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MSC/NASTRAN V70.5+ Linear Gap Capability page 1 “Linear Gap” New Capability Seminar October 2001

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MSC/NASTRAN V70.5+ Linear Gap Capability page 2 Linear Gaps n What is a “linear gap”? n Why do I want linear gaps? n What is theory/implementation? n Patran interface n Examples n Limitations n Conclusions

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MSC/NASTRAN V70.5+ Linear Gap Capability page 3 What is a “linear gap”? n The linear gap is a contact element in its simplest form: –DOF-to-DOF gaps with initial openings –Linear, therefore does not include: friction large displacements material non-linearity Uses iterative solver to determine open/closed status. Node 3 X Y Node 2 P = 30 lbs. U gap Node 1 U init

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MSC/NASTRAN V70.5+ Linear Gap Capability page 4 Why do I want linear gaps? n Successful analysis will use proper boundary conditions and load paths. n Linear gaps can solve a large class of problems Heel-toe interaction Hole bearing Simple contacts –Bridge Supports –Fitting contacts –Efficient when compared to nonlinear methods

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MSC/NASTRAN V70.5+ Linear Gap Capability page 5 Theory / Implementation n The linear gaps provide for simple contact, (compressive) forces only. n MPC’s are used to define the gaps –The displacements and mpcforces are used to determine if each gap is “welded” or “free” Displacement criteria: no penetration (MPC displacement >=0) MPCFORCE criteria: compressive force only (MPCforce <=0) –An iterative procedure is used to solve the model based on displacements/mpcforces

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MSC/NASTRAN V70.5+ Linear Gap Capability page 6 Node 3 X Y Node 2 P = 30 lbs. U gap Node 1 U init X Y U y (opening) U y (closing) U y (initial) Opening GridU y opening - positive disp will open the gap Closing GridU y closing - positive disp will close the gap Initial OpeningU y initial - initial separation between grids The equation for the gap displacement can be written as: U y gap = U y opening - U y closing + U y initial Rearranging in MPC format and setting U y closing as the dependant (first) term: U y closing - U y opening + U y gap - U y initial = 0

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MSC/NASTRAN V70.5+ Linear Gap Capability page 7 Theory / Implementation n SPOINTs are defined for U gap and U init SPOINT55155 n SUPORT puts SPOINT 55 (U gap ) in the R-set for iteration. SUPORT550 n SPC defines initial gap opening =.05 (U init ) SPC n MPC Entry: (Eq. of motion: U y3 - U y2 + U gap - U init = 0) $ SIDG1C1A1G2C2A2 MPC $ G3C3A3G4C4A

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MSC/NASTRAN V70.5+ Linear Gap Capability page 8 MSC.Patran Interface n PCL Utility developed to easily create linear gaps and write appropriate MSC.Nastran input entries. –Easy Creation/Deletion of linear gaps –Useful graphics for visualization –Special Verification –Creates complete, run-ready, MSC.Nastran job –Stores gaps on MSC.Patran db Session file support

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MSC/NASTRAN V70.5+ Linear Gap Capability page 9 Initial opening defined by nodal distance (automatically calculated) or by user specified value Create gaps within tolerance; if coincident nodes identify the opening node based on Node ID Select Nodes (and direction) on both sides of gap, interface will automatically determine “Opening” and “Closing” Nodes and check for SPC/MPC conflicts Initial Assumption: Opened or Closed Special Cases CREATING GAPS

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MSC/NASTRAN V70.5+ Linear Gap Capability page 10 Initial Assumption: Opened or Closed Initial opening defined by nodal distance (automatically calculated) or by user specified value User defines “Opening” Node(s), “Closing” Node(s), and directions. CREATING GAPS

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MSC/NASTRAN V70.5+ Linear Gap Capability page 11 Gap Display: No Options Gap Display: All Options (0.15) (0.15-S) (-S) VISUALIZING GAPS

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MSC/NASTRAN V70.5+ Linear Gap Capability page 12 DELETING GAPS

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MSC/NASTRAN V70.5+ Linear Gap Capability page 13 CREATING JOB

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MSC/NASTRAN V70.5+ Linear Gap Capability page 14 If any LBC (SPC’s) have been added during the session, “Reload” the form and select appropriate boundary conditions “Rechecks” any model changes related to MPC and/or SPC changes (MPC’s include RBAR, RBE2, RBE3, etc.) VERIFYING GAPS

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MSC/NASTRAN V70.5+ Linear Gap Capability page 15 L-Bracket Heel-Toe Analysis 1.0” 3.0” 2.0” 0.25” Thick Aluminum 100 Pounds Shear Bolt =.248 Diameter Shear Hole=.250 Diameter Linear gaps defined in radial direction to distribute bearing load Tension Bolt: 0.5 inches long,.250 Diameter, attached to plate with RBE3 and fixed at bottom “Gap to Ground” along bottom surface

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MSC/NASTRAN V70.5+ Linear Gap Capability page 16 Force Transfer at Shear Bolt Force Transfer at Tension Bolt Local Stress Distribution

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MSC/NASTRAN V70.5+ Linear Gap Capability page 17 Interference Fit Plate 5 X 4 X hole.40 from edge Pin.506 dia X.1 thick (All Aluminum) Interference Gaps: Opening node is plate Closing node is pin Initial Gap determined by nodal distance

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MSC/NASTRAN V70.5+ Linear Gap Capability page 18 Non-uniform force distribution caused by edge effect

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MSC/NASTRAN V70.5+ Linear Gap Capability page 19 Limitations n Remember “simple gaps” only –NO LARGE DISPLACEMENTS –NO FRICTION –NO MATERIAL NONLINEARITY n Otherwise use SOL 106 with CGAP/PGAP –with or without PARAM,LGDISP –with or without MATS1 –etc.

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MSC/NASTRAN V70.5+ Linear Gap Capability page 20 Additional Information n MSC.Nastran V70.5 Release Guide; Section 3.5, download from: n McCullough, John and Proctor, Lance, “LOCAL ANALYSIS OF FASTENER HOLES USING THE LINEAR GAP TECHNOLOGY OF MSC/NASTRAN,” 1999 MSC Aerospace Users’ Conference. Download from:

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MSC/NASTRAN V70.5+ Linear Gap Capability page 21 Conclusion n Simple gap contact is available in SOL 101 of MSC.NASTRAN V70.5 or later. – Constrained Displacement ITERative technique (CDITER). –Simple gaps -- no friction n Works with large models n Reduces the complexities inherent with SOL 106 (gap stiffness, convergence, etc.) n Allows use of GPFORCE (now available in SOL 106 in V2001) n Used in instances where non linearity's do not exist, but contact is required.

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