Hand Calculations
Hand Calculations
(OP)
I would consider myself possessing an ample knowledge of finite element analysis, applying proper LBC, material properties and so on. If I would want to double-check a simulation study, I would opt for solving a simpler or complexer study by changing mesh types.
I know it is common practice to double-check by means of a hand calc.
However I just can not wrap my head around hand calculations and tend to want to avoid them. Does anybody have suggestions on how to get better at them?
And most important, are hand calculations essential to be taken serious as an employee involved with finite element analysis or is that a bridge to far?
I know it is common practice to double-check by means of a hand calc.
However I just can not wrap my head around hand calculations and tend to want to avoid them. Does anybody have suggestions on how to get better at them?
And most important, are hand calculations essential to be taken serious as an employee involved with finite element analysis or is that a bridge to far?
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RE: Hand Calculations
RE: Hand Calculations
If the type of analyses that you are talking about is something like static, dynamic, or thermal then you can get books of problems (Schaum's or Problem Solving are two that come to mind).
RE: Hand Calculations
The hand calcs will keep you in check and tremendously improve your ability to think about the right way to set up the FEM and greatly improve the result.
I know someone who prides himself on his FEM ability, but had poor ability translating theory into practice. He has built some of the most poor, ineffective, and costly FEMs that I have seen. In some cases I overrode the results via napkin scribble and a calculator. The other thing is that learning hand calcs is a more valuable skill than running a FEM program. This will help you in career opportunity and gain you respect. Not to mention that you can take those skills with you and don't have to worry about what software the company runs.
Brian
www.espcomposites.com
RE: Hand Calculations
I would say that if you "know" what to expect in terms of result before you run the analysis and than get the expected result, it is probably correct. At least there is a good chance. Then you have probably understood the problem and modelled it properly.
Otherwise you are, worst case, just pushing buttons if I put it harsh
Regards
Thomas
RE: Hand Calculations
Tobalcane
"If you avoid failure, you also avoid success."
"Luck is where preparation meets opportunity"
RE: Hand Calculations
Get a copy of Roark's and a copy of Peterson's. It helps to have good references.
RE: Hand Calculations
Andries
RE: Hand Calculations
Once you're past that stage the level of confidence will increase if the results are similar to other results obtained in the past or they're 'in the right ball park' of what you expect, to use an americanism. That 'ball park' figure is best obtained from hand calculations.
A higher level of confidence is reached if the results from the model agree with measurements taken from an existing case, showing that your assumptions, material properties, etc., are validated. I wouldn't be necessarily highly confident that the model results were correct because they agreed with some 'noddy' calculations someone had made as the assumptions in them are generally very simple compared to a FE model, and of course mistakes could have been made in the hand calc itself.
Tara
RE: Hand Calculations
I'm now often in a position of checking over some of the younger engineers work before it goes into fabrication. It's not that unusual to find a design that's not even close to meeting the loading requirements. When I consult with the engineer I will always find they didn't have a clue as to what the results should look like. They just took the results of the FEA and put it on paper. Of course the results are accurate to ten decimal places but the structure will not handle the loading. That's scary.
RE: Hand Calculations
It is my belief that no "young engineer" should be allowed to use FEA until they are competent in hand calculations and the use of free body diagrams.
However what I find scary is the push by management in many companies to out-source FEA to cheap consultancies where the "analysts" know what buttons to press in the software to produce pretty pictures but have no understanding of stress analysis.
www.Roshaz.com quality, cost effective FEA solutions
RE: Hand Calculations
RE: Hand Calculations
FEA is a fantastic and phenomenally powerful tool but like powerful physical tools (hand held chainsaw) it can be a deadly weapon in untrained hands. Push button technology in every industry has made people mentally lazy (remember when staff in small shops used to have to add up the cost of goods in their heads? in £sd?). The situation is not helped by a culture (amongst ignorant managers) that loves seeing glossy contour plots and loathes any hand written calculations. So the hand calculations get put into excel or mathcad and you're back to the push button technology again where the spreadsheet just becomes a template for subsequent users to plug a few numbers into, again with little or no thought behind their actions.
www.Roshaz.com quality, cost effective FEA solutions
RE: Hand Calculations
Get a copy of Roark & Young and an older version of Stress Concentration Factors by Peterson (the new ones are too small and don't lie flat on your desk.)
Doug
RE: Hand Calculations
Tara
http://tinyurl.com/4ydjg7m
RE: Hand Calculations
As someone stated, FEA can be dangerous.. "FEA will make great engineer from a good one, but it will make dangerous one from a bad engineer" that's how we describe this in firm
To be better at FEA ? expierence is essential (from my point of view).
As for the hand calc.. if it isn't too time costy - why not. It's better to sleep well (sometimes checking critical points of problem it's enought).
"If an experiment works, something has gone wrong"
RE: Hand Calculations
I don't know if you are mechanical or structural or otherwise in your studies. I rely on statics, mechanics of materials and a variety of structural analysis methods (energy and numerical) to determine overall responses and or stresses.
Other good sources for this include Roarks Stress and Strain as well as other such as Practical Stress Analysis in Engineering Design by Blake.
I agree with the others, it's practice, practice, practice.
Regards,
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RE: Hand Calculations
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