Information Technology Reference
In-Depth Information
year, optimizing vessel movements can significantly reduce the economic and
environmental burdens of containerized shipping, and allow shippers to better
utilize repositioning vessels to transport cargo. The aim of the IVLSFRP is to
maximize the profit earned when repositioning a number of vessels from their
initial services to a service being added or expanded, called the goal service.
Liner shipping services are composed of multiple
slots
, each of which represents
a cycle that is assigned to a particular vessel. Each slot is composed of a number
of
visitations
, which can be thought of as port calls, i.e., a specific time when a
vessel is scheduled to arrive at a port. A vessel that is assigned to a particular
slot sequentially sails to each visitation in the slot.
Vessel sailing speeds can be adjusted throughout repositioning to balance
cost savings with punctuality. The bunker fuel consumption of vessels increases
cubically with the speed of the vessel.
Slow steaming
, in which vessels sail near or
at their minimum speed, therefore, allows vessels to sail more cheaply between
two ports than at higher speeds, albeit with a longer duration (see, e.g., [12]).
Phase-out and Phase-in.
The repositioning period for each vessel starts at a
specific time when the vessel may cease normal operations, that is, it may stop
sailing to its scheduled visitations and go somewhere else. Each vessel is assigned
a time when it may begin its repositioning, called its
phase-out
time. After this
time, the vessel may undertake a number of different activities to reach the goal
service. In order to complete the repositioning, each vessel must join slot on
the goal service before a time set by the repositioning coordinator, called the
phase in
time. After this time, normal operations on the goal service begin, and
all scheduled visitations on the service are to be undertaken. In other words,
the repositioning of each vessel and optimization of its activities takes place in
the period between two fixed times, the vessel's earliest phase-out time and the
latest phase-in time of all vessels.
Cargo and Equipment.
Revenue is earned through delivering
cargo
and
equip-
ment
(typically empty containers). We use a detailed view of cargo flows. Cargo
is represented as a set of port to port demands with a cargo type, a latest delivery
time, an amount of TEU
1
available, and a revenue per TEU delivered. We sub-
tract the cost of loading and unloading each TEU from the revenue to determine
the profit per TEU of a particular cargo demand. In contrast to cargo, which
is a multi-commodity flow where each demand is a commodity with an origin
and destination port, equipment can be sent from any port where it is in surplus
to any port where it is in demand. We consider cargo demands and equipment
consisting of either
dry
or
reefer
(refrigerated) cargo. Vessels have a limited ca-
pacity, and are therefore assigned a maximum number of reefer containers and
a maximum number of all types of containers.
Sail-On-Service (SOS) Opportunities.
While repositioning, vessels may use
certain services to cheaply sail between two parts of the network. These are called
SOS opportunities
. The two vessels involved in SOS opportunities are referred to
1
TEU stands for
twenty-foot equivalent unit
and represents a single twenty-foot
container.
