USFOS is the leading computer program for collapse analyses and accidental load analyses of fixed offshore structures, intact or damaged. The program accurately simulates the collapse process of space frame structures, from the initial yielding, through to the formation of a complete collapse mechanism and on to the final toppling of the structure. USFOS gives the engineers and designers a better understand and insight into the behaviour and safety of a structure.
The USFOS program has been in commercial use since 1985 by oil companies and engineering consultants all over the world. The program has proved significant cost savings in areas such as inspection planning, lifetime extension and integrity assessment of ageing structures, and in fire protection assessment for new designs. . It is verified through participation in extensive benchmark activities both in Europe and USA, through comparison with experiments and through extensive scientific publication.
The program is cost effective, design oriented and easy to use. USFOS has a low user threshold. FE models created for linear analysis can be used with minimal alterations. The program has a simple input structure and requires little specialized knowledge on nonlinear finite element analyses. Any combination of thermal load and/or mechanical loads can be analyzed.
Based on simple engineering concepts, the program combines classical, analytic solutions, accurate numerical procedures and conventional finite element formulations into an efficient tool for the engineer.
The underlying philosophy of the program is to use a very coarse finite element modeling of the structure, but still obtain results with excellent accuracy. In fact, the same finite element model may be used in the USFOS nonlinear analysis as in conventional linear analysis of the structure. This saves a lot of modeling effort in design and documentation projects.
USFOS has a particular strength for use in reassessment of structures and during operation / inspection of structures. The program includes a very efficient formulation of damaged structural members, that makes it specially suited to document the capacity of structures with damaged members, e.g. from ship impact or dropped objects.
USFOS has undergone extensive verification for design usage. Results from second-order global analyses are highly sensitive to the modelling of the structure – a robust procedure has been developed within the USFOS program to ensure that the nonlinear formulation produces results conforming to recognized ULS design equations.
Some program features
USFOS traces the entire collapse and post collapse behaviour of the structure, including global unloading, member unloading and redistribution of forces.
The program requires only one finite element per physical member of the structure.
The program employs efficient solution algorithms (SPARSE technology), performing complete collapse analyses or time-domain dynamic analyses in short time.
Robust incremental / iterative solution procedures are implemented, with automatic step scaling and verification of numerical solution accuracy.
The program comes with an extremely powerful and versatile graphical post processor with full 3D graphics and image plots.
The non-linear finite element formulation includes
- Member P-d effects
- Global P-D effects
- Efficient beam element predicting buckling with only one element
- 3-node and 4-node fully non-linear shell elements
- Non-linear springs, including gap/contact modeling
- Shim / internal pile modelling
- Hydrodynamics and Aerodynamic loads
- Buoyancy and hydrodynamic forces integrated to the instantaneous wet surface
- Ship Impact and Dropped Objects
- Fire and Blast loading
- Independent, prescribed motion in ‘unlimited’ number of nodes/d.o.f’s :
- Displacement history
- Velocity history
- Acceleration history
- Tubular Joint Behaviour
- Pile / Soil Interaction
- Spud-can modelling
- Efficient model for dented/damaged CHS and RHS, including local buckling and dent growth
- Rupture / fracture modelling with unloading and redistribution of forces