Indra,
By riser do you mean a riser attached to a platform or a drilling riser deployed from a floating vessel or jackup?
If its the latter then you will need to use dedicated FE software to accurately capture the combination of first order loads from waves and currents and the second order loads due to vessel movement.
for the former you may be able to use a hand calculation approach, but as a riser will be more heavily loaded by waves than a pipeline, you will end up converting a load of waves to distributed loads and working out bending moment ranges. You will then have to account for wave directionality and combine all the results.
Unless you have a lot of time available and are happy with only obtaining approximate results, I would suggest that you would be better getting a software package such as ORCAFLEX or FLEXCOM and use that to perform the analysis.