Optimum Contact Stiffness
The Contact Stiffness input on the Support component is optional, and if omitted, an optimum default is calculated during subsequent analyses. The associated calculation procedure is as follows:
a) For the initial static analysis step a high stiffness is assumed for all supports with the Contact Stiffness input omitted.
b) Immediately after this step the average surface reaction is calculated for each of the supports above.
c) If the Optimum Contact Stiffness option on the Project component is set to Largest then the largest average surface reaction from all related supports is extracted. This largest extracted value is combined with the power law equation for the ramp to provide an optimum stiffness value that achieves the same reaction at zero surface penetration. The optimum contact stiffness is then applied to all supports requiring default stiffness. Note that the initial high stiffness value in conjunction with the ramp would have prevented the pipe from actually reaching the contact surfaces as well as resulting in relatively long dynamic run times. However with the new optimised stiffness these limitations should be overcome.
d) A similar calculation is also carried out if the Optimum Contact Stiffness option is set to Individual, however rather than using the largest average reaction to calculate an overall optimum, each support average reaction is used to determine a specific optimum stiffness for individual supports. Note that this results in different contact stiffness for each support but nonetheless the values should still be of similar magnitude.
e) Steps b) to c) are also repeated at the end of the static analysis procedure so as to account for any significant changes in support reactions during the various analysis steps, thus ensuring realistic static results and also maximising subsequent dynamic run time performance.