Thomas Johansson DYNAmore Nordic AB. Drop Test Simulation

Transcription

1 Thomas Johansson DYNAmore Nordic AB Drop Test Simulation

2 Plastic Work Displacement LS-DYNA solve all your applications One Code for Multi-Physics Solutions Thermal Solver Implicit Double precision EM Solver Implicit Air (BEM) Conductors (FEM) Double precision Temperature Fluid Solver Implicit / Explicit ICFD / CESE ALE / CPM Double precision Mechanical Solver Implicit / Explicit Double precision / Single precision

3 Drop Testing Short duration Large deformations Non linearities Material properties Parts into contacts Explicit solver is the starting point => Core of LS-DYNA!!!

4 LS-DYNA Impact problems I Drop tests Most of non-coupled simulations Prediction of deceleration Prediction of failure Consumer goods (e.g. chain saw) Offshore applications oil pipes

5 Drop Test - modelling approach Geometry Standard element formulation Shells/Solid Appropriate material model More than 200 different model available Connection between parts Contacts Rivets/bolts/welds Initial velocity Gravity

6 Drop Test More options/possibilities exists of course.

7 LS-DYNA Impact problems II Coupled simulations Impact with birds Failure of turbine blade Watering

8 Case 1: Trawl gear impact on pipeline based on DNV RP F111 Methodology based on DNV RP F111 Non-linear FEA using LS-DYNA shell elements for the pipeline 1.5 million solid elements for the soil Impact duration 0.25 seconds Offshore impact analysis 8

9 Soil prestressing Offshore impact analysis 9

10 Impact simulation Offshore impact analysis 10

11 Case 2: Full scale FSI - Rock berm protected pipeline overtrawling Coupling: Fluid Structural DEM/DES Offshore impact analysis 11

12 Model set-up Artificial representation of trawl MMALE representation of water DEM representation of rock berm FEM (beam elements) representation of rigging gear Towing node, prescribed velocity 12

13 Simulation result Offshore impact analysis 13

14 LS-DYNA Drop Test Coupling ICFD structural DEM - structural

15 Dropping Frame LS-DYNA Explicit Scalability

16 Dropping Frame LS-DYNA Explicit Scalability Dropping frame on rigid plane deformable shell elements Uniform element size: 10 x 10 mm t = 0,5 s Initial velocity + gravity All nodes in the frame are in contact with the rigid plane 1 part made of steel defined using a isotropic material model. (true stress strain curve from tensile testing)

17 Dropping Frame LS-DYNA Explicit LS-DYNA R7 MPP 2 cores MPP 4 cores MPP 8 cores Very good scaling!

18 How to speed up the simulations??? How do I get results faster? 1. Buy more licenses!!!! 2. Clusters for parallel execution 3. Refine the model where it is needed 4. Simplify 5. Use built-in features, e.g SMS (Selective Mass Scaling)

19 t t n n n n n n i n e n n 2 1/ 1 2 1/ 2 1/ 1 ) ( v u u a v v f f M a Explicit Finite Elements Geometry update Mass matrix diagonal Stability I m m M n m e e e e e e e e e El m l E t min min 2 max Seminar, Porsche, 2013

20 Mass Scaling Conventional Mass Scaling: Adding mass to increase time step! Mass matrix still diagonal Shorter simulation time -> YES!. But higher mass also affect the Kinetic Energy. Selective Mass Scaling is a more advanced way of introducing mass to the system without affecting the kinetic energy (=mass) too much. Suppress high frequency content and leave low freqency modes unaffected (most deformations tend to deform in low frequency mode) ω/ ω 0 ω/ ω 0 i i CMS SMS Modify the structure of the added mass matrix to select affected modes

21 Selective mass scaling Implemented in LS-DYNA by DYNAmore Nordic AB Activated on *CONTROL_TIMESTEP Can be applied to specific Part sets in the simulation recommended!

22 Dropping Frame LS-DYNA Explicit, Selective Mass Scaling Using traditional mass scaling (scaling of density) can be used for a lot of analysis but NOT when the problem is dynamic. Selective mass scaling. 8 cores: 4h 38min - No mass scaling 8 cores: 29 min Selective mass scaling 9 times faster!!!! Kinetic energy

23 Comments Selective Mass Scaling Mass matrix not diagonal, requires solution of linear system of equations Ma f Penalty => too large time step will negatively affect CPU time Apply SMS to critical parts that require fine mesh Problem dependent => trial and error

24 Thank you! Your LS-DYNA distributor and more