Environmental Engineering Reference
In-Depth Information
where
E
(
X
) is the average total waiting time of trucks picking up containers
I
d
bay
i
E
(
X
) =
w
g
(
X
) +
(
X
)
v
bay
+
d
row
(
X
)
v
row
+
d
tier
(
X
)
v
tier
i
i
i
=
1
Subject to
I
x
it
≤
c
∀
t
∈ {
1,
...
,
T
}
(1)
i
=
1
T
x
it
≥
m
∀
i
∈ {
1,
...
,
I
}
(2)
t
=
1
x
it
∈ {
0, 1
}
(3)
The objective function is to minimize the total emissions from picking up contain-
ers at a block of import yard. The value of
E
(
X
) is calculated by using a simula-
tion model for the gate and import yard system, as described below. Constraint (
1
)
assures that the total of containers picked up in a period cannot exceed the capac-
ity of yard crane. Constraint (
2
) guarantees that the number of periods offered to
shipping company cannot be less than a desired number decided by the container
terminal. In a terminal without any arrival control, trucks can come at any time
in a day, so this number of available periods (the variable
m
) will be 24 h. In this
study, we would like to test what if the terminal operator provides half or one-third
of such available periods to a specific container, whether and how much the truck
waiting time and idling emissions can be reduced.
4 Solution Algorithm
In this section, we introduce the solution algorithm, including the genetic algo-
rithm, the simulation model and the procedure of the overall solution algorithm.
4.1 Genetic Algorithm
The decision variables in the mathematical model described above are represented
the available periods for picking up of import containers. There are thousands of
containers in a block and each container has several available periods for being
picked up. Hence, this is a combinatorial optimization of thousands of decision
variables. Moreover, in order to evaluate a feasible solution, we have to esti-
mate the total emissions which is proportional to the total waiting time of trucks.
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