Simulation study of a triple rail mounted gantry crane system

I am writing a research paper about a productivity increase by using a triple rail mounted gantry carne system serving a storage block. A part of this paper is a simulation study about the TRMG. For those who don't know what TRMG system means: A pair of twin cranes running on the same rails and a large cross-over crane running on its own rails are used for the storage block. My Question: Is it possible to simulate a TRMG system with Flexsim CT?


Thanks in advance


Jan

Yes. You can use the ResourceGroup object to control multiple cranes on the same block.

Are the conflicts among the three cranes considered and resolved by the ResoueGroup object?

This is the case for three end-loaded cranes. When I looked at the options available under the Dispatch Strategy in ResouceGroup, it seems they are used for side-loaded cranes.

The ResourceGroup should be able to handle end-loaded cranes, but not by simply using the default pick options. You can use the pick options as a starting point for writing custom code to control it exactly how you want.

It's not easy, but it is possible.

Actually, I don't know if the resource group is enough to do an end-loaded scenario with multiple cranes, that is, if you want the cranes to avoid each other properly. Often times in an end-loaded scenario, the crane will need to load a container and then wait for another crane to move out of the way, or just get out of the way of another crane. The resource group is specifically tasked with dispatching, not motion coordination once a stack/unstack task has already been dispatched.

For a project we did with Moffatt & Nichol a few years ago, we decided to break the problem into two pieces. First, we built a very simple, regular Flexsim model that just simulates one stack, that does all of the crane coordination, where they wait for each other and move out of each other's way, etc. Then, we figure out from that model the overall efficiency loss that you get through all of the waiting and get out of the way, and then just use that efficiency loss as an assumption in defining the load and unload times when we build a CT model with end-loaded cranes. So the CT model doesn't explicitly do crane coordination, but it does simulate it abstractly through defined extra load and unload times.

Dear Anthony,
the actual focus of my research paper is the first and very simple model that you described. It is my first time working with this software that is why I would like to ask you a couple of questions. What type of cranes and what type of stack did you use for your model? The Institute I am writing for just bought the CT license. Will I be still able to do the simulation or do I need a normal Flexsim license as well.

Jan,

the Flexsim CT licence includes Flexsim ("normal") GP, so you should be fine anyhow, no matter how you decide to build your model.

Good luck

Ralle
aka Ralf
Flexsim

In our scenario we simulated twin RMGs on an end-loaded stack. Other than that I don't know the exact crane type. But you should be able to do it using regular Flexsim, and you get a Flexsim license with CT, as Ralf mentioned.

Jan,

What you are trying to model is the CTB configuration of Automatic Stacking Crane (ASC) stacks, right? Is that HHLA you are working for? I think HHLA must have modeled it and studied its performance.

The model that we built is a standard twin end-loaded ASC block configuration with two ASCs working on the same pair of rails, one for waterside and one for landside. The three ASC configuration as seen in CTB will be more complicated and I know that the spreader of the bigger ASC has to be at a specific location to allow smaller ASCs passing.

Anyway, it is a interesting research topic. Good luck.

Alan,

yes I am trying to model the CTB (ASC) but I am not working for the HHLA. I am writing a paper for the University of Hamburg. Did you use the Object ResourceGroup for your project?

Jan,

No, we did not use ResourceGroup. It was a special logic written for two RMGs as described in Anthony's post. It basically follows a First In First Serve rule to solve the conflicts between two RMGs.

Thanks Alan. If I want to write a special logic myself where do I have to implement it? Do I place it in the travel sequence of the gantry crane or do I need to put it somewhere else?

You may actually use a regular crane object in Flexsim and put your logic in the onbeginoffset and onresourceavailable trigger.

To break the problem into 2 pieces seems to be a very good idea for me. But I doesn't understand the way you do it in detail. Can you explain it a bit more for me? Especially how you transfer the transports from the regular to the simple model. And the detailed way, you figured out the efficiency lost. I want to use this method for crane transports with the standard crane ( of the Discrete Object Lib ) and need to model transports between a lot of station at different places. Every crane can serve every station, but the cranes are on the same rails. Because I have to do it with many different plant layouts, I think this method would be very useful for me.

Thanks in advance
Michael

Originally Posted by Anthony Johnson

For a project we did with Moffatt & Nichol a few years ago, we decided to break the problem into two pieces. First, we built a very simple, regular Flexsim model that just simulates one stack, that does all of the crane coordination, where they wait for each other and move out of each other's way, etc. Then, we figure out from that model the overall efficiency loss that you get through all of the waiting and get out of the way, and then just use that efficiency loss as an assumption in defining the load and unload times when we build a CT model with end-loaded cranes. So the CT model doesn't explicitly do crane coordination, but it does simulate it abstractly through defined extra load and unload times.