opening factor of 0 as a fully closed gate. The position “1” is defined with an opening factor of 1, which represents a fully open gate. The tunnel’s loss_factor is divided by the gate position, which corresponds to infinite loss for closed gate. Thus, the loss_factor used to describe the tunnel should correspond to the situation of a fully open gate.
To prevent too frequent adjustment of the gate, the gate_adjustment_cost can be used. The cost is multiplied with the change in gate opening between each time step and the product is added to the objective function. To align the optimization with the current state of the gate, use the initial_opening attribute.
If the gate is not restricted to only the listed positions, but can be set to any position between the first and last listed position, set the continuous_gate parameter to 1. If the gate opening does not need to be optimized, it can be fixed to a schedule using the gate_opening_schedule attribute. Please note that the values in the schedule refers to the position of the gate (X-values of the gate_opening_curve).
It is possible to define limits for min and max flow in tunnels by the attributes min_flow and max_flow. The attributes min_flow_penalty_cost and max_flow_penalty_cost can be set to add the possibility of breaking the min_flow and max_flow constraints by taking a penalty, otherwise the constraints are hard limits.
Involving multiple tunnels#
Some rules for operating the tunnel system depend on the state of several tunnels simultaneously. A common situation is that not all reservoirs above a plant can have open tunnels at the same time. To represent these constraints, the involved objects must be connected to an interlock_constraint. The simplest case contains two reservoirs, of which only one can be connected to the plant at any given time. After adding a interlock_constraint and connecting the tunnels from each reservoir to that constraint, set the min_open and the max_open both equal to 1.
Results#
SHOP optimizes the gate opening in all tunnels, and this gate_opening factor between 0 and 1 is reported. The optimized flow in every tunnel is also saved. The end_pressure and physical_flow for all tunnels is also post-calculated by simulating the non-linear tunnel network equations based on optimized reservoir level and plant discharge results. A difference between flow and physical_flow means that the linearized optimization problem predicts a different flow than the non-linear post-simulation.
Examples#
References#
Attributes#
start_height#
The lowest part of the opening of the tunnel at the point defined as the starting point of the tunnel (xUnit: METER, yUnit: METER)
end_height#
The lowest part of the opening of the tunnel at the point defined as the ending point of the tunnel (xUnit: METER, yUnit: METER)
diameter#
The diameter of the tunnel. This is reserved for use in the simulation (xUnit: METER, yUnit: METER)
length#
The length of the tunnel. This is reserved for use in the simulation (xUnit: METER, yUnit: METER)
loss_factor#
Friction loss factor for the tunnel. The head loss in the tunnel is found by multiplying the loss_factor with the square of the flow. The loss_factor is also divided with the gate_opening_curve y-value if the gate is not fully open. (xUnit: S2/M5, yUnit: S2/M5)
weir_width#
Width of weir at tunnel entrance. Tunnel flow is limited by the amount of water that may flow over the weir, depending on the head of the reservoir above. (xUnit: METER, yUnit: METER)
time_delay#
The delay between the water leaving the tunnel and until it ends up in the downstream reservoir. This can only be used on tunnels with end_height above the HRL of the downstream reservoir (xUnit: NO_UNIT, yUnit: NO_UNIT)
gate_opening_curve#
Relationship between gate positions and related scaling of the pressure loss in the gate. The X-values represent an arbitrary position given by increasing numbers. The Y-values represent the corresponding opening factor for each position. The tunnel loss_factor is divided with the y-value if the gate is not fully open. An y-value of 0 represents a fully closed gate and will not be used for any division (xUnit: NO_UNIT, yUnit: NO_UNIT)
gate_adjustment_cost#
A cost for changing the gate position between each time step. The given cost is multiplied with the change in gate opening between each time step and the product is added to the objective function (xUnit: NOK, yUnit: NOK)
gate_opening_schedule#
Schedule for gate opening corresponding to the x-values of the gate_opening_curve (xUnit: NO_UNIT, yUnit: NO_UNIT)
initial_opening#
Initial position of the gate used as basis for calculating adjustment costs in the first time step (xUnit: NO_UNIT, yUnit: NO_UNIT)
continuous_gate#
Flag determining whether the gate can be set to any position between listed positions in the gate_opening_curve. A value of 0 means that it can only be set at the given positions while a value of 1 means that it can be set to any position between the first and last listed position (xUnit: NO_UNIT, yUnit: NO_UNIT)
end_pressure#
Resulting pressure from the optimization at the end of the tunnel (xUnit: METER, yUnit: METER)
sim_end_pressure#
Resulting pressure from the simulated at the end of the tunnel (xUnit: METER, yUnit: METER)
flow#
Resulting flow in the tunnel from the optimization (xUnit: M3/S, yUnit: M3/S)
physical_flow#
Post-calculated physical flow in the tunnel after all optimization decisions are fixed (xUnit: M3/S, yUnit: M3/S)
sim_flow#
Simulated flow in the tunnel (xUnit: M3/S, yUnit: M3/S)
gate_opening#
Resulting position of the tunnel gate after optimization (xUnit: NO_UNIT, yUnit: NO_UNIT)
network_no#
Network identification number set by the model to indicate which tunnel network this tunnel is part of (xUnit: NO_UNIT, yUnit: NO_UNIT)
min_flow#
Minimum allowed flow in this tunnel (xUnit: M3/S, yUnit: M3/S)
max_flow#
Maximum allowed flow in this tunnel (xUnit: M3/S, yUnit: M3/S)
min_flow_penalty_cost#
Given penalty cost for violating minimum flow in this tunnel (xUnit: NOK, yUnit: NOK)
max_flow_penalty_cost#
Given penalty cost for violating maximum flow in this tunnel (xUnit: NOK, yUnit: NOK)
min_start_pressure#
Minimum allowed pressure at the start of this tunnel (xUnit: METER, yUnit: METER)