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GRAV, ACCELERATION Model

Hi Everyone,

I am just trying to simulate the 6 axis simulation test. I have to apply acceleration in all direction as per the curve. The acceleration is time dependant. Is there any basic model to know the card needed to be defined in this analyis?

I have created one simple model (Acceleration in 1 direction) and I cannot able to run the model. Please have a look at it and let me know your suggestions/comments ASAP.

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Altair Forum User

Hi Uday,

Are you performing a dynamic analysis or a static analysis

Thanks,

Vikas

Udhayakumar Ramasamy

Hi vikas,

It is dynamic analysis similar to this video.

Altair Forum User

Hi Uday,

What is the component being tested?

You can perform this with a transient dynamic analysis. You can define the G loads using SPCD with ACCELERATION load type in all the 6 directions.

The SPCDs with ACCELERATION as load type depending on time can be defined via TABLED1 card.

Thanks,

Vikas

Udhayakumar Ramasamy

Thanks for your reply Vikas

Seat will be placed on the test device. We are going to apply pulse for particular period and will check the durability of the seat.

I am not familiar with these cards. Could you please send me the model which covers this topic or If possible could you please update the model which I have sent.

Altair Forum User

We shall send you a sample deck shortly

Thanks,

Vikas

Udhayakumar Ramasamy

Yes, Thanks Vikas.

Udhayakumar Ramasamy

Hi Vikas,

Could you please send the sample deck ASAP? Right now I am waiting for this to proceed further.

Thanks

Altair Forum User

Hi Udhay,

Please crate a load collector with no card image. Click on analysis > constraints > change load type to SPCD and pick the nodes where you want to define load.Give the unit value in all 6 directions (DOF 1-6)

create another load collector with card image tabled1 and define the acceleration vs time values here.

now create another load collector with card image as TLOAD1 and pick the SPCD load collector under EXECTID field Tabled1 under TID field and set the type to ACCE

call this TLOAD1 under DLOAD while creating the transient load step.

Currently I don't have acces to laptop, I can send the sample deck by tomorrow

Thanks

Vikas

Udhayakumar Ramasamy

Hi Vikas,

Thanks for your reply.

I have tried your suggestions and it is working without any error. I just have some more doubts in this analysis. Could you please have a look at it and let us know your comments. Basically our aim is to conduct fatigue test after transient direct analysis (time based acceleration).

1. We are using SPCD for giving acceleration and using TABLED1 for time history details. And both are referenced using Tload1. My query here is if I want to give x,y,z acceleration (separate SPCD, separate load collector for each dir.) for particular node means that particular node should be constrained by using SPC in x,y,z direction. Is this correct?

2. Damping card (using PARAM) is necessary for this analysis? Could you please explain the damping card functions in this analysis?

3. For conducting transient **** fatigue analysis, shall we use MATS1 card for material? We believe MATFAT card is only for conducting Fatigue load case. We just want to check the plastic behaviour of the structures in transient load case.

Thanks,

Udhay

Altair Forum User

Hi Uday,

Let me answer to your queries in order

1. YES

2. Damping is inherent property of any structure. It is necessary to provide damping to the structure to dampen the transient behavior over time and to find a steady state condition. There are several ways to define damping in OS. Please refer to our help manual for detailed information on the same.

3. The transient load case in OS is linear and do not take the effect of MATS1 card. If you would like to include them, then you must perform either NLSTAT or NLTRAN load cases.

Please add PARAM,NLFAT,YES to force OptiStruct to run models in which fatigue solutions reference small displacement nonlinear analysis (NLSTAT) subcases .

Thanks,

Vikas