Hardy-Cross Network Diagram Convergence

[Timmy!]

If I am given a set of diagrams for possible solutions to a Hardy-Cross network, and asked which one converges the quickest, how do I approach this problem? Might there be a key I can focus on to solve by inspection?

 

[cmp252]

I have always worked them by trial and error. There might be an easier way but none of my prof. never cared to share those methods. I can sit down and work a HC problem but for me it takes longer than 6 min. Its a pretty safe bet that there will be a HC problem or 3 reservoir problem if not both. When I took the test I skipped those longer problems and worked all the others that I knew I could do. If I have time to work one of the above problems great if not oh well. I passed without working either one of those type problems. To me they take up too much time to work when I know I can work most of the other problems. I would not get too hung up on one type of problem. thats just my $.02

 

[sceriana]

I agree with cmp252 ... I would not get hung up with these type of problems. These type of problems take more than 6-minutes to solve and your best bet is to use trial and error. Try to look at your answer choices and see if you can back in to them. I don't remember per say a HC problem in the last PE but there was a 3 reservoir problem. I tried to work through it and I know I didn't come up with one of the four answers, but I was able to eliminate one or two and make my best guess. I still passed thankfully! But don't get hung up too much on these type of problems ... it will drive you crazy. You'll end up concentrating on it too much only to realize you've just spent 20-minutes or however many minutes, become flustered and you need to move on!! Best of luck!

 

[vmi2000]

I agree that they are time consuming problems, however they really are easy plug and chug problems. If you take a first stab you may get lucky and if not you would have a good guess for second swipe. You just need to understand the HC method and be efficient at the plugging and chugging. :2cents:

 

[cantaloup]

I have always worked them by trial and error. There might be an easier way but none of my prof. never cared to share those methods. I can sit down and work a HC problem but for me it takes longer than 6 min. Its a pretty safe bet that there will be a HC problem or 3 reservoir problem if not both. When I took the test I skipped those longer problems and worked all the others that I knew I could do. If I have time to work one of the above problems great if not oh well. I passed without working either one of those type problems. To me they take up too much time to work when I know I can work most of the other problems. I would not get too hung up on one type of problem. thats just my $.02

You guys should not skip the Hardy Cross nor the 3 tanks problem. Why? Because the H-C method is the basic of water distribution modeling software which is applied everywhere from small utility companies to large cities. How often you guys need to design a spillway or dam ? Storm sewer drainage system (which includes detention/retention pond), sanitary sewer flow system, drinking water distribution system are the 3 backbones of hydraulics engineering. I figured out that for PM water resource module there must have about 15 to 17 questions on hydraulics, 4 to 5 questions on hydrology and 4 to 5 question on water treatment; total would be 26 questions which represents 65% of PM portion. They will give the problem in the exam, but they will not ask you to solve the whole thing, they will solve it partly and you will complete it, thus it would not take much time. The point is you need to know how to solve it, to know the concept.

 

[IlPadrino]

You guys should not skip the Hardy Cross nor the 3 tanks problem. Why? Because the H-C method is the basic of water distribution modeling software which is applied everywhere from small utility companies to large cities. How often you guys need to design a spillway or dam ? Storm sewer drainage system (which includes detention/retention pond), sanitary sewer flow system, drinking water distribution system are the 3 backbones of hydraulics engineering. I figured out that for PM water resource module there must have about 15 to 17 questions on hydraulics, 4 to 5 questions on hydrology and 4 to 5 question on water treatment; total would be 26 questions which represents 65% of PM portion. They will give the problem in the exam, but they will not ask you to solve the whole thing, they will solve it partly and you will complete it, thus it would not take much time. The point is you need to know how to solve it, to know the concept.

Cantaloup,

I disagree with your reasoning. Understanding concepts has nothing to do with the PE Exam. From a practical perspective, there are few (if any) review courses that would sacrifice learning how to answer the greatest number of questions correctly in the shortest time possible in exchange for knowledge or understanding of concepts. I remember very clearly what the head of my review course said: "I'm not here to teach you engineering - save that for the Universities or your work. I am here to teach you how to pass a test."

Any Engineer worth his salt can solve any single problem given enough time. To pass the PE exam, the Engineer needs to learn how to pass enough problems in sufficient time. That's the bottom line.

So... I don't disagree with your conclusion (you need to know how to solve it). But I do disagree that it has anything to do with the PE Exam.

I also passed on anything more than a cursory review of culverts and the six classes. It just didn't seem worth the time given I had plenty else I could work on.

 

[Fudgey]

So how much do you realistically they could ask on a Hardy/cross type question. It seems like an awful lot of work to iterate through to completion and the math is messy. Maybe like the flow at a node after one iteration? I saw a practice question like that once. i dont wanna waste a lot of time on a problem like that but can't afford to get picky.

 

[DeputyStateFireMarshal PE]

Cantaloup,
I disagree with your reasoning. Understanding concepts has nothing to do with the PE Exam. From a practical perspective, there are few (if any) review courses that would sacrifice learning how to answer the greatest number of questions correctly in the shortest time possible in exchange for knowledge or understanding of concepts. I remember very clearly what the head of my review course said: "I'm not here to teach you engineering - save that for the Universities or your work. I am here to teach you how to pass a test."

Any Engineer worth his salt can solve any single problem given enough time. To pass the PE exam, the Engineer needs to learn how to pass enough problems in sufficient time. That's the bottom line.

So... I don't disagree with your conclusion (you need to know how to solve it). But I do disagree that it has anything to do with the PE Exam.

I also passed on anything more than a cursory review of culverts and the six classes. It just didn't seem worth the time given I had plenty else I could work on.

ASSED2:When I took the Civil test in 1999, I self-studied using only the NCEES study materials and PASSED on the first try. IMHO - The test should be approached as a pass/fail task with emphasis on passing the test, not on achieving 100% perfection. Getting 60% of the way through the test with 100% correct answers is not as good as getting 100% through the test with 70% correct answers.

My preferred way to study was to work old test problems (from the NCEES study materials) and practice time efficiency and other test taking skills [like tabbing books and writing out your work in basic steps (to avoid errors and to facilitate checking your work & locating errors)]. Knowing where to quickly go to get a formula is very important, as well as getting the correct formula. Practice answering the prescribed number of problems in the prescribed time.

Remember this test is like the real world - it is time limited! If you can't work with deadlines, you'll have a hard time in most engineering jobs since people pay engineers to solve problems and in today's business environment, they want solutions yesterday.