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Shock Absorber

Altair Forum User

Hey guys, I'm looking for some help!

I'd like to set up a shock absorber model for a dynamic calculation with RADIOSS as a 1D element.

How can I do this?

The shock absorber I would like to simulate consists of two parts; a spring and a damper element.

Of those two parts I have also characteristic curves available, but how can I input them? (The two curves are

attached below)

The red line is the curve for the damper itself whereas the green line is just for the spring.

Really appreciate your help!

<?xml version="1.0" encoding="UTF-8"?>

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Altair Forum User

Hi,

You can model the suspension using Type 4 or Type 13 spring elements. You have the options available in the card to input the Force vs Displacement curve for stiffness and Force vs Velocity curve for damping.

I recommend you to watch this video where the suspension for a car is modeled using Type 4 spring is shown: https://www.youtube.com/watch?v=HMMbJXgiO2Q&list=PL1u26y75SCrA_BOCLaSewVCNY7xRvCTnA&index=2

<?xml version="1.0" encoding="UTF-8"?>

Altair Forum User

okay thank you for the answer.

I tried to implement your suggestions in a simple, single spring element and compared

the function based spring to a linear spring (putting K and C in).

The input of the spring stiffness via the Force Displacement function worked fine and I got the same result

as with a constant factor K!

Then when trying the same thing with the damping function, the solver tells me after 4 iterations that

the maximum energy error is reached and the runs has been killed. I don't know what I am doing wrong 'cause

I am assuming for C= 4 Ns/mm and my function's abscissa goes from 0mm/s to 500mm/s

and the ordinate goes from 0 N to 2000N which results in a slope of 4 Ns/mm and should be equal to the constant C...

Where is my mistake there?

And another question to the spring:

How can I implement different Force-Displacement curves for loading and unloading the spring?

Altair Forum User

Hi,

Any badly or wrongly defined material or property cards can result in such errors. Please recheck the function defined for damping. Also, please share the starter and engine out files of this run.

I strongly recommend you to go through our Crash Analysis with RADIOSS e-book, where all required details on spring elements (Page No:105 onward) are covered in detail. Please download the free e book from: http://www.altairuniversity.com/free-ebooks-2/ . Also please refer these webinars on springs http://www.altairuniversity.com/learning-library/v_b_spring-type-4-in-radioss/ and http://www.altairuniversity.com/learning-library/spring-type-13-in-radioss/ where Type 4 and Type 13 spring elements are explained with examples.

You can define unloading curve in the spring card. Please find the attached image,

<?xml version="1.0" encoding="UTF-8"?>

Altair Forum User

The starter and engine out files are below. I also attached the model itself so that you can take a look

at my damping function yourself. Apart from that I attached also two pictures of my spring property I tried to compare with.

(one where K and C got defined in its assigned box and one where I defined the two parameters via a function and as I have already

mentioned above, the spring comparison worked out fine, but the damping function has some failure in it...)

By studying your advised literature I came up with some ideas, even tough there is unfortunately no description of how to

input or set up a damping function...But my ideas failed every time, unfortunately...

May you come up with some further ideas when taking a look at my files /emoticons/default_wink.png' srcset='/emoticons/wink@2x.png 2x' title=';)' width='20' />

<?xml version="1.0" encoding="UTF-8"?>

Unable to find an attachment - read this blog

Altair Forum User

Hi,

I'll go through the files and will update you. Can you try the same with Type 13 spring?

Altair Forum User

Thanks! Tried it but got the same error occuring...

Altair Forum User

Hi,

Please recheck the values in the function defined. This can lead to errors. Rest everything in the model seems to be fine.

I'm attaching a sample spring model for your reference.

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