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Leaf spring analysis

Hi,

I am working on Leaf Spring nonlinear analysis using Hyper mesh and Radioss solver.

I have completed the run but results on Radioss differ from actual (experimental) results. I have attached .rad starter, engine file and output files.

Regards,

Pratik

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pratik gadve

Hi,

@George P Johnson

Altair Forum User

Hi Pratik,

We have discussed on a similar model.

As told before for achieving this simulation you will have to run this simulation for a long time in RADIOSS, which is not recommended. Else,instead of concentrated load we will have to try with an imposed load (imposed displacement) type so that we can simulate it in a short time.

The other option is to run with OptiStruct, where you can easily simulate this.

pratik gadve

Hi Pratik,

We have discussed on a similar model.

As told before for achieving this simulation you will have to run this simulation for a long time in RADIOSS, which is not recommended. Else,instead of concentrated load we will have to try with an imposed load (imposed displacement) type so that we can simulate it in a short time.

The other option is to run with OptiStruct, where you can easily simulate this.

Hi George,

Will you please explain what is imposed load and how to apply it ?

Imposed displacement is just to give displacement for bottom nodes of leaf spring but i didn't understand what you meant by imposed load.

Altair Forum User

Hi Pratik,

Imposed displacement is what I meant which you have to provide to the bottom nodes.

gopal_rathore

Hi Pratik,

This seems to be a quasistatic analysis and being solved in radioss. As George said, try with imposed displacement as boundary condition.

Use curve with foll. values in first trial run:

Time Displacment (mm)

0.0 0.0

0.1 100

pratik gadve

Hi Pratik,

This seems to be a quasistatic analysis and being solved in radioss. As George said, try with imposed displacement as boundary condition.

Use curve with foll. values in first trial run:

Time Displacment (mm)

0.0 0.0

0.1 100

Ok . Thank you.

Altair Forum User

Hi Pratik,

Moved your last query to OptiStruct sub forum and please follow up your query at:

pratik gadve

@George P Johnson : Regarding Leaf spring analysis you had solved on Radioss, I have query on relation between element time step, Run Time, minimum element length.

I have seen video you had shared regarding how to calculate element time step and relation between L, E and rho. But did not understand how to calculate termination time ?

My time step is very low. Why did you choose more number of animation files to be written and more RUN time ? ( How you decided 4 sec as termination time for my analysis ?? I tried lowering termination time to 2 sec but results fluctuated from original. )

Will you explain logic behind relation of (Engine file assistant parameters) minimum time step, termination time, minimum element size & number of animation files to be written to get smooth animation results without staggering effect ?

Altair Forum User

Hi Pratik,

Explicit scheme is a function of time and the explicit algorithm works in time step increments.Time step is the time required for a shock wave (governed by the speed of sound) to propagate across the smallest distance of the element. A run is a single model simulation and it starts at time zero and continues till the user defined endpoint is reached.

From the above relation, it is clear that both material modulus and density control the speed of sound. The solution time step is inversely proportional to the speed of sound. So, if the material is stiffer (higher modulus of elasticity), the speed of sound increases resulting in a lower solution time step. Thus, to keep a stable solution, the shock wave through a medium must not pass across more than one element per time step. This implies that the length of the element is the modeling parameter that affects the overall solution time.

Usually explicit analysis lasts only for a certain milliseconds, like crash, impact, drop...etc. Basically the user should get enough experienced in explicit analysis so that before running the analysis user can estimate a rough run time. Based on the energy plots once the system is stable we will terminate the run and thus a run time is calculated. In your simulation in order to achieve such a high deflection the run time was estimated for 4sec and hence I asked you to run with OptiStruct as your case is not an explicit one. Regarding the number of animation files, we always recommend to write 30-40 animation files which will give a smooth result.

pratik gadve

Hi Pratik,

Explicit scheme is a function of time and the explicit algorithm works in time step increments.Time step is the time required for a shock wave (governed by the speed of sound) to propagate across the smallest distance of the element. A run is a single model simulation and it starts at time zero and continues till the user defined endpoint is reached.

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

From the above relation, it is clear that both material modulus and density control the speed of sound. The solution time step is inversely proportional to the speed of sound. So, if the material is stiffer (higher modulus of elasticity), the speed of sound increases resulting in a lower solution time step. Thus, to keep a stable solution, the shock wave through a medium must not pass across more than one element per time step. This implies that the length of the element is the modeling parameter that affects the overall solution time.

Usually explicit analysis lasts only for a certain milliseconds, like crash, impact, drop...etc. Basically the user should get enough experienced in explicit analysis so that before running the analysis user can estimate a rough run time. Based on the energy plots once the system is stable we will terminate the run and thus a run time is calculated. In your simulation in order to achieve such a high deflection the run time was estimated for 4sec and hence I asked you to run with OptiStruct as your case is not an explicit one. Regarding the number of animation files, we always recommend to write 30-40 animation files which will give a smooth result.

George,

' Based on the energy plots once the system is stable we will terminate the run and thus a run time is calculated' did you mean my energy plots (Energy error, mass error) in engine output file got stable after 4 sec after I hit run ? And then you killed the process and decided run time as 4 second ?

Altair Forum User

Hi Pratik,

From the time history (T01) file we will plot the global energy curves. Please check the below global energy plot.

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

You can see that the total run time is 100 milliseconds. We can notice that after 80 milliseconds there is no much variation in the curves and it has become stable. Then we can conclude that there will not be much changes happening in the model and can terminate the run.

In your model I ran two runs and I understood that the model will take 4 seconds with the applied load to reach the expected deformation. You may have to do some iterations in your run and finally choose the termination time.