How to exert acceleration

Main Forum
1

Hi,

I want to model a vibrating seated driver using the SeatedHuman demo model. However, my data is accelerations measured from the seat-pan.
I was wondering if there is a way to exert acceleration (for example instead of force) to the seat-pan or another node.
In other words, I want the x-direction acceleration of the seat, and subsequently human hip, to be specified. How can I do that?

Thank you,
Sincerely Yours,
Mahdi

2

Hi again,
I have another question. I wanna exert force to the human pelvis(or any other point) in the SeatedHuman model. I added the lines below to the code but the outputs like the spine compression or muscle activities did not change at all. What is the problem?

AnyFolder Loads = {
      AnyForce3D PalmLoad = {
        F = {300*t, 0, 0};
        AnyRefFrame &PointOfAttack = Main.HumanModel.BodyModel.Trunk.ContactPoints.Pelvis;
      };
    };

Thank you,
Regars,
Mahdi

3

Hi Mahdi,

I can think of two possible reasons.

1.the force is not included inside the study you are running?, it either needs to be inside study or referred to by the study. Otherwise the study will not know it should apply this force.

  1. The force may be taken up by the support elements acting on pelvis. So it may not change muscles forces much. To check this try to add a very large force and look for differences.

Best regards
Søren

4

Hi Mahdi,

Two comments:

  • You can not directly apply an acceleration, it needs to be applied as e.g. a forces or as positions. In this case with a vertical acceleration i would do an AnyKinCoM measure on the human model and apply the force to this measure. If you apply e.g -9.81 * Bodymass as a force in the direction of gravity you will have double acting gravity (assuming you leave gravity in study unchanged) This quantity in the human model is a CoM measure Main.HumanModel.BodyModel.Interface.CenterOfMass that you can apply the force on.

  • The frequency can not be too high... it would not be realistic. The model will react instantly to any frequency you will apply so if you apply 500Hz you will see muscle fluctuations in 500Hz something not physiological possible. In reality a some point the muscles will not be able to react anymore. So frequency can only be so high that you will expect the human to be able to react actively to the applied loads, otherwise results will not be realistic.

Best regards
Søren

5

Thanks for your time and elaborate explanation. That was really helpful.

Best Regards

6

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