#SEU16. FEA in Solid Edge and FEMAP Mark Sherman

Transcription

1 FEA in Solid Edge and FEMAP Mark Sherman Realize innovation.

2 FEMAP Continuous development with the same core team! Since 1985 there have been more than 35 releases of FEMAP with only one major architecture change (DOS to Windows) FEMAP Development Team is all engineers turned programmers FEA By Engineers for Engineers Product development has been driven by FEA Analyst input Page 2

3 What you will learn Come learn how to apply finite element analysis techniques to your models using Solid Edge s built-in simulation as well as Femap, our CAD-independent, advanced simulation program. Digital simulation allows you to predict and improve the performance and reliability of your models, reduce time-consuming and costly physical prototyping, evaluate different designs and materials, and optimize your designs. This session will show you the benefit of integrating simulation in your design work, with emphasis on interpreting the results of an analysis to effectively influence product design. Page 3

4 Objectives of introducing 3D CAD? Page 4

5 Objectives introducing 3D CAD Top companies responded in 2001 General machinery Electric Transportation Precision machinery Other Page 5 Source: Survey by Japan society for the promotion of science

6 Objectives introducing 3D CAD Page 6 1 Shorten the development cycle 2 Eliminate the inconsistency in the design 3 Improve product quality 4 Reduce the number of prototypes 5 Reduce the number of development steps 6 Leverage the 3D design data for analysis 12 Expand the analysis by design engineers 16 Increase the types of analysis Source: Survey by Japan society for the promotion of science

7 Expand the analysis by design engineers CAE by designer 20% CAE by designer 30% CAE by specialist 80% CAE by specialist 70% Page 7 Analysis by design engineers is increasing Source: Survey by Japan society for the promotion of science

8 A Solution for Challenges in manufactures Time Development Design Validation Cost Materials Prototypes Warranty Quality Performance Innovation Simulation driven design Page 8

9 Why Simulation? Optimize design Failure analysis Reduce weight C Improve performance Q Reduce materials C Improve reliability Q Promote innovation Q Reduce recalls T C Q Virtual testing Reduce prototypes Reduce physical tests Speed time to market T T T C C T C Q Time Cost Quality Page 9

10 A Brief History of FEA and FEM The concept of a Finite Element was introduced by Prof. R.W. Clough of UC Berkeley in 1960 at an ASCE Conference. NASTRAN (NASA STRuctural ANalysis) was developed for NASA by a consortium of several companies for the analysis of the Saturn V rocket. acquired MSC.Nastran source code in 2003 and has greatly improved the performance and capabilities of NX Nastran through the latest release of NX Nastran 8.1 Finite Element Modelers(Pre/Post Processors), the tools used to generate Finite Element meshes and view results, were first commercialized in the 1970s. began the first commercial offering of FEM software with the introduction of SDRC SuperTab in the 1970 s. Siemens continues to support the analysis community with Femap and NX CAE pre/post-processors. Page 10

11 The Solution Consider a single degree of freedom system a simple spring: Apply the following conditions to generate a system of simultaneous equations where displacements are the unknowns: Equilibrium of forces and moments Strain- displacement relations Stress-strain relations? K u = P (static analysis) K: spring stiffness P: applied load u: displacement Page 11

12 Solution for Multiple DOFs Any real structure can be modeled as a collection of elements connected at nodes With many elements and nodal dof s, a matrix approach to the solution is adopted Element stiffness matrix k a k b k a = k 11 k 12 k 21 k All element matrices are assembled into a global stiffness matrix ka 11 ka 12 K gg = ka 21 ka 22 + kb 22 kb 23 kb 32 kb 33 Page 12

13 Modeling of Real Structures The behavior of the real structure is obtained by considering the collective behavior of the discrete elements. The user is responsible for the subdivision or discretization of real-world structures. Element choice has significant influence on the behavior A graphic preprocessor such as FEMAP/SE Simulation is the key tool for generating a model that accurately simulates real world structures Contributions from all other elements k a -k a K gg = -k a k a + k b -k b -k b k b n x n Page 13

14 Small Example Page 14

15 Small Example K u = P (static analysis) u = K -1 P Page 15

16 Small Example in FEMAP Page 16

17 Linear Static Analysis 90%+ of all FEA projects 100% Linear if you double the loads, you get double the response Material stays in the elastic range return to original shape Small Deformation Maximum Displacement much smaller than characteristic dimensions of the part being studied, i.e. displacement much less than the thickness of the part Loads are applied slow and gradually, i.e. not Dynamic or Shock Loading Page 17

18 Linear Static Analysis What can you expect to learn from a linear static Finite Element Analysis Displacements Load Paths Stress* Page 18

19 Important Guidelines Linear Analysis is small displacement, small angle theory Must use nonlinear analysis if the displacement changes the stiffness or loads Pressure loads on flat surfaces, have no membrane component unless nonlinear large displacement solution performed.(load carried by bending stiffness only) Linear contact is a misnomer, contact condition is iterative solution, but no other nonlinear effects are considered. Mesh density required is a function of the desired answers Must have enough nodes so model can deform smoothly like the real structure. In general, accurate stresses require more elements than accurate displacements. Goal is for a small stress gradient across any individual element Normal modes should always be run before any dynamic solution Confirm model behavior, stiffness and mass properties are correct Page 19

20 Normal Modes Function of stiffness and mass, both must defined correctly Understand fundamental vibration characteristics; shapes and frequencies All dynamic response is a linear combination of the normal modes of a structure Run Normal Modes to make sure your model is correct Page 20

21 Nonlinear Statics Material nonlinear effects: Material yielding Nonlinear stress/strain relationship Large displacement effects: displacement changes the stiffness; thin walled pressure vessel displacement changes the load direction; pressure, beam column Contact Page 21

22 Design Optimization Example Idler Pulley Page 22 Idler Pulley with following inputs to optimization Material is Aluminum 1060 (Yield Stress of 4000 psi) Torque Load of 1000 in-lbf Inner Cylinder/Geometry Fully Constrained Initial Solve indicates Max Von Mises Stress of 897 psi Optimization Inputs Initial Solution of 897 psi for Max Von Mises Objective Minimize Mass (Initial Mass is lbm) Design Limit Von Mises Stress Less than 1333 psi (ie. FOS of 3) Design Variables using Angle and Height Dimensions Max Iterations - 20

23 Design Optimization Example Continued UI Inputs Page 23

24 Design Optimization Example Final Solution Final Solution after 10 iterations Minimized Mass to lbm ( reduction of lbm from model) Max Von Mises Stress of 1285 psi (below 1333 psi ) with FOS of 3 Original angle dimension of 40 degrees now degrees Original Height of cutout of 3 in now 3.9 in Page 24

25 Frequency Response Response of structure vs frequency Load is function of frequency Examples: Washing Machine Generator in Power Plant Automobile Tire out of balance Page 25

26 Transient Response Response of structure is function of time. Load changes vs time Examples: Vehicle on road with potholes Building subjected to earthquake Impact loading; drop testing Rocket wind and thrust load Page 26

27 Nonlinear Transient Response Loading and structural response a function of time Large displacement effects considered Material nonlinear effects considered Implicit and Explicit Solvers Examples: Impact/crash where material stress exceeds yield Model from - National Crash Analysis Center Page 27

28 Solution from Siemens Page 28 Daily work SOLID EDGE SIMULATION Linear Static Normal Modes Heat Transfer Geometric Nonlinear Advanced Modeling & Analysis Dynamic Response Nonlinear Design Optimization Flow-Thermal Femap with NX Nastran Analysis expertise

29 Advanced Modeling Beam Like structures modeled as two node beam elements Thin structures (1 to 10) modeled as shells Rigid components modeled as Lumped Masses Model Size now smaller, Advanced Analyses now possible Page 29

30 Advanced Modeling Mid-Surface Extraction Model thin-shell structures with plate elements Reduces FEA model size significantly Quickly change thickness value to optimize design Page 30

31 Solid Edge Simulation Automatic Finite Element Model Creation Shell & Solid tetrahedral elements Local mesh size control Based on Femap meshing technology Full Boundary Condition Support Geometry based constraints & loads Handles help define direction and orientation Quick Bar input options Powerful Analysis Capability Industry standard solver - NX Nastran Statics, normal modes and buckling analysis Automatic element quality checks Comprehensive Post Processing Fringe, color plots and contours Displacement, animation and mode shapes Report generation Page 31 Synchronous Technology with model associativity Remove unnecessary features Change geometry shape quickly & easily Mesh automatic update

32 Customer Success GEA Farm Technologies FEA allows us to save money during the design process, and save iterations at the prototype step. We can reduce four to five physical prototypes down to just one, shaving the design cycle by months. Alexander Laprise Engineer GEA Farm Technologies Page 32

33 Customer Success Zumex The use of FEA has become a great time-saving device. During physical machine testing, the breakages that occur coincide exactly as predicted by the FEA analysis. Eloy Herrero Marketing Manager Zumex Page 33

34 Example An electric drive system Objective : Verify the bracket s strength so that the maximum deformation is within the design criteria. Design the better products reducing vibration level during operation, so that the noise level can be kept lower than the competitors eventually. Solution : Predict the maximum deformation of the bracket by applying linear statics analysis. Predict the product s dynamic characteristics by using the frequency response analysis. Page 34

35 CAD assembly of an electric drive system Bracket Motor Frame Page 35

36 Supporting structures Page 36

37 Connections defined between parts Glued connection Page 37

38 Connections defined between parts Glued connection Page 38

39 Constraints Fixed surfaces Page 39

40 Bearing load Page 40

41 Mesh for FEA Page 41

42 Static analysis - Result Result < Criteria Ok! Page 42

43 Linear Statics - Stresses To accurately recover stresses in shell and solid elements, the mesh must be very dense in areas of high stress gradients Stress Changing Too Fast Across One Element Page 43

44 Stresses from the Web Page 44

45 Linear Statics - Stresses To accurately recover stresses in shell and solid elements, the mesh must be very dense in areas of high stress gradients Stress Changing Less Across an Element More Accurate Page 45

46 Linear Statics - Stresses Keeping Model Size Reasonable Increase the Mesh Density where you need it, decrease it where you don t Page 46

47 Linear Statics - Stresses Page 47

48 Guidelines for Good Stress Interpretation - Singularities Page 48

49 Guidelines for Linear Static Analysis - Stresses Remember the limitations of Linear analysis Increase Mesh Density in High Stress Regions Ignore Stress Answers at Singularities Zero Radius Fillets Inside Corners Loaded and Constrained Nodes Page 49

50 Normal Modes - Result No Mode Frequency Mode Shape Hz Hz Hz Page 50

51 Normal Modes No Mode Frequency Mode Shape Hz Hz Hz Page 51

52 Results summary Category Item to check Results GO/NG Strength Deformation Stress < Design criteria GO Normal modes Modal frequencies Excitation frequencies (3000 RPM = 50 Hz) GO Page 52

53 Considerations Source input = Rotating motor = 3000 RPM = 50 Hz Resonance frequencies to avoid = n*rpm = 50 Hz, 100 Hz, 150 Hz, 200 Hz,.. Need to carefully investigate the vibration level around Mode 1 and 5 as these are close to the above input frequencies. Mode 1 = 206 Hz Mode 5 = 505 Hz Vibration level? Response Analysis Page 53

54 Switch to the dedicated CAE software In Solid Edge, you can save your simulation model as the Femap file. Direct file translation including the results Open the file in the Femap for the further analysis Page 54

55 Frequency Response Excitation = Force = Motor mass x Gravity = 2 [kg] x 9.8 [mm^2/s] = 19.6 [N] Page 55

56 Frequency Response Page 56

57 Flow Analysis Fan Vent Air volume Page 57 Flow velocity

58 Advanced Dynamics Examples Frequency response analysis is used to compute structural response to steady-state oscillatory excitation. Examples of oscillatory excitation include rotating machinery, unbalanced tires, and helicopter blades. In frequency response analysis the excitation is explicitly defined in the frequency domain. Excitations can be in the form of applied forces and enforced motions (displacements, velocities, or accelerations). Request responses between 50 and 80 Hz, every 0.05 Hz Page 58

59 Advanced Dynamics Examples Page 59

60 Two Takeaways Run Normal Modes on your Design to make sure everything is set up correctly, especially for assemblies Always be skeptical of a Stress Plot Page 60