,and I forgot to mention one more thing. The reason (according to what my mind says) that why couldn't you conduct an analysis without a force for a linear contact and you could for a non-linear contact might be that, as has already mentioned, the solver will try to push the cylinder away from the ring if there exists penetration more than the tolerance (before the analysis starts). This is when the force will automatically be developed from within the analysis without the need for an external force, and you would be seeing a reaction force coming from the contact. But since you already have no initial penetration (as shown in the contact tool figure I shared), therefore this is still not the reason why you are seeing a resultant force reaction at this contact.