DNV OS F201 combined loading
2. Description
The DNV OS F201 codecheck is based on Offshore standard DNVOSF201, Dynamic Risers,October 2010 .
3. Required results
To perform the codecheck, element forces and nodal displacements need to be stored from the simulation.
These time series will be used to calculate environmental loads.
Functional loads are taken from static results. The load step which should be used must be given.
4. Description of input parameters
The following user input is required.
4.1. Input for Load, resistance and reduction factors

Safety Class (Low/Normal/High)

Limit state category (SLS/ULS/ALS)

Safety class resistance factor \(\gamma_{SC}\) (read only, may be overridden)

Load effect factor for environmental loads \(\gamma_{E}\) (read only, may be overridden)

Load effect factor for functional loads \(\gamma_{F}\) (read only, may be overridden)

Load effect factor for accidental loads \(\gamma_{A}\) (read only, may be overridden)

Material resistance factor \(\gamma_{m}\) (read only, may be overridden)

Fabrication factor \(\alpha_{fab}\)
4.2. Input for fluid properties

pd  Design pressure at reference point

Reference point  Vertical reference position for design pressure, given in global coordinate system
4.3. Input for estimation of extreme values
If selected, Weibull distribution fitting may be used to estimate extreme utilization.
This requires the following input:

Sea state duration

Lower threshold for tail fitting
4.4. Structural properties
Structural properties is given either for a single element, all elements in a given segment or for the whole line.
Combined loading will be calculated for all elements that have specified structural properties.
4.4.1. Input for Riser geometry properties

Nominal diameter  Outside diameter of the pipe

Nominal thickness  Nominal (specified) pipe wall thickness

t corr  Corrosion/wear/erosion allowance

f0  Initial ovality
By default the nominal diameter and thickness is calculated based on cross section parameters.
5. Calculation of combined loading, Load and Resistance Factor Design
The following constants are calculated first:
Note that \(t_{2} = t  t corr\) is used in the following.
Burst resistance:
Elastic collapse pressure:
Plastic collapse pressure:
The collapse pressure is calculated as a function of elastic capacity,
plastic capacity and the ovality of the pipe and is solved using the analytical solution in
DNVOSF101 of the following equation:
Note DNV definition of ovality:
The following calculations are performed for each element/node and for each timestep of the dynamic analysis,
the utilization is then found as the maximum utilization from the resulting utilization timeseries.
Incidental design pressure:
Incidental external pressure:
Pressure difference:
Plastic bending stiffness:
Plastic axial force recistance:
Where \(\alpha_{c}\) is the fabrication factor calculated using formula in DNVOSF201,306.
The design bending moment:
Combined loading utilization for internal overpressure:
Combined loading utilization for external overpressure: