Hi,

I am working on a nonlinear contact problem with Abaqus. One of the parts

involved in the complete model is very small and as its behaviour needs to

be studied when it interacts with other parts, it is modelled with pretty

smaller elements as compared to other parts. When I do a Dynamic explicit

analysis then the time increment which Abaqus calculates from an Element by

element estimate is of the order 1e-8 due to that very small part. I did

mass scaling such that the increment becomes 1. e-7 (by DT= 1. E-7) and

used selective subcycling to complete my simulation. The percentage change

of mass in this process is 2.6 % which I think is pretty acceptable. But

there is one problem now. When I observe the transient response of my

simulation then I see that the part which is very small and of material

rubber is kind of jittering a lot as though it is modelled as fluid.

However, on the positive note this jittering is almost dying out at around

half-time of the simulation. I think that as the time increment size is very

less i.e. 1e-7 it could be high frequency vibrations that I see at the start

of the simulation. I tried increasing the default Bulk Viscosity parameter

to (0.25, 4.0) and I do observe that the high frequency jittering has

reduced at the start of the simulation itself. But I want to completely get

rid of with such high frequency vibrations (if I am right that they are the

same)...Is increasing the Bulk Viscosity parameter more further until I get

rid of them is the solution? Also there are limits to this value as

increasing the Bulk Viscosity parameter reduces the stable time increment

and affects accuracy also.

Thanks for your help.

Regards,

Manasvi

I am working on a nonlinear contact problem with Abaqus. One of the parts

involved in the complete model is very small and as its behaviour needs to

be studied when it interacts with other parts, it is modelled with pretty

smaller elements as compared to other parts. When I do a Dynamic explicit

analysis then the time increment which Abaqus calculates from an Element by

element estimate is of the order 1e-8 due to that very small part. I did

mass scaling such that the increment becomes 1. e-7 (by DT= 1. E-7) and

used selective subcycling to complete my simulation. The percentage change

of mass in this process is 2.6 % which I think is pretty acceptable. But

there is one problem now. When I observe the transient response of my

simulation then I see that the part which is very small and of material

rubber is kind of jittering a lot as though it is modelled as fluid.

However, on the positive note this jittering is almost dying out at around

half-time of the simulation. I think that as the time increment size is very

less i.e. 1e-7 it could be high frequency vibrations that I see at the start

of the simulation. I tried increasing the default Bulk Viscosity parameter

to (0.25, 4.0) and I do observe that the high frequency jittering has

reduced at the start of the simulation itself. But I want to completely get

rid of with such high frequency vibrations (if I am right that they are the

same)...Is increasing the Bulk Viscosity parameter more further until I get

rid of them is the solution? Also there are limits to this value as

increasing the Bulk Viscosity parameter reduces the stable time increment

and affects accuracy also.

Thanks for your help.

Regards,

Manasvi

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