Unlike the wind drag coefficients, the current drag coefficients are not the same for each draft. TANKER WIND AREASĪ comparison of surge and sway wind areas is shown above for three tanker sizes, each in three different load conditions. The hawser load may cause significant heeling of the tanker during a squall. The tanker will be swung around as shown in the figure above. The wind direction may quickly come onto the tanker beam. When sudden squalls occur, the wind direction often changes as the wind speed is increasing. WSEP has the highest wind speed and the direction changes during the time that the wind speed is increasing.īefore a wind shift, the moored tanker tends to be headed into the wind. It is important to note that, apart from WS1 (Wind Shift 1) the speed and direction changes are not instantaneous and do not occur in the same manner for the four measured wind shifts selected for analysis (WS6, WS7, WS13 and WS15). The purple triangles indicate the maximum change in the wind direction simulated during the wind shift. The red circles indicate the maximum wind speeds in each simulated wind shift. SUMMARY OF WIND SHIFT CONDITIONS MEASURED AND SIMULATED Simplified drawing of TLU3, as used in OrcaFlex model for SPM Mooring Analysis Study by STA in 2016. The SPMs are operated by OCENSA and ECOPETROL. Location of three SPMs (or TLUs, Tanker Loading Units) is shown above. The maximum direction change is 90 degrees, with 68 degrees change during the 80 seconds of rapid wind speed increase. The speed decreases fairly steadily to 22 knots at 1800 seconds. The speed starts at 15.7 knots, decreases slightly then increases to 35 knots over a time of only 80 seconds. The x-axis grid intervals are 10 minutes each. SQUALL, or SUDDEN WIND SHIFT CONDITIONSĪn example of sudden wind speed and direction change at Covenas, Colombia, is shown below. While STA SPM is an efficient and very fast tool to use for static SPM equilibrium solultions, we always continue with dynamic simulations using OrcaFlex.

For details of this user-interactive app, view the STA SPM USER MANUAL. The results are shown graphically in STA SPM, as shown below. STA SPMĮxample input and static equilibrium results for a single point moored tanker with tandem offtake tanker and tug, are shown in the figure below.

Preliminary static equilibrium can be quickly investigated with STA SPM.

Moored tankers are also modelled in the time domain with OrcaFlex with diffraction and added mass properties calculated with MDL Hydro, AQWA, WAMIT, Moses, and other frequency domain packages.ĭisplacement RAOs for the tankers can be quickly computed with STA BARMOT where load RAOs are not required (as is frequently the case). CALM buoys, mooring chains and underbuoy, or submarine, hoses are modelled in the time domain with OrcaFlex. STA specializes in the dynamic analysis of single point moorings.

Orcaflex wamit input