det_F < 0 in step-44

[seconds]

Hi,

I try to solve my  heart mechanic problem using two fields mixed finite element. And I write my program based on step-44. 

In one of my tests, only body force (no surface traction) is applied to a cube.The programm is sensitive to the magnitude of the external force I add.When the magnitude is small, the programm  can run well. But if  I increase the magnitude, the programm throw an exception det_F < 0.I wonder if  the magnitude contributes to the exception.

So I modify the original step-44 programm, just changing the following statement

 static const double p0 = -4.0/(parameters.scale * parameters.scale)

into 

                                                                                     static const double p0 = -400.0/(parameters.scale * parameters.scale)

Again, the programm throw an exception det_F< 0.

I guess  the magnitude leads to the exception. But I don't know how? Can anyone give me  some help.

Thanks

Seconds

[Andrew McBride]

 Hi Seconds

J = det F maps an infinitesimal volume from the reference configuration to the current. If J < 0 we have self-penetration of matter. In the discrete finite element setting it implies that the element is "too distorted”. The code has an assert that is triggered if this unphysical situation arises. 

Is this loading you apply physically meaningful? What displacement do you expect? I’m not surprised to see J<0 if the problem is constrained and the loading severe.

Andrew

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