Rolling Stock(Rail cars) Crashworthiness 2

[harishbm]

Hi

I am planning to excute rail crashworthiness simulation using LS dyna. I have one doubt should I consider the passenger mass for this simulation??

If anybody have worked on this, Please share your experience!!!

Thanks in advance!1

 

[jayrod12]

I have zero experience in this however I would be inclined to look at the passenger mass and compare it to just the rail car. If it's a reasonable percentage (that percentage is variable depending on the engineer and the situation) then I would be inclined to say yes include it.

To be honest, when life safety is an issue wouldn't it be prudent to design for both with and without occupant load?

 

[dhengr]

Harishbm:
Of course you should include the passenger mass, it’s your live load condition, your max. mass, longitudinal and lateral. Is it seated only, or standing room too (larger LL), as in short distance commuting? It’s probably not a real great number in comparison to the dead weight of the car body and running gear, but it has a fairly high C.G. and is a moveable load. Break the car body and the running gear into at least two separate masses and C.G’s. Trucks (running gear) maybe into two separate masses, front and back, depending on how they are connected to the underframe, locking center pins and the like, or free to separate. Are these powered trucks, much greater weight? Today, most car bodies (underframes) have anti-climber end details and crush zones at each end to help absorb crash energy.

 

[racookpe1978]

But, do NOT assume the same acceleration/deceleration forces on these "passengers" as for the rigid frame and then use a different acceleration/deceleration forces from the wheel/axle/springs/frames.

Those three forces will slow differently upon an impact on the coupler at the ends of the car.

The damage to the people as they more slowly decelerate will reduce the damage on their bodies.

 

[harishbm]

Thanks a lot !!! As racookpe1978 (Nuclear) rightly indicated accn/deccn are different for car body and passengers, I have a small explanation for non consideration of passenger mass in the simulations. I request you to post your views on this.

Thanks in advance !!

If we look at the sequential phenomena of the crashworthiness ,the collision of carbody occurs first then the passenger collision.

The acceleration/deceleration of the carbody is different from the acceleration/deceleration of passengers.

The acceleration/deceleration of the carbody is of prime importance compared to acceleration/deceleration of passengers (Sequential phenomena).

Based on the output(Acceleration/deceleration, displacement/deformation) obtained from the collision analysis of carbody with tare weight (only carbody weight) , allowable displacement/deformation can be worked out.

Definitely there will be a decrement in the acceleration/deceleration which passes on the passengers.

In the beginning of the simulation if passenger mass is considered, the output will be different, which may induce an error/deviation in the assessment of crash energy absorption capacity of carbody

 

[BUGGAR]

When modeling the passenger mass, you have to take into account the flexibility of the bodies on secondary impact. You will also have to determine the mix of male to female passengers as they each have their own flexibility matrix.
I think your first task would be to first determine the flexibility, both elastic and plastic of each of the respective sexes. For the purpose of human demand design, plastic deformation would be considered with impacts beyond "bone breaking" levels. Elastic deformation of bodies (human) would best be carried out by the palpating of representative bodies to determine soft areas and harder areas. Interestingly, during research of this subject, it was found that far more researchers were willing to palpate female participants than male, leaving us with less data for males involved in collision events.

 

[racookpe1978]

Hey!

if you're going to put body mass in there, make sure you add at least one tall, skinny male. (Some of us ain't got no body mass to act as a shock absorber compared to a short round better-padded female.) 8<)

 

[rconner]

I do not know the answer to your question but suspect you've been given some generally good advice, About the only thing I would add is that in addition to "normal design practice" a good thing to keep in mind is that the "mass of humanity" can be surprisingly large, when folks for whatever reason crowd together. A great example is what happened in 1987 when folks crowded on to the Golden Gate Bridge during the 50 year celebration. It is my understanding that well before the crowd got fully across, the span deflected 9 feet or more, maybe even accompanied by the towers leaning toward each other and some groaning of the structure (due to load eventually found to be much greater than normally considered heavy vehicle load per many sites including

http://www.mercurynews.com/ci_20695952/day-golden-gate-bridge-flattened).

Also to be considered is that sometimes folks crowded together for celebration walks/rides or otherwise do strange things e.g. marching in cadence like soldiers across a bridge, or grandstanded crowds stomping feet in cadence with structural span frequencies (again with examples in history).
While many modern designers think they are smart enough to minimize safety factors that are encroaching on short-term competitiveness, thankfully the bridge designer and/or builders in 1930 incorporated a good safety factor in that design (to avoid a Final Destination-type scenario below)!

All have a good weekend.

 

[harishbm]

Hi

I am modeling energy absorbing device for rail car (buffers/couplers). I am using LS dyna as solver(FEM). The energy absorbing device gives out reaction force of 1000 kN with displacement of 50 mm. After that the energy absorbing device collapses. The total mass of the rail-car is around 40 tonne. Can somebody suggest me a good configuration of MAT cards that suits the above application.

Thanks in advance.

 

[berkshire]

harishbm
You might check with Dowty Hydraulics. They did a great deal of work on Buffers and Retarders in the early 1960s, and there may be some published work available.
B.E.

You are judged not by what you know, but by what you can do.

 

[dhengr]

Harishbm:
What on earth are ‘MAT cards,’ size, number of cards, arrangement, etc.? Look also, at AAR draft gears and end-of-car cushioning units. Show us some sort of a sketch of your intended arrangement, and how it fits in the car body. Are these corner of car buffers or are they a type of draft gear behind a coupler, in the center sill?

 

[harishbm]

Hi
dhengr,

oh sorry for that, MAT cards refers to Material cards in LS-dyna(FEA code) software from LSTC incorporation. Yes, as you rightly pointed out the coupler is fixed in center sill with a draftgear behind the coupler. I have attached the line diagram of car and coupler for ref.


Thanks in adavance.

 

[dhengr]

Harishbm:
Come on... If you can’t provide a more meaningful sketch of what you’ve really got than that, you are not very likely to get much meaningful help here on E-Tips. We just can’t see it from here. Is it an existing draft gear, or is that what you are trying to design? What are the various major components, the draft arm, the center sill, the car body, etc., and how are they arranged? Who are you doing this for, a railroad, a car builder? You guys get so lost in your computer software that you can’t even see the various parts of your engineering problem, and you certainly don’t do a good job a describing it, and apparently don’t really understand it. I can’t help you much with your software, but I know a thing or two about railcars. You have to use your engineering judgement to provide the correct input, and the software might still not give you all the answers, and you better know the difference.