Variabilities Analysis

SnRD Post Stochastics and DoE module allows the analyst to investigate hundreds of simulation results in a powerful way. When multiple variational studies have been setup, and results imported, will automatically post process all the Rattle and Squeak results for high level and deep dive investigation. The analyst can have multiple goals out of this analysis. Some of them are detailed below:

1. Effect of variation on S&R performance

   When a material property or a fixation stiffness is identified to vary due to the manufacturing or the assembly process , it is important to understand the consequences on S&R performance.

   By selecting one of multiples parameters, analyst can quickly identify the range of response variation in the form of:

   • Relative displacement maximums and minimums
   • SnR Index ranking of all interfaces to see if failure is to occur. Failure in this case mean rattle and or squeak occurrence
   • Range of variations of selected parameter(s) that allow a risk zone free for S&R occurrence and therefore get important input to the project quality process
   The above mentioned information can be extracted and illustrated from a various range of graphics helping the diagnosis process as well as the communication of the results to the rest of the organization, especially the non-CAE community. Graphical representation of failed points per combination of variation and tabular view are show below as an example of visualization.

   
   

   

   
   Figure 1.

2. Aging effect on S&R performance

   A parameter variation, such as the fixation stiffness (PBUSH K_i values), can be representative of a loss of pre-tension between attached parts. This is one of the common root causes for squeak and rattle in assemblies, especially with time and use.

   Using the Stochastic/DoE capabilities allows the engineering team to understand the limits of the design choice implemented as well as the break point. SnR Analyst can show beyond which loss of stiffness problems will appear, where and how critical they are.

   This diagnosis process enables the project team to choose the right fixation and give better specification to their suppliers. Thus, anticipation of failure, rattle and/or squeak, can be detected and robust engineering solution implemented instead of post-production palliative measures.

3. Tendencies and Optimum

   Squeak and Rattle issues are often related to local stiffness issues rather than global stiffness. This means that solution implementation is often different from the NVH classical approach: stiffer is better.

   When using Design of Experiment, one can explore optimums around which the relative displacement responses are the lowest. Typically, engineering is trying to reduce weight and cost, so finding alternative combination where a softer material can be used while improving or keeping the performance is highly appreciated by the buyers

   In the example below, one can see that relative displacement is at its lower point when the Young Modulus of the lower cover (orange part) is at the minimum value. What conclusions from that?

   • Nominal material value causes performance issues
   • Softer material is cheaper and perform better
   • Aging, meaning loss of stiffness, will not affect the performance
   • In a cockpit module, driver lower cover is one of the key parts for occupant safety knee forces & occupant kinematics. Softer energy absorbing material can help Crash performance

   
   
   Figure 2.