Linear Static Stress Analysis vs. Mechanical Event Simulation Setup Comparison

Introduction

To see an analysis replay of the Mechanical Event Simulation for this model, click here.

1. Make an FEA model of the system's geometry.

• (LSSA) This is the same for both LSSA and MES. Work with existing CAD wireframes and solid models or use Superdraw sketching, modeling and meshing tools within FEMPRO to build finite element models. Then optionally refine surface meshes and create tetrahedral, brick or hex-dominant (hybrid) solid FEA meshes.
  
  
• (MES) This is the same for both LSSA and MES. Work with existing CAD wireframes and solid models or use Superdraw sketching, modeling and meshing tools within FEMPRO to build finite element models. Then optionally refine surface meshes and create tetrahedral, brick or hex-dominant (hybrid) solid FEA meshes.

2. Specify the model position.

• (LSSA) In the linear static world, the initial position of the model has no particular effect.
  
  
• (MES) Engineers must specify the initial position of all interacting parts in space because MES simulates the interaction between objects. 

3. Choose element types.

• (LSSA) Select from bricks, tetrahedra, beams, trusses, springs, plates/shells, 2-D, rigid or contact elements.
  
  
• (MES) In addition to the elements listed for LSSA, hydrodynamic and kinematic elements or motion-related engineering elements (such as dashpot, pulley, slider and actuator elements) can be added.

4. Specify material properties.

• (LSSA) Specify a linear material model and supply required data, including Young's Modulus, Poisson's Ratio and Shear Modulus. For orthotropic materials, these should be specified in multiple directions.
  
  
• (MES) Specify a linear material model with required data or specify a nonlinear material model with required data, including yield and ultimate stresses (if using MES with nonlinear material models). 

5. Specify material density.

• (LSSA) Specifying density enables engineers to calculate mass and then obtain the model's weight for use as loading.
  
  
• (MES) Specifying density contributes to gravity loading and the inertia of a part. Mass can be added or subtracted during the event to simulate the addition or removal of parts of the model.

6. Specify an analysis type.

• (LSSA) Choose linear static stress analysis. 
  
  
• (MES) Select MES to simulate physical events that may involve motion, impact or geometric nonlinearities. MES with nonlinear material models can also handle nonlinear material behavior and deformation.

7. Specify the duration of the event.

• (LSSA) With LSSA, loadings are applied over an infinite duration of time; therefore, the length of time cannot be specified in a static analysis.
  
  
• (MES) Because MES gives analysis results over time, the duration of the event must be specified. The event can be extended or shortened as needed once the analysis begins. Also, specify the capture rate, which is the output interval at which results are displayed. 

8. Specify constraints.

• (LSSA) Specify constraints to affix the model to set reference points with varying degrees of freedom. The part in question is isolated from interaction with other parts even though it may move freely in the real world. 
  
  
• (MES) This is done in the same manner as LSSA whenever the model is to be constrained from motion. However, with MES, engineers only need to apply actual physical constraints because MES can handle the interaction of several moving parts. 

9. Specify gravity field.

• (LSSA) This is the same for both LSSA and MES. 
  
  
• (MES) This is the same for both LSSA and MES. 

10. Specify acceleration field(s).

• (LSSA) Specify constant acceleration field(s) such as gravity or centrifugal loads.
  
  
• (MES) Specify constant or time-dependent acceleration field(s) (acceleration vs. time curves) such as gravity or centrifugal loads.

11. Specify revolution or angular acceleration.

• (LSSA) This is the same for both LSSA and MES. 
  
  
• (MES) This is the same for both LSSA and MES. For MES, revolution and angular acceleration of the model may initiate motion that, in turn, creates additional loads (stresses).

12. Account for potential contact.

• (LSSA) Linear contact and interaction between multiple bodies can be defined through right-click menus and dialogs in ALGOR's FEMPRO interface. Simply set the default contact type for the entire assembly through the contact branch of the tree view. Optional contact pairs between specific parts and/or surfaces can be interactively specified through the graphics window or tree view. Specify whether or not to include friction effects.
  
  
• (MES) Setup is the same for both LSSA and MES. However, MES automatically considers potential contact for objects that remain in contact or separate during the event. MES handles: 
  1. Contact between flexible bodies. 
  2. Contact between a flexible body and an impact wall, suitable for modeling a drop test or sliding behavior on a surface.

For LSSA, a force is applied. For MES, surface-to-surface contact is defined between the weight and the bar.

13. Specify displacements.

• (LSSA) This analysis type is limited to initial displacements that are static and can only be applied for one instant in time. These produce stresses and linear deformations.
  
  
• (MES) Handles initial displacements and displacements as functions of time, which generate stresses, produce motion and can be applied, modified or removed at any time during an event.

14. Specify force.

• (LSSA) LSSA uses forces to isolate the body from other objects. This interaction with other objects generally results in stresses. Additional work may be needed to determine the dynamic forces that are actually encountered.
  
  
• (MES) With MES, the event is structured so forces are calculated intrinsically and are based on changes in motion and flexing; therefore, engineers do not need to specify forces. When forces are known, they can be specified to get stresses as with LSSA. 

For LSSA, the weight is represented by a force, whereas it is modeled for MES.

15. Specify pressures.

• (LSSA) With LSSA, pressures are specified for an infinitely constant situation. Pressures are applied on the model surface and can be used to model the interaction of distinct parts. 
  
  
• (MES) Pressures can be functions of time with MES. Pressures, such as hydrostatic pressures, are easily specified with MES and can be applied to surfaces in the same manner as LSSA.

16. Specify pressure directions.

• (LSSA) Handles the initial direction of a pressure for all times.
  
  
• (MES) Can apply initial pressures in all directions as well as perpendicular to surfaces. All initial surface pressures can maintain their orientation as the part moves or deforms.

17. Process the analysis or event.

• (LSSA) Performs a process to obtain stresses and linear deformations resulting from the above specifications. 
  
  
• (MES) Initiates an interactive process to perform the event. Engineers can see the event unfold by live monitoring of motion, flexing and stresses. Both graphical plots of values vs. time and visual contours are available.

18. Produce result displays.

• (LSSA) Produces one set of graphical plots of stress contours, deformed shapes (with linear deformations exaggerated to facilitate viewing) for the one-step analysis based on an infinite amount of elapsed time.
  
  
• (MES) Produces graphical plots of stress contours, deformed shapes (linear and permanent deformation) for times defined by capture rate. See the event as it unfolds and view detailed graphical data of acceleration, stresses, displacements and more vs. time using the Superview IV Results environment.

19. Produce analysis replays.

• (LSSA) Produces a simulated analysis replay based on a linear extrapolation from very small linear deformations.
  
  
• (MES) Produces time-based analysis replays of the event from start to finish in real time, fast time or slow motion. 

LSSA yields one set of stress contours; MES gives full analysis replays of events and plots of time-dependent results.