special connecting element

Very urgent two enquires:

1. How to model rotational spring element in order to define a curve
like M=k*(theta) where theta is the rotaional angle? It seems that
abaqus could only provide F=kx model.

2. there is a dashpot connector element which behaves like F=C * V
(where C is a constant), can I ask how to model F=C*(dv/dt)=C*a(where a
is the derivative of change of velocity)?

Thanks.