DNV OS E301 mooring capacity

1. Purpose

Calculate the mooring line capacity.

2. Description

The DNV OS E301 code-check is based on Offshore standard DNV-OS-E301, Position Mooring, July 2021 .

The mooring line capacity is calculated using the utilization equation, see Section 2 in DNV-OS-E301.

3. Required results

To perform the code-check, the element forces 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 safety factors

  • Limit state category (ULS/ALS)

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

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

  • Last functional load group, i.e. the number of the last functional load group in the static calculation parameter that is part of the functional load

The tension capacity, \(S_{C}\), is a input on the cross section.

4.1.1. Statistics

The response extreme value are estimated using either

  • observed maximum

  • use distribution fitting for a given return period

4.1.2. Analysis Time Window

The time window can be set using

  • start time

  • end time

4.1.3. Output

Option to add intermediate results.

The intermediate results are stored together with the element results.

5. Calculation of mooring line capacity

The mooring line capacity can be expressed by the utilization factor, \(u\):

\[u = \frac{T_{pre}\cdot\gamma_{pret}+T_{C-env}\cdot\gamma_{env}} {S_C} \text{ where } u < 1\]

  • \(T_{pret}\) is the line pretension

  • \(T_{C-env}\), is the characteristic environmental tension

For details see DNV OS-E301,Section 2.