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Modelling in SACS Last updated on: October 30, 2008
SACS is a popular structural analysis software, used commonly in the analysis and design of offshore structures. This section attempts a brief introduction to using SACS and highlighting key features and differences from other software for a first time user. This section is by no means comprehensive and first time users are strongly recommended to read the official SACS manual and get to know its features, capabilities and limitations before using it. S o m e o f t h e k e y m o d e l li l i n g fe f e a t u r e s i n S AC AC S t h a t m a y d i ff ff e r f r o m o t h e r s o f tw tw a r e s u i t e s :
1. All m e m b e r s are identified by joint to joint ID (e.g., 1500–1505 designates a member, where 1500 and 1505 are joint numbers or node numbers. There are no separate member IDs. 2. G r o u p i n g feature is a sort of label to the member. Grouping helps in identifying the size, type of member and location if labelling is used effectively (e.g., PL1 for pile 1, LG1 for leg 1, MD1 for Main deck members, etc). A GRUP ID is a must when defining any member like 1500–1505. A group label can have a maximum of 3 characters. 3. Individual Individual members members cannot cannot be defined defined with material material propert properties. ies. Therefor Therefore, e, every member ha s to have a GRUP ID or else the system does not recognize the member. M a t e r i a l p r o p e r t i es e s can be defined to each group under Properties > Mem ber Group or Plate Group . C a u t i o n : All metric sizes are in cm, e.g., 660×25 tube shall be defined as 66×2.5 (Note: Centimeter or cm is a default in SACS. This is to reduce the overall stiffness matrix size, and corresponding time in computation). 4. W i s h b o n e s are dummy elements that have a finite length and the member has appropriate end releases to simulate system integrity. (Tip: It is a good idea to generate wishbones via SACS wizard that takes care of element definitions and offsets.) 5. M e m b e r e n d r e le l e a s es e s : [0 -- Fixed, 1 -- Free]. For e.g., if 1500–1505 is a moment released member at the end, then the end release would be defined as 000011. ix it i t i e s : [0 -- Free, 1 -- Fixed, 2 -- Retained]. For example, if 1500 is a 6. J o i n t f ix
Modelling in SACS | ckunte.com
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fixed joint, it would be defined as 111111 (fixed in all six degrees of freedom: x y z rx ry rz). 7. E le l e m e n t p r o p e r t i e s — K y, y , Kz K z , U n b r a c e d l e n g t h , Ef E f fe fe c t i ve ve l e n g t h : It is necessary to provide additional element properties in addition to the modelled length between joint to joint for a better and more accurate representation of the member, its connectivity, its effective length, etc. 8. S p r i n g s are required to be defined on joints with some appropriate spring stiffness (e.g., 100kN/m) to simulate a certain amount of mathematical stability to the structure or finite element model when performing analyses such as Lifting. 9. L o a d i n g o p t i o n s : Various loading options are available in SACS that include area and skid loading. (Tip: Use area loading with caution: check and verify load distribution.) Archives • Projects • © 2002–8 Chyetanya Kunte.
