how to maintain queue level and allow outlet rate positive all the time?

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Min Z6 asked Feb 9, '22 Min Z6 answered Feb 17, '22

how to maintain queue level and allow outlet rate positive all the time?

I have a continuous process. In the queue, it is initially empty. I first close the "output" of the queue and then fill the queue to a certain level. Afterwards, I open the output of the queue and allow outlet to flow. In the "process flow", I constructed a logic by adding a decision block, i.e. once the level in the queue is below certain level, I shut off the output. As a result, even though I can maintain the level in the queue, the outlet rate will drop to zero when output is shut off. I am wondering what logic I shall implement here to allow outlet flow positive all the time.

Software Version:

FlexSim 20.2.3

queue contiuous outlet

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Dan Bell commented · Feb 09, 2022 at 06:53 PM

Hi @Min Z6,

Could you clarify what you mean by constant "positive" outflow? Do you not want to have to close and open the ports?

It's also hard to know how to help without looking at your model. To receive a more accurate solution, please post your model or a sample model that demonstrates your question.

Proprietary models can be posted as a private question visible only to FlexSim U.S. support staff. You can also contact your local FlexSim distributor for phone or email help.

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Min Z6 Dan Bell commented · Feb 10, 2022 at 12:23 PM

Hi Dan:

Thank you for your reply. I figured out a way to solve this problem. Instead of using level control in process flow, I changed it to "Push to List" in 3D and then "Pull from the List" by assigning the criteria of pulling length above certain number or pulling age greater than a certain age. That way, I will not shut off the outlet completely. It seems to work. Can you please comment on this approach?

Many thanks,

Min Z6

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Ryan Clark commented · Feb 17, 2022 at 12:04 AM

Hi @Min Z6,

As @Zach T mentioned in a comment below, we prefer that you ask new questions as a separate post. This helps to keep the forum more organized for all of our users. We won't address any additional questions on this thread, but if you post a new question, we will be more than happy to assist you. Please see Best practices for using this Answers site - FlexSim Community for more info. Thanks!

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Answer 1 · 2022-02-10T09:56:57Z

Jason Lightfoot answered Feb 10, '22 Min Z6 commented Feb 10, '22

It sounds like you want a periodic release of items from the queue when the level is between two values. In the attached model I placed 3 labels on the queue to control the release.

I set the sendTo port of the queue to not release:

I created an object instanced process flow for the queue to push items to a list when they arrive and to release them at the interReleaseTime interval when the queue's content is between the levels.

Hope this is what you wanted.

Queue_interReleaseTime.fsm

1644486814112.png (5.9 KiB)

1644486861415.png (2.6 KiB)

1644486974807.png (24.5 KiB)

queue-interreleasetime.fsm (55.0 KiB)

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Min Z6 commented · Feb 10, 2022 at 12:29 PM

Jason:

Thank you so much for your answer. It appears to be the solution that I am looking for. I apologized that I did not find your answer when I replied to Dan's message. It seems that we look for a solution on the same trajectory.

Again, thank you very much,

Min

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Answer 2 · 2022-02-17T12:16:40Z

Min Z6 answered Feb 17, '22

@Dan Bell @Jason Lightfoot @Zach T Thank you all for the help. After going through a simple case, I figured out the issue in my model. Now the question that I asked has been resolved. Again, thank you very much for answering my previous questions.

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Answer 3 · 2022-02-11T21:12:08Z

Min Z6 answered Feb 11, '22 Zach T commented Feb 11, '22

@Dan Bell @Jason Lightfoot

Dan:

I created a CSTR operation. My intention is to allow the operation reach steady state and continue to feed out the products. At certain operation time, I need to stop the feed and then the contents in the queue should be pushed out.

Here is the file:

CSTR_SS_Opt.fsm

The file however once stopping the feed, the 100 items in the list will always be there. Do you know how I can push the 100 items in the list in Queue1 out if I stop feed from Processor1? I set the criteria in "Processor2" by using pull strategy with "Where QueueSize > 100".

Many thanks,

Min

cstr-ss-opt.fsm (33.1 KiB)

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Zach T commented · Feb 11, 2022 at 09:47 PM

Hi @Min Z6, one of the community guidelines is that when you have multiple questions to ask, you post each one in a separate question thread. This makes it easier for other people in the future to find an answer if they have the same or a similar question to yours. If each of your individual questions are buried in the same thread, its less likely that they will help someone else out in the future. Thank you.

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Answer 4 · 2022-02-11T20:13:35Z

Min Z6 answered Feb 11, '22

queue-interreleasetime_02112022.fsm

queue-interreleasetime-02112022.fsm (53.9 KiB)

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Answer 5 · 2022-02-11T20:11:16Z

Min Z6 answered Feb 11, '22

@Jason Lightfoot

@Dan Bell

Jason and Dan:

I have some questions to ask. If there is no feed, for example, after certain time t0, the feed is stopped. Have all the items in the queue been pushed into the list even though the feed is stopped? Will all the items in the list be counted as the queue size in the queue, i.e. can I use the number of all the items in the list to count the level in the queue? What is the role of interreleasetime? If I set interreleasetime to 0, will there be no items in the list once the release process gets started or maintain the hold level? I simulated using interreleasetime of 0, checked the list and found no item in the list. How does this parameter affect the overall productivity?

I also made modification of your case (Jason). See attached file. One problem is that if the items make the queue full, it will not release the item afterwards. How can I overcome this issue? In practice, there will be constraint on the queue size but the feed is still expected.

I apologized for so many questions for this topic.

Thank you,

Min

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