This paper presents the preliminary global static and dynamic analysis of the new 8” nominal diameter water injection flexible jumper and addresses the following analysis:
1. Extreme static and dynamic analysis under 100-year storm conditions to check the
feasibility of the layout and configuration,
2. Global fatigue analysis.
2. Analysis Condition
The following analysis condition has been considered.
- The hang-off location at FPU and TLP as shown in Figure 1.1 was selected based in technical, economical and constructability consideration. This hang-off location gives the shortest length, do not interfere existing mooring lines and easy installation especially at TLP side where the hang-off location is positioned above the sea level without providing any I-Jube.
- Hundred years extreme storm with operating density was considered.
- Vessel offset for damaged mooring system was considered as a conservative approach.
- The vessel offset, environmental data and bend stiffeners stress - strain data, shall be taken from Design Premise, Detailed Design of Jumper System (Doc. No. 1-1-4-230/DP01 Rev 03).
- The vessel static position was considered as per as built field layout drawing (Drawing No. 00123-FOIP/CVX-DWG-016), hence no installation tolerance was applied.
- In order to avoid clashing with the existing electrical jumper, the centenary of new 8” nominal diameter water injection flexible jumper was positioned above the existing electrical jumper.
- The interference analysis, hang off design, and auxiliaries designs are not covered and shall be submitted in separate reports.
The Flexible jumper will be designed according to API Spec 17J (5) and API RP 17B (6). The design criteria for the extreme analysis for the extreme analysis are 1.5 times storage MBR for normal operation and 1.25 times storage MBR for abnormal operation. The design MBR values are given in table 3.1. The maximum effective tension is to be less than the specified allowable in the table 3.1.
3.1 Fluid and Flexible Jumper Properties
The hydrodynamic coefficient used in both the static and the dynamic analyses are specified in table 3.2. Note that the drag diameter for marine growth sections will be increased to reflect the specific marine growth levels. Note that combination of using a high drag coefficient with a large drag diameter can be considered to be conservative. If required sensitivity studies will be performed to evaluate the effect of a reduce level of conservations on the results (1).
4. Environmental Data
4.1 Water Depth and Density
The seawater density is assumed to be 1025kg/m3with a water depth (LAT) of 1021m. All analysis will be performed with the water elevation at this nominal value.
4.2 Current Data
Current data divided into Meridian current and Zonal current. Median current is applied to current with ±14o from north or south. The Zonal current profile is applied to all other directions. In the global analysis the current profile will be interpolated linearly between the points given. All current data West Seno present at Table 4.1
4.3 Wave Data
Directional wave data is presented in table 4.2 for the 100-year return storm conditions. The wave spectrum type is JONSWAP spectrum with a peak enhancement factor g of 2.5. The fatigue sea state scatter given in table 4.3 for regular wave analyses, mean, upper and lower wave periods were calculated and analyses will be performed for all three wave periods. The design 100-year storm regular wave data is follows (1):
HMAX = Value present in table 4.2 below
TLOWER = 1.06 x Tz
TMEAN = TMax (values present in table 4.2 below)
TUPPER = 1.40 x Tz
Table 4.2 Design Wave Data 100-year Return Storm
The scatter diagram shown in Table 4.3 gives the estimated individual wave height distribution for a period. The fatigue analyses will be based on this scatter diagram.
Table 4.3 Fatigue Design Environmental Events
4.4 Marine Growth
Marine growth data for the West Seno field present in Table 4.4. Jumper properties with marine growth were determined assuming a marine growth density of 1300 kg/m3. The Pipe properties have been modified to include marine growth. The drag diameter of the jumpers will be increased to account for the marine growth. The effect of Marine growth will be included in all analyses (1).
Table 4.4 Jumper Properties with Marine Growth
4.5 Wind Loads
Wind Load assumed to be included in the offset of The FPU and TLP (1).
Main dimension FPU and TLP summarized in the Table 5.1
Table 5.1 FPU and TLP General Specification
The vessel offsets are assumed to include mean offset plus maximum expected low frequency offset, plus vessel first order motions. With the FPU and TLP both responding differently under the same environmental conditions this causes the separations between the vessels to vary. The maximum and minimum separations between the two vessels are presented in Table 5.2 for a 100-year storm under damaged mooring line conditions. Also for the extreme load case matrix are derived from the values given in Table 5.2. Vessel offsets to be used for fatigue analysis are assumed to be zero (1).
Table 5.2 Maximum & Minimum FPU to TLP (centre to centre) distance in 100-year storm conditions- Damaged Mooring System
