Acceleration vs time data input

Shiva Kumar

I have tried to input Acc vs Time data as a Motion to a translation joint. For testing i have created a cylinder and created a curve and gave a joint to the cylinder and the ground.

The curve contains Accelaration data in mm/s^2. When i solved the model, i the cylinder started to fall, not as expected from the curve. The data is 170sec recorded at 100Hz.

The cylinder keeps falling

Kindly please help me.

Thankyou.

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Christopher_Fadanelli

Hi @Shiva Kumar ,

Going off of @Orestis_YB and @Vishvam.

With self built vehicle models, there are extra checks that need to be done in order to validate the model. For example, are the joints properly defined, if there are redundant constraints due to the amount of joints in the model can lead to inaccurate results.

We highly suggest using our vehicle library. The default models in the assembly wizard are already validated so you don't have to worry about validating the initial setup.

Building a model from our vehicle library is a breeze! I am attaching a gif on how you can immediately load up a default model.

For transferring hardpoints we have a tool called Data Summary that allows you to export the models hardpoints (and other data like mass, moi, spring stiffness, etc) as a excel spreadsheet. You can update the hardpoints in excel and reimport back into MotionView. This helps our customers save a lot of time for inputting multiple hardpoints!

Once you have inputted your data into the model. Then you can use our vast amount of events to validate your model! The main one for this discussion being the n_Post Shaker.

For more information please refer to

Two Wheeler Library

MotionSolve v2023 for Vehicle Modeling

MotionSolve Introduction Training

Best,

Christopher Fadanelli

Vishvam

Hello @Shiva Kumar

Could you please attach this test model as archived zip folder to take a better look?

Shiva Kumar

Accelration testing_archive.zip

There you thankyou for the fast response, there are two curves, the first one is in mm/sec^2

and the other in G

Vishvam

Your data shows a sharp change in acceleration to -9807 mm/s² at time = 0 s, which is equivalent to standard gravitational acceleration.

When you apply acceleration data to a body through a translational joint in MotionView:

• The solver interprets this as a prescribed motion.
• The joint will attempt to accelerate the body according to the input profile.

So at time = 0s:

• The body will immediately start accelerating downwards
• Since it jumps from zero (assuming initial rest) to -9807 mm/s² instantly, it will behave like a free-falling body from that moment.

Also the direction of gravity is adding to this motion acceleration.
If the goal is to apply the displacement, you can double integrate this data, to convert it into displacement data and apply it on the translational joint.

Shiva Kumar

Thankyou sir,

But how to perform 2 poster 4 poster jig analysis without using acceleration data, does the integration values be same as the real world displacements, no right, then how to perform these simulations sir

Vishvam

In case of n-post event, the solver internally converts acceleration data to displacement data. Same as I mentioned in my earlier comment. Below is the documentation related to that.
For n-post you can directly feed the acceleration data in the n-post event editor.

https://help.altair.com/hwdesktop/hwx/topics/motionview/n-post_event_r.htm#reference_i4h_vzl_kjb__section_bpd_yhx_wxb

Shiva Kumar

how to convert the data into displacements using expressions, i have acc vs time data.

How can i double integrate and give it as an input

Vishvam

Hello @Shiva Kumar

The screenshot regarding double integration was for the n-post event. This is what's being done in the backend by the solver. The image is just for reference.
Once you load the acceleration data in the n-post event, a new csv for displacement is automatically created in the working directory.
You can use the example 2-wheeler model and try the n-post event with your acceleration data. This will give more clarity on it

If you quickly want to convert the data, you can run a n-post example event.

Shiva Kumar

I have tried to input the curve into the n post but it is not accepting the curves, is there any way that i can integrate z acceleration data into displacement using expressions.

Orestis_YB

Hello @Shiva Kumar,

what is that you are trying to model? Is it an N-post vehicle analysis? Here you can find the relative documentation regarding n_Post Shaker. As you can see you can add there your data as acceleration input. As @Vishvam described already your acceleration signal will convert to displacement and this will be applied as motion.

In general signal units should be the same as solver units (by default mm/s^2) otherwise you should apply the proper offset or scale to the signal to bring it to those units.

Best regards,
Orestes

Shiva Kumar

i am modelling a front suspension of a motorcycle, i have the acceleration data recorded at the front wheel. i have created a post on which the front suspension lies. Now i want to observe the stress caused using flex body and the data that i have.

i have created a curve using the data, but when i applied it in the motion it is not working properly,

I am not using n-post, i have created a base/post using a cylinder.

Thank you for your fast response

Vishvam

@Shiva Kumar
We have the ready-made n-Post event in the events folder by default. You can directly double-click and start using it. Provided the vehicle is built with Vehicle Tools and it has a driver.

You need to give the input curve here, and the displacement conversion is then done accordingly.

Vishvam

For more insights on creating vehicle and events, you can go through the tailor-made eLearning for Vehicle simulations:

MotionSolve v2023 for Vehicle Modeling

Shiva Kumar

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i only have this setup sir

Christopher_Fadanelli

Hi @Shiva Kumar ,

Going off of @Orestis_YB and @Vishvam.

With self built vehicle models, there are extra checks that need to be done in order to validate the model. For example, are the joints properly defined, if there are redundant constraints due to the amount of joints in the model can lead to inaccurate results.

We highly suggest using our vehicle library. The default models in the assembly wizard are already validated so you don't have to worry about validating the initial setup.

Building a model from our vehicle library is a breeze! I am attaching a gif on how you can immediately load up a default model.

For transferring hardpoints we have a tool called Data Summary that allows you to export the models hardpoints (and other data like mass, moi, spring stiffness, etc) as a excel spreadsheet. You can update the hardpoints in excel and reimport back into MotionView. This helps our customers save a lot of time for inputting multiple hardpoints!

Once you have inputted your data into the model. Then you can use our vast amount of events to validate your model! The main one for this discussion being the n_Post Shaker.

For more information please refer to

Two Wheeler Library

MotionSolve v2023 for Vehicle Modeling

MotionSolve Introduction Training

Best,

Christopher Fadanelli

Shiva Kumar

Thank you all for the response

Shiva Kumar

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Sir i got this after double integration, that is why it is falling down @Vishvam

Orestis_YB

Hello @Shiva Kumar,

your acceleration data contain also the component of gravity. You need to use the relative to the ground acceleration in your model (offset your data by the amplitude of gravitational acceleration). I would also suggest to filter your data. The above procedure is done in the n-post shaker event.

Hope this helps!

Best regards,

Orestes