Apparently, container optimization was unsolved for very large fleets. I did not know this.
Google OR improves existing solutions by 10%-20% utilization which is incredible.
Google OR improves existing solutions by 10%-20% utilization which is incredible.
The insight is to see time as a spatial dimension - then a set of shipping tasks - each with a length determined by time to complete the task - can be packed into a set of 1d bins representing boat schedules!
This is variously known as the supply chain optimization problem in logistics, the minimal makespan problem in manufacturing, and the multiprocessor scheduling problem in compsci. All of these problems have been classically formulated as bin packing problems.
Toy model: Single ship + Single container Bin Packing
Here is how it works for a single boat and a single package going between multiple ports. In this case, the problem is equivalent to a shortest path problem on a graph with weighted nodes, and more traditionally presented as a shortest path problem on a graph with weighted edges. I'll show the model and the graph translations!
The model consists of:
1. One bin - a 1 dimensional line representing the utilization of the ship over time
2. Line segments p_1 .. p_k representing the transit time for each of k possible shipping operations (taking the container from some port to some other port). For this model, assume p_1 = p_k = 0, representing the first and final transits
3. A port relation P_ik saying "transit k can immediately follow transit i," or equivalently, "transit i's arrival port is transit k's departure port"
A span is a sequence of line segments respecting the port relations, starting at p_0 and ending at p_k. The problem is to find a makespan - an optimal span.
This is the same as the shortest path on a directed graph G with nodes weighted p_1 .. p_k, where we draw an arrow i -> j iff P_ij.
This graph can also be "dualized" into a directed graph G' where nodes are ports, and arrows between ports are weighted by transit times. This is the most familiar form of this problem.
Define an equivalence relation i ~ j saying transit i and j are equivalent iiff P_ik = P_jk for all k (i and j arrive at the same port). Now give G' a node for each equivalence class [i], which we call ports. Finally, for any pair of ports [i] and [j], add an arrow [i] -> [j] with weight p_k if and only if there exists k such that
1. P_ik. (Transit k leaves from port [i])
2. k is in [j]. (Transit k arrives at port [j])
Now we have the traditional shortest route problem on a graph with weighted edges. However the bin packing model naturally scales to the case where we have many ships, larger cargo capacities, many containers, and complex transit constraints.
In this general case, we regain the geometric packing aspect as well! This is because the ships are represented by 4 dimensional bins, which are packed with containers in x, y, z AND t dimensions! The spatial part of this packing now has to obey efficiency constraints like minimizing the unpacking and reshuffling that happens at each port! Wild, huh?
Exactly.
I was exposed to this sort of conception of the packing problem when implementing Ant Colony Optimization (ACO) for a programming challenge.
https://en.wikipedia.org/wiki/Ant_colony_optimization_algori...
-heavier containers at the bottom for stability
-refrigerated containers on the inside to reduce heat loss
-containers to be unloaded first near the top
etc
And all in 3 dimensions!
In the same vein, port /starboard / bow / stern balance.
> -containers to be unloaded first near the top
Containers with the same destination in separate places so that multiple cranes can run in parallel without infringing on each other's work-zones.
Truly an interesting project for people who get stuck trying to optimize too many things at once. :p
It's strange to me that the cargo space has not been aggressively optimized. It's a pretty substantial part of civilization and, I believe, there's definitely some money sloshing around there.
To be fair, a completely optimal solution definitely seems out of reach, but I'm not interested in those.
There are also a lot more constraints than weight and balance and they're constantly changing; some may rule out big chunks of the state space which is very good, but it's still a Hard Problem.
But it's not like there aren't people already doing it.
Just imagine the contingency planning due to restrictions in unloading.
Also, because of the short time requirement, and some extreme low temperature requirements on some cargo, it needs to be in a place where it can be disconnected and very quickly craned off the ship.
The engineer making and breaking the connections will generally have to manually log the time of these actions and the time of the unload. It's all a very interesting and somewhat complicated process.
It should be straight forward to include full wagon power with the upcoming DAC4EU coupling (UIC 552 says that normal coaches are to have an 800A through connection that's regularly fed with 1000V 16.7Hz or 1500V 50Hz; this is single-wire earth(/track)-return).
Keep in mind that unlike North American freight trains, Europe mainline service is almost fully electrified. Thus the reefer would be grid-fed.
I'm asking because I'm looking to propose a change to the current plans for the electric coupler (use near-field RF instead of the currently-preferred single-pair Ethernet or it's fallback powerline; I think 802.11 has suitable PHY options, especially among the OFDM codes if the near-field chamber is dispersive and/or has problematic resonances in the channel), and throwing in "grid power for reefers" with actual numbers from the reefer container industry would be easy (a change to the coupler is a change, and the additional cable through the wagon shouldn't be that extensive either if it's an economical aluminum type; also this would allow passenger coaches that are currently using the pre-DAC4EU hook and chain coupling to be used with DAC4EU rolling stock).
IIRC international reefers require three phase power with a 50 amp breaker so even 800 amps won't get you very far if they all start up at once.
But an automated system sounds like it has its own problems, how does it make sure it has proper ventilation and comes on at the right time? Probably I don't want the container to start venting diesel fumes when it's deep in a stack of lego surrounded on all sides.
It has to be automated since it’s a refrigeration unit that needs to know when to turn on the cooler. The control circuit starts up the generator if it senses no power connection at that time, usually off a standard marine lead acid battery.